Anti-Lock Brake Control System Including a Procedure of Sampling of Input Time Data of Wheel Speed Sensor Signals and Method Therefor

1. An anti-skid brake control system for an automotive hydraulic brake system comprising: a hydraulic brake circuit including a wheel cylinder for applying braking force to a vehicle wheel; a pressure control valve disposed within said hydraulic circuit and operative to increase fluid pressure in said wheel cylinder in a first position thereof, to decrease the fluid pressure in said wheel cylinder in a second position thereof and to hold the fluid pressure in said wheel cylinder constant in a third position thereof; a wheel speed sensor means for producing sensor signal pulses separated by intervals representative of the detected wheel speed; a timer means for producing timer signals; a first means, responsive to said sensor signal, for sampling values of said timer signals and for storing the sampled timer signal values; a second means for processing the stored timer signal values to derive a wheel speed value, a wheel acceleration value or a wheel deceleration value and for producing a control signal in accordance with the derived wheel speed and acceleration values, which control signal actuates said pressure cntrol valve to one of said first, second and third positions so as to adjust the wheel rotational speed toward an optimal relationship with vehicle speed; a third means for selectively activating said first and second means, said third means being responsive to said sensor signal pulses to interrupt operation of said second means and activate said first means for sampling said timer signal values and storing the sampled timer signal values; and a fourth means for detecting overflow of said timer means, counting the number of occurrences thereof, and replacing the wheel speed and acceleration values used by said third means with fixed values when the number of occurrences of overflow exceeds a predetermined number.

2. The anti-skid brake control system as set forth in claim 1, wherein said fourth means set said wheel speed value and said wheel acceleration value and deceleration value respectively at zero.

3. The anti-skid control system as set forth in claim 2, wherein said timer means comprises a clock generator for producing a plurality of constant frequency clock signals and a clock counter having a counting capacity and adapted to count said clock signals.

4. The anti-skid brake control system as set forth in claim 3, wherein said fourth means comprises an overflow detector for detecting occurrences of overflow of said clock counter to reset the clock counter at every occurrence of said clock counter overflow, said fourth means responsive to completion of operation of said second means for resetting said overflow detector, and a command generator detecting the overflow of said clock counter to produce a command for setting said wheel speed value and said wheel acceleration value and deceleration value at said fixed values.

5. The anti-skid brake control system as set forth in claim 4, wherein said overflow detector is operative at every occasion of said clock counter overflow, and said command generator is activated cyclically at a given timing.

6. The anti-skid brake control system as set forth in claim 5, wherein said command generator is operative at a given time interval corresponding to a period of time indicated by the maximum counter value of said clock counter.

7. The anti-skid brake control system as set forth in claim 6, which further comprises a fifth means for counting in an interruption counter occurrences of interruption of said second means, counting down the interruption counter by 1 whenever said second means completes one cycle of operation, said fifth means being operative to repeatedly activate said second means unti said interruption counter has a value of zero.

8. The anti-skid control system as set forth in claim 7, wherein said third means processes sampled timer signal values to derive a wheel speed based on input time data of mutually adjacent pairs of sensor signal pulses and a wheel acceleration or deceleration based on three times signal values succeedingly sampled.

9. An anti-skid brake control system for an automotive vehicle comprising: a hydraulic brake circuit including wheel cylinders respectively corresponding to respective vehicle wheel for applying braking force to the corresponding wheel cylinder; a pressure control valve associated with each of said wheel cylinder for controlling fluid pressure to be applied to the corresponding wheel cylinder, said pressure control valve being operative to increase the fluid pressure in said wheel cylinder at a first position thereof, to decrease the fluid pressure in said wheel cylinder at a second position thereof and to maintain the fluid pressure in said wheel cylinder at a constant value at a third position thereof; a wheel speed sensor means for sequentially outputting sensor signal pulses measuring a time period by counting clock pulses and having pulse intervals respectively corresponding to instantaneous wheel rotation speed; a timer means for measuring a time period by counting clock pulses and sequentially outputting timer signals having a value indicative of a measured period of time corresponding to the number of said counted clock pulses, said timer means having a maximum count capacity and continue counting from zero every time the measured period of time overflows said maximum capacity; a controller operative in a first operation for receiving said sensor signal pulses and said timer signals for sampling said timer signals at a given number of sensor signal pulses and in a second operation for deriving a wheel speed and a wheel acceleration or deceleration based on said time signals and for deriving a control signal based on a slip rate determined based on said wheel speed and said wheel acceleration or deceleration, of said corresponding wheel for controlling valve position of said pressure control valve at a predetermined pattern for optimizing braking characteristics, said controller deriving said given number such that a difference of a period of time between two mutually adjacent intervals of said given number of sensor signal pulses is greater than a predetermined value, and interrupting operation for deriving said slip rate and wheel acceleration and deceleration for skid control in response to said sensor signal pulses to perform operation for sampling the time signals of the corresponding sensor signal pulses when said difference exceeds said predetermined value, and said controller counting occurrence of interruption of said second operation for increasing a counter value by 1 and decreasing the counter value each time said second operation is completed, and said controller detecting overflow of said timer means upon said timer means overflowing the maximum capacity thereof to count the number of overflow occurrences in an overflow counter and clearing the overflow counter at the end of said second operation, said controller setting said wheel speed and said wheel acceleration and deceleration at fixed constant values when said overflow counter value reaches a given value.

