GB2237355A - A hydroelastic support - Google Patents

Abstract

A hydroelastic support has a block (3) of elastomer interconnecting first and second components (1, 2) each connectable to a respective one of the engine and the chassis of a vehicle. The support has a partition member (5, 6, 7, 8) which separates a working chamber (A) from two concentric expansion chambers (B, C). The chambers (A, B, C) contain hydraulic fluid. The partition member has a fixed part (6, 7) incorporating an outer duct (15) which enables fluid communication between cavities A and B and an axially displaceable part (9, 10) incorporating an inner duct (18) enabling fluid communication between cavities A and C. The support effects damping of mechanical vibrations in a relatively wide frequency range including the resonant frequencies of both ducts (15, 18) and the displaceable part (9, 10) effects damping of relatively high frequency acoustic vibrations. in a further embodiment (Fig. 3) working chamber A is also split into two chambers. <IMAGE>

Description

IMPROVEMENTS RELATING TO A HYDROELASTIC SUPPORT This invention relates to a hydroelastic support and particularly to a hydroelastic support for use as part of the suspension of an automobile engine.

French Patent Application No. 7926137 describes a hydroelastic support comprising two components which are joined together by a block of an elastomer which defines, in part, a working chamber containing a hydraulic fluid.

One of the two components is intended to be connected to the automobile engine whereas the other member is intended to be connected to the vehicle chassis.

The working chamber is connected by a duct to an expansion chamber which is also filled with hydraulic fluid. The connecting duct is incorporated within the structure of a partition member which is attached to one of the two components and separates the working chamber from the expansion chamber.

The connecting duct has a damping effect on relatively high amplitude, low frequency mechanical vibrations.

However, such damping is relatively ineffective outside a relatively narrow frequency zone centred on the resonant frequency of the connecting duct.

The partition member also includes a displacement member which is free to undergo a small degree of axial displacement (of the order of a few tenths of a millimetre) to effect damping of relatively low amplitude, high frequency (acoustic) vibrations.

French Patent Application No. 8709650 describes a related hydroelastic support which has two ducts interconnecting the working cavity and the expansion cavity. The ducts have different lengths and cross-sectional areas, and so different resonant frequencies. Accordingly, the hydroelastic support has a damping effect on mechanical vibrations in a relatively wide frequency range containing the resonant frequencies of both ducts.

However, this arrangement degrades the damping effect on the higher frequency, acoustic vibrations.

According to the invention there is provided a hydroelastic support comprising two components each being connectable to a respective one of the engine and the chassis of a vehicle, a block made of an elastomer joining the components, a working chamber defined in part by the block, means defining at least two expansion chambers, and a partition member separating the working chamber from the expansion chambers, wherein the working chamber and the expansion chambers contain hydraulic fluid, the partition member incorporates a respective duct providing fluid communication between the working chamber and each expansion chamber, and the partition member comprises a first part which is fixed in relation to one of the components and a second part which is displaceable with respect to the first part whereby to effect damping of acoustic vibrations.

The hydroelastic support has a significant damping effect on both relatively low frequency, mechanical vibrations, in a frequency range embracing the resonant frequencies of both ducts and on relatively high frequency acoustic vibrations.

There are preferably only two said expansion chambers, the first part of the partition member incorporating a first said duct, providing fluid communication between the working chamber and one of the expansion chambers, and the second part of the partition member incorporating a second said duct providing fluid communication between the working chamber and the other of the expansion chambers.

The first and second ducts may have different lengths and/or cross-sectional areas, and may be arranged concentrically.

The expansion cavities may be bounded by a common membrane, which may be so profiled as to co-operate with the partition member to establish a fluid tight seal between the expansion cavities.

The hydroelastic support may have an elastic bellows arranged to separate the working cavity into an inner region and an outer region, wherein said first duct provides fluid communication between the inner region of the working cavity and said one of the expansion cavities and the second duct provides fluid communication between the working cavity and said other of the expansion cavities.

Hydroelastic supports embodying the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a longitudinal sectional view (on line 1-1 in Figure 2) through a hydroelastic support in accordance with the invention; Figure la shows an enlarged view of the region referenced C in Figure 1; Figure 2 shows a transverse sectional view on line A-A through the hydroelastic support of Figure 1; Figure 3 shows a longitudinal sectional view (on line 3-3 in Figure 4) through another hydroelastic support in accordance with the invention; Figure 3a shows an enlarged view of the region referenced D in Figure 3; Figure 4 shows a transverse sectional view on line A-A through the hydroelastic support of Figure 3; and Figures 5 a and b illustrate the variation, as a function of frequency f, of the loss factor tn and dynamic rigidity K respectively of a hydroelastic support in accordance with the invention.

