METHOD OF CONNECTING AN ELECTRICAL TERMINAL TO AN ELECTRICAL WIRE CABLE AND A WIRE HARNESS ASSEMBLY MANUFACTURED ACCORDING TO SAID METHOD

A method of connecting an electrical wire cable having a plurality of uninsulated wire strands to an electrical terminal is presented. The method includes the steps of crimping an electrical wire cable within a crimping feature of an electrical terminal having wire strands protruding from the crimping feature and fusing the wire strands of protruding portion, or “wire brush” so that the wire strands are in intimate contact, thereby eliminating voids between individual wire strands of the wire brush. The wires may be fused by laser welding, soldering, or brazing. The method may be especially beneficial for wire strands having an insulative oxide layer, such as aluminum. The bonding reduces the resistance between the wire strands due to insulating oxide layers on the surface of the wire strands and inhibiting of corrosion by eliminating inter-strand gaps where electrolytes in solution may enter and cause galvanic corrosion.

TECHNICAL FIELD OF THE INVENTION

The invention generally relates to method of attaching an electrical terminal to an electrical wire cable, and more particularly relates to a method of fusing wire strands of the cable protruding from the terminal so that the wire strands are in intimate contact, thereby eliminating voids between individual wire strands of the protruding portion.

BACKGROUND OF THE INVENTION

Aluminum wire cables are increasingly being incorporated in automotive wiring harnesses. There are several factors driving this trend. First, the market price of copper, traditionally used for automotive wiring, is significantly higher and more volatile than that of aluminum. Second, the weight of aluminum wiring is approximately half that of the equivalent copper wiring. The push for more fuel efficient vehicles is requiring weight to be taken out of the vehicle and aluminum-based wire cables provide a good opportunity to reduce weight by substituting aluminum cable for copper cable.

Aluminum does have some disadvantages in vehicle wiring. Aluminum cable typically has multiple strands in the wire cable to increase flexibility of the cable. Aluminum forms an oxide layer that has a lower conductivity than aluminum and is very hard. Because these aluminum oxides form almost instantaneously on the surface of the aluminum wires, individual wire strands in the cable do not connect well electrically to each other. Additionally, aluminum wire strands in a crimped connection can also deform over time due to stress relaxation and creep. As the aluminum wire in a termination changes shape, electrical resistance can increase causing increased connection resistance, heat build-up, and connector failure. Because of these challenges, conventional crimped connections to aluminum cable constructions with a large number of strands do not provide a robust low resistance connection that will withstand environmental exposure over time. Alternate connection technologies are required to help interconnect each strand in the cable core so they act as a single conductor. It may also be desirable to use existing terminals designed for copper cable connection systems to avoid the expense of designing new terminals made especially for aluminum cable.

BRIEF SUMMARY OF THE INVENTION

In accordance with one embodiment of this invention, a method of connecting an electrical wire cable having a plurality of uninsulated wire strands to an electrical terminal is provided. The method includes the step of crimping an uninsulated end of the electrical wire cable within a crimping feature of the electrical terminal. A portion of the plurality of uninsulated wire strands protrudes from the crimping feature. The method further includes the step of fusing the wire strands of said protruding portion so that the wire strands are in intimate contact, thereby eliminating voids between individual wire strands of the protruding portion. The wire strands of the protruding portion may be fused to the electrical terminal. The wire strands may be formed of aluminum.

In another embodiment of the present invention, a wiring harness assembly is provided. The wiring harness assembly includes an electrical wire cable including an end having a plurality of uninsulated wire strands and an electrical terminal that is attached to the electrical wire cable by the method described above.

Further features and advantages of the invention will appear more clearly on a reading of the following detailed description of the preferred embodiment of the invention, which is given by way of non-limiting example only and with reference to the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1illustrates a non-limiting example of an electrical wire cable10, such as an aluminum wire cable, having multiple uninsulated wire strands12. As used herein, aluminum may refer to pure aluminum or and aluminum based or aluminum containing alloy. The electrical cable10is electrically and mechanically attached to an electrical terminal14. The terminal14in the illustrated example is a female socket connector and includes at least a pair of crimp wings16configured to connect the terminal14to the wire strands12. The terminal14may be formed of a copper based material. As used herein, the copper based material may be pure copper, a copper based alloy, or a copper containing alloy. The copper based material may also be plated with another material, such as a tin based alloy, to enhance corrosion resistance of the terminal14. The design and manufacture of electrical terminals having crimp wings and the use of crimp wings to attach wire cables to electrical terminals are well known to those skilled in the art. The terminal14as illustrated inFIG. 1is a female socket terminal. Alternatively, other embodiments may include a male plug terminal, ring terminal, hook terminal, or other terminal types configured to be attached to wire cables via a crimping feature as are well known to those skilled in the art.

When an electrical terminal14that has a crimping feature16, such as a pair of crimping wings16illustrated inFIG. 1, is crimped to a wire cable10having multiple wire strands12, an end portion18of the individual wire strands12typically protrude from the crimp wings16, forming what may be called a “wire brush” as illustrated inFIG. 2.

FIG. 3illustrates a non-limiting example of an electrical wire cable10and electrical terminal14wherein at least a portion20of the individual wire strands12of the wire brush18are bonded to one another by a thermal process such as welding, brazing, or soldering to produce a metallurgical bond between at least a majority of the strands12of the cable10, thus providing a benefit of reducing the resistance between the wire strands12due to insulating oxide layers on the surface of the wire strands12. Laser welding may be an effective method of welding the strands12because of the small target area of the wire brush18and the precision required to fuse the strands12of the wire brush18without adversely affecting the terminal14or wire cable10.

