U.S. patent application number 09/928379 was filed with the patent office on 2002-03-14 for braking force control apparatus and method of motor vehicle.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. Invention is credited to Niwa, Satoru, Sakamoto, Junichi, Shimada, Michihito.
Application Number | 20020030408 09/928379 |
Document ID | / |
Family ID | 18765342 |
Filed Date | 2002-03-14 |
United States Patent
Application |
20020030408 |
Kind Code |
A1 |
Niwa, Satoru ; et
al. |
March 14, 2002 |
Braking force control apparatus and method of motor vehicle
Abstract
A braking force control apparatus and method control a braking
force of a motor vehicle that has (a) regenerative braking devices
for front wheels and rear wheels, respectively, and (b) a friction
braking device for each of the front wheels and the rear wheels. A
target braking force of the front wheels and a target braking force
of the rear wheels are calculated, based on a braking requirement
made by a driver of the vehicle and a ratio of braking forces of
the front wheels and the rear wheels. Initially, the regenerative
braking devices are controlled to generate regenerative braking
forces at the front wheels and the rear wheels, and then, if
necessary, the friction braking device is controlled to generate a
friction braking force at each of the front wheels and rear wheels,
so that a total braking force applied to the front wheels and a
total braking force applied to the rear wheels are controlled to
the front-wheel target braking force and the rear-wheel target
braking force, respectively.
Inventors: |
Niwa, Satoru; (Susono-shi,
JP) ; Shimada, Michihito; (Susono-shi, JP) ;
Sakamoto, Junichi; (Gotenba-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
TOYOTA-SHI
JP
|
Family ID: |
18765342 |
Appl. No.: |
09/928379 |
Filed: |
August 14, 2001 |
Current U.S.
Class: |
303/152 ;
903/916; 903/918; 903/947 |
Current CPC
Class: |
B60T 8/267 20130101;
B60W 2540/12 20130101; B60T 8/00 20130101; B60T 13/662 20130101;
B60K 6/44 20130101; B60W 10/18 20130101; B60W 20/13 20160101; Y02T
10/623 20130101; B60K 17/354 20130101; Y02T 10/6265 20130101; Y10S
903/947 20130101; B60W 2050/0002 20130101; B60W 30/18127 20130101;
B60K 6/543 20130101; B60K 17/356 20130101; B60W 20/00 20130101;
B60W 2720/106 20130101; Y10S 903/918 20130101; Y02T 10/62 20130101;
B60K 6/52 20130101; B60T 2270/608 20130101; Y10S 903/916
20130101 |
Class at
Publication: |
303/152 |
International
Class: |
B60T 008/66 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 14, 2000 |
JP |
2000-280516 |
Claims
What is claimed is:
1. A braking force control apparatus of a motor vehicle including
(a) first and second regenerative braking devices that are operable
to effect regenerative braking with respect to front wheels and
rear wheels, respectively, and (b) a friction braking device that
is operable to effect friction braking with respect to each of the
front wheels and the rear wheels, comprising: a controller that:
calculates a first target braking force of the front wheels and a
second target braking force of the rear wheels, based on a braking
requirement made by a driver of the vehicle and a ratio of braking
forces of the front wheels and the rear wheels; and initially
causes the first and second regenerative braking devices to
generate regenerative braking forces at the front wheels and the
rear wheels, and then, if necessary, causes the friction braking
device to generate a friction braking force at each of the front
wheels and rear wheels, so that a total braking force applied to
the front wheels and a total braking force applied to the rear
wheels are controlled to the first target braking force and the
second target braking force, respectively.
2. A braking force control apparatus according to claim 1, wherein
the controller: determines a first maximum regenerative braking
force that can be generated by the first regenerative braking
device, and a second maximum regenerative braking force that can be
generated by the second regenerative braking device; sets a first
target regenerative braking force to a smaller one of the first
target braking force and the first maximum regenerative braking
force, and sets a second target regenerative braking force to a
smaller one of the second target braking force and the second
maximum regenerative braking force; and controls the first
regenerative braking device for the front wheels so as to provide
the first target regenerative braking force, and controls the
second regenerative braking device for the rear wheels so as to
provide the second target regenerative braking force.
3. A braking force control apparatus according to claim 2, wherein
the controller: determines a first actual regenerative braking
force actually generated by the first regenerative braking device,
and a second actual regenerative braking force actually generated
by the second regenerative braking device; sets a first target
friction braking force of the front wheels to a value obtained by
subtracting the first actual regenerative braking force from the
first target braking force, and sets a second target friction
braking force of the rear wheels to a value obtained by subtracting
the second actual regenerative braking force from the second target
braking force; and controls the friction braking device for each of
the front and rear wheels so as to provide the first target
friction braking force and the second target friction braking
force.
4. A braking force control apparatus according to claim 1, wherein:
the controller comprises a braking control unit and a regenerative
braking control unit that transmit and receive information to and
from each other; and the braking control unit controls the friction
braking device so as to control braking pressures applied to the
front and rear wheels, and controls the regenerative braking
control unit so as to control the first and second regenerative
braking devices.
