U.S. patent application number 09/820219 was filed with the patent office on 2001-10-04 for control device for antilock brake device.
Invention is credited to Goto, Shinji, Ota, Atsuo.
Application Number | 20010026096 09/820219 |
Document ID | / |
Family ID | 18606679 |
Filed Date | 2001-10-04 |
United States Patent
Application |
20010026096 |
Kind Code |
A1 |
Ota, Atsuo ; et al. |
October 4, 2001 |
Control device for antilock brake device
Abstract
An ABS return control device for retracting an expander piston
to an ABS non-operation position by turning a crank mechanism by a
servomotor includes a first procedure of driving the servomotor
with a position precedent to a turning limit. At the turning limit,
the movement of the crank mechanism is limited by a stopper member.
A target angle and a second procedure of driving the servomotor by
updating the target angle with the turning limit is further
disclosed. The ABS return control device permits reduction of a
conventional actuator in size and weight by controlling the kinetic
energy of a positioning member of the crank mechanism turned by a
servomotor at the time of collision against the stopper member.
Inventors: |
Ota, Atsuo; (Saitama,
JP) ; Goto, Shinji; (Saitama, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
18606679 |
Appl. No.: |
09/820219 |
Filed: |
March 29, 2001 |
Current U.S.
Class: |
303/113.1 ;
303/9.64 |
Current CPC
Class: |
B60T 8/4266
20130101 |
Class at
Publication: |
303/113.1 ;
303/9.64 |
International
Class: |
B60T 008/34 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 29, 2000 |
JP |
2000-091189 |
Claims
What is claimed is:
1. A control device for an antilock brake system comprising: an
input hydraulic chamber in communication with a master cylinder; an
output hydraulic chamber in communication with a caliper cylinder
of a brake; a cut valve in communication with said input hydraulic
chamber and said output hydraulic chamber for providing a hydraulic
cutoff condition; an expander piston for opening said cut valve,
wherein said expander piston is located on an open end side of said
cut valve in an open position, and said expander piston closes said
cut valve by increasing a volume of said output hydraulic chamber
in a closed position, wherein said expander position is located in
a closed end side in said closed position; a crank mechanism for
displacing said expander piston; a servomotor for turning said
crank mechanism to a predetermined target angle; and a stopper
member for setting a turning limit for said crank mechanism, said
expander piston is displaced in a step of reaching said closed
position during an ABS operation and being retracted to said open
position during a non-ABS operation.
2. The control device according to claim 1, wherein a return
control for retracting the expander piston to said open and closed
positions comprises a first control procedure of driving said
servomotor with a position precedent and a target angle to said
turning limit, and a second control procedure of driving said
servomotor by updating said target angle with said turning
limit.
3. The control device according to claim 2, wherein said crank
mechanism is prevented from exceeding the turning limit by said
stopper member, said stopper member limiting a displacement of said
expander piston between said open and closed positions.
4. The control device according to claim 2, wherein said position
precedent to said turning limit is within an angular range in which
said cut valve maintains an open condition.
5. The control device according to claim 2, wherein said target
angle is progressively updated toward said turning limit by said
second procedure.
6. The control device according to claim 4, wherein said target
angle is progressively updated toward said turning limit by said
second procedure.
7. A method utilizing the control device according to claim 1,
wherein a return control retracts the expander piston to said open
and closed positions, said method comprising a first control
procedure of driving said servomotor with a position precedent and
a target angle to said turning limit, and a second control
procedure of driving said servomotor by updating said target angle
with said turning limit.
