US2425030A - Heating apparatus switch - Google Patents

Description

Aug' 5, 1947. E. K. CLARK ZAZ HEATING APPARATUS SWITCH Filed Sept. 22, 1942 5 Sheets-Sheen 2 55 sa 5a 15g.

INVENTOR EARL, V. CLARK ATTORNEY Allg. 5, 1947. E, K, CLARK 2,425,030

HEATING APPARATUS SWITCH Filed Sept. 22, 1942 3 Sheets-Sheet 3 L Ll C L"N 7 f LL 2.

Ufa

21 62. 22 c/ c! /y /45 /64'5 MNM/4L AAW/4L wlTNEss-s: n v C7 7 INVENTOR G F Emu. Ka (imm BY o I l* y A oRNEY Patented Aug. 5, 1947 2,425,030 HEATING APPARATUS SWITCH Earl K. Clark, Mansfield, Ohio, assigner to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Appiieeaep september 22, 1942, serial No. 459,253

7 Claims. l

This invention relates to heating apparatus and particularly to a control device therefor which is especially adapted to control the wattage input to the heating apparatus, and it has for an object to provide an improved device of the character set forth.

It is also an object of the invention to provide a control including a thermally-operated cycling switch wherein the wattage input to the heating apparatus is not materially affected by variations in ambient temperatures at the control and, therefore, it is not necessary to compensate for ambient temperature changes.

It is another object of the invention to provide a control including a thermallyoperated cycling switch in which the switching cycles are of substantially uniform duration irrespective of normal changes in ambient temperatures eilecting the control switch, and regardless of the selected wattage input to the heating apparatus to be con trolled.

It is a still further object of the invention to provide a thermally-operated cycling switch in which the circuit-making and circuit-breaking switching operations are such that the time interval during which the circuit is closed may be adjusted to an extremely short interval to provide a minimum wattage input to the circuit controlled by the switch.

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

Fig. l is a perspective view of an electric cooking range in which the present invention is incorporated;

Fig. 2 is an .elevational view of the present control with the cover thereof removed and parts shown in section;

Fig. 3 is a fragmentary elevational view corresponding to a portion of Fig. 2 and showing the movable parts in a position different from that in Fig. 2; I

Fig. 4 is a sectional view taken substantially on the line IV--IV of Fig, 2;

Fig. 5 is a. diagrammatic view of the control shown in the previous figures and including a wiring diagram to illustrate one application of the invention;

Figs. 6 and 7 are diagrammatic views similar to Fig. 5 but omitting the wiring diagram and showing the position of the switch contacts at different points in a cycle of operation of the control; and

(Cl. 20o-122) Figs. 8 and 9 are time-temperature graphs illustrating the cycle of the thermal motor employed in the present control and showing the ef fect of changes in ambient temperature at the motor.

The control, generally indicated I0, comprises two sets of contacts II electrically connected in series as shown particularly in Fig. 5 and a thermal motor, generally indicated as I2 in Figure 2, which intermittently opens and closes these contacts. When both sets of contacts are closed, they complete a circuit for an electrical resistance element such as I3 in Fig. 5, which may be a surface heating element or an oven heating element of the range shown in Fig. 1. The control isV adjustable so that the ratio between the length of time both sets of contacts are closed to the length of time one or the other of them is open to interrupt the circuit may be varied to provide a preselected Wattage input to the resistance element I3. y g

Thel control is arranged in a compact housing I4 preferably made of insulating material and provided with a cover (not shown). The housing may be conveniently mounted at the rear of the backsplasher of the range shown in Fig. 1, as illustrated by dotted lines, with its adjusting knob I5 accessible at the front. I'he housing carries two supply line terminals I8 having fixed contacts I 'I which are engageable by movable contacts I8 carried by long springs I9. These springs are fixed to terminal brackets 2| and 22 at the lower end of the housing- The movable contacts I8 are moved into and out of engagement with their respective fixed contacts II by means oi' a cam 23. This cam is provided with notches 24 laterally offset relative to each other and which are adapted to receive integral lug portions 25 of the springs I9 when the control is set at its off position. The off position of the control I0 is shown in Fig. 2 where it will be noted that the lugs 25 are received in the notches 24, the natural bias of the springs holding contacts I 'I and I8 open.

