EP1594189A1

EP1594189A1 - Clamping contacting element, insulation displacement connector, connector terminal block and method of manufacture thereof

Info

Publication number: EP1594189A1
Application number: EP04405292A
Authority: EP
Inventors: Sami Kotilainen; Christian Ohler
Original assignee: ABB Research Ltd Switzerland; ABB Research Ltd Sweden
Current assignee: ABB Research Ltd Switzerland; ABB Research Ltd Sweden
Priority date: 2004-05-07
Filing date: 2004-05-07
Publication date: 2005-11-09
Also published as: CN1694306A; CN1694308B

Abstract

The cable connector (19) for making an electrical contact with a cable conductor (2) of a cable (1) comprises two legs (190), at least one of which can make electrical contact with a cable conductor (2) inserted into the cable connector (19) into a contacting position, and the two legs (190) are capable of exerting a contacting force on a cable conductor (2) in the contacting position for holding the cable conductor (2) in the contacting position. When there is no cable (1) inserted in the cable connector (19), the legs (190) exert an non-vanishing initial force on each other. In other words, the cable connector has two prestressed legs. Ends of the legs press against each other with some force prior to the insertion of any cable into the connector. The cable connector can, e.g., be used as an insulation displacement connector and in connector terminal blocks. Methods for manufacturing such a cable connector (19) comprise methods, in which an elastic deformation in at least one section of the cable connector (19) is performed, while another section of the cable connector (19) is plastically deformed. Preferably, the cable connector is integrally made from one piece of bent sheet metal.

Description

Technical Field

The invention relates to the field of low-voltage electrical cable connections and cable connectors, and in particular to clamping contacting elements, insulation displacement connectors and connector terminal blocks as well as a method of production thereof. It relates to methods and apparatusses according to the opening clause of the claims. Such devices find application, e.g., in industrial cabinets or in residential installations.

State of the Art

Such a low-voltage cable connector is known from the published European patent application EP 0 893 845 A2. That connector is an insulation displacement connector (IDC), i.e, a connector that does not require stripping of a cable insulation prior to making the connection to the cable conductor. The IDC has a contact spring with two spring legs for contacting a cable. The insulation of a cable inserted into the IDC is cut through by means of the legs, such that the cable conductor ends up in an open slit formed between the two legs such that the legs electrically contact it and hold it.
In order to provide a sufficiently high force for cutting the cable insulation and for holding the cable conductor, in EP 0 893 845 A2 it is suggested to provide a separate power leaf spring in addition to the spring formed by the spring legs. The separate leaf spring is arranged to act against a further opening of the slit. Thus, the force available for cutting the insulation and holding the conductor in contact is greater than when the contact spring with the two spring legs would fulfill that task without the power leaf spring. Since the design and the materials of the contact spring and of the power leaf spring can be chosen independently, a reduced width of the cable connector can be achieved. Or, formulated alternatively, at a constant width of the cable connector, an enhanced cutting and holding capability can be achieved.
A disadvantage of such a cable connector is, that two separate parts (contact spring plus power spring) must be manufactured and assembled, and that the range of diameters of cable conductors that can be safely contacted by the cable connector is rather limited.

