US3803526A

US3803526A - Snap acting double break switch

Info

Publication number: US3803526A
Application number: US00309121A
Authority: US
Inventors: E Andersen
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1972-11-24
Filing date: 1972-11-24
Publication date: 1974-04-09
Anticipated expiration: 1991-04-09

Abstract

A snap acting double break switch comprising a housing, a pair of terminals mounted to the housing, and a pair of mutually spaced fixed contacts mounted within the housing and electrically coupled to the pair of terminals. A snap acting switch blade is mounted within the housing. A bridge spring transversely overlays a movable portion of the switch blade with a central portion of the bridge spring riveted to the switch blade movable portion and with two flexible eccentric portions of the bridge spring carrying a pair of movable contacts to make and break with the pair of fixed contacts upon actuation of the switch blade. The flexible eccentric portions of the bridge spring are spaced from the switch blade when the switch blade is in a predetermined position relative to the fixed contacts. Means are also provided for actuating the switch blade to cause the movable contacts to make and break with the fixed contacts by moving the switch blade relative to the fixed contacts while permitting the movable contacts flexible movement relative to the switch blade.

Description

United States Patent [1 1 Andersen Apr. 9, 1974 SNAP ACTING DOUBLE BREAK SWITCH [73] Assignee: General Electric Company, Fort Wayne, Ind.

[22] Filed: Nov. 24, 1972 [21] Appl. No.: 309,121

[52] US. Cl 337/338, 200/166 H, 337/347 [51] Int. Cl. H01h 37/52 [58] Field of Search 337/41, 86, 337, 338, 342,

Primary Examiner-Bernard A. Gilheany Assistant Examiner-F. E. Bell [5 7 ABSTRACT A snap acting double break switch comprising a housing, a pair of terminals mounted to the housing, and a pair of mutually spaced fixed contacts mounted within the housing and electrically coupled to the pair of terminals. A snap acting switch blade is mounted within the housing. A bridge spring transversely overlays a movable portion of the switch blade with a central portion of the bridge spring riveted to the switch blade movable portion and with two flexible eccentric portions of the bridge spring carrying a pair of movable contacts to make and break with the pair of fixed contacts upon actuation of the switch blade. The flexible eccentric portions of the bridge spring are spaced from the switch blade when the switch blade is in a predetermined position relative to the fixed contacts. Means are also provided for actuating the switch blade to cause the movable contacts to make and break with the fixed contacts by moving the switch blade relative to the fixed contacts while permitting the movable contacts flexible movement relative to the switch blade.

16 Claims, 9 Drawing Figures SNAP ACTING DOUBLE BREAK SWITCH BACKGROUND OF THE INVENTION This invention relates generally to electric switches, and particularly to snap acting double break type electric switches such as, for example, those employed as thermostatic controls.

For rapid make and break contact action, snap acting switch blades are typically employed in electric switches. These switch blades carry a movable contact which makes and breaks with a mating fixed contact. The snap movement of the blade typically results from the action of a toggle spring which may inherently be provided by the configuration and mounting of the switch blade itself. Where actuation is thermally induced, as in the case of thermostats, a thermoresponsive element such as a bimetallic blade is biased against the toggle spring. As the temperature of the thermoresponsive element changes the balance of forces between. the element and spring changes. At a preselected temperature the balance of forces becomes such as to cause the toggle spring to trip and effect switch actuation.

A significant problem hereinbefore encountered by the just described type of switch has been that of contact bounce. The movable contact as well as its support inherently has inertia. When it strikes the mating fixed contact it tends to rebound since all of its kenetic energy is not ordinarily absorbedby the fixed contact upon initial impact. A series of bounces may then follow of decreasing bounce height and frequence before contact closure becomes firmly established. These bounces are frequently accompanied by arcing. Where sufficient current densities occur this arcing may in turn cause the contacts to become welded together. If the weld is of sufficient strength the contact will not separate upon subsequent switch operation thereby rendering the switch inoperative.

Another problem previously experienced by the just described type of switch has been that of self induced heating. Current flow through the switch contacts and conductors generates heat which in turn is conducted to the thermoresponsive element. The thermoresponsive element thus senses temperatures elevated above ambient. This tends to reduce the thermal accuracy of the switch which in turn tends to increase the temperature differential of swing range where the switch is employed as a thermostatic control. I I

To shorten the current path and thereby lessen self induced heating double break type switches have been devised in which two movable contacts are adopted to make and break with two fixed contacts. The fixed contacts are often mounted directly upon internal extensions of the switch terminals. With this configuration current may be channeled through the switch by flowing directly between the terminals through the conductor upon which the two movable contacts are mounted.

