U.S. patent application number 13/363279 was filed with the patent office on 2012-08-02 for powertrain and method for a kinetic hybrid vehicle.
Invention is credited to Hongping He, Jing He.
Application Number | 20120197472 13/363279 |
Document ID | / |
Family ID | 46577796 |
Filed Date | 2012-08-02 |
United States Patent
Application |
20120197472 |
Kind Code |
A1 |
He; Jing ; et al. |
August 2, 2012 |
Powertrain and Method for a Kinetic Hybrid Vehicle
Abstract
A kinetic hybrid device and method for a vehicle may include a
planetary gear system configured as a continuously variable
transmission comprised of three or four ports. The kinetic hybrid
device and method may include a flywheel connected to a first port
of the system, a final drive connected to a second port of the
system, and the variator for the flywheel connected to a third or
fourth port of the system. The prime mover and/or other power
sources may share a port with the flywheel, but do not share a port
with the final drive.
Inventors: |
He; Jing; (Burbank, CA)
; He; Hongping; (Bakersfield, CA) |
Family ID: |
46577796 |
Appl. No.: |
13/363279 |
Filed: |
January 31, 2012 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61438267 |
Feb 1, 2011 |
|
|
|
61471213 |
Apr 4, 2011 |
|
|
|
61495993 |
Jun 11, 2011 |
|
|
|
Current U.S.
Class: |
701/22 ; 475/5;
903/903 |
Current CPC
Class: |
B60K 6/365 20130101;
F16H 2200/2007 20130101; Y02T 10/62 20130101; B60K 6/105 20130101;
F16H 3/724 20130101; Y02T 10/6204 20130101; Y02T 10/6282 20130101;
Y10T 477/675 20150115; Y10T 477/23 20150115; B60K 6/52 20130101;
F16H 2200/2005 20130101; Y02T 10/6265 20130101; F16H 2037/088
20130101 |
Class at
Publication: |
701/22 ; 475/5;
903/903 |
International
Class: |
B60W 20/00 20060101
B60W020/00; F16H 3/72 20060101 F16H003/72 |
Claims
1. A powertrain for a kinetic hybrid vehicle, comprising: i. a
planetary gear system configured as a continuously variable
transmission comprising a first port, a second port, and a third
port; ii. a flywheel coupled to the first port of the planetary
gear system; iii. a final drive of the vehicle, the final drive
being coupled to the second port of the planetary gear system; iv.
an internal combustion engine configured to be coupled to the first
port; and v. a first motor/generator coupled to the third port.
2. The powertrain of claim 1, wherein the flywheel is coupled to
the first port of the planetary gear system through an additional
gear set.
3. The powertrain of claim 1, further comprising a second
motor/generator coupled to one of the first port and the second
port of the planetary gear system.
4. The powertrain of claim 3, wherein the internal combustion
engine is coupled to the first port of the planetary gear system
through a clutch.
5. The powertrain of claim 3, wherein the internal combustion
engine is coupled to the first port of the planetary gear system
through an additional planetary gear set having three additional
ports, wherein one of the ports of the additional planetary gear
set is connected to the first port of the planetary gear system,
and the remaining two ports are each connected to a respective one
of the internal combustion engine and a brake connected to the
vehicle chassis.
6. The powertrain of claim 4, wherein the powertrain is configured
to operate the internal combustion engine within a peak efficiency
range while the engine simultaneously drives the final drive of the
vehicle and charges the flywheel using power from the engine that
exceeds the power needed to maintain the vehicle at the vehicle
speed desired by an operator of the vehicle.
7. The powertrain of claim 6, wherein the clutch at the first port
is operable for selectively connecting the engine to and from the
planetary gear system at the first port, including for
disconnecting the engine from the planetary gear system when the
rotational speed of the flywheel has reached an upper limit, and
for connecting the engine to the planetary gear system when the
rotational speed of the flywheel has dropped to a lower limit.
8. The powertrain of claim 5, wherein the powertrain is configured
to operate the internal combustion engine within a peak efficiency
range while the engine simultaneously drives the final drive of the
vehicle and charges the flywheel using power from the engine that
exceeds the power needed to maintain the vehicle at the vehicle
speed desired by an operator of the vehicle.
9. The powertrain of claim 8, wherein the brake connected to the
additional planetary gear set is operable for selectively
connecting the engine to and from the planetary gear system at the
first port, including for disconnecting the engine from the
planetary gear system by releasing the brake when the rotational
speed of the flywheel has reached an upper range, and for
connecting the engine to the planetary gear system by applying the
brake when the rotational speed of the flywheel has dropped to a
lower range.
10. A method of operating a kinetic hybrid vehicle that includes a
flywheel coupled to a first port of a continuously variable
transmission, a final drive coupled to a second port of the
continuously variable transmission, a variator coupled to a third
port of the continuously variable transmission, and a power source
coupled to the first port of the continuously variable
transmission, the method comprising: maintaining the vehicle speed
desired by an operator of the kinetic hybrid vehicle within a speed
range, by operating the kinetic hybrid vehicle to alternate between
a first mode and a second mode, wherein the first mode comprises
simultaneously driving a final drive of the kinetic hybrid vehicle
using a power source that is operated within a peak efficiency
range, and charging a flywheel of the kinetic hybrid vehicle using
the power from the power source that exceeds the power level needed
to maintain the desired vehicle speed, and the second mode
comprises driving the final drive using the flywheel with the power
source decoupled.
11. The method of claim 10, wherein the power source is an internal
combustion engine.
12. The method of claim 10, wherein the power source is powered by
electricity.
13. The method of claim 10, wherein the flywheel is connected to
the continuously variable transmission through an additional gear
set.
14. The method of claim 10, further comprising precharging the
flywheel when the kinetic hybrid vehicle is stopped.
15. The method of claim 10, further comprising simultaneously using
the flywheel and the power source to drive the final drive of the
kinetic hybrid vehicle to accelerate the vehicle when the
accelerative power demand exceeds what the flywheel alone can
provide.
16. The method of claim 11, wherein the variator on the third port
of the continuously variable transmission is a first
motor/generator, and the continuously variable transmission further
includes a second motor/generator on the first port, the method
further comprising using the second motor/generator on the first
port to use up the power generated by the first motor/generator on
the third port of the continuously variable transmission
17. The method of claim 16, further comprising simultaneously using
the flywheel, the engine, the first motor/generator on the third
port and the second motor/generator on the first port to drive the
vehicle in a configuration for the maximum acceleration.
18. The method of claim 16, further comprising decoupling the
engine and charging the flywheel during deceleration.
19. The method of claim 16, further comprising decoupling the
engine and the first motor/generator on the third port, and using
the second motor/generator on the first port as a generator to
recover energy stored in the flywheel to an electric storage
device.
20. The method of claim 16, further comprising decoupling the
engine, using the first motor/generator at the third port as a
motor and using the second motor/generator at the first port as a
generator to drive the final drive at the second port so that the
vehicle drives in reverse.
Description
CROSS REFERENCE TO RELATED APPLICATION(S)
[0001] This application claims priority from a U.S. Non-provisional
patent application Ser. No. 13/193,728, filed Jul. 29, 2011, and
from U.S. Provisional Patent Application Ser. Nos. 61/438,267 filed
Feb. 1, 2011; 61/471,213, filed Apr. 4, 2011; and 61/495,993, filed
Jun. 11, 2011, and which all are incorporated by reference
herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention pertains to a powertrain and method of a
kinetic hybrid vehicle, such as a gas and/or electric powered
vehicle that includes a flywheel. The powertrain and method may be
used to store and use energy of the flywheel device for vehicle
propulsion and optimizing fuel efficiency.
[0004] 2. Description of the Related Art
[0005] Improving fuel economy is an important objective in vehicle
design, since it enables reduced fuel consumption and reduced
emissions. Especially with the current situation of dwindling
fossil fuel resources and worsening environmental conditions, the
end goal of reducing fuel consumption and emissions becomes
particularly important. Although automotive technology has been
advancing and there have been improvements in fuel economy, there
still exists an inherent conflict between fuel economy and
accelerative power in conventional vehicles. In a conventional
vehicle powered by an internal combustion engine, fuel economy is
generally inversely related to vehicle performance, as the engine
generally cannot be downsized to be run at its optimal efficiency
without sacrificing performance. This inverse relationship is due
to the characteristics of the internal combustion engine. IC
engines are at their highest efficiency within a certain speed
range and at a fairly high load, but these conditions constitute
only a small region in the map of all loads and speeds the engine
is operable at. Both gasoline engines and diesel engines exhibit
this characteristic. As a non-limiting example, an engine may be
most efficient running at 2000 RPM and seventy-five percent of its
maximum load. Thus an IC engine achieves its best efficiency at
relatively high power; automotive vehicles, however, require only
low power most of the time. Acceleration performance is seen in how
much reserve power the vehicle has to overcome its own inertia and
increase its speed. The more reserve power, the more quickly the
desired acceleration or speed can be achieved, and the better the
performance of the vehicle. Hence for performance considerations,
the bigger the engine in conventional vehicles, the more reserve
power there is to accelerate the vehicle relatively quickly and
overcome inertia. On the other hand, this means that when the
vehicle is not accelerating, its engine is operating at a lower
load level and lower efficiency state, wasting the maximum
efficiency potential of the engine. If a smaller engine is used,
then the engine will be working at a higher efficiency to improve
fuel consumption, but there will be less reserve power, which means
poorer performance in acceleration. In addition, much of the
vehicle's kinetic energy is dissipated as heat in the brakes when
decelerating, reducing the vehicle's potential fuel efficiency.
[0006] Hybrid vehicle technologies have taken a large step forward
in resolving the compromise between performance and fuel economy.
Hybrid electric vehicles (HEVs), which are equipped with another
power source and energy storage, may recover a portion of the
vehicle's kinetic energy during deceleration, and can use a
downsized engine operating at optimal efficiency consuming the
least fuel for each unit of work done for increased fuel
efficiency. By supplementing the power from a smaller engine with
power from a traction motor, HEVs can run the engine at increased
efficiency compared to conventional vehicles without sacrificing
performance. HEVs can also recover a portion of the vehicle's
kinetic energy during deceleration. Although more efficient and
environment friendly than some conventional vehicles, these
electric hybrids may be difficult to produce without the added
costs of a large traction motor, controller, and electrochemical
and/or electric storage devices. These costs, which may outweigh
the amount of money saved from consuming less fuel, may result in
an increased price to consumers that limits market penetration.
[0007] Aside from cost, a main disadvantage of electric hybrids is
that they are greatly limited in the fuel economy improvements they
can provide. Part of conventional electric hybrids' efficiency
limitations comes from the fact that energy is not stored in the
same form it is used in. When energy from the engine or the vehicle
is stored as electricity, there are multiple conversions from
mechanical to electric, from electric to electrochemical, from
electrochemical to electric, and from electric to mechanical. There
are typically four energy transformations by the time the energy is
used, each resulting in a conversion loss. These conversion losses
typically comprise above one-third the original amount of energy
initially recovered, such as from braking. Another part of
conventional electric hybrids' efficiency limitations comes from
the inherent characteristics of motor/generators and
batteries--namely, their power transfer limitations and reduced
efficiency at high rates of charge and discharge. Even when the
electric storage consists of ultracapacitors, which are highly
efficient at high rates of charge and discharge, the energy
regenerated from deceleration is limited by the power of the
traction motor. Thus only a small portion of the vehicle's kinetic
energy may be recovered via regenerative braking in electric
hybrids.
[0008] To avoid conversion losses and improve fuel economy, an
alternative energy storage device is available: the flywheel, which
can also serve as a power source. As an energy storage device the
flywheel is analogous to electrical storage devices like batteries
and supercapacitors, and as a power source the flywheel can
function similarly to motors. Flywheels have much higher power
density and can give and receive much higher power than
motor/generators, and since flywheels store energy in the same form
that it is to be used in for vehicle propulsion, they are more
efficient than electrical energy storage devices used in hybrid
electric vehicles if the energy is released via a direct mechanical
path. The challenge with flywheels is how to control the amount of
energy transferred. Flywheel systems may use Continuously Variable
Transmissions (CVTs), traditionally mechanical, to store and
release energy. Mechanical CVTs typically achieve only about a 6:1
transmission ratio, and cost quite a bit. In the early days of
flywheel vehicle development and even now in some industrial
applications and Uninterruptible Power Supply (UPS) systems, energy
is stored into and released from the flywheel via one or more
motor/generator(s), traveling a 100 percent electromagnetic path
from source to destination; these flywheel systems also suffer
multiple energy conversions and limited efficiency due to
conversion losses. With these methods the flywheel was used only as
an energy storage device. More recently, flywheels have been used
with electrically controlled CVTs that have a direct mechanical
path as well as an electromagnetic path for the transfer of power,
increasing efficiency.
[0009] U.S. Pat. No. 7,341,534 by Schmidt discloses an electrically
variable hybrid transmission and powertrain equipped with a
flywheel energy storage device. In this configuration, based on
modifying a conventional Internal Combustion Engine (ICE)
driveline, the engine is coupled to the final drive through a
torque converter, an automatic transmission, and the transmission
shaft. The final drive may include a drive shaft, a differential, a
set of fixed gears, and wheels, but does not include a
transmission. Meanwhile, the flywheel is coupled to the final drive
through a three way power split transmission wherein a first
input/output port is coupled to the flywheel, a second is coupled
to a motor/generator, and the third is coupled to the transmission
output shaft. The motor/generator and the planetary gear set
comprise a CVT between the flywheel and the transmission output
shaft so that part of the energy recovered by the flywheel from the
wheels is transferred through a purely mechanical path The
motor/generator controls the transfer of energy between the
flywheel and the vehicle by adjusting the speed of the port to
which the motor/generator is connected, which in turn affects the
speeds of the other two ports of this CVT for the flywheel. The
placement of the flywheel and its CVT is after the transmission of
the engine, so the variator motor/generator in the flywheel's CVT
must operate over a wide range and needs two planetary gear sets to
perform the right function. Also, two transmissions are required;
an automatic transmission for the engine and the three port power
split CVT for the flywheel.
[0010] Document US2010/0184549 by Sartre, et. al discloses a
similar configuration for the same purpose of energy recovery.
Unlike Schmidt, the flywheel energy recovery system for Sartre is
located between the engine and the engine's transmission. It takes
advantage of the engine's transmission so that the energy recovery
system is more independent from the vehicle speed than that in U.S.
Pat. No. 7,341,534. The variator motor/generator for the flywheel
operates over a narrower range than in Schmidt.
[0011] In both the configurations of Schmidt and Sartre, the CVT
for the flywheel is a three way power split transmission embodied
by planetary gears and at least one motor/generator to vary the CVT
ratio for the aforementioned power split transmission. Both use
three-port power split devices as transmissions only for the
flywheel, so the engine needs a separate transmission. Another
disadvantage is that both systems may have critical points where
the variator motor/generator approaches zero speed (stall state,
maximum current) and the system has poor efficiency unless the
effect is mitigated through other means such as by mechanically
braking the variator port when the motor/generator approaches zero
speed. In the prior art, the electrically controlled CVTs used to
control the flywheel comprised planetary gear systems with three
input/output ports. Even where there was more than one planetary
gear system used, one of the ports of the additional planetary gear
system was fixed, with the remaining two ports functioning as fixed
gears, and only one planetary gear set was used to vary speed.
[0012] Both the configurations of Schmidt and Sartre have coupled
the engine and the final drive on the same port of the power split
transmission. With the engine and the final drive both connected to
the same port on the power split transmission, another transmission
may be needed between the engine and the final drive to vary the
relative speeds of the engine and the final drive. In these
configurations, the CVT only serves the flywheel, so the engine
needs its own separate transmission.
SUMMARY OF THE INVENTION
[0013] The conventional power split CVTs used in conjunction with a
flywheel have three input/output ports, and may include an
additional planetary gear set for gear reduction rather than as
part of the CVT. In other words, the conventional three-port CVT is
for use with only the flywheel, and a separate transmission is
needed for the engine.
[0014] In the present invention, a number of kinetic hybrid systems
and methods are demonstrated. Three-port power split CVTs and
four-port compound power split CVTs that do not require a separate
engine transmission are used in configurations and methods distinct
from the prior art. Only in retrofit systems that make use of the
existing transmission for the engine does the present invention use
two transmissions. A power split transmission may be a transmission
that includes at least two paths that power can travel through. A
compound power split transmission may be a power split transmission
where the inputs can be split and the outputs can be split.
[0015] One thing is common to all the embodiments of the present
invention: the final drive is connected to its own independent port
and does not share its port with any other power source. The
various power sources (flywheel, motor, and/or engine) may share
the remaining ports in one way or another. In contrast, the
conventional power split CVT's connect the engine and the final
drive to the same port through an additional transmission. For
embodiments using a three-port power split CVT, the present
invention connects and uses the three-port power split CVT in ways
that are distinct from the conventional system and methods.
[0016] In preferred embodiments of the present invention, one port
manipulated by a variator can change the speed ratio between the
other two or three ports. This allows the flywheel of the present
invention to exchange energy with the vehicle, and it can also
change the speed ratio between the engine and the final drive,
allowing the engine to effectively transfer power to the vehicle's
wheels across a full range of vehicle speeds. In other words, the
flywheel and the engine can share a single CVT.
[0017] In one aspect, a flywheel hybridizes a single motor electric
vehicle. The flywheel (the kinetic power source and kinetic energy
storage), the motor (the variator and electric power source), and
the final drive each have their own independent input/output
port.
[0018] In another aspect, a flywheel hybridizes a dual motor
electric vehicle. One motor, as variator, is connected to a third
port, the final drive is connected to a second port, and the other
motor serving as the electric power source and the flywheel serving
as the kinetic power source and energy storage share the first
port.
[0019] In further aspects, a conventional vehicle with an IC engine
is hybridized into a kinetic-gas hybrid system. The variator and
the final drive each has its own independent port while the
flywheel and engine can either share the first port and use the
same transmission simultaneously in a four-port configuration, or
connect to the CVT in a three-port configuration through clutches,
using the CVT in turns. The final drive is connected to a second
port and the other motor, as variator, is connected to a third
port. None of the above configurations need a second transmission,
reducing cost.
[0020] In a preferred aspect of the present invention, a four-port
compound split transmission, as used in the present invention,
ensures that there are enough independent ports for the engine, the
final drive, the flywheel and the variator motor/generator to be
separately coupled. However, the engine and the motor/generator
used for propulsion may share a port. The compound split CVT can be
considered as comprised of two CVTs, one for the engine and the
other for the flywheel. No other transmission is needed. It should
be noted that the compound split CVT of the preferred embodiments
of this invention is not equivalent to two separate CVTs that do
not have direct feedback.
