An electrical terminal and an electrical connector

Abstract

 The terminal (14) comprises a contact arm (26) and a wedge arm (28). When the terminal has been inserted into a cavity (22) of a housing (66), the wedge arm (28) is moved relative to the contact arm (26) inwardly of the cavity (22) to force the contact arm (26) against wire (2)to drive it against a wall (70) of the cavity (22).
In order to enable the size of the terminal (14) to be reduced, the wedge arm (28) is contiguous with, and is slidable along, the contact arm (26), the contact portion (34) of the latter initially extending across the leading end (40) of the wedge arm (28) so that the contact portion (34) is displaced towards the wall (70) by the wedge arm (28).

Description

[0001] This invention relates in general to the art of making electrical line connections and relates in particular to an electrical terminal and to an electrical connector which are suitable for the termination of fine wires, e.g. of A.W.G. (American-Wire Gauge) 32 to 50.

[0002] We have described in our United States Patent Specification No. 4,026,013 an electrical terminal for establishing electrical connection with a wire which extends into a cavity in a housing, the terminal comprising a contact arm and a wedge arm in juxtaposed relationship, the wedge arm being movable with respect to the contact arm in the longitudinal direction thereof, one end of the contact arm projecting beyond an end of the wedge arm; whereby upon the insertion of the terminal into the cavity with the one end of the contact arm leading and with the contact arm adjacent to the wire, and then advancing the wedge arm relative to the contact arm, into the cavity, the contact arm is moved against the wire to clamp the wire against the wall of the cavity to establish electrical connection with the wire.

[0003] Although this known terminal has indeed proved to be useful for terminating the windings of small electrical coils, there are nevertheless cases where the known terminal cannot be made small enough to comply with coil manufacturers requirements as to space limitations.

[0004] In the known terminal the contact arm and the wedge arm are spaced from one another by a transverse strut which connects the leading ends of the contact arm and the wedge arm, the strut being accordingly acutely angled with respect to the contact arm and obtusely angled with respect to the wedge arm. As the wedge arm is advanced, the strut is driven towards a position in which it extends at right angles to the contact arm, so that the whole terminal is in effect expanded in the cavity to move the contact arm against the wire.

[0005] The invention proceeds from the realization that the size of the terminal can be greatly reduced by arranging the contact arm and the wedge arm in contiguous relationship, the wedge arm being slidable along the contact arm to-straighten an obliquely extending contact portion of the contact arm so as to drive such portion against the wire.

[0006] According to one aspect of the invention, a terminal as defined in the second paragraph of this specification is characterised in that the contact arm comprises a substantially straight shank portion, and a contact portion extending obliquely from the shank portion and transversely of the wedge arm, the contact arm and the wedge arm being held in contiguous relationship and the wedge arm being slidable along the shank portion of the contact arm towards the one end of the contact arm to drive the contact portion thereof towards a position of longitudinal alignment with the shank portion thereof.

[0007] According to another aspect of the invention, there is provided an electrical connector comprising a housing of insulating material, a cavity extending into one surface of the housing, and an electrical terminal dimensioned for insertion into the cavity, the terminal comprising a contact arm and a wedge arm in juxtaposed relationship, the wedge arm being movable with respect to the contact arm in the longitudinal direction thereof inwardly of the cavity when the terminal has been inserted into the cavity; to cause the contact arm to force a wire extending between the contact arm and a wall of the cavity, against such wall; characterised in that the contact arm comprises an obliquely extending contact portion, the wedge arm being held against the contact arm and being slidable there along to straighten the contact portion so as to force it against the wire, in turn to force the wire against the wall of the cavity.

[0008] It is of advantage to provide means for resiliently urging the contact portion of the contact arm against the wire after the connection has been made so as to avoid loss of contact brought about by temperature changes or "creep" of the constituent materials.

[0009] If desired the terminal can be constructed so that it can be made by stamping and forming from a single sheet of metal.

[0010] The state of the art is further exemplified by United States Patent Specifications Nos. 2,134,775, 3,812,453, 3,950,067 and United Kingdom Patent Specification No. 1,386,678.