Unfortunately, the double break configurations just described have also encountered problems. For example, it has proven difficult to obtain substantially simultaneous make and break operations between the two sets of contacts and thus to obtain appropriate force gradients during switch operations. Without proper force gradients the problem of contact bounce continues to be present. It has also proven difficult to achieve good contact wiping action with such double contact arrangements in order to clean the surfaces of the contacts during switch operations.

Accordingly, it is a general object of the present invention to provide an improved snap acting double break switch.

More specifically, it is an object of the invention to provide a snap acting double break switch which closes with minimal contact bounce.

Another object of the invention is to provide a snap acting double break switch which closes with relative low force gradients to effect minimal contact bounce and yet whichopens with relative high force gradients to break any small welds between the contacts.

Another object of the invention is to provide a snap acting double break switch which closes with a wiping action between mating contacts.

Another object of the invention is to provide a snap acting double break switch in which the movable contacts operate with self seeking leveling action whereby the movable contacts make and break with fixed contacts substantially simultaneously.

Yet another object of the invention is to provide a snap acting double break switch which exhibits minimal current induced self heating.

SUMMARY OF THE INVENTION In one form of the present invention a snap acting double break switch is provided comprising a housing, a pair of terminals mounted to the housing, and a pair of mutually spaced fixed contacts mounted within the housing and electrically coupled to the pair of terminals. A snap acting switch blade is mounted within the housing. A bridge spring transversely overlays a movable portion of the switch blade with a central portion of the bridge spring riveted to the switch blade movable portion and with two flexible eccentric portions of the bridge spring carrying a pair of movable contacts to make and break with the pair of fixed contacts upon actuation of the switch blade. The flexible eccentric portions of the bridge spring are spaced from the switch blade when the switch blade is in a predetermined position relative to the fixed contacts. Means are also provided for actuating the switch blade to cause the movable contacts to make and break with the fixed contacts by moving the switch blade relative to the fixed contacts while permitting the movable contacts flexible movement relative to the switch blade.

BRIEF DESCRIPTION OF THE DRAWING FIG. 11 is a side view in elevation of a snap acting double break thermostatic switch embodying principles of the invention in one form;

FIG. 2 is an end view in elevation of the switch shown in FIG. ll;

FIG. 3 is a cross-sectional view of the switch shown in FIGS. 11 and 2 taken along line 3-3;

FIG. 4 is a plan view of the lower housing member of the switch shown in FIG. 3 and of switch components mounted therewithin;

FIG. 5 is a cross-sectional view of the switch shown in FIG. 3 taken along line 5-5;

FIG. 6 is an exploded view of switch contact support and actuating members shown in FIGS. 3 and 4;

FIG. 7 is a plan view of the top of a portion of the switch blade and contact carrying bridge spring assembly component of the switch shown in FIGS. 1-6",

FIG. 8 is a plan view of the bottom of the switch blade and bridge spring assembly shown in FIG. 7; and

DETAILED DESCRIPTION OF THE DRAWING Referring now in more detail to the drawing there is shown a snap acting double break thermostatic or electrical switch embodying principles of the invention in one form which may, for example, be used in controlling a room air conditioner. This particular switch comprises a lower housing member 10 and an upper housing member 12 secured together along a mating plane 14 by rivets 16. The housing members are dielectric being formed of a moldable, phenolic resin. To lower housing member 10 are secured three

terminals

17, 18 and 19, by rivets 15. For controlling a room air conditioner terminal 17 may be connected to line voltage, terminal 18 to the air conditioner compressor, and terminal 19 to the air conditioner fan.

Beneath

terminals

18 and 19 are secured

fixed contacts

20 and 21 respectively by

rivets

22 and 23. To terminal 17 is secured contact 24. To the lower housing member is also secured a snap acting means, such as switch blade 25, by means of rivet 26. The switch blade has three spaced leg portions 27, 28 and29 intermediate its ends. The two outer leg portions 27 and 29 are each' slightly crimped thereby placing their crimped sections in a plane above that section of inner leg portion 28 disposed therebetween. This configuration renders the switch blade snap acting in the manner of a toggle spring with the aid of toggle retainer spring 30. One end of the retainer spring is secured to switch blade 25, also by means of rivet 26, while the other end bears directly against inner leg 28.

