GB2246664A - Snap action switch - Google Patents

Abstract

In an electrical snap action retractive switch including snap springs 14 arranged between an actuator 12 and a contact carrier 13 which carries a contact 22 cooperable with a fixed contact on an external terminal, the depth of the switch is reduced by positioning the contacts and the springs 15 for returning the actuator 12 to its unactuated state away from the line of action of the actuator 12. This reduction in depth has particular advantages for mounting the switch in substantially flat panels such as for control of electrically operated doors. <IMAGE>

Description

Snap Action Switch The present invention relates to snap action switches and in particular to the provision of such a switch which has a relatively small depth.

It is known in the prior art to provide electrical switches which use pre-tensioned snap springs to provide a positive action. These switches provide an actuator and a contact carrier which have snap springs arranged between them. When the actuator is depressed and passes a critical point for the snap springs, the springs force the contact carrier to move in the opposite direction to the movement of the actuator.

A release spring is provided on the actuator which is active, on release of the actuator, to return the actuator and contact carrier to their original positions. The contact carrier carries means for making and breaking connections between terminals which may be connected to external circuitry. With the contact carrier in one position, contact is made between one pair of terminals and when the carrier is in the second position, contact is made between a second pair of terminals. Thus applying and releasing force on the actuator causes the connections within the switch to change, and due to the snap springs there is a very positive movement for both making and breaking the contacts.

In this type of switch the release spring, snap spring arrangement and electric contact arrangement are all generally provided substantially on the central axis of the actuator, or at least substantially in one plane passing through this axis. These three parts of the switch are thus all provided along the line of action of the actuator and this causes the dimension of the switch assembly in this direction (the depth) to be relatively great.

Switches of this type are commonly mounted in a substantially flat panel, for instance, for control of an electrically operated door. In such an application it is advantageous to use a switch with minimum depth.

It is therefore an object of this invention to provide a snap action switch which has a relatively small size in the line of action of the actuator. This is achieved according to present invention by not positioning the three parts of the switch identified above substantially on the line of action of the actuator.

There is also a problem known in the prior art of the contacts welding together due to arcing between contacts when they are opened. One method of overcoming the effect of this is shown in GB-A-2020111. Here, some wiping action is generated between the contacts to facilitate opening the contacts in the case that they have become welded together. This is achieved by the mechanical construction of the switch and hence complexity is added to the design of the switch.

Therefore, according to a preferred embodiment of this invention, magnets are provided within the switch which cause no increase the overall depth of the assembly, but which function to minimize the time during which arcing occurs. This in turn minimizes the amount of welding which occurs between the contacts, and hence the problems of welding is overcome without introducing the above mentioned complexity into the mechanical design of the switch.

A further feature of the present invention is the provision of a mechanical link which may be inserted between switches and which provides simultaneously operating of a plurality of switches.

In general terms this invention provides an electrical snap switch comprising an actuator, a contact carrier and first and second resilient means, wherein said first resilient means is arranged between said actuator and said contact carrier whereby to provide a positive snap movement of said contact carrier between a first position and a second position upon movement of said actuator between a corresponding first position and a corresponding second position, wherein said second resilient means is operative on said actuator to return it to its first position in the absence of any external force, further comprising an external terminal electrically connected to an internal contact and a further contact attached to the contact carrier wherein the contacts are arranged whereby when the contact carrier is in one of its first or second position said two contacts are in electrical connection and when the contact carrier is in the other of its first or second positions the contacts are not in electrical connection, wherein the second resilient means and the contacts are provided off the line of action of the actuator.

A preferred embodiment of a switch according to the present invention will be described by way of example with reference to the accompanying drawings inwhich: Figure 1 is a plan view of the preferred embodiment; Figure 2 is a sectional view along line II-II of figure 1; Figure 3 is a sectional view along line III III of figure 1; Figure 4 is an enlarged portion of figure 3 which is illustrative of the actionof the magnet; and Figure 5 is a simplified sectional view along line II-II of figure 1 illustrating the mechanical link.

Throughout the figures, the same numeral is used to identify the same part.

