TECHNICAL FIELD This invention relates to a retaining device. It is concerned with a retaining device to provide a constant retaining force between two components linked by the device. It is particularly concerned with a retaining device for use in relation to two components of which one is mounted within other so that the device serves to regulate the sliding of one of the components relative to the other.

DISCLOSURE OF INVENTION According to a first aspect of the present invention there is provided a retaining device having selected characteristics and adapted for location between a first component lying within, but spaced from, a second component; the retaining device comprising: anchoring means providing for retention of the device on one of the components so as to resists displacement of the device relative to that component; at least one resiliently loadable surface component adapted for frictional engagement with one or more regions of the other of the components so that in the event that one component is subject to loading relative to the other component the device acts to resist such loading until a threshold loading is exceeded when the device allows relative sliding movement between the device and the other of the components.

According to a first preferred version of the present invention in the retaining device is adapted to provide for axial displacement to be resisted. According to a second preferred version of the present invention in the retaining device is adapted to provide for rotational displacement to be resisted.

According to a third preferred version of the present invention or of any preceding preferred version thereof resiliently loadable surface is selected on the basis of: profile of a component of which the surface is a part; material of the component; thickness of the component; and the number of such surfaces utilised in the retaining device.

According to a fourth preferred version of the present invention or of any preceding preferred version thereof the whole device is a unitary fabrication of the resiliently loadable material.

According to a fifth preferred version of the present invention or of any preceding preferred version thereof the retaining device is adapted for use in an application where the device is adapted to operate in its plastic region with a relatively flat force deflection characteristic so as to provide for a relatively constant radial force between first and second components linked by way of the device.

According to a sixth preferred version of the present invention or of any preceding preferred version thereof the, or each, resiliently loaded surface is intended to function with a lubricant, coating or cladding.

According to a seventh preferred version of the present invention or of the preceding first to fifth preferred versions thereof the, or each, resiliently loaded surface is intended to function in the absence of a lubricant, coating or cladding. According to a second aspect of the present invention there is provided an assembly comprising two components lined by way of a retaining device according to the first aspect or of any preferred version thereof.

BRIEF DESCRIPTION OF DRAWINGS Exemplary embodiments of the invention will now be described with reference to the accompanying drawings of retaining devices of which: Figure 1 is a sectional elevation of a first embodiment; Figure 2 is a sectional elevation of a second embodiment; Figure 3 is a sectional elevation of a third embodiment; and Figure 4 is a sectional elevation of a fifth embodiment.

MODE FOR CARRYING OUT THE INVENTION

Figure 1 Retaining device 11 is in the form of a corrugated cylinder being a unitary component of spring steel. The device 11 has a longitudinal axis A. The device 11 has an outer flange 12 by means of which it is seated in a recess 13 in bore 14 of a sleeve member 15. By seating the device 11 in this way the device 11 resists axial displacement in the bore 14 relative to the sleeve 15. The bore 14 has extending through it a rod 16 which is spaced from the sleeve member 15 by the device 11.

The device 11 includes two regions, respectively regions 17, 18, which are of reduced internal diameter by comparison with the remainder of the device 11 whose outside diameter D corresponds to that of the internal diameter of bore 14. The inside diameter of the regions 17, 18 when the rod 16 is not present is slightly less than the outside diameter d of the rod 18. Subsequently when the rod 18 is inserted into bore 14 and through device 11 the regions 17, 18 flex outwardly and grip the rod 16 over outer surfaces 17 A, 18A of, respectively, regions 17, 18. In this case the outer surfaces 17A. 18A are finished to a predetermined, roughness. This provides that with the assembled components as shown in Figure 1 when then rod 16 is loaded axially up to a pre-determined threshold level then the rod 16 does not move relative to the sleeve 15. However once the axial loading on the rod 16 exceeds the threshold level then the rod 16 slides relative to the sleeve 15 through the surfaces 17A, 18A (which is anchored relative to the sleeve 15 by way of outer flange 12) until the loading cease or at least falls below the threshold level. At that point the rod 16 stops moving axially relative to the .15.

Figure 2 This second embodiment is similar in form and function to the first described in relation to Figure 1. However this embodiment provides for retaining device 21 to be retained on rod 26 rather on sleeve member 25.

Retaining device 21 is in the form of a corrugated cylinder being a unitary component of spring steel. The device 21 has a longitudinal axis A. Bore 24 has extending through it a rod 26 which is spaced from the sleeve member 25 by the device 21. The device 21 has an inner flange 22 by means of which it is seated in a recess 23 in rod 26. By anchoring the device 21 in this way the device 21 resists axial displacement relative to the rod 26.

