GB2291691A

GB2291691A - Hydraulically damped mounting device

Info

Publication number: GB2291691A
Application number: GB9514587A
Authority: GB
Inventors: John Philip West; Peter Michael Trewhell Fursdon; Trevor Howard Johnson
Original assignee: AVON CLEVITE Ltd
Current assignee: AVON CLEVITE Ltd
Priority date: 1994-07-19
Filing date: 1995-07-17
Publication date: 1996-01-31
Anticipated expiration: 2015-07-17
Also published as: GB9514587D0; GB9414565D0; DE19526069B4; GB2291691B; DE19526069A1; GB2291691A9

Abstract

A hydraulically damped mounting device has a central anchor part (10) connected to a sleeve (11) forming a second anchor part by a resilient wall (13). The resilient wall (13) divides the interior of the sleeve (11) into two parts. The lower part forms a working chamber (16) for hydraulic fluid which is connected to a compensation chamber (20) in the other part by a passageway (30). The compensation chamber (20) is bounded by a bellows wall (19). As the central anchor part (10) vibrates relative to the sleeve (11), hydraulic fluid is forced to move through the passageway (30), thereby damping the vibrations. In order to prevent excessive pressures in the working chamber, a bypass channel (41) is formed, e.g. by part of the passageway (30), which provides a relatively short route between the working and compensation chambers (16, 20). The bypass channel (41) is normally closed by a part (33) of the bellows wall (19), but at high pressures the part (33) deforms, thereby opening the bypass channel (41). <IMAGE>

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 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.

The present invention is concerned with the development of the bush type of mount disclosed in EP A-0172700. It has been found that, under high loads, excessive pressures may build up in the working chamber, and that could damage the mounting device.

At its most general, the present invention proposes that a bypass channel be provided leading from the working chamber to an opening releasably covered by the bellows wall. At high pressures, the bellows wall deforms to uncover that opening, thereby permitting fluid from the working chamber to pass directly into the compensation chamber.

Preferably, that bypass channel is formed by part of the elongate passageway connecting the working and compensation chambers. The passageway then has the opening at an intermediate point along the length thereof, so that the bypass is formed by the passageway from the working chamber to that opening.

Hence, at high pressures, the opening connects an intermediate part of the passageway to the working chamber, thereby reducing the resistance to flow of the connection between the working and compensation chambers, and so enabling excessive pressures to be reduced.

However, the bypass channel need not be part of the passageway, and could be a separate connection of the working and compensation chambers. Indeed, two bypass channels may be provided, one formed by part of the passageway and the other being independent.

Where the bypass channel is formed by part of the passageway, it is preferable that the opening in the wall of the passageway is relatively close to the entrance to the passageway from the working chamber.

It is necessary for the passageway to extend around the resilient wall, in order to reach the space which contains the compensation chamber, but excessive length of the bypass channel should be avoided so that the bypass channel does not, itself, cause a significant resistance to flow.

An embodiment 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 according to an embodiment of the present invention, at low pressures; Fig. 2 is a schematic perspective view showing the direction of fluid flow in the embodiment under the conditions shown in Fig. 1; Fig. 3 is a sectional view through the hydraulically damped mounting device of the embodiment of the present invention, at high pressures; and Fig. 4 is a schematic perspective view showing the direction of fluid flow in the embodiment under the conditions shown in Fig. 3.

As can be seen from Fig. 1, an embodiment of the present invention is in the form of a "bush" type mount in which 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. In the arrangement illustrated in Fig. 1, the load applied to the mounting device is small, and therefore the resilient wall 13 biases the central anchor part 10 upwardly in the Figure. A larger load biases the central anchor part downwardly e.g. to the central axis of the sleeve 11.

In this embodiment, the sleeve 11 comprises an outer cylindrical body 14 and a shaped inner member 15. The resilient wall 13 is attached to the inner member 15.

As can be seen from Fig. 1, the resilient wall 13 divides the interior of the sleeve 11 into two spaces.

The lower space 16 forms a working chamber for hydraulic fluid, and is partially bounded by a diaphragm 17 which is attached to the inner member 15 via an attachment piece 18. The other space contains a bellows wall 19 which interconnects the first anchor part 10 and the sleeve 11, thereby defining a compensation chamber 20. The inner member 15 is provided with a channel brace 21, which has projection towards the central anchor part 10 to limit upward movement thereof.

