U.S. patent application number 09/769489 was filed with the patent office on 2001-06-07 for braking force control system for automotive vehicle.
Invention is credited to Matsuno, Koji.
Application Number | 20010002770 09/769489 |
Document ID | / |
Family ID | 18115981 |
Filed Date | 2001-06-07 |
United States Patent
Application |
20010002770 |
Kind Code |
A1 |
Matsuno, Koji |
June 7, 2001 |
Braking force control system for automotive vehicle
Abstract
A vehicle speed, an actual steering angle, an actual vehicle yaw
rate, and a lateral vehicle acceleration are detected. On the basis
of the detected vehicle speed, the detected actual vehicle yaw
rate, and the detected lateral vehicle acceleration, the vehicle
body slip angular velocity calculating section (32) calculates a
vehicle body slip angular velocity. On the basis of the calculated
vehicle body slip angular velocity, the front wheel steering wheel
angle correcting section (33) corrects the actual steering angle.
On the basis of the detected actual yaw rate, the detected vehicle
speed, and the corrected actual steering angle, the target yaw
moment calculating section (34) calculates a target yaw moment. On
the other hand, the braked wheel selecting section (36) selects a
braked wheel. Further, on the basis of the target yaw moment, the
target braking force calculating section (35) calculates a target
braking force to be applied to the braked wheel. Further, the
braking signal output section (37) outputs a braking signal to the
brake driving section (16) so that the target braking force
calculated by the target braking force calculating section (35) can
be applied to the braked wheel selected by the braked wheel
selecting section (36). Therefore, even if the driver unavoidably
turns the steering wheel excessively on a slippery road, for
instance, the target braking force is not set to a large value
beyond necessity, with the result that a stable vehicle turning
travel can be attained.
Inventors: |
Matsuno, Koji; (Gunma-ken,
JP) |
Correspondence
Address: |
SMITH, GAMBRELL & RUSSELL, LLP
1850 M STREET, N.W., SUITE 800
WASHINGTON
DC
20036
US
|
Family ID: |
18115981 |
Appl. No.: |
09/769489 |
Filed: |
January 26, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09769489 |
Jan 26, 2001 |
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08979950 |
Nov 26, 1997 |
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6209972 |
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Current U.S.
Class: |
303/146 ;
303/140; 303/155 |
Current CPC
Class: |
B60T 2230/02 20130101;
B60T 8/1755 20130101 |
Class at
Publication: |
303/146 ;
303/140; 303/155 |
International
Class: |
B60T 008/24; B60T
008/60 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 29, 1996 |
JP |
319943/1996 |
Claims
What is claimed is:
1. A braking force control system for automotive vehicle,
comprising: vehicle speed detecting means for detecting a vehicle
speed; steering wheel angledetecting means for detecting a steering
angle; actual yaw rate detecting means for detecting an actual
vehicle yaw rate; lateral acceleration detecting means for
detecting a lateral vehicle acceleration; vehicle slip angular
velocity calculating means for causing a computer to calculate a
vehicle slip angular velocity on the basis of the detected vehicle
speed, the detected actual vehicle yaw rate, and the detected
lateral vehicle acceleration; steering wheel angle correctingmeans
for causing a computer to correct the detected steering wheel
angleon the basis of the calculated vehicle slip angular velocity;
target yaw moment calculating means for causing a computer to
calculate a target yaw moment on the basis of the detected actual
vehicle yaw rate, the detected vehicle speed, and the steering
wheel anglecorrected by said steering wheel angle correctingmeans;
braked wheel selecting means for causing a computer to select a
wheel to be braked on the basis of the detected actual vehicle yaw
rate and the target yaw moment calculated by said target yaw moment
calculating means; target braking force calculating means for
causing a computer to calculate a target braking force to be
applied to the wheel selected by said braked wheel selecting means
on the basis of the target yaw moment calculated by said target yaw
moment calculating means; and braking signal outputting means for
causing a computer to output a signal to a brake drive section, for
application of the target braking force calculated by said target
braking force calculating means to the wheel selected by said
braked wheel selecting means.
2. The braking force control system according to claim 1, wherein
when the vehicle slip angular velocity calculated on the basis of
the detected vehicle speed, the detected actual vehicle yaw rate,
and the detected lateral vehicle acceleration lies within a
predetermined set value, said steering wheel angle correctingmeans
outputs the value detected by said steering wheel angledetecting
means as it is to said target yaw moment calculating means as a
corrected value.
3. A braking force control system for automotive vehicle,
comprising: vehicle speed detecting means for detecting a vehicle
speed; steering wheel angledetecting means for detecting a steering
angle; actual yaw rate detecting means for detecting an actual
vehicle yaw rate; lateral acceleration detecting means for
detecting a lateral vehicle acceleration; vehicle body slip angle
calculating means for causing a computer to calculate a vehicle
body slip angle on the basis of the detected vehicle speed, the
detected actual vehicle yaw rate, and the detected lateral vehicle
acceleration; steering wheel angle correctingmeans for causing a
computer to correct the detected steering wheel angleon the basis
of the calculated vehicle body slip angle; target yaw moment
calculating means for causing a computer to calculate a target yaw
moment on the basis of the detected actual vehicle yaw rate, the
detected vehicle speed, and the steering wheel anglecorrected by
said steering wheel angle correctingmeans; braked wheel selecting
means for causing a computer to select a wheel to be braked on the
basis of the detected actual vehicle yaw rate and the target yaw
moment calculated by said target yaw moment calculating means;
target braking force calculating means for causing a computer to
calculate a target braking force to be applied to the wheel
selected by said braked wheel selecting means on the basis of the
target yaw moment calculated by said target yaw moment calculating
means; and braking signal outputting means for causing a computer
to output a signal to a brake drive section, for application of the
target braking force calculated by said target braking force
calculating means to the wheel selected by said braked wheel
selecting means.
4. The braking force control system according to claim 3, wherein
when the vehicle body slip angle calculated on the basis of the
detected vehicle speed, the detected actual vehicle yaw rate, and
the detected lateral vehicle acceleration lies within a
predetermined set value, said steering wheel angle correctingmeans
outputs the value detected by said steering wheel angledetecting
means as it is to said target yaw moment calculating means as a
corrected value.
5. A braking force control system for automotive vehicle,
comprising: vehicle speed detecting means for detecting a vehicle
speed; steering wheel angledetecting means for detecting a steering
angle; actual yaw rate detecting means for detecting an actual
vehicle yaw rate; lateral acceleration detecting means for
detecting a lateral vehicle acceleration; vehicle slip angular
velocity calculating means for causing a computer to calculate a
vehicle slip angular velocity on the basis of the detected vehicle
speed, the detected actual vehicle yaw rate, and the detected
lateral vehicle acceleration; actual yaw rate correcting means for
causing a computer to correct the detected actual vehicle yaw rate
on the basis of the calculated vehicle slip angular velocity;
target yaw moment calculating means for causing a computer to
calculate a target yaw moment on the basis of the detected vehicle
speed, the detected steering angle, and the actual vehicle yaw rate
corrected by said actual yaw rate correcting means; braked wheel
selecting means for causing a computer to select a wheel to be
braked on the basis of the detected actual vehicle yaw rate and the
target yaw moment calculated by said target yaw moment calculating
means; target braking force calculating means for causing a
computer to calculate a target braking force to be applied to the
wheel selected by said braked wheel selecting means on the basis of
the target yaw moment calculated by said target yaw moment
calculating means; and braking signal outputting means for causing
a computer to output a signal to a brake drive section, for
application of the target braking force calculated by said target
braking force calculating means to the wheel selected by said
braked wheel selecting means.
6. The braking force control system according to claim 5, wherein
when the vehicle slip angular velocity calculated on the basis of
the detected vehicle speed, the detected actual vehicle yaw rate,
and the detected lateral vehicle acceleration lies within a
predetermined set value, said actual yaw rate correcting means
outputs the value detected by said actual yaw rate detecting means
as it is to said target yaw moment calculating means as a corrected
value.
7. A braking force control system for automotive vehicle,
comprising: vehicle speed detecting means for detecting a vehicle
speed; steering wheel angledetecting means for detecting a steering
angle; actual yaw rate detecting means for detecting an actual
vehicle yaw rate; lateral acceleration detecting means for
detecting a lateral vehicle acceleration; vehicle body slip angle
calculating means for causing a computer to calculate a vehicle
body slip angle on the basis of the detected vehicle speed, the
detected actual vehicle yaw rate, and the detected lateral vehicle
acceleration; actual yaw rate correcting means for causing a
computer to correct the detected actual vehicle yaw rate on the
basis of the calculated vehicle body slip angle; target yaw moment
calculating means for causing a computer to calculate a target yaw
moment on the basis of the detected vehicle speed, the detected
steering angle, and the actual vehicle yaw rate corrected by said
actual yaw rate correcting means; braked wheel selecting means for
causing a computer to select a wheel to be braked on the basis of
the detected actual vehicle yaw rate and the target yaw moment
calculated by said target yaw moment calculating means; target
braking force calculating means for causing a computer to calculate
a target braking force to be applied to the wheel selected by said
braked wheel selecting means on the basis of the target yaw moment
calculated by said target yaw moment calculating means; and braking
signal outputting means for causing a computer to output a signal
to a brake drive section, for application of the target braking
force calculated by said target braking force calculating means to
the wheel selected by said braked wheel selecting means.
