GB2386170A

GB2386170A - A hydraulically damped mounting device of the bush type

Info

Publication number: GB2386170A
Application number: GB0304390A
Authority: GB
Inventors: Geoffrey James Soper; Trevor Howard Johnson
Original assignee: Avon Vibration Management Systems Ltd
Current assignee: Avon Vibration Management Systems Ltd
Priority date: 2002-03-04
Filing date: 2003-02-26
Publication date: 2003-09-10
Anticipated expiration: 2023-02-26
Also published as: GB0205020D0; GB2386170B; DE10309905B4; GB0304390D0; DE10309905A1

Abstract

A hydraulically damped mounting device has a first anchor part 10 within a second anchor part in the form of a hollow sleeve (not shown). The anchor parts are inter-connected by resilient walls 14, 15 spaced axially apart to define an enclosed space between the anchor parts, which space is divided into chambers 30, 31, 32, 33 for hydraulic fluid by axially extending deformable walls 90, 91, 92, 93. The chambers 30, 31, 32, 33 are inter-connected by a series of passageways 94, 95. Radial movement causes the chambers 30, 31, 32, 33 to change volume and so causes damping fluid movement though the passageways 94, 95. The resilient walls 14, 15 may be either symmetrical or asymmetrical about the axis of the device.

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 passageway, and damping is achieved due to the 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-0172700, 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- 0172700 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-0172700 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.

GB-A-2322427 departed from this, by locating the resilient walls at axially spaced apart locations, unlike the arrangements in EP-A-0172700 and GB-A-2291691, in which the main spring effect is provided by axially extending, circumferentially spaced, resilient walls.

The resilient walls of GB-A-2322427 thus defined an enclosed space within the sleeve, which extends circumferentially around the central anchor part, which space is axially bounded by the resilient walls.

It was then necessary to divide that space into two chambers, and connect those two chambers with a passageway, to form the hydraulic mounting device of the bush type. To provide that division, GB-A-2322472 proposed that axially extending walls extend between the central anchor part and the sleeve. Unlike the axially extending walls of the known arrangements, those walls do not need to provide a spring effect, since the spring effect is provided by the axially spaced resilient walls.

Therefore, it is not necessary for those axially extending walls to be bonded to the sleeve and/or central anchor part. Instead, they made abutting, un-bonded, contact.

This permitted a bypass to be formed between the chambers without the need for a separate bypass channel, as in GB-A-2291691. By suitably selecting the abutment

force of the axial walls against the sleeve and/or central anchor part, a pressure-sensitive seal was achieved. For pressures below a suitable level, the integrity of that seal was achieved by the force of abutment. For higher pressures, however, the seal was broken, thereby providing a path around the axial walls between the two chambers.

Where GB-A-2322427 was primarily concerned with damping types of radial vibration, GB-A-2360345 developed the idea and applied it to axial vibrations of the central anchor part relative to the sleeve, thus giving a bush mount capable of providing both radial and axial damping.

In GB-A-2360345, the resilient walls were shaped such that they did not form mirror images when reflected about the central radial plane of the mount. This was achieved by making the length of each wall different in all radial directions. The short length of one resilient wall was then matched with the long length of the other resilient wall in bounding the chambers for the hydraulic fluid. This meant that the chambers were different shapes at each end of the mount, and consequently axial movement of the central anchor part relative to the sleeve caused one chamber to increase in volume and the other chamber to decrease in volume; the opposite change occurred when

the central anchor part moved in the opposite axial direction. With such an arrangement, hydraulic fluid passed through the passageways under axial vibrations, thus damping the relative motion. The chambers were still able to react to radial vibrations as described in GB-A- 2322427, therefore GB-A-2360345 described a mount that could deal with both axial and radial vibrations.

The present invention seeks to develop a mount of the general type shown in both GB-A-2322427 and GB-A- 2360345, by addressing both radial and axial vibrations of the central anchor part relative to the sleeve.

According to a first aspect of the present invention, there is provided 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 ; first and second resilient walls interconnecting the first and second anchor parts, the first and second resilient walls being 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; at least three deformable walls, each extending

axially between the first and second resilient walls at circumferentially spaced locations, so as to divide the enclosed space into chambers for hydraulic fluid; a plurality of passageways, each passageway interconnecting two of said chambers, the passageways for flow of hydraulic fluid therethrough; wherein the deformable walls each have an edge forced into abutting, un-bonded contact with the sleeve or first anchor part.

