An insulation-displacement terminal fitting

Abstract: [Object] To improve contact reliability while preventing a terminal fitting from becoming larger. [Solution] An insulation-displacement groove 24 is formed between blades 20 formed to project at right angles from left and right side walls 22 by cutting and bending. The insulation-displacement groove 24 is formed such that a straight contact groove 26 is continuously provided below a guide groove 25 having an angled tapered shape by being defined by moderately sloped edges 31 at its upper side and steeply sloped edges 32 at its lower side. When a coated wire W is pushed in, cuts are made in a coating Wb by boundary portions 35 between the moderately sloped edges 31 and the steeply sloped edges 32 of the guide groove 25. As the coated wire W is further pushed, the coating Wb is cut and a core Wa thus exposed is pushed into the contact groove 26 while being guided toward the center of the contact groove 26 by the steeply sloped edges 32, consequently establishing a contact by being tightly held between contact edges 33.

Description: The present invention relates to an insulation-displacement terminal fitting. An insulation-displacement terminal fitting shown in FIG. 8 is known as one example of the convention insulation-displacement terminal fitting. This terminal fitting is as follows. A pair of blades 2 are formed to project from left and right side walls 1 and face each other by making cuts in the side walls 1 and bending cut portions at right angles. An insulation-displacement groove 3 is formed between the blades 2 such that a straight contact groove 5 is continuously provided below a tapered guide groove 4 whose width is gradually narrowed toward its bottom end. When a coated wire W is pushed toward the contact groove 5 from the guide groove 4, a coating Wb is cut by a boundary portion 6 between the guide groove 4 and the contact groove 5, and an exposed core Wa is connected with the blades 2 while being tightly held between contact edges 7 of the contact groove 5. Insulation-displacement terminal fittings having such a construction are disclosed, for example, in Japanese Unexamined Utility Model Publication No. 2-150764. The guide groove 4 of the insulation-displacement groove 3 functions mainly to guide the coated wire W to the center of the contact groove 5. There are various discussions on the shape of the guide groove 4 including its angle of inclination. For example, if the inclination of the guide groove 4 is moderate, the guiding function of guiding the coated wire W to the center of the contact groove 5 is poor, and not only the coating Wb but also the core Wa may be cut due to an acute angle of the boundary portion 6 between the guide groove 4 and the contact groove 5. However, the moderate inclination has an advantage that the blades 2 are allowed to have a short height. Conversely if the inclination of the guide groove 4 is steep, the terminal fitting becomes larger due to a larger height of the blades 2 and it is difficult to cut the coating Wb although it provides an excellent function of guiding the coated wire W to the center of the contact groove 5. EP-A-0 859 430 which is considered to represent the closest prior art discloses an insulation-displacement-terminal having a slot and a first and a second pair of slopes, where the slopes of each pair are opposed to each other and where the slopes becoming more steep in the direction towards the slot. The total height of the insulation-displacement-terminal is rather large. The present invention was developed in view of the above situation and an object thereof is to improve contact reliability while preventing a terminal fitting from becoming larger. This object is solved according to the invention by an insulation-displacement terminal fitting according to claim 1. Preferred embodiments are subject of the dependent claims. According to the invention, there is provided an insulation-displacement terminal fitting, comprising an insulation-displacement groove having at least one contact groove to be brought into contact with a core of an insulated wire and at least one tapered guide groove whose width is gradually narrowed in an insertion direction of the coated wire into the insulation-displacement groove, wherein the guide groove has an angled tapered or narrowed shape having a moderate inclination portion at a front side and a steep inclination portion at a back side with respect to the inserting direction of the coated wire into the insulation-displacement groove, wherein a height of the moderate inclination portion along the insertion direction is at least half the height of the guide groove. According to a preferred embodiment of the invention, the contact groove is continuously provided at a back side of the tapered guide groove in the insertion direction. Thus, there is provided an insulation-displacement terminal fitting, comprising an insulation-displacement groove which is formed such that a contact groove is continuously provided at a back side of a tapered guide groove whose width is gradually narrowed toward its back side, in which terminal fitting a coated wire is pushed toward the contact groove from the guide groove, thereby bringing a core exposed by cutting a coating of the coated wire into contact with contact edges of the contact groove, wherein the guide groove