GB2041654A - A snap-action electric switch - Google Patents

Abstract

A snap-action electric switch comprising an actuating lever 1 and a contact lever 2 arranged side-by-side and a snap-acting spring 3 connected to both levers has two stationary support, 56 spaced apart from each other laterally with respect to the levers, and the actuating lever 1 and the contact lever 2 are interconnected by a spring strip 4 at their ends remote from the snap spring 3, the strip 4 being so mounted on the supports 5,6 that a point moving from one end of the strip to the other passes round the supports in opposite senses, the spring strip 4 being urged against the supports by the snap spring 3 and an abutment member 31 or an actuator F. <IMAGE>

Description

SPECIFICATION A snap-action electric switch This invention relates to an electric snap switch comprising an actuating lever, a contact lever approximately parallel thereto and a snap spring connected to both said levers, particularly an omega spring.

Such snap switches are widely used, for example in the form of micro-switches. In these switches, when the actuating arm has been swung through a predetermined distance or has been loaded by a predetermined force, the contact arm snaps from a stable rest position to an operative position and, when the actuating lever is operated in the opposite direction, for example by means of an inherent resetting force, it snaps back again. The two levers are separately manufactured and mounted at a stationary location at their end remote from the snap spring by means of a joint or by a spring mounting.

In this case each lever must be separately manufactured, mounted and aligned. If it is desired that the snap spring should be set to a predetermined force, one of the stationary bearings must be adjustable.

The invention is based on the problem of providing an electric snap switch of the aforementioned kind which can be assembled in a simpler manner and makes simpler manufacture and adjustment possible.

This problem is solved according to the invention in that two stationary counterbearings are provided laterally offset from the levers, that the actuating lever and contact lever are interconnected by a spring strip at their end remote from the snap spring, and that, between two oppositely curved arcs embracing the counterbearings, the spring strip comprises a retaining section which extends tran verselytothe levers and is pressed against the counterbearings under the influence of the snap spring and a support acting on the actuating lever.

In this construction, the two levers are already interconnected by the spring strip before assembly.

Since the support prevents deflection of the actuating lever and the snap spring gives rise to oppositely directed force components extending through the levers in the direction of their length, a moment is produced in the retaining section which presses same positively against the counterbearings. This results in a self-supporting system which is suspended to two fixed points and is assembled simply by pushing it over the counterbearings from the side. The actuating force also ensures that one arc of the spring strip lies closeiy against the one counterbearing, so that the position of the system transversely to the levers is also accurately defined. The spring strip has the additional advantage that a special return spring can be dispensed with because at least one part of the spring strip is elastically deformed on displacement of the actuating lever.

Very simple components can be used for the counter-bearings. In particular, they can be formed by pins. This results in a kind.of roller bearing in which there is practically no friction.

The production can also be simplified in that the spring strip is made in one piece with the actuating lever and contact lever and the latter are stiffened by longitudinal profiling. This one-piece construction also results in a very low masts and consequently a low tendency to rebound when contact is made.

In a preferred embodiment, the section of the actuating lever adjacent to the snap spring is resilient. This has the advantage that snapping occurs before the contact pressure has dropped to zero.

In a preferred embodiment, the contact lever is connected to the retaining section by an arc of about 90 and the actuating lever is connected to the retaining section by a connecting section adjoining substantially at right-angles and by an arc of about 180 . The actuating lever is thereby associated with a longer section of the spring strip, which improves the resetting properties.

During normal operation, the support of the actuating lever can be simply brought about by means of the associated actuating element.

It is also favourable if support of the actuating lever in the rest position is effected by means of a fixed abutment. In this way, securing the system can be effected before an actuating element has been installed. In conjunction with the snap spring, the abutment ensures appropriate prestressing or clamping stress in the spring strip.

With particular advantage, the spacing between the retaining section and connecting section can be changed by providing a set screw passing through both sections. With the aid of this screw one can alter the prestress in the stressing spring and thus the snapping behaviour. The set screw is loaded substantially only in the axial direction. The spring forces that are thereby set up secure the set screw against rotation without the need for taking additional measures.