5. A braking force control apparatus according to claim 4, wherein
the braking control unit: determines a first maximum regenerative
braking force that can be generated by the first regenerative
braking device, and a second maximum regenerative braking force
that can be generated by the second regenerative braking device;
sets a first target regenerative braking force to a smaller one of
the first target braking force and the first maximum regenerative
braking force, and sets a second target regenerative braking force
to a smaller one of the second target braking force and the second
maximum regenerative braking force; and transmits signals
indicative of the first target regenerative braking force and the
second target regenerative braking force to the regenerative
braking control unit, and the regenerative braking control unit
controls the first regenerative braking device for the front wheels
and the second regenerative braking device for the rear wheels so
as to provide the first target regenerative braking force and the
second target regenerative braking force.
6. A braking force control apparatus according to claim 5, wherein:
the regenerative braking control unit determines a first actual
regenerative braking force actually generated by the first
regenerative braking device, and a second actual regenerative
braking force actually generated by the second regenerative braking
device, and transmits signals indicative of the first and second
actual regenerative braking forces to the braking control unit; the
braking control unit sets a first target friction braking force of
the front wheels to a value obtained by subtracting the first
actual regenerative braking force from the first target braking
force, and sets a second target friction braking force of the
second wheels to a value obtained by subtracting the second actual
regenerative braking force from the second target braking force;
and the braking control unit controls the friction braking device
for each of the front and rear wheels so as to provide the first
target friction braking force and the second target friction
braking force.
7. A braking force control apparatus according to claim 4, wherein:
the vehicle is a hybrid vehicle including an internal combustion
engine and a motor/generator that are operable to drive the
vehicle, and a hybrid drive-train control unit that controls the
internal combustion engine and the motor/generator; at least one of
the first and second regenerative braking devices comprises the
motor/generator; and the regenerative braking control unit
comprises the hybrid drive-train control unit.
8. A braking force control apparatus according to claim 1, wherein
the vehicle is a hybrid vehicle including an internal combustion
engine and a motor/generator that are operable to drive the
vehicle, and wherein at least one of the first and second
regenerative braking devices comprises the motor/generator.
9. A braking force control apparatus according to claim 1, wherein
the vehicle is a front-wheel-drive vehicle, and wherein the first
regenerative braking device for the front wheels comprises a
motor/generator that is operable to drive the vehicle.
10. A braking force control apparatus according to claim 1, wherein
the controller calculates a target deceleration of the motor
vehicle based on the braking requirement made by the driver, so as
to calculate the first target braking force of the front wheels and
the second target braking force of the rear wheels.
11. A braking force control apparatus according to claim 10,
wherein the friction braking device comprises a brake pedal, a
master cylinder operatively connected to the brake pedal, and a
hydraulic circuit that controls braking pressures applied to the
front and rear wheels, and wherein the braking requirement is
calculated based on at least one of an amount of depression of the
brake pedal by the driver and a pressure of the master
cylinder.
12. A braking force control apparatus according to claim 1, wherein
the ratio of braking forces of the front wheels and the rear wheels
is constant.
13. A method of controlling a braking force of a motor vehicle
including (a) first and second regenerative braking devices that
are operable to effect regenerative braking with respect to front
wheels and rear wheels, respectively, and (b) a friction braking
device that is operable to effect friction braking with respect to
each of the front wheels and the rear wheels, the method comprising
the steps of: calculating a first target braking force of the front
wheels and a second target braking force of the rear wheels, based
on a braking requirement made by a driver of the vehicle and a
ratio of braking forces of the front wheels and the rear wheels;
and initially causing the first and second regenerative braking
devices to generate regenerative braking forces at the front wheels
and the rear wheels, and then, if necessary, causing the friction
braking device to generate a friction braking force at each of the
front wheels and the rear wheels, so that a total braking force
applied to the front wheels and a total braking force applied to
the rear wheels are controlled to the first target braking force
and the second target braking force, respectively.
14. A method according to claim 13, further comprising: determining
a first maximum regenerative braking force that can be generated by
the first regenerative braking device, and a second maximum
regenerative braking force that can be generated by the second
regenerative braking device; setting a first target regenerative
braking force to a smaller one of the first target braking force
and the first maximum regenerative braking force, and setting a
second target regenerative braking force to a smaller one of the
second target braking force and the second maximum regenerative
braking force; and controlling the first regenerative braking
device for the front wheels so as to provide the first target
regenerative braking force, and controlling the second regenerative
braking device for the rear wheels so as to provide the second
target regenerative braking force.
15. A method according to claim 14, further comprising: determining
a first actual regenerative braking force actually generated by the
first regenerative braking device, and a second actual regenerative
braking force actually generated by the second regenerative braking
device; setting a first target friction braking force of the front
wheels to a value obtained by subtracting the first actual
regenerative braking force from the first target braking force, and
setting a second target friction braking force of the rear wheels
to a value obtained by subtracting the second actual regenerative
braking force from the second target braking force; and controlling
the friction braking device for each of the front and rear wheels
so as to provide the first target friction braking force and the
second target friction braking force.
16. A method according to claim 13, wherein: the vehicle includes a
braking control unit and a regenerative braking control unit that
transmit and receive information to and from each other; and the
braking control unit controls the friction braking device so as to
control braking pressures applied to the front and rear wheels, and
controls the regenerative braking control unit so as to control the
first and second regenerative braking devices.
