Suspension control system having damping coefficient discretely varied responsive to road conditions

• US 5,361,209 A
• Filed: 01/22/1993
• Issued: 11/01/1994
• Est. Priority Date: 12/08/1989
• Status: Expired due to Fees

• Current Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Tsutsumi, Yasuhiro
• Primary Examiner(s): Black, Thomas G.
• Assistant Examiner(s): PARK, COLLIN
• Application Number:
  US08/007,917
• Time in Patent Office: 648 Days
• Field of Search: 364/424.05, 380/703, 380/707, 380/840
• US Class Current: 701/37
• CPC Class Codes: B60G 17/01941 characterised by the use of piezoelectric elements, e.g. sensors or actuators
• CPC Class Codes: B60G 2202/12 Wound spring
• CPC Class Codes: B60G 2202/24 Fluid damper
• CPC Class Codes: B60G 2204/80 Interactive suspensions; arrangement affecting more than one suspension unit
• CPC Class Codes: B60G 2204/81 front and rear unit
• CPC Class Codes: B60G 2400/204 Vehicle speed
• CPC Class Codes: B60G 2400/32 Torque on propulsion shaft
• CPC Class Codes: B60G 2400/41 Steering angle
• CPC Class Codes: B60G 2400/60 Load
• CPC Class Codes: B60G 2400/61 Load distribution
• CPC Class Codes: B60G 2400/82 Ground surface
• CPC Class Codes: B60G 2400/821 Uneven, rough road sensing affecting vehicle body vibration
• CPC Class Codes: B60G 2400/90 Other conditions or factors
• CPC Class Codes: B60G 2400/91 Frequency
• CPC Class Codes: B60G 2401/10 Piezoelectric elements
• CPC Class Codes: B60G 2500/10 Damping action or damper
• CPC Class Codes: B60G 2500/102 stepwise
• CPC Class Codes: B60G 2500/104 continuous
• CPC Class Codes: B60G 2500/30 Height or ground clearance
• CPC Class Codes: B60G 2600/02 Retarders, delaying means, dead zones, threshold values, cut-off frequency, timer interruption
• CPC Class Codes: B60G 2600/14 : Differentiating means, i.e. differential control
• CPC Class Codes: B60G 2600/184 : Semi-Active control means
• CPC Class Codes: B60G 2800/162 : Reducing road induced vibrations
• CPC Class Codes: B60G 2800/22 : Braking, stopping
• CPC Class Codes: F16F 9/348 : Throttling passages in the form of annular discs or other plate-like elements which may or may not have a spring action, operating in opposite directions or singly, e.g. annular discs positioned on top of the valve or piston body F16F9/341, F16F9/3415 take precedence

Abstract

A suspension control system for controlling a suspension having a shock absorber provided for a wheel of a vehicle includes a damping force change rate detector which detects a damping force change rate indicating a rate of change of a damping force of the shock absorber, and a damping coefficient controller which alters the setting of the damping coefficient on the basis of a relationship between the damping force change rate and an adjustment reference value. The system also includes a damping coefficient alteration holding unit which continuously maintains the setting of the damping coefficient at a first level for a holding period after the damping coefficient controller alters the setting of the damping coefficient from a second level to the first level less than the second level, and a road surface condition judgement unit which judges whether or not a road surface on which the vehicle has traveled for the holding period is rough. Further, the system includes a holding period correction unit which elongates the holding period which is to be supplied to the damping coefficient alteration holding unit when the road surface condition judgment unit determines that the road surface is rough.

Claims

1. A suspension control system for controlling a suspension having a shock absorber provided for a wheel of a vehicle, said suspension control system comprising:

damping force change rate detecting means for detecting a damping coefficient change rate indicating a rate of change of a damping force of said shock absorber;

damping coefficient controlling means, coupled to said shock absorber and said damping force change rate detecting means, for setting a damping coefficient of said shock absorber to a first level from a second level less than the first level when the damping force change rate has exceeded an adjustment reference value;

damping coefficient alteration holding means, coupled to said shock absorber and said damping coefficient controlling means, for continuously maintaining the setting of the damping coefficient at the first level for a holding period after said damping coefficient controlling means alters the setting of the damping coefficient from the second level to said first level, said holding period being a first period starting from a time when said adjustment reference value becomes greater than said damping force change rate after said damping coefficient controlling means alters the setting of the damping coefficient from the second level to the first level;

road surface condition judgement means for judging whether or not a road surface on which said vehicle has traveled for said holding period is rough; and

holding period correction means, coupled to said damping coefficient alteration holding means and said road surface condition judgement means, for elongating said holding period so that said holding period is a second period which is longer than said first period and which starts from said time when said adjustment reference value becomes greater than said damping force change rate after said damping coefficient controlling means alters the setting of the damping coefficient from the second level to the first level.

2. A suspension control system as claimed in claim 1, wherein said road surface condition judgment means comprises:

frequency calculation means for calculating a frequency which indicates the number of times that said damping force change rate exceeds a learning reference value less than said adjustment reference value for a fixed period; and

judging means for judging whether or not said road surface is rough on the basis of said frequency calculated by said frequency calculation means.

