Road surface condition determination system for automotive vehicles and anti-skid braking system having the same

• US 6,266,602 B1
• Filed: 02/18/2000
• Issued: 07/24/2001
• Est. Priority Date: 02/18/1999
• Status: Expired due to Term

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Unisia Jecs Corporation (Hitachi, Ltd.)
• Inventors: Yamaura, Tamotsu
• Primary Examiner(s): Cuchlinski, Jr., William A.
• Assistant Examiner(s): MANCHO, RONNIE M
• Application Number:
  US09/506,598
• Time in Patent Office: 522 Days
• Field of Search: 701/80-83, 701/91, 701/93, 701/102, 701/110, 701/1, 701/70, 701/71, 701/78, 303/121, 303/160, 303/165, 303/168, 303/3, 303/112, 303/152, 303/154, 303/163, 318/383, 318/430, 405/91, 405/84, 340/905
• US Class Current: 701/80
• 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

Abstract

A road surface condition determination system for an automotive vehicle comprises wheel-speed sensors, and a control unit being configured to be electrically connected to the wheel-speed sensors for data-processing a wheel-speed data signal. The control unit calculates a wheel-speed fluctuation of each of the road wheels on the basis of a previous value of the wheel-speed data signal and a current value of the wheel-speed data signal, and calculates an absolute value of the wheel-speed fluctuation of each of the road wheels. A integration circuit is provided to produce a first integrated value of the absolute values of the wheel-speed fluctuations of the road wheels. A smoothing circuit is provided to make a smoothing operation to the integrated value to produce a smoothed value. A road-surface condition determining section is also provided to determine a road surface condition on the basis of the smoothed value. In an automotive vehicle with an ABS system, a skid control section uses the result of discrimination between good and bad roads, executed by the road-surface condition determining section, so as to vary a pressure-reduction threshold depending on the road surface condition detected.

Claims

1. A road surface condition determination system for an automotive vehicle, comprising:

wheel-speed sensors detecting wheel speeds of each of road wheels; and

a control unit being configured to be electrically connected to said wheel-speed sensors for processing a wheel-speed data signal from each of said wheel-speed sensors, said control unit comprising;

(a) a wheel-speed fluctuation arithmetic-calculation section which calculates a wheel-speed fluctuation of each of the road wheels on the basis of a previous value of the wheel-speed data signal and a current value of the wheel-speed data signal,

(b) a first absolute-value arithmetic-calculation section which calculates an absolute value of the wheel-speed fluctuation of each of the road wheels,

(c) a first integration section which produces a first integrated value of the absolute values of the wheel-speed fluctuations of the road wheels,

(d) a smoothing section which makes a smoothing operation to the first integrated value to produce a smoothed value, and

(e) a road-surface condition determining section which determines a road surface condition on the basis of the smoothed value.

2. The road surface condition determination system as claimed in claim 1, wherein the wheel-speed fluctuation arithmetic-calculation section comprises a first-order high-pass filter that attenuates the wheel-speed data signal at a frequency below a predetermined cutoff frequency lower than a resonance frequency of unsprung mass.

3. The road surface condition determination system as claimed in claim 2, wherein said control unit comprises a skid-control dependent wheel-speed fluctuation arithmetic-calculation section which calculates a skid-control dependent wheel-speed fluctuation of each of the road wheels, occurring due to skid control, on the basis of a previous value of the wheel-speed data signal and a current value of the wheel-speed data signal, a second absolute-value arithmetic-calculation section which calculates an absolute value of the skid-control dependent wheel-speed fluctuation of each of the road wheels, a second integration section which produces a second integrated value of the absolute values of the skid-control dependent wheel-speed fluctuations of the road wheels, and a correction section which calculates a wheel-speed fluctuation correction value by subtracting the second integrated value from the first integrated value, and wherein said smoothing section makes the smoothing operation to the wheel-speed fluctuation correction value in lieu of the first integrated value to produce the smoothed value.

4. The road surface condition determination system as claimed in claim 3, wherein the skid-control dependent wheel-speed fluctuation arithmetic-calculation section comprises a first first-order low-pass filter that attenuates the wheel-speed data signal at a frequency above a predetermined cutoff frequency lower than the resonance frequency of unsprung mass.

5. The road surface condition determination system as claimed in claim 3, wherein the skid-control dependent wheel-speed fluctuation arithmetic-calculation section comprises a second first-order low-pass filter that attenuates the wheel-speed data signal at a frequency above a predetermined cutoff frequency lower than the predetermined cutoff frequency of the first-order high-pass filter.

