Antiskid controller

• US 6,023,649 A
• Filed: 02/12/1996
• Issued: 02/08/2000
• Est. Priority Date: 07/19/1994
• Status: Expired due to Term

• Current Assignee: Nippondenso Co., Ltd. (DENSO Corporation)
• Original Assignee: Nippondenso Co., Ltd. (DENSO Corporation)
• Inventors: Terao, Hidenori, Masaki, Syouichi, Ochi, Tsuyoshi, Matsuura, Masahiro
• Primary Examiner(s): Cuchlinski, Jr., William A.
• Assistant Examiner(s): Donnelly, Arthur D.
• Application Number:
  US08/600,218
• Time in Patent Office: 1,457 Days
• Field of Search: 701/71, 701/74, 701/78, 701/79, 701/80, 303/150, 303/156, 303/169, 180/197
• US Class Current: 701/71
• CPC Class Codes: B60T 2210/12 Friction
• CPC Class Codes: B60T 8/172 Determining control parameters used in the regulation, e.g. by calculations involving measured or detected parameters B60T8/17551 takes precedence
• CPC Class Codes: B60T 8/17636 Microprocessor-based systems

Abstract

The invention provides an anti-skid controller capable of correctly executing ABS control by accurately estimating a road surface μ without using additional sensors. Each wheel speed is detected, and acceleration of the vehicle body in a case where a wheel speed difference between front and rear wheels exceeds a specified value is determined. In this case, by using a change rate within a specified period of time with respect to a wheel speed of one in which wheel speed changing is small as the acceleration, a road surface μ corresponding to the acceleration is determined. Corrections regarding turning, bad road travelling, road surface changing, etc. can be carried out, by determining a lateral G based on a speed difference between left and right wheels.

Claims

1. An anti-skid controller comprising:

wheel speed detecting means for detecting a wheel speed of each wheel of a vehicle;

vehicle body speed calculating means for calculating a vehicle body speed of the vehicle based on the wheel speed;

calculating means for calculating an average change gradient of a wheel speed over a specified period of time of one of front and rear wheels of the vehicle in which a chance in the wheel speed detected by the wheel speed detecting means within the specified period of time is smallest;

determining means for determining whether or not a change rate of a difference in wheel speeds between the front and rear wheels within the specified period of time reaches a specified value;

estimating means for estimating a friction coefficient between a road surface and the wheel, at a point in time where the change rate is found to reach the specified value or higher by the determining means based on the average change of gradient calculated immediately prior to the point in time; and

brake pressure control means for controlling brake pressure of a controlled wheel in accordance with anti-skid control reference determined by using at least the friction coefficient to prevent excess slipping of the controlled wheel based on a comparison between the vehicle body speed and a speed of the controlled wheel.

20. An anti-skid controller according to claim 1 or 3, wherein the determining means determines whether or not a change rate with respect to an integrated value obtained by periodically and sequentially integrating, within a specified period of time, wheel speed differences between the front and rear wheels of the vehicle reaches a specified value or higher.

2. An anti-skid controller comprising:

wheel speed detecting means for detecting a wheel speed of each wheel of a vehicle;

calculating means for calculating an average change gradient of a wheel speed over a specified period of time of one of front and rear wheels of the vehicle in which a change in the wheel speed detected by the wheel speed detecting means within the specified period of time is smallest;

forward and backward direction acceleration calculating means for converting the average change gradient calculated by the calculating means to a forward and backward direction acceleration of the vehicle corresponding to a road surface friction coefficient based on changes of the relative wheel speeds between the front and rear wheels detected by the wheel speed detecting means;

vehicle body speed calculating means for calculating the vehicle body speed by using at least the forward and backward direction acceleration; and

brake pressure control means for controlling brake pressure of a controlled wheel in order to prevent excess slipping of a controlled wheel based on comparison between the vehicle body speed and a wheel speed of the controlled wheel.

3. An anti-skid controller comprising:

wheel speed detecting means for detecting a wheel speed of each wheel of a vehicle;

vehicle body speed calculating means for calculating a vehicle body speed of the vehicle based on the wheel speed;

determining means for determining whether or not a change rate within a specified period of time with respect to a difference in speeds between the front and rear wheels reaches a specified value or higher;

forward and backward direction acceleration calculating means for calculating acceleration in forward and backward directions corresponding to a road surface friction coefficient of a road surface immediately before the determining means determines that the change rate reaches the specified value or higher;

estimating means for estimating a friction coefficient between the wheels and the road surface based on the forward and backward direction acceleration calculated by the forward and backward direction acceleration calculating means; and

brake pressure control means for controlling brake pressure of a controlled wheel in accordance with an anti-skid control reference determined by using at least the friction coefficient in order to prevent excess slipping of the controlled wheel based on a comparison between the vehicle body speed and a wheel speed of the controlled wheel.

