GB2194047A - Pneumatic vehicle suspension system with thermal actuator - Google Patents

Abstract

Apparatus for changing an operative condition of a vehicle suspension, e.g. to level a vehicle to compensate for changed vehicle loading, comprises a device (12) operable by a fluid under pressure; a chamber (14) containing a quantity (22) of a vaporisable liquid; heating means (28) operable upon the liquid in the chamber to cause the liquid to generate vapour at an increased pressure; means such as a piston (16) for communicating the pressure of the vapour in the chamber to the fluid; conduit means (30) for flow of the fluid under pressure to or from the device (12); and valve means (32) for controlling flow of the fluid in the conduit means.

Description

SPECIFICATION Vehicle suspension including fluid pressure operating device This invention relates to apparatus for effecting a change in an operative condition of a vehicle suspension, by changing the pressure of the fluid in a fluid pressure operating device.

Vehicle suspensions are known wherein springing is provided by fluid pressure devices which are, in effect, gas springs. The devices, which may be in the form of bellows or bags, or possibly rolling diaphragm units, are connected between the chassis or main structure of the vehicle and appropriate suspension components in such a way that downwards movement of the vehicle structure relative to the wheels and the ground on which the vehicle stands causes compression of the gas in the device so that such movement is resiliently resisted. If vehicle load is increased, however, this would cause the vehicle structure to assume a lower position, both when stationary and in terms of the mean position about which the suspension operates when the vehicle is being driven.If the additional load is added at one part only of the vehicle, e.g. the rear, the attitude of the vehicle would change, possibly to an undesirable extent. To avoid such conditions occurring, it has been proposed to provide means for adjusting the pressure of the gas within the fluid pressure devices of the suspension, or a selected one or ones of them to compensate for changes in load. For example, a compressor may be provided, possibly driven by an electric motor under the control of a suitable control system, in order to increase the pressure in the suspension devices by pumping. However, to provide such a compressor on a vehicle is relatively expensive, and a compressor is a relatively bulky piece of equipment to be accommodated on the vehicle. Further, a motor driven compressor may be noisy in operation.

In vehicle suspension, a fluid pressure operating device or devices may find application other than as the main springing means as above described. For example, a device may be used to assist another springing means, but again may be required to undergo a change in operating pressure to change its characteristics. The present invention, although described hereafter in relation to its application to a particular type of fluid pressure device, is applicable more generally wherever analogous requirements arise.

It is an object of the present invention to provide for a reduction of the above described disadvantages associated with the provision of a motor driven compressor for changing suspension characteristics.

According to the invention, we provide apparatus for changing an operative condition of a vehicle suspension, comprising a device operable by a fluid under pressure; a chamber containing a quantity of a vaporisable liquid; heating means operable upon the liquid in the chamber to cause the liquid to generate vapour at an increased pressure; means for communicating the pressure of the vapour in the chamber to the fluid; conduit means for flow of the fluid under said pressure to or from the device; and valve means for controlling flow of the fluid in the conduit means.

In apparatus according to the invention, heating of the liquid in the chamber to generate vapour thereof at an increased pressure, and communication of such pressure to the fluid for the fluid pressure device, effects a change in the operating conditions of the vehicle suspension equivalent to the change which could be effected by use of a motor driven compressor, but without the complexity, weight, bulk, and noise in operation, of such a compressor. By selection of a suitable vapourisable liquid, examples and desirable characteristics of which are described hereafter, pressure changes of the same order of magnitude as those achievable by a compressor, can readily be achieved. By the provision of valve means, it is not necessary continuously to maintain operation of the heating means.

The fluid for the fluid pressure device is preferably a gas and the device is one which operates as a gas spring, either alone or in combination with other springing means in the suspension.

The heating means preferably comprises an electrical heater, conveniently a resistance element disposed in a part of the chamber in contact with the liquid therein. The means for communicating the pressure of the vapour to the fluid may comprise a piston slidable within the chamber, or a flexible diaphragm separating a part of the chamber containing the liquid and its vapour from a part of the chamber containing the fluid and in communication with the conduit means.

The valve means for controlling the flow of fluid in the conduit means is preferably electrically operable. This gives the possibility of providing a vehicle suspension in which compensation for varying load conditions of the vehicle is automatic. If a suitable sensor or sensors is provided to detect the operative position of one or more fluid pressure devices, this can provide an input signal to an automatic control circuit which controls operation of the heating means and valve means until the required vehicle position or attitude is achieved.

It will be appreciated that in use of the invention it takes an appreciable time for the heating means to operate to cause a required displacement of fluid. However, for most vehicle applications a response time of several seconds, e.g. up to thirty seconds, is adequate for static load compensation in the suspension.

There may be provided means for introduction of the fluid to the device and conduit means from an external source, or release thereof. This enables maintenance and correction for possible leakage of the fluid, or facilitates compensation for a greater change in vehicle loading than can be achieved by operation of the heating means of the apparatus according to the invention. It will be appreciated that, in most suspension systems, the fluid will normally be at an initial pressure above atmospheric pressure.

