U.S. patent application number 09/369879 was filed with the patent office on 2001-06-07 for vehicle stability control apparatus and method.
This patent application is currently assigned to FOLEY & LARDNER. Invention is credited to YASUDA, SOTA.
Application Number | 20010002628 09/369879 |
Document ID | / |
Family ID | 16840001 |
Filed Date | 2001-06-07 |
United States Patent
Application |
20010002628 |
Kind Code |
A1 |
YASUDA, SOTA |
June 7, 2001 |
VEHICLE STABILITY CONTROL APPARATUS AND METHOD
Abstract
A vehicle stability apparatus and method with an on-off-switch,
to prevent the driving road wheel from applying excessive braking
force when the traction control apparatus is off. When a selectable
switch is selected off, a control unit does not exert the traction
control to decrease the engine output power to restrain the driving
wheels slip even if driving wheel slip is generating. Then the
control unit exerts the yaw moment control apparatus for optimizing
vehicle stability to control wheel braking force of respective road
wheels, and the control unit compulsory exerts the traction control
during generating wheel slip irrespective of the switch.
Inventors: |
YASUDA, SOTA; (ISEHARA-SHI,
JP) |
Correspondence
Address: |
FOLEY & LARDNER
3000 K STREET NW
SUITE 500
PO BOX 25696
WASHINGTON
DC
200078696
|
Assignee: |
FOLEY & LARDNER
|
Family ID: |
16840001 |
Appl. No.: |
09/369879 |
Filed: |
August 9, 1999 |
Current U.S.
Class: |
180/197 |
Current CPC
Class: |
B62D 37/00 20130101;
B60T 8/175 20130101 |
Class at
Publication: |
180/197 |
International
Class: |
B62D 055/12 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 10, 1998 |
JP |
P10-226110 |
Claims
What is claimed is:
1. A vehicle stability control apparatus which includes an engine
and at least one drive wheel driven by the engine, the apparatus
comprising: a wheel speed sensor to detect a wheel speed of the at
least one driving wheel; an engine power control apparatus to
control the engine output power in response to a first control
signal; a braking force applying apparatus to apply braking force
to at least the driving wheel in response to a second control
signal; a vehicle behavior detector to detect vehicle behavior; a
selectable switch to output an activation signal which places the
engine power control apparatus in active state and an inhibition
signal which places the engine power control apparatus in inactive
state according to a selection by the driver; and a control unit
operatively coupled with said wheel speed sensor, said engine power
control apparatus, said braking force applying apparatus, said
vehicle behavior detector, and selectable switch, wherein said
control unit calculates a vehicle velocity from the wheel speed
detected by the wheel speed sensor; said control unit calculate a
slip of the at least one drive wheel in response to the wheel speed
and the vehicle velocity; said control unit applies the first
control signal to said engine power control apparatus to decrease
the engine output power according to the slip of the at least one
drive wheel when said selectable switch is outputting the
activation signal; said control unit applies the second control
signal to said braking force applying apparatus according to the
vehicle behavior to adjust braking pressure to have the vehicle
generate moment in the stable direction; and said control unit
applies said first control signal to the engine power control
apparatus irrespective of a state of the selectable switch when the
second control signal is applied to said braking force applying
apparatus.
2. A vehicle stability control apparatus as claimed in claim 1,
wherein said braking force applying apparatus comprises a hydraulic
circuit fluidly disposed for applying braking force to the at least
one driving wheel, a source of braking fluid for supplying the
braking fluid to said hydraulic circuit; and an electromagnetic
valve included in said hydraulic for adjusting braking pressure
applied to the at least one driving wheel in response to said
second control signal.
3. A vehicle stability control apparatus as claimed in claim 2,
wherein said vehicle behavior detector comprises a yaw rate sensor
for detecting yaw rate of the vehicle.
4. A vehicle stability control apparatus as claimed in claim 3,
wherein said vehicle stability control apparatus comprises an
angular sensor for detecting angular positioning of steering wheel;
said control unit calculates a desirable yaw rate from the vehicle
velocity and the angular positioning of steering wheel; said
control unit calculates a yaw rate difference from the difference
of the yaw rate and the desirable yaw rate; and said control unit
calculates desirable wheel cylinder pressure according to the yaw
rate difference.
5. A vehicle stability control apparatus as claimed in claim 1,
wherein said control unit calculates a slip quantity of the at
least one driving wheel response to the wheel speed and the vehicle
velocity.
6. A vehicle stability control apparatus as claimed in claim 5,
wherein said control unit calculates the amount of decreasing
engine power according to the slip quantity.
7. A vehicle stability control apparatus as claimed in claim 6,
wherein said engine power control apparatus comprises a second
throttle valve disposed in series to a first throttle valve in an
intake passage for the engine; an actuating system to actuate said
second throttle valve according to the first control signal.
8. A vehicle stability control apparatus as claimed in claim 6,
wherein said engine power control apparatus comprises a fuel cutoff
control apparatus for cutting off a fuel supply to a part of
cylinders of the engine and controlling a fuel cut cylinder number
in accordance with the slip quantity.
9. A vehicle stability control apparatus as claimed in claim 6,
wherein the control unit continuously applies said first control
signal until the slip quantity becomes under a predetermined value
when the control unit applies irrespective of a state of the
selectable switch.
