GB2112210A

GB2112210A - Electrical snap-action switch

Info

Publication number: GB2112210A
Application number: GB08235918A
Authority: GB
Inventors: Bernhard Dietrich
Original assignee: SDS Elektro GmbH
Current assignee: SDS Elektro GmbH
Priority date: 1981-12-18
Filing date: 1982-12-17
Publication date: 1983-07-13
Also published as: DE3150210A1; DE3150210C2; FR2518797A1; CH659911A5; FR2518797B1; GB2112210B

Abstract

An electrical snap-action switch comprises pairs of fixed contacts (11, 12; 13, 14) secured to a housing (1, 2), a double-breaking contact bridge (15, 16) having contact platforms formed at both ends and at least one movable contact (26-29 (Fig. 3 not shown)) on each platform, and a plunger-like actuating element 5 which at the same time serves as a carrier for the contact bridge. In order to obtain increased reliability of contacting, the switch is provided with twin movable contacts (e.g. 26, 27 (Fig. 3 not shown)) in which the universal swinging of the contact system, required for the four- point support, is achieved in that two springs (19, 20) insulating members (17, 18) are each knife-edge mounted on insulating members (17, 18) and are point-supported (23, 24) on the actuating element (25). The point support (23, 24) provides possibilities of easily adjusting (by means of screw 37 (Fig. 5 not shown)) the snapping instant from outside the housing and allows a degree of distortion in the bridge (15, 16). <IMAGE>

Description

SPECIFICATION Electrical snap-action switch The invention relates to an electrical snapaction switch of the type comprising at least one pair of fixed contacts which are secured to a housing, a movable, snap-action, double-breaking contact bridge having contact platforms formed on the two ends thereof and at least one movable contact disposed on each platform, and a plungerlike actuating element which serves as a carrier for the contact bridge, a snap spring being provided on each side of the contact bridge, one edge of each snap spring being knife-edge mounted on the contact bridge or insulating members positioned between contact bridges disposed one above the other, and the other, opposite edge of which spring is supported in a depression in the actuating element.

Snap-action switches having connection elements which are knife-edge mounted both on the contact platforms and also on the actuating element, have the disadvantage that the movable contact bridge system and the actuating element form a relatively rigid system which only has one freedom of movement, this being in the direction of actuation. In the course of the tendency for switching loads to decrease to the mV and mA ranges, and with the simultaneously increasing demands on reliability with respect to the currentflow resistance, it is advantageous to provide the individual contact points with twin contacts.

Since the demands on the accuracy of the instant of switching have increased together with the increasing demands on the reliability of contacting, so that readjustment is necessarily required when exchanging the snap-action switches in systems having predetermined instants of switching, it is nowadays necessary to provide possibilities of effecting this adjustment on the snap-switching elements from the outside, that is, without removing parts of the housing and the like.

A distinction is made between two basic principles in the case of snap-action switches in accordance with the preamble, that is to say, between resilient contact bridges and rigid connection elements (between contact platform and actuating element) on the one hand and, on the other hand, rigid contact bridges and resilient connection elements.

Snap-action switches having a resilient contact bridge are known from German patent specification No. 975,831, and a snap-action switch having two resilient contact bridges, and which thus forms a two-circuit change-over switch, is described in German patent specification No. 1 7 65 712. A snap-action switch having one or two rigid contact bridges and resilient connection elements is known from German Offenlegungsschrift No. 28 17 815.

In the types of construction described in the above patent specifications, these principles have the common feature that the contact platforms each carry a contact for the break and make functions in the case of a single-bridge construction, and only one contact per contact point in the case of the two-bridge construction.

In the case of two-sided knife-edge mounting of the snap springs or of the rigid connection elements, the contact points are not doubled to form so-called twin contact in German patent specification No. 1 7 65 712. However, since snap-action switches of this kind also have to be provided with devices for forced opening, contact bridges which are flexible, that is to say, resilient, in the direction of the contact closing and opening movements are eliminated in accordance with the requirement of VDE 0660 (which defines switches having forced opening as those switches whose switching members, during switching-off, are reliably separated at least over a portion of the actuating travel without the interposition of resilient drive members).

Doubling of the contacts to form twin contacts hitherto required special constructions of the kind described in British patent specification No. 1,593,948. However, the separation of the contact system from the snap system required in the aforesaid patent specification involves considerable disadvantages with respect to reliability of contacting in the case of low actuation speeds, as has been described in the Journal ETZVol. (1980), Issue 4 on pages 220and221.