[0021] In a further aspect, the invention consists of a flywheel,
an electrically controlled continuously variable transmission with
preferably four ports for input/output, a prime mover, a control
unit, and a plurality of gears working together to provide the
vehicle with a powertrain, an additional power source, energy
storage, and an energy recovery system. The prime mover used with
the invention may be either an internal combustion engine or a
motor/generator. The prime mover, the flywheel, the CVT variator,
and the final drive are coupled to separate ports, allowing the CVT
to be used for both the prime mover and the flywheel. As a kinetic
energy storage device, the flywheel stores energy in the same form
it is used in. When provided a direct mechanical path by the CVT
for transfer of energy between the flywheel and the vehicle, the
flywheel can recover the vehicle's kinetic energy during
deceleration as well as directly power the drivetrain to drive the
vehicle during acceleration or cruise, all with minimal energy
conversion and conversion losses because of the direct mechanical
transfer of energy. Using the flywheel as a secondary mover can
also result in higher performance since flywheels have a much
higher power density than motors or batteries. In an embodiment
where the prime mover is a traction motor, an engine may be coupled
to the same port to extend the vehicle's range. In an embodiment
where the prime mover is an internal combustion engine, a torquer
motor/generator may share the same port to improve efficiency.
[0022] When the IC engine is configured to be the primary power
source and the flywheel is configured to be the secondary power
source and energy storage, the system is configured as a kinetic
hybrid vehicle. When the IC engine is not used, the torquer motor
is configured to be the primary power source, and the flywheel is
configured to be the secondary power source and energy storage, the
system is configured as a kinetic-electric hybrid vehicle. In a
four port compound CVT, the speed change in any input/output port
may cause speed changes in the other ports; therefore, with
appropriate methods to control the variator motor/generator, both
the engine and the torquer motor/generator can be controlled as
well so as to exchange energy between the flywheel and the
vehicle's wheels, to pass energy from the engine and/or torquer
motor/generator to the vehicle's wheels, to pass energy from the
engine and/or torquer motor/generator to the flywheel, and even to
pass energy from the flywheel through a motor/generator to charge
the battery pack. Besides physical embodiments or configurations,
good control methods are also important to achieving fuel economy.
The vehicle's operation during driving can typically be classified
into two states: a first state where the vehicle's speed is
significantly changing, such as during acceleration and
deceleration, where inertia and change in the vehicle's kinetic
energy are involved, and a second state where the vehicle's speed
is not changing significantly, such as during cruise. In the first
state both high efficiency and high performance are desired,
whereas in the second state only high efficiency is desired, since
there is no appreciable change in the vehicle's speed.
[0023] In yet another aspect of the invention, a "de-inertia
operation" method is provided for controlling the flywheel with the
powertrain so that the vehicle's inertial effects are drastically
reduced. The flywheel can be precharged so that when the vehicle's
kinetic energy is low (vehicle speed is low or zero), the flywheel
is at its maximum energy level. The flywheel provides most of the
power used to launch the vehicle from rest, starts the engine, and
continues to participate in accelerating the vehicle, thus helping
the vehicle overcome its rest inertia. There is an inverse
relationship between the kinetic energy in the flywheel and the
kinetic energy in the vehicle's wheels: the higher the vehicle
speed, the lower the amount of energy stored in the flywheel. When
deceleration is desired, the energy in the flywheel may be at a
relatively low level, and the flywheel can be charged back up to a
higher energy level using the vehicle's kinetic energy. The lower
the vehicle speed, the higher the amount of energy recovered in the
flywheel. Once deceleration is over, the recovered energy in the
flywheel may be used to accelerate the vehicle in the next
acceleration maneuver. In doing so, the flywheel helps the vehicle
to decelerate, helping reduce the effects of the vehicle's moving
inertia, which improves performance. It also improves efficiency by
recovering energy during deceleration and reusing that energy for
the next acceleration. This method provides optimal efficiency and
performance while the vehicle speed is changing, enabling
downsizing of the engine and the motor/generators compared to
conventional vehicles and hybrids. More specific steps to this
method will be described later with reference to the drawings.
[0024] Still another aspect of the invention provides a optimized
efficiency cruise method for controlling the powertrain to provide
power to the vehicle during cruise (when the vehicle's operator
does not desire acceleration or deceleration). In conventional
vehicles, when there is no need for acceleration, such as during
cruise, when there is no appreciable speed or kinetic energy
change, the engine load is relatively low, since there are only air
drag and rolling resistance to overcome, and efficiency is low. The
system and methods of the present invention can raise the engine
load and splits excess power generated from raising the load to the
flywheel. The flywheel can be charged while the vehicle is in
motion, and the engine is continuously run in its most efficient
state (e.g. within a range of speeds and within a range of load
that correspond to the engine's maximum efficiency). With the
engine running at its optimal efficiency, its output is suitably
divided between the flywheel and the vehicle. When the energy in
the flywheel reaches a certain level, the engine is turned off and
decoupled from the rest of the powertrain; the vehicle is then
driven by the flywheel until the energy in the flywheel reaches a
lower level or setting. At that point, the engine is coupled to the
powertrain again to charge the flywheel. This method of
alternatively using the engine to simultaneously charge the
flywheel and drive the vehicle, and then decoupling the engine to
let the flywheel drive the vehicle, allows for the engine to be run
in a start-stop manner. Although electric hybrids may also operate
the engine in a start-stop manner, it is often not practical for
them to do so because of multiple stage energy conversion losses.
Since the system of the present invention minimizes conversion
losses, it is beneficial to operate the engine this way more
often.
[0025] Whenever the engine is on, it is run in its highest
efficiency state within a certain speed range and preferably a
certain load, which can be adjusted or shared by the optional but
beneficial torque motor/generator on the same port. Whenever the
flywheel is driving the vehicle, the engine is off, and the vehicle
consumes no fuel. The speeder motor/generator, or the variator,
ensures that a constant power is delivered to the wheels so that
the vehicle remains in cruise, regardless of whether it is driven
by the engine or the flywheel. Hence, this method optimizes
efficiency during cruise. Cruise includes situations where the
vehicle operator does not intentionally accelerate or decelerate;
in one non-limiting example, the vehicle speed might change
slightly with road conditions such as a slope or incline that does
not lead the vehicle operator to appreciably change the position of
the throttle. Variations for a vehicle powered by a traction motor
as the prime mover are also provided.
[0026] An additional aspect of the invention provides a motorless
configuration, also capable of directing the storage and release of
energy to and from a flywheel to benefit vehicle propulsion.
Instead of using motors or a more complicated mechanical
transmission, this configuration uses just planetary gearing and
either a set of brakes or a slip clutch and a brake as
variators.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 illustrates some efficiency factors and calculations
to point out some of the current limitations in the overall
efficiency of an electric vehicle;
[0028] FIG. 2 shows an embodiment of the present invention for an
electric vehicle;
[0029] FIG. 3 depicts various vehicle operation states for
effective use of the embodiment illustrated in FIG. 2;
[0030] FIG. 4(a) illustrates one possible way of combining the
embodiment of FIG. 2 into an existing vehicle;
[0031] FIG. 4(b) illustrates a wheel hub implementation of the
system described in FIG. 2 as a mechanical schematic;
[0032] FIG. 5 shows a dual motor embodiment of the invention for an
electric vehicle;
[0033] FIG. 6 depicts various operation states associated with the
dual motor embodiment of FIG. 5 for an electric vehicle;
[0034] FIG. 7(a) shows a possible way of placing the dual motor
embodiment into an existing vehicle with an engine to form a hybrid
vehicle with three power sources;
[0035] FIG. 7(b) illustrates a wheel hub implementation of the
system described in FIG. 5 as a mechanical schematic;
[0036] FIG. 8 shows an embodiment of the present invention for a
vehicle having an engine as its prime mover, wherein the engine and
the flywheel share in turn a three-port power split device as an
electrically continuously variable transmission;
[0037] FIG. 9 demonstrates in more detail how the "share-in-turn"
configuration of FIG. 8 can be controlled;
[0038] FIG. 10(a) presents an embodiment of the invention for a
vehicle having an engine as its prime mover, wherein the engine
shares a port of the CVT with the flywheel through a clutch;
[0039] FIG. 10(b) presents a variation upon FIG. 10(a) where
instead of clutches the embodiment features a second planetary gear
set with a brake, enabling the selective coupling or decoupling of
the engine from the system without needing slip clutches, making
for a clutchless embodiment;
[0040] FIG. 11 shows various operation states over a range of
vehicle demands for the equivalent embodiments of FIG. 10(a) and
FIG. 10(b);
[0041] FIG. 12(a) illustrates a unique motorless embodiment of the
present invention where a pair of brakes act as variators to store
energy to and release energy from the flywheel;
[0042] FIG. 12(b) is an equivalent embodiment that is also
motorless, using a clutch and a brake instead as the method of
control for storing and releasing energy to and from the
flywheel;
[0043] FIG. 12(c) shows how the motorless brake-based embodiment of
FIG. 12(a) may be used to turn a conventional vehicle into a
hybrid;
[0044] FIG. 12(d) is a mechanical schematic of the brake-based
embodiment of FIG. 12(a);
[0045] FIG. 13 illustrates the preferred embodiment of a hybrid
powertrain with a flywheel and a four port compound split CVT;
[0046] FIG. 14 is a mechanical schematic for the preferred
embodiment;
[0047] FIG. 15 is a graphical representation of the method of
de-inertia operation, and shows how the kinetic energy in the
vehicle and the kinetic energy in the flywheel as vehicle speed
changes;
[0048] FIG. 16 presents the rotational speeds of the separate ports
of the four port compound CVT in the preferred embodiment across a
range of vehicle speeds during de-inertia method operation;
[0049] FIG. 17 demonstrates how the engine and the flywheel work
together for the method of optimized efficiency cruise;
[0050] FIG. 18 depicts various vehicle operation states that can be
implemented to effectively use the preferred embodiment for both
efficiency and performance over a range of vehicle demands;
[0051] FIG. 19 is a flowchart for controlling a preferred
embodiment and for de-inertia methods of acceleration and
deceleration;
[0052] FIGS. 20(a), 20(b), and 20(c) are flowcharts depicting
stationary, reverse, and restore operations of a preferred
embodiment;
[0053] FIG. 21 is a flowchart for optimized efficiency of a cruise
mode for a hybrid vehicle with an engine as its prime mover;
[0054] FIG. 22 shows a second four-port embodiment of the present
invention;
[0055] FIG. 23 is a third four-port embodiment of the invention;
and
[0056] FIG. 24 is a fourth four-port embodiment of the
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0057] Embodiment(s) of the present invention are described herein
with reference to the drawings. In the drawings, like reference
numerals represent like elements.
Current Limitations of Electric Vehicle Propulsion Systems
[0058] Although both fuel efficiency and performance are desired in
vehicles, they are conflicting goals in the design of a
conventional vehicle powered by an internal combustion engine. High
performance vehicles are equipped with large engines but suffer
from poor efficiency, whereas fuel efficient vehicles lack
performance.
[0059] Gas-electric hybrid vehicle technologies have made
considerable advances in resolving the deadlock conflict between
fuel efficiency and accelerative performance. These hybrid electric
vehicles, or HEVs, rely on a downsized engine that works at a
better efficiency converting fuel to mechanical power, while a
motor, as a secondary mover, supplements power to compensate for a
smaller engine's lack of reserve power for acceleration. In
addition, HEVs can recover part of the vehicle's kinetic energy
with a generator during deceleration, which is typically wasted and
completely dissipated as heat in the brakes when conventional
vehicles are decelerated.
[0060] Yet there still remains a core problem in vehicle propulsion
using electric power. Powering the vehicle with an electric machine
requires an electrical energy storage (henceforth referred to as a
battery pack, with the understanding that the "battery pack" can be
any combination of different electrical energy storage devices,
such as batteries and/or supercapacitors). The disadvantage to
using an electric power source is that energy is not stored in the
same form that it is used in. Even if each energy conversion can be
performed at a high efficiency each stage, having multiple stages
of energy conversion (such as in vehicle propulsion, where energy
is converted from a mechanical form to an electric form and then to
electrochemical form when energy from the engine or from
regenerative braking is stored into the battery pack through a
generator and inverter, then released and used to the vehicle's
drivetrain, undergoing conversion from electrochemical to electric
to mechanical form) results in considerable conversion losses.
Conversion losses significantly limit fuel efficiency; this is a
problem common to electric vehicles as well as to the electric
system components of hybrid vehicles. Another problem frequently
encountered by electric hybrid vehicles and by many electric
vehicles is that the higher the rate of charge and discharge of
power to and from the batteries, the less efficient the
transformation of energy will be.
[0061] FIG. 1 illustrates the energy conversion efficiency rates
for the batteries and motor/generator(s) of a typical electric
vehicle under various conditions or vehicle operation demands. Such
a vehicle is powered by a motor/generator 01 (which can also be
known as an electric machine or a traction motor), which draws
energy from the battery pack 05 through a controller/inverter 03;
the output from the motor 01 is then transmitted to the final drive
or gearbox 32 via the transmission 11; from the final drive 32, the
output torque from the motor/generator 01 drives the vehicle's
wheels 34 through the wheel axes 36. The element 07 of FIG. 1
refers to the inset curve representing the efficiency of the
battery as it varies with the charge or discharge rate, C. C
denotes a charge or discharge rate equal to the capacity of a
battery in one hour, so for example, a battery pack that has 6.5 Ah
capacity would charge or discharge at a rate of 6.5 A or 1 C with
96 percent efficiency but would charge or discharge at a rate of 65
A or 10 C with 73 percent efficiency. From the inset curve 07, it
can be seen that efficiency is inversely proportional to the rate
of charge or discharge. The faster the rate of charge or discharge,
the lower the efficiency; when charging, energy is converted from
an electrical form into a chemical form to be stored in the
batteries, and when discharging energy from the batteries, the
energy is converted to an electrical form for use by a motor. 08
and 09 are also inset curves, respectively showing the efficiency
mapping of the motoring mode and the efficiency mapping of the
generator mode of the same motor/generator. When the torque
direction is in the same direction as motion, the motor/generator
01 is functioning as a motor, converting electrical energy into a
mechanical form to propel the vehicle, and the motor's efficiency
in this state as rotational speed and torque vary is depicted by
inset curve 08, above the horizontal axis, where torque is
positive. When the torque direction is opposite to the direction of
motion, the motor/generator 01 is functioning as a generator,
converting mechanical energy into electricity to charge the battery
pack, and its efficiency in this state as rotational speed and
torque vary is depicted by inset curve 09, below the horizontal
axis, where torque is negative. Overall electric system efficiency
can be analyzed in the following cases.
[0062] Acceleration--accelerative vehicle demands include
overcoming inertia and various resistive forces acting on the
vehicle, and a large amount of accelerative power is desired. In
order to provide such power, the battery pack 05 would typically be
discharged at a relatively high rate, as shown by point a on the
inset curve 07; conversion efficiency as the energy stored in
electrochemical form is transformed into electricity is 77 percent
as the inverter 03 supplies current to the motor 01. Because the
motor 01 typically works at high torque and low RPM when converting
electrical energy to a mechanical form during acceleration, around
point d on the inset curve 08, the combined efficiency of the
inverter 03 and the motor 01 is around 80 percent. Overall
efficiency is then 62 percent (0.77*0.80=0.62).
[0063] Steady speed (cruise)--during cruise, the vehicle need only
overcome air drag and rolling resistance, as the kinetic energy of
the vehicle need not change. Thus the demand on electrical current
is low and the motor 01 would work at moderate speed and torque.
The battery pack 05 can work near point b and achieve 96 percent
efficiency, while the motor 01 and inverter 03 can work around
point f and reach 84 percent efficiency. Overall efficiency is then
81 percent (0.96*0.84=0.81).
[0064] Regenerative braking--when the vehicle needs to be
decelerated, the power demand on the generator 01 and the battery
pack 05 is usually greater than acceleration power demands. For
simplicity, however, assuming that the charge rate of the battery
pack 05 and torque demands of the motor/generator 01 are
symmetrical to the case for acceleration, the battery pack 05 works
again around point a, and the generator 01 would work near point h.
In regenerative braking, kinetic energy from the vehicle's wheels
34 is transmitted through the wheel axes 36 and the final drive 32
to the transmission 11 and the generator 01 to be converted into
electricity. From the generator 01, the electricity is passed to
the inverter 03 and the battery pack 05, where electricity is
transformed into a chemical form and stored. In the next
acceleration maneuver, this energy conversion process is reversed,
and the chemical energy in the battery pack 05 must be converted
into an electrical form and then a mechanical form before it can
accelerate the wheels 34. The path energy recovered from
deceleration must traverse (through the motor 01 operating around
point d) to reach the wheels 34 again thus involves four energy
transformations, and the resulting efficiency is 38 percent
(0.80*0.77*0.77*0.80). If other mechanical transmission losses and
the use of other means to slow down the vehicle are considered,
then efficiency is even lower.
[0065] It should be noted that the highest efficiency does not
occur where the motor/generator 01 or the battery pack 05 is most
efficient, but where the multiplicative product of their
efficiencies is maximum, as it is unlikely that the motor/generator
01 and the battery pack 05 will both operate at optimal efficiency
simultaneously. For example, when the motor/generator 01 works
close to its most efficient around point e or g, the battery pack
05 may be operating around point c, so that the overall system
efficiency is highest at 86 percent (0.94*0.91=0.86).
[0066] Thus it can be seen that in vehicles relying upon electric
machines for propulsion, efficiency can fluctuate quite a bit.
Especially in situations calling for acceleration or deceleration,
the amount of energy lost to conversion is significantly,
particularly when large currents are needed or produced. Another
factor to consider is that battery lifespan is inversely
proportional to the number of charge/discharge cycles and the
"depth" to these cycles. Reducing the rates of charge and discharge
also prolongs battery life. In summary, to improve efficiency in
electric systems for vehicle propulsion, it is important to use the
motor/generator 01 and the battery pack 05 under conditions
resulting in high efficiency, and it is important to avoid
converting energy to be stored into the battery pack as much as
possible, by reducing the rate (electric current) and the number of
cycles of charge and discharge in the battery pack.
[0067] Supercapacitors and ultracapacitors can directly store
energy in the electrical form, which is an improvement upon battery
alone, because capacitors only require two energy conversions
instead of the typical four conversions with batteries. These
capacitors have higher power density than batteries, but their
disadvantage is low energy density. The combination of capacitors
and batteries into a battery pack can increase efficiency and
extend battery life.
[0068] Should it be possible to directly store and release kinetic
energy and minimize energy conversions, efficiency can be
improved.
The Characteristics and Advantages of the Flywheel as a Mechanical
Storage and Mechanical Power Source
[0069] When it comes to vehicle propulsion, there is a fundamental
truth: the ultimate form of energy the vehicle gains and uses is
mechanical, and to be more specific, kinetic. If a kinetic power
source and energy storage replace electric machines and electrical
storage as a secondary power source or the secondary mover, then
the vehicle would become a kinetic-gas hybrid. Furthermore, if the
prime mover is not an internal combustion engine but an electric
system, then the resulting combination of a kinetic secondary mover
with an electric prime mover produces a kinetic-electric hybrid.