[0011] For a better understanding of the invention embodiments thereof will now be described by way of example with reference to the accompanying drawings in which:-

Figure 1 is an exploded perspective view of an assembly comprising an insulating housing in the form of a coil bobbin having winding of fine gauge wire and being provided with electrical terminals according to a first embodiment of the invention connecting tap wires of the windings to conductors on a flexible electrical circuit, a clamping member being also provided for clamping the flexible circuit to the bobbin;

Figure 2 is an end view of a terminal of the assembly;

Figure 3 is a plan view of the terminal showing part of a carrier strip thereon;

Figure 4 is a side view of the terminal;

Figures 5 to 7 are side views, shown partly in section, illustrating successive stages in the insertion of the terminal into a cavity in the bobbin to make electrical connection with a tap wire;

Figure 8 is a view taken in the direction of the arrows VIII _- VIII of Figure 5;

Figure 9 is a side view of an electrical terminal according to a second embodiment of the invention;

Figure 10 is a view similar-to that of Figure 1 but showing a modified coil bobbin provided with terminals according to Figure 9;

Figures 11 and 12 are diagrammatic views illustrating the manner in which a contact arm of a terminal according to the invention is loaded when the terminal is in use;

Figure 12 is a diagram illustrating the distribution of the loading on the contact arm when the terminal is in use; and

Figure 14 is a diagrammatic view illustrating the manner in which a wedge arm of a terminal according to the first embodiment of the invention is resiliently deformed when electrical contact between the terminal and a wire is made.

[0012] Terminals 14, as shown in Figure 1, are arranged to connect varnish insulated tap wires 2 of a coil bobbin 6 to conductors 16 of a flexible circuit 18. The bobbin 6 has juxtaposed deep recesses 8 extending there about and receiving bobbin windings 4, from which recesses shallow channels 24 extend along a top (as seen in Figure 1) surface 20 of the bobbin 6, to side surfaces 68 thereof, each channel 24 communicating with a cavity 22 for receiving an individual terminal 14 for one of the tap wires 2. The bobbin 6 has mounting ears 10 to receive screws 12 for clamping the flexible circuit 18 between the surface 20 and the surface of a housing (not shown) or other mounting means (not shown) in which the circuit 18 and the bobbin 6 are to be contained. Protecting solder tab portions 30 of the terminals 14 are soldered to the conductors 16 prior to the clamping operation. The bobbin shown by way of example in Figure 1 is intended to form part of the shutter control mechanism of a cinema camera. The wires 2 may be within the range AWG (American Wire Gauge) 32 to 50.

[0013] Each terminal 14 comprises, as best seen in Figures 2 to 4, an elongate contact arm 26 and a shorter wedge arm 28 disposed against a side 39 of the contact arm 26. The contact arm 26 has solder tab portion 30 at its rearward or trailing end, a wire contact portion 34 at its forward or leading end, and a shank portion 32 intermediate the portions 30 and 34, the portion 34 adjoining the portion 32 at 35 (see Figures 3 and 4). Insulation piercing serrations 36 extend transversely of the arm 26 adjacent to the free end 36 of the portions 34 on the side of the arm 26 is opposite to its side 39. The portions 30 and 32 of the arm 26 are coplanar, the contact portion 34 extending obliquely across the adjacent free leading end 40 of the wedge arm 28 as best seen in Figure 4. Retention barbs 33 extend from the lateral edges of the shank portion 32 adjacent to the contact portion 34 and are also coplanar with the portions 30 and 32 of the arm 26. As explained below, the barbs 33 penetrate the sidewalls of the cavity 22 to retain the contact arm in the cavity 22 after insertion thereinto.

[0014] The wedge arm 28 has retention barbs 42 adjacent to its free end 40, the barbs 42 extending obliquely from the plane of the arm 28 and'away from the arm 26 at an angle with respect to the barbs 33 as best seen in Figure 2. The trailing end portion 27 (Figure 3):ofthe wedge arm 28 is of uniform width, being slightly wider than the solder tab portion 30 of the contact arm 26. As shown in Figure 2, the portion 27 of the wedge arm 28 adjacent to its other free end 60 is formed integrally with a continuous carrier strip 50 by which it is connected to other terminals 14 (not shown) in side 137 side relationship. Each terminal is severed from the strip 50 (by means not shown) along shear lines 64 when the terminal 14 is being inserted into a cavity 22 by an insertion machine (not shown). The wedge arm 28 is held in assembled relationship with the contact arm 26 by laterally extending reversely formed ears 46 which are formed integrally with the shank portion 32 of the contact arm 26 and which embrace the wedge arm 28 immediately rearwardly of the retention barbs 42. The ears 46 are so formed that the wedge arm 28 is slidable forwardly from the position of Figure 4, in which the trailing ends 58 and 60 of the respective arms 26 and 28 are coplanar, to the position of Figure 7, the arms 28 sliding over the surface 39 of the contact arm 26 and the ears 46 serving to guide the wedge arm 28 along a rectilinear path during such sliding movement.