With this aspect of the present invention, there are more than two chambers for hydraulic fluid, with passageways interconnecting different pairs of chambers.

In this case, radial vibrations of different directions will cause a volume change in particular chambers, so hydraulic fluid will pass through the passageways, damping the vibration.

Preferably, the mount has four deformable walls giving four chambers, with the walls preferably equally circumferentially spaced around the first anchor part to give four regularly shaped chambers. The chambers radially opposite one another may then be interconnected via a passageway. This configuration of chambers allows the mount to react independently to two perpendicular directions of radial vibration, as will be described in detail below.

The passageways which interconnect the chambers may all be provided at one end of the mount.

Preferably, the mount will damp particular radial vibration directions differently. For example, the passageways interconnecting pairs of chambers may be of different lengths and/or cross-sectional areas.

It is desirable for the interconnecting passageways to be provided at the same end of the mount in order to facilitate the manufacture of the device. To achieve the desired result of different damping in different radial directions, it is necessary to cross-connect the chambers. For example, in a four-chambered mount, this means that the chambers positioned radially opposite one another are connected. This presents a problem when the passageways are to be at the same end of the mount. Since passageways are usually arranged so that their outlets are formed between the ring that supports the resilient wall and the second anchor part, it is not straightforward for them to share a radial plane, without intersecting. If they are in different radial planes (or planes spaced axially apart) they take up more space in the mount.

Therefore a development of the invention proposes a structure whereby the passageways may occupy the same axial plane, therefore the mount does not have to

increase in size depending on the number of chambers. The passageways are arranged as concentric or coaxial channels having the same axial plane around the axis of the first anchor part. Therefore, one passageway lies inside the other. To get over the problem that arises because the passageways need to cross over, the inner passageway may have an outlet at one or each end which extends directly through the respective resilient wall of each chamber. This removes the need for an outlet on the boundary between the second anchor part and the ring. The passageway may have outlets like this at both its ends, or it may only have one such outlet, the other outlet being on the boundary. In the latter case, the radially outer passageway does not extend completely around the mount, instead there is a gap in it through which the inner passageway extends to the edge of the ring. The gap may be formed by stops at the ends of the out passageway.

According to a second aspect of the present invention, there is provided a hydraulically damped mounting device for damping vibrations between two vibrating bodies, the device having a first anchor part for connection to one vibrating body ; a second anchor part for connection to the other

vibrating body, the second anchor part being in the form of a hollow sleeve containing the first anchor part, such that the first anchor part extends axially of the sleeve ; first and second resilient walls interconnecting the first and second anchor parts, the first and second resilient walls being 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 deformable walls, 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 length of each resilient wall is the same in all radial positions when the first and second anchor parts are connected to the vibrating bodies and the system is at rest, and the radial distance from the central longitudinal axis of the centroid of one resilient wall where it bounds a first of the chambers is different from the corresponding radial distance of the centroid of the other wall ;

the arrangement being such that the resilient walls are not mirror images of each other when reflected about the central radial plane of the device.

With this aspect, it should be noted that the deformable walls do not necessarily have un-bonded contact with the sleeve or the first anchor part. This aspect may also have more than two of the chambers, with passageways interconnecting different pairs of chambers to deal with radial vibrations as described above, but its main feature is its system of coping with axial vibrations. Unlike GB-A-2360345, the length of the resilient walls in the present invention is the same in all radial directions around the first anchor part when the first and second anchor parts are connected to the parts of machinery the vibration between which requires damping and when the system is at rest. However, by radially displacing the centroid of the radial crosssection of each resilient wall by a different amount around the central longitudinal axis of the second anchor part, the shape of the resilient walls is such that they are not mirror images of each other when reflected about the central radial plane of the mount. Accordingly, the chambers created by the deformable walls have different shapes at each end of the mount. Therefore, axial movement in one direction of the central anchor part

relative to the sleeve causes one chamber to increase in volume, and the other to decrease in volume, with the opposite volume change occurring when the central anchor part moves in the opposite axial direction.

With such an arrangement, when axial movement occurs, the relative change in volume of two chambers (one getting larger and one getting smaller) causes hydraulic fluid to pass through the passageway interconnecting the chambers, thereby providing a damping effect.

