U.S. patent application number 09/416524 was filed with the patent office on 2001-09-27 for yaw rate detecting system for a vehicle.
This patent application is currently assigned to TOZU, KENJI. Invention is credited to NISHIO, AKITAKA, TOZU, KENJI.
Application Number | 20010025210 09/416524 |
Document ID | / |
Family ID | 17973670 |
Filed Date | 2001-09-27 |
United States Patent
Application |
20010025210 |
Kind Code |
A1 |
TOZU, KENJI ; et
al. |
September 27, 2001 |
YAW RATE DETECTING SYSTEM FOR A VEHICLE
Abstract
The present invention is directed to a yaw rate detecting system
for a vehicle, which includes a yaw rate sensor for measuring a yaw
rate of the vehicle. The apparatus is adapted to determine a
stopped state of the vehicle, set a zero point at the yaw rate
measured by the yaw rate sensor when the stopped state of the
vehicle is determined, and calculate an actual yaw rate in response
to an output of the yaw rate sensor, on the basis of the zero
point. The actual yaw rate is calculated by subtracting the yaw
rate at the zero point from the yaw rate measured by the yaw rate
sensor. It may be so arranged that a desired yaw rate is set on the
basis of a vehicle speed and a steering angle, and the zero point
is corrected in response to a comparison of the desired yaw rate
and the actual yaw rate. For example, a temporary zero point is set
when the stopped state of the vehicle is determined, and a
deviation between the desired yaw rate and the actual yaw rate is
calculated. In this case, the actual yaw rate is calculated by
subtracting the yaw rate at the temporary zero point from the yaw
rate measured by the yaw rate sensor. Then, the zero point is
corrected on the basis of the temporary zero point in response to
the deviation.
Inventors: |
TOZU, KENJI; (YOKKAICHI
CITY, JP) ; NISHIO, AKITAKA; (OKAZAKI CITY,
JP) |
Correspondence
Address: |
BURNS DOANE SWECKER & MATHIS L L P
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Assignee: |
TOZU, KENJI
|
Family ID: |
17973670 |
Appl. No.: |
09/416524 |
Filed: |
October 12, 1999 |
Current U.S.
Class: |
701/1 ; 303/146;
701/41; 701/71 |
Current CPC
Class: |
B60T 8/172 20130101;
B60T 2250/06 20130101 |
Class at
Publication: |
701/1 ; 701/41;
701/71; 303/146 |
International
Class: |
B62D 006/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 13, 1998 |
JP |
10-307825 |
Claims
What is claimed is:
1. An apparatus for detecting a yaw rate of a vehicle comprising: a
yaw rate sensor for measuring a yaw rate of a vehicle; stoppage
determining means for determining a stopped state of said vehicle;
zero point setting means for setting a zero point at the yaw rate
measured by said yaw rate sensor when said stoppage determining
means determines the stopped state of said vehicle; and actual yaw
rate calculating means for calculating an actual yaw rate of said
vehicle in response to an output of said yaw rate sensor, on the
basis of the zero point set by said zero point setting means.
2. The apparatus as set forth in claim 1, wherein said actual yaw
rate calculating means is adapted to calculate the actual yaw rate
by subtracting the yaw rate at the zero point from the yaw rate
measured by said yaw rate sensor.
3. The apparatus as set forth in claim 1, wherein said stoppage
determining means includes a parking switch activated in response
to a state of a parking brake of said vehicle.
4. The apparatus as set forth in claim 1, further comprising:
vehicle speed detecting means for detecting a vehicle speed of said
vehicle; steering angle detecting means for detecting a steering
angle of said vehicle; desired yaw rate setting means for setting a
desired yaw rate on the basis of the vehicle speed detected by said
vehicle speed detecting means and the steering angle detected by
said steering angle detecting means; and zero point correcting
means for correcting the zero point set by said zero point setting
means in response to a comparison of the desired yaw rate set by
said desired yaw rate setting means and the actual yaw rate
calculated by said actual yaw rate calculating means.
5. The apparatus as set forth in claim 4, wherein said stoppage
determining means includes a parking switch activated in response
to a state of a parking brake of said vehicle, and wherein said
stoppage determining means is adapted to determine the stopped
state of said vehicle, when it is determined that said parking
brake is activated on the basis of an output of said parking
switch, and that the vehicle speed is lower than a predetermined
speed on the basis of the output of said vehicle speed detecting
means.
6. The apparatus as set forth in claim 4, wherein said zero point
setting means includes temporary zero point setting means for
setting a temporary zero point in response to the result determined
by said stoppage determining means, and wherein said zero point
correcting means includes deviation calculating means for
calculating a deviation between the desired yaw rate set by said
desired yaw rate setting means and the actual yaw rate calculated
by said actual yaw rate calculating means in response to the output
of said yaw rate sensor, on the basis of the temporary zero point
set by said temporary zero point setting means, and said zero point
correcting means is adapted to correct the zero point on the basis
of the temporary zero point, in response to the deviation
calculated by said deviation calculating means and the vehicle
speed detected by said vehicle speed detecting means.
7. The apparatus as set forth in claim 6, wherein said actual yaw
rate calculating means is adapted to calculate the actual yaw rate
by subtracting the yaw rate at the temporary zero point from the
yaw rate measured by said yaw rate sensor.