10. The anti-skid brake control system as set forth in claim 9, wherein said controller sets said wheel speed and said wheel acceleration and deceleration respectively at zero.

11. The anti-skid control system as set forth in claim 10, wherein said timer means comprises a clock generator for producing constant frequency clock signals and a clock counter having said maximum counting capacity.

12. The anti-skid brake control system as set forth in claim 11, wherein said overflow counter detects overflow of said clock counter to increment the overflow counter by 1 at every occurrence of said clock counter overflow and is responsive to completion of operation of said second operation for resetting said overflow counter, and a command generator detecting the overflow counter exceeding said given value to produce a command signal for setting said wheel speed and said wheel acceleration or deceleration at said fixed values.

13. The anti-skid brake control system as set forth in claim 12, wherein said overflow counter is operative at every occasion of said clock counter overflow, and said command generator is activated cyclically at a given timing.

14. The anti-skid brake control system as set forth in claim 13, wherein said command generator is operative at a given time interval corresponding to a period of time indicated by the maximum counter capacity value of said clock counter.

15. The anti-skid brake control system as set forth in claim 6, wherein said controller is further operative for counting in an interruption counter occurrences of interruption of said second operation each time interruptions occur, counting down the interruption counter by 1 whenever said second operation is completed and repeating said second operation until said interruption counter has a value of zero.

16. The anti-skid control system as set forth in claim 15, wherein said controller processes said sampled timer signals to derive wheel speed based on mutually adjacent pairs of sensor signal pulses and wheel acceleration and deceleration values based on sequentially sampled values of said timer signals.

17. A method for anti-skid controlling an automotive hydraulic brake system including a wheel cylinder and a pressure control valve, fluid pressure in said wheel cylinder being increased as said pressure control valve is placed at a first position thereof, is decreased as said pressure control valve is placed at a second position thereof and is maintained at a substantially constant value at a third position of said pressure control valve, said method comprising the steps of: detecting wheel rotation speed to sequentially produce sensor signal pulses having intervals between mutually adjacent sensor signal pulses representative of the wheel speed; measuring a period of time by means of a timer counter which counts clock pulses and having a maximum capacity, said timer counter producing a timer signal having a value representative of the number of counted clock pulses; sampling a value of said timer counts in response to a given number of said sensor signal pulses to store said timer counter value as input time data of the corresponding sensor signal pulses; performing arithmetic operations for processing said input time data of said sensor signal pulses for deriving a wheel speed value and a wheel acceleration value or deceleration value as control factors and for detecting slip data based on derived wheel speed and wheel acceleration and deceleration values for controlling said pressure control valve positions according to a predetermined pattern for optimizing braking characteristics at the vehicle wheel based on said slip rate data and said wheel acceleration value and deceleration value; interrupting said arithmetic operations in response to said every given number of sensor signal pulses for performing operations for sampling the timer counter value and storing the sampled timer counter value as said input time data; detecting occurrences of overflow of the maximum capacity of said timer counter and counting the number of occurrences of overflow in an overflow counter, the overflow counter value being cleared at the end of said arithmetic operations; and setting said wheel speed value and said wheel acceleration and deceleration values as said control factors to given fixed values when said overflow counter value becomes equal to or greater than a given value.

18. The method as set forth in claim 17, which further comprises a step of adjusting said given number to determine a sample mode such that a difference of intervals between successive groups of sensor signal pulses is greater than a predetermined value.

19. The method as set forth in claim 18, wherein said adjustment of said number of sensor signal pulses is repeated to increase the number of sensor signal pulses included in each group without sampling the corresponding input time data until the difference of the intervals becomes greater than said predetermined value.

20. The method as set forth in claim 19, wherein, in said step of performing arithmetic operations, wheel speed is derived based on an interval of the mutually adjacent sensor signal pulses and wheel acceleration and deceleration are derived based on input time data of three sequentially sampled timer counter values.

21. The method as set forth in claim 20, wherein said given fixed values are zero.

22. The method as set forth in claim 20, wherein said step for detecting said overflow counter value becoming equal to or greater than said given value is cyclically performed at a given timing.

23. The method as set forth in claim 22, wherein said step for detecting said overflow counter value becoming equal to or greater than said given value is performed at an interval corresponding to a maximum period of time to be measured by said timer.