GB2381846A

GB2381846A - A mounting device which is hydraulically damped

Info

Publication number: GB2381846A
Application number: GB0224192A
Authority: GB
Inventors: Matthew Iain Barker; Ian Nicholson
Original assignee: Avon Vibration Management Systems Ltd
Current assignee: Avon Vibration Management Systems Ltd
Priority date: 2001-11-09
Filing date: 2002-10-17
Publication date: 2003-05-14
Also published as: GB0224192D0; GB0126978D0

Abstract

A hydraulically damped mounting device has first and second anchor parts 10, 11, the anchor parts 10, 11 being a tube and a sleeve respectively and are joined by resilient walls 14, 15 which are axially spaced to define a space 18 within the sleeve 11. The space 18 is divided into two chambers for hydraulic fluid by two axial walls (50, 51 in Fig. 5). A passageway 20 provides fluid communication between the two chambers. The sleeve 11 partially defines the outer periphery of the passageway 20, the passageway being closed by an attachment ring 16 to which the resilient wall 14 is secured. Thus the attachment ring 16 is joined to the sleeve 11 at two paced apart locations on the sleeve, the radially inner of which is axially inward of the periphery of the passageway 20 which is axially furthermost from the centre of the mount.

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 passageway, and the damping is achieved by flow of fluid through that passageway.

In EP-A-0172700, a hydraulically damped mounting device of the"bush"type was disclosed which damped vibration between two parts of a piece of machinery, e. g. a car engine and a chassis. In a bush type of hydraulically damped mounting device, the anchor 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 coaxially of the sleeve. Resilient walls then interconnect the central anchor part and the sleeve to act as a resilient spring for loads applied to the mounting device. In EP-A-1072700, the resilient walls also defined one of the chambers (the"working chamber") in the sleeve, which chamber was connected via the elongate passageway 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.

In GB-A-2291691, the arrangement disclosed in EP-A- 1072700 was modified by providing a bypass channel from the working chamber to the compensation chamber. Under normal operating conditions, that bypass channel was

closed by part of the bellows wall bounding the compensation chamber. At high pressures, however, the bellows wall deformed to open the bypass channel, thereby permitting fluid from the working chamber to pass directly into the compensation chamber without having to pass through the full length of the passageway.

In both EP-A-1072700 and GB-A-2291691, the resilient walls extended generally axially along the interior of the mount. Those walls therefore formed axially elongate blocks of e. g. rubber material which were configured to achieve the desired static spring requirements. The material of the block was deformed primarily in shear, to give maximum durability. As the resilient walls also formed walls of the working chamber, the axial ends of the working chamber were closed with material being integral with the resilient walls. In practice, however, the spring effect of those ends walls was small, so that the spring characteristic of the mount could be determined by the axially extending resilient walls.

In GB 2322427A, a mount was disclosed in which the resilient walls were located at axially spaced apart locations. This was thus a departure from the arrangements in EP-A-0172700 and GB-A-2291691, in which the main spring effect was provided by axially extending, circumferentially spaced, resilient walls. The resilient walls in GB 2322427A defined an enclosed space within the sleeve that extended circumferentially around the central anchor part, which space was axially bounded by the resilient walls. Axially extending walls extended between the central anchor part and the sleeve to divide that space into two chambers. The chambers were connected with a passageway to form the hydraulic mounting device of the bush type.

As can be seen from Fig. 1, being one mount arrangement disclosed in GB 2322427A is in the form a bush type mount in which a first anchor part 110 is located within a sleeve 111 forming a second anchor part, to which one part of the vibrating machinery may be attached. The first anchor part 110 has a bore 112 to which another part of the vibrating machinery may be attached. The first anchor part 110 has projecting wings 113 from which extend resilient walls 114,115. The resilient walls 114,115 extend circumferentially around the first anchor part 110, and thus are generally in the shape of hollow frusto-cones with their frustums at the ridge 119 of the first anchor part 110, and their bases in contact with attachment rings 116,117 which are secured to the sleeve 111. Thus, the attachment ring 116, 117 forms the attachment for the resilient wall 114,115 and is further attached to the sleeve 111. The inclined shape of the resilient walls 114,115 defines an enclosed space 118 within the sleeve 111. That space 118 is axially bounded by the resilient walls 114,115, radially bounded outwardly by the sleeve 111 and radially bounded inwardly by the first anchor part, including parts of the projecting wings 113 of the first anchor part 110.

