ANTI SKID CONTROL SYSTEM

• US 3,832,008 A
• Filed: 02/02/1972
• Issued: 08/27/1974
• Est. Priority Date: 08/23/1971
• Status: Expired due to Term

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Anton Rodi, Heinz Leiber
• Inventors: Leiber, Heinz, Rodi, Anton
• Primary Examiner(s): Blix, Trygve M.
• Assistant Examiner(s): Kunin, Stephen G.
• Application Number:
  US05/222,780
• Time in Patent Office: 937 Days
• Field of Search: 188/181C 303/20,21 317/5 324/160-161 340/263
• US Class Current: 701/79
• CPC Class Codes: B60T 8/17613 based on analogue circuits or digital circuits comprised of discrete electronic elements

Abstract

An antilocking control system in which slip signals are generated for brake pressure modulation. In this control system the circuitry for generating slip signals includes a unit for generating a signal proportional to the wheel speed and a memory circuit for generating a reference signal approximating the vehicle speed and having two different discharge time constants. When the second constant is effective, the stored signal follows decreases of the wheel speed very slowly. This constant is made effective, when a locking tendency occurs and the memory circuit is switched back to the first time constant only, if a permissible slip value is reached and particularly the reacceleration phase is substantially completed. The slip signals are generated by comparing the reference signal from the memory circuit with the signal proportional to the wheel speed.

Claims

1. An antilocking control system in which wheel slip signals are generated for brake pressure modulation, wherein the means for generating such slip signals comprise:

1. means for generating a signal which is substantially directly proportional to the rotational speed of a vehicle wheel, 2. memory means for generating a reference signal approximating the vehicle speed, said memory means being connected to said generating means to receive the signal proportional to the rotational speed and including discharge means for causing the reference signal to vary at one of two different individually selectable discharge time constants, the first discharge time constant permitting the reference signal generated by said memory means to follow the signal proportional to the rotational speed substantially without delay and the second discharge time constant permitting the reference signal to correspond to a slow decrease in vehicle speed, 3. comparison means connected to said generating means and said memory means for comparing the signal proportional to the rotational speed with the reference signal from said memory means and for generating an output signal for brake pressure modulation, when the rotational speed of the vehicle wheel is below the reference signal and in a certain relationship thereto, and 4. switching means connected to said memory means and including sensing means operatively arranged to respond to the rotational behavior of such wheel for producing a control signal when such wheel shows a tendency to lock and for terminating such control signal when a permissible slip value is reached, said switching means switching said memory means to its second discharge time constant in response to the occurrence of the control signal produced by said sensing means when a locking tendency occurs and switching said memory means back to its first time constant in the absence of such control signal.

2. memory means for generating a reference signal approximately the vehicle speed, said memory means being connected to said generating means to receive the signal proportional to the rotational speed and including discharge means for causing the reference signal to vary at any one of at least three different individually selectable discharge time constants, the first discharge time constant permitting the reference signal generated by said memory means to follow the signal proportional to the rotational speed substantially without delay, the second discharge time constant permitting the reference signal to correspond to a very slow decrease in vehicle speed and the additional discharge time constants being different but higher than the first constant and lower than the second constant,

3. comparison means connected to said generating means and said memory means for comparing the signal proportional to the rotational speed with the reference signal from said memory means and for generating an output signal for brake pressure modulation, when the rotational speed of the vehicle wheel is below the reference signal and in a certain relationship thereto, and

4. An arrangement as defined in claim 3, wherein:

said accelerometer means comprises means for providing a positive acceleration signal as a second output signal from a second output means of said accelerometer means;

said second output means of said accelerometer means being coupled in said switching means so that said switching means is responsive to said second output signal for holding said memory circuit means in its second time constant condition whenever the positive acceleration of the braked wheel exceeds a given value, whereby said memory circuit means is switched to its first time constant whenever the wheel has passed below a permissible slip value and the reacceleration phase has been substantially completed.

5. An arrangement as defined in claim 1 wherein said sensing means includes accelerometer means for providing a signal representing the acceleration of the wheel, a normally open inlet valve coupled to an output of said comparison means, and wherein the second discharge time constant of said memory means remains effective as long as said inlet valve is closed and as long as said accelerometer means produces a positive acceleration signal indicating that the re-acceleration phase of the wheel has not yet been substantially completed.

6. An arrangement as defined in claim 1 wherein there are several comparison means each associated with a different vehicle wheel and the reference signal generated by said memory means in response to the speed of rotation of one vehicle wheel is fed to each of said comparison means.

7. An arrangement as defined in claim 6 wherein the one vehicle wheel is a nondriven wheel.

8. An arrangement as defined in claim 7 further comprising:

means responsive to the rotational speeds of additional vehicle wheels for developing speed-related signals; and

means responsive to said speed-related signals and output from said memory circuit means for developing said reference signal.

9. An arrangement as defined in claim 8 further comprising means responsive to said speed-related signals and the output of said memory circuit means for formulating said reference signal from the highest one of said speed-related signals whenever at least a substantial portion of it exceeds the output of said memory circuit means.

10. An arrangement as defined in claim 1 further comprising:

separate control means for the brake pressure at first and second wheels of one axle;

wherein there are two of said memory circuit means, the first wheel being associated with the first said memory circuit means and the second wheel being associated with the second said memory circuit means;

said first memory circuit means and said second memory circuit means being fed respectively with signals proportional to the rotational speed of the respective associated wheels;

the switching of the discharge time constants of the said two memory means being effected by signals which are derived from the associated wheel and which indicate a tendency of that wheel to lock;

each of said memory circuit means furnishing output signals; and

signal processing means coupled to an output means of said first memory circuit means and an output means of said second memory circuit means and responsive to said output signals for selecting the higher of said output signals as said reference signal.

