GB2045003A - Snap-action switch - Google Patents

Abstract

A snap action switch having at least one contact bridge (10, 11), which is actuated by an external actuating member (2) through the intermediary of snap springs (4,5) together with a striker (6) movable in the opposite direction to the actuating member (2) and which is mounted in a recess (9) of the striker (6) under the pressure of a compression coil spring (12), is characterised in that: the compression spring (12) exerts a force which is greater than the force component exerted against it by the snap springs (4, 5) in the region of the snap point, but is less than the force component exerted against it by the snap springs (4, 5) towards the end positions of the actuating member (2); the compression spring (12) exhibits a flatter characteristic than the snap springs (4, 5); and the compression spring (12) is supported in mutually facing supports (13, 14) which are movable apart from each other upon relaxation of the compression spring (12), this relaxation being limited by the length of the recess (9) in the striker (6). <IMAGE>

Description

SPECIFICATION -Snap or quick-action switch The invention relates to a snap or quick-action switch of a kind with double interruption and with at least one contact bridge, the latter being actuated by an external actuating member through the intermediary of snap springs together with a striker, and being mounted in a recess of the striker under the pressure of a helical or helicoidal compression spring, the latter being disposed with its axis extending along the direction of-movement of the striker, and the movements of the actuating member and striker, in use of the switch, being in coaligned but opposite directions.

German Patent Application P 27 52638.1 has as its object a snap switch of this kind, wherein, in the end position of the striker, a force component exerted by the snap springs, this being a component oriented in the direction of movement of the striker, determines, through the intermediary of the striker and the compression spring, the contact force with which the contact bridge bears upon the fixed contact. In these or cornparable switches the compression spring is always dimensioned so that it exerts a-force greater than any force component exerted by the snap springs upon the contact bridge.Now if-a-changeov- er-operation is initiated by moving the ends of the snap springs remote from the striker in the direction counterto the striker movement to be initiated, i.e., towards the snap point, then the force component exerted by the snap springs which produces the contact force varies continuously, and so therefore does the contact force, until it becomes zero in the region -of the snap point. This has the result that in the case of a slow actuation a contact force of approximate zero is maintained for a considerable period. This system is only fully serviceable -at limited actuating velocities.

It is an object of the invention, in snap or quick-action switches of the kind initially described herein, to make it possible to accelerate the opening or breaking operation, and also to maintain a minimum contact force, irrespectively of the actuat ing velocity, until the contact bridge is retracted from the fixed contacts.

According to the present invention, we provide a snap or quick-action switch of the kind first mentioned herein, characterised in that: the compression spring is of such dimensions that the force which it exerts, in the direction of the stroke of the actuating member, is greater than the force component ex erted against it by the snap springs in the region of the snap point, but is less than the force component exerted against it by the snap springs towards the end positions of the actuating member; the com pression spring exhibits a flatter characteristic than the snap springs; the supports of the compression spring have seatings which face one another in the direction of the helicoidal axis, these seatings having surfaces suitable for mutual abutment; and said seatings leave a free space open between them selves in the event of relaxation of the helicoidal compression spring, this relaxation being limited by the length of the recess in the striker.

Preferably the snap springs are adjustable. In a more preferred construction, the snap springs are adjustable, the striker has a head for engagement of the snap springs, and the striker head is subdivided into two elastically deformable parts by a slit runni.ng in the direction of the movement of the striker and at right angles to the plane in which the greatest area.is definable (in use of the switch) betweentbe-end positions of the snap springs, .means being provided to maintain adjustably-a given degreeof openness of the slit. Preferably the slit in the-striker head terminates in a conical bore into which a similarly conical grub screw with a self-tapping screw-thread is driven to a depth sufficient to maintain the said degree of openness of the slit.

The invention will be explained more fully with reference to the accompanying drawings, in which: Figure 1 is a fragmentary diagrammatic side vi.ew, mostly in section, of a snap-switch according to the invention, the left-hand half of the Figure showing a first position of its moving parts and the right-hand half of the Figure showing a second position of its moving parts, Figure 2 is a graph illustrating the functioning of -the snap switch of Figure 1, and Figure 3 is a fragmentary sectional view showing adjustment means in the hed of the striker of the snap switch of Figure 1, in a plane at right angles to that of Figure 1.

