US2618721A - Control with column loaded strip - Google Patents

Description

Nov. 18, 1952 .H F, CLARK 2,618,721

CONTROL um COLUMN LOADED STRIP WMM Nov. 18, 1952 H. F. CLARK 2,618,721

CONTROL. wrm comm Loman s'mzp' Filed June 16, 1945 2 Sl'iEETS-S-IEEI- 2 BwyjNI/TOR. :9 M WMM Patented Nov. 18, 1952 M 2.618.721 coN'raoL wrm COLUMN LOADED s'rmr Harry F. Clark, Oakwood, Ohio, assignor to General Motors Corporation, Dayton, Ohio, a corporation of Delaware Application June 16, 1945, Serial No. 599,791

(Cl. 20D-122) Claims. a 1 This invention relates to electrical apparatus and more particularly to motor starting and overload controls for electric motors.

Because of their apparent simplicity, there.

have been many attempts to provide satisfactory bimetal starting and overload controls for electric motors. One example of such a bimetal starting control is-shown in Fig. 2 of the Werner Patent No. 2,117,123. A number oi' dimculties have prevented the Wide use of such a control.

@ne of the most troublesome factors is the wide range of current values which must be conducted by the starting control. In such bimetal starting controls, the motor current is used to iirst rapidly heat the lloimetal operated starting switch until the starting circuit is opened. The motor current must then continue to heat the bi-v metal operated starting switch to keep the startf ing circuit open throughout the remainder of the running period oi the motor. It is well known that at the point of use or connection of a device connected to acommercial supply line, the voltage varies widely depending upon the conditions of the system. For example, a nominal 110 volt circuit may deliver current at a voltage of from 9D to 120 or 125 volts.

By testing such himetal starting controls, it has been found ii suflicient heat is provided for the starting control to give proper starting on a 9G volt current supply, that too rapid heating will occur upon a 120 volt supply. Or if the heating is reduced suiliciently to prevent overheating on 120 volts, the heating will be insufficient to cause the bimetal to hold the starting circuit open when the voltage supply drops to 90 volts. Even where the power supply and individual power circuit does not vary to this extent, a manufacturer of starting controls is still confronted with this problem, since the equipment he builds for a nominal 110 volt circuit may be used either upon a power circuit which frequently supplies current at the point of delivery at 90 volts o1' upon another circuit which may supply current at the point of delivery at 120 or 125 volts. It has, in the past, also been necessary to provide for the manufacture of several different variations of starting controls to accommodate diiierent current frequencies because the power supply in this country employs in different communities, 25,-50 and 60 cycle current. It is therefore desirable that one starting control be provided which will operate satisfactorily upon a wide variation of voltages and frequencies.

Another diiculty with such bimetal starting and overload controls is that the operation varies 2 according to changes in the room or environment temperature. Still another difficulty is that the overload protector may reset before the starting control resets.

It is an object of my invention to provide a practical bimetal starting control for controlling the energization oi the phase winding in which the bimetal will not be overheated under any operating condition.

' It is another object of my invention to provide a heating arrangement for a bimetal starting control which will supply sutllclent heat to provide proper operation under all expected conditions without supplying excess heating under any conditions.

It is another object of my invention to provide a simple inexpensive starting control in which the timing is kept within a desirable range regardless of the variations in voltage conditions.

It is another object of my invention to provide a starting control which will operate satisfactorily upon current of 25, 50 and 60 cycles.

It is another object of my invention to provide a starting control in which the timing is kept Within a desirable range regardless of changes ln the room or environment temperature.

It is another object of my invention to provide means for keeping the motor overload protector tripping point within a desirable range regardless of the change in the room or environment temperature.

It is another object of my invention to provide a bimetal starting and overload control in which the overload will reset at the same time or earlier than the starting control.

It is another object of my invention to provide an improved support and arrangement of the ends of a bimetal strip.

It is another object of my invention to provide l means for reducing the voltage drop and heating produced within an electro-thermal starting control during the starting period of the motor.

