GB1602291A - Pneumatic vehicle suspensions - Google Patents

Description

(54) IMPROVEMENTS RELATING TO PNEUMATIC SUSPENSIONS (71) We, DUNLOP LIMITED, a British Company of Dunlop House, Ryder Street, St. James's, London SW1, England, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to improvements in pneumatic vehicle suspensions.

Suspeilsion systems for vehicles are known utilising the resilient properties of a gas, such as air, in place of coil springs or elastomeric bodies to damp and absorb the shock loads applied between the groundengaging parts (wheels or crawler tracks) of a vehicle and its chassis as the vehicle moves over an uneven terrain. It is also known to vary the quantity of gas present in a pneumatic suspension system by means of a so-called "levelling valve" which can connect the system to a source of pressurised gas or exhaust gas from the system to raise and lower the chassis or to vary the resilience of the pneumatic system.This facility requires, however, that the vehicle is provided with a source of compressed gas and it is one object of the present invention to provide a pneumatic vehicle suspension which has variable characteristics without requiring that the vehicle has a source of compressed gas, such as a compressor.

Hydro-pneumatic vehicle suspension systems are known in which shock loads are transmitted by the wheels of the vehicle to one or more closed gas spring via hydraulic fluid, the hydraulic fluid being separated from the gas in the spring by a flexible membrane. By a "closed" gas spring is meant one which is normally sealed and is not normally in communication with an extraneous source of gas, so that under service conditions the quantity of gas in the spring is not varied and a vehicle incorporating the system requires no compressor to renew or supplement the gas in the spring.

Such hydro- pneumatic systems, known under the Registered Trade Mark "HYDRAGAS", have proven themselves in use in motor cars, but problems arise in the application of such systems to commercial vehicles where the variation in pay-load relative to the unladen weight of the vehicle is much greater. In commercial vehicles, such as lorries, coaches or buses, it is desirable that the quantity of fluid in the system (hydraulic liquid or gas or both) should be variable in proportion to variations of the pay-load of the vehicle.If it is desired to use closed gas springs so that the vehicle can dispense with a source of compressed gas the most convenient way to achieve such variation is to vary the quantity of hydraulic liquid in the system by means of the known levelling valve which operates in response to changes in the height of the chassis to exhaust liquid or to connect the system with a pump such as is present in almost all modern vehicles for the purposes of other hydraulic circuitry having different control functions.

If, however, the quantity of hydraulic liquid in the system is variable whereas the quantity of gas is fixed the "hardness" of the gas spring will clearly vary considerably with variations of the pay-load of the vehicle. If sufficient gas is present in the closed gas spring to function satisfactorily under conditions of maximum pay-load the gas spring will be too "soft" when the vehicle is unladen. The presence of too soft a spring in the unladen vehicle gives rise to handling difficulties and there is the further problem that in public transport vehicles it is undesirable that there should be any appreciable variation in the height of the mounting step for passengers as between the fully laden and the fully unladen state of the vehicle.

The present invention offers a solution to this problem which does not require the presence in the vehicle of a gas compressor.

In accordance with the invention there is provided a suspension system for a vehicle comprising a gas spring for absorbing shock loads transmitted to the gas spring by relative movements between the chassis and a ground-engaging part of the vehicle, and an isolated gas chamber separate from the gas spring but communicable therewith through flow-controlling means to vary the mass of the gas in the gas spring in response to variation of the height of the chassis relative to said ground engaging part thereby to permit an exchange of gas between the gas spring and the gas chamber which will tend to restore the chassis to its former height, means being provided to increase the gas pressure in the gas chamber in response to a decrease of height of the chassis relative to said ground engaging part, and vice-versa.

By an "isolated" gas chamber is meant one which is not communicable with a source of gas under pressure (other than the gas spring when the latter tends to discharge gas through the control valve).

The gas chamber may be incorporated in hydro-pneumatic means wherein it is divided by a diaphragm from a liquid chamber, the liquid chamber being communicable via a three-position valve alternatively with a source of liquid under pressure or with a reservoir for vented liquid thereby to vary the pressure applied by the diaphragm to gas in the gas chamber, the three-position valve and a flow-controlling means comprising a control valve being responsive to alterations of the height of the chassis relative to said ground engaging part to move from closed to open positions thereby respectively varying the gas pressure in the gas chamber and permitting an exchange of gas between the gas spring and the gas chamber tending to restore the chassis its former height.

A preferred embodiment of the invention will now be described with reference to the accompanying diagrammatic drawing illustrating a hydro-pneumatic suspension system in accordance with the present invention.

