GB2279821A

GB2279821A - Shearing clamping connection for a plug pin and wire

Info

Publication number: GB2279821A
Application number: GB9311755A
Authority: GB
Inventors: Jerry Ranger
Original assignee: B&R Electrical PLC
Current assignee: B&R Electrical PLC
Priority date: 1993-06-08
Filing date: 1993-06-08
Publication date: 1995-01-11
Anticipated expiration: 2013-06-08
Also published as: GB2279821B; GB9311755D0

Abstract

A method of permanently connecting two members, such as an electric conductor from a cable (10) and an electric terminal (1, 2) of an electric plug (30), is disclosed. A portion of a conductor of the cable (10) may be inserted into a hole (5) near to the end of the terminal (1, 2) and is then clamped in place in the hole (5) by an impact, for example on the end surface (6) of the terminal (1, 2), near the hole (5) so as to distort the shape of the hole. The impact may firstly define a portion on the end surface by cutting it, and then partially shear the portion from neighbouring material. The volume below the portion moves into the hole and thus clamps the conductor in place. <IMAGE>

Description

A TERMINAL ASSEMBLY FOR A NON-REWIRABLE ELECTRIC PLUG The present invention relates to a method of connecting two members together and in particular to a method of connecting an electric conductor to a terminal of an electric plug.

Standard electric plug assemblies are designed to be movable between one electrical appliance and another. Consequently it is necessary for the connections between the conductors leading to the appliances and the terminals or pins of such plugs to be releasable. Generally a releasable connection for such a plug is effected by clamping a conductor in a bore or slot through the terminal by means of a screw which bears against the conductor. The connection can be released by unscrewing the screw. This operation is time consuming and the operation of connecting an electrical plug to the conductors of an appliance is thus unsuitable in a process of mass-production of appliances. Further to this, if the screw is not properly tightened the conductor may become detached from the terminal, whereas if the screw is overtightened the clamped section of the conductor may be twisted such that it is weakened or broken, due to the rotational movement of the base of the screw against it as the screw clamps it in the bore or slot of the terminal.

Currently there is a trend towards nonrewirable plugs which will be fitted permanently to a cable extending from an appliance during the manufacture of the appliance, or which will be fitted permanently to a cable which is adapted to plug into the appliance.

This trend is happening in the interests of public safety, the aim being to prevent injuries due to incorrect connection of the conductors. In addition to the benefits of increased safety and convenience for the user of the appliance, there are benefits for the manufacturer. Firstly, a plug that is not intended to be attached and detached to the conductors of different appliances does not need to be rewirable and is thus not limited to having to have releasable connections such as those described above. It is thus possible for the connections between the conductors of appliances and the terminals of their plugs to be of a type that does not cause damage or fatigue to the ends of the conductors, as do the standard releasable screw-clamp connections, described above, each time they are released and reconnected. It is also possible for the connections to be of a type suitable to be made and connected as a part of a process of mass-production of appliances.

Various arrangements are known whereby a conductor of an appliances is connected permanently to a terminal of a plug.

For example, UK Patent GB 2,072,435B relates to an electric plug assembly in which each connection is made by positioning a bare end of a conductor in a hole which extends through a pin of the plug, and then distorting a part of the pin bounding the hole in a direction transverse to the axis of the hole in such a way that the bare end of the conductor is permanently clamped to the pin, without any portion of the pin material being sheared from the pin.

UK Patent 2,173,361B relates to an electric plug assembly in which the connections are made similarly to those according to GB 2,072,435B, but in which the bare ends of the conductors are placed in, and throughout the length of, the holes, and are then clamped to the pin uniformly throughout the length of the hole by pin material distorted in a direction transverse to the axis of the hole, without completely shearing any portion of the pin material from the pin, the distortion being of the form of an elongate depression which extends throughout, and is of substantially uniform transverse cross-section throughout, substantially the entire length of the hole.

