U.S. patent application number 10/823623 was filed with the patent office on 2004-10-14 for hybrid powertrain.
This patent application is currently assigned to Stridsberg Innovation AB. Invention is credited to Stridsberg, Lennart.
Application Number | 20040204286 10/823623 |
Document ID | / |
Family ID | 27580583 |
Filed Date | 2004-10-14 |
United States Patent
Application |
20040204286 |
Kind Code |
A1 |
Stridsberg, Lennart |
October 14, 2004 |
Hybrid powertrain
Abstract
A powertrain for a vehicle is of the combined serial and
parallel hybrid type. It comprises a thermal engine (403), an
electric generator/motor (409) mechanically coupled to the output
shaft of the engine, a clutch (407) which can connect the two
portions of the output shaft rigidly to each other, and an electric
motor (401) mechanically connected to the distant portion of the
output shaft. Both the generator/motor (409) and the electric motor
(401) can be driven by the engine to charge an electric accumulator
(404) and can receive electric power therefrom to provide extra
torque to the output shaft. The output shaft of the engine drives
the wheels of the vehicle through a differential. A mechanical
gearbox (406) connects the output shaft to the differential and
wheels (408). The use of a gearbox and two electric motors
significantly improves the total performance of the powertrain. In
the powertrain standard components already used for driving
vehicles can be used.
Inventors: |
Stridsberg, Lennart;
(Enskede, SE) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Assignee: |
Stridsberg Innovation AB
|
Family ID: |
27580583 |
Appl. No.: |
10/823623 |
Filed: |
April 14, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10823623 |
Apr 14, 2004 |
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09557902 |
Apr 21, 2000 |
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6740002 |
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Current U.S.
Class: |
477/14 ; 475/5;
903/903; 903/909; 903/910; 903/914; 903/916; 903/917; 903/919;
903/952 |
Current CPC
Class: |
B60K 6/442 20130101;
Y10S 903/919 20130101; B60W 10/11 20130101; Y10S 903/914 20130101;
B60W 10/026 20130101; B60W 10/06 20130101; Y10S 903/91 20130101;
F16H 2200/0047 20130101; B60W 2510/244 20130101; B60K 6/387
20130101; B60K 6/52 20130101; H02K 51/00 20130101; Y10S 903/917
20130101; B60K 1/02 20130101; B60K 6/485 20130101; B60K 6/46
20130101; B60W 2556/50 20200201; Y02T 10/62 20130101; Y10S 903/903
20130101; Y10S 903/916 20130101; Y10S 903/952 20130101; B60W 20/30
20130101; Y10S 903/909 20130101; B60W 20/00 20130101; B60W
2050/0031 20130101; B60K 6/48 20130101; B60W 10/08 20130101; B60K
6/547 20130101; B60K 6/405 20130101; Y02T 10/40 20130101; B60K 6/54
20130101 |
Class at
Publication: |
477/014 ;
475/005 |
International
Class: |
F16H 003/72; H02P
015/02 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 21, 1997 |
SE |
9703887-1 |
Jan 8, 1998 |
SE |
9800043-3 |
Jan 25, 1998 |
SE |
9800228-0 |
Jan 30, 1998 |
SE |
9800288-4 |
Mar 3, 1998 |
SE |
9800690-1 |
Mar 22, 1998 |
SE |
9800987-1 |
May 20, 1998 |
SE |
9801848-4 |
Jul 2, 1998 |
SE |
9802413-6 |
Aug 27, 1998 |
SE |
9802913-5 |
Sep 29, 1998 |
SE |
9803313-7 |
Claims
What is claimed:
1. A powertrain of a vehicle having wheels, the powertrain
comprising a thermal engine having an output shaft, which when
required can be mechanically connected to at least one of the
wheels for driving the at least one of the wheels, an energy
storage, an electric motor, which is mechanically connected to the
thermal engine or to the at least one wheel and which is
electrically connected to the energy storage and is supplied with
electric power from the energy storage for supplying or receiving
mechanical power or torque when required, wherein at least part of
filtered air from an air filter of the thermal engine is made to
pass in such a way that at least part of the electric motor will
obtain cooling from the filtered air.
2. A powertrain according to claim 1, wherein at least part of the
filter air is made to pass through an airgap of the electric
motor.
3. A powertrain according to any of claims 1-2, wherein at least
part of the air is made to pass along permanent magnets of the
electric motor.
4. A powertrain according to claims 1-2, wherein at least part of
the air is made to pass between windings of the electric motor.
5. In a vehicle having wheels and a powertrain including a thermal
engine and a electric motor for selectively driving the vehicle,
the electric motor being equipped for regenerative braking, a
method of cooling the electric motor comprising: passing air for
supply to the thermal engine through an air filter to produce
filtered air; providing at least part of filtered air from an air
filter of the thermal engine to the electric motor to provide
cooling thereof.
Description
TECHNICAL FIELD
[0001] The present invention is concerned with hybrid powertrains
for vehicles, i.e. the combined devices needed for propelling
vehicles including engines, motors, mechanical transmission means
such as shafts, gears, axles, etc., and finally the exterior
driving devices such as wheels and tires acting by friction on a
surface of the ground such as that of a road.
BACKGROUND
[0002] A powertrain or drive train for a vehicle generally
comprises some kind of motor or thermal or heat engine producing a
mechanical force or torque and some transmission means converting
the force or torque to a movement of the vehicle. The transmission
means thus normally comprise a gear box or generally some
mechanical conversion means, the wheels of the vehicle and various
shafts from the motor and between the components of the
transmission means. Such powertrains for vehicles can use a one or
two electric motors which are capable of driving the vehicle at
least at moderate power levels using energy stored in an electric
energy storage unit such as an electrochemical accumulator and at
the same time such a powertrain can use a thermal engine to charge
the electrical storage system and to possibly supply extra power
during time periods when high power levels are required.
Alternatively the thermal engine can ordinarily drive the vehicle
and simultaneously charge the energy storage, from which power is
supplied to an electric motor when extra driving power is required.
This kind of powertrains using two different motors of quite
different types is called hybrid powertrains.
[0003] Classical hybrid powertrains comprise two basic types, the
serial type, the construction of which is schematically illustrated
in FIG. 1, and the parallel type, the construction of which is
schematically illustrated in FIG. 2.
[0004] In the SEV ("Serial Hybrid Vehicle") system illustrated in
FIG. 1, an electric motor 101 directly drives the wheels 108 of a
vehicle and thus provides all of the power required by the wheels
for propelling the vehicle. The electric motor receives electric
power from an accumulator 104. At high power levels, the thermal
engine 103 is activated to drive a generator 102 and thus adds
through the generator additional power to the accumulator, this
additional power being the difference between the power required by
the electric motor and the power which can be directly taken from
the accumulator. At leas for longer trips, the thermal engine 103
and the generator 102 will when required charge the accumulator 104
and thereby supply most of the power required by the electric motor
101 for driving the wheels.
[0005] In most applications, a mechanical reduction 105 is used to
allow the use of electric motors 101 having a lower torque and a
higher speed than what is normally required for driving the wheels
108. The mechanical reduction 105 is thus connected between the
electric motor 101 and the wheels 108. However, the electric motor
101 must be dimensioned to provide all the power required by the
wheels at all times, and a torque which varies linearly with the
torque of the wheels.
[0006] Serial hybrid vehicle systems of the kind described above
are often designed to use small thermal engines which are
dimensioned to be capable of providing little more than the average
power required for driving the vehicle on a horizontal highway at
high speeds, such as in typical designs about some 10 kW. This
permits the thermal engine to work either at an optimum load point
or not at all, thereby keeping its average efficiency close to an
optimum point. During accelerations and short inclinations a much
higher power is taken from the accumulator, which can be an
electrochemical battery, a flywheel, a supercapacitor, etc. Long
heavy inclinations require a high power over a long time period for
driving the vehicle, what in turn either requires a thermal engine
having a high output power or an accumulator having a high energy
content.
[0007] In the PHV ("Parallel Hybrid Vehicle") system as
schematically illustrated by the block is diagram of FIG. 2 a
thermal engine 203 is connected to convey a torque to the
differential gearing and wheels 208 through a disengageable clutch
207 and a gearbox 206. The gearbox 206 can also receive input
torque from an electric generator/motor 201 through an optional
mechanical reduction 205. The electric generator/motor receives its
input power from an energy storage unit or accumulator 204. The
torques provided by the thermal engine 203 and the electric
generator/motor 201 are thus both input to the gearbox, this
implying &t also torque can be provided from e.g. the thermal
engine 203 to the electric generator/motor 201, when there is
sufficient power available in the thermal engine. In such cases the
accumulator can be charged by the electric generator/motor which
then operates as a generator.
[0008] Generally, the accumulator 204 and the electric
generator/motor 201 and its electronic drive circuits, not shown,
have to provide a power being the difference between the power
required for driving the wheels and the power which is provided by
the thermal engine 203. In many applications, a mechanical
reduction 205 is used to allow the use of electric motors having a
lower torque and a higher speed than those provided by the thermal
engine. When the thermal engine 203 is switched off it is also
disconnected from the wheels by operating the clutch 207. All of
the traction power is in this case supplied from the energy storage
204 through the electric motor 201 which can also work as an
electric generator. Te energy storage 204 can, as has already been
mentioned, be charged by the thermal engine 203 while the vehicle
is running. The parallel hybrid vehicle system as described above
has the disadvantage that the speed of the thermal engine 203 is
dependent on the peed of the tires of the wheels and the setting of
the gearbox 206 and therefore the thermal engine has a non-constant
speed during running and then also during charging the energy
storage or accumulator 204. The torque of the thermal engine 203
can however be maintained at a suitable value by selecting a
suitable torque (positive or negative) for the electric
generator/motor 201. As the engine will loose its load as soon as
the clutch is disengaged, the torque of the thermal engine 203 must
change quickly as soon as a gearshift is performed. For many
thermal engine designs, this operation in addition causes high
peaks of environmentally unwanted emissions.
