GB2060276A - Mounting a plug pin - Google Patents

Abstract

A pin 13, accommodated in an aperture 18 of a two part plug body, is provided with a recess in its wall to receive a resilient member 22 which projects beyond the surfaces of the pin to engage with a ledge 21 and a surface 20, each defined about the aperture 18, and thus secure the pin in the aperture. The resilient member may be a split ring as shown or a compression spring (35, Fig. 6, not shown). <IMAGE>

Description

SPECIFICATION Electric plugs This invention relates to electric plugs more particularly to, but not exclusively to, domestic three pin plugs and comprising an electrically insulating base portion, a cover formed from like material which can be secured to the base portion, electrically conductive pins extending through apertures respectively in the base portion into said cavity and connector means located at the ends of the pins within said cavity.

Electric plugs of the aforesaid type are well known in the art. For domestic application the plug is provided with three pins namely the earth pin, the neutral pin and the live pin. The pins extend through apertures in the base portion and when the plug is engaged with a socket the axial forces acting on the pins tend to move the pins towards the cover and whilst the pins may be firmly fixed in the base portion it is more usual for the cover to define abutments for engagement by the pins to withstand these axial forces. When the plug is withdrawn from the socket the axial forces acting on the pins are in the opposite direction and in order to resist such forces it is the practice to provide surfaces on the plug which co-operate with surfaces defined on the pins.

When the cover is removed from the base portion the pins can fall out of the apertures unless special precautions are taken to retain the pins in position. In the case where the pins are firmly fixed to the base portion this does not of course occur.

It is undesirable for the pins to fall out of the base portion once the cover is removed since parts can be lost and it is therefore known to provide means for retaining the pins in position when the cover is removed. Various arrangements have been suggested for retaining the pins, but in general these include clips which must be located in position during assembly of the plugs. The provision of such clips increases the cost of the plugs, both in terms of material cost and assembly cost.

The object of the present invention is to provide a plug of the kind specified in a simple and convenient form.

According to the invention in a plug of the kind specified each pin has a recess defined in a side wall thereof, a resilient member at least partially located in said recess, said resilient member locating against a ledge defined about the respective aperture in the base portion to withstand the axial force applied to the pin when the plug is withdrawn from a socket, said resilient member also engageing a side wall to restrain the pin against falling from the aperture when the cover of the plug is removed.

In the accompanying drawings: Figure 1 is a sectional side elevation through a portion of a plug in accordance with the invention, Figure 2 is an exploded perspective view of a portion of the base of the plug together with a pin, Figure 3 is a perspective view of the pin with a clip removed, and showing an alternative form of clip, Figure 4 is an exploded perspective view of the line pin, Figure 5 is an exploded perspective view of the fuse carrier, and Figure 6 is a side elevation showing a modified form of the invention.

Referring to Figure 1 of the drawings the plug comprises a base portion 10 and a cover 1 the latter being secured to the base portion by means of a retaining screw not shown. Defined between the base portion and the cover is a cavity 1 2~into which the cables which are to be connected to the pins of the plug, extend. The cover and base portion are formed from electrically insulating material.

Figure 1 shows the neutral pin 13 of the plug and it will be seen from Figures 1 and 2 that it has the usual rectangular section. It will also be noted that the pin itself does not have any projections. It does however have a shaped end portion to facilitate the smooth engagement of the pin with the socket portions in the socket and at its opposite end it is provided with a transverse aperture 14 into which can be passed a flexible electrical conductor. The conductor is retained in the aperture by means of a retaining screw 15.

From Figure 1 it will be observed that a cover 11 is provided with a recess 1 6 having a diameter which is slightly larger than the head of the retaining screw, however, the aperture is small enough so that surfaces on the cover can engage with the adjacent end surface referenced 1 7 in Figure 2, of the pin. The engagement of the surface 17 with the cover retains the pin in position when the plug is being engaged with a socket.

The pin 1 3 extends with a very slight clearance, through a complementarily shaped aperture 1 8 formed in the base portion and as will be seen from Figure 2, the base portion defines an upstanding hollow boss portion 19. The internal surface 20 of the boss portion 1 9 is of cylindrical form and it has a diameter substantially equal to the diagonal of the hole 18. The surface 20 is not however continuous since it is necessary to provide an entry for the cable.The cylindrical surface does however extend through approximately 300 . In view of the fact that the diameter of the cylindrical surface is approximately equal to the diagonal of the aperture 18, ledges 21 are defined about the aperture 18, the ledges which lead into the longer sides of the aperture being of substantially greater maximum width than the ledges which extend into the narrower sides of the aperture.

In order to withstand the axial forces applied to the pin when the plug is removed from a socket, a resilient member is carried by the pin. As shown in Figure 2 the resilient member comprises a split resilient ring 22 and this is located in recesses which are machined into the pin. The recesses are more clearly seen in Figure 3 and it will be observed that they, because of the rectangular section of the pin, are mostly formed in the narrower walls of the pin. The recesses are referenced 23. The ring 22 is located about the pin and portions of the ring locate within the recesses 23. The diameter of the ring is such that it will be compressed slightly when the pin 1 3 is passed through the aperture and the ring engages the cylindrical surface 20 of the boss portion 19.