Cam 23 is xed on a shaft 26, journaled in the rear wall of the. housing, as shown in Fig. 4. By rotating the knob I5 from its "ofP position, the lugs 25 ride on the cylindrical surface of the cam 23 to maintain the-movable contacts I8 in engagement with fixed contacts II as shown in Fig. 3.

It will be understood that supply conductors, such as L1 and La of a conventional Edison threewire system, are connected to the terminals I6 as shown in Fig. 5 and that the contacts Il and I8 comprise a double-pole line switch to control 3 the supply of electricity to the thermal motor I2 and to the circuit controlled by the device of the present invention.

The thermal motor I2 is mounted in the lower portion of the housing and comprises a bimetal member 21 xed to a bracket 28 which may be adjustably secured to the bottom wall of the housing to permit adjustment of the bimetal with respect to the cycling contacts II. The upper free end of this bimetal has riveted thereto a U-shaped spring 23 which is received in an opening 3l provided in a horizontal bar 32 and prevents lost motion between the bimetal and bar.

The bimetal 21 is intermittently heated by means of a resistance 33 which is shown schematically as wrapped about the bimetal, although it is to be understood that the bimetal heating means may be associated with the bimetal in any suitable manner. When the resistance is energized to heat the bimetal, the |bimetal bows to the left, as viewed in Fig. 2, and upon deenergization of the heater, the bimetal cools and moves to the right.

The right end of the bar 32, which, it will be understood is moved by the bimetal, is provided with a depending bracket 34 which carries a stop and switch-operating stud 35. This stud passes through and is journaled in an opening 33 provided in a plate 31 secured to the housing I4 by means of ears 38 integrally formed thereon and fastened to bosses 39 provided on the side wall of the housing.

By reference to Figs. 2 and 3, it will be noted that the travel of the bar 32 to the right is limited by engagement of the bracket 34 with the plate 31, as shown in Fig. 2, and travel to the left by engagement of shoulder 4I of the stud 35 with the plate 31, as shown in Fig. 3.

The stud 35 also operates a switch which controls the energization of the bimetal heating element 33. This switch comprises an adjustable contact screw 42 threaded into the side wall of the housing and a cooperating contact 43 carried by a snap-acting spring member 44, preferably of the so-called Valverde type. The snap-acting member 44 comprises three legs connected together at their ends, the outer legs 45 being made shorter than the central leg 43, as by crimping. The center leg 45 is ilxed to plate 31 by means of a stud 41.

The operation of the switch, comprising contacts 42 and 43 for the bimetal heater 33 is briefly as follows: In Fig. 2 the parts are shown in the position they assume when the bimetal 21 has cooled sufciently for the bar 32 to reach its extreme right position at which time the stud 35 has caused the snap-acting spring 44 to snap over to the position shown in this gure and close the contacts 42 and 43. With these contacts closed. a circuit is established from neutral conductor N of the supply source (Fig. 5), through the closed contacts 42--43, conductor 48, the heating element 33, conductor 49, terminal 22, right spring member I9 and closed contacts I8 and I1 of the line switch to L1 of the supply line. With this circuit complete, heating element 33 heats the bimetal causing it to bow to the left, as viewed, in Fig. 2, to move the bar 32 and the stud 35 carried thereby to the .position shown in Fig. 3 by which time nut 5I carried by the stud causes the snap-acting spring 44 to snap over to the position shown in Fig. 3 and open contacts 42 and 43 and thereby deenergize the bimetal heating element.

When the snap-acting spring 44 snaps over to open the contacts 42 and 43, the lower free end of this spring engages an adjustable stop 52 carried by the plate 31, as shown in Fig. 3. It will be appreciated that the contact screw 42 and stop 52 may be adjusted relative to each other and to the lower free end of the snap-acting spring 44 so that the snap-acting spring may be made to operate between the limits determined by the length of travel of the switch-actuating stud 35.