[0015] Each of the cavities 22 extends from the surface 20 of the bobbin 6 to the underside 66 thereof and communicates with the surface 68 via a slot 80 traversing the surface 68. As shown in Figure 8, each cavity 22 has opposed side walls 70 and 72, one of the channels 24 opening into the side wall 70 which is the innermost of the walls 70 and 72. As shown in Figures 5 to 7, the channel 24 merges with a shallow groove 76 in the side wall 70, such groove extending part way there along up to a ramp 78 which merges with the left hand (as seen in Figures 5 to 7) end portion of the side wall 70. The side walls 70 and 72 are connected by side walls 74 (Figure 8).

[0016] The slot 80 communicates with the cavity 22 so that a wire 2 can be placed in the corresponding channel 24 and passed through the slot 80 so that the wire 2 is located in the corresponding groove 76 and against the adjacent side wall 70. The inner (i.e. the left hand as seen in Figures 5 to 7) end 86 of each cavity 22 is adjacent to the surface 66 of the bobbin 6, the opposed sides 84 of the slot 80 converging adjacent to, and towards the inner end 86 of the cavity 22 to define in co-operation with the wall 70, a narrow positioning guide way 88 for the wire 2, adjacent to the surface 66. It will thus be apparent that if the wire is simply located in the channel 24, and passed through the opening 80 whilst being held taut under slight tension, the wire will automatically locates itself in the groove 76 and in the guide way 88 so that a portion of the wire extends along the side wall 70 between the ramp 78 and the guide way 88 as shown in Figure 5, a portion 2' of the wire 2 extending obliquely across the cavity 22. The wires 2 can be positioned in the cavities 22 at the time of winding the bobbin 6, preferably by means of automatic winding machinery (not shown).

[0017] After a wire 2 has been located into a cavity 22.as described above, a terminal 14 is inserted into such cavity 22 with the contact portion 34 leading and in such an orientation (Figure 5) that the contact portion 34 engages the wire 2, as shown in Figure 6. The terminal 14 is initially inserted into the cavity 22 to such a depth that the trailing edges 37 of the retaining ears 46 are coplanar with the surface 20 of the bobbin 6. An insertion force is then applied against the free end 60 of the wedge arm 28 to cause it to slide along the side 39 of the contact arm 26 until the wedge arm 28 is fully inserted into the cavity 22 as shown in Figure 7. During such movement of the wedge arm 28, the contact portion 34 of the contact arm 26 is driven towards the side wall 70 by the arm 28, i.e. towards a position of longitudinal alignment with the shank portion 32, so that the wire 2 is clamped between the insulation piercing serrations 36 of the contact portion 34, and the side wall 70, the serrations 36 penetrating the varnish insulation of the wire 2 to establish electrical contact with the electrically conductive core of the wire 2. The solder tab portion 30 of the arm 26 is then electrically connected by soldering to a conductor 16 of the flexible circuit 18 and the assembly comprising the bobbin 6 and the circuit 18 is secured by the fasteners 12 to the surface of said housing or other mounting means, after clamping the circuit 18 to the bobbin by means of the clamping member 102, which is provided with holes 104 for receiving the fasteners 12.

[0018] By virtue of its construction as described above, the terminal may be made in a relatively small size so as to be compatible with the wire gauge, the cavity 22 being correspondingly small. The terminal 14 may, for example, have an overall length of 5.588 mm., an overall width as measured between the barbs 33, of 2.032 mm., and an effective thickness of 0.889 mm., as measured between the outer surface of the contact arm 26 and innermost edge 34' (Figure 5) of the contact portion 34 of the contact arm 26. The dimensions of the cavity 22 should be only slightly greater than those of the terminal 14. For the wire gauge range mentioned above, the stock thickness of the terminal 14 may be 0.2032 mm.

[0019] It has been found that an extremely stable and effective electrical connection between the terminal l4 and the fine wire 2 is achieved. The wedge arm 28 is guided and confined during its movement along the contact arm 26 between the ears 46 and after the electrical connection has been established between the wire and the terminal the wedge arm 28 provides a reservoir of stored energy which continually urges the contact portion 34 of the contact arm 26 into engagement with the wire 2.