The snap-action switch is known from British patent specification No. 1,088,083 which is provided with two knife-edge mounted contact bridges which are electrically isolated from one another. Each contact bridge has two associated pairs of fixed contacts. In order to ensure reliable contacting, sufficient play is allowed at the support points of the contact bridges to allow the contact bridges to counterbalance one another, so that the two contact points of the double-breaking contact bridge come into abutment. The individual contact points are not provided with parallel closing twin contacts and, in this latter solution, it is also impossible to do this.

U.S. patent specification No.2,571,453 discloses a snap-action switch which has a resilient contact bridge with single contacts. The purpose of this switch is to cope with a large number of switching tasks by a simple modification. However, twin contacts are again not provided in this snap-action switch, and forced opening within the meaning of VDE 0660 is inconceivable.

A further snap-action switch is disclosed in U.S. patent specification No. 4,216,358 which is again provided with a resilient contact bridge which co-operates with two pairs of fixed contacts, and in which the contact bridge is provided with double-breaking. Special attention is drawn to the fact that welded contacts break open upon actuation. In order to ensure this, mutually oppositely located fixed contacts are disposed on pivotable plates which are movable by drivers on the actuating element. Welded contacts roll on one another untii the welded joint breaks open. Measures are not provided to increase the reliability of contacting by means of twin contacts.

In the snap-action disclosed in German Auslegeschrift No. 1,935,225, a further type of forced control is obtained in that a pivoted lever driven by a cam of the actuating element acts upon a resilient contact bridge. The moveable contact bridge is sheared off by this lever arm if the contact bridge is more than merely resiliently deflected. Here also, measures ar not provided for increasing the reliability of contacting.

German Offenlegungsschrift No.2 613 555 discloses a snap-action contact which reliably switches even with a minimum actuating stroke.

For this purpose, a wire bow-type spring serving as a compression spring is pivotably mounted between a wedge-shaped groove in a bifurcated contact lever and a wedge-shaped groove in the actuating element. In this manner, a simple change-over contact is provided which is controllable by various actuating elements.

Double-breaking is not provided and there is no recognizable possibility of constructing the individual contact points as twin contacts.

Moreover, none of the above-mentioned constructions of snap-action switches have had devices for adjusting the instant of change-over, that is to say, the instant of snapping. Only German Offenlegungsschrift No. 29 13 913 describes a relevant possibility. However, since the aforesaid Offeniegungsschrift involves a snapaction switch in which the contact system is separated from the snap mechanism, this principle is not, for the aforementioned reasons of contacting reliability, an optimum one in the case of a slow actuation speed. Moreover, the snap point can only be adjusted when the housing has been removed or when an appropriate opening in the housing is provided.

Proceeding from the snap-action switch described in German Offenlegungsschrift No. 2 817 815, the object of the present invention is to increase the contacting reliability in an arrangement of this kind, and to mount the contact bridge such that it is freely movable and all the contact points abut against the fixed contacts with the smallest possible contacting variations.

In accordance with the invention, there is provided an electrical snap-action switch comprising at least one pair of fixed contacts which are secured to a housing of the switch, a movable snap-action, double-breaking contact bridge which has contact platforms formed on the two ends thereof and which is constructed so as to be distortable, twin movable contacts disposed on said platforms on each side of the contact bridge and located adjacent to one another transversely of the longitudinal axis of the contact bridge, a plunger-like actuating element serving as a carrier for the contact bridge, and a respective snap-action spring disposed on each side of the contact bridge, one edge of each snap spring being knife-edge mounted relative to the contact bridge, and the other, opposite edges of the springs being supported in a circularly symmetrical depression in the actuating element providing punctiform support points for the two snap springs on mutually opposite sides of the actuating element.

In the case of twin contacts, the contact system is thereby enabled to orientate itself to the attitude of the fixed contacts. Slight residual differences in the positions of the four support points can additionally be compensated for by the contact bridges which, although solid, are disposed in the contact system so as to be easily distortable.With regard to the spatial fixed positioning of the centre of oscillation and hence the prevention of the contact bridge system from being pushed out laterally, a particularly preferred embodiment of the point mounting is distinguished by the fact that that portion of the actuating element on which the connecting elements are supported is of circular symmetrical construction and the supports for the connecting elements on the rotational body each have a preferably arcuate recess whose radii are greater than the radius of the rotational body on the support point.