8. A control device for an antilock brake system comprising: an
input hydraulic chamber in communication with a master cylinder; an
output hydraulic chamber in communication with a caliper cylinder
of a brake; a cut valve in communication with said input hydraulic
chamber and said output hydraulic chamber for providing a hydraulic
cutoff condition; an expander piston for opening said cut valve,
wherein said expander piston is located on an open end side of said
cut valve in an open position, and said expander piston closes said
cut valve by increasing a volume of said output hydraulic chamber
in a closed position, wherein said expander position is located in
a closed end side in said closed position; a return control for
retracting the expander piston to said open and closed positions,
said return control includes means for executing a first control
procedure for driving said servomotor with a position precedent and
a target angle to a turning limit, and means for executing a second
control procedure for driving said servomotor by updating said
target angle with said turning limit; a crank mechanism for
displacing said expander piston; a servomotor for turning said
crank mechanism to a predetermined target angle; and a stopper
member for setting said turning limit for said crank mechanism,
said expander piston is displaced in said closed position during an
ABS operation and retracted to said open position during a non-ABS
operation.
9. The control device according to claim 8, wherein said servomotor
is a DC servomotor and forms a servomotor section of a modulator
connected with a crank mechanism.
10. The control device according to claim 9, wherein the crank
mechanism comprises a pinion axially attached to a rotary shaft of
the servomotor, and a semicircular crank gear is engaged with the
pinion and axially supported by a crank gear.
11. The control device according to claim 10, wherein a crank pin
is eccentrically connected to the crank gear through a crank arm,
and said crank arm is connected to a second end of the crank
pin.
12. The control device according to claim 11, wherein a turning
range of the crank gear is limited by a stopper pin.
13. The control device according to claim 8, wherein said turning
limit is limited by a stopper pin.
14. The control device according to claim 11 further comprising a
potentiometer serving as a position sensor fitted to the crank
arm.
15. The control device according to claim 11 further comprising: a
cam bearing rotatably fitted to the crank pin, said cam bearing
pressable toward a first end by a spring force; and a return spring
contained in a spring containing portion for producing said spring
force. 48.
16. The control device according to claim 15, wherein the expander
piston is engageable with the cam bearing at a position symmetrical
with a pressing position of the return spring for facilitating an
opening and closing operation of said cut valve.
17. The control device according to claim 14, further comprising: a
control unit controlling a turning angle of the DC servomotor based
on a wheel speed value read from a wheel speed sensor, and an
output value of the potentiometer representing a crank angle of the
crank mechanism.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a control device for an
antilock brake system, and more particularly to a control device
for an antilock brake system in which braking hydraulic pressure is
controlled by a turning angle of a servomotor.
[0003] 2. Background Art
[0004] An antilock brake system (ABS) for performing optimum brake
control has been mounted on conventional vehicles. In the ABS, a
slip rate is calculated from the rotation speed of a wheel of the
running vehicle and the vehicle velocity, and the optimum brake
control is performed based on the calculated slip rate.
[0005] In an ABS according to the conventional art, as disclosed in
Japanese Pre-examination Patent Publication (KOKAI) No. Hei 5-79543
(1993), an actuator for an antilock brake for reducing, maintaining
and increasing the braking hydraulic pressure is connected between
a master cylinder and a caliper cylinder. The master cylinder is
responsible for converting a brake operation to hydraulic pressure.
The actuator incorporates a servomotor for displacing a crankshaft
of the actuator based on slip rate information of the vehicle, and
the crankshaft opens and closes a cut valve through an expander
piston, thereby controlling the braking hydraulic pressure applied
to the caliper cylinder.
[0006] Stopper members are preliminarily provided at an upper limit
position and a lower limit position of a turning range of the
crankshaft. When the upper limit position or the lower limit
position is given as a target angle to the servomotor, the
crankshaft or a member in the vicinity of the crankshaft is turned
until a positioning member provided in the vicinity of the
crankshaft/member comes to collide with the stopper member.
[0007] However, in the conventional art as mentioned hereinabove,
the positioning member collides against the stopper member at a
high speed when a target position for the servomotor is set at
either the upper limit position or the lower limit position.
Therefore, the positioning member and the stopper members must be
provided with sufficient mechanical strength. This structural
requirement further hinders size reduction and weight reduction
attempts of the designer of an actuator.
