GB2343931A

GB2343931A - Active suspension system

Info

Publication number: GB2343931A
Application number: GB0007902A
Authority: GB
Inventors: Koenraad Reybrouk
Original assignee: Monroe Auto Equipment Co
Current assignee: Tenneco Automotive Inc
Priority date: 1996-02-06
Filing date: 1997-02-04
Publication date: 2000-05-24
Anticipated expiration: 2017-02-04
Also published as: GB2343931B; GB2343932B; GB2343932A; GB0007905D0; GB0007902D0

Abstract

A piston and cylinder hydraulic actuator has an accumulator 156 providing damping fluid at a first pressure to the lower portion of a working chamber 142, a pump 154 in fluid communication with the accumulator 156 to provide damping fluid at a second pressure to upper and lower portions of the chamber 142, and flow control means to control the position of the piston 144 in the chamber 142 comprising a first variable restriction valve 150 controlling flow between the upper and lower portions of the chamber, and a second variable restriction valve 152 controlling flow between the accumulator 156 and the lower portion of the chamber.

Description

"ACTIVE SUSPENSION SYSTEM BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a suspension system for autonotive vehicles, and more particularly to an active suspension system.

2. Description of Related Art Suspension systems are provided to filter or "isolate"the vehicle body fron vertical road surface irregularities as well as to control body and wheel notion.

In addition, suspension systens are also used to maintain an average vehicle attitude to promote improved platform stability during naneuvering. The classic passive suspension system includes a spring and a damping device in parallel which are located between the sprung mass (vehicle body) and the unsprung rass (wheel and axles).

Hydraulic actuators, such as shock absorbers and/or struts, are used in conjunction with conventional passive suspension systems to absorb unwanted vibration which occurs during driving. To absorb this unwanted vibration, hydraulic actuators include a piston located within the pressure cylinder of the actuator which is connected to the body of the automobile through a piston rod. Because the piston is able to restrict the flow of damping fluid within the working chamber of the hydraulic actuator when the actuator is displaced, the actuator is able to produce a damping force which counteracts the vibration of the suspension. The greater the degree to which the flow of damping fluid within the working chamber is restriced by the piston, the greater the damping forces which are generated by the actuator.

In recent years, substantial interest has grown in automotive vehicle suspension systems can improved comfort and road holding over the performance offered by conventional passive suspension systems. In general, such improvements are achieved by utilization of an "intelligent" suspension system capable of electronically controlling the suspension forces generated by hydraulic actuators.

Different levelsinachievingtheideal "intelligent" suspension system, called "a full active suspension", are possible. Sometimes only dynamic forces acting against the movement of the piston in the actuator can be generated and Sometimes static or slowly changing push-out forces, independent of the velocity of the piston in the actuator, can be added to the damping forces, called slow leveling. The mcst elaborate systems, full active suspensions, can generate variable forces, as well in rebound as in compression of the actuator, recardless of the position and movement of the piston in the actuator. it would be desirable to find simply a system which comes as close as possible to the full active suspension. In addition, in the event that the hydraulic system should fail, it would be desirable to have the hydraulic actuator still function in a fail-safe mode.

SUMMARY OF THE INVENTION In accordance with the teachings of the present invention, a hydraulic actuator is disclosed which is operable to generate forces.

The present invention comprises a hydraulic actuator being operable to generate damping forces comprising: a pressure cylinder; a piston disposed within said pressure cylinder being operable to divide said pressure cylinder into first and second portions, said piston having first and second sides; a first source of damping fluid being operable to provide damping fluid at a first pressure to said second portion of said pressure cylinder; a pump in fluid communication with said first source and operable to provide damping fluid at a second pressure to said first and second portions of said pressure cylinder; and flow control means for controlling the flow of damping fluid to control the pressure on said first and second sides of said piston and the position of said piston in said pressure cylinder; wherein said flow control means comprise: a first variable restriction valve being operable to control the flow of damping fluid between said first portion of said pressure cylinder and said second portion of said pressure cylinder; a second variable restriction valve being operable to control the flow of damping fluid between said second portion of said pressure cylinder and said first source of damping fluid.

'An aim of the present invention is to provide a hydraulic actuator which is able to be used in an active suspension system which provides for variable damping and leveling.