To enable a construction requiring the least number of components, it is advantageous for the actuating element to be of one part construction or for a rotational body to be pressed into the actuating element in order to obtain a construction which is optimized with respect to wear. In this case, that part of the actuating element in which the rotational body is pressed is optimized relative to its friction partner "housing" with respect to friction and wear characteristics, and the rotational body is optimized with respect to its friction partner "connection element".

If the dimensions of the pressed-in rotation body are to be fixed to a tolerance limit, a snap adjustment can be achieved in that the end position of the rotational body pressed into the actuating element is displaceable in the direction of the longitudinal axis of the rotational body and towards the contact system or towards the contact bridge by means of an adjusting screw.

It can be advantageous to adjust the snap point in both directions. In this case, in accordance with a further development, the rotational body can be disposed so as to be freely longitudinaily displaceable in the actuating element and be adjustable by means of an adusting screw against the force of a compression spring which is supported between the rotational body and the actuating element.

In this case, it is advantageous that the prestressed force of the compression spring over its entire adjustable range should have a higher numerical value than the force component of the snap springs and/or of the resilient contact bridges which acts in the direction of the compression spring but which opposes the latter.

Furthermore, in order to obtain an additional overrrun travel the compression spring is to be dimensioned such that, after the snap switch has been actuated by the actuating element, and after the contact system and the rotational body have reached their end positions, the actuating element is provided with additional overrun travel by compressing the compression spring, possibly to its maximum extent.

If the reliability of contacting of the contact points provided with twin contacts, and the free movability of the point-mounted contact system to increase reliability of contact, are still inadequate in the case of very low actuating speeds, the compression spring interposed between the actuating plunger and the rotational body can be dimensioned such that it is stronger along the path of the actuating element than the component, acting against the compression spring, of the force exerted by the snap springs or the resilient contact bridge in the region of the snap point, although it is weaker than this component towards the end position of the actuating element, and such that the compression spring has a flatter characteristic than the snap spring or the resilient contact bridges.

The snap points are also adjustable in this embodiment in that the point of equilibrium between the compression spring and the component of the snap springs and/or contact springs acting thereagainst is adjustable by means of an adjusting screw.

In all embodiments, it is advantageous that a degree of freedom of the swinging movement of the contact system or contact bridge is restricted by lugs which are provided on the insulating member and which possibly come into frictional contact with the parts of the housing.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 shows a snap-action switch in accordance with the invention, the left hand side of the Figure showing the position of the contact system when the actuating element has been pressed and the right hand side showing the normal position; Fig. 2 is a section through the switch of Fig. 1 on the right of the centre line, taken along the line I-I, on the left of the centre line, taken along the line Il-Il; Fig. 3 is a section through the switch of Fig. 1, taken along the line Ill-Ill; Fig. 4 shows sections through the point mounting (rotational body and connection element);; Fig. 5 is a section through an actuating element and shows diagrammatically a contact system having only one contact bridge; and Fig. 6 is a section through an actuating element having a longitudinally displaceable rotational body.

The snap-action switch illustrated in Figures 1 to 3 comprises a housing 1 and a cover 2 which is held in bores 4 (Fig. 1) in the housing 1 by means of clips 3 (Fig. 2). An actuating element 5 is guided by an upper flange 6 (Fig. 1) of the housing 1, and in grooves 8 (Fig. 3) in the housing 1 by way of ribs 7 (Figs. 1 and 3). A cylindrical coil spring 9 (Fig. 1) presses the actuating element 5 into its normal position, the normal position of the actuating element 5 being fixed by a stop 10 (Fig.

1).

Fixed contacts 11, 12 are associated with the normally-open contact (make contact) of the switch and fixed contacts 13, 14 are associated with the normally-closed contact (break contact) of the switch. The contact system comprising contact bridges 1 5, 1 6 which are joined to form a unit by insulating bodies 17, 18, is freely movably located between the fixed contacts 11, 12 on the one hand and the fixed contacts 13, 14 on the other hand. Two snap springs 1 9, 20 are interposed between knife-edge supports 21,22 on the insulating bodies 1 7, 18 and two point supports 23, 24 in a rotational body 25.

The construction of the contact bridges will be further explained with reference to the plan view of Fig. 3.

