WO1994011922A1

WO1994011922A1 - Integral contact element

Info

Publication number: WO1994011922A1
Application number: PCT/US1993/011234
Authority: WO
Inventors: Udo Seidel; Karl Heinrich Heucke; Vern Radewald; Mary R. Baumler
Original assignee: Minnesota Mining And Manufacturing Company
Priority date: 1992-11-14
Filing date: 1993-11-12
Publication date: 1994-05-26
Also published as: ZA938399B; AU5671494A; DE4238534A1

Abstract

Integral contact element, particularly for a plug-type connector, comprising a U-shaped contact portion, having two approximately parallel legs interconnected by a web portion and defining a receiving slot therebetween for the receipt of a cable, with the edges of the legs facing the slot adapted to pierce the insulation of the cable and to engage the cable wire under resilient deformation of the legs. A preferably fork-shaped second contact portion is asymmetrically connected to the web portion oppositely to the legs of the first contact portion, with the leg of the second contact portion adjacent to the U-shaped contact portion having a smaller width than the other leg in order to achieve an approximately symmetrical stress distribution. And the legs of the fork-shaped element are chamfered on the surface facing away from the slot of the U-shaped portion.

Description

INTEGRAL CONTACT ELEMENT Background of the Invention

The invention refers to an integral contact element, particularly for a plug-type connector. PRIOR ART

U-shaped insulation displacement contact elements for the contacting of cables without removal of the insulation sheath in that the edges of the legs facing the cable-receiving slot pierce the insulation and displace it in order to engage the cable conductor are known in various designs. They are extensively used in telecommunication systems. Only for example, it is pointed to the US patents Nos. 4,773,875 or 5,022,868 disclosing such U- contacts.

Furthermore, contact elements are known where a U- shaped insulation displacement contact is combined with a further contact portion, e.g. a further U-contact as disclosed in the USA patent No. 4,552,429. From the

USA patent No. 4,564,254 it has become known to combine a plug-in portion with a U-shaped contact. In this connection, it has also become known from "Technical Report 4005 Super Mate Pluggable Module" 3M November 1989 to combine a fork-shaped contact portion with a U- contact and to turn the fork-shaped contact portion relative the U-contact about 90^*. Such contact elements which are preferably formed of flat material are located in a connector housing and for example are used in telecommunication connections. The fork-shaped contact portions for example coact with pin-shaped or strip-like contact portions of the other connector_vpart when a connection between the two connector parts is to be established. The connection of the two contact portions of the known contact elements is frequently such that the web of the U-contact is asymmetrically formed with respect to the axis of the cable receiving slot of the U-contact.

In U-shaped contacts, it is essential that a sufficient force is generated between the legs in order to pierce the insulation and to effectively engage the conductor of the cable. The contact force is to be maintained over a longer period. Upon insertion of a cable into the receiving slot of the U-contact the legs are resiliently deformed. It is essential that the elastic limit is not exceeded since otherwise, a plastic deformation takes place which does not provide the necessary resilient contact force. In the use of U-shaped contacts with an asymmetrical web, it has been learned that the stress distribution in the legs and the web is not symmetrical/ Particularly in the use of cables having a larger outer diameter it may happen that the leg which is more loaded or stressed is subject to fatigue and the insertion of the cable leads to a plastic deformation. This problem could be met by extending and/or broadening the legs of the U-contacts. Since normally such contact elements are used in connectors with standard sizes and pitch, the dimensions of such U-contacts cannot be enlarged arbitrarily. Besides, a broadening of the legs or extension would result in a larger contact force so that the wire may be unduly deformed.

From the USA patents 4,932,893, 4,564,254, 4,484,791 or 4,441,779, integral contact elements have become know wherein the U-shaped contact portions are formed with an asymmetrical web portion. The problems described above are not discussed in these publications.

In USA patent Re 31,714 or USA patent No. 4,988,311, contact elements are described wherein the legs of U-contacts are asymmetrically formed. The specific configuration of the legs has the purpose to retain a cable temporarily in an upper portion prior to this final insertion into the receiving slot. The portions of the legs contacting the wire of the cable are symmetrical.

