US2813173A - Thermal cycling switch - Google Patents

Description

Nov. 12, 1957 G. H, RlsACHER m-AL 2,813,173

THERMAL CYCLING SWITCH Filed June 21, 1955 n /r 7 4 2 2 8 4 l 2 5 6 4 |I. 6 u 2 G F A 8 4 7 2 f h2 4 lOQ TORN EY United States Patent O 2,813,173 n THERMAL CYCLING SWITCH Gerard H. Risacher and Harold P. Allen, Mansfield, Ohio, assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application .lune 21, 1955, Serial No. 516,964 6 Claims. (Cl. 200-122) This invention relates to a thermal cycling switch for controlling the rate of energization of an electric heater, particularly of the type used in range surface units.

It is an object of this invention to provide an improved switch of the above-mentioned type having manually operated means for adjusting the switch to infinitely vary the heat output of an electric heater between predetermined maximum and minimum rates of heating.

Another object of this invention is to reduce contact wear in a simple and inexpensive switch of the abovementioned type having means for positively making and breaking a heater circuit at the switch contacts.

A further object of this invention is to accelerate the contact separating movement `in a thermal cycling switch.

A further object of this invention is to accelerate the Contact separating movement in a thermal cycling switch having ambient temperature compensating means.

In accordance with this invention, a cycling contact is supported on the free end of a main bimetallic strip that is heated by an auxiliary heater. The cycling contact is actuated by the main bimetallic strip into and out of engagement with an adjusted contact to make and break an electrical circuit through the auxiliary heater and through -a main heater to be Controlled. The adjusted contact is actuated by a structure including a differential or contact accelerating bimetallic strip and an ambient temperature compensating bimetalli'c strip and cy a manually controlled cam. The cam adjusts the switch to permit infinite selection of the rate of heat output of the main heater.

These and other objects are effected by the invention as will be apparent from the following description taken in connection with the accompanying drawings, forming a part of this application, in which:

Fig. 1 is a front elevation of a thermal cycling switch with the front cover thereof removed;

Fig. 2 yis a vertical section taken along the line lI-II of Fig. 1;

Fig. 3 is a perspective view of the main bimetal subassembly removed from the switch shown in Fig. 1; and

Fig. 4 is a perspective View of the assembly of compensating and contact accelerating bimetals removed from the switch shown in Fig. 1.

The thermal cycling switch assembly comprises an open-front box-shaped casing 11 of yinsulating material having a base or rear wall 13. Supported within the casing 11 is a main switch 19 having a cycling contact 29 and an adjusted contact 30. The cycling contact 2G is supported and actuated by a structure or subassembly 22, shown in Fig. 3, comprising a main bimetallic strip 24 and an auxiliary heater 26. The'bimetallic strip 24 will deflect upwardly when heated tending to move contact away from contact 30. The subassembly 22 is supported by a terminal 27 mounted on the base 13.

The adjustable. contact 30 is positioned to cooperate with the cycling contact 20 by a subassembly 32, shown in Fig. 4, comprising a contact accelerating bmetallic to move Contact 3G toward Contact Ztl.

Patented Nov. 12, 1957 strip 34 and an ambient temperature compensating bimetallic strip 36. Both strips 34 and 36 when heated tend The subassembly 32 is supported in the casing by a terminal 37. The bimetal 34 has a small cross section and very small mass in comparison to the main bimetal 24 to permit it to be rapidly self-heated and quickly cooled for a purpose hereinafter' described. The switch circuit between the terminals 27 and 37 will be cyclically opened and closed at the contacts 20 and 3l) to control the rate of energiza` tion of a main heater (not shown) connected in series therewith across a suitable power source.

