GB2318168A

GB2318168A - Hydraulically damped mounting device

Info

Publication number: GB2318168A
Application number: GB9721078A
Authority: GB
Inventors: David Boast; Mary Louise Marfell
Original assignee: Avon Polymer Products Ltd
Current assignee: Avon Polymer Products Ltd
Priority date: 1996-10-10
Filing date: 1997-10-03
Publication date: 1998-04-15
Anticipated expiration: 2017-10-03
Also published as: DE19744634A1; GB9621177D0; GB9721078D0; GB2318168B

Abstract

A hydraulically damped mounting device, particularly for a vehicle seat has a partition which defines a working chamber 17 and a compensation chamber 23, and with a variable cross-section orifice 19. As shown, a spool 33 attached to boss 1, and which has outer portions 37, 41 of cross-section increasing away from a central portion 35, moves in the orifice. Alternatively the orifice may be an iris diaphragm; the area may be changed by use of an electrorheological fluid and electrodes adjacent the orifice. Thus in the event of shock, as fluid is forced between the chambers, the area through which fluid can pass is reduced, eg by movement of the spool, thus varying the damping effect.

Description

2318168 HYDRAULICALLY DAMPED MOUNTING DEVICE The present invention relates

to a hydraulically damped mounting device. Such a mounting device usually has a pair of chambers for hydraulic fluid, connected by a suitable orifice and damping is achieved due to the flow of fluid through that orifice.

EPA-0115417 disclosed various "cup and boss" type mounting devices, in which a "boss", forming one anchor part to which one of the pieces of machinery was connected, was itself connected via a deformable wall to the mouth of a "cup", which was attached to the other piece of machinery and formed another anchor part. In EPA-0115417 that wall was normally resilient. But the use of a resilient wall is not essential in a cup and boss type mount. The cup and the deformable wall then defined a working chamber for hydraulic fluid, which was connected to a compensation chamber by a passageway which provided the damping orifice. The compensation chamber was separated from the working chamber by a rigid partition.

GB-B-2221280 disclosed a hydraulically damped mounting device of the ", cup" and "boss" tyre for damping the movement of a vehicular seat. The mounting device had an axially expandable housing with a flexible wall positioned within the housing to partition the interior of the housing into a compressed air filled part and a liquid filled part. The liquid filled part was further divided by a partition to form first and second chambers. The partitions had an aperture with an aperture member in it which was capable of axial movement in the aperture and had the damping orifice therein to allow liquid to 5 pass from the first chamber to the second chamber.

Shocks applied to a vehicular seat when the vehicle is moving (e.g. due to potholes) tend to be of low amplitude but high frequency. Further, each shock applied to the vehicular seat will vary slightly in its amplitude and frequency depending on the cause and the speed the vehicle is moving. In addition, the vehicular seat may be subject to vibrations of lower frequency, arising from e.g. undulations in the road. Although the vehicle suspension may absorb and or damp both the shocks and the low frequency vibrations, some of the force will be transmitted to the vehicular seat. Therefore, the present applicants have found it desirable to provide a hydraulically damped mounting device which seeks to develop the cup and boss type of mount as described above, so as to allow a variation in the damping effect in dependence on the variation in the shock and vibration applied to the mount.

At its most general, the present invention proposes that a hydraulically damped mounting device has a means for varying the effective cross-sectional area of a damping orifice through which fluid can pass between a first chamber and a second chamber in dependance on the movement of the first anchor point relative to the second anchor point. The term "effective cross-sectional area,, refers to the area of the orifice available for fluid flow. That area may be changed by movement of the walls of the orifice, by movement within the orifice of a member of varying cross-section (which thus makes part of the orifice unavailable for fluid flow), or even by the use of an electrorheological fluid and electrodes adjacent the orifice.

When the two chambers of a hydraulically damped mounting device are connected by a orifice, and one anchor point vibrates relative to the other, there will be fluid flow through the orifice from one chamber to the other. This will exert a damping force on the movement of the anchor points, which damping force is dependent on the length and cross-section of the orifice, and the frequency and amplitude of the vibration. An increase in the cross-section and a decrease in the length of the orifice will reduce the damping effect. However, in order to vary the damping effect to correspond with variations in the shock applied to an anchor point the applicants propose that the area provided by the orifice through which fluid can pass is alterable in accordance with the movement of one anchor point relative to the other. The variation in area may be passive, in the sense of involving only physical movement of components connected to one or other of the anchor points, or may be active in the sense of detecting that movement and causing an appropriate change in the orifice area. The latter may 4 then permit the effect achievable by the present invention to be frequency dependent, as well as amplitude dependent. Thus, in accordance with the present invention there may be provided a hydraulically damped mounting device comprising: first and second anchor parts; a first deformable wall connecting said first and second anchor parts; a working chamber for hydraulic fluid at least partially bound by the first deformable wall; a compensation chamber at least partially bound by a second deformable wall; an orifice interconnecting the working and compensation chambers for flow of hydraulic fluid therethrough; and a means for varying the effective cross-sectional area of the orifice in dependance on the relative axial position of the first and second anchor parts. 20 Preferably, the means for varying the cross- section of the orifice may be an orifice member having a variable cross- section and disposed in the orifice and spaced apart from the walls of the orifice. Preferably, the orifice member is an elongate member having a point of narrowest transverse cross-section at its centre with a an increasing transverse cross-section towards its outer ends. Such an orifice member is hereinafter called a spool. In a resting position, when the mount is subject to its normal stated load, it is preferred that the spool rests with its centre i.e. the point of narrowest crosssection within the orifice and the outer ends extending beyond the orifice into the first and second chambers respectively. In order to alter the effective area through which fluid may pass between the chambers in dependance on the relative position of the first and second anchor parts, the spool may be mounted on either the first or the second anchor part. In this way, the orifice member moves axially within the orifice in accordance with the axial movement of the anchor part to which it is mounted.

