GB2069254A - Electric plug - Google Patents

Abstract

An electric plug, of the non- rewireable type, comprises a base member (6) and a cover member (8) secured to the base member, defining an aperture through which an electric cable secured to the plug extends into the interior of the plug. The plug comprises cable gripping means to absorb tension applied to the cable, provided by formations (26, 28, 30, 32) on opposite sides of the longitudinal axis, to engage the cable as it enters the plug, and to force part of the cable away from the longitudinal axis. Insert members (40, 42) of differing sizes, selected in accordance with the size of the cable being utilised, may be engaged with the formations, to provide the appropriate gripping force on the cable. <IMAGE>

Description

SPECIFICATION Improvements relating to electric plugs Description of Invention This invention relates to electric plugs. By the term "electric plug" as used herein, we mean a device comprising a hollow body of insulating material, and electrically conductive pins extending through the body into the interior thereof, connector means being provided to enable the conductive wires of a two or three core electric cable which extends through an opening in the body to be connected to the pins. Such plugs are adapted to be inserted into an electric socket, to bring the pins into conductive contact with terminals of the socket, whereby to establish a conductive path to the cable, and to an electric appliance conncted to the other end of the cable.

A conventional electric plug comprises a body member and a cover member releasably secured together, enabling the plug to be connected to and disconnected from the cable by a user of the appliance.

It is however becoming increasingly recognised, that it is desirable to provide an electric appliance with a plug of the non-rewireable type, that is to say a plug of the type which is permanently attached to the cable, so that a user of the plug cannot interfere with the interior of the plug, and in particular the connection of the cable to the pins of the plug.

Difficulties have however been encountered, in the provision of non-rewireable plugs, by the construction and arrangement of the plugs, which in general require either that the cable be secured to the pins, around which the plug body is then provided by an injection moulding operation, orthatthe plug body be made of two parts which, subsequent to the connection of cable to the plug pins, are permanently secured together by welding, heat sealing, gluing or similar methods which require the provision of special tools.

It is therefore one of the objects of this invention to provide a non-rewireable plug, which may be assembled without the requirement for special tools.

According to a first aspect of this invention there is provided a kit of parts for use in the assembly of an electric plug of the non-rewireable type, comprising a base member, a cover member, a plurality of apertures in one of the base member and the cover member, a plurality of hollow formations extending from the other of the base member and the cover member and which, when the base member and cover member are positioned together in the assembly of the plug each extend into one of said apertures, and a plurality of plug members each of which is adapted to be inserted into one of the hollow formations to prevent withdrawal of the hollow formations from the apertures.

Conveniently either the plug member, and/or the hollow formation, is tapered, enabling the plug to be retained within the hollow formation by frictional engagement. Prevention of withdrawal of the hollow formation from the aperture may be effected by engagement of a head of the plug member with a surface portion surrounding the aperture, or a radial expansion of the hollow formation into engagement with the surface bounding the aperture caused by the insertion of the plug into the hollow formation, or by both of these.

The base member and cover member may be secured together by a single such hollow formation located generally centrally of the base and covers members, but desirably more than one such hollow formations and corresponding apertures are provided.

Thus, by the use of the invention an electric plug of the non-rewireable type may be assembled, by connecting one end of an electric cable to the pins of the plug, and subsequently securing the base and cover members together, in a manner which provides a pleasing appearance, and which does not require the use of special tools.

This invention also provides a method of assembly of an electric plug of the non-rewireable type, and an assembled electric plug the pins of which are secured to one end of an electric cable, as set out above.

Another problem in the provision of electric plugs of the non-rewireable type, is that provision must be made for preventing strain on the cable being transmitted to the point of connection of the cable to the plug pins within the body of the plug. In conventional plugs of the non-rewireable type, manually operable means may be provided to fixedly secure the cable to the plug body, but in general automatic means is only operative to take up the strain of withdrawal (pulling) movement on the cable relative to the plug, and is not operative to take up the strain of movement of the cable relative to the plug in the opposite direction.Whereas this is disadvantageous in conventional electric plugs of the rewireable type, in view of the infrequency of this occurrence requiring a rewiring of the plug, automatic cable grips operating in this way have heretofore been acceptable. however where it is not possible for a user of the plug to reconnect the cable to the terminals, anautomatically operative cable grip which merely takes the strain of pulling forces applied to the cable is not acceptable.

It is therefore another of the objects of this invention to provide an electric plug with improved cable grip means.

According to a second aspect of this invention there is provided a kit of parts for use in the assembly of an electric plug, comprising cable grip means to restrain portions of the cable within the plug from movement relative thereto, said kit of parts comprising a base member, a cover member adapted to be secured to the base member, at least one formation on the base member or cover membey which bounds at least in part the path which will be adopted by an electric cable secured to the electric terminals of the plug, and a plurality of insert members adapted selectively to be engaged with said formation to vary the cross-sectional area of said path.

