US2770693A

US2770693A - Snap switch mechanism

Info

Publication number: US2770693A
Application number: US438014A
Authority: US
Inventors: Lester E Fickel
Original assignee: Ranco Inc
Current assignee: Robertshaw US Holding Corp
Priority date: 1954-06-21
Filing date: 1954-06-21
Publication date: 1956-11-13
Anticipated expiration: 1973-11-13
Also published as: GB783014A; DE1136762B

Description

L. E. FICKEL. 2,770,693

SNAP SWITCH MECHANISM Filed June 21, 1954 United States Patent SNAP SWITCH MECHANISM Lester E. Fickel, Columbus, Ohio, assiguor to Ranco Incorporated, Columbus, Ohio, a corporation of Ohio Application June 21, 1954, Serial No. 438,014

3 Claims. (Cl. 200-67) The present invention relates to an improved snap switch mechanism particularly suitable for use in control devices having a relatively slow moving switch actuator, such as in thermostatically operated control devices.

In general the invention has for its object to provide a snap switch mechanism having a movable contact carrying arm which is actuated with a snap movement to shift its contact between two fixed stops comprising one or two contacts, in response to movement of an actuator adapted to move at a relatively slow rate, and which provides firm contact pressure until the instant of snap movement of the contact arm.

A more specific object of the invention is the provision of a snap switch mechanism comprising a contact arm anchored at one end and having the other end oscillatable between two spaced stops, one or both of which may be contacts engaged by a contact carried on the arm, the arm being moved by a rigid toggle link extending generally parallel thereto and pivoted thereon at a point adjacent to the free end thereof, the toggle link being shiftable in the direction of oscillation of the contact arm between two spaced, fixed pivots about which the toggle is alternately rotated by a compression spring interconnecting the other end of the toggle link and an actuator, the actuator moving the spring to shift the line of force thereof from one side to the other of dead center relative to the toggle link whereby the link is shifted from one pivot to the other and rotated about i the engaged pivot to shift the contact arm. By this arrangement, the force of the spring is exerted on the contact arm to maintain the contacts closed either through urging the toggle link about one or the other of its stop pivots and/or by urging the link in a longitudinal direction until after the spring is moved past its dead center relative to the link; thus there can be no period of instability of contact pressures, regardless of slowness of movement of the actuator. Preferably, the contact arm is of flexible material, and the rocking movement applied to the contact arm by the link pivoting on either of its stops tends to roll the contacts and pry the contacts free of slight welds which tend to cause sticking of the contacts.

Other objects and advantages of the inventionwill be apparent from the following description of a preferred embodiment of the invention, reference being had to the accompanying drawings in which Fig. 1 is a plan view of a snap switch particularly suitable for use in a thermostatic control device;

mechanism showing the relative positions of various parts during actuation of the mechanism.

In the form shown, the switch mechanism is mounted in an open side, box-like base or frame 12, which is preferably formed of a suitable dielectric material, such as that known as Bakelite. The base 12 is arranged to be assembled in a housing of a thermostatic control device, not shown, and the switch actuated by a thermostatic power element; however, the switch could be used otherwise, if desired. A generally U-shaped bracket 13 is secured in one end of the base and comprises a current carrying member having two

lugs

14, 15 projecting inwardly and rearwardly from the lower ends of the legs thereof as viewed in Fig. 1. These lugs extend into slotted openings through the bottom wall 18 of the base and the lug 15 projects beyond the bottom wall and forms a terminal for the switch mechanism. The lug 14 terminates Within its opening. The lugs have shoulders 19 which rest on the inside of the wall 18 of the base on opposite sides of the openings in which they are received, and the lug 15 has shoulders 20 formed thereon which are staked over or spread to engage the bottom wall of the base and thereby secure the bracket 13 to the base. The end edges of the lug 14 are similarly spread to additionally secure the bracket to the base.

The yoke portion 21 of the bracket 13 has a tab 22 formed thereon which extends outwardly relative to the base wall 18 and at right angles to the bracket proper, and the tab has a rectangular opening 23 therein, the purpose of which is described hereinafter.

The ends of the legs of the bracket 13 also have inturned portions providing ledges 24, which extend parallel to the bottom wall 18 of the base, to which the open end of a U-shape, flat spring type contact arm 25 is attached as by screws 26 threaded into openings in the ledges. The contact arm 25 is formed of good electrical conducting material, such as beryllium copper.

