WO2003010444A1

WO2003010444A1 - Mechanical shock absorbing apparatus

Info

Publication number: WO2003010444A1
Application number: PCT/AU2002/000980
Authority: WO
Inventors: Aldo Contarino
Original assignee: Shock-Proof Solutions Pty Ltd
Priority date: 2001-07-23
Filing date: 2002-07-23
Publication date: 2003-02-06

Abstract

A mechanical shock absorbing apparatus is disclosed which includes a rheopectic polymeric material (18), a first structure (12) mechanically coupled to the rheopectic polymeric material (18) such that the first structure (12) is substantially immobilised relative to the rheopectic polymeric material (18) in at least one direction, a second structure (14) mechanically coupled to the rheopectic polymeric material (18) such that the second structure (14) is substantially immobilised relative to the rheopectic polymeric material (18) in the at least one direction, and compression means (22, 24) for applying a compression force to the rheopectic polymeric material (18) , the compression means (22, 24) being adjustable so as to adjust the compression force applied to the rheopectic polymeric material (18). The first structure (12), the second structure (14) and the compression means (22, 24) at least partially define an enclosure (16) for confining the rheopectic polymeric material (18) irrespective of the force applied to the rheopectic polymeric material (18) by the compression means (22, 24). In use, when a sudden load is applied to the first structure (12) or the second structure (14) in the at least one direction, the rheopectic polymeric material (18) is subjected to shear, and the rheopectic polymeric material (18) absorbs a proportion of said applied load dependent on the magnitude of the force applied by the compression means (22, 24).

Description

MECHANICAL SHOCK ABSORBING APPARATUS

The present invention relates to an apparatus that employs the shock absorbing properties of a rheopectic polymeric material to absorb a sudden load applied to a structure, for example, in a vehicle suspension.

International application No. PCT/CA99/00768 discloses a suspension system for bicycles having a damper assembly coupled to a first moveable frame portion of a bicycle which includes a hydraulic damper made of rheopectic polymeric material. The damper assembly has an outer casing from which extends an arm for applying a torque to the damper. The damper assembly further comprises a pair of bearings, transversally disposed to the axis of a shaft that passes through the rheopectic polymeric material, and which bear on opposite sides of the hydraulic damper. The bearings are affixed onto the casing and are designed to prevent axial displacement and flow of the rheopectic polymeric material out of the damper assembly. With the rheopectic polymeric material confined between the bearings it is placed under an initial hydrostatic pressure so as to completely fill the cavity inside the casing. When a torsional load is applied to the casing, the adherence of the rheopectic polymeric material to the adjacent surfaces of the shaft and the casing increases. As a result, the shock resistance of the rheopectic polymeric material increases with increasing loads being applied.

The damper assembly of PCT/CA99/00768 employs some of the unique properties of rheopectic polymeric material when placed under hydrostatic pressure. However, there are other advantageous properties of this type of rheopectic polymeric material which are not exploited in this prior art damper assembly. Furthermore, the shock absorbing properties of this type of material make it particularly well suited for many other applications where a sudden load or shock is applied to a mechanical structure.

The present invention was developed with a view to providing an improved mechanical shock absorbing apparatus that more effectively exploits the unique properties of rheopectic polymeric materials, such as polyurethane. According to one aspect of the present invention there is provided a mechanical shock absorbing apparatus including: a mechanical shock absorbing apparatus, said apparatus including: a rheopectic polymeric material; a first structure mechanically coupled to the rheopectic polymeric material such that the first structure is substantially immobilised relative to the rheopectic polymeric material in at least one direction; a second structure mechanically coupled to the rheopectic polymeric material such that the second structure is substantially immobilised relative to the rheopectic polymeric material in the at least one direction; and compression means for applying a compression force to the rheopectic polymeric material, the compression means being adjustable so as to adjust the compression force applied to the rheopectic polymeric material; the first structure, the second structure and the compression means at least partially defining an enclosure for confining the rheopectic polymeric material irrespective of the force applied to the rheopectic polymeric material by the compression means; wherein, in use, when a sudden load is applied to the first structure or the second structure in the at least one direction, the rheopectic polymeric material is subjected to shear, and the rheopectic polymeric material absorbs a proportion of said applied load dependent on the magnitude of the force applied by the compression means.

