Suspension system for vehicle

• US 5,384,706 A
• Filed: 10/20/1993
• Issued: 01/24/1995
• Est. Priority Date: 02/20/1991
• Status: Expired due to Term

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Tokico Limited (Hitachi, Ltd.)
• Inventors: Uchiyama, Masaaki, Ozaki, Hidekatsu, Nezu, Takashi, Nakamura, Kenichi
• Primary Examiner(s): Chin, Gary
• Application Number:
  US08/138,387
• Time in Patent Office: 461 Days
• Field of Search: 364/424.05, 280/707, 280/840
• US Class Current: 701/37
• CPC Class Codes: B60G 17/0152 characterised by the action on a particular type of suspension unit B60G17/01941 takes precedence
• CPC Class Codes: B60G 2202/154 with an accumulator
• CPC Class Codes: B60G 2400/102 vertical
• CPC Class Codes: B60G 2400/252 vertical
• CPC Class Codes: B60G 2400/51 in suspension unit
• CPC Class Codes: B60G 2500/112 Fluid actuation
• CPC Class Codes: B60G 2600/02 Retarders, delaying means, dead zones, threshold values, cut-off frequency, timer interruption
• CPC Class Codes: B60G 2600/182 Active control means

Abstract

A suspension system for a vehicle which has a hydraulic cylinder that extends and retracts in accordance with a change in the distance between a vehicle body and an axle to vary the volumetric capacity of a working chamber defined therein, an accumulator connected to the working chamber in the hydraulic cylinder, a control valve controlling the flow rate of oil charged into and discharged from the accumulator and the hydraulic cylinder, and a vehicle level sensor detecting a change in the above-described distance. The suspension system further has a control unit that controls the control valve, on the basis of a flow control signal obtained by multiplying the detected signal from the vehicle level sensor by an amplification factor, so as to restore the vehicle to a neutral state. The control unit is arranged to increase the amplification factor when the amount of the extension or retraction of the hydraulic cylinder is close to the extent of the full stroke thereof. When the vehicle is running on a normal road surface, the suspension system absorbs any changes in the road surface, thereby stably maintaining the attitude of the vehicle body, and in the case of large irregularities, it is possible to prevent full rebound or full bump which would otherwise occur when the hydraulic cylinder performs a full-stroke operation.

Claims

1. A suspension system of a vehicle, said system comprising:

a hydraulic cylinder connected to a body and an axle of the vehicle so as to extend and retract as the distance between the body and the axle of the vehicle changes, said hydraulic cylinder having preestablished full extension and retraction strokes, and a neutral position, and said hydraulic cylinder including a cylinder in which a working chamber is defined, the volume of said working chamber varying during the extension and retraction of the hydraulic cylinder;

an accumulator containing a gas, said accumulator communicating with said working chamber;

a pressurized oil supply;

a control valve operatively hydraulically interposed between said pressurized oil supply and said hydraulic cylinder so as to control the flow of oil into and from said working chamber;

a vehicle level sensor which detects changes in said distance between the body and the axle of the vehicle and issues a respective signal representative of each of said changes; and

a control unit, operatively connected to said vehicle level sensor and said control valve, which receives each said signal issued by the vehicle level sensor, and issues a control signal to said control valve that operates said control valve to cause a force to be generated that restores said hydraulic cylinder to said neutral position, which said control unit can generate a first control signal by executing an operation in which the signal issued by the vehicle level sensor is multiplied by a first vehicle level control amplification factor at the time said signal issued by the vehicle level sensor is indicative of the hydraulic cylinder being located anywhere between said neutral position and the full extension or the full retraction stroke thereof, respectively, and which said control unit can generate a second control signal by executing an operation in which the signal issued by the vehicle level sensor is multiplied by a second vehicle level control amplification factor at the time said signal issued by the vehicle level sensor is indicative of the hydraulic cylinder being at a location between said position short of the full extension or the full retraction stroke there and the associated full extension or retraction stroke,which said control unit selectively generates said first and said second control signals and issues the control signal so generated to said control valve as said control signal that operates the control valve, said first and said second vehicle level control amplification factors being different wherein the force generated to restore the hydraulic cylinder to said neutral position is larger when said second control signal is generated than when said first control signal is generated, which said control unit generates said second control signal only when the hydraulic cylinder is progressing from said position just short of the full extension or full retraction stroke thereof towards the associated full extension or full retraction stroke, respectively, and which said control unit generates said first control signal when the hydraulic cylinder is progressing from the full extension stroke or the full retraction stroke thereof towards said position just short of the full extension or full retraction stroke, respectively.

2. A suspension system of a vehicle as claimed in claim 1, wherein said control unit selectively generates said first and said second control signals on the basis of the speed at which the hydraulic cylinder is extending or retracting, and generates said second control signal only when said speed is greater than a predetermined value.

3. A suspension system of a vehicle as claimed in claim 1,

wherein said control unit issues said control signal to operate said control valve to cause a force to be generated which includes a component that tends to extend or retract said hydraulic cylinder to said neutral position and a component that tends to reduce the relative velocity between the body and the axle of the vehicle,

and which said control unit generates said control signal by summing (a) a vehicle level control variable which is the product of a value of the signal from said vehicle level sensor and said vehicle level control amplification factor and (b) a speed control variable which is the product of a speed amplification factor and a differentiated value that is the mathematical derivative of the signals from the vehicle level sensor,

which said control unit establishes said speed control amplification factor at a value not larger than a predetermined value when the value of the signal from said level sensor is within a predetermined range including a value corresponding to a signal indicative of the hydraulic cylinder being in said neutral position, and

which said control unit establishes said speed control amplification factor at a value larger than said predetermined value when the value of the signal from said level sensor is outside of said predetermined range.