One end of the main bimetal 24 is pivotally connected to the terminal 27 by means of a exible hinge strip 42. The hinge strip 42 is electrically insulated from the terminal 27 by thin mica sheets 44 to prevent the bimetal 24 from shunting the heater strip 26. The heater strip 26 extends from the terminal 27 along substantially the entire length of the main bimetal 24 adjacent the high expansion side thereof and has its `other end secured, as by welding, between the cycling contact 20 and the free end of the main bimetal 24. Thin electrically insulating mica sheets 46 are provided on both sides of the heater strip 26 along the main bimetal 24, and a brass plate 47 holds the heater strip 26 in good heat transfer relationship with thermain bimetal 24 by means of ears 48 bent around the edge of the latter. A small loop 49 is formed in the heater strip 26 adjacent the terminal 27 to minimize the efect of expansion and contraction of the strip on the operation of the main bimetal 24. The base 13 of the casing is partially cut away to the rear of the main bimetal 24 to permit circulation of air within the casing for cooling the main bimetal during its cycling operation.

The main bimetal 24 may be adjusted on its pivotal support by means of a rigid L-shaped lever 52 having its shorter arm rigidly connected thereto adjacent the hinge strip 42. An adjusting screw 56 extends through a hole in the stationary bracket 58 attached to the casing 11 and is threaded in the end of the longer arm `of the .lever 52. rl`his arm is biased away from the bracket 58 by a coil spring 54 to a position determined by the adjusting screw. Rotation of the screw will cause the lever 52 to be moved and thus adjust the pivotal position of the bimetal 24.

In the subassembly shown in Fig. 4, one end of each of the bimetals 34 and 36 is supported by the free end 64 of a resilient conducting strip 60. The strip 60 is riveted to the terminal 37 and extends generally parallel to the main bimetal 24 with its free end 64 positioned opposite an intermediate portion of the latter. The other end of the bimetal 34 supports the adjustable contact 30 in a position opposite the cycling contact 20 on the end of the main bimetal 24 as shown in Fig. l. The compensating bimetal 36 extends in the direction generally opposite the bimetal 34 and generally parallel to the resilient strip 60 on the side thereof remote from the main bimetal 24. The other end of the compensating bimetal engages a bearing surface 66 formed by the terminal 37.

An insulating member 68 of ceramic material is positioned between the adjacent ends of the bimetals 34 and 36 to reduce the heat transfer therebetween. The opposite faces of the insulating member 68 are channeled to receive the strip 60 and the bimetals 34 and 36 to prevent them from rotating relative to each other. A rivet 69 rigidly clamps the bimetals and the strip 60 in the channels with the strips 60 and 34 in good electrical contact with each other.

A portion 70 of the compensating bimetal strip 36 intermediate its ends is bent or formed out of the general plane of the strip to act as a cam follower on an active bearing surface 71 of a cam 72. The cam 72 is mounted for rotation about an axis generally parallel to the active surface 71 and normal to the plane of deflection of the bimetal strips 24, 34 and 36. An operating shaft 74 extends through the canL 72 and is keyed thereto by means of a hat surface 75 on the shaft. A bearing support for the cam 72 comprises a conic-ally tapered member 76 on the base 13 coaxial with the shaft and engaged by the surface of a conical recess 77 in the body of the cam 72. Spring 78, positioned between the cam 72 and the casing cover 79, biases the two conical surfaces into engagement with each other. This cam construction is described and claimed in a copending application of Joseph S. Wojcik, Serial No. 516,411, filed June 20, 1955, and assigned to the assignee of the present invention.

The active cam surface 7l that is engaged by the compensating bimetal strip 36 has a low or off portion S0, -a hi-gh or full heat portion S1 and an infinite number of intermediate portions for varying the rate of energization of the main heating element. The compensating bimetal .strip 36 is biased into engagement with the active l cam surface 71 by the resilient strip 60. The cam operates as a fulcrum, causing the force exerted by the resilient strip 60 on one end of the bimetal strip 36 to pivot the latter on the cam and maintain its other end in engagement with the bearing surface 66 in all positions of the cam. The three bimetallic strips 24, 34 and 36 deflect i in a plane generally parallel to the base 13. The high expansion sides of the birnetals face the same general direction, that is, toward the cam 72. l