In one arrangement, the at least one direction includes a direction corresponding to reciprocal movement of one of the first and second structures relative to the other of the first and second structures.

Alternatively, the at least one direction includes a direction corresponding to rotational movement of one of the first and second structures relative to the other of the first and second structures.

In one embodiment, the first structure includes a shaft and the second structure at least partially defining a chamber into which the shaft extends. Preferably, the chamber is substantially cylindrical and the rheopectic polymeric material is substantially annular.

The chamber may be at least part substantially spherical shaped and the rheopectic polymeric material may be at least part substantially spherical shaped, the rheopectic polymeric material including an aperture for receiving the shaft.

In an alternative embodiment, the first structure includes a ball and the second structure includes a socket. Preferably, the rheopectic polymeric material is substantially cup shaped.

Preferably, the first structure and the rheopectic polymeric material are provided with complementary first engaging means for substantially immobilising the first structure relative to the rheopectic polymeric material in the at least one direction. The complementary first engaging means may include at least one projection and at least one recess.

Preferably, the second structure and the rheopectic polymeric material are provided with complementary second engaging means for substantially immobilising the second structure relative to the rheopectic polymeric material in the at least one direction. The complementary second engaging means may include at least one projection and at least one recess.

Preferably, the complementary first and second engaging means facilitate movement of the first structure relative to the second structure in at least one direction.

In one arrangement, the compression means is arranged such that adjustment of the compression means effects an increase or decrease in the size of the enclosure defined by the first and second structures and the compression means. For this purpose, the compression means may include a pressure member slidably received in an aperture in communication with the enclosure, and a thrust bearing for applying a compressive force to the pressure member. In an alternative arrangement, the compression means includes clamp means for urging the first and second structures to move towards or away from each other so as to thereby respectively reduce or enlarge the size of the enclosure. Preferably, clamp means includes a first screw threaded portion associated with the first structure and a second complementary screw threaded portion associated with the second structure. In an embodiment which includes a shaft and a chamber into which the shaft extends, the shaft may be provided with the first screw threaded portion at a free end of the shaft.

Most preferably, the rheopectic polymeric material is a polyurethane material.

In order to facilitate a more comprehensive understanding of the nature of the invention, preferred embodiments of the mechanical shock absorbing apparatus according to the invention will now be described in detail, by way of example only, with reference to the accompanying drawings, in which:

Figures 1 and 2 illustrate a first embodiment of a mechanical shock absorbing apparatus in accordance with the present invention;

Figure 3 is an exploded view of a second embodiment of a mechanical shock absorbing apparatus in accordance with present invention;

Figure 4 is an exploded view of a third embodiment of a mechanical shock absorbing apparatus in accordance with the present invention;

Figure 5 illustrates the apparatus of Figure 3 in its assembled condition;

Figure 6 illustrates the apparatus of Figure 4 in its assembled condition;

Figure 7 illustrates a fourth embodiment of a mechamcal shock absorbing apparatus in accordance with the present invention;

Figure 8 is an exploded view of a fifth embodiment of a shock absorbing apparatus in accordance with the present invention;

Figure 9 illustrates a sixth embodiment of a shock absorbing apparatus in accordance with the present invention; and

Figure 10 illustrates a seventh embodiment of a shock absorbing apparatus in accordance with the present invention.

The present invention is based on an application of the unique properties of rheopectic polymeric materials, such as polyurethane. Thixotropy is the property exhibited by certain gels of becoming fluid when stirred or shaken (Macquarie Dictionary). Rheopectic is the opposite of thixotropic and is sometimes referred to as anti- thixotropic. Rheopectic materials exhibit fluid-like properties in which the viscosity increases with time under a constantly applied stress. Certain resins, including polyurethane are rheopectic. Another polymer with rheopectic properties is carboxymethyl cellulose.

Polyurethane acts like a liquid in "solid" form. Like a liquid, it is substantially incompressible. Its rheopectic properties make it ideally suited as a damping material. When first struck by an object the material acts like a liquid, however as the object decelerates the material solidifies. Typically the shorter the time frame of the load applied to the material, the quicker the material responds. The transition from "solid" to liquid state occurs very quickly, and the material also "resolidifies" very quickly. Surprisingly, when fully encapsulated or contained with a confined volume, and subject to a compression force, the rheopectic properties of the material change. The nature of this change is not fully understood. However, without being bound by theory, it appears that varying the compression force applied to the contained material modifies its shock absorbing properties such as stiffness, viscosity, elasticity and/or the degree to which it is able to deflect deform under loading.