SUMMARY OF THE INVENTION
[0008] The present invention overcomes the shortcomings associated
with the related art and achieves other advantages not realized by
the related art.
[0009] It is an aspect of the present invention to provide a
control device for an antilock brake system which solves the
above-mentioned problems in the prior art.
[0010] It is an aspect of the present invention to provide a
control device that permits an actuator to be reduced in size and
weight by moderating the collision of a positioning member against
a stopper member.
[0011] These and other aspects of the invention are accomplished by
a control device for an antilock brake system comprising an input
hydraulic chamber in communication with a master cylinder, an
output hydraulic chamber in communication with a caliper cylinder
of a brake, a cut valve in communication with the input hydraulic
chamber and the output hydraulic chamber for providing a hydraulic
cutoff condition, an expander piston for opening the cut valve,
wherein the expander piston is located on an open end side of the
cut valve in an open position, and the expander piston closes the
cut valve by increasing a volume of the output hydraulic chamber in
a closed position, wherein the expander position is located in a
closed end side in the closed position, a crank mechanism for
displacing said expander piston, a servomotor for turning said
crank mechanism to a predetermined target angle, and a stopper
member for setting a turning limit for said crank mechanism, said
expander piston is displaced in a step of reaching said closed
position during an ABS operation and being retracted to said open
position during a non-ABS operation.
[0012] These and other aspects of the invention are accomplished by
a control device for an antilock brake system comprising an input
hydraulic chamber in communication with a master cylinder, an
output hydraulic chamber in communication with a caliper cylinder
of a brake, a cut valve in communication with said input hydraulic
chamber and said output hydraulic chamber for providing a hydraulic
cutoff condition, an expander piston for opening said cut valve,
wherein said expander piston is located on an open end side of said
cut valve in an open position, and said expander piston closes said
cut valve by increasing a volume of said output hydraulic chamber
in a closed position, wherein said expander position is located in
a closed end side in said closed position, a return control for
retracting the expander piston to said open and closed positions,
the return control includes means for executing a first control
procedure for driving the servomotor with a position precedent and
a target angle to the turning limit, and means for executing a
second control procedure for driving the servomotor by updating the
target angle with the turning limit, a crank mechanism for
displacing the expander piston, a servomotor for turning the crank
mechanism to a predetermined target angle, and a stopper member for
setting a turning limit for the crank mechanism, the expander
piston is displaced in a step of reaching the closed position
during an ABS operation and being retracted to the open position
during a non-ABS operation.
[0013] According to the above description, a position precedent to
the turning limit is first set as a turning target angle for the
crank mechanism, so that the turning speed of the crank mechanism
is only reduced at the position precedent to the turning limit. The
target angle is then updated and the crank mechanism is again
turned to the turning limit. Accordingly, the kinetic energy of the
crank mechanism at the time of reaching the turning limit is
smaller as compared with the case where the turning limit is set as
the target angle from the beginning. The kinetic energy of the
crank mechanism at the time of collision with the stopper member at
the turning limit is advantageously reduced.
[0014] Further scope of applicability of the present invention will
become apparent from the detailed description given hereinafter.
However, it should be understood that the detailed description and
specific examples, while indicating preferred embodiments of the
invention, are given by way of illustration only, since various
changes and modifications within the spirit and scope of the
invention will become apparent to those skilled in the art from
this detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The present invention will become more fully understood from
the detailed description given hereinbelow and the accompanying
drawings which are given by way of illustration only, and thus are
not intended to limit the present invention to the embodiments
shown, and wherein:
[0016] FIG. 1 is a schematic view of a brake control system
according to an embodiment of the present invention;
[0017] FIG. 2 is a side view of a modulator according to an
embodiment of the present invention;
[0018] FIG. 3 is a schematic view of a portion of the control unit
of FIG. 1;
[0019] FIG. 4 is a flowchart of the operation of the invention
according to an embodiment of the present invention;
[0020] FIG. 5 is a graphical view of the operation of the invention
according to an embodiment of the present invention; and
[0021] FIG. 6 is a flowchart showing the operation of a return
control according to an embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] Hereinafter, the present invention will be described in
detail with reference to the accompanying drawings. FIG. 1 is a
schematic view of a brake control system according to an embodiment
of the present invention. FIG. 2 is a side view of a modulator
according to an embodiment of the present invention. FIG. 3 is a
schematic view of a portion of the control unit of FIG. 1. FIG. 4
is a flowchart of the operation of the invention according to an
embodiment of the present invention. FIG. 5 is a graphical view of
the operation of the invention according to an embodiment of the
present invention. FIG. 6 is a flowchart showing the operation of a
return control according to an embodiment of the present
invention.