Portions of the ring engage the ledges 21 and this engagement withstands the axial forces applied to the pin when the plug is withdrawn from the socket. Hence when the cover is in position the pin 13 is firmly retained against any substantial axial movement when the plug is inserted into and withdrawn from the socket. When the cover is removed the pins will not fall out of the apertures 18. The reason for this is the frictional engagement between the ring 22 and the surface 20. If when the cover is removed, a deliberate axial force is applied to the pin 13 then the frictional engagement of the ring with the surface 20 will be overcome however the force required is substantial so that the pin can be regarded as being firmly fixed even when the cover is removed.

In order to facilitate assembly of the pin the entrance portion of the surface 20 is flared. This flaring is not shown but it has the effect of compressing the ring 22 as the pin is moved axially through the aperture 1 8.

Figure 3 shows at 24 a modified form of resilient member. In this case the member is of substantially "U" shape and it is intended that in assembly the pin 13 should be passed through the aperture 18 and the retaining member passed through the entry into the recess provided for the cable. It is anticipated that the limbs of the member will deform during such movement.

The same form of arrangement can be used for the earth pin in this case however, since the earth pin has a larger cross section than both the line and neutral pins, the portion of the pin lying within the cavity 12 can be of reduced section. This reduces the size of the boss 19 required.

In Figure 4 there is shown the arrangement which is provided for the line pin since as will be appreciated, the line pin is connected to one clip shown at 25, for the fuse. The line pin 26 is shorter than the neutral pin and the clip 25 is provided with an integral terminal portion 27 which is passed over a projection 28 formed on the pin. The terminal portion bears against a surface 29 defined adjacent the projection and the aforesaid recesses which accommodate the ring 22 are defined between the connector portion and ledges 30 defined on the pin. The ring 22 conveniently is positioned adjacent the ledges 30 prior to the connector portion 27 being located about the projection 28 and the latter deformed to secure the clip 25 to the pin.

The other clip 31 for the fuse is also formed with a connector portion 32 and this is similarly secured to a terminal member 33 the latter being provided with an aperture 34 to receive a cable.

Figure 6 shows a modification wherein the resilient member is in the form of a coiled compression spring 35 which is located within a recess in this case a drilling 36 which passes through the pin. The aperture in the base portion is provided in its wider side walls, with two slots 37, 38 these slots extending from the opposite ends of the aperture and terminating in ledges for engagement by the opposite ends respectively of the spring. The ledge defined by the slot 37 cooperates with the spring to prevent the pin being withdrawn from the aperture when the plug is withdrawn from the socket and the ledge defined by a slot 38 in conjunction with the spring, opposes the axial force imparted to the pin when the plug is engaged with the socket. In this case the cover need not define surfaces for engagement with the pin to withstand the force applied to the pin when the plug is engaged with the socket and both the ledges and the spring clearly co-operate to prevent the pin falling out of the aperture when the cover is removed. In order to facilitate assembly of the spring and pin within the aperture, an inclined slot 39 is formed in the wall of the aperture opposite to the slot 37 so that as the pin is pushed into position the spring will be gradually compressed. It is important however, if the cover is not to be used for restraining the force applied to the pin, to ensure that a ledge for the spring is properly defined by the slot 38.

Claims (9)

1. An electrical plug more particularly but not exclusively, a domestic three pin plug and comprising an electrically insulating base portion, a cover formed from like material which can be secured to the base portion, electrically conductive pins extending through apertures respectively into a cavity defined by the base portion and the cover, connector means located at the ends of the pins within said cavity, a recess defined in a side wall of each pin, and a resilient member at least partially located in said recess, said resilient member locating against a ledge defined about the respective aperture to withstand the axial force applied to the pin when the plug is withdrawn from a socket, said resilient member also engaging a side wall to restrain the pin against falling from the aperture when the cover of the plug is removed.

2. A plug according to claim 1 in which said resilient member comprises a split resilient ring.

3. A plug according to claim 2 in which said pin is of rectangular section and two of said recesses are provided in the narrower walls of the pin.

4. A plug according to claim 1 in which said resilient member is of "U" shape.

5. A plug according to any one of the preceding claims in which said side wall is defined by the internal surface of a hollow boss or bosses upstanding from the base portion about the aperture or apertures.

6. A plug according to claim 2 in which said recess is defined between a ledge on the pin and a terminal portion adapted to be secured to the pin.

7. A plug according to claim 1 in which said recess is defined by a drilling passing through the pin, and said resilient member is defined by a coiled compression spring located in said drilling.

8. A plug according to claim 7 in which a pair of ledges are provided for engagement by the opposite ends of the spring, said ledges being defined by oppositely extending slots formed in opposite side walls of said aperture.

9. An electrical plug substantially as hereinbefore described with reference to the accompanying drawings.