In conventional shock absorbing assemblies that employ rubber or other polymeric materials, the shock absorbing material is generally arranged to absorb sudden loads or shocks by being placed in compression so as to produce a cushioning effect. However, with the rheopectic polymeric materials employed in the present invention, it has been found that they are most effective in absorbing a significant proportion of the load when placed in shear. Therefore, in each of the described embodiments of the invention that follow, the shock absorbing apparatus is designed so that when a sudden load or shock is applied to the apparatus the polymeric material is subjected to a shear force, rather than a compression force as in conventional shock absorbing materials.

Figures 1 and 2 illustrate a first embodiment of the shock absorbing apparatus in accordance with the invention that may be used, for example, in connection with the clutch plate of a motor vehicle engine. Figure 1 is a section view through the apparatus 10 along the line A-A in Figure 2. The clutch plate of a motor vehicle engine lies between the gearbox and the motor, and is designed to provide a smooth transition between gear changes. It generally does this by allowing a degree of slippage to occur between the drive shaft of the engine and the gearbox. In this way, the sudden load applied to the drive shaft of the engine is largely absorbed through friction as the two halves of the clutch plate slip with respect to each other. In the apparatus 10 of Figures 1 and 2, a disc 12 may, for example, be formed integral to one half of the clutch of a motor vehicle engine. A shaft 14 of the apparatus may, for example, be the drive shaft of the motor, or alternatively the main shaft of the gearbox. A chamber 16 within the disc 12 contains a rheopectic polymeric material 18. As can be seen more clearly in Figure 1, both the inner surface of the annular chamber 16 and the outer surface of the shaft 14 are toothed so as to grip the rheopectic material 18 and inhibit slippage between the polymeric material and the disc 12 and shaft 14 respectively.

The chamber 16 is closed on one side by a plate 20 bolted to the end of the shaft 14. On the other side, the chamber 16 is closed by a pressure plate 22 against which a compressive force is applied via thrust bearing 24. In this way, the polymeric material 18 within chamber 16 is subject, in use, to a compression force so that it fully occupies the chamber 16 and there are no air pockets or cavities. By varying the compression force applied to the polymeric material 18 via pressure plate 22 and thrust bearing 24, the mechanical properties of the rheopectic polymeric material 18 can be modified. In particular, as the compressive force applied to the polymeric material increases, it has been found that the response time of the polymeric material in its ability to absorb shocks decreases. The compression force may be applied using any suitable mechanism, such as by a lever mechanism, by using a nut 25, and so on.

From the above description, it will be seen that when a sudden load is applied to the shaft 14, for example, when the motor vehicles gears are engaged, the polymeric material 18 within chamber 16 will be subject to torsional shear due to the inertia of the disc 12. As the torque is transferred from shaft 14 to the disc 12 via the polymeric material 18, and disc 12 begins to accelerate, the shear forces applied to the polymeric material 18 gradually decrease until both the disc 12 and shaft 14 are rotating with the same velocity. However, even in this condition, the polymeric material 18 will still be subject to some shear. The rheopectic properties of the polymeric material 18 are such that initially when the torque of shaft 14 is applied to the inner surface thereof, it "gives" and shaft 14 appears to slip with respect to the disc 12. However, as the polymeric material 18 is subject to shear, its viscosity increases and the material appears to harden so that the torque is then transmitted through the material to the disc 12 via the inner surface of the chamber 16. In this way, the polymeric material is capable of absorbing a significant proportion of the load or shock that would otherwise be applied to the disc 12 by the torque transmitted from shaft 14.

Figures 3 and 5 illustrate a second embodiment 30 of a mechanical shock absorbing apparatus in accordance with the present invention. This embodiment of the shock absorbing apparatus is incorporated in a ball joint or swivel joint 30. The ball joint 30 comprises a first structure having a rigid support member 32 connected to a ball 34, which is received within a second structure comprising a socket 36 integral to the first part 38 of the housing. Between ball 34 and socket 36 a rheopectic polymeric material is received moulded in the shape of a cup 40. In its assembled condition as shown in Figure 5, a second part 42 of the housing effectively seals the cup-shaped polymeric material 40 between the ball 34 and socket 36 of the ball joint. The first part of the housing 38 is formed with a circular aperture 44 therein, in which a plug 46 is slidably received in close-fitting relationship. It will be seen therefore that the first and second parts of the housing 38 and 42, together with ball 34 and plug 46 effectively contain the rheopectic polymeric material therein.