Summary of the invention

Therefore, the goal of the invention is to create an electrical cable connector and a method for electrically contacting a cable that do not have the disadvantages mentioned above. A cable connector and a method for electrically contacting a cable shall be provided that can be used for safely contacting cables of a wide range of conductor diameters, and at the same time requires a small amount of space. Furthermore, a connector terminal block comprising such a cable connector and a method of production of such a cable connector is provided.
The problem is solved by the apparatusses and a method with the characteristics of the claims.
According to the invention, the cable connector for making an electrical contact with a cable conductor of a cable comprises two legs, at least one of which can make electrical contact with a cable conductor inserted into the cable connector into a contacting position, and the two legs are capable of exerting a contacting force on a cable conductor in the contacting position. The cable connector is characterized in that, when there is no cable inserted in the cable connector, the legs exert an non-vanishing initial force on each other. In other words, the cable connector has two prestressed legs. Ends of the legs press against each other with some force prior to the insertion of any cable into the connector.
The contacting force can be a contacting force for holding the cable conductor in the contacting position. The cable connector can make electrical contacts with one or more cable conductors, i.e., there can be two, three or more cables with cable conductors to be contacted by the cable counductor.
The cable connector with prestressed legs provides for a connector, which can make an electrical contact with cables of a wider range of cable sizes (cable conductor diameters), while having the same width and generally the size as a known connector; or, worded alternatively, the cable connector may be of a reduced width or of a generally reduced size, while still permitting to safely connect the same range of cable conductor diameters; or, the cable connector provides for a combination of both. A narrower connector or connector block permits a larger number of connectors or connector blocks on the same rail length and thereby an increased number of connections in the same cabinet space.
A cable connector according to the invention has a force-displacement-characteristic for the opening of the two opposing legs with an initial force greater than zero at zero opening, i.e., when the two legs touch at their tips or when a slit formed between the ends of the legs is not yet open.
This means that a contacting force at a small opening between the ends of the legs is higher than a contacting force without the prestress at the same small opening and/or a contacting force at a large opening, where a maximum permitted stress level of the leg material is reached, is smaller than a contacting force without the prestress at the same large opening.
The maximum permitted stress level is defined through the transition from elastic deformation of the legs to plastic deformation of the legs. Since a cable connector shall usually be used many times, i.e., many insertions and extractions of cables, it is necessary to remain in the elastic region, since otherwise a thin cable will afterwards not be safely contacted anymore.
Contacting a cable safely means on the one hand a contact with a sufficiently small contact resistance, so that the overall voltage drop across the connector at nominal current is smaller than required by applicable standards. This requires a certain minimal contacting force. On the other hand the cable conductor may not be damaged by excessive force, which is particularly important if not solid, but stranded cable conductors are to be contacted. If insulated cables are to be contacted and the cable connector is an insulation displacement connector (IDC), there must, independent from the cable conductor diameter, always be sufficient force for removing the cable insulation; preferably, that force will also be provided through the legs.
The initial force (offset in the force-displacement-characteristic) and the overall spring constant (slope of the force-displacement-characteristic) of the cable connector can be chosen such, that an optimized small and leight-weight cable connector can be designed. For example: Adjusting the initial force and the spring constant such, that cable conductors of a minimal diameter to be contacted are helt with a minimal required force, and cable conductors of a maximal diameter to be contacted widen the slit between the legs just so far, that a plastic deformation does just not yet take place.
If the cable connector is made from sheet metal, the invention allows for a more efficient use of the metal sheet material, in particular a wider range of cable sizes with the same connector width, or a smaller connector width for the same range of cable sizes.
An additional advantage is, that the force needed for the insertion of a cable (this force must usually be provided by an operator who makes the cable connection using the cable connector) can be chosen to be smaller, and also the range of forces to be applied for the insertion of a cables of a range of cable conductor diameters can be chosen to be smaller, which results in a more ergonomic operation of the connector.
The cable connector can be formed integrally, or it may comprise several parts. In particular, the force may be provided (mainly) by the legs, or by an additional power spring.
Preferably, both legs contact an inserted cable in the contacting position.
It is preferred, but not necessary, that the whole leg is electrically conductive.
Preferably, the cable connector is designed such that it is of symmetrical shape.
In a preferred embodiment, the cable connector has an insertion opening for inserting a cable conductor into the cable connector into the contacting position. By means of such an insertion opening, it is possible to provide the force needed to open the slit between the legs by means of the insertion movement of the cable. In case of an IDC, this opening can, with advantage, simultaneously be used as a cutting element for removing the cable insulation. Instead of an insertion opening one can also think of other means for opening the slit, e.g., like in standard U-shaped paper clamps with two flippable arms.
In a preferred embodiment the cable connector is designed for making electrical contact with cable conductors of a diameter between a minimum diameter and a maximum diameter, wherein the initial force amounts to at least 5%, in particular at least 10% or at least 20%, of the contacting force exerted on a cable conductor of the minimum diameter in the contacting position. It can also be preferred to be at least 50% of that force.
In another preferred embodiment the cable connector is designed for making electrical contact with cable conductors of a diameter between a minimum diameter and a maximum diameter, wherein the cable connector is deformed only elastically through insertion of a cable conductor of the maximum diameter into the contacting position.
A connector terminal block according to the invention is characterized in that it comprises at least one cable connector according to the invention and has the corresponding advantages.
The method of production of a cable connector for making an electrical contact with a cable conductor of a cable, the cable connector comprising two legs, at least one of which can make electrical contact with a cable conductor inserted into the cable connector into a contacting position, and with the two legs capable of exerting a contacting force on a cable conductor in the contacting position, comprises that the two legs are formed and arranged in such a way, that they exert a non-vanishing initial force on each other, when no cable is inserted between them.
This method can in particular be used to manufacture a cable connector according to the invention.
Preferably, during production of the cable connector an elastic deformation in at least one section of the cable connector is performed
a) through temperature change and/or
b) while another section of the cable connector is plastically deformed and/or
c) while the two legs are fixed with respect to each other,
In a preferred method according to method a)