The USA patents Nos. 3,605,072 and 4,084,877 describe double U-shaped contact elements having three legs in a common plane with receiving or entrance slots formed between adjacent legs. The USA patent No. 4,084,877 discloses an element wherein the center leg is rigid and is not deflected if a cable is inserted into the slot. The outer legs are symmetrically formed. Thus, also the stress distribution is asymmetrical. The element of USA patent No. 3,605,072 has a center leg which is provided with an elongated, closed slot. Thus, parallel leg portions are defined which are subject to bending stresses upon an insertion of a cable into the slots. The kind of load in the legs is therefore different and leads to a different stress distribution in the legs and the web joined thereto. The state of the art of the application includes fork-shaped contact elements to be plugged together with U-contacts such that the legs of the fork-shaped contact element overgrip a leg of the U- contact from the free end thereof. Such contact arrangements, for example, are used in the telecommunication technology. By means of a further connector part, a connection with cables can be made which in turn are electrically connected with a first connector part through U-shaped contact elements. By this, a further conducting path can be established parallel to the existing one without the necessity to interrupt the operation through the individual cables. Such a further communication path can be useful when a telecommunication system is to be changed to a digital system. The plugging¹ of fork-shaped contact elements on U- shaped contacts in a manner described above was satisfactory in the past. When turning to a digital system frequently there is the necessity to use cables with larger diameter wire and insulation in order to achieve an extension of the range. The result of this, however, was that with the same pitch of the connector parts the legs of the fork-shaped contact elements suffer a bending by the displaced insulation of the cable deformed in the U-shaped displacement contacts. The bending effect is increased if the insulation material is relatively hard. A bending of the fork- shaped contact elements, however, reduces the quality of the electrical connection. SUMMARY OF THE INVENTION

The invention provides an integral contact element wherein uniform bending stresses occur if a cable is inserted into a U-contact although the web of the U- contact has an asymmetrically shape.

The invention is for example applicable to a contact element wherein the web of the U-contact is asymmetrically joined to a fork-shaped contact in a position rotated about 90^*.

It has surprisingly turned out through calculations and experiments that a symmetrical load on an asymmetrical U-contact can be achieved when the leg adjacent to the other contact portion has a reduced width relative to the width of the other leg. As already mentioned, the U-contact is designed such that sufficient contact force is developed upon inpertion of a cable to allow a penetration and displacement of the insulation by the legs. If in such a U-contact one leg has a reduced width, this results in a symmetrical distribution of the bending stress throughout the shape of the U-contact inclusive of the web portion. Particularly in the use of cables having a larger diameter the danger that the cable wire is unduly deformed is reduced upon insertion of the cable.

By numerical methods (finite element analysis) and/or experiments and/or computer simulation, the relation of the width of both legs of the U-contact can be determined in order to achieve the desired uniform stress distribution.

In the invention, the free end portions of the legs of the fork-shaped contact element are provided with an inclined or oblique surface, preferably a straight oblique surface, whereby a tapering end is formed with such chamfer on the side of the legs facing away from the receiving slot between the legs of the U- contact element. It is conceivable to use a curved surface rather than a straight one. Furthermore, two or more oblique surfaces can be provided effecting the tapering end portion of the legs. In an embodiment of the invention, the end of the tapered end portion may be obtuse. The width of the obtuse end is approximately one half the thickness of the legs or smaller.

The relatively sharp free ends of the legs of the fork-shaped contact elements pierce the deformed insulation material in case it lies in the movement direction of the legs whereby a possible deformation of these legs away from the U-shaped contact is restricted. The position of the inclined surfaces or the chamfer, respectively, opposite to the side facing the cable effects a force component towards the cable if the legs pierce the insulation material whereby a bending of the legs is avoided. Therefore, ir. spite of more or less collected insulation material in the engagement area of both contact elements, the invention provides for a reliable electrical connection.

A contact element according to the invention has the following advantages: an overstressing of portions of the U-contact is avoided - the contact forces during the necessary life time of the contact are maintained additional manufacturing costs are not necessary the tool for the manufacture of the contact elements according to the invention needs only a relatively small modification - an undesired excessive deformation of the cable wire does not take place, undesired bending forces on the fork-shaped contact element upon a plugging-in with a U- shaped contact are avoided also with large diameter wires; the fork-shaped contact element according to the invention can be made by conventional techniques. It is not necessary to redesign the element. The additional expense for the manufacturing of the chamfer is small, particularly in mass production. BRIEF DESCRIPTION OF THE DRAWINGS

The invention is subsequently explained with reference to the accompanying drawings, wherein Fig. 1 is a plan view of a conventional contact element having two U-shaped insulation displacement contact portions;

Fig. 2 is a plan view of a contact element according to the present invention including a U-shaped insulation displacement contact portion and a fork- shaped contact portion;

Fig. 3 is a plan view of a contact element of Fig. 2 turned about 90°;

Fig. 4 is a plan view of the contact element corresponding to Fig. 2;

Fig. 5 is an enlarged view of a sample of the U- contact portion of the structure of Fig. 4; and

Fig. 6 is a cross-sectional view of the housings of two connector parts, one which is equipped with a contact element according to the invention. DETAILED DESCRIPTION OF THE DRAWINGS

Fig. 1 depicts a conventional contact element 10, for example formed of flat material . It includes two U-shaped insulation displacement contact portions 12, 14 which are interconnected through a common web 16. The contact portions 12, 14 each include legs 18,20 and 22,24, respectively, and a receiving slot 26 and 28, respectively, therebetween. As can be seen, the contact portions 12, 14 are completely symmetrical. If a cable is inserted into the receiving slots 26,28, the legs 18,20 and 22,24 respectively, are symmetrically deformed (not shown) .

