GB2330892A

GB2330892A - Hydroelastic support

Info

Publication number: GB2330892A
Application number: GB9723305A
Authority: GB
Inventors: Patrice Fort; Jacques Metais
Original assignee: Draftex Industries Ltd
Current assignee: Laird Holdings Ltd
Priority date: 1997-11-04
Filing date: 1997-11-04
Publication date: 1999-05-05
Also published as: GB9723305D0

Abstract

A hydroelastic engine support having a liquid-filled working chamber (16) interconnected to a flexibly walled compensation chamber (18) via a restricted-flow conduit (24) has within the working chamber (14) a block of cellular material 26 which acts as a gas reservoir. It is compressed and expanded in response to pressure changes in the liquid caused by small amplitude vibrations and thus damps them.

Description

HYDROELASTIC SUPPORTS The invention relates to hydroelastic supports. Such supports may be used, for example, as engine mounts in vehicles for hydroelastically supporting the engine from the chassis or body of the vehicle and controlling or damping its vibrations.

However, they can be used for many other purposes.

According to the invention, there is provided a hydroelastic support, comprising two relatively rigid elements for respective connection to two relatively vibratable members, a chamber containing a fluid and having a flexible wall interconnected with the two elements so as to flex in response to the vibrations and to cause consequent pressure variations within the chamber, and a control element within the chamber which is compressed and expanded by the pressure variations whereby at least partially to damp the vibrations.

According to the invention, there is further provided a hydroelastic engine support, comprising first and second rigid elements for respective connection to the engine and the vehicle's chassis or body, relatively stiff but resilient material interconnecting the two rigid elements for partially absorbing the vibrations, a liquid-filled working chamber having a flexible wall subject to flexing in response to the vibrations, a liquid-filled compensation chamber having a flexible wall and interconnected to the working chamber through a longitudinal interconnecting conduit of predetermined length and crosssectional area whereby to restrict liquid transfer between the two chambers in response to pressure variations therein caused by relatively large amplitude vibrations and thereby to damp such vibrations, and a control element within the working chamber made of flexible material defining a reservoir of gas which is compressed and expanded by pressure variations in the working chamber caused by a relatively small amplitude vibrations which are damped thereby.

Hydroelastic supports embodying the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings in which: Figure 1 is a side view, partially in section, of one of the supports; Figure 2 is a cross-section through a control element used in the support of Figure 1; Figure 3 shows a modified form of the control element of Figure 2; and Figure 4 corresponds to Figures 2 and 3 but shows a further modified form of the control element.

The hydraulic support 4 shown in Figure 1 may be used as an engine mount in a vehicle. It comprises a rigid base 5, such as made of steel, which is securely attached to the vehicles body or chassis, such as by means of bolts passing through holes of which one is shown at 6. A rigid element 8, such as also made of steel, has a threaded bore 10 in which may be received a bolt attached to the engine. Several such hydroelastic supports may be similarly mounted at different positions around the engine.

The rigid base 5 is generally cup-shaped and supports an annular rigid member 12. A relatively stiff rubber element 14, of frusto-conical shape, supportingly extends between the element 8 and the member 12. Vibration of the engine relative to the vehicle body is thus accommodated and partially damped by corresponding flexure of the rubber element 14.

In addition, the support 4 defines two chambers filled with hydraulic fluid: a working chamber 16 and a compensation chamber 18. Chamber 16 is defined between the interior of the rubber element 14 and a shallow dish-shaped member 20 which is held securely and sealingly in position by the base 5 and the rigid annular member 12.

The compensation chamber 18 is defined by a flexible membrane 22 and the underside of the shallow dish-shape member 20. The membrane 22 is sealingly clamped around its periphery between the dish-shaped member 20 and the base 5.

The working and compensation chambers 16,18 are interconnected by means of a conduit 24 which is formed circularly or helically in the dish-shaped member 20 and is respectively connected at two spaced positions (not shown) to the working chamber 16 and to the compensation chamber 18.

The working chamber 16 contains a control element 26 which is freely positioned within the chamber. The control element 26 comprises a block of compressible material of predetermined shape. Advantageously, it is made of plastics or elastomeric material of foamed or cellular form, preferably with closed cells. As shown in Figure 2, it can be produced by moulding so as to have closed cells 28 and a skin 30 completely covering its external surface. Instead, it may be cut from a pre-formed block of the material, in which case it will have closed cells 28 together with some open cells 32 where cutting takes place, all as shown in Figure 3.

As shown in Figure 1, the control element 26 is freely positioned within the working chamber 24. However, instead it could be secured along part of its surface within the working chamber 16 (such as being adhesively secured to an internal wall of the chamber) but still allowing it to be compressed and to resile.

In operation, vibrations of the engine are partially absorbed and damped by the rubber element 14. Such vibrations are of course transmitted to the working chamber 24, causing alternate compression and expansion of the chamber and corresponding pressure variations therein. Vibrations of small amplitude, producing corresponding small pressure variations, cause alternate compression and expansion of the material of the control element 26. In effect, the control element 26 acts as a reservoir of gas (the gas being contained within the closed cells 28). Such small amplitude vibrations are absorbed (damped) by this reservoir of gas in the alternately compressed and expanded control element 26.