at least one of the two legs comprises a memory-shaped alloy or a bimetal, and at least one production step is performed at a temperature that is different from the temperatures present under operating conditions of the cable connector and/or
the elastic modulus of the material of at least one of the two legs is changed thrrough the temperature change.

In a preferred method according to method b) the contact element is a bent piece of sheet metal.
In a preferred method according to method c) the two legs are welded to each other while being pressed against each other.
The method according to the invention for electrically contacting a cable having a cable conductor comprises the steps of:

firstly, applying a non-vanishing initial force to two legs of a cable connector before a slit formed by the two legs opens up, and then
applying additional force to the legs for opening the slit and for moving the cable conductor between the two legs in a direction substantially perpendicular to the slit, until the cable conductor is in a contacting position, in which the cable conductor is making electrical contact with at least one of the legs.

Further preferred embodiments and advantages emerge from the dependent claims and the figures.

Brief Description of the Drawings

Below, the invention is illustrated in more detail by means of preferred embodiments, which are shown in the included drawings. The figures show:

Fig. 1: a perspective view of an insulation displacement connector (IDC) with a cable, schematic ;
Fig. 2: force-displacement-characteristics according to the state of the art (dashed) and according to the invention (solid line);
Fig. 3: the contact resistance as a function of the contact force, schematically ;
Fig. 4: a cut through a cable connector indicating the region of maximum stress upon cable insertion;
Figs. 5a - 5d: a schematic sketch of a first method of production of a cable connector;
Figs. 6a - 6e: a schematic sketch of a second method of production of a cable connector;
Figs. 7a - 7e: a schematic sketch of a third method of production of a cable connector;
Fig. 8: a schematic side view of an IDC;
Fig. 9: a perspective view of a partially disassembled connector terminal block, partially schematic.

The reference symbols used in the figures and their meaning are summarized in the list of reference symbols. Generally, alike or alike-functioning parts are given the same reference symbols. The described embodiments are meant as examples and shall not confine the invention.

