U.S. patent application number 13/421356 was filed with the patent office on 2013-09-19 for transmission control during regenerative braking.
This patent application is currently assigned to FORD GLOBAL TECHNOLOGIES,LLC. The applicant listed for this patent is Daniel Scott Colvin, Marvin Paul Kraska, Bernard D. Nefcy, Walter Joseph Ortmann, Fazal Urrahman Syed, Mark Steven Yamazaki. Invention is credited to Daniel Scott Colvin, Marvin Paul Kraska, Bernard D. Nefcy, Walter Joseph Ortmann, Fazal Urrahman Syed, Mark Steven Yamazaki.
Application Number | 20130244829 13/421356 |
Document ID | / |
Family ID | 49044190 |
Filed Date | 2013-09-19 |
United States Patent
Application |
20130244829 |
Kind Code |
A1 |
Nefcy; Bernard D. ; et
al. |
September 19, 2013 |
Transmission Control During Regenerative Braking
Abstract
A system and method for controlling a hybrid electric vehicle
during regenerative braking is provided. The system and method
include a brake controller adapted to cause, for a selected
transmission gear, a first torque ratio to be applied to a
regenerative brake system during regenerative braking and a second
torque ratio, different from the first torque ratio, to be applied
when the vehicle is not regenerative braking. The first torque
ratio results in an increased braking torque generated by the
regenerative brake system compared with application of the second
torque ratio.
Inventors: |
Nefcy; Bernard D.; (Novi,
MI) ; Colvin; Daniel Scott; (Farmington Hills,
MI) ; Kraska; Marvin Paul; (Dearborn, MI) ;
Ortmann; Walter Joseph; (Saline, MI) ; Yamazaki; Mark
Steven; (Canton, MI) ; Syed; Fazal Urrahman;
(Canton, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nefcy; Bernard D.
Colvin; Daniel Scott
Kraska; Marvin Paul
Ortmann; Walter Joseph
Yamazaki; Mark Steven
Syed; Fazal Urrahman |
Novi
Farmington Hills
Dearborn
Saline
Canton
Canton |
MI
MI
MI
MI
MI
MI |
US
US
US
US
US
US |
|
|
Assignee: |
FORD GLOBAL
TECHNOLOGIES,LLC
Dearborn
MI
|
Family ID: |
49044190 |
Appl. No.: |
13/421356 |
Filed: |
March 15, 2012 |
Current U.S.
Class: |
477/15 ; 192/220;
192/3.34 |
Current CPC
Class: |
B60W 10/11 20130101;
B60W 10/196 20130101; B60W 30/18127 20130101; B60W 10/184 20130101;
Y10T 477/33 20150115; B60W 10/10 20130101; B60W 10/08 20130101;
B60W 2710/1005 20130101; Y10T 477/347 20150115; B60W 20/14
20160101 |
Class at
Publication: |
477/15 ; 192/220;
192/3.34 |
International
Class: |
B60L 7/18 20060101
B60L007/18; B60W 10/10 20120101 B60W010/10; B60W 10/08 20060101
B60W010/08; B60W 10/196 20120101 B60W010/196 |
Claims
1. A hybrid-electric vehicle control system comprising: a brake
controller adapted to cause, for a selected transmission gear, a
first torque ratio to be applied to a regenerative brake system
during regenerative braking and a second torque ratio different
from the first torque ratio to be applied otherwise, wherein
application of the first torque ratio results in an increased
braking torque generated by the regenerative brake system compared
with application of the second torque ratio.
2. The control system according to claim 1 wherein the regenerative
brake system comprises a powertrain regenerative brake system
including an electric machine and a transmission adapted to apply
the braking torque.
3. The control system according to claim 2 wherein the electric
machine is mechanically coupled to the transmission such that the
transmission is in-line with the electric machine.
4. The control system according to claim 2 wherein the powertrain
regenerative brake system further includes a battery connected to
the electric machine such that the battery stores regenerative
energy collected by the electric machine, wherein application of
the first torque ratio increases an amount of regenerative energy
collected when the electric machine is generating.
5. The control system according to claim 2 wherein the powertrain
regenerative brake system further includes a torque converter
connected between the electric machine and the transmission,
wherein for the selected gear of the transmission, while the torque
converter is locked, the transmission is configured to produce the
first torque ratio when the electric machine is generating, and to
produce the second torque ratio when the electric machine is
motoring.
6. The control system according to claim 5 wherein the torque
converter is mechanically coupled to and included in the
transmission.
7. The control system according to claim 1 wherein the brake
controller is adapted to apply the first torque ratio when a
commanded transmission output torque is negative and adapted to
apply the second torque ratio when the commanded transmission
output torque is positive.
8. The control system according to claim 1 wherein the first torque
ratio is greater than the second torque ratio.