It is another object of my invention to provide a thermal snap-acting starting control which will trip quickly upon vthe application of asmall amount of heat.

When the electric motor is connected to certain loads, such as for example, the compressor of a refrigerating system, the starting load upon the motor increases with the environment temperature and it is desirable that the lengthof the motor starting period be increased with increasing temperature to compensate for the slower acceleration`of tlie motor to the optimum phase switching speed.

- starting circuit open during the running period of the motor.

A bimetal thermal overload with an auxiliary heater is provided with greater heat storage capacity than the starting control, so that the starting control will reset before the thermal overload will reset. The heating of the starting l bimetal and its auxiliary heater produces a temperature controlled amount of heat within the switch casing to provide a temperature which varies less than the environment temperature so as to reduce the variation in the tripping value of the overload control to a minimum.

The starting bimetal is compensated for variations in its environment temperature by a second bimetal strip. Where the motor is to be used to drive a refrigerator compressor or a load having similar characteristics in which the starting period should increase with an increase in temperature, this bimetal is made over-compensating so as to increase the starting time as the environment temperature increases.

The contacts are arranged so that the bimetals are substantially straight when cool. Each bimetalv is column loaded to provide a snap action. The short-circuited stationary contact which coomrates with the starting bimetal system, is located outside the snap action range to facilitate the periodic opening and closing of the shortcircuiting contact during the running period of the motor. Each of the ends of each of the bimetals preferably is provided with a 18D degree edgewise turn and a lateral bend which is connected to the anchorage and is used to apply the adjustable column loading to the bimetals.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings, wherein a preferred form of the present invention is clearly shown.

In the drawings:

Fig. 1 is a horizontal sectional view taken along the lines i-i of Figs. 2 and 3, showing one form of control embodying my invention;

Fig. 2 is a sectional View taken along the lines ii-t of Fig. l;

we. 3 is a sectional view taken along the lines 3 8 of Figsl and 2;

Fig. 4 is a diagram including a refrigerating system and a wiring diagram of the motor and control system connected for the starting of the motor in which the energized portions are indicated by heavy lines and the deenergized portions by light lines;

Fig. 5 is a wiring diagram similar to Fig. e showing the changed connections and circuits at the completion of the starting period;

Fig. 6 is a Wiring diagram similar to Figs. d and showing the other form of connection and circuit assumed intermittently during the running period:

Fig. 'Z is aternperature-movement diagram of the starting bimetal illustrating the movement of the starting contact with the rise and .fall in the temperature of the bimetal; vand Fig. 8 is a graph illustrating the length of the starting period at difierent temperatures and voltages and also the starting contact trip and reset pressures at different temperatures.

Referring now more particularly to Fig. 4, there is shown an electric motor-2B having a main or running winding 22 and a phase or starting winding 2t. This motor 2t is shown connected diagrammatically to drive a refrigerator compressor 25 which withdraws evaporated refrigerant from the evaporator 2l and forces the compressed refrigerant into the condenser 2Q where it is liquened and returned to the evaporator 2li under the control of a suitable valve. IThe evaporator 2l is employed to cool the medium within the compartment 3i. During idle periods of the refrigerating system the evaporator 2i is warmed up and if the idle period is sufficiently long it will reach Ithe room temperature. The evaporation of the liquid refrigerant in the evaporator 27 produces a pressure in accordance with its temperature. The pressure in the condenser also increases as the environment temperature increases. This causes the starting load upon the compressor to increase as the environment temperature increases.

The electric motor 2t is supplied with electric energy through the supply conductor 2t which connects to the common junction of the windings 22 and 2d and the supply conductor 28 which connects through the control switch 33 to the starting and overload control designated generally by the reference character Sii. To provide a greater starting torque, the phase winding 2li is shown connected by the conductor 83 to a condenser or starting capacitor 23 to make the motor a capacitor start motor. However, if high starting torque is not required this starting capacitor 2t may be omitted. When so omitted the motor 2t is an ordinary split phase motor.