The device 21 includes two outward facing regions, respectively regions 27, 28, which are of increased outside diameter by comparison with the remainder of the device 21 whose inside diameter d correspond to the outside diameter of rod 26.

The uncompressed outside diameter of the regions 27, 28 (before insertion into the bore 24) is slightly greater than internal diameter D of the sleeve 25. When the rod 28 with the device 12 now anchored on the rod 26 is inserted into bore 24 the regions 27, 28 flex inwardly and the grip the wall of bore 24 over outer surfaces 27 A, 28A of, respectively, regions 27, 28. In this case the outer surfaces 27A. 28A are finished to a predetermined roughness. This provides that with the assembled components as shown in Figure 2 when the rod 26 is loaded axially up to a pre-determined threshold level then the rod 26 does not move relative to the sleeve 25. However once the axial loading on the rod 26 exceeds the threshold level then the rod 26 and device 21 slides relative to the sleeve 25 until the loading cease or at least falls below the threshold level. At that point the rod 26 stops moving axially relative to the sleeve 25.

Figure 3 This shows the use of several single retaining devices 31 A, 31B functioning collectively (in a similar way to that of retaining device 21 in Figure 2). The device 31 A seats in annular recess 33A in rod 36. Likewise the device 31B seats in annular recess 33B in rod 36. This location serves to prevent against significant relative axial movement of the devices 31A, 31B relative to rod 36.

The device 31 A, 31B each includes an outward facing region, respectively regions 37, 38, which are of increased outside diameter by comparison with the remainder of the device 31A, 31B.

The uncompressed outside diameter of the regions 37, 38 (before insertion into the bore 34) is slightly greater than internal diameter D of the sleeve 35. When the rod 36, with the devices 31A, 31B now anchored on the rod 36, is inserted into bore 34 the regions 37, 38 flex inwardly and grip the wall of bore 34 over outer surfaces 37A, 38A of, respectively, regions 37, 38. In this case the outer surfaces 37 A. 38A are finished to a predetermined roughness. This provides that with the assembled components as shown in Figure 3 when the rod 36 is loaded axially up to a pre-determined threshold level then the rod 36 does not move relative to the sleeve 35. However once the axial loading on the rod 36 exceeds the threshold level then the rod 36 and device 31A, 31B slide relative to the sleeve 35 until the loading cease or at least falls below the threshold level. At that point the rod 36 stops moving axially relative to the sleeve 35.

Figure 4 This shows a retaining device 41 which is retained against movement relative to sleeve 45 by an end flange (not shown) with which the device 41 is anchored to the sleeve 45. The device 41 is mounted between two slidable members, namely members 46, 47, which are slidable relative to each other and each also being slidable relative to the sleeve 45. In this case the device 41 has two sets of outer working surfaces: first set comprising : surfaces 41 A, 4113 and 41 C contacting member 47 and the second set comprising faces 41X and 41Y contacting member 46. In this case the outer surfaces 41 A - C, and surfaces 41X, Y are finished to a predetermined roughness. This provides that with the assembled components as shown in Figure 4 when the member 46 is loaded axially (that is to say perpendicular to the plane of the Figure 5) up to a pre¬ determined threshold level then the member 46 does not move relative to the member 47 or the sleeve 45. However once the axial loading on the member 46 exceeds the threshold level then the member 46 slides relative to the sleeve 45 and the member 47 until the loading cease or at least falls below the threshold level. At that point the member 34 stops moving axially relative to the sleeve 45 or the member 47.

INDUSTRIAL APPLICABILITY The exemplary embodiments serve to demonstrate some of the ways in which the present invention can function. One range of applications relates to meeting a need for controlled energy absorption in the event of an accident. Examples of vehicle applications include: vehicle bumper mounts, truck under-ride protection bar mounts, train bumper mounts, steering column collapse mechanisms and windscreen wiper drive shafts. Examples of static applications include roadside crash barriers and railway buffers.

The material and design features incorporated in a given device provide so that the device in use always operates in its plastic region where it deforms within a relatively flat region of the materials' force/deflection curve. In this way is provides a relatively constant radial force relatively independent of component tolerance. This will apply even when used in contact with components of materials having differing thermal expansion characteristics over a wide temperature range.

The invention proves a device which is compact.

In the exemplary embodiments the contact surfaces have a pre-determined roughness to provide for the required load limit threshold above which sliding is provided for. However the contact surfaces can be designed to work with, or without at least one lubricant, coating or cladding or a combination of two of these.

The exemplary embodiments refer to the use of the invention in a context of relative axial movement. However the invention can be embodied in a way where it provides for controlled resistance to relative rotation between the components involved. In such an embodiment the device will serve to transmit a given level of torque before allowing relative rotation between the components linked by the device.