It will be appreciated that an asymmetric mount will tend to cause the central anchor part to twist relative to the sleeve as it moves axially. This is not always a problem ; indeed there are some arrangements in which that twisting may provide steering of the vibrating parts which may be advantageous.

In both aspects of the present invention, the resilient walls may be in the shape of hollow frustocones, with their frustums at the central anchor part and their bases at the sleeve. The resilient walls thus operate in shear under load. They preferably extend substantially completely around the central anchor part.

Although it is possible for the axial walls to be simple flaps, it is preferable for them to be hollow and more preferably with a V-shaped cross section, with the base of the"V"being in contact with the sleeve.

Providing such hollow axial walls allows tuning of the dynamic stiffness of the mount independent of the static stiffness. Where the axial walls are hollow in this way, it may be necessary to provide voids in the resilient walls at the point where those resilient walls meet the axial walls.

The hydraulic mounting device may also be formed such that the first anchor part is offset transversely from the longitudinal axis of the second anchor part.

This permits the hydraulic mounting to bear greater loads in certain transverse directions.

Embodiments 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 partial sectional view through a first arrangement which is not an embodiment of the present invention but is useful in understanding the invention; Fig. 2 is a side view of part of the mount of Fig.

1 ; Fig. 3 is a perspective view of part of the mount of Fig. 1; Fig. 4 is a partial sectional view through a second arrangement which is not an embodiment of the present invention but is useful in understanding the invention Fig. 5 is longitudinal sectional view through the arrangement of Fig. 4.

Fig. 6 is a perspective view of a first embodiment of the present invention; Fig. 7 is a transverse sectional view through the mount of Fig. 6; Fig. 8 is a longitudinal sectional view through the mount of Fig. 6; Fig. 9 is a view of the base of the mount of Fig. 6 ; Fig. 10 is a perspective view of a second embodiment of the present invention; Fig. 11 is a longitudinal sectional view through the mount of Fig. 10; Fig. 12 is a transverse view of the top of the mount of Fig. 10; Fig. 13 is a side view of the mount of Fig. 10.

As can be seen from Fig. 1, a"bush"type mount which is not an embodiment of the invention but is useful in understanding the invention has a central 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 central anchor part 10 has a projecting ridge 13 from which extend resilient walls 14,15. The resilient walls 14,15 extend circumferentially around the central anchor part 10, and thus are generally in the

shape of hollow frusto-cones with their frustums at the ridge 13 of the central anchor part 10, and their bases in contact with rings 16,17 which are secured to the sleeve 11. The inclined shape of the resilient walls 14, 15 therefore 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 central anchor part, including parts of the projecting ridge 13 of the central anchor part 10.

In order for the hydraulically damped mounting device to act as such, it is necessary for the space 18 to be divided into chambers for hydraulic fluid. When those chambers are connected by a suitable passageway, hydraulic fluid flows through the passageway from one chamber to another as the mount vibrates, thereby to damp the vibration.

The mount described above is similar to that in GB-A-2322427. In both that document, and the present invention, walls extend axially between the first and second resilient walls 14,15 at circumferentially locations, so as to divide the space 18 into chambers for hydraulic fluid. The series of passageways, an example of a part of which is shown at 20 in Fig. 1 interconnects pairs of those chambers. However, in this mount, the

structure of the deformable walls is different from that of GB-A-2322427. As shown in Fig. 2, in which the sleeve 11 is removed, an axial wall 21 extends between the rings 16,17. With a similar wall on the opposite side of the mount from that shown in Fig. 2, the space 18 is thus divided into two chambers, one on the left side of wall 21 in Fig. 2 and one on the right. For radial vibrations, which thus move the central anchor part 10 sideways in Fig. 2, relative to the sleeve, one of those chambers will increase in size, and the other will decrease. Hydraulic fluid will pass from one chamber to the other, via the passageway 20.

Figs. 6 to 9 show a first embodiment of the present invention. Components which are similar to those of the mount of Figs. 1 to 5 are indicated by the same reference numerals. Note that the sleeve 11 is omitted from Figs.

6 to 9 for the sake of clarity.

In this embodiment, the chambers 30,31, 32,33 are separated by flaps forming axial walls 90,91, 92,93 spaced approximately 900 apart around the mount. The chambers 30,31, 32,33 are then mirror images of each other about the plane of those walls 90,91, 92,93.