9. The control system according to claim 1 further comprising a
friction brake system coupled to road wheels, wherein the brake
controller allocates a braking request between the regenerative
brake system and the friction brake system when the braking request
exceeds a capacity of the regenerative brake system.
10. A hybrid-electric vehicle comprising: an electric machine; and
a transmission coupled to the electric machine and configured to
produce, for a selected gear, a first torque ratio when the
electric machine is generating and a second torque ratio different
than the first torque ratio when the electric machine is motoring,
wherein production of the second torque ratio results in an
increased regenerative braking capacity relative to production of
the first torque ratio.
11. The hybrid-electric vehicle according to claim 10 wherein the
regenerative braking capacity is indicative of a powertrain braking
torque and wherein the transmission applies an increased powertrain
braking torque when the transmission is configured to produce the
first torque ratio relative to when the transmission is configured
to produce the second torque ratio.
12. The hybrid-electric vehicle according to claim 10 further
comprising a battery connected to the electric machine, wherein the
regenerative braking capacity is indicative of an amount of
regenerative energy stored by the battery, such that the battery
stores an increased amount of regenerative energy when the
transmission is configured to produce the first torque ratio
relative to when the transmission is configured to produce the
second torque ratio.
13. The hybrid-electric vehicle according to claim 10 further
comprising a torque converter connected to the transmission,
wherein for the selected gear while the torque converter is locked,
the transmission is configured to produce the first torque ratio
when the electric machine is motoring, and the transmission is
configured to produce the second toque ratio, different than the
first torque ratio, when the electric machine is generating.
14. The hybrid-electric vehicle according to claim 10 wherein the
first torque ratio is greater than the second torque ratio.
15. A method for controlling a hybrid-electric vehicle including a
regenerative brake system having a transmission and an electric
machine, the method comprising: applying a first torque ratio to
the transmission for a selected gear of the transmission if the
regenerative brake system is regenerative braking; and applying a
second torque ratio to the transmission for the selected gear if
the regenerative brake system is not regenerative braking, the
second torque ratio being different than the first torque ratio,
wherein application of the first torque ratio results in increased
braking torque generated by the regenerative brake system compared
with application of the second torque ratio.
16. The method according to claim 15 wherein the first torque ratio
is greater than second torque.
17. The method according to claim 15 further comprising: collecting
regenerative energy, wherein application of the first torque ratio
increases an amount of regenerative energy collected compared with
application of the second torque ratio.
18. The method according to claim 15 further comprising: receiving
a braking request based on a desired transmission output torque;
and applying the first torque ratio to the transmission when the
desired transmission output torque is negative.
19. The method according to claim 18 further comprising allocating
the braking request between the regenerative brake system and a
friction braking device.
20. The method according to claim 19 further comprising braking the
vehicle with the friction braking device if the braking request
exceeds a capacity of the regenerative brake system, wherein, for
the selected gear of the transmission, application of the first
torque ratio increases the capacity of the regenerative brake
system compared with application of the second torque ratio.
Description
TECHNICAL FIELD
[0001] This disclosure relates to control of transmissions in
hybrid vehicles during regenerative braking.
BACKGROUND
[0002] Hybrid electric vehicles (HEV's) utilize a combination of an
internal combustion engine and an electric motor to provide the
power needed to propel the vehicle. This arrangement provides
improved fuel economy over a vehicle that has only an internal
combustion engine.
[0003] HEV's also capture and store energy when the vehicle is
experiencing powertrain braking. The electric motor functions as a
generator when powertrain braking is performed. When the electric
motor functions as a generator, the generator absorbs energy
generated as a result of the powertrain braking and converts the
energy to electric energy which may be used to increase the state
of charge of a battery. Regenerative powertrain braking may be
desirable beyond recouping energy because the hybrid electric
vehicle's energy may be dissipated with minimal or no negative
torque supplied by the frictional wheel brakes--thus reducing wear
on the frictional wheel brakes.
[0004] During vehicle operation, the HEV may require frictional
braking when the driver's braking demand exceeds the powertrain
braking capability or when the battery is already charged to
capacity.
SUMMARY
[0005] A system and method for controlling a hybrid electric
vehicle is provided. In one embodiment of the invention, a brake
controller, for a selected transmission gear, applies a first
torque ratio to be applied to the regenerative brake system during
regenerative braking. The controller applies a second torque ratio
different from the first torque ratio to the transmission when the
vehicle is not regenerative braking. Application of the first
torque ratio results in an increased braking torque generated by
the regenerative brake system compared with application of the
second torque ratio.
[0006] In another embodiment, the system and method include
collecting and storing regenerative energy by the regenerative
brake system. The first torque ratio increases an amount of
regenerative energy collected when the vehicle is regenerative
braking.