4. An anti-skid controller comprising:

wheel speed detecting means for detecting a wheel speed of each wheel of a vehicle;

forward and backward direction acceleration calculating means for calculating acceleration in forward and backward directions corresponding to a road surface friction coefficient based on changes of relative wheel speeds between front and rear wheels detected by the wheel speed detecting means;

lateral direction acceleration calculating means for calculating acceleration in a lateral direction of the vehicle based on wheel speeds of left and right wheels detected by the wheel speed detecting means;

deceleration limit gradient calculating means for calculating a deceleration limit gradient of the vehicle based on the forward and backward direction acceleration and the lateral acceleration;

vehicle body speed calculating means for calculating a vehicle body speed of the vehicle by using at least the deceleration limit gradient; and

brake pressure control means for controlling brake pressure of a controlled wheel in order to prevent excess slipping of the controlled wheel based on a comparison between the vehicle body speed and a wheel speed of the controlled wheel.

6. An anti-skid controller according to claim 4 or 5, wherein the forward and backward direction acceleration calculating means calculates, when braking torque is applied to the front and rear wheels of the vehicle, acceleration in forward and backward directions corresponding to a road surface friction coefficient based on a changing rate of wheel speeds on a high speed side when a change in a difference between front and rear wheel speeds exceeding a specified value is produced.

7. An anti-skid controller according to claim 6, wherein the forward and backward direction acceleration calculating means calculates, when no change exceeding the specified value is produced in the difference between the front and rear wheel speeds and brake pressure control is started for the front or the rear wheels, the acceleration in forward and backward directions corresponding to the road surface friction coefficient based on the change rate of wheel speeds of the front or the rear wheels when the brake pressure control is started.

8. An anti-skid controller according to claim 4 or 5, further comprising:

determining means for determining whether a road surface is a bad road surface that causes wheel acceleration based on change conditions in wheel speed; and

correcting means for correcting, when the determining means determines that the road surface is bad, the deceleration limit gradient calculated by the deceleration limit gradient calculating means to handle the bad road.

9. An anti-skid controller according to claim 8, wherein the correcting means corrects the deceleration limit calculated by the deceleration limit gradient calculating means to a bad road deceleration limit gradient value specified beforehand in order to handle a bad road.

10. An anti-skid controller according to claim 4 or 5, further comprising:

determining means for determining whether a road surface is an extremely low friction road surface based on a changing condition of a wheel speed when at least braking torque changes; and

correcting means for correcting, when the determining means determines that the road travelled by the vehicle is an extremely low friction road surface,the deceleration limit gradient calculated by the deceleration limit gradient calculating means in order to handle the extremely low friction road surface.

11. An anti-skid controller according to claim 10, wherein the correcting means corrects a deceleration limit calculated by the deceleration limit gradient calculating means to a bad road deceleration limit gradient specified beforehand in order to handle the extremely low friction road surface.

19. An anti-skid controller according to claim 4 or 5, wherein the forward and backward direction acceleration calculating means calculates, in a case where an integrated value obtained by periodically and sequentially integrating wheel speed differences between the front and rear wheels reaches a specified value or higher after braking torque is applied to the front and rear wheels of the vehicle, acceleration in forward and backward directions corresponding to a road surface friction coefficient based on a change rate of a wheel speed on a high speed side.

5. An anti-skid controller comprising:

wheel speed detecting means for detecting a wheel speed of each wheel of a vehicle;

forward and backward direction acceleration calculating means for calculating acceleration in forward and backward directions corresponding to a road surface friction coefficient based on changes of relative wheel speeds between front and rear wheels detected by the wheel speed detecting means before starting brake pressure control after braking torque is applied to the front and rear wheels of the vehicle;

lateral direction acceleration calculating means for calculating acceleration in a lateral direction of the vehicle based on wheel speeds of left and right wheels detected by the wheel speed detecting means before starting brake pressure control after braking torque is applied to the front and rear wheels of the vehicle;

deceleration limit gradient calculating means for calculating a deceleration limit gradient of the vehicle based on the forward and backward direction acceleration and the lateral direction acceleration;

vehicle body speed calculating means for calculating a vehicle body speed by using at least the deceleration limit gradient; and

brake pressure control means for controlling brake pressure of a controlled wheel in order to prevent excess slipping of a controlled wheel based on a comparison between the vehicle body speed and a wheel speed of the controlled wheel.