In order for the hydraulically damped mounting device to act as such, it the space 118 is divided into two chambers for hydraulic fluid, the division being achieved by axially extending walls (not shown in Fig. 1) that extended axially between the resilient walls 114, 115 at circumferentially spaced locations. Each resilient wall 114,115 axially bounds both chambers.

The two chambers are connected by a passageway 120.

Hydraulic fluid may flow through the passageway 120 from

on chamber to the other as the mount vibrates, thereby damping the vibration.

The passageway 120 lies between the attachment ring 116 and the sleeve 111. The sleeve 111 is accordingly turned radially inwards to make the passageway 120 completely enclosed, and the attachment ring 116 meets the sleeve 111 at two radially separated points on the sleeve. The point of lesser radial distance, herein referred to as the'inner ring join'121 is commonly sealed by a sealing bead. The angle formed by the attachment ring 116 with respect to a line perpendicular to the sleeve axis is herein referred to as the'attachment ring angle'125. It should be noted that the way the resilient wall is bonded to the attachment ring 116 may result in the attachment ring 116 being covered with a thin layer of rubber so that there is a small amount of rubber between the sleeve 111 and the attachment ring 116 at the inner ring join 121. In practice such a layer is sufficiently thin to have no effect on the function of the attachment ring 116.

The cross sectional area and shape of the passageway are variables that determine the friction imposed on fluid-flow. It is desirable to be able to tune the hydraulically damped mounting device by adjusting the cross sectional area and shape of the passageway. A limitation of bush mounts of the arrangement described by GB 2322427A is that the dimensions of the mounting device impose restrictions on the size of the passageway.

The current inventors have found that the above limitations can be overcome or at least ameliorated by repositioning the passageway with respect to the inner

ring join. At its most general, the present invention proposes that the sleeve and the attachment ring are shaped so that the passageway which is delivered between them has its outer axial extremity at a greater axial distance from central radial plane of the mount than the axial position of the inner ring join. In existing bush type mounts, the axial extremity of the passageway, that is, the point of the passageway that is at greatest axial distance from the centre of the mount, is axially aligned with the inner ring join that bounds the passageway in the assembled condition. The present inventors have found that by positioning the axial extremity of the passageway (i. e. the point on the periphery which is the furthest from the centre) at greater axial distance from the centre than the inner ring join bounding the passageway in the assembled condition, a shallow attachment ring angle can be achieved without increasing the outside diameter or decreasing the internal diameter.

The outer diameter of the bush at the position of the passageway can be identical to that of the rest of the bush.

The present invention permits greater freedom of passageway shape and cross sectional area and thus allows the device to be tuned as desired. For example, the invention permits the use of a larger radius to form a near circular passageway and thus reduce friction fluid losses. The shallow attachment ring angle allowed by the passageway position in the current invention also allows a high ratio between axial and radial bush rates.

Thus, the present invention may comprise 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 within the sleeve; first and second resilient walls interconnecting the first and second anchor parts, the first and second resilient walls being axially spaced apart so as to define an enclosed space within the sleeve extending circumferentially around the first anchor part and axially bounded by the first and second resilient walls; first and second axial walls interconnecting the first and second anchor parts, each extending axially between the first and second resilient walls at circumferentially spaced locations, so as to divide the enclosed space into first and second chambers for hydraulic fluid; and a passageway interconnecting the first and second chambers for flow of hydraulic fluid therethrough; wherein the point of the periphery of the passageway which is axially furthermost from the centre of the mount is axially outward of the inner ring join bounding the passageway.

Preferably, the sleeve is shaped in a curve where it bounds the passageway. More preferably, the sleeve has the general profile shown in Fig. 2 where it bounds the passageway. In Fig. 2, lines LI, L2, L3, L4, and curves Cl, C2 and C3 have variable lengths. Preferably, the inner ring join is located at L3, C3 or L4.

The passageway is preferably lined with rubber on the inner tace of the attachment ring. Preferably, the rubber lining mirrors the geometry of the sleeve, and thus reduces friction in the passageway. Therefore, the

passageway according to the present invention preferably comprises a curved boundary in cross section. Ideally the passageway may be circular, but for practical purposes may be generally elliptical.

