GB2298019A

GB2298019A - Elastomeric vibration-damping bushing with hydraulic damping

Info

Publication number: GB2298019A
Application number: GB9503188A
Authority: GB
Inventors: Giacomo Sciortino
Original assignee: Delphi Automotive Systems France; ACG France SAS
Current assignee: Delphi Automotive Systems France; ACG France SAS
Priority date: 1995-02-18
Filing date: 1995-02-18
Publication date: 1996-08-21
Anticipated expiration: 2015-02-18
Also published as: GB9503188D0; GB2298019B

Abstract

The bushing (10) comprises an inner sleeve (12); an outer sleeve substantially coaxial with the inner sleeve; a block (16) of resilient material retained between the inner sleeve and the outer sleeve, and being shaped to define two working chambers (18,20) that are filled with hydraulic fluid and a channel (22) interconnecting the two chambers for fluid flow therebetween. A flow restriction passage (28) is positioned in the channel to restrict the flow of fluid through the channel between the two chambers for improved vibration damping for low frequency vibrations.

Description

A BUSHING The present invention relates to a bushing for use on a motor vehicle to suppress vibrations.

Vibration damping bushings are used on motor vehicles in association with suspension systems, steering systems, and engine and transmission mounting systems. A basic design of bushing comprises inner and outer coaxial metallic sleeves with a moulded elastomeric block therebetween. A development of this arrangement provided the formation of two working chambers in the elastomeric block with a channel interconnecting the chambers. Hydraulic fluid substantially fills the chambers. During vibration damping action of the bushing, fluid is pumped between the two chambers by way of the channel. An example of this prior art can be found in US Patent No. 5178375.

An example of a similar arrangement for engine mounts is disclosed in US Patent No. 4720086. These known arrangements have limited damping effect on low frequency vibrations.

It is an object of the present invention to overcome the above mentioned disadvantage.

To this end, a bushing in accordance with the present invention comprises an inner sleeve; an outer sleeve substantially coaxial with the inner sleeve; a block of resilient material retained between the inner sleeve and the outer sleeve, and being shaped to define two working chambers that are substantially filled with hydraulic fluid; a channel interconnecting the two chambers for fluid flow therebetween; and a flow restriction passage positioned in the channel to restrict the flow of fluid through the channel between the two chambers.

The present invention provides improvements in the laminar flow of hydraulic fluid through the channel, thereby providing a larger damping effect at low frequency vibrations when compared to previously known arrangements, and can also provide better control of the compliance and dynamic stiffness of the bushing.

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a cross-section view on the line I-I of Figure 2 of a bushing in accordance with the present invention; Figure 2 is a cross-sectional view on the line II-II of Figure 1; Figure 3 is a perspective view of the inner sleeve and elastomeric block of the bushing of Figure 1; Figure 4 is a schematic presentation of the channel and the fluid restriction passage of the bushing of Figure 1; Figure 5 is a graph of dynamic stiffness against frequency for a bushing in accordance with the present invention; Figure 6 is a graph of phase angle against frequency for a bushing in accordance with the present invention; and Figure 7 is a graph of damping energy against frequency for a bushing in accordance with the present invention.

Referring to Figures 1 to 3, a bushing 10 in accordance with the present invention comprises an inner sleeve 12, an outer sleeve 14, and a block 16 of resilient material therebetween. The inner and outer sleeves 12 and 14 are substantially cylindrical and coaxial, and formed from any suitable metallic material. Although shown as circular in crosssection, the inner sleeve may have another other suitable cross-section. The block 16 is moulded from elastomeric material onto the inner sleeve 12, with the outer sleeve 14 being attached thereafter. Formed within the block 16 are two working chambers, a pumping chamber 18 and a release chamber 20. The pumping chamber 18 has a smaller volume than the release chamber 20. The longitudinally extending walls 19,21 of each chamber 18,20 respectively curve outwardly from the inner sleeve 12 to the outer sleeve 14.Both chambers 18,20 are substantially filled with hydraulic fluid. A channel 22 is formed in the outer surface 23 of the block 16, extends circumferentially, and is connected at either end by openings 24,26 with the pumping chamber 18 and the release chamber 20 respectively. During damping operation of the bushing 10, the inner and outer sleeves 12,14 move relative to one another to cause hydraulic fluid to be pumped from one chamber 18,20 to the other chamber by way of the channel 22. As so far described, the bushing 10 is known to those skilled in the art.