Ways to implement the invention

Fig. 1 schematically shows a perspective view of a cable connector 19 according to the invention with a cable 1 having a cable conductor 2 and a cable insulation 3. The cable connector 19 is a cutting clamping connector 19 designed as an isulation displacement connector 20 (IDC). The cable connector 19 has two legs 190, the ends of which form a slit 192. Through an insertion opening 196, which in addition functions as a cutting element for removing the insulation 3, a cable 1 can be inserted into the slit 192. The cable conductor 2 reaches a contact position when it contacts the legs 190 and is helt in that position by a force applied to the conductor 2 via the legs 190. That force is symbolized in Fig. 1 as two open arrows. It is substantially perpendicular to the direction M of the movement of the cable during insertion. In dashed lines the cable 1 is indicated before the insulation 3 is cut and before the cable is in contacting position. The width of the cable connector 19 is indicated by the arrow with the letter W.
According to the invention, that width W can be reduced with respect to known cable connectors suitable for connecting a given range of cable conductor diameters by having prestressed legs 190, i.e., legs 190 that not only touch each other when no cable is inserted, but which exert an initial force on each other when no cable is inserted. The open arrows in Fig. 1 also symbolize that initial force.
Fig. 2 shows force-displacement-characteristics according to the state of the art (dashed) and according to the invention (solid line). The initial force f0 according to the state of the art is zero. This results in a contacting force f1 at an intended minimal conductor diameter d1. At an intended maximum conductor diameter d2, a contacting force f2 results.
According to the invention, the initial force f0' is greater than zero. This results in a contacting force f1' at the intended minimal conductor diameter d1, which can be greater than f1, even if the spring constant (slope of the line) is smaller than in the case of a cable connector according to the state of the art. Accordingly, a safe contact at small diameters (d1) can be achieved with a weaker and therefore smaller spring.
At an intended maximum conductor diameter d2, according to the invention a contacting force f2' results, which can be chosen to be smaller than f2. Thus, it is easily possible to avoid excessive forces acting on cables of large diameter (d2), so that a safe contact can be realized without damaging the cable conductor. And the cable connector 19 can be designed such, that at d2 only elastic deformations of the cable connector take place.
Due to the availability of the two parameters spring constant ( = slope) and initial force f0' ( = (positive) offset) the force-displacement-characteristic can be designed in an optimized way.
Fig. 3 show schematically the contact resistance R as a function of the contact force F. With a cable connector according to the state of the art, it can easily happen that the contact force f1 is so small that an unsafe contact of high contact resistance R is made with cables of small conductor diameter d1, whereas a very low resistance is achieved through a very high contact force f2 in the case of maximum conductor diameter.
By means of the use of a cable connector according to the invention having a smaller spring constant (cf. Fig. 2 above), the contact force f1' can easily be selected to be higher than f1, resulting in a strongly improved contact at small conductor diameters d1; and f2' may be chosen much smaller than f2, which difference δF of forces F nevertheless results only in a very small decrease δR of the contact resistance R, so that still a sufficiently small contact resistance is achieved for large diameters d2. In addition, even for large diameters (d2) only moderate insertion forces are required, and the range of forces to be applied is much smaller for the same range of diameters, both resulting in an improved operability of the cable connector.
Fig. 4 shows a cut through a cable connector 19 indicating the zone 195 of maximum stress upon cable insertion. The cut runs in a plane perpendicular to the direction M of the movement of the cable during insertion (cf. Fig. 1) The cable connector is of symmetrical shape with respect to the symmetry line S. The dashed line shows the leg 190 before cable insertion, the solid line shows the leg 190, when a cable is inserted into the contact position.
The cable connector 19 is substantiall "U"-shaped with bottom bends Bb, between which the "U" has a preferably straight bottom line; and with top bends Bt near the ends 191 of the legs 190. Between a bottom bend Bb and a top bend Bt the "U" is preferably of straight shape. From numerical simulations it has been found that for such a "U"-shaped cable connector 19 the zone 195 of maximum stress is on the inside of the bottom bends Bb.