With the bimetal heating element 33 deenergized, the bimetal 21 begins to cool and moves the bar 32 to the right until it reaches the position shown in Fig. 2 at which time the cycle described above will be repeated.

The bar is continuously reciprocated as long as the line switch contacts I1-I8 are closed and as will appear later intermittently opens and closes the switch contacts I I during the middle of its travel while effecting switching of contacts 42 and 43 at each end of its travel. In other words, the cycling switches II are actuated in spacedtime relation to the actuation ot the switch 42 43. Each set of cycling contacts II include an adjustable contact 53 and a movable contact 54 biased toward its respective adjustable contact 53. The contacts 53 are simultaneously adjustable relative to their respective movable contacts 54 to vary the length of time both sets of contacts 53--54 are closed during each half cycle of the thermal motor I2 to increase or decrease the average wattage input to the resistance I3 controlled by these contacts. The manner of operating these contacts and adjusting them to vary the wattage input to the controlled circuit is described hereinafter.

The adjustable contacts 53 are carried by contact bars 55 which are fixed to the free ends of a U-shaped spring member 55 iixed to the upper end wall of the housing I4. This spring member serves to electrically connect, the contact bars 55 and their contacts 53 and is so arranged that it biases the bars toward each other, to maintain adjustable stops or screws 51 carried thereby, in engagement with cams 58 and 53, respectively.

The cams 58 and 53, are fixed to the shaft 26, and are identical and arranged so that they simultaneously swing the contact bars 55 away from or toward each other as the shaft is turned by knob I5.

The movable contacts 54 are mounted on arms 5I which are, in turn, hingedly mounted on terminal brackets 52 and 22, respectively, by means of spring strips 53. These spring strips are so arranged that they tend to bias the contacts 54 into engagement with their respective adjustable contacts 53. The arms 6I extend through openings 64 and 55 provided in the reciprocating horizontal bar 32.

From the above description, it will be seen that with the line switch contacts I1 and I8 closed, the horizontal bar 32 continuously reciprocates and that by proper association 0f the openings 64 and 65 through which the arms 8l extend, these arms and their contacts 54 are alternately moved in a direction away from and, due to the bias of their hinge springs 63, toward their respective movable contacts 53.

Operation It will be seen that in the condition shown in Fig. 2, with the control knob I5 set at "off, the line switch contacts I1 and I8 are held open and that the right-hand pair of contacts 53 and 54 of the cycling switch are also open. However, on turning the adjusting shaft from its o position to an active position, the condition represented in Fig. will result, wherein the line switch contacts I1 and IB are now closed causing energization of the bimetal heater 33 as already explained. It will be understood that turning of knob I5 from its off position causes cams 58 and 53 to swing the movable contacts 53 outwardly away from each other and toward their respective movable contacts 54. With the re sistance 33 energized, the bimetal 21 begins to bow to the left and moves the horizontal bar 32 to the left permitting the right-hand contact arm 6I and its contact 54 to approach the right-hand adjustable contact 53 until the switches are in the position shown in Fig. 6. At this time both sets of the cycling contacts are closed since the bar 32 has not yet begun to move the left-hand Contact arm 5I. An energizing circuit for the resistance I3 is now complete. This circuit may be traced in Figs. 2 or 5 from one side L1 of the supply line, closed contacts Il and I8 of the line switch, through right spring I9, terminal bracket 22, right contact arm 6I, closed cycling contacts 53 and 54 and their connecting spring 56, left contact arm 6I, conductor 51 to one side of the Y heating element I3 and from the other side thereor through the left spring I9 and closed contacts Il and I8 of the line switch to the other side L2 of the supply line.

