GB2109498A - Control cable - Google Patents

Abstract

A control cable comprises a flexible sheath (2), a liner (5) composed of acetal resin within the sheath, and a control wire (6) having a coating (9) of oil-filled polyethylene resin deposited thereon mounted in the liner for axial movement relative to the sheath and the liner. The selection of oil-filled polyethylene and polyacetal resins improves the durability of the cable at high temperatures. <IMAGE>

Description

SPECIFICATION Control cable This invention relates to control cables.

Conventional control cables, as for example disclosed in US Patent Specification No. 31 76538 or British Patent Specification No. 1292597, comprise a flexible sheath composed, for example, of one or more helically wound wires. A liner of plastics material is positioned within the sheath and is either secured to the sheath or movable relative thereto depending upon whether the control cable is to transmit only tensional forces or both tensional and compressive forces. A wire having a coating of plastics material therein is mounted within the liner for axial movement relative to the sheath. The sheath and the wire can then be secured by appropriate end-fittings to a fixed and movable components respectively.

In motor vehicles the control cable is required to perform reliably over a large number of operating cycles. In some vehicles the control cable is subjected to high temperatures, for example where the control cable passes close to the engine of the vehicle.

We have found that the choice of materials for the liner and the coating in the wire affects durability of the control cable.

According to the present invention, there is provided a control cable comprising a flexible sheath, a liner composed of plastics material within the sheath, and a control wire having a coating of plastics material thereon mounted within the liner for axial movement relative to the sheath and the liner, characterised in that the coating on the wire is composed of a polyolefin resin and the liner is composed of an acetal resin.

Preferably the coating is composed of a high-density polyethylene resin which desirably incorporates a lubricant filler. Conveniently, the lubricant filler is in the form of a mineral oil entrapped within the micropores of the resin. Acetal copolymers are preferred for the material of the liner.

The invention is applicable equally to control cables adapted to transmit only tensile forces in the wire as to control cables adapted to transmit tensile and compressive forces in the wire.

A preferred embodiment of the invention will now be described by way of example only, with reference to the drawing which is an axial cross-section through a control cable in accordance with the invention.

Referring to the drawing, a control cable 1 adapted to transmit only tensile forces, such as encountered in motor vehicle handbrakes, comprises a flexible sheath 2 composed of two helically interwound strands 3,4, of equal circular radial cross-section. A liner 5 in the form of a tube composed of an acetal copolymer manufactured by Amcell Ltd. under the designation M25, is mounted loosely with the sheath 2. The acetal copolymer has a density of 1.4 g/cc, a Rockwell hardness of M78, and a Vicat softener point of 1 620C. A control wire 6 is mounted within the liner 5 for axial movement relative to the sheath 2 and the liner 5, as indicated by the arrow 7.The control wire 6 includes a braided wire core 8 which carries a thin coating 9 of an oil-filled polyethylene resin manufactured by Railko Ltd., under the designation Pal 01. This material has a density of 0.96 gm/cc, a Rockwell hardness of 27HRR, and a Vicat softening point of 1200 C.

The efficiency of the cable is measured by clamping the sheath of the cable in an S-shaped configuration, applying an input tensile load to one end of the control wire, measuring the output load at the other end of the control wire, and expressing the output load as a percentage of the input load. The durability of the cable is estimated by reciprocating the control wire for 60,000 cycles, the load in each cycle increasing smoothly from 0 to 1 650 Newtons. The travel of the control wire is increased from an initial 5 to 9 mm in the first 15,000 cycles to between 9 and 13 mm in the second 15,000 cycles, then to between 13 and 1 7 mm in the third 1 5,000 cycles and finally to between 1 7 and 21 mm in tife final 15,000 cycles. The efficiency of the cable is then measured after the durability test.

The initial efficiency of the cable was 86.0% on the final efficiency was 84.8%.

For the purposes of comparison, similar tests were carried out on control cables having a similar construction to that illustrated in the drawings, but incorporating liners 5 and coatings 9 of different materials. The results are tabulated below:

Efficiency Liner Coating Initial Final High density Nylon 84.8 82.9 polyethylene High density Oil-filled acetal 83.8 polyethylene copolymer Oil-filled Oil-filled acetal 81.5 polyethylene copolymer Acetal copolymer Nylon 81.5 It can be seen that the materials used in the cable of the present perform better than those used in the comparison tests.

Claims (4)

1. A control cable comprising a flexible sheath, a liner composed of a plastics material within the sheath, and a control wire having a coating of plastics material thereon mounted within the liner for axial movement relative to the sheath and the liner, characterised in that the coating on the wire is composed of a polyolefin resin and the liner is composed of an acetal resin.

2. A control cable according to claim 1 wherein the polyolefin resin is a high density polyethylene resin.

3. A control cable according to claim 1 or claim 2 wherein the polyethylene resin is oil-filled.

4. A control cable according to any one of claims 1 to 3 wherein the polyacetal resin is an acetal copolymer.