GB2050712A - Self-stripping terminal for an electrical connector - Google Patents

Abstract

A self-stripping terminal for an electrical connector has a resilient fork (9) whose two limbs (7 and 8) extend towards each other, perpendicular to the longitudinal axis (XX) of the terminal, to define a slot (13) having a bevel configuration (12) at the opening thereof. The limbs (7 and 8) are carried by resilient arms (5 and 6). The terminal may include a second fork which may be a semi-rigid fork (31), or another resilient fork whose limbs may have a groove for retaining the conductor to prevent any disengagement thereof from the slots in the forks. <IMAGE>

Description

SPECIFICATION Self-stripping terminal for an electrical connector The invention relates to electrical connectors which, associated with electrical conductors, make it possible electrically to connect different members within a circuit, and more particularly concerns a self-stripping terminal.

Increasing requirements tending towards a reduction in the size of connection members which, in most cases, are required to accept metal conductor wires of the same diameter, have resulted in the development of smaller and smaller contact terminals, providing a self-stripping connection, in regard to which insertion of a metal conductor wire into its housing on the contact terminal can be effected in a restricted space, by using punch members of small sizes. For this purpose, each contact terminal is anchored in an insulating carrier by means of retaining members and, at one of its ends, has a self-stripping member including one or more slots.When one or more metal wires with a solid core (single-strand conductor) or with a divided core (multi-strand conductor), covered with an insulating sheath or casing, are inserted, the function of the abovementioned slot or slots is to cut or displace the insulating sheath or casing on passing into a bevel configuration at the opening of the slot, until the conducting core of the conductor makes a sealed electrical junction in the narrowest part of the slot or slots. This connection simultaneously provides for mechanically holding the conductor in its housing on the contact terminal against outside forces which are applied to the conductor such as pulling forces, bending forces or vibration.

Self-stripping connecting devices have an additional advantage which lies in the speed at which they can be used and thus in the saving of time upon making the connection, in particular with respect to the conventional devices which are very widely used, with solder-less wound connections, soldered connections or connections with a wire-crimping action.

However, the self-stripping connecting devices which have been available on the market for many years comprise contact terminals which are cut out and bent in such a way that the self-stripping portion with which they are provided is formed by rigid or semi-rigid forks.

This is the case with the self-stripping terminals which are the subject of USA patent No.

3 162 501 and German patent application no.

2 040 805. This arrangement in USA patent No.

3 162 501 uses a pair of resilient members in the form of a V, each of which is formed by cutting and bending towards each other, two lugs which are cut out from the opposite sides of a U-shaped structure.

This therefore provides two V-shaped forks whose limbs, which are directly fixed by one end in the sides of the U-shaped structure, are applied against each other at their free end and have a certain degree of resiliency which permits them to move apart when a conductor is introduced, while cutting the sheath of the conductor.It is clear that the lugs which form the limbs of the forks are elements which behave like rigid beams fixed in the sides of the U-shaped structure, by virtue of their being cut out from said sides, and that the semi-rigid or semi-resilient forks which are thus produced retain a memory of the deformation which they have undergone, insofar as they do not permit a conductor of large diameter to be introduced, without the limbs of the forks opening to such an extent that there is plastic deformation of the limbs which will then no longer return resiliently towards each other, after the conductor has been disconnected. The semi-resilient forks which are provided in this way do not permit a high number of connections to be made.

Moreoever, the edge which is disposed most inwardly of the U-shaped structure, of the free end of the lugs which are bent towards each other, forms a sharp cutting edge which is capable not only of cutting the insulation of an electrical conductor but also very substantially cutting into the core of such a conductor and even cutting right through some of the conducting strands when the conductor has a multi-strand core. Also, when an axial force is applied to the electrical conductor, the limbs of one of the V-shaped forks are tightened, which can cause the conductor to be sheared by the sharp cutting edges presented by a fork of this kind.The arrangement disclosed in German patent application No. 2 040 805 uses a U-shaped blade-type spring whose sides, which are urged resiliently towards each other, carry at their free end the limbs of the self-stripping fork, the limbs being turned towards each other and being wider than the sides of the spring and being pre-stressed towards each other.This device also forms a semi-resilient fork and, when fitting conductors of substantial diameter, it is very difficult to ensure that flattening of the conductor, which occurs when the conductor is inserted into the slot between the two limbs of the fork, is not accompanied by a certain reduction in the section of the conductor, with the removal of metal particles, the effect of which is substantially to alter the characteristics of the conductor whose section has been reduced in this way, both from the point of view of tensile strength and from the point of view of bending strength.

