GB2178241A - Snap-acting switch with increasing contact pressure before snapping - Google Patents

Abstract

A snap-acting switch characterised by a centre contact 26 that moves in response to applied force over the surface of a first alternate contact 46 with a contact force thereon increasing continuously to a peak value at which it snaps into contact with a second alternate contact 44. The switch is characterised by a V-shaped actuator element 28 and means 42 responsive to an applied force to produce relative movement between such element and the alternate contacts. This movement causes the centre contact to describe a path of movement in two mutually perpendicular directions. <IMAGE>

Description

SPECIFICATION Snap-acting switch with increasing contact pressure before snapping This invention relates generally to snap-acting switches and more particularly to switches having centre contacts capable of maintaining full current carrying capacity up to the moment of snapping from one alternate contact to the other.

In many snap-acting switches of the type having two fixed alternate contacts and a centre contact movable from one to the other of the alternate contacts, the contact force of the centre contact against an alternate contact decreases as the switch actuator approaches the position at which the centre contact snaps to the other alternate contact. The loss of contact pressure just before the snap-action occurs is undesirable because it results in an increase in contact resistance, affecting the flow of electrical current. This may result in sparking, pitting of the contact surfaces, and reduction in the useful life of the switch.

It is a principal object of this invention to provide an improved switch in which the contact pressure increases rather than decreases as the snapping position is approached, whereby the current carrying capacity of the switch is undiminished up to the moment when the snap-action occurs.

A second object of the invention is to provide an improved switch in which the centre contact moves over the face of each alternate contact as the snapping position is approached. In certain embodiments this movement produces a wiping action between the centre contact and the alternate contact with a resulting improved current carrying capability.

A further object of the invention is to provide improved snap-acting switch construction in which the foregoing advantages can be achieved with single pole or double pole, single throw or double throw or normally open or normally closed configurations, and thermostatically operated forms, in any desired combination.

With the foregoing and other objects hereinafter appearing in view, this invention is characterised by a V-shaped actuator element and means responsive to an applied external force to produce relative movement between such element and the alternate contacts of the switch. This movement causes the centre contact to describe a path of movement in two mutually perpendicular directions, whereby an electrically conductive part thereof moves over one alternative contact with a contact force thereon increasing continuously until the position is reached at which the snap-action occurs. As this position is approached the Vshaped actuator portion has resilient bearing engagement with the centre contact means, the bearing engagement position approaching the apex of said V-shaped portion and reaching said apex at the moment when the snapaction occurs.

The foregoing features can be achieved in a large variety of switch configurations of either the single pole or double pole type. In all of these configurations the centre contact moves over each alternate contact with increasing bearing force thereon prior to reaching the snap-acting position, and such movement can be associated with either a wiping or a rolling engagement.

Other features of the invention will be appreciated from the following description of three illustrative embodiments.

Figs. 1 to 5 illustrate a single pole, double throw push button embodiment, Fig. 1 being a plan view in section, Figs. 2 and 3 being side elevations respectively showing the switch with the button undepressed and depressed, with the cover 12 removed, and Figs. 3 and 5 being end elevations in section taken on lines 3-3 and 5-5 of Figs. 2 and 4 respectively.

Figs. 6 to 8 illustrate a double pole, double throw push button embodiment, Figs. 6 and 8 illustrating the parts with the push button undepressed and depressed respectively and Fig.

7 being a plan view in section taken on line 7-7 of Fig. 6.

Fig. 9 illustrates a third embodiment in which the centre contact means include a roller resiliently bearing on the V-shaped actuator.

Referring to Figs. 1 to 5, a first embodiment comprises a body of insulating material including parts 12 and 14 fastened together by a pair of screws 16 and 18. These parts enclose a cavity 20 in which there is mounted a centre contact means 22 comprising a wire spring 24 and an electrically conductive sleeve 26 fixedly secured to the wire. The cavity also contains an actuator 28 formed of flat leaf spring material and including an elongate section terminating with a V-shaped portion 30 bent at right angles thereto. The actuator 28 has a number of folds, including a fold 32 received in a slot in the member 14 and folds 34 and -36 leading through another slot in the member 14 to a centre contact terminal 38.

The wire 24 has an end 40 bent over the fold 32 and in electrical contact therewith.

A slot in the member 14 receives a push button 42 of insulating material which bears upon the actuator 28.