[0009] Parallel hybrid vehicle systems are disclosed in U.S. Pat.
Nos. 4,533,011, 5,337,848, 5,492,189 and 5,586,613.
[0010] In FIGS. 3a and 3b block diagrams of two hybrid systems are
shown which can be described to be mixtures or combinations of the
serial hybrid vehicle systems and the parallel hybrid vehicle
systems as described above. Employing the terms used in the
published European patent application EP 0 744 314 A1 they can be
called PSHV ("Parallel Serial Hybrid Vehicle") systems.
[0011] The parallel serial hybrid vehicle system illustrated by the
block diagram of FIG. 3a is described in the cited EP 0 744 314 A1,
see the description of FIG. 9 in this document. The system
according to FIG. 3a has the advantage that it to some extent can
use both the advantages of a serial hybrid vehicle system and a
parallel hybrid vehicle system. Here the thermal engine 303 has an
electric generator/motor 309 directly mechanically coupled to its
output shaft, not shown. To the output shaft is also an electric
motor 301 connected but through a clutch 307. The output shaft thus
drives through the clutch 307, when it is engaged, the differential
gearing and the wheels 308. The electric generator/motor 309 and
the electric motor 301 can when required be powered by the electric
energy storage 304 and the electric generator/motor 309 can also
charge the energy storage.
[0012] When the clutch 307 is disengaged and freely running, the
vehicle system of FIG. 3a acts as an SHV system and gives a
constant or slowly varying load on the thermal engine 303,
permitting a high thermal engine efficiency and low emissions. When
the clutch 307 is engaged it gives the advantage of a PHV system,
i.e. a higher power transfer efficiency between the thermal engine
303 and the wheels 308. As pointed out in EP 0 744 314 A1, see
column 4, lines 6 ff., the last advantage is only applicable for
medium to high speed vehicle movements since the rotation speed of
the thermal engine and thus of the electric generator/motor 309 at
low vehicle speeds will be below the lower operational limit of the
rotational speed of the thermal engine.
[0013] In FIG. 3b a block diagram of a PSHV system is shown in
which the speed of the thermal engine 303 is independent of that of
the differential and wheels 308. The system of FIG. 3b is obtained
from that depicted in FIG. 3b by replacing the electric
generator/motor 309 with a planetary gear 310, the planetary gear
instead driving or being driven by the electric generator/motor
309. The thermal engine 303 thus drives the differential gearing
and the wheels 308 through this planetary gear 310 and the clutch
307, when the clutch is engaged.
[0014] In the state in which the thermal engine 303 drives the
wheels, the system can for analytic purposes be regarded as three
blocks, the first block of which is the thermal engine 303. The
second block 311 consists of the planetary gearbox 310, the
electric generator/motor 309 and a first aspect of the electric
motor 301. The second block operates as a continuously variable
transmission between the thermal engine 303 and the differential
and wheels 308. It transfers the power from the thermal engine 303
from one speed/torque combination suitable for efficient and
environmentally good operation of the thermal engine 303 to another
speed/torque combination suitable for the differential
gearing/wheels 308. The output torque of the second block will be
determined by the input torque and the speed relation of the input
and output shafts of the second block. The mechanical energy at the
input shaft of the second block minus conversion losses will appear
at the output shaft thereof as it would in a purely mechanical,
continuously variable transmission.
[0015] The third block consists of a different, second aspect of
the electric motor 301, which adjusts the output torque from the
variable transmission block 311 to the torque required by the
wheels. It does this by converting power from the accumulator 304
to a mechanical torque and adding this extra mechanical power to
the shaft of the motor 301 or by converting excess mechanical power
at the shaft to electric power and charging the accumulator 304.
The physical electric motor 301 is required to provide a torque
which is the sum of the two torques attributed thereto as a
component of both the second block and the third block in the
analysis given above.
[0016] The hybrid powertrain according to FIG. 3b has the advantage
of allowing that part of the power of the thermal engine 303 can be
transferred by a highly efficient mechanical path from a the
thermal engine 303 to the differential and wheels 308 and still
permitting the thermal engine 303 to run at a slowly varying speed.
The thermal engine speed and torque can therefore be selected to
optimize thermal engine efficiency and polluting properties
independently of the speed and torque of the differential gearing
and wheels 308.
SUMMARY
[0017] It is an object of the invention to provide a PSHV system
having a high overall efficiency path from a thermal engine of the
system to the wheels of a vehicle.
[0018] Another object of the invention is to provide a PSHV system
which permits a thermal engine of the system to operate at a high
overall efficiency.
[0019] Another object of the invention is to provide a PSHV system
which avoids variations of speed and torque of the thermal engine
faster than what is compatible with goals for emissions and
efficiency.
[0020] Another object of the invention is to provide a PSHV system
which gives an acceptable performance if the accumulator and/or
electric motor system capacity should be reduced or even if the
accumulator and/or electric motor system cease to operate.
[0021] Another object of the invention is to provide a PSHV system,
which is capable of recharging its accumulator even when the
vehicle is stationary.
[0022] Another object of the invention is to provide a PSHV system
having a long service life and a low cost, in particular a PSHV
system having a dramatically reduced slip and other moving friction
forces on components like clutch and gearbox components during
shifts of gear position or speed.
[0023] Another object of the invention is to provide a PSHV system
capable of driving a vehicle when ascending long steep slopes.
[0024] Another object of the invention is to provide a PSHV system
capable of braking a vehicle when descending long steep slopes.
[0025] Another object of the invention is to provide a PSHV system
which is capable of providing occasional high output power peaks
using electric motors and thermal engines having comparatively
modest power ratings.
[0026] Another object of the invention is to provide a PSHV system
which makes use of investments already made in designs and
automated equipment for manufacturing vehicles.
[0027] Another object of the invention is to provide a PSHV system
which permits the use of electric motors of the permanent magnet
type having considerable losses when spinning or rotating at low
loads without obtaining high losses during high vehicle speeds.
[0028] The problem solved by the invention is how a hybrid
powertrain of the combined serial and parallel type can be
constructed which as improved performance, in particular a reduced
fuel consumption and a high total efficiency.
[0029] Thus a powertrain for a vehicle is the combined serial and
parallel hybrid type as generally defined above. It comprises a
thermal engine, an electric generator/motor mechanically coupled to
the output shaft of the engine, a coupling device such as a clutch
which can connect the output shaft to the wheels for driving the
vehicle. Thus, the output shaft can be divided in two portions, the
coupling device connecting the two portions rigidly to each other
when required. An electric motor/generator is mechanically
connected to the wheels for driving them when required. It can be
connected to the distant portion of the output shaft, which can be
disconnected from the near portion by operating the coupling
device. The clutch can connect the output shaft of the engine to
the input shaft of a gearbox, the output shaft of which is
connected to the wheels of the vehicle through a differential. An
electric motor is mechanically connected to the differential or the
gearbox input- or output shafts. Both the generator/motor and the
electric motor can be driven by the thermal engine to charge an
electric accumulator and can receive electric power therefrom to
provide extra torque. The term "mechanically connected" means that
the electric motors have the motion of their rotation shaft coupled
to the respective shaft, such as having a common shaft, interacting
through a gearing, a belt, etc.
[0030] Generally, a powertrain of a vehicle comprises a mechanical
gear box and at least one thermal engine, ordinarily only one,
having an output shaft, which shaft when required can be
mechanically connected to at least one of the wheels of the vehicle
through the mechanical gear box for driving the at least one of the
wheels. Furthermore it comprises an energy storage and at least one
engine side electric motor and at least one tire side electric
motor. At least two different electric motors are thus provided and
they are connected to the energy storage and are supplied with
electric power from the energy storage for providing or receiving
mechanical power or torque when required. Connection means are
connected to the electric motors, to the output shaft of the
thermal engine and to the wheel or wheels for mechanically
connecting the engine side electric motor to the output shaft of
the thermal engine to be driven by the thermal engine and for
mechanically connecting the tire side electric motor to the wheel
or wheels for driving it/them.
[0031] Additional objects and advantages of the invention will be
set forth in the description which follows, and in part will be
obvious from the description, or may be learned by practice of the
invention. The objects and advantages of the invention may be
realized and obtained by means of the methods, processes,
instrumentalities and combinations particularly pointed out in the
appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] While the novel features of the invention are set forth with
particularly in the appended claims, a complete understanding of
the invention, both as to organization and content, and of the
above and other features thereof may be gained from and the
invention will be better appreciated from a consideration of the
following detailed description of non-limiting embodiments
presented hereinbelow with reference to the accompanying drawings,
in which:
[0033] FIG. 1 is a block diagram of a serial hybrid vehicle drive
train system,
[0034] FIG. 2 is a block diagram of a parallel hybrid vehicle
system,
[0035] FIG. 3a is a block diagram of a parallel serial hybrid
vehicle system having a fixed transmission ratio between a thermal
engine and the wheels of the vehicle,
[0036] FIG. 3b is a block diagram of a parallel serial hybrid
vehicle comprising two electric motors and a planetary gear device
connected between a thermal engine and the wheels of the
vehicle,
[0037] FIG. 4a is a schematic picture, partly in block shape, of a
parallel serial hybrid vehicle system comprising two electric
motors on the thermal engine side of a gearbox,
[0038] FIG. 4b is a schematic picture similar to FIG. 4a of a
parallel serial hybrid vehicle system comprising one electric motor
on the thermal engine side of a gearbox and one electric motor on
the other side of the gearbox,
[0039] FIG. 4c is a schematic picture similar to FIG. 4a of a
modified parallel serial hybrid vehicle system comprising one
electric motor on the thermal engine side of a gearbox and one
electric motor on the other side of the gearbox,
[0040] FIG. 4d is a schematic picture similar to FIG. 4a of a
parallel serial hybrid vehicle system comprising one electric motor
on the thermal engine side of a gearbox and one electric motor on
the other side of the gearbox suitable for slow steep slope
climbing,
[0041] FIG. 4e is a schematic picture of a parallel series hybrid
vehicle similar to that of FIG. 4c having one electric motor on the
thermal engine side of the gearbox and one electric motor directly
connected to each wheel,
[0042] FIG. 4f is a schematic picture of a parallel series hybrid
vehicle similar to FIG. 4a showing additional features such as
shaft dampers,
[0043] FIG. 5 comprise diagrams of torque, speed, etc. of the
components of the power train of FIG. 4a, and
[0044] FIG. 6 is a detailed sectional view of some components of a
power train according to FIG. 4a illustrating the components with
realistic relative dimensions.