Another object of the present invention is to provide a hydraulic actuator in which the damping forces generated by the hydraulic actuator are substantially independent of the position and velocity of the piston within the pressure cylinder.

It is a further object of the present invention to provide a hydraulic actuator which can be used in an active suspension systen. In this regard, it is a further object of the present invention to provide a hydraulic actuator which can be used with a relatively low pressure hydraulic system.

Another object of the invention is to provide a hydraulic actuator which enables a fail-safe suspension design in case of nassive hydraulic pressure losses.

Another object of the invention is to provide a hydraulic actuator which is relatively sinple and relatively inexpensive.

BRIEF DESCRIPTION OF THE D GS Various avantages of the present invention will becone apparent to one skilled in the art upon reading the following specification and by reference to the following drawings in which : FIG. 1 is a diagrammatic illustration of the hydraulic actuator according to the teachings of the preferred e,-, bodinent of the present invention shown in operative association with a conventional automobile ; FIG. 2 is a diagrammatic illustration of the hydraulic actuator according to the preferred embodiment of the present invention shown in FIG. 1 ; DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a plurality of hydraulic actuators 10 in accorcance with the teachings of the preferred embodiment of the present invention is shown.

The hydraulic actuators 10 are depicted in operative association with a conventional automobile 12 having a vehicle body 14. The automobile 12 includes a rear suspension 16 having a transversely extending rear axile assembly 18 adapted to support the rear wheels 20. The rear axle assembly 18 is operably connected to the automobile 12 by means of a pair ouf hydraulic actuators 10 as well as by helical coil sprinas 22. Sinilarly, the automobile 12 has a front suspension system 24 including a transversely extending front axle assembly 26 adapted to support the front wheels 28. The front axle assembly 26 is connected to the automobile 12 by means of a second pair of hydraulic actuators 10 and by a second pair of helical coil springs 30. While the automobile 12 has been depicted as a passenger car, the hydraulic actuators 10 may be used with other types of r, otor vehicles as well. Furtherrore, the structural association of the front and rear axle assemblies are exemplary in nature and are not intended to limit the sccpe of the present invention.

To allow the forces generated by the hydraulic actuators 10 to be controlled, a rode select switch 32 and an electrcnic control module 34 are provided. The rode select switch 32 is located within the passenger compartment 36 of the automobile 12 and is accessible by thé occupants of the automobile 12. The mode select switch 32 is used for selecting the damping characteristics which the hydraulic actuators 10 are to provide as well to adjust leveling. It will be appreciated, however, that the mode select switch 32 is optional.

The electronic control module 34 receives output from the mode select switch 32 as well as various sensors which are used for generating control signals for selectively controlling the forces generated by the hydraulic actuators 10. In fluid communication with each of the hydraulic actuators 10 is a closed-loop high pressure hydraulic system 38 which includes a pump 154 and a fluid reservoir 156 shown in Fia. 2 and more fully discussed below.

, The preferred embodiment of the present invention will now be described with reference to FIG. 3.

In this regard, the hydraulic actuator 110 comprises a pressure cylinder 140 having a piston 144 disposed therein. The piston 144 is able to divide the working chamber 142 into an upper portion as well as a lower portion. The piston 144 is secured at one end to a piston rod 146 which is able to impart movement to the piston 144.

To provide a first source of camping fluid, the hydraulic actuator 110 further includes an accumulator 156.

The accumulator 156 is operable to store damping fluid at a pressure which determines the static pressure of the hydraulic actuator 110 and therefore the static pus-out force of the hydraulic actuator 110. As will be appreciated by those skilled in the art, the static pressure can be adjusted by an external or internal system to provide slow load leveling. To provide a second source of damping fluid at a second pressure, the hydraulic actuator 110 further includes a pump 154. The pump 154 receives damping fluid from the accumulator 156 and is able to deliver the fluid at a relatively higher pressure to either the upper or lower portion of the working chamber 142, depending on the operating of restriction valves 150 and 152. The pump 154 is operated at a constant speed by the motor 160 and therefore is able to generate a relatively uniform flow of damping fluid.