10. A vehicle stability control apparatus which includes an engine
and at least one driving wheel driven by the engine, the apparatus
comprising: a slip sensor for detecting a slip of the driving
wheel; a traction control apparatus for decreasing the engine
output power according to the detected slip of the driving wheel; a
selectable switch for switching the traction control apparatus on
and off; a vehicle behavior detector for detecting vehicle
behavior; a braking force applying apparatus for applying braking
force to at least the driving wheel in response to a control
signal; and a control unit operatively coupled with the vehicle
behavior detection apparatus, wherein said control unit applies a
control signal to adjust vehicle behavior to a determined value,
and said control unit activates the traction control apparatus ON
irrespective of a state of the selectable switch based on the
control signal.
11. A vehicle stability control apparatus as claimed in claim 10,
wherein said braking force applying apparatus comprises a hydraulic
circuit fluidly disposed for applying braking force to the at least
one driving wheel, a source of braking fluid for supplying the
braking fluid to said hydraulic circuit; and an electromagnetic
valve included in said hydraulic for adjusting braking pressure
applied to the at least one driving wheel in response to said
second control signal.
12. A vehicle stability control apparatus as claimed in claim 10,
wherein said control unit calculates a slip quantity of the at
least one driving wheel response to the wheel speed and the vehicle
velocity.
13. A vehicle stability control apparatus as claimed in claim 11,
wherein said control unit calculates the amount of decreasing
engine power according to the slip quantity.
14. A vehicle stability control apparatus as claimed in claim 13,
wherein said engine power control apparatus comprises a second
throttle valve disposed in series to a first throttle valve in an
intake passage for the engine; a actuating system for actuate said
second throttle valve according to the first control signal.
15. A vehicle stability control apparatus as claimed in claim 13,
wherein said engine power control apparatus comprises a fuel cutoff
control apparatus for cutting off a fuel supply to a part of
cylinders of the engine and controlling a fuel cut cylinder number
in accordance with the slip quantity.
16. A vehicle stability control apparatus as claimed in claim 13,
wherein the control unit continuously applies said first control
signal until the slip quantity becomes under a predetermined value
when the control unit applies irrespective of a state of the
selectable switch.
17. A vehicle stability control apparatus which includes an engine
and at least one driving wheel driven by the engine, the apparatus
comprising: a slip sensor apparatus for detecting a slip of the
driving wheel; a traction control apparatus for decreasing the
engine output power according to the detected slip of the driving
wheel; a selectable switch for switching the traction control
apparatus on and off; a vehicle behavior detection apparatus for
detecting vehicle behavior; a braking force applying apparatus for
applying braking force to at least the driving wheel in response to
a control signal; and a control unit operatively coupled with the
vehicle behavior detection apparatus, wherein said control unit
applies a control signal to adjust vehicle behavior to a determined
value, and said control unit setting said selectable switch ON when
adjusting the vehicle behavior based on the control signal.
18. A vehicle stability control apparatus which includes an engine
and at least one driving wheel driven by the engine, the apparatus
comprising: means for sensing a wheel speed of the at least the
driving wheel; means for calculating a vehicle velocity from the
wheel speed sensing means; means for calculating a slip quantity of
the at least one driving wheel; traction control means for
decreasing an engine output power according to the calculated slip
quantity of the at least one driving wheel; means for switching
said traction control means either on or off; means for detecting a
vehicle behavior; means for controlling a yaw moment of the vehicle
by applying a braking force to at least the driving wheel in
response to the detected vehicle behavior; and means for turning
said traction control means either on or off irrespective of the
switching means when the braking force is applied.
19. A vehicle stability control method provided for an engine and
at least one driving wheel driven by the engine, the comprising:
(a) detecting a slip of the driving wheel; (b) decreasing, with a
traction control apparatus, the engine output power according to
the detected slip of the driving wheel; (c) switching, with a
switch, the traction control apparatus on and off; (d) detecting,
with a vehicle behavior detection apparatus, vehicle behavior; (e)
applying, braking force to at least the driving wheel in response
to a control signal; (f) applying, a control signal to adjust
vehicle behavior to a determined value; (g) adjusting, the vehicle
behavior to the determined value; and (h) setting, the traction
control apparatus ON irrespective of a state of the selectable
switch based on the control signal.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The entire contents of Japanese application Tokugan Hei
10-226110, with a filing date of Aug. 10, 1998 in Japan, are hereby
incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] This invention relates to a vehicle stability control
apparatus which has a yaw moment control apparatus for optimizing
vehicle stability to control wheel braking force of respective road
wheels and has a traction control apparatus arranged to restrain a
drive wheel slip at least by reducing engine torque.
[0003] As one example, Japanese Patent Kokai No. 9-286261 discloses
a traction control apparatus that decreases the engine output power
to restrain a driving wheel slip, by closing a second throttle
valve operated by a DC motor and provided in series to a first
accelerator connected with an accelerator pedal so that the opening
degree of the first throttle valve is determined by the depression
degree of the accelerator pedal, and by cutting off the fuel supply
to one or more cylinders of the engine. Furthermore, if the driving
wheel slip cannot be restrained by decreasing the engine output
power, the traction control apparatus applies the brakes to the
driving wheel.
[0004] This conventional apparatus is intended to decrease the
engine output power to restrain the drive wheel slip in the first
place, but if the wheel slip is not restrained by it, then the
traction control apparatus applies the brakes to the drive
wheel.