The range of cable diameters to be connected to a cable connector 19 determines its overall size and in particular its width W. This is because (1.) the deformation of the two legs when the largest permitted cable is inserted shall remain within the elastic limit of the material. If the insertion of the largest permitted cable would lead to a plastic deformation, the connector would be damaged for a potential subsequent use, e.g., the insertion of a cable of smaller size.
While the deformation of the connector must remain within the elastic limit, when the largest permitted cable is inserted, there must be (2.) a sufficiently high contact force available, when a cable of smallest permitted size is inserted.
Because, according to the state of the art, the edges of the two legs are at most just touching prior to insertion of any cable (opening displacement D of zero), the minimum contact force required for the smallest cable (f1 in Fig. 2) defines the spring constant for an opening between the two legs and hence also the force experienced by an inserted cable of largest size (f2 in Fig. 2). In consequence, this force (f2) cannot be freely chosen according to the actual cutting force requirement and contact resistance requirement (cf. Fig. 3). Often, the resulting force will be larger than the minimum force required for a sufficiently low contact resistance (cf. Fig. 3).
Given a particular size and geometry of the connector 19 (like, e.g., in Fig. 4), the combined requirements of the spring constant (resulting from the specification of the smallest cable size to be connected) and the largest opening (for the largest cable size to be connected) define the maximum strain state suffered by the material. That maximum strain state is reached at the transition from elastic to plastic deformation. Usually the maximum strain is reached at the inner radius of the bottom bend Bb (cf. Fig. 4).
There are, besides the invention, essentially two measures that could be taken to reduce the strain level when the same requirements are to be fulfilled: (1.) to increase the radius of the bottom bends, or (2.) to increase simultaneously the width of the legs 190 and the length of the legs 190 (along the symmetry line S). The first (1.) increases the width W of the connector, which is very undesirable. The second (2.) increases the mass of the cable connector and decreases the open space inside the connector (which defines the largest outer dimensions of a cable insertable in the cable connector).
According to the invention, this problem is solved differently. Prestressed legs are used, which works as indicated above.
Fig. 5 schematically sketches a first method of production of a cable connector 19. In order to achieve an easy and cost-efficient method production of the connector, the connectors are preferably manufactured by cutting and subsequently bending a piece sheet metal. Fig. 5 shows a schematic sketch of a first possible manufacturing sequence. The sheet metal 30 and the connector are shown in a cut along a plane perpendicular to the direction of the movement M of the cable during cable insertion (cf. Fig. 1), which corresponds to a plane perpendicular to the slit 192 (cf. Fig. 1). In Fig. 5a a suitably cut piece of sheet metal 30 is shown. Through plastic deformation (black arrows) two legs 190 and two bottom bends Bb are formed, see Fig. 5b. Preferably, the plastic deformation is such, that the ends of the legs 190 will then nearly touch each other. The dash-dotted line depicts the symmetry line of the connector. In Fig. 5c is shown, that the legs 190 are then, close to their ends, bent plastically (black arrows), while the legs 190 are spread elastically (open arrows). Through this, two top bends Bt are formed, and the two legs touch each other at their ends, and the legs 190 are prestressed, see Fig. 5d. The two open arrows in Fig. 5d shall idicate the initial force, which the legs 190 exert on each other.
In Fig. 6 a second manufacturing sequence is shown in the same kind of representation as Fig. 5. In Fig. 6a a suitably cut piece of sheet metal 30 is shown. Through plastic deformation (black arrows) two top bends Bt are formed, see Fig. 6b, which are located near the ends (contact edges) of the two legs to be formed. Then one bottom bend Bb is formed through plastic deformation (black arrow, Fig. 6c). Notably, the angle at the bottom bend Bb is selected to be larger than the angle that would bring the end exaclty to the dash-dotted symmetry line.
While making the second, final bottom bend Bb (Fig. 6e), the other leg is elastically opened up (relative to the bottom part of the "U" to be formed) so far, that the opposite leg can be bent to the same, but opposite angle as the other leg was bent before, see Fig. 6d. Once the elastic open-up of the first-bent leg is released, the two ends of the opposing legs press against each other with an initial force. A connector with prestressed legs, like in Fig. 5, has thus been manufactured (see Fig. 6e).