According to the invention there is provided a self-stripping terminal, for an electrical connector, having a slot therein in which the core of a singlestrand or multi-strand electrical conductor can be retained, the insulating sheath or casing of the electrical conductor being cut or displaced on being introduced into a bevel configuration at the opening of the slot as the conductor is introduced into the slot, the slot being provided in a fork formed by two adjacently disposed limbs of the terminal, in which one of the limbs is carried by the free end of a resilient arm which is fixed by its other end on a structure which also carries the other of the limbs thereby to permit bending of the resilient arm, to cause the limbs of the fork to move apart, when the conductor is introduced in the slot such that a progressively increasing force is required to engage the conductor in the slot and a permanent resilient contact is maintained, the limbs of the fork extend opposite each other, perpendicularly to the longitudinal axis of the terminal, corresponding to the longitudinal axis of the electrical conductor connected to the terminal, such that the slot has flat walls which are parallel to each other and to the longitudinal axis of the terminal, and the slot is disposed in alignment with the bevel configuration at the opening of the slot with the bevel configuration itself formed by inclined flat walls which extend parallel to the longitudinal axis of the terminal.

In such a self-stripping terminal, the operation of cutting the insulation can still be ensured, when the conductor passes the bevel configuration at the opening of the slot, and the pressure force applied by the limbs to the conductor wire, which is made progressive, can push back and flatten the metal, without causing a noticeable reduction in its section. The resilient mechanical contact can ensure a permanent electrical contact, and these good connecting conditions may be achieved in regard to conductors wherein the differences in diameters range up to 30% between the smallest diameter and the largest diameter.

Advantageously however, each of the two limbs of at least one fork of the terminal is carried by the unfixed end of a resilient arm.

If desired the resilient arms can be pre-stressed so that, in the initial condition, before any conductor has been inserted into the slot, the prestressed arms cause the limbs to bear against each other. This arrangement makes it possible to achieve a virtually constant pressure force of the limbs of the resilient fork against the cores of conductors of different diameters, which may themselves be protected by insulating sheaths of different thicknesses and different materials.

In a preferred embodiment, the terminal comprises a U-shaped structure and fixing of the resilient arms is achieved by mounting the resilient arms on side portions of the U-shaped structure, the resilient arms being bent towards the interior of the profile of the U-shaped strucutre and being inclined with respect to the longitudinal axis of the terminal. Moreover, the fork limbs carried by the resilient arms can be attached to the arms which carry them by a rounded portion.

Each resilient arm can be separated from the base of the U-shaped structure, to one of the sides of which the arm is attached, by a cut-out portion provided in said base, from the position of attachment of the arm to the corresponding side portion, and extending longitudinally under the arm and transversely towards the interior of the terminal, beyond the projection of the arm onto the plane of the base.

The effect of these various measures can be respectively to permit the terminal to be housed in a chamber of simplae shape in an insulating carrier of a connector, while providing for stiffening of the fixing of the resilient arms by bearing against the sides of the chambers of the insulating carrier, and to improve the resilient mounting of the arms.

The self-stripping terminal, in addition to the' resilient fork whose two limbs are carried by the ends, which are not fixed, of two resilient arms which are fixed by attachment of their other end to the sides of U-shaped structure, may include, on an extended portion of a base of the U-shaped structure, which base is extended below the resilient arms and beyond the resilient fork, a semi-rigid fork comprising two rigid limbs which are separated by a slot provided in the end of the base, parallel to the slot in the resilient fork.

It is also possible for the terminal to have a further resilient fork with the two resilient forks facing each other, each resilient fork comprising two limbs which are carried by the two non-fixed ends of two resilient arms which are fixed by attachment of their other end to the side portions of a U-shaped structure, the two U-shaped structures being connected by a common base.

