GB2106054A

GB2106054A - Vehicle suspension system

Info

Publication number: GB2106054A
Application number: GB08128414A
Authority: GB
Inventors: Alan Leslie Harris
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1981-09-19
Filing date: 1981-09-19
Publication date: 1983-04-07

Abstract

A vehicle suspension system of the self-levelling kind is provided with a cornering sensor in the form of a switch 11 associated with the steering mechanism, which inhibits levelling adjustments of the suspension units 1 whilst the vehicle is being steered in a curved path. In order that the ride height of the vehicle can be adjusted when the vehicle is parked with the steered wheels at an angle, the system includes drive sensor means in the form of a second switch 12. This second switch is associated with the vehicle's transmission selection mechanism in such a way that when drive is disengaged the second switch renders the cornering sensor 11 ineffective as regards inhibition of levelling adjustments. <IMAGE>

Description

SPECIFICATION Suspension systems for vehicles This invention relates to suspension systems for vehicles, particularly those which are designed to maintain a suitable height relationship between the sprung and unsprung parts of the vehicle despite changes in vehicle load.

In this context, "the sprung parts of the vehicle" means the body and its associated components, and "the unsprung parts of the vehicle" means those parts of the vehicle (including the wheels, axles and the drive mechanism for the wheels) from which the body is supported by springs or equivalent members.

Such suspension systems must include some sort of delay to ensure that adjustment of the height relationship between the sprung and unsprung parts (the nominal ride height) can occur only in response to genuine alterations in vehicle load, and not in response to to oscillatory motion of the springs.

Methods of achieving this aim include incorporating a delay into an electrical control system and damping the movement of a control valve.

It is also necessary to minimise any response due to lateral (roll-generating) forces produced whilst cornering. The effects of any such response will be apparent from a consideration of a vehicle driving through an 'S' bend. If the suspension system were allowed to compensate for the roll generated whilst cornering by bringing the vehicle back towards the level condition during the first part of the bend, the second part would be approached in a "pre-rolied" condition. This is clearly a very dangerous situation, and the condition would not be corrected rapidly because of the in-built delay referred to above.

Furthermore, even when the delay has been exceeded, the rate of adjustment is often quite slow, frequently being limited by the capacity of a pump used in the height adjustment system.

It has been suggested that the problem can be overcome by selecting the delay so as to ensure that cornering would be completed before the system starts to respond. This is impractical because of the conflict between the delay needed to prevent roll correction, and the need to ensure reasonably rapid attitude correction from start up in a fully laden condition. It is quite possible to maintain a cornering manoeuvre for 20-30 seconds on some of the large radius curves which are found at motorway intersections for example.

A more practical way of overcoming the problem has been proposed, which involves interposing a pendulum-operated spool valve in the fluid lines to and from struts used to adjust the nominal ride height of the vehicle. When the pendulum is substantially vertical (with respect to the vehicle), fluid can be fed to and from the struts via the spool valve so that the suspension system operates in the normal way. But during a cornering manoeuvre the pendulum swings to one side or the other and operates the valve to isolate the struts, so preventing height adjustment from taking place.

This arrangement still has drawbacks when the vehicle is running on a cambered road, because the pendulum may move out of vertical when the vehicle is travelling along a straight stretch of road, thus inhibiting the necessary corrections. Furthermore, the pendulum-operated valve adds considerably to the cost of the system.

According to the present invention, a suspension system for a vehicle comprises at least two suspension units installed on opposite sides of the vehicle and adapted to maintain a suitable height relationship between the sprung and unsprung parts of the vehicle despite changes in vehicle load, and cornering sensor means operably connected to the steering mechanism of the vehicle so as to respond when the vehicle is steered in a curved path, the cornering sensor means being arranged to inhibit adjustment of the suspension units when the vehicle is so steered, and for a predetermined period thereafter.

Preferably the cornering sensor means is arranged to respond when the steering mechanism has moved through more than a predetermined amount from the straight ahead position.

The system may to advantage include drive sensor means associated with the transmission selection mechanism of the vehicle and arranged to be operated when the drive to the wheels is engaged, the drive sensor means being arranged to prevent the cornering sensor means from inhibiting adjustment of the suspension units unless the drive is engaged. This permits the nominal ride height to be adjusted when the vehicle is parked with the drive disengaged and the steering wheels at an anle.

A preferred form of cornering sensor means comprises a switch arranged to inhibit an electrical height control circuit for maintaining the height relationship between the sprung and unsprung parts of the vehicle. The switch may be installed anywhere that would permit the necessary steering movements to be sensed.

The drive sensor means may also comprise a switch.

The invention will now be further described, by way of example only, with reference to the accompanying drawing which is a layout of the suspension system of a vehicle, in accordance with the invention.

For simplicity only a single suspension unit 1 and its associated control system is shown in Figure 1, but in a practical installation the body will be supported from each wheel of the vehicle, or at least from each wheel of one axle, by means of a similar suspension unit.

The suspension units may be of the ram type in which each unit is effective to adjust the mounting position of the associated suspension spring within the body. Alternatively each unit may comprise an integral gas spring and damper unit, as disclosed in British Patent Specification 857799 for example.

A high pressure hydraulic pump 2 is arranged to draw fluid from a reservoir 3 and pump it to the suspension unit 1 through first and second solenoidoperated valves 4 and 5. Both valves are operated in response to electrical signals from an electronic height control unit 6 which receives signals from an electrical ride height sensor 7. The sensor 7 is associated with the suspension unit 1 in such a way that it monitors the height between the sprung and unsprung parts of the vehicle in the vicinity of the suspension unit.

