GB2306615A

GB2306615A - Hydraulically damped mounting device

Info

Publication number: GB2306615A
Application number: GB9621682A
Authority: GB
Inventors: Michael Peter Trewhela Fursdon
Original assignee: Avon Vibration Management Systems Ltd
Current assignee: Avon Vibration Management Systems Ltd
Priority date: 1995-11-03
Filing date: 1996-10-17
Publication date: 1997-05-07
Anticipated expiration: 2016-10-17
Also published as: GB9621682D0; GB2306615B

Abstract

A hydraulically damped mounting device comprises an anchor part in the form of a hollow sleeve 11, and another anchor part in the form of a coaxiall rod or tube 10. The device has two chambers 14, 15 and a channel 17 extending therebetween which opens into one of the chambers 14, but having its mouth adjacent the other chamber 15 closed by a diaphragm 18 or additionally by a valve (50 figure 5, not shown). The two chambers 14, 15 which are both "working" chambers since they are both partially bonded by a resilient wall 13 are also connected by a passageway 16. The passageway may alternatively (figure 2, not shown) or additionally (figure 3, not shown) be in the rod. The sleeve may have vented gas pockets (32, 33 figures 4, 5 not shown), bounded by diaphragms.

Description

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.

In EP-A-0172700, a hydraulically damped mounting device of the "bush" type was disclosed for damping vibration between two parts of a piece of machinery, e.g.

a car engine and a chassis. In the bush type of mounting device, the anchor part for one part of the vibrating machinery is in the form of a hollow sleeve, and the other anchor part is in the form of a rod or tube extending approximately centrally and co-axially of the sleeve In EP-A-0172700, the tubular anchor part was connected to the sleeve by a resilient wall or resilient walls,, which defined one of the chambers (the "working chamber") in the sleeve That chamber was connected via an elongate passageway forming the orifice to a second chamber (the "compensation chamber") bounded at least in part by a bellows wall which was effectively freely deformable so that it could compensate for fluid movement through the passageway without itself resisting that fluid movement significantly.

It is also possible to have a second form of bush type of mount in which the resilient walls connecting the tubular part and the sleeve bounds both chambers of the mount. The resilient wall(s) thus divide the interior of the mount into two parts, each of which is filled with hydraulic fluid. Hence, unlike EP-A-0172700, there are two working chambers, rather than a working chamber and a compensation chamber.

The present invention is concerned with a development of a bush type of mount either of the second form, or of the form disclosed in the EP-A-017200.

As its most general, a first aspect of the present invention proposes that, in addition to the elongate passageway connecting the two chambers, there is a channel extending between the two chambers, with that channel being closed at some point along its length by a diaphragm.

When the two chambers of a hydraulically damped mounting device are connected by a passageway, and one anchor point vibrations relative to the other, there will be fluid flow through the passageway 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 passageway, and the frequency of the vibration. If the two chambers were connected by two passageways, hydraulic fluid would move through the passageway which gave rise, at the particular frequency of vibration, to the lower damping effect, and the passageway which gave the higher damping effect at that frequency would be of minimal influence on the behavior of the mount.However, if one of the two passageways is not open, but forms a channel closed by a diaphragm as in the first aspect of present invention, the movement of fluid in that channel is then limited by the stiffness of the diaphragm. Therefore the channel does not negate the influence of the elongate passageway interconnecting the channels. With such an arrangement, by suitable selection of the characteristics of the diaphragm, it is possible to determine the relative influences of the channel and the elongate passageway on the behaviour of the mount.

Preferably, the channel has a different crosssect ion and/or length from the elongated passageway.

This means that its main damping effect occurs at a different frequency from the passageway. Normally, the channel has a higher area to length ratio, so that it creates its damping effect at a higher frequency.

By suitable selection of the diaphragm characteristics, it is possible to arrange for the channel to have its maximum influence at a frequency of eg 25-35Hz. At frequencies below this value, the channel and its diaphragm are designed to provide a resistance to fluid movement which is greater than that of the elongate passageway, so that the behaviour of the mount under the effect of the low frequency vibrations is determined by the elongate passageway. With increasing frequency, the resistance to fluid movement in the elongate passageway increases, and the mount may therefore be designed to permit the effect of the channel and diaphragm to dominate at frequencies of 25Hz or higher. Frequencies above 35Hz, the resistance to fluid movement in the channel and diaphragm itself will increase.Furthermore, the damping effects of the channel and passageway may be designed to improve the stiffness characteristics of the mount.

Preferably, the diaphragm is at one end of the channel, so that one of its surfaces is exposed to hydraulic fluid in one of the two chambers of the mount, but the diaphragm could be at an intermediate position in the channel if necessary. It is also possible for there to be more than one diaphragm in the channel. For example, there may be a diaphragm at each end of the channel.