8. The apparatus as set forth in claim 6, wherein said zero point
correcting means is adapted to renew the zero point by the
temporary zero point, when the deviation calculated by said
deviation calculating means is lower than a predetermined value,
and such a state that the vehicle speed detected by said vehicle
speed detecting means exceeds a predetermined speed has continued
for a period longer than a predetermined time period.
9. The apparatus as set forth in claim 6, wherein said zero point
correcting means is prohibited from correcting the zero point, when
such a state that the deviation calculated by said deviation
calculating means exceeds a predetermined value has continued for
more than a predetermined time period.
10. A method for detecting a yaw rate of a vehicle, comprising the
steps of: measuring a yaw rate of a vehicle by a yaw rate sensor;
determining a stopped state of said vehicle; setting a zero point
at the yaw rate measured by said yaw rate sensor when the stopped
state of said vehicle is determined; and calculating an actual yaw
rate of said vehicle by subtracting the yaw rate at the zero point
from the yaw rate measured by said yaw rate sensor.
11. The method as set forth in claim 10, further comprising the
steps of: detecting a vehicle speed of said vehicle; detecting a
steering angle of said vehicle; setting a desired yaw rate on the
basis of the vehicle speed and the steering angle; and correcting
the zero point in response to a comparison of the desired yaw rate
and the actual yaw rate.
12. The method as set forth in claim 11, wherein the stopped state
of said vehicle is determined, when it is determined that a parking
brake is operated, and that the vehicle speed is lower than a
predetermined speed.
13. The method as set forth in claim 11, wherein a temporary zero
point is set when the stopped state of said vehicle is determined,
and wherein a deviation between the desired yaw rate and the actual
yaw rate is calculated in response to the output of said yaw rate
sensor, on the basis of the temporary zero point, and wherein the
zero point is corrected on the basis of the temporary zero point,
in response to the deviation and the vehicle speed.
14. The method as set forth in claim 13, wherein the actual yaw
rate is calculated by subtracting the yaw rate at the temporary
zero point from the yaw rate measured by said yaw rate sensor.
15. The method as set forth in claim 11, wherein the zero point is
renewed by the temporary zero point, when the deviation calculated
by said deviation calculating means is lower than a predetermined
value, and such a state that the vehicle speed detected by said
vehicle speed detecting means exceeds a predetermined speed has
continued for a period longer than a predetermined time period.
Description
[0001] This application claims priority under 35 U.S.C. Sec. 119 to
No.10-307825 filed in Japan on Oct. 13, 1998, the entire content of
which is herein incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a yaw rate detecting system
for a vehicle, and more particularly to an apparatus and method for
detecting the yaw rate of the vehicle for use in a vehicle motion
control system.
[0004] 2. Description of the Related Arts
[0005] Recently, a system for controlling a vehicle motion
characteristic, particularly a turning characteristic of a vehicle,
has been noted, and a vehicle motion control system which is
adapted to directly control a rotating moment by controlling a
difference of braking force applied to left and right wheels, is
now on the market. For example, when it is determined that the
excessive oversteer occurs during cornering, the braking force will
be applied to a front wheel located on the outside of the curve in
the vehicle's path for example, to produce a moment for forcing the
vehicle to turn in the direction toward the outside of the curve,
i.e., an outwardly oriented moment, in accordance with an oversteer
restraining control which may be called as a vehicle stability
control. When it is determined that the excessive understeer occurs
while a vehicle is undergoing a cornering maneuver, for example,
the braking force will be applied to force the vehicle to turn in
the direction toward the inside of the curve, i.e., an inwardly
oriented moment, in accordance with an understeer restraining
control, which may be called as a course trace performance control.
The above described oversteer restraining control and understeer
restraining control as a whole may be called as a steering control
by braking. Accordingly, irrespective of brake pedal operation, the
braking force applied to each wheel is controlled in response to a
comparison of a dsired yaw rate and an actual yaw rate, for
example.
[0006] In the vehicle motion control system as described above, a
sensor for detecting a vehicle yaw rate is employed, as described
in Japanese Patent Laid-open Publication No.5-314397, for example.
It is stated in that Publication that a prior apparatus for
processing a signal output from a sensor neglects compensation for
drift component included in the signal output from the sensor, so
that an apparatus for processing the sensor signal has been
proposed so as to calculate an accurate yaw rate irrespective of
the drifted amount of the yaw rate sensor. In practice, a zero
point signal of the yaw rate sensor is renewed to provide such a
relationship that each value of steering angle of positive or
negative value within a certain time period and each value of yaw
rate of positive or negative value within a certain time period
will coincide with each other, under a certain running condition.
Also proposed is such a method that an output of the yaw rate
sensor is renewed to be zero, in the case where an estimated
generating yaw rate estimated in response to the output of the yaw
rate sensor, e.g., steering angle, speed in the longitudinal
direction, and vehicle characteristic, is smaller than a
predetermined allowable yaw rate error, under such a running
condition that the yaw rate is not generated, as in the case where
the vehicle is running on a straight road at a low speed.
[0007] According to the apparatus for processing the sensor signal,
however, an output of a steering angle sensor with low resolution
is directly used for renewing the zero point. Therefore, it is
impossible to set or renew the zero point signal accurately for the
yaw rate sensor. Particularly, in calculating a vehicle side slip
angle for use in the steering control by braking, errors in the
output of the steering angle are accumulated to cause a large
error. Furthermore, the process for correcting the error of the
zero point by means of the apparatus for processing the output of
the sensor as disclosed in the Publication is complicated, so that
a relatively long processing time is needed.