[0005] Such conventional traction control apparatus can have a
selector switch to turn it on or off depending on the situation in
which a traction wheel is stuck in a muddy place or the like.
[0006] As another example, Japanese Patent Kokai No. 9-2316
discloses a yaw moment control apparatus which makes the vehicle's
behavior more desirable by operating the braking force on the
inside brake of the vehicle or on the outside brake of the vehicle
during cornering.
BRIEF SUMMARY OF THE INVENTION
[0007] It is an object of the present invention to provide a
vehicle stability control apparatus and method which has a yaw
moment control apparatus and has a traction control apparatus,
which can prevent the traction road wheel from applying excessive
braking force when the traction control apparatus is switched
off.
[0008] According to one aspect of the present invention, there is
provided a vehicle stability control apparatus which includes an
engine and at least one drive wheel driven by the engine, the
apparatus comprising: a wheel speed sensor to detect a wheel speed
of the at least one driving wheel; an engine power control
apparatus to control the engine output power in response to a first
control signal; a braking force applying apparatus to apply braking
force to at least the driving wheel in response to a second control
signal; a vehicle behavior detector to detect vehicle behavior; a
selectable switch to output an activation signal which places the
engine power control apparatus in active state and an inhibition
signal which place the engine power control apparatus in inactive
state according to the selection by the driver; and a control unit
operatively coupled with said wheel speed sensor, said engine power
control apparatus, said braking force applying apparatus, said
vehicle behavior detector, and selectable switch, wherein said
control unit calculates a vehicle velocity from the wheel speed
detected by the wheel speed sensor; the control unit calculates a
slip of the at least one drive wheel in response to the wheel speed
and the vehicle velocity; said control unit applies first control
signal to said engine power control apparatus to decrease the
engine output power according to the slip of the at least one drive
wheel when said selectable switch is outputting the activation
signal; said control unit applies the second control signal to said
braking force applying apparatus to according to the vehicle
behavior adjust the braking pressure to have the vehicle generate a
moment in the stable direction; and said control unit applies said
first control signal to the engine power control apparatus
irrespective of a state of the selectable switch when the second
control signal is applied to said the braking force applying a
apparatus. According to the invention, the vehicle stability
apparatus and method with an on-off-switch prevent the driving road
wheel from applying excessive braking force when the traction
control apparatus is off.
[0009] There is also provided a vehicle stability control apparatus
which includes an engine and at least one driving wheel driven by
the engine, the apparatus comprising: a slip sensor apparatus for
detecting a slip of the driving wheel; a traction control apparatus
for decreasing the engine output power according to the detected
slip of the driving wheel; a selectable switch for switching the
traction control apparatus on and off; a vehicle behavior detection
apparatus for detecting vehicle behavior; a braking force applying
apparatus for applying braking force to at least the driving wheel
in response to a control signal; and a control unit operatively
coupled with the vehicle behavior detection apparatus, wherein said
control unit applies a control signal to adjust vehicle behavior to
a determined value, and said control unit setting the traction
control apparatus ON irrespective of a state of the selectable
switch based on the control signal.
[0010] There is also provided a vehicle stability control apparatus
which includes an engine and at least one driving wheel driven by
the engine, the apparatus comprising: a slip sensor apparatus for
detecting a slip of the driving wheel; a traction control apparatus
for decreasing the engine output power according to the detected
slip of the driving wheel; a selectable switch for switching the
traction control apparatus on and off; a vehicle behavior detection
apparatus for detecting vehicle behavior; a braking force applying
apparatus for applying braking force to at least the driving wheel
in response to a control signal; and a control unit operatively
coupled with the vehicle behavior detection apparatus, wherein said
control unit applies a control signal to adjust vehicle behavior to
a determined value, and said control unit setting said selectable
switch ON when adjusting the vehicle behavior based on the control
signal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a schematic view showing a vehicle equipped with a
traction control apparatus and a yaw moment control apparatus
according to an embodiment of the present invention;
[0012] FIG. 2 is a schematic diagram showing one embodiment of a
braking force control apparatus according to the present
invention;
[0013] FIG. 3 is a flow chart illustrating the programming of the
digital computer as it is used for braking force control;
[0014] FIG. 4A is a time chart showing the speed of a drive wheel
of the vehicle according to an embodiment of the present
invention;
[0015] FIG. 4B is a time chart showing the movement of the second
throttle valve;
[0016] FIG. 4C is a time chart showing the braking pressure
(braking force) of the outside brake of the vehicle during
cornering;
[0017] FIG. 5 is a flow chart illustrating the programming of the
digital computer as it is used for braking force control of another
preferred embodiment of the present invention;
[0018] FIG. 6 is a schematic view showing a vehicle equipped with a
traction control apparatus and a yaw moment control apparatus
according to another embodiment of the present invention; and
[0019] FIG. 7 is a schematic view showing a vehicle equipped with a
traction control apparatus and a yaw moment control apparatus
according to another embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] FIG. 1 shows component parts employed in illustrated
embodiments of the present invention.
[0021] This invention will be described in connection with a
rear-drive type automotive vehicle supported on a pair of front
road wheels and a pair of rear road wheels. Front wheels 1FL and
1FR are provided as non-driving wheels, and rear wheels 1RL and 1RR
are provided as driving wheels, and a drive is transmitted from an
engine 32 to the rear road wheels 1RL, 1RR through an automatic
transmission 33, a propeller shaft 34 and a differential gear
35.
