US2374967A - Refrigerating apparatus - Google Patents

Description

y ,1945. D. F. ALEXANDER 2,374,967

REFRIGERATING APPARATUS Filed Aug. 27, 1942 7 IIIIIIIIII/IIIIIIII A ll 26.

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IIII/IIIIII"II III [ti l/I Profs: far Tamper-afar frequency of resetting Patented May 1, 1945 7 2,374,961 J anrmcca'n'rmo APPARATUS Donald F. Alexander, Oakwood, Ohio, assignor to General Motors Corporation, "Dayton, Ohio, :1 corporation 01' Delaware V ApplicationAugust 27, 1942, Serial No. 456,427 '9 Claims. (01. 200-122) This invention relate to' refrigerating apparatus and more particularly to protectors for electric circuits.

Automatic thermal overload protectors have:

thermal elements heated by the current flowing through the electric circuit to open the electric circuit when the thermal element becomes he'ate'd above certain temperatures. The reclosingof the circuit takes place when the thermal element cools to a predetermined temperature. The cooling of the thermal element depends upon the environment or ambient temperature. Under continuous overload conditions the overload protector will trip and reset continuously permitting successive rushes of current through the electric circuit. When the ambient temperature is low the protector will reset at a more rapid rate so' thatthe successive rushes of current are more frequent than when the ambient temperature is high. Where there are large electrical elements in the electric circuit, suchas an electric motor the increasingfrequency of the rushes of'current through the motor increases the; temperature of the motor windingsLand may damage the insulation.

It isan object of my invention to provide a protector having means for making the frequency of resetting substantially the same regardless of I variations in the ambient temperature.

It is another object of my invention to compensate for the varying rate ,of cooling the opprotector by an erating element of the overload automatic reset'adjustment.

.[t is another object of my invention to provide a protector having a reset adjustment responsive to ambient temperature.

It is still another object .of my invention to provide a protector having a: bimetal operated reset adjustment. I '1 I have found that protectors of certain types, such as the-bimetallic disk type, have inherently large differentials. Such protectors, particularly when they are mounted upon an electric motor, reset too slowly for certain applications, such as the preservation of frozen foodstuffs.

It is therefore another object ofmy invention to provide a means for-reducing the on-ofi temperature diiferential of thermal motor protectors and thereby reducing the resetting time.

It is another object of my invention to provide a bimetal operated device for reducing the differential of a thermal motor protector.

These objects are attained by providing a thermal motor protector with a bimetal operated reset adjustment for the toggle mechanism of the protector in which the bimetal is located in and responsive to the ambient air, so that the differential of the protector is increased under cold ambient temperature conditions in order that the under continued overload conditions is substantially the same, as under warm ambient temperature condition. modified form, a bimetal heated by an electric heater which is'energized'upon the opening of the protector changes the open circuit position of the bimetal so as to raise the resetting temperature of the protector in order to reduce the resetting time.

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

In the drawing:

Fig. 1 is a view, partly diagrammatic, showing' a motor protector embodying one form of my invention operating under cold ambient temperature conditions;

Fig. 2 is a view similar to Fig. 1 with the protector' tripped to open circuit position operating under high ambient temperature conditions;

Fig. 3 is a graph in which the time temperature cycles of the protector are plotted for high and low ambient temperatures both with and without compensation for cold ambient temperatures;

Fig. 4 is another form of motor protector embodying my invention;

- Fig. 5 is one form of wiring diagram for the protector shown in Fig. 4;

Fig. 6 is another form of wiring diagram for the protector shown in Fig, 4;-and

Fig. 7 is a graph illustrating the cycles of the motor protector of Fig. 4 without and with my invention.

Referring now to the drawing and more particularly to Figs. 1 and 2, there is shown a thermal overload protector 20 including a casing 22 of electrical insulating material provided with an operating bimetal 24 provided with an adjustment 26. The bimetal 24 is connected to one end of a tension toggle spring 28 having its other end connected to the free end of a toggle lever 30. The free end of the toggle lever 30 is opera- -tively connected to a contact carrying strip 32 carrying the movable switch contact 34 which cooperates with a stationary switch contact 36.

The stationary contact 36 is connected to one of the supply conductors 38 of an electric circuit, while the contact carrying strip 82 is connected to an electric heater 40 which is provided for heating the cantilever bimetal strip 24. The electric heater 40 is connected to the remainder of the electric circuit which may include an electric motor 42 which in turn is connected to the other supply conductor 44. The bimetal 24 is so adjusted by the adjusting screw 26 and the heater 40 is made of such a size that when an electric current suiiicient to endanger the electric. motor 42 passes through the circuit, the bimetal 24 will be heated suiiiciently to'cause it to In the curl upwardly as shown in Fig. 2 to trip the toggle spring." and the' toggle lever 30 to open circuit position as shown in Fig. 2.