17. A method according to claim 16, further comprising: in the
braking control unit, determining a first maximum regenerative
braking force that can be generated by the first regenerative
braking device, and a second maximum regenerative braking force
that can be generated by the second regenerative braking device; in
the braking control unit, setting a first target regenerative
braking force to a smaller one of the first target braking force
and the first maximum regenerative braking force, and setting a
second target regenerative braking force to a smaller one of the
second target braking force and the second maximum regenerative
braking force; and the braking control unit transmits signals
indicative of the first target regenerative braking force and the
second target regenerative braking force to the regenerative
braking control unit, and the regenerative braking control unit
controls the first regenerative braking device for the front wheels
and the second regenerative braking device for the rear wheels so
as to provide the first target regenerative braking force and the
second target regenerative braking force.
18. A method according to claim 17, wherein: in the regenerative
braking control unit, determining a first actual regenerative
braking force actually generated by the first regenerative braking
device, and a second actual regenerative braking force actually
generated by the second regenerative braking device, and
transmitting signals indicative of the first and second actual
regenerative braking forces to the braking control unit; in the
braking control unit, setting a first target friction braking force
of the front wheels to a value obtained by subtracting the first
actual regenerative braking force from the first target braking
force, and setting a second target friction braking force of the
second wheels to a value obtained by subtracting the second actual
regenerative braking force from the second target braking force;
and the braking control unit controls the friction braking device
for each of the front and rear wheels so as to provide the first
target friction braking force and the second target friction
braking force.
19. A method according to claim 16, wherein: the vehicle is a
hybrid vehicle including an internal combustion engine and a
motor/generator that are operable to drive the vehicle, and a
hybrid drive-train control unit that controls the internal
combustion engine and the motor/generator; at least one of the
first and second regenerative braking devices comprises the
motor/generator; and the regenerative braking control unit
comprises the hybrid drive-train control unit.
20. A method according to claim 13, wherein the vehicle is a hybrid
vehicle including an internal combustion engine and a
motor/generator that are operable to drive the vehicle, and wherein
at least one of the first and second regenerative braking devices
comprises the motor/generator.
21. A method according to claim 13, wherein the vehicle is a
front-wheel-drive vehicle, and wherein the first regenerative
braking device for the front wheels comprises a motor/generator
that is operable to drive the vehicle.
22. A method according to claim 13, further comprising calculating
a target deceleration of the motor vehicle based on the braking
requirement made by the driver, so as to calculate the first target
braking force of the front wheels and the second target braking
force of the rear wheels.
23. A method according to claim 22, wherein the friction braking
device comprises a brake pedal, a master cylinder operatively
connected to the brake pedal, and a hydraulic circuit that controls
braking pressures applied to the front and rear wheels, and wherein
the braking requirement is calculated based on at least one of an
amount of depression of the brake pedal by the driver and a
pressure of the master cylinder.
24. A method according to claim 13, wherein the ratio of braking
forces of the front wheels and the rear wheels is constant.
Description
INCORPORATION BY REFERENCE
[0001] The disclosure of Japanese Patent Application No.
2000-280516 filed on Sep. 14, 2000 including the specification,
drawings and abstract is incorporated herein by reference in its
entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of Invention
[0003] The invention relates generally to a braking force control
apparatus and method of a motor vehicle, and more particularly to a
braking force control apparatus and method of a motor vehicle
including regenerative braking devices and a friction braking
device for front wheels and rear wheels of the vehicle.
[0004] 2. Description of Related Art
[0005] A known type of a braking force control apparatus of a motor
vehicle, such as an automobile, is disclosed in, for example,
Japanese Laid-open Patent Publication No. 9-93711. In the known
braking force control apparatus, driven wheels are provided with a
hydraulic braking device (i.e., a friction braking device), and
drive wheels are provided with a regenerative braking device and a
hydraulic braking device. In operation, when the regenerative
braking force of the drive wheels reaches a predetermined value
that is equal to or smaller than a maximum value, the regenerative
braking force is kept at the predetermined value, and hydraulic
braking of the driven wheels is started. With the driven wheels
being hydraulically braked, the regenerative braking force applied
to the drive wheels is kept at the predetermined value, until the
ratio of the braking forces of the driven wheels and drive wheels
becomes equal to a predetermined ratio.
[0006] The braking force control apparatus as described above makes
it possible to suitably control the ratio of the braking forces of
the driven wheels and drive wheels to the predetermined ratio,
while performing regenerative braking of the drive wheels so that
the regenerative braking force applied to the drive wheels becomes
equal to the predetermined value, which in turn is equal to or
smaller than the maximum value.
[0007] In the known braking force control apparatus as described
above, hydraulic braking of the driven wheels is started when the
regenerative braking force of the drive wheels reaches the
predetermined value, and the regenerative braking force is kept at
the predetermined value until the ratio of the braking forces of
the driven wheels and drive wheels becomes equal to the
predetermined ratio. With this type of the braking force control
apparatus, however, the regeneration efficiency of the regenerative
braking device cannot be maximized. To the contrary, if an attempt
is made to maximize the regeneration efficiency of the regenerative
braking device, the ratio of the braking forces of the driven
wheels and the drive wheels cannot be controlled to the
predetermined ratio.
