GB2106053A - Vehicle suspension system - Google Patents

Abstract

A vehicle suspension system of a self-levelling kind is provided with a pressure-sensitive device in the form of a switch 9 located in the vehicle's power steering system. The switch 9 responds to a rise in fluid pressure produced when the vehicle is steered in a curved path and blocks all levelling adjustments of the suspension units during this pressure rise. <IMAGE>

Description

SPECIFICATION Suspension system 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 genuine alterations in vehicle load, and not in response 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-rolled" 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.

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 a pressure-sensitive device arranged in the power steering system of the vehicle to respond to a rise in fluid pressure produced when the vehicle is steered in a curved path, the device being arranged to inhibit adjustment of the suspension units during the rise in fluid pressure and for a period of time thereafter.

The pressure-sensitive device preferably comprises a pressure-sensitive switch arranged to inhibit an electrical height control circuit when the necessary rise to fluid pressure takes place.

The invention will now be further described, by way of example only, with reference to the accompanying drawings, of which: Figure 1 is a layout of the suspension system of a vehicle, according to the invention, and Figure 2 is a layout of the power steering system of the same vehicle.

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 857 799 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.

A pressure-sensitive switch 9, operated by the power steering system of the vehicle (see below), is connected to the height control unit 6. When the switch is operated, the height control unit is inhibited so that the valves 4 and 5 are maintained in the positions shown irrespective of signals from the height sensor 7.

Referring now to Figure 2, a pump 10 is arranged to supply oil, or other suitable fluid, from a reservoir 11 via a supply line 12 to a power steering valve 13.

The valve 13 is operated by the steering wheel 14 of the vehicle. When the steering wheel is in the straight ahead position (the position when the vehicle travels in a straight line) the valve directs the oil back to the reservoir 11 via a return line 15. But when the steering wheel is moved to either the left or the right, the valve 13 is operated to connect the supply line 12 to one or other of two power steering lines 16, 17, connected to a power steering ram 18.

The output rod 19 of the ram is connected to the steering linkage of the steered wheels (not shown).

The pump 10 feeds fluid under pressure via the valve 13 and the appropriate line 16 or 17 to the ram 19 causing the ram to move the steered wheels one way or the other in response to the movement of the steering wheel. whenever the vehicle is steered in a curved path there is a consequent rise in fluid pressure in the supply line 12 downstream of the pump 10. The magnitude of this pressure rise depends on the load in the steering linkage, which in turn reflects the dynamic loads upon the vehicle whilst cornering. During steady state cornering, the pressure will rise as a function of speed and turning radius. The pressure-sensitive switch 9 referred to above is inserted in this line. The switch is adjusted so that it operates when the oil pressure in the line rises above a predetermined magnitude, thereby preventing the ride height of the vehicle being adjusted in response to lateral forces produced whilst cornering. The pressure level at which the switch operates can be set so that adjustment of ride height can take place whilst the vehicle is being driven at moderate speed through a curve of large radius but is inhibited on curves of smaller radius or at higher speeds.

Claims (6)

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 a pressure-sensitive device arranged in the power steering system of the vehicle to respond to a rise in fluid pressure produced when the vehicle is steered in a curved path, the device being arranged to inhibit adjustment of the suspension units during the rise in fluid pressure and for a period of time thereafter.

2. A suspension system according to Claim 1, in which the pressure-sensitive device is a pressuresensitive switch arranged to inhibit adjustment of the suspension units by inhibition of an electrical height control circuit.

3. A suspension system according to Claim 1 or 2, in which the pressure-sensitive device is inserted between a fluid source and a steering wheel operated valve arrangement which controls the supply of fluid to power steering means.

4. A suspension system according to Claim 3, in which the steering wheel operated valve arrangement is arranged to return fluid to the source via a return line when the steering wheel is in the straight ahead position and feed fluid to the power steering means when the vehicle is steered in a curved path.

5. A suspension system according to any preceding claim, in which the fluid pressure level at which the pressure-sensitive device operates can be adjusted.

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