DETAILED DESCRIPTION
[0045] In FIGS. 4a-f and 6 embodiments of a hybrid power train of a
PSHV system type having enhanced performance are shown.
[0046] In FIGS. 4a and 4c two most preferred embodiments of the
hybrid powertrains are shown. Both embodiments include the classic
thermal engine powertrain including a thermal engine 403, a clutch
407 and a gearbox 406. To this configuration two electric motors
are added. One electric motor 409 is closely connected to the
thermal engine, driving the shaft thereof or being driven thereby
using some mechanical transmission and thus operating both as an
electric generator and an electric motor. The other electric motor
401 is connected on the tire side of the clutch, driving some shaft
in the transmission path from the clutch to the wheels or tires of
the vehicle, this electric motor also using some mechanical
transmission means. In the embodiment of FIG. 4a the second
electric motor 401 is placed on the thermal engine side of the
gearbox and in the embodiment of FIG. 4c on the tire side of the
gearbox.
[0047] The basic arrangement including a thermal engine, a clutch
and a gearbox has dominated conventional vehicles for almost a
century, and one likely reason thereof is that it is one of the
best solutions available in terms of cost, performance and
efficiency. By adding one electric motor on each side of the
clutch, the engine load can be kept continuous even during shifts
of the gear position or speed as the power from the engine can be
absorbed by the electric generator/motor 409 and transferred to the
other, traction motor 401. This permits the thermal engine to
operate without the pollution generating transients between high
torque (with engaged clutch) and basically no torque (disengaged
clutch).
[0048] Thus, in the parallel serial hybrid vehicle system of FIG.
4a, a thermal engine 403, e.g. an internal combustion engine, has
an output shaft which is connected to an input side of a clutch
407. The opposite, output side of the clutch 407 is connected to a
gear box 406, the output shaft of which drives the differential
gearing and the wheels 408. When the clutch 407 is engaged, the
thermal engine 403 is mechanically connected to the differential
and wheels 408 through the clutch 407 and the gear box 406. In this
mode the thermal engine 403 will be locked in speed to the wheels
408 by one of the available reduction ratios of the gearbox 406,
and possibly the reduction ratio in the path between the gear box
406 and the differential gearing 408. By a suitable selection of
reduction ratios to fit the legal speed limits, the most common
highway (=long distance driving) speed limits can be made to be
close to the optimum speed of the thermal engine 403. Long distance
driving can therefore be done having the thermal engine 403 running
close to an optimum speed and an optimum torque. The balance
between optimal thermal engine torque and wheel torque requirement
can be absorbed or delivered through an electric generator/motor
409 and/or an electric motor 401. The electric generator/motor 409
is directly mechanically connected to the output shaft of the
thermal engine 403. It can as illustrated have its shaft in common
with the output shaft of the thermal engine or have its rotor
rigidly attached to the output shaft. The electric motor 401 is in
a similar way directly mechanically connected to the output side
shaft of the clutch 407 by e.g. having its shaft in common with
said output side shaft of the clutch or its rotor rigidly attached
to this shaft. The electric generator/motor 409 and the electric
motor 401 are both connected to an electric energy storage 404 such
as an electrochemical battery, the connection being obtained
through inverters 410, 411 respectively.
[0049] The various parts of a complicated drive train as discussed
above in conjunction with FIGS. 1-4a are controlled by a suitable
controller, not shown, e.g. a suitable microprocessor, which
controls at least the thermal engine, the electric motors and the
generator/motor to drive the wheels and to charge or discharge the
electric energy storage. The control is based on among other things
the speeds of the various shafts of the system. In FIG. 4a the
control uses electrical signals representing the speed of the input
shaft of the gearbox as obtained from a speed sensor or position
encoder 412, the speed of the output shaft of the gearbox as
obtained from an encoder 413 and the speed of the engine shaft as
obtained from an encoder 414. Similar controllers are of course
used for the powertrains as illustrated in FIGS. 4b-4f and 6 to be
described hereinafter.
[0050] The operation of the PSHV systems as disclosed herein will
be described for different configuration modes. Basically, such a
system can be run as en electric vehicle, i.e. when the thermal
engine is switched off, as a series hybrid vehicle, i.e. when the
thermal engine is switched on and the clutch is disengaged, and as
a parallel hybrid, i.e. when the thermal engine is switched on and
the clutch is engaged.
[0051] Now the transfer efficiencies of the various powertrains of
FIGS. 1-4a will be discussed and then some assumptions on
efficiencies of the incorporated components will be used. It is
thus assumed that the efficiency of a gear in which the forces
transferring torque pass a single cog surface barrier can be set to
0.98 and that the efficiency of an electric motor and its inverter
can be set to 0.90. The discussion of the powertrain of FIG. 4a has
also relevance for the powertrains of FIGS. 4b-f and 6 which will
be described hereinafter.
[0052] Both the PSHV system of FIG. 4a and the PHV system of FIG. 2
will under this assumption have a transfer efficiency of about 0.98
from the thermal engine through the engaged clutch and through the
gearbox.
[0053] The transfer efficiency of the PSHV system of FIG. 4a is
better than that of the PSHV system of FIG. 3b. A part of the
torque from the thermal engine 303 of the PSHV system of FIG. 3b to
the clutch 307 goes through a single cog surface barrier with an
efficiency of about 0.98. The other part passes however through a
single cog surface barrier, the electric generator/motor 309 and
its associated power electronics and the motor 301 and its
associated power electronics. The transmission efficiency of this
path is about 0.98.multidot.0.90.multidot.0.90=0.79. Using the
assumptions given above, the total transmission efficiency of the
PSHV system of FIG. 3b will therefore vary from a value close to
0.79 to a value close to 0.98.
[0054] The transfer efficiency of the PSHV system of FIG. 1 is
obviously lower than that of all other systems in FIGS. 2-4a since
it uses two motors/generators connected serially and thus has a
total efficiency of about 0.90.multidot.0.90=0.81.
[0055] The total efficiency of the mode of the powertrains of FIGS.
1-4a in which the clutch is engaged also depends on the efficiency
of the devices which store excess power delivered by the thermal
engine to the accumulator and add power from the accumulator to the
wheels. In the following, this is called "Accumulator path
efficiency".
[0056] The accumulator path efficiency of the PSHV system of FIG.
4a is slightly better than that of the PHV system of FIG. 2 due to
a marginally higher efficiency when one of the two motors 401, 409
is idling. Since the PSHV system of FIG. 4a has two electrical
machines 401 and 409, its controller, not shown, can choose between
running both electric motors, thus reducing copper losses, or to
run one electric motor having the other electric motor rotating
idle, thus reducing iron losses of the electric motors. As an
illustration, assume that the electric motors 401 and 409 are
identical having an equivalent electrical resistance R. Running
both electric motors at the same torque using a current I will
result in a copper loss of 2.multidot.RI.sup.2; running one motor
at twice the torque will result in a copper loss of
R.multidot.(2.multidot.I- ).sup.2 or 4.multidot.RI.sup.2, which is
twice the copper loss of the first case. On the other hand,
activating an electric motor using current from an inverter will
induce iron losses in the electric motor since the motor inductance
will have to balance the voltages switched over its coils. It may
therefore at lower loads be advantageous to run only one electric
motor having the other motor idle. Providing electric motors having
different characteristics increases the possibilities of improving
efficiency by activating only one electric motor.
[0057] The accumulator path efficiencies of the PSHV systems of
FIG. 4a and of FIG. 3b cannot be easily ranked. The disadvantage of
the powertrain of FIG. 3b is that the planetary gear will impose
relations between the speed and torque of the thermal engine 303,
the electric generator/motor 309 and the electric motor 301. This
will force the controller, not shown, to seek compromises. If the
thermal engine is working at optimum power efficiency speed and
torque, the transfer efficiency and accumulator path efficiencies
might be poor. If the transfer efficiency and accumulator path
efficiencies are good, the thermal engine might be working at far
from optimum power efficiency speed and torque. It seems likely
that this will result in compromises in which both the thermal
engine, transfer and accumulator efficiencies will suffer.
[0058] A first object of the invention which comprises providing a
PSHV system having a high overall efficiency path from the thermal
engine of the system to the wheels of the vehicle, therefore seems
fulfilled by the system according to FIG. 4a and also by those
according to FIGS. 4b-4f and 6.