Thus, as can be seen from Fig. 7, the space 18 is divided into four chambers 30,31, 32,33. Although not visible in the figures, the chambers 30,31, 32,33 are axially

bounded by the resilient walls 14,15 because those walls axially bound the space 18. The chambers 30,31, 32,33 are filled with hydraulic fluid.

Fig. 9 shows the base of the mount, and especially the arrangement of the passageways which interconnect the chambers. It is desirable for the chambers 30,31, 32,33 to be cross-connected, i. e. where radially opposite chambers are connected to each other. In this embodiment, that means chamber 30 is connected to chamber 32, and chamber 31 is connected to chamber 33.

Previously, only one passageway was provided in each end of the mount, whereas in this embodiment, two passageways 94,95 are provided in the base of the mount.

The passageways 94,95 are axially bounded by the ring 16 and the sleeve 11 when fitted. The passageways 94,95 are in the form of concentric channels separated by a channel wall 103. Thus passageway 95, which is the outermost channel, is radially bounded by the channel wall 103 and the sleeve 11. Channel wall 104 separates the central anchor part 10 from the passageways, therefore passageway 94, which is located inside passageway 95, is radially bounded by channel walls 103 and 104.

A baffle 100 is provided which extends between channel wall 104 and the edge of ring 16, so that when the sleeve 11 is fitted, it provides an end to both passageways 94,95. In fact, the other side of the baffle 100 is also the other end of passageway 94, hence passageway 94 extends around all of the bore 12. However,

since one inlet 97 for passageway 94 is on the edge of the ring 16, passageway 95 cannot extend all the way round the bore 12. It is therefore stopped by stopper 105, which provides the other end of passageway 95.

There are four inlets 96,97, 98,99 which open into the chambers 30,32, 31 and 33 respectively. Inlets 97, 98 and 99 are indented sections in the edge of the ring 16, whereas inlet 96 is a channel which leads from the passageway 94 directly through the resilient wall 14 into chamber 30. Thus passageway 94 interconnects chambers 30 and 32 via inlets 96 and 97, and passageway 95 interconnects chambers 31 and 33 via inlets 98 and 99.

In the arrangement shown, both passageways 94,95 contain dead channel areas 101,102 respectively. These are areas through which liquid does not need to flow to get from one inlet to the other. The dead channel areas 101,102 may be filled with rubber to improve the function of the passageways 94,95.

In such a mount, if the direction of vibration is e. g. in the plane formed by the 45 bisection of the walls 91,92, the effect is that chambers 30,32 change in size under that vibration, but chambers 31,33 do not.

Thus, fluid passes into the inlets 96,97 and through the passageway 94 between the chambers 30 and 32. Similarly, in the perpendicular direction, i. e. in the plane of the 45 bisection of the walls 90,91, chambers 30,32 are unaffected, and chambers 31,33 change in size. This

time, the fluid movement is into the inlets 98,99 and through passageway 95. Hence, by providing different characteristics for the passageways 94,95, for example if they have different lengths or different crosssectional areas, different damping characteristics can be provided in mutually perpendicular radial directions.

The axial walls 90,91, 92,93 are bonded to the ridge 13 of the central anchor part 10, they are not bonded to the sleeve 11. Instead there are shaped so that they are forced into abutting contact with the sleeve. The force of abutment is predetermined so that, under normal operating conditions, the force of abutment exceeds any force applied to the axial walls 90,91, 92, 93 by fluid pressures in the chambers 30,31, 32,33, so that the abutment forms a seal at the sleeve 11. Under such conditions, the only way for fluid to pass between the chambers is via the passageways 94,95.

However, if the pressures in the chambers 30,31, 32,33 exceed predetermined values, which may occur under very high loads, the forces applied to the axial walls 90,91, 92,93 by the fluid pressures in the chambers 30, 31,32, 33 will be sufficient to overcome the force maintaining the seal between the axial walls 90,91, 92, 93 and the sleeve 11. The edges of the axial walls 90, 91, 92,93 will be forced away from the sleeve 11, thereby creating a bypass route between the chambers 30,

31,32, 33 between the edge of the axial walls 90,91, 92,93 and the sleeve 11. Thus, extreme overpressure, which may damage the mount, can be avoided.

It should be noted that this embodiment has an arrangement in which the axial walls 90,91, 92,93 are not bonded to the sleeve 11, but are bonded to the ridge 13 of the central anchor part. It would also be possible to have an arrangement in which the axial walls 90,91, 92,93 are bonded to the sleeve, but not the ridge 13, or even not bonded to either the ridge 13 or the sleeve 11, provided that the positions of the axial walls 90,91, 92,93 could be suitably maintained by their bonding to the resilient walls 14,15.