[0008] In addition, the driven wheels of the vehicle that employs
the braking force control apparatus disclosed in the
above-mentioned publication are not provided with a regenerative
braking device, and therefore regenerative braking is not effected,
namely, electric energy is not recovered during braking of the
driven wheels. Thus, the known braking force control apparatus
cannot increase the regeneration efficiency of the vehicle as a
whole by utilizing regenerative braking of the driven wheels, thus
leaving a room for improvement in this respect.
SUMMARY OF THE INVENTION
[0009] It is therefore one object of the invention to provide a
braking force control apparatus and method of a motor vehicle
having regenerative braking devices and a friction braking device
for front wheels and rear wheels, wherein the regenerative braking
devices and the friction braking device for the front and rear
wheels are optimally operated under suitable control, thus assuring
an improved regeneration efficiency of the vehicle as a whole,
while achieving a predetermined ratio of the braking forces of the
front and rear wheels.
[0010] To accomplish the above and/or other objects, there is
provided a braking force control apparatus and method of a motor
vehicle including (a) first and second regenerative braking devices
that are operable to effect regenerative braking with respect to
front wheels and rear wheels, respectively, and (b) a friction
braking device that is operable to effect friction braking with
respect to each of the front wheels and the rear wheels. A
controller of the braking force control apparatus calculates a
first target braking force of the front wheels and a second target
braking force of the rear wheels, based on a braking requirement
made by a driver of the vehicle and a ratio of braking forces of
the front wheels and the rear wheels. The controller initially
causes the first and second regenerative braking devices to
generate regenerative braking forces at the front wheels and the
rear wheels, and then, if necessary, causes the friction braking
device to generate a friction braking force at each of the front
wheels and rear wheels, so that a total braking force applied to
the front wheels and a total braking force applied to the rear
wheels are controlled to the first target braking force and the
second target braking force, respectively.
[0011] With the braking force control apparatus and method as
described above, the overall braking force of the motor vehicle is
suitably controlled in accordance with the braking requirement made
by the driver or vehicle operator, and the ratio of the braking
forces of the front and rear wheels is also suitably controlled to
a predetermined braking-force ratio. Furthermore, the regenerative
braking devices and friction control device for the front wheels
and the rear wheels can be optimally operated, thus assuring an
improved regeneration efficiency of the vehicle as a whole and
significantly improved fuel economy, as compared with conventional
braking devices controlled by a conventional braking force control
apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The foregoing and/or further objects, features and
advantages of the invention will become more apparent from the
following description of a preferred embodiment with reference to
the accompanying drawings, in which like numerals are used to
represent like elements and wherein:
[0013] FIG. 1 is a diagram schematically showing the construction
of a front-wheel-drive vehicle in which a hybrid-type drive-train
is installed, which vehicle includes one embodiment of a braking
force control apparatus of the invention;
[0014] FIG. 2 is a flowchart illustrating a braking force control
routine executed by a braking control unit of the embodiment of
FIG. 1;
[0015] FIG. 3 is a flowchart illustrating a regenerative braking
control routine executed by an engine control unit of the
embodiment of FIG. 1;
[0016] FIG. 4 is a graph showing the relationship between the
depression stroke Sp of the brake pedal and the target deceleration
Gst;
[0017] FIG. 5 is a graph showing the relationship between the
master cylinder pressure Pm and the target deceleration Gpt;
[0018] FIG. 6 is a graph showing the relationship between the final
target deceleration Gt obtained in the last control cycle and the
weight a given to the target deceleration Gpt; and
[0019] FIG. 7 is a graph showing the relationship between the
target braking force Fbft of the front wheels and the target
braking force Fbrt of the rear wheels.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0020] A preferred embodiment of the invention will be described in
detail with reference to the accompanying drawings.
[0021] FIG. 1 schematically shows the construction of a braking
force control apparatus according to one embodiment of the
invention, which apparatus is employed in a front-wheel-drive
vehicle in which a hybrid-type drive-train is installed.
[0022] In FIG. 1, a hybrid-type drive-train 10 that drives front
wheels includes a gasoline engine 12 and a motor/generator 14. A
continuously variable transmission 18 that incorporates a clutch
has an input shaft that is coupled to an output shaft 16 of the
gasoline engine 12 and is also coupled to an output shaft 20 of the
motor/generator 14. Rotary motion of the output shaft 19 of the
continuously variable transmission 18 is transmitted to axles 24FL
and 24FR of left and right front wheels via a front-wheel
differential 22, so as to drive and rotate left and right front
wheels 26FL and 26FR.
[0023] The gasoline engine 12 and the motor/generator 14 of the
hybrid drive-train 10 are controlled by an engine control unit 28,
depending upon an operating amount of an accelerator pedal (not
shown) by the driver and running conditions of the vehicle, for
example. The motor/generator 14 also functions as a generator of a
regenerative braking device 30 for front wheels. The engine control
unit 28 controls the motor/generator 14 when it functions as a
regenerative generator for recovering electric energy during
regenerative braking.
