US3763339A

US3763339A - Electrical switches

Info

Publication number: US3763339A
Application number: US00277138A
Authority: US
Inventors: R Holmes
Original assignee: Burgess Micro Switch Co Ltd
Current assignee: Johnson Electric International UK Ltd
Priority date: 1971-08-03
Filing date: 1972-08-01
Publication date: 1973-10-02
Anticipated expiration: 1990-10-02
Also published as: GB1392709A; DE2238059A1

Abstract

A snap-action switch has a contact arm pivotable on an actuator member and engaged by a spring that moves through an over-centre position when the actuator member is deflected, to switch the contact arm. The actuator member is of elongate form and an end remote from its pivot engagement with the contact arm is frictionally engaged with a fixed, externally directed contact. The member is wedged with said contact in a slot of the switch casing and the interengaging portions of said member and contact are arranged to permit their pre-assembly before insertion in said slot.

Description

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[ 1 ELECTRICAL swlTcHEs 2,853,573 9/1958 Wang 200/67 D 3,176,109 3/1965 Woodtke 200/67 D 1 Invent Y Holmes chester'lestreet 2,728,826 12 1955 Lauder 200/67 B England [73] Assignee: Burgess Micro Switch Company Primary Examiner David Smith JR Gateshead County Attorney-Ernest A. Greenside Durham, England v [22] Filed: Aug. 1, 1972 Appl. No.: 277,138

Foreign Application Priority Data Aug. 3, 1971 Great Britain 36,475/71 U.S. Cl. 200/67 1B, 200/166 CT Int. Cl. 1101b 13/28 Field of Search 200/67 D, 67 B, 67 R,

References Cited UNITED STATES PATENTS 7/1957 Reitler 200/67 B [57] ABSTRACT A snap-action switch has a contact arm pivotable on an actuator member and engaged by a spring that moves through an over-centre position when the actuator member is deflected, to switch the contact arm. The actuator member is of elongate form and an end remote from its pivot engagement with the contact arm is frictionally engaged with a fixed, externally directed contact. The member is wedged with said contact in a slot of the switch casing and the interengaging portions of said member and contact are arranged to permit their pre-assembly before insertion in said slot.

14 Claims, 3 Drawing Figures ELECTRICAL SWITCHES FIELD OF THE INVENTION This invention relates to snap-action electrical switches, particularly to switches of relatively small and compact construction.

BACKGROUND OF THE INVENTION Small electrical switch mechanisms are usually contained in housings, which may be moulded, and ease and simplicity of both construction and assembly are desirable To this end, soldered, screwed or bolted engagements between parts should be avoided, but it is nevertheless important to ensure good electrical contact is maintained where required. The manner of securing is particularly important in switch mechanisms involving the pivotting of a contact arm in a snapaction movement through an over-centre position with respect to a spring member engaging it, because the parts must maintain their positions in the assembly.

SUMMARY OF THE INVENTION According to the invention, there is provided snapaction electrical switch having a housing containing a contact arm, a resiliently flexible electrically conducting actuator member having a fixed portion mounted in the housing and a displaceable portion remote from the fixed portion, the contact arm being pivotally supported on the displaceable portion for displacement therewith on flexure of the actuator member, and an over-centre spring member holding the contact arm against the said displacement portion and arranged to pivot the contact arm, when the contact arm is displaced, with a snap-action over-centre movement so that it engages or disengages at least one fixed electrical contact, the said fixed portion of the actuator member being held in position by frictional engagement with adjacent parts of the switch and having a contact portion urged against a further electrical contact.

Preferably said fixed portion of the actuator member makes an at least three-point frictional engagement with adjacent parts whereby it is wedged relative to the housing, one of the.said at least three points being engagement of the said contact portion with the said further electrical contact. suitably two other points of the said at least three engagement points are with walls of a slot in the housing.

Said fixed portion of the actuator member adjacent thereto may have a projecting or corner element providing an edge element arranged to bear against an engaging part of the surface of the further electrical contact element in such manner as to bed into said surface part in order to improve electrical contact therebetween. Conveniently, to assist the initial location of the actuator member to said further electrical contact element, it can be arranged that a terminal portion of the actuator member which is to be the fixed portion is inserted through an aperture in said further contact element in which case the said terminal portion can have a reverse bend to be located through the aperture and to provide two engagement points with adjacent parts of the switch. A final cranked end element of the terminal portion can then provide said edge element such that it acts as a knife-edge, bedding into the surface of the further contact element adjacent the aperture.