Switch blade is actuated by means of a thermoresponsive element in the form of bimetallic blade 33. The bimetallic blade is secured to housing plate 34 by bimetallic adjust screw 35 at one end thereof while the other end is coupled to switch blade 25 by a mechanical coupling means, such as a dielectric link 37 having tab s'38 and 39 which pass through

slots

40 and 41 in bimetallic blade 33 and switch blade 25, respectively. Housing plate 34 is in turn secured to upper housing member 12 by means of four bend tab extensions 44 from superstructure plate 45 which superstructure plate is riveted to the upper housing member by rivets 16. An apertured guard 46 for the bimetallic blade is secured at one end to two of the' tab extensions 44 by tabs 47, and at the other end to superstructure plate tab 48. Rotation of the bimetallic blade is inhibited by lock plate 49 which is secured to adjust screw 35 and which has a hole through which shaft 50 passes in close proximity.

Shaft 50, having a cam 52 mounted thereto, is rotatably journalled through the lower and

upper housing members

10 and 12 and through housing plate 34. A plastic shaft over-lay 54 is secured about the lower portion of shaft 50 and projects out from the bottom of the lower housing member through switch mounting bracket 55. An end portion of the shaft over-lay is contoured to fixedly receive a switch operating knob, not shown, press fitted thereabout. A retaining ring 56 and a torque washer 57 are seated about the extension of shaft 50 projecting to the exterior of housing plate 34. A spline 59 secures the ring to the shaft whereby the axial position of the shaft is set.

To the movable end of switch blade 25 is secured a resilient means, such as an elongate bridge or leaf spring by means of a rivet having a rivet head 72 from which a rivet shank extends thereby to constitute an interconnecting means. The bridge spring is preferably formed of a soft conductor such as a beryllium copper or cadium copper alloy which provides high electric conductivity and low force gradients. The diameter of the rivet shank steps down with the largest size portion 73 extending through a stiffening means, such as a washer 78, sandwiched between rivet head 72 and bridge spring 70, with the intermediate size portion 74 extending through a central portion of bridge spring 70, and with the smallest size portion 75 extending through an apertured bulge section of switch blade 25. The terminal portion of the rivet shank extending beneath the switch blade bulge section is riveted over against the bottom surface of the bulge section as shown at 76.

To two eccentric or opposite end portions of bridge spring 70 are secured two

movable contacts

82 and 83 by means of

rivets

84 and 85, respectively. These two eccentric portions are spaced from switch blade 25 as may be seen by reference to FIG. 9. Being resilient, these portions may each be flexed towards the switch blade by the application of a force directed downwardly upon the movable contacts. To inhibit or prevent appreciable rotation of the bridge spring about the axis of the rivet securing the bridge spring to the switch blade the bridge spring includes an integral tab 88 which is disposed between two offset

switch blade projections

90 and 91 within a slot communicating with a side edge of the switch blade.

To calibrate the switchtoggle adjust screw 93 is set to establish the spring bias of switch blade 25. Temperature differential screw 94 is then set to establish the limit of travel for the switch blade and in so doing the differential or temperature swing range. Bimetal adjust screw 35 is then set in adjusting the bias of the bimetal with respect to that of the switch blade.

For operation, shaft 50 is manually rotated by means of a knob attached to shaft overlay 54. By this action an overlay projection 96 is rotated out of engagement with switch arm 98, as may best be seen by reference to FIG. 4, causing movable contact 99 carried thereby to make with contact 24. Electrical connection is thereby established between

terminals

17 and 19. With terminal 17 coupled with line voltage and terminal 19 with a room air conditioner fan, the fan becomes energized. Rotation of shaft 50 also positions bimetallic blade 33 which has a bulge in sliding contact with cam 33 attached to shaft 50.

FIG. 3 shows the switch components positioned with

movable contacts

82 and 83 made with fixed

contacts

20 and 21, respectively. In this position bridge spring 70, which has relatively low electrical resistance and is but a fraction of an inch in length, couples terminal 18 with terminal 19 and, as previously explained, with terminal 17. With terminal 18 connected to a room air conditioner compressor the compressor is energized. Thus, FIG. 3 illustrates the switch in condition for cooling, that is to say with bimetallic blade 33 sensing a temperature elevated about a preselected minimum. As the sensed temperature of the bimetal decreases due to the cooling effect of the air conditioner,it will exert increasing downward bias against link 37, as viewed in FIG. 3, and thus against the switch blade 25. When this force reaches a preselected magnitude the force of the bimetal overcomes the counterbiasing force of the switch blade causing it to snap and thereby break

contacts

82 and 83 with contacts and 21. This action disconnects terminal 18 from terminal 19 thereby removing the air conditioner condenser from line volt age. The room will then begin to reheat thereby elevating the temperature of the bimetal to a point where the forces between the switch blade and bimetal again pass out of equilibrium causing the switch blade, link, and bimetallic blade to snap upwardly thereby remaking the movable contacts with the fixed contacts to start a new operative cycle.

