GB2119474A - Fluid damped elastomeric mounting - Google Patents

Abstract

A chamber is formed by a box- like body which is made of rigid material and whose one open end is closed by a flexible wall 22. A liquid or plastic material (in general, said material has a viscosity not lower than 50,000 centipoises) fills said chamber. The body is mounted on a supporting structure e.g. a vehicle. A rigid rod 23, connected to an oscillating mass e.g. the engine and extending through said wall 22, has one end thereof in said material and said one end carries a plate-like annulus 30. In one embodiment, movement of the rod moves the plate (fixed directly to the rod) in said material. In other embodiments, movement of the rod moves a device (fixed directly to the rod) which only engages the plate if the oscillation amplitude is greater than a predetermined minimum. The thickness of the wall, made of elastomeric material, may vary from portion to portion. This variation, or the movable mounting of the plate, enables high frequency oscillations to be accommodated without damping. <IMAGE>

Description

SPECIFICATION Shock-absorbing support The present invention relates to a shockabsorbing support.

A shock-absorbing support is used for connecting a body subjected to escillations, vibrations and the like, (as, for instance, the internal combustion engine of a motor-vehicle) to a supporting structure, (as, for instance, the body of a motor-vehicle), and there are shock-absorbing supports of the type using a fluid enclosed in a chamber to carry out the shock-absorbing action.

Conventional shock-absorbing supports of this type can be divided into two groups.

Conventional shock-absorbing supports belonging to the first group make use of a lowviscosity fluid enclosed in a chamber having rigid walls and also comprise a rigid wall tightly slidable within the chamber. The wall is provided with a small opening through which the fluid is constrained to flow as a consequence of the wall movement, thereby dissipating energy due to the fluid lamination. The chamber enclosing the fluid is secured to the supporting structure (for instance, the body of a motor-vehicle) whilst the slidable wall is connected to the element which is subjected to escillations, vibrations and the like (as, for instance, the engine of the motor-vehicle) by means of a rod which slides in a fluid-tight manner through the chamber wall(s).

Conventional shock-absorbing supports which belong to the second group have a fluidcontaining chamber into which moves a small plate which is secured to the element (say, a motor vehicle engine) which is subjected to escillations, vibrations and the like by means of a rod which passes through a wall of the fluidcontaining chamber. The fluid filling the chamber has a high viscosity and the chamber, having rigid walls, is connected to the supporting structure, (as, for instance, the body of the motor-vehicle).

The conventional shock-absorbing supports of these two groups have several disadvantages: Supports of the first group require very accurate construction and very close working tolerances and, consequently, their service life is unsatisfactory because in the course of time their working surfaces are subjected to rapid wear, with leaks of the liquid contained in the chamber having rigid walls, since said liquid has a low viscosity, as well as to variations in the characteristics of behaviour of the shockabsorbing support because the wear of the small opening (through which the fluid must continuously pass owing to the movements of the slidable wall) leads to enlargement of the said small opening with the result of an alteration of its ability to carry out good lamination.

Supports belonging to the second group are stronger and have a longer service life by comparison with that of the first group when a fixed anchorage between the rod and a flexible membrane (forming the wall of the chamber to be passed through by said rod) is provided in place of the anchorage constituted by the rod passing through the chamber with rigid walls and by the wall passed through by said rod. Moreover, said supports of the second group do not require such close working tolerances as these belonging to the first group.

However, the supports belonging to the second group possess the serious disadvantage of being negatively influenced by high-frequency vibrations, which are vibrations associated to lowamplitude oscillations; in these conditions, owing to the high viscosity of the fluid contained in the chamber, said support becomes completely rigid and transmits said high-frequency vibrations instead of absorbing them.

The present invention aims at eliminating all the disadvantages of the conventional shockabsorbing supports discussed above by providing a shock-absorbing support, classifiable as belonging to the second group, which can even absorb high-frequency shocks.

Accordingly, the present invention consists in a shock-absorbing support for connecting an oscillating body to a structure for supporting it, said support comprising a box-like rigid body open at one end thereof, a disc-like element of elastomeric material tightly connected to said body at said one end thereof in order to provide between said body and said element a closed space completely filled with a liquid, a rigid rod rigidly secured to said element and extending through the element to penetrate into the closed space and supporting a small plate in said:liquid, means being provided for absorbing the high frequency vibrations.

Other features of a shock-absorbing support according to the present invention are described in the appended Claims 2 to 7.

