Method and system for controlling active suspensions of a vehicle

• US 5,515,274 A
• Filed: 10/21/1994
• Issued: 05/07/1996
• Est. Priority Date: 09/27/1990
• Status: Expired due to Fees

• Current Assignee: Fuji Heavy Industries Limited (Subaru Corp.)
• Original Assignee: Fuji Heavy Industries Limited (Subaru Corp.)
• Inventors: Kamimura, Katsuyoshi, Hiwatashi, Yutaka, Mine, Atsushi
• Primary Examiner(s): Teska, Kevin J.
• Assistant Examiner(s): LOUIS JACQUES, JACQUES H
• Application Number:
  US08/327,445
• Time in Patent Office: 564 Days
• Field of Search: 364/424.05, 364/424.01, 280/703, 280/707, 280/714, 280/840, 280/709, 280/6.11, 280/708, 280/702, 307/10.1, 180/41
• US Class Current: 701/38
• CPC Class Codes: B60G 17/0162 mainly during a motion involving steering operation, e.g. cornering, overtaking B60G17/0164 takes precedence
• CPC Class Codes: B60G 2202/154 with an accumulator
• CPC Class Codes: B60G 2400/102 vertical
• CPC Class Codes: B60G 2400/104 lateral or transversal with regard to vehicle
• CPC Class Codes: B60G 2400/106 longitudinal with regard to vehicle, e.g. braking
• CPC Class Codes: B60G 2400/252 vertical
• 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 2600/20 Manual control or setting means
• CPC Class Codes: B60G 2600/604 low pass
• CPC Class Codes: B60G 2800/012 Rolling condition

Abstract

An active suspension system of a vehicle has a feed back control system for controlling four suspensions for the four wheels to maintain a reference vehicle height responsive to detected vertical relative displacements between the wheels and the vehicle body at said suspensions, and a feed forward control system for controlling the suspension to maintain an intended rolling of the vehicle responsive to detected lateral acceleration. There is further provided a circuit for changing the reference vehicle height which is responsive to the absolute value of the detected lateral acceleration, and operates to reduce the reference vehicle height with increase of the absolute value so that the vehicle body is lowered while the rolling is maintained whereby a better driver'"'"'s sensation during a vehicle turn is obtained and the capability of turning of the vehicle is improved.

Claims

1. A method for controlling active suspensions of a vehicle, comprising the steps of detecting vertical relative displacements between a vehicle body and respective wheels of the vehicle, controlling charging and discharging of a fluid into and out of respective fluid suspensions for the respective wheels to extend and contract the suspensions independently so as to maintain the suspensions to have a reference vehicle height, detecting lateral acceleration being applied to the vehicle with lateral acceleration detection means, and controlling said charging and discharging of the fluid so as to maintain rolling of the vehicle at a predetermined value, said method further comprising the steps of:

changing the reference vehicle height in response to the lateral acceleration detected by said lateral acceleration detection means by reducing the reference vehicle height as the absolute value of the detected lateral acceleration increases; and

lowering the vehicle body while the rolling of the vehicle is maintained at said predetermined value.

2. The method according to claim 1,

wherein the reference vehicle height is linearly reduced with an increase of said absolute value.

3. The method according to claim 1, wherein the reference vehicle height is gradually reduced with an increase of said absolute value.

4. A system for controlling active suspensions of a vehicle, having fluid suspensions provided for respective wheels, means for charging and discharging a fluid into and out of the respective fluid suspensions to extend and contract the suspensions independently, suspension stroke sensors provided for the respective wheels to detect vertical relative displacements between a vehicle body and the respective wheels, feed back control means responsive to the relative displacements detected by the suspension stroke sensors for independently controlling said means for charging and discharging so as to maintain said suspensions to have a reference vehicle height, a lateral G-sensor for detecting lateral acceleration applied to the vehicle, and feed forward control means responsive to the lateral acceleration for independently controlling said means for charging and discharging so as to maintain rolling of the vehicle during a turn at a predetermined value, said system further comprising:

means responsive to the detected lateral acceleration for changing the reference vehicle height, said changing means supplying an output thereof to said feed back control means so as to reduce the reference vehicle height as the absolute value of the lateral acceleration increases, to lower the vehicle body while the rolling of the vehicle is maintained at said predetermined value.

5. The system according to claim 4, further comprising:

selecting means for selecting rolling direction and degree to output a selection signal; and

reference vehicle height correcting means responsive to the detected lateral acceleration and to said selection signal for calculating a correcting amount and for supplying an output corresponding to said correcting amount to said feed back control means so as to correct the reference vehicle height in a manner to constantly maintain a set rolling angle of the vehicle determined by said selected rolling direction and degree.

6. The system according to claim 5, further comprising:

calculating means responsive to the lateral acceleration for calculating and outputting a rolling moment;

computing means responsive to the rolling moment for calculating and outputting a lateral load shift quantity;

means responsive to the load shift quantity for calculating and outputting a suspension reaction force variation;

control means responsive to the suspension reaction force variation for calculating and outputting a control quantity for supplying to the feed back control means;

first correcting means responsive to the detected lateral acceleration and to said selection signal for correcting the rolling moment calculated in said rolling moment calculating means;

second correcting means responsive to said selection signal for correcting the suspension reaction force variation calculated in said suspension reaction force variation calculating means; and

third correcting means responsive to said selection signal for correcting the control quantity calculated in said control quantity calculating means.

7. The system according to claim 4 wherein the reference vehicle height is linearly reduced with an increase in said absolute value.

8. The system according to claim 43 wherein the reference vehicle height is continuously reduced with an increase in said absolute value.

9. An apparatus for controlling active suspension of a vehicle, comprising:

means for detecting vertical relative displacements between a vehicle body and respective wheels of the vehicle;

means for controlling charging and discharging of a fluid into and out of respective fluid suspensions for the respective wheels to extend and contract the suspensions independently to maintain the suspensions at a reference vehicle height;

means for detecting lateral acceleration being applied to the vehicle;

means for controlling said charging and discharging of the fluid in an effort to maintain a degree of rolling of the vehicle at a predetermined value; and

means for reducing the reference vehicle height in accordance with an increase in the detected value of lateral acceleration experienced by the vehicle while negotiating a curve so as to lower the vehicle body while the rolling of the vehicle is maintained at said predetermined value whereby riding comfort is improved during vehicle turning.

10. The apparatus according to claim 9 wherein the reference vehicle height is reduced linearly in accordance with an increase in an absolute value of the lateral acceleration.

11. The apparatus according to claim 9 further comprising a selection switch for selecting a rolling direction and degree setting.

12. An apparatus according to claim 9 further comprising a vehicle height adjusting switch for setting a vehicle to either a high or a low suspension setting.