[0024] In the embodiment as shown in FIG. 1, in particular, the
hybrid drive-train 10 is operable in a selected one of operating
modes including a normal driving mode, an electric vehicle mode,
and an engine brake mode. When a shift lever (not shown) is placed
in a D (Drive) range during normal running of the vehicle, the
hybrid drive-train 10 operates in the normal driving mode in which
driving force or engine brake force is generated by the gasoline
engine 12 or by both the gasoline engine 12 and the motor/generator
14. When the shift lever is placed in the D range but the load is
low, the hybrid drive-train 10 operates in the electric vehicle
mode in which driving force is generated solely by the
motor/generator 14. When the shift lever is placed in a B range,
the hybrid drive-train 10 operates in the engine brake mode in
which driving force or engine brake force is generated by the
gasoline engine 12 and the motor/generator 14, such that the engine
brake force generated in this mode is greater than that generated
when the shift lever is placed in the D range. When the shift lever
is placed in the D range and a brake pedal 32 is depressed by the
driver, the motor/generator 14 functions as the regenerative
generator as mentioned above.
[0025] In FIG. 1, rotary motion of left and right rear wheels 34RL
and 34RR, serving as driven wheels, is transmitted to a
motor/generator 42 of a regenerative braking device 40 for rear
wheels, via axles 36RL and 36RR of left and right rear wheels and a
rear-wheel differential 38. The engine control unit 28 as indicated
above is also operable to control regenerative braking effected by
the motor/generator 42. Thus, the engine control unit 28 functions
as a regenerative braking control unit for controlling the
regenerative braking devices 30, 40.
[0026] A hydraulic circuit 46 of a friction braking device 44 is
operable to control braking pressures applied to wheel cylinders
48FL, 48FR, 48RL and 48RR corresponding to the left and right front
wheels 26FL, 26FR and left and right rear wheels 34RL, 34RR so as
to control friction braking forces of the respective wheels 26FL,
26FR, 34RL, 34RR. Although not shown in the drawings, the hydraulic
circuit 46 includes a reservoir, an oil pump, and various valve
devices. The friction braking device 44 including the hydraulic
circuit 46 is controlled by a braking control unit 52. During
normal operations, the braking pressures applied to the respective
wheel cylinders are controlled by the braking control unit 52,
depending upon the pressure of a master cylinder 50 that is driven
in accordance with the amount or degree of depression of the brake
pedal 32 by the driver.
[0027] The engine control unit 28 receives, from an accelerator
pedal sensor 54, a signal indicative of an amount of depression of
the accelerator pedal, and receives, from a shift position sensor
56, a signal indicative of a current shift position of the
continuously variable transmission 18. The engine control unit 28
further receives, from the braking control unit 52, a signal
indicative of a target regenerative braking force Frgft of front
wheels and a signal indicative of a target regenerative braking
force Frgrt of rear wheels.
[0028] The braking control unit 52 receives a signal indicative of
a depression stroke Sp of the brake pedal 32 from a stroke sensor
58, and receives a signal indicative of a pressure Pm of the master
cylinder 50 from a pressure sensor 60. The braking control unit 52
further receives, from pressure sensors 62fl, 62fr, 62rl, 62rr,
signals indicative of braking pressures Pfl, Pfr, Prl, Prr applied
to the wheel cylinders 48FL, 48FR, 48RL, 48RR of the left and right
front wheels and left and right rear wheels.
[0029] Each of the engine control unit 28 and the braking control
unit 52 may have a general configuration or arrangement that
includes a microcomputer including CPU, ROM, RAM, input and output
devices, and a drive circuit.
[0030] As will be described in detail, the braking control unit 52
calculates a final target deceleration Gt of the vehicle that
represents a braking requirement made by the driver, based on the
stroke Sp of depression of the brake pedal 32 and the master
cylinder pressure Pm, according to a routine as illustrated in FIG.
2. The braking requirement means a braking amount or degree that is
requested or desired by the driver. The braking control unit 52
then calculates target braking forces Fbft and Fbrt for the front
wheels and the rear wheels, respectively, based on the final target
deceleration Gt and a predetermined ratio of the braking forces
distributed to the front wheels and the rear wheels, respectively.
Where Frgfmax and Frgrmax represent the maximum regenerative
braking forces that can be generated by the regenerative braking
devices 30 and 40, respectively, the braking control unit 52
employs the smaller one of the target braking force Fbft and the
maximum regenerative braking force Frgfmax as a target regenerative
braking force Frgft for the front wheels, and employs the smaller
one of the target braking force Fbrt and the maximum regenerative
braking force Frgrmax as a target regenerative braking force Frgrt
for the rear wheels. The braking control unit 52 then outputs or
transmits signals indicative of the front-wheel and rear-wheel
target regenerative braking forces Frgft and Frgrt to the engine
control unit 28.
[0031] The engine control unit 28 controls the motor/generator 14
of the front-wheel regenerative braking device 30, using the
front-wheel target regenerative braking force Frgft as an upper
limit thereof, and calculates the actual regenerative braking force
Frgfa actually generated by the front-wheel regenerative braking
device 30, based on voltage and current generated by the
motor/generator 14. Similarly, the engine control unit 28 controls
the motor/generator 42 of the rear-wheel regenerative braking
device 40, using the rear-wheel target regenerative braking force
Frgrt as an upper limit thereof, and calculates the actual
regenerative braking force Frgra actually generated by the
rear-wheel regenerative braking device 40, based on voltage and
current generated by the motor/generator 42. The engine control
unit 28 then outputs signals indicative of the actual regenerative
braking forces Frgfa and Frgra, to the braking control unit 52.
