The invention relates to a combined spring and damper such as would be used, for example, in a vehicle suspension. Conventional practice is to provide spring and damper as distinct independent units. The present invention employs a spring of unconventional form, which leads to the possibility of employing the spring itself in a dual function in that the spring element also forms a part of the damper. It is anticipated that this will lead to the possibility of saving of materials, cost and weight for the combined unit. All of these are particularly desirable objectives, especially in the automotive field.

Accordingly the present invention provides a combined spring and damper comprising a plurality of spring elements and a mass of resilient material, each spring element being in the form of a continuous strip of resilient material which is disposed when unstressed in the form of a zig-zag consisting of a plurality of limbs and link portions of reflex form which join together adjacent pairs of limbs by one end thereof, the spring elements each extending in the same general direction, and being disposed in radial planes with respect to a common axis, the mass of resilient material being located on the said axis, whereby on compression of the spring elements in the direction of the said axis, the resulting radially inward movement of the radially inner reflex portions is resisted resiliently by the mass of resilient material, and the resulting axial movement of the radially inner reflex portions is resisted by contact with the mass of resilient material and axial compression thereof.

The spring elements may very conveniently be of fibre reinforced plastics material.

Spring elements of this kind are disclosed and claimed in my co-pending International Patent Application No OB/84/OO207.

Alternatively the spring elements may be of metal.

The mass of resilient material will generally have a much greater elasticity than the material of the spring elements.

The mass of resilient material is suitably of an elastemeric substance, such as natural or synthetic rubber.

The surface of the mass of resilient material may be provided

with a layer of wear resistant material, at least in the regions which can be contacted by the spring elements.

This coating may be for example of metal, a hard plastics material, or a low friction material such as polytetrafluoroeth lene. The coating may define concavities in which the inner reflex portions are receivable, whereby sliding movement between the spring elements and the resilient mass is minimised. Damping is then achieved primarily as a result of deformation of the resilient material and consequent internal energy dissipation, ie hysteresis losses.

The invention will now be described by way of example only with reference to the accompanying drawings, of which Figure 1 shows a combined spring and damper in accordance with the invention, when in an unstressed state, and Figure 2 shows the combined spring and damper of Figure 1 when in a compressed state.

As shown in the Figures, the combined spring and damper com¬ prises a pair of spring elements 1, each spring element being in the form of a continuous strip of fibre-reinforced plastics material disposed in the form of a zig-zag. Each element consists of six links 2, and five link portions 3 which join together each adjacent pair of links by one end.

The spring elements 1 are disposed in radial planes with respect to a common axis AA. Although only two spring elements 1 are illustrated, in practice it may be preferred to provide three or four or more spring elements 1, similarly disposed in radial planes with respect to the axis AA, and normally arranged symmetrically.

The spring elements 1 are integrally joined at their upper ends by an end-piece , and at their lower ends by an end-piece 5 pro- vided with a central aperture 6.

Enclosed within the spring elements 1 and lying on the axis AA, there is provided a core comprising a mass 7 of a resilient elastomeric material, for example a ployurethane or synthetic rubber. The radially inner ones of the reflex portions 3 bear upon the core, which is pro- vided with longitudinal rubbing strips of a wear resistent flexible plastics material 8 which extend along the longitudinal lines of

contact. The core is fixed eg by adhesive Q to the end-piece k.

In use, for example as a suspension unit for an automobile, the unit is.attached to the body of the vehicle or other device, which is indicated at 10. The sprung mass (eg vehicle wheels, axles, brakes etc) to be suspended from the body 10 is connected to the lower end-piece 5 eo as directly to load the spring elements 1, but not directly to load the mass 7 of elastomeric material, as indicated by the arrows P (Figure 2).

When a load is applied as indicated at P, the action of the device is as follows. The spring elements 1 cure compressed, and they therefore deform in such a way that the inner ones of the reflex portions 3 more inwardly due to the bending movement and upwardly from their position as shown in Figure 1 to the positions shown in Figure 2. As shown therein, the lower end of the elastomer mass 7 can freely enter the aperture 6. As this movement occurs, the resilient mass 7 is thereby compressed radially inwards. At the same time, by virtue of the frictional engagement between the inner reflex portions 3 *nd the rubbing strips δ, there is a degree of frictional sliding contact between these components, and at the same time some longitudinal compression of the resilient mass occurs.

A damping effect is therefore obtained from three factors, ie the radial and longitudinal deformation of the elastomeric mass 7- which results in energy dissipation on account of internal hysteresis losses (internal friction in the material), and also from the afore- said frictional sliding contact.

By appropriate choice of materials, the effect of the sliding friction can be varied - eg if polytetrafluoroethylene is used as the rubbing strip material, the sliding friction will be low, and the possibility of "stick-slip" will be reduced. As an alternative to the use of strips 8, a ring (not illustrated) presenting a concave outer surface could be provided at each axial location of the inner reflex portions 3* so that each reflex portion is positively located by a ring. The rings can be fixed, eg by insert moulding or by adhesive, to the elastomer mass 7 _* Frictional sliding contact would thus be minimised, so reducing wear, but the axial co preεsive effect on the elastomer mass would be increased. A similar effect could be obtained by use of individual concave

contact pieces fixed to the elastomer mass 7- one corresponding to each inner reflex portion 3 _*

It should be especially noted that the invention provides a suspension member having the inherent property that its stiffness increases as the compresεive deformation increases.