One function of bonding the wire strands12together is to minimize inter-strand electrical resistance. It is also desirable to bond the wire brush18to the electrical terminal14, thus providing a low resistance connection between the wire cable10and the terminal14. This may occur as a plating material on the electrical terminal14melts and bonds to the welded strands12in the bonded portion20. However, bonding the wire brush18to the electrical terminal14is not necessary. The crimp wings16may include features to break-up oxides on the wires to improve electrical conductivity between the wire strands12and the terminal14. An example of such features may be found in U.S. Pat. No. 8,485,853 granted to Seifert, et al on Jul. 16, 2013. Additives such as flux, solder paste, brazing rod/wire or welding rod/wire may be applied the bonded portion20to improve the quality of the metallurgical bond between the strands12.

Another benefit of metallurgically bonding the wire strands12of the wire brush18is the inhibition of corrosion at the bonded portion20. Whenever two different types of metal, such as an aluminum-based wire and a copper based terminal, are in contact with each other in the presence of an electrolyte in solution, there is risk of galvanic corrosion. The aluminum-based wire will act as an anode in a galvanic reaction and can corrode when in contact with a copper-based terminal. If the bonding process reflows metal to fill the open spaces between the strands12, it can seal the bonded portion20at the front of the crimped connection between the wire cable10and the terminal14to prevent electrolytes in solution from entering inter-wire spaces, voids, or gaps in the crimped connection. Use of sacrificial metals, such as zinc or magnesium, in the welding/brazing process (e.g. zinc additives in a solder paste, solder flux, or a brazing/welding rod) may provide enhanced corrosion protection. Because these sacrificial metals are more anodic relative to aluminum in the galvanic series, the sacrificial metals will corrode before the aluminum, thus preserving the integrity of the termination. Additional corrosion protection, such as the application of a sealant, may be applied to the end of the terminal14opposite the bonded portion20where the uninsulated wire strands12exit the crimp wings16. An example of such a method of applying a sealant to a crimped wire connection may be found in U.S. Pat. No. 8,181,343 granted to Martauz, et al on May 22, 2012.

As illustrated inFIG. 3, the cut end of the wire cable10protruding from the front of the crimping wings16is fused to become the bonded portion20. Alternatively, the uninsulated wire strands12protruding from the back of the crimping wings16opposite the cut end may also be fused to become a bonded portion20.

FIG. 4illustrates a non-limiting example of a method100of connecting an electrical wire cable10having a plurality of uninsulated wire strands12to an electrical terminal14.

In step110, CRIMP AN UNINSULATED END OF AN ELECTRICAL WIRE CABLE WITHIN A CRIMPING FEATURE OF AN ELECTRICAL TERMINAL, an uninsulated end of the electrical wire cable10is crimped within a crimping feature16of the electrical terminal14. A portion18of the plurality of uninsulated wire strands12protrudes from the crimping feature16forming a “wire brush”. The crimping feature16of the electrical terminal14may define a pair of crimp wings16as illustrated inFIGS. 1-3.

In step112, APPLY A SOLDER PASTE TO A PROTRUDING PORTION OF THE WIRE STRANDS, according to one embodiment, a solder paste is applied to the protruding portion18of the wire strands12, otherwise referred to as the wire brush18. The solder paste may comprise zinc, such as a tin-zinc or zinc-aluminum solder, to serve as a sacrificial metal to inhibit corrosion of an aluminum wire cable crimped to a copper electrical terminal. Step112may be performed prior to step116.

In step114, SHAPE AN END OF THE PROTRUDING PORTION, according to one embodiment, the wire brush18or protruding portion18is shaped to provide a smooth end of the wire brush18because the end of the wire brush18may be uneven following the crimping of the wire in step110. The end of the wire brush18may be shaped by trimming the ends of the individual wire strands12by cutting or grinding. Step114may be performed prior to step116.

In step116, FUSE THE WIRE STRANDS OF THE PROTRUDING PORTION, the wire strands12of the wire brush18as fused so that the wire strands12are in intimate contact, thereby eliminating voids between individual wire strands12of the protruding portion18. The end face of the wire brush18may be fused or the wire strands12of the entire protruding portion18may be fused. According to one embodiment, the wire strands12are fused by irradiating the protruding portion18with laser radiation (e.g. coherent light beam) in a process commonly known as laser welding. Only the protruding portion18of the wire strands12is irradiated. According to another embodiment, thermal energy is applied to the protruding portion18using a process such as brazing, soldering, or welding.

In step118, FUSE THE WIRE STRANDS OF THE PROTRUDING PORTION TO THE ELECTRICAL TERMINAL, according to one embodiment, the wire strands12of the protruding portion18are also fused to the electrical terminal14.

In step120, APPLY A FILLER MATERIAL TO THE protruding portion18, according to one embodiment, a filler material, such as solder paste, welding rod, or brazing rod is applied to the protruding portion18. The filler material may comprise zinc. Step120may be performed as part of step116.

Accordingly, a method100of connecting an electrical wire cable10having a plurality of uninsulated wire strands12to an electrical terminal14and a wiring harness assembly22manufactured by the method100and having an electrical wire cable10and an electrical terminal14is provided. The wire cable10is attached to the terminal14by a crimping feature16and the wire strands12of a portion18of the cable10that protrudes from the crimping feature16are fused, bonded, or welded to metallurgically bond the wire strands12to one another. This bonding of the strands12reduces inter-strand resistance and seals the bonded portion20against the infiltration of electrolytes that may cause galvanic corrosion of the wire cable10.

While this invention has been described in terms of the preferred embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow. Moreover, the use of the terms first, second, etc. does not denote any order of importance, but rather the terms first, second, etc. are used to distinguish one element from another. Furthermore, the use of the terms a, an, etc. do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items.