[0059] Thermal engine efficiency
[0060] A second object of the invention is to provide a PSHV system
which permits the thermal engine to operate at a high overall
efficiency. Obviously the thermal engines of FIGS. 1, 3a, 3b, 4a
and also those of FIGS. 4b-4f and 6 can all be selected to run at
an optimal load point in the serial mode, i.e. for FIGS. 3a, 3b,
4a-4f when the clutch 307 or 407 respectively runs freely. As
pointed out above, the PSHV system of FIG. 3b can in principle run
at the thermal engine optimal efficiency point for any vehicle
speed also in the parallel mode when the clutch 307 is engaged, but
at a penalty of lower transfer and accumulator efficiencies.
[0061] A disadvantage of the powertrain of FIG. 4a and also of that
of FIGS. 4b-4f and 6 is that the speed of the thermal engine cannot
be set independently of the vehicle speed. This disadvantage will
be diminished if the thermal engine 403 has a high efficiency over
a fairly wide rpm range or speed range and/or the gearbox 406 has
many ratios.
[0062] To permit a comparison with prior art hybrid systems a
simulation model has been built.
[0063] The simulated vehicle shown in table 1 is based on the
automobile 318i/328i manufactured by the company BMW. The current
power train has been replaced by an Opel C18NZ internal combustion
thermal engine, two electric motors in the configuration shown
according to FIG. 4a and a currently available gear box and front
wheel drive differential. The mass has been increased by about
120(=140-20) kg. The additional mass of 140 kg includes the mass of
electric motors, inverters, and the accumulator batteries and
hopefully leave sufficient margins to encompass cabling, battery
cell encasement and other ignored components. The mass of the fuel
tank has been reduced by 20 kg.
[0064] The C18NZ thermal engine was used in the Opel Vectra and is
selected because a non-confidential thermal engine efficiency map
was available. The efficiency map is based on measurements made in
Finland and has been obtained from Mr. Olavi H. Koskinen, Chief
engineer, Ministry of Transport and Communications, P.O. Box 33,
FIN-00521 HELSINKI, Finland.
[0065] The battery system assumed is 120 UHP NiMH cells type 17
from the company Varta. The battery model used was too
conservative. A NiMH model used by another highly qualified
research group gives a noticeably lower fuel consumption for the
vehicle, and recently received data on existing NiMH cells show a
higher charge-discharge efficiency than that which was used in the
simulation model.
[0066] Electric motor and inverter efficiencies have been simulated
using data published by Unique Mobility, Inc. for the Unique
Mobility SR218H motor and CA-40-300L inverter as published by UQM
on the Internet at www.uqm.com.
[0067] The components have been selected because non-confidential
data are available. The two electric motors have the same
specification. The simulations do therefore not show an optimized
vehicle. It seems reasonable to assume that the fuel consumption
would be lower if specially developed components had been used and
if the maximum torque and speed had been selected for the
application from a wide selection of already available components.
The tires used for the simulations of the vehicle having "current"
tires have a static rolling friction of 0.09 N/kg and a dynamic
friction of 0.0018 N/kg/(m/s). For the simulations of the vehicle
with "improved" tires these two values have been reduced by
30%.
[0068] No non-confidential data on high efficiency thermal engines
has been available. For the simulations of the vehicle having
"improved" tires and thermal engine, the fuel consumption of the
C18NZ has been reduced by a factor of 220/262 (from 262 g/kWh to
220 g/kWh). This corresponds to 38% thermal efficiency as claimed
for the motor-car Prius from the company Toyota. Peak efficiency
data for the Prius car are taken from an efficiency plot in an
EVS-14 conference paper by Sasaki et al., "Toyota's Newly Developed
Electric-Gasoline Thermal engine Hybrid Powertrain System", 1997.
The model of the "improved" tires and thermal engine therefore
assumes that the efficiency of the advanced thermal engine varies
with torque and speed in the same manner as that of the C18NZ.
[0069] To permit simple direct comparisons of the fuel consumption,
the controller driving strategy has been adjusted to obtain the
same battery charge before and after the driving cycle. Almost no
effort has been made to optimize strategy in other ways.
[0070] To make it possible for independent researchers to check the
efficiencies of the simulations, a detailed listing of the energy
flow and losses for the ECE (European mixed driving cycle) has been
prepared in 6096 0.2 sec steps. The vehicle shown in these listings
has a vehicle mass of 1561 kg, an area of 2.22 m.sup.2 and a Cv of
0.28.
[0071] The simulation results as shown in this listing have been
checked by two research workers at the Royal Military College of
Science, Cranfield University, UK, who worked independently of each
other. No significant errors were found.
[0072] The simulation model has also been checked by running it for
a conventional vehicle using a detailed thermal engine efficiency
map for a vehicle which had been supplied under a Confidentiality
Agreement. The simulation model gave a slightly lower (1.2%) fuel
consumption than the real life tests.
[0073] The simulation model and the verification have been focused
on fuel consumption. Acceleration has been modelled in a
straightforward way to get a first idea of the potential.
Acceleration data have not been verified by any independent
researcher.
[0074] The simulation model ignores thermal engine start up energy
consumption. Preliminary measurements of thermal engine start up
fuel consumption indicate that the start-up will increase the
consumption values shown by 1 to 2%. The model of the electric
motors does not consider the effects of battery voltage variations
(The Unique Mobility data are only given for constant battery
voltage).
[0075] The present simulation always starts the thermal engine up
to about a start point having a predetermined speed (1200 rpm) and
a predetermined torque (100 Nm). Only when this operating point is
almost reached the control system will start to adjust the thermal
engine speed and torque to fit the speed required for a closed
clutch. This control method is intended to simplify start up
exhaust control but will result in an unnecessary long time in the
serial mode and a higher fuel consumption.
[0076] According to the verification efforts described above, the
model seems to be sufficiently reliable to permit some conclusions
of the efficiency of the proposed powertrain when compared to prior
art designs.
1TABLE 1 Simulation model results. Col. A Col. B Col. C Cal. D Cal.
E Cal. F Cal. G Col. H Powertrain type Conv Conv Hybrid Hybrid
Hybrid Hybrid Hybrid Hybrid Tires and engine n.a. n.a. current
improved current improved current improved Area, m.sup.2 2.08 2.06
2.08 2.08 2.08 2.08 2.08 2.08 Drag coeff. Cd 0.27 0.29 0.27 0.27
0.27 0.27 0.27 0.27 Vehicle mass, kg 1360 1470 1480 1480 1480 1480
1480 1480 Driving cycle ECE ECE ECE ECE 10-M 10-M FTP FTP Spec.
cons. 8.4 9.6 4.15 2.96 3.37 2.45 3.77 2.65 litres/100 km (EU)
Spec. cons. 11.9 10.4 24.1 33.8 29.6 40.7 26.5 37.7 km/litre (JAP)
Spec. cons. mpg (US) 28.0 24.5 56.7 79.5 69.7 95.9 62.4 88.7 Engine
relative efficiency, % 95.1 94.4 94.1 94.3 94.2 94.2 Time to 100
km/h, s 10.7 7.4 7.8 7.8 7.8 Time to 130 km/h, s 17.7 12.0 13.0
13.0 13.0
[0077] Some results from the simulations:
[0078] 1. The average thermal engine efficiency is 94 to 95% of the
optimal efficiency. The average efficiency of the thermal engine is
surprisingly high and rather constant for the three different
driving cycles used. The average efficiency depends on the
characteristics of the thermal engine. In the three columns above
for "current" thermal engine and tires, data for the Opel C18NZ
thermal engine have been used. The C18NZ was not designed for use
in hybrid powertrains. Future thermal engines designed for use in
hybrid powertrains could give an even better average efficiency
when used with the hybrid powertrain as proposed herein.
[0079] 2. In the ECE driving cycle (the one verified by external
researchers), of 100 energy units which could have been obtained if
the engine was to run at its optimum speed and torque, 95 energy
units (on the average) was obtained as mechanical power on the
output shaft of the thermal engine. Of these 95 energy units, 74
were directed to the gear box and 71 reached the tires through the
mechanical chain. Another 21 energy units are directed to the
electric link.
[0080] 2. The fuel consumption is very low. This is what could be
expected when a very high average efficiency of the thermal engine
is combined with a predominantly mechanical, high efficiency
transfer from the thermal engine to the tires.
[0081] 3. The transients in the thermal engine torque and speed are
small. This should give low emission levels, similar to the levels
already demonstrated for hybrid powertrains using planetary
gears.
[0082] 4. The fuel consumption is approximately 1/3rd of present
fuel consumption.
[0083] At the time of writing, the automobile Prius manufactured by
Toyota seems to be the most efficient hybrid powertrain vehicle
known. Data given for the Prius are related to the fuel consumption
when tested using the Japanese 10-Mode test cycle. The model of the
powertrain of FIG. 4a has been run against the same (?) test cycle,
see table 1, column F. The fuel consumption of the 1530 kg Prius is
given as 28 km/litre whereas the simulation model indicates a
consumption of 41 km/litre for a 1430 kg vehicle. Both simulations
refer to a vehicle having a peak thermal engine efficiency of 38%,
using high power NiMH batteries, two electric motors, low friction
tires and a low Cd value (0.30 against 0.27). The mass of the Prius
is based on verbal communications from competitors which have
purchased a Prius.
[0084] The simulation model shows that the average relative
efficiency of the thermal engine is 94 to 95% when an thermal
engine designed for another type of vehicle is combined with a
standard gear box designed for another type of vehicle. It seems
very likely that systems using thermal engines and gear boxes
designed to fit powertrains according to FIG. 4a would give an even
better average efficiency.
[0085] A second object of the invention, which is to provide a PSHV
system which permits the thermal engine to operate at a high
overall efficiency, therefore seems fulfilled.