Returning to Fig. 3, consider now axial vibrations of the central anchor part 10 relative to the sleeve.

Since the two chambers are symmetric, they will not change in volume and thus there will be no damping due to fluid movement through the passageway 20. Instead, damping is provided by fluid movement within the wall 21.

A second arrangement which is not an embodiment of the present invention but is useful in understanding the invention will now be described with reference to Figs. 4 and 5. In the mount of Fig. 3, the resilient walls are symmetric about the central radial plane of the mount.

The resilient walls are in the shape of hollow frusto-

cones. In the mount of Figs. 4 and 5, however, the resilient walls are not circumferentially symmetric, and they are not mirror images when reflected about a radial plane of the mount. Instead, the length of those walls as they extend between the central anchor part and the sleeve varies around the central anchor part. They are still frusto-cones, but with their bases inclined to the perpendicular to the axis of the cone.

Thus, referring to Figs. 4 and 5, the parts which are similar to the arrangement of Figs. 1 to 3 are indicated by the same reference numerals. However, each resilient wall comprises a short part 14a, 15a and a long part 14b, 15b and the walls are arranged so that the two chambers 30,31 formed by the division of the space 18 by the axial walls are bounded by one long part of a resilient wall and one short part of a resilient wall.

Thus, one chamber 30 is bounded by short wall 14a and long wall 15b and the other chamber 31 is bounded by long wall 14b and short wall 15a. It can be noted that the ridge is itself not symmetric, having one part 13a close to one axial end, and another part 13b close to the other axial end. Again, the chambers 30,31 are filled with hydraulic fluid and have a passageway 20 interconnecting them.

Consider now axial movement of the sleeve 10

downwardly in Figs. 4 and 5. The effect of this will be to increase the volume of chamber 30 but to decrease the volume of chamber 31. Thus, hydraulic fluid is forced in the passageway 20 from chamber 31 to the chamber 30, thus providing a damping effect. If the central anchor part 10 moves upwardly in Figs. 4 and 5, the fluid flow is reversed as the chamber 30 decreases in volume and the chamber 31 increases in volume.

Figs. 10 to 13 show a second embodiment of the present invention. Again, components which are similar to those of the mount in Figs. 1 to 5 are indicated by the same reference numerals. Note that the sleeve 11 has been omitted from Figs. 10 to 13 for clarity.

In this embodiment, the resilient walls each comprise two portions; one resilient wall (equivalent to wall 14 in Figs. 1 to 3) comprises portions 140,141 and the other resilient wall (equivalent to wall 15 in Figs.

1 to 3) comprises portions 150,151. Each portion is one half of a frusto-cone that has been bisected by a plane through the axis of the cone. Portions 140,150 are smaller than portions 141,151.

Hence, the walls 14,15 are still in the shape of frusto-cones, but as seen in Fig. 12, in this embodiment each wall is formed by joining together portions from two frusto-cones with different diameters.

Rings 16,17 have protrusions 16a, 17a, which extend from rings 16,17 towards ridge 13 in the same direction as portions 140,150 respectively. Portion 150 then extends between and interconnects ridge 13 and the end of protrusion 17a. Likewise, portion 140 extends between and interconnects ridge 13 and the end of protrusion 16a.

Since portions 140,150 are closer to central anchor part 10, the rings 16,17 need to extend further towards the central anchor part 10. When the protrusion is added on to the end of this extension, the rings have grooves 16b, 17b. It is preferable that the chambers 30,31 are bounded by the material used in the resilient walls, and not by the grooves 16b, 17b, so the portions 140,150 extend over the protrusions 16a, 17a and are connected to resilient rings 142,152 which fill grooves 16b, 17b.

Ridge 13 is also covered by the material used in the resilient walls. In addition to providing the chamber with a boundary composed of a uniform material, covering the rings 16,17 and ridge 13 in this way enables the resilient part of the mount to be cast as a single body.

Ridge 13 also has two protrusions 13a, 13b which extend from ridge 13 towards rings 16,17 respectively in the same direction as portions 141,151. Indeed, portions 141,151 extend between and interconnect the ends of protrusions 13a, 13b and rings 16,17 respectively.