According to the two documents referred to above, the process of distortion by which the end part of the plug pins are made to clamp the bare ends of the conductors is simply a punching process, such as controlled impact punching of the relevant face of the pin. In general, since the force from the punching process is in the direction towards the holes in the pins, and since each hole is a weakness in the structure of the pin, the material of the pins will generally distort in such a way as to clamp the ends of the conductors as required. It is possible for other distortions to occur in the material of the pins, particularly if there are defects or inconsistencies in the material. For example, one or both of the side portions of the pin material extending beside the hole through the pin may buckle under the impact from the punching process; this may not prevent the end of the conductor from being clamped, but would result in a pin of an irregular shape different to the preferred shape of the pins according to the documents.

It is thus advantageous if the direction of the distortion occurring as a result of the punching process can be controlled. Embodiments of the method of the present invention aim to provide control of the direction of distortion by cutting or scoring portions of the material of the terminals, in such a way as to provide weaknesses in the structures of the terminals.

When a suitable impulse is provided at a suitable position of the terminal, distortions to the pin material will preferentially be caused to the required volume of pin material, in the required direction, as a result of the selected weakness in the pin material.

The size of the impulse required to cause the distortion may also be reduced.

According to the present invention there is provided a method of connecting a first member to a second member comprising the steps of: forming a hole near to an end surface of said first member, said hole extending in a direction substantially perpendicular to a longitudinal axis of said first member; inserting a part of a second member into said hole in said first member; and providing an impact at a selected position of said end surface of said first member, whereby to partially shear a volume of material of said first member below said selected position of said end surface from the neighbouring material of said first member and distort the shape of the hole below the partially sheared portion to clamp the part of the second member into the hole in the first member, and thus to clamp the first member and the second member together.

Connections made according to the present invention are of particular use in moulded" plugs which are permanently attached to an electric cable for supplying power to an electrical appliance, generally during the production of the appliance.

The invention will now be described by example with reference to the following drawings, in which: Figure la shows a standard earth terminal of an electric plug, prior to preparation for connection according to the method of the present invention; Figure ib shows an earth terminal, prepared for connection according to the method of the present invention; Figure 2 shows the step of inserting electric conductors into the earth and neutral terminals of an electric plug, prepared for connection according to the method of the present invention; Figure 3 shows a method of forming a connection of a live terminal to a fuse; Figure 4 shows terminals formed according to the present invention, prior to insertion of the terminals into the body of the plug; and Figure 5 shows the electric plug of Fig. 4 prior to moulding of the insulating body.

Referring to Figs. la and ib, Fig. la shows a terminal 1 of an electric plug, in this case an earth terminal 1, prior to the steps of the connecting method according to the present invention. This terminal, and the other or others in the respective cases of two- and three-pin plugs, may be determined according to practical considerations.

In Fig. ib the earth terminal 1 is shown prepared for connection to a bared end of an insulated wire leading to an electrical appliance. The terminal is rectangular in cross-section as it is for a 13 amp plug as used in U.K.

At a position near to the end face 6 of the terminal 1, a through hole 5, slightly larger in diameter than the wire to be connected to it, is provided in the side 4 of the terminal 1. Preferably the hole 5 runs in a direction parallel to the plane of the end face 6. At a position on the end face 6, an area 8 is defined above a part of the hole 5 as indicated by the lines 7, which are made by any suitable means such as a cutter cutting to a depth sufficient to weaken the structure of the end of the terminal 1. The weakening of this structure is such that the portion of material between the area 8 and the hole 5 is preferentially distorted when subjected to punching or stamping, the area 8 being at least partially sheared from the remainder of the end face 6. Preferably the area 8 is a rectangle.

Referring to Fig. 2, the earth terminal 1 is shown prepared for insertion of the end of the earth conductor 11 of cable 10. Similarly, the neutral terminal 2 is shown prepared for insertion of the end of the neutral conductor 12 of cable 10. The live terminal in this example is to be connected to a conductor in a different manner to the earth and neutral terminals, and is instead connected to a fuse (not shown) which is in series with a fuse-contact means 20, 21 and the end of the live conductor 13 of the cable 10. The live connection will be described briefly later.