[0086] Speed and torque variations
[0087] A third object of the invention is to provide a PSHV system
which avoids variations of speed and torque of the thermal engine
faster than what is compatible with goals for emissions and
efficiency.
[0088] The diagram of FIG. 5 illustrates some basic performance
possibilities of the parallel/serial hybrid system of FIG. 4a. The
diagram illustrates a simulation in which a vehicle is driven
during a 52 second start-stop movement typical of city traffic. In
this case the simulation model is based on data from a thermal
engine which is less suited than the C18NZ. During the first 4
seconds in FIG. 5 the vehicle is driven by the electric motor 401.
The torque and the speed of the electric motor 401 are shown as
"507 mot torque" and "508 mot is rpm" in FIG. 5. The speed and
torque of the wheels (tires) are shown by curves 501 and 502. Power
to the electric motor 401 comes from discharging the battery, shown
as "510 Batcharge" in FIG. 5, the power being negative during the
first 4 seconds of FIG. 5.
[0089] Some 3 seconds after vehicle start, the controller, not
shown, will cause the electric generator/motor 409 to force the
thermal engine 403 to start. In the control method shown, the start
up always follows the same pattern up to a fixed thermal engine
entry point having a moderate speed and high torque. Using one or a
few start up ramps facilitates optimal control of exhaust
transients. As long as the clutch 407 is disengaged, the electric
generator/motor 409 absorbs the thermal engine power as shown in
curve "505 gen torque". This causes a short positive charging of
the battery as shown, see the curve 510.
[0090] The vehicle controller, not shown, seeks to adjust the
gearbox setting to the values estimated to be optimal, and to
adjust thermal engine speed and torque to permit a low slip clutch
engagement. In the case shown, the gear is changed from 1 to 2 and
the clutch 407 can be engaged, see curve 509, about 4.5 seconds
after vehicle start.
[0091] At the 7:th second, the controller initiates a gear change,
indicated by the box "511 gear change event" in FIG. 5. The gear
change shown is made without driver intervention. The electric
generator/motor 409 will absorb the torque from the thermal engine
403 by rapidly increasing its torque, see curve 505, thus
permitting a slip-free opening of clutch 407, see curve 509. The
vehicle controller will also reduce the torque, see curve 507, of
the electric motor 401 to zero. The controller can now disengage
the previous gear as virtually no torque is transferred over it and
rapidly change the speed of the electric motor 401 to fit the
required speed for the forthcoming gear. Using the speed/position
encoders 412 and 413 connected to the input and output shafts to
the gear box 406, see FIG. 4a, the speed and also the relative
position of the two shafts can be synchronized to permit a
virtually slip-free engagement of the forthcoming gear
position.
[0092] The clutch 407 is now open as shown by the curve 509
"Clutch" and the thermal engine torque 504 is absorbed by the
electric generator/motor 409, see curve 505. In the case shown, the
electric generator/motor 409 will absorb the power of the thermal
engine during about one second until the thermal engine speed has
been adjusted enough to permit a low slip clutch closure, which
happens in the end of the time slot shown in the box 511 indicated
by "gear change event". The encoder 414, see FIG. 4a, provides
information on the rotation speed of the output shaft of the
thermal engine 403.
[0093] As can be seen, the transients in the thermal engine torque,
curve 504, and speed, curve 506, are small. The thermal engine
speed and torque change rate can be selected by parameters input to
or set for the controller. In this way mechanically identical
vehicles can be given different properties in different markets or
different areas by setting different weight to emission levels and
efficiency.
[0094] As shown, the gear change will neither affect the load on
the thermal engine 403, nor the response of the vehicle assuming
that the power available from the electric motor 401 is sufficient
to give the required performance. As seen in the curve 502
indicated by "tyre torque", disengaging the clutch will only cause
a short absence of torque provided to the tires. Since the gear
change can be made very fast, the no-torque period is shorter than
in conventional vehicles. During engaging and disengaging, the
clutch will carry very small torque, and will therefore experience
very small slip and wear.
[0095] In the figure, the torque from the electric generator/motor
409 is always positive, i.e. it is working as a generator. A more
detailed simulation would have shown it to work as a starter motor,
and an optimum use of the two electric machines in the parallel
hybrid mode would most likely have resulted in that in some
instances both electric motors would have been used as electric
motors or as generators, even if one electric motor is mostly used
as a generator and the other electric motor is mostly used as a
motor.
[0096] In systems or driving situations in which power performance
is given priority over exhaust levels, high power gear changes can
be achieved. The electric generator/motor 409 can rapidly force the
speed of the thermal engine 403 down to the speed anticipated to
fit the gearbox input speed after the gear change. This permits a
very short time period with a reduced power to the wheels while
still maintaining an almost slip-free operation of the clutch.
[0097] A third object of the invention is to provide a PSHV system
which avoids variations of speed and torque of the thermal engine
faster than what is compatible with goals for emissions and
efficiency and this object thus seems fulfilled.
[0098] Thermal engine switched off
[0099] When the thermal engine is switched off, the main difference
between the powertrains according to FIGS. 1-3b and the embodiments
of FIGS. 4a-4f and 6 is the existence of a mechanical gearbox
connected between the electric traction motor and the tires. A
gearbox permits the controller to select a gear position which
gives the highest efficiency for the electric motor/inverter
combination and also permits electric motors having a lower maximum
torque to drive the vehicle on ascending slopes. The 5-speed
gearboxes used in contemporary vehicles permit a range of
approximately 1 to 5 for the input speed at a given vehicle speed.
This permits the electric motor 401 of FIG. 4a to have the same top
speed as the electric motor of FIG. 4c but at only 1/5th of the
rated torque. Alternatively, the two electric motors may have the
same rated torque but in that case the electric motor working in
the embodiment of FIG. 4a will only run at 1/5th of the speed at
high vehicle speeds. For electric motor designs using permanent
magnets the iron losses at high speeds and low loads are
considerable. The advantage of a low top speed may more than
compensate for the disadvantage of having one more cog transfer
between the electric motor and the tires.
[0100] Like in all serial hybrid systems, the electric
generator/motor 409 can act as a starter motor of the thermal
engine.
[0101] Power peaks
[0102] During high power operation, such as hill climbing or
overtake, a PSHV system as that of FIG. 4a should normally operate
having the clutch 407 engaged.
[0103] When compared to the powertrains of FIGS. 1-3b, the
powertrains of FIG. 4a and also of FIGS. 4b-d, see the description
hereinafter. can divide the required mechanical power between the
two electrical motors 401 and 409 and the thermal engine 403, and
divide the required power supply between the accumulator 404 and
the thermal engine 403.
[0104] This gives an advantage compared to the powertrain of FIG.
1, in which the full mechanical power must be provided by only the
electric motor 101. The electric motor 101 of the serial hybrid
system of FIG. 1 must therefore have a much higher rating than the
electric motors of FIGS. 4a-d and 4f. As part of the engine power
in the PSVH of FIG. 3b passes through the electric motors 309 and
301, at least the electric motor 301 must have a higher rating than
the corresponding electric traction motor 401 in the power trains
of FIGS. 4a-d and 4f. As part of the power of the thermal engine in
the PSVH of FIG. 3b passes through the electric motors 309 and 301,
at least the electric motor 301 must have a higher rating than in
the power trains of FIGS. 4a-4d.
[0105] Reliability
[0106] Some components of a hybrid vehicle system, particularly the
accumulators, will in the beginning have little proven record of
reliability. This may be a serious obstacle to a wide market
acceptance of hybrid powertrain vehicles. At the time of writing,
hybrid vehicles must either use time proven low capacity lead-acid
batteries, resulting in a low performance, proven but very
expensive NiCd batteries or systems like lithium or NiH pulse
batteries or supercapacitors, which may have a potential to become
affordable but which has an unproven reliability. A fourth object
of the invention is therefore to provide a PSHV system which gives
an acceptable or at least tolerable performance if the accumulator
and/or the electric motor system capacity should be reduced or even
if the electric motor system ceases to operate.
[0107] This is only possible for the PHV system of FIG. 2 and the
PSHV system of FIGS. 4a-4f, in both cases assuming the existence of
a starter motor, not shown, similar to that of a conventional car
or automobile. The PSHV system of FIG. 3a is similar to a
conventional car with the gearbox locked in gear position No. 4 and
is therefore unlikely to be able to start. The PSHV system of FIG.
3b has the same problem if the error conditions will lock the
electric motor 309. If the error conditions will permit the
electric generator/motor 309 to spin freely, it will eliminate any
output torque to the wheels even if the thermal engine 303 runs at
full speed.
[0108] Other objects
[0109] A fifth object of the invention is to provide a PSHV system
which is capable of recharging its accumulator even when the
vehicle is stationary. This is possible for all the powertrains
according to FIGS. 1-4f, assuming that a brake, not shown, permits
locking the shaft between the planetary gear 310 and the clutch 307
of the PSHV system of FIG. 3b.
[0110] A sixth object of the invention is to provide a PSHV system
having a longer service life and a lower cost and particularly a
dramatically reduced slip and other moving friction forces on
components like clutch and gearbox components during shifts of the
gear position. This is obtained by the capability of the electric
motors 40i and 409 of absorbing torque from the thermal engine and
supplying all vehicle movement torque before a clutch release and
of synchronising the gearbox shafts at shifts of gear position. The
use of the electric motor 401 to synchronize the gearbox 406
permits a longer gear box life for the same component quality or
permits the use of parts of low costs. The cost and mass of the
gearbox may be reduced further as components etc. required for the
synchronisation in manually operated gearboxes can be eliminated.