In this case, in order to retain the conductor to prevent it from any radial disengagement through the slots in the forces, the Ushaped structure of one of the resilient forks is arranged to permit said terminal to co-operate with a connection terminal of complementary shape, the other resilient fork being such that each of its limbs has a groove to retain the conductor to prevent it from being radially disengaged by way of the slots of the forks.

The groove is advantageously in the form of a cut-out portion in the limb, which opens onto the slot and towards the base, and such that the part of the slot which is closest to the base is wider than the part of the slot which is closest to the bevel configuration, these two parts each being defined between two flat walls which are parallel to each other and to the longitudinal axis of the terminal, and the walls of the two parts being connected, on each limb, by a flat wall which is perpendicular to the walls of said two parts.

Electrical connectors provided with terminals according to the invention, of complementary shapes and anchored in insulating carriers, can have the fixing of the resilient arms stiffened by the side portions of the U-shaped structure bearing against facing sides of the insulating carrier on which each terminal is anchored.

Likewise, it is possible to provide that, as from a certain degree of opening of the slot, the fixing of the resilient arms is stiffened by a portion of the arms bearing against the sides of the insulating carrier.

The invention is diagrammatically illustrated by way of example in the accompanying drawings, in which: Figure 1 shows a perspective view of a first embodiment of a self-stripping terminal according to the invention, provided with a resilient fork associated with a semi-rigid fork, of known kind: Figure 2 shows a plan view from above of the resilient fork of the terminal of Figure 1 anchored in an insulating carrier; Figure 3 shows a perspective view of a second embodiment of a self-stripping terminal according to the invention, provided with two resilient forks; Figure 4 shows a view from above of part of the terminal of Figure 3; and Figure 5 shows a perspective view from below, of a modified embodiment of the terminal of Figure 3, provided with complementary means for radially retaining a conductor.

The contact terminals shown in Figures 1 to 5 are of female type, one end of which is arranged to permit co-operation with male-type terminals of complementary shape.

For better comprehension of Figures 1 to 5, means for anchoring the contact terminal in an insulating carrier of a connector, and and end-oftravel abutment with which the terminal may be provided in order to limit the introduction of a male terminal of complementary shape, are not shown.

Referring to Figure 1, a contact terminal comprises a generally U-shaped structure 1 whose sides 2 and 3 are extended at one end to define resilient limbs of gripping means 4 of known shape, intended to permit the insertion and then the retention of a male terminal of complementary shape.

At the other end, the sides 2 and 3 are extended in the form of two resilient arms 5 and 6, to form, at their free ends, two limbs 7 and 8 of a fork 9 whose configuration is similar to that of a semi-rigid fork 31 of known kind, which is carried by the corresponding end of an extended base 11 of the U-shaped structure 1. However, the fork 9 is resilient since its limbs 7 and 8 are carried by resilient arms 5 and 6 which can flex since they are not rigid with the base 11 in the way that the sides 2 and 3 of the U-shaped structure 1 are.The functions of the limbs 7 and 8 with the respective arms 5 and 6 is formed by a rounded portion 10 and the resilient arms 5 and 6 are bent inwardly of the configuration of the U-shaped structure t and are inclined to the longitudinal axis XX of the terminal, which axis corresponds to the longitudinal axis of an electrical conductor when connected to the terminal. The two limbs 7 and 8 extend opposite to each other, perpendicularly to the longitudinal axis XX of the terminal, and between them form a slot 13 with flat walls, which are parallel to each other and to the axis XX, the slot 13 being disposed in alignment with a bevel configuration 12 at the opening of the slot 13, which bevel configuration 12 is itself formed by inclined flat walls extending parallel to the axis XX.

Parallelism of the flat walls of the slot 13 with respect to each other and with respect to the axis XX is a condition which should be observed with a high degree of precision. For example, when the width of the slot 13 in the rest condition is 0.15 mm, the deficiency of parallelism must be less than 0.05 mm.

Upon inserting a conductor whose metal core is surrounded by an insulating sheath which may be of various thicknesses and nature, between the limbs 7 and 8 of the resilient fork 9, cutting and/or displacement of the insulating sheath occurs first.