[0007] According to another embodiment, the method and system
include wherein production of the second torque ratio results in an
increased regenerative braking capacity relative to production of
the first torque ratio.
[0008] In a further embodiment, the system and method includes a
torque converter connected between to electric machine and a
transmission. For the selected gear of the transmission, while the
torque converter is locked, the transmission produces the first
torque ratio when the electric machine is generating, and produces
the second torque ratio different than the first torque ratio, when
the electric machine is motoring.
[0009] In an alternate embodiment, the system and method applies
the first torque ratio when a commanded transmission output torque
is negative and applies the second torque ratio when the commanded
transmission output torque is positive.
[0010] According to another embodiment, the first torque ratio is
greater than the second torque ratio.
[0011] Embodiments according to the present disclosure may provide
various advantages. For example, systems and methods for
controlling a hybrid electric vehicle during regenerative
powertrain braking according to the present disclosure may
performed may be performed to decelerate the hybrid vehicle even
for an extended period to further reduce usage of mechanical wheel
braking operations. In addition, regenerative powertrain braking
operations may be performed for longer durations to charge the
battery to capacity which may improve fuel economy and reduce
emissions.
[0012] The above advantages and other advantages and features will
be readily apparent from the following detailed description of
representative embodiments when taken in connection with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a schematic view of a hybrid vehicle according to
an embodiment of the disclosure;
[0014] FIG. 2 is a graph illustrating operating characteristics of
the transmission of FIG. 1 according to an embodiment of the
disclosure; and
[0015] FIG. 3 is a flowchart illustrating a method for controlling
the hybrid vehicle during regenerative powertrain braking according
to an embodiment of the disclosure.
DETAILED DESCRIPTION
[0016] As required, detailed embodiments of the present invention
are disclosed herein; however, it is to be understood that the
disclosed embodiments are merely examples of the invention that may
be embodied in various and alternative forms. The figures are not
necessarily to scale; some features may be exaggerated or minimized
to show details of particular components. Therefore, specific
structural and functional details disclosed herein are not to be
interpreted as limiting, but merely as a representative basis for
teaching one skilled in the art to variously employ the present
invention.
[0017] FIG. 1 illustrates a schematic diagram of a hybrid vehicle
10 according to an embodiment of the disclosure. The vehicle 10
includes an engine 12, and an electric machine, which, in the
embodiment shown in FIG. 1, is a motor generator (M/G) 14, and
alternatively may be a traction motor. The M/G 14 is configured to
transfer torque to the engine 12 or to the vehicle wheels 16. Each
of the wheels 16 may include a friction brake device 18.
[0018] The M/G 14 is connected to the engine 12 using a first
clutch 20, also known as a disconnect clutch or the upstream
clutch. A second clutch 22, also known as a launch clutch or the
downstream clutch, connects the M/G 14 to a transmission 24, and
all of the input torque to the transmission 24 must flow through
the launch clutch 22. The launch clutch 22 can be controlled to
isolate the driveline 26, which includes the M/G 14 and the engine
12, from the transmission 24, differential 28 and the vehicle drive
wheels 16. Although the clutches 20, 22 are described and
illustrated as hydraulic clutches, other types of clutches, such as
electromechanical clutches may also be used. Alternatively, the
clutch 22 may be replaced with a torque converter and bypass
clutch.
[0019] In the embodiment illustrated in FIG. 1, the transmission 24
is disposed between the M/G 14 and vehicle drive wheels 16. The M/G
14 can operate as a motor to provide torque to the vehicle wheels
16, and can also operate as a generator, receiving torque from the
engine 12 and/or vehicle wheels 16, thereby charging a battery
32.
[0020] While FIG. 1 shows one example of a hybrid vehicle
powertrain configuration, various other hybrid configurations are
also contemplated. With regards to a full series type hybrid
powertrain system, the engine may be operated to generate a form of
energy suitable for use by the one or more motors. For example,
with a full series type hybrid electric vehicle, the engine may
generate electricity via a motor/generator that may be used to
power an electric motor for propelling the vehicle. With regards to
a parallel type hybrid propulsion system, the engine and one or
more motors may be operated independently of each other. As one
example, an engine may be operated to provide torque to the drive
wheels, while a motor may be selectively operated to add or remove
torque delivered to the wheels. As another example, the engine may
be operated without the motor or the motor may be operated without
the engine. Further, in addition to the embodiment in FIG. 1 it is
also contemplated that the hybrid electric vehicle may have with
either series or parallel type hybrid powertrain systems, or
combinations thereof to cooperatively generate electric power as
well as output torque.
[0021] The engine 12 is a direct injection engine. Alternatively,
the engine 12 may be another type of engine or prime mover, such as
a port injection engine, a fuel cell, or a second electric machine.