As can be seen most clearly in Figure 3, ball 34 is formed with a series of radially extending projections 48 on the lower hemisphere thereof which are received in a corresponding number of grooves 50 on the inner surface of the cup-shaped polymeric material 40. Similarly, the cup-shaped polymeric material 40 is formed with a series of radially extending projections 52 on the outer surface thereof which are received in a corresponding number of radially extending grooves 54 within the socket 36. The effect of these interlocking projections and grooves is that the ball 34 is substantially immobilised rotationally about its central axis 56 relative to the polymeric material 40. Likewise, the socket 36 is also substantially immobilised rotationally about the central axis 56 relative to the polymeric material 40. Pivotal movement of the support member 32 from side to side in any plane defined by the radially extending projections 48 and grooves 50 will subject the rheopectic polymeric material 40 to shear and the support member is thereby urged to return to a generally upright orientation. It will be seen that the upper surface of the second part 42 of the housing is of conical shape to accommodate the pivoting movement of the support member 32.

If a sudden torque is applied to the support member 32 about its longitudinal axis 56, the cup-shaped rheopectic polymeric material 40 will be subject to shear and is capable of absorbing a significant proportion of the shock, in a similar manner to the polymeric material 18 of the previous embodiment. Furthermore, the mechanical properties of the rheopectic polymeric material may be modified by increasing or decreasing the compression force applied thereto by means of the plug 46. The compression force may be applied to the plug 46 in any suitable way, such as by a lever mechanism, by providing an externally screw threaded thrust member which engages with a corresponding internally screw threaded portion on the circular aperture 44, and so on. This particular embodiment may find application in any situation where the first structure is subject to torsional loading but must be capable of pivotal movement with respect to the second structure, such as in universal coupling for the power transmission in trucks and cars. Figures 4 and 6 illustrate a third embodiment 30(a) of the mechanical shock absorbing apparatus in accordance with the present invention. This embodiment is similar to the second embodiment 30 illustrated in Figures 3 and 5, and identical parts have been identified with the same reference numerals. Similar parts have been identified with the same reference numerals but using the suffix "a". The only difference between this embodiment and that of Figures 3 and 5 is that the radially extending projections and grooves are replaced with circumferentially extending projections 48a on the lower hemispherical surface of the ball 34a, and with circumferential grooves 50a on the inner surface of the cup-shaped rheopectic polymeric material 40a. Likewise, the polymeric material 40a is formed with circumferentially extending annular projections 52a on its outer surface which are received in circumferentially extending annular grooves 54a on the surface of the socket 36a. This means that in this embodiment the support member 32a is free to rotate without hindrance about its longitudinal axis 56a. However, due to the interlocking of the projections 48a and grooves 50a the ball 34a is substantially immobilised relative to the polymeric material 40a when subject to pivoting movement. Likewise, socket 36a and the first part 38a of the housing are substantially immobilised relative to the polymeric material 40a other than in a plane substantially parallel to the annular projections 52a and grooves 54a.

Therefore, this embodiment of the shock absorbing apparatus is particularly suitable for absorbing sudden loads applied to the support member 32a which cause it to pivot relative to the central axis 56a, or a load applied longitudinally to the support member 32 along its central axis 56a. As with the previous embodiment, the rheopectic polymeric material 40a will be subject to shear when a load is applied to the support member 32a in these ways, and is capable of absorbing a significant proportion of the load. As with the previous embodiment, the mechanical properties of the polymeric material 40a, including its response time, may be modified by increasing or decreasing the compressive force applied to the polymeric material via the plug 46 in any suitable way. This embodiment 30a of the apparatus would be suitable, for example, to provide vibration resistant engine mounts in a motor vehicle. Alternatively, an enlarged version could be one of several shock absorbing mounts provided for supporting a building structure in an earthquake-prone zone.