In Fig. 7 a third manufacturing sequence is shown in the same kind of representation as Figs. 5 and 6. In Fig. 7a a suitably cut piece of sheet metal 30 is shown. Like in the procedure of Fig. 6, through plastic deformation (black arrows) two top bends Bt are formed, see Fig. 7b, which are located near the ends (contact edges) of the two legs to be formed. Then, near the dash-dotted symmetry line, a dent Bd is formed through plastic deformation (black arrow, Fig. 7c). This center dent Bd points towards the location, where the ends of the legs will end up. Then, two bottom bends Bb are formed by plastic deformation, such that the two legs are bent towards each other, preferably until they touch each other at the symmetry line, see Fig. 7d.
Finally, the two legs are helt in their position, and the direction of the center bend is reversed through plastic deformation (black arrow, Fig. 7e), so that it points away from the ends of the legs. During the reversal of the dent Bd through plastic deformation, an elastic deformation takes place near the bottom bends (not indicated). As a consequence, the ends of the opposing legs press against each other with an initial force. A connector with prestressed legs is thus formed. The depth of the dent Bd is typically smaller than indicated in Fig. 7.
Besides the described manufacturing methods (Figs. 5, 6, 7), there are several other methods one can think of, which achieve the same goal. Such manufacturing sequences have in common, that during production of the cable connector, an elastic deformation of at least one section of the workpiece is performed, while another section of the workpiece is plastically deformed. In Fig. 5, the legs 190 are spread, such that an elastic deformation at the bottom bends Bb take place, while the ends of the legs are plastically bent. In Fig. 6, an elastic bending (opening) of one bottom bend Bb takes place, while the second bottom bend is created through plastic deformation. And in Fig. 7, an elastic strain at the bottom bends Bb takes place during the (plastic) reversal of the dent Bd.
In these manufacturing of a prestressed IDC connector, the possibility is exploited to deform the workpiece elastically not only after the connector is finished, but also during the manufacturing process itself.
The steps indicated in the above manufacturing methods do not necessarily have to be performed in exactly the depicted order. For example, in Fig. 6, it is also possible to firstly create the first bottom bend Bb (see Fig. 6c) and then provide for the top bends Bt (see Fig. 6b). Or, in Fig. 7, first the center dent Bd (see Fig. 7c) can be created, and then the top bends Bt are done (see Fig. 7b).
It is furthermore not necessary to have two bottom bends Bb; one bottom bend Bb can be enough. And it is also not necessary that the connector is of symmetrical shape.
There is a number of further possibilities to manufacture a prestressed connector. For example, one can use of a memory-shaped alloy, which converts its shape to some prelearned shape through a heat treatment. Accordingly, the (not-yet-prestressed) connector is formed at a temperature different from the envisaged working temperature of the connector, such that the connector changes its shape when cooling down or heating up to a temperature corresponding to the operating conditions. Instead of a memory alloy, or in addition, a bimetal can be used in the same way.
Another possibilty would be to fix two formerly separate legs with respect to each other, e.g., by welding, by glueing, or by mechanically fixing, while the legs are pressed against each other (elastically), such that there is a prestress between the two legs in the cable connector after the fixing.
Yet another possibility would be to attach to the two legs a separate power spring, which provides for an initial force, with which the legs press against each other before any cable insertion. In that case the legs by themselves may, but do not have to have an initial prestress. A spring clamp around a U-shaped connector as a power spring can be used for that purpose.
Fig. 8 shows a schematic side view of an IDC or a connector terminal, which can incorporate a connector according to the invention.
The task of this connector terminal is to electrically contact a cable 1, which has a cable conductor 2 and a cable insulation 3. The IDC comprises a guiding means 4 for receiving an end 1a of the cable 1 and for moving the end 1a of the cable 1 into a cutting element 5 and a clamping contacting element 19. The clamping contacting element 19 incorporates the functions of a contact element 6, which is to electrically contact the cable conductor 2, and a holding means 18, which shall hold the cable conductor 2 in electrical contact with the contact element 6, in this case by clamping between two legs of the connector 19. The cutting element 5 cuts through the cable insulation 3 by means of its cutting edge 5a, so that the contact element 6 can electrically contact the cable conductor 2. Preferably, the cutting element 5 and the connector 19 are united in one unit, as, e.g., shown in Fig. 1. The contact element 6 is in electrical contact with an electrically conductive interconnection element 13 in order to provide an electrical connection to another electrical device. e.g., another IDC.