The engine 12 may use various fuel sources, such as diesel,
biofuel, natural gas, hydrogen, or the like.
[0022] In some embodiments, the vehicle 10 also includes a starter
motor 30 operatively connected to the engine 12, for example,
through a belt or gear drive. The starter motor 30 may be used to
provide torque to start the engine 12 without the addition of
torque from the M/G 14. This allows the upstream clutch 20 to
isolate the M/G 14 during engine 12 start and may eliminate or
reduce torque disturbances that would otherwise occur if torque is
transferred from the M/G 14 to the engine 12 to assist the engine
start.
[0023] The M/G 14 is in communication with a battery 32. The
battery 32 may be a high voltage battery. The M/G 14 may be
configured to charge the battery 32 in a regeneration mode, for
example when a driver demands negative wheel torque, through
regenerative powertrain braking, or the like. In one example the
battery 32 is configured to connect to an external electric grid,
such as for a plug-in electric hybrid vehicle (PHEV) with the
capability to recharge the battery from an electric power grid,
which supplies energy to an electrical outlet at a charging
station.
[0024] In some embodiments, the transmission 24 is an automatic
transmission and connected to the drive wheels 16 in a conventional
manner, and may include a differential 28. The vehicle 10 is also
provided with a pair of non-driven wheels, however, in alternative
embodiments, a transfer case and a second differential can be
utilized in order to positively drive all of the vehicle
wheels.
[0025] The M/G 14 and the clutches 20, 22 may be located within a
motor generator case 34 which may be incorporated into the
transmission 24 case, or alternatively, is a separate case within
the vehicle 10. The transmission 24 has a gear box to provide
various gearing ratios for the vehicle 10. The transmission 24
gearbox may include clutches and planetary gear sets, or other
arrangements of clutches and gear trains as are known in the
art.
[0026] The transmission 24 is controlled using a transmission
control unit (TCU) 36 to operate on a shift schedule, such as a
production shift schedule, that connects and disconnects elements
within the gear box to control the ratio between the transmission
output and transmission input. The TCU 36 also acts to control the
M/G 14, the clutches 20, 22, and any other components within the
motor generator case 34.
[0027] The engine 12 output shaft is connected to the disconnect
clutch 20, which in turn is connected to the input shaft for the
input shaft to the M/G 14. The M/G 14 output shaft is connected to
the launch clutch 22, which in turn is connected to the
transmission 24. In the embodiment illustrated in FIG. 1, the
components of driveline 26 of the vehicle 10 are positioned
sequentially in series with one another.
[0028] An engine control unit (ECU) 38 is configured to control the
operation of the engine 12. A vehicle system controller (VSC) 40
transfers data between the TCU 36 and ECU 38. The VSC is also in
communication with various sensors for detecting the operating
conditions of the engine 12 and transmission 24 such as throttle
position sensors, mass air flow sensors, oxygen sensors, manifold
pressure sensors or any other powertrain sensors for determining
driver input and operating conditions of the battery 32 and M/G
14.
[0029] The VSC 40 may also communicate with or include a brake
controller 42. The brake controller 42 may be connected with a
variety of sensors including brake pedal sensors, accelerator pedal
sensors or wheel speed sensors or any other brake system sensors.
The brake controller 42 may control and operate friction brakes 18
for mechanical braking of the wheels 16. The brake controller 42
may also control the regenerative brake system 48. The regenerative
brake system may include the M/G 14 driven by and driving the
wheels 16 of an HEV and the battery 32.
[0030] The control system 44 for the vehicle 10 may include any
number of controllers, and may be integrated into a single
controller, or have various control modules. Some or all of the
controllers may be connected by a controller area network (CAN) or
other system. The control system 44 may be configured to control
operation of the various components of the transmission 24, the
motor generator assembly 34, the starter motor 30 and the engine 12
under any of a number of different conditions. For example, the
control system 44 may control operation of the various systems and
components in a way that minimizes or eliminates torque
disturbances and impact to the driver.
[0031] Under normal powertrain conditions, the VSC 40 interprets
the driver's demands, such as acceleration deceleration demand and
then determines the wheel torque command based on the driver
demand, powertrain and battery limits. In addition, the VSC 40
determines how much torque each power source needs to provide in
order to meet the driver's torque demand, in order to maintain
state of charge of the battery 32, and to achieve the operating
point (torque and speed) of the engine 12.
[0032] Some hybrid electric vehicle configurations may control the
engine 12, transmission 24, M/G 14 or any combination thereof, to
provide powertrain braking during a braking request from the
operator. A braking request may include any operator request to
brake the vehicle during a braking event. Therefore a braking
request from the operator may include depressing the brake pedal 50
for greater braking or merely releasing the accelerator pedal 52
during gradual or lower braking events.