(Note that the definition of hybrid used here refers to any vehicle
having two or more sources of power for propulsion. There is a
prime mover or primary power source, and a secondary mover or
secondary power source, along with an energy storage that is used
by the secondary power source; the energy supplied to the secondary
power source generally comes from the prime mover, or from
recovering the kinetic energy of the vehicle.) With a kinetic power
source, the vehicle may directly use the stored energy without need
for energy conversion, at least in a portion of the stored energy,
or a majority of the stored energy, to move the vehicle, improving
overall efficiency. (100 percent of the energy the vehicle uses
from electric power sources must undergo conversion.)
[0070] Flywheels make for both a kinetic energy storage and a
kinetic power source; a flywheel is analogous in function to both a
battery pack (energy storage) and a motor/generator (power source
and a means for recovering energy) combined into one device. A
major benefit of a flywheel is that the form of the energy stored
is kinetic, which is the same form of energy that the vehicle needs
to use. Hence there are no energy conversion losses, only energy
transmission losses. This characteristic provides the basis for
improving fuel economy.
[0071] Another important characteristic of the flywheel is its
extremely high power density, easily over ten times the power
density of electric machines for vehicle propulsion. As flywheels
can output or absorb large rates of power while still remaining
lightweight, they can vastly improve the vehicle's performance.
Flywheels have considerable energy density as well, which is an
often neglected fact. Some flywheels may have more energy stored
per unit weight than any type of battery. Unlike batteries,
flywheels do not suffer degradation from use, and can easily
outlast vehicle lifetimes. They do not create hazardous byproducts
or wastes either in the manufacturing process or disposal.
Flywheels also have a simple, cost-effective structure; they are
simply a solid mass of material in a simple shape.
[0072] Owing to the aforementioned advantages, effective use of
flywheels for vehicle propulsion may increase efficiency, reduce
emissions, improve the vehicle's performance, and reduce cost of
manufacture compared to electric hybrids comparable in power and
size. The challenge is in how to utilize a flywheel just so to make
the best use of the flywheel's characteristics for vehicle
propulsion.
Basic Configuration of a Kinetic-Electric Hybrid System, with
Methods
[0073] FIG. 2 shows a configuration for a vehicle with both a
traction motor 01 and a flywheel 10 as power sources. This
configuration is that of a kinetic-electric hybrid vehicle equipped
with a three port CVT; on the basis of an electric vehicle, there
is now a flywheel. With the traction motor 01 as the prime mover,
this embodiment adds the flywheel 10 as a secondary power source
and energy storage to an electric vehicle, making for a single
motor kinetic-electric hybrid vehicle. Compared to the electric
vehicle of FIG. 1, the embodiment features the flywheel 10, and the
transmission 11 of FIG. 1 has been replaced by the planetary gear
set 12. The planetary gear set 12, which is the core structure of
the system, is a power split CVT with three input/output ports: the
ring gear R, connected to the rotor of the motor/generator 01 as
both the prime power source and as the variator; the sun gear S,
connected to the flywheel 10 with a one-way clutch 24, which
prevents the flywheel (the secondary power source and kinetic power
source) from spinning in the reverse direction; and the planetary
carrier C, coupled to the final drive 32 (through an output shaft
33), which transmits power to the wheels 34. The planetary gear set
12 is the transmission for the motor/generator 01, and these two
combined comprise the transmission for the flywheel 10. The
motor/generator 01 adjusts the speed of the ring gear R, which in
turn variates the speed and torque of the carrier gear C and the
sun gear S to control the exchange of energy between the vehicle
and the flywheel. The energy for the motor/generator 01 is supplied
by the battery pack 05 through the controller/inverter 03. There is
also an interface 62, which connects to the vehicle's ECU 60 to
gather relevant real-time data to help control the two power
sources so that through the exchange of energy in the system,
better efficiency and fuel economy is achieved. A variator may be a
mechanism or device that can change its parameters, or parameters
for other devices. For example, in an embodiment, a variator may be
a mechanism through which the speed ratio in the planetary gear
sets can be altered to correspondingly adjust the overall
continuously variable transmission ratio.
[0074] The transmission in FIG. 2 need not be a power split device
actualized as a planetary gear set 12, but the power split device
shown here has its advantages--it provides a transmission to both
the motor/generator 01 and the flywheel 10 using an extremely
simple and cost-effective design. Changing the speed and/or torque
on any one of the three input/output ports changes the speed and/or
torque of the other two ports. The planetary gear set 12 is the
transmission for the motor/generator 01. Together, the planetary
gear set 12 and the motor/generator 01 comprise the continuously
variable transmission for the flywheel 10. Since the
motor/generator 01 can manipulate the speed and torque on the ring
gear R, the speed and the torque of the planetary carrier C and the
sun gear S can be varied, enabling the exchange of kinetic energy
between the flywheel 10 and the wheels 34. The relationship of the
motion of the three input/output ports in a planetary gear set can
be expressed in the following equation:
(k+1).omega..sub.c=k.omega..sub.r+.omega..sub.s (1)
[0075] Where .omega..sub.c, .omega..sub.r, and .omega..sub.s are
respectively the speeds of the planetary carrier C, the ring gear
R, and the sun gear S, and the constant k represents the physical
gear ratio between the ring gear R and sun gear S.
[0076] Even with an appropriate physical embodiment, the hybrid
system must have an appropriate method of control to increase fuel
efficiency effectively using a flywheel. FIG. 3 depicts different
operation states for controlling the vehicle from the beginning to
the end of a journey. In FIG. 3, the components of the system and
their connections are simplified. M or G denotes the
motor/generator 01, W denotes the vehicle's wheels 34, F is the
flywheel 10, and B is the battery pack 05. For convenience, the
final drive 32 has been omitted from FIGS. 3(a) through 3(i), and
it is assumed that the speed of the planetary carrier C is
proportional or equal to the speed of the wheels W. In the
rotational diagrams representing the planetary gear set 12 and its
ports, the thick filled arrows represent motion direction, and the
thick unfilled arrows represent torque direction. In the component
representations, a broken line signifies that for those components
there is temporarily no connection or interaction. A solid line
with an arrow indicates direction of energy flow or transfer. A
solid line without an arrow means that the component connected to
the planetary gear set is inactive, and there is also no energy
transfer into or out of that component.
[0077] At the start of the drive or when stopped at an
intersection, the hybrid system can pre-charge the flywheel F, as
shown in FIG. 3(a). From equation (1), we can determine that when
the vehicle is braked and the wheels W and .omega..sub.c=0,
.omega..sub.s=-k.omega..sub.r. It is assumed that the forward
direction of motion in the vehicle's wheels W is clockwise in the
planetary gear set 12 for the non-limiting examples of FIG. 3. As
long as the motor M rotates the ring gear R in the counterclockwise
direction (CCW) by some .omega..sub.r, the flywheel F will spin in
the clockwise (CW) direction at .omega..sub.s=-k.omega..sub.r. In a
non-limiting example, when the physical gear ratio k between R and
S is 4, when the speed of M reaches 2500 RPM, F will reach 10000
RPM. It should be noted that in the rotational diagram of FIG. 3(a)
the gear turning in the CCW direction between the sun gear and the
ring gear represents planetary pinion gears, which do not indicate
the motion of the planetary carrier port but serve as a direct
mechanical path for the power transfer between the ring gear port
of the ring gear R and the sun gear port of the sun gear S. Hence,
according to the operation state depicted in FIG. 3(a), the motor M
can operate at a suitably low current so that the combined
efficiency of the motor M and the battery pack B is optimal during
this phase of pre-charging the flywheel F.
[0078] FIG. 3(b) shows that once the flywheel F is charged and
acceleration is desired, the vehicle's brakes are released, and the
motor/generator G reverses the direction of its torque to act as a
generator, reducing the speed of the ring gear R by providing a
braking torque in the direction opposite that of motion. The sun
gear S obtains a reaction torque from the ring gear R, allowing for
the release of energy from the flywheel F. Energy from the flywheel
F is split into two paths: the majority of the power flows from S
to C to accelerate the vehicle's wheels W, while a small portion is
used by the generator G to produce the braking torque on R, which
also charges the battery pack B in the process. In this operation
state for acceleration the speeds of the flywheel F and the
generator G, as well as the sun gear port of the sun gear S and the
ring gear port of the ring gear R they are connected to, decrease,
while the speeds of the planetary carrier port and the wheels W
increase. Aside from the small portion of power supplied to the
speed ratio variator G, the transfer of accelerative power from the
flywheel F to the wheels W is extremely efficient, and the
drivability of the vehicle at low speeds is improved by supplying
accelerative power from the flywheel F, which has very high power
density.
[0079] The first acceleration state portrayed in FIG. 3(b) only
works until the speed of the ring gear R drops to zero, which may
happen when very large amounts of accelerative power is needed,
such as at high vehicle speeds. When this is the case, then the
system may be operated in the second acceleration state, as shown
in FIG. 3(c). By the time .omega..sub.r reaches zero, .omega..sub.c
and the speed of the wheels W will have reached 1/(k+1) the
flywheel F's speed, .omega..sub.s. The motor/generator M then
incrementally increases the speed of R in the same direction,
acting as a motor now instead of a generator. At this point the
power received by the wheels W is the sum of the power of the motor
M and the power of the flywheel F. Typically with a power split
device, the motor/generator (either M or G) uses less than
one-third the total power to control over two-thirds of the total
power in the flywheel F.
[0080] From the pre-charge phase to the acceleration phase, the
motor stores energy into the flywheel at a high efficiency and the
flywheel can be controlled to release energy at a high power and a
high efficiency, which explains why the flywheel can increase both
the vehicle's efficiency and performance.
[0081] It should be mentioned that the acceleration at the start of
a journey or drive can also occur without a flywheel pre-charge
phase. In that scenario, although the forward or CW motion of the
motor/generator M (causing the ring gear R to also rotate CW) would
otherwise cause the sun gear S and flywheel F to spin in the
reverse or CCW direction, the one-way cltuch 24 locks down this
port so that .omega..sub.s=0. The planetary gear set 12 then
becomes a fixed ratio transmission with (k+1)/k as the transmission
ratio. To accelerate the vehicle without pre-charging the flywheel
F would therefore involve the motor M working alone at a larger
current and torque (lower efficiency and also lower performance,
since the power density of motor/generators are lower, compared to
operation states 3(a) through 3(c). If the flywheel F is not
pre-charged as in 3(a), then it must wait for the next deceleration
maneuver to be charged and be of use in the subsequent acceleration
maneuver.
[0082] FIG. 3(d) depicts the cruise operation state. In the latter
part of acceleration or during cruise, the energy of the flywheel F
will eventually be released to zero. By then, the motor M will have
already started rotating CW to provide power directly to the wheels
W, no longer serving as the variator for the flywheel F. After
.omega..sub.s reaches zero, the one-way clutch 24 locks the
flywheel F and the port S, preventing them from spinning in the
reverse direction, so .omega..sub.s remains at zero. The motor M
alone provides power to the wheels W, but since during cruise the
vehicle only has to overcome air drag and rolling resistance, the
power required to maintain cruise is not high, and the motor M by
itself can drive the vehicle with a relatively high system
efficiency (the combined efficiency of the battery pack B and the
motor M).
[0083] If the flow of energy from the battery pack B to the
motor/generator M/G is stopped, the rotor of the motor/generator
M/G and the ring gear R it is connected to can spin freely without
transmitting torque. Thus both the vehicle's wheels W and the
flywheel F can remain in the same state, and do not affect one
another (as there is no torque on the ring gear R). This is
equivalent to a neutral state, seen in FIG. 3(e). If the vehicle
was in motion, it will remain in motion, which is considered
coasting. If the vehicle was stopped, it will remain stopped.
[0084] During deceleration, if the speed of the flywheel F is less
than k+1 times the vehicle speed (also expressed as
.omega..sub.s<(k+1).omega..sub.c) then the motor/generator G
acts as a generator, applying a torque in the CCW direction
opposite the CW direction of motion, reducing the speed
.omega..sub.r of the ring gear R, depicted in FIG. 3(f). The
reaction torque produced and the decrease in .omega..sub.r have the
effect of reducing the speed of the carrier gear port and the
wheels W, and accelerating the sun gear S and the flywheel F in the
forward (CW) direction. The portion of the vehicle's kinetic energy
that becomes stored in the flywheel F is transferred via a direct
mechanical path from the planetary carrier C to the sun gear S at
very high efficiency. The portion of energy required by the
variator G to produce the torque directing the transfer of the
vehicle's kinetic energy into the flywheel F travels an
electromagnetic path and becomes regenerated as electricity and
stored into the battery pack B.
[0085] The second deceleration state, shown in FIG. 3(g), occurs
when the flywheel F has accrued enough energy so that its speed is
greater than k+1 times the vehicle speed, which can be expressed as
.omega..sub.s>(k+1).omega..sub.c. The motor/generator M becomes
a motor to push the ring gear R to spin in the CCW direction to
enable the flywheel F to spin more quickly and store more energy
than is otherwise possible. This second deceleration state
continues until the vehicle speed, or .omega..sub.c, is zero. Of
the total energy stored into the flywheel F, a portion comes from
the vehicle's kinetic energy, and a portion comes from the motor
M.
[0086] To drive in reverse, the operation state depicted in FIG.
3(h) is used. The motor M rotates in reverse, causing the wheels W
to turn in the reverse direction, and charging the flywheel F.
[0087] At the end of the drive, indicated by FIG. 3(i), it may be
desirable to transfer the energy in the flywheel F to the battery
pack B. To do so, the planetary carrier C is mechanically braked so
that w.sub.c=0, and the generator G regenerates the energy from the
flywheel F as electricity to the battery pack B at a small current
and at a high system efficiency.
[0088] With a flywheel as the secondary power source and energy
storage, the motor/generator can work consistently in a high
efficiency state. Especially during acceleration and deceleration,
the motor/generator is not responsible for the entire vehicle's
power, but only a small portion of the total power; because a much
larger portion of the vehicle's power comes from the flywheel, the
power requirements of the motor/generator are lowered. Furthermore,
because the flywheel can handle a significant portion of energy
storage and release at a high rate, the portion of energy that
passes through the battery pack is reduced, not only increasing the
efficiency (less energy conversions) but also extending the battery
pack's life.
[0089] In summary, compared to conventional electric vehicles, a
kinetic-electric hybrid vehicle has the following advantages. It
increases fuel efficiency by enabling the motor/generator and the
battery pack to continuously work at high efficiency, through
decreasing the charge or discharge rate of the battery pack. It
also increases accelerative performance, since the flywheel has a
much higher power density than a motor/generator, and for
acceleration both the flywheel and motor/generator can contribute
their power. A kinetic-electric hybrid vehicle can also reduce the
cost of the vehicle since it allows for downsizing of the
motor/generator and extends the life of the battery pack (it uses
the flywheel as an energy storage buffer, decreasing the number of
charge/discharge cycles).
[0090] As a variation, the kinetic-electric hybrid system described
in FIG. 2 may be placed in an existing vehicle. In a non-limiting
example, the configuration of FIG. 2 may be placed at the rear
wheels 34 of a front wheel drive vehicle powered by an IC engine
20, forming a retrofit four wheel drive kinetic-gas-electric hybrid
vehicle seen in FIG. 4(a).
[0091] FIG. 4(b) illustrates another implementation where the basic
kinetic-electric hybrid configuration of FIG. 2, including the
motor, flywheel, and the planetary gear system, is installed inside
a wheel hub. S is the sun gear, C is the planetary carrier gear
connected to the wheel hub, and R is the ring gear of the planetary
set 12; the flywheel 10 is connected to the sun gear S in the
housing 110. The one-way clutch 24 which prevents the flywheel from
spinning in reverse is connected to the sun gear S. There is also a
motor/generator stator 101, which is fixed to the chassis, and a
motor/generator rotor 103, which is connected to the ring gear R.
The mechanical brakes 50 of the wheel 34 are drawn, as is the tire
39. This implementation is ideal for modifying or upgrading an
existing wheeled vehicle to a hybrid, since it features the
advantages of convenience, space conservation, and
cost-effectiveness in addition to increasing fuel efficiency and
providing more accelerative power. This configuration may also be
implemented to drive electric vehicles, electric motorcycles, and
hybrid motorcycles.
Dual Motor Kinetic-Electric Hybrid System and Methods
[0092] There is room for improvement for the basic hybrid system
configuration. FIG. 5 demonstrates a kinetic-electric hybrid system
using two motor/generators, 01 and 02. The major difference in this
configuration compared to FIG. 2 is the addition of the
motor/generator 02 on the sun gear S of the planetary gear set 12
along with the controller/inverter 04 for the motor/generator 02.
There is also the addition of a DC bus 06, which supplies both the
controller/inverters 03 and 04 with current from the battery pack
05. The physical gear ratio of the ring gear R to the sun gear S,
k, is reduced compared to the single motor configuration. With a
smaller value of k, the difference in speeds between the
motor/generator 01 and the motor/generator 02 is less likely to be
so great that it affects efficiency. Everything else remains the
same as the basic configuration of FIG. 2, except that the flywheel
10 now needs a gear set 17 to increase operation speed. The
additional motor/generator 02 and controller/inverter 04 may
increase cost, but are well worth it in the end, as both efficiency
and ease of control are improved. Further details regarding the
configuration are explained in FIG. 6, which reveals various ways
the system may be used.
[0093] To pre-charge the flywheel F, the dual motor configuration
of FIG. 6(a) can use one of the motors M1 and M2, or both. M1 would
need to rotate in the CCW direction and/or M2 would rotate in the
CW direction to spin the flywheel F CW. Efficiency and the speed of
the flywheel 10 should be the primary factors in determining
whether one or both of the motor/generators is used in the
pre-charge phase. What is illustrated in FIG. 6(a) is the use of
motor M2 only to charge the flywheel F.
[0094] For acceleration, illustrated in FIG. 6(b), the variator G1
produces a torque in the direction opposite the motion of the ring
gear R. The resulting reaction torque transfers power from the
flywheel F to the wheels W. This is the same process compared to
the first acceleration state in the basic single motor
configuration, with the distinction that the electricity generated
by the variator G1 is used by the motor M2 to spin the sun gear S
in the same direction as the flywheel F, instead of charging the
battery pack B. Thus the vehicle is propelled by both the motor M2
and the flywheel F on the sun gear S. There are three advantages to
this change. Firstly, efficiency is increased, since the
electricity generated by the variator G1 is spared two stages of
conversion (electric to chemical, chemical to electric) and the
conversion losses associated. This, in turn, prolongs the life of
the battery pack B, since battery life is inversely proportional to
the number of charge/discharge cycles. Also, by adding the power of
M2 to vehicle propulsion, performance is improved.