When higher amplitude vibrations occur, the control element 26 is effectively saturated - that is, compressed to the maximum extent by the increase of pressure in the working chamber 16.

When this occurs, fluid is forced between the working chamber 16 and the compensation chamber 18 through the conduit 24. The conduit 24 is shaped to restrict the flow of fluid oscillating therealong so as to damp the flow and consequently to damp the vibrations.

Figure 4 shows how the control element 26 may be produced from two layers 26A and 26B of the cellular material. Layer 26A has a thickness el and the diameters of the closed cells 28 have a size 01. In layer 26B, the thickness is e2 and the diameter of the closed cells 28 is 2, where 2 is greater than 81. In this way, the force/compressibility characteristic of the control element 26 can be varied. Clearly, such variation can be made more complex by the use of more than two layers or by other modifications.

In hydroelastic mounts having working and compensation chambers (similar to chambers 16 and 18) interconnected by a conduit (like conduit 24), it is known to provide a direct connection between the two chambers (that is, by-passing the conduit) which is controlled by a movable valve element. Such a valve element is mounted in position within the direct connection so as to be capable of limited bodily movement, or limited flexing, between a position in which the direct connection is open and positions in which the direct connection is closed. For example, the valve element may be disc-shaped and supported between closely spaced grills, one grill being open to the working chamber and the other grill being open to the compensation chamber. In this way, small amplitude vibrations of the engine cause small pressure changes in the chambers which in turn cause of the valve element to move or flex, resulting in consequent limited movement of the hydraulic fluid between the two chambers, thus damping such small amplitude vibrations. For large amplitude vibrations, the valve element cannot respond and tends to be held in the closed position; transfer of fluid between the two chambers thus occurs through the circular or helical conduit, causing damping of the vibrations in the manner already described. It will thus be seen that the control element 26 shown in Figure 1 takes the place of such a valve element. It is constructionally much simpler than such a valve element and requires no corresponding direct connection between the two chambers. Problems of wear occurring with the use of a valve element are avoided. Movement of the valve element can cause an unsatisfactory "clicking" noise, and thus is also avoided by the use of the control element 26. By appropriate design of the control element (such as shown, by way of example only, in Figure 4), more complex damping characteristics can be achieved than is easily possible with the use of the valve element.

Claims

CLAIMS 1. A hydroelastic support, comprising two relatively rigid elements for respective connection to two relatively vibratable members, a chamber containing a fluid and having a flexible wall interconnected with the two elements so as to flex in response to the vibrations and to cause consequent pressure variations within the chamber, and a control element within the chamber which is compressed and expanded by the pressure variations whereby at least partially to damp the vibrations.
2. A support according to claim 1, in which the control element comprises means defining a reservoir of gas.
3. A support according to claim 1 or 2, in which the control element is freely disposed within the chamber.
4. A support according to any one of claims 1 or 2, in which the control element is secured within the chamber against bodily movement but not against compressive or expansive movement.
5. A support according to any preceding claim, including relatively stiff but resilient material extending between the two rigid elements so as to flex in response to the vibrations and to cause partial damping of the vibrations.
6. A support according to claim 5, in which the flexible wall of the chamber is at least partially defined by the relatively stiff but resilient material.
7. A support according to any preceding claim, including a second chamber containing fluid and which is flexibly walled and interconnected with the first-mentioned chamber through a longitudinal conduit whereby fluid flows through the longitudinal channel between the two chambers in response to vibrations of large amplitude which cause substantially maximum compression of the control element.
8. A support according to any preceding claim, in which the fluid is a liquid.
9. A hydroelastic engine support, comprising first and second rigid elements for respective connection to the engine and the vehicle's chassis or body, relatively stiff but resilient material interconnecting the two rigid elements for partially absorbing the vibrations, a liquid-filled working chamber having a flexible wall subject to flexing in response to the vibrations, a liquid-filled compensation chamber having a flexible wall and interconnected to the working chamber through a longitudinal interconnecting conduit of predetermined length and crosssectional area whereby to restrict liquid transfer between the two chambers in response to pressure variations therein caused by relatively large amplitude vibrations and thereby to damp such vibrations, and a control element within the working chamber made of flexible material defining a reservoir of gas which is compressed and expanded by pressure variations in the working chamber caused by a relatively small amplitude vibrations which are damped thereby.
10. A support according to claim 9, in which the control element is freely disposed within the working chamber.
11. A support according to claim 9, in which the control element is secured against bodily movement within the working chamber but not against compressive or expansive movement.
12. A support according to any preceding claim, in which the control element comprises resilient cellular material.
13. A support according to claim 12, in which the cellular material is formed with cellular plastics or elastomeric material.
14. A support according to claim 13, in which the material is a predetermined shape and produced by moulding.
15. A support according to claim 12 or 13, in which the cellular material is of predetermined shape and is produced by cutting or shaping from a larger piece thereof.
16. A support according to any one of claims 12 to 15, in which the support element comprises portions of material in which the cells are of respectively different sizes to produce a predetermined force/compressibility characteristic.
17. A hydroelastic support, substantially as described with reference to Figure 1 of the accompanying drawings.
18. A hydroelastic support, substantially as described with reference to Figure 1 of the accompanying drawings as modified by any one of Figures 2,3 and 4 thereof.