To provide means for controlling the flow of damping fluid from the pump 154 to the accumulator 156, the hydraulic actuator 110 further includes a first variable restriction valve 150 and a second variable restriction valve 152. One side of the first variable restriction valve 150 fluidly communicates with the upper portion of the working chamber 142 as well as the output of the pump 154. The other side of the first variable restriction valve 150 fluidly communicates with the lower portion of the working chamber 142 as well as one side of the second variable restriction valve 152. The second side of the second variable restriction valve 152 fluidly cormunicates with the input of the pump 154 as well as the accumulator 156.

When it is desirable to move the piston 144 downward by increasing the pressure within the upper portion of the working chamber 142, the first variable restriction valve 150 is closed while the second variable restriction valve 152 is open. The pump 154 is therefore able to deliver damping fluid to the upper portion of the working chamber 142. At the same time, damping fluid in the lower portion of the working chamber 142 is able to flow into the accumulator 156 through the second variable restriction valve 152. When it is desirable to move the piston 144 in an upward direction, the first variable restriction valve 150 is opened while the second variable restriction valve 152 is closed. This causes the pressure of the damping fluid in both the upper and lower portions of the working chamber 142 to become substantially the same. Since the surface area of the piston 155 upon which damping fluid in the lower portion of the working chamber 142 acts is larger than the surface area of the piston 144 upon which damping fluid in the upper portion of the working chamber 142 acts, the piston is displaced upwardly.

As evidenced from the foregoing, those skilled in the art will appreciate that the present invention is able to provide a hydraulic actuator which is able to be used in a suspension system to provide both variable damping and leveling. In addition, the hydraulic actuator is able to provide damping forces which are substantially independent from the position of the piston within the pressure cylinder. The hydraulic actuator allows a conventional spring to be mounted in parallel with the actuator without appreciable loss of performance of the suspension system.

Since conventional springs may be used, only dynamic forces have to be generated by the pump thereby permitting only relatively low pressures to be used within the hydraulic system. This permits relatively standard components to be used in the piston valve and other co. ;, ponents of the hydraulic actuator. However, with the embodiment shown in FIG. 2, the different actuators must be connected to different pumps. These pumps can be combine to one or two central units (keeping the hydraulic circuits separated), but the. pumps can also be integrated with different actuators.

It will also be noted that the hydraulic actuator of the present invention is operable to minirize the impact of a hydraulic system failure. In this regard, the hydraulic actuator can be used in parallel with a spring.

In such an implementation, the failure of the hydraulic system will cause the hydraulic actuacor to work as firm passive damper.

Claims

CLAIMS A hydraulic actuator being operable to generate damping forces comprising: -a pressure cylinder; a piston disposed within said pressure cylinder being operable to divide said pressure cylinder into first and second portions, said piston having first and second sides; a first source of damping fluid being operable to provide damping fluid at a first pressure to said second portion of said pressure cylinder; a pump in fluid communication with said first source and operable to provide damping fluid at a second pressure to said first and second portions of said pressure cylinder; and flow control means for controlling the flow of damping fluid to control the pressure on said first and second sides of said piston and the position of said piston in said pressure cylinder; wherein said flow control means comprise: a first variable restriction valve being operable to control the flow of damping fluid between said first portion of said pressure cylinder and said second portion of said pressure cylinder; a second variable restriction valve being operable to control the flow of damping fluid between said second portion of said pressure cylinder and said first source of damping fluid.
2. The hydraulic actuator of claim 1, wherein said first source of damping fluid comprises an accumulator.
3. The hydraulic actuator of claim 1 or 2, further comprising a motor operable to drive said pump at a substantially constant speed.
4. The hydraulic actuator of any one of claims 1 to 3, wherein said second source of damping fluid is in fluid communication with said first source of damping fluid.
5. A method of controlling the actuator of any one of claims 1 to 4, said method comprising the steps of: opening said first variable restriction valve and closing said second variable restriction valve so as to connect the second source of damping fluid to both of said first and second portions of said pressure ; and activating said pump so as to pump damping fluid to said second portion of said pressure chamber.
6. A method of controlling the actuator of any one of claims 1 to 4, said method comprising the steps of: closing said first variable restriction valve and opening said second variable restriction valve so as to connect said first source of damping fluid to said second portion of said pressure cylinder and to connect said second source damping fluid to said first portion of pressure cylinder.
7. A hydraulic actuator constructed and arranged substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.
8. A method substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.