[0095] By the time the ring gear R is turning CW, the variator M1
is no longer functioning as a generator, but as a motor; this marks
the second acceleration state, which can be seen in FIG. 6(c). The
motors M1 and M2, as well as the flywheel F, all propel the
vehicle, which is accelerated with the combined torque of all three
power sources.
[0096] The neutral or coasting state shown in FIG. 6(d) is achieved
when electricity is neither supplied to nor generated from the
motor/generators M1 and M2. When the motor/generator M1 is
electrically off, the ring gear R rotates freely, and the vehicle
is in a neutral or coasting state. When M1 and M2 are off, there is
no torque to transfer energy between the vehicle and the flywheel
F, and the rotors of the motors M1 and M2, connected respectively
to port R and port S, spin freely.
[0097] During cruise, the dual motor configuration seen in FIG.
6(e) offers a little more flexibility compared to the single motor
configuration illustrated in FIG. 2. The power that the vehicle
needs during cruise is very little, and especially at lower speeds
the motor may not be able to operate at optimal efficiency.
Increasing the load of a motor may increase efficiency. Hence, in a
dual motor configuration, the motor M2 may charge the flywheel F
while simultaneously driving the vehicle in cruise, raising
efficiency. The amount of energy stored in the flywheel F can be
controlled in real-time while the vehicle is in motion, so that
there can be reserve power for situations calling for sudden
acceleration. The variator G1 can also maintain the transmission
speed ratio at an optimal efficiency so that both motor/generators
G1 and M2 as well as the battery pack B may operate near points c,
e, and g in FIG. 1.
[0098] In the second cruise state depicted in FIG. 6(f), the
flywheel F has accrued enough energy that it is now desired to
release its energy to drive the vehicle. The variator G1 continues
to control the vehicle speed by adjusting the transmission speed
ratio. The motor M2, however, transitions to another operation
state where it only uses the electricity generated by G1 and none
from the battery pack B. When cruising at a low vehicle speed, the
first and second cruise states may be used in turn to improve
efficiency. Also, the kinetic energy can be reserved at a certain
level for possible acceleration demand. At a higher speed, however,
a third cruise operation state may be desired.
[0099] The third cruise state illustrated in FIG. 6(g) depicts the
case when vehicle speed is very high; both the motor/generators M1
and M2 act as motors, ensuring that the CVT ratio is suitable for
high speeds. Equilibrium will be reached so that there is no
transfer of energy into or out of the flywheel F, which merely
serves to stabilize the vehicle speed.
[0100] A fourth cruise state shown in FIG. 6(h) may use the same
mode as the configuration in FIG. 2, where only M1 is used. The
motor M2 is electrically off so that only the variator G1 is in
operation to release energy from the flywheel F; additionally, even
if the energy in the flywheel F is completed depleted, the one-way
clutch mechanism 24 can lock the sun gear S so that the flywheel F
does not affect the drivability of the vehicle when the
motor/generator M1 takes over to propel the vehicle by itself as a
motor at a fixed gear ratio of (K+1)/K. Without the use of the
flywheel F, acceleration will be affected, but the motor M2 is
available to provide more power. It is possible that at the start
of this cruise state, there is excess amount of energy in the
flywheel F; in that scenario, the generator G1 can release the
energy from the flywheel F to the vehicle, before changing its
state of operation to that of a motor M1, to drive the vehicle as
described above.
[0101] Which of these four cruise states is best for efficiency
depends on many conditions and may be determined in real-time by
the vehicle's ECU 62, which can generate signals needed to control
the hybrid system.
[0102] For the first deceleration state, shown in FIG. 6(i), the
variator G1 produces a braking torque on the ring gear R, which is
initially turning in the same direction as the planetary carrier C
and the vehicle's wheels W. The braking torque slows the ring gear
R and the planetary carrier C, but it also speed up the sun gear S
and the flywheel F, thereby passing the vehicle's kinetic energy to
the flywheel F through a mechanical path without conversion. The
electricity generated by G1 may be used by M2 to produce torque and
accelerate (charge) the flywheel F, which extends battery life by
reducing the number of charge/discharge cycles for the battery pack
B.
[0103] The ring gear R will at some point be completely braked by
the torque produced by the variator G1, and will start to turn in
the opposite direction as the planetary carrier C and the wheels W.
This marks the beginning of the second deceleration phase,
illustrated in FIG. 6(j), where the variator M1 works as a motor to
further increase the speed of the ring gear port in the reverse
direction and force more energy from the vehicle into the flywheel
F, until the vehicle speed and the speed of the planetary carrier
port drops to zero.
[0104] When it is desired to drive the vehicle in reverse, the
motor M1 turns the planetary carrier port in the reverse direction
while the generator G2 acts as a variator to produce a braking
torque, so that energy is passed from the ring gear port to the
planetary carrier port, shown in FIG. 6(k). This induces the
planetary carrier port and the wheels W to turn in the reverse
direction also.
[0105] FIG. 6(m) demonstrates how energy may be restored from the
flywheel F to the battery pack B. The motor/generator G2 simply
works as a generator, absorbing the energy from the flywheel F and
regenerating it as electricity to store into the battery pack B
while the motor/generator G1 is off. Since there is no torque on R,
there is no influence to the speed of the vehicle's wheels W. Thus
flywheel energy restoration may be performed when the vehicle is
moving (coasting) as well as when the vehicle is stopped.
[0106] In summary, the dual motor hybrid configuration demonstrated
by FIGS. 5 and 6 offer more flexibility for control and higher
performance while simultaneously improving efficiency by reusing
electricity generated by the variator back into the powertrain
instead of continually recharging the battery pack, which also
extends the battery life.
[0107] A powertrain in an automobile may be the collection of
components that work as a system to generate and transmit power
from a power source to the road surface (e.g., the engine, motor,
flywheel, gears, transmission, and wheels). As shown in FIG. 7(a),
the configuration of FIG. 5 can also be placed into a vehicle
where, as a non-limiting example, an IC engine 20 is the prime
mover driving the front wheels 35 through the transmission 21. The
hybrid system can be connected to the final drive 32 at the rear of
the vehicle and drive the rear wheels 34 through the axes 36. Thus
an existing vehicle combined with the system of the present
invention can be upgraded to a four wheel drive
kinetic-gas-electric hybrid, similar to FIG. 4(a).
[0108] Another implementation is illustrated in FIG. 7(b). Here,
the motor/generators 01 and 02, the flywheel 10, and the planetary
gear set 12 are all built into a wheel hub; besides better
efficiency and performance, this implementation basically has the
same features and advantages as the configuration in FIG. 4(b),
although the structure has now been modified to fit two
motor/generators. The rotor 103 of motor/generator 01 is connected
to the ring gear R, and the rotor 106 of motor/generator 02 is
connected to the sun gear S; both the stator 101 of the
motor/generator 01 and the stator 105 of the motor/generator 02 are
affixed to the chassis. In all other aspects, the structure of this
wheel hub implementation is the same as the simpler wheel hub
implementation of FIG. 4(b).
Three-Port Hybrid System Configuration with Flywheel and Engine on
Separate Ports
[0109] As seen in FIGS. 4(a), 7(a), it is possible to combine two
independent powertrains to form what is similar to a four wheel
drive hybrid. The power sources in these implementations each has
its own independent transmission and can be operated separately or
together. However, because of the separate transmissions, the
implementations of 4(a) and 7(a) are somewhat complex. FIG. 8 shows
a more integrated arrangement.
[0110] On the basis of the dual motor kinetic-electric hybrid
system, the configuration of FIG. 8 introduces an IC engine 20 into
the powertrain as the prime mover. The flywheel 10 can be used as
the secondary power source or mover, and the two electric
motor/generators provide a third power source for vehicle
propulsion. Note that although there are now additional power
sources, no additional transmission is required. The planetary gear
set 12 remains at the core of the system, combining three different
power sources in a symmetric arrangement--the IC engine 20 coupled
to the ring gear R through a clutch 22, the flywheel 10 coupled to
the sun gear S through clutch 16 and the gear set 17, and the
motor/generators 01 and 02, respectively connected to R and S. The
planetary carrier C is the input/output port connected to the
output shaft 33 that transmits power to the final drive 32 and from
there to the wheels 34 through the axes 36. The system interface 60
and ECU 62 generate signals to the controller/inverters 03 and 04,
which in turn operate the respective motor/generators 01 and 02 to
direct the power flow within the hybrid system.
[0111] The configuration of FIG. 8 introduces a planetary gear
system serving as an electrically variable CVT that is controlled
by the motor/generators 01 and 02. This CVT can be used by the
prime mover (the engine 20), the secondary mover (the flywheel 10),
and even by the third power source, one of the motor/generators 01
or 02, in turns.
[0112] When the clutch 22 is disengaged, decoupling the engine 20
from the drivetrain, while the clutch 16 is engaged, coupling the
flywheel 10 to the drivetrain, the system is in the
kinetic-electric mode seen in FIG. 5, wherein the planetary gear
set 12 and the variator motor/generator 01 comprise the
electrically variable CVT for the flywheel 10. The variator 01 can
adjust the speed ratio between ports S and C of the CVT to control
the transfer of energy between the vehicle's wheels 34, connected
to port C, and the flywheel 10 on port S. The motor/generator 02
also serves as a mover, reusing the electricity generated from the
variator 01 to produce torque back to the powertrain so that the
regenerated energy does not have to be stored in the battery pack
05, which increases efficiency and performance and prolongs battery
life.
[0113] When the clutch 16 is disengaged, decoupling the flywheel 10
from the drivetrain, but the clutch 22 is engaged, the system is in
the fuel-electric hybrid mode. The planetary gear set 12 and the
motor/generator 02 comprise an electrically variable CVT for the
engine 20 controlling the speed ratio and energy transfer from the
ring gear port R to the planetary carrier port C. In this mode the
variator 02 acts as a generator, and the motor 01 reuses the
electricity from the variator 02 to produce torque back to the
powertrain to avoid conversion losses in the battery pack 05. The
motor 01's power supplements that of the engine 20.
[0114] Disengaging both clutches 16 and 22 permits operation in a
pure electric mode. Either motor/generator may act as a traction
motor or as a variator for the other motor/generator in the CVT.
Either one or both motors may be used for vehicle propulsion. With
01 as the variator and 02 propelling the vehicle, the transmission
speed ratio is greater than (k+1), suitable for low vehicle speeds;
with 02 as the variator and 01 propelling the vehicle, the
transmission speed ratio is greater than (k+1)/k, more suitable for
moderate vehicle speeds; with both 01 and 02 acting as motors
propelling the vehicle, the transmission speed ratio is adjustable
and less than (k+1)/k, suitable for high vehicle speeds.
Additionally, there are single motor modes available for use with
the configuration of FIG. 8. With the clutch 22 engaged and the
clutch 16 disengaged, as well as with the generator 01 and the
engine 20 off, the motor 02 can drive the vehicle by itself; due to
the one-way clutch 24 that will lock down the ring gear R and
prevent it from rotating in the reverse direction, the gear ratio
between S and C will be K+1, which is appropriate for low vehicle
speeds. In another mode, the clutch 16 can be engaged, with the
clutch 22 disengaged and the motor/generator 02 off, which would
allow the motor 01 to drive the vehicle by itself; the energy in
the flywheel 10 will be completely released, and then the one-way
clutch 18 would prevent the sun gear S from rotating in the reverse
direction, so the gear ratio between R and C would be (K+1)/K, more
appropriate for moderate speeds. At higher vehicle speeds, 01 and
02 can work together for high efficiency.
[0115] The methods used to control the system of FIG. 8 can be
described along with the vehicle's operation states shown in FIG.
9. Since the engine E in FIGS. 9(a)-9(c) is disengaged throughout
these three operation states, FIGS. 9(a)-9(c) are equivalent to
FIGS. 6(a)-6(c).
[0116] FIG. 9(d) depicts the system starting the engine E during
acceleration. Since the ring gear R is already rotating in the
forward direction from the second acceleration state in FIG. 9(c),
the engine E can be started by engaging the clutch 22. Thus, both
motor/generators M1 and M2, as well as the engine E and the
flywheel F, contribute power to move the vehicle after the engine E
starts. Should the energy in the flywheel F be depleted, the clutch
16 can be disengaged, decoupling the flywheel F from the drivetrain
so it does not adversely affect drivability.
[0117] FIG. 9(e) depicts a first cruise state, wherein the flywheel
F is disengaged, and the engine E provides the power that the
vehicle needs while the variator G2 manipulates the speed ratio of
the CVT to control vehicle speed. The motor M1 reuses the
electricity generated by the variator G2 to also propel the
vehicle, reducing the number of charge/discharge cycles for the
battery pack B, extending battery life. In a second cruise state
shown in FIG. 9(f), the motor/generator G1 acts as a generator to
not only generate electricity for the battery pack B and to
increase the load of the engine E and thereby improve efficiency,
while the motor/generator G2 controls the speed ratio. Under a
third cruise state, seen in FIG. 9(g), when the state of charge in
the battery pack B is too high, the engine E is shut off and
disengaged from the powertrain, and either one or both
motor/generators M1 and/or M2 would be used to maintain the
vehicle's cruise speed. At higher vehicle speeds, using both
motor/generators would be preferred, since they can both split the
load to operate at a better efficiency.
[0118] The deceleration states demonstrated by FIGS. 9(h), 9(i)
also do not involve an active engine, so they are equivalent to the
states depicted in FIGS. 6(i), 6(j). In FIG. 9(j), the engine E
charges the battery pack B via the generator G1, while the flywheel
is decoupled and the motor/generator M/G2 is off. Since the CVT is
neutral, this battery charge state can be used regardless of
whether the vehicle is moving or stopped. For the states of reverse
(FIG. 9(k)) and flywheel restore (FIG. 9(m)), the process and the
method for control are exactly the same as in FIGS. 6(k) and
6(m).
[0119] Fuel-electric hybrids save fuel primarily by virtue of
running a small engine in a fuel efficient region of operation.
Although the downsized engine has low reserve power, performance is
not compromised because the hybrid relies upon the electric power
source and energy storage to compensate for the engine's poor
performance. The electric power source and energy storage also
enable regenerative braking to recover a portion of the vehicle's
kinetic energy that is normally completely lost when a conventional
vehicle is decelerated. As analyzed and discussed in FIG. 1, the
same limitations exist and apply for electric hybrids and for pure
electric vehicles. These vehicles face the challenges of
efficiency, performance, and cost due to the fact that in
acceleration and deceleration high power is needed to propel the
vehicle and to regenerate or recover the vehicle's kinetic energy.
Efficiency is limited because energy conversions are needed to use
or store energy in the batteries. To have good performance, the
vehicle would need a large traction motor, a large battery pack,
and a high power controller/inverter, which increase cost of
manufacture.
[0120] Power split fuel-electric hybrid vehicle powertrains are
well known, but if a flywheel is integrated into the powertrain,
the vehicle becomes a kinetic-fuel-electric hybrid like the one
shown in FIG. 8. Using a flywheel as a kinetic energy storage and a
power buffer can go a long way in overcoming the aforementioned
challenges faced by electric propulsion systems. Flywheels store
and release kinetic energy, which is the same form of energy the
vehicle uses; with a power split CVT as in FIG. 8, the majority of
the energy to and from the flywheel may be transferred via a direct
mechanical path, with only 30 percent or so of the total power
traveling an electric path. This represents a significant increase
in system efficiency, as energy conversion losses are drastically
reduced. Flywheels also increase performance, as they have high
power density. The electric variator for the power split CVT should
be rated for 30 percent of the total power used to propel the
hybrid vehicle. Since the power demands on the electric propulsion
system are reduced with the addition of a flywheel, the electric
propulsion system components (motor/generator(s), inverter(s), and
battery pack) can be considerably downsized, reducing cost. Having
a flywheel to buffer energy and power instead of storing and
releasing energy to the battery pack also has the advantage of
reducing the number of charge/discharge cycles for the battery
pack, which extends battery life.
Three-Port Hybrid System Configuration with Flywheel and Engine
Sharing Same Port
[0121] FIG. 8 illustrates a hybrid system with a three-port power
split CVT where the prime mover IC engine 20 and the secondary
mover flywheel 10 are on separate input/output ports of the power
split CVT. In this arrangement, the flywheel 10 and engine 20 may
not be able to use the CVT simultaneously. Hence, with the engine
20 controlling the CVT during cruise, the flywheel 10 may not be of
use in the cruise state(s).
[0122] Another arrangement is possible while maintaining the
principle of keeping the final drive 32 independent on its own
input/output port in a three-port power split CVT. Placing a power
plant on the same port as the final drive 32 may result in an
additional transmission being needed for that power plant. Thus,
the engine 20 and the flywheel 10 may either each command one of
the remaining two ports, as with the configuration of FIG. 8, or
share a common port, leaving the third port alone to a variator
motor/generator 01, which can then control the transmission speed
ratio for both the engine 20 and the flywheel 10, as in FIGS. 10(a)
and 10(b).
[0123] For the configuration of FIG. 10(a), the IC engine 20 is
connected to the sun gear port of the planetary gear set 12 through
a clutch 22. Also connected to the sun gear port are the flywheel
10, connected through a gear set 17 which increases the speed of
the flywheel 10 relative to the sun gear S, the motor/generator 02,
and a single one-way clutch 24. This configuration saves a clutch
and a one-way clutch compared to the configuration of FIG. 8, and
can be controlled to significantly improve fuel efficiency during
cruise. The variator motor/generator 01, connected to the ring gear
port R, controls the speed ratio between the sun gear port S and
the planetary carrier port C. The final drive 32 is connected to
the planetary carrier port C through a shaft 33, and drives the
vehicle's wheels 34 through the axes 36. The motor 02 improves
efficiency, both by reusing electricity generated from the variator
01 back into the powertrain to assist the flywheel 10 in propelling
the vehicle, and by sharing the load of the engine 20 (also on port
S) so that the engine's efficiency is improved. While the engine 20
and the motor 02 are both operated within a suitable speed range
for optimal fuel efficiency, the gear set 17 permits the flywheel
10 to be simultaneously charged to spin at a faster speed than the
other power sources on the same port, increasing the amount of
energy that can be stored into the flywheel 10.
[0124] Apart from propelling the vehicle, an important function of
the engine 20 is to charge the flywheel 10, maintaining the
flywheel 10's RPM within a certain range. The RPM range of the
flywheel 10 can be controlled dynamically, for example, as a
function of the current vehicle speed. The flywheel 10's speed can
be inversely related to the vehicle speed, so that the sum of the
vehicle's kinetic energy and the flywheel 10's kinetic energy at
any given moment is approximately a constant value, which in one
non-limiting example can be equal to the maximum safe energy
storage capacity of the flywheel 10. Should the flywheel 10 drop
below a lower speed or energy setting at any moment, the engine 20
may be engaged with the clutch 22 to charge the flywheel 10; when
the flywheel 10 is above some higher speed or energy setting, the
engine 20 may be disengaged and turned off or in idle. The engine
20 can be operated in a start-stop manner, either driving the
vehicle and charging the flywheel 10 at the engine's maximum
efficiency, or using no fuel when the engine 20 is disengaged and
shut off. The flywheel 10 may be thought of as an energy buffer for
the engine 20, gradually releasing the excess energy generated as a
result of running the engine 20 in its most fuel efficient state.
