EP0287352A2

EP0287352A2 - Improvements relating to electrical plugs

Info

Publication number: EP0287352A2
Application number: EP88303327A
Authority: EP
Inventors: Terence E. King
Original assignee: Bradshaw Raymond; Lapidus Alfred David Henry; Lapidus Robyn Griffith; Lapidus Samuel Henry Alfred
Current assignee: Bradshaw Raymond; Lapidus Alfred David Henry; Lapidus Robyn Griffith; Lapidus Samuel Henry Alfred
Priority date: 1987-04-13
Filing date: 1988-04-13
Publication date: 1988-10-19
Also published as: GB2204750B; GB2204750A; GB8708775D0; EP0287352A3; GB8808706D0

Abstract

An electrical plug of a type for domestic use consists of a body portion 1 and an insert portion 2 enterable into the body portion 1. The insert portion 2 comprises an axially directed lead receiving bore 7 in communication with radially directed conductor receiving channels 9 intersected by respective insulation displacement backup pieces 11. In use, a power supply lead is assembled to the insert portion 2 by the placement of conductors 15 in the conductor receiving channels 9 and the insert portion 2 can then be entered into the body portion 1 where insulation piercing pins 4 drive the conductors 15 into insulation displacing contact with the backup pieces 11 and pierce into insulation on the conductors to establish electrical connection between the plug and the power supply lead. The lead can be clamped to the insert portion 2 by way of a radially expandable and contractible clamping core 8 which co-operates with a complementarily shaped recess in the insert portion to clamp the lead when the insert portion is urged inwardly by insert portion driving member 3.

Description

This invention concerns improvements relating to electrical plugs and particularly, though not exclusively, concerns electrical plugs of the type employed for coupling domestic and other electrical appliances to socket outlets of the mains electrical supply.
The present invention results from our continuing development of an electrical plug of the above-mentioned type which can be simply and securely assembled to an appliance flex or cable without requiring use of a screwdriver or other tools. As is well known, the search for an electrical plug which truly can be said to be assemblable to a flex or cable without use of a screwdriver, wire-strippers etc. has long occupied many minds and the art is replete with failed screwless plugs, that is to say plugs alleged to achieve the aim of simple screwless attachment to a flex or cable but which for one reason or another have failed to achieve commercial success.
Our own efforts in this direction stem from an idea first disclosed in International Patent Publication No. WO82/00387 and now the subject of our European Patent Specification No. EP0063120. In accordance with this idea, an electrical plug of the aforementioned type comprised a plug body portion with terminal pins to be inserted into the corresponding openings of a socket outlet, and an insert portion to which an appliance cable is assembled as a simple screwless operation as a preliminary step in the connection of the plug to the cable, the insert portion being enterable into a recess in the body portion of the plug for completing the connection of the plug to the cable by virtue of the plug body portion and the insert portion having contact-establishing means which cooperate when the insert portion is entered into the recess. In the preferred embodiment described in EP0063120, the plug body portion has within its said recess insulation-piercing pins connected to the plug terminal pins and arranged to enter into conductor-receiving channels provided in the insert portion as the insert portion is entered into the recess; by threading the cable conductors into the conductor-receiving channels in the insert portion, without stripping the insulation from the conductors, as a preliminary step in the assembly of the plug to the cable, it is ensured that the entry of the insert into the recess results in the insulation-piercing pins piercing the conductor insulation of the conductors received in the channels and making electrical connection thereto. The insert portion is advantageously designed to accept cable conductor portions all of the same length and incorporates it own integral cable grip and thus can be assembled to the end of a cable by the simplest of operations.
Refinements of the basic idea described in EP0063120 are disclosed in our European Patent Application No. 85302871.0 (Publication No. EP0162597) and the most fundamental of these is to provide a means associated with the body portion of the plug for providing a mechanical advantage for facilitating the insertion of the insert portion into the plug body recess and thus, in the embodiment provided with insulation-piercing pins, enabling the mechanical resistance to piercing of the insulation to be overcome more readily. As described in EP0162597, the means for providing the mechanical advantage can advantageously comprise an additional internally screw-threaded component adapted for cooperation with an externally screw-threaded portion of the plug body to drive the insert portion positively into its accommodating recess when the internally screw-threaded component is manually screwed down onto the plug body portions. By virtue of this arrangement it is ensured that even the aged and infirm and others of weak manual strength can readily use the subject plug, and additional advantages are obtained by virtue of the fact that the additional component positively secures the insert within the plug body so that it cannot become detached during use.
The present invention provides yet further refinements of the basic invention of EP0063120 and primarily, though not exclusively provides for a metal backup to the conductor-piercing pins so that the forces developed as the pins pierce the insulation of the cable conductors, and thereafter by virtue of the presence of the pins pierced through the insulation and through the stranded cable conductors, are not resisted or backed up simply by the moulded plastics material of the insert. It is believed that by virtue of such an arrangement an even better and more secure electrical connection between the stranded conductors of the cable and the insulation-piercing pins will be obtained. In an exemplary embodiment as described in outline herinafter, generally flat bladed conductor piercing pins are utilised and metal backup pieces of generally flat U-shaped configuration are provided in the insert so that each piercing pin in use penetrates into the open end of a respective U-shaped backup piece, the backup pieces being oriented generally transversely to the flat pins.
In another aspect, the present invention provides an improved cable clamping arrangement which utilises a clamping cone of generally frusto-conical external configuration formed with an axial cable-receiving cylindrical bore, the cone being defined by a plurality of conical generatrices connected, in zig-zag fashion, each to the preceding generatrix at the bottom of the cone and to the succeeding generatrix at the top of the cone. By virtue of this arrangement, the cone is expandible and contractible in concertina fashion. The cone can thus be fitted over a cable sheath and, with a complementary conical clamping recess formed in the back of the insert, can be forcibly contracted down onto the cable as the insert driving component is screwed down onto the plug body.
These and further features and advantages of the present invention will become apparent from consideration of the following description given with reference to the accompanying drawings wherein:

Fig. 1 is an exploded view showing principal parts of an exemplary electric plug constructed in accordance with the present invention;
Fig 1A is a detailed showing of the piercing pin locator affixed to the fanning block (insert portion) and with cable conductors received in their respective conductor-receiving channels;
Fig. 2 is a sectional view showing the assembly of a cable and its conductors with the fanning block (insert portion), the section being taken on the line A--A in Fig 3;
Fig. 3 is a front end elevation view of the fanning block (insert portion) and piercing pin locator; and
Fig. 4 is a detailed showing of the combined effect of a piercing pin and its associated metal backup piece on an insulated, stranded conductor of a cable.

Referring to Fig. 1, there is schematically shown therein an electrical plug comprising a body portion 1 which, as is described in EP0063120 and EP0162597 afore-mentioned, is provided with a recess (not shown) into which there can be introduced an insert portion or fanning block 2, the plug body portion being provided with an externally screw-threaded portion (not shown) which cooperates with an internally screw-threaded insert driving portion 3 (see Fig 2) which, as described in EP0162597, provides a mechanical leverage for the insertion of the insert portion 2 into the plug body recess.
The plug body portion 1 is provided with three flat bladed piercing pins 4 each of which is electrically connected to a respective one of the L, N and E plug terminal pins 5. As described in EP0063120 and EP0162597, the insulation piercing pins 4 project into the recess formed in the plug body portion for making insulation-displacing electrical contact with conductors pre-assembled into the insert portions when the insert portion is fully entered into the recess.
In the illustrated embodiment, the insert portion or fanning block 2 (so called since it serves to fan out the L, N and E conductors of a cable) comprises an externally cylindrical moulding 6 formed with an internal bore 7 or conductor-receiving channel (see Fig 2) which at its rearmost end is frusto-conical for receiving a cable-clamping cone 8 and otherwise is as shown in Fig 2. At its forward face, the bore 7 communicates with three radially-directed conductor-receiving channel portions 9 each of which is intersected by a recess 10 for receiving a flat metal backup piece 11 configured as shown in Fig 1. An apertured fanning block end cap 12, which as shown in Fig 3 can be hingedly connected to the fanning block 2 by means of a moulded hinge, serves as a piercing pin locator for guiding the piercing pins 4 into the conductor receiving channels 9 of the fanning block 2 as can best be seen from Fig 2. Integrally formed popper pins 13 are provided on the pin locator cap 12 for engagement in bores 14 provided in the end face of the fanning block 2 to secure the pin locator cap 12 in closed condition.
Fig 1A and Fig 2 show how the conductors 15 of a cable are inserted, in use of the plug, through the central bore of the fanning block and are fanned out and laid into the respective cones of the conductor-receiving channels 9, the same being colour coded and/or provided with indicia to guide correct assembly. Once the conductors have been laid into the channels 9, the pin locator 12 cap can be closed. Insertion of the fanning block into the plug body recess will then cause the insulation piercing pins 4 to enter into the front end of the fanning block, guided by the apertures in the pin locator cap 12. When the pins 4 encounter the insulated conductors 15, they will initially compress the conductors into the open ends of the U-shaped backup pieces 11 and then will begin to pierce into the insulation. As the fanning block is forcibly driven into the plug body recess by tightening of the insert-driving portion 3, so the backup pieces 11 will also pierce through the insulation of the conductors as shown in Fig 4. As a result, an excellent electrical connection is obtained between the insulation piercing pins and the conductors of the cable which is independent of any back pressure derived from the plastics material of the fanning block itself, which is considered to be advantageous.