Thus in the assembly of the electric plug, an insert member appropriate to the cross-sectional dimensions of the cable will be selected, and engaged with the said formation so as to place the electric cable, when the base and cover members are secured together, under some degree of radial compression or deformation.

Conveniently the cable grip means comprises two formations, one on each of the base and cover members, each of which bounds part of the path on opposite sides thereof. Said formations may be arranged on diametrically opposite sides of the path, or may be spaced in directions longituinally of the path so as to effect a deformation of the cable from the longitudinal axis of the path. The arrangement is desirably such that an insert member may be engaged with one or with both of said formations, in accordance with the cross-sectional area of the cable.

By use of this aspect of the invention, frictional engagement of the cable with the formation or formations, and/or one or more insert members, may be arranged to prevent movement of that part of the cable on the interior of the plug relative to the pins of the plug.

This invention also provides an electric plug comprising cable grip means, as set out above.

It is to be appreciated that whereas the second aspect of this invention has been devised primarily in relation to the provision of cable grip means for a non-rewireabie plug, and in particular for a nonrewireable plug in accordance with the first aspect of the invention, the cable grip means of the second aspect may be used in a conventional plug of the rewireable type.

There will now be given a detailed description, to be read with reference to the accompanying drawings, of an electric plug which has been selected for the purposes of illustrating the two aspects of this invention by way of example. In the accompanying drawings: Figure lisa side sectional view of the preferred embodiment; Figure2 is an exploded sectional view, illustrating the permanent securing of parts of the plug together; Figure 3 is a plan view of a base member of the plug; Figures 4, 5 and 6 are views corresponding to Figure 1 illustrating the assembly of the plug with electric cable of differing cross-sectional areas; and Figure 7is a view of an insert member of cable gripping means of the plug.

The electric plug which is the preferred embodi ment of this invention comprises a housing of electrically insulating material, comprising a base member 6 and a cover member 8. Extending from the base member are plug pins 10, arranged in a conventional manner; these plug pins are provided on their end portions within the interior of the plug body, with means 11 by which the wires of an electric cable C may be secured thereto (see Figure 3): however the live wire of the cable is connected to the live pin by way of a fuse F, accessible for replacement from the exterior of the base member.

The base member is provided with at least one, and preferably three, stepped apertures 12, and the cover member 8 is provided with three, similarlyspaced hollow cylindrical formations 14. The outside diameter of the formations 14 when at rest are slightly less than the diameters of the apertures 12, and when the cover member is brought into position relative to the base member in the assembly of the plug, each of the formations 14 passes through an associated one of the apertures 12.

The plug also comprises three plug members 16, each comprising a head 18, and a shank a central portion 20 of which is tapered, and an end portion 22 of which is parallel-sided, having an outside diameter such as to be a sliding fit within the interior of the corresponding formation 14.

Thus, a plug 16 may be inserted through the wall of the base member 6 into the interior of each of the hollow formations 14, the tapered portion 16 of the shank effecting a radial outward deformation of the formation 14 into gripping engagement with the circumferential surface bounding the aperture 12.

Further, the end portion of each formation 14 is deformed to a diameter greater than that of the aperture 12, and separative movement of the base and cover members is prevented, by each formation 14, firstly by engagement of the formation 14 within the aperture 12, secondly by engagement of the enlarged end portion oftheformation 14 with a radial surface 13 bounding the aperture 12, and thirdly by engagement of the head 18 with a radial shoulder 17 spaced outwardly of the aperture 12.

In this manner the base and cover members may be secured together in a manner in which separation of the two is prevented, both simply, and without the need for special tools.

The electric plug which is the preferred embodiment of this invention also comprises means to restrain relative movement between the cable C and the interior of the plug housing, the cable extending into the plug through a sleeve S. Said means comprises formations 26,28 on the interior of the cover member, and formations 30,32 on the interior of the base member, the formations 26,28,30 and 32 bounding in partthe path adopted by the cable C when secured to the electric terminals of the plug.

The formations 26 and 30 are arranged on diametrically opposite sides of the longitudinal axis of the plug, and extend towards the longitudinal axis by a distance, such that when a cable C or large diameter is connected to the terminals, and the base and cover members are secured together, the cable will be placed under radial compression by the formations 26 and 30.

The formations 28 and 32 are spaced longitudinally of said axis, and the formation 28 (as is shown in Figure 1) effects a displacement of the cable from the longitudinal axis.

Thus, the cable C is engaged by all four formations 26, 28, 30 and 32, and restrained against movement relative to the plug by frictional engagement therewith.

The electric plug which is the preferred embodi mentofthis invention also comprises a plurality of insert members, two of which, 40 and 42, are shown in Figures 4 and 5.