It is also possible for a mount according to the present invention to incorporate other features which permit further control of the characteristics of the mount. For example, either or both of the chambers may be partially bounded by a further diaphragm, which further diaphragm separates the fluid in the corresponding chamber from gas That gas may be air, with the side of the further diaphragm remote from the hydraulic fluid being exposed to air, or may be a gas pocket. This use of such a further diaphragm, when vented to air, is also disclosed in EP-A-017270G referred to above. Where the further diaphragm separates the hydraulic fluid from a gas pocket, that gas pocket may have a valved outlet, permitting the characteristics of the further diaphragm to be varied by control of the valve.

In a further development of the present invention, the channel is itself valved. Again, the valve may be controlled in dependence on an external characteristic, such as engine frequency, indeed, this idea of having a valved channel interconnecting two chambers of the mount, in addition to a passageway, represents a second aspect of the present invention, since it is not necessary for such a valved channel to contain a diaphragm, as in the first aspect.

Embodiments of the present invention will now be described in detail, by way of example, with reference to the accompanying drawings, in which: Fig. 1 shows a hydraulically damped mounting device being a first embodiment of the present invention; Fig. 2 shows a hydraulically damped mounting device being a second embodiment of the present invention; Fig. 3 shows a hydraulically damped mounting device being a third embodiment of the present invention; Fig. 4 shows a hydralically damped mounting device being a fourth embodiment of the present invention; Fig. 5 shows a hydraulically damped mounting device being a fifth embodiment of the present invention.

Referring first to Fig. 1, a central anchor part 10 is located within a sleeve 11 forming a second anchor part, to which one part of vibrating machinery may be attached The central anchor part 10 has a bore 12 to which another part of the vibrating machinery may be attached. The central anchor part 10 and the sleeve 11 are interconnected by a resilient wall 13. As can be seen from Fig. 1, the resilient wall 13 divides the interior of the sleeve 11 into two spaces forming respective chambers 14, 15 for hydraulic fluid. The two chambers 14, 15 are connected by an elongate passageway 16 formed within the sleeve 11, that passageway 16 having a convoluted path.

The two chambers 14, 15 also have a channel 17 extending therebetween. The channel 17 opens into one of the chambers 14, but its mouth adjacent the other chamber 15 is closed by a diaphragm 18. The diaphragm 18 separates the hydraulic fluid in the channel 17 from the hydraulic fluid in the chamber 15.

The mount in Fig. 1 is thus related to that disclosed in EP-A-0172700 in that it is of the bush type, but the two chambers 14, 15 are both "working" chambers, since they are both partially bounded by the resilient wall 13, and hence will be affected in a similar way by vibrations between the central anchor part 10 and the sleeve 11. The type of mount shown in Fig. 1 thus has no "compensation" chamber as in EP-A-0172700.

As can be seen rom Fig 1, the channel 17 has a shorter length, and a larger cross-section, than the passageway 16. however, the fact that the channel 17 is closed by the diaphragm 18 means that fluid movement therein is restricted by movement of the diaphragm 18, which itself is restricted by the pressure of the fluid in the chamber 15. As a result, by selection of the characteristics of the diaphragm 18, low frequency vibrations will cause movement of fluid through the passageway 16, as the central anchor part 10 moves relative to the sleeve 11, and so changes the volumes of the chambers 14, 15.

At higher frequencies, however, fluid movement in the channel 17 will dominate over fluid movement in the passageway 16, thereby allowing the characteristics of the channel 17 and the diaphragm 18 to dominate over the effect of the passageway 16, at a range of frequencies which may be selected in dependence on the design of the mount.

In Fig. 2, shows the second embodiment which is similar to that of Fig. 1, and the same reference numerals are used to indicate corresponding parts. In this second embodiment, however, the passageway 20 extends within a bore in the central anchor part 10, rather than in the sleeve 11.

In the third embodiment, shown in Fig. 3, the arrangement of the various components is similar to that of the embodiment of Fig. 1, and corresponding parts are indicated by the same reference numerals. In the embodiment of Fig. 3, however, the passageway 16 is not convoluted. In addition, each of the chambers 14, i5 is partially bounded by a diaphragm 30, 31, each of which separates the corresponding chamber 14, 15 from a gas pocket 32, 33 formed in the sleeve 11. Each of those gas pockets 32, 33 has a corresponding vent 34, 35 to the exterior of the sleeve 11. The wall of the sleeve 11 radially outwardly of the diaphragms 30, 31 limits excessive movement of those diaphragm 30, 31 in the radially outwardly, and snubber plates 36, 37 which extend over the diaphragms 30, 31 limit movement of the diaphragms 30, 31 in the radial inward direction.These diaphragms 30, 31, and associated gas pockets 32, 33 offer similar advantages to the diaphragm and gas pocket arrangement as disclosed in EP-A-0172700.

