Process for manufacturing a compact-stranded wire conductor for wire harnesses

Abstract: A compact-stranded wire conductor (1) made by circularly compressing peripheral element wires (3) provided around a central element wire (2), in which the central element wire (2) is selected to have a hardness higher than that of the peripheral element wire (3) in order to achieve higher strengths for small diameters of the wire conductor.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a process for forming a compact-stranded wire conductor and in particular to forming acompact-stranded wire conductor to be used in wire harnesses for motor vehicles. Description of the Prior Art Wire harnesses are typically used in the various electrical systems of motor vehicles, and with the growing advancement in the technology of such electrical systems, the number and complexity of associated wirings has had to increase accordingly. This increase in complexity is especially evident for the-growing number of electrical systems that operate on low electrical currents, such as indicator lights and the like. For this reason, the current trend has been to try to reduce the overall weight of the wire harness by reducing the diameter of the individual wire conductors comprising the wire harness. In response to the current trends mentioned above, a thinner wire harness was proposed by making use of compacted-stranded wire conductors, that is, wire conductors made by circularly compressing a bundle of individual wires (Japanese Laid-Open Patent Application No. JP-A-60-91573). The reasoning behind this suggestion was that since the diameters of the compact-stranded wire conductors can be made relatively small, thein use would therefore lead to an overall reduction in the size of the wire harness. Now, in order to gain a better understanding of the prior art compact-stranded conductor, a cross sectional view of one example of such a conductor is illustrated in Fig. 1. As shown in this figure, a compact-stranded wire conductor 1 comprises a central element wire 2 and peripheral element wires 3 provided around the central element wire 2, with spaces 4 and 4' existing between the element wires 3 and the central element wire 2 and between the element wires 3 themselves, respectively. In the example described above, Fig. 1 further illustrates that the element wires 2 and 3, having originally been circular in cross section, become deformed when they are circularly compressed, such as by die drawing, to form the the compact-stranded wire conductor 1. As a result of this deformation, the spaces 4 and 4' are reduced in size relative to what they were before the element wires 2 and 3 were circulary compressed, thus leading to reduction in the overall size of the wire conductor 1. Unfortunately, however, the prior art compact-stranded wire conductors have many inherent disadvantages because they employ wires made from the same material (such as hard or soft copper) and having the same physical properties for both the central element wire 2 and the peripheral element wires 3. These disadvantages can best be explained by referring once again to Fig. 1. Namely, as shown in Fig. 1, both the central element wire 2 and the peripheral element wires 3 undergo deformation and thereby take on somewhat random shapes, which in turn causes the spaces 4 and 4' to become a little scattered and also take on somewhat random patterns. As a result, the compact-stranded wire conductor so produced does not possess sufficient overall strength if its diameter is made relatively small, and it is even possible that the electrical conductivity of one or more of the element wires could be adversely affected due to such deformations. Moreover, the slightly random nature of the deformations tends to give rise to a loss in the overall circularity of the wire conductor, which necessitates the provision of a thicker layer of insulating material in order to properly cover the wire conductor. GB-A-2 160 554 describes a method of producing a compact conductor by laying-up pre-shaped wires around a circular central conductor. SUMMARY OF THE INVENTION In view of the disadvantages of the prior art compact-stranded wire conductors, it is an object of the present invention to provide a method of forming a compact-stranded wire conductor having sufficient strength and electrical characteristics even when the wire conductor is formed to have a relatively small diameter. It is another object of the present invention to provide a method of forming a compact-stranded wire conductor having high circularity. It is still another object of the present invention to provide a method of forming a compact-stranded wire conducto requiring only a thin layer of an insulation covering. It is still a further object of the present invention t provide a method of forming a compact-stranded wire conducto in which only the peripheral element wires undergo substantial deformation when the compact-stranded wire conductor is manufactured. The objects stated above are solved by a process for forming a compact stranded wire comprising: providing a central element wire enclosing the central element wire with a plurality of peripheral element wires; and compressing the peripheral element wires against the central element wire to reduce the size of the spaces between the wires characterized by providing a central element wire with a hardness greater than that of the peripheral element wires. The foregoing, and other objects, features, and advantages of the present invention will become more apparent from the detailed description of the preferred embodiments taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross-sectional view of a prior art compact-stranded wire conductor. Fig. 2 is a cross-sectional view of a compact-stranded wire conductor according to the present invention. Fig. 3 is a graph showing the associated limiting currents for the various diameters of the same wire conductors shown in Fig. 4. Fig. 4 is a graph showing the associated breaking loads for various diameters of two compact-stranded wire conductors according to the present invention in comparison with defined standards. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to Fig. 2, one embodiment of the present invention will be described. Namely, as shown in Fig. 2, a compact-stranded wire conductor 1 comprises a central element wire 2 and peripheral element wires 3 concentrically placed around the central element wire 2. In this construction, either single or stranded wires can be employed for both the central element wire 2 and the peripheral element wires 3, but any and all choices made must be such that the central element wire 2 has a higher hardness than that of the peripheral element wires 3. In the embodiment described above, the use a wire having both high hardness and high strength for the central element wire 2 is preferred, such as a wire made from stainless steel, copper alloy or the like. In this connection, it should be noted that the choice should be made even at the sacrifice of a small loss in the limiting current, because for low currect electrical systems such a minor loss will have no adverse effect. For the peripheral element wires 3, soft or hard copper wires or copper alloy wires may be used so long as they have hardnesses smaller than that of the wire chosen for the central element wire 2. However, it is recommended that wires having slightly high hardnesses, such as stainless steel wires, be used for the peripheral element wires 3 when a high-hardness copper alloy wire is being employed for the central element wire 2. As a direct consequence of the choices for wires based on hardness mentioned above, it can be seen from Fig. 2 that only the peripheral wires 3 undergo substantial deformation when the wire conductor 1 is circularly compressed during its manufacture. Moreover, since these deformations are roughly uniform for each of the peripheral wires 3, there occurs a reduction in the dispersion and size of spaces 4 and 4' existing between the element wires 3 and the central element wire 2 and between the element wires 3 themselves, respectively. The end result is that the wire conductor 1 will have both high strength and high circularity. Now, for the purpose of demonstrating the features and advantages of the present invention described above, several examples of the present invention were made and tested against prior art standards both in terms of strength and limiting current for various diameters thereof. The particular construction of these examples and standards, i.e., examples A and B and standards C and D, is listed in Table 1, with the resulting test data thereof being displayed in Figs. 3 and 4. With reference first to Fig. 3, the limiting currents of examples A and B and standards C and D are shown for various diameters, with the dashed line P indicating a minimum limiting current of 3 amperes re quired for wire conductors which are to be used in wire harnesses for motor vehicles. For the data shown, tests were carried out under conditions in which the maximum temperature and the ambient tem perature of the conductor during use were 80°C and 60°C, respectively. From Fig. 3, it can be seen that even though the limiting currents of examples A and B are slightly smaller than those of standards C and D, these currents are still above the minimum limiting current line P. Thus, these examples show that the wire conductors made according to the present invention can achieve sufficient electrical current flow, even when the diameter of the wile conductor is reduced to about 0.5mm. Next, with reference to Fig. 4, there is shown the associated breaking loads for various diameters of the examples A and B and standards C and D. In this graph, L represents a minimum breaking load a 10kgf that must be achieved in order for the wire conductor to be considered to have adequate strength characteristics. As can be seen from Fig. 4, in order for standard C to have sufficient strength so as to meet the mini mum breaking load requirement of 10kgf, it must have a diameter of at least 0.7mm. However, a direc comparison reveals that example A can achieve the same strength requirement with a diameter of only 0.5mm. This means that it is possible to achieve a reduction in diameter of about 29%, and consequently a reduction in cross-sectional area of about 50%. Thus, it is quite clear that present invention allows high strength to realized for very small diameters of a wire conductor. Finally, it is to be understood that even though the present invention has been described in its preferred embodiments, many modifications and improvements may be made without departing from the scope of the invention as defined by the appended claims.

Claims: A process for forming a compact stranded wire comprising: providing a central element wire (2); enclosing the central element wire (2) with plurality of peripheral element wires (3); and compressing the peripheral element wires (3) against the central element wire (1) to reduce the size of the spaces (4, 4') between the wires by substantial deformation thereof; characterized by: providing a central element wire (2) with a hardness areater than that of the peripheral element wires.

Inventors: IKEGAYA AKIRA, IKEGAYA, AKIRA
Applicants: YAZAKI CORP, YAZAKI CORPORATION
Application year: 1989
Main classification: H01B5
IPC codes: H01B5, H01B7