In the drawing there is shown a hydropneumatic suspension system intended for a public transport road vehicle, which comprises two similar vessels 10 and 11 each comprising a lower half shell 12 crimped at its periphery over the periphery of an upper half shell 13 and a flexible membrane 14 or 14A e.g. of butyl rubber spanning the interior of each vessel 10 and 11 to divide it into an upper chamber 15 or 15A filled with air and a lower chamber 16 or 16A filled with an hydraulic liquid.

The chamber 16 of the vessel 10 communicates via a pipe 17 with a chamber 18 of variable dimensions formed by a rolling lobe diaphragm 19 located in an open-ended housing 20, the smaller end 21 of the rolling lobe diaphragm 19 being secured to a piston 22 axially displaceable into and out of the housing 20 to exchange the incompressible liquid between the chambers 18 and 16.

The chamber 16A of the vessel 11 is connected via a pipe 23 with a three-position levelling valve 30 of a kind known per se which is adapted to exhaust liquid from the chamber 1 6A of the vessel 11, or introduce additional liquid from a pump or to adopt a neutral position closing the pipe 23 in response to variations of the pay-load of the vehicle resulting in variation of the height of the chassis of the vehicle relative to its wheels.

In accordance with the present invention the chambers 15 and 15A of the vessels 10 and 11 are mutually connected by a pipe 24 which is controlled by a two-position valve 25 adapted to open or close the pipe 24 in response to changes in the height of the chassis relative to the wheels resulting from variations of the pay-load of the vehicle.

Suitable ways in which the three-position levelling valve 30 and the two-position valve 25 can be made to respond to variations in the height of the chassis relative to the wheels are known per se and therefore will not be particularly described, it being optional whether such means are mechanical or electronic. In the simplest mechanical arrangements the valve housing would be secured relative either to the chassis or a wheel and the valve member would be connected either to a wheel or to the chassis, relative movements of the chassis and wheel serving to move the valve member relative to its housing.

The piston 22 is connected to a wheel of the vehicle and the vessel 10 and the housing 20 are fixed relative to the chassis of the vehicle. Shock loads received by the wheel as the vehicle travels over an uneven terrain therefore cause reciprocation of the piston 22 in the housing 20 causing an exchange of incompressible hydraulic liquid between the chambers 18 and 16 via the pipe 17. Under normal conditions, i.e. so long as the pay-load of the vehicle remains within limits such that there is no appreciable variation of the height of the chassis relative to the wheels the valve 25 remains closed. Under these conditions air in the chamber 15 of the vessel 10 is compressed by the membrane 14 as the chamber 16 fills with liquid so that the shock loads are cushioned by the gas spring constituted by air in the chamber 15.

In response to a drop in the height of the chassis the three-position levelling valve places the chamber 16A of the vessel 11 in communication with the pump 31 whereby additional hydraulic liquid is supplied to the chamber 1 6A of the vessel 11 thereby compressing the gas in the chamber 15A of the vessel 11 and simultaneously, or almost simultaneously the valve 25 opens. Since gas in the chamber 15A is now at a higher pressure than gas in the chamber 15 there will be an exchange of gas from the chamber 15A to the chamber 15 which will tend to raise the chassis back to its normal position under the heavier pay-load conditions, whereupon the valve 25 will close and the levelling valve 30 resumes the neutral position isolating the chamber 16A.Conversely if the pay-load of the vehicle is reduced so that the chassis tends to rise through expansion of the gas in chamber 15 liquid is evacuated from the chamber 16A of the vessel 11 by operation of the levelling valve 30 so that compression of the gas in chamber 15A of the vessel 11 is reduced.

Simultaneously, or almost simultaneously, the valve 25 is opened so that gas now at higher pressure in the chamber 15 flows to the chamber 15A until the consequent reduction in pressure acting on the diaphragm 14 allows the chassis to drop, whereupon the valve 25 closes and the levelling valve 30 resumes the neutral position. This arrangement ensures that there is no appreciable difference in the step-height of the vehicle as between its fully laden and fully unladen conditions.

The drawing is a simplified, schematic illustration and it will be appreciated that in use an assembly 19, 20, 22 will be associated with each wheel of the vehicle. Preferably the hydraulic assemblies associated with ihe wheels on the same side of the vehicle are connected with a common vessel 10 and isolated from the assemblies on the other side of the vehicle.

The described embodiment of the invention is a hydro-pneumatic system in which loads are transmitted between the piston 22 and the membrane 14 of the vessel 10 by an incompressible liquid in the chambers 16 and 18, but it will be appreciated that the hydraulic system could be dispensed with and the loads transmitted mechanically between the wheels of the vehicle and the membrane 14 of the or each associated vessel 10. Likewise the hydraulic height adjustment system for the membrane 14A could be replaced by a mechanical heightadjustment system acting mechanically on the membrane 14A of vessel 11.