The contact element of Figs. 2 and 3 includes a U- shaped insulation displacement contact portion 32 and a fork-shaped contact portion 34. Contact portion 32 includes legs 36,38 and a receiving slot 40 therebetween. Legs 36,38 are interconnected through a web 42 to which also contact portion 34 is joined. As can be seen in Fig. 2, contact portion 34 is offset relative to the axis of U-contact portion 32. It is further rotated about 90^*. This results in an asymmetrical configuration of web 42. The fork-shaped contact portion 34 includes legs 44,46 and a receiving slot 48 therebetween which is also symmetrically structured. It has now turned out that an insertion of a cable into the receiving slot 40 of U-contact portion 32 leads to a symmetrical distribution of the stresses.

The contact element 50, see Fig. 4 includss a U- shaped insulation displacement contact portion 52 having approximately parallel legs 54,56 and a receiving slot 58 therebetween. The legs 54,56 are interconnected through a web 60 to which a fork-shaped contact portion 62 is joined in the same manner as contact portion 34 of the embodiment of Figs. 2 and 3. Contact portion 62 is discussed in more detail hereinafter. It may for example be pushed onto leg 18 of contact portion 12 in order to establish an electrical connection between contact elements 10,50 which are located in housings of different connector parts (not shown) . The receiving slots 26, 28 of contact element 10 and receiving slot 58 of contact element 50 may receive a cable in a conventional manner (not shown) . By this, parallel communication paths can be established, e.g. in telecommunication systems. This eliminates the necessity to interrupt the communication if for example a change to a digital system is to take place. As can be recognized, leg 54 adjacent to contact portion 62 is significantly smaller than leg 56. Leg 54 has an average width of "a" which is smaller than the corresponding width "b" of leg 56 which leg has an increasing width towards web 60. The outer edge 64 of leg 56 is oblique while the 'outer edge 66 of leg 54 is parallel to the axis of contact portion 52, or parallel to the axis of slot 58.

The width of web 60 is not constant. The smallest width c is measured approximately beneath slot 58, while the largest width d is measured on the opposite side of contact portion 62. As can be seen, d is larger than b, while c is approximately equal to a. Besides, the following sizes are valid for contact element 50: Total length - 8,1 mm

Width of web 60 transverse to legs 54,56 = 3,95 mm Length of legs 54,56 = 2, 6 mm a = 1, 05 mm b 1,15 mm c = 1, 05 mm d = 1,5 mm Thickness of sheet material = 0,4 mm The sheet material is phosphor-bronze.

With such a design of a U-contact it turned out that despite geometrical asymmetry a symmetrical stress distribution takes place upon insertion of a cable, with the load peaks located lower as is the case for example with known contact elements as contact element 30 of Figs. 2 and 3. In Fig. 5, an example on the U-contact portion of Fig. 4 is shown, here designated with 52a. It includes legs 54a, 56a and a cable receiving slot 58a therebetween. The web 60 is asymmetrically shaped and the lower web portion 70 can for example be joined to a further contact portion, e.g. contact portion 62 of Fig. 4. As can be seen, leg 54a is significantly narrower than leg 56a. Despite this fact, it surprisingly turned out the leg 54 is less laterally deflected than 56a if cable (not shown) is inserted into slot 58a. This has yielded through investigations and calculations. In Fig. 5 the initial state is indicated by dashed lines and the deformed state is drawn with continuous lines. The distribution of the bending stresses in legs 54a, 56a and web 60a is approximately uniform as found out by investigations and calculations, too.

It can be seen in Figs. 2 and 3 that the legs 44,46 have a chamfer 44a,46a in the free end portion thereof. This chamfer 44a,46a is made such that the end portion tapers toward an obtuse free end formed with a rounded contour in the plane of legs 44,46 (Fig. 3) . The chamfer is in the surface of the contact element 30 opposite the surface closest to the cable- receiving slot 40 in the contact element 30. A similar champfer 63 is shown on the fork-shaped portion 62 of contact element 50.

