GB2235168A

GB2235168A - A vehicle suspension system having an adjustable anti-roll bar

Info

Publication number: GB2235168A
Application number: GB8919262A
Authority: GB
Inventors: Paul Bloor
Original assignee: GKN Technology Ltd
Current assignee: GKN Technology Ltd
Priority date: 1989-08-24
Filing date: 1989-08-24
Publication date: 1991-02-27
Also published as: GB8919262D0

Abstract

An hydraulic system for adjusting springing means, such as an anti-roll torsion bar, in a vehicle suspension system comprises two valves (12, 13) each with three ports, arranged and connected to one another to supply fluid under pressure from a source (P) thereof to either side of an actuator (10, 11) for the springing means or to return fluid to a reservoir by way of a relief valve (14). Separate front and rear anti-roll bars are provided. <IMAGE>

Description

VEHICLE SUSPENSION SYSTEMS This invention relates to vehicle suspension systems, and more particularly to the active control of vehicle suspension systems, that is to say the automatic adjustment of a system part or parts in response to vehicle operating parameters in order to provide an improved suspension performance.

In our international patent application published under no. WO 89/04262, there is disclosed a vehicle suspension system which comprises springing means (particularly an anti-roll torsion bar) which is common to at least two vehicle wheels; adjustment means operable on the springing means to positionally adjust it, to change its loading; means for measuring the position of the springing means as adjusted and providing a signal representative of its position; acceleration sensing means for sensing vehicle acceleration and providing a signal representing the acceleration; and control means for controlling the operation of the adjustment means, the control means being responsive to the acceleration signal to determine a required position of the springing means, and operable to cause the springing means position to be adjusted until the required position thereof is reached.Such a system will hereafter be referred to as a suspension system of the kind specified.

Such a vehicle suspension system is particularly advantageous for controlling vehicle roll when cornering.

Adjustment of an anti-roll torsion bar in response to vehicle lateral acceleration can at least reduce, or possibily even totally eliminate, vehicle roll. The anti-roll torsion bar can be adjusted by a torsional actuator, or by some other form of actuator for positionally adjusting the torsion bar. There may be respective actuators associated with anti-roll torsion bars for the front wheels and the rear wheels of the vehicle. Preferably the actuators are hydraulic actuators.

It is the object of the present invention to provide an hydraulic system for operating the actuator or actuators in a suspension system of the kind specified.

According to the invention, we provide a hydraulic system for a vehicle suspension system of the kind specified, comprising: a source of fluid under pressure; an actuator for positionally adjusting the springing means, having two fluid connections to which the application of fluid under pressure causes the actuator to produce outputs in respective opposite senses; two valves each having a first, a second and a third port and operable between a first position wherein a connection is established between the first and third ports only and a second position wherein a connection is established between the first and second ports only; and a pressure relief valve for returning fluid to a reservoir thereof and openable at a predetermined pressure lower than that at which fluid is supplied by said source thereof;; the first ports of the valves being connected respectively to the fluid connections of the actuator; the second ports of the valves being connected to each other and to said source of fluid under pressure; and the third ports of the valves being connected to each other and to said pressure relief valve.

A system according to the invention uses readily available valves, and provides the necessary actuator operation simply and economically.

Preferably there are two actuators, respectively associated with anti-roll torsion bars at the front and rear of the vehicle, the fluid connections of the actuators being in parallel with one another.

Preferably a further valve is provided in the connections to the actuator associated with the anti-roll torsion bar at the front wheels of the vehicle, such further valve isolating the fluid connections to the actuator from one another and from the rest of the system when not subject to any control signal. This provides, as described hereafter, that if there should be any failure the system will revert to a state in which the vehicle has safe handling characteristics.

The invention will now be described by way of example with reference to the accompanying drawings, in which Figures 1, 2 and 3 show a system according to the invention in three different operational conditions.

Referring firstly to Figure 1 of the drawings, there is shown an hydraulic system according to the invention for controlling a vehicle suspension system of the type disclosed in our International Patent Application Publication No. W089/04262. Particularly, Figure 3 of the said published application is referred to, wherein there is disclosed a suspension which comprises anti-roll torsion bars disposed at the front and rear of the vehicle inter-connecting the respective pairs of wheels of the vehicle, and respective hydraulic actuating rams associated with the anti-roll torsion bars. In practice, it will be appreciated that the actuating rams may be rotary hydraulic actuators rather than actuators having a linear output.

In Figure 1 of the present disclosure, hydraulic actuators for the front and rear anti-roll torsion bars of the suspension are indicated at 10, 11, respectively.

Each actuator has two hydraulic connections, the piston and output member of the actuator being driven in either direction according to which one of the actuator connections hydraulic fluid under pressure is supplied to, whilst fluid is released from the actuator at its other connection.

The system comprises a source P of hydraulic fluid under pressure, such means comprising a pump and accumulator. From the source P, hydraulic fluid is delivered to two valves 12, 13 each of which is a solenoid operated three-way proportional valve. The valve 12 has three ports A, B, C, and when the solenoid of the valve is not energised the state of the valve is as depicted in Figure 1, such that a fluid connection is provided between the ports A and C of the valve. When the solenoid of the valve is actuated, the connection between ports A and C is closed and a connection between ports A and B established, the flow capacity of the connection being proportional to the magnitude of the signal supplied to the solenoid of the valve.Valve 13 is of the same type as valve 12, having three ports D, E, F, and the normal state of the valve is that depicted in Figure 1 wherein a connection is established between the ports E and F of the valve. The fluid output from the source P is connected to the port B of valve 12 and the port D of valve 13. Port C of valve 12 and port E of valve 13 are connected together, and to a pressure relief valve 14 which, when supplied with fluid at a pressure exceeding a predetermined level, permits excess fluid to flow back to a tank or reservoir T thereof from which the fluid source P draws its supply.

