GB2191157A - Control valve with damping means - Google Patents

Abstract

A hydraulic pressure regulator 10 for an automobile suspension system comprises a pilot-operated control valve having damping means 40 to damp movement of the valve member in the direction for fluid pressure dumping, whereby audible clicks produced by sudden dumping of high pressure fluid to tank are reduced or eliminated. The damping means is preferably a piston 40 and cylinder 44 arrangement which allows progressive rather than sudden opening or closing of the main valve 26. <IMAGE>

Description

SPECIFICATION Control valves This invention relates to control valves. More particularly, but not exclusively, the invention relates to control valves for hydraulic pressure control systems, such as are provided in automobile suspension systems.

An example of the application of the invention is to the hydraulic pressure regulators fitted to all current Citroen cars which have a central hydraulic system supplied by a high pressure pump. Models in current production are the CX and BX. Previous Citroen models using the system are the DS/D, the SM, and the GS/GSA. These regulators are also supplied to other car manufacturers, for example Maserati and Rolls-Royce.

Such a hydraulic pressure regulator is ofthe pilot valvetype,and its function isto maintainthe pressure in the hydraulic system between certain preset upper and lower limits. When the pressure falls to below the lower limit, the main valve in the regulator directs high pressure fluid from the pump intothemain high pressuresystem.Whenthe pressure reaches its maximum, the main valve switches the fluid from the pump into the reservoir and circulation continues from pumpto reservoir and back, until the pressure in the main system falls to the point of "cut in",whereuponthe pump is reconnected to the high pressure system.

The regulator, though efficient, is however not silent in operation. In use, it emits a fairly loud click which can be a source of irritation to drivers of the more silent models. The use of these regulators in Rolls-Royce cars has meant that the sound ofthe regulator operating is just about the only mechanical noise to be audiblewithin the car, clearlyan unsatisfactory situation.

Despite the existence of the above-identified problem for a significant period of time no acceptable solution to it has been found. It has been generally accepted that the "click" emitted bythe pressure regulator is caused by its main valve portion striking the limit stop at the end of itstravel.

Attempts to silence the regulator on this basis have proved ineffective. My investigations have lead me totheconclusionthatthesound isnotcausedbythe piston striking the stop, and some other source ofthe sound needed to be identified.

An object of the present invention is to provide a control valve and a hydraulic circuit incorporating same, for example an automobile hydraulic system, in which one or more improvements in relation to matters discussed above are provided, or improvements generally.

According to the invention there is provided a control valve and a fluid pressure control system and an automobile suspension system as defined in the accompanying claims. The invention also provides corresponding apparatus not limited by all features of any particular claim herein, but comprising any novel feature or novel combination of features disclosed herein and which provides any technical effect or improvement disclosed or suggested herein.

In an embodiment described belowthere is provided a pressure regulator of the pilot valvetype for use in an automobile hydraulic system in which the loud click emitted by such regulators in prior art apparatus is substantially reduced or eliminated. In the embodiment, the reduction or elimination of this click occurs at the time when the valve switches the pressure supply from the pump so that instead of supplying high pressure to the relatively high pressure circuit, the fluid is delivered to reservoir or tank. Research and development has shown thatthe sound emitted by the prior art apparatus is caused by a shockwave or "slug" of high pressure fluid (about 175 bar) passing at high speed through the main valve and into the low pressure return system beyond it.In the embodiment, the movement of the main valve piston is slowed by damping whereby opening of the valve is progressive and the previous "slugging" action is thereby reduced or prevented and the click hitherto emitted is reduced to a gentle hiss which is largely inaudible inside the passenger compartment of an automobile.

In the embodiment, a liquid/gas accumulator sphere which provides the reserve of pressure in the hydraulic system can become discharged after several years of service in an automobile. When this occurs, the time interval between "cut in" and "cut out" movements of the valve (i.e. connection ofthe pump to the high pressure circuit and to the tank respectively) becomes extremely short. In this condition, control of the main valve has to be highly sensitive since (dueto the lack of cushioning hitherto provided by the accumulator) fluid pressure rises very rapidly on cut-in. Likewise, in the absence ofthe accumulator, there is a tendencyforfluid pressureto drop somewhat rapidly.Accordingly, there is a need for the valve to be able to respond to these requirements. In the embodiment, the progressive opening of the valve against retracting movement of the damper permits pressure to rise more slowly on cut-in, than would otherwise be the case. Likewise, when cut-out is required the piston of the dam per can extend (in a vacuum-producing direction) relatively rapidly. Accordingly, the damper has almost no effect on main valve movement during fast cycle times, so the correct system pressure is maintained even underthese adverse conditions.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows a section through a pressure regulator and accumulator assembly; and Figure2 shows a portion of the assembly of Figure 1 illustrating same in the absence ofthe damping means of the present invention.