The yoke end of the contact arm 25 has a double contact member 27 attached thereto, and this end of the armoscillates between fixed-

contacts

28, 29 to alternately engage contact 27 with latter contacts.

The contact 28 is attached to the end of a screw 31 which extends through an opening in the base wall 18 and is threaded in an opening through a plate 32 lying 1 against the wall and which has a terminal prong 33 projecting through a slotted opening in the wall. The prong 33 forms a terminal post and has shoulders (not shown) formed thereon similar to the shoulders 20 by which the plate 32 is secured to the base. By rotating the screw 31 one way or the other, the position of the contact 28 can be adjusted, which is desirable in assembling the mechanism and facilitates securing proper operation of the switch mechanism.

The contact 29 is attached to the arch of a U shaped terminal bracket 35, one leg of which has a foot portion a a 36 held to the wall 18 by a prong 37 formed thereon and Fig. 2 is a sectional view taken substantially along line 2-2 of Fig. 1; M

'Fig. 3 is a sectional view taken substantially along line 33 of Fig. 2;

Fig. 4 is a sectionalview taken substantially along line 44 of Fig. 2; t

Fig. 5 is a fragmentary view taken approximately along line 5-5 of Fig. 1; and a L a p Figs. 6 to 11 are schematic illustrations of the switch extending through a slotted opening in the wall and secured therein by shoulders 38 spread against the edges of the opening. The prong 37 forms anotherterminal post for the switch mechanism. The other leg of the bracket35 has a foot 39 having a prong: extending into a slotted opening in the wall 14 and secured in the opening by turning end edges thereof against the sides of the opening, as described with reference to thelug 15.

An actuating member in the form of a flat, A-shaped spring 42 has the ends of its legs riveted to shoulders 43 a formed at opposite sides of the base 12. The member 42 the contact '27 against contact 29.

the legs to weaken'at the rivets. The movable portion of member 42 is reinforced along its edges by marginal flanges, and the cross piece 47 thereof is integral with the member and is bowed or dished to provide a curved surface for engagement with a power member, such as the lever of .a thermostatic device, not shown. The free portion of member 42 is normally outwardly relative to the base wall 18, as seen in Fig. 2, and this position is assumed by the inherent bias of the member.

The actuator 42 is connected with the contact arm 25 through a C-shaped spring 50 and a rigid toggle link 51. The'link 51 extendsjthrough the rectangular opening 22 ofthe bracket tab '21 and one end'is pivoted to the arm 25' by a V"bea'ring 52, which engages the edge of the arm at the yoke portion, and the opposite end of the link'is pivoted by a similar V bearing 53 to an end edge of the spring'5'0f The V notches receiving the edges of the contact arm 25 and the spring 50 form pivot joints having'a minimum of friction, as is well known in the art. The spring 50 is connected'to the actuator 42 by a knife edge bearing arrangement 54 formed by a shallow V at one end of the spring which receives an edge of a bulged portion 55 of the yoke of the actuator.

As mentioned previously, the toggle link 51 extends through the rectangular opening 22 in the tab 21, and the

opposite end walls

56, 57 of the opening form spaced stops about which the link 51 may pivot. The dimensions' of the opening 22 and the link 51 are such that the link has a slight free movement between the end edges of the opening. Preferably, in forming the tab 22 on the bracket 13, the material thereof is compressed so that the thickness of the tab is considerably less than that of the bracket proper to provide point-like pivots for the link.

Referring to Figs. 6 to 11, when the actuator 42 is in what may be referred to as its normal position, as shown in Fig. 6 the spring 50 urges the link 51 downwardly against the stop 57 and counterclockwise about the pivot formed by the stop so that the right hand end of the link forces the contact arm 25 upwardly to engage contact 27 with contact 29. Additionally, the force of spring 50exerts'a longitudinal bias on the link which also urges When the actuator 42 is moved downwardly as by a thermostatic device, the direction of the force of the spring 50, which .is represented by a straight line through

pivots

53, 54, reaches a dead center position with respect to the link, which is defined herein as a line through the

link pivots

52, 53 and is illustrated in Fig. 7 by the line DC. In this position it is clear that rotational effort of the link about the stop 57 is' nil, but that the longitudinally biased toggle link still exerts a substantial force along line DC to urge contact arm 25 to contact 29. The instant the line of force of the spring moves below line DC the toggle link is moved from stop 57 to stop 56 by a snap action, as seen in Fig. 8, causing the link to pivot clockwise about stop 56 and move the contact arm downwardly whereby contact27 is snap moved from contact 29 to contact 28. The contact arm is held in this position by the clockwise movement of the toggle link aswell' as by the force of the spring 50 acting longitudinally through the link, as may beseen in Fig. 9.v