has an angled tapered shape having a moderate inclination at a front side and a steep inclination at a back side with respect to a pushing direction of the coated wire. When the coated wire is pushed toward the contact groove from the guide groove, the coating is cut by boundary portions between the moderately sloped edges and the steeply sloped edges of the guide groove and the core thus exposed is pushed into the contact groove while being guided toward the center of the contact groove by the steeply sloped edges, consequently establishing a contact by being tightly held between the contact edges. By forming the guide groove to have an angled tapered shape by the moderately sloped edges at its front side and the steeply sloped edges at its back side with respect to the pushing direction, the depth of the entire insulation-displacement groove can be suppressed, i.e. the terminal fitting is prevented from becoming larger, the coating can be satisfactorily cut and the core can be precisely guided to the center of the contact groove. Therefore, contact reliability can be remarkably improved. Preferably, the insulation-displacement groove is formed between a pair of blades projecting from left and right side walls of the insulation-displacement terminal fitting to substantially face each other. Further preferably, the insulation-displacement groove is formed in a portion of a bottom wall of the insulation-displacement terminal fitting bent at an angle different than 0° or 180°, preferably substantially normal to the bottom wall. Still further preferably, the insulation-displacement groove is formed between a pair of blade portions projecting inwardly substantially in V-shape when viewed in the inserting direction of the coated wire. Thus preferably, the insulation-displacement groove is formed between a pair of blades projecting from left and right side walls of the insulation-displacement terminal fitting to face each other, and/or the pair of blades project inwardly in V-shape when viewed in the pushing direction of the coated wire. The present invention is effectively applicable to insulation-displacement terminal fittings of the type in which the coating is cut open by getting caught by V-shaped blades. Specifically, since a portion for cutting the coating open has a large area in the V-shaped blade portions, if an attempt is made to forcibly cut the coating open, the coating may be torn over a wide area to expose the core after connection by insulation displacement and a contact failure may occur resulting from loosening of the core. However, in the present invention, the coating can be more easily cut open by the boundary portions between the moderately sloped edges and the steeply sloped edges of the guide groove. Thus, a cut-open portion of the coating is kept minimum in size, thereby preventing the exposed portion of the core Wa from becoming larger. According to still a further preferred embodiment, cuts are made in a coating of the coated wire by boundary portions between the moderate inclination portions and the steep inclination portions of the guide groove, when the coated wire is at least partly inserted into the insulation-displacement groove. Preferably, a first angle formed between the moderate inclination portion and a line normal to the wire insertion direction is about 45° or larger and a second angle formed between the steep inclination portion and this line is between the first angle and 90°. Further preferably, a spacing A between boundary portions between the moderate and steep inclination portions of the guide groove, a diameter B of a core of the coated wire and a width C of the insulation-displacement groove satisfy a relationship A ≥ B ≥ C. Most preferably, two insulation displacement grooves are provided in longitudinally spaced positions, respective distal portions of blade portions thereof being coupled by one or more coupling portions. Most preferably, the contact groove and/or the tapered guide groove is defined between a pair of blades being formed by making cuts in side walls and bending the cut portions by an angle different from 0° or 180°, preferably by substantially 90° with respect to the side walls. These and other objects, features and advantages of the present invention will become more apparent upon reading of the following detailed description of preferred embodiments and accompanying drawings. It should be understood that even though embodiments are separately described, single features thereof may be combined to additional embodiments. FIG. 1 is a perspective view partly cut away showing a first embodiment of the present invention, FIG. 2 is a section along X-X of FIG. 1, FIG. 3 is a section along X-X of FIG. 1 when connection by insulation displacement is completed, FIG. 4 is a perspective view of a second embodiment, FIG. 5 is a perspective view of a third embodiment, FIG. 6 is a plan view of a fourth embodiment, FIG. 7 is a lateral section of the fourth embodiment, and FIG. 8 is a lateral section of a prior art. Hereinafter, preferred embodiments of the present invention are described with reference to the accompanying drawings. <First Embodiment> A first preferred embodiment of the present invention is described with reference to FIGS. 1 to 3. A coated wire W has a known structure in which a core Wa e.g. made by twisting strands is covered with a