8. The braking force control system according to claim 7, wherein
when the vehicle body slip angle calculated on the basis of the
detected vehicle speed, the detected actual vehicle yaw rate, and
the detected lateral vehicle acceleration lies within a
predetermined set value, said actual yaw rate correcting means
outputs the value detected by said actual yaw rate detecting means
as it is to said target yaw moment calculating means as a corrected
value
9. The braking force control system according to anyone of
preceding claims, wherein said braked wheel selecting means decides
a vehicle cornering direction on the basis of the detected actual
vehicle yaw rate; and when a direction of the target yaw moment is
the same as the vehicle cornering direction, a rear inside wheel is
selected as the wheel to be braked; on the other hand, when the
direction of the target yaw moment is opposite to the vehicle
cornering direction, a front outside wheel is selected as the wheel
to be braked.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a braking force control
system for an automotive vehicle, which can improve vehicle
cornering stability by applying an appropriate braking force to a
vehicle wheel during vehicle cornering.
[0003] 2. Description of the Prior Art
[0004] In recent years, various braking force control systems for
improving vehicle cornering stability have been developed and
further put to practical use, by which an appropriate braking force
can be applied to the vehicle wheel on the basis of some forces
applied to the vehicle during cornering.
[0005] For instance, in the case of Japanese Published Unexamined
Patent Application No. 5-24422, a technique for applying an
appropriate braking force to a predetermined vehicle wheel is
disclosed such that a target yaw rate is calculated on the basis of
steering wheel angle and vehicle speed, and further a target
braking force is calculated under due consideration of cornering
power of a vehicle model (determined in accordance with various
vehicle items and equations of motion) on the basis of detected
loads applied to the vehicle wheels so that the actual yaw rate can
become closer to the target yaw rate.
[0006] In the above-mentioned prior art technique, however, since
the braking force is so controlled that the actual yaw rate may
become closer to the target yaw rate obtained by calculation, in
case the target yaw rate is set to an erroneous value, the braking
force is determined erroneously, with the result that there exists
a possibility that the vehicle can be lead into spin or drifts out.
Therefore, for instance, when the driver turns the steering wheel
excessively (e.g., to its full lock angle) to keep the vehicle away
from an obstruction on a slippery road, there exists a problem in
that such a large target yaw rate at which a stable vehicle driving
cannot be attained is set
[0007] In addition, when a braking force is applied to the vehicle
wheel in such a way that the actual yaw rate become closer to the
target yaw rate, there exists a possibility that the vehicle can be
lead into spin or drift out.
SUMMARY OF THE INVENTION
[0008] With these problems in mind, therefore, it is a object of
the present invention to provide a braking force control system for
automotive vehicle, by which the vehicle can be driven stably
during cornering, without setting an excessive target braking
force, even when the driver unavoidably turns the steering wheel
excessively on a slippery road, for instance.
[0009] To achieve the above-mentioned object, the first aspect of
the present invention provides a braking force control system,
comprising: vehicle speed detecting means for detecting a vehicle
speed; steering wheel angle detecting means for detecting a
steering angle; actual yaw rate detecting means for detecting an
actual vehicle yaw rate; lateral acceleration detecting means for
detecting a lateral vehicle acceleration; vehicle slip angular
velocity calculating means for causing a computer to calculate a
vehicle slip angular velocity on the basis of the detected vehicle
speed, the detected actual vehicle yaw rate, and the detected
lateral vehicle acceleration; steering wheel angle correcting means
for causing a computer to correct the detected steering wheel angle
on the basis of the calculated vehicle slip angular velocity;
target yaw moment calculating means for causing a computer to
calculate a target yaw moment on the basis of the detected actual
vehicle yaw rate, the detected vehicle speed, and the steering
wheel angle corrected by said steering wheel angle correcting
means; braked wheel selecting means for causing a computer to
select a wheel to be braked on the basis of the detected actual
vehicle yaw rate and the target yaw moment calculated by said
target yaw moment calculating means; target braking force
calculating means for causing a computer to calculate a target
braking force to be applied to the wheel selected by said braked
wheel selecting means on the basis of the target yaw moment
calculated by said target yaw moment calculating means; and braking
signal outputting means for causing a computer to output a signal
to a brake drive section, for application of the target braking
force calculated by said target braking force calculating means to
the wheel selected by said braked wheel selecting means.
[0010] Here, it is preferable that when the vehicle slip angular
velocity calculated on the basis of the detected vehicle speed, the
detected actual vehicle yaw rate, and the detected lateral vehicle
acceleration lies within a predetermined set value, said steering
wheel angle correcting means outputs the value detected by said
steering wheel angle detecting means as it is to said target yaw
moment calculating means as a corrected value.
[0011] Further, the second aspect of the present invention provides
a braking force control system, comprising: vehicle speed detecting
means for detecting a vehicle speed; steering wheel angle detecting
means for detecting a steering angle; actual yaw rate detecting
means for detecting an actual vehicle yaw rate; lateral
acceleration detecting means for detecting a lateral vehicle
acceleration; vehicle body slip angle calculating means for causing
a computer to calculate a vehicle body slip angle on the basis of
the detected vehicle speed, the detected actual vehicle yaw rate,
and the detected lateral vehicle acceleration; steering wheel angle
correcting means for causing a computer to correct the detected
steering wheel angle on the basis of the calculated vehicle body
slip angle; target yaw moment calculating means for causing a
computer to calculate a target yaw moment on the basis of the
detected actual vehicle yaw rate, the detected vehicle speed, and
the steering wheel angle corrected by said steering wheel angle
correcting means; braked wheel selecting means for causing a
computer to select a wheel to be braked on the basis of the
detected actual vehicle yaw rate and the target yaw moment
calculated by said target yaw moment calculating means; target
braking force calculating means for causing a computer to calculate
a target braking force to be applied to the wheel selected by said
braked wheel selecting means on the basis of the target yaw moment
calculated by said target yaw moment calculating means; and braking
signal outputting means for causing a computer to output a signal
to a brake drive section, for application of the target braking
force calculated by said target braking force calculating means to
the wheel selected by said braked wheel selecting means.
[0012] Here, it is preferable that when the vehicle body slip angle
calculated on the basis of the detected vehicle speed, the detected
actual vehicle yaw rate, and the detected lateral vehicle
acceleration lies within a predetermined set value, said steering
wheel angle correcting means outputs the value detected by said
steering wheel angle detecting means as it is to said target yaw
moment calculating means as a corrected value.
[0013] Further, the third aspect of the present invention provides
a braking force control system, comprising: vehicle speed detecting
means for detecting a vehicle speed; steering wheel angle detecting
means for detecting a steering angle; actual yaw rate detecting
means for detecting an actual vehicle yaw rate; lateral
acceleration detecting means for detecting a lateral vehicle
acceleration; vehicle slip angular velocity calculating means for
causing a computer to calculate a vehicle slip angular velocity on
the basis of the detected vehicle speed, the detected actual
vehicle yaw rate, and the detected lateral vehicle acceleration;
actual yaw rate correcting means for causing a computer to correct
the detected actual vehicle yaw rate on the basis of the calculated
vehicle slip angular velocity; target yaw moment calculating means
for causing a computer to calculate a target yaw moment on the
basis of the detected vehicle speed, the detected steering angle,
and the actual vehicle yaw rate corrected by said actual yaw rate
correcting means; braked wheel selecting means for causing a
computer to select a wheel to be braked on the basis of the
detected actual vehicle yaw rate and the target yaw moment
calculated by said target yaw moment calculating means; target
braking force calculating means for causing a computer to calculate
a target braking force to be applied to the wheel selected by said
braked wheel selecting means on the basis of the target yaw moment
calculated by said target yaw moment calculating means; and braking
signal outputting means for causing a computer to output a signal
to a brake drive section, for application of the target braking
force calculated by said target braking force calculating means to
the wheel selected by said braked wheel selecting means.
[0014] Here, it is preferable that when the vehicle slip angular
velocity calculated on the basis of the detected vehicle speed, the
detected actual vehicle yaw rate, and the detected lateral vehicle
acceleration lies within a predetermined set value, said actual yaw
rate correcting means outputs the value detected by said actual yaw
rate detecting means as it is to said target yaw moment calculating
means as a corrected value.
[0015] Further, the fourth aspect of the present invention provides
a braking force control system, comprising: vehicle speed detecting
means for detecting a vehicle speed; steering wheel angle detecting
means for detecting a steering angle; actual yaw rate detecting
means for detecting an actual vehicle yaw rate; lateral
acceleration detecting means for detecting a lateral vehicle
acceleration; vehicle body slip angle calculating means for causing
a computer to calculate a vehicle body slip angle on the basis of
the detected vehicle speed, the detected actual vehicle yaw rate,
and the detected lateral vehicle acceleration; actual yaw rate
correcting means for causing a computer to correct the detected
actual vehicle yaw rate on the basis of the calculated vehicle body
slip angle; target yaw moment calculating means for causing a
computer to calculate a target yaw moment on the basis of the
detected vehicle speed, the detected steering angle, and the actual
vehicle yaw rate corrected by said actual yaw rate correcting
means; braked wheel selecting means for causing a computer to
select a wheel to be braked on the basis of the detected actual
vehicle yaw rate and the target yaw moment calculated by said
target yaw moment calculating means; target braking force
calculating means for causing a computer to calculate a target
braking force to be applied to the wheel selected by said braked
wheel selecting means on the basis of the target yaw moment
calculated by said target yaw moment calculating means; and braking
signal outputting means for causing a computer to output a signal
to a brake drive section, for application of the target braking
force calculated by said target braking force calculating means to
the wheel selected by said braked wheel selecting means.
[0016] Here, it is preferable that when the vehicle body slip angle
calculated on the basis of the detected vehicle speed, the detected
actual vehicle yaw rate, and the detected lateral vehicle
acceleration lies within a predetermined set value, said actual yaw
rate correcting means outputs the value detected by said actual yaw
rate detecting means as it is to said target yaw moment calculating
means as a corrected value.