However, the present invention is not limited to the use of such an orifice. For example, the means for varying the cross-section of area of the orifice may be a diaphragm operating in a similar way to an iris shutter used in cameras. The diaphragm may comprise an plurality of orifice plates arranged around the orifice which rotate about pivots to open out in a direction away from the axis of the orifice to provide the maximum orifice cross-section and close in a direction towards the axis to provide a smaller cross-section. The degree of movement of the plates may be controlled mechanically or electronically to correspond with the movement of the anchor parts relative to each other. For example, if a shock is applied to one anchor part such that it moves towards the other anchor part, a signal corresponding to the frequency and amplitude of the movement may be given to a drive element which in turn coordinates the movement of the orifice plates in order to provide the desired damping effect.

Preferably, the second deformable wall of the compensation chamber partially defines a further chamber which may be filled with compressed air. This further chamber, hereinafter called the air chamber, acts to compensate the movement of fluid between the working chamber and the compensation chamber. The compressed air may be supplied to the air chamber by a compressor via an air inlet. It may be noted that such an air chamber, containing compressed air, is not present in EP-A0115417, is present in GB-B-2221280. One reason for this is that EP-A-0115417 has a resilient wall joining the cup and boss. In GB-B-2221280, the wall joining the cup and boss is a flexible wall. The use of the flexible wall is also preferred in the present invention. In such an arrangement, the pressure in the air chamber provides the force which maintains the mounting device in a suitable rest position when under load. If the wall joining the cup and boss is flexible, rather than resilient, some spring force must be provided in the structure of the mounting device to resist static load.

The device may be used in a number of situations: as a mounting device for a vehicular seat, for absorbing shock and vibration applied to the seat when the vehicle is moving; as a combined spring damper unit for cab suspension in such vehicles as tractors and trucks; as a combined spring damper unit for a wide range of off-road vehicles, such as 4x4 trucks and motor bikes; and as a combined spring damper for mountain bike fork and seat post applications.

An embodiment of the present invention will now be described in detail, by way of example, with reference to the accompanying drawing, in which the sole figure is a sectional view through a hydraulically damped mounting device being an embodiment of the present invention.

The figure shows a hydraulically damped mounting device for damping vibration between two parts of a structure (not shown). The mounting device has a boss 1 connectable via a fixing bolt 3 to one of the parts of the structure. The other part of the structure is connectable to a generally U-shaped cup 5. The cup 5 is made up of a series of rings (five are shown) which are held in place by fixing bolts (not shown) inserted into recesses 7,9 formed by the rings. A first flexible wall, 11 of e.g. rubber interconnects the boss 1 and the cup 5 as can be seen from the drawing, the first flexible wall 11 is convoluted and fits over a projecting flange 12 at the mouse of the cup 5, and has its other edge clamped between two parts la, 1b of the boss.

A partition 13 is also attached to the cup 5 adjacent a ring 15, and extends across the mouth of the cup 5. Thus a working chamber 17 is defined within the mount, bounded by the boss 1, the first flexible wall 11 and the partition 13.

8 The partition 13 defines an orifice 19, one end 21 of which opens into the working chamber 17 and the other end 23 of which opens into a compensation chamber 23. Thus, when the boss 1 vibrates axially relative to the cup 5 (in the vertical direction in Fig. 1), the volume of the working chamber 17 will change, and hydraulic fluid in that working chamber 17 will be forced through the orifice 19 into the compensation chamber 23. The volume of the compensation chamber 23 needs to change in response to such fluid movement, and therefore the compensation chamber 23 is bounded by a second flexible wall 27.

The flexible wall 27 partially defines a further chamber 29 which is filled with compressed air. The compressed air is supplied by a compressor (not shown) via an inlet 31. This compressed air chamber 29 supports the flexible wall 27 in the resting position, and acts as an air spring during vibration.

Within the orifice 19 there is a spool 33 which is divided into three portions, namely: a central portion 35 which, in the rest position, e.g. the position where the mount is subject to its normal static load, lies within but spaced apart from walls of the orifice 19 and has a relatively narrow transverse cross-section; a first portion 37 which extends into the working chamber 17 and increases in transverse cross-section away from the central portion 35 towards its outer end 39; and a second portion 41 which extends into the compensation chamber 23 9 and again increases in transverse cross-section away from the central portion 35 towards its outer end 43. The increase in transverse cross- section is symmetrical towards both outer ends 39,43. In other words the outer 5 ends 39,43 will have the same transverse cross-section.