The overload protector The conductor 2@ through the switch 33 specilically connects to an L-shaped mounting bracket 32 (see Figs. 1 to 3) having its lower portion beneath the switch mounting base 55d. This lower portion is riveted to the base 3d by a hollow rivet threaded to receive the fastening screw 35 which fastens the supply conductor 28 to the bottom of this Lshaped mounting bracket 32. The upper portion of the L-shaped mounting bracket 32 extends upwardly through a slot in the switch mounting base 3d. To it is fastened by Welding or soldering one end of the coiled electric heater 36. The other end of this electric heater 36 is supported by an L-shaped stationary contact 40 which extends through the base 3 and is riveted thereto. In an engagement with the stationary contact 4t is a movable contact 42 carried by the middle of a column loaded bimetal strip it which serves as the actuating bimetal of the overload control. The stationary contact iii is so located that when engaged by the movable contact t2 the bimetal strip M will be held substantially straight. v

To rmly support the bimetal strip it the ends are welded to the upturned ends t5 and d8 of bow to the left at its mid-portion such plain anchored ends of the strip would tend to bend counterclockwise at the top and clockwise at the bottom so as to i'orce the midpoint of the bimetal strip 44 to the right.

To prevent this opposition and to make both effects supplement each other I provide edgewise curves or bends 43 and 45 through an angle 'of 180 degrees at each end of the strip 44 and bend eachof these turned portions at right angles and weld their ends 41 and 49 to the upturned ends 48 and 48 oi the main bracket 50. Upon heating this causes the bimetal ends to accentuate thc bowing to the left of the mid-portion ot the strip 44 by bending clockwise at the top and counterclockwise at the bottom and this makes it possible to make the control smaller.

The upturned end 48 is provided with an adjusting screw 52 which may be adjusted to provide any desired column loading upon the bimetal strip 44 by engaging the free portion of this welded right angled portion 49 of the strip 44. In this column loading the right angled portion .49 acts as a compound cantilever spring for applying the column loading in direct alignment with the strip 44 when in the closed position. This column loading insures a snap opening and closing of these contacts which can be separately adjusted.

The adjustment provided by the screw 52 varies the force required to close the overload contacts 42 and 4U. This force is obtained by the cooling of the bimetal strip and thus the adjusting screw 52 may be set to vary the closing temperature of the overload contacts. The opening of the contacts is adjusted by moving the stationary contact 40 toward or away from the strip 44. Moving the contact 40 toward the strip 44 will reduce the contact opening temperature while moving the contact 40 away from the strip will increase the contact opening temperature. The initial curvature, type, width, thickness and length of the bimetal strip 44 and the resistance of the auxiliary heater 36 may be varied to provide the proper overload tripping and resetting characteristics for different motors.

The starting control The upturnedend 48 of the bracket 50 supports the lower end of the starting bimetal strip E0 which, like the overload bimetal strip 44, has its end portions turned edgewise 180 degrees, as indicated by the reference characters 6I and G3, and then at right angles for similar reasons. The end of the right angled portion 59 is welded to the upturned portion 48 and is provided with a set-screw 68 for applying a resilient column loading to the strip 60. The right angled portion 59 acts as a compound cantilever spring which applies the column loading in substantially direct alignment with the strip 60 when in contact with the starting contact 18. At the upper end of the strip 60 the right angled portion 85 is Welded to the upturned end 84 of a separate bracket 66 extending alongside of the bracket 50 and likewise riveted at two points to the switching mounting base 34. It is provided with a longitudinal stiilening rib.

At its midpoint the starting bimetal strip 6!) carries a double-ended contact which when the strip 53 is cooled engages with considerable contact pressure the starting contact member 18. The starting contact member 18 is in the form of an L-shaped bracket extending beneath the switch mounting base 34 and is riveted thereto.

tends through the switch The auxiliary heater Connected to the bracket 65 is one end of an electric heater 56 which extends along the outer side of the starting bimetal strip and has its other end fastened to the L-shaped back contact member 14. This back contact member 14 exmounting base 34 and is riveted thereto. On its bottom face it is provided with a binding screw 15 which connects this back contact member 14 with the conductor 88 of the main winding circuit.