Operation of the just described switch has been found'to result in extremely little contact bounce. Indeed, such switches have typically exhibited contact bounce of less than 1 millisecond. Oscilloscopic observations demonstrate more of a scrubbing or wiping contact closure as opposed to one or a series of bounces. This in turn has drastically reduced the incidence of contact welding and has reduced corrosive build-up upon the contact surfaces. The interdependency of the two sets of fixed and movable contacts has led to efficiency of the movable contacts in positional self seeking which in turn has reduced the risk of contact welding. In the event a small weld does occur the high force gradient provided by the stiffening washer 7b coupled with the switch blade and bridge spring 70 usually breaks the weld during a contact break operation with both a shear and tension forces being applied thereto. With the fixed and movable contacts closed very little self induced heating has been observed.

It should, of course, be understood that the just described embodiment merely illustrates principles of the invention. Many modifications may be made thereto without departure from the spirit and scope of the invention asset forth in the following claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A snap acting double break switch comprising a I housing, a pair of terminals mounted to said housing,

a pair of mutually spaced fixed contacts mounted within said housing and electrically coupled to said pair of terminals, a snap acting switch blade mounted within said housing, a bridge spring transversely overlaying a movable portion of said switch blade with a central portion of said bridge spring riveted to said switch blade movable portion and with two flexible eccentric portions of said bridge spring carrying a pair of movable contacts to make and break with said pair of fixed contacts upon actuation of said switch blade, said flexible eccentric portions of said bridge spring being spaced from said switch blade when said switch blade is in a predetermined position relative to said fixed contacts, means for actuating said switch blade to cause said movable contacts to make and break with said fixed contacts by moving said switch blade relative to said fixed contacts while permitting said movable contacts flexible movement relative to said switch blade, said bridge spring beingriveted to said switch blade with a rivet having a head and a shank, and wherein said rivet head overlays said bridge spring with a washer sandwiched therebetween about said rivet shank whereby said flexible eccentric portion of said bridge spring may be flexed more easily towards than away from said switch blade.

2. A snap acting double break switch in accordance with claim 1 wherein said actuating means comprises a thermo-responsive element.

3. A snap acting double break switch in accordance with claim 1 wherein said switch blade comprises three spaced leg portions with a section of one of said leg portions adjacent to and offset from a plane defined by sections of said two other leg portions adjacent said one leg section to form a toggle spring.

4. A snap acting double break switch in accordance with claim 1 wherein an edge of said switch blade defines a notch, and wherein said bridge -spring includes a tab projecting into said notch to inhibit rotation of said bridge spring about the rivet.

5. A snap acting double break switch in accordance with claim ll wherein said switch blade movable portion has an apertured bulge surrounded by a substantially planar section, and wherein said rivet shank passes through the bulge aperture and is spread over against a portion of the bulge about the bulge aperture.

6. Means for making and breaking a pair of movable contacts with a pair of fixed contacts in a snap acting double break switch, said means comprising a snap acting switch blade having a movable portion, a bridge spring secured to said switch blade movable portion by fastening means, said bridge spring having two contact support sections disposed about opposite sides of said fastening means with each of said contact support sections being flexibly movable with respect to said switch blade movable portion, and stiffening means sandwiched between said fastening means and said bridge spring whereing said contact support sections are more easily flexed away from said stiffening means than toward it.

7. A snap acting, double break electrical switch comprising a housing having a pair of fixed contacts mounted thereto, means movably mounted in said housing for snap action in opposite directions and normally biased in one direction, means for actuating said snap action means in the other direction; resilient means extending substantially transversely of said snap action means for overlaying engagement therewith and including a pair of movable contacts for engagement with said fixed contacts, means disposed between said movable contacts for interconnecting said resilient means and said snap action means in overlaying engagement, said resilient means being movable with said snap action means upon its biasing actuation in the one direction to engage said movable contacts with said fixed contacts and said resilient means being thereafter yieldable about said interconnecting means in response to a force in excess of a predetermined value exerted thereon in the one direction by said snap action means, and means contained in abutment between said resilient means and said interconnecting means for stiffening said resilient means, said resilient means being yieldable about said stiffening means in response to another force in excess of another predetermined value greater than the first named predetermined value exerted on said resilient means by said snap action means upon actuation thereof in the opposite direction by said actuating means to insure disengagement of said movable contacts from said fixed contacts in the event of minor welding engagement therebetween.