However, the bimetal continues to be heated until the bar reaches substantially its extreme left position, as shown in Fig. 3, but before this occurs, the left pair of cycling contacts 53 and 54 will have opened, as shown in Fig. '7, to interrupt the circuit just described. .Thus, the energizing circuit for the heating element I3 is completed during a portion only of \the time it takes the bar 32 to travel from right\to left through the heating-up period of the bimetal 2l. Similarly during the cooling-down period of the bimetal, the same sequence of operations described above in connection with the cycling switch contacts 53 and 54 is repeated except that the left pair of cycling contacts53 and 54 close to complete the circuit and the rigift pair of contacts open to interrupt the circuit. It will be understood thatv cams 58 and 59 adjustably position the contacts 53 to fix the ratio between the period o! time the contacts 53 and 54 are simultaneously closed to the period they are open for each cycle of the bar 32. Thus, if contacts 53 and 54 are both closed for one-half the time cycle of the bar 32, one-half wattage input is Provided for the heating element I3.

For each complete cycle of the bimetal motor, that is, a complete reciprocation of the bar 32, the energizing circuit for the heating element is established twice and by selecting a bimetal 21 and heater which provides a two minute cycle, the heating element I3 is energized twice every two minutes. Thus, while this .is an on and off control, the cycle is suiliciently short so that the eiect is substantially the same as varying continuous wattage input. A further advantage arising from the present arrangement of the cycling contacts is that for each half cycle of the bimetal motor, one pair of cycling contacts completes the energizing circuit and the other pair o! cycling contacts interrupts the circuit so that the life of these contacts is doubled as compared to cycling contacts wherein the same set of contacts interrupts and completes the circuit.

The cams 53 and 59, which position the contact arms 55 and their contacts 53 with respect to the associated movable contacts 54, are preferably shaped so that, within the low wattage range of adjustment which provides relatively short on periods for the heating element i3, relatively great movement of the knob is require-d to effect a small change in the wattage input and the adjustment in the higher wattage input range is relatively coarse so that a small movement of the adjusting shaft effects a substantial change in the wattage input to the heating ele ment I3. It is understood that the knob i5 will be provided with a suitable scale. v

By providing the on period for the resistance element I3 lat the center el" the heating and cooling periods of the bimetal motor, it is possible to obtain a minimum time on interval. to provide an extremely low wattage input to the resistance element. For example, if the on interval were at either end of the thermal cycle of the Minetti motor, the three following factors would ce instrumental in adding to the minimum time on interval obtained at the minimum switch setting. These factors are:

(l) .Annulment of the bimetal deflection as a result of engagement of the bimetal with the cycling switch contact. `That is, movement oi the bimetal is arrested until it develops enough crce to overcome the spring bias exerted by the switch contact arm.

(2) Annulment of the bimetal deflection as a result of operating the bimetal motor switch,

f which must be snap-acting.

(3) The time interval required for the himetal to change its direction of deection at the end of its thermal cycle due to thermal storage and lag of the bimetal heating element.

The present control eliminates factor 2 in that the cycling contacts are actuated at a time other than when the bimetal is actuating snapacting bimetal switch and it also eliminates iacm tor 3 since the bimetal actuates the cycling con tacts in the middle of its travel, while the thermal storage and lag of the bimetal heating element is eiective only at` the ends of the heating and cooling periods of the bimetal.

The graphs of Figs. 8 and 9 illustrate the fact that normal changes in ambient temperature at the bimetal 21 have little effect on the cycling period of the bimetal and the wattage input to been plotted against time for a complete cycle of the thermal motor. 'The lower horizontal line A represents the temperature at which the bimetal heater switch 42--43 closes and the upper horl- Zontal line B the temperature at which this kswitch opens. Thus, beginning at the point C in the graph of Figli, the himetal temperature rises along the curve D initil the upper temperature limit B is reached, asA indicated 'oy point at which time the switch 42-43 opens to deenerM gize the bimetal heater. The himetal then cools along the curve F until the lower temperature limit A is reached at point G when the switch 42-43 again closes to begin. a new cycle. The graph of Fig. 8 gives an'approi-.imate timetemperature indication with an assumed ambient temperature of'ilO F. at the bimetal.