Positioned within the channel 22 is a flow restriction passage 28. The passage 28 is preferably moulded integrally with the block 16. Alternatively, an additional metal sleeve (not shown) may be positioned between the outer sleeve 14 and the block 16 to provide a metallic lining for the channel and to define the flow restriction passage. The presence of the passage 28 in the channel 22 provides better damping at low frequency vibrations for the bushing 10.

The channel 22 is preferably formed with a predetermined length L and a predetermined maximum diameter or width D (see Figure 4) either side of the flow restriction passage 28. In a preferred arrangement, the ratio of L/D lies in the range of 1 to 18. Further, the passage 28 is preferably formed with a predetermined length 1 and a predetermined maximum diameter or width d (see Figure 4). In a preferred arrangement, the ratio of l/d also lies in the range of 1 to 18, and is preferably the same as the ratio of L/D. The values for L, D, 1 and d are predetermined to provide the required compliance verses vibration frequency characteristics and the required dynamic stiffness verses vibration frequency characteristics for the bushing 10. The passage 28 is preferably situated at the mid-point of the channel 22.It is possible that the maximum diameter or width of the channel 22 may be different on either side of the passage 28. However, it is preferable that the maximum diameter or width of the channel 22 remains substantially constant along the length of the channel. The cross-sectional shape of the channel 22 is preferably substantially V-shape as shown, or semicircular.

The graphs of Figures 5 to 7 indicate plots of dynamic stiffness K*, phase angle +, and damping energy or compliance C, respectively, against frequency f for the bushing 10 of Figures 1 to 4. The critical operating frequency is indicated by the line fcrit fcrit is an intermediate frequency at which the dynamic stiffness K* increases rapidly, and so the damping energy C is much larger and the phase angle Q is at a maximum. Increasing L will move the peak of graph Q against f to the left as viewed in Figure 6 and as indicated by the dashed line f(L). Increasing D will move the peak of graph Q against f to the right as viewed in Figure 6 and as indicated by the dashed line f(D). Any such movement affects the critical frequency fcrit and hence, the dynamic stiffness and compliance of the bushing 10. It will be appreciated, therefore, that the bushing 10 can be tuned to meet any predetermined requirements for damping.

As an alternative to the above described arrangement, the block may be formed from any suitable plastics material.

Attention is drawn to our patent application nos. (Ref. No. MJD/H-187270) and (Ref. No. MJD/H-187271), filed the same day as the present application, the disclosures in which are incorporated herein by reference.

Claims

Claims:

1. A bushing comprising an inner sleeve; an outer sleeve substantially coaxial with the inner sleeve; a block of resilient material retained between the inner sleeve and the outer sleeve, and being shaped to define two working chambers that are substantially filled with hydraulic fluid; a channel interconnecting the two chambers for fluid flow therebetween; and a flow restriction passage positioned in the channel to restrict the flow of fluid through the channel between the two chambers.

2. A bushing as claimed in Claim 1, wherein the channel has a predetermined length and a predetermined maximum diameter either side of the flow restriction passage.

3. A bushing as claimed in Claim 2, wherein the ratio of the predetermined length to the predetermined maximum diameter of the channel lies in the range of 1 to 18.

4. A bushing as claimed in any one of Claims 1 to 3, wherein the passage has a predetermined length and a predetermined maximum diameter.

5. A bushing as claimed in Claim 4, wherein the ratio of the predetermined length to the predetermined maximum diameter of the passage lies in the range of 1 to 18.

6. A bushing as claimed in any one of Claims 1 to 5, wherein the passage is situated substantially at the mid-point of the total length of the channel.

7. A bushing as claimed in any one of Claims 1 to 6, wherein the channel extends circumferentially around the outer surface of the block.

8. A bushing as claimed in any one of Claims 1 to 7, wherein the block is moulded from elastomeric material and wherein the block, the channel, and the passage are moulded as an integral formation.

9. A bushing as claimed in any one of Claims 1 to 7, wherein the channel and the passage are defined by a metallic insert positioned between the block and the outer sleeve.

10. A bushing substantially as herein described with reference to, and as shown in, the accompanying drawings.