Referring now to Figure 1, the hydroelastic support comprises two components 1,2, each being connectable to a respective one of the engine and the chassis of a vehicle.

The components 1,2 are interconnected by an arched body 3 made from an elastomer which abuts facing surfaces of the two components.

Component 2 has a generally frusto-conical wall which assists the fitting of body 3, and is formed as an extension of one part 4 (the upper part in the drawing) of a casing, of which the other (lower) part comprises a dish-like member 12 having a shaft 13 for connection to the engine or chassis. The upper part 4 of the casing surrounds and supports a central partition member, shown generally at 5, and may be provided with fixing lugs.

Partition member 5 incorporates two concentric ducts 15,18, each having the form, in plan, of an interrupted annulus, as represented in the sectional view of Figure 2. The outer duct 15 is bounded by respective surfaces of two generally annular members 6,7 which are supported in abutting relation between the upper and lower parts 4,12 of the casing, and which define a housing for an axially displaceable body comprising two plate-like members 9,10.

The axially displaceable body is located freely within the housing by means of a flanged retainer 8, and members 9 and 10 have complementary, inter-fitting shapes which, in combination, define the inner duct 18 in the partition member.

The upper surface of the partition member 5 and the internal surface of body 3 define a working (or pulsating) chamber A on the upper side of the partition member, and a resilient membrane 11, which is secured peripherally between the lower part 12 of the casing and the annular element 7, is so profiled as to define two concentric expansion (or compensating) chambers B,C on the lower side of the partition member. The membrane 11 is formed with a ridge having a beading, of circular cross-section, which is trapped in a clearance between the inner peripheral surface of element 7 and the outer peripheral surface of retainer 8, thereby to form a fluid-tight seal between the inner and outer chambers, C and B respectively.

The outer duct 15 is in fluid communication with chamber A through an opening 14 in member 6, at one end of the duct, and is in fluid communication with chamber B through an opening 16 in member 7 at the opposite end of the duct. Similarly, the inner duct 18 is in fluid communication with chamber A through an opening 17 in plate 9, at one end of the duct, and is in fluid communication with chamber C through an opening 19 in plate 10, at the opposite end of the duct.

The afore-mentioned chambers A, B and C, the openings and the ducts contain a hydraulic liquid of the kind commonly used in hydroelastic supports, and fluid can pass between chambers A and B, via the outer duct, and between chambers A and C, via the inner duct, in response to relative displacement of the two components 1,2.

The axially displaceable body, formed by members 9 and 10, is capable of axial displacement relative to the surrounding structure defined by members 6, 7 and 8. The small degree of axial play (J) possible, typically of the order of a few tenths of a millimetre, has a damping effect on low amplitude, high frequency acoustic vibrations which are generally responsible for the generation of noise. Axial displacement of members 9,10 prevents the transmission of noise.

The axially displaceable body has no significant damping effect on relatively high amplitude, low frequency mechanical vibrations, and in this regard, the frequency response of the hydroelastic support structure is determined by movement of fluid between the working and the expansion chambers.

The response characteristic of the hydroelastic support structure depends on the geometry of the ducts and, in particular, on such parameters as the duct length and the cross-sectional area of the duct, across which flow can take place.

The outer duct 15, being longer, has a lower resonant frequency than the inner duct .18. When mechanical vibrations occur at, or around, the lower resonant frequency (i.e. that of duct 15) fluid may still pass along the inner duct (which has a higher resonant frequency) but is prevented from passing along the outer duct giving rise to a first level of damping. Similarly, when mechanical vibrations occur at, or around, the higher resonant frequency (that of duct 18) fluid may pass along the outer duct (which has a lower resonant frequency), but is prevented from passing along the inner duct, giving rise to a second level of damping.

The damping effect attainable by the hydroelastic support is illustrated in Figure 5, in which the damping level is represented in terms of the loss factor tg of the support as a function of frequency.

The curve shown in broken outline in Figure 5a, represents the variation in loss factor tg , as a function of frequency, in a hydroelastic support of hitherto known construction, and this curve has only one damping maximum. The solid curve, on the other hand, represents the variation in loss factor tg in the hydroelastic support disclosed herein, and this curve has two damping maxima. Figure 5b shows the corresponding variation of the dynamic rigidity of the hydroelastic support.

Since the inner duct is enclosed within the assembly defined by members 9 and 10, which is capable of axial displacement relative to the housing, the "filtration function" achieved enables the hydroelastic support to have a less rigid structure than would normally be permitted in the high frequency regime.