Then, when the conductor is introduced into the slot 13, the limbs 7 and 8 of the resilient fork 9 can move apart, while applying a progressive pressure force to the metal of the core of the conductor which is thus flattened and pushed back without significant reduction in the core section.

Being of circular section before the insertion operation, the core is progressively deformed by its section becoming oval, until it has two lateral flats against which the limbs 7 and 8 of the fork 9 resiliently bear to provide for a permanent electrical contact.

Using a conductor core which is made of a metal of known properties, which has been subjected to a determined heat treatment, it is easy to select the width and the thickness of the resilient arms 5 and 6, the length of the resilient arms 5 and 6 from their fixing points, and the initial width of the slot 13, before engagement of a conductor therein, in order to make it possible to connect conductors whose cores have differences in diameter of 25 to 3096 between the smallest and the largest diameter, or else in order to suit the pressure forces applied by the limbs 7 and 8 of the resilient fork 9 to the core of a determined conductor.

In order for the conductor better to be held mechanically to the contact terminal, it is possible for the resilient fork 9 to have associated therewith the semi-rigid fork 31 of known kind, comprising two rigid arms which are separated by a slot, as shown in Figure 1, in particular if the size of such a terminal is to be limited.

The contact terminal which is provided with a -resilient fork, as described hereinbefore, is anchored in an insulating carrier 20, Figure 2. It is advantageous for the fixing of the resilient arms such as 5 and 6 to be stiffened by providing for the sides 2 and 3 of the U-shaped structure 1 and even, as from a given degree of opening, the arms 5 and 6 themselves, to bear against the sides of the insulating carrier 20. The large support surface area thus obtained can avoid damage to the contact terminal when a conductor is connected or reconnected thereto, in contrast to what occurs with the terminals provided with forks of known kind.

In a preferred embodiment, two resilient forks are associated, on the same terminal, as shown in Figures 3 and 4. The U-shaped structure 1 is connected to a second U-shaped structure 14 by way of their common base 11. Mounted by sides 15 and 16 of the U-shaped structure 14 are resilient arms 1 7 and 18 which carry limbs 25 and 26 of a resilient fork 1 9 which is turned towards the fork 9 and which is constructed in a similar manner to the fork 9. Thus the limbs 25 and 26 are opposite each other, extend perpendicular to the axis XX, and are connected by rounded portions 10 to the arms 17 and 18 which are bent towards the interior of the configuration of the Ushaped structure 14, the walls of the slot 27 which is defined between the limbs 25 and 26 being parallel to each other and to the axis XX.

Each of the resilient arms 5, 6, 17 and 18 is separated from the base 11 of the U-shaped structures 1 and 14 by a cut-out portion 29 or 30 provided in the base 11, and extending to the junction of the arms 5, 6, 17 and 1 8 respectively with the sides 2, 3, 1 5 and 16; the cut-out portions 29 and 30 thereby extend longitudinally below the arms 5 and 17, and 6 and 18 respectively, and transversely, towards the interior of the terminal, beyond the projections onto the plane of the base 11 of the arms 5 and 17, 6 and 1 8 respectively.

In the two embodiments described with reference to Figures 1 to 3, it will be seen that the provision of a second fork, whether semi-rigid as at 31 or resilient as at 14, considerably improves mechanical holding of the conductor, compared with the holding action of the resilient fork 9, and protects the electrical connection against longitudinal forces which may accidentally be applied to the conductor. However, this mechanical anchoring action is relatively weak in regard to possible stresses which produce forces in directions substantially parallel to the slots of the forks. Figure 5 shows a terminal similar to that shown in Figures 3 and 4, which has been modified to remedy this weakness and which provides an anchoring action which is much better than that produced by means of the terminals shown in Figures 1 to 4.Identical components of the two terminals shown in Figures 3 and 4 will not be described again and will be denoted by the same reference symbols.

The feature differentiating a resilient fork 19 of Figure 5 from the resilient fork 9 is a groove 21 in each of the limbs 25 and 26. The groove 21, is in the form of a cut-out portion in the limbs 25 and 26, which opens out of the slot 27 and towards the common base 11, so that a part 22 of the slot 27, which is closest to the base 11, is wider than a part 23 of the slot 27 which is closer to the bevel configuration 24 at the mouth of the slot in the fork 19, the two parts 22 and 23 each being defined between two flat walls which are parallel to each other and to the axis XX, and the walls of the two parts 22 and 23 being connected, on each limb 25 or 26, by a shoulder formed as a flat'wall 28 which is perpendicular thereto and which forms the operative part of the groove 21.As in the bevel configuration 1 2, the bevel configuration 23 is formed by inclined flat walls which are parallel to the axis XX.