SUMMARY OF THE INVENTION
[0008] Accordingly, it is an object of the present invention to set
a zero point of a yaw rate sensor accurately, to detect a yaw rate
of a vehicle on the basis of the zero point.
[0009] In accomplishing the above and other objects, an apparatus
for detecting the yaw rate of the vehicle is adapted to include a
yaw rate sensor for measuring a yaw rate of the vehicle, a stoppage
determining device for determining a stopped state of the vehicle,
a zero point setting device for setting a zero point at the yaw
rate measured by the yaw rate sensor when the stoppage determining
device determines the stopped state of the vehicle, and an actual
yaw rate calculating device for calculating an actual yaw rate in
response to an output of the yaw rate sensor, on the basis of the
zero point set by the zero point setting device. According to the
actual yaw rate calculating device, the actual yaw rate can be
calculated by subtracting the yaw rate at the zero point from the
yaw rate measured by the yaw rate sensor.
[0010] Preferably, the apparatus may further include a vehicle
speed detecting device for detecting a vehicle speed of the
vehicle, a steering angle detecting device for detecting a steering
angle of the vehicle, a desired yaw rate setting device for setting
a desired yaw rate on the basis of the vehicle speed detected by
the vehicle speed detecting device and the steering angle detected
by the steering angle detecting device, and a zero point correcting
device for correcting the zero point set by the zero point setting
device in response to a comparison of the desired yaw rate set by
the desired yaw rate setting device and the actual yaw rate
calculated by the actual yaw rate calculating device. The stoppage
determining device may be constituted by the vehicle speed
detecting device and a parking switch activated in response to a
state of a parking brake of the vehicle, and adapted to determine
the stopped state of the vehicle, when it is determined that the
parking brake is activated on the basis of an output of the parking
switch, and that the vehicle speed is lower than a predetermined
speed on the basis of the output of the vehicle speed detecting
device.
[0011] It may be so arranged that the zero point setting device
includes a temporary zero point setting device for setting a
temporary zero point in response to the result determined by the
stoppage determining device, and the zero point correcting device
includes a deviation calculating device for calculating a deviation
between the desired yaw rate set by the desired yaw rate setting
device and the actual yaw rate calculated by the actual yaw rate
calculating device in response to the output of the yaw rate
sensor, on the basis of the temporary zero point set by the
temporary zero point setting device, and the zero point correcting
device is adapted to correct the zero point on the basis of the
temporary zero point, in response to the deviation calculated by
the deviation calculating device and the vehicle speed detected by
the vehicle speed detecting device. The actual yaw rate calculating
device may be adapted to calculate the actual yaw rate by
subtracting the yaw rate at the temporary zero point from the yaw
rate measured by the yaw rate sensor.
[0012] The zero point correcting device may be adapted to renew the
zero point by the temporary zero point, when the deviation
calculated by the deviation calculating device is lower than a
predetermined value, and such a state that the vehicle speed
detected by the vehicle speed detecting device exceeds a
predetermined speed has continued for a period longer than a
predetermined time period. Furthermore, the zero point correcting
device may be prohibited from correcting the zero point, when such
a state that the deviation calculated by the deviation calculating
device exceeds a predetermined value has continued for a period
longer than a predetermined time period.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The above stated object and following description will
become readily apparent with reference to the accompanying
drawings, wherein like reference numerals denote like elements, and
in which:
[0014] FIG. 1 is a block diagram illustrating an embodiment of an
apparatus for detecting a yaw rate of a vehicle according to an
embodiment of the present invention;
[0015] FIG. 2 is a schematic block diagram of a vehicle having a
brake control system including the yaw rate detecting apparatus
according to an embodiment of the present invention;
[0016] FIGS. 3A and 3B are flowcharts showing a main routine of the
brake control;
[0017] FIG. 4 is a flowchart showing a subroutine for calculating
an actual yaw rate .gamma.a for use in the steering control by
braking executed in FIGS. 3A and 3B;
[0018] FIG. 5 is a flowchart showing a subroutine for setting a
desired slip rate for use in the steering control by braking
executed in FIGS. 3A and 3B;
[0019] FIG. 6 is a flowchart showing a hydraulic pressure servo
control in the steering control by braking executed in FIGS. 3A and
3B;
[0020] FIG. 7 is a diagram showing a region for determining start
and termination of the oversteer restraining control for use in the
steering control by braking executed in FIGS. 3A and 3B;
[0021] FIG. 8 is a diagram showing a region for determining start
and termination of the understeer restraining control for use in
the steering control by braking executed in FIGS. 3A and 3B;
[0022] FIG. 9 is a diagram showing a relationship between a vehicle
slip angle and a gain for calculating the parameters for use in the
steering control by braking executed in FIGS. 3A and 3B; and
[0023] FIG. 10 is a diagram showing a relationship between the
pressure control modes and parameters for use in the steering
control by braking executed in FIGS. 3A and 3B.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0024] Referring to FIG. 1, there is schematically illustrated an
apparatus for detecting a yaw rate of a vehicle according to an
embodiment of the present invention. The apparatus includes a yaw
rate sensor YS for measuring a yaw rate of the vehicle, a stoppage
determining device PD for determining a stopped state of the
vehicle, a zero point setting device ZS for setting a zero point at
the yaw rate measured by the yaw rate sensor YS when the stoppage
determining device PD determines the stopped state of the vehicle,
and an actual yaw rate calculating device YA which is adapted to
calculate an actual yaw rate in response to an output of the yaw
rate sensor YS, on the basis of the zero point set by the zero
point setting device ZS. According to the apparatus as constituted
in the above, the zero point can be set accurately, because the
output of the steering angle sensor as used in the prior art is not
directly used for setting the zero point.