A switch according to the invention can be arranged so that movement of said displaceable portion of the actuating member is arranged to impart to the contact arm tangential and rotational components of motion relative to its engaging fixed electrical contact whereby a wiping action can take place between said contact and the contact arm on engagement and disengagement therebetween.

In a preferred form of switch according to be invention, a terminal portion of the actuator member, remote from said clamped portion is engaged by an operating element projectinG externally of the housing to switch the mechanism. Conveniently, if the actuator member is made of sheet material, said terminal portion engaged by the operating element can be formed from material between a pair of arms on which said contact arm is supported, the over-centre spring then passing through the space thus left between the arms.

DESCRIPTION OF A PREFERRED EMBODIMENT An embodiment of the invention will be described with reference to the accompanying drawings in which FIG. 1 is a side elevation of an electrical switch according to the invention with one side of its housing removed, the movable parts of the mechanism being shown in one alternative end position;

FIG. 2 is a section on line A-A of FIG. I; and,

FIG. 3 is a perspective view of the actuator member of the switch of FIG. 1.

Referring to the drawings, housing 2 of the switch has a cavity into which external contact members 4, 6 and 8 have portions projecting. The members 4, 6 have opposed electrical contact faces 10 and a contact arm 14 has one end provided with contact buttons 16 that lie between the faces 10. The arm 14 is pivotably mounted on a displaceable portion 18a of a resiliently flexible actuator member 18 which has a portion 18b fixed relative to the housing 2. The contact arm 14 is displaceable with the displaceable portion 18a and is pivotable thereon to bring one or other of the contact buttons 16 into engagement with its adjacent contact face 10. For

.the mounting of the arm 14, the displaceable portion 18a of the actuator member 18 has a pair of spaced end legs 20 extending at an angle to the main part of the portion 18a and formed with recesses 22. The arm 1d is held against the legs 20, with projections 23 located in the recesses 22, by a spring 24 that passes through the space between the legs 20, opposite ends of the spring being attached to an aperture 26 in the arm adjacent the buttons 16 and to a boss 28 integral with the switch housing. The spring 24 also provides the contact pressure between the faces 10 and the buttons 16.

The fixed end 18b of the member 18 is, as described below, wedged or clamped relative to the casing and the contact member 8, the member thus projecting in cantilever manner from the region of clamping. The member 18 being formed from a rectangular strip (see FIG. 3), the legs 20 are bent to leave the material between them projecting as a spur 30 upon which bears an operating member 32 slidably mounted to project from the housing.

In the normal, stable position of the switch, the spring 24 urges the actuator member 18 upwards to the position illustrated in FIG. 1, in which the spur 30 bears on the operating member 32 to urge it to its outermost position. The spring 24 thereby maintains a relatively high contact pressure between the engaging contact button 16 and contact face 10 in either position of the switch.

At the same time, the configuration has the effect of reducing the force required to depress the operating member to change over the switch from the illustrated position. Such depression flexes the actuating member 18 to move the end of the arm 14 downwards below the axis of the spring 24 so that there is an over-centering action of the spring, whereby the arm 14 is pivoted in a snap-action movement to bring the upper button 16 against the upper contact face 10. The location of the operating member 32 at the extreme opposite end of the actuating member 18 to its fixed portion 18b also has the effect of reducing the operating force required because of the mechanical advantage obtained.

lt is to be noted that the recesses 22 carrying the arm 14 swing substantially about a centre at the region of clamping of the member 18. One result of this is that displacement of the arm 14 to contact one or other of the members 4, 6 is accompanied by some initial movement parallel to the faces so that before contact is broken between a face 10 and its engaging contact button, there is rolling and sliding between these parts. This gives a wiping, self-cleaning action and minimises the risk of malfunctioning of the switch through arcing or local welding between the buttons 16 and their contact faces 10.

At its fixed portion 18b, the member 18 has a double cranked end portion including a reverse bend 34 that is located in an aperture 36 in the contact member 8 for pre-assembly of these parts before they are placed in the housing. Oppositely bent tip 38 of the cranked end portion bears against a lower surface 37 of the contact 8 close to the aperture 36, providing one engagement point of a three point engagement which holds the actuator member in position in the assembled switch, the other two engagement points being provided by

opposite sides

34a, 34b of the reverse bend 34 which respectively bear on an upper face 40 and a lower face 41 of a slot 43 in the housing. The combined material thicknesses of the actuator member 18 and the contact member 8 is slightly less than the spacing between the

surfaces

40, 42 of the housing However, the spacing of

faces

40 and 41 is such as to ensure an interference fit with the actuator member 18 so thatit is gripped between the

surfaces

37, 41 and 40 and so that tip 38 is urged into the surface 37. The actuator member 18 is thus held in the desired position in the assembled switch by the frictional forces at the three points of engagement.