The cam 72 has a second active surface 34 in a rear portion of the casing 11 to actuate a pair of L- shaped spring arms 85 and 86, operating a pilot light switch 82 and a line switch 83, respectively. The spring arms 8S and 86 have fixed ends fastened together on a terminal 87. The free end of the arm 8S supports the movable contact of the pilot light switch 82. An intermediate cam follower portion 91 of the spring arm 85 projects toward the cam surface 84, and an adjacent portion 92 extends in the opposite direction to engage the other spring arm 36 intermediate its ends and move it in response to movement of the cam 72. The free end of the spring arm 86 supports the`movable contact of the line switch 83.

Both of the spring arms 85 and 86 are self-biased towards the cam surface 84. A single high point 96 on this cam surface is located Vso that both the pilot light switch and the line switch are opened only when the cam surface 7l is adjusted to the olf position. ln all other adjusted positions of the cam, the cam `surface 84 is too low to engage the spring arm 85, so that the switches 82 and S3 are closed.

The cam is provided adjacent the cover 79 with a starwheel V97 having a plurality of notches 98 spaced about theV shaft 74. A leaf spring 99 having opposite ends supported in recesses 100 in the casing wall 12 has a detent '101 at its Vcenter biased upwardly into engagement with the starwheel 97. The detent 101 and notches 9S permit the cam to be readily adjusted to any one of a plurality of active positions and to an off position. However, the cam may be adjusted to an infinite number of positions in which the detent 1911 does not slip into one of the notches 98, but rather rides on a portion of the surface of the starwheel 97 between the notches.

This thermal cycling control and the main heater (not shown) may be electrically connected with the switches 83 and 19 arranged, respectively, on opposite sides of the heater in the energizing conductors that are connected to a power source. Y

Operation Y in which the switch 19 is open. At the Sametime, the

cam surfae'portion 96 is in engagement with the switch arm S5 to maintaln the switches 32 and 83 in open position. The switches 19 and 83, when open, isolate the heater from both sides of the power source.

Upon actuation of the control from the off position to an intermediate heat position, the cam portion 96 moves out of engagement with the switch arm 85, permitting the switches 32 and 33 to close. At the same time, an intermediate portion of the active cam surface 71 engages the compensatingbirnetal 36 and raises it to bring the contact 39 into engagement with the contact 29, to begin intermittent or cycling operation. When current flows through these contacts, it also ows in series therewith through the auxiliary heater 26 to gradually heat the main bimetal 24, and through the self-heated bimetal 34 to rapidly heat the latter. Both bimetals deliect upwardly in response to an increase in temperature, but the bimetal 34 initially tends to deect at a more rapid rate than the bimetal 24 because of its physical characteristics. The bimetal 34 will thus press toward the main bimetal and increase the contact pressure during the first portion of the movement of the main bimetal 24 as the latter deliects upon heating. I

As the two bimetals 24 and 34 deflect together in respense to heating, the bimetal 34 will reach its point of maximum deflection after a period of time and will stop, but the main bimetal 24 will continue deflecting upwardly until it separates the contacts 20 and 30. The thermal inertia of the main bimetal structure causes the latter to deflect slightly further in contact opening direction, whereas the bimetal 34 quickly cools, due to its small mass, to deect in the opposite direction at a rapid rate. The bimetal 34 thus accelerates the contact Iseparation and, when cooled, stops in a position slightly higher than that in which the contacts were lirst engaged while the cam surface was being adjusted from off to a cycling position. The main bimetal 24 cools and causes the contact 20 to reengage contact 30. The main bimetal will continue to deflect downwardly to a slight extent, due to its thermal inertia, after the contacts are engaged. The current owing through the heater 26 and the selfheated bimetal 34 will cause the bimetals 24 and 34 to again deflect upwardly. r[he bimetal 34 again tends to deflect to increase the contact pressure during the first portion of the movement of the latter.