[0025] As shown in FIG. 1, such components may be further provided
as a vehicle speed detecting device VS for detecting a vehicle
speed of the vehicle, a steering angle detecting device SA for
detecting a steering angle of the vehicle, a desired yaw rate
setting device YT for setting a desired yaw rate on the basis of
the vehicle speed detected by the vehicle speed detecting device VS
and the steering angle detected by the steering angle detecting
device SA. And, a zero point correcting device ZA may be provided
for correcting the zero point set by the zero point setting device
ZS in response to a comparison of the desired yaw rate set by the
desired yaw rate setting device YT and the actual yaw rate
calculated by the actual yaw rate calculating device YA.
[0026] According to the actual yaw rate calculating device YA, the
actual yaw rate can be calculated by subtracting the yaw rate at
the zero point from the yaw rate measured by the yaw rate sensor
YS.
[0027] In the case where the vehicle is on a ferryboat, or the
vehicle is on a rotating turntable, the yaw rate sensor YS is swung
or rotated, while it is in a stopped state relative to the vehicle,
thereby to cause an error in the output of the sensor YS. In order
to avoid this error, therefore, the present embodiment is so
arranged that the zero point setting device ZS includes a temporary
zero point setting device TZ for setting a temporary zero point in
response to the result determined by the stoppage determining
device PD, and that the zero point correcting device ZA includes a
deviation calculating device YD for calculating a deviation between
the desired yaw rate set by the desired yaw rate setting device YT
and the actual yaw rate calculated by the actual yaw rate
calculating device YA in response to the output of the yaw rate
sensor YS, on the basis of the temporary zero point set by the
temporary zero point setting device TZ. And, the zero point
correcting device ZA is adapted to correct the zero point on the
basis of the temporary zero point, in response to the deviation
calculated by the deviation calculating device YD and the vehicle
speed detected by the vehicle speed detecting device VS.
[0028] In practice, the actual yaw rate calculating device YA is
adapted to calculate the actual yaw rate by subtracting the yaw
rate at the temporary zero point from the yaw rate measured by the
yaw rate sensor YS. And, the zero point correcting device ZA is
adapted to renew the zero point by the temporary zero point, when
the deviation calculated by the deviation calculating device YD is
lower than a predetermined value, and such a state that the vehicle
speed detected by the vehicle speed detecting device VS exceeds a
predetermined speed has continued for a period longer than a
predetermined time period. Therefore, the zero point to the yaw
rate sensor can be corrected certainly, even in the case where the
vehicle is placed on the ferryboat, the rotating table, and the
like. When such a state that the deviation calculated by the
deviation calculating device YD exceeds a predetermined value has
continued for a period longer than a predetermined time period, it
is determined to be abnormal, so that the zero point correcting
device ZA is prohibited from correcting the zero point.
[0029] Referring to FIG. 2, there is schematically illustrated a
vehicle including the yaw rate detecting apparatus according to an
embodiment of the present invention. The vehicle has an engine EG
provided with a fuel injection apparatus FI and a throttle control
apparatus TH which is arranged to control a main throttle opening
of a main throttle valve MT in response to operation of an
accelerator pedal AP. The throttle control apparatus TH has a
sub-throttle valve ST which is actuated in response to an output
signal of an electronic controller ECU to control a sub-throttle
opening. Also, the fuel injection apparatus FI is actuated in
response to an output signal of the electronic controller ECU to
control the fuel injected into the engine EG. According to the
present embodiment, the engine EG is operatively connected with the
front wheels FL, FR through a transmission GS to provide a
front-drive system, but the present embodiment is not limited to
the front-drive system. The wheel FL designates the wheel at the
front left side as viewed from the position of a driver's seat, the
wheel FR designates the wheel at the front right side, the wheel RL
designates the wheel at the rear left side, and the wheel RR
designates the wheel at the rear right side.
[0030] With respect to a braking system according to the present
embodiment, wheel brake cylinders Wfl, Wfr, Wrl, Wrr are
operatively mounted on the wheels FL, FR, RL, RR of the vehicle,
respectively, and which is fluidly connected to a hydraulic braking
pressure control apparatus BC. The pressure control apparatus BC in
the present embodiment may be arranged as illustrated in FIG. 1
which will be explained later in detail. According to the present
embodiment, a so-called diagonal circuit system has been
employed.
[0031] As shown in FIG. 2, at the wheels FL, FR, RL and RR, there
are provided wheel speed sensors WS1 to WS4 respectively, which are
connected to the electronic controller ECU, and by which a signal
having pulses proportional to a rotational speed of each wheel,
i.e., a wheel speed signal is fed to the electronic controller ECU.
Also provided are a parking switch PB, which turns on when a
parking brake (not shown) is operated to hold the vehicle in the
stopped state, a brake switch BS which turns on when the brake
pedal BP is depressed, a front steering angle sensor SSf for
detecting a steering angle .delta.f of the front wheels FL, FR, a
lateral acceleration sensor YG for detecting a vehicle lateral
acceleration, and a yaw rate sensor YS for detecting a yaw rate of
the vehicle. These are electrically connected to the electronic
controller ECU. According to the yaw rate sensor YS for use in the
apparatus of the present invention, a varying rate of rotational
angle of the vehicle about a normal on the center of gravity of the
vehicle, i.e., a yaw angular velocity or a measured yaw rate
.gamma.as is fed to the electronic controller ECU.