[0022] The front road wheels 1FL, 1FR and the rear road wheels 1RL,
1RR are associated with respective disc brakes 7 which are placed
for application of brakes to the respective wheels. These disc
brakes 7 generate braking force by braking pressure provided from
and controlled by the braking force control apparatus 10.
[0023] Wheel speed sensors 13FL, 13FR are provided for off and
right front wheels 1FL, 1FR. Wheel sensors 13RL, 13RR are provided
for left and right rear wheels 1RL, 1RR. A yaw rate sensor 44 is
provided to detect the yaw rate of the vehicle. Angular sensor 46
is provided to detect angular positioning .theta. of steering
wheel.
[0024] A selectable switch 48, which selects between operating
conditions and non-operating conditions of the traction control, is
installed near the driver's seat. This selectable switch 48 outputs
a switch signal S.sub.OFF when the driver selects condition which
activates the traction control, the switch signal S.sub.OFF is
"ON", when the driver selects condition which does not activate the
traction control, S.sub.OFF is "OFF".
[0025] A stability control unit 29 receives wheel speed signals
from the wheel speed sensor 13FL.about.13RR, detects an occurrence
of slip in accordance with a wheel speed difference between a
driving wheel speed and a non-drive wheel speed, and produces
driving force reduction request signals when the slip occurs. A
driving force reduction request signals is sent to an actuating
system 39 for actuating the second throttle valve 52.
[0026] The actuating system 39 is associated with an engine 32 for
controlling the power of the engine. The first throttle valve 51 is
connected with an accelerator pedal so that the opening degree of
the first throttle valve 51 is determined by the depression degree
of the accelerator pedal. A second throttle valve 52 is further
provided in the intake passage 53 of the engine. The second
throttle valve 52 of this example is disposed on the upstream side
of the first throttle valve. The second throttle valve 52 is a
normally open-valve.
[0027] FIG. 2 shows a schematic diagram showing one embodiment of a
braking force control apparatus according to the embodiment of the
present invention.
[0028] A brake pedal 11 is operated by the operator and connected
to a master-cylinder 24 that has two cells. One of the cells is
connected to wheel cylinders 12FL, 12FR through a conduit to
provide an operator's demand for braking pressure. The other one is
connected with wheel cylinders 12RL, 12RR through a conduit to
provide an operator's demand for braking pressure. A motor 13 is
driven on a command from the control unit to operate front and rear
road wheel pumps 14F, 14R so as to force the braking fluid to
respective accumulators 15F, 15R.
[0029] The front road wheel pump 14F has an exhaust or discharge
port connected through a conduit 16F to pressure increasing valves
18FL, 18FR and hence to the respective wheel cylinders 12FL, 12FR.
A check valve 20FL is connected in parallel with the pressure
increasing valve 18FL to permit flow only toward the 16F while
preventing back flow. A check valve 20FR is connected in parallel
with the pressure increasing valve 18FR to permit flow only towards
the 16F while preventing back flow.
[0030] The pressure increasing valves 18FL and 18FR, which are
substantially the same in structure, are in the form of solenoid
valves operable, on a control signal fed thereto from the control
unit 29, to occupy one of two positions. The first or open
position, illustrated in FIG. 2, is occupied in the absence of the
control signal to increase the braking fluid pressure P.sub.FL,
P.sub.FR furnished to the corresponding one of the wheel cylinders
12FL and 12FR. The second or closed position is encountered in the
presence of the control signal to hold the braking fluid pressure
in the corresponding wheel cylinder. The front road wheel pump 14F
has an intake or suction port connected through a conduit 17F to
pressure reducing valves 19FL and 19FR and hence to the respective
wheel cylinders 12FL and 12FR.
[0031] The pressure reducing valves 19FL and 19FR, which are
substantially the same in structure, are in the form of solenoid
valves operable, on a control signal fed thereto from the control
unit 29, to occupy one of two positions. The first or closed
position, illustrated in FIG. 2, is occupied in the absence of the
control signal to hold the braking fluid pressure P.sub.FL,
P.sub.FR in the corresponding one of the wheel cylinders 12FL and
12FR. The second or open position is encountered in the presence of
the control signal to reduce the braking fluid pressure in the
corresponding wheel cylinder.
[0032] Similarly, the rear road wheel pump 14R has an exhaust or
discharge port connected through a conduit 16R to pressure
increasing valves 18RL and 18RR and hence to the respective wheel
cylinders 12RL and 12RR. A check valve 20RL is connected in
parallel with the pressure increasing valve 18RL to permit flow
only towards the 16F while preventing back flow. A check valve 20RR
is connected in parallel with the pressure increasing in parallel
with the pressure increasing valve 18RR to permit flow only towards
the 16R while preventing back flow.
[0033] The pressure increasing valves 18RL and 18RR, which are
substantially the same in structure, are in the form of solenoid
valves operable, on a control signal fed thereto from the control
unit 29, to occupy one of two positions. The first or open
position, illustrated in FIG. 2, is occupied in the absence of the
control signal to increase the braking fluid pressure P.sub.RL,
P.sub.RR furnished to the corresponding one of the wheel cylinders
12RL and 12RR. The second or closed position is encountered in the
presence of the control signal to hold the braking fluid pressure
in the corresponding wheel cylinder.
[0034] The rear road wheel pump 14R has an intake or suction port
connected through a conduit 17R to pressure reducing valves 19RL
and 19RR and hence to the respective wheel cylinders 12RL and 12RR.