The system further comprises a valve 15 which is a solenoid operated valve having four ports G, H, J, K.

When the solenoid of valve 15 is not energised, ports G and H of the valve are connected together, whilst ports J and K are each isolated. When the solenoid of the valve is energised, as shown in Figure 2, connections are established respectively between the ports G and J of the valve and between ports H and K thereof. Port A of valve 12 is connected to port G of valve 15 and to the connection to the left-hand side of the piston of actuator 11. Port F of valve 13 is connected to the port H of valve 15 and to the connection at the right-hand side of the piston of the actuator 11. The connections to the left and right-hand sides of the piston of actuator 10 are connected respectively to ports J and K of valve 15.

The system further comprises, as disclosed in W089/04262, sensors associated with the actuators 10, 11 for detecting their respective positions and for feeding back signals representing such positions to a suitably programmed controller. The controller also receives a signal representing vehicle lateral acceleration, and supplies outputs to the solenoids of the valves to control operation thereof in the manner hereafter described.

When the system is in operation, the solenoid of valve 15 will be energised so that the connections to the left-hand side of the pistons of both actuators 10, 11 will be connected to port A of valve 12. Similarly the connections to the right-hand side of the pistons of the actuators will be connected to port F of valve 13. When the vehicle is travelling in a straight line, the solenoids of valve 12 and 13 are not energised, so that the connections to the fluid spaces on both sides of the pistons of both actuators are all connected together.

The actuators 10, 11 can have no influence on the respective anti-roll torsion bars with which they are associated. This condition is shown in Figure 2.

When, however, the vehicle corners or another condition arises causing vehicle lateral acceleration to be present and detected in the manner disclosed in our published international application aforesaid, either the valve 12 or the valve 13 is actuated according to the direction of the lateral acceleration. Figure 3 shows the valve 13 actuated, to establish a connection between its ports D and F so that fluid under pressure can flow to the connections to the spaces at the right-hand side of the pistons of the actuators 10, 11. The pistons are thus driven to the left, whilst fluid displaced from the spaces to the left of the pistons is returned to the fluid reservoir T by way of the pressure relief valve 14.

It will be appreciated that the pressure at which the pressure relief valve 14 opens will be appreciably less than the pressure at which fluid is supplied by the source P. When the actuators have reached the required positions to counteract the vehicle lateral accelaration, the valve 13 is returned to a position at which a small quantity only of fluid is delivered from the source P to the actuators, to maintain actuator position allowing for slight leakage of fluid across the pistons of the actuators.

When the condition causing vehicle lateral acceleration no longer exists, valve 13 returns to its original position so that the actuators can also return to their starting positions, although if a more rapid return to the starting positions is required valve 12 may be actuated to supply fluid under pressure to the actuators positively to restore them to their original positions.

When no electrical signal whatsoever is applied to the solenoids of the valves 12, 13 and 15, it will be appreciated from a consideration of Figure 1 that a fluid connection is established between the spaces on opposite sides of the piston of the actuator 11 associated with the anti-roll torsion bar at the rear of the vehicle. No such connection is established, however, between the piston spaces of the actuator 10 associated with the anti-roll torsion bar at the front of the vehicle. The effect of this is that, while the anti-roll torsion bar at the rear of the vehicle is able to make no contribution to the roll stiffness of the vehicle's rear suspension, that at the front of the vehicle does provide some roll stiffness. The tendency is thus for the handling characteristic of the vehicle when cornering to be that of understeering, which is considered to be the safest handling mode. Therefore, if there should be any failure of the control system of the described suspension, the handling characteristics of the vehicle will revert to those which are generally considered to be safe.

Claims

1. An hydraulic system for a vehicle suspension system of the kind specified, comprising: a source of fluid under pressure; an actuator for positionally adjusting the springing means, having two fluid connections to which the application of fluid under pressure causes the actuator to produce outputs in respective opposite senses; two valves each having a first, a second and a third port and operable between a first position wherein a connection is established between the first and third ports only and a second position wherein a connection is established between the first and second ports only; and a pressure relief valve for returning fluid to a reservoir thereof and openable at a predetermined pressure lower than that at which fluid is supplied by said source thereof; the first ports of the valves being connected respectively to the fluid connections of the actuator; ; the second ports of the valves being connected to each other and to said source of fluid under pressure; and the third ports of the valves being connected to each other and to said pressure relief valve.

2. A system according to Claim 1 wherein there are two actuators, respectively associated with anti-roll torsion bars at the front of the vehicle and rear thereof and having their fluid connections in parallel with one another.

3. A system according to Claim 2 comprising a further valve in the connections to the actuator associated with the front anti-roll torsion bar, the further valve isolating the fluid connections to the actuator from one another and from the rest of the hydraulic system when not subject to any control signal.

4. A system substantially as hereinbefore described with reference to the accompanying drawings.