[0032] Subsequently, the braking control unit 52 sets a target
friction braking force Fbpft of the front wheels to a value
obtained by subtracting the front-wheel actual regenerative braking
force Frgfa from the front-wheel target braking force Fbft, and
sets a target friction braking force Fbprt of the rear wheels to a
value obtained by subtracting the rear-wheel actual regenerative
braking force Frgra from the rear-wheel target braking force Fbrt.
The braking control unit 52 then calculates target braking
pressures Pbtfl and Pbtfr applied to the left and right front
wheels, based on the front-wheel target friction braking force
Fbpft, and calculates target braking pressures Pbtrl and Pbtrr
applied to the left and right rear wheels, based on the rear-wheel
target friction braking force Fbprt. The braking control unit 52
then controls the braking pressure of each wheel so that the
braking pressures Pi (i=fl, fr, rl, rr) of left and right front
wheels and left and right rear wheels become equal to the target
braking pressures Pbti (i=fl, fr, rl, rr) of the corresponding
wheels.
[0033] It is to be understood that the engine control unit 28 may
control the operating mode of the hybrid drive-train 10 and the
gasoline engine 12 in different known manners from those of the
illustrated embodiment, since these controls do not constitute the
principle of the invention.
[0034] Next, a braking force control routine to be executed by the
braking control unit 52 of the present embodiment will be explained
with reference to the flowchart as shown in FIG. 2. The control
according to the flowchart of FIG. 2 is started upon closing of an
ignition switch (not shown), and is repeatedly executed at
predetermined time intervals.
[0035] In step S10, the braking control unit 52 reads a signal
indicative of a depression stroke Sp of the brake pedal 32 detected
by the stroke sensor 58, and a signal indicative of a pressure Pm
of the master cylinder 50 detected by the pressure sensor 60. In
step S20, a target deceleration Gst is calculated based on the
brake-pedal depression stroke Sp, using a map corresponding to the
graph as shown in FIG. 4. In step S30, a target deceleration Gpt is
calculated based on the master cylinder pressure Pm, using a map
corresponding to the graph as shown in FIG. 5.
[0036] In step S40, a weight .alpha. (0.ltoreq..alpha..ltoreq.1)
that is given to the target deceleration Gpt based on the master
cylinder pressure Pm is calculated, on the basis of the final
target deceleration Gt obtained in the last control cycle, using a
map corresponding to the graph as shown in FIG. 6. In step S50, the
final target deceleration Gt is calculated as a sum of the weighted
target deceleration Gpt and the weighted target deceleration Gst,
according to the following equation (1):
Gt=.alpha..multidot.Gpt+(1-.alpha.)Gst (1)
[0037] In step S60, the target braking force Fbft for the front
wheels and the target braking force Fbrt for the rear wheels are
calculated according to the following equations (2) and (3), where
Kf and Kr are positive constants that represent the proportions of
the braking force applied to the front wheels and the braking force
applied to the rear wheels.
Fbft=Kf.multidot.Gt (2)
Fbrt=Kr.multidot.Gt (3)
[0038] In step S70, the target regenerative braking force Frgft for
the front wheels and the target regenerative braking force Frgrt
for the rear wheels are calculated according to the expressions (4)
and (5) indicated below, and signals indicative of the target
regenerative braking forces Frgft and Frgrt thus obtained are
transmitted to the engine control unit 28. In the expressions (4)
and (5) as indicated below, MIN means an operation to select the
smaller one of numerical values in the parentheses ( ). While the
maximum regenerative braking forces Frgfmax and Frgrmax are
determined as positive constants in the present embodiment, these
braking forces may be varied depending upon the operating mode of
the hybrid drive-train 10 and the vehicle speed.
Frgft=MIN(Fbft, Frgfmax) (4)
Frgrt=MIN(Fbrt, Frgrmax) (5)
[0039] In step S80, the braking control unit 52 reads, from the
engine control unit 28, signals indicative of the actual
front-wheel regenerative braking force Frgfa and actual rear-wheel
regenerative braking force Frgra that have been achieved through
regenerative braking control performed by the engine control unit
28 as described later with reference to FIG. 3. In step S90, the
target front-wheel friction braking force Fbpft and the target
rear-wheel friction braking force Fbprt are calculated according to
the following equations (6) and (7):
Fbpft=Fbft-Frgfa (6)
Fbprt=Fbrt-Frgra (7)
[0040] In step S100, the target braking pressures Pbtfl and Pbtfr
applied to the left and right front wheels are calculated based on
the target front-wheel friction braking force Fbpft, and the target
braking pressures Pbtrl and Pbtrr applied to the left and right
rear wheels are calculated based on the target rear-wheel friction
braking force Fbprt. In step S110, the braking pressure of each
wheel is controlled in a feedback manner so that the braking
pressures Pi of the left and right front wheels and left and right
rear wheels become equal to the respective target braking pressures
Pbti of the corresponding wheels. After executing step S110,
control returns to step S10.
[0041] Referring next to the flowchart as shown in FIG. 3, a
regenerative braking control routine to be executed by the engine
control unit 28 in the present embodiment will be now explained.