Figure 7 illustrates a fourth embodiment 60 of the mechanical shock absorbing apparatus in accordance with the present invention. In this embodiment, a rheopectic polymeric material 62 is substantially contained within a cylindrical shell 64. Each end of the shell 64 is closed off by a series of nested, concentric rings 66 mounted about a central shaft 68. Rings 66 are tightly nested and have a close fit with their adjacent rings so as to effectively encapsulate the polymeric material 62 within the shell 64. Likewise, the outer most ring 66 has an outer diameter having a close tolerance fit within the inner circumference of the shell 64, and the inner most ring 66 has an inside diameter having a close tolerance fit with the outer surface of the central shaft 68. A pair of parallelogram links 70 and 70a are pivotally connected at one end to the shaft 68 and at the other to the shell 64.

The rheopectic polymeric material 62 is subject to a compression force by applying a force to the polymeric material 62 through the rings 66. The compression force may be applied in any suitable way, such as by a lever mechanism, by including shims or similar between adjacent rings 66, and so on.

The outer surface of shaft 68 is formed with a plurality of circumferential grooves in order to provide a grip for the polymeric material 62. In this way, shaft 68 is substantially immobilised relative to the polymeric material 62 in the longitudinal direction of the shaft 68. Hence, when a load is applied to the shaft 68 in a longitudinal direction, as indicated by arrow 72, the polymeric material 62 will be subject to shear as the shaft 68 moves relative to the shell 64. Parallelograms 70 and 70a together with the concentric rings 66 accommodate this movement. As with the previous embodiments, due to its rheopectic properties, the polymeric material 62 is capable of absorbing a significant proportion of the load applied to the shaft 68.

Figure 8 illustrates a fifth embodiment 80 of the shock absorbing apparatus in accordance with the invention. The apparatus 80 of this embodiment incudes a first structure 82 comprising a ring member 84 and a connecting member 86 which may, for example, be a tie rod in a motor vehicle which is connected by means of a swivel joint to a shaft 88. Ring member 84 has a plurality of grooves 90 formed on its inner circumference which are adapted to receive a plurality of projections 92 formed on the outer surface of the two halves of a shell 94. When the two halves of shell 94 are joined together they form a part-sphere within which is contained a part-sphere of rheopectic polymeric material 96.

The inner surfaces of the two halves of shell 94 are formed with grooves 98 therein which are adapted to receive a plurality of projections 100 formed on the outer surface of the polymeric material 96. The polymeric material 96 is also formed with a central bore therethrough having a recessed surface adapted to receive a toothed outer surface of shaft 88 therein, in interlocking relationship. Accordingly, in its assembled condition, it will be seen that shaft 88 is mechanically coupled to the polymeric material so as to be substantially immobilised relative thereto in a rotational direction about its central axis 102 and the shell 94 is likewise mechanically coupled to the polymeric material so as to be substantially immobilised relative thereto in a rotational direction about axis 102. Shell 94 is in turn locked to the inner circumference of ring 84 of the first structure in a rotational direction about the axis 102. However, because of the curvature of the outer surface of shell 94, ring 84 can swivel from side to side so that the connecting member 86 is not necessarily perpendicular to the axis 102.

The rheopectic polymeric material 96 is substantially contained within shell 94 by means of a pair of end plates 104 mounted respectively on either side of the polymeric material 96. Like the polymeric material 96, end plates 104 have a central aperture which is adapted to interlock with the toothed outer periphery of shaft 88 so as to be rotationally locked thereto. However, end plates 104 are free to slide longitudinally along the shaft 88. By applying pressure to the end plates 104 via suitable thrust bearings (not shown), the polymeric material contained within the shell 94 is subject to a compression force. The compression force may be applied in any suitable way, such as by a lever mechanism, and so on. Furthermore, if a torque is applied to the ring 84 via connecting member 86 or toothed shaft 88, it will be seen that the polymeric material 96 is subject to shear. In a manner similar to that of the previous embodiment, the polymeric material 96 is thereby capable of absorbing a significant proportion of a sudden load applied to the first structure 82 and/or the shaft 88. The mechanical properties of the polymeric material 96 can be modified by varying the pressure applied to the end plates 104.

Figure 9 illustrates a sixth embodiment 110 of a mechanical shock absorbing apparatus in accordance with the present invention. In this embodiment, a rheopectic polymeric material 111 of generally cylindrical configuration is contained in a cavity defined by interengaging female and male portions 112 and 114 respectively.

