Ignition Cable

Abstract

An ignition cable having an interior conductive core directly and tightly engaged by surrounding insulation, the engaged layers of the core and insulation being of material that are relatively nonadherent.

Parent Case Text

This invention relates to ignition cables. This application is a continuation-in-part of my copending application, Ser. No. 121,859 filed Mar. 8, 1971 now abandoned.

Description

One usual construction of automobile ignition cable includes a central conductive core of glass filaments bonded together with conductive rubber, surrounded with one or more layers of rubber insulation. Such cables are connected to terminals by stripping the insulation from a length of the conductive core, bending back the stripped portion of the core, and then crimping the terminal tightly in position engaging the bent-over portion.

Providing a cable construction which provides the required substantially airtight core-to-insulation interface and, at the same time, permits relatively easy stripping, has presented a major problem. In the past, it has been possible to solve this problem only by either sacrificing the highly desirable tight interface, or by providing an extra, otherwise superfluous, layer of some type of special "releasing agent" between the core and insulation. A second problem, providing a core of the necessary conductivity, has required impregnation of the core fibers with conductive particles such as graphite. One typical construction is shown in U.S. Pat. No. 2,284,751 to Barker, wherein the glass core fibers are impregnated with conductive graphite particles and a "releasing layer," of conductive graphite which must be uniformly distributed and which affects the overall conductivity of the cable, is provided between the core and insulation.

Principal objects of the present invention include providing a cable which has all the desirable characteristics, i.e., airtight interface, suppression of interference and ease of stripping, of prior art constructions, but which does not require either the inclusion of any extra and special "releasing" layer between the core and insulation, or impregnation of the core fibers with conductive particles. Other objects include providing such a cable that is less expensive to manufacture than are existing constructions and which may be constructed using conventional equipment.

In one aspect, the invention features an ignition cable including a central conductive core directly and tightly engaged by a layer of surrounding insulation, the core comprising a plurality of flexible fibers bonded together with conductive rubber which defines the outer core surface, and the adjacent surfaces of the conductive rubber and surrounding insulation being relatively nonadherent. A second aspect features a core which is free from impregnating conductive particles and consists essentially of the flexible fibers and bonding conductive rubber layer. In preferred embodiments which include both aspects, there is featured a conductive silicone dispersion of conductivity matching that of the graphite-impregnated fibers bonding the fibers together and insulation comprising a layer of synthetic, hi-dielectric rubber surrounded by braided glass reinforcement, which is in turn surrounded by an outer jacket of synthetic rubber.

Other objects, features and advantages will appear from the following detailed description of preferred embodiments of the invention, taken together with the annexed drawing. The single view is a perspective, partially in section, of a flexible ignition cable constructed in accord with the present invention.

The cable, generally designated 10, has at its center a pluality of individual elements 12 of glass fibers impregnated and bonded together with a layer 14 of a conductive silicone dispersion rubber (sold by Dow Corning Corp.). A layer 16 of insulating rubber, typically a hi-dielectric styrene butadiene rubber, is extruded directly over the outer cylindrical surface of conductive layer 14 so that the adjacent surfaces of the two layers, outer surface of conductive layer 14, and inner layer of insulating layer 16, tightly engage each other in an airtight manner. To increase the overall cable strength, a glass fiber overbraid 18 and an insulating rubber outer jacket 20 preferably are applied over insulation layer 16.

In a first preferred embodiment, glass fibers 12 are rendered conductive by impregnation with conductive graphite particles, and the conductivity of the silicone dispersion is matched to that of the graphite-impregnated fibers so that both layer 14 and impregnated fibers 12 have a conductivity in the range of 3,000 to 7,000 ohms per foot. In this first embodiment, the fibers 12, the impregnating graphite, and the bonding silicone dispersion of layer 14 together form the conductive core of cable 10.

In a second preferred embodiment, the core fibers 12 are free from impregnating conductive particles, and the conductive cable core is formed by fibers 12 and layer 14 alone.

In using cables of either embodiment, a length of the insulation, namely layers 16, 18, and 20, is stripped to expose the interior core, so that the stripped core portion may be bent back over the insulating outer layer and attached to a terminal. Although the adjacent surfaces of the core and insulation are in tight engagement, the material of the inner layer of insulation, layer 16, does not adhere to the material of the outer layer of the core, layer 14, thereby facilitating stripping of the insulation.

Other embodiments within the scope of the following claims will occur to those skilled in the art.

Claims

What is claimed is:

1. An ignition cable comprising:

a core; and,

insulation surrounding and tightly engaging said core,

said core comprising a plurality of flexible fibers bonded together with a conductive silicone dispersion rubber, said conductive rubber defining the outer surface of said core,

said insulation including a layer of insulating rubber defining the inner surface of said insulation, there being no intervening layer intermediate the inner surface of said insulation and the outer surface of said core whereby said surfaces directly engage each other, and directly engaging said outer surface of said core,

the conductive silicone dispersion rubber defining the outer surface of said core and the insulating rubber defining the inner surface of said insulation being relatively nonadherent whereby stripping of said insulation from said core is facilitated.

2. The cable of claim 1 wherein the interface between said surfaces is substantially airtight.

3. The cable of claim 1 wherein said core includes discrete particles of conductive graphite impregnating said fibers.

4. The cable of claim 3 wherein the conductivity of said conductive rubber and of said fibers impregnated with graphite are each in the range of 3,000 to 7,000 ohms per foot.

5. The cable of claim 1 wherein said insulating rubber layer is synthetic, hi-dielectric rubber and, the interface between said surfaces is substantially airtight.

6. The cable of claim 1 wherein the conductivity of said conductive rubber is in the range of 3,000 to 7,000 ohms per foot.

7. The cable of claim 1 wherein the insulation includes at least two layers of insulation and a layer of reinforcing braid intermediate said layers of insulation.

8. The cable of claim 7 wherein said conductive rubber has a conductivity matching the conductivity of the other portions of said core.

9. The cable of claim 8 wherein the inner one of said layers of insulation is a synthetic, hi-dielectric rubber.

10. The cable of claim 8 wherein the inner one of said layers of insulation is a hi-dielectric styrene butadine rubber.

11. The cable of claim 10 wherein the interface between said surfaces is substantially airtight.

12. The cable of claim 1 wherein said core is free from conductive particles impregnating said fibers and consists essentially of said fibers and said conductive rubber.

13. The cable of claim 12 wherein the interface between said surfaces is substantially airtight.

14. The cable of claim 12 wherein the conductivity of said conductive rubber is in the range of 3,000 to 7,000 ohms per foot.

15. The cable of claim 12 wherein said insulation includes at least two layers of insulation and a layer of reinforcing braid intermediate said layers of insulation.

16. The cable of claim 15 wherein the inner one of said layers of insulation is a synthetic, hi-dielectric rubber.

17. The cable of claim 16 wherein the inner one of said layers of insulation is a hi-dielectric styrene butadine rubber.

18. The cable of claim 17 wherein the interface between said surfaces is substantially airtight.