GB2240217A

GB2240217A - Electrical switches

Info

Publication number: GB2240217A
Application number: GB9001398A
Authority: GB
Inventors: Bruce Stewart Bridgestock; Keith Fletcher
Original assignee: Otter Controls Ltd
Current assignee: Otter Controls Ltd
Priority date: 1990-01-22
Filing date: 1990-01-22
Publication date: 1991-07-24
Anticipated expiration: 2010-01-22
Also published as: GB9001398D0; GB9101350D0; GB2240217B; GB2240218B; GB2240218A

Abstract

An electrical switch incorporating a snap-acting actuator 5 for actuating switch contacts 4, 9 has a latching mechanism for ensuring that the switch, once operated, does not auto-reset. The latching mechanism comprises a spring biased moulded plastics latching member 11 which is received in click-fit manner in a recess in a moulded plastics body part 1 of the switch. The latching member 11 interferes with a movable contact carrying member 5 after it has moved to a contact open position to prevent reclosure of the switch contacts 4, 9 until it is subjected to a resetting movement. The latching member 11 does not load the actuator 5 until after the switch contacts 4, 9 have opened. The actuator 5, which may be bimetallic, may constitute the movable contact carrying member 5 or act on a separate member. <IMAGE>

Description

IHPROVKKENTS IN OR RELATING TO ELECTRIC SWITCHES This invention relates to electric switches incorporating a snap-acting actuator comprising a stressed disc, sheet or strip of resilient sheet material movable with a snap action 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 such latching member is positively displaced to permit return movement of the movable contact carrying member. Such switches will hereinafter be referred to as "of the kind described".

The disc, sheet or strip of resilient material in a switch of the kind described may be of bimetallic material to provide a thermally-responsive switch, for example, or it may be made of a suitable spring metal in which case the switch will be manually actuatable.

The actuator blade 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.

Exemplary switches of the kind described are the subject of our UK Patents Nos. 2061009 and 2110474.

Whilst such switches have been successfully exploited at a commercial level, the search has nonetheless continued for a more simple latching mechanism enabling automatic switch assembly and reduced manufacturing costs. The present invention results from our efforts in this regard and provides a switch of the kind described wherein a moulded plastics body part of the switch has a moulded plastics latching member engaged therewith in a click-fit manner such that the latching member is capable of limited movement when thus engaged with the body part, the latching member having spring biassing towards a particular positional orientation relative to the body part and being arranged to interfere with the movable contact carrying member of the switch when it moves into its contacts-open condition and to prevent reclosure of the switch contacts until it is subjected to a switch resetting movement.

In some exemplary embodiments of the invention which are described in detail hereinafter, the body part of the switch has a slotted through recess into which the latching member is fitted, and the movable contact carrying member of the switch (constituted by a bimetallic switch actuator) has a nose portion which extends into the slotted recess for co-operation with the latching member. The latching member is shaped to click fit into the recess and to be retained therein, and is capable of movement in a rocking and pivotal fashion generally in the plane of the slotted recess.

A spring, which can be formed integrally with the latching member or can be a separate part, biasses the latching member into a central position where it does not interfere with the switch actuator when the switch contacts are closed. As the actuator moves to open the switch contacts, so it interferes with the latching member and displaces it against its spring bias until a ledge portion of the latching member lodges under the actuator and prevents it from resetting. A head portion of the latching member projects outwardly from the body part of the switch and enables the latching member to be moved for resetting the switch.

The invention, together with further features and advantages thereof, will best be appreciated from consideration of the following detailed description of exemplary embodiments illustrated in the accompanying drawings wherein: Figures 1A to 1E are various different showings of a first exemplary embodiment; Figures 2A to 2E are similar showings of a second exemplary embodiment; and Figures 3A to 3D illustrate alternative spring biassing arrangements for the latching member.

Referring first to Figures 1A to 1E, these show a top plan view of the switch, an end elevation, a part sectional view with the switch in contacts closed condition, a similar part sectional view with the switch in contacts open condition and latched out, and a perspective enlarged view of the latching member, respectively. As shown, the switch comprises a moulded plastics switch body 1 formed of nylon for example and capturing terminal parts 2 and 3 formed of brass for example. An extended limb of one terminal 2 serves as a mounting for a fixed contact 4 of the switch, preferably formed of silver, and an extended limb of the other terminal 3 serves as a mounting for a moving contact carrying member 5 in the form of a generally well known Otter type snap-acting bimetallic element.The bimetallic element comprises a dished blade having a generally U-shaped cut-out defining a central tongue 6 extending between outer legs 7 bridged by a nose portion 8 of the blade, and the blade is secured to the terminal 3 by virtue of the free end of the tongue 6 being spot welded to the extended limb of the terminal and carries a moving contact 9 on its nose portion 8. As will be appreciated, the switch is thermally responsive both to ambient temperature conditions and to overload current flow through the switch to open its contacts.

The moulded nylon body 1 of the switch is formed with a generally rectangular slotted through recess 10 into which there is fitted a moulded plastics latching member 11 which is shown more clearly in the enlarged view of Figure 1E, a biassing spring 12 being interposed between the switch body 1 and an enlarged head portion of the latching member. The latching member 11 and its accommodating recess 10 are formed so that the latching member can be click fitted into the recess and then will be retained therein with a limited degree of freedom of movement as is required to enable the latching member to perform its required function; the detailed shapes of the recess and the latching member can best be seen from Figures 1C,1D and 1E.