[0017] Further, in above-mentioned first to fourth aspects of the
present invention, it is preferable that said braked wheel
selecting means decides a vehicle cornering direction on the basis
of the detected actual vehicle yaw rate; and when the target yaw
moment is the same as the vehicle cornering direction, a rear
inside wheel is selected as the wheel to be braked; on the other
hand, when the target yaw moment is opposite to the vehicle
cornering direction, a front outside wheel is selected as the wheel
to be braked.
[0018] In the first aspect of the braking force control system
according to the present invention, said vehicle speed detecting
means detects a vehicle speed; said steering wheel angle detecting
means detects a steering angle; said actual yaw rate detecting
means detects an actual vehicle yaw rate; and said lateral
acceleration detecting means detects a lateral vehicle
acceleration. Further, said vehicle slip angular velocity
calculating means causes a computer to calculate a vehicle slip
angular velocity on the basis of the detected vehicle speed, the
detected actual vehicle yaw rate, and the detected lateral vehicle
acceleration; said steering wheel angle correcting means causes a
computer to correct the detected steering wheel angle on the basis
of the calculated vehicle slip angular velocity; said target yaw
moment calculating means causes a computer to calculate a target
yaw moment on the basis of the detected actual vehicle yaw rate,
the detected vehicle speed, and the steering wheel angle corrected
by said steering wheel angle correcting means; said braked wheel
selecting means causes a computer to select a wheel to be braked on
the basis of the detected actual vehicle yaw rate and the target
yaw moment calculated by said target yaw moment calculating means;
said target braking force calculating means causes a computer to
calculate a target braking force to be applied to the wheel
selected by said braked wheel selecting means on the basis of the
target yaw moment calculated by said target yaw moment calculating
means; and said braking signal outputting means causes a computer
to output a signal to a brake drive section, for application of the
target braking force calculated by said target braking force
calculating means to the wheel selected by said braked wheel
selecting means.
[0019] Here, when the vehicle slip angular velocity calculated on
the basis of the detected vehicle speed, the detected actual
vehicle yaw rate, and the detected lateral vehicle acceleration
lies within a predetermined set value, said steering wheel angle
correcting means outputs the value detected by said steering wheel
angle detecting means as it is to said target yaw moment
calculating means as a corrected value, without executing any
correction processing.
[0020] Further, in the second aspect of the braking force control
system according to the present invention, said vehicle speed
detecting means detects a vehicle speed; said steering wheel angle
detecting means detects a steering angle; said actual yaw rate
detecting means detects an actual vehicle yaw rate; and said
lateral acceleration detecting means detects a lateral vehicle
acceleration. Further, said vehicle body slip angle calculating
means causes a computer to calculate a vehicle body slip angle on
the basis of the detected vehicle speed, the detected actual
vehicle yaw rate, and the detected lateral vehicle acceleration;
said steering wheel angle correcting means causes a computer to
correct the detected steering wheel angle on the basis of the
calculated vehicle body slip angle; said target yaw moment
calculating means causes a computer to calculate a target yaw
moment on the basis of the detected actual vehicle yaw rate, the
detected vehicle speed, and the steering wheel angle corrected by
said steering wheel angle correcting means; said braked wheel
selecting means causes a computer to select a wheel to be braked on
the basis of the detected actual vehicle yaw rate and the target
yaw moment calculated by said target yaw moment calculating means;
said target braking force calculating means causes a computer to
calculate a target braking force to be applied to the wheel
selected by said braked wheel selecting means on the basis of the
target yaw moment calculated by said target yaw moment calculating
means; and said braking signal outputting means causes a computer
to output a signal to a brake drive section, for application of the
target braking force calculated by said target braking force
calculating means to the wheel selected by said braked wheel
selecting means.
[0021] Here, when the vehicle body slip angle calculated on the
basis of the detected vehicle speed, the detected actual vehicle
yaw rate, and the detected lateral vehicle acceleration lies within
a predetermined set value, said steering wheel angle correcting
means outputs the value detected by said steering wheel angle
detecting means as it is to said target yaw moment calculating
means as a corrected value, without executing any correction
processing.
[0022] Further, in the third aspect the braking force control
system according to the present invention, said vehicle speed
detecting means detects a vehicle speed; said steering wheel angle
detecting means detects a steering angle; said actual yaw rate
detecting means detects an actual vehicle yaw rate; and said
lateral acceleration detecting means detects a lateral vehicle
acceleration. Further, said vehicle slip angular velocity
calculating means causes a computer to calculate a vehicle slip
angular velocity on the basis of the detected vehicle speed, the
detected actual vehicle yaw rate, and the detected lateral vehicle
acceleration; said actual yaw rate correcting means causes a
computer to correct the detected actual vehicle yaw rate on the
basis of the calculated vehicle slip angular velocity; said target
yaw moment calculating means causes a computer to calculate a
target yaw moment on the basis of the detected vehicle speed, the
detected steering angle, and the actual vehicle yaw rate corrected
by said actual yaw rate correcting means; said braked wheel
selecting means causes a computer to select a wheel to be braked on
the basis of the detected actual vehicle yaw rate and the target
yaw moment calculated by said target yaw moment calculating means;
said target braking force calculating means causes a computer to
calculate a target braking force to be applied to the wheel
selected by said braked wheel selecting means on the basis of the
target yaw moment calculated by said target yaw moment calculating
means; and
[0023] said braking signal outputting means causes a computer to
output a signal to a brake drive section, for application of the
target braking force calculated by said target braking force
calculating means to the wheel selected by said braked wheel
selecting means.
[0024] Here, when the vehicle slip angular velocity calculated on
the basis of the detected vehicle speed, the detected actual
vehicle yaw rate, and the detected lateral vehicle acceleration
lies within a predetermined set value, said actual yaw rate
correcting means outputs the value detected by said actual yaw rate
detecting means as it is to said target yaw moment calculating
means as a corrected value, without executing any correction
processing.
[0025] Further, in the fourth aspect of the braking force control
system according to the present invention, said vehicle speed
detecting means detects a vehicle speed; said steering wheel angle
detecting means detects a steering angle; said actual yaw rate
detecting means detects an actual vehicle yaw rate; and said
lateral acceleration detecting means detects a lateral vehicle
acceleration. Further, said vehicle body slip angle calculating
means causes a computer to calculate a vehicle body slip angle on
the basis of the detected vehicle speed, the detected actual
vehicle yaw rate, and the detected lateral vehicle acceleration;
said actual yaw rate correcting means causes a computer to correct
the detected actual vehicle yaw rate on the basis of the calculated
vehicle body slip angle; said target yaw moment calculating means
causes a computer to calculate a target yaw moment on the basis of
the detected vehicle speed, the detected steering angle, and the
actual vehicle yaw rate corrected by said actual yaw rate
correcting means; said braked wheel selecting means causes a
computer to select a wheel to be braked on the basis of the
detected actual vehicle yaw rate and the target yaw moment
calculated by said target yaw moment calculating means; said target
braking force calculating means causes a computer to calculate a
target braking force to be applied to the wheel selected by said
braked wheel selecting means on the basis of the target yaw moment
calculated by said target yaw moment calculating means; and said
braking signal outputting means causes a computer to output a
signal to a brake drive section, for application of the target
braking force calculated by said target braking force calculating
means to the wheel selected by said braked wheel selecting
means.
[0026] Here, when the vehicle body slip angle calculated on the
basis of the detected vehicle speed, the detected actual vehicle
yaw rate, and the detected lateral vehicle acceleration lies within
a predetermined set value, said actual yaw rate correcting means
outputs the value detected by said actual yaw rate detecting means
as it is to said target yaw moment calculating means as a corrected
value, without executing any correction processing.
[0027] Further, in above-mentioned first to fourth aspects of the
present invention, said braked wheel selecting means decides a
vehicle cornering direction on the basis of the detected actual
vehicle yaw rate; and when the target yaw moment is the same as the
vehicle cornering direction, a rear inside wheel is selected as the
wheel to be braked; on the other hand, when the target yaw moment
is opposite to the vehicle cornering direction, a front outside
wheel is selected as the wheel to be braked.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a functional block diagram showing a first
embodiment of the braking force control system according to the
present invention;
[0029] FIG. 2 is a diagrammatical block diagram showing the first
embodiment of the braking force control system according to the
present invention;
[0030] FIG. 3 is an illustration for assistance in explaining the
vehicle braking operation caused under the braking force control
executed by the first embodiment of the braking force control
system according to the present invention;
[0031] FIG. 4 is a flowchart for controlling the braking force by
the first embodiment of the braking force control system according
to the present invention;
[0032] FIG. 5 is a flowchart of a braked wheel selecting routine
executed by the first embodiment of the braking force control
system according to the present invention;
[0033] FIG. 6 is a functional block diagram showing a second
embodiment of the braking force control system according to the
present invention;
[0034] FIG. 7 is; a flowchart for controlling the braking force by
the second embodiment of the braking force control system according
to the present invention;
[0035] FIG. 8 is a functional block diagram showing a third
embodiment of the braking force control system according to the
present invention;
[0036] FIG. 9 is a flowchart for controlling the braking force by
the third embodiment of the braking force control system according
to the present invention;
[0037] FIG. 10 is a functional block diagram showing a fourth
embodiment of the braking force control system according to the
present invention; and
[0038] FIG. 11 is a flowchart for controlling the braking force by
the fourth embodiment of the braking force control system according
to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0039] Preferred embodiments of the present invention will be
described in detail hereinbelow with reference to the attached
drawings.
[0040] 1st embodiment
[0041] A first embodiment thereof will be explained with reference
to FIGS. 1 to 5. FIG. 1 is a functional block diagram showing the
first embodiment of the braking force control system; FIG. 2 is a
diagrammatical illustration showing the same braking force control
system; FIG. 3 is an illustration for assistance in explaining the
vehicle braking operation by the same braking force control system;
FIG. 4 is a flowchart showing the operation of the same braking
force control system; and FIG. 5 is a flowchart of a routine for
selecting the braked wheel.