Some embodiments of support according to the present invention will now be described, by way of non-limiting examples, with reference to the accompanying drawings, in which: Figure 1 is a sectional view, taken along line I-I of Figure 2, of a first embodiment of shockabsorbing support; Figure 2 is a plan view of the support shown in Figure 1; Figure 3 is a sectional view, taken along line Ill-Ill of Figure 4, of a second embodiment of shock-absorbing support; Figure 4 is a sectional view, taken along line lV-lV of Figure 3, of the support shown in that Figure; Figure 5 is a sectional view, taken along line V-V of Figure 6, of a third embodiment of a shock-absorbing support;; Figure 6 is a sectional view, taken along line VI--VI of Figure 5, of the support shown in that Figure; Figure 7 is a sectional view, taken along line VIl-VIl of Figure 8, of a fourth embodiment of shock-absorbing support; and Figure 8 is a sectional view, taken along line Vill-Vill of Figure 7, of the support shown in that Figure.

According to the general inventive idea underlying the present invention, a shockabsorbing support comprises a box-like body which has a flexible wall and which is filled with a high-viscosity liquid; a small plate carried by the end of a rigid rod which extends through the flexible wall is immersed in said liquid, and said support provides means for absorbing the highfrequency vibrations. The means for absorbing the high frequency vibrations are such as will prevent the high viscosity fluid from increasing its viscosity under the action of the high frequency vibrations; said means may be constituted by a variation in the flexibility of said flexible wall or by the possibility for the small plate to carry out very small displacements in the direction of the longitudinal axis of the rigid rod or by both of these measures.

Referring to Figures 1 and 2, a shock-absorbing support comprises a box-like body 1 open at one end at which a flange 2 is provided. Preferably, but not exclusively, the box-like body 1 has a circular plan configuration and therefore has a substantially cylindrical wail 3 and a flat base 4.

Said wall 3 and said base 4 are made of a rigid, for instance metallic, material.

A rod 5 is provided in central position in the base 4 and is tightly fastened to it (for example, by welding as shown). The rod 5 serves as part of means to connect the shock-absorbing support to a supporting structure which might be, for instance, the body of a motor-vehicle. The wall 3 is provided with an opening which is closed by a screw-threaded plug 6.

'A flexible wall 7, having the plan configuration of a disc-like body and being made of an elastomeric or other suitable material, is mounted on the box-like body 1. More particularly, the wall 7 is secured along its radially outer periphery to an annular body 8 which is provided with radially outwardly directed projection 9 intended to be gripped by the crimped-over flange 2; a portion of the elastomeric material of the wall 7 is interposed between a surface of the flange 2 and a surface of the projection 9 in order to effect a liquid-tight joint.

In this way, a liquid-tight closed chamber 10 is formed which contains a high-viscosity fluid such as, for instance, a silicone grease. In general, a fluid having a viscosity not lower than 50,000 centistokes should be used.

A rigid rod 11 is secured in the wall 7 and extends therethrough along the axis of symmetry A of the latter and is connected by means of a rubber/metal bending to the elastomeric material forming said body. Asmall rigid (e.g. metal) plate 13 is rigidly secured (for example by a screw driven into a tapped hole in the rod 11) to that end 12 of the rod 11 which is inside the chamber 10 and has a diameter far smaller than those of chamber 1 0. The rod 11 is provided at its other end 14, external to the chamber 10, with a cavity 15 (e.g. a tapped hole) to enable the shockabsorbing support to be connected to a body subjected to oscillations, vibrations and the like (as, for instance, the internal combustion engine of a motor-vehicle).

The main feature of the shock-absorbing support shown in Figure 1 is that of providing a thickness variation in the elastomeric material of the wall 7. Preferably, said thickness variation is provided in such a way as to be symmetrical with respect to the axis A; in Figures 1 and 2, said thickness variation occurs in opposite quadrants, the elastomeric material of quadrants 16 and 17 having a thickness smaller than that of said material in quadrants 1 8 and 19.

The operation of the shock-absorbing support of Figures 1 and 2 will now be described with reference to its use between the chassis (or body) and the engine of a motor vehicie:-- The vibrations transmitted from the engine cause an oscillatory movement in the direction of the axis A of the rod 11 and consequently an oscillatory movement of the small plate 13.Said oscillation of the small plate 13 resuits, in the event of high frequency vibrations, in a variation of the pressure of the high-viscosity fluid contained in chamber 1 0. This pressure variation, by virtue of the greater degree of deformability existing in some portions of the wall 7 than in other portions thereof, does not lead to an increase of the apparent viscosity of the fluid and therefore does not result in a stiffening of the support; instead, the pressure variation merely causes deformation of the quadrants 16, 1 7 which are of reduced thickness. This deformation of said quadrants means that there is absorption of the high frequency vibrations which are, therefore, not transmitted to the vehicle chassis.

