WO2009112881A1

WO2009112881A1 - Electrical terminal system

Info

Publication number: WO2009112881A1
Application number: PCT/IB2008/002148
Authority: WO
Inventors: Thomas Pabst; Mirko Posmik; Armin Studt
Original assignee: Fci
Priority date: 2008-03-11
Filing date: 2008-03-11
Publication date: 2009-09-17
Also published as: EP2266167A1; CN101999192B; EP2266167B1; CN101999192A

Abstract

The invention relates to an electrical terminal system (3), comprising at least one cable (20) comprising a stranded wire; at least one elongated terminal (10) for reception of the cable, which terminal has a contacting portion for electrical and/or mechanical connection and a welding portion (12) for electrical connection between the terminal and the stranded wire. At the free end of the cable the stranded wire is compacted and welded into an essentially solid portion (23); and said essentially solid portion (23) is welded directly to the welding portion (12) of the terminal to achieve electrical continuity therebetween.

Description

Electrical terminal system

Field of the invention

The invention relates to an electrical terminal system, in particular for automotive applications, comprising an elongated terminal and a wire or cable attached thereto as well as a method for the production of such an electrical terminal system.

Prior art

Electrical terminal systems comprising a terminal having a contacting portion for electrical connection and a mounting part for the attachment of a cable or wire are known from the art. As used herein, the term cable denotes a single conductor comprising a conducting wire or wires and an insulating sheath surrounding and insulating the wire or wires. The term wire denotes the conductive core of the cable and may consist of one or more wire strands. The terminal is commonly formed of bend and stamped metal sheet. Typically, the terminal is formed integrally from a piece of metal sheet, which can be folded at one end in the form of a box to receive an end of a separate contact pin, or is shaped so that it is adapted to connect with a second terminal counterpart, and on the other end it is provided with means for connecting a cable or wire, respectively surrounded by an insulating sheath. The cable or wire is mechanically and electrically connected at one end to the terminal and at the other end for example with some kind of power source or electrical device or similar. In the case of for example airbag ignition systems the other end of the cable or wire is usually connected to airbag control means for triggering the airbag inflation. A usual practice to achieve electrical connectivity between a cable and a terminal, consists in fitting the terminal with end sleeves which are crimped around the wire strands of the cable. However gas could be entrapped inside the crimped connection and further the crimped elements may tend to "spring back", what can create fluctuations of the overall connection electrical resistance, at an eventually unacceptable level for critical applications.

This can be overcome by welding or brazing the wire to the terminal instead of crimping.

The shape of a stranded wire termination is usually not well defined, since the individual strands spread randomly around the wire axis. For this reason, the welding of such wire strands is difficult, since when e.g. the welding electrode presses the strand bundle onto the terminal portion to be welded with, the electrical contact area is not well defined. Therefore the welding power is changing from a terminal to another for the same tuning of the welding apparatus and during a welding operation the heat generation is not evenly spread over the welding area, so that some individual strands receive more heat than others. For these reasons the welding quality may not be satisfying.

Still further, such electrical terminal systems, i.e. the terminal and the respective wire or cable connected therewith, are mass products so that production costs and the reliability of the manufacturing process with respect to quality and the reduction of defective products is of high importance.

It is therefore an object of the present invention to provide an electrical terminal system which reduces the above described problems and drawbacks and which is in particular cost efficient to produce.

Another object of the invention is to get a more constant and better quality welding of a wire (or wires) with a terminal. Summary of the invention

According to the invention an electrical terminal system is provided, comprising at least one cable having a stranded wire and at least one elongated terminal for reception of at least a portion of the wire strands of the cable. The terminal has a contacting portion for mechanical and/or electrical connection with another electronic device and a holding or welding area to provide for an electrical connection between the terminal and a portion of the stranded wire of the cable. The cable is preferably an insulated cable having a stranded wire of for example a copper alloy. At the free end of the cable, i.e. the end which is connected to the terminal, the stranded wire is compacted and welded into an essentially solid portion. The stranded wire is for example compacted in a suitable press and then at the same time resistance welded by applying a charge or voltage to the compacted strands. This compacted and essentially solid portion of the stranded wire of the cable is welded directly onto the welding portion of the terminal to achieve electrical continuity therebetween. Preferably, the compacted and essentially solid portion of the stranded wire has an essentially rectangular cross section, most preferably a square cross section. Compacting, advantageously but not necessarily in a rectangular shape, allows well defined and constant shapes and dimensions of the stranded wire, which in turn allows stable welding characteristics. The location of the wire relative to the terminal and the welding electrode is accurate. In one aspect of the invention the elongated terminal is formed from a piece of metal sheet. The preferred material for the terminal is copper alloy. In a most preferred embodiment the terminal has a metal sheet frame, at the end of which the contacting portion is folded in the form of a box to receive e.g. a separate connector pin and formed in form of an open rounded channel at the receiving end for the cable. In a advantageous embodiment the welding portion of the elongated terminal - A -