[0042] In FIG. 2, an engine 1 is mounted on the front side of an
automotive vehicle. A driving force generated by the engine 1 is
transmitted from a clutch mechanism 2 to a center differential gear
4 through a transmission mechanism 3. Further, the driving force is
transmitted from the center differential gear 4 to a rear wheel
final reduction gear 8 via a rear drive shaft 5, a propeller shaft
6 and a drive pinion shaft 7. On the other hand, the driving force
is transmitted to a front wheel final reduction gear 12 via a
transfer gear drive 9, a transfer driven gear 10, and a front drive
shaft (i.e., a drive pinion shaft) 11. Here, the above-mentioned
clutch mechanism 2, the transmission mechanism 3, the center
differential gear 4, the front wheel final reduction gear 12, etc.
are all arranged within a casing 13 together.
[0043] The driving force inputted to the rear wheel final reduction
gear 8 is transmitted to a rear left wheel 15rl via a rear wheel
left drive shaft 14rl and to a rear right wheel 15rr via a rear
wheel right drive shaft 14rr. On the other hand, the driving force
inputted to the front wheel final reduction gear 12 is transmitted
to a front left wheel 15fl via a front wheel left drive shaft 14fl
and to a front right wheel 15fr via a front wheel right drive shaft
14fr.
[0044] Further, in FIG. 2, a master cylinder 18 connected to a
brake pedal 17 depressed by a driver is coupled to a brake drive
section 16. Therefore, when the driver depresses the brake pedal
17, braking pressure is introduced from the master cylinder 18 to
each of four wheel cylinders (i.e., a front left wheel cylinder
19fl, a front right wheel cylinder 19fr, a rear left wheel cylinder
19rl, and a rear right wheel cylinder 19rr) mounted on each of the
four wheels (the front left wheel 15fl, the front right wheel 15fr,
the rear left wheel 15rl, and the rear right wheel 15rr) through
the brake drive section 16, with the result that the four wheels
can be braked, respectively.
[0045] The above-mentioned brake drive section 16 is a hydraulic
unit provided with a pressure source, pressure reducing valves,
pressure intensifying valves, etc. Further, the brake drive section
16 can introduce brake pressure into each of the wheel cylinders
19fl, 19fr, 19rl and 19rr, independently in response to an input
signal applied thereto.
[0046] Further, a steering wheel angle sensor 21 for detecting a
steering wheel angle .theta. is mounted on a steering column of a
steering wheel 20. A vehicle speed sensor (vehicle speed detecting
means) 22 for detecting the number of revolutions of a rear wheel
output shaft is mounted on the casing 13. Further, a lateral
acceleration sensor (lateral acceleration detecting means) 23 for
detecting the acceleration in the vehicle lateral direction
(lateral acceleration a.sub.y) and a yaw rate sensor (actual yaw
rate detecting means) 24 for detecting an actual vehicle yaw rate
.gamma.(t) are both mounted on a vehicle body.
[0047] Further, in FIG. 2, a controller 30 is composed of a
microcomputer and its peripheral units, to which the steering wheel
angle sensor 21, the vehicle speed sensor 22, the lateral
acceleration sensor 23 and the yaw rate sensor 24 are all connected
to generate a drive signal to the brake drive section 16.
[0048] As shown in FIG. 1, a controller 30 is mainly composed of a
front wheel steering wheel anglecalculating section 31, a vehicle
body slip angular velocity calculating section 32, a front wheel
steering wheel angle correcting section 33, a target yaw moment
calculating section 34, a target braking force calculating section
35, a braked wheel selecting section 36, and a brake signal
outputting section 37.
[0049] In response to a signal applied from the steering wheel
angle sensor 21, the front wheel steering wheel anglecalculating
section 31 calculates an actual front wheel steering wheel
angle(actual steering wheel angle .delta.F(t)) on the basis of the
steering wheel angle .theta. under consideration of the steering
gear ratio N, and outputs the calculated actual steering wheel
angleto the front wheel steering wheel angle correcting section 33.
Here, the steering wheel angle sensor 21 and the front wheel
steering wheel anglecalculating section 31 constitute steering
wheel angledetecting means.
[0050] In response to signals applied from the vehicle speed sensor
22, the lateral acceleration sensor 23 and the yaw rate sensor 24,
the vehicle body slip angular velocity calculating section 32
calculates a vehicle body slip angular velocity d.beta./dt in
accordance with the following formula (1). The vehicle body slip
angular velocity calculating section 32 is vehicle body slip
angular velocity calculating means.
d.beta./dt=ay/V-.gamma.(t) (1)
[0051] On the basis of the vehicle body slip angular velocity
d.beta./dt calculated by the vehicle body slip angular velocity
calculating section 32, the front wheel steering wheel angle
correcting section 33 corrects the actual steering wheel angle
.delta.F(t)calculated by the front wheel steering wheel
anglecalculating section 31 in accordance with the following
formula (2). The corrected actual steering wheel angle
.delta.F(t)is outputted to target yaw moment calculating section
34. Here, the front wheel steering wheel angle correcting section
33 is steering wheel angle correctingmeans.
.delta.F(t)=(.delta.F(t).multidot.G.gamma.+d.beta./dt)/G.gamma.
(2)
[0052] where GY denotes a steady-state gain at the target yaw rate
(described later).
[0053] Further, the correction in accordance with the formula (2)
is executed only when an absolute value
.vertline.d.beta./dt.vertline. of the vehicle body slip angular
velocity d.beta./dt is larger than a predetermined set value VBC (a
positive number) previously obtained on the basis of experiments
and calculations. Therefore, when this absolute value is smaller
than the set value VBC, the actual steering wheel angle .delta.F(t)
obtained by the front wheel steering wheel anglecalculating section
31 is outputted as it is to the target yaw moment calculating
section 34, so that it is possible to eliminate an unnecessary
correcting control when the vehicle is being driven stably on a
usual non-slippery road.
[0054] When the above-mentioned correction is executed in
accordance with the formula (2), even if the vehicle tends to be
spun when the yaw rate .gamma.(t) has a positive sign (i.e., when
the vehicle is turning to the left) on a slippery road with a low
friction (.mu.), since the vehicle body slip angular velocity
d.beta./dt becomes a negative value, the actual steering wheel
angle .delta.F(t) is corrected to a smaller value. Therefore, even
if the driver unavoidably turns the steering wheel excessively on a
slippery road, for instance, since an excessive actual steering
wheel angle .delta.F(t) can be corrected to an optimum actual
steering wheel angle .delta.F(t), it is possible to obtain a stable
control by use of the corrected actual steering wheel angle
.delta.F(t).
[0055] The target yaw moment calculating section 34 (the target yaw
moment calculating means) 34 calculates a target yaw moment Mz(t)
on the basis of the vehicle speed V obtained by the vehicle speed
sensor 22, the actual yaw rate .gamma.(t) obtained by the yaw rate
sensor 24, and the corrected actual steering wheel angle
.delta.F(t) obtained by the front wheel steering wheel angle
correcting section 33.
[0056] Here, the method of calculating the target yaw moment Mz(t)
will be described in detail hereinbelow. When the vehicle is
linearized by replacing it with a two-wheel model, the equation of
motion thereof can be expressed as follows:
Iz.multidot.d.gamma.(t)/dt=2.multidot.LF.multidot.CF(t)-2.multidot.LR.mult-
idot.CR(t)+Mz(t) (3)
[0057]
M.multidot.V(d.beta.(t)/dt+.gamma.(t))=2.multidot.CF(t)+2.multidot-
.CR(t) (4)
[0058]
[0059] where CF(t) is the front wheel cornering force and CR(t) is
the rear wheel cornering force both expressed as follows:
CF(t)=kF.multidot.(.delta.F(t)/N-.beta.(t)-LF.multidot..gamma.(t)/V)
(5)
CR(t)=kR.multidot.(-.beta.(t)+LR.multidot..gamma.(t)/V) (6)
[0060] where M denotes the vehicle mass, Iz denotes the vehicle yaw
inertia; .gamma.(t) denotes the yaw rate; Mz(t) denotes the yaw
moment (target yaw moment) caused by the braking force; .beta.(t)
denotes the vehicle body slip angle, LF denotes the distance
between the front wheel and the vehicle gravity center; LR denotes
the distance between the rear wheel and the vehicle gravity center;
kF denotes the equivalent front wheel cornering power; kR denotes
the equivalent rear wheel cornering power, and N denotes the
steering gear ratio.