Figures 3 and 4 show an alternative hydroelastic support in accordance with the invention, which also has separate chambers containing hydraulic fluid and exhibits the same general damping charactertstic as that of the hydroelastic support described with reference to Figures 1 and 2.

The components 1,2 and the body 3 of elastomer are substantially the same as the corresponding components shown in Figure 1, and, as before, the partition member (referenced 20) has an axially displaceable body, formed by interfitting members 9,10, which incorporates an inner duct 18.

The duct 18 has a length commensurate with desired damping characteristics.

In this embodiment, the axially displaceable body is located by a pair of rings 21,22, which have a generally S-shaped profile.

The lower of these rings serves to trap a beading formed in the membrane 11 in the region of the ridge formed therein, thereby to create a fluid-tight seal between the two expansion chambers referenced at N and P.

The upper ring 21 serves to anchor an elastic bellows, made of a rubber or a plastics material, around its periphery, thereby to separate the working chamber, defined by the partition member 20 and the arched body 3, into two discrete parts; that is, an outer working chamber M and an inner working chamber L.

The outer duct 15 is defined by generally annular elements 25,26 and has a length commensurate with the desired damping effect.

The construction of the arched body 3, and the manner by which air in the space between the lower casing part 12 and the diaphragm 11 is discharged to the exterior (via openings in the casing), in response to a displacement of membrane 11, are exactly the same as for the hydroelastic support described with reference to Figures 1 and 2, as are the means of connection to the engine and chassis.

The outer duct 15 enables fluid communication between the working chamber M and the expansion chamber N, through the openings 14 and 16 at opposite ends thereof.

Similarly, the inner duct 18 enables fluid communication between the inner working chamber L and the inner expansion chamber P via the openings 19 and 17 at opposite ends of the duct.

Thus, fluid can flow between the chambers M and N, on the one hand, and L and P on the other hand. This exchange of fluid takes place in an interactive manner, so that the volume of fluid being transferred between the upper and lower chambers (M,L; N,P) remains constant.

With this arrangement, the two maxima in the response curve corresponding to that shown in Figure 5 for the hydroelastic support of Figures 1 and 2, would be even more pronounced, and may be spaced apart more in frequency, thereby providing a greater level of damping over a wider frequency range.

Claims (11)

1. A hydroelastic support comprising two components each being connectable to a respective one of the engine and the chassis of a vehicle, a block made of an elastomer joining the components, a working chamber defined, in part, by the block, means defining at least two expansion chambers, and a partition member separating the working chamber from the expansion chambers, wherein the working chamber and the expansion chambers contain hydraulic fluid, the partition member incorporates a respective duct providing fluid communication between the working chamber and each expansion chamber, and the partition member comprises a first part which is fixed in relation to one of the components and a second part which is displaceable with respect to the first part whereby to effect damping of acoustic vibrations.

2. A hydroelastic support as claimed in claim 1, wherein there are only two said expansion chambers, the first part of the partition member incorporates a first said duct providing fluid communication between the working chamber and one of the expansion chambers, and the second part of the partition member incorporates a second said duct providing fluid communication between the working chamber and the other of the expansion chambers.

3. The hydroelastic support as claimed in claim 1 or claim 2, wherein the ducts have different lengths and/or cross-sectional areas.

4. A hydroelastic support as claimed in claim 3, wherein the ducts are arranged concentrically.

5. A hydroelastic support as claimed in any one of claims 2 to 4, wherein the expansion chambers are bounded, in part, by the partition member and, in part, by a common membrane attached at its periphery to the first component.

6. A hydroelastic support as claimed in claim 5, wherein the membrane is so profiled as to co-operate with the partition member to define a fluid-tight seal between the expansion chambers.

7. A hydroelastic support as claimed in claim 6, wherein a portion of the membrane is trapped between abutting components of the partition member whereby to effect the seal.

8. A hydroelastic support as claimed in any one of claims 5 to 7, wherein the expansion cavities are arranged concentrically.

9. A hydroelastic support as claimed in any one of claims 1 to 8, wherein the second part of the partition member is displaceable on a longitudinal axis of the support.

10. A hydroelastic support as claimed in claim 2, including a bellows arranged to separate the working cavity into an inner region and an outer region, wherein said first duct provides fluid communication between the inner region of the working cavity and said one of the expansion cavities and the second duct provides fluid communication between the working cavity and said other of the expansion cavities.

11. A hydroelastic support substantially as herein described with reference to the accompanying drawings.