has an essentially semi-circular cross section forming an open rounded channel for the reception of the essentially solid portion of the compacted stranded wire. Due to this half-shell shape, which is advantageously but not necessarily semi-circular, an easy positioning of the wire relatively/within the terminal is possible.

For resistance welding it is required that the electrode, at least at the beginning of the welding process, reaches the wire without contacting the metal sheet of the terminal. As an advantageous solution to this end, dimensions of half-shell shape and compacted wire are adapted so that the upper face of the compacted wire projects above upper face of the half -shell.

Another aspect of the invention relates to a method for the production of an electrical terminal system, in particular for automotive applications. The method comprises the steps of providing a cable comprising a stranded wire, compacting and welding the stranded wire on a free end of the cable to form an essentially solid portion. Further, an elongated terminal is provided, for example a terminal as described above, for the reception of the cable, having a contacting portion for mechanical and electrical connection with e.g. an electronic device and a welding portion for electrical connection between the terminal and the stranded wire. After compacting and welding the stranded wire, the same is mounted with the terminal such that the essentially solid portion is arranged in the welding portion. In a next step, the essentially solid or compacted portion of the stranded wire is welded with the terminal to achieve electrical continuity therebetween. Preferably, the stranded wire and the terminal are welded by means of resistance welding. In a preferred embodiment, the stranded wire of the cable is also compacted by means of resistance welding. Description of the preferred embodiments

In the following, the invention is described exemplarily with reference to the enclosed figures, in which:

Fig. 1a is a schematic illustration of a terminal.

Fig. 1b is a cross sectional view as seen from the line A-A;

Fig. 2a is a schematic illustration of a cable comprising a stranded wire.

Fig. 2b is a cross sectional view of a compacted and welded portion of the stranded wire; and

Fig. 2c is a schematic cross sectional view of a wire and a terminal wall after the same have been welded together.

Fig. 3 is a schematic illustration of an electrical terminal system according to the invention.

Fig. 4a is a sectional schematic view of the electrical terminal system shown in figure 3.

Fig. 4b is a schematic front view of the terminal system of figure 4a.

Fig. 1a shows a schematic view of a terminal 10 comprising a cable connecting end 11 having two fixing flanges 14, which are shown in their bent position after fastening on the insulating sheath of a cable (not shown). For mounting a cable and the terminal 10, the cable is first inserted between the flanges 14 which are then crimped around the outer insulating sheath of the cable. Terminal 10 further comprises a welding portion 12 in the form of a rounded open channel. The cross section of the channel can best be seen from figure 1b (see hatched area), which is a sectional view seen along the line A-A of figure 1a. Terminal 10 is further provided with contacting portion 13 into which for example a separate connector pin may be inserted. As the skilled person understands from figure 1a, terminal 10 is made from a piece of stamped and bend metal sheet, preferably from a piece of copper alloy or the like.

Fig. 2a shows a cable 20 comprising a stranded wire 22 and an insulating sheath 21 formed around the stranded wire 22 to electrically insulate the same from the environment. The stranded wire 22 comprises for example a number of single strands 24 (see fig. 2b), for example between ten and twenty strands. As can best be seen from figure 2a the insulating sheath 21 is removed from the end of cable 20. The portion of the stranded wire 22 where the insulating sheath is removed is then compacted and welded into an essentially solid portion 23. This is preferably achieved by compacting and resistance welding of the strands. Figure 2b shows a cross section of the compacted and resistance welded strands 24. As can be seen from the figure almost all the surfaces of the single strands 24 are bounded together. Figure 3 shows a schematic view of an electrical terminal system 3 before welding the wire 20 on the terminal 10 according to the invention. The terminal 10 is further provided with a separate contact pin 15 for inserting into e.g. a female counter part (not shown). It is of course also possible to provide the electrical terminal 10 in form of a female terminal, into which a pin of a corresponding male counterpart can be inserted. The cable 20 is mounted to the terminal 10 and mechanically fastened to the same by means of the flanges 14, which are bent or crimped around the cable 20 respectively around its insulating sheath 21. The cable 20 is arranged such that the compacted solid portion 23 of the stranded wire is arranged in the welding portion 12 of terminal 10. Figures 4a and 4b show a sectional view of the terminal system 3 shown in figure 3. As can be seen from the figure the cross section of the welding portion 12 (see hatched area) is essentially semi-circular and has the form of an open rounded pipe. The solid portion 23 rests in the rounded channel of the welding portion 12. Since the solid portion 23 has preferably a square cross section a space 40, 40' remains between the inner channel wall of welding portion 12 and the two lateral side walls of portion 23.

