Snap-action electric switches

Abstract

 A snap-action electric switch providing a sequence of three stable switching operations comprises a housing (2) containing a switching mechanism (4) having a pair of contact elements (24,26) each resiliently biased into a normal rest position, and an operating button (16) depression of which first of all causes snap-acting movement of a first of the contact elements (24) to a displaced position and then, on continued depression of the operating button (16), causes snap-acting movement of the other contact element (26) to a displaced position.

Description

[0001] This invention relates to snap-action electric switches and more particularly to such switches incorpor­ating snap-acting mechanisms of the over-center type.

[0002] Snap-action switches commonly comprise a housing in which is mounted a snap-acting mechanism movable, by means of an operating member projecting from the housing, between a rest position and a displaced position to make or break associated electric-circuits.

[0003] A first known switch of this type incorporates a single contact arm carrying a contact member adapted for snap-acting movement, under the influence of resilient means in the form of a coil spring, between a pair of fixed terminal members to make or break circuits associated with said terminal members.

[0004] A further known switch of this type incorporates a pair of contact arms each carrying a contact member adapted for simultaneous snap-acting movement, under the influence of common resilient means in the form of a coil spring, between an associated pair of fixed terminal members to make or break electrical circuits associated with said terminal members.

[0005] However, in both cases, the switches only have two stable positions one either side of snap-action, and consequently, where switching sequences requiring more than two stable positions are concerned, it is necessary to use two or more of the above-detailed switches in combination, for example one on the other or side-by-­side.

[0006] Clearly the use of two or more switches, as compared with one, involves extra space, weight and expense.

[0007] It would be desirable to be able to provide a snap-­action electric switch having more than two stable positions associated therewith and such as to provide a corresponding number of different electrical circuits switchable thereby.

[0008] According to the present invention there is provided a snap-action electric switch comprising a housing in which is mounted a snap-acting switching mechanism, said switching mechanism including a pair of contact elements each resiliently biased into a normal rest position, and an operating button depression of which causes snap-­acting movement of a first contact element from its normal position to a displaced position, continued depression of said operating button subsequently causing snap-acting movement of the other contact element from its normal position to a displaced position.

[0009] Preferably the contact elements are each movable between an associated pair of terminal members, said contact elements, in their normal rest positions, engaging a first terminal member of the associated pair and said contact elements, in their displaced positions, engaging the other terminal member of the associated pair.

[0010] Conveniently, the other terminal member associated with one contact element is electrically connected to the first terminal member associated with the other contact element.

[0011] Although the switching mechanism may be of the snap-­acting leaf spring type, a preferred mechanism includes a pair of contact arms one to each side of an intermediate abutment member and a coil spring reacting between the two contact arms to urge one end of each contact arm into pivotal engagement with an associated region of the abutment member, the other end of each contact arm being located between the terminal members of the associated pair of terminal members, the arrangement being such that, on depression of the operating button, the abutment member is moved to alter the positions of the regions of engage­ment of the contact arms with the abutment member relative to the line of action of the spring whereby the first contact arm snaps over from its normal position to its displaced position and subsequently the other contact arm snaps over from its normal position to its displaced position.

[0012] In a preferred arrangement, the regions of engagement of the two contact arms with the intermediate abutment member are axially displaced from one another along the line of movement of the abutment member whereby snap-­action of the other contact arm follows snap-action of the first contact arm.

[0013] In one embodiment of the invention, the line of movement of the operating button comprises a continuation of the line of movement of the abutment member.

[0014] In an alternative embodiment of the invention, the line of movement of the operating button is parallel with but spaced from the line of movement of the abutment member, in which case a lever may react between the operating button and the abutment member, said lever being pivotal about one end thereof, the operating button engaging with the lever at or adjacent the other end thereof and the abutment member engaging an inter­mediate region of said lever, depression of the operating button pivoting said lever about the one end thereof whereby the abutment member is moved by said intermediate region of the lever.

[0015] Such an arrangement is convenient when it is desired to provide, for a given degree of movement of the abutment member, a greater degree of movement of the operating button.

[0016] Conveniently the regions of engagement of the contact arms with the abutment member comprise notches formed in the opposed faces of said abutment member and with which the one ends of the contact arms make bearing engagement.

[0017] Preferably depression of the operating button and consequent movement of the abutment member is effected against resilient means, conveniently a coil spring, biasing the mechanism into a normal rest position.

[0018] By way of example only, an embodiment of the invention will now be described in greater detail with reference to the accompanying drawings of which:

Fig. 1 is a perspective view of a switch according to the invention with a side of the housing removed;

Fig. 2 shows the switching mechanism of the switch of Fig. 1 in more detail;

Figs. 3a, b and c show the switching mechanism of Fig. 2 in each of its three stable positions;

Figs. 4a, b and c show the electrical connections effected by the switching mechanism in the positions of Figs. 3a, b and c respectively, and

Fig. 5 shows a alternative switch according to the invention, partly in vertical section, with a side of the housing removed.