The compensating bimetal The starting bimetal strip 3l is also provided with a compensating bimetal strip |2| which may either exactly compensate or under or over compensate for the eilects of environment temperature upon the starting bimetal strip 33. This compensating bimetal strip I 2| is bent inwardly at its central portion and fastened to the strip 80 by the double contacts 10 which may be riveted or welded together. The compensating bimetal strip I2| extends in both directions from its mid-portion spaced away from the strip 50 a suillcient distance to prevent it from receiving any material amount of heat from the strip 80. Each of th-e ends of the compensating strip 2| is provided with an extremely small projection |23 which bears lightly against the adjacent end portions of the starting bimetal strip 40. The compensating bimetal strip |2| is notched at each end as indicated by the reference character |25 so as to avoid contact with the right angled portions 59 and 85 of the starting bimetal strip B0 and the 4upturned portions 48 and 84 of the brackets 60 and 56. The surface contact resistance of the projections |23 upon the ends of the starting bimetal strip 60 is so high that no appreciable amount of current flows through the compensating strip I2| The compensating strip |2I is made of such initial curvature, length, width, :thickness and type of bimetal that it will pro'ide just the amount of compensation desire The switch mounting base 34 is made of some suitable electrical insulating material and is preierably mounted within a casing 90 likewise of insulating material. The mounting base 34 is held in place against the shoulders 94 provided in the corners by -the projections 92 upon the sides of the casing 9U.

Current flow through the control With this arrangement, when the motor 20 is first connected to the power line through the closing of the switch 33, as illustrated by the heavy lines in Fig. 4, the current will flow 'from the supply conducto; 28 through the switch 33 to the bracket 32, thence through the heater 35 alongside the overload bimetal strip 44 to the stationary contact 40 and the movable contact 42. From this point the current will divide and flow in opposite directions throughout the overload bimetal strip 44 until it reaches the points 7 at which it is welded to the upturned ends Il and I8 of the main bracket B0.

The characteristics of the heater 3G and the characteristics and adjustment of the 'bimetal strip 44, andthe position of the stationary contact d will determine the current values which will cause the overload bimetal strip l! to trip open to deenergize the motor 2li upon an overload. The column load imposed by the setscrew 52 will determine the temperature to which the overload bimetal strip M will iall and thus the resetting time required before it will snap to its closed position. This resetting time must be made longer than the resetting time of the starting bimetal strip St. By arranging the contacts so that the overload bimetal strip d4 is held straight when closed, the tripping current can separately be adiusted by bending or adjusting the location of the stationery contact dt, since the column loading has little eect as long as the bimetal lstrip llt is straight. The resetting time and temperature can be separately adjusted by adjusting Ithe column loading through the adjusting screw E52.

From the ends of theoverload bimetal strip it current will flow through the main bracket 5u to'the point at which the right angled portion 5s of the starting bimetal strip d@ is welded to the u-pturned end dd. All this current will then pass upwardly through the lower portion o1 the starting bimetal strip 6i) to the double contact l@ at its mid-point. There more than half the current will flow through the contacts i@ and i8 to the starting or phase winding circuit including conductor Si?, capacitor 23 and the phase winding 2d to the supply conductor 2t. The re mainder of the current will flow through the up per portion of the starting bimetal strip t@ to the bracket te and thence through the heater 5t to the back contact member it which connects to the main winding circuit including the conductor 88 and the main winding 22 which connects to the supply conductor it.

Operatimz Upon the initial starting of the motor, the bimetals d@ and et will be at room temperature and the control will be in the positions shown in Figs. 1 to 4. This is indicated by the point i2@ upon the diagram shown in Fig. 7, although it is held substantially straight by the starting contact i8, at room temperature. The initial curvature of the starting bimetal strip G@ tends to bow it to the left so as to press tightly against the starting contact i8. The flow of current through this starting bimetal strip dii will gradually raise its temperature as illustrated by the vertical line extending up from the point i253 in Fig. 7 to cause it to rapidly reduce its tendency to bow to the left. The starting bimetal stri-p d@ is of such length, thickness, width, initial curvature and characteristics that at the most desirable time for terminating the starting period it will become straight.