The solid portion 23 is welded to the walls of the terminal 10 by means of, for example, spot resistance welding or a welding seam in order to achieve a good electrical continuity therebetween. It is also possible to use a brazing operation instead of welding. Figure 2c shows the wire 23 with a wall of the welding portion 12 of the terminal after welding. Due to the pressure of electrode on the wire 23 during welding, the wire is squeezed together with the walls of the welding portion of the terminal to a more or less flat cross-sectional shape.

For resistance welding it is required that the electrode reaches the wire without contacting the metal sheet of the terminal. To this end, as can be seen on figure 4b, the upper face of compacted wire 23 projects above the upper face of the half-shell of the welding portion wall. To that effect, the half-shell may have been cut sufficiently low. In any case, after welding the resulting terminal has to be rigid enough. The welding portion 12 complies nevertheless with this requirement because the wire and metal sheet hold firmly together after welding. The front and rearward zones of the welding portion 12 , as seen on figure 1a, are reinforced, i.e. the walls of contacting portion 13 are e.g. higher to increase the cross section, with an as short as possible slope portion in the transition zone between the welding and the contacting portions.

Due to the use of a compacted wire portion with a well defined shape, the welding power is well defined and better spread over the welding area so that a better and manageable welding quality can be achieved.

It should be noted, that the figures show the embodiments in an enlarged view. In reality the length of the terminal 10 is for example in the range of a few centimeters, for example 2 to 4 cm, and the strength of the metal sheet from which the terminal is made of is in the range of 0,1 to 0,5 mm, preferably around 0,2 mm. The solid portion 23 may have a length in the order of 1 cm, for example 0,3 to 1 cm, and a thickness of maybe 0,5 mm up to 2 mm.

Claims

1. Electrical terminal system (3), comprising

- at least one cable (20) comprising a stranded wire (22); - at least one elongated terminal (10) for reception of the cable, which terminal has a contacting portion (13) for electrical and/or mechanical connection and a welding portion (12) for electrical connection between the terminal and the stranded wire, characterized in that

- at the free end of the cable the stranded wire (22) is compacted and welded into an essentially solid portion (23); and

- said essentially solid portion (23) is welded directly to the welding portion (12) of the terminal to achieve electrical con- tinuity therebetween.

2. Electrical terminal system according to claim 1, wherein the stranded wire (22) is compacted by means of resistance welding.

3. Electrical terminal system according to any of the preceding claims, wherein the welding portion (12) of the elongated terminal (10) has an essentially semi-circular cross section forming a rounded open channel for reception of the essentially solid portion (23) of the compacted stranded wire.

4. Electrical terminal system according to any of the preceding claims, wherein the terminal (10) comprises at least a wall which is reinforced in a front zone of the welding portion (12) by increasing its height and consequently its the cross sectional area.

5. Method for the production of an electrical terminal system (3), particularly for airbag ignition systems, comprising the following steps:

- providing a cable comprising a stranded wire at a free end;

- compacting and welding the stranded wire at the free end of the cable to form an essentially solid portion (23);

- providing an elongated terminal (10) for reception of the cable having a contacting portion for electrical and/or mechanical connection between the terminal and the stranded wire and a welding portion (12) for electrical connection between the terminal and the stranded wire,

- mounting the free end of the cable with the compacted portion of the stranded wire with the terminal so that the essentially solid portion lies in the welding portion; and

- welding the compacted portion of the stranded wire with the terminal to achieve electrical continuity therebetween.

6. Method according to claim 5, wherein the stranded wire is compacted by means of resistance welding.

7. Method according to claims 5 or 6, wherein the solid portion (23) has an essentially rectangular cross section, preferably square.

8. Method according to any of the claims 5 to 7, wherein the welding portion (12) of the elongated terminal (10) has an essentially semi- circular cross section forming a rounded open channel for reception of the essentially solid portion (23) of the compacted stranded wire.