The female portion 112 includes an inwardly facing cylindrical wall 116 having a transversely disposed first gripping surface 118.

The male portion 114 includes a shaft 120 extending through the rheopectic polymeric material 111 and into a stepped cavity 121 formed in the female portion 112. The male portion 114 also includes an outwardly facing second gripping surface 122.

When the male portion 114 is received in the female portion 112, the first and second gripping surfaces 118, 122 engage with third and fourth gripping surfaces 124 and 126 respectively provided on the rheopectic polymeric material 111 so as to substantially prevent relative movement between the first and third gripping surfaces and the second and fourth gripping surfaces about a longitudinal axis of the shaft 120.

A compression force is applied to the polymeric material 111 using a bolt 128 which extends inwardly of the female portion 112 and engages with an end of the shaft 120. A friction minimising device, in this example a thrust washer 130, is also provided between a head of the bolt 128 and the female portion 112 so as to minimise friction between the bolt and the female portion 112.

When a load is applied to the male portion 114 which urges the male portion 114 to rotate about a central axis of the shaft 120, the polymeric material 111 will be subject to shear as the male portion rotates relative to the female portion. As with previous embodiments, due to its rheopectic properties, the polymeric material 111 is capable of absorbing a significant portion of the load applied to the male portion 114.

As with previous embodiments, the mechanical properties of the rheopectic material 111 can be modified by varying the force applied by the bolt 128.

The embodiment shown in Figure 10 is similar to the embodiment in Figure 9 in that a polymeric material 111 is disposed in a generally cylindrical cavity defined by male and female portions, in this embodiment indicated by reference numerals 142 and 144 respectively.

As with the previous embodiment, the female portion 142 includes an inwardly facing cylindrical wall 146 and a first gripping surface 148. However, with this embodiment, a force is applied to the rheopectic material 111 using an internal screw thread portion 149 provided on the female portion 42 which engages with an external screw threaded portion 150 of a step bolt 152 extending through a sleeve 154 provided on the male portion 144. As with the previous embodiment, the male portion 144 includes a second gripping surface 156 and the polymeric material 111 includes third and fourth gripping surfaces 158 and 160 respectively which engage with the first and second gripping surfaces provided on the female and male portions 142, 144. A friction minimiser, in this example in the form of a thrust washer 160, is also provided between a head of the step bolt 152 and the male portion 144.

It will be understood that this embodiment operates in a similar way to the embodiment shown in Figure 9 and rotation of the male portion 144 subjects the polymeric material 111 to shear, the polymeric material 111 absorbing a significant portion of the load applied to the male portion 144.

As with previous embodiments, the mechanical properties of the rheopectic material 111 can be modified by varying the force applied by the step bolt 152.

The embodiments shown in Figures 9 and 10 are particularly suited to suspension units and drive shafts.

It will be appreciated that in all embodiments, the rheopectic polymeric material is confined in an enclosure and subjected to a compression force which is adjustable, the rheopectic polymeric material remaining confined within the enclosure irrespective of the applied compression force. In this way, the shock absorbing properties of the rheopectic polymeric material may be readily controlled and modified according to application.

Now that several embodiment of the shock absorbing apparatus in accordance with the present invention have been described in detail, it will be apparent that it provides a number of significant advantages, including the following:

(a) It is of relatively simple construction with no moving parts. (b) The shock absorbing properties of the polymeric material can be easily modified by varying the compression force applied thereto, (c) It is relatively lightweight, the polymeric material itself having very little weight, and any associated housing and other structures can be made from any suitably rigid material, including plastics materials and anodised aluminium. (d) No lubrication is required and the apparatus is virtually maintenance free.

Numerous variations and modifications will suggest themselves to persons skilled in the mechanical arts, in addition to those already described, without departing from the basic inventive concepts. For example, the dimensions of the components in each of the described embodiments of the shock absorbing apparatus can be scaled up or down depending on the application. Furthermore, as is evident from the range of embodiments described, the shape, size and arrangement of the components in the apparatus can be varied considerably depending upon the application, to provide the desired functionality. However, in each case, it is essential that the polymeric material be substantially fully contained and subject to shear in use. All such variations and modifications are to be considered within the scope of the present invention, the nature of which is to be determined from the foregoing description.

