Ignition cable terminal construction

Abstract

A method and means for improving the connection between a resistive core ignition wire and a terminal is disclosed. The improvement comprises placing a conductive metallic band around the outer insulation of the wire after exposing the core, and folding the core back over the conductive metallic band before crimping the terminal in place. The invention is best suited for use with ignition wire of the type having a conductive elastomeric or polymeric coating around the central core, and eliminates possible loss of electrical contact between the core and the terminal which may occur due to plastic deformation of the wire at elevated temperatures.

Description

FIELD OF THE INVENTION

The present invention relates generally to termination of ignition cable, and more particularly to strip-and-fold-back termination of resistive core ignition cable.

DESCRIPTION OF THE PRIOR ART

Resistive core ignition cables for use in automotive vehicle ignition systems to dampen current oscillations following the firing of a spark plug, and minimize electromagnetic interference to electronic receiving equipment, such as radios and televisions, conductor, having a wrap of metallic foil around the outer insulation, according to the invention.

FIG. 3 is a perspective view of an ignition cable according to the invention, with a wrap of metallic foil, and with the central resistiveFIGS. FIG. 1, with central core 2 and layer 3 exposed and folded back over a sheet material shown as metallic foil wrapping 6 and the outer insulation layer 5. This sequence of operations, without the step of wrapping the cable with metallic foil, is known as a "strip-and-fold-back" termination method.

FIG. 4 shows the ignition cable of FIG. 3 after an ignition terminal 8 has been clamped in place. Ignition terminal 8 includes terminal ferrule 7, adapted to be clamped to an ignition cable, and connector portion 9, adapted to connect to a conventional spark plug stud and including spring clip 10 adapted to retain connector portion 9 to a conventional spark plug stud. As shown in FIG. 4, clamping terminal ferrule 7 of ignition terminal 8 onto cable 1 causes elastic deformation of cable 1, including central core 2 and layer 3. Of course, a solid wire core or stranded wire core would not be subject to the same elastic deformation. In the absence of foil wrapping 6, when repetitively subjected to high temperatures, followed by cooling, this elastic deformation relaxes, and core 2 with layer 3 tends to embed itself into outer insulation layer 5, losing contact with terminal ferrule 7. Upon firing in this condition, a spark jumps between layer 3 and ferrule 7, which causes erosion of core 2 and layer 3, and eventual complete failure of the termination. In accordance with this embodiment of the invention, foil 6 deforms with wire 1, and maintains a conductive path between layer 3 and terminal ferrule 7 even if conductor 3 and terminal ferrule 7 are not in firm and direct contact, yielding a more reliable termination. This advantage is also attained when the invention is applied to solid wire core or stranded wire core types of ignition cable. Of course, with these types of cable used, there is no conductive layer surrounding the conductive core.

FIG. 5 illustrates a second embodiment of the invention. As shown in FIG. 5, a sheet material shown as a C-shaped conductive metallic strip 10 is placed over outer insulating layer 5, covering approximately 270° of the circumference of layer 5. This embodiment has been used to advantage with a C-shaped stainless steel strip 10, approximately 0.015 inches (0.038 cm) thick, having identations 11 adjacent either end, placed on cable 1 by pushing cable 1 through strip 10.

FIG. 6 illustrates a third and preferred embodiment of the invention. A piece of sheet material shown as strip 12 is a strip of stainless steel bent around cable 1, with overlapping ends 13. In a workable embodiment, strip 12 has been found formed from a strip of stainless steel, 0.156 inches (0.396 cm) wide, 0.012 inches (0.030 cm) thick, and approximatey 1 inch (2.54 cm) long, applied to cable 1 by automated equipment after the automated stripping operation, to form a band, with an overlapping section disposed so that layer 3 or a solid wire core or a stranded wire core will not be pinched by it when terminal ferrule 7 is applied, encircling cable 1.

As shown in FIG. 8, a terminal 8 including ferrule portion 7, is crimped in place over outer layer 5, core 2 and layer 3, and strip 12, with ferrule portion 7 causing primarily elastic deformation of cable 1. Strip 12 is also deformed, but this deformation does not relax when the terminal is repeatedly subjected to high and low temperatures, serving to maintain conductive layer 3 in firm contact with terminal ferrule portion 7, and provide additional electrical contact area between the portion of conductive layer 3 adjacent outer insulation layer 5, and terminal ferrule 7, over a substantial portion of its circumference. Therefore, the addition of strip 12 (or strip 10) to restive core ignition cable, solid wire core ignition cable or stranded wire core ignition cable can be quickly and conveniently performed with automated equipment in a high-speed mass-production line, and results in a substantial increase in reliability of the ignition cable assembly at a minimal additional expenditure.