The control according to the flowchart of FIG. 3 is also started
upon closing of the ignition switch (not shown), and is repeatedly
executed at predetermined time intervals.
[0042] In step S210, the engine control unit 28 reads, from the
braking control unit 52, signals indicative of the target
regenerative braking force Frgft for the front wheels and the
target regenerative braking force Frgrt for the rear wheels. In
step S220, the engine control unit 28 causes the front-wheel
regenerative braking device 30 to effectuate regenerative braking,
using the target regenerative braking force Frgft as an upper limit
thereof. In step S230, the actual regenerative braking force Frgfa
actually applied to the front wheels by the front-wheel
regenerative braking device 30 is calculated.
[0043] Similarly, in step S240, the engine control unit 28 causes
the rear-wheel regenerative braking device 40 to effectuate
regenerative braking, using the target regenerative braking force
Frgrt as an upper limit thereof. In step S250, the actual
regenerative braking force Frgra actually applied to the rear
wheels by the rear-wheel regenerative braking device 40 is
calculated. In step S260, signals indicative of the actual
front-wheel regenerative braking force Frgfa and the actual
rear-wheel regenerative braking force Frgra are transmitted to the
braking control unit 52. After executing step S260, control returns
to step S210.
[0044] In the embodiment as described above, the target
deceleration Gst is calculated in step S20 based on the depression
stroke Sp of the brake pedal 32, and the target deceleration Gpt is
calculated in step S30 based on the master cylinder pressure Pm. In
step S40, the weight .alpha. given to the target deceleration Gpt
is calculated based on the final target deceleration Gt obtained in
the last control cycle.
[0045] Subsequently, the final target deceleration Gt is calculated
in step S40 as a sum of the weighted target deceleration Gpt and
the weighted target deceleration Gst, and the target front-wheel
braking force Fbft and the target rear-wheel braking force Fbrt are
calculated in step S60 based on the predetermined ratio of the
front-wheel and rear-wheel braking forces and the final target
deceleration Gt. In step S70, the target front-wheel regenerative
braking force Frgft is obtained as the smaller one of the target
braking force Fbft and the maximum front-wheel regenerative braking
force Frgfmax, and the target rear-wheel regenerative braking force
Frgrt is obtained as the smaller one of the target braking force
Fbrt and the maximum rear-wheel regenerative braking force Frgrmax.
Then, signals indicative of the target regenerative braking forces
are transmitted to the engine control unit 28.
[0046] In step S220 of the regenerative braking routine as shown in
FIG. 3, the engine control unit 28 controls the motor/generator 14
of the front-wheel regenerative braking device 30, using the target
front-wheel regenerative braking force Frgft as an upper limit
thereof. In the next step S230, the actual regenerative braking
force Frgfa generated by the front-wheel regenerative braking
device 30 is calculated based on voltage and current generated by
the motor/generator 14. In step S240, the engine control unit 28
controls the motor/generator 42 of the rear-wheel regenerative
braking device 40, using the rear-wheel target regenerative braking
force Frgrt as an upper limit thereof. In the next step S250, the
actual regenerative braking force Frgra generated by the rear-wheel
regenerative braking device 40 is calculated based on voltage and
current generated by the motor/generator 42.
[0047] Turning to the flowchart of FIG. 2, the front-wheel target
friction braking force Fbpft is calculated in step S90 by
subtracting the actual regenerative braking force Frgfa from the
target regenerating force Fbft, and the rear-wheel target friction
braking force Fbprt is calculated in step S90 by subtracting the
actual regenerative braking force Frgra from the target braking
force Fbrt. In step S100, the target braking pressures Pbtfl and
Pbtfr applied to the left and right front wheels are calculated
based on the target front-wheel friction braking force Fbpft, and
the target braking pressures Pbtrl and Pbtrr applied to the left
and right rear wheels are calculated based on the target rear-wheel
friction braking force Fbprt. In step S110, the braking pressure of
each wheel is controlled in a feedback manner so that the braking
pressures Pi of the left and right front wheels and left and right
rear wheels become equal to the target braking pressures Pbti of
the corresponding wheels.
[0048] Thus, in the illustrated embodiment, the final target
deceleration Gt that represents a braking requirement made by the
driver is calculated based on the pedal stroke Sp as an operating
amount of the brake pedal 32 and the master cylinder pressure Pm,
and the braking force of the vehicle as a whole, namely, the sum of
the braking forces applied to the front and rear wheels by the
friction braking device and the regenerative braking devices, is
controlled to a value corresponding to the final target
deceleration Gt. Thus, the braking force of the vehicle as a whole
can be reliably controlled in accordance with the braking
requirement made by the driver.
[0049] In the illustrated embodiment, the ratio of the total
braking force applied to the front wheels by the friction braking
device and the regenerative braking device to the total braking
force applied to the rear wheels by the friction braking device and
the regenerative braking device is always controlled to be equal to
the predetermined braking-force ratio, Kf/Kr. Thus, the ratio of
the braking forces distributed to the front and rear wheels can be
surely controlled to the predetermined braking-force ratio,
irrespective of the proportion of the braking force generated by
the friction braking device and the braking force generated by the
regenerative braking device. It is thus possible to certainly avoid
deterioration of the stability of the vehicle and changes in
steering characteristics, which would otherwise occur when the
ratio of the braking forces applied to the front and rear wheels
differs from the predetermined ratio.