To reverse the switch movement, the actuator 42 is moved upwardly, from that shown in Fig. 9 which moves the center of force of spring 50 in line with the centerline of the toggle link 51, as indicated by line DC. In

this position. the rotational effort of the toggl'elink about stop 76 is nil, but it is apparent that the-force of the spring ur ging' the link longitudinal-1y acts to hold the contact armso that contact 27 is firmly engaged'with contact. 28. 'When the actuator moves upwardly further, thecenter of force of the spring 50 snaps the toggle link downwardly against the stop 57 which causes the link topivotcounterclockwise about this stop a'ndmove the contact arm to shift contact 27 from contact 28 to contact 29, as seen in Fig. 6.

It will be noted that should the contacts tend to stick, which frequently occur by slight welding action from arcing, the movement of the toggle link 51 about either stop 56 or 57 tends to flex the contact arm adjacent to the contact 27 and effects a prying or rolling action which breaks the welds. Thus, the switch is positively operated by a minimum of power.

It will be apparent that the invention provides a snap switch mechanism having a movable contact that has a double throw action and which is maintained in firm engagement with either of the fixed contact until the instant of its movement to the other contact, irrespective of the gradual movement of the actuator. The switch mechanism is compact, easy to assemble, reliable in operation and provides relatively high current carrying capacity for the chart required to actuate the same.

Although but one form of the invention has been described it will be apparent that other forms, modifications and adaptations may be made, all falling within the scope of the claims which follow.

I claim:

1. In a snap switch mechanism, a contact arm having one end free to move '.in opposite directions between limits, spaced stopsfor-ming' limits of movement of said end of said contact arm, a relatively rigid toggle link having one end pivoted to said arm adjacent to said one end, a pair of fixed spaced pivots for said link, one on opposite sides thereof and intermediate the ends thereof, said stops forming alternate pivots for said link when said link is shifted in the directions of said movements of said contact arm, a spring having one end pivotally connected'to the other end of said link and urging said link in the direction of its said one end and to one or the other of said fixed pivots, and means pivotally connected' to the other end of said spring for moving said spring'generally parallel to the movement of said one end of said contact arm to shift the line of force of said springfrom one side to the other of the longitudinal centerline of said link.

2. In a snap'switch mechanism, a contact arm having one end free to move in opposite directions between limits, spaced stops forming limits'of movement of said end of said contact arm, a relatively rigid toggle link having one' end pivoted to said arm adjacent to said one end, a pair of fixed spaced pivots for said link, one on opposite sides thereof and intermediate the ends thereof, said stops forming alternate pivots for said link when said link is shifted in thedirections of said movements of said contact arm, a spring having one end pivotally connected to the other end of said link and urging said link in the direction of its said one end and to one or the other of said fixed pivots, said stops and pivots being spaced apart respectively to cause said link to lie to one side of said contact arm when said link .is urged to one of said pivots by said spring and said contact arm is nected to the other end of said spring for moving said spring generally parallel to the movement of said one end of said contact arm to shift the line of force of said spring from one side to the other of the longitudinal centerline of said link.

3. ha snap switch mechanism, a flexible contact arm having one end free to shift between limits, a contact carried on said arm adjacent to said free end thereof, two spaced stops forming limits of movement of said free end of said arm, at least one of saidstops comprising a contact, a relatively rigid toggle link having one end pivoted to said arm adjacent to' said one end, a pair of fixed, pivots for said link, onev on oppositesides' thereof and operative toform alternate pivots for said link when said link isshifted in the directions of said movements of said'contact arm; a'C-shape' spring having one end pivotally connected to the other end of said link and urging said link in the direction of its said one end and to one or the other of said fixed pivots, and means pivotally connected to the other end of said spring and moving said spring to shift the line of force of said spring from one side to the other of the longitudinal centerline of said link.

References Cited in the file of this patent UNITED STATES PATENTS Engholdt July 18, 1950 Persons Nov. 14, 1950 Allan Apr. 10, 1951 Raney June 12, 1951