In comparison, HEVs may use the same control strategy at times with
electric storage devices as buffers for the excess energy generated
by the engine, but electric storage results in more energy
conversion losses and lower overall system efficiency.
[0125] The configuration portrayed in FIG. 10(b) is a variation on
the arrangement in 10(a). In 10(b), the clutch 22 connecting the
engine 20 to the powertrain has been replaced by the planetary gear
set 14 and the brake 50, which comprise a coupling/decoupling
mechanism that is equivalent to the clutch 22. The sun gears S1 and
S2 of planetary gear sets 12 and 14, respectively, are connected.
The engine 20 is connected to the planetary carrier C2 of planetary
gear set 14, and so when the ring gear R2 of 14 is braked by 50
(equivalent to engaging the engine 20), the engine 20 can transmit
power to the flywheel 10 and the planetary gear set or CVT 12. When
the ring gear R2 is not braked (which is equivalent to disengaging
the engine 20), both C2 and R2 are able to spin freely and the
engine 20 can be turned off.
[0126] FIGS. 11(a)-11(m) provide more detail on how to control the
equivalent embodiments of FIGS. 10(a) and 10(b).
[0127] When pre-charging the flywheel, illustrated in FIG. 11(a),
the variator G1 is off, so the wheels W on the planetary carrier
port are free to maintain their current speeds while the motor M2
charges the flywheel F. The flywheel F can be pre-charged in this
way with the vehicle stopped (wheels W braked) or moving (wheels W
at the same velocity as their velocity just prior to pre-charge).
The engine E may be used to pre-charge the flywheel F if the state
of charge in the battery pack B is low, or if doing so would be
more efficient. To start the engine E with the flywheel F, all that
has to be done is to engage the engine E after the flywheel F has
accrued a certain level of energy, as shown in FIG. 11(b). When
acceleration is desired, the variator G1 or M1 produces a torque in
the same direction as the desired direction of motion for the
wheels W, which produces a reaction torque from the ring gear port
of the ring gear R that enables power from the sun gear port of the
sun gear S to transfer to the planetary carrier port of the
planetary carrier C. When acceleration first begins, the ring gear
R that had been spinning freely in the reverse direction is braked
by the torque from the variator G1, which acts as a generator in
this first accelerative state of FIG. 11(c). Because the torque
provided by the variator G1 or M1 does not change direction
throughout the process of acceleration, the ring gear R will reach
a point (if acceleration continues to very high vehicle speeds)
when it is completely braked and its speed is zero, then start to
rotate in the same direction as port C, which marks the start of
the second accelerative state of FIG. 11(d). Then, since the torque
direction is the same direction as motion of the ring gear port of
the ring gear R, the variator M1 is now acting as a motor, not as a
generator. If the motor/generator G1 and M2 and the engine E are
all inactive or disengaged, the vehicle is in a neutral and/or
coasting state, shown in FIG. 11(e), and the speed of the flywheel
F remains unchanged.
[0128] During cruise, the configurations of FIG. 10(a) and FIG.
10(b) are capable of using the flywheel F to buffer the energy
produced by the engine E so that the engine E can always operate in
its most efficient state, in a start-stop manner. In the first
cruise state presented in FIG. 11(f), the engine E not only
provides energy to the sun gear port of the sun gear S to
accelerate the wheels W on the planetary carrier port of the
planetary carrier C, but also charges the flywheel F. In this
scenario, the rotational speed of the flywheel F is lower than a
certain level or setting for the flywheel F's speed compared to the
current vehicle speed. The engine E operates within a suitable
speed range for fuel efficiency, and the variator G1 and motor M2
may adjust the engine load dynamically to ensure that the engine E
runs at its best efficiency.
[0129] Once the flywheel F's energy reaches a certain level or
setting, the engine E can be disengaged and either turned off or in
idle, allowing the vehicle to be propelled primarily by power from
the flywheel F, shown in FIG. 11(g). When the energy in the
flywheel F drops below a certain level or setting, the engine E can
be engaged again to simultaneously charge the flywheel F and drive
the wheels W. The flywheel F serves an important function of
providing an energy reserve and buffer: when there is demand for
change in the vehicle's speed (such as during deceleration or
acceleration), the flywheel F exchanges kinetic energy with the
vehicle; when cruise is desired, the flywheel F passes energy
between the engine E and the vehicle such that the engine E
operates at an optimal efficiency. In this process of energy
exchange, only a small portion of the energy from the engine E
passes through the generator G1 and the motor M2, and the battery
pack B is used minimally, reducing the number of energy conversions
and increasing efficiency, while also extending the battery life.
Whereas conventional hybrids suffer from multiple energy
conversions (using three different forms of energy), which decrease
efficiency when transferring energy in and out of the battery pack,
the exchange of energy between the flywheel and the engine does not
require conversion and thus occurs at higher efficiency. The system
alternates between the states of FIG. 11(f) and FIG. 11(g) to
optimize the vehicle's efficiency for the entire duration of the
cruise period.
[0130] The first and second deceleration states, presented in FIGS.
11(h) and 11(i), function in the same way as FIGS. 6(i) and 6(j),
respectively, since the engine E is disengaged (not involved in
deceleration). At any point in the drive where the state of charge
in the battery pack B is too low, however, energy from the engine E
and/or the flywheel F can be used to charged the battery pack B
through the generator G2 in the neutral battery charge state of
FIG. 11(j). Since the variator G1 is off, there is no exchange
between the sun gear port of the sun gear S and the planetary
carrier port of the planetary carrier C, and the battery pack B may
be charged regardless of whether the vehicle is stopped or
moving.
[0131] FIG. 11(k) and FIG. 11(m) respectively show the operation
states for reverse and flywheel energy recovery, similar to FIG.
6(k) and FIG. 6(m).
Brake-Based, Motorless Kinetic Energy Recovery System, Embodiments
and Methods
[0132] Conventional vehicles dissipate all of the kinetic energy of
the vehicle every time the vehicle is braked to a full stop. For
converting existing vehicles into hybrids, or for new vehicles
where the primary focus of fuel efficient design is to recover the
vehicle's kinetic energy during deceleration, an embodiment of the
present invention includes a brake-based, motorless hybrid system
configuration in FIG. 12(a), as well as a variation thereupon in
FIG. 12(b).
[0133] The flywheel 10 in the configuration of FIG. 12(a) is
connected to the sun gear S2 of the planetary gear set 14,
designated as port-1. The planetary carrier C1 of the planetary
gear set 12 and the planetary carrier C2 of the planetary gear set
14 are connected to each other and to a transmission shaft 33 that
is also connected to the wheels 34 through the final drive 32 and
the axes 36. Any point along the shaft 33, on the planetary carrier
C1, or on the planetary carrier C2 is considered to be on port-2.
The brake 50, which may be electrically controlled, is connected to
R1 of 12, designated as port-3. The sun gear 51 of 12 and the ring
gear R2 of planetary gear set 14 are connected, and comprise
port-4, to which the brake 52, which may also be electrically
controlled, is connected. The planetary gear set 14 is the CVT for
the flywheel 10, coupling to the flywheel 10 via its sun gear S2;
the control for this CVT comes from the ring gear R2, which is
connected to the sun gear 51 of the planetary gear set 12 as well
as directly to the brake 52. For the majority of the time, both
brakes 50 and 52 are maintained in the disengaged or "open"
position.
[0134] When deceleration (kinetic energy recovery) or acceleration
(kinetic energy release) is desired, the slipping brakes 50 and 52
are the means to change the speed of port-3 and port-4, replacing
the motor variator of the previous embodiments and the prior art.
They will and should slip when engaging. Only one of the slipping
brakes 50 or 52 is used at a time; 50 for vehicle deceleration, and
52 for vehicle acceleration.
[0135] During deceleration, if the brake 50 is engaged, the
interaction between the torques on port-3 (ring gear R1) and port-2
(planetary carriers C1 and C2) leads to torque being passed to
port-4 (sun gear S1 and ring gear R2). S1 receives torque in the
opposite direction of the motion of C1 and causes R2 to rotate in
the reverse direction. Consequently, the sun gear S2 on port-4
accelerates, storing energy into the flywheel 10, while the vehicle
decelerates. When the brake 50 has completely braked port-4, the
flywheel 10's maximum speed can reach -(k.sub.1k.sub.2-1) times the
speed of port-2, where k.sub.1 and k.sub.2 respectively represent
the physical gear ratio of the ring gear to the sun gear in the
planetary gear sets 12 and 14. Once this maximum ratio between the
speeds of port-1 and port-2 is reached, or perhaps when the speed
of port-1 compared to the speed of port-2 is close enough to this
ratio, the brake 50 should be released or disengaged, or else the
flywheel 10 would actually prevent the vehicle from further
decelerating. After this maximum speed ratio is reached (when the
energy stored in the flywheel 10 is at a maximum) and the brake 50
disengaged (to prevent releasing energy from the flywheel 10, which
would interfere with further deceleration), the vehicle must be
further decelerated by another braking mechanism if further
deceleration is desired.
[0136] The brake 52 should be engaged if it is desired to release
the energy stored in the flywheel 10 for accelerating the vehicle.
Braking port-4 with the slipping brake 52 can release energy in the
flywheel 10 all the way down to zero to propel the vehicle. The
brake 52 should be disengaged immediately thereafter, or else the
flywheel 10 may start spinning in the reverse direction, negatively
impacting the vehicle's drivability.
[0137] FIG. 12(b) demonstrates a variation on the configuration of
FIG. 12(a). Here, the only changes are the replacement of the
planetary gear set 12 with the gear set 13, and the replacement of
the brake 50 by the slip clutch 51 that is connected to the gear
set 13 and the ring gear R of the planetary gear set 14. The gear
set 13 has a fixed gear ratio. To recover kinetic energy during
deceleration, the slip clutch 51 is engaged to charge the flywheel
10. If it is assumed that k.sub.3 is the physical gear ratio of
ring gear R to sun gear S in 14, and k.sub.4 is the physical gear
ratio of the gear set 13, then in relating the gear speeds of 13 it
follows that .omega..sub.r=-k.sub.4.omega..sub.c; it also follows
that from substituting -k.sub.4.omega..sub.c for .omega..sub.r in
equation (1) and replacing k with k.sub.3, the equation
.omega..sub.s=(k.sub.3k.sub.4+k.sub.3+1).omega..sub.c (2)
can be derived for when the clutch 51 is completely engaged. The
flywheel 10 can therefore be charged up to
(k.sub.3k.sub.4+k.sub.3+1) times the vehicle speed .omega..sub.c
before the clutch 51 should be disengaged. Releasing the energy
stored in the flywheel 10 involves only the brake 52, and the
flywheel 10's energy can be totally released to zero before
disengaging the brake 52.
[0138] FIG. 12(c) illustrates an actual implementation of the
configuration of FIG. 12(a) in a vehicle, similar to FIGS. 4(a) and
7(a).
[0139] FIG. 12(d) is a mechanical schematic of FIG. 12(a) for an
implementation like the one shown in FIG. 12(c).
The Preferred Four-Port Embodiment of the Present Invention
[0140] FIG. 13 shows the preferred four-port embodiment of the
present invention. There are three power sources: an internal
combustion (or IC) engine 20, which serves as the prime mover; the
flywheel 10, which is both a kinetic energy storage and a kinetic
power source, and serves as the secondary mover most of the time;
and the motor/generators 01 and 02, additional electric power
sources. The motor/generators 01 and 02 are controlled by the
controller/inverters 03 and 04, respectively, which draw energy
from the battery pack 05. The three different power sources
interact with one another through a compound power split
transmission, which has four input/output ports. This core unit,
henceforth referred to as the compound CVT (40), is comprised of
two planetary gear sets 12 and 14, with the carrier gear C1 of 12
connected to the ring gear R2 of 14, and the carrier gear C2 of 14
connected to the ring gear R1 of 12.
[0141] This configuration yields a four-port power split system,
with port-G coming off the sun gear S1 of the planetary gear set 12
that is connected to the variator motor/generator 01, port-F coming
off the sun gear S2 of the planetary gear set 14 that is connected
to the kinetic power source flywheel 10 through the clutch 16,
port-W that is connected to C1 and R2 and to the wheels 34 through
the final drive 32, and port-EM, which is connected to the ring
gear R1 and the planetary carrier C2 as well as the electric power
source motor/generator 02 and the IC engine 20 through the clutch
22 and secured with the one-way clutch 24. The system mainly
functions as a flywheel hybrid, and with an adequately large
battery pack 05 it can also function as a plug-in flywheel hybrid
electric vehicle. The interface to the system 62 may contain a
series of sensors generating signals to the ECU 60, including
sensors to detect RPM of various ports of the CVT, the engine load,
and the state of charge of the battery pack 05, and etc. The
interface 62 also processes the control signals from the ECU 60 to
perform operations to the system, such as providing signals to the
controller/inverters 03 and 04 or generating signals to couple or
decouple the flywheel 10 and/or the engine 20.
[0142] The compound CVT is the key to controlling the system's
three power sources. The motion of the rotational components in the
compound CVT is governed by the following planetary gear
equations:
(k.sub.1+1).omega..sub.c1=k.sub.1.omega..sub.r1+.omega..sub.s1
(3)
(k.sub.2+1).omega..sub.c2=k.sub.2.omega..sub.r2+.omega..sub.s2
(3)
The constant k.sub.1 is the physical gear ratio of the ring gear R1
to the sun gear S1, chosen to fit high efficiency RPM ranges for
the motor/generators 01 and 02. The constant k.sub.2 is the
physical gear ratio of the ring gear R2 to the sun gear S2, chosen
in consideration of the energy level of the flywheel 10.
[0143] .omega..sub.c1 and .omega..sub.r2 represent the angular
speed of port-W, directly related to the vehicle speed.
.omega..sub.r1 and .omega..sub.c2 represent the angular speed of
port-EM, which is the angular speed of both the motor/generator 02
and the engine 20. .omega..sub.s1 is the angular speed of port-G
and represents the speed of the motor/generator 01, and
.omega..sub.s2 is the angular speed of port-F, which is the speed
of the flywheel 10. Supposing that .omega..sub.w is the speed of
the wheels 34 (disregarding the final drive 32), .omega..sub.em is
the speed of both the engine 20 and motor/generator 02,
.omega..sub.g is the speed of the motor/generator 01, and
.omega..sub.f is the speed of the flywheel 10, we can rewrite
equations (3) and (4) as follows.
(k.sub.1+1).omega..sub.w=k.sub.1.omega..sub.em+.omega..sub.g
(5)
(k.sub.2+1).omega..sub.em=k.sub.2.omega..sub.w+.omega..sub.f
(6)
[0144] The speed change(s) of any port(s) will affect the speed(s)
of the others. The planetary gear set 12 governed by equation (5)
allows the engine 20 and motor/generator 02 to drive the wheels 34,
with the motor/generator 01 acting as the variator of the planetary
gear set 12 and the compound CVT 40. Changing the speed of the
motor/generator 01 varies the transmission speed ratio, which is
.omega..sub.em/.omega..sub.w, which can be used to control the
vehicle speed. The planetary gear set 14 governed by equation (6)
is for the control of the flywheel 10 to store and release its
kinetic energy when the clutch 16 is in the engaged position. The
speed of the vehicle, .omega..sub.w, is used as the variator in the
planetary gear set 14 to control the exchange of kinetic energy
between the flywheel 10 and the vehicle.
[0145] FIG. 14 is one possible mechanical schematic for the core
components of the embodiment of FIG. 13. The planetary gear sets 12
and 14 comprise a compound power split device 40 with four ports to
provide infinitely variable speed ratios and to distribute power
throughout the hybrid system. A flywheel 10 is connected to a first
port through a clutch 16. The second port of the compound CVT 40 is
connected to the final drive or gearbox 32 through the shaft 33,
which is then connected to the vehicle's wheels 34 through wheel
axes 36. The motor/generator 01 is connected to a third port. Both
an IC engine 20 and a second motor/generator 02 are connected to
the fourth port of the compound CVT 40. The port also features a
slip or friction clutch 22 and a one-way clutch 24 for the engine
20.
[0146] Even the best physical configuration for a hybrid vehicle
needs to be controlled appropriately to achieve the desired
characteristics. For control strategies, the two key considerations
are performance and efficiency. The present invention also provides
two operation methods that optimize these two key considerations;
which method is used depends upon whether the vehicle's speed is
changing (acceleration, deceleration) or steady (cruise).
Introducing Inertia and What it Means for Vehicle Propulsion
[0147] The energy consumed by the vehicle can generally be
categorized into two portions: one portion is used for overcoming
frictional forces such as drag and rolling resistance, and is
unrecoverable; the other portion of the energy used goes into the
kinetic and/or potential energy of the vehicle. When the vehicle is
either accelerating or decelerating, the kinetic energy of the
vehicle must either increase or decrease. Inertia always plays a
negative or resistive role in changing the vehicle's speed. It
takes energy to speed the vehicle up, and when the vehicle needs to
be slowed or stopped, the vehicle's kinetic energy is dissipated as
heat when braking in conventional vehicles. The energy wasted to
braking during deceleration is a result of having to overcome the
vehicle's inertia. Most of the reserve power from the vehicle's
prime mover is for performance during acceleration, also driven by
the need to overcome the vehicle's inertia. In other words, a
conventional vehicle must be equipped with an engine powerful
enough to overcome inertia in short periods of time for
acceleration, but this means that for the remainder of the drive,
since relatively little power is needed, the vehicle operates at
low engine load and, consequently, low efficiency. The tradeoff in
performance and efficiency is necessary because of inertia. If
there was no inertia, then fuel or electricity used for vehicle
propulsion would only be expended for overcoming drag, rolling
resistances, and other frictional forces. Removing inertia from the
vehicle is the motivation for the method of performing a
"de-inertia operation" enabled by the present invention. The system
of the present invention offers both improved performance and
efficiency while drastically reducing the vehicle's inertial
effects.
Overview of De-inertia Operation Methods
[0148] The de-inertia process starts from an initial state wherein
the speed of .omega..sub.w on port-W is zero (the vehicle is
stationary), and the speed of the flywheel or port-F,
.omega..sub.f, is high (it is assumed the flywheel 10 was
pre-charged or charged from the last deceleration maneuver). By
equation (6), therefore, the speed of port-EM equals
.omega..sub.f/(k.sub.2+1), and by equation (5) the speed of port-G
can be expressed as -k.sub.1.omega..sub.em or
-k.sub.1.omega..sub.f/(k.sub.2+1). The variator 01 in the planetary
gear set 12 thus rotates in the negative direction at the speed
.omega..sub.g=-k.sub.1.omega..sub.f/(k.sub.2+1). The engine 20 and
the motor/generator 02 rotate in the positive direction at the
speed .omega..sub.em=.omega..sub.f/(k.sub.2+1), which is controlled
within a relatively stable range around the engine 20's RPM that
corresponds to its best efficiency state for maximum efficiency.