The pressure reducing valves 19RL and 19RR, which are substantially
the same in structure, are in the form of solenoid valves operable,
on a control signal fed thereto from the control unit 29, to occupy
one of two positions.
[0035] The first or closed position, illustrated in FIG. 2, is
occupied in the absence of the control signal to hold the braking
fluid pressure PFL, PRR in the corresponding one of the wheel
cylinders 12RL and 12RR. The second or open position is encountered
in the presence of the control signal to reduce the braking fluid
pressure in the corresponding wheel cylinder. A reservoir 21R is
connected to the conduit 17R. The reservoir 21R acts as an
accumulator for accumulating the braking fluid pressure discharged
through the pressure reducing valves 29FL and 29FR. A reservoir 21R
is connected to the conduit 17R. The reservoir 21R acts as an
accumulator for accumulating the braking fluid pressure discharged
through the pressure reducing valves 19RL and 19RR.
[0036] A cutting valve 22F is installed between the master-cylinder
24 and the conduit 16F, and a cutting valve 24F is installed
between the accumulator 15F and the conduit 16F. Similarly a
cutting valve 22R is installed between the master-cylinder 24 and
the conduit 16R, and a cutting valve 24R is installed between the
accumulator 15R and the conduit 16R.
[0037] The cutting valves 22F, 22R, which are substantially the
same in structure, are in the form of solenoid valves operable, on
a control signal fed thereto from the control unit 29, to occupy
one of two positions. The first or open position, illustrated in
FIG. 2, is occupied in the absence of the control signal to let the
braking fluid flow. The second or closed position is encountered in
the presence of the control signal to cut off the conduits. The
cutting valves 24F, 24R, which are substantially the same in
structure, are in the form of solenoid valves operable, on a
control signal fed thereto from the control unit 29, to occupy one
of two positions. The first or closed position, illustrated in FIG.
2, is occupied in the absence of the control signal to keep the
pressure inside of the accumulators high. The second or opened
position is encountered in the presence of the control signal to
supply the high pressure braking fluid for braking pressure.
[0038] The control signals applied to the respective solenoid
valves 18FL, 18FR, 18RL, 18RR, 19FL, 19FR, 19RL, 19RR, 22F, 22R,
24F and 24R are repetitively determined from calculations performed
by the control unit 29.
[0039] FIG. 3 is a flow chart illustrating the programming of the
digital computer as it is used for the vehicle stability control
apparatus that combines the traction control unit and the braking
force control unit.
[0040] At the step S1, a determination is made as to whether or not
the switch S.sub.OF is OFF. If the answer to this question is
"yes", i.e. switch S.sub.OFF is OFF, the control unit proceeds to
the step S2.
[0041] At the step S2, the control unit makes that flag FS is "0",
and then proceeds to the step S4.
[0042] Otherwise, if the answer to this question is "no" at the
step S1, i.e. switch S.sub.OFF is ON, the control unit proceeds to
the step S3.
[0043] At the step S3, the control unit makes that flag FS is "1",
and then proceeds to the step S4.
[0044] At the step S4, wheels speed V.sub.WFL, V.sub.WFR,
V.sub.WRL, V.sub.WRR yaw rate .psi., and angular positioning
.theta. of steering wheel are read into the computer memory.
[0045] At the step S5, vehicle speed Vc is calculated from wheels
speed V.sub.WFL, V.sub.WFR, V.sub.WRL and V.sub.WRR by calculating
the average of V.sub.WFL, V.sub.WFR which are speeds of non-driving
wheels while the vehicle is not braked, or by calculating selecting
the highest speed of all of the wheels while the vehicle is
braked.
[0046] At the step S6, slip quantity S of the driving wheels is
calculated as shown in equation (1)
S=(V.sub.WFL+V.sub.WFR-V.sub.WRL-V.sub.WRR)/2 (1)
[0047] At the step S7, desirable yaw rate is calculated by the
following equation (2) and equation (3) from the yaw rate .psi.,
and angular .theta. of steering wheel respectively.
.psi.*=Vc/R (2)
R=Ks L/tan (.theta./N) (3)
[0048] where R is the radius of the cornering, L is the gear ratio
of steering and Ks is the stability factor. Stability factor Ks is
a coefficient that corresponds to a vehicle's driving stability
during cornering. Generally, a vehicle develops a tendency to
understeer as the stability factor is greater.
[0049] At the step S8, the yaw rate difference .DELTA..psi. is
calculated by subtracting the yaw rate from a desirable yaw
rate.
[0050] At the step S9, the traction control unit compares the
absolute value .vertline..DELTA..psi..vertline. of the yaw rate
difference with a predetermined yaw rate threshold .psi.TH. If
.vertline..DELTA..psi..vertl- ine..ltoreq..psi.TH, then the control
unit judges that the yaw rate difference is so small that the
vehicle does not need to be exerted yaw moment control, and
proceeds to the step S10.
[0051] At the step S10, the control unit makes that flag FY is "0",
and then proceeds to the step S13.
[0052] At the step S9, if
.vertline..DELTA..psi..vertline.>.psi.TH, then the control unit
judges that the yaw rate difference is so great that the vehicle
should be exerted yaw moment control, and proceeds to the step
S11.
[0053] At the step S11, the control unit makes that flag FY is "1",
and then proceeds to the step S12.
