GB2139814A

GB2139814A - Electrical switch

Info

Publication number: GB2139814A
Application number: GB08313357A
Authority: GB
Inventors: Leon Wachnianin
Original assignee: REARSBY AUTOMOTIVE Ltd
Current assignee: REARSBY AUTOMOTIVE Ltd
Priority date: 1983-05-12
Filing date: 1983-05-12
Publication date: 1984-11-14
Also published as: ES287026Y; DE3417554C2; GB8313357D0; ES287026U; DE3417554A1; GB2139814B

Abstract

A miniature electrical slide action switch is suitable for motor vehicles, for example as a hand brake warning switch. A slide member 4 carries an electrical contact member 16 which passes into a longitudinal slot 24 in the slide member 4 through a slot 22 in an end wall thereof. The portion of the contact member extending outwardly of the slide member provides a seat for a return spring 10 and is provided with a fulcrum edge 20 which defines a pivotal axis for the contact member 16. The portion of the contact member 16 located in the longitudinal slot 24 is biassed radially outwardly against a side wall of a casing 2, in which are exposed one or more first electrical terminal conductors 28. Axial movement of the contact member 16 relative to the slide member 4 is prevented by the fact that the return bias for the slide member 4 is transmitted wholly through the contact member 16. <IMAGE>

Description

SPECIFICATION Electrical switch The invention relates to electrical slide-action switches, and particularly but not exclusively to minaturized switches suitable for motor vehicles. Ail such switches comprise a slide member which extends axially from a casing and which can be depressed into the casing against the bias of a return spring to effect switch actuation. Such switches exist and are used, for example, to actuate warning lights such as handbrakewarning lights in motor vehicles, to indicate when vehicle handbrakes are engaged.

Current designs of such slide-action switches employ free-floating electrical contact members which bridge two electrical contacts to complete a circuit in one switching position, and which break that circuit in another switching position. Such switches are not as reliable as they might otherwise be, as the free-floating nature of the electrical contact members inevitably permits some limited movement of the contact members axially of their slide members, which in turn introduces a risk that the contact members twist and jam in the recess in the slide members in which they are mounted. Also, the switches are essentially on-off switches and there is very little potential for flexibility of design.

There is a clear need for a slide-action switch which is reliable in use, which avoids the problem of jamming of the contact members, which is simple to assemble and economical to manufacture and which permits a range of different terminal configuration and other design flexibilities from uniform body mouldings.These and other advantages are possible according to the invention, which provides a minature electrical slide-action switch in which a slide member extends axially from a casing and can be depressed in to the casing against the resilient bias of a return spring to effect switch actuation, wherein an electrically conductive contact member carried by the slide member comprises a fulcrum edge seated on an end surface of the slide member under the bias of the return spring and a cantilever portion extending through an end slot the slide member into a longitudinal recess in the slide member, means being provided for urging an electrical contact zone of the cantilever portion of the contact member transversely of the recess against a side wall of the casing in which are exposed one or more first electric terminal conductors.

Because the contact member of the switch of the invention is a lever that is urged against the end wall of the slide member by the return spring, there is no permittent axial movement of the contact member relative to the slide member. The edge defining the pivotal axis of the contact member also maintains the contact member in axial alignment with the slide member (except for its permitted movement) so that it is possible to maintain at all times a clearance between the sides and end of the contact member and the walls of the recess in the slide member. Thus there is no likelihood of the contact member becoming twisted and jamming, as in the prior art switches which utilize free-floating contact members.

Because the return spring bears directly onto the contact member, an electrical path is formed from the first electrical terminal, via the contact member and return spring to a second electrical terminal which provides a reaction seat for the return spring.

This enables the first and second terminals to be spaced apart far more easiiy than in the prior art switches which rely on the contact member bridging two electric contacts to complete the electric circuit.

Also it makes it very simple to modify the switch design from a simple ON/OFF switch, with one 'first' terminal to a two-way switch which has two 'first' terminals axially displaced one from the other.

Preferably the first terminal is a simple electrical 'spade' contact male member which comprises an anchorage portion receivable as a snap-fit in a transverse slot in the casing, and a spade contact portion extending therefrom. Advantageously the transverse slot is symmetrical so that the contact member can be inserted with the contact portion extending from either side of the casing.

Preferably the second terminal is another electrical 'spade' contact male member which comprises an anchorage portion receivable as a snap-fit in a transverse slot in an end of the casing to provide the reaction seat for the return spring, and a spade contact portion. The two portions may be aligned so that the spade contact portion extends perpendicularly to the axis of the casing, or they may be mutually angled, for example perpendicular. In the latter case the spade contact portion may extend longitudinally outwardly fron the end of the casing or it may extend over the top of the casing for electrical contact with an anchorage strap straddling the casing all these different terminal configurations are possible, however, using the same mouldings for the casing and slide member.