[0033] As discussed above, when the M/G 14 provides powertrain
braking, the M/G 14 creates negative torque to slow the vehicle
during a braking period. In turn, M/G 14 generates electric energy
(e.g. charge (Q) or current (I)) from braking the vehicle which may
be transferred to the battery 32. When M/G 14 functions as the
generator, kinetic or potential energy of the vehicle is converted
to electric energy in order to brake the vehicle. This operation
may be known as regenerative braking. In a HEV, regenerative
powertrain braking may also be considered a type of powertrain
braking.
[0034] However, regenerative braking may be limited by the state of
charge of the battery 32. In particular, during a braking period
the battery 32 may be charged to capacity and cannot accept any
additional energy. In other words, regenerative powertrain braking
may be performed as long as the battery 32 state of charge is not
substantially full. Therefore, when a regenerative powertrain
braking event is in progress in a HEV, it may be important to
determine the amount of torque received by the M/G 14 from the
transmission 24 so that the amount of powertrain braking and the
amount of regenerative energy captured can be accurately accounted
for to allow the battery 32 to recapture as much energy as
possible. Accurately accounting for the amount of regenerative
energy captured through powertrain braking may allow HEV's to have
smaller capacity batteries, thereby saving space and cost.
[0035] In addition, accurately accounting for the amount of
regenerative energy captured through powertrain braking may also
allow regenerative powertrain braking period to be extended.
Extending regenerative powertrain braking operation may further
reduce wear on the friction wheel brakes 18, increase vehicle fuel
efficiency, increase the amount of energy stored by the battery and
decrease vehicle emissions. Extending regenerative braking may also
improve driver perceptions and HEV feel when the vehicle is
required to switch between regenerative powertrain braking and
friction braking since the vehicle may be required to switch
between the two braking functions less often when regenerative
powertrain braking is extended.
[0036] During regenerative powertrain braking events, torque from
the wheels 16 is transmitted to the M/G 14 through the transmission
24. However, the amount of torque received by the M/G 14 is a
function of the gear ratio and losses in the transmission 24.
Turning to FIG. 2, the torque, gear ratio and losses of the
transmission 24 are represented graphically. The ideal gear ratio
of the transmission 24 is equal is a ratio of the torque input
(.tau..sub.in) and torque output (.tau..sub.out), where
.tau..sub.in is the torque at the input shaft 60 and .tau..sub.out
is the torque at the output shaft 62. The ideal gear ratio may also
be considered an ideal torque ratio. For example, if the gear ratio
is 4:1, for a +100 Nm input torque .tau..sub.in, the output torque
.tau..sub.out would be 400 Nm. Therefore, the ideal torque ratio is
represented by line 110 in FIG. 2 where the slope of the line is
the ideal torque ratio.
[0037] Traditionally, the torque input to torque output is a linear
relationship where the linear line can be described with the
formula:
y=m*x+b
[0038] where y is output torque and x is input torque. The slope m
is the torque ratio output/input and b is therefore the output
torque when the input torque is zero.
[0039] Ideally without losses, the slope would be the ideal torque
ratio and the offset would be zero. The slope with no losses is the
ideal torque ratio. Therefore, the formula for the line 110 is:
.tau..sub.out=(.tau..sub.in*TR.sub.ideal) Equation (1)
[0040] However, the transmission 24 is not perfectly efficient and
has some losses. The losses in the transmission may be a function
of friction, heat, spin losses or many other factors. The losses in
the transmission may be characterized as `proportional losses` and
`non-proportional losses`. `Proportional losses` are essentially a
slope which varies as a function of the current gear and speed,
whereas `non-proportional losses` are independent of torque. The
efficiency for a step ratio transmission 24 is usually measured
across the transmission 24 with a torque converter 56 locked, or
modeled without a torque converter.
[0041] Therefore, the intercept b is equal to the `non-proportional
loss` T.sub.s illustrated at 112 in FIG. 2. Line 114. Line 114
illustrates the ideal torque ratio when accounting for
non-proportional losses T.sub.s Therefore, the formula for the line
114 is:
.tau..sub.out=(.tau..sub.in*TR.sub.ideal)-T.sub.s Equation (2)
[0042] Proportional transmission losses must also be accounted for.
The actual torque ratio of the transmission 24 of .tau..sub.out to
.tau..sub.in can be measured empirically in different gears. The
empirical modeling of the transmission 24, without the torque
converter 56 (locked, or not included), allows for representation
of the `proportional to torque` losses separate from
`non-proportional to torque` losses. The slope with proportional
losses is equal to the actual torque ratio. By knowing the ideal
torque ratio and torque input-output relationship and measuring
only a few points of the actual torque ratio input-output
relationships, the difference between the slopes of the ideal
torque ratio and the actual torque ratio can be determined. Then,
by subtracting off the portion of .tau..sub.in that comes from the
difference in the slopes between the ideal torque ratio and the
actual torque ratio, we can account for the proportional torque
losses. The linear formula for the transmission when accounting for
proportional and non-proportional losses, shown as line 116 in FIG.