[0019] Referring to Figs. 1 and 2, the illustrated switch comprises a housing 2 containing a switching mechanism indicated generally at 4 and from which housing project four electrical terminals 6,8,10 and 12, the terminals 6 and 8 constituting a first pair and the terminals 10 and 12 constituting a second pair.

[0020] The switching mechanism 4 includes a central, metal plate or abutment member 14 to the upper end of which is force-fitted an operating button 16 slidably mounted in, to project from, the upper wall of the housing 2. A coiled compression spring 18 reacts between the bottom wall of the housing 2 and the lower end of the plate 14 to urge said plate 14 and button 16 to a normal rest position as shown in Figs. 1 and 2. It will be appreciated that depression of the operating button 16 moves the plate 14 downwardly in the housing 2 against the bias of the spring 18.

[0021] The switching mechanism further includes a pair of metal contact arms 20,22, one either side of the plate 14, each arm carrying at its outer end an associated contact button 24,26, respectively. A coil extension spring 28 extends between the two contact arms, the ends of the spring 28 being hooked into apertures in the associated arms 20 and 22 whereby the inner end of each arm 20,22 is urged into pivotal bearing contact with the associated side face of the plate 14.

[0022] More particularly, each side face of the plate is formed with a notch adapted to receive therein the inner end of the associated contact arm 20 or 22, the notch receiving the contact arm 20 being slightly lower down in the plate 14 - i.e. further from the button 16 - than that receiving the contact arm 22 for reasons which will become apparent.

[0023] In the normal rest position of the switching mechanism 4 shown in Figs. 1,2 and 3a, the location of the notches in the plate 4 and the resilience of the spring 28 determine that the contact buttons 24,26 of the arms 20,22 are urged into engagement with the termin­als 8,10 respectively.

[0024] Initial depression of the operating button 16 results in downward movement of the plate 14 and, conse­quently, the inner ends of the contact arms 20,22 by virtue of their enforced bearing engagement with the notches in the plate 14 until the lowermost notch, and therefore the inner end of the contact arm 20, is moved to a position just below the level of the centreline of the spring 28. At this instant, the over-centring movement of the contact arm 20 relative to the spring 28 results in upward snap-action of the contact arm 20 about its pivotal connection on the plate 14 such that the contact button 24 breaks from the terminal 8 and makes contact with the terminal 6. This position of the mechanism is shown in Fig. 3b.

[0025] On continued depression of the operating button 16 and therefore the plate 14, the other notch, together with the inner end of the contact arm 22, is moved to a level below the centreline of the spring 28 whereby the contact arm 22 is caused to snap over to a displaced position in which the contact button thereon breaks from the terminal 10 and makes with the terminal 12. This position of the mechanism is shown in Fig. 3c.

[0026] It will thus be appreciated that the described switch has three stable positions determined by the operating button being in a normal rest position, a first displaced position and a further displaced position.

[0027] The plate 14 acts as an electrical shorting bar between the contact buttons 24 and 26, whereby said buttons are in continuous electrical connection one with the other.

[0028] It will be appreciated that, in the above-described arrangement, the plate 14 moves with, under the direct influence of, the operating button 16. From the practical point of view, and in order to ensure precision of operation, the distance between the notches in the plate 14 should be quite small. Consequently, the movement of the operating button 16 associated with movement of the switching mechanism 4 between its first displaced position and its further displaced position is also quite small.

[0029] Fig. 5 illustrates a switch which maintains the small movement of the plate 14 for precision purposes but which allows a greater degree of movement of the operating button 16 associated with said small movement of the plate 14.

[0030] Referring to Fig. 5, in which components equivalent to those of the switch of Figs. 1 and 2 are similarly referenced, the switch further comprises a lever 30 one end of which is pivotally mounted at 32 to the housing 2. The other end of the lever 30 is located beneath, for pivotal movement by, the operating button 16, which button 16 is provided with a resilient cowl 34 for sealing purposes.

[0031] A plastic anti-wear cap 36 is located over the upper end of the plate 14, said cap 36 being urged by the spring 18 into engagement with an intermediate region of the lever 30, the other end of said lever, in turn, being urged upwardly to locate the operating button 16 in its uppermost position.

[0032] On depression of the operating button 16, the lever 30 is pivoted in an anti-clockwise direction as viewed in the drawing about the pivot 32 whereby the plate 14 is depressed by said movement of the lever 30, the presence of the cap 36 preventing undue wear of the region of contact of the lever 30 with the plate 14. It will be appreciated that the travel of the operating button 16 associated with the necessary travel of the plate 14 to move the switching mechanism to its first and further displaced positions is greater than that of the operating button of Figs. 1 and 2, thus effectively magnifying the sequence of switching actions. Other arrangements, either internally or externally of the housing 2, may be provided to achieve this greater travel of the operating button 16 between switch-overs.