[0023] FIG. 1 is a schematic view of a brake control system
according to an embodiment of the present invention. A description
of a brake control system incorporating an embodiment of the
present invention will be made with reference to an example of the
system to the front wheel.
[0024] The brake system includes a disk plate 10 arranged at a
rotational shaft of the front wheel, a brake lever 20 fitted to a
steering handle portion of the vehicle, a control unit 30, and a
modulator 40 acting as an actuator for controlling the braking
hydraulic pressure.
[0025] A caliper cylinder 11 supplied with braking hydraulic
pressure from the modulator 40 generates a braking force. A wheel
speed sensor 12 is mounted to the disk plate 10 along with the
caliper cylinder 11. The rotating speed of the front wheel detected
by the wheel speed sensor 12 is inputted to the control unit
30.
[0026] A DC servomotor M of the modulator 40 is connected with a
crank mechanism 50. As shown in FIG. 2, the crank mechanism 50
comprises a pinion 51 axially attached to the rotary shaft of the
DC servomotor M. A semicircular crank gear 52 is engaged with the
pinion 51. A crankshaft 41 axially supports the crank gear 52. A
crank pin 44 is eccentrically connected to the crank gear 52
through a crank arm 42, and a crank arm 46 is connected to a second
end of the crank pin 44. The turning range of the crank gear 52 is
limited by a stopper pin 53. A potentiometer 43 serving as a
position sensor is fitted to the crank arm 46.
[0027] A cam bearing 45 is rotatably fitted to the crank pin 44,
and is normally pressed toward one end by a spring force of a
return spring 47 contained in a spring containing portion 48. An
expander piston 60 is disposed in contact with the cam bearing 45
at a position symmetrical with a pressing position of the return
spring 47. Therefore, as the cam bearing 45 is moved up and down,
the expander piston 60 is displaced up and down in response
thereto. This relationship results in the opening and closing of a
cut valve 61.
[0028] A cut valve containing portion 62 incorporating the cut
valve 61 is provided at an upper portion of the expander piston 60.
A master cylinder 67 is connected to an input hydraulic chamber 64
of the cut valve containing portion 62 through piping 65. The
caliper cylinder 11 is connected to an output hydraulic chamber 66
of the cut valve containing portion 62 through piping 68. It shall
be appreciated by one of ordinary skill in the art that piping 65
and 68 may include multiple sections of piping or tubing for
accomplishing distribution of pressurized braking fluid to multiple
locations.
[0029] The master cylinder 67 and the caliper cylinder 11 are
connected to each other through the piping 65, the modulator 40 and
the piping 68. This hydraulic oil/braking circuit is filled with a
hydraulic oil suitable for the vehicle's braking system. The master
cylinder 68 converts an operation on the brake lever 20 into an oil
pressure, and transmits the oil pressure to the cut valve
containing portion 62.
[0030] The control unit 30 controls the turning angle of the DC
servomotor M based on wheel speed information read from the wheel
speed sensor 12 and an output value of the potentiometer 43
representing the angle of the crank mechanism 50 at the position of
the crank arm 46.
[0031] In the arrangement described hereinabove, when the ABS is
not operated, the crank gear 52 has been turned to a turning limit
restricted by the stopper pin 53. Therefore, the expander piston 60
is located at one end side, and the cut valve 61 is open, so that a
braking pressure in response to a brake operation is supplied to
the caliper cylinder 11.