[0054] At the step S12, the control unit calculates a desirable
wheel cylinder pressure P.sub.WC*.sub.FL.about.P.sub.WC*.sub.RR of
the respective wheel cylinders according to the yaw rate difference
.DELTA..psi.. While the control unit drives the motor 13 to operate
front and rear road wheel pumps 14F, 14R and changes the position
of the cutting valve 22F from opened position to closed position.
Similarly the cutting valves 22R, 24F and 24R are changed from an
opened position to a closed position. Furthermore the pressure
increasing valves 18FL, 18FR, 18RL and 18RR are changed from the
opened position to the closed position. Consequently the pressure
inside of the conduits 16F, 16R is kept high pressure for supplying
the braking pressure to wheel cylinders. The control unit 29
outputs the increase and decrease signals to increase or decrease
the wheels cylinder pressure according to the difference of
desirable wheel cylinder and the braking fluid pressure in the
corresponding wheel cylinder. At the step S13, the control unit
judges whether or not the slip quantity S calculated at the step S6
is greater than a predetermined slip quantity threshold STH. If
S.ltoreq.STH, then the control unit judges that the slip quantity
is so small that the vehicle does not need to be exerted traction
control, and terminates this routine. If S>STH, then the a
predetermined slip quantity threshold STH judges that the slip
quantity is so great that the vehicle should be exerted traction
control, and proceeds to the step S14.
[0055] At the step S14, the control unit judges whether or not the
switch flag FS is set as "1". If switch flag FS is set to "1", the
traction control proceeds to the step S15.
[0056] At the step S15, the control unit calculates a deviation
.epsilon. of the calculated actual slip quantity S from a a
predetermined slip quantity threshold STH for optimum driving
performance (.epsilon.=S-STH), and further calculates a desired
second throttle valve closed degree T from the deviation .epsilon.
according to a predetermined control law. In this example, the
desired second throttle valve closed degree TH is determined
according to a PID control law, and given by the following
equation;
TH=KP.multidot..epsilon.+KI.multidot..intg..epsilon.dt+KD.multidot.d.epsil-
on./dt (4)
[0057] Where KP is the proportional gain of the proportional
control action, KI is an integral gain of the integral control
action, and KD is a derivative gain of the derivative control
action.
[0058] At the step S15, if the switch flag FS is set to "1", the
control proceeds to the step S16.
[0059] At the step S16, the control unit judges whether or not the
switch flag FY is set as "1". If the switch flag FS is set as "1",
the control proceeds to the above-mentioned step S15, and if the
switch flag FY is set as "0", the control terminates this
routine.
[0060] In this example, the steps S7.about.S12 correspond to the
yaw moment control means, the steps S6.about.S15 correspond to the
traction control unit, and the steps S14.about.S16 correspond to
the compulsion exert unit.
[0061] For example, when driving straight ahead on a high
coefficient of friction road like a dry-paved road with the switch
signal S.sub.OFF="ON" to activate the traction control, wheel slip
does not generate on the rear wheels 1RL, 1RR.
[0062] Therefore, slip quantity S calculated at the step S6 becomes
nearly zero and the desirable yaw rate calculated at the step S7
becomes nearly zero.
[0063] On this condition, yaw rate .psi. sensed at the yaw rate
sensor 16 also becomes nearly zero. Therefore, the yaw rate
difference .DELTA..psi. calculated at the step S8 becomes nearly
zero and is less than predetermined yaw rate threshold .psi.TH. The
control unit judges that the yaw moment control is unnecessary for
the vehicle and does not exert the yaw moment control at the step
S12. The control unit judges that the traction control is
unnecessary for the vehicle and terminates without exerting the
traction control at the S15 because the slip quantity is nearly
zero and is less than the slip quantity threshold STH.
[0064] For example, after this condition, the vehicle is regarded
as turning in a right direction while accelerating, with wheel
slip, and over steering.
[0065] Yaw rate .psi. becomes larger than desirable yaw rate
.psi.*, and the absolute value .vertline..DELTA..psi..vertline. of
the yaw rate difference exceeds a predetermined yaw rate threshold
.psi.TH.
[0066] Accordingly, the traction control unit proceeds from the
step S9 to the step S11, makes that flag FY is "1", and then
proceeds to the step S12.
[0067] At the step S12, the control unit calculates a desirable
wheel cylinder pressure P.sub.WC*.sub.FL.about.P.sub.WC*.sub.RR of
the respective wheel cylinders according to the yaw rate difference
.DELTA..psi.. While the control unit drives the motor 13 to operate
the front and rear road wheel pumps 14F, 14R and changes the
position of the cutting valve 22F from opened position to closed
position. Similarly the cutting valves 22R, 24F and 24R are changed
from opened position to closed position. Furthermore, the pressure
increasing valves 18FL, 18FR, 18RL and 18RR are changed from opened
position to closed position. Consequently the pressure inside of
the conduits 16F, 16R is kept high for supplying the braking
pressure to wheel cylinders. The control unit 29 outputs the
increase and decrease signals to the pressure increasing valves
18FL, 18FR, 18RL and 18RR, and the pressure decreasing valves 19FL,
19FR, 19RL and 19RR to increase or decrease the wheels cylinder
pressure according to the difference of desirable wheel cylinder
and the braking fluid pressure in the corresponding wheel
cylinder.
[0068] The braking force produced on the outside wheel at cornering
and increased according to the pressure of the wheel cylinder of
the disc brake restrains the vehicle's over steer tendency and
ensures the vehicle stability.