The working chamber 16 and the compensation chamber 20 are connected by a passageway 30, formed between the member 15 and the outer cylindrical wall 14. In fact, as illustrated in Fig. 2, that passageway 30 - has a folded path, as indicated by arrows 31. The passageway 30 extends from the working chamber 16 around the interior of the sleeve 11, and passes over the channel brace 21. Then, the passageway is folded back on itself, and passes over the top of the channel brace 21 and through an opening (not shown in Fig. 1) into the compensation chamber 20.

Fig. 1 also shows that the inner member 15 has an opening 32 in the wall thereof, which opening 32 is covered by part 33 of the bellows wall 19. When pressures are low, the shaping of the part 33 of the bellows wall 19 is such as to maintain it in contact with the adjacent part of the channel brace 21, so that the opening 32 is covered. Hence, as the central anchor part 10 moves downwardly, so reducing the volume of the working chamber 16, the hydraulic fluid passes through the passageway 30 along the full length thereof, to the compensation chamber 20. The length of the passageway 30, and the resistance to fluid movement therethrough, provides a damping effect.

However, at high pressures, that resistance to flow may result in the pressures in the working chamber 16 increasing excessively. In this embodiment of the present invention, to prevent this occurring excessively, the bellows wall 19 is designed so that, at sufficiently high pressures, the part 33 of the bellows wall 19 covering the opening 32 will deform as shown in Fig. 3. That deformation moves the part 33 away from the channel brace 21, thereby uncovering the opening 32 and permitting hydraulic fluid to pass directly through that opening 32 into the compensation chamber 20, as indicated by arrows 40.

Thus, a bypass channel is formed by the part 41 of the passageway 30 between the working chamber 16 and the opening 32, providing a relatively short route between the working and compensation chambers 16, 20 so that pressures in the working chamber can be reduced rapidly. The resistance to flow due to the passageway 30 is no longer significant, since hydraulic fluid does not have to pass along the full length thereof in order to pass from the working chamber 16 to the compensation chamber 20.

Fig. 4 shows that a second bypass channel 42 may be formed in the inner member 15, the second bypass channel 42 extending from the working chamber 16 and terminating in an opening 43. At low pressures, that opening 43 will be covered by a part of the bellows wall 19 in a similar way to the covering of the opening 32 by the part 33 of the bellows wall 19. At high pressures, as in Fig. 3, that part of the bellows wall will uncover the opening 43, thereby permitting fluid to pass from the working chamber 16 to the compensation chamber 20 as indicated by arrows 44.

Hence, there are two bypass channels in this embodiment, one of which is formed by part of the passageway 30,- and one which is independent of the passageway 30. It is possible for the bypass channel to be wholly independent of the passageway, if desired. Thus, provision of the bypass channel, or bypass channels, prevents excessive pressures building-up in the working chamber 16, thereby preventing the mounting device being damaged.

Claims

1. A hydraulically damped mounting device having: a first anchor part; a second anchor part in the form of a hollow sleeve containing the first anchor part, such that the first anchor part extends axially of the sleeve and a space is defined within the sleeve radially of the first anchor part; a resilient wall within the space connecting the sleeve and the first anchor part and dividing the space into two parts, the resilient wall being adapted to be compressed when a load is applied between the anchor parts and defining, together with the sleeve, a working chamber for hydraulic fluid in one part of the space; a bellows wall in the other part of the space, the bellows wall defining, at least in part, a compensation chamber for hydraulic fluid; an open passageway for hydraulic fluid interconnecting the working and compensation chambers; and at least one bypass channel for hydraulic fluid extending from the working chamber to the compensation chamber, the bypass channel being releasably closed.

2. A hydraulically damped mounting device according to claim 1, wherein the releasable closing of the bypass channel is pressure sensitive.

3. A hydraulically damped mounting device according to claim 1 or claim 2, wherein the bypass channel is releasably closed by a part of the bellows wall, deformation of said part of the bellows wall permitting hydraulic fluid from the working chamber to pass to the compensation chamber via the at least one bypass channel.

4. A hydraulically damped mounting device according to any one of the preceding claims, wherein the at least one bypass channel is formed by a part of said passageway.

5. A hydraulically damped mounting device according to any one of the preceding claims, wherein the bypass channel is shorter than the passageway.