[0020] The wedge arm 28, the contact arm 26, and the cavity 22 should be dimensioned and the materials used should be so chosen that the contact arm 26 is deformed and loaded by the wedge arm 28 as illustrated in the diagrams of Figures 11 to 13. In Figure 11, the contact portion 34 of the contact arm 26 is shown diagrammatically in its normal or unstressed condition. The free end 40 of the wedge arm is shown as being located at the inner end 35 of the contact portion 34. After the terminal has been inserted into the cavity 22 and the wedge arm 28 has been moved to its fully inserted position, the wedge arm 28 supports the contact portion 34 in the manner shown in Figure 12 in which the end 40 of the wedge arm 28 is shown as being located at the end 38 of the contact portion 34, an intermediate portion of the wedge arm 28 extending past and supporting the end 35 of the contact portion 34. The contact portion 34 is thus loaded in the manner of a simple beam which is freely supported at its ends 35 and 38, the load, C, on the portion 34 being, of course, the load imposed by the wire, which has been forced against the wall 70 of the cavity 22. As shown in Figure 13, this load is distributed along the length of the contact portion of the contact arm with the maximum load being located centrally of the beam i.e. the contact portion 34. It will be apparent that the contact portion 34 in its loaded condition is capable of compensating for any relaxation in the bobbin 6 or in the wire 2, for example, relaxation resulting from temperature fluctuations or material flow. By virtue of this phenomenon, a stable electrical connection is achieved over a wide range of temperatures and for a prolonged period of time.

[0021] Figure 14 shows, in end view the wedge arm 28 looking towards its free end 40, the condition of the wedge arm 28 being shown in full lines, prior to its movement relative to the contact arm 26. After the completion of such relative movement the obliquely extending barbs 42, will, as indicated in broken lines, be flexed downwardly as seen in Figure 14 towards the contacts arm 34 which is also shown in broken lines, such flexure of the barbs 42 being imparted to them by the load imposed on the wedge.arm 28 by the contact portion 34.

[0022] Figure 14 shows in fact the conditions which exist at the right hand end of the diagram of Figure 12. The support for the end 38 of the contact portion 34 must be stable and unremitting if optimum contact between the wire and the terminal is to be maintained. The resilient flexure of the barbs 42 provides such stability in that dimensional changes which may be brought about, for example, by temperature fluctuations are counteracted by the flexure of the barbs 42. In other words, the barbs 42 tend to return to their solid line positions of Figure 14 so as to follow the contact portion 34 thereby to maintain the stability of the beam system shown in Figure 12.

[0023] Although Figures 11 to 14 are explanatory of the phenomena which contribute to the stability of the electrical connections which are maintained within the limited confines of the cavities 22, these Figures are not intended to be quantative representations.

[0024] According to the embodiment of Figures 9 and 10, a terminal 14' which operates in a similar manner to the terminal 14 described above is formed in one piece. The terminal 14' comprises a contact arm 26' and a wedge arm 28', connected by a flexible, generally triangular shaped (as seen in Figure 9) strap 92, having a generally central bight 98 from one side of which extends a strap portion 94 connected to the rear or trailing end of the arm 26' and projecting obliquely there from, and from the other side of which extends a strap portion 96 connected to and projecting obliquely from the rear or trailing end of the arm 28'. On the outer face of the portion 96, is formed a rounded contact boss 100. The wedge arm 28' is provided with barbs 42' on each of its lateral edges and with a central elongate resilient boss 101 slidably engaging the contact arm 26'. The contact portion 34' of the contact arm 26' has insulating piercing serrations 36' on its outer surface, retaining barbs 33' being provided on the lateral edges of the arm 26'. The strap 92 serves to hold the arms 26' and 28' in contiguous relationship.

[0025] In use of this second embodiment, a wire 2 is positioned in the cavity 22 as described above and the terminal 14' is inserted into the cavity 22 to position the contact portion 34' against the wire 2.

[0026] The wedge arm 28' is then advanced into the cavity until the portion 96 of the strap 92 extends horizontally and thus parallel to the top surface 20 of the bobbin 6, during such advance, the boss 101 of the arm 28' slides along the inner face 39' of the contact arm 26' and drives the contact portion 34' towards a position of longitudinal alignment with the shank portion 32' and thus against the wire so that the serrations 36' are driven through the insulation of the wire and the wire is wedged between the contact portion 34' and the adjacent wall 70 of the cavity 22 as described above with reference to the first embodiment.

[0027] As shown in Figure 10, the clamping member 102' has holes 103 to reduce the amount of material used in manufacturing the member 102'. Portions of the flexible circuit 18 are forced by the strap portions 96, against the member 102', as the fasteners 12 are tightened, the bosses 100 making firm electrical contact with the conductors 16 of the circuit 18, no soldering operation being required in this case.