Fig. 4 shows another embodiment, which is a modification of the embodiment of Fig. 3. Parts which correspond to those in Fig. 3 are indicated by the same reference numerals. In the embodiment of Fig. 4, each of the vents 34, 35 contains a valve 40, 41. By control of the valves 40, 41, gas flow into and out of the gas pockets 32, 33 may be controlled in dependence on an external characteristic, such as vibration frequency. If a valve 40, 41 is closed, the corresponding gas pocket 32, 33 is sealed and has a strong air-spring effect. If, on the other hand, the valve 40, 41 is wholly open, the characteristic of the mount then approaches the embodiment of Fig. 3. Thus, the valving of the vents 34, 35 permits the characteristics of the mount in Fig. 3 to be varied.

Fig. 4 also shows an air-spring decoupler device 42 connected to one of the vents 34. A similar decoupler may be connected to the other vent 35 if desired. The action of the air-spring decoupler device on the gas pocket 32 is discussed in more detail in GB-A-2269217, and therefore will not be discussed in more detail now.

It can also be seen from Fig. 4 that, in this embodiment, there are two passageways interconnecting the chambers 14, 15, in addition to the channel 17. One passageway 16 passes through the sleeve 11, as in the first and third embodiments, whilst the second passageway 20 extends through the tubular anchor point 10, as in the second embodiment.

Fig. 5 shows a further embodiment of the invention, in which the embodiment of Fig. 1 is modified by the inclusion of a valve 50 in the channel 17. The embodiment of Fig. 5 is otherwise similar to the embodiment in Fig. 1, and corresponding parts are indicated by the same reference numerals. If the opening and closing of the valve 50 is controlled in dependence on an external characteristic, such as frequency of vibration, the effect of the channel 17 and the diaphragm 18 on the characteristic of the mount may be varied. If the valve 50 is wholly closed, there can be no fluid movement in the channel, so its effect is negated. If, on the other hand, the valve 50 is wholly open, the characteristics of the mount of this fifth embodiment will then correspond to that of the first embodiment. By controlling the valve 50, the characteristics of the mount can therefore be varied between these two extremes.

Indeed, since the valve 50 permits control of the fluid movement in the channel, it is then possible to omit the diaphragm 18 and still enable the channel to have an affect only at a desired frequency range. For example, if the valve 50 is wholly open within that frequency range, and wholly closed outside it, the fluid will pass through the channel 17 between the chambers 14, 15 only within that frequency range. As a result, within that frequency range, the damping characteristics of the mount will be determined by the channel 17, rather than the passageway 16. At other times, when the valve closes the passageway 17, the passageway 16 will be more important.

Claims

1. A hydraulically damped mounting device comprising: a hollow sleeve forming a first anchor part; a second anchor part extending within the sleeve; a flexible wall interconnecting the sleeve and the second anchor part, the flexible wall dividing the interior of the sleeve into two parts; a first chamber for hydraulic fluid in one of the interior parts of the sleeve, the first chamber being at least partially bounded by the flexible wall; a second chamber for hydraulic fluid in the other of the interior parts of the sleeve; a passageway interconnecting the first and second chambers for fluid communication between the two chambers; and a channel entending between the first and second chambers, the channel being closed by at least one diaphragm.

2. A hydraulically damped mounting device according to claim 1, wherein the diaphragm is at one end of the channel and separates hydraulic fluid in the channel from hydraulic fluid in one of the two chambers.

3. A hydraulically damped mounting device according te claim 1, wherein the diaphragm is at an intermediate point along the channel, with opposIte ends of the channel opening into respective ones of the two chambers.

4. A hydraulically damped mounting device according =e any one of the preceding claims, wherein the channel has a closeable valve therein.

5. A hydraulically damped mounting device comprising: a hollow sleeve forming a first anchor part; a second anchor part extending within the sleeve; a flexible wall interconnecting the sleeve and the second anchor part, the flexible wall dividing the interior of the sleeve into two parts; a first chamber for hydraulic fluid is one of the interior parts of the sleeve, the first chamber being at least partially bounded by the flexible wall; a second chamber for hydraulic fluid in the other of the interior parts of the sleeve; a passageway interconnecting the first and second chambers for fluid communications between the two chambers; and a channel extending between the first and second chambers, the channel having a closable valve therein.

6. A hydraulically damped mounting device according to claim 4 or claim 5, wherein the valve is controlled in dependence on a frequency signal.

7. A hydraulically damped mounting device according to any one of the preceding claims, wherein the length anchor area of the channel is different from the passageway.

8. A hydraulically damped mounting device according to any one of the preceding claims, wherein the area to length ratio of the channel iS larger than that of the passageway.

9. A hydraulically damped mounting device according to any one of the preceding claims, wherein the flexible wall is resilient.

10. A hydraulically damped mounting device according to any one of the preceding claims, wherein the second chamber is partially bounded by the flexible wall.

11. A hydraulically damped mounting device according to any one of the preceding claims, wherein at least one of the chambers is partially bounded by a corresponding further diaphragm, the further diaphragm separating fluid in the corresponding chamber from gas.

12. A hydraulically damped mounting device substantially as herein described with reference to and as illustrated in Fig.1, Fig.2, Fig.3, Fig.4, or Fig.S.