8. A snap acting double break thermostatic switch in accordance with claim 7 wherein said snap action means comprises a switch blade having three spaced leg portions with a section of one of said leg portions adjacent to and offset from a plane defined by sections of said two other leg portions thereby forming a toggle spring.

9. A snap acting double break thermostatic switch in accordance with claim 7 comprising means on said snap acting means for inhibiting said bridge spring resilient means from rotating about said interconnecting means.

10. A'snap acting, double break electrical switch as set forth in claim 7 wherein said resilient means comprises an elongate substantially planar leaf spring.

11. A snap acting, double break electrical switch as set forth in claim 10 wherein said leaf spring comprises a central protion secured to said snap action means in overlaying engagement therewith by said interconnecting means, and opposite yieldable end portions integral with said central portion, said movable contacts being respectively disposed on said end portions.

12. A snap acting, double break electrical switch as set forth in claim 7 wherein said strengthening means comprises a washer disposed about said interconnecting means and contained in abutment between said resilient means and'said interconnecting means.

13. A snap acting, double break electrical switch as set forth in claim 7 wherein said interconnecting means comprises means extending through said strengthening means, said resilient means and said snap action means and including a pair of opposed means disposed in displacement preventing engagement with said stiffening means and said snap action means and urging them into abutment with said resilient means.

14. A snap acting, double break electrical switch as set forth in claim 7 wherein said interconnecting means comprises a rivet having a head and a shank, said rivet head overlaying said stiffening means urging it into engagement with said resilient means and urging said resilient means into engagement with said snap action means, and said shank passing through said stiffening means, resilient means and snap action means for displacement preventing engagement with a portion of said snap action means.

15. A snap acting, double break electrical switch as set forth in claim 7 wherein said actuating means comprises a thermoresponsive element.

16. A snap acting, double break electrical switch as set forth in claim 15 comprising means for mechanically coupling said thermoresponsive means with said snap action means.

Claims

1. A snap acting double break switch comprising a housing, a pair of terminals mounted to said housing, a pair of mutually spaced fixed contacts mounted within said housing and electrically coupled to said pair of terminals, a snap acting switch blade mounted within said housing, a bridge spring transversely overlaying a movable portion of said switch blade with a central portion of said bridge spring riveted to said switch blade movable portion and with two flexible eccentric portions of said bridge spring carrying a pair of movable contacts to make and break with said pair of fixed contacts upon actuation of said switch blade, said flexible eccentric portions of said bridge spring being spaced from said switch blade when said switch blade is in a predetermined position relative to said fixed contacts, means for actuating said switch blade to cause said movable contacts to make and break with said fixed contacts by moving said switch blade relative to said fixed contacts while permitting said movable contacts flexible movement relative to said switch blade, said bridge spring being riveted to said switch blade with a rivet having a head and a shank, and wherein said rivet head overlays said bridge spring with a washer sandwiched therebetween about said rivet shank whereby said flexible eccentric portion of said bridge spring may be flexed more easily towards than away from said switch blade.

4. A snap acting double break switch in accordance with claim 1 wherein an edge of said switch blade defines a notch, and wherein said bridge spring includes a tab projecting into said notch to inhibit rotation of said bridge spring about the rivet.

5. A snap acting double break switch in accordance with claim 1 wherein said switch blade movable portion has an apertured bulge surrounded by a substantially planar section, and wherein said rivet shank passes through the bulge aperture and is spread over against a portion of the bulge about the bulge aperture.

6. Means for making and breaking a pair of movable contacts with a pair of fixed contacts in a snap acting double break switch, said means comprising a snap acting switch blade having a movable portion, a bridge spring secured to said switch blade movable portion by Fastening means, said bridge spring having two contact support sections disposed about opposite sides of said fastening means with each of said contact support sections being flexibly movable with respect to said switch blade movable portion, and stiffening means sandwiched between said fastening means and said bridge spring wherein said contact support sections are more easily flexed away from said stiffening means than toward it.

10. A snap acting, double break electrical switch as set forth in claim 7 wherein said resilient means comprises an elongate substantially planar leaf spring.

11. A snap acting, double break electrical switch as set forth in claim 10 wherein said leaf spring comprises a central portion secured to said snap action means in overlaying engagement therewith by said interconnecting means, and opposite yieldable end portions integral with said central portion, said movable contacts being respectively disposed on said end portions.

12. A snap acting, double break electrical switch as set forth in claim 7 wherein said strengthening means comprises a washer disposed about said interconnecting means and contained in abutment between said resilient means and said interconnecting means.