The member 18 is preferably plated, e.g., with silver, to improve electrical contact with the contact member 8 and with the arm 14 (it is usually more convenient to electroplate the whole surface of the member 18 than to plate only its end regions where these contacts are made). In addition, the tip 38 of the member 18, being at an angle to the surface 37 of the contact member 8 presents a knife edge to that surface: the surface 37 of the member 8 may be formed by a silver or like conductive inlay 44 into which the angulate edge of the tip 38 can bed under the clamping pressure to ensure good electrical contact.

What I claim and desire to secure by Letters Patent l. Snap-action electrical switch having a housing containing a contact arm, a resiliently flexible electrically conducting actuator member having a fixed portion mounted in the housing and a displaceable portion remote from the fixed portion, the contact arm being pivotally supported on the displaceable portion for displacement there-with on fiexure of the actuator member, and an over-centre spring member holding the contact arm against the said displaceable portion and arranged to pivot the contact arm, when the contact arm is displaced, with a snap-action over-centre movement so that it engages or disengages at least one fixed electrical contact, the said fixed portion of the actuator member being held in position by frictional engagement with adjacent parts of the switch and having a contact portion urged against a further electrical contact.

2. Snap-action electrical switch according to claim 1 wherein said fixed portion of the actuator member makes an at least three-point frictional engagement with adjacent parts whereby it is wedged relative to the housing, one of said three frictional points of engagement being between said contact portion of said actuator member and said electrical contact.

3. Snap-action electrical switch according to claim 2 wherein two other points of the said at least three engagement points are with walls of a slot in the housing.

4. Snap-action electrical switch according to claim 1 wherein the said contact portion of the said fixed portion of the actuator member has an edge element which is urged against a surface of the said further electrical contact so as to bed into the said surface.

5. Snap-action electrical switch according to claim 1 wherein the said further electrical contact has an aperture and the fixed portion of the actuator member passes through the aperture whereby the actuator member and the said further electrical contact can be interengaged before assembly in the switch.

6. Snap-action electrical switch according to claim 1 having an operating element projecting externally of the housing and engaging the said actuator member at a point remote from the fixed portion, inward movement of the operating element causing the said displacement of the displaceable portion and hence switching action of the switch.

7. Snap-action electrical switch according to claim 6 wherein the said operating element engags the actuator member at a point further from the fixed portion of the actuator member than the point of support of the contact arm on the actuator member.

8. Snap-action electrical switch according to claim 1 wherein movement of said displaceable portion of the actuating member is constrained to impart to the contact arm tangential and rotational components of motion relative to its engaging fixed electrical contact whereby a wiping action can take place between said contact and the contact arm on engagement and disengagement therebetween.

9. Snap-action electrical switch according to claim 1 wherein the actuator member is formed of metal sheet or strip, the said displaceable portion having two arms angularlY related to the sheet or strip, on which arms the contact arm is supported, the spring mmber passing between the arms.

10. Snap-action electrical switch according to claim 9 having two arms formed from marginal portions of the member, said two arms having a combined width less than the width of said sheet or strip at said marginal portions leaving thereby an intermediate portion between the marginal portions, an operating element projecting externally of the housing engaging said intermediate portion, inward movement of the operating element causing the said displacement of the displaceable portion and hence switching action of the switch.

11. Snap-action electrical switch according to claim 1 wherein the fixed portion of the actuator member has a reverse bend which extends into an aperture of said further electrical contact and which provides the said frictional engagement with two spaced points on said furt her contact on opposite sides of said aperture.

12. Snap-action electrical s witch according to claim 1, wherein said displaceable portion of the actuating member is substantially more remote from the fixed portion thereof than from said pivotal support of said contact arm of said actuator member.

