EP0237500A2

EP0237500A2 - A screened electrical cable

Info

Publication number: EP0237500A2
Application number: EP87830082A
Authority: EP
Inventors: Giuseppe Codrino
Original assignee: Cavis Cavetti Isolati SpA
Current assignee: Cavis Cavetti Isolati SpA
Priority date: 1986-03-10
Filing date: 1987-03-05
Publication date: 1987-09-16
Anticipated expiration: 2007-03-05
Also published as: DE3783787T2; EP0237500B1; DE3783787D1; IT8621177V0; IT208614Z2; ES2037741T3; EP0237500A3

Abstract

A screened electrical cable has an inner core (2) of mechanically strong filaments surrounded by an inner semi-conductor layer (3) around which is wound an electrically conductive helix (4) surrounded by an insulating layer (5) clad in an outer cladding layer (6) of temperature resistant material capable of resisting aggressive chemical agents.

The ends of the screened cable are provided with terminals in the form of longitudinally split connector bodies (11) having aligned, likewise longitudinally split generally cylindrical clinching collars (13) inwardly from which project piercing elements (15, 20) which pass through the outer cladding layer (6) and insulating layer (5) to make electrical contact with the conductive helix (4) when the clinching collar (13) is crimped onto the end of the cable.

Description

The present invention relates to a screened electrical cable, that is an electrical cable having a screen against interference which may be caused to nearby sensitive electrical equipment, particularly radio and television receivers.
Considerable difficulties are currently encountered in the production of screened electrical cables, in particular as far as the mechanical strength of the cable is concerned; the problem up to now has been the difficulty in obtaining a good electrical screening combined with adequate mechanical strength of the cable. Another disadvantage of the prior art is constituted by the fact that known screened electrical cables currently available on the market are not able to resist relatively high temperatures or aggressive external chemical agents.
The object of the present invention is to provide a screened electrical cable which has not only a high mechanical strength but also an excellent screening against interference so as to obtain a product which has good properties both from a mechanical and an electrical point of view.
According to the present invention there is provided a screened electrical cable, characterised in that it comprises a core of aromatic polyamide filaments surrounded by a semi-conductor layer around which is wound a helix of electrically conductive wire, the said helix being disposed within an insulating layer covered by an outer cladding layer, and in that at least one end of the cable is provided with a contact terminal fixed to the cable by a crimping collar having at least one piercing element which passes through the said outer layer and the said insulating layer to make electrical contact with the electrically conductive helix.
One advantage of the present invention is that it provides a screened electrical cable which can be quickly and easily formed to connector terminals at its ends thus facilitating electrical connection operations.
Another advantage of the present invention is that it provides a screened electrical cable having an outer cladding layer which is able to resist even the most severe working conditions without being subject to damage of any type.
A further advantage of the present invention is that it provides a screened electrical cable which is able to offer the widest guarantees of reliability and safety in use.
One embodiment of the present invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a schematic partly cut-away perspective view of a screened electrical cable formed as an embodiment of the invention;
Figure 2 is a perspective view on an enlarged scale of a first type of electrical connector terminal with which the screened cable of the invention may be fitted;
Figure 3 is a cross section through a screened cable fitted with the connector terminal of Figure 2;
Figure 4 is a perspective view, again on an enlarged scale, of a second type of electrical connector terminal with which the screened cable of the invention may be fitted; and
Figure 5 is a cross section through a screened cable fitted with the connector terminal of Figure 4.