Figures 3 and 4 represent an alternative embodiment which comprises a box-like body 20 of rigid (e.g. metaliic) material which is open at one end and which is provided at said one end with a flange 21 having (in section) a channel-like shape. The open end body 20 is closed by means of a wall 22 of elastomeric material which has a centrally disposed rigid rod 23 extending therethrough. The rod 23 has its longitudinal axis coincident with the axis of symmetry of the wall 22.

The wall 22 is moreover secured (e.g by bonding) at its outer edge to an annular member 24 having a radially outwardly directed flange 24' which extends into the channel-like flange 21; the flange 21 is crimped onto the flange 24t, a part of the elastomeric material of the wall 22 being interposed between said flanges to ensure a fluidtight joint.

Spokes 26, U-shaped in section, are secured by their respective ends 27 to the end 25 of the rod 23 in a conventional manner; the spokes have their several axes lying in a place perpendicular to the longitudinal axis of the rod 23 and are situated symmetrically with respect around it. Each spoke 26, by virtue of its U-shape, has two spaced arms 28 and 29 and a small annulus 30 is carried by the spokes 26; the annulus 30 is coaxial with the rod 23 and the thickness of said annulus 30 is smaller than the distance between the arms 28, 29. In this way, a clearance is provided to allow for the movement of the spokes relatively to the annulus 30 along the axis of the rod 23.

Between the wall 22 and the inner surface of the body 20 there is a high viscosity fluid and a pin 32 is secured to the base 31 of the body 20 for the purpose of mounting the shock-absorbing support on the vehicle chassis or body, and a tapped hole 34 is formed in the end 33 of the rod 23 in order to facilitate connecting the shockabsorbing support to the vehicle engine.

The operation of the shock-absorbing support of Figures 3 and 4 is as follows:- Under the action of high frequency vibrations which have a reduced amplitude and which are transmitted by the engine to the rod 23, said rod carries out alternating movements. These movements are transmitted to the spokes 26 but, due to the fact that the annulus thickness is less than the spacing between the arms 28, 29, the small amplitude movements are not transmitted to the annulus. If such movements were to be transmitted to said annulus, they might originate pressure increases in the liquid (due to the large surface area of said annulus) and these might be the cause of such an increase in the apparent density of the liquid as to cause the support to stiffen and to transmit the high frequency vibrations to the chassis (body).

Consequently, by virtue of the movement of the rod 23 and of the attached spokes 26 without movement of the annulus 30, it is possible to carry out the absorption of the high frequency vibrations by way of the resistance encountered by the small surface areas of the arms 28, 29 as they move through the surrounding liquid.

Figures 5 and 6 illustrate another embodiment of a shock-absorbing support which is identical to that shown in Figures 3 and 4, with the exception of the means for connecting the small annul us 30 (which has a central hole 36 therein) to the end 25 of the rod 23. Said means consist of a grooved bush 35 in whose U-shaped grove 35' the radially inner periphery of the annulus 30 is housed. In view of the fact that the width of the groove 35' (measured axially of the support) is greater than the thickness of the annulus 30, the latter can move with respect to the bush and, therefore, with respect to the end 25 of the rod 23.

The operation of the support embodiment represented in Figures 5 and 6 is identical to that described in respect of the embodiment illustrated in Figures 3 and 4. Obviously, in the embodiment represented in Figures 5 and 6, in the event of frequencies of high value imparted to the rod 23 by an engine, they are practically dissipated only by virtue of the surface area of the end 25 of said rod by the walls of the grooved bush 35 facing into the cavity or chamber which is filled with viscous liquid.

Figures 7 and 8 represent yet another embodiment of a shock-abosrbing support which comprises a box-like body 37 open at one end, a flange 38 at said end and of channel shape, an edge 39 of a flexible wall 40 of elastomeric material, a ring 41, a radially outwardly directed flange 41' on said ring, and said ring being joined to the elastomeric material by means of a rubber/metal bonding. The entire arrangement is so similar to the ones already described with reference to Figures 1 to 6 that it is considered unnecessary to describe them again.

Between the flexible wall 40 and the inner surface of the body 37, there is defined a space 42 which is completely filled with a high viscosity liquid, as for instance a silicone grease and, in general, a liquid having a viscosity not smaller than 50,000 centistokes.