This might also reduce the mechanical losses in the gearbox.
[0111] A seventh object of the invention is to provide a PSHV
system capable of driving the vehicle when ascending long steep
slopes. This is provided by the gear box, thus permitting large
tire torques delivered by a moderate size electric motor 401 and/or
thermal engine 403. As the thermal engine power is transferred by a
highly efficient, predominantly mechanical transmission, the losses
and the rise of temperature in the transmission components will be
low. The powertrains of FIGS. 1 and 3a will transfer all power at
low vehicle speed through the electric motors 102, 101 and 309, 301
respectively, and the powertrain of FIG. 3b will as described above
transfer part of the thermal engine torque through the electric
motors.
[0112] An eighth object of the invention is to provide a PSHV
system capable of driving the vehicle when descending long steep
slopes, which is provided by the gear box and clutch permitting the
thermal engine 403 to operate as an air compressor which can absorb
the excess power which the accumulator 404 cannot receive or
accept.
[0113] A ninth object of the invention is to provide a PSHV system
capable of delivering occasional high power peaks for comparatively
modest power ratings of electric motors and the thermal engine.
This is achieved since the thermal engine power at power peaks is
transferred mechanically, whereas the powertrain of FIG. 1 will
transfer all the power of the thermal engine through the electric
motors 102, 101 and that of FIGS. 3a and 3b will transfer part of
the thermal engine power through the electric motors 309 and
301.
[0114] A tenth object of the invention is to provide a PSHV system
which utilizes investments already made in designs and automated
equipment for manufacturing thermal engines of moderate sizes and
gearboxes of normal sizes. Depending on the design goals, the gear
box of a PSHV system as of that of FIG. 4a-f can be considerably
simplified compared to the gear boxes of conventional cars. To
maintain the ability to operate even with failing electric motors
and/or accumulator, a reverse gear is required. If a full operating
ability for failing electric motors and/or accumulator is not
considered necessary, the reverse gear can be eliminated, thus
reducing cost and weight.
[0115] An eleventh object of the invention is to provide a PSHV
system which permits the use of electric motors of the permanent
magnet type having considerable losses when spinning or rotating at
low loads without obtaining high losses for high vehicle speeds.
This is in the embodiments shown in FIG. 4a-4f obtained by the use
of the gearbox.
[0116] Other embodiments
[0117] Whereas the embodiment according to FIG. 4a comprising a
single clutch 407 and an electric motor 401 mounted on the thermal
engine side of the gearbox 406 has been used in the discussion
above, most of the advantages can be obtained with some other
structures.
[0118] In FIG. 4b is shown an embodiment of a PSHV system similar
to that of FIG. 4a but having the electric motor 401 connected on
the tire side of the gearbox 406. The electric motor 401 is thus
connected between the gearbox 406 and the differential gear, such
as having its shaft in common with the output shaft of the gearbox.
This eliminates the loss of torque during a gearbox change, giving
the advantage of a smoother acceleration. In this case, having the
electric motor 401 mounted on the outgoing shaft from the gearbox
406, one encoder 413 connected to this shaft can be used both for
the commutation and other control data for electric motor 401 and
at the same time be used for engaging the clutch with a low slip.
The differential gearing is here seen to be driven by a cog wheel
421 on the output shaft of the gearbox 406, the cog wheel 421
cooperating with a cog wheel 422 on the input shaft of the
differential gearing. The gear ratio between the cog wheels 421 and
422 normally is in the range of 1:2 to 1:5. Therefore the torque of
the electric motor 401 at low speeds must be higher than that of
the electric motor of FIG. 4a, which at the lowest gear or speed
position has a ratio to the wheels of approximately 12:1.
[0119] In FIG. 4c another embodiment of a hybrid power train system
is shown which is similar to the system of FIG. 4a but has the
electric motor 401 connected on the tire side of the gearbox 406.
In this case, the electric motor 401 is mounted on an own shaft.
This requires an extra path from the electric motor 401 to the
differential and wheels 408. In the embodiment shown, this is
arranged by a cog wheel 423 on the shaft of the electric motor 410
cooperating with the cog wheel 422 on the input shaft of the
differential gearing. The motor encoder 416 can (except for some
unlikely combinations of gears) no longer be used for gear changes
made with a low wear. To achieve a low wear gear change, a total of
three encoders 412, 413 and 416 are required, the encoder 416
sensing the speed of the output shaft of the electric motor 401.
The gear ratio between the cog wheels 423 and 422 can is this case
be optimized for the electric motor 401, which in the case of high
speed motors often is in the order of 10:1.
[0120] In FIG. 4d yet another embodiment of a hybrid powertrain is
shown which is similar to that of FIG. 4c. Another clutch 415 is
connected between the thermal engine 403 and the electric
generator/motor 409. By adding this second clutch 415 both of the
electric motors 409 and 401 can supply torque while the thermal
engine is disconnected. The thermal engine 403 can be disconnected
using the added clutch 415 while the electric generator/motor 409
can add torque to the wheels through the engaged first clutch 407.
This can permit a capability if climbing steep slopes at slow
speeds which would otherwise have required a large torque
capability of the electric motor 401. In FIG. 4d no encoders are
provided having fixed positions in relation to the shafts of the
gearbox 406. To permit an adjustment of the position of the gearbox
cogs using the electric motor 409, another two encoders would
normally be required.
[0121] In FIG. 4e a parallel series hybrid vehicle system having
one electric motor on the thermal lo engine side of the gearbox and
one electric motor 424-427 directly connected to the axle of each
wheel is shown, such as having the shaft of the electric motor in
common with or assembled to the wheel axle as illustrated. This
permits a full regenerative braking for higher decelerations. At
decelerations above a certain limit all four wheels should
participate to some extent, and this would in the embodiments of
FIGS. 4a-4d require the use of friction brakes. For presently
available electric motor technology, full braking forces will
always be predominantly done using conventional friction brakes.
The electric generator/motor 409 connected close to the thermal
engine can be generally called an engine side electric motor and
the electric motor or motors 401; 424-427 connected close to the
wheels can be generally called tire side electric motors or
traction motors. The engine side electric motors and the tire side
electric motors always have some device for mechanically
disconnecting them arranged in the power transmission line from the
thermal line to the wheels and tires.
[0122] In FIG. 4f an embodiment of a parallel series hybrid vehicle
system similar to that of FIG. 4a is shown, but some additional
features has been added. The electric generator/motor 409 has been
illustrated as an outside rotor motor, the rotor enclosing the
stator. The active rotor parts are in such motors located radially
outside the active parts of the stator. Such a motor may have
sufficient inertia to permit it to be used as a flywheel, thus
replacing the conventional flywheel. This reduces the extra mass of
the hybrid powertrain.
[0123] Conventional clutches normally have some torsional
flexibility to reduce the torque ripple from the thermal engine.
This damping device is shown in FIG. 4f as item 432. Another torque
ripple damper 434 has been added between the electric traction
motor 401 and the input shaft of the gearbox 406 thus providing two
serially connected. mechanical low pass filters to further reduce
the torque ripple from the thermal engine. As the encoder 412 in
this case does not have any rigid connection to the electric motor
401, an extra encoder 433 rigidly connected to the electric motor
401 has been added.
[0124] An electric traction motor such as 401 has a large inertia
compared to the part of a normal car clutch which is rigidly
connected to the input shaft of a gearbox. This imposes much higher
requirements on the regulation of the speed of the electric motor
401 before the next gear position is attempted. As has been
described above, the electric motor 401 and its encoder 433 permits
a high gain servo loop. This permits the speed and even the phase
of the electric motor 401 to be adjusted to the speed and phase of
the output shaft of the gear box, the shaft carrying the encoder
413. Transients in the speed of the tires due to obstacles in the
road could cause large forces on the gearbox if the splines of a
new gear were fractionally in grip when the tire speed transient
appears. The damper 434 will dramatically reduce the spline loads
from such tire speed transients as the inertia of the motor 401
will be connected through a much softer path.
[0125] During a change of gear or speed position the torque and
inertia of the electric motor 401 will permit a steady rotational
speed of the motor 401. The gears on the gearbox input shaft and
its encoder 412 might possibly oscillate. The moments of inertia of
the rotor of the electric motor 401 and of the input shaft gears
and of the torsion spring in the damper 434 constitute a resonance
circuit. If the damping of this circuit is low, any torsional
resonance which has been initiated for any reason might continue
for a relatively long time. The energy in this resonance circuit is
however much lower than the energy stored in the friction plates of
a conventional clutch and can be easily absorbed by most
clutches.
[0126] A resonance which may cause more concern is that one which
may develop between the inertia of the gearbox output shaft, the
inertia of the differential, the inertia of the tires and their
shafts and the elasticity of the cogs on cog wheels 421 and 422 and
between the cog wheels in the differential. The elasticity is
highly non-linear, being extremely soft when the play between the
cogs are open and very stiff when the cogs are deformed during the
maximum amplitude of the oscillations between the shafts. Such
oscillations may create signals from the encoder 413 which are
difficult to distinguish from transients caused by obstacles on the
road surface. This problem might motivate the insertion of a torque
generation device which in the diagram of FIG. 4f is drawn as a
small electric motor 437 connected to the output shaft of the
gearbox 406. For the purpose of stabilising the speed of the
gearbox output shaft a rather small motor is sufficient. By
supplying a suitable torque, the small electric motor 437 can
rapidly reduce any oscillations between the output shaft of the
gearbox and the differential and/or the tires. In the case of a
small electric motor 437, it could detect oscillations using the
encoder 413 and actively damp them out. Regardless of type, the
device in position 437 should apply its torque before the reduction
of the torque from the thermal engine 403 and/or the electric
generator/motor 409. It should preferably apply a torque of the
same sign as that obtained from the thermal engine 403 and/or the
electric generator/motor 409. In that case, the torque transferred
through the cog wheels 421 and 422 and the differential gears will
keep its sign when the torque from the engine 403 and/or the
electric generator/motor 409 is withdrawn.
