Electricity: conductors and insulators – Conduits – cables or conductors – Combined
Reexamination Certificate
1999-10-06
2002-03-12
Nguyen, Chau N. (Department: 2831)
Electricity: conductors and insulators
Conduits, cables or conductors
Combined
Reexamination Certificate
active
06355888
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for securing electrical cables, which have a screen for electromagnetic compatibility (EMC), having a retaining body and a contact-maker device, in which case the contact-maker device is arranged inside the retaining body and an electrical connection can be produced between the screen and the retaining body by means of the contact-maker device, in which case, in the operating state, the screen is fixed in a force-fitting manner, in particular being clamped, by means of a tightening element, which acts radially inwards, between the contact-maker device and the retaining body.
2. Description of the Related Art
Electromagnetic compatibility (EMC) of equipment or cables is becoming evermore important with regard to the increasing use, both commercially and in the private field, of electrical or electronic equipment and machines which influence one another by virtue of interference radiation.
Electrical cables equipped with a screen prevent the emission of electromagnetic radiation, since the interference radiation emitted, for example, by the equipment or the assembly, is reliably dissipated to zero potential via the screen. EMC-proof cable installations comprise cable unions which allow an electrical connection to be made between the screen and the equipment housing.
By way of example, a cable union is known in practice, which is equipped with a contact-maker device within the retaining body, in order to produce the electrical connection between the screen and the retaining body. The contact-maker device comprises two conical rings and an endless spring washer. When the compression screw is tightened, the two conical rings act radially inwards onto the spring washer. This reduces the diameter of the spring washer, and the screen makes contact with the cable passing through, whose outer casing has been removed in the contact region. Any electromagnetic interference radiation is passed from the metallic retaining body, via the metallic conical rings and the metallic spring washer, to the screen and, finally, to zero potential.
A problem with this apparatus is that, in mechanical terms, the contact to the screen is produced only by the spring washer resting against the screen. Even a slight reduction in the pressure exerted by the compression screw on the conical rings the [sic] can lead to an interruption in the contact, since the diameter of the spring washer again increases. Furthermore, the production and assembly of the known apparatus or EMC cable union are quite complex owing to the three components—namely two conical rings and a spring washer.
EP 0 598 261 A2 discloses a solution to the problem of securing the electrical contact between the screen and the retaining body by the screen making direct contact with the retaining body and being clamped between the contact-maker device and the electrically conductive retaining body. For this purpose, the screen mesh is exposed and the contact-maker device is then pushed on. The mesh is then bent back, and the clamping process is carried out by means of the retaining body and a tightening element. The clamping process takes place exclusively in the radial direction with respect to the longitudinal axis of the screw union. In addition, the screen must be bent around the contact-maker device in a complex way, thus resulting in an increased assembly effort for connecting the cable to the cable screw union. The retaining body and the screw sleeve have no end face.
OBJECT AND SUMMARY OF THE INVENTION
With this prior art, which is known from EP 0 598 261 A2, as the starting point, the invention is based on the primary object of specifying an apparatus of the type under discussion, which is functionally reliable, results in low production costs and, furthermore, reduces the assembly effort overall.
The above object is achieved in accordance with the invention, an apparatus of the type under discussion which is designed in such a way that the application of force produced by the tightening element on the contact-maker device is directed coaxially with respect to the longitudinal axis of the retaining body, so that the screen is pressed against the end face of the retaining body.
According to the invention, it has first of all in principle been recognized that the assembly effort can be reduced if there is no need to bend the screen around to match the contact-maker device once the cable insulation has been stripped off. Furthermore, it has been recognized that there is no need to bend the screen around if the tightening element applies force to the contact-maker device not only radially but also coaxially. The coaxially directed application of force moves the contact-maker device towards the screen, which is gradually pressed against the end face of the retaining body and, in consequence, is fixed. The preparation of the cable could, for example, be limited to exposing the screen, in which case engagement elements are then provided on the contact-maker device which deform the mesh such that sufficient material is available for clamping. Alternatively, the screen could simply be pushed back and a bead could be formed, against which the contact-maker device is pressed coaxially—without any special engagement elements. In any case, the screen preparation steps which result from the teaching of the prior art of this generic type and increase the assembly effort, comprising weaving the mesh, bending it to the rear, and cutting off the screen, are eliminated in the claimed teaching in favour of reduced assembly effort and thus more cost-effective production, while at the same time ensuring the functional reliability of the claimed apparatus.
A particularly effective connection between the contact-maker device and the screen is produced if the contact-maker device engages in the mesh of the screen and presses the latter against the inner surface, virtually compressing it in the process. If the outer casing of the cable is removed and the screen is just exposed, special engagement elements are required on the contact-maker device, which deform the mesh so that sufficient material is available, which can be clamped between the contact-maker device and the retaining body.
It is of particular advantage with respect to a contact-maker device of simple design and without any special engagement elements for the screen to be pushed back after the outer casing is removed from the cable, so that it forms a bead. The bead extends at right-angles to the longitudinal axis of the cable and parallel to the end face of the retaining body, and offers a good surface for the contact-maker device to act on.
In order to produce the clamped connection between the contact-maker device and the retaining body with the interposition of the screen, the tightening element (which, as is known, is part of the retaining body) is tightened, during which process pressure is applied to the contact-maker device.
According to a preferred exemplary embodiment, the tightening element is a union nut having an internal thread which, at its end facing away from the rest of the retaining body, has an internal design which converges in the direction of this end. This refinement in particular additionally leads to the application of pressure to the contact-maker device, which is directed radially inwards, being supplemented by pressure which is directed coaxially with respect to the longitudinal axis of the retaining body being applied to the contact-maker device according to the invention. The coaxial application of pressure, which is directed at least parallel to the longitudinal axis, results in the contact-maker device being moved towards the screen which, as a result of the convergent internal design, is gradually pressed against the end face of the retaining body, and is fixed by it. As an alternative to the union nut having a convergent internal design, a stepped reduction in cross section would also be possible. Furthermore, instead of a union nut, it would also be possible
Nguyen Chau N.
Reed Smith LLP
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