A METHOD OF MAKING A HIGH TENSION IGNITION CABLE

Abstract: A tension member (1) consisting of organic or inorganic fibrous material is covered by an vulcanizable elastomer compound containing fluorinated elastomer, vulcanizing agent, ferromagnetic material and anti-oxidant by an extrusion process under condition which restrains vulcanization of the elastomeric ingriedients, followed by winding fine wire of resisive conductor (3) in a way that enough tension is imposed in order to embed each turn of the resistive conductor (3) into the layer (2) having still plastic nature. The cable core ( 3 ) thus formed is subjected to the seond extrusion process of an electrical insulating material, which is vulcanized at an elevated temperature under steam atmosphere while the same will take place in the plastic layer (2) made by the first extrusion. An overbraid (5) and a plastic sheath (6) are formed over the electrical insulation layer (4) for protection purposes. The method of producing high tension ignition cable with excellent electro-magnetic and mechanical properties is disclosed. Also discribed are the cable configuration according to the method of the present invention. Finally the high tension ignition cable manufactured by the method of the present invention, especially according to the specific way of manufacturing the same as described in the preferred embodiments of the present invention is also claimed.

Description: Summary of the Invention An object of this invention is to provide a method of making a high tension ignition cable with an increased value of inductance and with enough mechanical properties which makes ordinary cable connection possible by removal of additional layers (insulation (4), overbraid (5), and sheath (6)) from the cable core ( 3 ) without causing any fluctuation of coil structure once formed. Desired electrical properties are obtaind by extruding unvulcanized fluoro elastomer compound over the tension member (1) of preferrably aromatic polyamide fiber yarns as a tension member (1), followed by winding a fine resistive conductor (3) made of nichrom (Ni-Cr-Fe) or stainless steel in a coil form with minimum gap between turns over the extruded, unvulcanized plastic layer (4). The fluoro elastomer compound is substantially composed of fluoro elastomer, ferromagnetic material, vulcanizing agent, anti-oxidant, and the fillers and additives if necessary and these constitute the cable core ( 3 ) of ignition cable. The cable core ( 3 ) is then vulcanized simultaneously after extruding an electrical insulation compound over it at an elevated temperature under steam atmosphere. Each turn of the fine wire of resistive conductor (3) has been embedded into the uncured plastic layer (2) and has become integrated into one coil form after vulcanization takes place. This structure enables the cable core ( 3 ) to be taken out at the cable end for connection purpose. Object of the Present Invention Object of the present invention is to provide a method of manufacturing high tension ignition cable having rigid, and closely wound coil structure of resistive conductor (3) between the plastic layer (2) of cable core ( 3 ) and the insulation layer (4). Another object of the present invention is to provide a coil of resistive conductor (3) which is wound around the plastic layer (2) with minimum distance between turns, embedded in the plastic layer (2) and is capable of maintaing it's original coil structure even after being exposed against thermal treatment during the extrusion process of an insulation layer (4). Another object of the present invention is to afford the product ignition cable with very high degree of inductance per unitary cable length, and thus excellent noise-free ignition cable for motor vehicle is achieved. The above and further advantageous features of the present invention will be more fully explained by the following description of preferred embodiments of the present invention when the same is understood in connection with accompanying drawings. Background of The Invention In the conventional method of making high tension ignition cable, the first process establishing a layer (2) of plastic materials with or without a ferromagnetic material such as ferrite powder over a tension member (1) made of yarns of high tensile material. The plastic materials commonly used are silicone rubber, chlorinated polyolefinic elastomers including chlorinated polyethylene and they are extruded over the tension member concentrically, followed by cross-linking the plastic material at elevated temperature under pressure. The second process is coiling of resistive conductor (3) around the extruded plastic layer (2) and the third processes is making an insulation layer (4), overbraid (5) and finally formation of protective plastic materials as a sheath (6) in it's outermost circumference of the cable core ( 3 ). Technical approach has been taken to increase inductance of the cable per unitary length. It is recently proposed for that purpose that the resistive conductor (3) should be wound more closely to provide more turns around the plastic layer (2). A problem has been raised, however, that initially formed coil of resistive conductor can easily be deformed by the step of extrusion of elastomeric polymer over it resulting in fluctuation of coil alignment and contact between coil-turns causes the cable inductance higher than that was expected on a design-stage. Some of the alternatives for preventing the coil alignment from fluctuation from were disclosed in previous