The first portion 37 of the spool 33 is attached to the boss 1 via a mounting device 45. The mounting device 45 engages the boss at a fixing point 47 and the spool at its outer end 39. As a result the movement of the spool 33 is dependent on the movement of the boss 1.

In use, if a shock is applied to the boss 1, it will move towards the cup 5 changing the volume of the working chamber 17. As the volume changes fluid is forced through the orifice 19 into the compensation chamber 23. However, as the boss 1 moves so the spool 33 is forced through the orifice 19 such that the central portion 35 of the spool 33 leaves the orifice 19 and extends into the compensation chamber 23. The first portion 37 of the spool 33 enters the orifice 19 and thereby reduces the area through which fluid can pass between the working chamber 17 and the compensation chamber 23. Depending on the actual amplitude and frequency of the movement of the boss the damping effect will be altered accordingly.

Likewise, if the shock is applied to the cup 5, the boss 1 will move away from the cup 5 as fluid is forced into the working chamber 17 from the compensation chamber 23. As the boss 1 moves away from the cup 5, the spool 33 is also moved allowing the second portion 41 of the spool 33 to enter the orifice 19 thereby reducing the area through which fluid may pass and as a result increasing the damping effect as required.

In a similar way, movement tending to separate the cup 5 and boss 1 will be damped by movement of the fluid from the compensation chamber 3 to the working chamber 17. Again, the movement of the boss 1 relative to the cup 5 will move the spool 33 in the orifice 19, again varying the damping effect as the movement continues.

Thus, with the present invention, the damping effect changes with displacement. This is not true in the prior art arrangements mentioned earlier, in which the damping force of the orifice connecting the working in the compensation chambers is independent of displacement.

The variation in the effective cross-sectional area of the orifice with movement of the boss relative to the cup will depend on the particular amplitude and frequency of vibrations being damped. In the arrangement shown in the drawing, there is a stepwise change in the width of the spool 33. More gradual changes may also be used, and indeed the shape of the spool 33 may vary in dependence on the particular type of damp desired. The arrangement shown in the drawing is thought to be particularly suitable for damping the vibrations of a particular seat, where the amplitude of vibrations is very small and there is a very large variation in the frequency of such vibrations. Pot holes, and similar abrupt changes in the road surface cause high frequency vibrations, whereas 11 more gradual undulations may cause low frequency vibration. Indeed, because of the effect of the suspension of the vehicle, such different types of vibrations may occur at different speeds; in general the abrupt shocks are more apparent at low speeds, and the more gradual undulations more evident at high speeds. Previous attempts to solve this problem have concentrated on one or other of the types of vibrations but have not been successful in damping both.

It can be noted that many variations to the above embodiment are possible within the present invention. For example, although the embodiment has a relatively short orifice, the present invention may be applied to arrangements in which the orifice is in the form of an elongate passageway, as in EP-A-0115417. Indeed, it would be possible within the present invention for the orifice not to be in the partition, but in some other part of the mount.

12

Claims

CLAIMS 1. A hydraulically damped mounting device comprising: first and

second anchor parts; a first deformable wall connecting said first and second anchor parts; a working chamber for hydraulic fluid at least partially bound by the first deformable wall; a compensation chamber at least partially bound by a second deformable wall; an orifice interconnecting the working and compensation chambers for flow of hydraulic fluid therethrough; and a means for varying the effective cross-sectional area of the orifice in dependence on the relative position of the first and second anchor parts.
2. A hydraulically damped mounting device according to claim 1 wherein the means for varying the cross-section of the orifice is an orifice member having a variable crosssection movable in the orifice.
3. A hydraulically damped mounting device according to claim 2 wherein the orifice member is an elongate member having a point of narrowest transverse cross-section at its centre with an increasing transverse cross-section towards the outer ends.
4. A hydraulically damped mounting device according to claim 2 or claim 3 wherein the orifice member is mounted on either said first or second anchor part and the orifice is fixed relative to the other anchor part such 13 that the orifice member moves axially within the orifice in accordance with the movement of the anchor part to which it is mounted.
5. A hydraulically damped mounting device according to claim 1 wherein the means for varying the cross-section of the orifice is a diaphragm of a variable size.
6. A hydraulically damped mounting device according to claim 5, wherein the diaphragm comprises a plurality of orifice plates arranged around the orifice which rotate about pivots to open out in a direction away from the axis of the orifice to provide the maximum orifice crosssection and close in a direction towards the axis to provide a smaller cross-section.
7. A hydraulically damped mounting device according to any one of the preceding claims wherein the second deformable wall of the compensation chamber partially defines an air chamber filled with compressed air.
8. A hydraulically damped mounting device according to claim 7 wherein the compressed air is supplied to the air chamber by a compressor via an air inlet.
9. A hydraulically damped mounting device according to claim 7 or claim 8 wherein the first deformable wall is flexible.
10. A hydraulically damped mounting device substantially as herein described with reference to and as illustrated in the accompanying drawing.
11. A seat supported by a hydraulically damped mounting device according to any one of the preceding claims.