When the temperature gets so high that the pressure against the starting contact itl reaches zero, the starting bimetal strip d@ will snap and bow to the right to the position shown in Fig. 7 due to the column loading and the temperature pointing action of the bimetal. This snapping or tripping temperature is indicated by the reference character; V22 and the movement of the contact it at this temperature is designated by the horizontal line connecting the point @22 and the point E26. r This snapping or tripping temperature may be raised or lowered by bending the starting contact away or toward the starting bimetal strip B0, thus increasing or reducing the length of the starting period. By arranging the starting contact 18 so that the strip tt is held substantially straight during the starting period, there is substantially no resistance to the movement of the starting contact '18 and less heating of the bimetal strip is required and a heavier bimetal material may be used. It also reduces the energy consumed by the starting control during the starting period as well as during the running period, thus increasing the net amount available for the motor. The starting bimetal strip Bil is also less likely to overheat under such an arrangement.

r The compensating bimetal strip li is so ar-s ranged that when cooling its end portions bow to the left thus forcing the end portions of the starting bimetal strip t0 to the left and at the same time the mid-portion of the strip t@ is pulled to the right. As shown in Fig. 8, the starting contact tripping pressure is lowest when the temperature is lowest and this pressure rises in almost a straight line as the temperature rises. Without this compensating bimetal the starting contact tripping pressure would fall as the temperature rises thereby reducing the starting time or starting period as the temperature increases. While this may be satisfactory for some applications, such as when a motor is driving a device working upon viscous uid, which provides decreasing opposition to movement as the temperature increases, it is not suitable for many other applications and often the rate of change is not suitable even though the variation may be in the right direction. Hence the bimetal strip i2! may be under-compensating for such loads.

` For many other applications the load does not change materially with temperatures and therefore the starting contact tripping pressure should be uniform. In such a case the compen-l sating bimetal strip im is made of such a length,

width, thickness and characteristics that it.

exactly compensates for the eect of environment temperature upon the starting bimetal strip 6B. This would produce a substantially straight horizontal line for the starting contact tripping pressure dn the graph Fig. Y8. It would also provide a substatnially straight horizontal line for the length of the starting period or starting time at different temperatures and diierent voltages.

Some starting loads, for example refrigerator compressors, are heavier as the ambient or environment temperature rises. Under such conditions it will take longer for the motor to reach the proper switching speed at which the phase winding should be disconnected. For such loads the compensating bimetal strip i2! should be of such length, width, thickness, initial curvature. and characteristics that it will over-compensate for the eiect of environment temperature on the starting bimetal strip Gd to produce a rising contacttripping pressure as shown in Fig. 8. This also provides a gradual increasing starting time with rising ambient temperatures at different voltages. 'Ihe starting time is inherently lengthened at low voltages since the heating effect is slower and this is desirable since the motor has less power under low voltage con' ditions and requires more time to reach the optimum speed for switching. Thus by the use of an over-compensating bimetal strip i2i the starting bimetal strip tt will provide a starting 9 time,which is adjusted to the starting load of thev refrigerator compressor 25 and the time required for the motor to reach its optimum speed for switching under all temperature conditions.

The starting bimetal strip 60 travels rapidly away from the starting contact 10 under the force oi' the snap action column loading and reaches the back contact '|4 without a pause. In this operation the phase winding 24 is disconnected from the power source 28 for the remainder of the running period of the motor. The column loading of the bimetal strip 60 is such that at the tripping temperature indicated by the horizontal line |22 to |24, the contact 10 will just be in contact with the back contact 14 without any contact pressure. In action, however, due to inertia, the contact 18 will strike the back contact 14 with considerable force. This contact immediately shunts both the heater 59 and the upper half of the starting bimetal strip 60 and arranges the circuits as shown in Fig. 5. The main winding current ilowing through the lower half of the starting bimetal 60 to the back contact 'I4 is insuillcient to prevent the bimetal 60 from cooling slowly but it is sulcient to prevent rapid cooling. This causes the bimetal 60 to gradually creep away from the back contact 'I4 nearly to the position illustrated in Fig. 6.