Similarly to portions 140,150 above, portions 141,151 extend over protrusions 13a, 13b so that the chambers 30, 31 are uniformly bounded.

When the mount is connected to machinery for use, i. e. sleeve 11 is connected to one part of vibrating machinery, and another part is connected to the central anchor part 10 via bore 12, the vibration between the two parts being that which requires damping, the lengths of the portions 140,141, and portions 150,151 are the same. In the embodiment shown, the length of the resilient walls are also the same as each other. Thus in the case of portions 140,150, the distances between ridge 13 and the ends of protrusions 16a, 17a respectively are the same. In the case of portions 141, 151, the distances between the ends of protrusions 13a, 13b and rings 16,17 respectively are the same as each other and the same as the length of portions 140,150.

The embodiment is arranged so that portion 140 is positioned under portion 151, and portion 141 under portion 150. Fig. 11 shows the longitudinal sectional view of the embodiment, and it can be seen that the centroids of the radial cross-section of wall portions 140,150 are at different radial distances from the axis of the sleeve 11 (in this case the vertical line through the middle of bore 12) from the centroids of portions

151,141 respectively. In the embodiment shown, the centroids of portions 140,150 and of portions 141,151 are respectively the same distance from the axis of the sleeve 11, but the distance of the centroid at any point on one resilient wall is always different from the corresponding point on the other resilient wall (i. e. the centroid of the other wall which is in the same axial plane and on the same side of the first anchor part).

As can be seen in Fig. 13, the sides 210,211 of the axial wall 21 extend back from the edge so that they meet the wall. Therefore side 210 must extend back further at the top of the mount than side 211 so that it reaches portion 150.

Thus, the resilient walls 14,15 are not mirror images when reflected about the central radial plane of the mount. The mount in Figs. 4 and 5 achieved this by the length of each wall being different at all radial positions, but in this invention it is achieved with the length of the walls being the same at all radial positions.

The walls 14,15 are arranged so that when the sleeve 11 is present, two chambers 30,31 are formed by the division of space 18 by the axial wall 21 and another axial wall not shown in the figures positioned about 180 around the central anchor part 10 from axial wall 21.

Thus each chamber is bounded by the sleeve 11, ridge 13, one wall with a short radius (e. g. portion 150) and one wall with a long radius (e. g. portion 151). The chambers 30,31 are connected by a passageway not shown in the figures, but similar to passageway 20 in Figs. 4 and 5.

Again, the chambers 30,31 are filled with hydraulic fluid.

Consider now axial movement of the central anchor part 10 downwardly in Figs. 10 and 11. The effect of this will be to decrease the volume of chamber 30, but to increase the volume of chamber 31. Thus hydraulic fluid is forced in the passageway from chamber 30 to chamber 31, thus providing a damping effect. If the central anchor part 10 moves upwardly in Figs. 10 and 11, the fluid flow is reversed as chamber 31 decreases in volume and chamber 30 increases in volume.

In both embodiments of the present invention, the axial walls 90, 91,92, 93 or 21 are hollow and have voids 40,41, 42,43 therein. These voids are preferable, rather than essential, but enable the dynamic stiffness of the mount to be tuned independently of the static stiffness as explained in GB-A-2291691. Since it is preferable for the resilient walls 14,15 and the axial walls 90,91, 92,93 or 21 to be integrally moulded, there will be voids 50,51, 52,53 in the resilient walls 14,15 aligned with the voids 40,41, 42,

43 in the axial walls 90,91, 92,93 or 21 as can be seen in Figs. 7 and 12. If such voids are provided, they then form gaps in the circumferential extent of the resilient walls 14,15 around the central anchor part 10. They do not significantly affect the spring characteristic of the mount, since the mount will not normally be positioned so that the principal direction of vibration is along the diameter joining those gaps 50,51, 52,53.

It should be noted that this embodiment has an arrangement in which the axial walls are not bonded to the sleeve 11, but are bonded to the ridge 13 of the central anchor part. It would also be possible to have an arrangement in which the axial walls are bonded to the sleeve, but not the ridge 13, or bonded to both the sleeve 11 and the ridge 13, or even not bonded to either the ridge 13 or the sleeve 11, provided that the positions of the axial walls could be suitably maintained by their bonding to the resilient walls 14,15.

The features of the first and second embodiments of this invention can also be combined; for example, the arrangement in Figs. 10 to 13 may comprise more than two chambers as described in the first embodiment, so that the mount can also have different damping characteristics for vibrations in different radial directions.