13. Snap-action electrical switch having a housing containing a contact arm, a resiliently flexible electrically conducting actuator member having a fixed portion mounted in the housing and a displaceable portion remote from the fixed portion, the contact arm being pivotally supported on the displaceable portion of the actuatormember for displacement therewith on flexure of the actuator member, and an over-center spring member holding the contact arm aginst the said displaceable portion and arranged to pivot the contact arm, when the contact arm is displaced, with a snap-action over-center movement so that it engages or disengages at least one fixed electrical contact, the said fixed portion of the actuator member being held in position by frictional engagement with adjacent parts of the switch and having a contact portion urged against a further electrical contact, said further electrical contact being formed with anaperture through which the fixed portion of the actuator member passes whereby the actuator member and said further electrical contact can be interengaged before assembly in the switch.

14. A switch having a housing containing therewithin three fixed contacts, each having a portion extending inwardlyof the housing for connection to an external instrumentality, two of said fixed contacts terminating with end portions thereof in said housing in spaced apart overlying relation, a movable contact arm within said terminating in contact button means at one of its ends between said two fixed contacts for alternate engagement therewith, the remaining fixed contact having an end portion within said housing in super-posed relation to said fixed contacts and spaced therefrom, a displaceable resiliently flexible conducting means interconnecting the remaining fixed contact with the end of said contact arm opposite said one of its ends, said conducting means being fixed at one end portion thereof to the housing and forming at that end a fixed electrical connection with said remaining fixed contact, said conducting means at another end portion remote from said one end portion providing a pivotal connection for said opposite end of the contact arm, and spring means acting on said contact arm for maintaining said contact arm in engagement with said conducting means, said conducting means being displaceable in a region thereof closer to its pivotal connection with said movable contact then its pivotal connection with said remaining fixed contact.

Claims

1. Snap-action electrical switch having a housing containing a contact arm, a resiliently flexible electrically conducting actuator member having a fixed portion mounted in the housing and a displaceable portion remote from the fixed portion, the contact arm being pivotally supported on the displaceable portion for displacement there-with on flexure of the actuator member, and an over-centre spring member holding the contact arm against the said displaceable portion and arranged to pivot the contact arm, when the contact arm is displaced, with a snap-action over-centre movement so that it engages or disengages at least one fixed electrical contact, the said fixed portion of the actuator member being held in position by frictional engagement with adjacent parts of the switch and having a contact portion urged against a further electrical contact.

11. Snap-action electrical switch according to claim 1 wherein the fixed portion of the actuator member has a reverse bend which extends into an aperture of said further electrical contact and which provides the said frictional engagement with two spaced points on said further contact on opposite sides of said aperture.

12. Snap-action electrical switch according to claim 1, wherein said displaceable portion of the actuating member is substantially more remote from the fixed portion thereof than from said pivotal support of said contact arm of said actuator member.

13. Snap-action electrical switch having a housing containing a contact arm, a resiliently flexible electrically conducting actuator member having a fixed portion mounted in the housing and a displaceable portion remote from the fixed portion, the contact arm being pivotally supported on the displaceable portion of the actuatormember for displacement therewith on flexure of the actuator member, and an over-center spring member holding the contact arm aginst the said displaceable portion and arranged to pivot the contact arm, when the contact arm is displaced, with a snap-action over-center movement so that it engages or disengages at least one fixed electrical contact, the said fixed Portion of the actuator member being held in position by frictional engagement with adjacent parts of the switch and having a contact portion urged against a further electrical contact, said further electrical contact being formed with an aperture through which the fixed portion of the actuator member passes whereby the actuator member and said further electrical contact can be interengaged before assembly in the switch.

14. A switch having a housing containing therewithin three fixed contacts, each having a portion extending inwardly of the housing for connection to an external instrumentality, two of said fixed contacts terminating with end portions thereof in said housing in spaced apart overlying relation, a movable contact arm within said terminating in contact button means at one of its ends between said two fixed contacts for alternate engagement therewith, the remaining fixed contact having an end portion within said housing in super-posed relation to said fixed contacts and spaced therefrom, a displaceable resiliently flexible conducting means interconnecting the remaining fixed contact with the end of said contact arm opposite said one of its ends, said conducting means being fixed at one end portion thereof to the housing and forming at that end a fixed electrical connection with said remaining fixed contact, said conducting means at another end portion remote from said one end portion providing a pivotal connection for said opposite end of the contact arm, and spring means acting on said contact arm for maintaining said contact arm in engagement with said conducting means, said conducting means being displaceable in a region thereof closer to its pivotal connection with said movable contact then its pivotal connection with said remaining fixed contact.