Figure 1 shows a plan view of a preferred embodiment of this invention. It can be seen that the switch comprises a main body, an actuator 12 and terminals 1, 2, 3, 4 for making external electrical connections. The main body has a generally cruciform shape with arms 5, 6, 7, 8. The internal constructions of this switch is symmetrical about the line II-II and the switch is operative such that when un-actuated the terminals 1, 2 are connected together and when the switch is actuated, the terminals 1, 2 are disconnected from each other and the terminals 3, 4 are connected together.

In this switch, the release spring, snap spring arrangement and electric contact arrangement are not all positioned substantially on the line of action of actuator 12. Instead, as will be explained in more detail below, the elements of the switch are arranged such that the mechanical operation of the switch occurs generally in the arms 5, 6 of the cruciform shown in figure 1 and the electrical operation occurs generally in the arms 7, 8. It is this arrangement which allows the considerable reduction in the depth of this snapswitch over the prior art.

The internal construction and operation of the switch of figure 1 is shown in figures 2 and 3. In addition to being symmetrical about the line II-II in figure 1, the internal construction is also symmetrical about the centre lines A and B in figures 2 and 3 respectively. In each of figures 2 and 3, the righthand half illustrates the switch un-actuated, and the left-hand half illustrates the switch actuated.

Referring to figure 2 it can be seen that the switch comprises a housing 10, 11, actuator 12, a contact carrier 13 with contact bridge 22, snap springs 14 and release springs 15. Snap springs 14 are mounted with one end in groove 16 in actuator 12 and the other end in groove 17 in contact carrier 13. Release springs 15 are active to apply a separating force between the actuator 12 and the lower part of the housing 11.

The construction and operation of the switch will be described in relation to the orientation shown in figures 2 and 3 although it is understood that the switch may work satisfactorily in any orientation.

It may be seen from figure 2 that there is a release spring 15 provided in each of arms 5 and 6.

These are therefore away from the line of action of actuator 12 (co-linear with centre line A). One end of each snap spring 14 is substantially on the line of action of actuator 12 and therefore if the release spring were to be positioned on this line of action, it would have to be positioned either above or below the snap spring arrangement. This would cause an increase in the overall depth of the switch.

However, because release springs 15 are positioned away from the line of action of actuator 12 they may be positioned generally on a level with the snap spring arrangement ie. the release and snap springs are at approximately the same height above the base of the switch, as illustrated in figure 2, and hence they cause no increase in the overall depth of the switch.

Referring to figure 3 it can be seen that the switch further comprises contact strips 18, 20 with contacts 18a, 20å, in addition to actuator 12, contact carrier 13, and-contact bridge 22 with contacts 22a, 22b. Contact strip 18 is arranged so as to electrically connect contact 18a to terminal 2, and contact strip 20 is arranged to electrically connect contact 20a to terminal 4. According to the preferred embodiment illustrated in figure 3, the switch further comprises magnet 23.

Figure 3 is a section along line III-III in figure 1 and is a section through arm 7 of the main body of the switch. There is an arrangement of contacts and contact strips connected to terminals 1 and 3 in arm 8 of the main body similar to that illustrated in figure 3. Contact bridge 22 extends substantially across the width of the switch, ie into both arm 7 and 8, and hence provides an electrical connection path between these two arms.

Thus while the release springs 15 are provided in arms 5 and 6 of the main body, the electrical contact arrangements are positioned in arms 7 and 8. The electrical contact arrangements are therefore also positioned away from the line of action of actuator 12, and are positioned generally on a level with the snap spring arrangement and release springs 14. Hence the electrical contacts do not cause any increase in the overall depth of the switch.

The operation of the switch will now be described in conjunction with figures 2 and 3.

The right-hand half of figure 2 shows the switch in its un-actuated state. Spring 15 is extended and pushes actuator 12 upwards such that it rests against the inside of the upper part of the housing 10.

Snap spring 14 exerts a force at grooves 16 and 17 as indicated by arrows P which forces contact carrier 13 downwards with respect to actuator 12. Contact carrier 13 is thus held in its lower un-actuated position.