WHAT WE CLAIM IS: 1. A suspension system for a vehicle comprising a gas spring for absorbing shock loads transmitted to the gas spring by relative movements between the chassis and a ground-engaging part of the vehicle, and an isolated gas chamber separate from the gas spring but communicable therewith through flow-controlling means to vary the mass of the gas in the gas spring in response to variation of the height of the chassis relative to said ground engaging part thereby to permit an exchange of gas between the gas spring and the gas chamber which will tend to restore the chasis to its former height, means being provided to increase the gas pressure in the gas chamber in response to a decrease of height of the chassis relative to said ground-engaging part, and vice-versa.

2. A suspension system as claimed in claim 1, wherein the gas chamber is incorporated in hydro-pneumatic means wherein it is divided by a diaphragm from a liquid chamber, the liquid chamber being communicable via a three-poslttion valve alternatively with a source of liquid under pressure or with a reservoir for vented liquid thereby to vary the pressure applied by the diaphragm to gas in the gas chamber, the three-position valve and a flow-controlling means comprising a control valve being responsive to alterations of the height of the chassis relative to said ground-engaging part to move from closed to open positions thereby respectively varying the gas pressure in the gas chamber and permitting an exchange of gas between the gas spring and the gas chamber tending to restore the chassis to its former height.

3. A suspension system for a vehicle substantially as herein described with reference to and as illustrated in the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. tend to raise the chassis back to its normal position under the heavier pay-load conditions, whereupon the valve 25 will close and the levelling valve 30 resumes the neutral position isolating the chamber 16A. Conversely if the pay-load of the vehicle is reduced so that the chassis tends to rise through expansion of the gas in chamber 15 liquid is evacuated from the chamber 16A of the vessel 11 by operation of the levelling valve 30 so that compression of the gas in chamber 15A of the vessel 11 is reduced. Simultaneously, or almost simultaneously, the valve 25 is opened so that gas now at higher pressure in the chamber 15 flows to the chamber 15A until the consequent reduction in pressure acting on the diaphragm 14 allows the chassis to drop, whereupon the valve 25 closes and the levelling valve 30 resumes the neutral position. This arrangement ensures that there is no appreciable difference in the step-height of the vehicle as between its fully laden and fully unladen conditions. The drawing is a simplified, schematic illustration and it will be appreciated that in use an assembly 19, 20, 22 will be associated with each wheel of the vehicle. Preferably the hydraulic assemblies associated with ihe wheels on the same side of the vehicle are connected with a common vessel 10 and isolated from the assemblies on the other side of the vehicle. The described embodiment of the invention is a hydro-pneumatic system in which loads are transmitted between the piston 22 and the membrane 14 of the vessel 10 by an incompressible liquid in the chambers 16 and 18, but it will be appreciated that the hydraulic system could be dispensed with and the loads transmitted mechanically between the wheels of the vehicle and the membrane 14 of the or each associated vessel 10. Likewise the hydraulic height adjustment system for the membrane 14A could be replaced by a mechanical heightadjustment system acting mechanically on the membrane 14A of vessel 11. WHAT WE CLAIM IS:

1. A suspension system for a vehicle comprising a gas spring for absorbing shock loads transmitted to the gas spring by relative movements between the chassis and a ground-engaging part of the vehicle, and an isolated gas chamber separate from the gas spring but communicable therewith through flow-controlling means to vary the mass of the gas in the gas spring in response to variation of the height of the chassis relative to said ground engaging part thereby to permit an exchange of gas between the gas spring and the gas chamber which will tend to restore the chasis to its former height, means being provided to increase the gas pressure in the gas chamber in response to a decrease of height of the chassis relative to said ground-engaging part, and vice-versa.

2. A suspension system as claimed in claim 1, wherein the gas chamber is incorporated in hydro-pneumatic means wherein it is divided by a diaphragm from a liquid chamber, the liquid chamber being communicable via a three-poslttion valve alternatively with a source of liquid under pressure or with a reservoir for vented liquid thereby to vary the pressure applied by the diaphragm to gas in the gas chamber, the three-position valve and a flow-controlling means comprising a control valve being responsive to alterations of the height of the chassis relative to said ground-engaging part to move from closed to open positions thereby respectively varying the gas pressure in the gas chamber and permitting an exchange of gas between the gas spring and the gas chamber tending to restore the chassis to its former height.

3. A suspension system for a vehicle substantially as herein described with reference to and as illustrated in the accompanying drawing.