Cable terminal for mechanically retaining and electrically...

Details Cable terminal for mechanically retaining and electrically... Cable terminal for mechanically retaining and electrically...

2000-02-25

2001-07-17

Abrams, Neil (Department: 2839)

Electrical connectors

With stress relieving means for conductor to terminal joint

Conductor gripped by or entirely within connector housing

C174S068300

Reexamination Certificate

active

06261121

ABSTRACT:

TECHNICAL FIELD
The invention relates to a cable terminal for mechanically retaining and electrically connecting a cable, comprising a two-piece housing and a clamping device for a cable to be inserted into the housing.
BACKGROUND OF THE INVENTION
Such a cable terminal may be put to use, for example, in a switchboard cubicle where it needs to satisfy differing requirements. For one thing, it needs to permit a reliably good electrical connection of the cable. At the same time it is to provide strain relief by means of which the cable is retained in the cable terminal such that tensile strain introduced into the cable is not transferred to the electrical connection, it instead being directed away into the housing beforehand. Finally, such a cable terminal may also be made use of to provide electrical shielding of the cable joint with the electrical connection.
Known from prior art are two concepts by means of which it is attempted to ensure both a reliable mechanical retention of the cable in the cable terminal and good electrical shielding. One concept provides for configuring a cable receptacle provided with several screws which in the screwed-in condition engage the sheath of the cable. If the cable is provided with a shielding this can be folded back through 180° on the cable sheath and contacted there. Another concept provides for crimping a retaining ring onto the cable sheath. This ring is then inserted into an accommodating receptacle in the housing and acts as a strain relief. If the shielding is exposed prior to crimping the retaining ring and is folded back on the sheath the retaining ring is able to contact this shielding and serve together with the electrically conducting receptacle to ensure a good shielding of the cable terminal.
The drawback in these concepts is the high expenditure involved in inserting and securng the cable.
BRIEF SUMMARY OF THE INVENTION
The object of the invention consists of improving a cable terminal of the aforementioned kind so that a cable to be inserted into the cable terminal can be reliably mechanically retained with minimum complication.
This object is achieved in a cable terminal for mechanically retaining and electrically connecting a cable. The cable terminal comprises a two-piece housing having a first housing shell and a second housing shell, and a clamping device adapted to receive the cable. The clamping device defines a longitudinal axis and comprises at least two pairs of deforming elements arranged opposite each other. The deforming elements of a first of the pairs are arranged opposite each other in a clamping direction which is different from a clamping direction in which the deforming elements of a second of the pairs are arranged opposite each other. The first and the second pairs are arranged in sequence along the longitudinal axis. The term “clamping direction” is understood to be the direction along which the two deforming elements of a pair exert a clamping force on the inserted cable; this direction generally coinciding with the direction of the shortest connection between the two deforming elements.
Termed in general, the gist of the cable terminal in accordance with the invention is based on the retaining force to be made available for the purpose of strain relief being furnished by at least two pairs of deforming elements arranged in sequence. These deforming elements are configured such that the deformation of the cable caused by them differs directionally. When, for example, the first and the second pair of deforming elements deform the cable from its initial round cross-section into an oval cross-section the direction defined by the longer main axis of the oval cross-section in the region of the first pair of deforming elements differs from the direction defined by the longer main axis of the second oval cross-section. However, the resulting deformation must not necessarily result in an oval or elliptical cross-section of the cable. Depending on the configuration of the deforming elements and the deformation response of the cable, a constricted cross-section may also be produced, for instance. In any case a reduction in the diameter of the cross-section occurs in the clamping direction in which the deforming elements are arranged opposite each other, whilst at right angles to this clamping direction, for instance, an enlargement of the diameter of the cross-section materializes. Due to the differing orientation of the deformed cross-sections of the cable, any tendency of the cable to be pulled out from the cable terminal is counteracted by a resistance to a change in shape in addition to the friction forces produced at the “bite” locations of the deforming elements on the cable; namely, for the cable to be pulled out, each point of the cable deformed in a first direction by a pair of deforming elements would need to be deformed in another direction in the subsequent pair of deforming elements. It is this resistance to a change in shape resulting from the material stiffness of the cable that counteracts the multiple deformation of the cross-section.
In accordance with a preferred embodiment of the invention it is provided for that the clamping direction dictated by the first pair of deforming elements differs by roughly 90° from the clamping direction dictated by the second pair of deforming elements. This configuration produces a maximum resistance in the case of tensile forces acting on the cable.
In accordance with the preferred embodiment of the invention a third pair of deforming elements is provided, the second pair of deforming elements being disposed between the third pair of deforming elements and the first pair of deforming elements and the clamping direction dictated by the third pair of deforming elements roughly coinciding with the clamping direction dictated by the first pair of deforming elements. In this configuration three deformed cross-sections of the cable are produced, each of which differs from the adjacent cross-section to thus further enhance the strain relief effect.
It is preferably provided for that a deforming element of a pair is applied to the first housing shell and the associated other deforming element is applied to the second housing shell. In this configuration a minimum assembly requirement is involved, the cable merely needing to be inserted into the one of the housing shells. The strain relief then materializes automatically when the second housing shell is mounted and connected to the first housing shell.
In accordance with the preferred embodiment of the invention it is further provided for that a deforming element consists of a rib extending in a plane perpendicular to the longitudinal axis of the cable to be accommodated in the cable terminal. Using a rib as a deforming element offers various advantages. For one thing it is simple to manufacture, especially when the two housing shells are fabricated as injection molded parts. For another, the deformation of the cable and the thereby resulting resisting and retaining forces can be freely adjusted by the geometrical configuration of the rib, for example of the edge engaging the cable and the width of this edge.
It is, for example, possible that the rib engages the cable by a straight edge which, as regards a tangent to the outer circumference of the cable to be inserted, is slightly inclined. In this configuration inserting the cable is facilitated; apart from this the risk of the cable being damaged on insertion is reduced.
Preferably the two edges are opposite each other in a clamping direction which is roughly perpendicular to the direction in which the housing is closed. In this configuration the pushing forces needed to clamp the cable in place are applied on closing the housing. Since due to the wedge effect no particularly high forces are needed to close the housing, just a few screws are sufficient to reliably close the housing. Apart from this, no particular precautions are needed to prevent deformation of the housing.
As an alternative it is provided for that the rib engages the cable by a protuberance. This c

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