coating Wb made e.g. of a synthetic resin. An insulation-displacement terminal fitting 10 of this embodiment is formed into a shape shown in FIG. 1 preferably by successively cutting and bending or folding a metallic plate by means of a press, and is provided with a connecting portion 11, an insulation-displacement portion 12 and a barrel portion 13 in this order from its leading end (end to be connected with an unillustrated mating connector). The connecting portion 11 is substantially in the form of a rectangular tube which is hollow in forward and backward or longitudinal directions. A metal locking portion 15 is formed at the lateral or upper wall of the connecting portion 11 preferably by cutting and bending and/or embossing, and an elastic contact piece (not shown) is provided inside preferably by folding back a tongue extending from the front end of the bottom wall. A tab of an unillustrated male terminal fitting is or can be inserted into the connecting portion 11 preferably from front to be elastically or resiliently brought into contact with the elastic contact piece. In the barrel portion 13 at the rear end, a pair of crimping pieces 18 project from left and right short side walls 17 while being displaced or spaced from each other in forward and backward or longitudinal directions. The coated wire W is or can be fastened to the insulation-displacement terminal fitting 10 by crimping or bending or folding the crimping pieces 18 into connection with the coated wire W connected or connectable with the insulation-displacement portion 12 by insulation displacement. The insulation-displacement portion 12 is in the form of a channel or groove having an open upper surface, and two blade portions 21 each comprised of a pair of left and right blades 20 are provided while being spaced apart in forward and backward or longitudinal directions. Specifically, the blades 20 are preferably formed by making cuts in the left and right side walls 22 and bending cut portions at an angle different from 0° or 180°, preferably at substantially right angles so as to substantially oppose to each other at a specified spacing, and an insulation-displacement groove 24 is formed or defied substantially between the facing edges of the blades 20. As shown in FIG. 2, an upper part of the facing edge of each blade 20 is formed into a slanted edge 30 which gradually project inwardly as it extends toward its bottom end and a remaining part thereof is formed into a contact edge 33 which preferably is substantially straight in vertical direction or arranged at about 90° with respect to the bottom edge of the insulation-displacement groove 24. The slanted edge 30 is comprised of a moderately slanted edge 31 as a preferred moderate inclination portion at its upper part and a steeply slanted edge 32 as a preferred steep inclination portion at its lower part whose inclination is steeper than that of the moderately slanted edge 31. In other words, the insulation-displacement groove 24 is formed such that the substantially straight contact groove 26 is continuously provided below a guide groove 25 having an angled tapered shape by being defined by the moderately sloped edges 31 at its upper side and the steeply sloped edges 32 at its lower side. Here, if it is assumed that A, B and C are a spacing between left and right boundary portions 35 between the moderately and steeply slanted edges 31, 32 of the guide groove 25, a diameter of the core Wa of the coated wire W and a width of the insulation-displacement groove 24, respectively, a relationship A≥B≥C is satisfied. Further, it is desirable that an angle α formed between the moderately slanted edges 31 and a horizontal line normal to a wire pushing direction is 45° or larger and an angle β formed between the steeply slanted edges 32 and this horizontal line is between α and 90°. This embodiment functions as follows. At the time of connection by insulation displacement, an end portion of the coated wire W is inserted or pushed into the insulation-displacement portion 12 along an insertion or pushing direction ID as shown by an arrow in FIG. 1 to be placed on the guide grooves 25 of the insulation-displacement grooves 24 of the front and rear blade portions 21 as indicated by phantom line of FIG. 2, and the coated wire W is at least partly pushed between the front and rear blade portions 21 and at the front and rear sides of the front and rear blade portions 21 preferably by an unillustrated pressing jig. When the coated wire W is pushed, cuts are made in the coating Wb by the boundary portions 35 between the moderately sloped edges 31 and the steeply sloped edges 32 of the guide grooves 25. As the coated wire W is further pushed, the coating Wb is cut and the core Wa thus at least partly exposed is pushed into the contact groove 26 as shown in FIG. 3 while being guided substantially toward the center of the contact groove 26 by the steeply sloped edges 32, consequently establishing a contact by being tightly held between the contact edges 33. As the coated wire W is connected by insulation displacement, the barrel portion 13 is crimped or bent or folded into connection therewith at a position behind its portion connected by insulation displacement or at a side opposed to the connecting portion 11. According to this embodiment, following advantages can be provided by forming the guide