11. An arrangement as defined in claim 10 wherein the reference signal, derived from the braked nondriven axle of the vehicle, is also used to control the brake pressure at the driven wheels.

12. An arrangement as defined in claim 10 further comprising:

means responsive to the rotational speeds of additional vehicle wheels for developing speed-related signals; and

means responsive to said speed-related signals and the output from said processing means for developing said reference signal.

13. An arrangement as defined in claim 12 further comprising means responsive to said speed-related signals and the output of said processing means for formulating said reference signal from the highest one of said speed-related signals whenever at least a substantial portion of it exceeds the output of said processing means.

14. An arrangement as defined in claim 13 further comprising an additional memory means to which the speed-related signal which is proportional to the highest rotational speed of the additional wheels is fed, said additional memory means having a first time constant and a second time constant;

and further comprising means for switching said additional memory means to its second time constant as long as a signal proportional to the highest rotational speed of the additional wheels exceeds the reference signal obtained from the undriven axle, the output of said additional memory means furnishing then the reference signal.

15. An arrangement as defined in claim 12 comprising further processing means generating the reference signal and receiving the output signal of said processing means, which is the higher output of the outputs of said two memory means, and the highest speed-related signal of the other wheels, said further processing means forming, as reference signal, an average of at least substantial portions of its input signals.

16. An arrangement as defined in claim 1 further comprising:

separate control means for the brake pressure at first and second wheels of one axle;

wherein there are two of said memory circuit means, the first wheel being associated with the first said memory circuit means, and the second wheel being associated with the second said memory circuit means;

said first and second memory being fed respectively with signals proportional to the rotational speed of the respective associated wheels;

the switching of the discharge time constants of the said two memory means being effected by signals which are derived from the associated wheel and which indicate a tendency of that wheel to lock each of said memory circuit means furnishing output signals; and

signal processing means coupled to an output means of said first memory circuit means and an output means of said second memory circuit means and responsive to said output signals for forming an average of said output signals, said average constituting the reference signal.

17. An arrangement as defined in claim 16 wherein the reference signal, derived from the braked nondriven axle of the vehicle, is also used to control the brake pressure at the driven wheels.

18. An arrangement as defined in claim 16 further comprising:

means responsive to the rotational speeds of additional vehicle wheels for developing speed-related signals; and

means responsive to said speed-related signals and the output from said processing means for developing said reference signal.

19. An arrangement as defined in claim 18 further comprising means responsive to said speed-related signals and the output of said processing means for formulating said reference signal from the highest one of said speed-related signals whenever at least a substantial portion of its exceeds the output of said processing means.

20. An arrangement as defined in claim 19 further comprising an additional memory means to which the speed-related signal which is proportional to the highest rotational speed of the additional wheels is fed, said additional memory means having a first time constant and a second time constant;

and further comprising means for switching said additional memory means to the second time constant whenever a signal proportional to the highEst rotational speed of the additional wheels exceeds the reference signal obtained from the undriven axle, the output of said additional memory means furnishing then the reference signal.

21. An arrangement as defined in claim 1 further comprising:

separate means responsive to the rotational speeds of additional wheels for producing separate signals directly proportional to the individual speeds of the additional wheels; and

means responsive to the output of said memory circuit means and to said separate signals for switching said memory circuit means to said second time constant whenever any one of said separate signals exceeds the output of said memory circuit means.

22. An antilocking control system in which wheel slip signals are generated for brake pressure modulation, wherein the means for generating such slip signals comprises:

23. An arrangement as defined in claim 22 wherein, said switching means acts to switch said memory means back to its first time constant when the vehicle wheel re-acceleration phase is substantially completed.

24. An arrangement as defined in claim 22 wherein said sensing means includes accelerometer means for sensing vehicle deceleration and providing switching signals for the time constants when certain vehicle deceleration thresholds are reached.

25. An arrangement as defined in claim 22 wherein only three discharge time constants are provided and wherein the discharge time constant between the highest and the lowest constants is made effective by switching signals when a locking tendency occurs, and wherein the highest discharge time constant is made effective by switching signals when during the antilocking control the signal proportional to vehicle speed falls below a given slip threshold.

26. An arrangement as defined in claim 22 further comprising means connected for measuring the brake pressure at the wheel and wherein the individual discharge time constants are made effective by switching signals corresponding to brake pressure at the wheel during control, the lower the brake pressure the higher the effective discharge time constant.

27. An arrangement as defined in claim 22 wherein only three discharge time constants are provided and wherein the discharge time constant between the lowest and the highest discharge constants is made effective by switching signals when a locking tendency occurs, and wherein the highest discharge time constant is made effective by switching signals when brake pressure is decreased for a given time within a time period.

28. An arrangement as defined in claim 22 wherein only three discharge time constants are provided, and further comprising a wheel accelerometer, and wherein the highest discharge time constant is made effective by means of switching signals when a locking tendency occurs and wherein the discharge time constant between the lowest and the highest constants is made effective by switching signals when during antilocking control an acceleration threshold is exceeded as indicated by said wheel accelerometer.

29. An antilocking control system in which wheel slip signals are generated for brake pressure modulation, wherein the means for generating such slip signals comprise: