GB2294525A

GB2294525A - Hydraulically damped mounting device

Info

Publication number: GB2294525A
Application number: GB9522005A
Authority: GB
Inventors: John Philip West; Peter Michael Trewhell Fursdon
Original assignee: AVON CLEVITE Ltd
Current assignee: AVON CLEVITE Ltd
Priority date: 1994-10-31
Filing date: 1995-10-27
Publication date: 1996-05-01
Also published as: GB9421892D0; GB9522005D0; DE19540612A1

Description

1 2294525 HYDRAULICALLY DAMPED MOUNTING DEVICE The present invention

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

EP-A-0115417 and EP-A-0172700 discussed two different types of hydraulically damped mounting devices for damping vibration between two parts of a piece of machinery, e.g. a car engine and a chassis. EP-A-0115417 disclosed various "cup and boss" type of 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 (normally resilient) wall to the mouth of a "cup", which was attached to the other piece of machinery and formed another anchor part. The cup and the resilient wall then defined a working chamber for hydraulic fluid, which was connected to a compensation chamber by a passageway (usually elongate) which provided the damping orifice. The compensation chamber was separated from the working chamber by a rigid partition, and a flexible diaphragm was in direct contact with the liquid and, together with the partition formed a gas pocket.

In EP-A-0172700 the mounting devices disclosed were of the "bush" type. In this type of mounting 2 device, the anchor part for one part of the vibrating machinery is in the form of a hollow sleeve with the other anchor part in the form of a rod or tube extending approximately centrally and coaxially of the sleeve. In EP-A-0172700 the tubular anchor part was connected to the sleeve by resilient walls, which defined one of the chambers in the sleeve. The chamber was connected via a passageway to a second 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. In the hydraulically damped mounting devices disclosed in the specifications discussed above, there was a single passageway. It is also known, from other hydraulically damped mounting devices, to provide a plurality of independent passageways linking the chambers for hydraulic fluid. 20 In EP-A-0115417, there was a single diaphragm, which was configured to give a specific influence on the vibration characteristics of the hydraulically damped mounting device. Those characteristics depended on the stiffness of the diaphragm, by which is meant the change in applied pressure needed to cause unit change in the volume displaced by the diaphragm. Furthermore, the surface of the diaphragm which is in contact with the fluid in the

3 working chamber must be covered by a snubber plate, with openings therein for fluid communication therethrough between the upper surface of the diaphragm and the rest of the working chamber, and it has been found that the size of those openings also affects the characteristics of the mount.

In EP-A-0115417, those openings were in the form of holes in a relatively thin plate, so that the diameter of the holes was much greater than their axial length. In EP-A-0115417, the intention was that hydraulic fluid would pass relatively freely through those holes, from the working chamber to the diaphragm.

The applicants have now discovered that resonancd of fluid in the opening may be tuned to frequencies which offer desirable characteristics for the mount. For very short openings, such as the known holes, it is not possible to cover the desired scope of frequencies. However, if the openings have greater length than width, then resonance can be then created at all desired frequencies. The size and shape of such openings can be designed for a particular mount characteristic. Such openings, having an axial length greater than width will be referred to herein as channels, to distinguish them from the known holes.

In practice, the channels are likely to have an axial length which is greater than twice the width, 4 and sometimes greater than three times the width. It should also be understood that such a channel represents the opening in the upper snubber plate of the partition. There will be a space between that snubber plate and the diaphragm containing hydraulic fluid, at least when the diaphragm is not in contact with the snubber plate, but that space does not form part of the channel.

Such an opening may be entirely separate from the passageway connecting the working and compensation chambers, or may be at least partially integral with it.

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 is a sectional view through a hydraulically damped mounting device being a first embodiment of the present invention; and Fig. 2 is a sectional view through a hydraulically damped mounting device being a second embodiment of the present invention.

Referring first to Fig. 1, a first embodiment of a hydraulically damped mounting device according to the present invention is shown for damping vibration between two parts of a structure (not shown). The mount has a boss 1 connected via a fixing bolt 2 to one of the parts of the structure, and the other part of the structure is connected to a generally U-shaped cup 4. A resilient spring 5 of e.g. rubber interconnects the boss 1 and the cup 4. A partition 7 is also attached to the cup 4 adjacent a ring 6, and extends across the mouth of the cup 4. Thus, a working chamber 8 is defined within the mount, bounded by the resilient spring 5 and the partition 7.

The interior of the partition 7 defines a convoluted passageway 9 which is connected to the working chamber 8 via an opening 10 and is also connected via an opening 11 to a compensation chamber 12. Thus, when the boss I vibrates relative to the cup 4 (in the vertical direction in Fig. 1), the volume of the working chamber 8 will change, and hydraulic fluid in that working chamber 8 will be forced through the passageway 9 into, or out of, the compensation chamber 12. This fluid movement causes damping. The volume of the compensation chamber 12 needs to change in response to such fluid movement, and therefore the compensation chamber 12 is bounded by a flexible wall 13.