Because k.sub.1 and k.sub.2 are constant, and .omega..sub.em, is
near-constant, the k.sub.1.omega..sub.em, and
(k.sub.2+1).omega..sub.em, in equations (5) and (6) are
near-constant. The variator 01 meanwhile rotates in the negative
direction, acting as a generator most of the time to provide the
reaction force needed to transmit the power from the movers 20 and
02 to the wheels 34 through the direct mechanical path from port-EM
to port-W of the CVT (R1 to C1 of 12).
[0149] When acceleration is desired, by decreasing the speed
.omega..sub.g of the variator 01 in the negative direction and
having the motor/generator 02 hold .omega..sub.em, to be relatively
steady, the speed .omega..sub.w of the vehicle's wheels increases,
since k.sub.1 in equation (5) is constant. In the planetary gear
set 14, described by equation (6), k.sub.2 is also a constant, and
the rise of .omega..sub.w while .omega..sub.em is constant will
cause .omega..sub.f to drop, also releasing energy to port-W and
serving to increase .omega..sub.w. This is the process of
acceleration, whereby the engine 20, whereby the flywheel 10, the
motor 02, and/or the engine 20 exchange energy with port-W to
accelerate the vehicle. Under the control of the variator 01, the
vehicle accelerates, which increases its kinetic energy, while the
flywheel 10 decelerates as its kinetic energy decreases. Most of
the flywheel 10's energy is transferred from port-F to port-W to
accelerate the vehicle via a mechanical path, and approaching 100
percent efficiency. A smaller portion of the flywheel 10's energy
travels an electrical path through the variator 01 on port-G, and
is reused by the motor 02 on port-EM to also accelerate the vehicle
at port-W. This process, governed by the speed relationships of
equations (5) and (6), is such that decreasing the speed of the
variator 01 releases kinetic energy stored in the flywheel 10 to
the vehicle's wheels 34, thereby accelerating the vehicle.
Conversely, increasing .omega..sub.g in the negative direction will
cause a decrease in .omega..sub.w and an increase in .omega..sub.f
when .omega..sub.em is maintained to be constant or near constant,
resulting in deceleration while also charging the vehicle's energy
into the flywheel 10.
[0150] To prevent the flywheel 10 from reducing drivability when
vehicle speed is low and there is not enough energy in the flywheel
10, the flywheel 10 can be pre-charged; alternatively, it can also
be decoupled from the drivetrain by keeping the clutch 16 in the
disengaged position if it is desired to charge the flywheel 10
later, during deceleration. In the pre-charge state (which is also
explained in detail later with FIG. 18(a), the IC engine 20 is
decoupled temporarily from the drivetrain by keeping the clutch 22
disengaged, while the motor 02 draws energy from the battery pack
05 through the controller/inverter 04 to charge up the flywheel 10.
From equation (6), it can be seen that if .omega..sub.w=0 (the
vehicle is stationary), the flywheel 10 can be charged to
.omega..sub.f=(k.sub.2+1) .omega..sub.em, k.sub.2+1 times the speed
of the motor/generator 02 up to the maximum safe rotational speed
of the flywheel 10.
[0151] Note that the speed .omega..sub.w of the wheels 34 is the
speed of the vehicle, which directly relates to the kinetic energy
level of the vehicle; similarly, the speed .omega..sub.f of the
flywheel 10 determines the flywheel 10's kinetic energy level.
During acceleration, the vehicle's kinetic energy increases and the
flywheel 10's kinetic energy decreases. During deceleration, the
vehicle's kinetic energy decreases and the flywheel 10's kinetic
energy increases. The speed of the flywheel 10 is inversely related
to the vehicle's speed. The vehicle's kinetic energy level and the
flywheel 10's kinetic energy level are related, but they change in
opposite directions, so that during acceleration kinetic energy is
released from the flywheel 10 to speed up the vehicle's wheels 34,
and during deceleration the kinetic energy of the vehicle is
recovered and stored back into the flywheel 10. Therefore,
accelerating and decelerating the vehicle simply entails energy
exchange between the flywheel 10 and the vehicle, and little to no
external energy need be provided to accelerate the vehicle, as long
as the vehicle's speed is in the range covered by the flywheel 10.
The engine 20, therefore, does not need to work at higher power to
overcome the vehicle's inertia, and is primarily used to overcome
resistive forces such as drag and rolling resistance. The effect is
that the flywheel 10 always acts against the vehicle's inertia and
reduces or eliminates inertial effects, thus achieving "de-inertia"
operation. In the configuration of the present invention, adjusting
the speed .omega..sub.g of the motor/generator 01 to suitably
control vehicle speed automatically performs the de-inertia
function described above during acceleration or deceleration. When
a change in the vehicle's speed is desired, the vehicle's kinetic
energy can be recovered and reused with little loss, increasing
both efficiency and performance.
[0152] FIG. 15 illustrates one possible example of the kinetic
energy exchange between the vehicle and the flywheel 10. For the
calculations used to generate this figure it was assumed that the
flywheel 10 is a 20 kg steel ring-shaped flywheel with radius of 18
cm and thickness of 5 cm. When the vehicle is at rest (vehicle
speed 0 km/h) it has already been pre-charged to the setting of its
maximum safe operation speed, 1040 rad/s or 10,000 RPM. The
flywheel in this example at this speed has a maximum capacity for
kinetic energy of about 100 Wh, which is equivalent to the kinetic
energy of a 1600 kg vehicle moving at 75 km/h. When the vehicle is
stationary, the kinetic energy of the vehicle is zero, while the
kinetic energy of the flywheel is at a maximum or at a high level.
The kinetic energy of the flywheel is continuously released as
.omega..sub.w (vehicle speed) continuously increases, and as
vehicle speed increases, the vehicle's kinetic energy increases,
and the flywheel's kinetic energy decreases.
[0153] In the lower speed range depicted in the diagram, the
vehicle can be boosted to over 30 km/h solely through the energy
released from the flywheel 10, while the engine 20 is off and/or
decoupled from the hybrid powertrain. Since at and below 30 km/h
the flywheel 10 of this example can totally cover the kinetic
energy gained by the vehicle, and the motor 02 covers drag and
rolling forces, and since the flywheel 10 has a tremendous power
density, the vehicle is easily accelerated, and the resulting
effect is that it is as though the vehicle has little or no
inertia.
[0154] As the speed of the vehicle .omega..sub.w gets higher and
higher, 02 gradually increases its power to contribute to the
vehicle's acceleration. The IC engine 20 may be started to supply
power to accelerate the vehicle as .omega..sub.w enters higher
speed ranges. The speed of the motor 02 is then controlled to be
held at the speed of the engine's ideal efficiency, which is
assumed to be 2000 RPM for the purpose of this example. The speed
of the variator 01, .omega..sub.g, can be controlled to increase
.omega..sub.w and accelerate the vehicle (also see FIG. 18(c)).
[0155] It is feasible for the present invention to release the
energy in the flywheel 10 entirely to zero; for the sake of
performance, however, it is better to reserve a certain level of
kinetic power in the flywheel 10 even as the vehicle speed
increases. In the case of heavier acceleration to a higher speed,
the torquer motor/generator 02 can help share the engine load to
optimize efficiency. In cases where the heaviest acceleration is
desired, the engine 20, motor 02, motor 01, and the flywheel 10 may
all contribute driving power for maximum performance of the vehicle
(also see FIG. 18(d)).
[0156] FIG. 15 may also be used to understand deceleration
de-inertia operation. For deceleration, the process starts towards
the right side of the graphical representation, when the vehicle
speed is high, and works its way left, to where the vehicle speed
reaches zero. (See FIGS. 18(h) and 18(i)). Because the figure
models the de-inertia process, air drag and rolling resistances are
not represented. The kinetic energy trajectories for the vehicle
and for the flywheel 10 remain unchanged; at any given instant, the
height of the unshaded area below the dotted line now represents
the amount of the vehicle's kinetic energy that can still be stored
into the flywheel 10; the difference between the vehicle's kinetic
energy trajectory and the dotted line now represents the portion of
the vehicle's kinetic energy that can either be regenerated as
electricity by the motor/generators 01 and/or 02, and/or wasted to
friction in mechanical braking. Note that this is a non-limiting
example, where the size and speed of the flywheel 10 greatly
impacts the trajectory of the kinetic energy in the flywheel 10, as
well as the dotted line representing how much energy may still be
charged into the flywheel 10 at any given vehicle speed.
[0157] FIG. 16 shows the speeds of each of the ports of the
compound CVT in the configuration shown in FIG. 13 for acceleration
or deceleration. Suppose that the physical gear ratio k.sub.1 of
the planetary gear set 12 is 1.5 and the physical gear ratio
k.sub.2 of the planetary gear set 14 is 4. In order to pre-charge
the flywheel 10 when the vehicle is stationary, the motor/generator
02 would rotate in the positive direction about 2000 RPM and the
motor/generator 01 rotates in the negative direction up to 3000
RPM. The flywheel 10 would then reach the speed of 10000 RPM by the
equations (5) and (6). As the vehicle speeds up, port-EM is held
steady around 2000 RPM, which is the speed at which the engine 20
and motor 02 work most efficiently; as the variator 01 decreases
its speed in the negative direction, the speed of the flywheel 10
decreases and the speed of the final drive 32 and the wheels 34
increases, resulting in de-inertia operation for acceleration. For
deceleration, the variator 01 increases its speed in the negative
direction, which allows for power to be transferred to the flywheel
10 as the vehicle decelerates. In the range from where the
rotational speed of port-W is negative to where it reaches zero,
the vehicle can be in reverse or moving forward at up to a speed of
approximately 120 km/h. The rotational speed of the flywheel on
port-F is highest when the vehicle speed is zero, and as vehicle
speed increases the rotational speed of port-F decreases,
demonstrating de-inertia. The engine 20 and the motor 02 have a
rotational speed maintained to be around the speed corresponding to
optimal efficiency; the dotted line for port-EM signifies that the
engine 20 is off. The speed of port-G, the variator port, is
negative throughout the range of vehicle speeds since the
motor/generator 01 is efficient over a wider range (from -3000 RPM
to -400 RPM on the diagram). Note that all the motor/generators and
the engine are operating at optimal efficiency across a large range
of vehicle speeds, with the speed of the engine 20 and motor 02
varying only very little or not at all; neither the motor/generator
01 nor 02 cross the zero speed point (very low efficiency for
motor/generators) under the normal range of vehicle speeds, a
characteristic that vastly improves upon prior art. Under
situations that call for very high vehicle speeds or acceleration,
the motor/generator 01 can cross zero speed and rotate as a motor
in the positive direction.
Optimized Efficiency Cruise Operation Methods
[0158] "De-inertia operation" methods use the flywheel 10 to
diminish the effects of inertia, which comes into play during
acceleration and deceleration. Using the flywheel in this manner
improves the system's efficiency and increases performance. When a
steady vehicle speed is desired, without significant demand for
change in vehicle speed, or when vehicle speed changes only
slightly, as during cruise, inertia is no longer an issue, and the
main concern is fuel efficiency. (Steady vehicle speeds may be
considered to mean constant, near-constant, or fluctuating only a
little within a certain speed range based off a percentage of the
vehicle's current speed; for instance, in a non-limiting example,
if the current vehicle speed is 100 km/h, a steady speed may
fluctuate within a 10 percent vehicle speed range, or 5-15 percent
of the current speed, such as 95 km/h to 105 km/h.) For optimized
fuel efficiency, it would be undesirable to not take advantage of
the flywheel's capabilities and to let it sit there as "dead
weight." During a period of driving where steady speed is desired,
the flywheel 10 can still be used to improve the vehicle's fuel
efficiency. The difference between the steady speed optimized
efficiency method of the present invention and the "de-inertia
operation" explained earlier is that during a preferred
implementation of steady speed (cruise) operation the flywheel 10
is charged by the engine 20 and then transfers the energy to the
vehicle, whereas in a preferred implementation of "de-inertia
operation" the flywheel 10 exchanges energy with the vehicle
only.
[0159] In the description that follows regarding optimized
efficiency cruise methods, some steps of FIG. 21, a logic flow
chart of the optimized efficiency cruise method, are cross
referenced, although FIG. 21 will also be explained in detail
later. The process of optimized efficiency cruise also corresponds
to the operation states shown in FIG. 18(f) and FIG. 18(g).
[0160] If the motor 02 is the prime mover, as in the case for an
electric vehicle (EV) embodiment, the most efficient control method
when driving at a steady speed is simply to adjust the speeds
.omega..sub.em and .omega..sub.g so that both the motor/generators
01 and 02 are operating in high efficient RPM regions of a
predetermined efficiency map. Alternatively, the motor/generators
01 and 02 can be dynamically controlled and adjusted in real time
to minimize electric current while maintaining the same vehicle
speed, which also improves the charge/discharge efficiency in the
battery pack 05. In electric vehicle mode, with the engine 20 off
and the clutch 22 in the engaged position, the one-way clutch 24
can lock the port-EM and prevents the motor 02 and the engine 20
from turning in the negative direction, so that the variator
motor/generator 01 alone can drive the vehicle in the lower speed
range. In the higher speed range, both the motor/generators 01 and
02 work together to provide more power, with both controlled to
work at the optimal efficiency possible.
[0161] If the engine 20 is the prime mover, as in hybrid vehicle
embodiments, the efficiency of the engine 20 should be the focus.
Engine efficiency is determined by engine speed and load. The
highest efficiency state for a conventional IC engine is usually
constrained within a limited range of engine speed .omega..sub.em
and occurs at a relatively high engine load, close to two-thirds or
three-fourths of the maximum torque that the engine 20 can produce.
For a conventional vehicle in cruise, only power to overcome air
drag and other resistive forces is needed, so the engine is
operated at low power, which means lower efficiency; the lower the
vehicle speed (less power needed to maintain the speed), the less
efficiently the engine runs. When .omega..sub.em, is controlled to
be in the optimal range, as is possible with the present invention,
placing a suitably high enough load on the engine 20 is the key to
optimizing fuel efficiency. In a non-limiting example for the
configuration of FIG. 13, the speed of port-EM should be maintained
within a range for optimal efficiency, such as around 2000 RPM.
Since one of the variables determining the engine efficiency is
held to be near constant, all that remains is to ensure that the
engine operates within an optimal load range.
[0162] Should the load level be too high for a given vehicle speed
(determined in step 1202, FIG. 21), such as may be the case when
driving uphill or running against a strong wind, the
motor/generator 02 acts as a torque adjuster to provide extra power
while sharing a portion of the torque with the IC engine 20 to
ensure that engine load remains within the most efficient operation
region (step 1204). If the engine load is within the most efficient
range for the current driving condition (no in step 1202 and also
no in step 1206), the motor 02 is operated at just enough minimal
power to use the electricity generated by the variator 01 as it
controls the CVT ratio (step 1208). If the engine load is too low
for a given driving condition, the optimal control strategy is more
complicated. For most situations when the vehicle is not in
acceleration or deceleration, the power needed to maintain the
vehicle speed during cruise is very low. The lower the cruise
speed, the lower the power needed to maintain it. Conventional
vehicles usually cannot operate the engine at high efficiency
during cruise (except at very high cruise speeds), as this would
mean generating more power than needed, accelerating the vehicle
and forcing it out of cruise; consequently, most conventional
vehicles can only operate the engine at a low load during
cruise.
[0163] Low engine load means low engine efficiency, and it seems
simple to just turn off the engine 20 in a hybrid vehicle and let
the motor 02 take over as the power source moving the vehicle.
However, since in HEVs electric energy may originally be derived
from the fuel for the vehicle or another chemical energy source,
which has to go through four energy conversions, it may not always
be desirable to turn off the engine 20 and let the motor 02 take
over due to conversion losses. Suppose that the efficiency for each
conversion is 90 percent and mechanical gear to gear transmission
loss is ignored, then the efficiency of the electric energy that
gets output to the wheels is 0.9 4=0.6561, about 66 percent, which
means that 34 percent of the energy was lost to energy conversions.
It is thus not advisable to turn off the engine 20 and use only the
motor 02 to propel the vehicle unless the efficiency drop from the
best efficiency region is more than 34 percent (66 percent relative
efficiency or lower; relative efficiency is defined as the engine
efficiency under current operation conditions divided by the
maximum engine efficiency when operating under optimal conditions
for efficiency). Using the motor 02 with electric energy from the
battery before the engine efficiency has dropped 34 percent from
its best efficiency will use more fuel in the long haul, since more
energy has been lost through conversion than the energy that was
conserved or gained by operating the engine at the maximum
efficiency. When the engine load drops below a certain threshold,
which is related to 66 percent relative efficiency in the HEV case,
which can be calculated by estimating the conversion losses, the
engine 20 is turned off and motor 02 takes over until the state of
charge in the battery pack 05 drops to a lower state of charge
limit. Then, the engine 20 starts and the variator 01 and traction
motor 02 can act as generators to increase the load seen by the
engine 20, controlling the engine 20 to work at optimal load and
optimal efficiency while .omega..sub.em, is fixed in the most
efficient range of the engine 20 by the generator 02, and the CVT
ratio is controlled by the generator 01 to maintain the same
vehicle speed. The power generated by the variator 01 and the
traction motor 02 charge the battery pack 05 until an upper state
of charge limit is reached. The engine 20 is then shut off and the
motor 02 is then used to drive the vehicle until the lower state of
charge limit is reached. Under this control strategy for HEVs, the
IC engine 20 is ensured to work at 66 percent relative efficiency
or better.
[0164] In a preferred embodiment of the present invention, the
addition of the flywheel 10 brings a kinetic power source and
kinetic energy storage to the vehicle, which will be heretofore
referred to as the kinetic hybrid vehicle or KHV. A kinetic hybrid
vehicle may be a vehicle that includes a kinetic power source and a
kinetic energy storage in addition to having a prime power source
(e.g., a prime mover) and the energy source for the prime mover.
Since the energy is stored in the flywheel in the same form it is
used in, the energy exchange between the flywheel 10 and the wheels
34 of the vehicle takes place along a direct mechanical path, with
no energy conversion. There is a mechanic-electric energy split
between port-G and port-EM for the control of the CVT ratio. With a
compound CVT, typically around 25 or less percent of the total
power goes through the electric path, and 75 percent or more of the
power is transferred via a direct mechanical path. The same
assumptions used for the HEV example, namely that each energy
conversion stage is 90 percent efficient and that the mechanical
gear to gear loss is negligible, may be used to estimate the
percentage of energy lost to storing and releasing energy to and
from the flywheel 10 in the KHV.