3. A suspension control system as claimed in claim 2, wherein said road surface condition judgment means comprises:

averaging means for averaging a plurality of frequencies, each being obtained by said frequency calculation means for each said fixed period and for outputting a frequency average; and

comparing means for comparing said frequency average with a predetermined threshold frequency and for outputting a comparison result which indicates whether or not said road surface is rough.

4. A suspension control system as claimed in claim 1, further comprising speed detection means for detecting a vehicle speed of said vehicle, wherein said adjustment reference value comprises a component which increases as the vehicle speed increases.

5. A suspension control system as claimed in claim 1, further comprising:

determining means for determining whether or not said road surface condition judgment means judges that said road surface is rough during a period between an end of said first period and an end of said second period; and

means for stopping said damping coefficient alteration holding means from holding the setting of the damping coefficient at the first level when said determining means determines that said road surface condition judgment means judges that said road surface is not rough, so that the setting of the damping coefficient is restored to said second level from said first level.

6. A suspension control system for controlling a suspension having a shock absorber provided for a wheel of a vehicle, said suspension control system comprising:

damping coefficient change rate detecting means for detecting a damping force change rate indicating a rate of change of a damping force of said shock absorber;

damping coefficient alteration means, coupled to said shock absorber and said damping coefficient change rate detecting means, for determining whether or not said damping force change rate is outside a first range and for setting said damping force to a first level from a second level greater than said first level when it is determined that said damping force change rate is outside said first range; and

damping coefficient restoration means, coupled to said damping force change rate detecting means, said damping coefficient alteration means and said shock absorber, for determining whether or not said damping force change rate is continuously within a second range, which is narrower than said first range and within said first range during at least a predetermined period after said damping coefficient alteration means alters the setting of the damping coefficient from said second level to said first level and for restoring the setting of the damping coefficient from said first level to said second level when it is determined that said damping force change rate is continuously within said second range for said predetermined period.

7. A suspension control system as claimed in claim 6, wherein said damping coefficient restoration means comprises:

first means for detecting a time when said damping force change rate goes into said second range; and

second means for timing said predetermined period which starts from a starting time corresponding to said time when said damping force change rate goes into said second range.

8. A suspension control system as claimed in claim 7, further comprising resetting means for resetting said second means to said starting time when said damping coefficient restoration means determines that said damping force change rate goes outside of said second range.

9. A suspension control system as claimed in claim 6, further comprising:

speed detection means for detecting a vehicle speed of said vehicle; and

adjustment means, coupled to said speed detection means and said damping coefficient restoration means, for adjusting said second range on the basis of said vehicle speed.

10. A suspension control system as claimed in claim 9, wherein said adjustment means comprises:

comparing means for comparing said vehicle speed with a predetermined vehicle speed and for outputting a comparison result; and

means for increasing said second range when the comparison result output by said comparing means indicates that the vehicle speed is greater than said predetermined vehicle speed and for decreasing said second range when the comparison result output by said second comparing means indicates that the vehicle speed is equal to or less than said predetermined vehicle speed.

11. A suspension control system as claimed in claim 6, further comprising:

speed detection means for detecting a vehicle speed of said vehicle; and

adjustment means, coupled to said speed detection means and said damping coefficient restoration means, for adjusting said predetermined period on the basis of said vehicle speed.

12. A suspension control system as claimed in claim 11, wherein said adjustment means comprises:

comparing means for comparing said vehicle speed with a predetermined vehicle speed and for outputting a comparison result; and

means for decreasing said predetermined period when the comparison result output by said comparing means indicates that the vehicle speed is greater than said predetermined vehicle speed and for increasing said predetermined period when the comparison result output by said second comparing means indicates that the vehicle speed is equal to or less than said predetermined vehicle speed.

13. A suspension control system as claimed in claim 6, further comprising:

speed detection means for detecting a vehicle speed of said vehicle;

first adjustment means, coupled to said speed detection means and said damping coefficient restoration means, for adjusting said second range on the basis of the vehicle speed; and

second adjustment means, coupled to said speed detection means and said damping coefficient restoration means, for adjusting said predetermined period on the basis of said vehicle speed.

14. A suspension control system for controlling a suspension having a shock absorber provided for a wheel of a vehicle, said suspension control system comprising:

damping force change rate detecting means for detecting a damping force change rate indicating a rate of change of a damping force of said shock absorber;

damping coefficient alteration means, coupled to said shock absorber and said damping force change rate detecting means, for determining whether or not said damping force change rate is outside a first range and for setting said damping coefficient to a first level from a second level greater than said first level when it is determined that said damping force change rate is outside said first range;

first damping coefficient restoration means, coupled to said damping force change rate detecting means, said damping coefficient alteration means and said shock absorber, for determining whether or not said damping force change rate is continuously within a second range, which is narrower than said first range and within said first range during at least a first period after said damping coefficient alteration means alters the setting of the damping coefficient from said second level to said first level and for restoring the setting of the damping coefficient from said first level to said second level when it is determined that said damping force change rate is continuously within said second range for said predetermined period;

holding period calculation means, coupled to said damping coefficient alteration means and said first damping coefficient restoration means, for calculating a holding period from a time when the setting of the damping coefficient is altered to the first level by said damping coefficient alteration means to a time when the setting of said damping coefficient is restored to said second level by said first damping coefficient restoration means; and

second damping coefficient restoration means, coupled to said holding period calculation means and said shock absorber, for determining whether or not said holding period becomes longer than a second period and for restoring the setting of the damping coefficient from said first level to said second level when it is determined that said holding period has become longer than said second period.