A rigid rod 43 connected to the wall 40 carries a cylindrical bush 48 which has radial projections 50 at its end 49 and which has radial projections 52 at its other end 51. Said two sets of projections 50, 52 (which are offset around the longitudinal axis of the rod, as can be seen in Figure 7) define a groove in which is accommodated the radially inner periphery of an annulus 45 whose thickness is less than the axial dimension of said groove. Thus, it will be understood that there can be movement of the rod 43/projections 50, 52 relatively to the annulus 45.

A detailed description of the mode of operation of this particular embodiment is not considered to be necessary because it is identical with that of the preceding two embodiments.

It will have been noted from the descriptions of the various embodiments represented in Figures 3 to 8, all of which operate in the same way as regards the absorption of high frequency vibrations, that they differ from one another only in respect of the radially outwards extension of the elements whose surfaces are moved through the viscous liquid and which lead to the high frequency vibrations being absorbed therefore, according to the type of high frequency vibrations involved, a technician skilled in this art can make a choice among the various embodiments described (and among others which can be deduced from the inventive teaching in the Specification) to find the most suitable solution.

A further alternative embodiment of a shockabsorbing support according to the present invention, not represented in the Figures, is carried out by replacing the wall of disc-like body of elastomeric material described with reference to any of Figures 3, 4, 5, 6, 7 and 8 by the wall or disc-like body of elastomeric material described with reference to Figures 1 and 2.

From the above description, it will have been understood already that the stated aims of the invention are achieved by means of the shockabsorbing supports disclosed. In fact, first of all, the parts constituting a shock-absorbing support according to the invention do not require close manufacturing tolerances because too high a degree of precision would have a negative effect on their ability to absorb high frequency vibrations.

This brings in its train a simplified construction of shock-absorbing supports, their absolute reliability over their service life and their ability to absorb high frequency vibrations (which was impossible to achieve and to maintain by means of the conventional shock-absorbing supports) and all this without losing their efficiency in absorbing low frequencies.

Claims (9)

1. A shock-absorbing support for connecting an oscillating mass to a supporting structure, said support comprising a box-like rigid body open at one end thereof, a disc-like element of elastomeric material tightly connected to said one end in order to provide between said body and said element a closed space completely filled with liquid, a rigid rod rigidly secured to said body and extending through said body so that one end of the rod is in the closed space, said one end of the rod carrying a small plate, and means being provided for absorbing the high frequency vibrations.

2. A support as claimed in Claim 1, wherein said means for absorbing high frequency vibrations comprise a variation in the thickness of the disc-like element of elastomeric material.

3. A support as claimed in Claim 1, wherein said means for absorbing high frequency vibrations comprise a connection of said small plate to the end of said rod such as will allow said small plate to carry out oscillatory movements in the direction of the rod axis.

4. A support as claimed in Claim 3, wherein said connection comprises spokes radially extending in cantilever fashion from said one end of the rod, said spokes having an outwardly directed U-shaped section and the small plate lying between the arms of the various spokes, the thickness of the plate being smaller than the distance between the arms of each spoke.

5. A support as claimed in Claim 3, wherein said connection comprises a bush which is provided with a circumferential groove and which is secured to said one end of said rod, a throughhole in the central portion of the small plate, the radially inner periphery of said plate which defines said through-hole being housed in the bush groove, and the width of the bush groove measured axially of the support being greater than the thickness of the small plate.

6. A support as claimed in Claim 3, wherein said connection comprises a cylindrical bush secured to said one end of the rod, said bush being provided at both of its ends with a plurality of projections extending radially outwardly in cantilever fashion, the projections at one end of said bush being offset with respect to those at the other end thereof, the distance between the planes containing the facing surfaces of the two sets of projections being greater than the thickness of the small plate which is provided in its central portion with a through-hole, the radially inner periphery of said plate which defines said through-hole being housed between said two sets of projections.

7. A support as claimed in any one of the preceding Claims 3 to 6, wherein the means for absorbing high frequency vibrations additionally comprise a variation or variations in the thickness of said element.

8. A shock-absorbing support for connecting an oscillating mass to a supporting structure, said support being constructed, arranged and adapted to operate substantially as hereinbefore described with reference to and as illustrated in Figures 1 and 2 or Figures 3 and 4 or Figures 5 and 6 or Figures 7 and 8 of the accompanying drawings.

9. Any features of novelty, taken singly or in combination, of the embodiments of the invention hereinbefore described with reference to the accompanying drawings.