In Fig. 9 the same cycle has been plotted out with an assumed ambient temperature of F. It will be noted that with the higher ambient tem perature the heating period of the loimctal is shorter but the cooling period is longer than with 7 the lower ambient temperature, with the result that the length cf the cycles is substantially the same for the different ambient temperatures.

As previously explained, both sets of cycling contacts 53--54 are closed during the middle of the travel of the bimetal on its heating and cooling periods, and the length of time these contacts are closed for each cycle of the bimetal determines the average wattage input to the heating element I3.

Ln Figs. 8 and 9, the horizontal lines H and I respectively indicate the lower and upper bimetal temperature limits between which the bimetal causes both sets of cycling contacts 53--54 to be closed for a particular setting of the knob I5. It will be understood that different settings of the knob change these limits to provide different average wattage inputs to the heating element I3, The points J, K, L, and M where the lines H and I intersect the curves D and F, represent the points at which the bimetal effects switching of the contacts |53 and 54. The horizontal distance between related points J, K, and L, M determines the time the contacts 53-54 are closed for a complete cycle of the bimetal. The ratio of the time between J and K, represented by X, to the total heating-up period, represented by Y gives the per cent of maximum wattage input to the heating element for the heating-up period of the bimetal. Similarly the ratio between the time X', the horizontal distance between L and M, to the coollng-down period Y' gives the per cent of maximum wattage input to the heating element for the cooling-down period of the bimetal. These ratios are substantially identical.

It will be noted from Figs. 8 and 9 that, since the portion of each of the heating and cooling curves during which the contacts are closed is located in the center of the curve, its slope will be substantially the same as the general slope of the complete heating or cooling curve. This is true even though the slope of the curve changes for different ambient temperatures. Accordingly, the percentage of time that the contacts are closed during each heating or cooling period remains substantially the same upon change in ambient temperature.

The present control is particularly adapted for use in a control system like that disclosed in Pat ent No, 2,399,423 of Edward Bletz, assigned to the assignee of the present invention. The Bletz control system includes a thermostatic switch which is responsive to the temperature of a body to be heated. such as a cooking vessel or the like placed on a surface heating element of a range, and arranged so that maximum wattage input is initially supplied to the heating element to rapidly heat the body. When the body reaches a predetermined temperature, it causes the thermostatic switch to open, and control of the energization of the heating element is shifted to a wattage selector which may, for example, be the present control.

As shown particularly in Figs. 2 and 5, such a thermostatic switch, generally indicated T, may be connected in parallel to the cycling contacts 63-54 so that when the thermostatic switch is closed these contacts are shunted and continuous energization of the resistance I3 is provided but when the temperature of the heated body and the thermostatic switch reaches a preselected value, the thermostatic switch opens and energization of the resistance I3 is then controlled by the cycling contacts 53-54.

While I have shown my invention in but one form, it will be obvious to those skilled in the art 8 that it is not so limited, but is susceptible of various changes and modifications without departing from the spirit thereof, and I desire. therefore, that only such limitations shall be placed thereupon as are specifically set forth in the appended claims.

What I claim is:

1. A control comprising a pair of series connected switches each including an adjustable contact and a movable contact, means for adjusting said adjustable contacts relative to their respective movable contacts, and reciprocating means for moving said movable contacts to close .both pairs of contacts during the intermediate portion of its travel. to open one pair of ccntacts at one end of its travel and to open the other pair of contacts at the other end of its travel. said last-mentioned means comprising a thermal motor and a heater therefor, and switch means actuated by said motor and independent of said first-mentioned switches for controlling said heater. 4

2. A control device comprising a casing, a rotatable shaft in said casing and having handle means thereon for manually rotating said shaft. cam means carried by said shaft within said casing, adjustable contact arms disposed within said casing and biased into engagement with said cam means, a pair of movable contact arms mounted within said casing and having contact portions adapted to engage contact portions on said adjustable contact arms, means for moving said pair of movable contact arms in a regularly repeated cycle, said last-mentioned means being operable during each cycle to move one movable contact arm out of and into engagement with its associated contact portion and then to move the other movable contact arm out of and into engagement with its associated contact portion. said cam means being effective on adjustment of said shaft to position said contact portions of said adjustable contact arms to engage said movable contact portions for varying periods.