[0061] Here, the above formulae (3) and (4) can be expressed by an
input/output system by setting the output of the vehicle motion as
.gamma.(t) as follows:
A(P).multidot..gamma.(t)=BM(p).multidot.Mz(t)+BF(t).multidot..delta.F(t)
(7)
[0062] where 1 A ( p ) = p 2 - ( a11 + a22 ) ( 2 / V ) p + ( a11
a22 - a12 a21 ) ( 2 / V ) 2 + 2 a12 = p 2 - ayl ( 2 / V ) p + ay2 (
2 / V ) 2 + 2 ay3 BM ( p ) = p / Iz + 2 ( kF + kR ) / ( M Iz V ) =
( p - a22 ( 2 / V ) ) / Iz BF ( p ) = b11 ( 2 / N ) p + ( a12 b21 -
a22 b11 ) ( 4 / N V ) = by1 ( 2 / N ) p + by2 ( 4 / N V )
[0063] where
[0064] a11=-(LF.sup.2.multidot.kF+LR.sup.2.multidot.kR)/Iz
[0065] a12=-(LF.multidot.kF+LR.multidot.kR)/Iz
[0066] a21=-(LF.multidot.KF+LR.multidot.KR)/M
[0067] a22=-(KF+KR)/M
[0068] ay1=a11+a22
[0069] ay2=a11.multidot.a22-a12.multidot.a21
[0070] ay3=a12
[0071] b11=LF.multidot.KF/Iz
[0072] b21=KF/M
[0073] by1=b1
[0074] by2=a12.multidot.b21-a22.multidot.b11
[0075] p.times.d/dt (i.e., differential operator)
[0076] Further, the following formula is established as an
normative model of the vehicle motion.
dxm(t)/dt=-am.multidot.Xm(t)+bm.multidot..delta.F(t) (8)
ym(t)=Xm(t) (9)
[0077] Here, am and bmare both constants. Therefore, when the
target yaw rate ym(t)is determined in accordance with the formulae
(8) and (9), the steady-state gain GY of the target yaw rate for
the actual steering wheel angle.delta.F(t) can be expresses as
G.gamma.=bm/am (10)
[0078] Successively, such a yaw moment Mz(t)that the output
.gamma.(t) can asymptotically follow the output ym(t)of the
normative model is taken into account, by use of the detectable
signals .gamma.(t), .delta.F(t), and Mz(t).
[0079] Here, the following two stable polynomials Q(p)and D(p)are
introduced:
Q(p)=Q1(p).multidot.D(p) Q1(p)=p+q1 D(p)=p+d1 (11)
[0080] where g1>0 and d1>0
[0081] Therefore, when A(p) and BM(p) of the formula (7) are both
expressed by using Q(p) and D(p), the following formulae can be
obtained:
A(p)=Q(p)-A1(p) (12)
BM(p)=b1.multidot.D(p)+b0 (13)
[0082] where 2 A1 ( p ) = ( q1 + d1 + ay1 ( 2 / V ) ) p + q1 d1 -
ay2 ( 2 / V ) 2 - 2 ay3 b1 = I / Iz b0 = ( - a22 ( 2 / V ) - d1 ) /
Iz
[0083] Here, when the formulae (12) and (13) are substituted for
the formula (7),
(Q(p)-A1(p).multidot..gamma.(t)=(b1.multidot.D(p)+b0).multidot.Mz(t)+BF(p)-
.multidot..delta.F(t)
[0084] Therefore,
Qp.multidot..gamma.(t)=A1(p).multidot..gamma.(t)+(b1.multidot.D(p)+b0).mul-
tidot.Mz(t)+BF(P).multidot..delta.F(t) (14)
[0085] Further, on the basis of the formulae (8) and (9), since
(p+q1).multidot.ym(t)-q1.multidot.ym(t)=-am.multidot.ym(t)+bm.multidot..de-
lta.F(t)
Q1(p).multidot.ym(t)=(q1-am).multidot.ym(t)+bm.multidot..delta.F(-
t) (15)
[0086] Here, since Q(P)=Q1(P).multidot.D(p) in the formula (11),
the formula (14) can be expressed as
Q1(p).multidot.D(p).multidot..gamma.(t)=A1(p).multidot..gamma.(t)+(b1.mult-
idot.D(p)+b0).multidot.Mz(t)+ BF(t).multidot..gamma.F(t)
[0087] so that the following formula can be obtained
Q1(P).multidot..gamma.(t)=A1(P).multidot.D.sup.-1(P).multidot..gamma.(t)+(-
b1+b0.multidot.D.sup.-1(P).multidot.Mz(t)+
BF(P).multidot.D.sup.-1(P).mult- idot..delta.F(t) (16)
[0088] Here, when the output error e(t) is defined as
e(t)=ym(t)-.gamma.(t) (17)
[0089] the following error equation can be obtained on the basis of
the formulae (15) and (16):
Q1(p).multidot.e(t)=(q1-am).multidot.ym(t)+bm.multidot..delta.F(t)-A1(p).m-
ultidot.D.sup.-1(p).multidot..gamma.(t)-(b1+b0.multidot.D.sup.-1(p)).multi-
dot.Mz(t)-BF(p).multidot.D.sup.-1(p).multidot..delta.F(t) (18)
[0090] Here, when Mz(t)is so selected that the right side of the
formula (18) can be zeroed, 3 Mz ( t ) = 1 / b1 ( - A1 ( P ) D - 1
( p ) ( t ) - b0 D - 1 ( p ) Mz ( t ) - BF ( p ) D - 1 ( p ) F ( t
) + ( q1 - am ) ym ( t ) + bm F ( t ) ( 19 )
[0091] Further, when Q1 is substituted for the formula (11),
Q1(p).multidot.e(t)=(p+q1).multidot.e(t)=0
[0092] Therefore, since
de(t)/dt=-g1.multidot.e(t) (20)
[0093] when q1>0, e(t) can be zeroed, so that it is possible to
obtain the output .gamma.(t) corresponding to the normative
model.
[0094] The target yaw moment Mz(t) calculated by the target yaw
moment calculating section 34 is inputted to the target braking
force calculating section 35 and the braked wheel selecting section
36, respectively.
[0095] The target braking force calculating section (the target
braking force calculating means) 35 calculates the target braking
force FB on the basis of the target yaw moment Mz(t) as
follows:
FB=Mz(t)/(d/2) (21)
[0096] where d denotes a vehicle tread.
[0097] Further, the braked wheel selecting section (the braked
wheel selecting means) 36 decides the vehicle cornering direction
on the basis of the actual yaw rate .gamma.(t) obtained by the yaw
rate sensor 24. When the target yaw moment Mz(t) calculated by the
target yaw moment calculating section 34 is the same as the vehicle
cornering direction, the braked wheel selecting section 36 selects
the rear inside wheel as the wheel to be braked. On the other hand,
when the target yaw moment Mz(t) calculated by the target yaw
moment calculating section 34 is opposite to the vehicle cornering
direction, the braked wheel selecting section 36 selects the front
outside wheel as the wheel to be braked. Therefore, the following
combinations can be determined, where the signs of the actual yaw
rate .gamma.(t) and the target yaw moment Mz(t) are positive (+)
when the vehicle is turning to the left but negative (-) when
turning to the right.
[0098] Further, in order to decide that the vehicle is driven in
straight, .epsilon. is set to a positive number near zero
previously obtained on the basis of experiments or calculations.
Further, in order to decide that the target yaw moment Mz(t) is
roughly zero in turning state, .epsilon.Mz is set to another
positive number near zero previously obtained on the basis of
experiments or calculations.
[0099] (Case 1) When .gamma.(t)>.epsilon. and
Mz(t)>.epsilon.Mz; that is, when the vehicle is turning to the
left in under-steering tendency, the rear left wheel is braked.
[0100] (Case 2) When .gamma.(t)>.epsilon. and
Mz(t)<-.epsilon.Mz; that is, when the vehicle is turning to the
left in over-steering tendency, the front right wheel is
braked.
[0101] (Case 3) When .gamma.(t)<.epsilon. and
Mz(t)>.epsilon.Mz; that is, when the vehicle is turning to the
right in over-steering tendency, the front left wheel is
braked.
[0102] (Case 4) When .gamma.(t)<.epsilon. and
Mz(t)<-.epsilon.Mz; that is, when the vehicle is turning to the
right in under-steering tendency, the rear right wheel is
braked.
[0103] (Case 5) When
.vertline..gamma.(t).vertline..ltoreq..epsilon. in straight drive
or when .vertline.Mz(t).vertline..ltoreq..epsilon.Mz in turning
drive, any braked wheel is not selected.
[0104] The above-mentioned braking control is summarized in FIG.
3.
[0105] The braked wheel selected by the braked wheel selecting
section 36 is outputted to the target braking force calculating
section 35. Further, the selected braked wheel is outputted to the
braking signal outputting section 37 together with the target
braking force FB calculated by the target braking force calculating
section 35.
[0106] The braking signal outputting section (the braking signal
outputting means) 37 outputs a braking signal to the braking drive
section 16 so that the target braking force FB calculated by the
target braking force calculating section 35 is applied to the
braked wheel selected by the braked wheel selecting section 36.
[0107] The braking force control of the first embodiment will be
explained in further detail with reference to flowcharts shown in
FIGS. 4 and 5. The braking force control program is executed for
each predetermined time (e.g., 10 ms) when the vehicle is
running.
[0108] Upon start of the program, in step S101, a vehicle speed V
is read from the vehicle speed sensor 22, a steering wheel angle
.theta. is read from the steering wheel angle sensor 21, an actual
yaw rate .gamma.(t) is read from the yaw rate sensor 24, and a
lateral acceleration ay is read from the lateral acceleration
sensor 23. Further, in step S102, an actual steering wheel
angle.delta.F(t) is calculated on the basis of the steering wheel
angle .theta. by the front wheel steering wheel anglecalculating
section 31 under consideration of a steering gear ratio N.
[0109] Further, in step S103, a vehicle body slip angular velocity
d.beta./dt is calculated by the vehicle body slip angular velocity
calculating section 32 on the basis of the vehicle sped V, the
actual yaw rate .gamma.(t) and the lateral acceleration ay in
accordance with the formula (1).
[0110] Here, the steps from S104 to S106 are processing executed by
the front wheel steering wheel angle correcting section 33. In more
detail, in step S104, the absolute value
.vertline.d.beta./dt.vertline. of the vehicle body slip angular
velocity d.beta./dt is compared with the set value VBC (a positive
number) previously obtained by experiments or calculations. When
the absolute value .vertline.d.beta./dt.vertline. of the vehicle
body slip angular velocity d.beta./dt is smaller than the set value
VBC (i.e., .vertline.d.beta./dt.vertline..ltoreq.VBC), in step S105
.delta.F(t)=.delta.F(t) is set. That is, the value .delta.F(t)
obtained by the front wheel steering wheel anglecalculating section
31 is outputted from the front wheel steering wheel angle
correcting section 33 as it is without any correction. In other
words, when the absolute value .vertline.d.beta./dt.vertline. of
the vehicle body slip angular velocity d.beta./dt is small and
therefore when the vehicle is running normally on a non-slippery
road, it is possible to eliminate an unnecessary control.