12. An anti-skid controller according to claim 5, further comprising:

determining means for determining, based on a change of a wheel speed with respect to an increase or decrease in brake pressure after starting anti-skid control, whether the deceleration limit gradient calculated by the deceleration limit gradient calculating means is suitable for the road surface; and

correcting means for correcting the deceleration gradient during antiskid control when the determining means determines that the deceleration limit gradient is not suitable for the road surface.

13. An anti-skid controller according to claim 12, wherein the determining means determines, when wheel speed reduction is below a reference value even after brake pressure is increased over a specified amount, that the deceleration limit gradient is not suitable for the road surface.

14. An anti-skid controller according to claim 12, wherein the determining means determines, when wheel speed reduction is over a reference value even after brake pressure is decreased, that the deceleration limit gradient is not suitable for the road surface.

15. An anti-skid controller according to claim 12, wherein the determining means determines, when brake pressures applied to a plurality of wheels are simultaneously increased in anti-skid control based on a wheel speed of each wheel, that the deceleration limit gradient is not suitable for the road surface.

16. An anti-skid controller according to claim 12, wherein the determining means determines, when wheel speed reaches the vehicle body speed or higher, that the deceleration limit gradient is not suitable for the road surface.

17. An anti-skid controller comprising:

wheel speed detecting means for detecting a wheel speed of each wheel of a vehicle;

vehicle body speed calculating means for obtaining a vehicle body speed based on the wheel speed of each wheel;

calculating means for calculating an average change gradient within a specified period of time with respect to the vehicle body speed calculated by the vehicle body speed calculating means;

determining means for determining whether a change rate within a specified period of time with respect to a speed difference between a rear wheel speed and the vehicle body speed or a speed difference between a front wheel speed and the vehicle body speed reaches a specified value or higher;

estimating means for estimating, when the determining means determines that the change rate reaches the specified value or higher, a friction coefficient between a road surface travelled by the vehicle and the wheels based on the average change gradient immediately before the chance rate reaches the specified value or higher; and

brake pressure control means for controlling brake pressure of a controlled wheel according to an anti-skid control reference determined by using at least the friction coefficient to prevent excess slipping of the controlled wheel based on a comparison between the vehicle body speed and the speed of the controlled wheel.

18. An anti-skid controller comprising:

wheel speed detecting means for detecting a wheel speed of each wheel of a vehicle;

vehicle body speed calculating means for obtaining a vehicle body speed based on the wheel speed of each wheel;

calculating means for calculating an average change gradient within a specified period of time with respect to a vehicle body speed calculated by the vehicle body speed calculating means;

determining means for determining whether either a change rate within a specified period of time with respect to a speed difference between a rear wheel speed and the vehicle body speed or a change rate within a specified period of time with respect to a speed difference between a front wheel speed and the vehicle body speed reaches a specified value or higher;

estimating means for estimating, when the determining means determines that one of the change rates reaches the specified value or higher, a friction coefficient between a road surface travelled by the vehicle and the wheels based on the average change gradient calculated by the calculating means immediately before the chance rate reaches the specified value or higher; and

brake pressure control means for controlling brake pressure of a controlled wheel corresponding to an anti-skid control reference determined by using at least the friction coefficient to prevent excess slipping of the controlled wheel based on a comparison between the vehicle body speed and the speed of the controlled wheel.

21. An apparatus for a vehicle comprising:

wheel speed detection means for detecting a wheel speed of each of front and rear wheels of a vehicle;

wheel deceleration calculation means for calculating a wheel deceleration of each wheel from the detected wheel speed;

speed difference calculation means for calculating a difference in the detected speeds of the front and rear wheels;

timing determination means for determining, from the calculated speed difference, a timing of estimating a friction coefficient of a road surface; and

estimation means for estimating the friction coefficient from the calculated wheel deceleration, and irrespective of the calculated speed difference, at the determined timing of estimating.

22. An apparatus according to claim 21, wherein:

the speed difference calculation means further calculates a change rate of the calculated speed difference in a predetermined time period; and

the timing determination means determines the timing of estimating the friction coefficient from the calculated change rate attaining a predetermined reference.

23. An apparatus according to claim 21, wherein the estimation means estimates the friction coefficient from the calculated wheel deceleration of one of the wheels which has the smallest change in its detected wheel speed in a predetermined time period as compared to the change in wheel speed of the other wheels.

24. An apparatus according to claim 21, wherein the estimation means estimates the friction coefficient from the calculated wheel deceleration of one of the front and rear wheels which has the smallest change in its detected wheel speed in a predetermined time period as compared to the change in wheel speed of the other wheels.