In creeping away from back contact 14 the movement soon is opposed by the gradually increasing resistance due to the column loading of the bimetal strip 60. This movement, however, is beyond the snap action range and is represented by the curve between the points |24 and |26 in Fig. 7 which shows that as the temperature falls the movement becomes less, due to this increasing resistance. The snap action range is :indicated by the horizontal line between the points |28 and |30. However, as soon as the bimetal contact 1|) leaves the back contact 'i4 the shunt for the heater 56 and the upper portion of the bimetal strip 60 is opened and the current again ows through the upper portion of the strip 6D and the heater 56. This heat is sufficient to slow down the movement of the strip 60 and to stop it and reverse its movement so that it again moves into contact with the back contact 74. This reversal takes place at some point on the curve between the points |24 and |26 in Fig. 7. The point of reversal is not fixed but depends somewhat upon the environment temperature which governs the rate of cooling of the upper portion of the bimetal strip 60 and the heater 56 as well as the speed at which the temperature is restored.

This contacting of the contact 1U with the back contact 14 and the subsequent creeping away and again contacting the back contact takes place repeatedly during the normal running period of the motor. In Fig. 7 this is represented by repeated movements from the point |24 downwardly a. variable distance along the line toward the point |26. It is through this cycling on the back contacts that the temperature of the bimetal strip 60 is kept substantially constant during the normal running period and is prevented from overheating. The resetting time of the starting bimetal strip 6|) is regulated by this cycling temperature. This cycling temperature may be raised or lowered by bending the back contact i4 6|) or by increasing or reducing the column loading by adjusting the set-screw B8 or both. It also is provided through this means with sumaway or toward the strip i0 cient heat to prevent it from snapping backto the starting position. This cycling on the back contact takes place outside of the snap action range provided by the column loading of the strip lli. The cycling on the back contact provides thermostatically controlled heating oi' the interior of the casing lll so as to reduce the variations in temperature therein due to changes in room temperatures. As shown in the graph, Fig. 8, the starting contact resetting pressure does not vary because the column loading o1' the bimetal strip which determines the resetting pressure does not vary with temperature changes. When the motor circuit is opened to shut oi! the motor by opening the'switch Il the bimetals and heaters will cool. In cooling the bimetal it will reach the point of maximum resistance o! the snap action column loading applied to it immediately after it passes in cooling below the point |23 in Fig. 7. It will then cool without much movement until it cools to the point designated by the reference character' |25 where it enters the snap action zone or range of movement. Upon passing this point without any appreciable cooling the bimetal strip 80 will snap immediately into contact .with the starting contact 18. This movement is designated by the horizontal line extending from the point, |28 to the point |30 located on the vertical line between the points |20 and |22. The strip 8l will cool without further movement.

Should there be an excessive current flowl through the circuit, the 60 will cycle on the back ing its temperature until bimetal strip 44 is heated starting bimetal strip contact thereby limit-v the thermal overload to its tripping point so as to apply a column loading to the thermal overload bimetal strip 44 rwhich will insure that the overload'contacts will not close until after the starting bimetal strip 60 has reset to its initlal position.

This application is a continuation-impart of my copending applications S. N. 473,892, tiled January 29, 1943, now Patent No. 2,451,535, issued October 19, 1948, and S. N. 552,166, tiled August 31, 1944, now Patent No. 2,417,912, issued March 25, 1947.

While the form of embodiment of the invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted, as may come within the scope of the claims which follow.