[0111] On the other hand, in step S104, when the absolute value
.vertline.d.beta./dt.vertline. of the vehicle body slip angular
velocity d.beta./dt is larger than the set value VBC (i.e. ,
.vertline.d.beta./dt.vertline.> VBC), in step S106 the actual
steering wheel angle .delta.F(t) is corrected in accordance with
the formula (2). Therefore, even if the driver unavoidably turns
the steering wheel excessively on a slippery road, an excessive
actual steering wheel angle .delta.F(t) can be corrected to an
optimum actual steering wheel angle .delta.F(t).
[0112] After the actual steering wheel angle .delta.F(t) is set or
corrected in step S105 or S106, in step S107 a target yaw moment
Mz(t) is calculated by the target yaw moment calculating section 34
on the basis of the vehicle speed V, the actual yaw rate
.gamma.(t), and the corrected actual steering wheel angle
.delta.F(t) in accordance with the formula (19).
[0113] After that, in step S108, a braked wheel is selected by the
braked wheel selecting section 36 in accordance with a braked wheel
selecting routine (described later) as shown in FIG. 5. Further, in
step S109, a target braking force FB is calculated by the target
braking force calculating section 35 on the basis of the target yaw
moment Mz(t) and in accordance with the formula (21). Further, in
step S110, a signal is outputted to the brake drive section 16 so
that the target braking force FB calculated by the target braking
force calculating section 35 can be applied to the wheel selected
by the braked wheel selecting section 36, ending the program.
[0114] Here, the braked wheel selecting routine executed by the
braked wheel selecting section 36 will be explained hereinbelow
with reference to FIG. 5.
[0115] First, in step S201, the actual yaw rate .gamma.(t) is
compared with the value .epsilon. to discriminate whether the
vehicle is turning to the eft excessively to some extent. When the
actual yaw rate .gamma.(t) is less than .epsilon., in step S202 the
actual yaw rate .gamma.(t) is compared with the value -.epsilon. to
discriminate whether the vehicle is turning to the right
excessively to some extent.
[0116] When the vehicle is decided to be not turning to the right
excessively in step S202; that is, if the actual yaw rate
.gamma.(t) lies between .epsilon. and -.epsilon.
(.epsilon..gtoreq..gamma.(t).gtoreq.-.ep- silon.), since the
vehicle motion is roughly in straight state, in step S211 any
braked wheel is not selected (without braking the vehicle).
[0117] Further, in step S201 when the vehicle is decided to be
turning to the left excessively to some extent; that is, if the
actual yaw rate .gamma.(t)>.epsilon. , in step S203 it is
discriminated whether the target yaw moment Mz(t) is roughly zero;
that is, .vertline.Mz(t).vertlin- e..ltoreq..epsilon.MZ.
[0118] Further, in step S203, when
.vertline.Mz(t).vertline..ltoreq..epsil- on.Mz; that is, when the
target yaw moment Mz(t) is decided to be roughly zero, the routine
proceeds to step S211. However, in the other case (i.e., in the
case of under-steering or over-steering tendency), the routine
proceeds to step S204.
[0119] In step S204, it is decided whether the steering tendency is
under-steering (Mz(t)>.epsilon.Mz) or over-steering
(Mz(t)<-.epsilon.Mz) on the basis of the positive or negative
(direction) of the target yaw moment Mz(t). In the case where
Mz(t)>.epsilon.Mz and further the sign of the target yaw moment
Mz(t) is positive (the left direction) in the same way as that of
the actual yaw rate .gamma.(t), the under-steering tendency is
decided. Therefore, in step S205, the rear left wheel 15rl is
selected as the wheel to be braked by the target braking force FB
calculated in step S109, ending the routine. On the other hand, in
the case where Mz(t)< -.epsilon.Mz and further the sign of the
target yaw moment Mz(t) is negative (the right direction) being
different from that of the actual yaw rate .gamma.(t), the
over-steering tendency is decided. Therefore, in step S206, the
rear right wheel 15fr is selected as the wheel to be braked by the
target braking force FB calculated in step S109, ending the
routine.
[0120] On the other hand, in step S202 when the vehicle is decided
to be turning to the right excessively to some extent; that is, if
the actual yaw rate .gamma.(t)<-.epsilon., in step S207 it is
discriminated whether the target yaw moment Mz(t) is roughly zero;
that is, .vertline.Mz(t).vertline.<.epsilon.Mz.
[0121] Further, in step S207, when
.vertline.Mz(t).vertline..ltoreq..epsil- on.Mz in; that is, when
the target yaw moment Mz(t) is decided to be roughly zero, the
routine proceeds to step S211. However, in the other cases
(under-steering or over-steering tendency), the routine proceeds to
step S208.
[0122] In step S208, it is decided whether the steering tendency is
under-steering (Mz(t)<-.epsilon.Mz) or over-steering
(Mz(t)>.epsilon.Mz) on the basis of the positive or negative
(direction) of the target yaw moment Mz(t). In the case where
Mz(t)<-.epsilon.Mz and further the sign of the target yaw moment
Mz(t) is negative (the right direction) in the same way as that of
the actual yaw rate .gamma.(t), the under-steering tendency is
decided. Therefore, in step S209, the rear right wheel 15rr is
selected as the wheel to be braked by the target braking force FB
calculated in step S109, ending the routine. On the other hand, in
the case where Mz(t)> .epsilon.Mz and further the sign of the
target yaw moment Mz(t) is positive (the left direction) being
different from that of the actual yaw rate .gamma.(t), the
over-steering tendency is decided. Therefore, in step S210, the
front left wheel 15fl is selected as the wheel to be braked by the
target braking force FB calculated in step S109, ending the
routine.
[0123] Further, when the routine proceeds from the steps S202, S203
or the steps S207 to the step S211, the braked wheel is not
selected (without vehicle braking), ending the routine.
[0124] As described above, in the first embodiment of the present
invention, since the braking force can be controlled by correcting
the actual steering wheel angleon the basis of the vehicle body
slip angular velocity and further by calculating the target yaw
moment on the basis of the corrected actual steering angle, the
vehicle speed, and the actual yaw rate, even if the driver
unavoidably turns the steering wheel excessively on a slippery
road, for instance, the wheel braking force can be controlled under
optimum conditions on the basis of the corrected actual steering
angle, with the result that a stable vehicle turning travel can be
attained without setting the target braking force to an excessively
large target braking force. Further, since the actual steering
wheel angleis not corrected when the vehicle body slip angular
velocity lies within a predetermined set value, it is possible to
eliminate the braking force control when the vehicle is running
normally on a non-slippery road and thereby the correction is not
required.
[0125] Further, since the braked wheel can be selected immediately
on the basis of the actual yaw rate and the direction of the target
yaw moment, it is possible to execute the braking force control
accurately and effectively at high response speed.
[0126] 2nd embodiment
[0127] A second embodiment of the present invention will be
described hereinbelow with reference to FIGS. 6 and 7.
[0128] FIG. 6 is a functional block diagram showing the second
embodiment of the braking force control system; and FIG. 7 is a
flowchart showing the operation of the same braking force control
system. The feature of this second embodiment is that the vehicle
body slip angle is first calculated; the actual steering wheel
angleis corrected on the basis of the calculated vehicle body slip
angle; and the target yaw moment is calculated on the basis of the
corrected actual steering angle. Further, in FIGS. 6 and 7, the
same reference numerals have been retained for the similar parts or
elements having the same functions as with the case of the first
embodiment.
[0129] As shown in FIG. 6, a controller 40 is mainly composed of a
front wheel steering wheel anglecalculating section 31, a vehicle
body slip angular velocity calculating section 32, a vehicle body
slip angle calculating section 41, a front wheel steering wheel
angle correcting section 42, a target yaw moment calculating
section 34, a target braking force calculating section 35, a braked
wheel selecting section 36, and a brake signal outputting section
37.
[0130] On the basis of a vehicle body slip angular velocity
d.beta./dt calculated by the vehicle body slip angular velocity
calculating section 32, the vehicle body slip angle calculating
section 41 calculates a vehicle body slip angle .beta. by
integrating the inputted vehicle body slip angular velocity
d.beta./dt, and outputs the obtained vehicle body slip angle .beta.
to the front wheel steering wheel angle correcting section 42.
Here, the vehicle body slip angle .beta. can be expressed as
follows:
.beta..sub.k=.beta..sub.k-1+d.beta./dt.multidot..DELTA.t (22)
[0131] where .beta..sub.k denotes the newly set vehicle body slip
angle; .beta..sub.k-1 denotes the vehicle body slip angle
calculated at the last time; and .DELTA.t denotes the calculation
cycle of the arithmetic unit (microcomputer).
[0132] In other words, in the case of the first embodiment, the
vehicle body slip angular velocity calculating section 32 is the
vehicle body slip angular velocity calculating means. In the case
of the second embodiment, however, the vehicle body slip angular
velocity calculating section 32 and the vehicle body slip angle
calculating section 41 constitute the vehicle body slip angle
calculating means.
[0133] On the basis of the vehicle body slip angle .beta. inputted
by the vehicle body slip angle calculating section 41, the front
wheel steering wheel angle correcting section (steering wheel angle
correctingmeans) 42 corrects an actual steering wheel angle
.delta.F(t) inputted by the front wheel steering wheel
anglecalculating section 31 in accordance with the following
formula and outputs the corrected actual steering wheel angle
.delta.F(t) to the target yaw moment calculating section 34.