groove 25 of the insulation-displacement groove 24 to have an angled tapered shape by being defined by the moderately sloped edges 31 at its upper side, i.e. a front side with respect to the wire pushing direction and the steeply sloped edges 32 at its lower side, i.e. a back side with respect to the wire pushing direction. First, the coating Wb can be satisfactorily cut by suitably sharpening the boundary portions 35 between the moderately sloped edges 31 and the steeply sloped edges 32 of the guide groove 25. Since the steeply sloped edges 32 are formed at the back side of the guide groove 25 with the wire pushing direction, the exposed core Wa can be precisely guided inwardly, preferably substantially to the center of the contact groove 24 and the core Wa is not cut since an angle between the steeply sloped edges 32 and the contact edges 33 is a relatively large obtuse angle β+90°). As a result, contact reliability can be remarkably improved. Further, by preferably forming the moderately sloped edges 31 over more than half the dimension of the guide groove 25 with respect to height direction, the entire depth of the insulation-displacement groove 24, i.e. the height of the blades 20 can be suppressed to a small value, thereby preventing the insulation-displacement terminal fitting 10 from becoming larger. <Second Embodiment> FIG. 4 shows a second preferred embodiment of the present invention. In the second embodiment, unlike the blade portion 21 made by linearly arranging two blades 20, a unitary blade portion 40 formed with an insulation-displacement groove 41 beforehand is formed by making a cut in the bottom plate and bending a cut portion at a angle different from 0° or 180°, preferably substantially normal to the bottom plate. Specifically, an insulation-displacement groove 41 is formed such that a substantially straight and bottomed contact groove 43 is provided below a guide groove 42 having an angled tapered shape by being defined by moderately sloped edges 31 at its upper side and steeply sloped edges 32 at its lower side similar to those of the first embodiment. The same function and effects as the first embodiment can be obtained in the second embodiment. <Third Embodiment> FIG. 5 shows a third preferred embodiment of the present invention. Similar to the second embodiment, the third embodiment is provided with blades 40 formed with insulation-displacement grooves 41 beforehand by cutting and bending. In order to prevent the blade portions 40 from being inclined during connection by insulation displacement, the upper or distal ends of the front and rear blade portions 40 are coupled by coupling or bridging portions 45. In the third embodiment, the insulation-displacement groove 41 of each blade portion 40 is similarly formed such that a straight and bottomed contact groove 43 is provided below a guide groove 42 having an angled tapered shape by being defined by moderately sloped edges 31 at its upper side and steeply sloped edges 32 at its lower side. The same function and effects as the first embodiment can also be obtained in the third embodiment. <Fourth Embodiment> FIGS. 6 and 7 show a fourth preferred embodiment of the present invention. The fourth embodiment illustrates an insulation-displacement terminal fitting provided with so-called V-shaped blades. Specifically, left and right blade portions 51 are formed by embossing left and right or lateral side walls 52 to substantially face each other at a specified spacing, and an insulation-displacement groove 54 is defined between facing edges of the blades 51. The insulation-displacement groove 54 is formed such that a substantially straight contact groove 58 having a width smaller than a diameter of a core Wa of a coated wire W is provided below a guide groove 55 having an angled tapered shape by being defined by moderately sloped edges 56 as preferred moderate inclination portions at its upper side and steeply sloped edges 57 as preferred steep inclination portions at its lower side. When the coated wire W is pushed, cuts are made in a coating Wb by boundary portions 59 between the moderately sloped edges 56 and the steeply sloped edges 57 of the guide groove 55, the core Wa is exposed while the coating Wb is being turned up or cut or teared. The core Wa is then guided substantially toward the center of the contact groove 58 by the steeply sloped edges 56, pushed therein and tightly held between contact edges to thereby establish a contact. Since a portion for cutting the coating open has a large area in the V-shaped blade portions, if an attempt is made to forcibly cut the coating open, the coating may be torn over a wide area to expose the core after connection by insulation displacement and a contact failure may occur resulting from loosening of the core. However, since the coating Wb can be more easily cut open by the boundary portions 59 between the moderately sloped edges 56 and the steeply sloped edges 57 of the guide groove 55 in this embodiment, a cut-open portion of the coating Wb is kept minimum in size, thereby preventing the exposed portion of the core Wa from becoming larger. Each blade portion 51 may be formed by providing two portions 51' projecting inwardly from the side walls 52 (e.g. by cutting and bending and/or embossing), wherein distal ends thereof are contacted to form an overall embossed shape (see FIG. 6). Similar