The switch will repeat the `same cycle of contact closing and contact opening by the bimetals as described immediately above. As `long as the adjusted cam 72 remains in a fixed cycling position, the succeeding cycles of operation of the switch will be substantially identical, except for the change in the movement of contacts 20 and 30 in response to changes in ambient temperature.

The percentage of closed contact or on time with respect to total cycling time may be varied by adjusting the cam surface 71. As'the cam moves or biases the adjusted contact 30 farther in the direction toward the cycling contact 20, the percentage ofV on time relative the total cycling timewill be increased, since it will take longer for the main bimetal 24 to be heated and deflected away from the bimetal 34.

When the ambient temperature within the casing 11 rises, the main bimetal-24V will respond to this temperature rise and will deect further in contact opening direction, thereby tending to decrease the percentage of the total cycling time that the contacts 20 and 30 are engaged. To compensate for the additional deflection of the main bimetal and the Contact 20 due to an'ambient temperature rise, the compensating bimetal 36 deects in response to the rise in ambient temperature to move or bias the Ycontact 30 in the direction of the cycling contact 20 to maintain the percentage of on time relative the total cycling time substantially independent of changes in ambient temperature. When the ambient temperature drops, the main bimetal will not move as far in contact opening `direction and the compensating bimetal will deliect, moving contact 30 in theV direction away from contact 20, so as to keep the percentage Yof on time substantially constantY for each position of cam 72.

When the cam 72 is adjusted to the maximum or full heat position with the bimetal 36 engaging the cam portion 81, the adjusted contact 30 will be moved and biased upwardly to such extent that the main bimetal 24 cannot deflect sufficiently, even when continuously heated by the heater strip 26, to move the cycling contact 20 out of engagement with the adjusted contact 30.

While the invention has been shown in but one form, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various changes and modifications without departing from the spirit thereof.

What is claimed is:

l. A thermal cycling switch assembly comprising a casing, a resilient electrically conducting strip within said casing and having one en d rigidly supported therein, a first bimetal strip having one end fastened to the free end of said resilient strip, an adjustable contact attached to the other end of said bimetal strip, a compensating bimetal strip having one end supported by the free end of said resilient strip, a bearing ysurface supported by the casing for engaging the other end of said compensating bimetal strip, an adjustable cam having an active surface engaging an intermediate portion of said compensating bimetal, said compensating bimetal being biased into engagement with said cam by forces exerted thereon by said resilient strip and said bearing surface, a main bimetal strip having one end supported in said casing, a cycling contact supported on the other end of said main bimetal and positioned thereby to cooperate with said adjustable contact, and a heater for said main bimetal, said heater being connected in series with said contacts and said first bimetal strip, and means for clamping said heater to said main bimetal and electrically insulating the same therefrom along at least a part of its length, said bimetal strips being positioned with their high expansion sides facing the same general direction.

2. A thermal cycling switch assembly comprising a base, a resilient electrically conducting strip having one end fixed on said base and a movable second end, a first bimetal having one end fastened to the movable end of said resilient strip, an adjustable contact attached to the opposite end of said bimetal, a compensating bimetal having one end supported by the movable end of said resilient strip, a bearing surface supported by the base for engaging the other end of said compensating bimetal, an adjustable cam having an active surface engaging an intermediate portion of said compensating bimetal, said compensating bimetal being pivotally biased into engagement with said cam and said bearing surface by said resilient strip, a main bimetal having one end supported on said base, a cycling contact supported on the other end of said main bimetal and positioned thereby to engage said adjustable Contact, a heater adjacent said main bimetal, said heater being connected in series with said contacts and said first bimetal, means for clamping said heater to said main bimetal and electrically insulating the same therefrom along at least a part of its length, said bimetals being positioned with their high expansion sides facing the same general direction, and thermal insulating means positioned between the ends of said rst mentioned bimetal and said compensating bimetal adjacent the free end of said resilient strip to reduce the transfer of heat therebetween.