In particular, the set screw may pass through a through hole in the connecting section and have a self-cutting screwhead for engaging the retaining section. It is therefore necessary to stamp only a small hole in the retaining section; the set screw will then cut its own screwthread.

The present invention also provides a snap-action electric switch comprising an actuating lever and a contact lever arranged side-by-side and a snapacting spring connected to both levers, wherein two stationary supports are provided which are spaced apart from each other laterally with respect to the levers, and the actuating lever and the contact lever are interconnected by a spring strip at their ends remote from the snap spring the strip being so mounted on the Supports that a point moving from one end of the strip to the other passes round the supports in opposite senses and the spring strip being urged against the supports by the snap spring and a member abutting or for abutting the actuating lever.

Three snap action electric switches constructed in accordance with the invention will now be described by way of example only, with reference to the accompanying drawing, wherein Figure 1 is a diagrammatic side elevation of a first switch; Figure 2 illustrates a second switch, and Figure 3 shows a third switch.

Referring to the accompanying drawings and first to the snap-action electric switch comprises an actuating lever 1, a contact lever 2 and a snap.spring which is articulated to both sections and is in the form of an omega spring. The two levers are interconnected by a spring strip 4 which, adjoining the contact levers 2, has a 90" are 5, a retaining section 6, an 1800 arc 7, a connecting section 8 and a 90 bend or arc 9. The spring strip 4 and the two levers 1 and 2 are made in one piece from spring material. For stiffening purposes, the two levers have longitudinal profiling 10 in the form of flanges at the edge of the levers.

Two counterbearings 11 and 12 are provided which are in the form of pins, disposed at a fixed location and are offset from each other transversely to the levers 1 and 2. The 90" are 5 embraces the counterbearing 11 and the 180 arc embraces the counterbearing 12. An actuating element 30 acts on the actuating lever 1 on the side remote from the counterbearings. In addition, this side is provided with a possibly adjustable abutment 31 which defines the rest position of the actuating lever 1. The snap spring 3 produces a force component P1 in the contact lever 2 and a force component P2 in the actuating lever 1.These force components act in opposite directions and produce a torque in the retaining section 6that brings about positive abut mentofthis retaining section againstthecounter- bearings 11 and 12. Deflection of the actuating lever 1 is prevented by the actuating element 30 or, in the rest position, by the abutment 31. Depending on displacement of the actuating lever 1, part of the connecting section 8 is resiliently deformed so that this part serves as a return spring. Consequently, a supporting force F is produced at the actuating element 30. The switch may may be displacement dependent, the actuating lever 1 being moved through a dead-centre position by displacement of the actuating element 30.However, it is preferred if the switch is force dependent snap-over occurring when the element 30 produces an actuating force on the lever 1 exceeding the force F.

A set screw 13 passes through a through hole in the connecting section 4 and has a self-cutting screwthread 14 for engagement with the retaining section 6. When this set screw 13 is thightened, there is a change in the spacing of the joints 15 and 16 between the stressing spring 3 and the levers 1 and 2 respectively. In this way one can change the prestress in the stressing spring 3 and thus the switching point of the snap switch. Since the retaining section 6 and connecting section 8 are pressed apart by the stressing spring, the set screw 13 is loaded axially and therefore secured against turning about its axis.

The contact system comprises a fixed contact 17 and two movable contacts 18 and 19 provided on a respective spring 20 and 21 fixed with respect to the housing. These movable contacts are associated with a fixed abutment 22 and 23, respectively. The contact lever 2 carries an entrainment member 31 which, in the illustrated stable rest condition, lifts the movable contact 19 from the fixed contact 17 and holds it against the abutment 23. When the actuating lever 1 is displaced in the direction of the force F, the system snaps over after a predetermined distance, the entrainment member 31 being suddenly moved to the left so that the movable contact 19 comes into contact with the fixed contact 17 and the movable contact 18 is lifted off until it abuts the abutment 22.