Still greater freedom in passageway design, and therefore in tuning, may be accomplished if the centroid of the cross sectional area of the passageway, is axially outward of the inner ring join. Described differently, in this arrangement the centroid of the cross sectional area of the passageway is at greater axial distance from the centre of the mount than is the inner ring join. For the avoidance of doubt, the centroid of a set is defined by the point whose co-ordinates of the points in the set, as defined by Mathematics Dictionary, Fifth Edition, 1992. For the passageway, the relevant set of points are those (infinite) points which define the cross sectional angle of the passageway.

In the present invention, the sleeve may have the same outer diameter at the position of the passageway as it has over rest of the bush. Preferably, however, the radial extremity of the passageway, i. e. the point of the passageway at greatest radial distance from the centre of the mount, is positioned outboard of, i. e. at greater radial-distance than, the centreline of the inner ring join.

More preferably, the centroid of the cross sectional area of the passageway lies outboard of the centreline of the inner ring join.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a longitudinal section through of a hydraulically damped mounting device of the bush type, as a demonstration of the prior art and has already been described; Figure 2 illustrates the general profile of the sleeve shaping the passageway used in the present invention; Figure 3 is a longitudinal section through an embodiment of a hydraulically damped mounting device according to the present invention; Figure 4 is an enlargement of the passageway in Figure 3, and Figure 5 is a transverse sectional view through the embodiment of Figure 3.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: An embodiment of the present invention shown in Fig.

3 is a bush type mount comprising a first anchor part 10 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 first-anchor part 10 has a projecting wings 13 from which extend resilient walls 14,15. The resilient walls 14,15 extend circumferentially around the first anchor part 10, and thus are generally in the shape of hollow frustocones with their frustums at the ridge 19 of the first anchor part 10, and their bases in contact with attachment rings or'bottom metal'16,17, which are secured to the sleeve 11. Thus, the bottom metal 16,17 forms the attachment for the resilient wall 14,15 and is further attached to the sleeve 11. The bottom metal

forms a'bottom metal angle'25 with a line perpendicular to the sleeve axis. The inclined shape of the resilient walls 14,15 defines an enclosed space 18 within the sleeve 11. That space 18 is axially bounded by the resilient walls 14, 15, radially bounded outwardly by the sleeve 11, and radially bounded inwardly by the first anchor part, including parts of the projecting wings 13 of the first anchor part 10.

In order for the hydraulically damped mounting device to act as such, it the space 18 is divided into two chambers for hydraulic fluid, the division being achieved by axially extending walls (not shown in Fig. 2) that extended axially between the resilient walls 14,15 at circumferentially spaced locations. Each resilient wall 14,15 axially bounds both chambers. The two chambers are connected by a passageway 20. Hydraulic fluid may flow through the passageway 20 from on chamber to the other as the mount vibrates, thereby damping the vibration.

The passageway 20 lies between the attachment ring 16 and the sleeve 11. The sleeve 11 is accordingly turned radially inwards to make the passageway 20 completely enclosed, and the bottom metal 16 joins the sleeve-11 at two radially separated points. In this embodiment, the radially inner point, or inner ring join, is sealed by a bead and may therefore be referred to as the sealing bead interface 21. The sleeve 11 where it bounds the passageway 20 is swaged so that it extends axially to form the radially outer wall of the passageway 20, curves radially inward to form the axially outer wall of the passageway 20, curves axially inward and extends axially past the centroid 23 of the cross section area of the passageway 20 to form part of the radially inner wall

of the passageway 20, then curves radially inward to the sealing bead interface 21. This can be seen in detail in Figure 2.

Thus, the centroid 23 of the cross section area of the passageway 20 is axially and radially outward of the sealing bead interface 21, and the axially outer extremity of the passageway 20 (line L2 in Fig. 2) (i. e. the point of the periphery of the passageway which is axially furthermost from the centre of the mount) is axially outward of the inner ring join. The passageway 20 is lined with rubber 24 on the axially inner face, where it is bounded by the bottom metal 16. The rubber lining 24 mirrors the geometry of the sleeve 11 bounding the passageway 20, making the passageway 20 oval in cross section.