3. A control device for an electrically-energized element comprising rst switch means'for controlling the supply of electrical energy to said element, reciprocating means movable in a nxed path and actuating said switch means to cause alternate energization and deenergization of said element, the energization of said element taking place in a central portion of said path and deenergization of said element taking place in each end portion of said path, thermal-motor means including a temperature-responsive means and a heater therefor for moving said recpirocating means, and second switch means for controlling energization o! said heater and actuated by said reciprocating means at the ends of said path.

4. A control device for an electrically-energized element comprising first switch means for controlling the supply of electrical energy to said element, reciprocating means for actuating said switch means to cause alternate energization and deenergization of said element. said reciprocating means actuating said switch means to close the circuit therethrough in the central portion of its travel and to open the circuit therethrough in each end portion of its travel, and thermal-motor means including a temperature-responsive means and a heater therefor for driving said reciprocating means, and second switch means for controlling the energization of said heater and actuated by said reciprocating means at the ends of its travel.

5. A control device for an electrically-enerbring the movable contact of said iirst switch into engagement with its adjustable contact and subsequently move the movable contact of the second switch out of engagement with its adjustable contact when moving in one direction and to bring the movable contact of said second switch into engagement with its adjustable contact and subsequently move the movable contact of said first switch out of engagement with its adjustable contact when moving in the opposite direction, thermal-motor means for moving said reciprocating means in said path, said thermalmotor means including a switch actuated by said reciprocating means in spaced-time relation to the actuation of said first-mentioned switches.

6. An electrical control device comprising nrst switch means for opening and closing a circuit therethrough and including first and Second actuating members each of which is adapted when actuated to open said circuit, reciprocating thermal-motor means for' alternately actuating said members, said thermal-motor means including reciprocating temperature-responsive means and a heater therefor, and second switch means for initiating energization of said heater when said thermal-motor means reaches one end of its travel and for initiating deenergization of said heater when said thermal-motor means reaches the other end of its travel, said thermal-motor means being operable throughout one end portion of its travel to actuate one of said members to open the iirst switch means and throughout the other end portion of its travel to actuate the other member to open said rst switch means, said nrst switch means being closed only during a central portion of the travel of said thermal-motor means.

7. A control comprising a pair of switches connected in series with each other, each o! said switches including an adjustable contact and a movable contact, means including a common manually-actuated member for adjusting said adjustable contacts with. respect to said movable contacts, said last-mentioned means being operable to adjust 4both of said adjustable contacts toward their associated movable contacts upon movement of said member in one direction and away from the same upon movement in the opposite direction, motor means for moving said movable contacts into and out of engagement with said adjustable contacts in a regularly repeated cycle, said last-mentioned means being operable during each cycle to move one movable contact out of and into engagement with its associated adjustable contact while the other contacts are in engagement and then to move the other movable contact out of and into engagement with its associated adjustable contact while the first contacts remain in engagement, whereby the circuit through the series-connected switches is opened once by each switch duringeach cycle of operation and whereby\both periodscf circuit opening in each cycle are adjusted by said common manually-actuated member,

EARL K CLARK.

file of this patent:

UNITED STATES PATENTS Number Name Date 498,312 Scribner May 30, 1893 2,202,725 Bear May 28, 1940 2,224,596 Desfachelles Dec. 10, 1910 1,637,155 Marden July 26, 1927 2,172,189 Clark Sept. 5, 1939 2,254,054 Vaughan et al Aug. 26, 1941 2,331,737 Scoggin Oct. 12, 1943 1,187,897 Friedman June 20, 1916 1,928,907 Noble Oct. 3, 1933 2,002,467 Blodgett May 2l, 1935 2,129,477 Parks Sept. 6, 1938 2,243,615 Werner et al May 27, 1941 2,272,975 Jacobs Feb. 16, 1942

Images