Method of terminating wire wound type noise preventing resistance cable

Abstract: The end portion (a) of a wire wound noise preventing resistance cable (1) in which a resistance wire (3) is transversely wound around a core (2) formed from an elastomeric compound is terminated such that the resistance wire (3) is fully embedded in the core by applying heat and high pressure to the leading end that remains exposed after the cable is cut and the end portion thereof is stripped of a covering layer. This construction of the end portion of the core prevents unravelling of the resistance wire (3) and maintains a good electrical connection between the resistance wire (3) and a metal terminal (6).

Description: The present invention relates to an improved method of terminating a wire wound noise preventing resistance cable (hereinafter referred to simply as a "cable") for use in the ignition system of an engine for an automotive vehicle after the cable has been cut and stripped of the outer insulating cover at the end thereof. Generally, there are two types of method of terminating a wire wound noise preventing resistance cable of this kind: one method is referred to as a "contact pin type" in which an electrical connection between a solderless terminal and a resistance wire is attained via a contact pin disposed at the end of the resistance wire, and the other method referred to as a "folding type" in which a direct electrical connection between the terminal and the resistance wire is attained by removing an outer insulating cover from the end of the cable to expose a wire wound core therein and folding back the exposed wire wound core over the cable. The "contact pin type" method consumes labor in disposing a pin at the end of the resistance wire, and a superior electrical connection can be attained with the "folding type" method. Thus, the latter terminating method has been more and more utilized recently. For example, the folding and connecting structure of a strand type resistance wire is disclosed in U.S. Patent Nos. 3,787,800 and 3,266,008. However, in a case where the "folding type" method is used for terminating a wire wound type resistance cable, a resistance wire easily unravels when the end portion of the wire is stripped of the outer insulating cover, thereby causing leakage problems. In addition, it is known that a magnetic substance is included in the core of the cable of this type so as to improve the noise preventing capability. However, there is a drawback in that if a great quantity of magnetic substance is included in the core, the tensile strength and extensibility of the core is deteriorated, and cracks are generated during a terminating operation when the leading end of the wire wound core is folded back over the cable, the resistance wire being thereby broken. A general connecting structure for the end portion of a wire wound noise preventing resistance cable is disclosed in U.S. Patent No. 3,518,606, but there is no statement in regard to a method of preventing unraveling of a resistance wire in this patent. In order to solve the above drawbacks, the development of a new resistance cable has been desired in which a resistance wire is prevented from unraveling when removing the outer insulating cover from the end thereof, and in which a core has good mechanical properties such as the tensile strength and so forth. The inventor of the present invention discloses a method of manufacturing a resistance cable in which a resistance wire can be wound around a core in a compact fashion at a uniform pitch, and in which the resistance wire is prevented from unraveling in the official gazette of Japanese Patent Public Disclosure No. 16891/1988. In the cable manufactured in accordance with the method disclosed in the above official gazette, since a core is made from a fluorine rubber compound by extruding the same in an unvulcanized state, and since a resistance wire is wound around the core so made, the resistance wire is partly embedded in the surface of the core. Due to this construction, with the resistance cable disclosed in the official gazette, even when extruding an insulating cover, as well as removing the insulating cover from the end of the resistance cable, the resistance wire that is wound around the core in a compact fashion is prevented from being displaced and/or unraveling. In addition, although fluorine rubber is a compound that contains a great quantity of magnetic substance, it remains superior in regard to tensile strength, extensibility and so forth even after it has been vulcanized, the core being thus made free from the above-mentioned cracking problem. However, although it is possible to solve the unraveling problem arising at the time of removing the outer insulating cover, it often happens during a cable-terminating operation after the removal of the outer insulating cover, especially, when a solderless terminal is manually press fitted over the end of the cable that the hand of a worker touches the exposed wire wound core, thereby often causing the leading end of the resistance wire to unravel. With a view to solving the above-mentioned problem, an adhesive is conventionally applied to the leading end of the wire wound core that is exposed by removing the outer insulating cover so as to prevent unraveling. However, with this method in which an adhesive is applied to the wire wound core there are drawbacks in that the application of adhesive to the wire wound core takes time and that electrical connection errors between the terminal and the resistance wire are caused due to the application of adhesive to the portions needing no application of adhesive, thus making the quality of a product unstable. An object of the present invention is to obtain a method of terminating a wire wound noise preventing