In order to actuate the switch a force is applied to actuator 12 as indicated by arrow F. When this force is greater then the upward force applied to the actuator 12 by the release spring 15 and the snap spring 14 as indicated by arrow P, actuator 12 moves in the direction of arrow F. Initially contact carrier 13 remains in its un-actuated position, until a critical point occurs when the groove 16 is level with the groove 17.

When actuator 12 moves beyond this critical position such that groove 16 is below groove 17 the action of snap spring 14 changes such that is exerts a force which forces contact carrier 13 upwards with respect to actuator 12. This causes the switch to snap into its actuated position shown in the left-hand half of figure 2.

In order for the switch to remain in the actuated state, a force as indicated at F must continue to be applied to overcome the force of spring 15 to hold actuator 12 in its actuated state. Snap spring 14 exerts a force a grooves 16 an 17 as indicated by arrows Q which holds contact carrier 13 in its upper actuated position.

When the force indicated by arrow F is removed, the upwards force on actuator 12 due to release spring 15 is greater than the downwards force due to snap spring 14 and therefore actuator 12 moves upwards.

When the critical point described above is passed, the snap springs become active to snap the switch into its un-actuated state as shown in the right-hand half of figure 2.

When the switch is in its un-actuated state as illustrated in the right-hand half of figure 3, the contact carrier 13 and contact bridge 22 are in the lower position. Contact 22a is in contact with contact 18a and hence electrical connection is made between terminal 2 and contact bridge 22. Due to the similar construction within arm 8, electrical connection is made, in this un-actuated state, between terminal 1 and terminal 2.

When a force is applied to actuator 12 and the switch moves to its actuated state as described above in relation to figure 2, contact carrier 13 and contact bridge 22 move to their upper position as illustrated in the left-hand half of figure 3. Contact 22a is not in contact with 18a, and hence terminal 1 is not connected to terminal 1 is not connected to terminal 2. Contact 22b is in contact with contact 20a and hence electrical connection is made between terminal 4 and contact bridge 22. Due to the similar construction in arm 8, electrical connection is made in this actuated state, between terminal 3 and terminal 3 and terminal 4.

The construction of the switch as described above allows the switch housing to have a substantially smaller depth than the prior art switches. This is achieved by mounting aapair of release springs 15 in the arms 5 and 6 which act to return the actuator 12 to the un-actuated position, and by positioning the electrical contacts in the arms 7 and 8. In the prior art, either one of these elements was commonly positioned substantially on the central axis of the actuator and this led to the overall assembly having a greater depth than the present invention.

-Expressed in different terms in conjunction with figure 1, the reduction in depth is achieved as a result of positioning the snap springs and the release springs substantially on line II-II, and the terminals and contact arrangements substantially on lines parallel to Il-Il. As can be seen, terminals 2 and 4 and the contact in arm 7 all lie substantially on line III-III, and terminals 1 and 3 and the contacts in arm 8 all lie substantially on another line parallel to II-II.

As stated above, the snap springs and release springs are all positioned substantially on line II-II, and the release springs are further advantageously positioned at a greater distance from the line of action of the actuator than the snap springs.

A further advantage of the arrangement of this invention is that magnet 23 may be conveniently mounted without the need to increase the overall depth. The function of magnet 23 will be described with reference to figure 4.

Figure 4 shows the centre portion of figure 3 enlarged, in the un-actuated state, ie contact carrier 13 and contact bridge 22 are in the lower position. The north and south poles of magnet 23 are indicated by N and S respectively, and lines representative of the magnetic field of magnet 23 are also shown. The function of magnet 23 is to "blow-out" any arc which forms between the contacts when contact is broken.

When the actuator 12 is released and the switch snaps back to its un-actuated state as shown in figure 4 an arc may form between contact 20a and 22b.

It is preferable that any arc which does form lasts for as short a period as possible. Arcing causes welding between the contacts, causing them to stick, and therefore reducing the length of time that the arc is present reduces the amount of welding which occurs.

In such an arc, the current and the current carrying particles move substantially directly between the contact 20a and 22b. Thus they move in a direction which lies substantially in the plane of figure 4, and perpendicular to the lines of the magnetic field of magnet 23. According to well known physical laws this causes a force to be exerted on the current carrying particles which causes them to be deflected in a direction perpendicular to the plane of figure 4. This increases the effective resistance of the gap in which the arc is formed and hence minimizes the time for which the arc lasts.