[0050] Furthermore, the target front-wheel braking force Fbft is
achieved or realized by controlling the regenerative braking force
and friction braking force of the front wheels such that the
front-wheel regenerative braking device provides the maximum
regenerative braking force. Similarly, the target rear-wheel
braking force Fbrt is achieved by controlling the regenerative
braking force and friction braking force of the rear wheels such
that the rear-wheel regenerative braking device provides the
maximum regenerative braking force. Thus, the regenerative braking
force and friction braking force can be controlled so that the
regeneration efficiency of the vehicle as a whole is maximized
while at the same time the ratio of the braking forces distributed
to the front wheels and the rear wheels is kept at the
predetermined braking-force ratio.
[0051] In general, even if a regenerative braking device, in
particular, a regenerative braking device having a motor/generator
mounted in a hybrid drive-train, is controlled so as to provide a
target regenerative braking force, the actual regenerative braking
force actually generated by the regenerative braking device does
not coincide with, but becomes smaller than the target regeneration
braking force because of various restrictions.
[0052] In the illustrated embodiment, the engine control unit 28
controls the motor/generator 14 of the front-wheel regenerative
braking device 30 and the motor/generator 42 of the rear-wheel
regenerative braking device 40, using the target front-wheel
regenerative braking force Frgft and target rear-wheel regenerative
braking force Frgrt as the upper limits of the respective braking
forces. The engine control unit 28 then calculates the actual
regenerative braking forces Frgfa, Frgra of the front and rear
wheels, based on the voltage and current generated by the
respective motor/generators, and calculates the target front-wheel
friction braking force Fbpft and the target rear-wheel friction
braking force Fbprt by subtracting the actual regenerative braking
forces Frgfa, Frgra from the target braking forces Fbft, Fbrt,
respectively. Accordingly, the friction braking forces applied to
the front wheels and rear wheels can be controlled with improved
accuracy so that the braking force of the vehicle as a whole
precisely corresponds to the braking requirement made by the
driver, as compared with the case where the target front-wheel
friction braking force Fbpft and target rear-wheel friction braking
force Fbprt are calculated by subtracting the target regenerative
braking forces Frgft, Frgrt from the target braking forces Fbft,
Fbrt, respectively.
[0053] While the invention has been described with reference to a
preferred embodiment thereof, it is to be understood that the
invention is not limited to the preferred embodiments or
constructions. To the contrary, the invention is intended to cover
various modifications and equivalent arrangements. In addition,
while the various elements of the preferred embodiments are shown
in various combinations and configurations, which are exemplary,
other combinations and configurations, including more, less or only
a single element, are also within the spirit and scope of the
invention.
[0054] In the illustrated embodiment, the target deceleration Gt is
calculated based on the depression stroke Sp of the brake pedal 32
and the master cylinder pressure Pm, and the front-wheel target
braking force Fbft and the rear-wheel target braking force Fbrt are
calculated based on the target deceleration Gt. However, the target
braking forces Fbft, Fbrt of the front and rear wheels may be
calculated based on the depression stroke Sp of the brake pedal 32
or the master cylinder Pm.
[0055] While the ratio Kf/Kr of the braking force applied to the
front wheels to the braking force applied to the rear wheels is
constant with no regard to the magnitude of the target total
braking force in the illustrated embodiment, the proportion Kr of
the braking force of the rear wheels with respect to that of the
front wheels may be reduced as the target total braking force
increases, as indicated by a broken line in the graph of FIG.
7.
[0056] In the illustrated embodiment, signals indicative of the
target regenerative braking forces and the actual regenerative
braking forces of the front wheels and the rear wheels are
transmitted between the engine control unit 28 and the braking
control unit 52. This embodiment may be modified as follows.
Initially, target regenerative braking torque is calculated based
on the target regenerative braking force, and a signal indicative
of the target regenerative braking torque is transmitted from the
braking control unit 52 to the engine control unit 28, so that the
engine control unit 28 controls regenerative braking, using the
target regenerative braking torque as the upper limit. On the other
hand, a signal indicative of the actual regenerative braking torque
is transmitted from the engine control unit 28 to the braking
control unit 52, and the actual regenerative braking force is
calculated based on the actual regenerative braking torque received
from the engine control unit 28.
[0057] In the illustrated embodiment, a driving system for driving
the vehicle takes the form of the hybrid drive-train 10 including
the gasoline engine 12 and the motor/generator 14, and the
motor/generator 14 is operable as a generator for regenerative
braking. However, the hybrid drive-train may include another type
of internal combustion engine, such as a diesel engine. Also, the
driving system for driving the vehicle may be a generally known
internal combustion engine, and a generator for regenerative
braking may be provided independently of the engine.
[0058] While the vehicle takes the form of a front-wheel-drive
vehicle in the illustrated embodiment, the invention may be equally
applied to a rear-wheel-drive vehicle or a four-wheel-drive
vehicle. While the motor/generator 40 provided for the rear wheels
functions solely as a generator for regenerative braking in the
illustrated embodiment, the embodiment may be modified such that
the rear-wheel motor/generator functions as an auxiliary drive
source for driving the rear wheels as needed.
* * * * *