[0069] On the other hand, when rear wheels 1RL, 1RR are slipping,
the slip quantity S is larger than slip quantity threshold STH, so
the traction control unit proceeds from the step S13 to the step
S14. Thereafter the traction control unit proceeds to the step S15
because the switch flag FS is set to "1". At the step S15, the
control unit calculates the desirable engine torque to restrain the
drive wheel slip, and outputs the second throttle valve open degree
indicating signal TH to the engine power control module 9.
[0070] Next, when the driver turns the selectable switch 48 and the
switch signal S.sub.OFF="OFF" is outputted to be inactivate the
traction control, the driving wheel slip is not restrained by a
decrease in the engine output power. As described in connection
with the illustrated embodiments, however, when the flow chart
showed in the FIG. 3 is executed, the switch flag FS is set as "0"
at the step S2. The yaw moment control is executed likewise at the
step S12, and the control unit calculates a desirable wheel
cylinder pressure P.sub.WC*.sub.FL.about.P.s- ub.WC*.sub.RR of the
respective wheel cylinders according to the yaw rate difference
.DELTA..psi., and outputs the increase and decrease signals to the
braking force control apparatus to increase or decrease the wheels
cylinder pressure according to the difference of desirable wheel
cylinder and the braking fluid pressure in the corresponding wheel
cylinder.
[0071] On the other hand, the traction control unit proceeds from
the step S13 to the step S14 because the slip quantity S is larger
than slip quantity threshold STH, the control unit proceeds from
the step S14 to the step S16 because the switch flag FS is reset to
"0", and the control unit forcibly proceeds from the step S16 to
the step S15 because the flag FY is set to "1".
[0072] Therefore, the drive wheel slip is restrained by the
traction control according to slip quantity S, and at the step S12
the control unit exerts necessary braking force on the traction
road wheel so as to set the vehicle's behavior with a desirable
behavior.
[0073] When the yaw moment apparatus is exerted with the traction
control apparatus not being under operating conditions by
selectable switch 48, the second throttle valve is kept fully open
as described with a broken line in FIG. 4b in spite of generating
wheel slip at a point of time t1 as described with a broken line in
FIG. 4a.
[0074] Because wheel slip is increased without restraint by the
traction control, the control unit must apply excessive braking
force to accommodate the amount of the engine output power, which
should be decreased by the traction control apparatus as described
by a broken line in FIG. 4c.
[0075] According to the present invention, even if the wheel slip
generates at a point of time t1, the second throttle valve is
closed until nearly zero as described a solid line in FIG. 4b, and
as a consequence of decreased engine power, the wheel slip is
restrained as described in FIG. 4a. As a consequence, the control
apparatus only has to apply the least breaking force on the driving
wheels as described in FIG. 4c.
[0076] Furthermore, the control apparatus has an advantage of
applying the least breaking force on the disc brake of driving
wheels and of improving the durability of the disc brakes.
[0077] If the absolute value .vertline..DELTA..psi..vertline. of
the yaw rate difference .DELTA..psi. becomes less than the
predetermined yaw rate threshold .psi.TH according to the yaw
moment control, the traction control proceeds from the step S9 to
the step S10 and flag FY is reset to "0". As the traction control
unit terminates this routine without proceeding to the step S15
even if the traction control is exerted, the traction control is
not under operating conditions, and the control unit can stop the
undesirable traction control of the driver as soon as possible.
[0078] FIG. 5 shows a second embodiment of the present invention.
In this embodiment, the control unit judges whether the traction
control is being exerted or not at the moment the yaw moment
control is finished after forcefully exerting traction control
during the exerting of the yaw moment control, and if the traction
control is exerted, the control unit continuously exerts the
traction control until wheel slip has been restrained.
[0079] This embodiment is substantially similar to the first
embodiment of FIG. 3 except the addition of the steps S21, S22 and
S23. That is, the control unit proceeds from the step S16 to the
step S21 when the flag FY is set as "1" at the step S16. At the
step S21, the control unit sets the flag FT to "1", which shows
that the control unit forcefully starts the traction control, and
proceeds to the step S15. When the flag FY is set as "0" at the
step S16, the control unit proceeds to the step S22 and judges
whether or not the flag FT is set to "1". If the flag FT is set to
"1", the control unit proceeds to the step S15, and if the flag FT
is set to "0", the control unit terminates this routine. And when
the result of the step S13 is S.ltoreq.STH, the control unit resets
the flag to "0", and terminates this routine.
[0080] In this embodiment, when the vehicle is regarded as turning
in a right direction while accelerating, incurring wheel slip, and
becoming in over steer with switch off as the above-mentioned
embodiment, the control unit sets the flag FY to "1" at the step
S11 and exerts the yaw rate control. At the step S16 through the
steps S13, S14, the control unit proceeds to the step S21 because
the flag FY is set to "1". At the step S21, the control unit
proceed to the step S15 and exerts the traction control after sets
the flag FT is set to "1".
[0081] After that, the control unit proceeds from the step S9 to
the step S10 according to the convergence of yaw rate difference
.DELTA..psi. and resets the flag FY to "0". If wheel slip is
generating on the rear wheels which are the driving wheels, the
control unit proceeds to the step S16 through the steps S13, S14,
and proceeds to the step S22 because the flag FY is set to "0". At
the step S22, the control unit proceeds to the step S15 because the
flag FT is set to "1", and exerts the yaw moment control.
