US2254593A - Refrigerating apparatus - Google Patents

Description

p 2, 1941- R. J. EISINGER EI'AL 2,254,593

REFRIGERATING APPARATUS Filed Oct. 19, 1937 CONDENSER i4 7 Ll e4 24-; w

COHPRESSO 6| MOTOR RIB PO N 3 IV: DIV I CE DIR VALVE WITNESSES: R J IEVENTORS UDOLFH IsING=RRNI g' 'fj Ci E. RAYMOND J. Rana.

A'ITOR Patented Sept. 2, 1941 2,254,593 REFRIGERATING APPARATUS Rudolph J. Eisinger, Prospect Park, and Raymond J. Bi e, Lansdowne, Pa. asaignoro to Westingho e Electric & Manufacturing Company,

East Pittsburgh, Pm, a corporation of Pennsylnla Application October 19, 1937, Serial No. 169,758

3 Claims.

Our invention relates to refrigerating apparatus, more particularly to mechanism for unloading the compressor of such apparatus during the starting period thereof in order to reduce the starting current of the motor driving the compressor.

One way of unloading a compressor is to provide an unloader valve which permits flow of refrigerant from the high pressure side to the low pressure side of the system for equalizing the pressures therein. The valve is closed only during operation of the compressor, so that the pressures are equalized while the compressor is shut down. This method oi unloading has a disadvantage in certain cases where the com pressor crank case containing a supply of lubrieating oil is connected to the low pressure side and a refrigerant miscible in oil, such as dichlorodmuoromethane, is used. The pressure in the crank case is raised by the pressure equalization to such an extent that the oil absorbs an excessive quantity of refrigerant while the comnressor is shut down. Upon starting, slugs of oil may be carried into the cylinders, due to the foaming of the oil caused by vaporization of the refrigerant absorbed therein.

Another method. of unloading is to equalize the pressures at the moment of starting the compressor. Since the starting current rises rapidly, this method involves the problem of cheating the pressure equaliflng now almost instantaneously, which is diflicuit with refrigersting apparatus of the larger sizes.

It is an object of our invention to provide improved unloader mechanism for a oomprmor.

A more particular object is to provide unloader mechanism which permits the presure diiference betweenthetwosidesoithesystemtobemaintained while the compressor is shut down, and which eifects substantially complete unloading beforetheoomstarlssotbatthestarting mix-rent is efl'ec'tively limited.

In with our invention, we proade 'IIIIJH an ea including 7 unload omflfin f no u 0| sex-a isde aredtcrn o permit the The starting of the compressor and the closing of the unloader valve may be eifected in timed relation to the action of the master or automatic control, the closing of the unloader valve being delayed suiiiciently to permit the compressor to come up to speed. Alternatively, the compressor may be started in response to pressure difference in the high and low pressure sides of the refrigerating system, and the unloader closed in response to speed c! the compressor.

The above recited and other objects are effected by my invention as will be apparent from the following description and claims taken in connection with the accompanying drawing, forming a part of this application, in which:

Fig. l is a diagrammatic view of one embodiment of our invention in which the starting of the compressor and closing of the unloader valve are efi'ected in timed relation to the closing of a gtheotthemotor thermostatic switch; and

Fig. 3 is a wiring diagram or a modified form of control mechanism in winch the compressor is started in response to the diiierence between the pressures in the high and low pressure sides of the compressor.

Referring to Fig. 1 in detail, the refrigerating system ncludes a compressor 3% driven by a motor The compressor and motor are onclosed in a common owing, thereby forming av hermetically sealed motor compressor unit. The outlet of the compressor, shown at 12, is connected through a discharge conduit to a condenser i, of any suitable type. The refrigerant condensed in the condenser is is conveyed through a conduit I to an evaporator ii, the flow thereof being controlled by a thermostatic expansion valve i'l, not: well known in the art. The refrigerant is vaporized in the evaporator and conveyed through a suction conduit'il to r unit, being prei'erahly admitted to the end thereof contaming the motor. so octopus in contact with the'motor parts tor cooling same before being to cylinders at flue cumm'esor.

The ID is oftho reciprocating type andhasacrankcnseoontainingabodyoiofl a l the motor unit. The crank case is connected to the low pressure side A conduit I is to 1?:du1t II adlaoentthe outlet ll ated in any suitable manner as by a solenoid 22, which opens the valve when energized and closes same when deenergized. A check valve 2! may be interposed in the discharge conduit l9 beyond the connection with the conduit II to prevent back-flow of compressed refrigerant from the condenser when the valve 2| is opened.

The control mechanism for the motor compressor unit includes a master control device, preferably automatic, which may be 01 any suitable conventional form. For example, it may comprise a thermostatic switch 24 responsive to the temperature of an enc osed space which is cooled by the evaporator l The thermostatic switch 24 is adapted to close its contacts when the temperature exceeds apredetermined value and to open its contacts when the temperature decreases substantially below said predetermined value.

