GB2149577A - Electric switch - Google Patents

Abstract

An electric switch has two fixed spaced-apart contact elements (21), and two movable contact elements (31,32) which under the influence of contact pressure springs (41) are pressed against the fixed contact elements (21) on opposite sides thereof to form parallel current paths in the closed position of the switch. Closing and opening of the switch are effected by means of a wedge-shaped member (53), displaceable between the movable contact elements (31, 32). The wedge-shaped member is on a linearly displaceable contact carrier (51). The movable contact elements (31, 32) are guided in such a way that they move at right angles to the direction of displacement of the contact carrier (51). Between each of the movable contact elements and the associated contact pressure spring, there is located a guide member (61) which is fixed in the contact carrier (51). The guide member (61) is formed so that upon closing of the electric switch, it is displaced, by the associated movable contact element, from a rest position, in which the movable contact element is not influenced from the associated contact pressure spring, to an operating position, in which the movable contact element is influenced by the contact pressure spring via the guide member (61). <IMAGE>

Description

SPECIFICATION Electric switch This invention relates to a single-pole or multi-pole electric switch, and in particular, but not exclusively, to a low voltage load or safety switch of the kind which, in each pole, has two fixed spacedapart contact elements on a switch body and an elongate movable contact element which, under the influence of a contact pressure spring is pressed against both fixed contact elements in the closed position of the switch. Closing and opening of the switch are effected by means of a wedgeshaped member which is displaceable, the movable contact element being guided in such a way that, during the displacement of the wedge-shaped member, the movable contact element moves substantially at right angels to the direction of displacement of the wedge-shaped member.

A switch of the above-mentioned kind is previously known from British Patent Specification No.

2,062,355. In the known design a pair of movable contact elements are influenced by the forces from respective contact pressure springs during the entire closing or opening operation. This results in significant frictional resistance having to be overcome during the movement of the contact elements along the tapered end of the wedge-shaped member, which in turn implies that the switch has to be provided with a sufficiently strong operating device to overcome the frictional drag, which is space-demanding and expensive. In addition, the wedge-shaped member and other moving parts in the switch are subjected to relatively considerable wear.

One aim of the present invention is to improve the above-mentioned known design, so that the amount of energy necessary for a closing or opening operation is considerably reduced, which means that it will be possible to use a smaller and less expensive operating device.

What constitutes a switch design in accordance with the invention is defined in the following claim 1.

With a design according to the invention, the contact pressure can be applied, upon closing of the switch, only when this is really needed, namely during the final stage of the closing operation. In this way, the expenditure of energy necessary to alter the state of the switch is reduced, and a smaller and less expensive operating device becomes adequate. Since, in addition, during the first part of the closing operation the contact movement takes place in an almost friction-less manner, a greater contact acceleration is possible, which results in making a more positive electrical contact with a reduced risk of contact welding upon closure in the case of a short circuit. The safe current carrying capacity of the switch is thereby increased.

The invention will now be described in greater detail, by way of example, with reference to one embodiment of switch design shown in the accompanying drawings, wherein Figure 1 shows a plan of the central part of a load switch according to the invention, in the open position with the upper portion of the switch body removed, Figure 2 shows a schematic view, in the direction of the arrow II in Figure 1, of the contact system and the contact carrier of the switch, and Figures 3a-3c show a partial view from the side, in the direction of the arrow Ill in Figure 1, of the contact system and the contact carrier in the open position (Figure 3a), in an intermediate position during a closing operation (Figure 3b) and in the closed position (Figure 3c).

The load switch, part only of which is shown in the drawings, is designed, with the exception of the movable contact device, substantially in the same way as the switch disclosed in British Patent Specification No. 2,062,355.

The switch has a body 11 made of an electrically insulating material, in which are located two fixed, spaced apart contact elements 21 and 22. The distance between the fixed contact elements 21, 22 is capable of being bridged by two parallel movable contact elements 31, 32, which, in the closed position of the switch and under the influence of respective contact pressure springs 41, 42, are pressed against the fixed contact elements 21, 22 on opposite sides thereof, to provide two electrically parallel contact bridges.

Those parts of the fixed and the movable contact elements which perform the making and breaking functions are formed with contact tongues 23 and 33, respectively, which extend into breaking chambers 12, 13 of the switch body.

The movable contact elements 31, 32 are attached to a contact carrier 51 in the form of a rectangular plate which is displaceable in a groove 14 in the switch body 11. The contact carrier 51 has an opening 52 formed therethrough, one side of which opening defines a wedge-shaped member 53 tapering in the direction of displacement of the contact carrier 51. The movable contact elements 31, 32 extend through the opening 52, to be positioned on opposite sides of the wedge-shaped member in the open position of the switch.

Between each of the movable contact elements 31, 32 and the associated contact pressure spring 41 or 42, a guide plate 61 and 62, respectively, is arranged. The guide plates are movable in a slot 54 in the contact carrier 51 and are each formed with a rectangular aperture 63 in which the associated contact pressure spring is located. The contact pressure springs are helical springs which are clamped between an edge of the aperture 63 and a support in the contact carrier 51, which support is provided with a guiding projection 55 in the carrier 51.