The resetting of the. protector depends upon the rate or cooling of the bimetal 24. The graph in Fig. 3 shows, in the light solid line, a temperature time curve designated by the reference character mwmen the bimetal 24 1s illustrated as heating up to, predetermined high temperature at which the-protector trips to the open position as shown in Fig.2 The protector then cools to a temperature, for example; of 135 F. at which temperature the bimetal has cooled suiilciently to reset-the protector contacts. The graph illustrates the successive tripping and resetting of the protector in regular cycles during the continuing of the overload.

The light dotted line designated by the rererence character 48 illustrates a slightly slower rise in temperature of the bimetal 24 under overload conditions in acold room followed by more rapid cooling to the same resetting temperature foli in its lowermost positionthe diflerential oi the ambienttemperature conditions-to lower the retoggle is 'reduced'so that theresettingtemperature israised .to 135, F. It should b'e'noted thlt the opening of the protector isnot affected in any set temperature under low' ambient temperature conditions, Iprovide a cantilever bimetal-Bl out- 1 side the vcasing 52 'where it is responsive to ambient temperature, The high expansive ma lowed by tripping and subsequent resetting in 0 regular cycles. It will be seen from this graph that where the resetting temperature is the same,

that about three cycles of the protector takes place under high ambient temperature conditions,

while about four cycles takes place under cold room-conditions. Also, for each cycle'the length of time the current is allowed to rush through the circuit is just as long or in fact a trifle longer 4. under the cold ambient temperature conditions .than under the high ambient temperature conditions. The greater length'of time the motor 42 is connected to the supply source. the more its windings will be heated. If the protector is adjusted to allow the highest possible loading of the motor .durlng warm room. conditions, under which it is ordinarily desired that the motor operate to its fullest capacity, then the motor will be adeduately protected under low ambient temperature conditions and the insulation of the windings may be damaged if an overload should occur under the low ambient temperature conditions.

I overcome this dimculty bylowering the reterial ofthe bimetal is located on the upper side so that as the ambient'temperature' rises it will curl downwardly and move the pin 52 downward ,ly to raise the resetting temperature of the protector, for example, to-155 F. When the ambient temperature is low the bimetalgfl will curl upwardly, as shown in Fig z L to allow pin 52 to move'upwardly tolowerfthe resetting temperature ,of the protector,' for example to 120 F. The bimetal 54- may assume intermediate position or temperatures for intermediate ambient temperatures. The bimetal 54 may be adjusted byithe adjusting screw 56 to vary the resetting tempera tu'res. Byrthis device I provide adequate-adjustment for amblenttemperature, so that the frequency of the resetting cycles of the protector is substantially the-same undervaryingambient temperature conditions. At the same time, the

tripping temperatures are kept substantially the same since they are substantially entirely govemed by the heating effect of the'electric heater 40. e

setting temperature under low ambient temperature conditions so that the frequency of the resetting cycles is Just, as long or possibly a trifle longer during low ambient temperaturecondi- .tions. For example, I may reduce the resetting temperature under'low ambient temperature conditions to about 120 F. This will. extend the cooling cycle of the protector under law ambient temperature conditicns'as illustrated by the double dot and'dash lines designated by the reference character in Fig.3. This change in the reset I temperature extends the first cooling cycle of the graph 48 to a lower temperature thereby increasits length so that when the protector closes, the next heating cycle of the protector will bring the tripping point' of the protector substantially at the same time as the protector would trip under high ambient temperatures. In this way the frequency of tripping and'resetting is made substantially the same for high temperature conditions.

and low ambient To carry this out, I haveprovided a movable reset regulating pin 52 which determines the cir cuit closing tripping position of the toggle lever '30. When this movable resetting pin 52 is in its uppermost positionv th'e diflerential of the toggle is increased so that the bimetal 24 must'be' cooled through a temperature of 120 F., before the toggle will permit tripping of the protector to the closed circuit position. When the pin 52 is In Fig. 4 I have shown another formlof my,

invention in which the thermal operating element- |2| is in the form of a dished bimetal disk-enclosed within a casing I23 ofelectrical insulating m'aterialwhich is provided with a-gro'ove125 for re taining the-edges of the disk |2|. The disk "I f carries a movable contact which is adapted to make contact with. a stationary contact i2]. The stationary contact I2Iis connected to a supply conductor I30 while the disk .is connected to a conductor 32. The disk I 2| is heated by an 130:-

tric heater I34, so chosen as to heat the bimetal disk 2| suificiently when the safe operating cur rent of the electric circuit is exceeded to cause it to snap to the dot and dash line position, shown in These bimetal disks havean inherently large temperature'diflerential between their snapping where such disks are used for certain applications,

from one position to another. It has been found that the-resetting time is too long. One example of this is the refrigeration of frozen foodstuffs wherein if the system is deenergized for a con siderable period of time, the frozen ioods will vrise above freezing temperature thereby reducing their rqu'ality and subjecting them to possible spoilage.