The control system further includes an instant reset, time-delay relay mechanism 25 including solenoid 28, a contactor arm 21 adapted to engage arcuate contacts 2| and 29, and a dash-pot Ii connected to the solenoid 26. The dash-pot 1i includes a piston 32 operating in a cylinder 83. The piston is formed with an opening it adapted to be closed by a check valve It, so that the piston retards only upward movement of relay but permits instantaneous downward movement under force of a spring 36 when solenoid II is deenergized.

The arcuate contact 28 is disposed to be engaged by the contact arm 2'! from the lower end of its travel throughout most but not all of the upward movement. The arcuate contact 1! is disposed to be engaged by the contact arm 21 shortly before the latter disengages the contact I! and to remain in engagement with said arm at the upper end of its travel. The contacts II and I! are adjustable with respect to the arm 21. for example, each contact may be provided with a slotted member. 81 engaged by a binding screw ll.

Electric energy for the control system is supplied irom line conductors L1 and La. The several control circuits extend in common fromline conductor Li through conductor II and the thermostatic switch 24 so that they are deenergized when the switch 24 is opened. Thence, one circult extends through the solenoid ll to the line conductor in so that the solenoid is energised as long as the thermostatic switch is closed. A circuit tor the solenoid 12 extends irom the thermostatic switch 14 through the contact arm 21. the contact segment "and a conductor Ii to the solenoid I2, and thence to the line conductor In. A relay 4! is preferably provided for controlling thesupply line I! to the compressor motor ii. The relay 4! is controlled by a circuit extending from the thermostatic switch 24 through the arm I1, the contactsegment 2 0. a conductor 44 and the relay 4! to the line conductor is.

Orrasrron unloader valve 2i. Accordingly, compressed reirigerant at the outlet of the compressor is released to the low pressure side thereof, thereby equalizing the pressure in the inlet and outlet sides of the compressor. The compressor is thus unloaded, thereby reducing the starting current of the motor Ii. When the check valve II is employed, which is optional, only a relatively small volume 01' compressed gas is released, the compressed gas in the condenser being held back from the pressure equalizing conduit II by the check valve.

The contact arm 21 moves upwardly under force of the solenoid 28, the movement thereof being retarded by the dash-pot ll. At the end or a predetermined period of time, sufllcient for unloading, the arm engages the contact 29, there? by completing the circuit controlling the compressor motor. The compressor is thereby started. The arm now engages both the contacts 2'! and 29 so that the unloader valve remains open during the starting period. The arm continues its upward movement and at the end of a further predetermined period 01' time, suflicient tor the motor compressor unit to attain substantially the normal running speed, it disengages the contact 2!, thereby opening the circuit through the solenoid 23 and closing the unloadcr valve 22. The compressor is thereby loaded andnormal operation of the refrigerating system begins.

When the controlling temperature is reduced substantially below the predetermined value, the thermostatic switch ll opens, thereby opening the circuit through the relay II to terminate opera tion of the compressor. At the same time, the solenoid 28 is deenergized, so that the arm 21 is moved to the lower end of its travel. This movement is eiiected rapidly or substantially instantaneously, since the check valve II permits the fluid below the piston tb escape through the opening N. The purpose oi instantly resetting the time delay mechanism is to insure that, in the event or opening of the switch 24 for a'short period, the compressor is again unloaded during the starting period. When the arm 21 is moved to the lower end or its travel, it again engages the contact II but the circuit through the solenoid 22 is opened by the thermostatic switch 24 so that the unloader valve remains closed. The circuit is conditioned, however, to be energized when the thermostatic switch II recloses.

Figure 2 tact l4, irom which a circuit extends through the solenoid 22. or a contact Ill. from which a ciredit extends through the coil of the relay. 2.

this contact arm I! is actuated by a suitable mechanism, indicateddiagrammatically at I.

which is responsive to the speed of the motor compressor unit. to! example. a centrifugal tiy- 7 ball governor or a pressure responsive element which may be responsive to the pressure developed by the oil pump 1 the compressor. 'lhe contact arm it engages the contact ll when the speed is below a predetermined value, and it engem the contact It when the speed is above the predetermined value. The predetermined speed is preferably slightly below the normal running speed; for example, if the motor compressor imit operates at 1170 R. P. 11.. then the switch may be operated at 1050 R. P. M. A suitable form of snap-acting m (not shown as it is well understood in the art) is preferably-provided to move the contact arm I! rapidly from one contact to the other.