The invention will now be described by way of example with reference to the accompanying drawing, which is a schematic diagram of one form of apparatus according to the invention.

The illustrated apparatus comprises the main eiements of a pressure generator 10, a fluid pressure operating device in the form of a rolling diaphragm actuator unit 12, and conduit means in the form of pipe 30 connecting the pressure generator 10 with the actuator 12.

Valve assemblies 48 and 32 are provided in the pipe 30 between the pressure generator and actuator. In the arrangement illustrated, a further actuator 1 2a is connected in parallel with the actuator 12 since in many applications of vehicle suspension two or more such actuators would be provided, e.g. one at each side of the vehicle.

The pressure generator 10 comprises a closed chamber 14 containing a slidable piston 16 which divides the chamber 14 into an upper portion 18 containing a gas and a lower portion 20 containing a volatile liquid 22. In the bottom of the chamber 14, within the liquid 22 so as to be able to heat the liquid so that it vapourises at an increased vapour pressure there is disposed an electrical heater 28, illustrated as a resistance heating coil. The piston 16 is slidable between a lower position indicated generally at 24 and an upper position indicated generally at 26, but although the movement of the piston is illustrated as vertical for convenience of illustration, it could be in any orientation suitable for accommodating the pressure generator in a motor vehicle.Instead of the piston 16, a flexible diaphragm could be provided to separate the part of the chamber containing the liquid 22 from the upper part 18 containing the gas. Whether a diaphragm is provided or a piston as illustrated, it preferably is constructed so as to minimise heat transfer between the two parts of the chamber.

The actuator 12 is a rolling diaphragm strut unit, having a part 34 telescopically movable relative to a housing 36 and sealed by a rolling diaphragm 42. The part 34 is movable from a retracted position to an extended position as indicated in broken lines at 40. The part 34 contains a damping assembly of generally known type. In use, actuator 12 would be connected in a vehicle suspension so as to be movable between its retracted and extended conditions by movement of the vehicle's wheel or wheels relative to the chassis or other structure of the vehicle. Level or position sensors may be associated with the or each actuator 12 to provide signals, in generally known manner, to a suitable control circuit for controlling operating of the apparatus in the manner described hereafter.

The valve 32 in the pipe 30 is normally biased by springs 50 to a position wherein the valve is closed. The valve 30 is openable in one sense by a solenoid 46, and in the other sense by a pilot actuator 60. The latter provides for connection between the pipe 30 and a connector 44 which is connectable to an external source of pressurised fluid, e.g. a compressed air line or a source of compressed inert gas. The solenoid 46 is operable to open the valve to permit flow through the pipe 30, but not provide communication with the connector 44.

The valve 48 is normally open and is biased by a spring 52 to this condition, so that connection is provided between the space 18, above the piston 16 in the chamber 14, and the pipe 30. The valve 48 is operable by a solenoid 54 to provide communication between the pipe 30 and a port 56 leading to the external atmosphere.

Although the pressure generator 10 and valves 32, 48 have been shown as separate components, themselves separate from actuators 12, it would be possible for one or more of these components to be incorporated in a combined unit or units.

The operation of the apparatus will now be described. Initially it will be assumed that the vehicle to which the apparatus is fitted is static and level in an unloaded condition. The gas above piston 16, and in pipe 30 and above the diaphragm in actuators 12, 1 2a is at a pre-charged pressure to act as a gas spring.

Typically such a pre-charged pressure may be of the order of two atmospheres or so. The pre-charging of the system to such a pressure will be performed at construction of the vehicle, and at desired intervals of maintenance thereof. Introduction of gas under the pre-charged pressure is provided through the valve 32 by connecting an external source of pressurised gas to the connector 44, which pressure applied through the pilot actuator 60 causes the external source of gas to be connected to the pipe 30 and to the space above the piston 16 in the chamber 14. Disconnection of the external source of pressurised gas from the connector 44 will de-actuate the pilot actuator 60, so that valve 32 resumes its closed position, hence sealing the gas under pre-charge pressure in the pipe 30, actuators 12, and chamber 14.

If now the vehicle load is increased so that the actuator 12 is compressed (a state of equilibrium being reached when the pressure of the gas therein and in pipe 30 is matched to the increased vehicle load) the apparatus is operated in the following manner to restore the actuator to its previous condition of extension and hence the vehicle to its previous attitude. By a suitable control system, heater 28 is operated to increase the temperature of liquid 22 and the vapour pressure thereof. Simultaneously with or slightly after operation of heater 28, solenoid 46 is energised so that valve 32 opens to provide communication for flow of gas between the actuator 12 and the pressure generator 10 by way of pipe 30.

When the liquid 22 has been heated sufficiently for its vapour pressure to equal and then exceed the pressure of gas in pipe 30, piston 16 will be displaced upwardly in chamber 14 to compress the gas 18 above the piston.