[0032] As shown in FIG. 2, the electronic controller ECU is
provided with a microcomputer CMP which includes a central
processing unit or CPU, a read-only memory or ROM, a random access
memory or RAM, an input port IPT, and an output port OPT, and etc.
The signals detected by each of the wheel speed sensors WS1 to WS4,
brake switch BS, front steering angle sensor SSf, yaw rate sensor
YS and lateral acceleration sensor YG are fed to the input port IPT
via respective amplification circuits AMP and then to the central
processing unit CPU. Then, control signals are fed from the output
port OPT to the throttle control apparatus TH and hydraulic braking
pressure control apparatus BC via the respective driving circuits
ACT. In the microcomputer CMP, the read-only memory ROM memorizes a
program corresponding to flowcharts as shown in FIGS. 3A, 3B to
FIG. 6, the central processing unit CPU executes the program while
the ignition switch (not shown) is closed, and the random access
memory RAM temporarily memorizes variable data needed to execute
the program. A plurality of microcomputers may be provided for each
control such as throttle control, or may be provided for performing
various controls, and electrically connected to each other.
[0033] According to the present embodiment as constituted above, a
program routine for the vehicle motion control including the
steering control by braking, anti-skid control and so on is
executed by the electronic controller ECU, as will be described
hereinafter with reference to FIGS. 3A, 3B to FIG. 6. The program
routine starts when an ignition switch (not shown) is turned on. At
the outset, the program for the brake control as shown in FIGS. 3A,
3B provides for initialization of the system at Step 100 to clear
various data. At Step 101, the signals detected by the wheel speed
sensors WS1 to WS4 are read by the electronic controller ECU, and
also read are the signal (steering angle .delta.f) measured by the
front steering angle sensor SSf, the signal (actual yaw rate
.gamma.as) measured by the yaw rate sensor YS, and the signal
(lateral acceleration Gya) measured by the lateral acceleration
sensor YG.
[0034] Then, the program proceeds to Step 102 where the wheel speed
Vw** (** represents one of the wheels FL, FR, RL, RR) of each wheel
is calculated, and differentiated to provide the wheel acceleration
DVw**. At Step 103, the maximum of the wheel speeds Vw** for four
wheels is calculated to provide an estimated vehicle speed Vso on a
gravity center of the vehicle (Vso=MAX[Vw**]), and an estimated
vehicle speed Vso** is calculated for each wheel, respectively, on
the basis of the wheel speed Vw**. The estimated vehicle speed
Vso** may be normalized to reduce the error caused by a difference
between the wheels located on the inside and outside of the curve
while cornering. Furthermore, the estimated vehicle speed Vso is
differentiated to provide an estimated vehicle acceleration DVso.
Next, the program proceeds to Step 104, where the desired yaw rate
.gamma.t is calculated in accordance with the following
equation:
.gamma.t={.delta.f/(N.multidot.L)}.multidot.Vso/(1+Kh.multidot.Vso.sup.2)
[0035] where "Kh" is a stability factor, "N" is a steering gear
ratio, and "L" is a wheelbase of the vehicle. Then, at Step 105, an
actual yaw rate .gamma.a is calculated, as will be described
later.
[0036] At Step 106, also calculated is an actual slip rate Sa** on
the basis of the wheel speed Vw** for each wheel and the estimated
vehicle speed Vso** (or, the estimated and normalized vehicle
speed) which are calculated at Steps 102 and 103, respectively, in
accordance with the following equation:
Sa**=(Vso**-Vw**)/Vso**
[0037] Then, at Step 107, on the basis of the vehicle acceleration
DVso and the actual lateral acceleration Gya measured by the
lateral acceleration sensor YG, the coefficient of friction .mu.
against a road surface can be calculated in accordance with the
following equation:
.mu..apprxeq.(DVso.sup.2+Gya.sup.2).sup.1/2
[0038] In order to detect the coefficient of friction against the
road surface, various methods may be employed other than the above
method, such as a sensor for directly detecting the coefficient of
friction against the road surface.
[0039] The program proceeds to Step 108, where a vehicle slip
angular velocity D.beta. is calculated, and then a vehicle slip
angle .beta. is calculated. This vehicle slip angle .beta. is an
angle which corresponds to a vehicle slip against the vehicle's
path of travel, and which can be estimated as follows. That is, at
the outset, the vehicle slip angular velocity D.beta., which is a
differentiated value d.beta./dt of the vehicle slip angle .beta.,
is calculated at Step 108 in accordance with the following
equation:
D.beta.=Gy/Vso-.gamma.a
[0040] Then, the vehicle slip angle .beta. is calculated in
accordance with the following equation:
.beta.=.intg.(Gy/Vso-.gamma.a)dt
[0041] where "Gy" is the lateral acceleration of the vehicle, "Vso"
is the estimated vehicle speed of the vehicle measured at its
gravity center, and ".gamma.a" is the actual yaw rate. According to
the present embodiment, the actual yaw rate .gamma.a is provided
for calculating the vehicle slip angle .beta. and vehicle slip
angular velocity D.beta..