The above structure is generally similar to that described in EP-A0115417, and the manner of operation is similar. As in EP-A-0115417, the partition supports a diaphragm 20 which acts as a boundary between fluid in the working chamber 8 and a gas pocket 21.

In this embodiment, the space 22 between the 6 diaphragm 20 and the snubbing surface 23 of the partition is connected to the working chamber 8 by a channel 24. That channel 24 thus provides a column of hydraulic fluid between the working chamber 8 and the diaphragm 20, which will provide a resonant effect when the boss 1 vibrates relative to the cup 4. The length and cross-section of that channel 24 will then determine the resonant frequency of that fluid column. In accordance with the present invention, the channel 24 has an axial length (from its opening into the working chamber 8 to its opening into the space 23) which is greater than its maximum transverse width.

In the embodiment of Fig. 1, the opening of the channel 4 to the working chamber 8 is the same opening 10 as the opening of the passageway 9 into the working chamber 8. They could be separated, but such common opening is preferable where, as in the embodiment of Fig. 1, the partition 7 is formed by an upper partition part 25, a lower partition part 26, and a plate 27 sandwiched therebetween. Both the passageway 9 and the channel 24 may then be formed by suitable shaping of recesses in the upper part 25, with the plate 27 then closing those recesses except where the channel 24 is to open into the space above the diaphragm 20, the upper part 25 and the plate 27 then acting as the numbering plate of the present invention. The lower part 26 may 7 then have a relatively direct connection to the compensation chamber 12.

As is known from EP-A-0115417, the gas pocket 21 may have a bleed orifice 28 leading therefrom, to permit pressure control of the gas in the gas pocket 21. In the embodiment of Fig. 1, that bleed orifice 28 leads to a value 29 which may control the passage of gas through the bleed orifice in dependence on e.g. frequency or some other suitable characteristic.

It may also be noted that, in the embodiment of Fig. 1, the diaphragm 20 has a lower snubber plate 30 formed by a projection within the gas pocket 21.

Fig. 2 shows a second embodiment of the present invention. That embodiment is generally similar to the embodiment of Fig. 1, and the same reference numerals will be used to indicate corresponding parts.

In the embodiment of Fig. 2, there is a second diaphragm 40. In this embodiment, the second diaphragm 40 is annular, but it may alternatively be circular. In order to locate that second diaphragm 40, the upper surface of the upper part 25 of the partition 7 has an annular recess therein, which receives the second diaphragm 40, and which is then covered by a cover plate 41. A second gas pocket 42 is formed on the opposite side of the second diaphragm 40 from the working chamber 8, and that 8 second gas pocket 42 has a bleed orifice 43 leading therefrom, in a similar way as to the bleed orifice 28 leading from the gas pocket 21. Again, that bleed orifice 43 has a valve 44 to control movement of gas therethrough, e.g. in dependence on frequency or some other characteristic.

It can be noted that the use of such a double diaphragm is referred to in our UK patent application number GB 2282430 and, as shown in Fig.

2, the second diaphragm 40 may be convoluted, again as in application GB 2282430. Alternatively, the second diaphragm may be flat. Moreover, in these embodiments, the first diaphragm 20, to which the channel 24 extends is not convoluted, or at least only partially convoluted. Also, in these embodiments, the diaphragm to which the channel extends is not annular.

In the above embodiments, there is a single channel. It would, of course, be possible to provide multiple channels.

9

Claims

CLAIMS 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 bounded by the first deformable wall, a compensation chamber for hydraulic fluid at least partially bounded by a second deformable wall, a passageway interconnecting the working and compensation chambers for flow of hydraulic fluid there through, a diaphragm in contact with the hydraulic fluid in the working chamber, the diaphragm separating the working chamber and a gas pocket, and a snubber plate in the working chamber extending over the diaphragm, the snubber plate having at least one opening therein for hydraulic fluid flow therethrough, the at least one opening having a greater length than width.
2. A hydraulically damped mounting device according to claim 1, wherein the snubber plate is part of a rigid partition separating the working and compensation chambers, that rigid partition also separating the diagram.
3. A hydraulically damped mounting device according to claim 1 or claim 2, wherein the axial length of the at least one opening is greater than twice the width of the opening.
4. A hydraulically damped mounting unit according to any one of the preceding claims, wherein the passageway and the at least one opening have a common mouth.
5. A hydraulically damped mounting device according to any one of the preceding claims, wherein the diaphragm is 5 circular.
6. A hydraulically damped mounting device according to any one of the preceding claims, having a further diaphragm in contact with the hydraulic fluid in the working chamber, the further diaphragm separating the working chamber and a 10 further gas pocket.
7. A hydraulically damped mounting device according to claim 6, wherein the further diaphragm is on the snubber plate.
8. A hydraulically damped mounting device substantially 15 as herein described with reference to and as illustrated in Fig. 1 or Fig. 2 of the accompanying drawings.