25. An apparatus according to claim 21, further comprising:

vehicle body speed detection means for detecting a vehicle body speed from the detected wheel speed of each wheel;

control reference setting means for variably setting a control reference in accordance with the estimated road surface friction coefficient; and

brake control means for controlling a braking operation of the vehicle using the set control reference and based on the detected vehicle body speed and the detected wheel speed of each wheel.

29. An apparatus according to claim 21, wherein:

the speed difference calculation means further calculates a parameter using the calculated speed difference; and

the timing determination means determines the timing of estimating the friction coefficient only when the calculated parameter attains a predetermined reference.

30. An apparatus according to claim 29, wherein the speed difference calculation means calculates a change rate of the calculated speed difference in a predetermined time period as the parameter.

31. An apparatus according to claim 21, wherein the estimation means estimates the friction coefficient variably in accordance with the calculated wheel deceleration.

26. A method comprising the steps of:

detecting a wheel speed of each of front and rear wheels of a vehicle;

calculating a wheel deceleration of each wheel from the detected wheel speed;

calculating a difference in the detected speeds of the front and rear wheels;

determining, from the calculated speed difference, a timing of estimating a friction coefficient of a road surface; and

estimating the friction coefficient from the calculated wheel deceleration, and irrespective of the calculated speed difference, at the determined estimation timing.

32. A method according to claim 26, wherein the determining step calculates a change rate of the calculated difference and determines the timing of estimating the friction coefficient only when the calculated change rate is smaller than a predetermined reference.

27. A method for controlling a vehicle comprising the steps of:

detecting a wheel speed of each of front and rear wheels of a vehicle;

calculating a wheel deceleration from the detected wheel speed;

determining from the detected wheel speed a timing of estimating a friction coefficient of a road surface;

estimating the friction coefficient from the calculated wheel deceleration, and irrespective of the calculated speed difference, at the determined estimation timing; and

controlling an operation of the vehicle using the estimated friction coefficient.

33. A method according to claim 27, wherein the determining step integrates a difference in the detected wheel speeds of the front and rear wheels at a first predetermined interval and calculates a change rate of the integrated difference at a second predetermined interval longer than the first predetermined interval, to thereby determine the timing of estimating the friction coefficient only when the calculated change rate is less than a predetermined reference.

28. A method of controlling a vehicle comprising the steps of:

detecting a wheel speed of each of front and rear wheels of a vehicle;

calculating a wheel deceleration of each wheel from the detected wheel speed;

determining which one of the wheels has the smallest change in the calculated wheel speed as compared to the change in wheel speed of the other wheels;

estimating a friction coefficient from the calculated wheel deceleration of the determined one wheel; and

controlling an operation of the vehicle using the estimated friction coefficient.

34. A method according to claim 28, further comprising the steps of:

calculating a difference in the detected wheel speeds of the front and rear wheels at a first predetermined interval;

calculating a change rate of the calculated wheel speed difference at a second predetermined interval longer than the first predetermined interval; and

determining a timing of estimating the friction coefficient only when the calculated change rate is less than a predetermined reference.

35. A control system for a vehicle comprising:

speed detecting means for detecting a speed of each of vehicle front and rear wheels;

deceleration calculating means for calculating a deceleration of a vehicle body;

difference calculating means for calculating a difference in the detected speeds of the front wheel and the rear wheel;

timing determining means for determining a timing of estimating a road surface friction coefficient based on the calculated speed difference; and

estimating means for estimating the friction coefficient based on the calculated deceleration, and irrespective of the calculated speed difference, at the timing determined by the timing determining means.

36. A control system according to claim 35, further comprising:

skid control means for controlling a skidding of the vehicle front and rear wheels when a skid control condition is established; and

changing means for changing the skid control condition based on the estimated friction coefficient.

37. A control system for a vehicle comprising:

speed detecting means for detecting a speed of each of vehicle front and rear wheels;

deceleration calculating means for calculating a deceleration of a vehicle body at every predetermined period based on the detected wheel speed;

difference calculating means for detecting a difference in the detected speeds of the front wheel and the rear wheel;

integration means for integrating the calculated difference for the predetermined period;

comparison means for comparing the integrated difference with a predetermined reference;

holding means for holding the calculated deceleration unchanged irrespective of changes in the calculated deceleration when a comparison output indicates that the integrated difference exceeds the predetermined reference; and

control means for controlling a braking operation of the vehicle based on the calculated deceleration.

38. A control system according to claim 37, further comprising estimating means for estimating a friction coefficient of a road surface based on the calculated deceleration, the estimated friction coefficient being used by the control means in controlling the braking operation.