6. The road surface condition determination system as claimed in claim 2, wherein the smoothing section comprises a first-order smoothing low-pass filter that attenuates the wheel-speed data signal at a frequency above a predetermined cutoff frequency lower than the predetermined cutoff frequency of the first-order high-pass filter.

7. The road surface condition determination system as claimed in claim 5, wherein the smoothing section comprises a first-order smoothing low-pass filter that attenuates the wheel-speed data signal at a frequency above a predetermined cutoff frequency lower than the predetermined cutoff frequency of one of the first and second first-order low-pass filters.

8. An anti-skid braking system having a road surface condition determination system for an automotive vehicle, comprising:

wheel-speed sensors detecting wheel speeds of each of road wheels;

a hydraulic brake unit regulating wheel-brake cylinder pressures of wheel-brake cylinders mounted to each of the road wheels; and

a control unit being configured to be electrically connected to said wheel- speed sensors and hydraulic brake unit for processing a wheel-speed data signal from each of said wheel-speed sensors and for execute skid control based on the wheel-speed data signal from each of said wheel-speed sensors, said control unit comprising;

(a) a wheel-speed fluctuation arithmetic-calculation section which calculates a wheel-speed fluctuation of each of the road wheels on the basis of a previous value of the wheel-speed data signal and a current value of the wheel-speed data signal,

(b) a first absolute-value arithmetic-calculation section which calculates an absolute value of the wheel-speed fluctuation of each of the road wheels,

(c) a first integration section which produces a first integrated value of the absolute values of the wheel-speed fluctuations of the road wheels,

(d) a skid-control dependent wheel-speed fluctuation arithmetic-calculation section which calculates a skid-control dependent wheel-speed fluctuation of each of the road wheels, occurring due to skid control, on the basis of a previous value of the wheel-speed data signal and a current value of the wheel-speed data signal,

(e) a second absolute-value arithmetic-calculation section which calculates an absolute value of the skid-control dependent wheel-speed fluctuation of each of the road wheels,

(f) a second integration section which produces a second integrated value of the absolute values of the skid-control dependent wheel-speed fluctuations of the road wheels,

(g) a correction section which calculates a wheel-speed fluctuation correction value by subtracting the second integrated value from the first integrated value,

(h) a smoothing section which makes a smoothing operation to the wheel-speed fluctuation correction value to produce a smoothed value,

(i) a road-surface condition determining section which determines a road surface condition on the basis of the smoothed value, and

(j) a skid control section preventing wheel lock of each of the road wheels in response to the wheel-speed data signal from each of the wheel-speed sensors, said skid control section executing the skid control depending on the road surface condition determined by the road-surface condition determining section.

9. The anti-skid braking system as claimed in claim 8, wherein, when a bad road surface condition is detected by the road surface condition determining section, the skid control section sets a pressure-reduction threshold value at a lower value as compared to a road surface condition except the bad road surface condition.

10. A road surface condition determination system for an automotive vehicle, comprising:

wheel-speed sensors detecting wheel speeds of each of road wheels; and

a control unit being configured to be electrically connected to said wheel-speed sensors for processing a wheel-speed data signal from each of said wheel-speed sensors, said control unit comprising;

(a) a wheel-acceleration arithmetic-calculation section which calculates a wheel-acceleration data signal as a difference between a previous value of the wheel-speed data signal and a current value of the wheel-speed data signal,

(b) a wheel-speed fluctuation arithmetic-calculation section which calculates a wheel-speed fluctuation of each of the road wheels on the basis of the wheel-acceleration data signal,

(c) a first absolute-value arithmetic-calculation section which calculates an absolute value of the wheel-speed fluctuation of each of the road wheels,

(d) a first integration section which produces a first integrated value of the absolute values of the wheel-speed fluctuations of the road wheels,

(e) a smoothing section which makes a smoothing operation to the first integrated value to produce a smoothed value, and

(f) a road-surface condition determining section which determines a road surface condition on the basis of the smoothed value.

11. The road surface condition determination system as claimed in claim 10, wherein the wheel-speed fluctuation arithmetic-calculation section comprises a first-order high-pass filter that attenuates the wheel-acceleration data signal at a frequency below a predetermined cutoff frequency lower than a resonance frequency of unsprung mass.