A pair of fixed alternate terminals 44 and 46 extend through slots in the body 14 and comprise a pair of abutments having fixedly spaced apart surfaces extending in the direction perpendicular to the direction of extent of the wire 24.

Fig. 2 illustrates the switch in the position when no external force is applied to the push button 42. The actuator 28 being of spring material biased in an upward direction bears on a shoulder 48 of the push button, raising it to the position shown. In this position the apex 50 of the V-shaped portion 30 is located so that the electrically conductive sleeve 26 bears resiliently on a surface of the contact 46 within an aperture 52 formed in the member 14.

When the push button 42 is depressed, the V-shaped portion 30 bears upon the sleeve 26, and as the motion continues the sleeve moves in wiping contact with the surface of the contact terminal 46. As the sleeve 26 continues to be deflected, the contact force of the V-shaped portion 30 thereon increases and develops an increasing reaction contact force between the sleeve 26 and the contact terminal 46. These forces increase until the centre line of the sleeve 26 reaches the apex 50 of the V-shaped portion 30. When the movement reaches this position the component force previously causing the sleeve 26 to bear on the contact terminal 46 is suddenly removed and the sleeve passes over the apex, snapping into engagement with the contact terminal 44 as shown in Fig. 4.

Still further downward movement of the push button 42 may occur, causing a wiping action of the sleeve 26 on the contact terminal 44 until the actuator strikes the inner wall of the cavity 20 at 54.

If the push button 42 is released, the parts are restored to the position shown in Fig. 2 with the bearing engagement position of the sleeve 26 on the V-shaped portion 30 progressing toward the apex 50, and at an intermediate position passing said apex and snapping back into contact with the terminal 46.

The embodiment of Figs. 6, 7 and 8 illustrates a double pole embodiment of the invention, in which the actuator comprises a spool 60 having an annular V-shaped portion 62 or solid of revolution which replaces the flat Vshaped portion 30 in the embodiment of Figs.

1 to 5. This provides a pair of oppositely directed V-shaped portions respectively having bearing engagement with a pair of spring wires 64. Each of these spring wires is cantilever mounted on a post 66 or 68 secured to a body comprising insulating parts 70 and 72.

The spring wires 64 are preferably held in a variable deflected state by contact with the Vshaped portion 62 of the spool 60.

The spool 60 is formed of insulating material and has an integral push button 74 extending therefrom through an aperture in the part 72. A compression spring 76 urges the push button to the position shown in Fig. 6, in which position the apex 78 of the V-shaped portion 62 is located so that the wires 64 are snapped into engagement with fixed normally closed alternate contacts 80.

Opposing each of the contacts 80 are fixed normally open alternate contacts 82.

In operation, when the push button 64 is depressed, the V-shaped portion bears upon the spring wires 64 with increasing bearing engagement force, this force increasing as the position of engagement approaches the apex 78. At the same time, each of the wires 64 moves with a wiping action across one of the contacts 80, passing through a series of positions 84 (Fig. 7), moving with a contact force upon the contacts 80 which increases continuously until the bearing engagement position of the wires on the V-shaped portion 62 reaches the apex 78. Further movement then causes the wires 64 to pass over the apex and to snap into contact with the contacts 82.Typically, when the wires 64 first engage the contacts 82 the portions thereof engaging the Vshaped portion 62 are in engagement with an intermediate position on the latter spaced from the apex 78, and further downward movement of the push button 74 as viewed in the drawing, causes the wires to slide over the portion 62 in the direction away from the apex 78, producing a wiping movement of the wires across the contacts 82 similar to the movement depicted at 84 in Fig. 7. Fig. 8 depicts the push button 74 in its limit position with the spool 60 abutting the inner wall of the part 70.

Upon the release of externally applied pressure to the push button 74, the parts return to the position of Fig. 6, producing the same forces upon and motions of the wires 64 previously described, with the wiping motion and increased contact pressure being applied to the contacts 82 prior to the snapping of the wires 64 back into contact with the contacts 80.

With respect to the embodiments of Figs. 1 to 5 and 6 to 8, it will be apparent that the electrically conductive parts of the centre contact means that engage the fixed abutting alternate contact terminals 44 and 46 or 80 and 82 may have frictional contact therewith as illustrated, or may be fitted with rollers for rolling engagement with these terminals. Likewise, the portions of the centre contact wires engaging the V-shaped portion of the actuator may have frictional contact therewith or may be fitted with rollers for rolling contact. also, the spring wires shown in the drawings may be replaced, if desired, with helically wound elongate springs.