15. A suspension control system as claimed in claim 14, further comprising correction means for determining whether or not said holding period becomes longer than a third period and for correcting said second range so that said first damping coefficient restoration means restores the setting of the damping coefficient to said second level from said first level more quickly than before said second range is corrected when it is determined that said holding period has become longer than said third period.

16. A suspension control system as claimed in claim 15, further comprising:

determining means for determining whether or not said second range corrected by said correction means becomes wider than a limited range;

means, coupled to said shock absorber and said determining means, for restoring the setting of said damping coefficient to said second level when said determining means determines that said second range has become longer than said limited range.

17. A suspension control system as claimed in claim 16, further comprising initialization means for setting said second range to an initial range when said determining means determines that said second range has become longer than said limited range.

18. A suspension control system as claimed in claim 17, further comprising:

frequency calculation means for calculating a first frequency which indicates the number of times that said second range becomes wider than said limited range during a predetermined period;

first comparing means for comparing said first frequency with a predetermined reference frequency and for outputting a comparison result; and

first initial range correction means for correcting said initial range when said comparison result shows that said first frequency is less than said reference frequency, so that said first damping coefficient restoration means alters the setting of the damping coefficient from said first level to said second level more quickly than before said initial range is corrected.

19. A suspension control system as claimed in claim 18, further comprising:

correction frequency calculation means for calculating a correction frequency which indicates the number of times that said correction means corrects said second range during said predetermined period;

second comparing means for comparing said correction frequency with a first reference correction frequency and for outputting a comparison result when said comparison result output by said first comparing means shows said first frequency is equal to or greater than said predetermined reference frequency; and

second initial range correction means for correcting said initial range when said comparison result output by said second comparing means shows that said correction frequency is less than said first reference correction frequency, so that said first damping coefficiency restoration means alters the setting of the damping coefficient from said first level to said second level more quickly than before said initial range is corrected.

20. A suspension control system as claimed in claim 19, further comprising:

third comparing means for comparing said correction frequency with a second reference correction frequency less than said first reference correction frequency and for outputting a comparison result; and

third initial range correction means for correcting said initial range when said comparison result output by said third comparing means shows that said correction frequency is less than said second reference correction frequency, so that said first damping force restoration means alters the setting of the damping force from said first level to said second level more slowly than before said initial range is corrected.

21. A suspension control system as claimed in claim 14, further comprising correction means for determining whether or not said holding period becomes longer than a third period and for correcting said first period so that said first damping coefficient restoration means restores the setting of the damping coefficient from said first level to said second level more quickly than before said first period is corrected when it is determined that said holding period has become longer than said third period.

22. A suspension control system as claimed in claim 21, further comprising:

determining means for determining whether or not said second period corrected by said correction means becomes greater than a limited period; and

means, coupled to said shock absorber and said determining means, for restoring the setting of said damping coefficient to said second level when said determining means determines that said second period has become greater than said limited period.

23. A suspension control system as claimed in claim 22, further comprising initialization means for setting said second period to an initial period when said determining means determines that said second range has become longer than said limited range.

24. A suspension control system as claimed in claim 23, further comprising:

frequency calculation means for calculating a first frequency which indicates the number of times that said second period becomes longer than said limited period during a predetermined period;

first comparing means for comparing said first frequency with a predetermined reference frequency and for outputting a comparison result; and

first initial period correction means for correcting said initial period when said comparison result shows that said first frequency is less than said reference frequency, so that said first damping coefficient restoration means alters the setting of the damping coefficient from said first level to said second level more quickly than before said initial period is corrected.

25. A suspension control system as claimed in claim 24, further comprising:

correction frequency calculation means for calculating a correction frequency which indicates the number of times that said correction means corrects said second range for said predetermined period;

second comparing means for comparing said correction frequency with a first reference correction frequency and for outputting a comparison result when said comparison result output by said first comparing means shows said first frequency is equal to or greater than said predetermined reference frequency; and

second initial period correction means for correcting said initial period when said comparison result output by said second comparing means shows that said correction frequency is less than said first reference correction frequency, so that said first damping coefficient restoration means alters the setting of the damping coefficient from said first level to said second level more quickly than before said initial period is corrected.

26. A suspension control system as claimed in claim 19, further comprising:

third comparing means for comparing said correction frequency with a second reference correction frequency less than said first reference correction frequency and for outputting a comparison result; and

third initial range correction means for correcting said initial range when said comparison result output by said third comparing means shows that said correction frequency is less than said second reference correction frequency, so that said first damping force restoration means alters the setting of the damping force from said first level to said second level more slowly than before said initial range is corrected.