On its edge surface facing the associated movable contact element, each guide plate 61, 62 is formed from sheet metal and is provided with two projections 64, 65, which in the closed position of the switch are located on opposite sides of the mid-portion of the respective contact element.

In the open position of the switch (Figure 3a), the guide plates 61, 62 rest with their projections 64 against the tapering edge portion of the wedgeshaped member 53, a clearance slot 70 thus being created between the wedge-shaped member and the respective guide plate, the width of each slot being greater than the thickness of the mid-portion of the respective contact element 31, 32.

Upon closing of the switch from the open position shown in Figure 3a, the contact carrier 51 is displaced in the direction of the arrow A by means of an operating device (not shown), the wedgeshaped member 53 is thus pulled away from its position between the movable contact elements 31, 32. These contact elements are guided both in slots 56 in the contact carrier 51 and in slots 15 in the switch body 11, whereby they will move at right angles to the direction of displacement of the contact carrier 51. During the first part of the clos ing movement the movable contact elements 31, 32 are not influenced by the contact pressure springs at all, the contact movement thus being performed in an almost friction-less manner. The springs 41, 42 with their guide plates 61, 62 do not move in relation to the contact carrier during this stage of the closing operation.In the intermediate position shown in Figure 3b, the mid-portions of the contact elements make contact with the projections 64 of the guide plates and start to push the plates down off the tapered end of the wedgeshaped member 53. The force from the springs 41, 42 will thereafter be applied to the movable contact elements via the respective guide plate, which is now locked to the respective contact element 31, 32, since the projections 64, 65 on each plate are pressed down on opposite sides of the respective contact element. The making of the electrical contact first takes place at the tip of the contact tongues, 23, 33, whereafter the movable contact elements roll somewhat on the fixed contact elements 21, 22 to the final closed position shown in Figure 3c.

Upon opening of the switch, the contact carrier 51 is displaced in the opposite direction, whereby the tapered end of its wedge-shaped member 53 is moved in between the movable contact elements 31, 32 and presses these elements apart, initially against the action of the springs 41, 42. The contact elements 31, 32 will thereby be rotated slightly so that the contact tongues 33 of the movable elements 31, 32, roll on the contact tongues 23 of the fixed contact elements 21, 22. The breaking of electrical contact will thus take place at the outer extremity of the contact tongues, which results in the advantage that the contact surfaces which carry the normal load current are not those likely to be subjected to arc damage.

During the opening movement, the movable contact elements are pressed against the projections 65 of the guide plates, the guide plates thus being pulled up to their rest position on the wedge-shaped member 53 while the movable contact elements are again disengaged from any influence from the contact pressure springs 41, 42.

Although a pair of opposed movable contact elements 31, 32 would normally be used, it will be appreciated that the improvement afforded by the invention could be used with just a single contact element.

Claims (8)

1. An electric switch comprising two spaced apart fixed contact elements and an elongate mov able contact element which is arranged, in the closed position of the electric switch, under the in fluence of a contact pressure spring to be pressed against both the fixed contact elements and pro vide electrical communication therebetween, clos ing and opening being effected by means of a displaceable wedge-shaped member, the movable contact element being guided during displacement of the wedge-shaped member such that the mova ble contact element moves substantially at ri the associated contact pressure spring, a guide mem ber is arranged, which guide member is arranged such that, upon closing of the electric switch, it is displaced by the movable contact element from a rest position, in which the movable contact ele ment is disengaged from the associated contact pressure spring, to a working position in which the movable contact element is influenced by the contact pressure spring via the guide member.

2. A switch according to claim 1, in which two movable contact elements are provided in contact with the wedge-shaped member and a guide member and spring are provided for each movable contact element, which movable contact elements sandwich the spaced-apart fixed contact elements between them in the closed position of the switch, each movable contact element being released from spring influence as they move apart due to the intrusion therebetween of the wedge-shaped member.

3. A switch according to claim 2, in which each guide member is formed with a projection which in said rest position rests against the tapered end of the wedge-shaped member such that a clearance slot is formed between the wedge-shaped member and the guide member, the clearance slot being clear of the respective movable contact element, which movable contact element is arranged to be pressed, towards the end of a closing movement, against the projection and thereby to displace each guide member from its rest position.

4. A switch according to any preceding claim, in which the or each guide member is formed with a second projection, which is arranged such that the or each movable contact element, upon opening of the electric switch, bears against the second projection and moves the or the respective guide member up the tapered end of the wedge-shaped member to its rest position thereon.

5. A switch according to any preceding claim, in which the or each guide member is made from sheet metal.

6. A switch according to any preceding claim, in which the or each contact pressure spring is in the form of a helical spring.

7. A switch according to any of the preceding claims, in which the or each guide member has an aperture therein for the associated contact pres sure spring, which spring rests with one endcarrier used to move the wedge-shaped member.

8. An electric switch substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.