When it is desired to secure to the plug a cable of cross-sectional area smaller than that shown in Figure 1 ,the insert member 40 may be positioned on the formtion 28. Thus, when the base and cover members are secured together, the insert member 40 engages the cable C', and displaces the cable from the longitudinal axis, into engagement with the formations 30 and 32. Thus relative movement of the cable C' is prevented by frictional engagement with the insert member 40, and with the formations 30 and 32 (see Figure 4).

As is shown in Figure 5, in addition to the use of an insert member 40, a further insert member 42 is engaged with said formations 30, 32 to reduce further the cross-sectional area of the path adopted by the cable C". As described previously, the restraint provided by the engagement between the cable and the insert members 40,42 is primarily frictional, caused by a combination of compression of the cable, and deformation of the cable away from the longitudinal axis. When cable of yet smaller diameter is used (C"', Figure 6) the insert member 42 may be replaced by a larger insert member 44.

Claims (21)

1. An electric plug comprising a base member, a cover member secured to the base member, parts of the base and cover members defining an aperture through which an electric cable secured to the plug extends into the interior of the plug, the plug comprising cable gripping means to restrain portions of the cable within the plug against movement relative thereto, said cable gripping means being operative to force part of the cable within the plug away from the longitudinal axis of the aperture.

2. An electric plug according to Claim 1 wherein said cable gripping means is operative at one position to force the cable away from the longitudinal axis of the aperture, and at another position to force the cable towards the longitudinal axis.

3. An electric plug according to one of Claims 1 and 2 wherein said cable gripping means is operative to cause the cable to adopt a serpentine configuration.

4. An electric plug according to any one of the preceding claims wherein the cable gripping means comprises a formation on each of the base and cover members, which extend towards the longitudinally axis on opposite sides thereof.

5. An electric plug according to Claim 4wherein said formations are on diametrically opposite sides of the longitudinal axis.

6. An electric plug according to one of Claims 4 and 5 wherein said formations are spaced longitudinally of said axis.

7. An electric plug according to any one of Claims 4,5 and 6 wherein the cable gripping means comprises at least three formations spaced longitudinally of the axis on alternately opposite sides thereof.

8. An electric plug according to any one of the preceding claims wherein the cable gripping means comprises at least one insert member selected in accordance with the diameter of the cable being used, and which may be engaged with the base and/or cover members to extend towards the longitudinal axis, to engage the cable and so force part of the cable away from the longitudinal axis of the aperture.

9. A kit of parts for use in the assembly of an electric plug comprising a base member, a cover member adapted to be secured to the base member, said kit of parts comprising cable gripping means to restrain portions of the cable within the plug against movement relative thereto, and which comprises at least one formation on the base member or cover member which bounds at least part of the path which will be adopted by an electric cable when secured to terminals of the plug, and a plurality of insert members adapted selectively to be engaged with said formation to vary the effective crosssectional area of said path.

10. A kit of parts according to Claim 9 wherein the cable gripping means comprises two such formations, one on each of the base and cover members, each of which, when the base and lower members are secured together, bounds part of the path on opposite sides thereof.

11. A kit of parts according to Claim 10 wherein said formations are on diametrically opposite sides of the path.

12. A kit of parts according to Claim 10 wherein said formations are spaced in directions longituclinally of the path so as to effect deformation of the cable from the longitudinal axis ofthe path.

13. A kit of parts according to any one of Claims 9 to 12, the construction and arrangement being such that an insert member may be engaged with one or with both of said formations, in accordance with the cross-sectional area of the cable with which the plug is intended to be used.

14. The invention according to any one of the preceding claims comprising a sleeve secured or adapted to be secured within and extending from the aperture, through which sleeve the cable extends into the plug.

15. The invention according to Claim 14 wherein the sleeve comprises a flange which is engaged by the base and cover members to secure the sleeve in position within the aperture.

16. The invention according to any one ofthe preceding claims in which the base and cover members are, or are adapted to be, non-releasably secured together.

17. The invention according to Claim 16 comprising a plurality of apertures in one of the base and cover members a plurality of hollow formations extending from the other of the base and cover members and which, when the base and cover members are positioned together in the assembly of the plug each extend into one of said apertures, and a plurality of plug members, each of which is adapted to be inserted into one of the hollow formations to prevent withdrawal of the hollow formations from the aperture.

18. An electric plug constructed and arranged substantially as hereinbefore described with reference to the accompanying drawings.

19. A kit of parts for use in the assembly of an electric plug substantially as herein before described with reference to the accompanying drawings.

20. A method of assembly of an electric plug involving the use of a kit of parts substantially as hereinbefore described with reference to the accompanying drawings.

21. Any novel feature or combination of novel features herein described and/or illustrated in the accompanying drawings.