Fig. 9 illustrates an embodiment having a combination of elements in which the fixed and moving elements are reversed with respect to the embodiments of Figs. 1 to 8. A base 90 has an integral V-shaped actuaor portion 92. The base, preferably made of an insulating material, has an upstanding end portion 94. A pair of alternate contact members 96 and 98 of flat spring metal are secured at one end to the portion 94 by an insulating assembly pin 100 or by screws as illustrated.

The opposite ends of the members 96 and 98 are free to flex but are secured in fixed relationship by brackets secured to an insulating bar 102.

A roller 106 of electrically conductive material is located upon the surface of the base 90 between the members 96 and 98 which are preferably so spaced that the roller 106 is constantly in rolling contact with the V-shaped portion 92. A member 108 of flat spring metal is secured by screws 1 10 to the portion 94 of the base and is constantly in resilient engagement with the roller 106, being thereby in continuous electrical contact with the roller. Thus the element 108 in combination with the roller 106 comprises a centre contact means and the members 96 and 98 comprise alternate contacts or abutments for alternate electrical connection with the centre contact means.

It will be apparent that the V-shaped portion 92 of the base may be located so that either of the members 96 or 98 is a normally open or normally closed contact.

It will be apparent that the embodiment of Fig. 9 can be modified to incorporate a centre contact means of the type used in either of the embodiments of Figs. 1 to 5 or Figs. 6 to 8 or a similar type. Thus an elongate spring wire may be supported centrally on the portion 94 of the base, extending parallel to the members 96 and 98 and axially through the roller 106. If the wire is rotatable in the part 106 the latter rolls over the V-shaped portion 92 as previously described. If the wire is fixedly secured to the part 106 the latter does not roll but slides on the V-shaped portion 92. In either case the wire is preferably arranged to provide a continuous downward force on the part 106, as viewed in the drawing, in order to maintain continuous contact between the part 106 and the V-shaped actuator portion.

Claims (14)

1. A snap-acting switch comprising, in combination, a support, centre contact means including an electrically conductive part movable relative to the support, in first and second perpendicular directions, a pair of abutments mounted on the support and having fixedly spaced apart surfaces extending in said first direction on opposite sides of said electrically conductive part, at least one abutment comprising an electrically conductive contact, an actuator having a V-shaped portion in resilient bearing engagement with the centre contact means and, means responsive to an applied external force to produce relative movement in the said second direction between said V-shaped portion and the abutments, said movement causing the bearing engagement position to approach the apex of said V-shaped portion and the electrically conductive part to move in the first direction over one abutment surface with a contact force thereon increasing oontinuously until said bearing engagement position reaches said apex, further movement causing the centre contact means to pass over said apex and the electrically conductive part to snap into contact with the other abutment surface.

2. A switch according to claim 1, in which the centre contact means is an elongate spring fixed to the support and extending in a third direction perpendicular to the first and second directions.

3. A switch according to claim 2, in which the spring is cantilever mounted on the support with the electrically conductive part adjacent its free end.

4. A switch according to claim 1, in which the centre contact means include a spring urging the electrically conductive part into bearing engagement with said V-shaped portion.

5. A switch according to claim 4, in which the electrically conductive part is a roller.

6. A switch according to claim 1, in which the abutments are fixed to the support and the actuator is movable relative to the support.

7. A switch according to claim 6, in which the actuator comprises a leaf spring mounted on the support.

8. A switch according to claim 1, in which said V-shaped portion is fixed to the support and said abutment surfaces are movable relative to the support.

9. A switch according to claim 8, in which the abutments comprise leaf springs resiliently mounted on the support.

10. A switch according to claim 1, in which both of the abutments comprise electrically conductive contacts.

11. A switch according to claim 9, in which the parts are relatively located so that in the absence of said external force the electrically conductive part is in contact with one of the abutment surfaces.

12. A switch according to claim 1, in which further said movement after said snapping causes the electrically conductive part to move in the fixed direction over the other abutment surface.

13. A switch according to claim 1, in which the V-shaped portion has oppositely directed V-shaped cross sectional outlines, the centre contact means comprising a pair of electrically conductive parts resiliently bearing on opposite sides of said portion, and including a pair of said abutments for each said part.

14. A snap-acting switch substantially as herein described with reference to Figs. 1 to 5, 6 to 8 or 9 of the drawings.