[0042] Then, the program proceeds to Step 109 where the mode for
the steering control by braking is made to provide a desired slip
rate for use in the steering control by braking, wherein the
braking force applied to each wheel is controlled at Step 118
through the hydraulic pressure servo control which will be
explained later. The steering control by braking is to be added to
each control performed in all the control modes described later.
Then, the program proceeds to Step 110, where it is determined
whether the condition for initiating the anti-skid control is
fulfilled or not. If it is determined that the condition is in the
anti-skid control mode, the program proceeds to Step 111, where a
control mode performing both the steering control by braking and
the anti-skid control start.
[0043] If it is determined at Step 110 that the condition for
initiating the anti-skid control has not been fulfilled, then the
program proceeds to Step 112 where it is determined whether the
condition for initiating the front and rear braking force
distribution control is fulfilled or not. If it is affirmative at
Step 112, the program further proceeds to Step 113 where a control
mode for performing both the steering control by braking and the
braking force distribution control is performed, otherwise it
proceeds to Step 114, where it is determined whether the condition
for initiating the traction control is fulfilled or not. If the
condition for initiating the traction control is fulfilled, the
program proceeds to Step 115 where a control mode for performing
both the steering control by braking and the traction control is
performed. Otherwise, the program proceeds to Step 116 where it is
determined whether the condition for initiating the steering
control by braking is fulfilled or not. If the condition for
initiating the steering control by braking is fulfilled, the
program proceeds to Step 117 where a control mode for performing
only the steering control by braking is set. On the basis of the
control modes as set in the above, the hydraulic pressure servo
control is performed at Step 118, and then the program returns to
Step 101. If it is determined at Step 116 that the condition for
initiating the steering control by braking has not been fulfilled,
the program proceeds to Step 119 where solenoids for all of the
solenoid valves are turned off, and then the program returns to
Step 101. In accordance with the control modes set at Steps 111,
113, 115 and 117, the sub-throttle opening angle for the throttle
control apparatus TH may be adjusted in response to the condition
of the vehicle in motion, so that the output of the engine EG could
be reduced to limit the driving force produced thereby.
[0044] FIG. 4 shows a flowchart for calculating the actual yaw rate
.gamma.a which is to be provided at Step 105 in FIG. 3A for the
operation of the steering control by braking. At the outset, is
calculated at Step 201 a deviation .DELTA..gamma. between the
desired yaw rate .gamma.t calculated at Step 104 and the measured
yaw rate .gamma.as measured by the yaw rate sensor YS (i.e.,
.DELTA..gamma.=.gamma.t-.gamma.as). Then, it is determined at Step
202 whether the vehicle is in its stopped state, or not. That is,
it is determined whether the parking switch PB has been turned on,
and the estimated vehicle speed Vso is zero. If these conditions
are fulfilled, it is determined that the vehicle is in the stopped
state, then the program proceeds to Step 203 where the measured yaw
rate .gamma.as is set at a temporary zero point .gamma.tm, and
further proceeds to Step 204. If the conditions are not fulfilled
at Step 202, the program jumps to Step 204. Although it is selected
as one of the conditions at Step 202 that the estimated vehicle
speed Vso is zero, in the present embodiment, it may be selected as
one of the conditions that the estimated vehicle speed Vso is equal
to or smaller than a predetermined speed.
[0045] At Step 204, it is determined whether the temporary zero
point .gamma.tm is to be actually set for the zero point. Namely,
it is determined whether (1) the temporary zero point .gamma.tm has
been set, (2) an absolute value of the deviation .DELTA..gamma.
between the desired yaw rate .gamma.t and the measured yaw rate
.gamma.as is smaller than a predetermined value .epsilon., and (3)
the estimated vehicle speed Vso exceeds a predetermined speed Kv,
and these conditions (1)-(3) have continued for a predetermined
time period T1 (e.g., 0.5 sec). If all of these conditions have
been fulfilled, the program proceeds to Step 205 where the zero
point .gamma.ao is reneweed by the temporary zero point .gamma.tm,
and then the temporary zero point .gamma.tm is cleared to be zero
at Step 206. Unless the conditions at Step 204 have been fulfilled,
the program proceeds to Step 207, where it is determined whether
the estimated vehicle speed Vso has exceeded the predetermined
speed Kv, or not. If the estimated vehicle speed Vso is lower than
the predetermined speed Kv, the program jumps from 207 to Step 210.
In other words, the Step 205 is not executed, but the previous zero
point which was provided when the vehicle was in the stopped state,
is used, in the case where the absolute value of the deviation
.DELTA..gamma. is equal to or greater than the predetermined value
.epsilon., or the case where such a state that the estimated
vehicle speed Vso exceeds the predetermined speed Kv has continued
for the period less than the predetermined time period T1.
[0046] If it is determined at Step 207 that the estimated vehicle
speed Vso exceeds the predetermined speed Kv, the program further
proceeds to Step 208, where it is determined whether such a state
that the absolute value of the deviation .DELTA..gamma. is greater
than the predetermined value .epsilon. has continued for a
predetermined time period T2 (e.g., 2 seconds). If the result is
negative, the program proceeds to Step 210. However, in the case
where the estimated vehicle speed Vso exceeds the predetermined
speed Kv, and such a state that the absolute value of the deviation
.DELTA..gamma. exceeds the predetermined value .epsilon. has
continued for the predetermined time period T2, then the temporary
zero point .gamma.tm is cleared to be zero at Step 209, and further
proceeds to Step 210. In other words, the zero point will not be
renewed, hereinafter, until the vehicle stops. Accordingly, at Step
210, the zero point .gamma.ao is subtracted from the measured yaw
rate .gamma.as of the yaw rate sensor YS to provide the actual yaw
rate .gamma.a (i.e., .gamma.a=.gamma.as-.gamma.ao). In this case,
the zero point .gamma.ao is renewed at Step 205. In the case where
the result was negative at Step 204, however, the zero point
.gamma.ao, which was renewed previously, i.e., prior to the
previous calculation timing, is used.