A contact portion 34,62 for example has a thickness of 0.4mm. The chamfer 44a,46a,63 may make an angle of 20^* relative to the longitudinal axis of legs 44,46 and the tapering takes place to a width of 0.2mm, i.e., half the thickness of legs 44,46. By means of the fork-shaped contact portion 34,62 as shown in Figs. 2,3 and 4 a satisfactory electrical connection can be achieved with cables up to a wire diameter of 0.9 mm and an outer insulation diameter of 1.95 mm, also if the insulation consists of a HD-polyethylene. Conventional cables have an outer diameter of 1.65 mm and a wire thickness of 0.65 mm.

Fig. 6 illustrates a cross section through a housing 80 which accommodates one or more rows of contact elements, only one contact element is shown at 50 within recess 82. The receiving slot 58 of element 50 is adapted to receive a cable 84 in the manner described above. A further housing 85 shown also in cross section accommodating a plurality of contact elements, one thereof shown at 10. It corresponds to element 10 in Fig. 1. It receives a cable 90 and one leg co-acts with the fork-type contact portion 62 which projects beyond housing 80. The configuration of the housing 80,86 and the positioning of the elements 10, 50 are generally known. In Fig. 6 it can be seen that the fork-shaped contact portion 62 engages leg 18 of U-contact portion 12 of contact element 10. The chamfer 63 of the legs of the fork-shaped portion 62 is located opposite to the side facing slot 58 or conductor 84, respectively. Such tapered end portion enables the legs of the fork- shaped portion 62 to pierce through the insulation material 88 surrounding the cable 90. The effect of the position of the chamfer 63 is such that the legs are not bent away from cable 90. In contrast, the chamfers rather develop a force component towards cable

90.

As can be seen further, the obtuse end of the legs of the fork-shaped portion 62 does not disturb the function described.

Claims

1. An integral contact element, particularly for a plug-type connector, comprising a U-shaped contact portion, having two approximately parallel legs (36,38) interconnected by a web (42) and forming a cable- receiving slot therebetween (40) , with the edges of said legs defining said slot for piercing the insulation of said cable and resiliently engaging the conductor upon insertion of a said cable into said slot, and a preferably fork-shaped second contact portion (34) joined to said web (42) opposite to said legs (36,38) characterized in that the portion of said web (42) located oppositely to said legs of said U- contact portion is located asymmetrically in relationship to the axis of said cable-receiving slot (40), such that said one leg (36,54,54a) of said U- shaped contact portion (32,52) adjacent to said second contact portion (34,62) is provided with a reduced width compared with that of the other leg (38,56,56a) such that the bending stress distribution in said U- shaped contact portion is approximately uniform upon a said cable being inserted into said slot (40,58,58a).

2. The contact element of claim 1, wherein said second contact portion (34,62) is a fork-shaped contact portion rotated about 90' relative to the U-shaped contact portion (32,52).

3. The contact element of claim 1, wherein the edges of said one of said legs (36,54,54a) of reduced width extend approximately parallel to each other.

4. The contact element of claim 2, wherein the edges of said one of said legs (54) of reduced width extend approximately parallel to each other.

5. The contact element of claim 1, wherein the shortest distance (c) between said receiving slot (58) and the free edge of said web portion (60) interconnecting said legs is approximately equal to the width (a) of said smaller leg (54) .

6. The contact element of claim 1, wherein the thickness of the sheet material of said contact element (30,50) is between 0.35 and 0.5 mm for cable diameters of 0.32 to 0.9 mm if phosphor bronze or brass is used for said material.

7. A contact element for a plug-type connection including connector parts, wherein one connector part has a fork-shaped contact element (34,62) having a web (42,60) with opposite surfaces and a free end with a slot (48) formed therein to define two spaced legs

(44,46) and the other part has at least one U-shaped insulation displacement contact element (32,52) defined by a web (42,60) having spaced legs (36,38 54,56) formed at the free end with a cable-receiving slot (40,58) therebetween, with said legs (44,46) of said fork-shaped element being adapted for making gripping engagement with a said leg (36,54) of a said U-shaped contact element (32,52) from the free end thereof, wherein said free end portions of said legs of said fork-shaped element are provided with an oblique surface defining a chamfer (44a,46a, 63) on one side such that said legs (44,46) of said fork-shaped contact element taper towards the free end thereof.

8. The contact -element of claim 7, wherein a straight chamfer is provided.

9. The contact element of claim 7, wherein the end of the legs is obtuse.

10. The contact element of claim 9, wherein the thickness of the obtuse end of the legs 44,46) is not more than approximately half of the thickness of said web (42,60) .