Insulation displacement terminal

Description

BACKGROUND OF THE INVENTION
This invention relates to an insulation displacement terminal which can effect stable insulation displacement connection with a conductor comprising a number of fine strands.
For convenience of explanation, a conventional insulation displacement terminal will be described below by referring to the drawings. FIG. 6A is a perspective view of a conventional insulation displacement terminal.
FIGS. 7A and 7B are graphs which illustrate relationships between a slot width and the number of cutoff strands and between the slot width and a contact resistance, respectively.
Heretofore, in order to connect a conductor in an electric cable, for example, a wire harness for an automotive vehicle or the like to a terminal in a manner of insulation displacement connection, an insulation displacement terminal 1, as shown in FIG. 6A, has been used which is provided with a slot 1a having a given slot width WS. The slot 1a in the insulation displacement terminal 1 is provided on an open part with a pair of slopes 1 b each having a wire (electric cable) guide angle a with respect to a longitudinal axis of the slot or a direction of insertion of the electric cable. Such an insulation displacement terminal requires a maximum force when an insulation sheath in the electric cable is stripped. This maximum force is called a stripping force for an insulation sheath.
In a design of the insulation displacement terminal, after a relationship between the wire guide angle a and the stripping force for insulation sheath has been found, the wire guide angle a is selected so that a force applied to the insulation displacement terminal or an insulation displacement tool becomes minimum. In order to maintain stabilization of insulation displacement connection of the conductor, the slot width SW is set so that the strands of the conductor are compressed without causing any cutoff of the strands, so that the strands behave as if they were a single wire as a whole, and so that the contact resistance between the conductor and the insulation displacement terminal becomes stable. That is, as shown in FIG. 7A, the slot width WS is designed so that no cutoff of the strands is caused and the contact resistance is in an allowable area of stabilization.
On the other hand, an electric cable to be used in movable parts in an apparatus which effects a sliding, rotating, or bending motion requires high flexibility. A conductor having a number of fine strands is suitable for satisfying such a requirement (hereinafter referred to a flexible conductor). Such a flexible conductor has a nominal cross sectional area and a number of strands, such as more than fifteen (15) in 0.3 mm.sup.2, more than nineteen (19) in 0.5 mm.sup.2, more than thirty (30) in 0.75 mm.sup.2, more than thirty-seven (37) in 1.25 mm.sup.2, or the like.
However, since the strands of the flexible conductor move irregularly and are not stable as a whole when a load is applied to the conductor, there is a problem in which the contact resistance is not stable, if a inflexible conductor having the same nominal cross sectional area is combined with a flexible conductor in which the contact resistance becomes stable in the slot width WS.
If the slot width WS is set to be narrower in order to make the contact resistance of the flexible conductor stable, a part of the strands are cut at the edges b on the intersections between the slopes 1b each having the wire guide angle a and the flat surfaces of the slot 1a when the conductor is inserted into the slot 1a, and thus the strands are not compressed fully. Consequently, a contact load between the strands or between the strands and the terminal does not become great and ultimately the contact resistance does not remain stable.
Even if the slot width WS is changed to find the stable area of the flexible conductor, as shown in FIG. 7B, the strands move irregularly and become unstable as a whole when the slot width WS is wide, while the stands are cut when the slot width is narrow. Accordingly, there is no slot width WS in which the contact resistance is in the stable area and the insulation displacement connection can not be effected.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an insulation displacement terminal which effects an insulation displacement connection with the conductor with strands being compressed into a slot width in which a contact resistance is in a stable area and the strands are not cut.
In order to achieve the above object, an insulation displacement terminal in accordance with the present invention is adapted to be connected to a conductor in an electric cable in a manner of insulation displacement connection. The electric cable includes the conductor which comprises a plurality of strands and an insulation sheath which covers an outer periphery of the conductor. The insulation displacement terminal comprises: a slot having a given slot width WS; a first pair of slopes opposed to each other and formed on an open part of the slot at an upper side with respect to a direction of insertion of the electric cable, the first pair of slopes being adapted to guide the electric cable into the slot; and a second pair of slopes opposed to each other and formed on the open part of the slot at a lower side with the direction of insertion of the electric cable. The second pair of slopes are adapted to compress and rearrange the strands in the electric cable. The slot width WS, an opening width WS1 of the first pair of slopes, an opening width WS2 of the second pair of slopes, an outer diameter D of the insulation sheath in the electric cable, and an outer diameter d of the conductor in the electric cable are set to satisfy the following relationship:
WS1>D>d>WS2>WS; and 0.8.gtoreq.WS2/d.gtoreq.0.7.
The inventors of this invention have examined a behavior of the flexible conductor in a process of insulation displacement connection of the flexible conductor into the slot and have created a structure of the insulation displacement terminal which can effect stable insulation displacement connection. This process will be described below by referring to FIG. 6B. FIG. 6B is a perspective view of an apparatus which carried out a compression experiment of the electric cable with the flexible conductor.
As shown in FIG. 6B, an electric cable 2 with a flexible conductor 2a is compressed by insertion between two pairs of plates 10a, 10a and 10b, 10b which are made like the insulation displacement terminal 1. A distance between them is set to be WS. In accordance with this experiment the inventors have found that a specific slot width WS exists which does not cause any cutoff of the strands of the conductor and maintains the contact resistance in the stable area.
However, in this case, it is necessary to strip the insulation sheath beforehand, and otherwise the insulation displacement connection can not be obtained since conduction can not be made between the conductor and the terminal even if the conductor is compressed.
The inventors have examined how the insulation sheath is stripped in a process of actual insulation displacement connection. In the process, the insulation sheath 2b comes into contact with the edges b on the intersections between the slopes 1b each having the wire guide angle a and the flat surfaces of the slot 1a and the insulation sheath 2b is broken at the contact portion by a local great load onto the contact portion. Then, the edges enter the broken portion to widen it. Consequently, the insulation sheath 2b is stripped.
Also, the inventors have examined in which step the strands are cut upon insertion of the flexible conductor 2a into the slot 1a having the narrow slot width WS. When the strands are inserted rapidly into the narrow slot 1a, a great force is applied to the strands and the edges so as to rapidly deform the strands. This will cause cutoff of the strands.
In accordance with the above examination, the inventors have come into the following conclusion. It is difficult to strip the insulation sheath 2b by means of only the pair of edges b and at the same time to push the strands into the narrow slot 1a rapidly. If the insulation displacement terminal has a structure which can divide the process of insulation displacement connection into two steps of stripping the insulation sheath 2b and of pushing the strands into the slot 1a, it will be possible to carry out insulation displacement connection of the flexible conductor 2a.
The insulation displacement terminal of the present invention adopts the structure described above. The edges on the intersections between the first and second pairs of slopes firstly strip the insulation sheath and the second pair of slopes secondly guide the strands of the conductor into the narrow slot while gradually compressing and rearranging the strands in the process of insulation displacement of the terminal in accordance with the present invention.
Preferably, the second slope is formed into a smooth curve which changes a curvature continuously in the slot. It is possible to smoothly push the strands into the narrow slot in the terminal without causing any cutoff of the strands while compressing and rearranging the strands gradually. There is also no possibility of cutoff of the strands on the edges since there is no edge on the intersection between the second slope and the flat surface of the slot.
Preferably, a nominal cross sectional area of the conductor and the number of the strands are set to be more than fifteen (15) in 0.3 mm.sup.2, more than nineteen (19) in 0.5 mm.sup.2, more than thirty (30) in 0.75 mm.sup.2, and more than thirty-seven (37) in 1.25 mm.sup.2. However, the present invention is not limited to the nominal cross sectional area of the conductor and the number of the strands mentioned above.

BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a front elevational view of an insulation displacement terminal in accordance with the present invention;
FIG. 1B is a schematic cross sectional view of an electric cable having a flexible conductor, illustrating a dimensional relationship between the electric cable and the terminal shown in FIG. 1A;
FIG. 2 is a front elevational view of an alteration of the insulation displacement terminal shown in FIG. 1A;
FIGS. 3A and 3B are perspective views of another alterations of the insulation displacement terminal shown in FIG. 1A;
FIG. 4 is a perspective view of still another alteration of the insulation displacement terminal shown in FIG. 1A;
FIG. 5 is a detailed cross sectional view of the electric cable having the flexible conductor, illustrating the figure similar to FIG. 1B;
FIG. 6A is a perspective view of a conventional insulation displacement terminal;
FIG. 6B is a perspective view of an apparatus which is subject to a compression test of the electric cable with the flexible conductor; and
FIGS. 7A and 7B are graphs which illustrate relationships between a slot width and the number of cutoff strands and between the slot width and a contact resistance, respectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings, embodiments of an insulation displacement terminal in accordance with the present invention will be explained below. In the embodiments, the same structures and operations as those in the prior art described above are illustrated in FIGS. 1A to 5 by the same signs and reference numbers as those in FIGS. 6A, 6B, 7A and 7B and a detailed explanation of them is omitted.
As shown in FIGS. 1B and 5, an electric cable 2 includes a conductor 2a and an insulation sheath 2b which covers an outer periphery of the conductor 2a. The conductor 2a comprises a plurality of flexible and fine strands 21.
The conductor 2a comprises the flexible and fine strands 21, which is used in an actual work at present, has a nominal cross sectional area and the number of strands of more than fifteen (15) in 0.3 mm.sup.2, more than nineteen (19) in 0.5 mm.sup.2, more than thirty (30) in 0.75 mm.sup.2, and more than thirty-seven (37) in 1.25 mm.sup.2.
It is assumed hereinafter that an outer diameter of the insulation sheath 2b in the electric cable 2 is "D" and an outer diameter of the conductor 2a in the electric cable 2 is "d". The outer diameter d of the conductor 2a is a diameter of the minimum circumcircle which circumscribes the strands 21 disposed on the outermost periphery of the conductor 2a.
As shown in FIG. 1A, an insulation displacement terminal 5 is provided with a slot 5a having a given slot width WS in which a contact resistance of the strand 21 of the conductor 2a is in a stable area. The slot 5a is provided on the open part at an upper side and a lower side with respect to a direction of insertion A of the electric cable 2 with a first pair of slopes 5b for guiding the electric cable 2 and with a second pair of slopes 5c for compressing and rearranging the strands 21 in the electric cable 2, respectively. The first and second pairs of slopes 5b and 5c are opposed to each other in the slot 5a, respectively. It is assumed hereinafter that an opening width of the first pair of slopes 5b is "WS1" and an opening width of the second pair of slopes 5c "WS2".
In a process for making an insulation displacement connection between the insulation displacement terminal 5 and the conductor 2a in the electric cable 2, firstly, the electric cable 2 is guided into the slot 5a by the first pair of slopes 5b and the insulation sheath 2a is stripped by a pair of edges 5d on intersections between the first pair of slopes 5b and the second pair of slopes 5c (corresponding to the opening width WS2 of the second pair of slopes 5c).
Secondly, the strands 21 of the conductor 2a are gradually compressed and rearranged by the second pair of slopes 5c and then the strands 21 are pushed into the slot 5a having the narrow slot width WS as they are.
Thus, the conductor 2a can be pushed into the narrow slot 5a without causing any cutoff of the strands 21 of the conductor 2a. Also, the second pair of slopes 5c and slot 5a can fully compress the conductor 2a into the slot width WS in which the contact resistance is in the stable area.
In order to guide the electric cable 2 between the first pair of slopes 5b, it is necessary that the opening width WS1 of the first pair of slopes 5b is greater than the outer diameter D of the insulation sheath 2b in the electric cable 2, that is, WS1>D. Also, in order to strip the insulation sheath 2b in the electric cable 2 by the pair of edges 5d on the intersections between the first pair of slopes 5b and the second pair of slopes 5c, it is necessary that the opening width WS2 of the second pair of slopes 5c is smaller than the outer diameter D of the insulation sheath 2b in the electric cable 2, that is, WS2<D.