[0047] FIG. 5 shows a flowchart for the operation of the steering
control by braking executed at Step 109 in FIG. 3A, which includes
the oversteer restraining control and the understeer restraining
control. Through this flowchart, therefore, the desired slip rates
are set in accordance with the oversteer restraining control and/or
the understeer restraining control. At the outset, it is determined
at Step 301 whether the oversteer restraining control is to be
started or terminated, and also determined at Step 302 whether the
understeer restraining control is to be started or terminated. More
specifically, the determination is made at Step 301 on the basis of
the determination whether it is within a control zone indicated by
hatching on a .beta.-D.beta. plane as shown in FIG. 7. That is, if
the vehicle slip angle .beta. and the vehicle slip angular velocity
D.beta. which are calculated when determining the start or
termination, are fallen within the control zone, the oversteer
restraining control will be started. However, if the vehicle slip
angle .beta. and the vehicle slip angular velocity D.beta. come to
be out of the control zone, the oversteer restraining control will
be controlled as indicated by the arrow in FIG. 7 thereby to be
terminated. Therefore, the boundary between the control zone and
non-control zone (as indicted by two dotted chain line in FIG. 7)
corresponds to the boundary of a starting zone. And, the braking
force applied to each wheel is controlled in such a manner that the
farther they remote from the boundary between the control zone and
non-control zone (two dotted chain line in FIG. 7) toward the
control zone, the more the amount to be controlled will be
provided.
[0048] On the other hand, the determination of the start and
termination is made at Step 302 on the basis of the determination
whether it is within a control zone indicated by hatching in FIG.
8. That is, in accordance with the variation of the actual lateral
acceleration Gya against a desired lateral acceleration Gyt, if
they become out of the desired condition as indicated by one dotted
chain line, and fallen within the control zone, then the understeer
restraining control will be started. If they come to be out of the
zone, the understeer restraining control will be controlled as
indicated by the arrow in FIG. 8 thereby to be terminated.
[0049] Then, the program proceeds to Step 303, where it is
determined whether the oversteer restraining control is to be
performed or not. If the oversteer restraining control is not to be
performed, the program further proceeds to Step 304 where it is
determined whether the understeer restraining control is to be
performed or not. In the case where the understeer restraining
control is not to be performed, the program returns to the main
routine. In the case where it is determined at Step 304 that the
understeer restraining control is to be performed, the program
proceeds to Step 305 where the desired slip rate of each wheel is
set to a desired slip rate which is provided for use in the
understeer restraining control. If it is determined at Step 303
that the oversteer restraining control is to be performed, the
program proceeds to Step 306 where it is determined whether the
understeer restraining control is to be performed or not. In the
case where the understeer restraining control is not to be
performed, the program proceeds to Step 307 where the desired slip
rate of each wheel is set to a desired slip rate which is provided
for use in the oversteer restraining control. In the case where it
is determined at Step 306 that the understeer restraining control
is to be performed, the program proceeds to Step 308 where the
desired slip rate of each wheel is set to a desired slip rate which
is provided for use in both of the oversteer restraining control
and the understeer restraining control.
[0050] With respect to the desired slip rate for use in the
oversteer restraining control set at Step 307, the vehicle slip
angle .beta. and the vehicle slip angular velocity D.beta. are
employed. With respect to the desired slip rate for use in the
understeer restraining control, a difference between the desired
lateral acceleration Gyt and the actual acceleration Gya is
employed. The desired lateral acceleration Gyt is calculated in
accordance with the following equations:
Gyt=.gamma.t.multidot.Vso
[0051] At Step 305, the desired slip rate of a front wheel located
on the outside of the curve of the vehicle's path is set as
"Stufo", the desired slip rate of a front wheel located on the
inside of the curve is set as "Stufi", and the desired slip rate of
a rear wheel located on the inside of the curve is set as "Sturi".
As for the slip rate, "t" indicates a desired value, which is
comparable with a measured actual value indicated by "a". Then, "u"
indicates the understeer restraining control, "f" indicates the
front wheel, "r" indicates the rear wheel, "o" indicates the
outside of the curve, and "i" indicates the inside of the curve,
respectively.
[0052] At Step 307, the desired slip rate of the front wheel
located on the outside of the curve is set as "Stefo", and the
desired slip rate of the rear wheel located on the inside of the
curve is set as "Steri", wherein "e" indicates the oversteer
restraining control. Whereas, at Step 308, the desired slip rate of
the front wheel located on the outside of the curve is set as
"Stefo", the desired slip rate of the front wheel located on the
inside of the curve is set as "Stufi", and the desired slip rate of
the rear wheel located on the inside of the curve is set as
"Sturi". That is, when both of the oversteer restraining control
and the understeer restraining control are performed
simultaneously, the desired slip rate of the front wheel located on
the outside of the curve is set to be the same rate as the desired
slip rate for use in the oversteer restraining control, while the
desired slip rates of the rear wheels are set to be the same rates
as the desired slip rates for use in the understeer restraining
control. In any cases, however, a rear wheel located on the outside
of the curve, i.e., a non-driven wheel of the front drive vehicle
is not to be controlled, because this wheel is employed as a
reference wheel for use in calculation of the estimated vehicle
speed.