The means biassing the contact portion of the contact member laterally outwardly of the recess may be a spring between the contact member and the base of the recess. For example the spring may be a coiled compression spring one end of which engages a nose portion of the contact member facing the base of the recess, and the other end of which engages locating means such as a locating well in the recess. The invention provides an interesting and novel method of assembly of such a switch. The recess in the slide member should be of a size freely to receive the coiled compression spring when the spring is laid longitudinally therein. Insertion of the contact member, nose portion first, through the end slot causes the nose portion to pick up the end of the coiled spring and lift the spring to its operative position transversely of the slide member.

An alternative embodiment of the invention utilizes as the means biasing the contact member laterally outwardly of the recess, the return spring itself. By offsetting the fulcrum edge of the contact member from a line of engagement between the contact member and spring, the axial bias of the return spring on the contact member can impart sufficient angular moment to bring the contact portion of the contact member into good electrical contact with the wall of the casing in which the first terminal or terminals is or are exposed.

Drawings Figure 1 is an axial section through a first embodiment of a switch according to the invention; Figure 2 is a plan view from above of the switch of Figure 1; Figures 3 and 4 are end views, in the directions III and IV respectively, of the switch of Figure 1; Figure 5 is a perspective view of the contact member of the switch of Figure 1; Figure 6 is an axial section through the contact member and slide member of Figure 1, illustrating the method of assembly; Figure 7is an axial section through a second embodiment of a switch according to the invention; and Figure 8 is a perspective view of the contact member of the switch of Figure 7.

Referring first to the embodiment of Figures 1 to 6, the switch comprises a casing 2 in which is axially slidable a plunger or slide member 4. The plunger 4 is received in the casing as a snap-fit, the casing being deformed during insertion by an inclined cam surface of a detent lug 6 of the plunger 4, and springing back into its natural shape when the detent lug 6 is received wholly within a slot 8 in the casing 2.

The plunger 4 is biassed to the position illustrated in Figure 1 underthe influence of a return spring 10 one end of which is seated on a reaction surface of a terminal member 12, and the other end of which engages a cross piece 14 of a rockable contact member 16 the shape of which is more clearly apparent from Figure 5. A tail portion 18 of the contact member 16 extends partially into the spring 10, acting as spring retainer.

An edge surface 20 of the contact member 16 engages a left-hand end surface of the plunger 4, to serve as a fulcrum edge about which the contact member can rock. If desired, this edge 20 can be shaped as a knife edge or a rounded edge to improve the freedom of the contact member 16 to rock.

The major part of the contact member 16 extends through an end slot 22 in the plunger 4 as a cantilever portion located in a longitudinal recess 24 in the plunger. At a forward end of the contact member 16, that is the end remote from the return spring 10, the contact member is bent downwardly to present a rounded electrical contact zone 26 which is shown in Figure 1 as being in electrical contact with a first terminal 28, and a spring retainer nose portion 30 which extends laterally of the longitudinal recess 24. The spring retainer nose portion 30 is engaged by one end of a coiled compression spring 32 the other end of which is received in a well 34 in the plunger 4. The spring 32 urges the electrical contact zone 26 transversely of the recess against either the top inside wall of the casing or the first terminal 28, depending on the axial position of the plunger 4.

In use, when the plunger 4 is in the position shown in Figure 1, the switch if ON, with an electrically conducted path being formed from the first terminal 28 through the contact member 16 and the return spring 10 to the second terminal 12. Depression of the plunger 4 in the direction of the arrow III of Figure 1 causes the electrical contact zone 26 of the contact member 16 to move away from the first terminal 28 and into abutment with the top side wall of the casing 2, so that the switch assumes the OFF condition.

The flexibility of the design can be appreciated by a comparison of Figures 2 to 4. A metal support strap 36 is placed around the casing 2 to secure the switch to, for example, a motor vehicle body. The first terminal 28 comprises a spade contact portion 29 extending laterally from the casing 2, and the terminal portion which provides the anchorage of the terminal in the casing. The terminal is retained by an out-turned detent lug 38 of conventional form.

The same terminal 28 could have been inserted into its slot in the casing 2 from the right-hand side of Figure 2, so that its spade contact porition would have assumed the position 29' shown in phantom lines in Figure 2. Thus with exactly the same components the switch could have had its first terminal 28 accessible from either the right-hand side or the left-hand side, which is of importance in the motor vehicle industry where the design of left-hand and right-hand drive vehicles makes the mirror imaging of components highly desirable.

The second terminal 12 is shown in Figures 2 to 4 as comprising an integral spade contact portion 13 lying generally perpendiculary to the anchorage portion of the terminal. The spade contact portion 13 can be positioned to lie over the top of the casing 2, as shown in solid lines in Figures 1 and 2, or it can be turned to the position shown as 13' so that it extends longitudinally from the end of the casing. In the former position it is in electrical contact with the anchorage strap 36 which provides an electrical path to earth. In the latter position the switch becomes a two-terminal switch which is isolated from earth.

This can be important in some motor vehicles, especially those which employ microprocessor controls, and it is of particular advantage that the switch of the invention enables identical components to be assembled in either of two alternative ways, to form either the single terminal or the two terminal options.

It will be appreciated that the switch could just as easily have been designed as a two-position switch rather than a simple ON/OFF switch, merely by the provision of more than one first terminal 28 axially displaced one from the other along the casing 2.