2, could be written as:
.tau..sub.out=(.tau..sub.in*TR.sub.ideal)-T.sub.s-.tau..sub.in*(TR.sub.i-
deal-TR.sub.actual) Equation (3A)
[0043] Cancelling out the terms in the loss equation, the formula
for line 116 in FIG. 2 can be simplified as:
.tau..sub.out=(.tau..sub.in*TR.sub.actual)-T.sub.s Equation
(3B)
[0044] For example for a +100 Nm input torque, actual torque ratio
of 4.0, ideal torque ratio of 4.1, and non-proportional loss of 5
the .tau..sub.out may be determined as:
[0045] Using Equation (3A)
.tau..sub.out=(100*4.1)-5-(100*(4.1-4.0))=395 Nm
[0046] Using Equation (3B) .tau..sub.out=(100*4.0)-5=395 Nm
[0047] Next power can be determined by knowing that power is equal
to torque multiplied by the speed of the shafts 60, 62, illustrated
by the equation:
P=.tau.*.omega.
[0048] Using an input speed of 400 rad/sec, we can determine the
power calculations.
P.sub.in=100*400=40,000 Watts
P.sub.out=395*(400/4.1)=38,536 Watts
[0049] The difference between the power at the transmission input
60 and the transmission output 62 is the amount of power loss
because of transmission inefficiencies.
P.sub.in-P.sub.out=1,464 Watts
[0050] The loss formulas in Equation (3) can accurately describe
the transmission including losses in a traditional powertrain. The
loss formulas in Equation (3) can also accurately describe the
transmission including losses in a HEV powertrain when the vehicle
10 is motoring. However, the problem comes when the vehicle 10 is
putting power into the transmission output 62 and extracting it
from the transmission input 60, such as during regenerative
powertrain braking in a HEV. In this situation, the torque values
are negative. The loss formulas in Equation (3) do not apply the
same when the torque values are negative.
[0051] The problem with the loss formulas in Equation (3) during
regenerative powertrain braking can be illustrated by another
example. For example, for negative torques, where the input torque
.tau..sub.in is -100 Nm input torque, the actual ratio is 4.0, the
ideal ratio is 4.1, and non-proportional losses (T.sub.s) 5 the
following .tau..sub.out is found:
[0052] Using Equation (3A)
.tau..sub.out=(-100*4.1)-5-(100*(4.1-4.0))=-405 Nm
[0053] Using Equation (3B) .tau..sub.out=(-100*4.0)-5=-405 Nm
[0054] Using an input speed of 400 rad/sec, we can determine the
power calculations:
P.sub.in=-100*400=-40,000 Watts
P.sub.out=-405*(400/4.1)=-39,512 Watts
P.sub.in-P.sub.out=P.sub.loss=-488 Watts
[0055] Using the standard formulas arrives at a negative loss
calculation, which is impossible. For example, it is impossible
that 40,000 Watts of regenerative energy are collected at the
transmission input 60 when only 39,512 Watts of regenerative energy
is going into the transmission output 62 from the wheels 16. The
power going in the transmission output 62 is smaller than the power
coming out of the transmission input 60 to the battery 32, which is
impossible.
[0056] For regenerative braking events, two lines fit the data
better than one line. The first line, illustrated as line 118 in
FIG. 2, is for positive output torque .tau..sub.out and input
torque .tau..sub.in when the vehicle 10 is motoring. The second
line, illustrated as line 120 in FIG. 2, is for negative output
torque and input torque when the HEV is regenerative braking.
[0057] The non-proportional losses are calculated the same during
motoring and regeneration. Therefore, line 118 and line 120 both
use the same offset term b for non-proportional torque loss
T.sub.s. However, during regeneration, `proportional to torque`
losses are not correctly accounted for using the standard
equations.
[0058] The correct .tau..sub.in for a given .tau..sub.out value is
correctly computed only when the proportional torque losses are
summed in the correct direction. The term in proportional loss term
in Equation (3A), that is
.tau..sub.in*(TR.sub.ideal-TR.sub.actual), must be a positive
value, regardless if the transmission is receiving negative torque
during regeneration. Because .tau..sub.in is negative during
regeneration and the proportional loss expression in Equation (3A)
must be positive, the ideal torque ratio must actually be less than
actual torque ratio during regeneration. Therefore, the
proportional losses in the transmission actually add to the
regenerative energy. This is best illustrated in the following
example.