Claims

1. An electrical terminal for establishing electrical connection with a wire (2) which extends into a cavity (22) in a housing (6), the terminal comprising a contact arm (26 or 26') and a wedge arm (28 or 28') in juxtaposed relationship, the wedge arm (28 or 28') being movable with respect to the contact arm (26 or 26') in the longitudinal direction thereof, one end (38) of the contact arm (26 or 26') projecting beyond an end (40) of the wedge arm (28 or 28'); whereby upon the insertion of the terminal (14 or 14') into the cavity (22) with the one end (38) of the contact arm (26 or 26') leading and with the contact arm (26 or 26') adjacent to the wire (2), and then advancing the wedge arm (28 or 28') relative to the contact arm (26 or 26'), into the cavity (22), the contact arm (26 or 26') is moved against the wire (2) to clamp the wire (2) against the wall of the cavity (22) to establish electrical connection with the wire (2), characterised in that the contact arm (26 or 26') comprises a substantially straight shank portion (32 or 32'), and a contact portion (34 or 34') extending obliquely from the shank portion f32 or 32') beyond and transversely of the wedge arm (28 or 28'), the contact arm (26 or 26') and the wedge arm (28 or 28') being held in contiguous relationship and the wedge arm (28 or 28') being slidable along the shank portion (32 or 32') of the contact arm (26 or 26') towards the-one end (38) of the contact arm (26 or 26') to drive the contact portion (34 or 34') thereof towards a position of longitudinal alignment with the shank portion (32 or 32') thereof.

2. A terminal according to Claim 1, characterised in that the contact arm (26) and the wedge arm (28) are held in contiguous relationship by a pair of ears (46) which extend from one arm (26) and which embrace the other arm (28).

3. A terminal according to Claim 1, characterised in that the contact arm (26') and the wedge arm (28') are held in contiguous relationship by means of a flexible strap (92) formed integrally with both these arms (26' and 28').

4. A terminal according to Claim 1, 2 or 3, characterised bv resilient means (42 or 101) acting between the contact portion (34 or 34') and the wedge arm (28 or 28') to retain the contact portion (34 or 34') in engagement with the wire (2).

5. A terminal according to any one of the preceding claims, characterised in that the contact arm (26 or 26') and the wedge arm (28 or 28') each have barbs (33 or 33', 42 or 42') extending from their lateral edges for retaining the terminal (14 or 14') in the cavity (22).

6. An electrical connector comprising a housing (6) of insulating material, a cavity (22) extending into one surface (20) of the housing (6), and an electrical terminal (14 or 14') dimensioned for insertion into the cavity (22), the terminal (14 or 14') comprising a contact arm (26 or 26') and a wedge arm (28 or 28') in juxtaposed relationship, the wedge arm (28 or 28') being movable with respect to the contact arm (26 or 26') in the longitudinal direction thereof inwardly of the cavity (22) when the terminal (14 or 14') has been inserted into the cavity (22); to cause the contact arm (26 or 26') to force a wire (2) extending between the contact arm (26 or 26') and a wall (70) of the cavity (22), against such wall (70), characterised in that the contact arm (26 or 26') comprises an obliquely extending contact portion (34 or 34'), the wedge arm (28 or 28') being held against the contact arm (26 or 26') and being slidable there along to straighten the contact portion (34 or 34') so as to force it against the wire (2), in turn to force the wire (2) against the wall (70) of the cabity (22).

7. A connector according to Claim 6, characterised in that the cavity (22) extends from the one surface (20) of the housing (6) into a second and opposite surface (66) thereof, a slot (80) extending through a surface (68) of the cavity (6) adjacent to the two first mentioned surfaces (66 or 70), the slot (80) communicating with the cavity (22) so that the wire (2) can be passed through the slot (80) laterally of the longitudinal axis of the wire (2) to position the wire (2) in the cavity (22), the cavity (22) having a wire guide way in the form of a reduced cross- section portion (88) in the vicinity of the second surface (66) for locating an end portion (2') of the wire (2) with respect to the wall (70).

8. A connector according to Claim 7, characterised in that the wall (70) is provided with a ramp (78) for locating the wire (2) in the cavity (22) so that the end portion (2') of the wire (2) extends obliquely across the cavity (22) for engagement by the contact portion (34 or 34') of the contact arm (26 or 26') as the terminal (14 or 14') is inserted into the cavity (22).

9. A connector according to Claim 7, 8 or 9, characterised in that when the terminal (14 or 14') has been inserted into the cavity (22), the contact portion (34 or 34') of the contact arm (26 or 26') is maintained in a flexed condition by the wedge arm (28 or 28') which resiliently loads the contact portion (34 or 34') at either end.

10. A connector according to Claim 9, characterised in that the wedge arm (28 or 28') is provided with lateral projections (42) which are resiliently deflected by engagement with the contact portion (34 or 34') of the contact arm (26 or 26') as the wedge arm (28 or 28') is slid along the contact arm (26 or 26').

Drawing