The metal backup pieces 11 are generally U-shaped as shown in Fig 1 with the open mouth of the U shaped to define inwardly converging opposed surfaces which serve to guide a conductor laid into one of the channels 9 centally between the spaced-apart legs of the U. Inwardly of the converging opposed surfaces of the mouth of the U, there is provided a generally parallel throat portion which serves an insulation displacement function as the conductor is forced into the U-shaped piece. The arrangement of the recesses 10 is such that the U-shaped pieces 11 lie transversely to conductors laid into the channels 9, and the flat bladed pins 4 align with the conductors, as shown in Fig 4.
Referring to Figs 1 and 2, the clamping cone 8 may be seen to be in the form of a radially expandible and contractible frusto-conical member having an internal cylindrical bore which can be fitted over the sheath of a cable and, when introduced into the complementarily shaped frust-concial recess in the back of the fanning block and urged inwardly by the action of the fanning block driving member 3, will clamp down onto the cable thereby forming an effective cable clamp for the plug. As can be best seen from Fig 1, the clamping cone 8 is formed as a plurality of conical generatrices which are connected at their opposite ends to the generatrices on either side, and as can best be seen from Fig 2 each generatrix is wedge shaped so that as the clamping cone is forced into the recess in the back of the fanning block a radially inwardly camming action is exerted upon the generatrices of the clamping cone.
From the foregoing it will be appreciated that the present invention provides an easy-assembly domestic electrical plug in use of which the conductors of a cable need only be threaded into the central bore of the fanning block and then fanned out into their respective conductor-receiving channels whereupon, after trimming off any excess length of conductor with scissors, insertion of the fanning block into the plug body recess and driving home of the fanning block by means of the screw component completes the connection of the cable to the plug, with the cable conductors pierced by insulation-piercing pins backed up with metal backup pieces, and also securely clamps the cable to the plug.
It is to be appreciated that the embodiment hereinbefore described is exemplary only and that many modifications and variations are available without departure from the broad ambit of the invention. Thus, for example, whilst in the illustrated embodiment the fanning block 6 has its conductor-receiving channels defined by the internal bore 7 and the communicating channel portions 9, it could alternatively be formed with conductor receiving channels more in the form of those described in EP0063120 and EP0162597. Also, the configuration of the clamping cone is susceptible to variation and a single division in an otherwise continuous hollow frusto-conical member could be employed, for example, rather than the multiple interconnected generatrix arrangement described, the essential requirement being that the cone be capable of radial deformation under the camming action of the recess in the rear of the fanning block.

Claims

1. An electrical plug for use for connecting the power supply lead of a domestic electrical appliance to a socket outlet of a mains electrical distribution system, the said plug comprising a body portion having a plurality of terminal pins to be inserted into the corresponding openings of a socket outlet and an insert portion to which a power supply lead as aforesaid can be assembled as a preliminary step in the connection of the plug to the power supply lead, the said insert portion thereafter being enterable into a recess in said body portion for completing the connection of the plug to the power supply lead, the insert portion comprising an axially directed lead receiving bore in communication with a plurality of transversely directed conductor-receiving channels intersected by respective insulation displacement type backup means, each of the receiving channels being arranged for receiving a respective one of the conductors of the power supply lead to which the plug is to be connected and each being arranged in co-operation with the metal backup means for supporting a conductor end portion therein at a location to be accessed for making electrical contact between the respective conductor and a respective one of said pins when the insert portion is entered into said recess, and a plurality of separate insulation displacement type contact-establishing means being provided in said recess for co-operating with respective ones of said backup means and thereby establishing electrical contact between each of said terminal pins and a respective conductor end portion received at a respective one of said locations when said insert portion is entered into said recess.