patent publications. In Japanese Utility Model Unexanmined Publication No.146,812/1984 teaches coil configuration which was wound around insulation layer of the core of high tension ignition cable with fin-like portions which are outwardly projecting from the cable surface and are extending along the longitudinal surface of the insulation. By providing such a surface the wound coil is, as a whole, embedded in the insulation and thus it's wavering is restricted. In another instance which was disclosed in Japanese Patent Unexamined Publication No.106,884/1979, resistive conductor was wound over the preheated, softened surface of thermoplastic insulating material which had been extruded concentrically over high tension ignition cable core. The resulting coil structure was kept embedded when the insulation surface was chilled. Both alternatives under discussion were unsuccessful to achieve unchanged coil structure after extrusion of sheath elastomer since in the first example utmost high tension was required for resistive conductor in order to obtain rigid coil structure, and since in the second example to obtain uniformly softened elastomer surface was hardly successful. Brief Description of The Drawings Fig. 1 (a) is a schematic diagram showing a method of making a plastic layer (2) over a tension member (1) by an extrusion process in the present invention. Fig. 1 (b) shows a winding process for resistive conductor (3) over the plastic layer (2) in the present invention. Fig. 1 (c) shows a schematic diagram showing a method of making an insulation layer (4) over the cable core ( 3 ) by an extrusion process in the present invention. Detailed Description of The Preferred Embodiment Referring to the drawings the mothod of the present invention is described in details. To an extruder (12), as can be seen in Fig. 1 (a), a tension member consisting either of organic or inorganic fibrous material was introduced out of a supply spool (11). The suitable tension member is selected from such fibrous materials as Kevlar, E.I. Dupont Nemours and Company, glass fiber yarns, or boron fiber, in a form of either yarns or strands. To the extruder (12) a homogeneous compound of a fluorinated elastomer such as Aflas, grade 150E or 150L, of Asahi Glass Kogyo, Japan, was charged. The preferred compound of fluorinated elastomer consists of the following ratios of the ingredients: The best results were obtained when the fluorinated elastomer compound contains about four times the weight ratio (400 parts by weight) of powdered ferrite to that of the elastomer (100 parts by weight) and a small quantity of vulcanizing agent. Extrusion of the elastomer compound was carried out over the tension member (1) while keeping the extrusion temperature in a range which did not exceed about 100°C, measured at die and nipple of the extruder, in order to avoid initiation of cross-linking due to being subjected to heat. The tension member covered with unvulcanized plastic layer, was wound up around a take-up spool (13). Fig. 1 (b) illustrates the winding mechanism of the resistive conductor (3) over the plastic layer (2). As shown in the figure, the cable core consisting of a tension member (1) and a plastic layer (2) was lead into the center hole of the rotating axis of rotor head (22) of a winding device and was pulled up vertically by a pair of capstans (15) and (16). A fine resistive conductor (3), of 20 to 100 µm in diameter , made of a resistive metal such as Nichrome Resistance Wire, Manganin Resistance Wire, or stainless steels, was drawn out of the supply bobbin (24) and was wound around the plastic layer (2) as it proceeded in a coil form with small gaps between neighboring turns. As described before, the plastic layer (2) of fluoro elastomer had not been subjected to vulcanization yet and, therefore, it retained plasticity of the surface of the layer (2) and the wound coil was embedded in the plastic layer (2) and thus smooth, evenly and closely coiled wire turns cover the outer surface of the plastic layer (2) with homogeneous, slight roughness so that the second, extrusion of electrical insulation material could be applied evenly and without serious fluctuation of the coil structure once formed. Fig. 1 (c) illustrates a process for providing the cable core ( 3 ) with an insulation layer (4) utilizing an extruder (19). The cable core ( 3 ) having a closely wound coil structure around it's outer surface was supplied out of the take-up reel (17) of the core (3) in Fig. 1 (b) to the extruder. The extruder (19) was charged with an electrical insulating thermoplastic polymer compound. The suitable polymer compound for providing the cable core ( 3 ) with an insulation layer (4) was composed of thermo plastic polymeric material, cross-linking or vulcanizing agent, anti-oxidizing agent (s) and inorganic fillers if necessary. The thermoplastic polymeric material was selected from EPDM, polyethylene, or silicone resins. In an vulcanizer (20) the product was subjected to continuous heat treatment at about 200°C for about 40 seconds under steam atmosphere and vulcanization took place at both the plastic layer (2) and the insulation layer (4) simultaneously. The vulcanized cable product was taken up by a take-up reel (21) followed by over-braiding (5) of organic/inorganic yarns and finally, outermost protective sheath (6) of the thermoplastic resin, preferrably of polyvinyl chloride was formed over the overbraid (not shown in the figures). Advantages of The Present Invention In Fig.2 a longitudinal cross-sectional