The terminal of Figure 5 operates in the following manner: upon insertion of a conductor between the limbs 7 and 8 of the resilient fork 9 and between the limbs 25 and 26 of the resilient fork 19, as the conductor passes the bevel configurations 12 and 24 at the openings of the slots 1 3 and 27, the insulating sheath of the conductor is firstly cut and/or displaced. Then, when the conductor is introduced into the slots 13 and 27, the limbs 7 and 8 on the one hand and 25 and 26 on the other hand move apart, while applying a pressure force to the core of the conductor if the conductor is a single-strand conductor, or to the cluster of strands within the sheath if the conductor is a multi-strand conductor.

The core or cluster of strands, which was circular in section before the insertion operation, is deformed, into an oval configuration, until it has two lateral flats against which the limbs 7 and 8 of the fork 9 will constantly bear resiliently in order to ensure permanent electrical contact, as well as providing for excellent mechanical retention of the conductor to the terminal, capable of resisting any accidental longitudinal force applied thereto. The resilientforce of the limbs 25 and 26 bearing against the core of cluster of strands will occur only while the core or cluster is passing through the narrow part 23 of the slot 27 of the fork 19.

After the conductor has passed through that part 23, the limbs 25 and 26 of the fork 19 are resiliently pushed towards each other by the resilient arms 1 7 and 18 so that the fork 1 9 closes again and the conductor is held in the wider part 22 of the slot 27, thereby providing for radial anchoring of the conductor. In fact, following any force which is applied in the direction of the slots 13 and 27, the conductor comes to bear against and is retained against the flat shoulder walls 28 which act as abutments, of the grooves 21, without the danger of causing the fork 19 to be opened.

The presence of a groove 21 on each of the limbs 25 and 26 of the fork 19 makes it possible to avoid the necessity for using either retaining elements which are integrated in the insulating carrier in which the terminal is positioned, or additional elements for holding the conductors in the forks, as is the case with the prior art selfstripping terminals, in particular those disclosed in USA parent No. 3 162 501.

In addition to the possible ways of adjusting the pressure forces which are applied to a given conductor, and the possibilities of connecting conductors of different diameters, which are provided by the self-stripping terminal with resilient fork, by virtue of the many parameters which it is easy to adjust, further substantial advantages can derive from the invention. In particular, the terminals with resilient fork may be re-cabled a large number of times (from 10 to 20 times) without resulting in any substantial change in the mechanical and electrical characteristics of the connection. In addition, the terminals can provide for advantageous connection, in the case of multi-strand conductors. Indeed, inserting such conductors in forks of known kind is often accompanied by the strands which come most into contact with the edges of the slot being cut, and relaxation of the cluster of strands tend to cause the cluster to become more oval than would be appropriate. Breaks in the electrical contact may then occur, if the terminal is subjected to vibration. The elastic forks however need not suffer from these disadvantages. On insertion of the multi-strand conductor, opening of the limbs of the fork makes it possible to avoid cutting the strands. The strands are simply displaced relative to each other and any relaxation of the cluster of strands is accompanied by a tightening of the limbs, due to the resilience of the arms, so that electrical continuity is ensured. Multi-strand or single-strand conductors can thus be connected with a high degree of stability in regard to contact resistance.

Finally, by association of resilient forks with forks of the same kind or with forks of a different kind, which are rigid or semi-rigid, on the same contact terminal, or within the same connector, it is possible to provide the connection with widely varying mechanical and electrical properties, thereby permitting a high degree of facility of adaptation to the space available for making the connection, or to the climatic conditions of use.