[0059] During a regenerative braking event, where the transmission
input torque .tau..sub.in is -100 Nm, the actual torque ratio is
4.2, the ideal torque ratio, being less than the actual ratio, is
4.1, and non-proportional loss T.sub.s is 5, .tau..sub.out can be
determined as follows:
[0060] Using Equation (3A)
.tau..sub.out=(-100*4.1)-5-(-100*(4.1-4.2))=-425 Nm
[0061] Using Equation (3B) .tau..sub.out=(-100*4.2)-5=-425 Nm
[0062] Using an input speed of 400 rad/sec, we can determine the
power calculation:
P.sub.in=-100*400=-40,000 Watts
P.sub.out=-425*(400/4.1)=-41,463 Watts
P.sub.in-P.sub.out=P.sub.loss=1463
[0063] When the output torque and input torque are both positive
the actual measured slope is less than the ideal torque ratio.
However, when the output torque and input torque are both negative,
the actual measured slope, or TR.sub.actual is greater than the
mechanical torque ratio, or TR.sub.ideal. The actual torque ratio
for negative torque is measured to be 4.2. If the measured positive
torque ratio of 4.0 is used for the negative torque situation, then
Equation (3) will calculate that more energy is being collected at
the transmission input 60 than is being input into the transmission
output 62 during regeneration.
[0064] To account for the difference in the actual torque ratio and
ideal torque ratio, the a proportional loss coefficient C1 is
calculated for each gear using the following formula:
C1=.tau..sub.in*(TR.sub.ideal-TR.sub.actual) Equation (4)
[0065] During motoring, the proportional loss coefficient C1 is
included in Equation (3B) to derive the loss equation as
follows:
.tau..sub.out=(.tau..sub.in*(TR.sub.actual-C1)-T.sub.s Equation
(5)
[0066] Conversely, based on a desired torque output .tau..sub.out,
in order to derive the required torque in .tau..sub.in during
motoring, the following equation applies:
.tau..sub.in=(.tau..sub.out+T.sub.s)/(TR.sub.ideal-C1) Equation
(6)
[0067] During a regenerative braking event, when the torque values
are negative, the actual torque ratio is greater than the ideal
torque ratio by the same amount that the ideal torque ratio is
greater than the actual torque ratio during motoring. Therefore,
the sign of C1 changes during regenerative braking. During
regeneration, Equation (6) is modified so that C1 is positive, as
follows:
.tau..sub.in=(.tau..sub.out+T.sub.s)/(TR.sub.ideal-C1) Equation
(7)
[0068] Therefore, the transmission is better characterized by two
lines to differentiate between the different torque ration during
motoring and regeneration. Line 120 in FIG. 2 illustrates the line
accounting for proportional losses which add to regenerative
braking. Line 120 can be characterized instead by the equation:
.tau..sub.out=(.tau..sub.in*(TR.sub.ideal-C1))-T.sub.s Equation
(8)
[0069] Now the inclusion of a torque converter, pump losses, and
dynamic inertia losses can easily be consistent across the
transmission controls development process. For example, when the
vehicle includes a torque converter 56, the torque input
.tau..sub.in when the vehicle is motorizing may be determined from
the following equation:
.tau..sub.in=((.tau..sub.out+T.sub.s)/(TR.sub.ideal-C1))*(1/TR.sub.torqu-
e.sub.--.sub.converter) Equation (9)
[0070] When the M/G 14 is generating or when the vehicle is
regenerative braking such that the transmission output torque is
negative, Equation (9) is modified so that the torque input
.tau..sub.in may be determined from the following equation:
.tau..sub.in=((.tau..sub.out+T.sub.s)/(TR.sub.ideal-C1))*(1/TR.sub.torqu-
e.sub.--.sub.converter) Equation (10)
[0071] The torque converter 56 may be connected between the M/G 14
and the transmission 24. The torque converter 56 may also be
included in the transmission 24. When the torque converter 56 is
locked, the torque ratio of torque converter 1:1.
[0072] FIG. 3 is a flowchart illustrating a method for controlling
the hybrid vehicle during regenerative powertrain braking according
to an embodiment of the disclosure. As those of ordinary skill in
the art will understand, the functions represented by the flowchart
may be performed by hardware and/or software. Depending on the
particular processing strategy, such as event driven, interrupt
driven, etc., the various functions may be performed in an order or
sequence other than that illustrated in FIG. 3. Likewise, one or
more steps or functions may be repeatedly performed although not
explicitly illustrated. Similarly, one or more of the steps or
functions illustrated may be omitted in some applications or
implementations. In one embodiment, the functions illustrated are
primarily implemented by software instructions, code, or control
logic stored in a computer-readable storage medium and executed by
a microprocessor based computer or controller to control operation
of the vehicle, such as the VSC 40 or the brake controller 42 (FIG.