As shown in the drawings, a pressure regulating control valve 10 formes part of a hydraulic system of an automobile, including the suspension thereof.

Pressure regulator 10 isconnectedtoan accumulator 12 and by inlet and qutlet connectors 14 and 16 respectively to a high pressure hydraulic pump and to an hydraulic reservoir respectively. The valve is also connected through a port (not seen in the section taken in Figure 1) to a high pressure hydraulic circuitforwhich the pressure regulator constitutes a pressure-maintaining control valve.

Arrow 18 designates the high pressure output from valve 10. The pump supplying inletl4drawsfluid through a filter from the reservoir to which outlet port 16 is connected.

Accumulator 12 comprises a diaphragm 20 containing a high pressurevolumeofgas22which is separated by the diaphragm from hydraulic fluid within the portion 24 ofthe accumulator. Pressure in chamber 24 acts on one side of a slide valve 26, and on the other side thereof is a coiled compression spring 28 acting between the slide valve and the housing 30. A non-return ball valve 32 permits fluid pressure communication from inlet 14to chamber 26, but prevents fluid return, through a drilling 34.

A pilot valve 36 acting against a spring 38 serves to control main valve 34 in accordance with the downstream pressure in line 18.

Acting between slide valve 26 and housing 30 is damping means 40 in the form of a piston 42 and a cylinder 44 slidably received one within the other. In the embodiment, the diameter ofthe piston is approximately 0.5 inches (1.27 centimetres) and the clearance between the piston and the cylinder is approximatelyfourthousandths of an inch (0.0102 centimetres). The cylinder 44 is closed at its end remote from valve 26, wherebythe headside chamber has nofluid escape path other than through the clearance between the piston 42 and cylinder44.

This limited annular path of width fourthousandths of an inch itself provides the damping effect by restricting the fluid escape path.

It is particularly to be noted thatthe arrangement of the piston 42 and cylinder 44 is such that movement of slide valve 26 to the fluid dumping (to reservoir) position involves retraction of piston 42 into cylinder 44, which necessarily involves escape of hydraulic fluid between the piston 42 and the cylinder 44. On the other hand, movementofvalve 26 in the opposite directin can occur more rapidly by extension of piston 42 from cylinder 44 by producing avacuum in the headsidechamber.

In use, valve 10 regulates fluid pressure in the usual way but damping device 40 serves to damp movementofvalve 26 in the direction for fluid dumping to tank, whereby the latter occurs in a controlled manner and the audible click hitherto produced is thereby avoided.

Figure 2 shows the prior art apparatus which in use produces substantial audible clicks. As can be seen, valve 26 can move rapidlyto its fluid dump position merely against the action of spring 28.

Amongst other modifications which could be made in the above embodiment while remaining withinthescopeofthe invention arethe provision of alternative damping means, for example a piston and cylinder assembly having an orifice for controlling fluid flow into and out of the headside chamber. It might be possible to provide other damping arrangements to achieve a comparable result likewise.

Claims (8)

1. An automobile suspension system comprising an hydraulicfluid pressure control system having a control valve for controlling the supply offluid pressure from a pressure source to a pressurised circuit and to a lower pressure circuit or reservoir, characterised in that damping means is provided to limit the rate of movement of a valve member in the direction permitting fluid flow towards said reservoir.

2. Asystem according to claim 1 characterised in that said damping means comprises a piston and cylinder assembly.

3. A system according to claim 2 characterised in that said damping is provided by clearance between said piston and cylinder.

4. A system according to claim 3 characterised in that said piston and cylinder assembly are arranged to retract when the valve member moves in a direction to permitfluidflowtosaidreservior.

5. A system according to any one of the preceding claims characterised by accumulator meansto maintain hydraulic pressure in said circuit.

6. An automobile suspension system comprising a pressure regulatorvalve having damping means substantially as described herein with reference to the accompanying drawings.

7. A control valve for controlling the supply of fluid pressure from a pressure source to a pressurised circuit and a lower pressure circuit or reservoir, characterised in that damping means is provided for a valve member two limit the rate of movement thereof in a direction permitting flow of fluid pressure towards said reservoir.

8. A control valve substantially as described herein with reference to the accompanying drawings.