[0053] The desired slip rates Stefo for use in the oversteer
restraining control is calculated in accordance with the following
equation:
Stefo=K1.multidot..beta.+K2.multidot.D.beta.
[0054] where K1, K2 are constants which are set so as to provide
the desired slip rate Stefo which is used for increasing the
braking pressure (i.e., increasing the braking force). However, the
desired slip rate Steri of the rear wheel located on the inside of
the curve is set to be zero.
[0055] On the contrary, the desired slip rates Stufo, Sturi for use
in the understeer restraining control are calculated in accordance
with the following equations, respectively:
Stufo=K3.multidot..DELTA.Gy
Sturi=K4.multidot..DELTA.Gy
Stufi=K5.multidot..DELTA.Gy
[0056] where K3 is a constant for providing the desired slip rate
Stufo which is used for increasing the braking pressure (or,
alternatively decreasing the braking pressure), while K4, K5 are
constants for providing the desired slip rate, which are used for
increasing the braking pressure.
[0057] FIG. 6 shows the hydraulic pressure servo control which is
executed at Step 118 in FIG. 3A, and wherein the wheel cylinder
pressure for each wheel is controlled through the slip rate servo
control. At Step 401, the desired slip rates St**, which are set at
Step 305, 307 or 308, are read to provide the desired slip rate for
each wheel of the vehicle. Then, the program proceeds to Step 402
where a slip rate deviation .DELTA.St** is calculated for each
wheel, and further proceeds to Step 403 where a vehicle
acceleration deviation .DELTA.DVso** is calculated. At Step 402,
the difference between the desired slip rate St** and the actual
slip rate Sa** is calculated to provide the slip rate deviation
.DELTA.St** (i.e., .DELTA.St**=St**-Sa**). And, at Step 403, the
difference between the estimated vehicle acceleration DVso on the
center of gravity of the vehicle and the vehicle acceleration DVw**
of a selected wheel is calculated to provide the vehicle
acceleration deviation .DELTA.DVso**. The actual slip rate Sa** and
the vehicle acceleration deviation .DELTA.DVso** may be calculated
in accordance with a specific manner which is determined in
dependence upon the control modes such as the anti-skid control
mode, traction control mode or the like, the explanation of which
will be omitted.
[0058] Then, the program proceeds to Step 404 where a parameter Y**
for providing a hydraulic pressure control in each control mode is
calculated in accordance with the following equation:
Y**=Gs**.multidot..DELTA.St**
[0059] where "Gs**" is a gain, which is provided in response to the
vehicle slip angle .beta. and in accordance with a diagram as shown
by a solid line in FIG. 9. The program further proceeds to Step 405
where another parameter X** is calculated in accordance with the
following equation:
X**=Gd**.multidot..DELTA.DVso**
[0060] where "Gd**" is a gain which is a constant value as shown by
a broken line in FIG. 9. On the basis of the parameters X** and
Y**, a pressure control mode for each wheel is provided at Step
406, in accordance with a control map as shown in FIG. 10. The
control map has a rapid pressure decrease zone, a pulse pressure
decrease zone, a pressure hold zone, a pulse pressure increase
zone, and a rapid pressure increase zone which are provided in
advance as shown in FIG. 10, so that any one of the zones is
selected in accordance with the parameters X** and Y** at Step 406.
In the case where no control mode is performed, no pressure control
mode is provided (i.e., solenoids are off).
[0061] At Step 407, is performed a pressure increase and decrease
compensating control, which is required for smoothing the first
transition and last transition of the hydraulic pressure, when the
presently selected zone is changed from the previously selected
zone at Step 406, e.g., from the pressure increase zone to the
pressure decrease zone, or vice versa. When the zone is changed
from the rapid pressure decrease zone to the pulse pressure
increase zone, for instance, the rapid pressure increase control is
performed for a period which is determined on the basis of a period
during which the rapid pressure decrease mode, which was provided
immediately before the rapid pressure increase control, lasted.
Then, the program proceeds to Step 408, where the solenoid of each
valve (not shown) in the hydraulic pressure control apparatus BC is
energized or de-energized in accordance with the mode determined by
the selected pressure control zone or the pressure increase and
decrease compensating control thereby to control the braking force
applied to each wheel. The structure of the hydraulic pressure
control apparatus BC is the same as the apparatus installed in the
prior vehicle motion control system, and it is not directly related
to the present invention, its explanation will be omitted.
[0062] Then, the program proceeds to Step 409 where a motor for
driving pressure pumps (not shown) is actuated. Although the slip
rate is used for the control in the present embodiment, any value
corresponding to the braking force applied to each wheel, such as
the braking pressure in each wheel brake cylinder, may be employed
as the desired value for the control.
[0063] It should be apparent to one skilled in the art that the
above-described embodiment is merely illustrative of but one of the
many possible specific embodiments of the present invention.
Numerous and various other arrangements can be readily devised by
those skilled in the art without departing from the spirit and
scope of the invention as defined in the following claims.
* * * * *