[0127] The control system should seek to maximize the total
efficiency of the powertrain. One way to estimate the efficiency of
the thermal engine 403 is to measure its speed and torque. These
two data will, when inserted in a table, give a good estimate of
the efficiency. Even better estimates can be obtained by adding
other information such as temperatures in various components of the
engine, air pressure after compressors (if any), etc.
[0128] Information on the speed of the thermal engine is directly
available from the encoder 414 attached to the drive shaft or
crankshaft of the thermal engine. When the clutch 407 is
non-engaged, thermal engine torque can easily be calculated from
the torque of the electric generator/motor 409. The torque of an
electric motor can be calculated with moderate accuracy from its
electrical current, current phase angle and the temperature of its
magnets.
[0129] When the clutch 407 is engaged, some other torque
measurement method is required. The torsional deformation of one or
both of the two elastic dampers 432 and 434 can be used to measure
the total torque passing them. Preferably, the encoders should be
located close the damper used. One solution is to locate the
encoders 433 and 412 close to the damper 434. This requires a
sufficient resolution in the encoders 433 and 412. The use of the
damper 432 seems to require an additional encoder on the left side
of the damper 432.
[0130] Instead of using the torsional deflection of dampers 432 or
434, conventional torque measuring devices can be used. In FIG. 4f
torque transducers 435 and 436 are placed on the left and right
tire axle respectively. In most positions of conventional torque
transducers, the torque measured will be the sum of the torque from
the thermal engine 403 and one or more of the electric motors 409
and 401. As the torque from the electric motors can be estimated
from their currents, etc., as mentioned above, the torque of the
thermal engine can be found as the difference between the total
measured torque and the torque from the electric motor(s).
[0131] Encoders based on magnetic principles seem well suited to
the environment close to the shafts. Magnetically biased Hall
sensors can sense the position of cog-like parts. They can either
be cogs from cogwheels being part of the gearbox or cog-like
details protruding from motor rotors, clutch components or similar
devices.
[0132] A detailed design example
[0133] FIG. 6 shows a layout of some of the essential components of
a powertrain having an electric generator/motor on the shaft of the
thermal engine a conventional clutch and an electric traction motor
on the thermal engine side of the gear box. The layout is intended
to illustrate that hybrid powertrains like those shown in FIGS. 4a
and 4f can be implemented within acceptable dimensions. As water,
oil and air cooling arrangements are illustrated using the same
layout, some details are far from optimal for some of the cooling
types.
[0134] The shaft 601 of the thermal engine has the rotor 602 of the
electric generator/motor attached to it using a rigid connection
603 as shown or a connection comprising means for elastic vibration
damping, not shown. The rotor 602 has the shape of a cup with the
magnets 604 of the electric generator/motor located inside the cup.
This gives the electric generator/motor rotor a high inertia which
is approximately equal to that of a conventional flywheel. The
stator 605 of the electric generator/motor is mounted inside the
cup-shaped rotor and is attached to a disc 606 which is mounted to
the thermal engine. The cooling of the electric generator/motor
stator can be arranged by having oil enter, at 607, from inside the
thermal engine as indicated by the arrows of the figure to an exit
608. Water cooling in channels in the stator hub 609 of the
electric generator/motor is an alternative cooling method. For
somewhat different dimensions and suitable openings in the rotor
602, the airflow from 636 to 637 in the figure could pass the
magnets 604 and the stator 605 of the electric generator/motor.
[0135] The right surface 610 of the electric generator/motor rotor
acts as a component in a conventional clutch also including a
conventional friction disc 611 and a pressure plate 612. In the
engaged state shown, the friction disc 611 is fixed between surface
610 and member 612. The torque from the thermal engine is
transferred through vibration damping springs 613 to a spine 614 on
the shaft 615 of the electric traction motor. The pressure on the
plate 612 is in the conventional way supplied by a spring 617. The
clutch arrangement is quite conventional except that the member 612
is much thinner that normal. This is possible because the heat
dissipated is much less than in conventional clutches due to the
almost synchronized speeds of the two shafts during clutch closure
time.
[0136] To release the clutch a hydraulic device 618 is provided.
The device shown has a left shield 623 which rotates with the rotor
602 of the electric generator/motor and a right shield 624 that
rotates with the rotor 620 of the electric traction motor. The
hydraulic device receives for operation thereof oil supplied
through a tube 622. The stator 619 of the electric traction motor
is cooled by channels 621 around the outer side of the stator for
cooling oil or water.
[0137] The shaft 615 of the electric traction motor is rigidly
attached to its rotor 620. The left part ends in a bearing 616 in
the end surface of the shaft 601 of the thermal engine. The other
end, i.e. the right part is radially attached to the input shaft
625 of the gearbox using a PTFE lubricated bearing 639. Axially it
is fixed between the engine shaft bearing 616 and another PTFE
lubricated ring 640 which transfers the pressing force to the input
shaft 625 of the gear box through a vibration damping device 627.
PTFE bearings are assumed to be sufficient since the relative
rotation is limited to a few degrees. The surface material of the
ring 640 should be selected to obtain a suitable damping of
possible oscillations between the rotor 620 of the electric motor
and the input shaft of the gear box. The pressing force is provided
by a disc or cup spring 638 which forces the bearing 616 in the
engine shaft 601 to the right. During assembly, the outer ring part
of bearing 616 is kept from falling out by the rotor 602. The
vibration damper has a first element 627 torsionally fixed to the
gearbox input shaft using a spline. A second element 628 is fixed
to the rotor 620 of the electric traction motor and springs 629
connecting the elements act as damping elements.
[0138] The electric traction motor shown can change its speed from
a speed used for one gear to a speed suitable for the next gear in
some 15 ms while still using moderate currents.
[0139] The input shaft 625 of the gearbox has several cogwheels,
only the active ones of which are shown. The cogwheel 631
cooperates with the cogwheel 632 on the output shaft 633. A
permanently used cogwheel 634 cooperates with the input cogwheel
635 of the differential.
[0140] A hybrid vehicle system has several forced air flows, such
as the thermal engine input air, turbocharger input air, air for
the cooling- of cooling oil or water and air for cooling of battery
cells. Therefore several flows of reasonable cool, filtered air are
available. Some of this air can be entered into the electric motor
enclosure and forced to cool the surface magnets of the rotor(s).
Two airflow arrows illustrate this fact. They enter at the input
opening 636, pass either through the airgap 639 or between the
surface mounted magnets 638 of the electric traction motor, pass
the traction motor winding head 640 and exit at 637 after having
passed the outer side of the electric generator/motor rotor 602. In
this way, the temperature of the magnets can be kept low. This
permits the use of magnet material having a higher flux density and
will also keep the flux from a given magnet material at a higher
intensity as the temperature coefficient of currently used
permanent magnet materials is negative.
[0141] If the stators 608 and/or 619 of the electric
generator/motor and the electric traction motor respectively have
their windings arranged as separate coils, each on wound around a
stator pole as shown around the stator pole 605, the air flow could
be directed to flow between the coils. If the rotor or rotors have
surface mounted magnets with considerable space between the
magnets, the air flow could be directed to flow between the
magnets. For electric motors having both those features, the
cooling air can flow between the coils. through the air gap and
between the magnets, thus providing cooling of the surface of the
coils as well as cooling of the magnets.
[0142] As is obvious for those skilled in the art, the embodiments
shown in FIGS. 4a-f and 6 are not the only ones comprised within
the general scope of the invention. The mechanical connection
between an electric generator/motor 409 which in some settings
permit the absorption of the thermal engine power when the thermal
engine 403 lacks a direct mechanical torque transfer to the wheels
can be made in many ways. Of these, only the most simple ones
having shafts in common with other devices and with or without
clutches are shown. Similarly, the connection of another electric
traction motor 401 or several electric motors 424-427 to the wheels
of the vehicle during the time periods when the thermal engine 403
lacks a direct mechanical torque transfer to the wheels can be made
in many ways. They include the use of cog wheels, belts, chains,
etc. The paths from the electric motor 401 and the thermal engine
403 to the differential gear 408 can be anything from fully shared,
as in FIG. 4a, to completely separate, as in FIG. 4c. The electric
traction motor can be anything from a single motor 401 to motors
like 424-427 which are each one directly connected to one wheel.
Many intermediate forms may be used. One such form could be to is
have one electric motor like 401 acting on the front wheel
differential and another motor acting on a rear differential
through a clutch. The clutch can be disengaged to eliminate the
losses of this rear traction motor during normal driving and
engaged during braking and conditions requiring four wheel drive.
Yet another such form could be to have one electric motor like 401
acting on the front wheel differential and two hub motors acting
directly on the two rear wheels.
[0143] Another such form is to use a mechanical four-wheel
transmission in place of the two wheel transmissions shown in FIGS.
4a-d. This would permit the recovery of break energy in a system
having only two electric motors.
[0144] Another general modification within the basic scope of the
invention is to connect the electric generator/motor 409 and/or the
electric traction motor(s) through clutches. This permits the
system to let one or several of the motors to stay idle. This can
be advantageous owing to the fact that the losses at high speed and
no load can have some importance, especially for permanent magnet
motors.
[0145] Whereas the preferred embodiment has a manual type gearbox
with automated, non-manual shifts of gear position, the powertrain
principle can be used with other gearbox principles:
[0146] 1. A manual shift of gear position with gear shift
suggestions from the system. In this embodiment, the system
controller cannot execute a gearshift but can suggest a gearshift
based on actual and anticipated load.