[0165] In the fuel-kinetic hybrid mode of operation, the KHV's
strategy during cruise is to keep the engine 20 working within its
optimal efficiency region; although more power will be generated as
a result, the output power from the engine 20 can be split into two
portions, one of which drives the vehicle's wheels 34 to maintain
the desired cruise speed, and another which is split to the
flywheel 10 to store up to a level either predetermined or
calculated in real time. Once the energy in the flywheel 10 has
reached that level, the engine 20 is turned off and disengaged,
allowing the flywheel 10 to propel the vehicle and maintain the
desired cruise speed.
[0166] It follows from equation (5) that if the clutch 22 is
engaged and the speed of the engine 20 .omega..sub.em is increased
a certain increment, and the speed of the variator 01 .omega..sub.g
in the reverse direction is increased by k.sub.1 times that
increment, the vehicle speed .omega..sub.w will remain unchanged.
It also follows from equation (6) that if the speed .omega..sub.em
of the engine 20 is increased a certain increment but the vehicle
speed .omega..sub.w remains the same, the speed of the flywheel 10,
.omega..sub.f, must increase by k.sub.2+1 times that increment.
Thus a steady cruise speed can be maintained while the engine 20
runs at optimal efficiency.
[0167] Once the kinetic energy of the flywheel 10 reaches some
upper limit, the clutch 22 is disengaged and the engine 20 is
turned off; from equation (5), it follows that if the variator 01
decreases its speed .omega..sub.g in the reverse direction by
k.sub.1 times a certain decrement and the motor 02 decreases its
speed .omega..sub.em by one time that decrement, the vehicle speed
.omega..sub.w remains unchanged. According to equation (6), if the
vehicle speed .omega..sub.w remains the same, and the motor 02
decreases its speed .omega..sub.em by a certain decrement, then the
speed of the flywheel 10, .omega..sub.f, must decrease by k.sub.2+1
times that decrement. In other words, the system controls the
flywheel 10 to release energy to the vehicle's wheels 34 to
maintain the desired cruise speed. Once the kinetic energy of the
flywheel 10 reaches some lower limit, the clutch 22 is engaged and
the engine 20 is started to begin the next cycle; the engine 20 and
the flywheel 10 propel the vehicle in turns in this manner.
Whenever the engine 20 is on, it works at optimal efficiency, and
whenever the flywheel 10 propels the vehicle, it does so at a very
high efficiency, since the flywheel 10 transfers kinetic energy to
the vehicle mechanically, without conversion loss. With the engine
20 and the flywheel 10 working together in this way, the vehicle's
efficiency during cruise can be optimized and can improve
significantly.
[0168] The flywheel 10 in the preferred embodiment of the KHV is
used as a kinetic energy and kinetic power buffer to enable the
prime mover engine 20 to be operated in the most efficient manner.
Most of the energy transferred into and out of the flywheel 10 is
transferred mechanically, and with negligible loss. What energy
conversion losses there are in the KHV comes from the portion of
energy that travels the electric path, through the variator 01 and
the motor 02 (refer to FIG. 18(f) and FIG. 18(g)). In each cycle,
the energy from the engine 20 travels through the compound CVT at
most twice, once when the excess power is driving the flywheel 10
and the energy is stored into the flywheel 10, and once when energy
is released from the flywheel 10 to drive the vehicle. Each time,
approximately 25 percent of the total power travel the electric
path, and that portion of the energy is converted into electricity
by the variator 01, then converted back into kinetic energy and
used back into the powertrain by the motor 02, so each trip through
the compound CVT the portion of energy lost to conversion is
0.25*(1-0.9*0.9), 4.75 percent of the total energy. When energy is
stored into the flywheel 10, approximately 75 percent is stored
kinetically into the flywheel 10 via a purely mechanical path, 4.75
percent is lost to conversion, and 20.25 percent is stored back
into the flywheel 10 via an electromagnetic path by the motor 02.
The efficiency for storing kinetic energy to the flywheel 10 is
0.75+0.2025=0.9525, 95.25 percent, compared to 81 percent for HEVs.
When energy is released from the flywheel 10, another 4.75 percent
is lost to conversion. Recall, however, that originally 95.25
percent of the total energy was stored into the flywheel 10; the
percent lost to conversion out of the total energy from the
beginning would thus be
0.0475+0.9525*0.0475=0.0475+0.04525=0.09275, or approximately 9
percent. The overall system efficiency, assuming that gear to gear
loss is negligible, is then approximately 91 percent, which is a
drastic improvement compared to 66 percent when the same control
method is applied to the HEV using the HEV's batteries as the
energy buffer instead of the flywheel buffer unique to the KHV.
Although in practice mechanical gear to gear losses may decrease
the KHV's system efficiency from its estimated value, the same
effect also applies to HEVs, so the conclusions drawn from
theoretically comparing the KHV to HEVs would still hold in real
world applications.
[0169] FIG. 17 presents the difference in efficiencies between the
preferred embodiment of the KHV of this invention and conventional
HEVs during steady speed operation. On the left side of the figure
is an efficiency (or BSFC) map for a conventional internal
combustion engine. This engine needs to work around 2000 RPM for
best efficiency. The threshold engine load in the preferred
embodiment of the KHV of the present invention is about 130 N-m,
where the efficiency of the engine is 91 percent of its maximum
efficiency. The region below this threshold covers the areas A and
B in which the engine of this example can perform optimized
efficiency cruise operation and work in a start-stop mode to save
fuel and increase efficiency. Meanwhile, the threshold engine load
for a typical HEV is about 67 N-m, where the efficiency of the
engine is 66 percent of its maximum efficiency. In this case, the
HEV can stop the engine only when the engine load has dropped below
67 N-m, i.e. area B. Here is an example: in area A with the
preferred embodiment of the KHV of the invention, where the engine
efficiency is about 80 percent of maximum efficiency, operating the
engine in a start-stop manner yields a relative efficiency increase
of 11 percent than if the engine was operated continuously. For a
conventional HEV, if the engine operates in a start-stop manner,
it's a loss in relative efficiency of 14 percent compared to
operating it continuously. Thus the preferred embodiment of the KHV
of the present invention is more advantageous for improving fuel
economy under a broader range of driving conditions than the
typical HEV.
[0170] The right side of FIG. 17 illustrates the energy changes
during start-stop operation where vehicle speed is held steady.
From t1 to t2 and again from t3 to t4 the engine is on, and from t2
to t3 and again from t4 to t5 the engine is off. Each time when the
engine is on, the engine's output power can be divided into two
portions, indicated by the areas C and D. The area C represents the
power needed to maintain the steady speed of the vehicle, and the
area D is the excess power generated by the engine in order to
operate at optimum efficiency. The excess power represented by D is
charged into the flywheel when the engine is on, and when the
kinetic energy in the flywheel reaches a preset value, it is
released from the flywheel when the engine is off, in area E. A
constant level of power is delivered to the wheels throughout,
while the engine is operated in a start-stop manner.
[0171] With a preferred embodiment of the KHV of this invention, it
is worthwhile to perform start-stop operation as long as the
efficiency of the engine has dropped by 9 percent compared to its
highest efficiency (100%). For a preferred embodiment of the KHV of
the present invention, the IC engine 20 may work at 91 percent
relative efficiency or better, and the engine load that corresponds
to 91 percent relative efficiency in the speed range of
.omega..sub.em can be used as a threshold load condition to trigger
the optimized efficiency cruise operation or start-stop operation
of the engine 20. If in cruise the engine 20 would be operating at
a "current" load below the threshold load condition (step 1206,
FIG. 21), then the engine 20 is operated at the optimal efficiency
load, the output power from the engine 20 is split to drive the
vehicle with the "current" load or power needed to maintain the
current vehicle speed, and to charge the flywheel 10 (step 1214)
with the remaining power that is the difference between the optimal
efficiency load and the "current" load until the flywheel 10's
upper speed setting is reached (step 1210). Once the flywheel 10
has a certain amount of reserve energy (upper speeding setting
exceeded, step 1210), the flywheel 10 can drive the vehicle when
the engine 20 is off (step 1216), with the motor 02 reusing the
electric energy generated by the variator 01 to reduce energy
conversion losses and prolong the life of the battery pack 05.
[0172] In a slightly more condensed form than was described
previously, the preferred method to optimize efficiency of cruise
(steady vehicle speed) operation for the preferred embodiment of
the KHV of the present invention is as follows. If the load is too
high (step 1202) from road conditions for the engine 20, the motor
02 shares the extra load and lets the engine 20 work in its most
efficient state (step 1204). When the load is just right (step
1208), the motor 02 maintains the minimum power needed to absorb
the electricity from the variator 01, and the engine 20 provides
the remaining torque needed. If the engine load is below a
threshold (determined by step 1206), the engine load is controlled
to increase to the highest efficiency load level of the engine 20
(step 1214) by increasing the engine speed .omega..sub.em
incrementally; the speed of the generator 01, .omega..sub.g, is
increased k.sub.1 times the increment of the change in
.omega..sub.em in the opposite direction to keep the speed
.omega..sub.w of the vehicle stable (equation (5)). At the same
time, .omega..sub.f, the speed of the flywheel 10, is increased
k.sub.2+1 times the incremental change in .omega..sub.em (equation
(6)), so the energy is charged to the flywheel 10 from the engine
20. When the speed .omega..sub.f of the flywheel 10 reaches a
preset upper value (determined by step 1210), the engine 20 is
turned off (step 1216), and the flywheel 10 is used to drive the
wheels 34. At this point, the control goes as follows: the speed
.omega..sub.g of the generator (and transmission ratio variator) 01
is decreased k.sub.1 times an incremental speed in the negative
direction, and the speed of the motor/generator 02, .omega..sub.em,
is decreased that incremental speed in the positive direction to
keep .omega..sub.w stable. As a result, the speed .omega..sub.f of
the flywheel 10 is decreased by k.sub.2+1 times the incremental
speed, and energy is released from the flywheel 10 to drive the
wheels 34. When .omega..sub.f drops to or below a lower preset
value (determined by step 1224), the engine 20 is started again
(step 1214) to begin another cycle of this operation, where a
portion of the energy is delivered to the vehicle at a constant
rate, but another portion is transmitted from the engine 20 to the
flywheel 10 and stored in the flywheel 10 until used. The flywheel
10 functions as both an energy storage device and as a power
source.
[0173] The method of the optimized efficiency cruise operation
described above (and described in more detail with FIG. 21)
maximizes the use of the flywheel 10, and minimizes the use of the
battery pack 05, extending the life of the battery pack 05. The IC
engine 20 always works at optimized efficiency when it is on
because charging the flywheel 10 while driving the vehicle also
increases the engine load for better fuel efficiency. In
conventional flywheel hybrids in the prior art, the flywheel was of
little or no use during cruise, and was only significantly useful
during substantial acceleration or deceleration of the vehicle. In
preferred embodiments, the present invention optimally uses the
flywheel to increase the vehicle's efficiency both in situations
where speed changes (de-inertia operation) and in situations where
speed is steady (optimized efficiency cruise operation), improving
upon conventional methods and systems.
Vehicle Operation States for the Preferred Four-Port Embodiment
[0174] FIG. 18 depicts the general range of operation states the
vehicle is capable of undergoing with a preferred embodiment of the
hybrid powertrain. Some steps are cross-referenced from the
corresponding logic flowcharts FIGS. 19-21 to be described in
detail later. The operation states 18(a) through 18(m) are listed
in the order in which they occur in a typical journey. Again in
FIG. 18, the flywheel is represented as F, motor/generator 01 is
represented as M1 or G1, the motor/generator 02 is represented as
M2 or G2, the engine is represented as E, the vehicle's wheels are
represented as W, the battery pack is represented as B, and the
input/output ports of the planetary gear sets 12 and 14 correspond
respectively to the sun gear S1, the planetary carrier C1, and the
ring gear R1 for planetary gear set 12 and the sun gear S2, the
planetary carrier C2, and the ring gear R2 for planetary gear set
14. Large filled arrows indicate the direction of motion, large
unfilled arrows indicate the direction of torque, and the small
arrows indicate the direction of energy transfer, while dotted
lines indicate the component(s) are decoupled or are not used, and
solid lines without arrows indicate a physical connection (same
port).
[0175] At the beginning of the journey prior to launching the
vehicle, it would be desirable to charge up the flywheel F before
starting the engine E so that the flywheel F enhances drivability
and efficiency. To pre-charge the flywheel F while the vehicle
remains stationary and braked at the wheels W (which applies just
as the vehicle is started and there is not yet enough energy in the
flywheel, or when the vehicle is stopped at a signal light and the
energy in the flywheel is not yet at maximum state of charge), the
engine E is decoupled from the drivetrain and the motor M2 draws
energy from the battery pack B charge the flywheel F at optimal
efficiency (at a current maximizing combined efficiency), as shown
in FIG. 18(a). Since .omega..sub.w=0 (wheels W fully braked), from
equation (6) it follows that .omega..sub.f=(k.sub.2+1)
.omega..sub.em. This means that for every increment of change in
the speed of motor M2, the speed in the flywheel F changes by
k.sub.2+1 times that increment. G1 is electrically off (spinning
freely) during pre-charge so that there is no reaction torque to
transfer the power from the flywheel F and M2 to the wheels W.
[0176] Once the flywheel F is sufficiently charged, the vehicle is
ready to be started by the flywheel; the variator G1 reduces its
speed in the reverse direction, producing a reaction force enabling
the transfer of kinetic energy from the flywheel F and the motor M2
to the wheels W, which is no longer braked, launching the vehicle
from rest. Either the motor MG2 or the flywheel F may supply the
torque needed to start the engine E, depicted by FIG. 18(b).
[0177] Following the start of the engine E, the vehicle is launched
from rest by the flywheel F and accelerates. In FIG. 18(c), the
first mode of acceleration, which follows starting the engine in
FIG. 18(b), M2, the engine E, and the flywheel F all contribute
torque to accelerate the vehicle, of which the flywheel F would be
the prime contributor at lower vehicle speeds. G1, the variator,
provides the reaction torque necessary to transmit power from the
engine E and the flywheel F to the wheels W. Referring to equations
(5) and (6), decreasing .omega..sub.g in the negative direction
while holding the M2 speed .omega..sub.em steady results in an
increase in .omega..sub.w, the speed of the wheels W and hence
vehicle speed. Meanwhile, an increase in .omega..sub.w while
.omega..sub.em remains steady results in a drop in .omega..sub.f,
meaning that energy is simultaneously released from the flywheel F
to accelerate the vehicle. This is the process of the de-inertia
method for acceleration, in which the flywheel F's energy is
transferred to the vehicle, improving both performance and fuel
efficiency. In the latter stage of acceleration (higher speeds),
power is primarily provided by the engine E and the traction motor
M2 (which reuses the energy generated by the variator G1 back into
the powertrain to prevent charging the batteries, increasing
efficiency and extending battery life). Occasionally, at very high
vehicle speeds when considerable acceleration is still needed, M/G1
can go into the motoring state to transmit more power to the wheels
W. Thus in FIG. 18(d), M1, M2, the engine E and the flywheel F can
all contribute power to propel the vehicle. Using all four power
sources gives the greatest power output to the vehicle's wheels,
and should the energy in the flywheel F be depleted this way, M1,
M2, and E can continue to drive the vehicle at the maximum combined
output of these remaining three power sources.
[0178] Following acceleration, cruising or coasting may be desired
for some period of time. In the coasting state shown in FIG. 18(e),
every component of the drivetrain is inactive, which puts the
vehicle in neutral. In the following cruise states, there is very
little change in the vehicle's speed and little in the way of
inertial effects, so in the event of driving the vehicle with only
the engine E, as is the case with conventional vehicles, the engine
load would be low, which also means low efficiency. Raising the
efficiency of the engine E is the primary goal of the optimized
efficiency cruise states in FIGS. !8(f), 18(g). In the first cruise
state illustrated in FIG. 18(f), the goal is to increase the
efficiency of the engine E by increasing the engine load and
storing the reserve power, so G1 acts as the variator controlling
the speed ratio of the CVT, while the power from the engine E is
split to charge up the flywheel F and to drive the wheels W, and M2
acts as a torquer motor to use the electricity from G1. Once the
maximum safe or desired speed (equivalently, upper desired kinetic
energy setting) on the flywheel F has been reached, the engine E
can be decoupled from the drivetrain, allowing the flywheel F
controlled by the variator G1 to function as the mover in a second
cruise state, depicted in FIG. 18(g). Kinetic energy is released
from the flywheel F to the wheels W at precisely (or as near
precisely as possible) the power needed to maintain the cruise
speed of the vehicle. Until cruise is no longer desired, the KHV
cycles through the two cruise states of 18(f) and 18(g),
alternating between either using the prime mover engine E at its
optimal efficiency or not using it at all. More detailed
descriptions of the optimized efficiency cruise methods have
already been introduced with the previous figures and so will be
omitted here.
[0179] For deceleration, there are also two states. In FIG. 18(h),
showing de-inertia methods during deceleration (and hence opposite
to the de-inertia mode for acceleration shown in FIG. 18(c)). The
engine E is decoupled and off. The system is focused on charging as
much energy as possible to the flywheel F, and the variator M1
enters the motoring state to increase the speed of S1 negatively to
control the kinetic energy from the wheels W to transfer to the
flywheel F via a mechanical path from ring gear R2 to sun gear S2.
The generator G2 produces a braking torque to hold the speed
.omega..sub.em, steady and to supply power to the variator M1. By
the planetary gear relationships expressed in equations (5) and
(6), the kinetic energy of the vehicle is transferred from the
wheels W to the flywheel F via a mechanical path from ring gear R2
to sun gear S2. The second deceleration state, shown in FIG. 18(i),
is entered when the flywheel F has been charged to its maximum safe
energy capacity. Here, both motor/generators of the system act as
generators G1 and G2 to regenerate any remaining kinetic energy
left in the vehicle as electricity to be stored in battery pack
B.
[0180] The last three states of FIG. 18 show miscellaneous other
functions desired in the vehicle. Should the state of charge of the
battery pack B drop to a very low level, the engine E may be used
to charge the battery pack B through G2 while the vehicle coasts or
remains stationary, depicted in FIG. 18(j). To reverse the vehicle,
shown in FIG. 18(k), M2 drives the wheels directly in the reverse
direction, while the generator G1 provides the reaction torque, and
both the engine E and the flywheel F are decoupled. Finally, at the
end of the drive, the flywheel F may have some energy left over and
it may be more desirable to store this energy into the battery pack
B; in FIG. 18(m), the flywheel F releases its energy through the
generator G2 to the battery pack B while other components of the
system (M1, E) are inactive and decoupled.
Control Methods
[0181] FIGS. 19, 20(a), 20(b), 20(c), and 21 comprise logic flow
charts describing the methods to control the system of the
invention.
[0182] In the flow charts, M/G1 refers to the motor/generator 01,
M/G2 refers to the motor/generator 02, and both Engine and ICE
refer to the engine 20, while CL(E) refers to the clutch 22
connecting the engine 20 to the drivetrain, and CL(F) refers to the
clutch 16 connecting the flywheel 10, which is just expressed as
Flywheel.