One of the advantages of the arrangement of the present invention is that it allows the mounting of the magnet in the housing without any increase in the overall depth of the switch being necessary. Further, the magnet may be mounted close to the contacts where any arc will form, thus increasing the efficiency of its "blow-out" function.

In the prior art the effects of welding were reduced by provided some degree of mechanical sliding between the contacts. The present invention minimizes the effects of welding by the above described provision of a magnet which acts to reduce the arcing time without any need for a complicated mechanical arrangement.

A plurality of switches according to the present invention may be stacked and operated simultaneously as shown in figure 5. Figure 5 shows a similar section to that shown in figure 2, but the detail showing the contact carrier 13 and snap springs 14 has been removed. The switch is in all respects identical to that described in relation to figure 2, and there is further added mechanical line 24.

Mechanical line 24 abuts the lower surface of actuator 12 as indicated by numeral 25. Thus, when actuator 12 is pushed downwards to actuate the switch, link 24 will also move downwards. The underside of link 24 abuts the top of a second identical switch, the actuator of which is indicated by numeral 12a, and hence force will be transmitted to actuator 12a to actuate the second switch simultaneously with the first.

It is clear that more than two switches may be mounted as described above, with mechanical links 24 between them, and all acting simultaneously. The limiting factor in the number of switches which may be operated in this way is the magnitude of the operating force on the top switch, and the strength of the actuators 12 to transmit the force.

Claims (9)

CLAIMS:

1. An electrical snap switch comprising an actuator, a contact carrier and first and second resilient means, wherein said first resilient means is arranged between said actuator and said contact carrier whereby-to provide a positive snap movement of said contact carrier between a first position and a second position upon movement of said actuator between a corresponding first position and a corresponding second position, wherein said second resilient means is operative on said actuator to return it to its first position in the absence of any external force, further comprising an external terminal electrically connected to an internal contact and a further contact attached to the contact carrier wherein the contacts are arranged whereby when the contact carrier is in one of its first or second position said two contacts are in electrical connection and when the contact carrier is in the other of its first'or second positions the contacts are not in electrical connection, wherein the second resilient means and the contacts are provided off the line of action of the actuator.

2. An electrical snap switch according to claim 1 wherein said first resilient means comprises a pair of pre-tensioned snap springs.

3. An electrical snap switch according to claim 1 or 2 wherein said second resilient means comprises a pair of helical compression springs.

4. An electrical snap switch according to claim 1, 2 or 3 comprising at least one further external terminal electrically connected to an internal contact and wherein contacts are so arranged on the contact carrier that two of the external terminals are in electrical connection when the contact carrier is in one of its first or second positions and said two terminals are not in electrical connection when the contact carrier is in the other of its first or second positions.

5. An electrical snap switch according to claim 4 comprising two pairs of external terminals wherein when the contact carrier is in its first position a first pair of external terminals are in electrical connection and when the contact carrier is in its second position a second pair of external terminals are in electrical connection, and wherein the components of the switch are so arranged that the first and second resilient means lie substantially on a first straight line which passes on through the actuator, a first one of each pair of external terminals and their associated internal contacts lie substantially on a second straight line and the second of each pair of external terminals and their associated internal contacts lie substantially on a third straight line, and said three straight lines are parallel to each other.

6. An electrical snap switch according to any preceding claim which has a body which is substantially cruciform and wherein said second resilient means is provided in one pair of opposite arms of said cruciform, and the contacts are provided in the other pair of opposite arms of said cruciform.

7. An electrical snap switch according to any preceding claim and further comprising at least one magnet adjacent said contacts having its poles arranged whereby the magnetic field generated is operative, in the presence of an arc between contacts,-to deflect said arc in order to minimize its duration.

8. A switching arrangement comprising a plurality of snap switches each according to any preceding claim and a plurality of linking members, each linking member being arranged to transmit force between the actuator of one switch and the actuator of another switch whereby all of the plurality of switches may be operated simultaneously.

9. An electrical snap switch as hereinbefore described with reference to the accompanying drawings.