GB2112576A - Electric switches - Google Patents

Abstract

A thermally-responsive electrical switch 1 has a snap-acting bimetallic switch-actuating element 2 provided with a latching arrangement which is so designed that, once the element 2 has moved from one to the other of its two temperature stable conditions, it cannot automatically reset until such a time as the latching arrangement has first been manually actuated and then been positively released. A spring strip 7 cooperates with a projection 6 formed on the switch-actuating element 2 so as to prevent the element 2 from automatically resetting, and a cut-out 8 is formed in an edge of the strip 7 so that when a bowed end portion 9 of the strip 7 is manually depressed the cut-out 8 can register with the projection 6 which drops into the cut-out 8 without resetting the switch, and when the bowed end portion 9 is subsequently released an inclined edge 11 of the projection 6 cams the spring strip 7 out from under the projection 6 so releasing the element 2 to reset the switch. <IMAGE>

Description

SPECIFICATION Improvements in or relating to electric switches This invention concerns improvements relating to electric switches and particularly to electric switches incorporating a snap-acting actuator comprising a stressed disc, sheet or strip of resilient sheet material movable with a snapaction between two configurations to control the making and breaking of the switch contacts, and a latching member which when the actuator has snapped in one sense to break or make the switch contacts restrains return movement of a movable contact carrying member to prevent re-making or re-breaking of the contacts, i.e. the resetting of the switch, until said latching member is positively displaced to permit return movement of the movable contact carrying member. Such switches will hereinafter be referred to as "switches of the kind described".The disc, sheet or strip of resilient material may be of bimetallic material to provide a thermally-responsive switch, or it may be made of a suitable spring metal in which case the switch will be manually actuatable. The actuator itself may constitute the movable contact carrying member, or alternatively the actuator may act upon a contact carrying or controlling strip of resilient sheet material to make or break the contacts.

Thermally responsive switches of the kind described find widespread use in many areas of technology, particularly for protecting apparatuses and appliances, such as electric motors and heaters for example, against overheating. The latching member prevents the occurrence of a cycling behaviour in that the switch requires to be reset before any further operation of the apparatus or appliance can take place. Otherwise the actuator blade would simply snap back into its original configuration only to snap act yet again on further overheating and thus perform cycles indefinitely.

Electric switches of the kind described are known for example from our British patent applications nos. 8031960 (GB2061 009A) and 8233455 the disclosures whereof are incorporated herein by way of reference. Exemplary switches disclosed in our applications abovementioned comprise a per se known form of snap-acting bimetallic switch-actuating element having associated therewith a latching member which prevents the bimetallic element from recycling and has to be reset to enable the switch-actuating element to return to a closed switch condition.In the embodiments described in application no. 8031960 the latching member is a generally L-shaped spring member one of the limbs of which is arranged to lodge under a projection formed on the bimetallic element when the element operates so as to latch the element in its operated condition, and the other limb of which serves as a resetting element which when depressed causes the first-mentioned limb to move away from its latching position thereby allowing the bimetallic element to reset. In the embodiment described in application no. 8233455, the latching is achieved similarly but the latching member is not formed of spring material but rather is relatively rigid and the spring function is performed by means of a separate spring.

In all of the embodiments described in the applications aforementioned, depression of the latching member resets the bimetallic blade. It has now been recognised that a requirement exists for a latching arrangement wherein depression of the latching member does not of itself reset the bimetal, but rather prepares the bimetal for being reset, and wherein the bimetal is not reset until the latching member having been actuated is then released.

Described hereinafter in outline is an arrangement which satisfies the above requirement. In the accompanying drawing, Fig. 1 represents a top plan view showing the latching arrangement only of a switch of the kind with which the present invention is concerned, and Fig. 2 is a cross-sectional view taken on the line II.. II of Fig. 1. It is to be appreciated that all switch parts such as contacts, terminals, etc. have been omitted from the drawing for the sake of clarity.

Referring to Fig. 1 a switch body 1 has a snap-acting bimetallic switch actuating element 2 of per se known type mounted thereon by means of an attachment 3 at the free end of the tongue 4 which is released from the element 2. With temperature changes, the bridge portion 5 of the element 2 will move up and down transversely to the general plane of the element.

For latching the element 2 in its position whereat, as viewed in Fig. 1, the bridge portion 5 has moved upwardly with a snapaction, a projection 6 is formed on the bridge portion for cooperation with a latching member 7 constituted by a copper alloy spring strip which is captive in a recess formed through the switch body 1 but can be moved lengthwise of the said recess.

As may be seen clearly in Fig. 2, the spring strip 7 has a rectangular cut-out 8 in its upper edge. As shown in Fig. 1, in the rest condition of the spring strip 7 this cut-out 8 is displaced from the location whereat the projection 6 on the bimetal bears upon the upper edge of the spring strip 7 to latch the bimetal 2. However, if the bowed end 9 of the spring strip 7 is depressed towards the switch body 1, the cut-out 8 will move towards the projection 6 until such a time as the projection drops down into the cut-out, further movement of the cut-out being prevented by engagement of the stop edge 10 formed on the spring strip 7 wih the edge of the switch body 1.The dropping down of the projection 6 into the cut-out 8 is arranged in itself to be insufficient to reset the bimetal 2, but if the bowed end 9 of spring strip 7 is now released so that the strip springs back to its rest position, then the inclined edge 11 formed on the projection 6 cams the spring strip 7 out from under the projection 6 and the bimetal 2 is enabled to reset. Resetting is thus accomplished not merely on depression of the bowed end 9 of the spring strip 7 but only after the spring strip is subsequently released.

As has been said, the drawing and connected description are intended only to portray the gist of the invention and many modifications and variations will occur to those possessed of appropriate skills. For example, whilst the described embodiment employs a spring latching member, as is the case in application no. 8031960 aforementioned, as is the case in application no. 8031960 aforementioned, a rigid member provided with separate spring bias, as in the case of application no. 823345 would be feasible as an alternative construction.

Claims (6)

1. A switch of the kind described wherein the latching arrangement is such that operation of the latching member does not of itself enable the actuator to reset, but rather prepares the actuator for being reset, and the actuator is not reset until the latching member having been operated is then released whereupon the actuator can reset.

2. A switch as claimed in claim 1 wherein the latching member is movable under spring action in a first direction from an inoperative position into an operative latching position when the actuator moves from one to the other of its said two configurations, and is further movable against spring action transversely to said first direction in response to a switch reset enabling action to engage a camming portion of said actuator with a cam following portion of the latching member such that upon release of said reset enabling action the latching member returns oppositely to said transverse direction under spring action and is calmed oppositely to said first direction by engagement of said camming and cam following portions so as to move into its inoperative position and permit the actuator to reset.

3. A switch as claimed in claim 2 wherein the latching member has a recess defining said cam following portion and the actuator has a portion formed with a camming surface engageable with said recess when, with the latching member in its operative latching position, the latching member is moved in said transverse direction in response to a switch reset enabling action.

4. A switch as claimed in claim 2 or 3 wherein the latching member comprises an elongate element supported with spring action for movement in the direction of its length and also transversely thereto.

5. A switch as claimed in claim 4 wherein the latching member comprises a strip of material captive in a recess in the switch body providing for movement of the strip in the direction of its length and also transversely thereto and a bowed end portion of the strip is secured to the switch body and is formed of spring material to provide the requisite spring action.

6. A switch as claimed in any of the preceding claims and substantially as herein described with reference to the accompanying drawings.