view of the product, high tension ignition cable manufactured by the method of the present invention is illustrated. In the left side cable end portion insulation layer (4), protective sheath (6) and overbraid (5) of fibrous material were removed from the cable for connection purpose. As the cable core ( 3 ) and the plastic layer (2) were tightly integrated by the closely wound coil structure of the resistive conductor (3) which was embedded in the plastic layer (2) giving a smooth, even surface, removal of the layer (4) associated with overbraid (5) and the protective sheath (6) was carried out quite easily without releasing the wound coil structure. According to the method of the present invention the cable core ( 3 ) with surrounding coil structure of the resistive conductor (3) is easily taken out and thus the high tension ignition cable is capable of being connected with a metallic terminal by a conventional method such as crimping described in U.S. Patents 3,787,800 and 3,284,751. Another advantage of the method of the present invention is that since the plastic layer (2) has not yet been cross-linked when the coil structure is formed, it allows for a person of ordinary skill to wind such a fine resistive conductor as 20 to 100 µm in diameter with close turns. When it was done on the surface of a cross-linked elastomer, each of the turns of the coil had not been embedded in the insulation layer (2) since less degree of plastic nature existed than it was in the case of unvulcanized material. A large amount of magnetic ingredients in the cable core improves noise attenuation characteristic of the ignition cable while it will usually deteriorate physical properties of the elastomeric plastic layer (2). According to the extensive study of the inventor it has been proved that the cross-linked fluorinated elastomer maintains its tensile strength of 40 kgs and elongation 200% of the original even though 400 parts by weight of powdered ferrite were compounded with 100 parts by weight of the fluorinated elastomer. It is clearly understood that according to the method of the present invention a high tension ignition cable having high value of inductance due to the closely wound coil structure of resistive conductor and good attenuation characteristics derived from ferromagnetic ingredients in the cable core associated with desirable physical properties was obtained. Furthermore cable connecting operation through conventional insulation removal is successfully carried out. Numerals in The Drawings 1. tension member 2. plastic layer 3. resistive conductor 3 . cable core 4. insulation layer 5. overbraid 6. protective sheath 11. supply spool 12. extruder 13. take-up spool 14. cooling bath 15. capstan 16. capstan 17. take-up reel 18. 19. extruder 20. steam vulcanizer 21. take-up reel 22. rotor head 23. wire guide 24. supply bobbin

Claims: A method of making a high tension ignition cable, which comprises: Advancing a tension member through a device for extruding a fluoro elastomer compound containing fluoro elastomer, vulcanizing agent, powdered ferromagnetic material, antioxidant, and other additives when necessary; Extruding the elastomer compound around the tension member under thermal and atmospheric condition where no vulcanizing or curing of the elastomer ingredients will take place during this first extrusion process; Winding a resistive conductor around the plastic layer of the unvulcanized fluoro elastomer with enough tension to enable each turn of the wound conductor to be embedded in the plastic layer to form a coil on the outer surface of the cable core; Providing the cable core with a layer of thermoplastic insulating polymer by extruding a compound containing a polymeric material, vulcanizing or cross-linking agent, antioxidant, and other additives when necessary, by the second extrusion process; Vulcanizing or Cross-linking the product under steam at elevated temperature where the same will take place in the fluoro elastomer formed by the first extrusion process; Providing the insulated cable core with protective layers of overbraid made or organic/inorganic yarns and a sheath of thermoplastic polymeric material. The method of making a high tension ignition cable as defined in claim 1 wherein the tension member is yarn or strands made of aromatic polyamide fiber. The method of making a high tension ignition cable as defined in claim 1 and claim 2 wherein the fluoro elastomer compound used for the first extrusion process contains the main ingredients in a parts by weight ratio of: The method of making a high tension ignition cable defined in claim 1 wherein the resistive conductor is selected from resistance wires of Nichrome Resistance Wire, Manganin Resistance Wire, or wire of stainless steels. The method of making a high tension ignition cable as defined in claim 1 wherein the insulation layer of the cable core is made by extruding a compound of a curable thermoplastic polymeric material selected from those of polythylene, EPDM (Ethylene Propyrene Diene Mixture), and silicone resins. The method of making a high tension ignition cable as defined in claim 1 and claim 3 wherein the thermal and atmospheric condition under which the second extrusion process is carried out to meet those conditions for complete vulcanization or curing of the uncured fluoro elastomer in the cable core prepared by the first extrusion process.

Inventors: TERUTSUGU, FUJIMOTO
Applicants: SUMITOMO WIRING SYSTEMS, LTD.
Application year: 1987
Main classification: H01B13
IPC codes: H01B7, H01B13