[0033] The switches of the invention have many applications wherever a sequence of three stable switching operations is required. It is envisaged that prime applications of the switch will be in the actuation of a central door-­locking mechanism for motor vehicles, and in a warning device associated with advising of the condition of the doors of motor vehicles. In the latter case, the device may be so arranged that a first condition of the switch is associated with the door being fully latched, no signal being transmitted by the device. With the door closed but not fully latched - i.e. ajar - the device will transmit a warning signal of that condition. With the door fully open, the device will serve to switch on the interior light of the vehicle. Other uses, such as providing a warning of over-travel or excessive movement of an associated device, said device effecting the depression of the operating button 16, will be apparent to those skilled in the art.

[0034] For example, where it is desired to switch between three different outputs with a central position in which no electrical connection is effected, the terminals 6 and 10 are permanently connected to each other by a shorting lead 29 shown in Fig. 1.

[0035] In the rest position of the switch shown in Figs. 1,2 and 4a, with the contact buttons 24,26 engaging the terminals 8 and 10 respectively, the terminals 6,8 and 10 are electrically connected while terminal 12 is dis­connected therefrom as shown in Fig. 4a.

[0036] In the first displaced position of the switch shown in Fig. 3b, the contact buttons 24,26 engage the terminals 6,10 respectively whereby the common terminals 6,10 are disconnected from terminals 8 and 12 which are themselves electrically isolated as shown in Fig. 4b. Thus the switch has a null position where no electrical connect­ions are effected.

[0037] In the further displaced position of the switch shown in Fig. 3c, the contact buttons 24,26 engage the terminals 6,12 respectively such that the common terminals 6,10 are electrically connected to the terminal 12, while terminal 8 is disconnected therefrom as shown in Fig. 4c.

Claims

1. A snap-action electric switch comprising a housing (2) in which is mounted a snap-acting switching mechanism (4), said switching mechanism (4) including a pair of contact elements (24,26) each resiliently biased into a normal rest position, and an operating button (16), characterised in that depression of the operating button (16) causes snap-acting movement of a first contact element (24) from its normal position to a displaced position, continued depression of said operating button (16) subsequently causing snap-acting movement of the other contact element (26) from its normal position to a displaced position.

2. A snap-action electric switch as claimed in claim 1 in which the contact elements (24,26) are each movable between an associated pair of terminal members (6,8 and 10,12), said contact elements (24,26), in their normal rest positions, engaging a first terminal member (8,10) of the associated pair, and said contact elements (24,26), in their displaced positions, engaging the other terminal member (6,12) of the associated pair.

3. A snap-action electric switch as claimed in claim 2 in which the other terminal member (6) associated with one contact element (24) is electrically connected to the first terminal member (10) associated with the other contact element (26).

4. A snap-action electric switch as claimed in claim 2 or claim 3 in which the switching mechanism (4) includes a pair of contact arms (20,22) one to each side of an intermediate abutment member (14) and a coil spring (28) reacting between the two contact arms (20,22) to urge one end of each contact arm (20,22) into pivotal engagement with an associated region of the abutment member (14), the other end (24,26) of each contact arm (20,22) being located between the terminal members (6,8 and 10,12) of the associated pair of terminal members, the arrangement being such that, on depression of the operat­ing button (16), the abutment member (14) is moved to alter the positions of the regions of engagement of the contact arms (20,22) with the abutment member (14) relative to the line of action of the spring (28) whereby the first contact arm (20) snaps over from its normal position to its displaced position and subsequently the other contact arm (22) snaps over from its normal position to its displaced position.

5. A snap-action electric switch as claim in claim 4 in which the regions of engagement of the two contact arms (20,22) with the intermediate abutment member (14) are axially displaced from one another along the line of movement of the abutment member (14) whereby snap-action of the other contact arm (22) follows snap-action of the first contact arm (20).

6. A snap-action electric switch as claimed in claim 5 in which the line of movement of the operating button (16) comprises a continuation of the line of move­ment of the abutment member (14).

7. A snap-action electric switch as claimed in claim 5 in which the line of movement of the operating button (16) is parallel with but spaced from the line of movement of the abutment member (14).

8. A snap-action electric switch as claimed in claim 7 and comprising a lever (30) reacting between the operating button (16) and the abutment member (14), and pivotal about one end thereof, the operating button (16) engaging with the lever at or adjacent the other end thereof, and the abutment member (14) engaging an intermediate region of said lever (30), depression of the operating button (16) pivoting said lever (30) about the one end thereof whereby the abutment member (14) is moved by said intermediate region of the lever.

9. A snap-action switch as claimed in any one of claims 5 to 8 in which the regions of engagement of the contact arms (20,22) with the abutment member (14) comprise notches formed in the opposed faces of said abutment member (14) and with which the one ends of the contact arms (20,22) make bearing engagement.

10. A snap-action switch as claimed in any one of claims 4 to 9 in which depression of the operating button (16) and consequent movement of the abutment member (14) is effected against resilient means (18) biasing the mechanism (4) into a normal rest position.

Drawing