Thus the gas pressure in actuator 12 is increased to reach a state of equilibrium at a suspension position corresponding to that before the vehicle was loaded. When such condition has been reached, as detected by a suitable level sensing device, solenoid 46 is de-energised and the heater 28 brought out of operation. Valve 32 is closed by de-energisation of solenoid 46, so that the gas in the actuators 12 remains at the increased pressure which compensates for the increased vehicle load. In the pressure generator, as it cools the vapour generated from liquid 22 will condense and the piston 16 returned to its starting position.

If the vehicle now is unloaded, so that, unless compensated for, the actuator part 34 would tend to move towards its extended position as indicated at 40, it is necessary to release gas from the actuator by way of pipe 30. To do this, solenoid 46 is energised without the heater 28 having been brought into use, so that gas will flow back to the pressure generator 10.

Maintenance of a vehicle will occasionally require the checking and possible replenishment of the gas in the actuators 12, pipe 30, and above the piston 16. As above described, gas can be introduced by way of connector 44. Valve 48 may also or in addition be used for such maintenance purposes. Valve 48 is normally spring biased to its condition wherein port 56 is not connected to the rest of the system, but when solenoid 54 is actuated the port 56 is so connected. If solenoid 54 is actuated to connect the port 56 to the system, whilst piston 16 is at its lowermost position, the space above the piston 16 will be filled with gas at atmospheric pressure. If solenoid 54 is de-energised to close port 56, and then solenoid 46 energised to open the valve 32 whilst the heater 28 is operated, the piston 16 will be driven up to displace the charge of air into the actuator 12.Successive such operations, each followed by closing of valve 32 and opening the port 56 will pump successive quantities of air into the actuator.

Typically, the volume of the space 18 above the piston 16 when in its lowermost position will be of the same order as the total volume of the gas normally contained above the diaphragms of actuator or actuators 12, 12A.

The liquid used in the pressure generator 10 may be pentane or dimethyl-acetylene, or similar organic liquids or mixtures of liquids which have boiling points at atmospheric pressure of less than 100 degrees C. and have a normal liquid state at atmospheric pressure and in a temperature range of, for example, -40 degrees C to +40 degrees C. Such liquids must have a vapour pressure sufficiently high to operate the apparatus at temperatures easily achieved in safety, e.g. up to 140 degrees C.

Such liquids must, of course, be chemically neutral with respect to the material of the chamber 14 and piston 16, and safe from the health point of view in case of accidental leakage thereof. It is contemplated that the pressure generator may operate at pressures up to about 8 atmospheres. Desirably, a safety valve or other safety device would be provided in association with the pressure generator 10. If a liquid having an appropriate operating temperature range is chosen, the pressure generator 10 may be able to be constructed from plastics materials, for economy in production and light weight.

The heating means 28 would be designed to operate so that the suspension can compensate for vehicle loading in a reasonable time period, e.g. of several seconds. Faster operation could be achieved by use of a more powerful heating means, but this is not generally required in a typical motor vehicle.

As above referred to, the heating means, and valves, of the apparatus may be automatically controlled in response to signals provided by suitable level or position sensing devices provided in association with the vehicle suspension. Such control circuits are known in suspensions wherein correction for vehicle load is achieved by means other than the present invention, and may readily be adapted for use with the present invention. Alternatively or in addition, manual control may be provided for.

Claims (11)

1. Apparatus for changing an operative condition of a vehicle suspension, comprising a device operable by a fluid under pressure; a chamber containing a quantity of a vaporisable liquid; heating means operable upon the liquid in the chamber to cause the liquid to generate vapour at an increased pressure; means for communicating the pressure of the vapour in the chamber to the fluid; conduit means for flow of the fluid under said pressure to or from the device; and valve means for controlling flow of the fluid in the conduit means.

2. Apparatus according to Claim 1 wherein said fluid is a gas, and the fluid pressure device operates as a gas spring.

3. Apparatus according to Claim 1 or Claim 2 wherein the heating means comprises an electrical heater.

4. Apparatus according to any one of the preceding claims wherein the means for communicating the pressure of the vapour to the fluid comprises a piston slidable in the chamber.

5. Apparatus according to any one of Claims 1 to 3 wherein the means for communicating the pressure of vapour to the fluid comprises a diaphragm in the chamber.

6. Apparatus according to any one of the preceding claims wherein said valve means is electrically operable.

7. Apparatus according to any one of the preceding claims comprising means for introduction of the fluid to the device and conduit means from an external source of the fluid under -pressure.

8. Apparatus according to any one of the preceding claims wherein said fluid is air.

9. Apparatus according to Claim 8 further comprising means for admission of air from the external atmosphere to the conduit means.

10. Apparatus according to any one of the preceding claims further comprising sensing means responsive to the relative position assumed by vehicle suspension components, and a control means having an input from the sensing means and outputs controlling the valve means and heating means in accordance therewith.

11. Apparatus substantially as hereinbefore described with reference to the accompanying drawings.