GB2155143A

GB2155143A - Temperature regulation in hydropneumatic suspension units

Info

Publication number: GB2155143A
Application number: GB08503938A
Authority: GB
Inventors: Alain Guesdon
Original assignee: Delti SA
Current assignee: Delti SA
Priority date: 1984-02-29
Filing date: 1985-02-15
Publication date: 1985-09-18
Also published as: IT8421012A1; FR2560323A1; DE3418572A1; SE8500722L; IT1176154B; SE8500722D0; FR2560323B1; ES8606596A1; ES540814A0; IT8421012A0; JPS60205038A; GB8503938D0

Abstract

A unit for a vehicle suspension includes a volume of gas and a volume of liquid which are separated in sealed manner by a deformable membrane 16. A device is provided to regulate the temperature of the gas, said device comprising a temperature sensor 28 and a heating means (e.g. resistance 30) disposed in the volume of gas and connected to a regulator circuit 32 for maintaining the temperature of the gas substantially at the maximum value which it could reach during use of the suspension. This ensures a uniform performance from the suspension unit. The membrane 16 deforms radially into the shape of a cross in X-section (Fig 2). The gas may be within the membrane instead of around it. The resistance 30 may be replaced by a microwave heater element, in which case the gas contains particles sensitive to microwaves e.g. particles of iron oxide. <IMAGE>

Description

SPECIFICATION A regulator device for an oleo strut, and an oleo strut including the device The invention relates to a regulator device for an oleo strut, and to an oleo strut including the device, in particular for a vehicle suspension.

Background of the invention Generally speaking, an oleo strut for a vehicle (i.e. an oil-and-air shock absorber strut, and not necessarily for an aircraft) comprises a tubular piston which is slidably mounted and sealed inside a body which is closed in a sealed manner, together with means constituting a sealed barrier between a volume of gas and a volume of liquid such as a deformable membrane housed in the piston, for example, whereby movements of the piston in the body cause variations in the volume of the gas and thus compress or relax said volume of gas.

When an oleo strut is used, the flow of liquid through non-return valves or throttles causes to liquid to heat and thus heats the gas contained in the oleo strut. Thus the temperature of the gas which is substantially equal to ambient temperature when the strut has not been in use for some time, progressively rises to a maximum value which is a function of conditions under which the strut is used and which is reached when the suspension including the strut is working under its toughest or most difficult conditions. The temperature of the gas in the strut may rise, for example, up to about 60"C to 800C, and this temperature rise leads to an accompanying rise in pressure thus changing the response curve of the strut which becomes progressively "harder".Since the viscosity of the liquid used an oleo strut also varies as a function of temperature, the behavior of the strut can vary rather widely as a function of its conditions of use and cannot therefore be determined with any accuracy in advance.

Devices are already known either for heating the liquid contained in an oleo strut to modify its viscosity and thus increase or decrease its shock absorbing effect, or else for heating the gas contained in the strut in order to modify the trim of a vehicle as a function of its load.

However, none of these known devices serves to make the oleo strut operate along a predetermined stroke-force curve. Further, these known devices have structural drawbacks such that either they do not operate in the expected manner, or else they are too unreliable to be used in practice.

Preferred embodiments of the present invention avoid these drawbacks and propose a regulator device which ensures pre-determined behavior of an oleo strut regardless of the ambient temperature and the conditions under which a suspension including the strut is used.

Summary of the invention According to the invention, the regulator device comprises means for detecting the temperature of the gas and means for raising this temperature to the maximum value which it may reach during use of the suspension, and for maintaining the temperature at said value.

The means for heating the volume of gas contained in an oleo strut may be of any appropriate type, for example an electrical resistance or a microwave heater, in which case the gas preferably includes sensitive elements which are not transparent to microwaves, for example iron oxide particles.

Thus, once the vehicle has started, the invention makes it possible to obtain a predetermined temperature in the volumes of gas contained in oleo struts in its suspension and thus causes the suspension to operate along a predetermined force or response curve. The temperature of the gas is raised very rapidly and is quickly communicated to the liquid contained in each oleo strut, thus ensuring a predetermined viscosity.

Advantageously, the invention also provides means for adjusting the temperature to which the gas is raised and maintained during use of the suspension, together with means enabling the vehicle driver to control said adjusting means.

Thus, as a function of the path to be followed, the driver can harden or soften the response of the suspension at will.

The invention also relates to an oleo strut which is fitted, either during manufacture or subsequently, with a temperature regulator device of the above-defined type.

In a preferred embodiment of the invention, the heating means are mounted at one end of the piston, and the membrane housed in the piston is of tubular shape, is disposed along the axis of the piston, and is of a type which is deformable in the radial direction only without extending or stretching under the effects of variations in gas pressure.

This serves to avoid, inter alia, the membrane coming into contact with the heater means which could damage it. Further, since the membrane deforms only radially under the effect of variations in gas pressure without any extension or stretching, the sealing or separation between the gas and the liquid is improved and the danger of the membrane becoming porous under the effect of excessive extension or stretching is avoided.

Depending on circumstances, the gas may be contained inside the membrane or outside the membrane.

Brief description of the drawing An embodiment of the invention is described by way of example with reference to the accompanying drawing, in which: Figure 1 is an axial section through an oleo strut in accordance with the invention; and Figure 2 is a cross-section through said strut, on a line ll-ll of Figure 1. More detailed description The drawings show, by way of example, a particular embodiment of an oleo strut in accordance with the invention. The strut comprises a tubular steel piston 10 whose top end is closed in sealed manner and whose bottom end is fitted with a stopper or cap 12 which is fixed to the annular rim 14 at the bottom end of a tubular membrane 16 made of elastomer or the like, thereby fixing the membrane to the piston in sealed manner.The cap further includes one or more orifices 18 which may optionally be fitted with non-return valves and which provide communication with the inside of the membrane 16.