What is claimed is as follows:

1. A control comprising a bimetal strip portion having one portion turned edgewise substanmeans for rigidly supporting said strip portion at the one terminus of said turned portion'and at a portion separated a substantial distance from the opposite terminus of said turned portion, and a control device operably connected to and operated by the part of the strip portion between said points of support.

2. A control comprising a bl'metal strip portion provided with a substantially straight portion at each end of which are degrees edgewise directions, means for supporting said strip portion solely by said turned portions, and a control device operably connected to and operated by said straight portion.

3. A control including a bimetal strip portion,

' a, normally stationary contact positioned to hold bimetal strip portion in response to ambient tem-f peratures, and means for heating the nrst men tioned strip portion independently ofthe second.

s. A control including a bimetal strip portion, means for supporting said strip portion at two separated points, with the strip portion free to bend between the points of support, contact means connected to said strip portion between said points of support, compensating means including a second bimetal strip portion having an operative connection with said nrst strip portion to apply a load thereto substantially in accord ance with its own temperature, and means for heating said first strip portion substantially independently of said second strip portion.

5. A control including a bimetal strip portion,

means for supporting said strip portion' at two `separated. points, with the strip portion free to bend between the points of support, contact .means connected to said strip portion between said points of support, compensating means in= cludina a second bimetal strip portion operatively connected to said first strip portion adiacent said contact means and atleast one other point separated therefrom, and means for heating said nrst strip portion substantially independently of saidv second strip portion.

6. A control including a strip portion a normally stationary contact positioned to hold the strip portion substantially straight when contact is made, means for applying a column loading to said strip portion so that it is in substantial direct alignment with the strip portion when contact is made for providing a snap=acting movement ci the strip away from the contact substantially without opposition from the column loading, said strip portion being provided with means tending to force it toward and away from said contact, and temperature responsive means for applying el load to said strip portion in accordance with ambient temperatures.

7. A control comprising a bimetal strip portion adapted to move in a rst direction when 'cooling and in a second direction when heating,

a normally stationary contact positioned to stop the movement of the strip portion upon cooling, a thermal means responsive to environment temperatures for applying an increasing load upon 12 l said strip portion in said second direction 'upo cooling. and means for heating said strip portion with electrical energy.

8. A control comprising a bimetal strip portion having one portion turned edsjewise substantially 180 degrees, rigid'supporting means for rigidly supporting said strip portion substantially at the one terminus of said 180 degree portion, said bimetal strip portion having a second portion extending substantially straight from the opposite terminus oi said 180 portion and a control device operatively connected to and operated by said second portion of the strip portion remote from 'said 180 portion.

9. A control comprising a bimetal strip portion having a substantially straight mid-portion at one end of which is a 180 degree edsewise turn, said one end adjacent the terminus oi the 180 degree turn being bent substantially at right angles to said mid-portion, means for applying a column loading to said portion bent at right angles, and a control device operably connected to and operated by said mid-portion.

10. A control comprising a bimetal strip portion having a substantially straight mideportion at each end of which are 180 degree edgewise turns in opposite directions of rotation, each ci the ends adjacent the terminus of their 180 degree turns being bent substantially at right angles to said mid-portion, means for applying a column loading to said portions bent substantially at right angles in substantially direct alignment with said mid-portion, and a control device operably connected to and operated by said j mid-portion.

REFERENGES @MED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 1,578,119 Hall Mar. 9, 1926 2,016,244 Gregory Oct. 1, 1935 2,095,579 Werner Oct. 12, 1937 2,132,888 Werner Oct. 11, 1938 2,133,309 Schmidinger Oct. 18, 1938 2,175,032 Schaefer Oct. 3, 1939 2,177,671 Schmidinger Oct. 31, 1939 2,207,422 Vaughan et al. July 9, 1940 2,254,054 Vaughan et al Aug. 28, 1941 2,255,169 Ireland Sept. 9, 1941 2,288,640 Paulus July 7, 1942 2,332,518 Kooi Oct. 26, 1943 2,374,967 Alexander May 1, 1945 2,379,802 Stickel Juy 3, 1945

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