Figurre 6 illustrates the assembly of the switch of Figures 1 to 5, and in particular the manner in which the spring 32 is mounted between the nose 30 of the contact member 16 and the well 34 of the recess 24.

The recess 24 is of a size to receive the spring 32 which can lie longitudinally of the recess 24 when the spring is relaxed as shown in Figure 6. When the nose 30 of the contact member 16 is inserted through the end slot 22 in the plunger 4 it automatically engages the spring 32. By a combination of rotary movement in the direction of the arrow A and sliding movement in the general direction of the arrow B, the contact member 16 is fed through the slot 22 and raises the spring 32 from the horizontal position of Figure 6 to the vertical position of Figure 1. Light finger pressure on the curved portion 26 of the contact member 16 is then all that is necessary to maintain the spring 32 compressed, while the plunger 4 is inserted into the casing 2 in the direction of the arrow Ill of Figure 1.

Figures 7 and 8 show an alternative embodiment of the invention, the same parts as those of Figure 1 being indicated by identical reference numerals. The embodiment of Figure 7 differs from that of Figure 1 solely in that it avoids the use of a compression spring 32 to urge the electrical contact zone 26 of the contact member 16 radially outwardly of the slot 24.

Instead, the return spring 10 provides the necessary bias by virtue of the fact that the fulcrum edge 20 of the contact member 16 is displaced laterally from the zone of contact with the spring 10. This lateral displacement provides the necessary angular moment to maintain the contact zone 26 of the contact member 16 in good electrical contact with the first terminal 28 when the plunger is in the position shown in Figure 7.

Claims

1. A minature electrical slide-action switch in which a slide member extends axially from a casing and can be depressed into the casing against the resilient bias of a return spring to effect switch actuation, wherein an electrically conductive contact member carried by the slide member comprises a fulcrum edge seated on an end surface of the slide member under the bias of the return spring and a cantilever portion extending through an end slot in the slide member into a longitudinal recess in the slide member, means being provided for urging an electrical contact zone of the cantilever portion of the contact member transversely of the recess against a side wall of the casing in which are exposed one or more first electric terminal conductors.

2. A switch according to claim 1, wherein a single first electric terminal conductor is exposed in the side wall of the casing.

3. A switch according to claim 1 or claim 2, wherein the or each first terminal conductor comprises a spade contact with an anchorage portion received as a snap-fit in a transverse slot in the casing and an integral spade contact portion extending laterally from the casing.

4. A switch according to claim 3, wherein the transverse slot is provided symmetrically across the full width of the casing so that the terminal conductor can be mounted from either side.

5. A switch according to any preceding claim, wherein the return spring provides an electrical path through the switch from the contact member to a second terminal conductor at an end of the casing.

6. A switch according to claim 5, wherein the second terminal conductor comprises a spade contact with an anchorage portion that is received as a snap-fit in an end slot in the casing to provide a reaction seat for the return spring, and an integral spade contact portion.

7. A switch according to claim 6, wherein the anchorage and spade contact portions of the second terminal conductor are mutually perpendicular.

8. A switch according to claim 7, wherein the second terminal conductor is receivable in the end slot in two alternative positions, with the spade contact portion extending longitudinally from the end of the casing or with the spade contact portion lying closely over the top of the casing in electrical contact with a mounting strap for securing the switch in a working position.

9. A switch according to any preceding claim, wherein the means urging the electrical contact zone of the cantilever portion of the contact member transversely of the recess comprises spring means between the cantilever portion and a base of the recess.

10. A switch according to claim 9, wherein the spring means comprises a coiled compression spring having one end located in a wall in the base of the recess and the other end located on a laterally projecting nose portion of the contact member.

11. A switch according to claim 10, wherein the contact member comprises a bent strip of metal having near one end a cross-piece which provides both a seating for the return spring and the fulcrum edge for the contact member, and at the other end a bent-over portion providing a rounded shoulder which is the electrical contact zone and a shaped nose for engaging the coiled compression spring.

12. A switch according to any of claims 1 to 8, wherein the means urging the electrical contact zone of the cantilever portion of the contact member transversely of the recess comprises a lateral spacing between the fulcrum edge and the zone of engagement between the return spring and the contact member, so that the axial bias of the return spring on the contact member also imparts an angular moment urging the contact member pivotally to rock about its fulcrum edge to bring its electrical contact zone into engagement with the side wall of the casing.

13. A method of assembly of a switch according to claim 10 or claim 11, which comprises laying the coiled compression spring longitudinally in the recess in which it is freely received; inserting the contact member through the end slot in the slide member so that the nose portion picks up the end of the coiled compression spring; and raising the coiled compression spring to a position extending transversely of the housing by continued movement of the contact member through the end slot until its fulcrum edge contacts the end wall of the slide member.

14. A minature electrical slide-action switch substantially as described herein with reference to Figures 1 to 6 of the drawings.

15. A minature electrical slide-action switch sub stantiaily as described herein with reference to Figures 7 to 8 of the drawings.