The earth and neutral connections are made by inserting the respective ends of the earth and neutral conductors 11, 12 into the holes 5 in the earth and neutral terminals 1, 2. They are secured in place by punching or stamping the areas 8 such that the portions of material between the areas 8 and the holes 5 are particularly sheared for the end surfaces of their respective terminals and move towards and into the holes 5 in the direction of preferential distortion caused by definition of the area 8 as indicated by the lines 7.

The conductors are thus clamped in place against the lower part of their respective holes 5, by a simple process suitable for mass-production. The clamping is effectively permanent, being highly secure and unlikely to release, while avoiding the potential for damage to the conductors caused by the screws in conventional plug connections rotating as they clamp the conductors.

Also shown in Fig. 2 is a contact member 20 for electrical connection to the live conductor 13 and a fuse (not shown). The end of the live conductor is shown ready to be inserted into a crimped part 200 of the contact member 20. The contact member is preferably made of a high conductivity metal such as copper whose resilience is such that it may be easily bent into a preferred shape but will hold its shape almost rigidly.

The connection between the conductor 13 and the contact member 20 is made by inserting the bared end of the conductor 13 into the crimp part 200 of the contact member 20, and then pressing, stamping or otherwise bending the crimp part 200 around the end of the conductor 13 such that the end of the conductor is clamped firmly to, and with a good electrical connection to, the contact member 20. The contact member 20 has a shaped spring clip for electrical connection to, and mechanical retention of, a standard fuse.

Figure 3 shows the steps of a process for preparing a second contact member 21 and attaching it to a terminal of a plug, which in this general example, is the live terminal of a three-pin plug. Fig. 3a shows a J-shape cut from a flat sheet of a conductive material, preferably of a high conductivity metal such as copper with a suitable resilience as described in relation to the contact member 21. A hole 210 is formed in the shape. Figs 3b and 3c show the cross-bars of the Jshape bent so as to form a spring-clip 211 suitable for electrical contact to, and mechanical retention of, a standard fuse. Fig. 3d shows the completed contact member 21 ready to be attached to the live terminal 3 by means of a post 212 on the end face of the terminal and the hole 212 in the contact member 21. The post 212 and the hole 210 may engage by a snap-action, and may be substituted by other coupling means which provide good electrical and mechanical contact.

If a fuse is not required to be placed in the plug, the live connection could, like the earth and neutral connection, be made according to the method described earlier.

Figs. 4 and 5 show perspective views of a 13 amp plug for use in the U.K.

Referring to Fig. 4, the three conductors of the cable 10 are shown connected to the terminals 1, 2, 3, the connections to the earth and neutral terminals 1, 2 being made by the method described in relation to Figs. 1 and 2. (The connection to the live terminal 3 in this example is made through the fuse-contact means 20, 21 and the fuse 26 (see Fig.5), the reason being to allow removal and replacement of the fuse after the plug has been assembled, as will be explained briefly later).

The conductors are clamped firmly in the holes 5 due to the areas 8 having been stamped such as to form recessed areas 8.

The terminals 1, 2, 3 are shown in Fig. 4 positioned ready to be inserted into the lower portion 30 of the insulating body of the plug, which is generally made out of a plastic material suitable for moulding .

Referring to Fig. 5, the terminals 1, 2, 3 are shown inserted into the lower portion 30 of the body of the plug. The cable 10 is held in a lower housing portion 31 of the lower portion 30 of the body of the plug. Sufficient space is left in the plug body for the conductors to run from the cable 10 to their respective connections without straining the connections or wearing down the insulation on the conductors by friction against other components in the plug. As can be seen from Figs. 4 and 5, the fuse-contact means 20, 21 extends through a fuse compartment wall such that it is effectively outside the plug body, but inside the fuse compartment 22. The fuse 26 can thus be held in place by the resilience of the spring clips 211 of the fusecontact means 20, 21 which electrically complete the connection in series of between the fuse 26, the fusecontact means 20, 21, the live conductor 13 (see Fig. 2) and the live terminal 3. The fuse is also held by an insulating fuse holder 24 which allows it to be removed without the danger of the fuse being touched by a user while still in the electrical circuit, or linked to residual charges in an appliance to which the cable 10 is connected. The fuse can thus be easily and safely removed without disassembling the plug body, merely by removing the insulating fuse holder 24, which may be held in place by a snap-action.