An operator operating the connector terminal provides the force necessary for moving the guiding element 4 with the cable end 1 a and for cutting the insulation 3 and for acting against the initial force of the prestressed legs and for providing additional force for opening the slit between the legs, such as to contact and hold the cable conductor 2. A tool 14, e.g., a standard tool like a screw-driver, can be used by the operator in order to move the guiding means 4, preferably in lever action, as indicated in Fig. 1. Therefore, the guiding means 4 has as a force receiving means 11 an opening 11 for the tool 14. A pivotal point 15 for the lever action is in Fig. 1 provided by a housing 10 of the IDC. The arrow indicates how the tool 14 is moved when the IDC is operated. The tool 14 could, for example, also be moved laterally and sliding instead of in lever action for moving the guiding means 4.
When the IDC is to be operated, the cable 1 is inserted into a cable receiving opening 16 of the guiding means 4, and the tool 14 is entered into the force receiving means 11. When then the guiding means 4 is moved, extra force has to be applied in order to act against a spring device 7, which in Fig. 1 is illustrated as a coil spring 7, which is helt between to spring holders 7a,7b. Spring holder 7a is integrated in the guiding means 4 and spring holder 7b is fixed to the housing (not shown in Fig. 1). After the guiding means 4 has been moved over a certain length and the cable conductor 2 is in contact with and helt by the connector 19, a locking mechanism 8 will terminate the action of the spring device 7. In Fig. 1 the locking mechanism 8 is provided by the guiding means 4 together with an elastically helt tip 8. When the locking mechanism 8 is activated, the cable 1 is in safe contact with the contact element 6 because of the holding means 18.
In this final, contacting state (not shown in Fig. 8), the force exerted on the guiding means 4 and the cable 1 by the spring 7 is zero or at least greatly reduced. The operator will feel and maybe hear the activation of the locking mechanism 8. If the operator would terminate his action before the activation of the locking mechanism 8, the spring 7 would act so as to push back the guiding means 4 and the cable 1 towards or preferably into the initial state. A situation, in which there is no contact between the cable conductor 2 and the contact element 6 is therefore easily visible, and bad contacts are impossible to come about and are therefore successfully avoidable if the spring device and the locking mechanism are designed and arranged suitably.
Fig. 9 shows a perspective view of a connector terminal block meant for two IDCs and comprising one IDC according to the invention. For reasons of clarity, the left side of the connector terminal block is illustrated in a state not equipped with an IDC. A housing 12 of the connector terminal block comprises the tool insertion opening 17, which also provides for the pivotal point 15 for a lever action of an inserted tool. The housing 12 also comprises the cable insertion opening 16. The spring device 7 is a leaf spring, preferably made from spring steel, which comprises the locking mechanism and, in addition, an opening mechanism.
In the IDC shown in Fig. 9 the guiding means 4 and the end 1 a of the cable is moved with respect to the housing 12. The guiding means 4 can be made in a single piece from a polymer material. The IDC comprises a cutting clamping connector 20, which unites the function of the cutting element 5 and the contact element 6 and a holding means. The connector 20 has a cutting zone 198, where the insulation is cut, and a contacting zone 199, where the conductor is in electrical contact with the connector 20. The cutting clamping connector 20 can be formed from one piece of metal. At the end of the cutting clamping connector 20 opposite to the cutting edge 5a, the cutting clamping connector 20 is electrically connected to the electrically conductive interconnection element 13, which preferably is a piece of sheet metal, and possibly the same piece of sheet metal as the connector 19,20. When both sides of the connector terminal block are equipped with IDCs, one single piece of metal can be used as the electrically conductive interconnection element 13 for connecting the two IDCs with each other, which IDCs may be integrally formed with each other.
Typical ranges of cable conductor diameters of cables to be contacted are 0.75 mm² to 1.5 mm². Typical forces exerted on a maximum diameter cable inserted in a connector according to the invention are in the range of 50 N to 100 N or 150 N. For minimum diameter cables, typical forces range between 10 N and 30 N. The initial force can typically range between 0.5 N and 5 N or between to 1.5 N and 15 N.
List of Reference Symbols

