GB2298020A

GB2298020A - Elastomeric vibration-damping bushing with hydraulic damping

Info

Publication number: GB2298020A
Application number: GB9503245A
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: GB9503245D0; GB2298020B

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 shaped to define two working chambers (18,20) that are filled with hydraulic fluid. Each working chamber is defined in part by a pair of walls (19,21) of predetermined thickness (T 1 ,T 2 ) which extend between the inner sleeve and the outer sleeve and which curve outwardly from the inner sleeve to the outer sleeve. A channel (22) interconnects the two chambers for fluid flow therebetween. The thickness of the walls of one working chamber is different from the thickness of the walls of the other working chamber in order to improve the control of compliance characteristics for the bushing.

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 opportunity for optimal tuning of the bushing.

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, each working chamber being defined in part by a pair of walls of predetermined thickness which extend between the inner sleeve and the outer sleeve and which curve outwardly from the inner sleeve to the outer sleeve; and a channel interconnecting the two chambers for fluid flow therebetween; wherein the thickness of the walls of one working chamber is different from the thickness of the walls of the other working chamber.

By having walls of different thicknesses, the compliance of a bushing in accordance with the present invention is better set and controlled, thereby allowing optimum tuning of the damping characteristics of the bushing for a particular application.

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; Figures 5 and 6 are graphs of damping energy and dynamic stiffness respectively against frequency for the bushing shown in Figures 1 to 3; Figures 7 and 8 are graphs of damping energy and dynamic stiffness respectively against frequency for another embodiment of bushing in accordance with the present invention; and Figures 9 and 10 are graphs of damping energy and dynamic stiffness respectively against frequency for a prior art bushing.

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.The walls 19 of the pumping chamber 18 have a substantially constant predetermined thickness T1.

The walls 21 of the pumping chamber 20 have a substantially constant predetermined thickness T2.

Both chambers 18,20 are substantially filled with hydraulic fluid. The shape of the walls 19,21 substantially prevents loss of fluid pressure in the chambers 18,20 when the inner sleeve 12 moves relatively towards the outer sleeve 14. 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.

In accordance with the present invention, T1 has a different value to T2. In a preferred arrangement T1 is greater than T2 although in certain cases T2 may be greater than T1. The preferred range for the ratio T1:T2 is between 1 and 20.

A flow restriction passage 28 is preferably positioned within the channel 22. 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 and 6 indicate plots of dynamic stiffness K* and damping energy or compliance C, respectively, against frequency f for the bushing 10 of Figures 1 to 4, the case where T1 is greater than T2. The graphs of Figures 7 and 8 indicate plots of dynamic stiffness K* and damping energy or compliance C, respectively, against frequency f for the bushing 10 of Figures 1 to 4, the case where T2 is greater than T1. By comparison, the graphs of Figures 9 and 10 indicate plots of dynamic stiffness K* and damping energy or compliance C, respectively, against frequency f for a bushing where T1 is equal to T2. It will be appreciated that providing a bushing 10 with different wall thicknesses for the pumping and release chambers 18,20 changes the compliance and dynamic stiffness characteristics of the bushing 10, and that the compliance characteristics can be easily controlled by such different wall thicknesses. Consequently, 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-182114) 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, each working chamber being defined in part by a pair of walls of predetermined thickness which extend between the inner sleeve and the outer sleeve and which curve outwardly from the inner sleeve to the outer sleeve; and a channel interconnecting the two chambers for fluid flow therebetween; wherein the thickness of the walls of one working chamber is different from the thickness of the walls of the other working chamber.

2. A bushing as claimed in Claim 1, wherein one of the working chambers has a smaller volume than the other working chamber.

3. A bushing as claimed in Claim 2, wherein the thickness of the pair of walls of said one working chamber is greater than the thickness of the pair of walls of the said other working chamber.

4. A bushing as claimed in any one of Claims 1 to 3, wherein a flow restriction passage is positioned in the channel to restrict the flow of fluid through the channel between the two chambers.

5. A bushing as claimed in any one of Claims 1 to 4, wherein the channel extends circumferentially around the outer surface of the block.

6. A bushing as claimed in any one of Claims 1 to 5, wherein the block is moulded from elastomeric material and wherein the block and the channel are moulded as an integral formation.

7. A bushing as claimed in any one of Claims 1 to 5, wherein the channel is defined by a metallic insert positioned between the block and the outer sleeve.

8. A bushing substantially as herein described with reference to, and as shown in, Figures 1 to 8 of the accompanying drawings.