.delta.F(t)=(.delta.F(t).multidot.G.gamma.+.beta..multidot.G.beta.1)G.gamm-
a. (23)
[0134] where G.beta.1 denotes a constant for deciding the
correction degree of the vehicle body slip angle.
[0135] Further, the correction in accordance with the formula (23)
is executed only when an absolute value .vertline..beta..vertline.
of the vehicle body slip angle .beta. is larger than a
predetermined set value BC (a positive number) previously obtained
on the basis of experiments and calculations. Therefore, when this
value is smaller than the set value BC, the actual steering wheel
angle .delta.F(t)obtained by the front wheel steering wheel angle
calculating section 31 is outputted as it is to the target yaw
moment calculating section 34, so that it is possible to eliminate
an unnecessary correcting control when the vehicle is being driven
stably on a usual non-slippery road.
[0136] When the above-mentioned correction is made in accordance
with the formula (23), even if the vehicle tends to be spun when
the yaw rate .gamma.(t) has a positive sign (i.e., when the vehicle
is turning to the left) on a road with a low friction (p), since
the vehicle body slip angle .beta. becomes a negative value, the
actual steering wheel angle .delta.F(t)can be corrected to a
smaller value. Therefore, even if the driver unavoidably rotates
the steering wheel excessively on a slippery road, for instance,
since an excessive actual steering wheel angle .delta.F(t)can be
corrected to an optimum actual steering wheel angle .delta.F(t), it
is possible to obtain a stable control by use of the corrected
actual steering wheel angle .delta.F(t).
[0137] The braking force control of the second embodiment will be
explained in further detail with reference to a flow-chart shown in
FIG. 7, which corresponds to the flowchart shown in FIG. 4.
[0138] In step S103, after a vehicle body slip angular velocity
d.beta./dt has been calculated by the vehicle body slip angular
velocity calculating section 32 on the basis of the vehicle sped V,
the actual yaw rate .gamma.(t) and the lateral acceleration ay, in
step S301 the vehicle body slip angle .beta. is calculated by the
vehicle body slip angle calculating section 41 on the basis of the
vehicle body slip angular velocity d.beta./dt and in accordance
with the formula (22).
[0139] Here, the steps S302 to S304 are the processing executed by
the front wheel steering wheel angle correcting section 42. In more
detail, first in step S302, the absolute value
.vertline..beta..vertline. of the vehicle body slip angle .beta. is
compared with the set value BC (a positive number) previously
obtained by experiments or calculations. When the absolute value
.vertline..beta..vertline. of the vehicle body slip angle .beta. is
smaller than the set value BC (i.e.,
.vertline.d.beta..vertline..ltoreq.BC), in step S303
.delta.F(t)=.delta.F(t) is set. That is, the value .delta.F(t)
obtained by the front wheel steering wheel anglecalculating section
31 is outputted from the front wheel steering wheel angle
correcting section 42 as it is without any correction. In other
words, when the absolute value .vertline..beta..vertline. of the
vehicle body slip angle .beta. is small and therefore when the
vehicle is running normally on a non-slippery road, it is possible
to eliminate an unnecessary control.
[0140] Further, in step S302, when the absolute value
.vertline..beta..vertline. of the vehicle body slip angle .beta. is
larger than the set value BC (i.e.,
.vertline..beta..vertline.>BC), in step S304 the actual steering
wheel angle.delta.F(t)is corrected in accordance with the formula
(23). Therefore, even if the driver unavoidably turns the steering
wheel excessively on a slippery road, an excessive actual steering
wheel angle .delta.F(t) can be corrected to an optimum actual
steering wheel angle .delta.F(t).
[0141] After the actual steering wheel angle.delta.F(t)is set or
corrected in step S303 or S304, in step S107 a target yaw moment
Mz(t) is calculated by the target yaw moment calculating section 34
on the basis of the vehicle speed V, the actual yaw rate
.gamma.(t), and the corrected actual steering wheel angle
.delta.F(t) in accordance with the formula (19).
[0142] Further, the other steps from S108 to S110 are the same as
with the case of the first embodiment shown in FIG. 4.
[0143] As described above, in the second embodiment of the present
invention, since the braking force can be controlled by correcting
the actual steering wheel angleon the basis of the vehicle body
slip angle and further by calculating the target yaw moment on the
basis of the corrected actual steering angle, the vehicle speed,
and the actual yaw rate, even if the driver unavoidably turns the
steering wheel excessively on a slippery road, for instance, the
wheel braking force can be controlled under optimum conditions on
the basis of the corrected actual steering angle, with the result
that a stable vehicle turning travel can be attained without
setting the target braking force to an excessively large target
braking force.
[0144] Further, since the actual steering wheel angleis not
corrected when the vehicle body slip angle lies within a
predetermined set value, it is possible to eliminate the braking
force control when the vehicle is running normally on a
non-slippery road and thereby the correction is not required.
[0145] Further, the first embodiment can be modified in such a way
that the vehicle body slip angle is obtained on the basis of the
vehicle body slip angular velocity and further the actual steering
wheel angleis not corrected when the obtained vehicle body slip
angle lies within a predetermined value. In contrast with this, the
second embodiment can be modified in such a way that the actual
steering wheel angleis not corrected when the obtained vehicle body
slip angular velocity lies within a predetermined value.
[0146] 3rd embodiment
[0147] A third embodiment of the present invention will be
described hereinbelow with reference to FIGS. 8 and 9.
[0148] FIG. 8 is a functional block diagram showing the third
embodiment of the braking force control system; and FIG. 9 is a
flowchart showing the operation of the same braking force control
system. The feature of this third embodiment is that the vehicle
body slip angular velocity is first calculated; the actual yaw rate
is corrected on the basis of the calculated vehicle body slip
angular velocity; and the target yaw moment is calculated on the
basis of the corrected actual yaw rate. Further, in FIGS. 8 and 9,
the same reference numerals have been retained for the similar
parts or elements having the same functions as with the case of the
first embodiment.
[0149] As shown in FIG. 8, a controller 45 is mainly composed of a
front wheel steering wheel anglecalculating section 31, a vehicle
body slip angular velocity calculating section 32, a yaw rate
correcting section 46, a target yaw moment calculating section 34,
a target braking force calculating section 35, a braked wheel
selecting section 36, and a brake signal outputting section 37.
[0150] On the basis of a signal applied by the yaw rate sensor 24
and a signal applied by the vehicle body slip angular velocity
calculating section 32, the yaw rate correcting section (actual yaw
rate correcting means) 46 corrects the actual yaw rate .gamma.(t)
on the basis of the vehicle slip angular velocity d.beta./dt and in
accordance with the following formula (24), and outputs the
corrected actual yaw rate .gamma.(t) to the target yaw moment
calculating section 34.
.gamma.(t)=.gamma.(t)-d.beta./dt (24)
[0151] Further, the correction in accordance with the formula (24)
is executed only when an absolute value
.vertline.d.beta./dt.vertline. of the vehicle body slip angular
velocity d.beta./dt is larger than a predetermined set value VBC (a
positive number) previously obtained on the basis of experiments
and calculations. Therefore, when this value is smaller than the
predetermined set value VBC, the actual yaw rate .gamma.(t)
obtained by the yaw rate sensor 24 is outputted as it is to the
target yaw moment calculating section 34, so that it is possible to
eliminate an unnecessary correcting control when the vehicle is
being driven stably on a usual non-slippery road.
[0152] When the above-mentioned correction is executed in
accordance with the formula (24), even if the vehicle tends to be
spun when the yaw rate .gamma.(t) has a positive sign (i.e., when
the vehicle is turning to the left) on a road with a low friction
(.mu.), since the vehicle body slip angular velocity d.beta./dt
becomes a negative value, the actual yaw rate .gamma.(t) is
corrected to a larger value. Therefore, even if the driver
unavoidably turns the steering wheel excessively on a slippery
road, for instance, since the actual yaw rate .gamma.(t) can be
corrected to an optimum yaw rate .gamma.(t), it is possible to
obtain a stable control by use of the corrected actual yaw rate
.gamma.(t).
[0153] Further, on the basis of the vehicle speed V obtained by the
vehicle speed sensor 22, the actual steering wheel
angle.delta.F(t)obtained by the front wheel steering wheel
anglecalculating section 31, and the actual yaw rate .gamma.(t)
obtained by the yaw rate correcting section 46, the target yaw
moment calculating section 34 calculates the target yaw moment
Mz(t). In other words, in this third embodiment, the actual
steering wheel angle.delta.F(t)obtained by the front wheel steering
wheel anglecalculating section 31 is inputted to the target yaw
moment calculating section 34 without any correction.
[0154] The braking force control of the third embodiment will be
explained in further detail with reference to a flowchart shown in
FIG. 9, which corresponds to the flowchart shown in FIG. 4.
[0155] In step S103, after a vehicle body slip angular velocity
d.beta./dt has been calculated by the vehicle body slip angular
velocity calculating section 32 on the basis of the vehicle sped V,
the actual yaw rate .gamma.(t) and the lateral acceleration ay, the
program proceeds to step S401.
[0156] Here, the steps S401 to S403 are the processing executed by
the yaw rate correcting section 46. In more detail, first in step
S401, the absolute value .vertline.d.beta./dt.vertline. of the
vehicle body slip angular velocity d.beta./dt is compared with the
predetermined set value VBC (a positive number) previously obtained
by experiments or calculations. When the absolute value
.vertline.d.beta./dt.vertline. of the vehicle body slip angular
velocity d.beta./dt is smaller than the set value VBC (i.e.,
.vertline.d.beta./dt.vertline..ltoreq.VBC), in step S402
.gamma.(t)=.gamma.(t) is set. That is, the value .gamma.(t)
obtained by the yaw rate sensor 24 is outputted from the yaw rate
correcting section 46 to the target yaw moment calculating section
34 as it is without any correction. In other words, when the
absolute value .vertline.d.beta./dt.vertline. of the vehicle body
slip angular velocity d.beta./dt is small and therefore when the
vehicle is running normally on a non-slippery road, it is possible
to eliminate an unnecessary control.