In the snap switch shown in Figure 1, an external actuating member 2 in the form of a push-button is guided longitudinally in a switch housing 1, and has supports 3 and 31 for snap springs 4 and 5. The snap springs engage at their other ends in supports 7 and 8 on a striker 6 guided in the housing 1. The striker exhibits a recess 9. In the recess 9, contact bridges 10 and 11 are mounted under the pressure of a compression spring 12, the axis of which is oriented.

along the direction of movement of the striker 6. The compression spring 12 is engaged in two supports 13 and 14 which exhibit mutually confronting sea tings 15 and 16. The seatings 15 and 16 have surfaces designed for mutual abutment, on which they abut mutually as shown at.17 in the condition illustrated in the left-hand half of Figure 1. However, when the compression spring 12 is relaxed and the contact bridge1 0 is an abutment with the top - boundary surface of the recess 9, theseatings 15 and 16 leave a free space open between themselves at the level shown at 17.

In the position shown in the left-hand half of Figure 1 ,.the snap spring 4 exerts an upwardly directed force upon the striker 6. This acts through the lower contact bridge 11 and the supports 14 and 13 upon the upper contact bridge 10, and determines the contact force which is exerted upon upper fixed contacts 18 and 19.

If the switching movement is now initiated, e.g., by a counterspring not shown, then the outer actuating member 2 moves upwards. This reduces the vertical interval of the supports 3 and 7, with the result that there is a progressive reduction in the upwardly directed component of force exerted by the snap spring 4 upon the striker 6, and hence in the contact force of the contact bridge 10 upon the fixed contacts 18 and 19. In the case of the prior-art constructions the snap point would be attained when the supports 3 and 7 were at the same height. The contact force would then be approximately zero, and the duration of this unstable state would depend upon how quickly the other actuating member 2 passed through the snap point.In the case of the embodimentofthe invention illustrated, however, a critical position is reached along the stroke of the actuating member even before the support 3 reaches the height of the support 7. In the critical position, given the dimensioning of the compression spring 12 according to the invention, the force stored in the latter is greater than the counterforce exerted by the snap spring component. The compression spring 12 can now relax before the snap point is attained.

Braced through the intermediary otthe top support 13 and the contact bridge 10 against the stationary fixed contacts 18 and 19, it urges the lower support 14, and hence both the contact bridge 11 and the striker 6, downwards. This has the following results: 1. Before the actuating member 2 with its support 3 has reached the height of the support 7, the striker 6, braced against the fixed contacts 18 and 19, is drawn rapidly through the snap point independently of the speed of the actuating member 2 by the compression spring 12, the support 7 being lowered.

2. Because of the flatter characteristic of the compression spring 12, the contact force of the contact bridge 10 upon the fixed contacts 18 and 19 retains a minimum value determined by the residual force of the compression spring 12 until the contact bridge 10 separates from contacts 18 and 19.

3. Because of the rapid transition through the snap point, the vertical component of the force exerted by the snap spring 4, which is now directed downwards, grows stronger very rapidly. The lower contact bridge 11 is quickly brought into abutment upon the lower fixed contacts 20 and 21 with a sufficiently high contact force determined by the residual force of the compression spring 12. In its further movement, the striker 6 descends with respect to the contact bridge 11 until the seatings 15 and 16 come into abutment at 17. The vertical component of the force exerted by the snap springs 4 and 5 now acts as contact force.

The position shown in the right-hand half of Figure 1 is attained after completion of the switching movement. The snap spring 5 behaves and moves in the same sense as the snap spring 4 during the switching operation.

If the external actuating member 2 now moves downwards again due to pressure upon it against a counterspring, then the process described hereinbefore is repeated in the opposite direction.

In Figure 2 the curve of the contact force P is plotted over the stroke of the member 2 when forced into the housing against a counterspring; above the horizontal axis, it relates to the contact bridge 10 in Figure 1, which here has an opening function, and below that axis it relates to the contact bridge 11 in Figure 1, which here has a closing function. Within the tolerance range 22 dictated by the tolerances of the snap spring, the contact force diminishes along the stroke of the actuating member, until, between the points 24 and 25, it becomes of equal value to the counterforce ofthe compression spring 12 lying in the tolerance range 23, and the compression spring 12 initiates the snap process.But since the compression spring 12 never totally relaxes, a minimum contact force, which corresponds to the region between the points 26 and 32, is always maintained even when the force exerted by the snap spring becomes zero at 27. In the case of the countermovement, starting from the point 34, there is a similar sequence of events, but here the contact bridge 11 has the opening function and the contact bridge 10 has the closing function.