3. A thermal cycling switch comprising a base, a first contact-actuating structure including an ambient temperature compensating bimetal and a second bimetal rigidly connected to one end of said compensating bimetal, a pair of spaced bearing surfaces on said base engaged by said supporting structure, a resilient member connected to said base and biasing said structure into engagement with said bearing surfaces, a first contact attached to one of said bimetals at a point spaced from each of said bearing surfaces, a second contact-actuating structure including a main bimetal supported at one end by said base, a second contact attached to the other end of said bimetal and posivtioned thereby to cooperate with said first contact, electrical heating means for said main bimetal, said heating means, said second bimetal and said contacts being connected in series, each of said compensating and second bimetals being arranged to move said first contact in the direction toward said second contact upon being heated, said main bimetal being arranged to move said second contact in the same direction, away from said first contact, upon being heated.

4. A thermal cycling switch assembly comprising a casing, a resilient electrically conducting strip mounted within said casing, a rst bimetal strip having one end fastened to a deflectable portion of said strip, an adjustable contact attached to the other end of said bimetal strip, an ambient temperature compensating bimetal strip having one end supported by said resilient strip adjacent said first bimetal strip, a bearing surface supported by the casing and engaging the other end of said compensating bimetal strip, an adjustable cam having an active surface engaging an intermediate portion of said compensating bimetal strip, the latter strip being biased into engagement with said cam by forces exerted thereon by said resilient strip and said bearing surface, a main bimetal strip supported in said casing, a contact attached to a deflectable portion of said main bimetal strip and positioned thereby to cooperate with said adjustable contact, said main bimetal strip being deflectable in contact separating direction upon being heated, electrical heating means connected in series with said contacts and said first bimetal strip for heating said main bimetal strip, said bimetal strips being positioned with their high expansion sides facing the same general direction.

5. A thermal cycling switch assembly comprising a casing, a resilient electrically conducting strip mounted within said casing, a first bimetal strip having one end fastened to a deiiectable portion of said strip, an adjustable contact attached to the other end of said bimetal strip, an ambient temperature compensating bimetal strip having one end supported by said resilient strip adjacent said first bimetal strip, thermal insulating means positioned between the ends of said first-mentioned bimetal strip and said compensating bimetal strip at the defiectable portion of said resilient strip to reduce the transfer of heat between the bimetal strips, a bearing surface supported by the casing and engaging the other end of said compensating bimetal strip, an adjustable cam having an active surface engaging an intermediate portion of said compensating bimetal strip, the latter strip being biased into engagement with said cam by forces exerted thereon by said resilient strip and said bearing surface, a main bimetal strip supported in said casing, a contact attached to a deflectable portion of said main bimetal strip and positioned thereby to cooperate with said adjustable contact, said main bimetal strip being deflectable in contact separating direction upon being heated, electrical heating means connected in series with said contacts and said first bimetal strip for heating said main bimetal strip, said bimetal strips being positioned with their high expansion sides facing the same general direction.

6. A thermal cycling switch assembly comprising a casing, a resilient electrically conducting strip mounted within said casing, a first bimetal strip having one end fastened to a deectable portion of said strip, an adjustable contact attached to the other end of said bimetal strip, an ambient temperature compensating bimetal strip having one end supported by said resilient strip adjacent said first bimetal strip, thermal insulating means positioned between said first-mentioned bimetal strip and said compensating bimetal strip to reduce the transfer of heat therebetween, said first-mentioned bimetal strip and said compensating bimetal strip extending in opposite directions from said dellectable portion of said resilient strip, a bearing surface supported by the casing and engaging the other end of said separating direction upon being heated, electrical heating 10 CTI l8 means connected in series with said contacts and said first bimetal strip for heating said main bimetal strip, said birnetalistrips being positioned Vwith their high expansion sides facingthe same general direction.

References Cited in the le of this patent UNITED STATES PATENTS Hanser et a1. July 4, 1933 Clapp Mar. 30, 1954

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