Claims (13)

1. A self-stripping terminal, for an electrical connector, having a slot therein in which the core of a single-strand or multi-strand electrical conductor can be retained, the insulating sheath or casing of the electrical conductor being cut or displaced on being introduced into a bevel configuration at the opening of the slot as the conductor is introduced into the slot, the slot being provided in a fork formed by two adjacently disposed limbs of the terminal, in which one of the limbs is carried by the free end of a resilient arm which is fixed by its other end on a structure which also carries the other of the limbs thereby to permit bending of the resilient arm, to cause the limbs of the fork to move apart, when the conductor is introduced in the slot such that a progressively increasing force is required to engage the conductor in the slot and a permanent resilient contact is maintained, the limbs of the fork extend opposite each other, perpendicularly to the longitudinal axis of the terminal, corresponding to the longitudinal axis of the electrical conductor connected to the terminal, such that the slot has flat walls which are parallel to each other and to the longitudinal axis of the terminal, and the slot is disposed in alignment with the bevel configuration at the opning of the slot with the bevel configuration itself formed by inclined flat walls which extend parallel to the longitudinal axis of the terminal.

2. A self-stripping terminal according to claim 1, in which said other of the limbs is also carried by the free end of a resilient arm.

3. A self-stripping terminal according to claim 1 or claim 2, in which one at least of the resilient arms is pre-stressed so that, in an initial condition, it applies a force causing one of the limbs to bear against the other.

4. A self-stripping terminal according to claim 2, in which said structure is a U-shaped structure and the resilient arms are mounted on side portions thereof, the resilient arms being bent towards the interior of the profile of the U-shaped structure and being inclined with respect to the longitudinal axis of the terminal.

5. A self-stripping terminal according to claim 4, in which the fork limbs are carried on the resilient arms with a rounded portion between each fork limb and its respective resilient arm.

6. A self-stripping terminal according to claim 4 or claim 5, in which the base of the U-shaped structure, beneath each of the resilient arms is cut away, each portion cut away extending longitudinally from the position of attachment of the arm to the corresponding side portion below the arm and transversely inwardly of the terminal, beyond the projection of inner face of the arm onto the plane of the base.

7. A selfstripping terminal according to any one of claims 1 to 6, in which the two limbs of the resilient fork are carried by the non-fixed ends of respective resilient arms which are fixed by attachment of their other ends to the sides of a Ushaped structure whose base, which extends below the resilient arms and beyond the resilient fork, is shaped to form a semi-rigid second fork comprising two rigid limbs which are separated by a slot provided in the end of the base, parallel to the slot in the resilient fork.

8. A self-stripping terminal according to any one of claims 1 to 6, including a further fork facing said fork, said further fork also comprising two limbs which are carried by the non-fixed ends of two resilient arms which are fixed by attachment of their other end to the sides of a U-shaped structure with the two U-shaped structures connected by a common base.

9, A self-stripping terminal according to claim 6, in which the U-shaped structure of one of the resilient forks is so disposed as to permit the terminal to co-operate with a connection terminal of complementary shape, and the other resilient fork has a groove provided in each of its limbs in order to restrain the conductor from radial disengagement from the slot in said other fork, the grooves each being in the form of a cut-out portion in the respective limb, which cut-out portion opens into the slot and towards the base, and being such that the part of the slot which is closest to the base is wider than the part of the slot which is closest to the bevel configuration, said two parts each being defined between two flat walls which are parallel to each other and to the longitudinal axis of the terminal, and the walls of said two parts being connected, on each limb, by a flat wall which is perpendicular to the walls of said parts.

1 0. An electrical connector of the kind comprising a contact terminal anchored in an insulating carrier and capable of co-operating with a contact terminal of complementary shape also anchored in an insulating carrier, in which at least one of said contact terminals is a terminal according to any one of claims 1 to 9.

11. An electrical connector according to claim 10, provided with at least one contact terminal, in accordance with claim 4, in which the fixing of the arms is stiffened by the sides of the U-shaped structure bearing against facing sides of the insulating carrier in which said terminal is anchored.

12. An electrical connector according to claim 11, in which, as from a certain degree of opening of the slot, the fixing of the resilient arms is stiffened by a portion of the arms bearing against the sides of the insulating carrier.

13. A self-stripping terminal for an electrical connector substantially as hereinbefore described and illustrated with reference to Figure 1, Figure 2, Figures 3 and 4 or Figure 5 of the accompanying drawings.