The section from point 33 to point 27 corresponds to the stroke of the external actuating member 2 from the rest position up to the position in which the supports 3, 7, 8 and 31 lie in one line. The section from point 27 to point 34 is the possible overrun of the external actuating member 2. The section from point 35 to point 36 corresponds to the possible opening between the seatings 15 and 16.

In order to keep the influence of the unavoidable spring tolerances as small as possible and thus to be able to adjust the snap point more precisely with respect to the stroke of the actuating member 2, we provide, as a preferred feature of the invention, for the snap springs to be adjustable. Assuming that the snap switch has a striker 6 whch has a head for engagement of the snap springs (4,5), the striker head can be subdivided into two elastically deformable parts by a slit 28 running in the direction of the movement of the striker 6 and at right angles to the plane in which the greatest area is definable (in use of the switch) between the end positions of the snap springs (4,5), means being provided to maintain adjustably a given degree of openness of the slit28.

As shown in Figure 3, the aperture of the slit 28 in the striker head is advantageously adjusted by providing for it to terminate in a conical bore 29 into which a similarly conical grub screw 30 with a self-tapping screw-thread is driven to a depth sufficient to maintain the said degree of openness of the slit 28.

These measures have the effect that the snap springs 4 and 5 can be more or less strongly pre-tensioned and thereby suited to the characteristic of the compression spring 12.

Figure 3 is a section made along the centre line in Figure 1. It shows how the slit 28 in the head of the striker 6 is enlarged into the conical bore 29, and how the conical grub screw 30 with a self-tapping screw-thread is introduced into the bore 29, to enable the width of the slit 28 to be adjusted more or less widely. By this means one can adjust the horizontal interval of the supports 7 and 8, and hence the interval with reference to the external actuating member 2, which determines the pre-tension of the snap springs 4 and 5.

Claims (5)

1. Snap or quick-action switch with double inters ruption and with at least one contact bridge, the latter being actuated by an external actuating mem berthrough the intermediary of snap springs together with a striker, and being mounted in a recess of the striker under the pressure of a helical or helicoidal compression spring, the latter being disposed with its axis extending along the direction of movement of the striker, and the movements of the actuating member and striker, in use of the switch, being in coaligned but opposite directions, characterised in that: the compression spring (12) is of such dimensions that the force which it exerts, in the direction of the stroke of the actuating member (2), is greater than the force component exerted against it by the snap springs (4, 5) in the region of the snap point, but is less than the force component exerted against it by the snap springs (4, 5) towards the end positions of the actuating member (2); the compression spring (12) exhibits a flatter characteristic than the snap springs (4, 5); the supports (13, 14) of the compression spring (12) have seatings (15,16) which face one another in the direction of the helicoidal axis, these seatings having surfaces suitable for mutual abutment; and said seatings (15, 16) leave a free space open between themselves in the event of relaxation of the helicoidal compression spring (12), this relaxation being limited by the length of the recess (9) in the striker (6).

2. Snap switchaccording to claim 1, characterised in that the snap springs (4, 5) are adjustable.

3. Snap switch according to claim 2, whose striker has a head for engagement of the snap springs, characterised in that the striker head is subdivided into two elastically deformable parts by a slit (28) running in the direction of the movement of the striker (6) and at right angles to the plane in which the greatest area is definable (in use of the switch) between the end positions of the snap springs (4, 5), means being provided to maintain adjustably a given degree of openness of the slit (28).

4. Snap switch according to claim 3, characterised in that the slit (28) in the striker head terminates in a conical bore (29) into which a similarly conical grub screw (30) with a self-tapping screw-thread is driven to a depth sufficient to maintain the said degree of openness of the slit (28).

5. Snap switch according to claim 1, substantially as described with reference to Figures 1 and 3 of the accompanying drawings.