1: cable
1a: end of cable
2: cable conductor
3: cable insulation
4: guiding means
5: cutting element
5a: cutting edge
6: contact element
7: spring device, spring
7a: spring holder
9b: opening
10: housing (of cable connector), insulating housing
11: force receiving means, opening
12: housing (of connector terminal block)
13: electrically conductive interconnection element (current bar)
14: tool
15: pivotal point
16: cable insertion opening (of connector terminal block or of guiding means)
17: tool insertion opening
19: cable connector; clamping contacting element
20: cutting clamping connector
30: piece of sheet metal
190: leg of cable connector
191: end of leg of cable connector
192: slit
195: zone of maximum stress
196: insertion opening
198: cutting zone
199: contacting zone

Bb: bottom bend
Bt: top bend
Bd: dent
D: opening displacement
d1: minimal diameter of cable conductor
d2: maximum diameter of cable conductor
F: force
δF: difference of forces
f0, f0': initial force
f1, f1': contacting forces
f2, f2': contacting forces
M: direction of insertion movement
R: contact resistance
δR: difference of contact resistances
S: symmetry line
W: width of cable connector

Claims

Cable connector (19) for making an electrical contact with a cable conductor (2) of a cable (1), comprising two legs (190), at least one of which can make electrical contact with a cable conductor (2) inserted into the cable connector (19) into a contacting position, and with the two legs (190) capable of exerting a contacting force (f1';f2') on a cable conductor (2) in the contacting position, characterized in that with no cable (1) inserted in the cable connector (19), the legs (190) exert an non-vanishing initial force (f0') on each other.
Cable connector (19) according to claim 1, characterized in that both legs (190) make electrical contact with a cable conductor (2) inserted into the cable connector (19) into a contacting position.
Cable connector (19) according to claim 1 or claim 2, characterized in that each of the two legs (190) has an end (191), with the two ends (191) forming a slit (192).
Cable connector (19) according to one of the preceding claims, characterized in that it is of symmetrical shape.
Cable connector (19) according to one of the preceding claims, characterized in that it has an insertion opening (196) for inserting a cable conductor (2) into the cable connector (19) into the contacting position.
Cable connector (19) according to one of the preceding claims, characterized in that it is one piece of bent sheet metal.
Cable connector (19) according to one of the preceding claims, characterized in that it has a cutting element (5) for cutting through a cable insulation (3) of the cable (1).
Cable connector (19) according to one of the preceding claims, characterized in that it is designed for making electrical contact with cable conductors (2) of a diameter between a minimum diameter (d1) and a maximum diameter (d2), and wherein the initial force (f0') amounts to at least 5%, in particular at least 10% or at least 20%, of the contacting force (f1') exerted on a cable conductor (2) of the minimum diameter (d1) in the contacting position.
Cable connector (19) according to one of the preceding claims, characterized in that it is designed for making electrical contact with cable conductors (2) of a diameter between a minimum diameter (d1) and a maximum diameter (d2), and wherein the cable connector is deformed only elastically through insertion of a cable conductor (2) of the maximum diameter (d2) into the contacting position.
Connector terminal block, characterized in that it comprises at least one cable connector (19) according to one of the preceding claims.
Connector terminal block according to claim 10, characterized in that it comprises an electrically insulating housing (12) accommodating the at least one cable connector (19), and further comprising an electrically conductive interconnection element (13) for electrically connecting the at least one cable connector (19) to another electric device.
Method of production of a cable connector (19) for making an electrical contact with a cable conductor (2) of a cable (1), in particular a cable connector (19) according to one of the claims 1-9, the cable connector (19) comprising two legs (190), at least one of which can make electrical contact with a cable conductor (2) inserted into the cable connector (19) into a contacting position, and with the two legs (190) capable of exerting a contacting force (f1';f2') on a cable conductor (2) in the contacting position, wherein the two legs (190) are formed and arranged in such a way, that they exert a non-vanishing initial force (f0') on each other, when no cable is inserted between them (190).
The method according to claim 12, characterized in that during production of the cable connector (19), an elastic deformation in at least one section of the cable connector (19) is performed

a) through temperature change and/or

b) while another section of the cable connector (19) is plastically deformed and/or

c) while the two legs (190) are fixed with respect to each other,

such that there is a prestress between the two legs (190) in the cable connector (19) under operating conditions.
The method according to claim 13 a), wherein

at least one of the two legs (190) comprises a memory-shaped alloy or a bimetal, and at least one production step is performed at a temperature that is different from the temperatures present under operating conditions of the cable connector (19), and/or

the elastic modulus of the material of at least one of the two legs (190) is changed through the temperature change.
The method according to claim 13 b), wherein the contact element (19) is a bent piece of sheet metal.
The method according to claim 13 c), wherein the two legs (190) are welded to each other while being pressed against each other.
Method for electrically contacting a cable (1) having a cable conductor (2), comprising the steps of:

firstly, applying a non-vanishing initial force (f0') to two legs (190) of a cable connector (190) before a slit (192) formed by the two legs (190) opens up, and then

applying additional force to the legs (190) for opening the slit (192) and for moving the cable conductor (2) between the two legs (190) in a direction substantially perpendicular to the slit (192), until the cable conductor (2) is in a contacting position, in which the cable conductor (2) is making electrical contact with at least one of the legs (190).