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.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     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. 
     2. Background Art 
     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. 
     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. 
     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. 
     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 
     The present invention overcomes the shortcomings associated with the related art and achieves other advantages not realized by the related art. 
     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. 
     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. 
     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. 
     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. 
     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. 
     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 
     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: 
     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; and 
     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 
     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. 
     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. 
     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. 
     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 . 
     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 . 
     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 . 
     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. 
     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&#39;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 . 
     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 . 
     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 . 
     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 . 
     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. 
     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 λf of a wheel based on the vehicle velocity V and the wheel speed Wf. A target angle determining section  303  determines a target angle θt for the crank mechanism  50  based on the slip rate λf. 
     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. 
     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. 
     In FIG. 5, the relationship between the target angle θt and actual angle θo 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. 
     In step S 1 , a value representing the non-operating condition of ABS (OFF representative value) is set into an ABS flag (Fabs) described later. In step S 2 , 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 S 3 , 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 S 4 , the slip rate λf is calculated in the slip rate calculating section  302  based on the wheel speed Wf and the vehicle velocity V In step S 5 , wheel acceleration a, is calculated by differentiating the wheel speed Wf. 
     In step S 6 , a reference slip rate λref given as a function of the wheel acceleration a and the slip rate λf are compared with each other. Here, when the slip rate λf exceeds the reference slip rate λref at time t 1  in FIG. 5, step S 7  is entered to operate the ABS. In step S 7 , a value representing the operating condition of the ABS (ON representative value) is set in the ABS flag (Fabs). 
     In step S 8 , in an ABS executing section  303   a  of the target angle determining section  303 , the target angle θt 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 θo of the crank mechanism  50  detected by the potentiometer  43  to coincide with the target angle θt is executed, and a duty ratio for driving pulses supplied to the servomotor M is determined. 
     In step S 9 , 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 λf exceeds the reference slip rate λref. 
     Thereafter, at time t 2  in FIG. 5, the slip rate λf becomes less than the reference slip rate λref. When the slip rate λf is detected to be less than the reference slip rate λref in step S 6  (FIG.  4 ), step S 10  is entered. In step S 10 , the ABS flag (Fabs) is determined to have an ON representative value and step S 11  is entered. In step S 11 , a value representing an ABS return control (return representative value) is set into the ABS flag (Fabs). 
     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 . 
     In step S 12 , a return timer Trtn initiates counting. In step S 13 , the ABS return control is executed by a return executing section  303   b  of the target angle determining section  303 . 
     FIG. 6 is a flowchart showing the operation of the ABS return control according to an embodiment of the present invention. In step S 131 , 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 S 132 . 
     In step S 133 , and as shown in expanded detail in the lower side of FIG. 5, the target angle λt for the crank mechanism  50  is set at a position θp precedent to the turning limit θlmt, and the process returns. Therefore, in the next step S 9 , a control for turning the actual angle θo of the crankshaft to the position θp precedent to the turning limit θlmt is executed. The precedent angle θp is set in an angle range in which the cut valve  61  can be maintained in an opened condition. 
     Returning to FIG. 4, in the next period the process goes from step S 10  to step S 14 , where the ABS flag (Fabs) is discriminated as a return representative value, and step S 15  is entered. In step S 15 , it is determined if a return timer Trtn has timed-out. If the return timer Trtn has not yet timed-out, the step S 13  is entered, and the return control with the position θp precedent to the turning limit θlmt as a target angle θt is continued. 
     Thereafter, at time t 3  in FIG. 5, the target angle fixing timer Tfix times-out. When this is detected in step S 134  of the ABS return control (FIG.  6 ), step S 135  is entered, wherein the target angle θt is brought closer to the turning limit θlmt by a predetermined unit angle Δθ than the present position θp. In step  136 , it is determined if the updated target angle θt is equal to or less than the turning limit θlmt. In the beginning, the target angle θt is greater (precedent) than the turning limit θlmt, and the process returns. Therefore, in the next step S 9 , a control for bringing the actual angle θo of the crankshaft closer to the turning limit θlmt than the present value by the unit angle Δθ is executed. 
     The process of progressively reducing the target angle θt is continued until the target angle θt reaches the turning limit θlmt. Therefore, the turning angle of the crank mechanism  50 , angularly controlled based on the target angle θt, is also progressively reduced toward the turning limit θlmt, as shown in FIG.  5 . 
     Thereafter, at time t 4  in FIG. 5, when the target angle θt comes to be equal to or less than the turning limit θlmt and this is detected in step S  136 , the target angle θt is fixed at the turning limit θlmt in step S 137 . The duty ratio determining part  304  executes the PID control for causing the actual angle θo of the crank mechanism  50  to coincide with the target angle θt, and a duty ratio of driving pulses supplied to the servomotor M is determined. 
     In the PID control at the time of return control, gain of term D is increased (as compared with the PID control in step S 8 ) so that an abrupt return action does not degrade convergence properties. 
     In the next step S 9 , a motor control for causing the actual angle θo to coincide with the turning limit θlmt is executed. Thereafter, when the return timer Trtn comes to time-out at time t 5  and this is detected in step S 15 , the return timer Trtn is reset in step S 16 . In step S 17 , an OFF representative value is set into the ABS flag (Fabs). 
     Thus, in the present embodiment, at the time of finishing the ABS control by moving the crank mechanism  50  to the turning limit θlmt, the target angle θt is not set at the turning limit θlmt from the beginning. Instead, the target angle θt is once set at the position θp precedent to the turning limit θlmt and thereafter updated with the turning limit θlmt. Therefore, the turning speed o the crank mechanism  50  is reduced immediately, before the turning limit θlmt is reached. 
     Thereafter, the target angle θt is updated, and the crank mechanism  50  is again turned to the turning limit θlmt. 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 θlmt is smaller than that in the case where the target angle θt is set at the turning limit θlmt 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 θlmt can be advantageously reduced. 
     In addition, since the position θp precedent to the turning limit θlmt 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&#39;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 θlmt does not at all affect the driver&#39;s brake operation. 
     While in the present embodiment, the cancelling of fixation of the target angle θt 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 of change of the actual angle θo comes is less than a predetermined value, or at the time point when the differential between the target angle θt and the actual angle θo is less than a predetermined value. 
     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 turner to the turning limit. 
     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. 
     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&#39;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&#39;s braking operation. 
     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. 
     The invention being thus described, it will 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.