2. A plug as claimed in claim 1 further comprising inset portion urging means associated with the body portion of the plug for providing a mechanical advantage for facilitating the manual insertion of the insert portion with the power supply conductors assembled thereto into the said recess in the plug body portion and facilitating the associated operation of the insulation displacement type contact establishing means and the insulation displacement type backup means.

3. An electrical plug as claimed in claim 2 wherein the said insert portion urging means comprises an internally screw-threaded component adapted for co-operation with an externally screw-threaded portion of the plug body to drive the insert portion positively into its accommodating recess in the plug body portion when the said screw threads are engaged with each other and the internally screw-threaded component is manually screwed down onto the plug body portion.

4. An electrical plug as claimed in claim 3 wherein the plug body portion has a generally cylindrical hollow protrusion from its rear surface and the external surface of such protrusion is screw-threaded for co-operation with the internally screw-threaded surface of said insert portion urging means, the said recess in the plug body portion aligning with the hollow interior of the protrusion, and the said insert portion and the said urging means co-operating with each other such that when the insert portion is introduced into the recess and the said urging means is thereafter screwed onto the said protrusion the said urging means drives the insert portion in the recess.

5. An electrical plug as claimed in any of the preceding claims wherein a generally conical cable clamping member co-operates with a complementarily shaped rearmost end portion of the lead receiving bore to provide a cable clamping arrangement at one end of said insert portion which is outermost of said recess when the insert portion is fully entered into said recess, said cable clamping arrangement serving for clamping a power supply lead to the insert portion, and the co-operating contact-establishing means are each provided at the opposite end of said insert portion from the cable clamping arrangement in the direction of insertion of the insert portion into the recess and at a co-operating surface of said recess.

6. An electrical plug as claimed in claim 5 as dependent upon claim 2 wherein the said cable clamping member is formed as a plurality of conical generatrices defining an internal substantially cylindrical axial lead receiving bore through which a power supply lead can be passed in said preliminary step, each of said generatrices being substantially wedge shaped and each being connected at one end to the preceding generatrix and at the other end to the succeeding generatrix thereby to form a radially expandable and contractible clamping member which, when introduced into the complementary end portion and urged inwardly by said urging means, serves to clamp the lead to the insert portion.

7. An electrical plug as claimed in any of the preceding claims wherein said insulation displacement type backup means is generally U-shaped with the open end portions of the U defining inwardly converging opposed surfaces and the limbs of the U being spaced to provide a conductor receiving portion providing an insulation displacement function when said conductors are received in said respective receiving channels.

8. An electrical plug as claimed in claim 7 wherein said backup means are oriented substantially perpendicular to respective receiving channels with the limbs of the U being positioned on either side of said receiving channel.

9. An electrical plug as claimed in any preceding claim wherein said contact establishing means comprise generally flat bladed insulation piercing pins oriented substantially parallel to respective receiving channels and arranged to drive the conductors contained therein into insulation displacing contact with said respective backup means and to pierce into insulation on the conductor thereby to establish said electrical contact when said insert portion is entered into said recess.

10. An electrical plug as claimed in any of the preceding claims wherein the insert portion and the recess are arranged such that the insert portion is enterable into the said recess in only a predetermined orientation of the insert portion relative to the plug body portion and is movable within the recess for completing the connection of the plug to a power supply lead only by linear movement of the insert portion relative to the plug body portion without relative rotation therebetween.

11. An electrical plug as claimed in any one of the preceding claims wherein said insert portion further comprises an apertured end cap which apertures co-operate with said contact-establishing means to guide the same towards respective conductors when said insert portion is entered into said recess.

12. An electrical plug as claimed in claim 11 wherein said apertured end cap is hingedly connected at one end of said insert portion which end is inmost of said recess, thereby to facilitate assembly of conductors into said respective conductor-receiving channels in said preliminary step.

13. An electrical plug as claimed in claim 11 or claim 12 wherein press fit retaining pins are integrally provided on the apertured end cap which retaining pins are arranged to co-operate with bores on said inmost end of the insert portion to secure said end cap in closed condition.

14. An electrical plug as claimed in any of the preceding claims wherein said co-operating contact-establishing means are constituted by said body portion having insulation displacement terminals projecting into said recess from an inner end wall thereof and said insert portion being arranged such that when, in use of the plug, the insert portion is fully entered into the recess the said terminals enter into electrical contact with conductor end portions received at said locations in said conductor-receiving channels.