Further, since the edges 5d must reach the outermost periphery of the conductor 2a in order to completely strip the insulation sheath 2b after the insulation sheath 2b comes into contact with the edges 5d, it is necessary that the outer diameter d of the conductor 2a is greater than the opening width WS2 of the second pair of slopes 5c, that is, d>WS. Accordingly, in order to strip the insulation sheath 2b without causing any cutoff of strands 21 of the conductor 2a, it is necessary to satisfy the following relationship: WS1>D>d>WS2>WS.
The slot width WS is determined by making various terminals each having the WS which satisfies the above-mentioned relationship among the WS1, WS2, D, and d and then by their connection characteristics; or by using the simple method shown in FIG. 6B and then by observing a behavior in which the contact resistance is in the stable area without causing any cutoff of the strands 21 of the conductor 2a.
Also, a wire guide angle "a" for a wire (electric cable) defined by the first slope 5b with respect to the direction of insertion A is determined by the conventional method or by surely bringing the edge 5d on the intersection between the first slope 5b and the second slope 5c into contact with the insulation sheath 2b in the electric cable 2.
In addition, an angle b defined between the first slope 5b and the second slope 5c is preferably set so that the intersection forms the edge 5d correctly, for example, to be less than 160.degree..
On the other hand, the inventors have verified by experiment a relationship between the outer diameter d of the conductor 2a to be connected into the slot 5a in the insulation displacement terminal 5 and the opening width WS2 of the second pair of slopes 5c. Consequently, it has been found that the contact resistance can compress the strands into the stable area without causing any cutoff of the strands when the relationship between the opening width WS2 of the second pair of slopes 5c and the outer diameter d of the conductor 2a satisfies the following condition.
That is, the relationship between the outer diameter d of the conductor 2a and the opening width WS2 must satisfy the condition: 0.8.gtoreq.WS2/d.gtoreq.0.7. If WS2/d is greater than 0.8 (WS2/d>0.8), separation (cutting) of the insulation sheath 2b in the electric cable 2 becomes poor and the strands 21 of the conductor 2a hardly come into contact with the slot 5. If WS2/d is smaller than 0.7(WS2/d<0.7), cutoff of the strands is apt to cause.
It is necessary from the foregoing to set 0.8.gtoreq.WS2/d.gtoreq.0.7 in addition to WS1>D>d>WS2>WS described above.
Since there is no need to specify an edge 5f on an intersection between the second slope 5c of the insulation displacement terminal 5 and a flat surface of the slot 5a, it is possible to form the second pair of slopes 5c into a smooth curve which changes a curvature continuously to the slot 5a, as shown in FIG. 2. This structure will preclude the possibility of cutoff of the strands on the edges 5f.
The insulation displacement terminal 5 may be altered to various kinds of configuration such as a configuration in which a pair of insulation displacement terminal 5, 5 stand on the ends of the bottom wall in parallel to each other, as shown in FIG. 3A, a configuration in which a pair of insulation displacement terminals 5,5 are provided on side walls, as shown in FIG. 3B, or a configuration in which a pair of insulation displacement terminals 5,5 are punched up from a bottom wall of a U-shaped member, as shown in FIG. 4.
It will be apparent from the foregoing that it is possible to push the strands into the narrow slot in the terminal without causing any cutoff of the strands, to fully compress the strands into the slot width in which the contact resistance is in the stable area, and to enable low costs and a compact size to be obtained by employing the insulation displacement connection for the flexible conductor, since the edges on the intersections between the first and second pairs of slopes firstly strip the insulation sheath and the second pair of slopes, secondly guide the strands of the conductor into the narrow slot while gradually compressing and rearranging the strands in the process of insulation displacement of the terminal in accordance with the present invention.
In the case where the second pair of slopes are smooth curves which changes the curvature continuously, the conductor can be readily inserted into the narrow slot and there is no possibility of cutoff of the strands on the edges since there is no edge on the intersection between the second slope and the flat surface of the slot.
The entire disclosure of Japanese Patent Application No. 9-29383 filed on Feb. 13th, 1997 including specification, claims, drawings and summary is incorporated herein by reference in its entirety.