[0032] When the ABS is in an operating state, the crank gear 52 is
turned by the servomotor M, and the expander piston 60 is lowered
toward the other end side. By this action, the cut valve 61 is
closed, and the volume of the output hydraulic chamber 66 is
increased according to the position of the expander piston 60.
Accordingly, the braking pressure supplied to the caliper cylinder
11 is reduced according to the position of the expander piston
60.
[0033] While the above description has been made in accordance with
a brake control system arranged for a front wheel of a vehicle, a
similar brake control system can also be arranged for the rear
wheel.
[0034] FIG. 3 is a schematic view of a portion of the control unit
30 shown in FIG. 1. A wheel speed calculating part 300 calculates
the wheel speed Wf based on an output signal from the wheel speed
sensor 12. A vehicle velocity calculating section 301 calculates
vehicle velocity V based on engine revolution number Ne and speed
change gear stage G (or the wheel speed Wf or the like). A slip
rate calculating section 302 calculates slip rate .lambda.f of a
wheel based on the vehicle velocity V and the wheel speed Wf. A
target angle determining section 303 determines a target angle
.theta.t for the crank mechanism 50 based on the slip rate
.lambda.f.
[0035] A duty ratio determining section 304 determines a duty ratio
of driving pulses supplied to the servomotor M by PID control. A
pulse generating section 305 generates a train of pulses based on
the determined duty ratio. A driver 306 drives the servomotor M
based on the generated train of pulses.
[0036] Next, the operation of the present embodiment will be
described referring to the flowcharts of FIGS. 4 and 6, and the
graphical time chart of FIG. 5. FIG. 4 is a flowchart of the
operation of the invention according to an embodiment of the
present invention. FIG. 5 is a graphical view of the operation of
the invention according to an embodiment of the present invention.
FIG. 6 is a flowchart showing the operation of a return control
according to an embodiment of the present invention.
[0037] In FIG. 5, the relationship between the target angle
.theta.t and actual angle .theta.o of the crank mechanism 50,
controlled according to the relationship between the vehicle
velocity V and the wheel speed Wf, is shown for both the prior art
and the present invention.
[0038] In step S1, a value representing the non-operating condition
of ABS (OFF representative value) is set into an ABS flag (Fabs)
described later. In step S2, an output signal from the wheel speed
sensor 12 is taken into the wheel speed calculating section 300,
and the wheel speed Wf of the front wheel is calculated. In step
S3, the vehicle velocity V is obtained in the vehicle velocity
calculating section 301. In this embodiment, the vehicle velocity V
is obtained based on the relationship between the engine revolution
number Ne and the speed change gear stage G. In step S4, the slip
rate .lambda.f is calculated in the slip rate calculating section
302 based on the wheel speed Wf and the vehicle velocity V. In step
S5, wheel acceleration .alpha. is calculated by differentiating the
wheel speed Wf.
[0039] In step S6, a reference slip rate .lambda.ref given as a
function of the wheel acceleration .alpha. and the slip rate
.lambda.f are compared with each other. Here, when the slip rate
.lambda.f exceeds the reference slip rate .lambda.ref at time t1 in
FIG. 5, step S7 is entered to operate the ABS. In step S7, a value
representing the operating condition of the ABS (ON representative
value) is set in the ABS flag (Fabs).
[0040] In step S8, in an ABS executing section 303a of the target
angle determining section 303, the target angle .theta.t for the
crank mechanism 50 is determined according to the relationship
between the vehicle velocity V and the wheel speed Wf, as shown by
a broken line in FIG. 5. In the duty ratio determining section 304,
a PID control for causing the actual angle .theta.0 of the crank
mechanism 50 detected by the potentiometer 43 to coincide with the
target angle .theta.t is executed, and a duty ratio for driving
pulses supplied to the servomotor M is determined.
