LEAF SPRINGS OF COMPOSITE MATERIAL

Abstract: A composite spring with a bush (14), specifically a metal-rubber-metal bush (16, 17, 18) held to an end portion (10) of the spring by a clamping member (11, 21), for receiving a mounting bolt, wherein the clamping member is projection welded to the bush to prevent movement of the bush relative to the clamping member. The use of projection welding to hold the bush and clamping member together ensures that the bush is not degraded by heat from the welding operation.

Description: Leaf Springs of Composite Material This invention relates to leaf springs made of compo¬ site, fibre reinforced resin, material. More particularly, the invention relates to means by which such a spring is secured to a motor vehicle or other apparatus or equipment where it is to be used. It has been proposed, in EP-A-0070122, that a bush for receiving a mounting bolt or like element can be secured to a composite leaf spring by being positioned within a transverse recess at an end portion of the spring, and clamped to it by a clamping member, eg of steel. It is important that the bush is not able to move relative to the spring and clamping member in service, and the present invention aims to satisfy this requirement. It is proposed in EP-A-0070122 that the bush can interfit mechanically with the clamping member, or be adhesively secured thereto, to prevent endwise movement of the bush, but such expedients can be unreliable or involve extra operations in production. According to the invention, we provide a composite spring including at least one end fitting comprising a bush adapted to receive a mounting bolt or the like and secured to the spring by a clamping member extending around part of the periphery of the bush and embracing a part of the spring and secured thereto, wherein the clamping member and bush are held together by projection welding. The bush is preferably a metal-rubber-metal bush, such as is commonly used in spring mounting applications for motor vehicles. It has been found that by use of the technique of projection welding for securing the bush to the cl nping member, damage to the rubber clement of the bush due to heat from the welding process does not occur, or is negligible. This is because of the very short length of time for which the welding current flows during the welding operation, and the "heat sink" effect of the metal element of the bush. Even if some degradation of the rubber in the bush does occur it is extremely localised and does not affect the performance of the bush as a whole. If the spring is one intended for heavy duty application, eg in a large commercial vehicle, large forces have to be resisted and a clamping member of large dimensions may be necessary, such that even to projection weld it to the bush may heat the bush sufficiently to cause damage. In this case, the invention provides that a number of individual clamping members may be utilised, disposed alongside one another and each held to the bush by projection welding, such that the welding of each clamping member to the bush individually does not cause sufficient heating thereof to damage the bush. In use, one clamping member would be projection welded to the bush, after which a cooling time would be allowed before the next clamping member would be welded. Thus an assembly sufficient to take the loads encountered in service can be built up, without damaging the bush. An additional advantage is that a less powerful welding machine would be required to weld the individual clamping members to the bush, compared with that which would be necessary if a single large clamping member were used. The indivdual clamping members may be connected at a positional position remote from the bush, eg by spot or projection welding a further element to them. The position of such further element must be sufficiently far from the bush for heat generated during welding thereof not to affect the bush. - .. . . The invention will now be described by way of example with reference to the accompanying drawings, of which Figure 1 is an elevation of the end of a spring according to the invention Figure 2 is a section on the line 2-2 of Figure 1. Figure 3 is a plan view of a modified embodiment of the invention. Figure 4 is a view of a spring. Referring firstly to Figure 1 of the drawings, this shows the end portion of a leaf spring 10 of composite, fibre reinforced resin, material. Adjacent its end, the spring is formed with a transverse recess in which lies a bush 14 for receiving a mounting bolt or the like. The spring extends around the periphery of the bush to a point 13 » so that the bush is securely located lengthwise of the spring. A clamping element 11 of sheet metal extends around the end of the portion of the spring and the bush 14 to hold the bush to the spring. A fastener 12 such as a bolt or rivet secures the clamping element 11 to the spring. The bush 14 is projection welded to the clamping element at 15. The bush is a conventional metal-rubber-metal bush. Referring to the section shown in Figure 2 this clearly shows the construction of the bush 14 with inner and outer tubular metal elements 16, 17 and the intervening rubber element 18. For welding by the technique known as projec¬ tion welding, the clamping element 11 is provided externally with indentation 19 which appear inside the clamping element as projections which are the sole contact areas between the clamping element and outer metal element 17 of the bush for welding. With these components in their required relative position, electrodes are applied to them and a welding current passed therebetween. Welding occurs where the projections inside the clamping element contact the bush, where the entire current must flow between these components. The result is that the bush is fixed to the clamping element, and thus securely fixed to the spring in service. Referring now to Figure 3 of the drawings, this is a plan view of an end portion of a leaf spring 20, having two clamping members 21 disposed alongside one another and embracing a bush and spring end portion in the same manner as the embodiment of Figures 1 and 2. The clamping members 21 are secured to the outer tubular metal element of a metal-rubber-metal bush by projection welds 29. The inner tubular metal element of the bush is shown as 26. The clamping members 21 are held together by a member 22, spot or projection welded to the clamping members at a distance from the bush. As referred to above, the embodiment of Figure 3 is useful where a single clamping member, having the same dimensions as clamping members 21 together, may be such that projection welding it to the bush may heat the bush sufficiently to cause damage. It is possible to avoid this by welding the clamping members 21 individually to the bush, with a suitable cooling time between welding operation. Referring now to Figure 4 of the drawings, this shows a composite leaf spring suitable for installation in a motor vehicle having two end fittings each of the type described above.

Claims: CLAIMS 1. A composite spring including at least one end fitting comprising a bush (14) adapted to receive a mounting bolt or the like, held to the spring by a clamping member (11, 21) extending around part of the periphery of the bush and embracing a part of the spring and secured thereto, characterised in that the clamping member (11, 21) and bush (17) are held together by projection welding (19, 29). 2. A composite spring according to -Claim 1 further characterised in that the bush is a metal-rubber-metal bush (16, 17, 18). 3. A composite spring according to Claim 2 further characterised in that there are a number of clamping members (21) disposed alongside one another and each held to the bush by projection welding (29), such that the welding of each clamping member to the bush individually does not cause sufficient heating of the bush to damage it. 4. A composite spring according to Claim 3 further characterised in that said clamping members are secured together (22) at a position remote from the bush. 5. A composite spring according to any of the preceding claims further characterised in that said bush lies within a transverse recess at an end portion of the spring.

Inventors: DEVILLE ARTHUR ERNEST, DEVILLE, ARTHUR, ERNEST
Applicants: GKN TECHNOLOGY LTD, GKN TECHNOLOGY LIMITED
Application year: 1984
Main classification: F16F1
IPC codes: B60G11, F16F1