to the above foregoing embodiments, the fourth embodiment can improve contact reliability while preventing the insulation-displacement terminal fitting from becoming larger. The present invention is not limited to the above described and illustrated embodiments, and various changes can be made without departing from the scope of the present invention as defined in the claims. LIST OF REFERENCE NUMERALS W coated wire Wa core Wb coating 10 insulation-displacement terminal fitting 12 insulation-displacement portion 20 blade portion 22 side wall 24 insulation-displacement groove 25 guide groove 26 contact groove 31 moderately sloped edge 32 steeply sloped edge 33 contact edge 35 boundary portion (between the moderately sloped edge 31 and the steeply sloped edge 32) 40 blade portion 41 insulation-displacement groove 42 guide groove 43 contact groove 50 insulation-displacement terminal fitting 51 blade portion 54 insulation-displacement groove 55 guide groove 56 moderately sloped edge 57 steeply sloped edge 58 contact groove 59 boundary portion (between the moderately sloped edge 56 and the steeply sloped edge 57)

Claims: An insulation-displacement terminal fitting (10; 50), comprising an insulation-displacement groove (24; 41; 54) having at least one contact groove (26; 43; 58) to be brought into contact with a core (Wa) of an insulated wire (W) and at least one tapered guide groove (25; 42; 55) whose width is gradually narrowed in an insertion direction (ID) of the coated wire (W) into the insulation-displacement groove (24; 41; 54), wherein the guide groove (25; 42; 55) has an angled tapered shape having a moderate inclination portion (31; 56) at a front side and a steep inclination portion (32; 57) at a back side with respect to the inserting direction (ID) of the coated wire (W) into the insulation-displacement groove (24; 41; 54), characterized in that a height of the moderate inclination portion (31; 56) along the insertion direction (ID) is at least half the height of the guide groove (25; 56). An insulation-displacement terminal fitting according to claim 1, wherein the contact groove (26; 43; 58) is continuously provided at a back side of the tapered guide groove (25; 42; 55) in the insertion direction (ID). An insulation-displacement terminal fitting according to one or more of the preceding claims, wherein the insulation-displacement groove (24; 54) is formed between a pair of blades (21; 51) projecting from left and right side walls (22; 52) of the insulation-displacement terminal fitting (10; 50) to substantially face each other. An insulation-displacement terminal fitting according to claim 1 or 2, wherein the insulation-displacement groove (41) is formed in a portion of a bottom wall of the insulation-displacement terminal fitting bent at an angle different than 0° or 180°, preferably substantially normal to the bottom wall. An insulation-displacement terminal fitting according to one or more of the preceding claims, wherein the insulation-displacement groove (54) is formed between a pair of blade portions (51) projecting inwardly substantially in V-shape when viewed in the insertion direction (ID) of the coated wire (W). An insulation-displacement terminal fitting according to one or more of the preceding claims, wherein cuts are made in a coating (Wb) of the coated wire (W) by boundary portions (35; 59) between the moderate inclination portions (31; 56) and the steep inclination portions (32; 57) of the guide groove (25; 42; 55), when the coated wire (W) is at least partly inserted into the insulation-displacement groove (24; 41; 54). An insulation-displacement terminal fitting according to one or more of the preceding claims, wherein a first angle (α) formed between the moderate inclination portion (31; 56) and a line normal to the wire insertion direction (ID) is about 45° or larger and a second angle (β) formed between the steep inclination portion (32; 57) and this line is between the first angle (α) and 90°. An insulation-displacement terminal fitting according to one or more of the preceding claims, wherein a spacing A between boundary portions (35; 59) between the moderate and steep inclination portions (31, 32; 56, 57) of the guide groove (25; 42; 55), a diameter B of a core (Wa) of the coated wire (W) and a width C of the insulation-displacement groove (24; 41; 54) satisfy a relationship A≥B≥C. An insulation-displacement terminal fitting according to one or more of the preceding claims, wherein two insulation displacement grooves (41) are provided in longitudinally spaced positions, respective distal portions of blade portions (40) thereof being coupled by one or more coupling portions (45). An insulation-displacement terminal fitting according to one or more of the preceding claims, wherein the contact groove (26) and/or the tapered guide groove (25) is defined between a pair of blades (20) being formed by making cuts in side walls (22) and bending the cut portions by an angle different from 0° or 180°, preferably by substantially 90° with respect to the side walls (22).

Inventors: AOYAMA MASAHIKO, KOJIMA EIJI, AOYAMA, MASAHIKO, KOJIMA, EIJI, AOYAMA, MASAHIKO, C/O SUMITOMO WIRING SYSTEMS, LTD, Kojima, Eiji, c/o Sumitomo Wiring Systems, Ltd.
Applicants: SUMITOMO WIRING SYSTEMS, SUMITOMO WIRING SYSTEMS, LTD.
Application year: 2001
Main classification: H01R4
IPC codes: H01R4