The pairs of twin contacts 26, 27 and 28, 29 associated with the contact platforms 1 5a and 15b are interconnected by narrow ribs Al and A2 and are electrically interconnected by narrow ribs B1 and B2. The contact system is largely able to adapt itself, by way of the point supports 23, 24, to any differences in position existing between the pairs of contacts 26, 27/28, 29 and the four supports points of the fixed contacts (the two support points of the fixed contacts 11 are designated 11 a and 11 b in Fig. 2), that is to say, to an extent to which three of the four contact points have come into contact.Since the point supports relatively easily permit distortion of the contact bridges which are deliberately constructed so as to be distortable by the narrow ribs Al, A2 and B1, B2, the fourth contact point also comes into abutment with small differences in the contact pressure during the course of the snap-over operation.

The free tumbling movement of the contact system requires guidance relative to the housing parts 1,2. For this purpose, the lugs 1 7a and 1 7b are formed on the insulating body 17, and the lugs 1 8a and 1 8b are formed on the insulating body 18.

The various possibilities for securing a switch of the construction which has been described are set forth in German patent application No. P 31 39 701.8 and in HGm G 81 29 211.2.

The point supports 23, 24 between the connection elements, the snap springs 1 9 and 20 and the rotational body 25 in the illustrated embodiment, will be further described with reference to Fig. 4. The rotational body 25 has a circumferential groove 30. In order to prevent excursion of the snap springs 1 9, 20 in the direction of the arrow C, that is to say, to prevent them from leaving their intended symmetrical position, the snap springs have arcuate cutaway portions 31 whose radii have to be equal to or greater than the radius of a circle defined by the points 24, 32, 33 located on its circumference, in order to ensure the correct location of the point supports in all possible positions of ths rotational body 25 relative to the position of the connecting elements 23, 24. The points 32, 33 are the points of intersection of the line Xl -X2 with the line Y1-Y2 and of the line Y1-Y2 with the circumferential line Z.

The possibility of adjusting the spatial position of the rotational body 25 which is rigidly pressed into the actuating element 5, is explained with reference to Fig. 5. During the course of assembly, the rotational body 25 is pressed into a bore 5a in the actuating element 5 until it abuts against a surface 34. The journal 35 of the rotational body 25 extends into the bore 5a and has undercuts 36 in order to obtain a well-defined press fit. When the parts 5 and 25 are abutting against the surface 34, the distance D ensues as pre-travel, and the distance E ensues as overrun travel. The theoretical snap point ensures when the distance D has become zero.

In the embodiment of Fig. 5, the contact system only comprises one contact bridge 49 which is acted upon by the symbolically illustrated snap springs 50, 51 by way of insulating members 52, 53 and knife-edge supports 21, 22. The fixed contacts are designated 54a, 54b and 55a, 55b.

In the arrangement illustrated here by way of example, it is structurally advantageous for the dimensions of the individual parts determining the pre-travel to be such that adjustment always has to proceed from a condition where the amount of pre-travel is too large.

In order to reduce the distance D, a screw 37 abutting against the rotational body 25 at 38 is adjusted so that the rotational body 25 is pressed out of the bore 5a such that the undercuts 35 dig into the bore 5a. The distance D is then reduced by the amount by which the rotational body 25 is forced out of the actuating element 5, and the over-run increases by the same amount. The switching-back point ensues from the sum of the adjusted distance E plus the contact gap F. It will be appreciated that it is always possible to construct the rotational body 25 and the screw 37 in one piece. This only necessitates designing the rotational body such that it is longitudinally displaceable and is provided with means for preventing unintentional rotation. It can then be inserted into the actuating element 5.

In Figure 6, the rotational body 39 is mounted in the actuating element 40 so as to be freely displaceable in a longitudinal direction G, the travel of the actuating element 40 being determined by stops 41 and 42. In this embodiment, the return spring 43 has been disposed at the bottom end 44 of the rotational body 39. Security against rotation is provided by a square portion 39a.

Snap conditions similar to those shown in Fig.

5 ensue when the compression spring 45 is dimensioned such that its force over the entire adjustable range exceeds the component of the force of the snap spring which acts against the force of the compression spring 45. The difference between this construction and the construction shown in Fig. 5 resides in the very important advantage that, after the rotational body 39 has reached its end position (corresponding to distance D plus E of Fig. 5), the actuating element 40 can be pressed in even further until either the actuating element abuts at 42 or the compression spring 45 is fully compressed. The instant of snapping can be adjusted in both directions by means of an adjusting nut 46 which abuts against a shoulder of the actuating element at 47, the adjusting nut 46 being pressed against the latter shoulder by the compression spring 45.