12. The road surface condition determination system as claimed in claim 11, wherein said control unit comprises a skid-control dependent wheel-speed fluctuation arithmetic-calculation section which calculates a skid-control dependent wheel-speed fluctuation of each of the road wheels, occurring due to skid control, on the basis of a previous value of the wheel-acceleration data signal and a current value of the wheel-acceleration data signal, a second absolute-value arithmetic-calculation section which calculates an absolute value of the skid-control dependent wheel-speed fluctuation of each of the road wheels, a second integration section which produces a second integrated value of the absolute values of the skid-control dependent wheel-speed fluctuations of the road wheels, and a correction section which calculates a wheel-speed fluctuation correction value by subtracting the second integrated value from the first integrated value, and wherein said smoothing section makes the smoothing operation to the wheel-speed fluctuation correction value in lieu of the first integrated value to produce the smoothed value.

13. The road surface condition determination system as claimed in claim 12, wherein the skid-control dependent wheel-speed fluctuation arithmetic-calculation section comprises a first first-order low-pass filter that attenuates the wheel-acceleration data signal at a frequency above a predetermined cutoff frequency lower than the resonance frequency of unsprung mass.

14. The road surface condition determination system as claimed in claim 12, wherein the skid-control dependent wheel-speed fluctuation arithmetic-calculation section comprises a second first-order low-pass filter that attenuates the wheel-acceleration data signal at a frequency above a predetermined cutoff frequency lower than the predetermined cutoff frequency of the first-order high-pass filter.

15. The road surface condition determination system as claimed in claim 11, wherein the smoothing section comprises a first-order smoothing low-pass filter that attenuates the wheel-acceleration data signal at a frequency above a predetermined cutoff frequency lower than the predetermined cutoff frequency of the first-order high-pass filter.

16. The road surface condition determination system as claimed in claim 14, wherein the smoothing section comprises a first-order smoothing low-pass filter that attenuates the wheel-acceleration data signal at a frequency above a predetermined cutoff frequency lower than the predetermined cutoff frequency of one of the first and second first-order low-pass filters.

17. An anti-skid braking system having a road surface condition determination system for an automotive vehicle, comprising:

wheel-speed sensors detecting wheel speeds of each of road wheels;

a hydraulic brake unit regulating wheel-brake cylinder pressures of wheel-brake cylinders mounted to each of the road wheels; and

a control unit being configured to be electrically connected to said wheel-speed sensors and hydraulic brake unit for processing a wheel-speed data signal from each of said wheel-speed sensors and for execute skid control based on the wheel-speed data signal from each of said wheel-speed sensors, said control unit comprising;

(a) a wheel-acceleration arithmetic-calculation section which calculates a wheel-acceleration data signal as a difference between a previous value of the wheel-speed data signal and a current value of the wheel-speed data signal,

(b) a wheel-speed fluctuation arithmetic-calculation section which calculates a wheel-speed fluctuation of each of the road wheels on the basis of a previous value of the wheel-acceleration data signal and a current value of the wheel-acceleration data signal,

(c) a first absolute-value arithmetic-calculation section which calculates an absolute value of the wheel-speed fluctuation of each of the road wheels,

(d) a first integration section which produces a first integrated value of the absolute values of the wheel-speed fluctuations of the road wheels,

(e) a skid-control dependent wheel-speed fluctuation arithmetic-calculation section which calculates a skid-control dependent wheel-speed fluctuation of each of the road wheels, occurring due to skid control, on the basis of a previous value of the wheel-acceleration data signal and a current value of the wheel-acceleration data signal,

(f) a second absolute-value arithmetic-calculation section which calculates an absolute value of the skid-control dependent wheel-speed fluctuation of each of the road wheels,

(g) a second integration section which produces a second integrated value of the absolute values of the skid-control dependent wheel-speed fluctuations of the road wheels,

(h) a correction section which calculates a wheel-speed fluctuation correction value by subtracting the second integrated value from the first integrated value,

(i) a smoothing section which makes a smoothing operation to the wheel-speed fluctuation correction value to produce a smoothed value,

(j) a road-surface condition determining section which determines a road surface condition on the basis of the smoothed value, and

(k) a skid control section preventing wheel lock of each of the road wheels in response to the wheel-speed data signal from each of the wheel-speed sensors, said skid control section executing the skid control depending on the road surface condition determined by the road-surface condition determining section.

18. The anti-skid braking system as claimed in claim 17, wherein, when a bad road surface condition is detected by the road surface condition determining section, the skid control section sets a pressure-reduction threshold value at a lower value as compared to a road surface condition except the bad road surface condition.