GB2064062A

GB2064062A - Hydraulic damping units with elongate by-pass slots

Info

Publication number: GB2064062A
Application number: GB7920338A
Authority: GB
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1979-06-12
Filing date: 1979-06-12
Publication date: 1981-06-10

Abstract

In a hydraulic piston-cylinder damper, to provide a by-pass passage from one side of the piston to the other, there is provided an insert 8 within which the piston 1 slides, the insert 8 having or defining an elongate aperture 11 which preferably has the variation in shape shown. The insert may be made of spring steel, or rigid or resilient plastics. <IMAGE>

Description

SPECIFICATION Damping units This invention relates to damper units.

Damper units have many applications, among which are their uses in vehicle seats to damp the shocks caused by the vehicle travelling along bumpy tracks or over rough country, and in vehicle suspension systems. The damper units generally comprise a piston working in a cylinder containing a damping fluid, the cylinder being closed at one end and the piston having a piston rod which extends sealingly through the other end of the cylinder. The piston commonly has a damping valve arrangement to restrict the flow of damping liquid from one side of the piston to the other.

It is often desirable that the unit has different damping characteristics for different loadings. In a vehicle suspension system, for example, it is desirable that the unit only lightly damps smallamplitude oscillations of the wheel when travelling over a smooth surface, for example on a motorway, but heavily damps larger-amplitude oscillations which might occur when travelling along a bumpy road. Furthermore, it is desirable that the damping characteristics of the unit take account of possible changes in non-transient loading of the unit, for example changes in the number of people in the vehicle in the case of a vehicle suspension unit or a change in the occupant of a seat incorporating a unit. Such units are conveniently termed "displacement conscious" units, since the damping characteristics of the unit is dependent upon the displacement of the piston within the cylinder.

Previously proposed displacement conscious damping units have involved complex valve arrangements in the piston and the aim of the present invention is to provide a damping unit which can be displacement conscious and which is relatively easy and cheap to produce.

In accordance with the invention, there is provided a damper unit comprising a cylinder, a piston working in the cylinder and having a piston rod which extends sealingly through one end of the cylinder, wherein the cylinder comprises an outer tube and an insert within which the piston is slidable, wherein the insert has an elongate aperture therein which acts as a by-pass passage permitting fluid by-pass from one side of the piston to the other when the piston is adjacent the aperture.

Preferably the aperture comprises a slit or slot in the insert, which slit extends longitudinally of the insert along the whole length thereof.

The edges of the aperture are preferably so contoured as to provide a varying damping effect dependent upon the position of the piston within the insert. The slit may have a cross-sectional area which decreases from a medial part thereof of the respective ends of the insert.

The insert may be formed from any suitable material, which may depend on the application.

For example, the insert may be of steel, for example spring steel, for heavy duty applications or may be of rigid of resilient plastics material.

A damper unit in accordance with the invention will now be described, by way of example, with reference the the accompanying drawings, in which: FIGURE 1 is an axial cross-sectional view of the damper unit; FIGURE 2 is a perspective view of an insert of the unit of Figure 1; and FIGURE 3 is a plan view of a blank for the insert of Figure 2.

The damper unit comprises a cylinder 1 which is closed at one end by a cap 2 and at the other end of which is a guide 3 and seal 4 for a piston rod 5 carrying a piston 6 working in the cylinder 1.

The cylinder comprises an outer tube 7 connected to the cap 2 and guide 3 and a thin inner insert 8 which is located at its ends by the cap 2 and a support 9 for seal 4. Extending longitudinally of the insert 8 is a slit 11 which as shown varies progressively in width from a median point to the ends of the insert 8. The slit 11 could, however, be of any desired shape and any desired width and may be an aperture in the insert.

In operation, the slit 11 provides a by-pass passage through which fluid in the cylinder 1 can pass from one side of the piston 6 to the other.

The width of the slit at a particular axial point determines the degree of damping of the piston when it passes that point. Thus, with the illustrated insert 9, the damping of the piston 6 increases progressively from the normal medial position of the piston to the ends of the cylinder where the width of the slit 11 is smallest.

The insert 8 may be made of any suitable material using any desired process which will enable the slit 11 to be formed with reasonable accuracy. For example, the edges 12 of the slit 11 may be formed by shearing or stamping the edges of a thin blank 13 of material (Figure 3) and the blank may then be rolled into the generally cylindrical shape of the insert 8. The material of the insert may, for example, be spring steel, or resilient or rigid plastics. In the case of plastics material, the insert may be moulded into its generally cylindrical shape.

It will be appreciated that an infinite variety of shapes of slit 11 is possible by varying the configuration of the edges 12 of the slit 1 Thus, an infinite variety of damping effects can be obtained for different applications of the damper unit.

The above-described unit has many possible applications. For example, it could be used as a shock absorber in a vehicle seat to reduce the effect on the occupant'of vibration and shocks obtained for example when travelling over rough country or over bumpy tracks. Another application of the unit is in automatic washing machines where it could damp the out-of-balance force resulting from change-over from a wash cycle to a spin cycle. The unit could also be used as a suspension unit for a motor vehicle, the unit enabling different damping effects to be achieved for different weight conditions.

The illustrated slit 11 provides only a small damping effect under smooth, low amplitude conditions and a greater damping effect under rougher, higher amplitude conditions. As applied to a vehicle seat or a vehicle suspension system, the damper unit would have only a small damping effect when the vehicle is running on a smooth surface, for example on a motorway, and the amplitude of wheel movement is small, but would have a much larger damping effect when the road conditions are rougher and wheel amplitudes are greater. The slit 11 also provides different damping characteristics for different loading conditions of the unit. For example, if the seat or vehicle had a greater load than normal, the piston rod 5 would extend further into the cylinder 1 to a position where the piston 6 is damped more than in the normal position illustrated in Figure 1.

Claims

1. A damper unit comprising a cylinder, a piston working in the cylinder and having a piston rod which extends sealingly through one end of the cylinder, wherein the cylinder comprises an outer tube and an insert within which the piston is slidable, wherein the insert has an elongate aperture therein which acts as a by-pass passage permitting fluid by-pass from one side of the piston to the other when the piston is adjacent the aperture.

2. A damper unit in accordance with claim 1, wherein the aperture comprises a slit or slot in the insert, which slit extends longitudinally of the insert along the whole length thereof.

3. A damper unit in accordance with claim 1 or 2, wherein the aperture has edges which are so contoured as to provide a varying damping effect dependent upon the position of the piston within the insert.

4. A damper unit in accordance with claim 3 as dependent upon claim 2, wherein the slit has a cross-sectional area which decreases from a medial part thereof to the respective ends of the insert.

5. A damper unit in accordance with any of claims 1 to 4, wherein the insert is made of spring steel.

6. A damper unit in accordance with any of claims 1 to 4, wherein the insert is of plastics material.

7. A damper unit constructed and arranged substantially as herein described with reference to the accompanying drawings.