Claims

1. An insulation displacement terminal adapted to be connected to a conductor in an electric cable in a manner of insulation displacement connection, said electric cable including said conductor which comprises a plurality of strands and an insulation sheath which covers an outer periphery of said conductor, comprising:
a slot having a given slot width WS:
a first pair of slopes opposed to each other and formed on an open part of said slot at an upper side with respect to a direction of insertion of said electric cable, said first pair of slopes being adapted to guide said electric cable into said slot; and
a second pair of slopes opposed to each other and formed on said open part of said slot at a lower side with respect to said direction of insertion of said electric cable, said second pair of slopes being adapted to compress and rearrange said strands in said electric cable;
wherein said slot width WS, and opening width WS1 of said first pair of slopes, an opening width WS2 of said second pair of slopes, an outer diameter D of said insulation sheath in said electric cable, and an outer diameter d of said conductor in said electric cable are set to satisfy the following relationship: WS1>D>d>WS2>WS; and 0.8.gtoreq.WS2/d.gtoreq.0.7.
2. The insulation displacement terminal according to claim 1, wherein a nominal cross sectional area of said conductor and the number of said strands are set to be more than fifteen (15) in 0.3 mm.sup.2, more than nineteen (19) in 0.5 mm.sup.2, more than thirty (30) in 0.75 mm.sup.2, and more than thirty-seven (37) in 1.25 mm.sup.2.
3. The insulation displacement terminal according to claim 1, wherein said second slope is formed into a smooth curve which changes a curvature continuously in said slot.
4. The insulation displacement terminal according to claim 3, wherein a nominal cross sectional area of said conductor and the number of said strands are set to be more than fifteen (15) in 0.3 mm.sup.2, more than nineteen (19) in 0.5 mm.sup.2, more than thirty (30) in 0.75 mm.sup.2, and more than thirty-seven (37) in 1.25 mm.sup.2.

Priority Claims (1)

Number	Date	Country	Kind
9-029383	Feb 1997	JPX

US Referenced Citations (1)

Number	Name	Date	Kind
5030132	Hayes et al.	Jul 1991

Foreign Referenced Citations (4)

Number	Date	Country
0101290	Feb 1984	EPX
2621423	Apr 1989	FRX
4028987	Mar 1992	DEX
4108133	Sep 1992	DEX

Non-Patent Literature Citations (1)

Entry
Search Report EP 98 30 0981.

Insulation displacement terminal

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