When the setting element loading the actuating lever 1 returns, the actuating lever 1 returns under the spring strip resetting forces to cause snapping back to the illustrated rest position. Connecting terminals associated with the contact are indicated at 24, 25 and 26.

If it is necessary for the snap spring 3 and part of the actuating lever 1 to extend through the plane of the contact lever 2, the latter can be provided with an appropriate slot or recess.

The spring strip 4 need not have parallel side edges. It may, for example, be possible to make the connecting section wider than the retaining section to increase the resetting force.

In the switch of Figure 2, the system consisting of the actuating lever 1, contact lever 2, snap spring 3 and spring strip 4 has the same construction and the same mounting as in Figure 1. What is different is that a movable contact 27 is carried directly by the contact lever 2, for which reason the spring strip 4 is connected to the connecting terminal 24. The movable contact co-operates with two fixed contacts 28 and 29 which are mounted at a fixed location. This system functions in the same way as a conventional micro-switch.

The Figure 3 switch differs from that of Figure 1 only in that the actuating lever 1 has a resilient section 30 at the end adjacent to the snap spring, the resilient section causing the joing 15 to follow while simultaneously producing an additional stress. The result of this is that a self-completing snapping-over action is initiated before the contact pressure between the contacts 27 and 29 or 27 and 28 has decreased to zero.

Actuation of the snap switch can, as usual, be manual or automatic in response to a thermostat, pressostat or the like.

Claims (11)

1. A snap-action electric switch comprising an actuating lever and a contact lever arranged side-byside and a snap-acting spring connected to both levers wherein two stationary supports are provided which are spaced apart from each other laterally with respect to the levers, and the actuating lever and the contact lever are interconnected by a spring strip at their ends remote from the snap spring, the strip being so mounted on the supports that a point moving from one end of the strip to the other passes round the supports in opposite senses and the spring strip being urged against the supports by the snap spring and a member abutting or for abutting the actuating lever.

2. A switch as claimed in claim 1, wherein the supports are formed by pins.

3. A switch as claimed in claim 1 or claim 2, wherein the spring strip is made in one piece with the actuating lever and the contact lever and the latter is stiffened by longitudinal profiling.

4. A switch as claimed in claim 3 wherein part of the actuating lever adjacent to the snap-acting spring is resilient.

5. A switch as claimed in any one of claims 1 to 4, wherein the contact lever is connected to the said part of the spring strip by a portion of that strip which is bent round one of the supports through about 90 and the actuating lever is connected to the said part of the spring strip by a portion of that strip which is bent round the other support through about 180'.

6. A switch as claimed in any one of claims 1 to 5 wherein the member abutting the actuating lever is an actuating element.

7. A switch as claimed in any one of claims 1 to 6, wherein the member abutting the actuating lever is a fixed abutment.

8. A switch as claimed in any one of claims 1 to 7, wherein, a set screw passes through the said part of the spring strip and another part of that strip lying alongside the said part, the screw being arranged to vary the spacing between those parts.

9. A switch as claimed in claim 8, wherein the set screw passes through a hole in the said other part of the spring strip and has a self-tapping screwthread for engaging a hole in the first-mentioned part of that strip.

10. An electric snap switch comprising an actuating lever, a contact lever approximately parallel thereto and a snap spring connected to both said levers, particularly an omega spring, characterised in that two stationary counterbearings are provided laterally offset from the levers, that the actuating lever and contact lever are interconnected by a spring strip at their end remote from the snap spring, and that, between two oppositely curved arcs embracing the counterbearings, the spring strip comprises a retaining section which extends transversely to the levers and is pressed against the counterbearings under the influence of the snap spring and a support acting on the actuating lever.

11. A snap-action electric switch substantially as hereinbefore described with reference to, and as illustrated by Figures 1,2, or 3 of the accompanying drawings.