resistance cable in which unraveling of a resistance wire is well prevented and in which a proper electrical connection between the resistance wire and a metal terminal is well maintained. The present invention is characterized in that a resistance wire wound around a core formed from an elastomeric compound is fully embedded into the core that is subjected to a plastic deformation by applying heat and high pressure to the exposed leading end of the wire wound core after a resistance cable having therein such a core is cut and stripped of the outer insulating cover. It is preferable that the elastomeric compound used is a fluorine rubber compound. When applying heat and high pressure to the leading end of the wire wound core, the core is softened and subjected to a plastic deformation. When the core is plastically deformed, the resistance wire wound around the core so deformed is then fully embedded in the core, thus preventing the unraveling of the resistance wire from the leading end of the core with an electrical connection with the terminal being attained by the resistance wire wound around the portion of the core where the above-mentioned heat and high pressure is not applied. Fig. 1 shows an embodiment of a terminating method according to the present invention; Fig. 2 is an enlarged cross-sectional view showing the portion of a cable that is terminated by utilizing the terminating method of the present invention; Fig. 3 is an enlarged cross-sectional view showing the portion of the cable over which a metal solderless terminal is fitted; and Fig. 4 is a graph showing the temperature characteristics of a fluorine rubber used in the embodiment of the present invention. Referring to Figs. 1 to 4, an embodiment of a method of terminating a wire wound noise preventing resistance cable according to the present invention will now be described. In Fig. 2, reference numeral 1 denotes a wire wound noise preventing resistance cable, and a core 2, around which a wire is wound, of the cable 1 is formed from a fluorine rubber compound containing a certain quantity of ferrite [ferrite:fluorine rubber = 400:100 (part by weight ratio)]. The temperature characteristics of a fluorine rubber (produced by ASAHI GLASS CO., LTD.: AFRAS) used in the embodiment of the present invention are shown in Fig. 4. The core 2 is extruded and formed in an unvulcanized state, and a resistance wire 3 is transversely wound around the core 2 in such a manner that the resistance wire 3 is partly embedded in the core 2. In addition, a covering layer 4 comprising an insulation layer, a braid, a sheath and so forth is provided over the wire wound core 2, and afterwards, the cable so formed is vulcanized. As shown in Fig. 2, the cable 1 formed as described above is cut, and the covering layer 4 is removed from the end portion a (about 15 mm) of the cable 1 so as to expose the core 2 around which the resistance wire 3 is wound. The leading end b (about 3 mm) of the exposed end portion a is crushed by means of a press machine 5 as shown in Fig. 1. Subsequently, the exposed end portion a of the wire wound core 2 is folded back over the cable as shown in Fig. 3, and a metal terminal 6 is press fitted thereover. An electrical connection between the metal terminal 6 and the wire wound core 2 is attained via the portion c of the wire wound core 2 where the resistance wire 3 remains exposed. The press machine 5 is mounted on a cable cutting and stripping machine, and the cable 1 is automatically conveyed to the press machine 5 by means of a conveyor or the like after the covering layer 4 is removed from the end portion a thereof so as to be pressed. A heater, as a heating source, is installed in an upper die 7 of the press machine 5, and the upper die 7 is vertically moved by a hydraulic cylinder or the like. The temperature of the heater, pressing time and pressing pressure are adjusted such that the fluorine rubber compound constituting the core can be plastically deformed so that the resistance wire is fully embedded in the core. In the embodiment of the present invention, the high-pressing time, pressing pressure and the temperature for heating the portion to be crushed are 0.5 seconds, 4 kg/cm² and 100°C, respectively. In this embodiment, a fluorine rubber compound having superior mechanical properties is used as the best material for the core. However, other elastomers such as chlorinated polyethylene, polyolefin resin, EPDM rubber, silicone rubber and so forth may also be used. With the terminating method of the present invention, since the resistance wire may be fully embedded in the core only at the leading end, the resistance wire on the exposed portion of the core is prevented from unraveling even after the cable is cut and stripped of the covering layer, and an electrical connection between the press fitted metal terminal and the resistance wire can be attained as in the case of the prior art cables. In addition, the conventional process of applying an adhesive may be omitted.

Claims: A method of terminating a wire wound noise preventing resistance cable (1), said cable comprising a resistance wire (3) transversely wound around a core (2) formed from an elastomeric compound, the method including the steps of cutting the cable (1) and stripping a covering layer (4) from the end portion (a) thereof, CHARACTERISED IN THAT said resistance wire (3) is then fully embedded into said core (2) by applying heat and high pressure to the exposed leading end (b) thereof. A method as set forth in Claim 1, wherein said elastomeric compound is a fluorine rubber compound.

Inventors: FUJIMOTO TERUTSUGU, FUJIMOTO, TERUTSUGU
Applicants: SUMITOMO WIRING SYSTEMS, SUMITOMO WIRING SYSTEMS, LTD.
Application year: 1990
Main classification: H02G15
IPC codes: H01R4, H01B7, H02G1, H01R11