'To hasten the resetting of the bimetal' disk |2| to closed circuit position, I provide a second bimetal I38 against which the bimetal disk stops when' in the open'circuit position. This bimetal I38 is heated by an electric heater I38 which is placed in shunt with the protector switch I21, 30 that when the protector contactsare opened the heater I38. will be energized to heatthe bimetal' m to cause the bimetal I36 to curl toward the bimetal. disk |2| forthe purpose'otpushi'ng mechanically the bimetal disk-J 2| toward its closed circuit position. This will raise the temperature to which the bimetal disk I2I snaps to closed circuit position.

The heater I34 may be arranged in the circuit as shown in Fig. 5 in which it is in series with the switch contact I21 and the heater I38, or as shown inFig. 6 in which the heater I34 is in series only with the switch contact I 2l and in parallel the reclosing of said electric circuit, a casing en- I4Il is closed to allow the heater I38 to operate and assist the resetting of the disk I2 I, so that the resetting occurs at the higher temperature and in a shorter time, As shown the resetting is accomplished in less than half the time the heater I36 is used. Thus this device increases the usefulness of this type of protector, and also other types of thermal protectors which do not reset rapidly enough. Obviously the heater I38 could be used upon the protector the bimetal 54.

' 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 shown in Fig. 1 to heat adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. A protector for an electric circuit including an operating element, means for operating said operating element in response to current-flow through the electric circuit, means controlled by said operating element for opening said electriccircuit, reset regulating means for regulating only the reclosing of said electric circuit, and means forvarying said regulating means in response to ambienttemperatures.

2. A protector fpr an electric circuit including a thermal operating element, means for heating said element in response to the flow of electric energy through said circuit, means controlled by said operating element for opening said electric circuit when said operating element reaches a; predetermined temperature, reset regulating means for regulating the temperatures at which the operating means recloses the electric circuit, and bimetal means for varying said reset regulating means.

3. A protector for an electric circuit including a thermal operatingelement, means for heating said element, in response to the fiowof electric energy through said. circuit, means controlled by said operating element for opening said electric circuit when said operating element reaches a predetermined temperature, temperature responsive means for changing the temperature at which the circuit is 'reclosed independently of the circhit-opening temperature, and heating means energized in response-to the opening of said pro-v tector for heating said temperature responsive means. I v

4. A protector for an electric circuit including an operating element, means for operatingsaid closing said element and all said above mentioned means, and temperatureresponsive means located outside said casing and having an operating connection with said reset regulating means for varying said reset regulating means.-

5. A protector for an electric circuit including an operating element, means for operating said operating element response to current-flow through the electric circuit, means controlled by said operating element for opemng said electric circuit, reset regulating means ior regulating Only the reclosing of said electric circuit, a casing enclosing said element and all said above mentioned means, and a bimetal strip located outside of and subject to the environment temperature of said casing and having an operating connection with said reset regulating means for varying said reset regulating means according to environment temperature's. A i

6. Aprotector for an electric circuit including an operating element, means foroperating said operating element in response to current-flow through the electric circuit, means controlled by said operating element for opening-said electric circuit, reset regulating means for regulating only the. reclosing of said 'electriccircuit, a casing en closing said element and all said above mentioned means, and temperature responsive means located outside said casing and having an operatingconnection with said reset regulating means for varying said reset regulating means and means for bimetal operating element, an electric heating means located in heat transfer relationship with said operating element'and connected in series with said electric circuit for operating said oper-\ ating element, means controlled by said operating element for opening said electric circuit, and reset regulating means for regulating only the reclosing of the electric circuit comprising a cantilever mounted bimetal trip and arranged to reduce the operating differential of the protector upon a rise operating element in response to current-flow,

through the electric circuit, means controlled by circuit, reset regulating means for regulating only said operating element for opening said electric in ambient temperature.

' 9. A protector for an electric circuit including a thermal operating element, means for heatin said element in response to the flow of electric energy through said circuit, means controlled by said operating element for opening said electric circuit when saidqoperating element reaches a predetermined temperature and for closing said circuitcwhen said operating element cools, temperature responsive means for varying th operation or said operating-element and means controlled thereby, and heating means energized in response to the opening of said protector for heating said temperature responsive means.

DONALD F. ALEXANDER.

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