A so-called double-snap function, as described in German Offenlegungsschrift No. 29 13 913, is obtained by dimensioning the compression spring 45 such that it is stronger along the path of the actuating element than the component, acting against the compression spring of the force exerted by the snap springs and/or the resilient contact bridge in the region of the snap point, although it is weaker than this component towards the end position of the actuating element, and such that it has a flatter characteristic than the snap spring or the resilient contact bridges. The difference between the solution in accordance with the invention and that disclosed in German Offenlegungsshrift No. 29 13 913 resides in the great advantage that no supports are required in the actuating element, and it is possible to adjust the snapping instant externally by way of the adjusting nut 46.

In this construction, the amount of the pretravel results from the distance D shown in Fig. 5 less the amount X (not illustrated) by which the compression spring 45 is compressible by the shoulder 48. The switching-back point is also reduced by this amount X, that is to say, the differential travel which (when the compression spring 45 is not compressible by the force component of the snap spring) normally corresponds to the contact gap F (Fig. 5) increased by the amount 2 times X, that is to say, F+ (2 times X).

The function of the forced opening device can be explained with reference to Figs. 1 and 2. Two forced-opening levers 56, 57 are mounted at 56a and 57a in the housing 1 and cover 2 respectively. After the actuating element 5 has been pressed, and the switch-over point of the contact system has been reached, even though switch-over is prevented for some reason or other, the rotational body is operatively connected to the contact bridge at 58 and 59 after a further distance has been covered which takes into account pitting of the contacts occurring during operation, and thus forcibly triggers the opening of the normally-closed contact (break contact).

Claims

1. An electrical snap-action switch comprising at least one pair of fixed contacts which are secured to a housing of the switch, a movable snap-action, double-breaking contact bridge which has contact platforms formed on the two ends thereof and which is constructed so as to be distortable, twin movable contacts disposed on said platforms on each side of the contact bridge and located adjacent to one another transversely of the longitudinal axis of the contact bridge, a plunger-like actuating element serving as a carrier for the contact bridge, and a respective snapaction spring disposed on each side of the contact bridge, one edge of each snap spring being knifeedge mounted relative to the contact bridge, and the other, opposite edges of the springs being supported in a circularly symmetrical depression in the actuating element providing punctiform support points for the two snap springs on mutually opposite sides of the actuating element.

2. An electrical snap-action switch as claimed in claim 1, wherein the support points of the snap springs on the actuating element each have an arcuate recess whose radii are greater than the radius of the actuating element at the support point.

3. An electrical snap switch as claimed in claim 1 or 2, wherein the actuating element is bipartite, and includes a rotational part carrying the depression.

4. An electrical snap-action switch as claimed in claim 3, wherein an end of the rotational part is inserted into the body of the actuating element with a friction fit therebetween and is displaceable in the direction of the longitudinal axis of the rotational part and away from the actuating element by means of an adjusting screw.

5. An electrical snap-action switch is claimed in claim 3, wherein the rotational part is disposed with play in the body of the actuating element so as to be longitudinally displaceable and is adjustable by means of an adjusting screw against the force of a compression spring which is supported between the rotational part and the actuating element.

6. An electrical snap-action switch as claimed in claim 5, wherein the force of the pre-stressed compression spring is greater over its entire adjustable range than the force component of the snap springs which acts in the direction of the compression spring but which opposes the latter.

7. An electrical snap-action switch as claimed in claim 5 or 6, wherein the force of the compression spring is dimensioned such that, after the snap-action switch has been actuated by the actuating element, and after the contact system and the rotational part have reached an end position, the actuating element is provided with additional overrun travel by compressing the compression spring.

8. An electrical snap-action switch as claimed in any of claims 5 to 7, wherein the compression spring is dimensioned such that it is stronger along the path of the actuating element than the component, acting against the compression spring, of the force exerted by the snap springs in the region of the snap point, although it is weaker than this component towards the end position of the actuating element, and wherein it has a flatter characteristic than the snap spring or the resilient contact bridges.

9. An electrical snap-action switch as claimed in any of the preceding cliams, wherein the rotary movement of the contact system or contact bridge about the axis of the rotational part is restricted by lugs which are provided on the insulating member and which face respective adjacent housing walls.

10. An electrical snap-action switch as claimed in any of the preceding ciaims, wherein forceopening levers are mounted in the housing part and, after pressing by the actuating element, and when the contact system has not snapped over, establish frictional connection between the rotational part and the insulating intermediate member or contact system.

11. An electrical snap-action switch substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.