[0082] After that, wheel slip quantity S is under slip quantity
threshold STH due to the convergence of wheel slip, and the control
unit proceeds from the step S13 to the step S23. At the step S23,
the control unit resets the flag to "0" and terminates the routine
without proceeding to the step S15, and the traction control is
finished.
[0083] When wheel slip generates on the rear wheels which are the
driving wheels on the condition such as acceleration of the vehicle
or low friction road like an icy road, a rain-dampened road or the
like, the control unit proceeds to the step S16 through the steps
S13, S14. As the flag FY is set to "0" at the step S16, the control
unit proceeds to the step S22, and as the flag FT is also set to
"0", the control unit terminates the routine without proceeding to
the step S15. So the traction control is not exerted as the drivers
intend.
[0084] Otherwise, when the yaw rate control is exerting, the
control proceeds from the step S13 to the step S23, and the
traction control is terminated as the flag is reset to "0".
[0085] In this embodiment, when the traction control is
continuously being exerted as non-convergence of wheel slip when
the yaw rate control is terminated, the control unit returns from
an exerting condition to a non-exerting condition until the
traction control is terminated. Because the traction control is
stopped after the vehicle behavior stabilizes, this embodiment can
let the vehicle stability improve more than terminating the
traction control while the wheel slip is generating.
[0086] Referring to FIG. 6, there is shown a third embodiment of
the present invention. This embodiment is substantially similar to
the first embodiment of FIG. 1 except a traction control unit and a
yaw moment control unit 69 are respectively installed.
[0087] The yaw moment control unit 69 receives wheel speed signals
from the wheel speed sensor 13FL.about.13RR, yaw rate from the yaw
rate sensor 44 and angular positioning of steering wheel from the
angular sensor 46. The yaw moment control unit 69 calculates a
desirable wheel cylinder pressure in the same way explained in the
first embodiment, and outputs increase and decrease signals to the
braking force control apparatus.
[0088] The traction control unit 49 receives wheel speed signals
from the wheel speed sensor 13FL.about.13RR and ON-OFF signal from
the selectable switch. The traction control unit 49 calculates the
desirable engine torque to restrain the driving wheel slip, and
only if the traction control unit judges that the selectable switch
is ON, outputs the driving force reduction request signals to an
engine control module 59.
[0089] An engine control module 59 receives driving force reduction
request signals from the traction control unit, and performs a fuel
cutoff control so that fuel supply is cut off to a predetermined
number of engine cylinders determined in accordance with a required
reduction of the vehicle driving torque. The engine control module
59 can perform the fuel cutoff control by stopping the output of
the fuel injection pulse signal or signals to one or more engine
cylinders.
[0090] The yaw moment control unit 69 also outputs a signal whether
it is outputting the increase and decrease signals to the braking
force control apparatus or not to the traction control unit. If the
yaw moment control unit 69 outputs the signal to the traction
control unit, the traction control unit 49, outputs the driving
force reduction request signals to an engine control module 59
according to the calculated desirable engine torque irrespective of
selectable switch.
[0091] According to the present invention, when the yaw moment
control is exerting, the engine control module can perform a fuel
cutoff control so that fuel supply is cut off to a predetermined
number of engine cylinders determined in accordance with a required
reduction of the vehicle driving torque even if the selectable
switch is OFF. As a consequence, the control apparatus only has to
apply the least breaking force on the driving wheels.
[0092] Referring to FIG. 7, there is shown a fourth embodiment of
the present invention. This embodiment is substantially similar to
the first embodiment of FIG. 6 except a yaw moment control unit is
69 connected to the selectable switch 48. The yaw moment control
unit 69 compulsory sets the selectable switch as ON when it is
exerting the yaw moment control.
[0093] According to the present invention, when the yaw moment
control 69 is exerting, the engine control module can perform a
fuel cutoff control so that fuel supply is cut off to a
predetermined number of engine cylinders determined in accordance
with a required reduction of the vehicle driving torque because the
selectable switch is compulsory changed ON even if selected
OFF.
[0094] Although both of the first and second above embodiments have
been described where the second throttle valve decreases the engine
power as the traction control apparatus, it is understood that the
invention can be used with other types of the traction control
system. For example, the invention is applicable to the fuel
cutting off system and the brakes to the driving wheels.
[0095] Although the embodiments have been described in which the
desirable yaw rate .psi.* was computed for control processing based
on vehicle velocity Vc and angular position .theta. of steering
wheel, it is understood that the lateral acceleration sensor can be
applied to vehicle velocity Vc and angular .theta. of steering
wheel to compute the desirable yaw rate. Moreover, it is understood
that desirable yaw rate can be computed based on regular yaw
rate.
[0096] Although the embodiments have been described for a desirable
yaw rate computed for control processing based on equation (2) and
equation (3), it is understood that the control unit can be
programmed to store a map that provides the relationship between
angular .theta. of steering wheel which has parameters of vehicle
velocity Vc.
[0097] Although the embodiments have been described for the wheel
cylinder pressure directly detected under exerting yaw moment
control, it is understood that the wheel cylinder pressure may be
determined by computing.
[0098] Furthermore, although the embodiments have been described
for a rear-drive type automotive vehicle, it is understood that
this invention can be applicable also to a front-wheel drive
vehicle or a four-wheel drive vehicle.
* * * * *