Referring now to the drawings, the screened electrical cable of the invention, which is generally indicated with the reference numeral 1, comprises a core 2 composed of a plurality of filaments of aromatic polyamide fibre, commonly commercially known by the trade mark KEVLAR, which serve as a mechanically strong support. Around the core 2 is provided a layer of semi-conductor material 3, which is preferably made of a ferrite with polyvinyl chloride. Outside the semi-conductor layer 3 there is helically wound an electrically conductive wire 4 which, advantageously, is composed of ferro-nickel, which provides an extremely effective screening action against electrical interference.
Around the conductive helical winding 4 is provided an insulating layer 5 which is formed by means of extrusion of a medium to high density E.P.D.M. rubber. The insulating layer is, in turn, clad in an outer layer 6 which is able to resist high temperatures and aggressive chemical agents and which is preferably made of HYPALON.
Electrical connection to the cables can be made by means of terminals such as those shown in Figures 2 to 5. In Figure 2 the terminal shown is generally indicated with the reference numeral 10 and comprises a contact body 11 of longitudinally split generally cylindrical form which is connected, by means of a narrow bridging portion 12, to a correspondingly shaped longitudinally split generally cylindrical clinching collar 13.
As is illustrated in Figures 2 and 3, the clinching collar 13 is provided with pointed piercing elements 15 which can be pressed through the outer cladding layer 6 and the insulating layer 5 to made electrical contact with the helical winding 5. The piercing elements 15 are disposed in several rows extending circumferentially with respect to the cable, and are formed by punching out elongate isosceles triangles from the material of the collar 13.
Upon clinching of the collar 13 onto the end of the cable 1, the piercing elements 15 penetrate through the layers 6 and 5 and come into contact with the conductive helix 4 so that electrical connection between the terminal 10 and the helix 4 is made in a very rapid and effective manner.
As is illustrated in Figures 4 and 5, the alternative embodiment in which like reference numerals indicate the same parts as in the embodiment of Figures 2 and 3, electrical connection is effected by means of a pair of arms 20, which can also pierce the outer layer 6 and the insulating layer 5, to come into electrical contact with the helix 4; the pair of arms 20 effectively constitute a fork element which again can be formed directly, by means of punching out of the clinching collar 13. The arms 20 are disposed substantially orthogonally of the axis of the cable in such a way as to come into contact with the helix 4 without passing through it or in any way cutting it, but merely embracing it externally thus ensuring electrical contact therewith.
Externally accessible electrical terminals connected to the inner conductor are thus easily provided on the screened electrical cable automatically upon crimping of the terminals themselves to the ends of the cable.

Claims

1. A screened electrical cable (1), characterised in that it comprises a core (2) of aromatic polyamide filaments surrounded by a semi-conductor layer (3) around which is wound a helix (4) of electrically conductive wire, the said helix (4) being disposed within an insulating layer (5) covered by an outer cladding layer (6), and in that at least one end of the cable (1) is provided with a contact terminal (10) fixed to the cable (1) by a crimping collar having at least one piercing element (15, 20) which passes through the said outer layer (6) and the said insulating layer (5) to make electrical contact with the electrically conductive helix (4).

2. A screened electrical cable (1) according to Claim 1, characterised in that the filaments of the said core (2) are composed of KEVLAR.

3. A screened electrical cable according to Claim 1 or Claim 2, characterised in that the said semi-conductor layer (3) is composed of a ferrite compound with polyvinyl chloride.

4. A screened electrical cable according to any of Claims 1 to 3, characterised in that the said conductive helix (4) is made of ferro-nickel wire.

5. A screened electrical cable according to any preceding Claim, characterised in that the said insulating layer (5) is made by extrusion of a medium to high density E.P.D.M. rubber.

6. A screened electrical cable according to any preceding Claim, characterised in that the said outer cladding layer (6) is made of HYPALON.

7. A screened electrical cable according to any preceding Claims, characterised in that the said piercing element (15) introduceable through the outer cladding layer (6) and the insulating layer (5) to make electrical contact with the conductive helix (4) is constituted by at least one point (15) projecting inwardly from the inner surface of the crimping collar (13) and of a length such as to be brought into contact with the conductive helix (4) upon application of the crimping collar onto the end of the electrical cable.

8. A screened electrical cable according to any preceding Claim, characterised in that there are two said piercing elements (20) introduceable through the outer cladding layer (6) and the insulating layer (5) to make electrical contact with the said conductive helix (4), these two piercing elements (20) being formed by punching out from the crimping collar (13) to form a fork capable of straddling the said conductive helix (4) in a direction substantially perpendicular to the axis of the electrical cable.