An advantage of the invention in this embodiment is that the oral cross section of the passageway 20 produces lower friction fluid loss than an angular cross section.

This gives a high level mass-damping effect. Increasing the cross section area of the passageway 20 requires less increase in bottom metal angle 23 than would be required by a similar increase in cross section area of passageways in the prior art. The passageway 20 in this embodiment has a large radius, which further reduces friction fluid losses, and a small bottom metal angle 23 relative to (bush mounts of similar dimension in) the prior art.

The smaller bottom metal angle allows a higher ratio between axial and radial bush rates and allows the diameter of the sleeve to be smaller and the diameter of the first anchor part to be larger.

In the embodiment of Figs. 3 and 4, the passageway 20 is lined with rubber 24, and there may also be rubber

on the axially outer surface of the bottom metal 16 so that there is rubber between that bottom metal 16 and the sleeve 11 at both ends of the bottom metal 16. In practice, the amount of such rubber is very small and the formation of the mount tends to compress it further, so that any spacing between the bottom metal 16 and the sleeve 11 at the inner and outer ring joins is negligibly small. Thus, since the amount of such rubber is so small, it is straight forward to determine the points on the sleeve corresponding to the inner and outer ring joins since the inner metal 16, even if it does not actually contact the sleeve 11 (and it may do in such circumstances) is very close indeed to the sleeve at the inner and outer ring joins.

Many variations to the embodiment illustrated in Figs. 3 and 4 are possible. Fig. 2 illustrates the general shape of the sleeve 11 as it extends around the passageway and, as has previously been mentioned, the dimensions of the lengths LI to L4 and the curves Cl to C3 may be varied and indeed lengths L2 or L3 may be 200.

The above discussion of the embodiment of Figs 3 and 4 has concentrated on the configuration of the passageway 20 and surrounding components. However, other components of the-mount may be varied in many ways, and still achieve the advantages of the invention. For example, features of the mount discussed in GB 2322427A may be present. In particular, and as shown in Fig. 5, the embodiment has axially extending walls 50,51 at circumferentially spaced locations so that the enclosed space 18 is divided into two chambers 52,53. In Fig. 5, the axially extending walls 50,51 are hollow at 40,41 and may make abutting unbonded contact with the sleeve 11, but alternatives are possible in which they make

abutting unbonded contact with the first anchor part as in GB 2322427A. Other features disclosed in that document may also be incorporated into the mount according to the present invention.

Claims

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 within the sleeve; first and second resilient walls interconnecting the first and second anchor parts, the first and second resilient walls being axially spaced apart so as to define an enclosed space within the sleeve extending circumferentially around the first anchor part and axially bounded by the first and second resilient walls; first and second axial walls interconnecting the first and second anchor parts, each extending axially between the first and second resilient walls at circumferentially spaced locations, so as to divide the enclosed space into first and second chambers for hydraulic fluid; and - a passageway interconnecting the first and second chambers for flow of hydraulic fluid therethrough, the passageway being defined between a part of the sleeve and an attachment ring attached to the resilient wall, the attachment ring being joined to the sleeve at two spaced apart locations on the sleeve, the radially inner of those locations being an inner ring join;

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wherein the point of the periphery of the passageway which is axially furthermost from the centre of the mount is axially outward of the inner ring join bounding the passageway.
2. A mounting device according to claim 1, wherein the sleeve is shaped in a curve where it bounds the passageway.
3. A mounting device according to claim 1 or claim 2, wherein the passageway is lined with rubber on the inner face of the attachment ring.
4. A mounting device according to any one of the preceding claims, wherein in cross section the passageway has a curved boundary.
5. A mounting device according to any one of the preceding claims, wherein the centroid of the cross sectional area of the passageway, is axially outward of the inner ring join.
6. A mounting device according to any one of the preceding claims, wherein the radial extremity of the passageway is at a greater radial distance from the

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centre of the mount than the centreline of the inner ring join.
7. A mounting device according to claim 6, wherein the centroid of the cross-sectional area of the passageway is at a greater radial distance from the centre of the mount then the centreline of the inner ring join.
8. A hydraulically damped mounting device substantially as herein described with reference to and as illustrated in Figs. 3 to 5 of the accompanying drawings.