The plug is completed by positioning the upper portion 32 of the plug body onto the lower portion 30, such that the cable 10 is securely held between the upper housing portion 33 and the lower housing portion 31. The upper and lower sections of the plug body may be attached to each other by any standard method such as a snap-action mechanism, but are preferably moulded together permanently by ultrasound, heat, adhesives, or otherwise. By clamping the cable 10 firmly between the lower and upper housing portions 31,33 when the lower and upper sections 30,32 are moulded together, it can be ensured that any strain tending to pull the conductors from their connections to the terminals is prevented, even if the cable itself is subjected to strain.

Claims

CLAIMS:

1. A method of connecting a first member to a second member comprising the steps of: forming a hole near to an end surface of said first member, said hole extending in a direction substantially perpendicular to a longitudinal axis of said first member; inserting a part of a second member into said hole in said first member; and providing an impact at a selected position of said end surface of said first member, whereby to partially shear a volume of material of said first member below said selected position of said end surface from the neighbouring material of said first member and distort the shape of the hole below the partially sheared portion to clamp the part of the second member into the hole in the first member, and thus to clamp the first member and the second member together.

2. A method according to claim 1, wherein the portion of the surface below which said volume of material is partially sheared is defined by a cutter penetrating the surface to a predetermined depth prior to the impulse for distorting the shape of the hole in the first member.

3. An electric plug comprising an insulating body and at least two electric terminals which protrude from said body, each terminal being electrically connected to an electric conductor at a connection location inside said body, wherein a terminal of said plug has a hole extending in a direction substantially perpendicular to a longitudinal axis of said terminal, said hole being near to an end surface of said terminal; a part of an electric conductor is received in said hole of said terminal; and a volume of the material of said terminal is in a partially sheared condition with respect to the remainder of said end-surface; and wherein the hole in said terminal is of a distorted shape below said partially sheared volume of the material such that the part of said electric conductor in the hole is clamped to the terminal.

4. An electric plug according to claim 3, wherein there are three electric terminals electrically connected to an earth conductor, a neutral conductor and a live conductor respectively.

5. An electric plug according to claim 3 or 4, wherein a contact means for a fuse is electrically connected in series with a selected one of said electric terminals and a selected one of said electric conductors.

6. An electric plug according to claim 5, wherein said contact means comprises a first fuse contact member and a second fuse contact member, said first fuse contact member being electrically and mechanically connected to said selected one of said electric conductors, and said second fuse contact member being electrically and mechanically connected to said selected one of said electric terminals.

7. An electric plug according to claim 6, wherein said first fuse contact member includes a clamping means in which a part of said selected one of said electric conductors is clamped, and a retention means for releasably retaining a first terminal of a fuse in electrical contact with said first fuse contact member.

8. An electric plug according to claim 6 or 7, wherein said second fuse contact member includes an engaging means which is permanently engaged with a part of said selected one of said electric terminals, and further includes a retention means for releasably retaining a second terminal of a fuse in electrical contact with said second fuse contact member.

9. An electric plug according to any of claims 5 to 8, wherein said selected one of said electric terminals is a live terminal and said selected one of said electric conductors is a live conductor.

10. An electric plug according to claim 9, wherein a part of an earth conductor is permanently connected to an earth terminal of said electric plug and a part of a neutral conductor is permanently connected to a neutral terminal of said electric plug.

11. An electric plug according to any of claims 5 to 10, wherein said contact means for a fuse is adapted to releasably retain a fuse in a position that is accessible from outside said insulating body.

12. An electric plug according to any of claims 3 to 11, wherein said insulating body is a single moulded body.

13. A method of connecting an electric conductor to an electric terminal substantially as hereinbefore described with reference to the description and drawings.

14. An electric plug substantially as hereinbefore described with reference to the description and drawings.