In this embodiment, the compressor is started when the p in the inlet and outlet sides of the compressor have been substantially equalized. The circuit for initially energizing the relay 4! extends through the switch 2| and then through a switch 51 actuated by a pressure responsive diaphragm 88. The latter is subjected, in switch opening direction, to the pressure at the outlet of the compressor, which pressure is conveyed through a tube 58. It is biased in switch closing direction by the pressure in the inlet side of the compressor conveyed through a tube ii. The switch 51 is biased in closing direction by a spring 82, which is preferably adjustable in order to vary the pressure diiference at which the switch opens and closes. As will be noted from the drawing, the switch I! is in parallel with the contact I! of the switch 53.

Figure 2-Operction As sooh as the pressures in the inlet and outlet 40 sides of the compressor have been substantially.

equalized by the flow through the unloader valve,

the spring 82 closes the switch Bl to close the circuit for the relay 4!. The latter closes the circuit supplying current to the compressor motor to start operation thereof. The unloader valve remains open for the time being in order that the compressor may be brought up to speed, thereby reducing the starting current of the motor. As the motor compressor unit approaches the normal operating speed, the arm 52 is moved from the contact 5! to the contact II. The unloader valve is closed so that the compressor becomes effective to compress refrigerant. The compressor immediately begins to build up a pressure difference so that, within a short time, the diaphragm 58 opens the switch 51. The circuit for the relay 42 remains closed, however, i'or the rea'iion that the contact arm 82 is moved into engagement with the contact I! at the same time that the unloader circuit was opened. The refrigerating apparatus now remains in normal operation as long as the thermostatic switch is closed.

When the switch 24 opens, the circuit through the coil of the relay .2 is deenergized to terminate operation of the motor compressor unit. As the speed of the motor compressor unit drops below 1050 R. P. M., the contact arm 52 e gages the contact 54, but the solenoid 22 remains deenergized because of the opening of the switch 24. The circuit is conditioned, however. to be reclosed immediately upon reclosing of the switch 24, in which case the compressor is again uniii necessary to unload as the motor compressor is operating at sumcient speed. However, when the speed once drops below 1050 R. P. M., then the compressor must be unloaded before it can be restarted.

If the .motor compressor unit is shut down for a greater length of time, the pressures in the high and low side of the compressor may be substantially equalized by slight leakage through the compressor valves or other part of the refrigerating system. In such case, the switch 51 is closed and the compressor starts immediately upon the closing of the switch 24. The unloader valve 2! remains open, however, to avoid placing load on compressor until it has come up to the predetermined speed, for example, 1050 R. P. M.

From the above description, it will be seen that we have provided refrigerating apparatus wherein the unloader valve is closed while the motor compressor unit is shut down so that absorption of refrigerant in the crank ca se coil is avoided or minimized, and wherein starting of the motor compressor unit is delayed, when the master or automatic control calls for operation, to provide time for the pressure equalizing flow to be effected for unloading the compressor.

While we have shown our invention in two forms, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various other changes and modifications without departing from the spirit thereof, and we desire, therefore, that only such limitations shall be placed thereupon as are imposed by the prior art or as are specifically set forth in the appended claims.

What we claim is:

1. In a mechanical compression refrigerating system, the combination of a compressor havin a crank case containing a body of lubricating oil connected in the low pressure side of the system. a normally closed pressure-equalizing valve connected between the inlet and the outlet sides of the compressor, an electrically actuated device for operating said valve and arranged to open said valve when energized 'and to close said valve when deenerglzed, an automatic control switch which closes in response to an operating condition indicating demand for operation of the compressor, a time delay device set into operation by closing of said automatic control switch and having a first set of contacts which are closed for a predetermined period of time after closin of the automatic control switch and then opened and a second set of contacts which are open for a predetermined period of time after closing of i the automatic control switch and then closed, an electrical circuit for the operating mechanism of said valve extending through said automatic control switch and said first set of contacts in series, and an electrical circuit for controllin operation of the compressor extending through said automatic control switch and said second set of contacts in series, whereby said unloader valve is opened only for a predetermined period sure side and a high-pressure side and including 5 a. motor compressor unit for translating reirigerant vapor from the low-pressure side to the highpressure side, a normally closed. pressure-equalizing valve connected between the low-pressure side and the high-pressure side oi. the system, an 10 electrically energized valve-operating device directly connected to said valve, master control means for controlling the operation of the motor compressor unit, and means operable automatically in response to action of the master con- 15 trol means callin: for operation of the motor compressor unit to control said valve-operating device to open said valve substantially instantaneously while delaying starting of the motor compressor unit for a period of time after said valve is opened to provide pressure-equalizing now and then to start the motor compressor unit.

3. A refrigerating system as set forth in claim 2, wherein the automatically-operable means controls said valve-opening device to close said valve at the end or a predetermined period of time after the motor-compressor unit is started.

RUDOLPH J. EIBIN'GER. RAYMOND J. RIDGE.

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