It should also be noted that a wrapping, or even a small pad, of nonconductive sheet material placed between insulation layer 5 and conductive layer 3 will also prolong the life of the cable termination by locally increasing the force pressing conductive layer 3 against ferrule 7, and preventing the folded-back core from becoming embedded in the outer insulation. Although functional, this is less desirable since it does not provide an alternate conductive path between conductive layer 3 and ferrule 7.

It is to be understood that one skilled in the art may be capable of practising practicing and carrying out the invention in various ways, and with various modifications of the disclosed embodiments, without departing from the spirit of the invention and scope of the appended claims.

Claims

1. A method of attaching a terminal to an ignition cable for use with internal combustion engines, said cable having a central resistive conductive core, an inner insulation layer concentric with said core and an outermost insulating layer concentric with and surrounding said inner insulation layer, comprising the steps of;

removing a portion of said inner insulation layer and of said outermost insulating layer from said conductive core for a predetermined distance from an end of said cable to form an exposed core end portion;

placing a narrow strip of conductive sheet material in contact with at least a portion of the circumference of said outermost insulating layer adjacent said core end portion;

bending said core end portion back over said sheet material; and

clamping a terminal ferrule over said core end portion, said sheet material and said outermost insulation layer to make direct electrical contact between said core end portion and said ferrule.

2. A method according to claim 1, wherein:

said step of placing said sheet material in contact with said outermost insulating layer includes the step of wrapping a strip of metal foil around said outermost layer of said cable.

3. A method according to the claim 1, wherein:

said step of placing said sheet material in contact with said outermost insulating layer includes the step of placing a C-shaped metal strip around said outermost layer of said cable.

4. A method according to claim 1, wherein:

said step of placing said sheet material in contact with said outermost insulating layer includes the step of bending a metal strip around the periphery of said outermost layer of said cable to form a band around said cable.

5. An ignition cable assembly having an outermost insulating layer, an inner insulating layer concentric with said outermost layer and a central resistive conductive core and a terminal ferrule fastened to said cable at an end thereof, characterized in that a predetermined length of said conductive resistive core is exposed at said end of said cable, a portion of said exposed core is bent back over said outermost insulating layer, a narrow strip of conductive sheet material is interposed between said bent back portion of said exposed core and said outermost insulating layer, said sheet material, and said bent back portion of said exposed core, to form make a permanent electrical connection between said core and said ferrule, said sheet material being adapted to prevent plastic deformation of said cable due to elevated ambient temperature from affecting said electrical connection.

6. An ignition cable according to claim 5, wherein said sheet material is a narrow strip of conductive metallic foil wrapped around said outermost insulating layer.

7. An ignition cable according to claim 5, wherein said sheet material is a narrow conductive metal strip substantially concentric with at least one half of the periphery of said outermost conducting insulating layer.

8. A method of attaching a terminal to a cable, said cable having a central conductive core, and an outermost insulating layer concentric with and surrounding said central conductive core, comprising the steps of:

forming an exposed core end portion by removing said outermost layer from said central conductive core for a predetermined distance from an end of said cable; then

placing a narrow strip of conductive sheet material in a circumferential direction with respect to said cable and in contact with substantially more than half of the circumference of said outermost insulating layer adjacent said core end portion; then

bending said core end portion back over said sheet material; and then

clamping a terminal ferrule over said core end portion, said sheet material and said outermost insulation layer to make direct electrical contact between said core end portion and said ferrule.

9. A cable assembly having an outermost insulating layer and a central conductive core and a terminal ferrule fastened to said cable at an end thereof, characterized in that a predetermined length of said conductive core is exposed at said end of said cable, a portion of said exposed core is bent back over said outermost insulating layer, and a narrow strip of sheet material is disposed in a circumferential direction with respect to said cable and in contact with substantially more than half of the circumference of said outermost insulating layer and interposed between said bent back portion of said exposed core to form a permanent electrical connection between said core and said ferrule.