[0147] 2. An automated gearshift with gear set suggestions from the
driver. In this embodiment, the system controller executes all
gearshifts but the driver can suggest a gearshift based on an
anticipated load or speed change. The driver can also indicate that
a gearshift which he anticipates that the system will make should
be avoided, for example when accelerating up to a lower than normal
queue speed.
[0148] Whereas the preferred embodiment has a manual type gearbox
with automated clutch control, the powertrain principle can be used
with other clutch control principles, such as:
[0149] 3. A manual gearshift using a manual clutch control. As soon
as the driver applies enough force on the clutch pedal, the system
can disengage the clutch. As soon as the clutch is disengaged and
the gear handle has been moved so much that the system can detect
the gear position which the driver intends to use, the electric
motor 401 can adjust the speed input to the gearbox to fit the new
gear position. The system controller can delay the clutch
engagement even if the driver has released the clutch pedal until
the thermal engine speed has been adjusted to the new gear
setting.
[0150] 4. A manual gear shift using a manual clutch control
obtained by operating a lever or pedal can be replaced or combined
with sensors which detect the movement of the gearshift lever. As
soon as the driver applies enough force on the handle, the system
can disengage the clutch. As soon as the clutch is disengaged, the
electric motor can adjust the input speed to the gearbox to fit the
new gear, and the system controller can engage the clutch as soon
as the thermal engine speed has been adjusted to the new clutch
setting.
[0151] Whereas the preferred embodiment has a gearbox with one
input shaft and one output shaft, the powertrain principle can be
used with other shaft arrangements of the gearbox. In order to
further decrease the delay from one gear position to the next gear
position, a gearbox having several input shafts or several output
shafts can be used. As an example, two output shafts can be used,
each for example being connected to the input cogwheel of the
differential gear through a clutch. As a gear box of a hybrid
vehicle can operate without a reverse gear, the problems to find
space for two output shafts should be easier than in a conventional
gearbox. The total length could be reduced as each output shaft
would carry only half the normal number of gears, even if the
clutches would consume some of these gains. The cogwheels for the
even gear positions can be located on one of the output shafts and
the cogwheels for odd gear positions can be located on the other
shaft. This permits the controller to synchronize the estimated
forthcoming gear on the inactive shaft (with a non-engaged output
clutch) while the other shaft transfers torque through the
gearbox.
[0152] An actual gear shift operation, for example from gear
position No. 2 to gear position No. 3, would then consist of a
release of the thermal engine clutch, release of the even gear
output shaft clutch, engagement of the odd gear output shaft clutch
and change of the speed of the electric generator/motor. The actual
timing of the three last operations will most likely depend on the
release and engage times of the clutches, which normally is longer
(some 100 ms when controlled by 24 V DC on-off control) than the
time required to change the speed of the generator/motor. Using a
more sophisticated control of the clutch coil voltage, the time
from the ensured release of one clutch to the ensured engagement of
the next one could be kept to some 30 ms, virtually eliminating the
gap in providing torque to the tires.
[0153] Yet another alternative is to use a conventional automatic
transmission in place of the gearbox.
[0154] All embodiments shown use a single thermal engine. In some
applications more than one thermal engine may advantageously be
used. One such application is the city bus. For city busses, it
might be attractive to use gasoline engines as present diesels have
considerable exhaust of small particles. The health consequences of
these may be a problem. As most gasoline engines produced are too
weak to cover all power needs of a bus, it might be advantageous to
use two or more gasoline engines. This can either be implemented as
two complete powertrains acting on the front and rear wheels
respectively, or as one powertrain having for example two thermal
engines 403 each having an electric generator/motor 409 and a
clutch 407 acting on the same input shaft of a common gearbox. In
most inter-city driving conditions, only one thermal engine would
be used, while high speed or uphill operation could engage both
engines.
[0155] Thermal engine on/off control strategies
[0156] If the internal combustion thermal engines of a hybrid
system as the ones shown are to give a low total energy
consumption, some criteria must be used for the controller to
determine when the thermal engine is to be switched on and off.
FIG. 5 and the simulation results of table I show the result of a
fairly simple control strategy. The thermal engine is started if
the speed of the tires is above a certain limit at the same time as
the torque demanded for the tires is above a certain limit. The
thermal engine is switched off when the torque demand on the tires
goes below another limit. One or several of the three limit values
can be changed as a function of the charge status of the battery.
When the charge status of the battery is low, the parameters should
be changed in a way that will cause the thermal engine to be
switched on earlier and switched off later.
[0157] The control strategies can be arranged to accept input from
the driver. as the driver knows his own plans, for example that a
long steep slope will appear soon or that he plans to accelerate to
overtake a car.
[0158] The control strategies can also be arranged to accept input
from a GPS system or other systems capable of determining the
position of the vehicle. This information can be set in relation to
a data base comprising data of a road system, for example presently
available systems which use GPS data to show a map of the immediate
vicinity of the vehicle. This information permits a much better
possibility to estimate whether a change of torque demanded by the
driver as given by the accelerator and brake pedals indicates
temporary or longer time period requirements of power to be
provided by the thermal engine. If the driver has keyed in his
desired target, the control computer can use the information in the
GPS system and the local map system to make an even better estimate
of the immediate and long term power requirements and thus further
optimize switch on and switch off times of the IC thermal engine.
If the driver has not keyed in his desired target, the GPS system
can be used to recognize common patterns like when the driver seems
to be on a frequent route like home-to-work, and in other cases
assume that the driver is going to follow the main routes.
[0159] Gear and thermal engine torque control strategies
[0160] If the IC thermal engines of a hybrid system as the ones
shown are to give a low total energy consumption, some criteria
must be used for the controller to determine the gear which is to
be used and the torque which should be demanded from the thermal
engine.
[0161] The simulation model which has provided the data illustrated
in FIG. 5 and in the simulation results of table 1 shows the result
of a fairly simple control strategy. This partial strategy has as a
given fact that the thermal engine is on or off and that the driver
has requested a certain torque on the tires. This leaves two
decisions for the local control strategy:
[0162] 1. To keep or change the gear position.
[0163] 2. The torque which is to be demanded from the thermal
engine.
[0164] To reach a decision on these two variables, the controller
calculates the total losses incurred for each gear position, and
for each gear, the total losses (generator, battery, thermal engine
etc.) incurred for a number of alternatives of the torque obtained
from the thermal engine.
[0165] If the lowest losses should occur for any thermal engine
torque for the present gear position or speed, the controller will
keep the gear but change the torque to the optimal one if this is
within the maximum torque change rate set by the limitations set by
exhaust control system. Otherwise the torque is changed as far as
possible in the desired direction.
[0166] If the lowest losses should occur for anv thermal engine
torque for another gear position than the present one, the
controller will test if the potential long range improvement is
large enough to motivate a change. Each change will cause some
transient losses (a low efficient electric power transfer instead
of a more efficient mechanical power transfer) and very frequent
gear changes may irritate the passengers. In the simulation model
generating FIG. 5, this is achieved by a constant minimum gain
between the present and next gear. Better results will be obtained
if some information on the expected future torque demand can be
included when making the decision. Decisions on gear changes can be
substantially improved using GPS data or by collecting a large
amount of driving information to permit statistically better
estimates on power demands for the near future.
[0167] Clutch or movable spline
[0168] The clutch must not have slip capacity. It can be replaced
by other disconnectable torque transfer devices, for example by a
sliding splined tube normally used to lock or release a cog wheel
inside a gearbox. It can also be completely eliminated and its
function replaced by using the neutral setting of the gearbox as an
equivalent of a non-engaged clutch. This requires a sufficiently
good synchronisation of the two shafts of the gearbox. If the
clutch 407 of FIG. 4b or 4c is replaced by a solid shaft, the
angular speed and phase of the two gearbox shafts can be controlled
by the two electric motors 409 and 401, thus permitting gear
engagement at very low speed differences (for example less than 20
rpm) or even at negligible speed differences.
[0169] Depending on the reliability level required and the
reliability assumed for the electric components, i.e. motors,
inverters, batteries, etc., the system may have anything from a
normal clutch having a normal thermal capacity to a clutch having
low thermal capacity which allows it to operate as a conventional
clutch only for driving patterns adjusted to reduce the thermal
load on the device to devices like splined tubes which can absorb
only very small slips or speed differences between the two shafts
to be connected by the clutch.
[0170] A clutch-free design will however in most cases require that
the torsion vibration dampers found in normal vehicle clutch design
are installed somewhere else in the powertrain. One solution to
this is to arrange a similar, torsionally flexible connection
between the thermal engine 403 and the electric generator/motor 409
or at the electric traction motor.
[0171] To further reduce losses in the powertrain, the normal
immersion of cogs in oil can be replaced by spray or drop
lubrication.
[0172] As the inner diameter of the active parts of the electric
motors 409 and 401 can be rather large, it may be conceivable to
place the clutch device inside the rotor of one of the electric
motors 409 and 401 or even inside both rotors. The term "inside"
here means that the clutch device is placed radially inside, as
seen from the common axis of the clutch device and the respective
rotor, the active parts of the respective rotor. While specific
embodiments of the invention have been illustrated and described
herein, it is realized that numerous additional advantages,
modifications and changes will readily occur to those skilled in
the art. Therefore, the invention in its broader aspects is not
limited to the specific details, representative devices and
illustrated examples shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents. It is therefore to be
understood that the appended claims are intended to cover all such
modifications and changes as fall within a true spirit and scope of
the invention.
* * * * *
References