Start of the Drive and the Vehicle Stationary State
[0183] The vehicle is started at step 1002. When the vehicle is
first started, it is presumed that the vehicle is first stationary
(step 1004), and the flywheel 10 can be pre-charged while it is
stationary. The vehicle stationary step 1004 also includes the
vehicle state when the vehicle is stopped in traffic. The process
represented by step 1004 consists of the steps 1110 through 1132,
explained in more detail in FIG. 20(a). Steps 1110 through 1132
ensure that while the vehicle is stopped, the flywheel is charged
to a maximum level for improved performance upon acceleration, and
also allows the battery pack to be charged if SOC is too low when
the vehicle is stationary. At first both the clutches 16 and 22 are
disengaged, and the engine 20 and both the motor/generators 01 and
02 are off (step 1112). The vehicle stationary state, apart from
the start of the drive, may also apply when the vehicle is stopped
temporarily at an intersection or a stop sign. 1110 represents when
the system first enters the vehicle stationary loop. The system
continually reads in inputs from sensors in its interface 62 or
from the vehicle's ECU 60 to evaluate whether the operator's intent
is for the vehicle to remain stationary (step 1114). As soon as it
is detected that moving the vehicle is desired, determined in step
1114, the system exits the vehicle stationary loop (step 1120) and
proceeds on to step 1006.
Battery Charge and Flywheel Charge or Restore
[0184] As long as the vehicle remains in the stationary state, the
system will make decisions as to whether the battery pack 05 and/or
the flywheel 10 should be charged. First, it detects the state of
charge in the battery pack 05 and determines in step 1116 whether
it needs charging. If so, the system proceeds to step 1118,
engaging the clutch 22 to connect the engine 20, which then drives
the generator 02 to charge the battery pack 05, as in FIG. 18(j).
While the battery pack 05 is being charged the system can continue
to monitor whether it is desired for the vehicle to leave the
stationary state in step 1114 (through 1118 to 1126 to 1114). Once
it is determined that the battery charge is complete (step 1126),
the system performs step 1128, shutting off the engine 20 and the
generator 02, and disengaging the clutch 22 before returning to
1114. As long as the state of charge in the battery pack 05 is
adequate, following 1114 the system proceeds from 1116 to 1122, to
see if the flywheel 10 needs charging. If yes, the system executes
step 1124, engaging the clutch 16 to connect the flywheel 10, and
using the motor 02 to charge up the flywheel 10, as in FIG. 18(a).
If the flywheel 10 does not need to be charged (step 1122), or if
it is still being charged and the charge is not yet complete (step
1130), the system returns to step 1114 to check if it is desired
for the vehicle to leave the vehicle stationary state. Whenever it
is determined that the vehicle is to leave the stationary state in
step 1114, the system exits the loop (step 1120).
[0185] Variations on battery charging and flywheel charging. In one
conceivable but less preferred variation, the system may determine
whether the flywheel 10 needs charging before determining whether
the battery pack 05 needs to be charged. In another variation, the
steps 1126 and 1128 may be omitted. In another variation, the steps
1130 and 1132 may be omitted. In still another variation, the steps
1126, 1128, 1130, and 1132 may all be omitted. The system would
still work with these variations, just at less optimal
efficiency.
[0186] Of course, another possibility for when the vehicle is
stationary is if the end of the drive has been reached (step 1006)
and it is time to turn off the vehicle. If so, then the system
performs the flywheel restore function that corresponds to the
state in FIG. 18(m) in step 1014, where energy in the flywheel 10
is converted and stored into the battery pack 05, before shutting
down (step 1016). The flywheel restore function is described in
more detail by steps 1140 through 1148 in FIG. 20(c). In step 1142,
the clutch 22 disengages the engine 20 from the drivetrain. The
clutch 16 connecting the flywheel 10 to the drivetrain is in the
engaged position, allowing the flywheel 10 to drive the generator
02 in step 1144. The flywheel 10 continues to drive the motor 02 to
charge the battery pack 05 until the energy in the flywheel 10 is
depleted (.omega..sub.f=0). Once it has been determined that the
flywheel 10 has stopped in step 1146, the flywheel restore
operation is complete, and the system then exits the loop in step
1148, and the vehicle can shut down.
Driving in Reverse
[0187] Once again following the logic flow chart in FIG. 19 from
the very beginning, when the vehicle is first started in step 1002,
once it is desired for the vehicle to start moving (determining in
step 1006 that the operator does not intend to end the drive), it
may be desirable to reverse the vehicle (step 1010). The reverse
state, which is depicted in FIG. 18(k), is represented by step 1008
in FIG. 19 and the steps from 1133 through 1138 in FIG. 20(b). From
step 1010, the system enters the reverse loop, step 1133. The
reverse mode is carried out in electric mode. To prepare to drive
the vehicle in reverse, step 1134, both clutches 22 and 16 are
disengaged, the engine 20 is off, and both the motor/generators 01
and 02 are on (01 as a variator/generator, 02 as a motor). For the
duration of the drive in reverse (step 1135), the motor 02 provides
the power to drive the vehicle, while the variator 01 provides a
braking torque so the power from the motor 02 can be transmitted to
the wheels 34. The system will continually monitor whether the
operator brakes the vehicle, step 1136. As long as the operator has
not given a signal to stop the vehicle, the system loops back to
step 1135 to keep driving the vehicle in reverse until it is
desired that the vehicle should be stopped (step 1136), at which
point the system leaves the reverse loop, step 1138. From there,
the vehicle is momentarily in the vehicle stationary state (step
1104), and proceeds to step 1006, which determines whether the
operator of the vehicle intends to end the drive. If so, then the
system proceeds to step 1014 to transfer the flywheel's energy to
the battery pack 05.
De-Inertia Acceleration
[0188] After the vehicle has been started (step 1004 of FIG. 19),
and it is not desired to drive the vehicle in reverse (step 1008)
or end the drive (step 1006), the system waits for a signal to
accelerate the vehicle (step 1018). It is presumed that the system
has pre-charged the flywheel 10 in step 1004 of FIG. 19, and more
specifically in step 1124 of FIG. 20(a), when the vehicle was
stationary at the very beginning of the drive, or following a
deceleration maneuver. Please also refer back to FIG. 16 for
reference to the four different ports and how their rotational
speeds are interrelated. If the system detects a signal from the
operator of the vehicle to accelerate (step 1018), the system
proceeds to step 1020. In step 1020, or de-inertia acceleration,
the flywheel 10 is spinning at some angular velocity, and
decreasing the negative angular velocity of port-G while holding
port-EM at a steady angular velocity (selected to correspond to the
most efficient region of operation for the engine 20) will cause
the flywheel velocity .omega..sub.f to decrease and the speed of
port-W, which is coupled to the final drive 32 and the wheels 34,
to increase (according to equations (5) and (6)), thus increasing
the vehicle speed. In this manner the vehicle is accelerated while
the speed of the flywheel 10 is decreased; the flywheel transfers
its kinetic energy to the vehicle, helping the vehicle to
accelerate while diminishing its inertial effects, increasing both
efficiency and performance. The engine 20 may also be started to
provide even more power to acceleration. The system continually
checks for signals indicating the end of acceleration (step 1022)
and will continue implementing de-inertia acceleration, step 1020
(and FIGS. 18(c) and 18(d)), until acceleration is no longer
needed. Following de-inertia acceleration, step 1026 checks whether
there is demand for deceleration; if so, the system enters step
1028 for de-inertia deceleration, and if there is no deceleration
demand, the system enters optimized efficiency cruise in step
1024.
De-Inertia Deceleration
[0189] After some period of acceleration has ended (determined in
step 1022), the system detects whether it is desired that the
vehicle be decelerated, step 1026. The de-inertia deceleration
state is represented by step 1028 in FIG. 19 and depicted in FIGS.
18(h) and 18(i), and is basically the opposite of the acceleration
process in step 1020. During deceleration, no power is needed, so
the clutch 22 is disengaged and the engine 20 may be turned off to
save fuel. FIG. 16 can also serve as a reference for how the port
speeds are interrelated. In this process, the motor/generator 01
increases its velocity .omega..sub.g on port-G in the negative
direction, while motor/generator 02 holds the speed of port-EM,
steady. With .omega..sub.em steady and the quantity .omega..sub.g
decreasing, .omega..sub.w and the vehicle speed on port-W must
decrease (equation (5), FIG. 16). By the planetary relationships of
equation (6), this would mean that with the speed of port-EM
.omega..sub.em steady and the vehicle speed .omega..sub.w
decreasing, the flywheel speed .omega..sub.f on port-F must
increase, which means that the vehicle's kinetic energy is stored
into the flywheel 10. Step 1028 enables the vehicle to reduce its
speed while recovering its kinetic energy at the same time, which
will be used in the future to accelerate the vehicle, diminishing
inertial effects and increasing efficiency. Should deceleration in
step 1028 take the vehicle speed all the way down to zero,
determined in step 1030, then since that would mean the vehicle is
once again stationary, the system returns to step 1004, the vehicle
stationary state. If deceleration has occurred from step 1028 but
the vehicle speed is not yet zero, then the system returns to step
1022, from where the system can accelerate (step 1020), continue to
decelerate (step 1026), or enter optimized efficiency cruise (step
1024).
Optimized Efficiency Cruise
[0190] After some period of acceleration, the vehicle can enter
into an optimized efficiency cruise state (FIGS. 18(f) and 18(g))
if deceleration is not desired in step 1026. If neither
acceleration nor deceleration is desired (no in step 1022 and in
step 1026), then it is equivalent to say that it is desired to
maintain the current vehicle speed. Since there are no inertial
effects or acceleration to consider, the sole objective is
efficiency. If this is the case, then the system enters into
optimized efficiency cruise, step 1024, which is also represented
in more detail by the steps 1200 through 1226 of FIG. 21. Since the
engine 20 is assumed to be the prime mover, it is of the utmost
importance to ensure that the engine 20 runs in its best efficiency
state. Engine RPM, .omega..sub.em, is controlled to operate near
the speed corresponding to the engine 20's peak efficiency region,
while the system of the invention can also adjust engine load with
the motor/generator 02 to increase efficiency. Step 1200 is the
point of entry for the optimized efficiency cruise method. The
system of the invention will continually monitor any signals
generated by the operator of the vehicle to ensure that the
operator intends to stay in cruise. Steps 1212, 1218, and 1220 all
determine that, in the case that the operator no longer wishes to
maintain a steady speed (i.e. a speed change is desired), the
system exits the optimized efficiency state loop in step 1226.
[0191] In step 1202, the system detects whether the current engine
load or torque value is higher than the load corresponding to the
engine 20's best efficiency state (encountered when there is strong
wind or incline). If so, then the motor 02 shares the load in
excess using energy from the battery pack 05 to allow the engine 20
to run at a better efficiency. If the engine load is not too high,
then the system detects whether the engine load is too low in the
next step, step 1206. If the engine load is neither too high nor
too low, then because engine speed .omega..sub.em is approximately
fixed at the ideal speed for efficiency, the system determines that
the engine 20 is already running at optimal efficiency, and in step
1208 controls the motor 02 to only reuse the power generated by the
variator 01 as the variator 01 behaves mostly as a generator to
vary the transmission ratio for the engine 20. Following 1204 or
1208, the system checks whether the operator intends to change the
vehicle speed in step 1212: if not, the system returns to step 1202
to keep looping; if yes, the system exits the optimized efficiency
cruise loop in step 1226.
[0192] If the engine load is too low, as is usually the case when
the vehicle is in cruise (inducing low engine efficiency in
conventional vehicles), the adjustment of the engine load becomes
key. The following steps use the flywheel 10 to increase the load
of the engine 20 to ensure the greatest efficiency in operating the
engine 20. When the load of the engine 20 is less than the lower
limit of the load range for optimal efficiency (determined from
steps 1200 to 1206), the system will proceed to step 1210 to
determine whether the flywheel 10 has enough energy stored to drive
the vehicle on its own for a period of time. During cruise the
flywheel speed .omega..sub.f is controlled to be no lower than a
lower setting and no higher than an upper setting. The lower
setting represents power reserved in the flywheel 10 in the event
that it is desired to stop cruising and accelerate the vehicle. The
difference between the maximum safe flywheel speed and the upper
setting represents the amount of energy the flywheel 10 can still
safely recapture in case of deceleration. These lower and upper
speed settings for the flywheel 10 under cruise can be
predetermined or dynamically determined according to parameters
such as vehicle speed, which can be read from the interface to the
system 60 or the vehicle's ECU 62.
[0193] Should the flywheel 10 speed .omega..sub.f be greater than
the upper setting in step 1210, it means the flywheel 10 has enough
energy stored to drive the vehicle on its own (FIG. 18(g)), and the
system proceeds to step 1216 to release energy from the flywheel 10
to the vehicle's wheels 34. The engine 20 is temporarily turned off
and disengaged by keeping the clutch 22 "open". Hence, with the
engine 20 disengaged the speed of port-EM, .omega..sub.em, is
controlled by the motor 02 and should be decreased by a certain
increment. If the variator G1 changes its speed .omega..sub.g by a
certain increment, then by equation (5) .omega..sub.em must change
in the opposite direction by 1/k.sub.1 times that increment to
maintain the same vehicle speed .omega..sub.w for cruise. Since
.omega..sub.w is also steady in equation (6), any incremental
change in .omega..sub.em, the speed of M2, will be accompanied by a
change of (k.sub.2+1) times that increment in .omega..sub.f, the
speed of the flywheel F, to maintain steady vehicle speed.
[0194] After discharging the flywheel in step 1216, the system
proceeds to step 1220 to make sure that the vehicle should still be
operated in cruise. Then as long as the flywheel speed is above the
lower setting in step 1224, the system continues to release energy
from the flywheel to maintain a steady vehicle speed while the
engine is off, step 1216, FIG. 18(g). Once the flywheel speed
.omega..sub.f drops lower than the lower setting, then it becomes
desirable to store more energy into the flywheel 10, and as long as
a speed change is not desired in step 1220, the system proceeds to
step 1214 to charge the flywheel 10, FIG. 18(f). If a speed change
is desired in step 1220, it marks the end of the optimized
efficiency cruise loop and the system exits (step 1226).
[0195] If in step 1210 it is determined that the flywheel speed
.omega..sub.f is not above the upper setting, or if the flywheel
speed .omega..sub.f has already dropped below some lower setting in
step 1224, the system then charges the flywheel 10 up to the upper
setting (FIG. 18(f)) in step 1214. For step 1214 the clutch 22 is
held in the "closed" position to engage the engine 20, and both the
engine 20 and the motor 02 increase their speed to operate in the
range of the ideal RPM for the engine 20's best efficiency state.
The engine 20 outputs higher power than previously, a portion of
which is used to maintain the current vehicle speed, and another
portion of which is used to accelerate the flywheel 10. From
equations (5) and (6), it follows that when the motor/generator 01
increases its speed .omega..sub.g in the negative direction at k1
times the rate of increase in .omega..sub.em, (the speed of the
engine 20 and the motor 02), the flywheel speed .omega..sub.f
increases as it is charged at k.sub.2+1 times the rate of increase
in .omega..sub.em, and the vehicle speed stays stable or steady
(also see FIG. 16). Functionally, what is happening is that the
engine 20 and motor/generator 02 drive the vehicle, and the
variator 01 splits the power from port-EM in FIG. 13 so that just
enough power goes to port-W to maintain a steady vehicle speed, and
the rest of the power goes to charge the flywheel 10 on port-F,
illustrated in FIG. 18(f). After step 1214, the system once again
determines whether a speed change is desired in step 1218. If not,
then the system returns to step 1210. If yes, the system then goes
to step 1226 and exits the optimized efficiency cruise operation
loop.
[0196] The optimized efficiency cruise method primarily consists of
step 1214, charging the flywheel 10, and step 1216, releasing
energy from the flywheel 10. These two steps are alternatively used
until there is a demand for a change in vehicle speed. In step
1214, the engine 20 is operated within an optimal efficiency range,
simultaneously driving the vehicle's wheels 34 and charging the
flywheel 10. The vehicle maintains the same speed since any power
in excess of what is needed to maintain the cruise speed is stored
into the flywheel 10. In step 1216, the engine 20 is off and
consumes no fuel, and the power needed to maintain the same vehicle
speed comes from the flywheel 10. Any time the engine 20 is used,
it is operated in its best efficiency state, hence optimizing the
vehicle's fuel efficiency during cruise.
Other Four-Port (Compound CVT) Configurations
[0197] FIG. 22 demonstrates an alternative configuration. The
difference between this configuration with the first preferred
configuration in FIG. 13 is that the carrier gear C1 of the
planetary gear set 12 is connected to the carrier gear C2 of the
planetary gear set 14 and the ring gear R1 of the planetary gear
set 12 is connected to the ring gear R2 of the planetary gear set
14. The resulting planetary gear equations derived from (3) and
(4):
(k.sub.1+1).omega..sub.w=k.sub.1.omega..sub.em+.omega..sub.g
(7)
(k.sub.2+1).omega..sub.w=k.sub.2.omega..sub.em+.omega..sub.g
(8)
[0198] The configuration in FIG. 22 functions almost equally well
except for the fact that the physical gear ratio k.sub.2 should be
increased by 1 to achieve the same flywheel speed .omega..sub.f
with the same increment in .omega..sub.em as compared to the
configuration of FIG. 13.
[0199] For the alternative configurations shown in FIG. 23 and FIG.
24, the variator 01 is connected to the ring gear R1 instead of the
sun gear S1 in the planetary gear set 12. This change affects the
speed range of the variator 01 so that it may have to work from
negative to positive RPM as the vehicle speeds up. This signifies
that there will be a zero speed point which is inefficient because
it is a momentary point of stall. Otherwise these two
configurations will also work.
[0200] For the configuration of FIG. 23 the planetary equations
are:
(k.sub.1+1).omega..sub.w=k.sub.1.omega..sub.g+.omega..sub.em
(9)
(k.sub.2+1).omega..sub.em=k.sub.2.omega..sub.w+.omega..sub.f
(10)
[0201] For the configuration of FIG. 24 the planetary equations
are:
(k.sub.1+1).omega..sub.w=k.sub.1.omega..sub.g+.omega..sub.em
(11)
(k.sub.2+1).omega..sub.w=k.sub.2.omega..sub.em+.omega..sub.f
(12)
[0202] The relationship between the configurations of FIG. 23 and
FIG. 24 is similar to the relationship between the configurations
of FIG. 13 and FIG. 22. To achieve the same flywheel speed
.omega..sub.f, the configuration in FIG. 24 needs to have k.sub.2
increased by 1 to match the output of the configuration in FIG. 23.
Any other compound CVT configurations, where the flywheel 10 is not
on the sun gear S2, are not practical since less energy can be
stored.
* * * * *