[0041] In step S9, a train of pulses generated by the pulse
generating section 305 and based on the duty ratio is supplied to
the servomotor M through the driver 306. A normal control of ABS
such as this may be continued as long as the slip rate .lambda.f
exceeds the reference slip rate .lambda.ref.
[0042] Thereafter, at time t2 in FIG. 5, the slip rate .lambda.f
becomes less than the reference slip rate .lambda.ref. When the
slip rate .lambda.f is detected to be less than the reference slip
rate .lambda.ref in step S6 (FIG. 4), step S10 is entered. In step
S10, the ABS flag (Fabs) is determined to have an ON representative
value and step S11 is entered. In step S11, a value representing an
ABS return control (return representative value) is set into the
ABS flag (Fabs).
[0043] The ABS return control is a process of turning the crank
gear 52 to a turning limit restricted by the stopper pin 53 and
retracting the expander piston 60 to one end side on the upper
side, in order to finish the ABS control and reopen the cut valve
61 and permit inactive ABS braking control, i.e. direct control
with brake lever 20.
[0044] In step S12, a return timer Trtn initiates counting. In step
S13, the ABS return control is executed by a return executing
section 303b of the target angle determining section 303.
[0045] FIG. 6 is a flowchart showing the operation of the ABS
return control according to an embodiment of the present invention.
In step S131, it is determined if a target angle fixing timer Tfix
has been started. Since the target angle fixing timer Tfix is not
yet started at the beginning, it is started in step S132.
[0046] In step S133, and as shown in expanded detail in the lower
side of FIG. 5, the target angle .lambda.t for the crank mechanism
50 is set at a position .theta.p precedent to the turning limit
.theta.lmt, and the process returns. Therefore, in the next step
S9, a control for turning the actual angle .theta.0 of the
crankshaft to the position .theta.p precedent to the turning limit
.theta.lmt is executed. The precedent angle .theta.p is set in an
angle range in which the cut valve 61 can be maintained in an
opened condition.
[0047] Returning to FIG. 4, in the next period the process goes
from step S10 to step S14, where the ABS flag (Fabs) is
discriminated as a return representative value, and step S15 is
entered. In step S15, it is determined if a return timer Trtn has
timed-out. If the return timer Trtn has not yet timed-out, the step
S13 is entered, and the return control with the position .theta.p
precedent to the turning limit .theta.lmt as a target angle
.theta.t is continued.
[0048] Thereafter, at time t3 in FIG. 5, the target angle fixing
timer Tfix times-out. When this is detected in step S134 of the ABS
return control (FIG. 6), step S135 is entered, wherein the target
angle .theta.t is brought closer to the turning limit .theta.lmt by
a predetermined unit angle .DELTA.0 than the present position
.theta.p. In step 136, it is determined if the updated target angle
.theta.t is equal to or less than the turning limit .theta.lmt. In
the beginning, the target angle .theta.t is greater (precedent)
than the turning limit .theta.lmt, and the process returns.
Therefore, in the next step S9, a control for bringing the actual
angle .theta.0 of the crankshaft closer to the turning limit
.theta.lmt than the present value by the unit angle .DELTA.0 is
executed.
[0049] The process of progressively reducing the target angle
.theta.t is continued until the target angle .theta.t reaches the
turning limit .theta.lmt. Therefore, the turning angle of the crank
mechanism 50, angularly controlled based on the target angle
.theta.t, is also progressively reduced toward the turning limit
.theta.lmt, as shown in FIG. 5.
[0050] Thereafter, at time t4 in FIG. 5, when the target angle
.theta.t comes to be equal to or less than the turning limit
.theta.lmt and this is detected in step S136, the target angle
.theta.t is fixed at the turning limit .theta.lmt in step S137. The
duty ratio determining part 304 executes the PID control for
causing the actual angle .theta.0 of the crank mechanism 50 to
coincide with the target angle .theta.t, and a duty ratio of
driving pulses supplied to the servomotor M is determined.