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; first and second resilient walls interconnecting the first and second anchor parts, the first and second resilient walls being 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; at least three deformable walls, each extending axially between the first and second resilient walls at circumferentially spaced locations, so as to divide the enclosed space into chambers for hydraulic fluid; a plurality of passageways, each passageway interconnecting two of said chambers, the passageways for flow of hydraulic fluid therethrough ; wherein the deformable walls each have an edge forced into abutting, un-bonded contact with the sleeve or first anchor part.

2. A hydraulically damped mounting device according to claim 1, wherein all the passageways are provided at one end of the mounting device.

3. A hydraulically damped mounting device according to claim 1, wherein there are four deformable walls and four chambers for hydraulic fluid.

4. A hydraulically damped mounting device according to claim 3, wherein there are two passageways, each interconnecting two chambers which are positioned radially opposite one another.

5. A hydraulically damped mounting device according to any one of the preceding claims, wherein the deformable walls are regularly spaced around the circumference of the first anchor part.

6. A hydraulically damped mounting device according to any one of the preceding claims, wherein the chambers are arranged to deform differently under different radial vibrations.

7. A hydraulically damped mounting device according to any one of the preceding claims, wherein the passageways have different lengths and/or cross sections.

8. A hydraulically damped mounting device for damping vibrations between two vibrating bodies, the

device having a first anchor part for connection to one vibrating body; a second anchor part for connection to the other vibrating body, the second anchor part being in the form of a hollow sleeve containing the first anchor part, such that the first anchor part extends axially of the sleeve; first and second resilient walls interconnecting the first and second anchor parts, the first and second resilient walls being 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 deformable walls, 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 length of each resilient wall is the same in all radial positions when the first and second anchor parts are connected to the vibrating bodies and the system is at rest, and the radial distance from the central longitudinal axis of the centroid of one resilient wall where it bounds a first of the chambers is different from the

corresponding radial distance of the centroid of the other wall where it bounds that chamber; the arrangement being such that the resilient walls are not mirror images of each other when reflected about the central radial plane of the device.

9. A hydraulically damped mounting device according to claim 8, wherein the deformable walls each have an edge forced into abutting, un-bonded contact with the sleeve or first anchor part.

10. A hydraulically damped mounting device according to either one of claims 8 or 9, wherein the device has more than two of said chambers and there are passageways interconnecting pairs of said chambers.

11. A hydraulically damped mounting device according to claim 10, wherein each passageway interconnects two chambers positioned radially opposite one another.

12. A hydraulically damped mounting device according to either one of claims 10 or 11, wherein the chambers are arranged to deform differently under different radial vibrations.

13. A hydraulically damped mounting device according to any one of claims 10 to 12, wherein the passageways have different lengths and/or cross sections.

14. A hydraulically damped mounting device according to any one of the preceding claims, wherein the deformable walls are hollow.

15. A hydraulically damped mounting device according to claim 14, wherein the resilient walls contain gaps aligned with the hollow interiors of said deformable walls.

16. A hydraulically damped mounting device according to any one of the preceding claims, wherein the resilient walls are in the shape of hollow frusto-cones with their frustums at the first anchor part and their bases at the second anchor part.

17. A hydraulically damped mounting device according to any one of the preceding claims, wherein the frusto-cones open in opposite axial directions.

18. A hydraulically damped mounting device according to any one of the preceding claims, wherein the

resilient walls extend substantially completely around the first anchor part.

19. A hydraulically damped mounting device according to any one of the preceding claims, wherein said first anchor part is offset radially from the central longitudinal axis of the second anchor part.

20. A hydraulically damped mounting device according to any one of the preceding claims, wherein passageways are arranged as concentric or coaxial channels having the same axial plane around the axis of the first anchor part.

21. A hydraulically damped mounting device according to claim 20, wherein one passageway lies inside the other and the inner passageway has an outlet at one or each end which extends directly through the respective resilient wall of each chamber.

22. A hydraulically damped mounting device substantially as herein described with reference to and as illustrated in Figs. 6 to 9 or Figs. 10 to 13 of the accompanying drawings.

23. An assembly for damping vibrations, comprising

a first vibrating body; a second vibrating body, the vibrating body vibrating relative to one another during use; and a hydraulically damped mounting device according to any one of the preceding claims for damping vibrations between the two vibrating bodies.