The top end of the membrane is closed in sealed manner by a plug 20 and a collar 22 which clamps the top end of the membrane onto the plug 20.

The piston 10 is slidably and sealingly mounted in a cylindrical bearing 24 of a body 26 which is filled with a suitable liquid, generally an oil, while the volume outside the membrane 16 and inside the piston 10 is filled with a gas, for example air.

As indicated above, the membrane 16 is tubular in shape and deforms only radially relative to the longitudinal axis of the piston 10 without extending or stretching in any way under the effect of displacements of the piston relative to the body 26.

The shape of the cross-section of the membrane varies between a cross having several arms as shown in solid lines in Figure 2 and a circle as shown in dot-dashed lines, with the perimeter of the membrane cross-section remaining substantially the same in both cases.

In accordance with the invention, this oleo strut is fitted with a gas temperature regulator device comprising firstly a temperature sensor 28 and secondly heater means 30 which are constituted in this case by an electrical resistance together with an electric circuit 32 having two terminals 34 for receiving electrical current, for example from a vehicle battery, an input connected to the temperature sensor 28, and two output terminals connected to the terminals of the heating resistance 30.

Preferably, the sensor 28 and the heating resistance 30 are disposed inside the piston in the volume of gas, but they could alternately be mounted on the wall of the piston and outside the volume of gas.

The electric circuit 32 is designed in such a manner as to provide high electrical power to the heating means 30 in order to rapidly raise the temperature of the gas contained in the piston 10 to a predetermined value, and then to maintain the temperature at this value. The predetermined value for the gas temperature is substantially equal to the maximum temperature which the gas could reach under the toughest conditions of use for the suspension including the oleo strut, and this tem perature may be adjustable, e.g. by means of a potentiometer, which is placed directly on the circuit 32 and thus only accessibie to a maintenance engi neer, or else by means of a control circuit 36 which is made accessible to the vehicle driver, thus ena bling the set temperature to be varied between predetermined values corresponding to predeter mined degrees of suspension "hardness".

By way of numerical example, in one embodi ment the circuit 32 delivers a maximum power of 2.5 watts to the heater element 30 if the heater element 30 is in direct contact with the gas inside the piston 10 or a maximum power of about 8 watts if the heater element 30 is not in direct contact with the gas.

The piston 10 is the component of the suspension which is subjected, in operation, to the greatest temperature variations with heating coming from friction between the piston and its sealing rings and from the throttled flow of the liquid through the non-return valves mounted at the bottom end of the piston, and to the repeated compression and de-compression of the gas. For this reason the temperature sensor 28 is preferably placed inside the piston so as to be sensitive to variations in the temperature of the gas, of the liquid, and of the piston itself.

Depending on the particular embodiment of the oleo strut, the gas may be outside the membrane 16 as shown in Figures 1 and 2, or else it may be inside the membrane, which would correspond approximately to an embodiment in which the piston 10 is turned upsidedown relative to the body 26 so that its top end becomes its bottom end and is open for the passage of liquid.

The invention is applicable to any suspension including an oleo strut, and in particular to vehicle suspensions.

Claims

1. A device for regulating an oleo strut of the type comprising a volume of gas separated in sealed manner from a volume of liquid, wherein the device comprises means for detecting the temperature of the gas, and means for raising said temperature to the maximum temperature the gas may reach in operation of the strut, and to maintain the gas temperture at said value.

2. A device according to claim 1, further including means for adjusting the temperature to which the gas is raised and at which it maintained during use of the oleo strut.

3. A device according to claim 2 wherein the means for adjusting the said temperature are controllable by the driver of a vehicle including said oleo strut.

4. A device according to claim 1, 2 or 3, wherein the temperature detection means are connected to an input of a regulator circuit which is supplied with electrical current, for example from the battery of a vehicle equipped with the oleo strut, with the output of said regulator circuit being connected to the means for heating the gas.

5. A device according to any one of claims 1 to 4, wherein the heating means comprise an electrical resistance.

6. A device according to any one of claims 1 to 4, wherein the heating means comprise a microwave heater element and wherein the gas includes elements which are sensitive or non-transparent to microwaves, for example particles of iron oxide.

7. An oleo strut, in particular for a vehicle suspension, comprising a tubular piston slidably mounted in sealed manner in a body which is closed in sealed manner, and means, such as an elastically deformable housed in the piston, constituting a sealed barrier between a volume of gas and a volume of liquid, wherein the oleo strut further includes a gas temperature regulator device according to claim 1, and wherein the said membrane is tubular in shape and is disposed along the axis of the piston, and is deformable in the radial direction only, without extension or stretching.

8. A strut according to claim 7, wherein the cross-section of the membrane varies under the effect of variations in pressure between a cross having a plurality of arms and a circle, with the perimeter of the membrane cross-section remaining substantially constant.

9. A strut according to claim 7 or 8, wherein the volume of gas is outside the membrane and the bottom end of the membrane is fixed to the bottom end of the piston while the top end of the membrane is closed at a distance from the top end of the piston, with the top end of the piston carrying the heating means.

10. A strut according to claim 7 or 8, wherein the volume of gas is located inside the membrane and the top end of the membrane is fixed in sealed manner to the top end of the piston which carries the heating means.

11. A device for regulating an oleo strut, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

12. An oleo strut substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.