1).
[0073] During regenerative powertrain braking in a HEV, the driver
requests a braking event in .tau..sub.out units, as represented by
block 210. Electronic throttle control systems, replaced the
traditional mechanical throttle cable system with an "electronic
linkage" provided by sensors and actuators in communication with an
electronic controller. This allows control of the powertrain
independent of the accelerator pedal 52 position. Driver inputs may
be assessed by pedal position sensors in communication with the
brake pedal 50 or accelerator pedal 52, to determine the driver's
intent to apply the brakes or intent to provide positive wheel
torque. The driver's braking request may also be assessed from
inputs as brake pedal force, accelerator position, gear position,
and other variables known to those skilled in the art. In the
electronic throttle control system, the driver's braking request is
provided in units based on desired .tau..sub.out. Alternatively,
the driver's request for braking may also include determining
another output parameter which is then converted or used to
determine the desired .tau..sub.out.
[0074] First, the controller converts .tau..sub.out to .tau..sub.in
based on the ideal torque ratio of the transmission, as represented
by block 212. Next, the controllers determine the value for the
current gear, or alternatively the actual torque ratio, as
represented by block 214. The actual torque ratio may be stored in
a lookup table which corresponds to the current gear, or
corresponds to whether the vehicle is motoring or regenerative
powertrain braking, as described above.
[0075] The actual torque ratio is used with the transmission
speeds, either estimated or actual, to determine the
non-proportional loss, as represented by block 216. The
non-proportional loss values may stored in a lookup table which
corresponds to the current gear and is accessed or indexed by the
transmission speeds, as described above.
[0076] The controller determines the torque proportional loss, as
represented by block 218 of FIG. 3. The proportional loss values
may also be stored in a lookup table with a separate set of values
for each of the available gears or torque ratios, as well as
negative torque values or positive torque values.
[0077] Block 220 represents determination of a proportional loss
coefficient based on the currently selected gear. This factor may
be used to fine-tune or calibrate the engine torque determination
for any additional losses which may not be included in the torque
loss terms described above.
[0078] The controller then determines .tau..sub.in is based on the
transmission losses, including non-proportional losses and torque
proportional losses when the vehicle is regenerative powertrain
braking, so that .tau..sub.out is negative, as represented by block
222. In accounting for losses, the controller may also consider
pump loss, gear ratio, final drive ratio, converter multiplication,
and scaling factor or any other system losses which effect
computing .tau..sub.in, as represented in block 222.
[0079] In one embodiment, the brake controller 42 may perform the
steps or functions described in blocks 212 through 222. The brake
controller 42 may communicate the data to the VSC 40, as
represented by block 228, for coordination with the engine 12 and
transmission 24, as necessary.
[0080] Next, the controller apportions the braking request between
the friction braking system and regenerative powertrain braking
system, as represented by block 320. The controller may apportion
the braking request based on a maximum regenerative powertrain
braking limit and inputs of the M/G 14 and battery 32, as
represented by block 232. The regenerative powertrain braking
limits, the M/G inputs and the battery inputs may be based upon
system considerations, such as the temperature of the battery,
state of charge of the battery and other system parameters known to
those skilled in the art and suggested by this disclosure.
[0081] The regenerative powertrain braking limits, the M/G inputs
and the battery inputs may also be influenced by the regenerative
powertrain braking functions in steps 212 through 222. The
regenerative powertrain braking functions in steps 212 through 222
allow the controller to accurately account for the proportional
losses in the transmission and increase accuracy of regenerative
powertrain braking torque calculations. Therefore, the friction
brake system may be applied later, as shown in block 240, and the
M/G may apply regenerative powertrain braking longer, as shown in
block 234.
[0082] The controller applies regenerative powertrain braking
torque in .tau..sub.in units, as represented by block 234. The
controller applies regenerative powertrain braking as long as the
limits of the regenerative powertrain braking system, including the
M/G and battery, are within a threshold capacity. The threshold
capacity of the regenerative powertrain braking system may be based
on the state of charge of the battery, the torque capacity of the
M/G, the quantity of the braking request or any other parameters
known to those skilled in the art and suggested by this
disclosure.
[0083] Once the capacity of the regenerative powertrain braking
system is exceeded, the controller may apply to the friction
braking system to fulfill the braking request, as represented by
block 240.
[0084] While exemplary embodiments are described above, it is not
intended that these embodiments describe all possible forms of the
invention. Rather, the words used in the specification are words of
description rather than limitation, and it is understood that
various changes may be made without departing from the spirit and
scope of the invention. Additionally, the features of various
implementing embodiments may be combined to form further
embodiments of the invention.
* * * * *