[0051] In the PID control at the time of return control, gain of
term D is increased (as compared with the PID control in step S8)
so that an abrupt return action does not degrade convergence
properties.
[0052] In the next step S9, a motor control for causing the actual
angle .theta.0 to coincide with the turning limit .theta.lmt is
executed. Thereafter, when the return timer Trtn comes to time-out
at time t5 and this is detected in step S15, the return timer Trtn
is reset in step S16. In step S17, an OFF representative value is
set into the ABS flag (Fabs).
[0053] Thus, in the present embodiment, at the time of finishing
the ABS control by moving the crank mechanism 50 to the turning
limit .theta.lmt, the target angle .theta.t is not set at the
turning limit .theta.lmt from the beginning. Instead, the target
angle .theta.t is once set at the position .theta.p precedent to
the turning limit .theta.lmt and thereafter updated with the
turning limit .theta.lmt. Therefore, the turning speed of the crank
mechanism 50 is reduced immediately, before the turning limit
.theta.lmt is reached.
[0054] Thereafter, the target angle .theta.t is updated, and the
crank mechanism 50 is again turned to the turning limit .theta.lmt.
Since the turning speed of the crank mechanism 50 is once reduced,
the kinetic energy of the crank mechanism 50 at the time of
reaching the turning limit .theta.lmt is smaller than that in the
case where the target angle .theta.t is set at the turning limit
.theta.lmt from the beginning. Therefore, the kinetic energy of the
crank gear 52 at the time of collision with the stopper portion 53
at the turning limit .theta.lmt can be advantageously reduced.
[0055] In addition, since the position .theta.p precedent to the
turning limit .theta.lmt is set in an angular range in which the
cut valve 61 can be maintained in the opened condition, namely, at
a position where the driver's brake operation is reflected in the
braking force, the reduction of the turning speed of the crank
mechanism 50 immediately before the turning limit .theta.lmt does
not at all affect the driver's brake operation.
[0056] While in the present embodiment, the cancelling of fixation
of the target angle .theta.t in the ABS return control is set at
the point of timing-out of the target angle fixing timer Tfix.
However, the present invention is not limited to this setting. The
cancellation may be set at the time point when the rate of change
of the actual angle .theta.0 comes is less than a predetermined
value, or at the time point when the differential between the
target angle .theta.t and the actual angle .theta.0 is less than a
predetermined value.
[0057] According to the invention, the following advantages and
effects can be accomplished over previous systems found in the
conventional art. Since a position precedent to the turning limit
is set in the beginning as the target angle for turning of the
crank mechanism, the turning speed of the crank mechanism is
necessarily only reduced once at the position precedent to the
turning limit. Thereafter, the target angle is updated and the
crank mechanism is again turned to the turning limit.
[0058] Since the turning speed of the crank mechanism is reduced,
the kinetic energy of the crank mechanism at the time of reaching
the turning limit is smaller than that in the case where the target
angle is set at the turning limit from the outset. Therefore, the
kinetic energy of the crank mechanism at the time of collision
against the stopper portion at the turning limit is significantly
reduced.
[0059] Since the position precedent to the turning limit is made to
be the target angle in the beginning, and the position precedent is
set in the angular range in which the cut valve can be maintained
in the opened condition, namely, at a position where the driver's
brake operation is reflected in the braking force, the reduction of
the turning speed of the crank mechanism does not at all impact the
driver's braking operation.
[0060] Since the updating of the target angle from the position
precedent to the turning limit to the turning limit is executed so
that the target angle is progressively changed to the turning
limit, the kinetic energy of the crank mechanism at the time of
collision with the stopper portion when the turning limit is
reached is further reduced.
[0061] The invention being thus described, it will be obvious that
the same may be varied in many ways. Such variations are not to be
regarded as a departure from the spirit and scope of the invention,
and all such modifications as would be obvious to one skilled in
the art are intended to be included within the scope of the
following claims.
* * * * *