As shown in Figures lC and 1D, the recess 10 has a minor portion 13 towards the upper surface of the switch body 1 and a major portion 14 towards the under surface of the switch body, and the forward edge of the minor portion (that is to say the edge nearest to the bimetal blade 5) is inclined. The latching member 11 as shown in Figure 1E has an enlarged head 15, a shoulder portion 16 shaped and dimensioned to click fit through the juncture of the minor and major portions 13, 14 of the recess 10 and into the major portion and then not to be returnable past the juncture, and an end portion 17 which, as will hereinafter be described, performs the latching function. The latching member 11 is symmetrically shaped about the direction of its insertion into the recess 10 so as to facilitate its automatic insertion as a stage in the fully automatic manufacture of the switch.

When the switch contacts are closed, as shown in Figure lC, the spring 12 acts to centralize the latching member 11 so that it sits out of contact with the free end of the nose portion 8 of the bimetallic blade 5 which projects into the major recess portion 14. In response to an appropriate temperature change, the bimetallic blade 5 will snap into its oppositely dished configuration as shown in Figure 1D and in so doing will brush past the end portion 17 of the latching member 11, the latching member displacing to accommodate such blade movement and then recentralizing.When the bimetallic blade subsequently cools and seeks to snap back into its original condition, the free end of the nose portion of the blade engages the ledge provided on the end portion 17 of the latching member 11 and so the switch is latched in a contacts open condition as shown in Figure 1D. The latch can be released and the switch reset by pressing the head 15 of the latching member in towards the bimetallic blade so that the end portion 17 moves out of engagement with the blade. An abutment member 18 formed in the major recess portion 14 serves as a back stop for the bimetallic blade 5 when it switches into its contacts open condition and also co-operates with inclined camming surfaces provided on the end portion 17 of the latching member 11 to ensure that the release action of the latching member is sufficiently positive.

Figures 2A to 2E show a second embodiment of the invention which is substantially identical to the first embodiment described above other than for the detailed form of the latch member 11. As can best be seen in Figures 2C, 2D and 2E, the latch member 11' of this embodiment lacks the camming surfaces just mentioned above as provided in the first embodiment and instead is formed with a fulcrum 19 which bears upon the upper surface of the switch body when the head of the latching member is pushed forwardly to release the latch and causes a positive rearward movement of the end portion 17'.As with the latching member 11 of the first embodiment, that of the second embodiment is symmetrically formed for facilitating automatic assembly of the switch; the V-shaped cut-out 20 provided at the front of the minor recess portion 13 and defining the inclined front edge thereof in both embodiments accommodates the inoperative fulcrum 19' so that it does not inhibit the release movement of the latching member. The operation of the second embodiment is the same as for the first embodiment.

Figures 3A, 3B and 3C illustrate the formation of the spring biassing means associated with the latching member as a coil spring in Figure 3A (and in the two above-described embodiments), as a leaf spring in Figure 3B, and as an integrally formed plastics spring in Figure 3C where the head portion of the latching member has resilient ears which perform the required spring function.

The moulded plastics latching member has to be able to withstand the temperatures attained by the bimetal blade (up to 200 C for example), has to resist wear caused by the nose of the bimetal blade pushing against it, and has to be capable of being click fitted into the body moulding. These requirements are met by use of Stanyl as the plastics material from which the latching member is formed.

In addition to be structured for automatic assembly, the switches above described have the significant advantage that the bimetallic blade is permitted to move a sufficient distance to open the switch contacts before any contact is made with the latching member so that there is no mechanical resistance to operation of the switch as a cut-out.

In previous switch designs where the latching arrangement loaded the switch actuator prior to the switch contacts being opened, the loading of the actuator affected its switching characteristics.

Where the actuator was a bimetallic blade, loading of the blade by the latching arrangement affected the blade operating temperature and its speed of response, and the amount of the affect was in turn a function of manufacturing tolerances and could not readily be predicted. These problems are avoided in the abovedescribed switches. As compared to prior art switches employing metal leaf springs as latching members, the switches of the present invention, by virtue of their use of moulded plastics parts, can be fabricated to more precise manufacturing tolerances.

Having thus described improved switches in accordance with the present invention, it is to be appreciated that the described switches are exemplary only and that many modifications and variations could be made thereto without departure from the spirit and scope of the invention as set forth in the appended claims.

Claims

PT.w.C

1. A switch of the kind described wherein a moulded plastics body part of the switch has a moulded plastics latching member engaged therewith so as to be capable of limited movement, the latching member being biassed towards a particular positional orientation relative to the body part and being arranged to interfere with the movable contact carrying member of the switch when it moves into its contacts open condition and to prevent reclosure of the switch contacts until it is subjected to a switch resetting movement.

2. A switch as claimed in claim 1 wherein the moulded plastics latching member is arranged to make a click-fit engagement with the body part of the switch.

3. A switch as claimed in claim 1 or 2 wherein the body part of the switch is formed with a recess for accommodating the latching member.

4. A switch as claimed in claim 3 wherein the moving contact carrying member of the switch has a portion which extends into said recess for co-operation with the latching member.

5. A switch as claimed in any of the preceding claims wherein the latching member is arranged so that it does not load the switch actuator in a contacts opening operation of the switch until after the switch contacts have opened.

6. A switch as claimed in any of the preceding claims wherein the switch actuator is a bimetallic element.

7. A switch as claimed in claim 6 wherein the bimetallic element serves additionally as the moving contact carrier of the switch.

8. A switch as claimed in any of the preceding claims wherein the biassing of the latching member is effected by virtue of the latching member itself being formed with a resilient biassing portion.

9. A switch of the kind described wherein the latching member is arranged so that it does not load the switch actuator until, in a contacts opening operation of the switch, the contacts have opened an appreciable distance.

10. A switch substantially as herein described with reference to any of the accompany drawings.