[0157] Further, in step S401, when the absolute value
.vertline.d.beta./dt.vertline. of the vehicle body slip angular
velocity d.beta./dt is larger than the predetermined set value VBC
(i.e., .vertline.d.beta./dt.vertline.>VBC), in step S403 the
actual yaw rate .gamma.(t) is corrected in accordance with the
formula (24). Therefore, even if the driver unavoidably turns the
steering wheel excessively on a slippery road, an actual yaw rate
can be corrected to an optimum actual yaw rate .gamma.(t).
[0158] After the actual yaw rate .gamma.(t) is set or corrected in
step S402 or S403, in step S107 a target yaw moment Mz(t) is
calculated by the target yaw moment calculating section 34 on the
basis of the vehicle speed V, the actual steering wheel angle
.delta.F(t), and the corrected actual yaw rate .gamma.(t) in
accordance with the formula (19).
[0159] Further, the other steps from S108 to S110 are the same as
with the case of the first embodiment shown in FIG. 4.
[0160] As described above, in the third embodiment of the present
invention, since the braking force can be controlled by correcting
the actual yaw rate on the basis of the vehicle body slip angular
velocity and further by calculating the target yaw moment on the
basis of the corrected actual yaw rate, the vehicle speed, and the
actual steering angle, even if the driver unavoidably turns the
steering wheel excessively on a slippery road, for instance, the
wheel braking force can be controlled under optimum conditions on
the basis of the corrected yaw rate, with the result that a stable
vehicle turning travel can be attained without setting the target
braking force to an excessively large target braking force.
[0161] Further, since the actual yaw rate is not corrected when the
vehicle body slip angular velocity lies within a predetermined set
value, it is possible to eliminate the braking force control when
the vehicle is running normally on a non-slippery road and thereby
the correction is not required.
[0162] 4th embodiment
[0163] A fourth embodiment of the present invention will be
described hereinbelow with reference to FIGS. 10 and 11.
[0164] FIG. 10 is a functional block diagram showing the fourth
embodiment of the braking force control system; and FIG. 11 is a
flowchart showing the operation of the same braking force control
system. The feature of this fourth embodiment is that the vehicle
body slip angle is first calculated; the actual yaw rate is
corrected on the basis of the calculated vehicle body slip angle;
and the target yaw moment is calculated on the basis of the
corrected actual yaw rate. Further, in FIGS. 10 and 11, the same
reference numerals have been retained for the similar parts or
elements having the same functions as with the case of the first
embodiment.
[0165] As shown in FIG. 10, a controller 50 is mainly composed of a
front wheel steering wheel anglecalculating section 31, a vehicle
body slip angular velocity calculating section 32, a vehicle body
slip angle calculating section 41, a yaw rate correcting section
51, a target yaw moment calculating section 34, a target braking
force calculating section 35, a braked wheel selecting section 36,
and a brake signal outputting section 37.
[0166] On the basis of a vehicle body slip angle .beta. inputted by
the vehicle body slip angle calculating section 41, the yaw rate
correcting section (actual yaw rate correcting means) 51 corrects
the actual yaw rate .gamma.(t) obtained by the yaw rate sensor 24
in accordance with the following formula (25), and outputs the
corrected actual yaw rate .gamma.(t) to the target yaw moment
calculating section 34.
.gamma.(t)=.gamma.(t)-.beta..multidot.G.beta.2 (25)
[0167] where G.beta.2 denotes a constant for deciding the
correction degree on the basis of the vehicle body slip angle.
[0168] Further, the correction in accordance with the formula (25)
is executed only when an absolute value .vertline..beta..vertline.
of the vehicle body slip angle .beta. is larger than a
predetermined set value BC (a positive number) previously obtained
on the basis of experiments and calculations. Therefore, when this
value is smaller than the set value BC, the actual yaw rate
.gamma.(t) obtained by the yaw rate sensor 24 is outputted as it is
from the yaw rate correcting section 51 to the target yaw moment
calculating section 34, so that it is possible to eliminate an
unnecessary correcting control when the vehicle is being driven
stably on a usual non-slippery road.
[0169] When the above-mentioned correction is made in accordance
with the formula (25), even if the vehicle tends to be spun when
the yaw rate .gamma.(t) has a positive sign (i.e., when the vehicle
is turning to the left) on a road with a low friction (.mu.), since
the vehicle body slip angle .beta. becomes a negative value, the
actual yaw rate .gamma.(t) is corrected to a larger value.
Therefore, even if the driver unavoidably turns the steering wheel
excessively on a slippery road, for instance, since the actual yaw
rate .gamma.(t) can be corrected to an optimum yaw rate .gamma.(t),
it is possible to obtain a stable control by use of the corrected
actual yaw rate .gamma.(t).
[0170] Further, on the basis of the vehicle speed V obtained by the
vehicle speed sensor 22, the actual steering wheel
angle.delta.F(t)obtained by the front wheel steering wheel
anglecalculating section 31, and the actual yaw rate .gamma.(t)
obtained by the yaw rate correcting section 51, the target yaw
moment calculating section 34 calculates the target yaw moment
Mz(t). In other words, in this fourth embodiment, the actual
steering wheel angle.delta.F(t)obtaine- d by the front wheel
steering wheel anglecalculating section 31 is inputted to the
target yaw moment calculating section 34 without any
correction.
[0171] The braking force control of the fourth embodiment will be
explained in further detail with reference to a flowchart shown in
FIG. 11, which corresponds to the flowchart shown in FIG. 7.
[0172] In step S301, after a vehicle body slip angle .beta. has
been calculated by the vehicle body slip angle calculating section
41, the program proceeds to step S501.
[0173] Here, the steps from S501 to S503 are the processing
executed by the yaw rate correcting section 51. In more detail,
first in step S501, the absolute value .vertline..beta..vertline.
of the vehicle body slip angle .beta. is compared with the
predetermined set value BC (a positive number) previously obtained
by experiments or calculations. When the absolute value
.vertline.d.beta./dt.vertline. of the vehicle body slip angle
.beta. is smaller than the set value BC (i.e.,
.vertline..beta..vertline..ltoreq.BC), in step S502
.gamma.(t)=.gamma.(t) is set. That is, the value .gamma.(t)
obtained by the yaw rate sensor 24 is outputted from the yaw rate
correcting section 51 to the target yaw moment calculating section
34 as it is without any correction. In other words, when the
absolute value .vertline..beta..vertline. of the vehicle body slip
angle .beta. is small and therefore when the vehicle is running
normally on a non-slippery road, it is possible to eliminate an
unnecessary control.
[0174] Further, in step S501, when the absolute value
.vertline..beta..vertline. of the vehicle body slip angle .beta. is
larger than the predetermined set value VBC (i.e.,
.vertline..beta..vertline.>VBC), in step S503, the actual yaw
rate .gamma.(t) is corrected in accordance with the formula (25).
Therefore, even if the driver unavoidably turns the steering wheel
excessively on a slippery road, an actual yaw rate can be corrected
to an optimum actual yaw rate .gamma.(t).
[0175] After the actual yaw rate .gamma.(t) is set or corrected in
step S502 or S503, in step S107 a target yaw moment Mz(t) is
calculated by the target yaw moment calculating section 34 on the
basis of the vehicle speed V, the actual steering wheel angle
.delta.F(t), and the corrected actual yaw rate .gamma.(t) in
accordance with the formula (19).
[0176] Further, the other steps from S108 to S110 are the same as
with the case of the first embodiment shown in FIG. 4.
[0177] As described above, in the fourth embodiment of the present
invention, since the braking force can be controlled by correcting
the actual yaw rate on the basis of the vehicle body slip angle and
further by calculating the target yaw moment on the basis of the
corrected actual yaw rate, the vehicle speed, and the actual
steering angle, even if the driver unavoidably turns the steering
wheel excessively on a slippery road, for instance, the wheel
braking force can be controlled under optimum conditions on the
basis of the corrected yaw rate, with the result that a stable
vehicle turning travel can be attained without setting the target
braking force to an excessively large target braking force.
[0178] Further, since the actual yaw rate is not corrected when the
vehicle body slip angle lies within a predetermined set value, it
is possible to eliminate the braking force control when the vehicle
is running normally on a non-slippery road and thereby the
correction is not required.
[0179] Further, the third embodiment can be modified in such a way
that the vehicle body slip angle is obtained on the basis of the
vehicle body slip angular velocity and further the actual steering
wheel angleis not corrected when the obtained vehicle body slip
angle lies within a predetermined value. In contrast with this, the
fourth embodiment can be modified in such a way that the actual
steering wheel angleis not corrected when the obtained vehicle body
slip angular velocity lies within a predetermined value.
[0180] As described above, in the braking force control system
according to the present invention, since the parameters used to
calculate the target yaw moment are previously corrected
appropriately and further since the braking force is controlled on
the basis of the target yaw moment calculated by use of the
corrected parameters, even if the driver unavoidably turns the
steering wheel excessively on a slippery road, for instance, the
target braking force is not set to a large value beyond necessity,
with the result that a stable vehicle turning travel can be
attained.
[0181] While the presently preferred embodiments of the present
invention have been shown and described, it is to be understood
that this disclosure is for the purpose of illustration and that
various changes and modifications may be made without departing
from the scope of the invention as set forth in the appended
claims.
* * * * *