Claims

CLAIMS:

1. A mechanical shock absorbing apparatus, said apparatus including: a rheopectic polymeric material; a first structure mechanically coupled to the rheopectic polymeric material such that the first structure is substantially immobilised relative to the rheopectic polymeric material in at least one direction; a second structure mechanically coupled to the rheopectic polymeric material such that the second structure is substantially immobilised relative to the rheopectic polymeric material in the at least one direction; and compression means for applying a compression force to the rheopectic polymeric material, the compression means being adjustable so as to adjust the compression force applied to the rheopectic polymeric material; the first structure, the second structure and the compression means at least partially defining an enclosure for confining the rheopectic polymeric material irrespective of the force applied to the rheopectic polymeric material by the compression means; wherein, in use, when a sudden load is applied to the first structure or the second structure in the at least one direction, the rheopectic polymeric material is subjected to shear, and the rheopectic polymeric material absorbs a proportion of said applied load dependent on the magnitude of the force applied by the compression means.

2. An apparatus as claimed in claim 1, wherein said at least one direction includes a direction corresponding to reciprocal movement of one of said first and second structures relative to the other of said first and second structures.

3. An apparatus as claimed in claim 1, wherein said at least one direction includes a direction corresponding to rotational movement of one of said first and second structures relative to the other of said first and second structures.

4. An apparatus as claimed in any one of claims 1 to 3, wherein the first structure includes a shaft and the second structure at least partially defines a chamber into which the shaft extends.

5. An apparatus as claimed in claim 4, wherein the chamber is substantially cylindrical and the rheopectic polymeric material is substantially annular.

6. An apparatus as claimed in claim 4, wherein the chamber is at least part substantially spherical shaped and the rheopectic polymeric material is at least part substantially spherical shaped, the rheopectic polymeric material including an aperture for receiving the shaft.

7. An apparatus as claimed in any one of claims 1 to 3, wherein the first structure includes a ball and the second structure includes a socket.

8. An apparatus as claimed in claim 7, wherein the rheopectic polymeric material is substantially cup shaped.

9. An apparatus as claimed in any one of the preceding claims, wherein the first structure and the rheopectic polymeric material are provided with complementary first engaging means for substantially immobilising the first structure relative to the rheopectic polymeric material in said at least one direction.

10. An apparatus as claimed in claim 9, wherein the complementary first engaging means includes at least one projection and at least one recess.

11. An apparatus as claimed in any one of the preceding claims, wherein the second structure and the rheopectic polymeric material are provided with complementary second engaging means for substantially immobilising the second structure relative to the rheopectic polymeric material in said at least one direction.

12. An apparatus as claimed in claim 11, wherein the complementary second engaging means includes at least one projection and at least one recess.

13. An apparatus as claimed in claim 9, wherein the complementary first and second engaging means facilitate movement of the first structure relative to the second structure in at least one direction. i

14. An apparatus as claimed in any one of the preceding claims, wherein the compression means is arranged such that adjustment of the compression means effects an increase or decrease in the size of the enclosure at least partially defined by the first and second structures and the compression means.

15. An apparatus as claimed in claim 14, wherein the compression means includes a pressure member slidably received in an aperture in communication with the enclosure.

16. An apparatus as claimed in claim 15, further including a thrust bearing for applying a compressive force to the pressure member.

17. An apparatus as claimed in claim 14, wherein the compression means includes clamp means for urging the first and second structures to move towards or away from each other so as to thereby respectively reduce or enlarge the size of the enclosure.

18. An apparatus as claimed in claim 17, wherein the clamp means includes a first screw threaded portion associated with the first structure and a second complementary screw threaded portion associated with the second structure.

19. An apparatus as claimed in claim 18 when dependent on claim 4, wherein the shaft is provided with the first screw threaded portion at a free end of the shaft.

20. An apparatus as claimed in any one of the preceding claims, wherein the rheopectic polymeric material is a polyurethane material.

21. A clutch of a motor vehicle including an apparatus as claimed in any one of the preceding claims.

22. A ball joint including an apparatus as claimed in any one of claims 1 to 19.

23. A tie rod including an apparatus as claimed in any one of claims 1 to 19.

24. A drive shaft including an apparatus as claimed in any one of claims 1 to 19.

25. A suspension device including an apparatus as claimed in any one of claims 1 to 19.