The pump 2 is under the control of the control unit 6 so that the pump only operates when fluid is required by the suspension unit 1. Alternatively, the pump could be provided with means to reduce the load on the pump when fluid is not required.

At a certain ride height, the valves 4 and 5 are in the positions shown in the drawing, that is, the second valve 5 connects the suspension unit 1 to the first valve 4, but the first valve 4 is closed. Thus, fluid is trapped in the suspension unit so that the nominal ride height of the vehicle remains constant. In order to increase the nominal ride height, the first valve 4 is moved to its alternative position so that fluid can be pumped from the reservoir 3, via valves 4 and 5, into the lower chamber of the suspension unit, thus increasing its length. When the required nominal ride height has been reached, as detected by the sensor 7, the first valve 4 is moved back to its closed position shown.In order to reduce the nominal ride height, the second valve 5 is moved to its alternative position in which the suspension unit 1 is connected to the reservoir through a return line 8, thus enabling fluid to be dumped from the suspension unit to reduce its length. When the required height relationship has been achieved the second valve 5 is returned to its initial position.

The height control unit 6 has a pair of inhibit connections 9, 10, which can be connected together to cause the unit 6 to keep the valves 4,5 in the positions shown, irrespective of signals from the ride height sensor 7. A pair of switches 11, 12, are connected in series with the connections 9, 10. The first of these switches, 11, is arranged to be operated by the steering mechanism of the vehicle (not shown). When the steering mechanism is in the straight ahead position (the position when the vehicle travels along a straight path) the switch 11 is open, but when the steering wheel of the vehicle is turned either way sufficient to move the steering mechanism beyond a predetermined amount, the switch closes. The other switch 12 is arranged to be operated by the transmission selection mechanism of the vehicle.This second switch 12 is open whilst the drive to the wheels is disengaged, but closes when drive is engaged.

The height control unit 6 also includes a delay facility which maintains the inhibit status for a predetermined period, typically 10 seconds, afterthe steering has been returried to the straight ahead position.

When the vehicle is driven along, the second switch 12 is closed and normal adjustment of ride height can take place as long as the vehicle is driven along a straight path. But when the vehicle is steered in a curved path the first switch 11 closes to make a circuit between the inhibit terminals 9, 10, via the closed second switch 12. Adjustment of nominal ride height is therefore inhibited and remains so until the steering mechanism moves back to the straight ahead position causing the first switch 11 to open again and has remained in that state for the predetermined period. The delay ensures that the suspension cannot make adjustments during an oversteer condition in which the steered wheels may be required to point straight ahead whilst the vehicle is still cornering.

When the vehicle is stopped and drive disengaged, the second switch 12 opens so that adjustment of ride height cannot be inhibited even if the vehicle is parked with the steered wheels at an angle.

The second switch could be omitted if this facility is not required.

In another embodiment (not shown) the height control unit may be modified so that it is inhibited when the connections 9, 10 are open circuited. In this case the switches 11 and 12 are connected in parallel across the connections and they are arranged to operate the other way around, that is, switch 11 is closed when the steering mechanism is in the straight ahead position and switch 12 is closed when drive is disengaged.

Claims

1. A suspension system for a vehicle, comprising at least two suspension units installed on opposite sides of the vehicle and adapted to maintain a suitable height relationship between the sprung and unsprung parts of the vehicle despite changes in vehicle load, and cornering sensor means operably connected to the steering mechanism of the vehicle so as to respond when the vehicle is steered in a curved path, the cornering sensor means being arranged to inhibit adjustment of the suspension units when the vehicle is so steered, and for a predetermined period thereafter.

2. A suspension system according to Claim 1, in which the cornering sensor means is arranged to respond when the steering mechanism has moved through more than a predetermined amount from the straight ahead position.

3. A suspension system according to Claim 1 or 2, which includes drive sensor means associated with the transmission selection mechanism of the vehicle and arranged to be operated when the drive to the wheels is engaged, the drive sensor means being arranged to prevent the cornering sensor means from inhibiting adjustment of the suspension units unless the drive is engaged.

4. A suspension system for a vehicle, which is substantially as described with reference to and as shown in the accompanying drawings.

4. A suspension system according to any preceding claim, in which the cornering sensor means comprises a switch arranged to inhibit an electrical height control circuit for maintaining the height relationship between the sprung and unsprung parts of the vehicle.

5. A suspension system according to claim 4 when appended to claim 3, in which the drive sensor means comprises a switch connected to the height control circuit.

6. A suspension system for a vehicle, which is substantially as described with reference to and as shown in the accompanying drawings.

New claims or amendments to claims filed on 10.8.82 Superseded claims 1-6 New or amended claims:

1. A suspension system for a vehicle, comprising at least two suspension units installed on opposite sides of the vehicle and adapted to maintain a suitable height relationship between the sprung and unsprung parts of the vehicle despite changes in vehicle load, cornering sensor means operably connected to the steering mechanism of the vehicle so as to respond when the vehicle is steered in a curved path, the cornering sensor means being arranged to inhibit adjustment of the suspension units when the vehicle is so steered, and for a predetermined period thereafter, and drive sensor means associated with the transmission selection mechanism of the vehicle and arranged to be operated when the drive to the wheels is engaged, the drive sensor means being arranged to prevent the cornering sensor means from inhibiting adjustment of the suspension units unless the drive is engaged.

2. A suspension system according to Claim 1, in which the cornering sensor means comprises a switch arranged to inhibit an electrical height control circuit for maintaining the height relationship between the sprung and unsprung parts of the vehicle.

3. A suspension system according to Claim 2, in which the drive sensor means comprises a switch connected to the height control circuit.