US2274337A - Refrigerating apparatus - Google Patents

Description

Feb. 24, 1942.

J. G. RITTYER REFRIGERATING APPARATUS Fil'ed May 16, 1939 WITNESSES:

INVENTOR JOHN G. P/TTER ATTOR I Patented Feb. 24, 1942 ,Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application May 16, 1939, Serial No. 273,845 7 6 Claims.

My invention relates to a motor compressor unit, more particularly to a mechanism for unloading the compressor for starting, and it has for an object to provide an improved mechanism.

Another object is to provide an unloader mechanism whereby satisfactory operation can be obtained easily and with a high degree of certainty.

A particular object is to provide an unloadermechanism which operates satisfactorily to maintain the compressor unloaded until it ap-.

proaches normal running speed and then to load the compressor. 1

One known method of unloading a compressor for starting is to unload the compressor in response to the oil pressure developed by the oil" pump; While this method is usually satisfactory,

I have found that, in one instance, the oil pressure loaded the compressor prematurely and prevented it from attaining normalrunning speed. Also, the speed at whichthe compressor is loaded is affected by the viscosity of the oil, which alters the relation of. oil pressure to speed.

Another known method of unloading a compressor for starting is to provide a pressureequalizing valve which is operated in response to the motor current. The'high value of motor The abov and other objects are efi'ected by my invention as will be apparent from the Joblowing description and claims taken in connec-- tion with the accompanying drawing, forming apart of this application, in which:

The single figure is a diagrammatic view of a refrigerating system including .a motor compressor unit having my novel unloader mechanism incorporated therein, the latter being shown in section. Referring to the drawing in detail, I show a refrigerating systemcomprising an evaporator start current opens the-valve to equalize the pressures for starting and a spring 'closes the valve as the motor current decreases to normal value. Such a type of unloader has been found satisfactory for small compressors but is not so suitable for large compressors because of the size of valve; required. It must be carefully made to prevent leakage of refrigerant and gas during normal operation, when theforce-holding the valve closed is relatively small.

In accordance with my invention, I provide an unloader mechanism which is operated by the oil pressure developed by the oil pump. In addition, -I provide a valve operated by a coil which is responsive to the motor current. The high motor current" during starting opens the valve so that'the oil is allowed'to escape and the compressor remains unloaded. As the motor compressor unit approaches normal running speed,

the decrease in motor current allows the valve to close, whereupon the oil pressure is imposed upon the unloader mechanism to load the compressor. I have found that such an unloader mechanismpperates very satisfactorily. -It is very reliable in obtaining unloading during the starting period to permit the motor to bring the unit up to speed and to load the compressor during normal operating speed. v

10, a motor compressor unit a condenser l2, and an expansion valve l3. The refrigerating system operates in the usual manner of such apparatus, the refrigerant being compressed by the motor compressor unit ll, condensed in the condenser l2, expanded in the'expansion valve l3 and vaporized in the evaporator Ill.

The motor compressor unit comprises a reciprocating compressor l4 and a motor [5 directly,

connected to the compressor for driving the same. The compressor It includes a crankcase I6, the lower portion of which constitutes an oil reservoir. It is provided with an oil pump ll disposed in the crankcase I6 and driven by the compressor. The oil pump "has its inlet l8 disposed below the oil level in the crankcase and discharges oil under pressure through suitable passages l9 to the several surfaces to be lubricated.

The compressor is provided with an unloader mechanism heretofore known. This mechanism 'is adapted to hold the suction valve, shown at 2 l,

in open position so that on the upstroke of the piston the gas in the cylinder is returned to the suction side and is notcompressed. The unloader mechanism includes a stem. 32 which is spring 33 and is moved in upward direction by a same upwardly. A conduit 36 connects the oil' pump discharge with the bellows 35 for imposadapted to hold the suction valve 2| downwardly in open position. Itis biased downwardly by a lever 34. A pressure-responsive bellows 35 engages we: end of the lever 34 for moving the ing the oil pressure on the bellows.

.There is interposed in the conduit 36 a valve 37 which is adapted to permit the oil'to escape from the conduit.36.,The escaping oil is returned to the reservoir in the crankcase, as by" I means of a conduit 38. The valve 31 is biased in closed direction by a spring 39. A coil ll is 'connected to. th valve 31 and is-connected in the motorcircuitll, so that the motorcurrent passes throngh the coil and biases the valve in opening direction. The coil 49 and the spring 39 are so designed that the current drawn by the motor at normal operating speed thereof is insufficient to overcome the force of the spring 39, but is suflicient to overcome the force of the spring 39 and to open the valve 31 when the speed of the unit is appreciably below the normal operating speed.

The operation of the refrigerating apparatus is controlled in any suitable manner, for example, a thermostat 42 may be connected in the motor circuit 4| and operate in response to the temperature of the air cooled by the evapora:

- tor l0.

Operation Assuming the apparatus to have been previously shut down, the motor .circuit 4,| may be closed either by the action of the thermostat 42 or by the switch 43. The closing of the circuit 4| energizes the motor 5. The current drawn by the motor during the starting period is much greater than that normally drawn, so that the coil 40 opens the valve 31 against the force of the spring 39. The opening of the valve 31 permits oil discharged from the oil pump l1 to escape from the conduit 36 and return tothe reservoir through the conduit 38. therefore, no appreciable pressure imposed on the .bellows 35, so that the spring 33 forces the stem 32 downwardly to hold the suction valve 2| in open position. Accordingly, the compressor is unloaded while the motor "compressor unit is started. As the speed of the unit increases, the pressure developed by the oil pump l1 increases, but it is ineffective to act on the bellows 35 since the oil is released by the valve 31. As the speed of the unit approaches the normal running speed, the current drawn by the unit decreases sufllciently so that the valve 31 is closed by the force of the spring 39. The oil pressure is now imposed on the bellows 35, whereupon the latter moves the stem 32 upwardly'through the lever 34. The suction valve 2| is now permitted to close on the upstroke. of the piston, so that the compressor is eflfective to compress refrigeran slight.

An important advantage ofthe invention is the, fact that the pressure developed by the oil pump and the pressure at which the bellows operates the unloader need, not be exactly correlated, itjbeing necessary only that ample oil pressure be provided at normal operating speed. It will also be apparent that variations in operating results produced by variations in viscosity of the oil, are entirely avoided; It is notessen- There is,

tial that the valve 31 be entirely fluid-tight, since a small amount of leakage of oil from the oil, pump tothe reservoir is unobjectionable.

I desire it'to be understood that various expedients which will be apparent to those skilled in the art. may be used in connection with the apparatus shown and described. For example, the thermostat 42 may control'the motor circuit 4| through a relay instead ofdirectly. Also, the motor may be of any suitable'type known in the art.

While I have shown my invention in but one form, it will be obvious-to those skilled in the art that it is not so limited, but is susceptible of various changes and modifications without departing from the spiritthereof, 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. The combination with a compressor and an electric motor for driving the same, of a pressure-operated unloader mechanism adapted to load the compressor -upon application of suflicient fluid pressure thereto, a pump driven simultaneously with the compressor at a speed pro portional to that of the compressor and developing a fluid pressure which is sufiicient, at normal operati g speed of the compressor, to actuate the unloader mechanism to load the compressor, means including and controlled by a valve for imposing said fluid pressure on the unloader mechanism, and means responsive to theelectric current drawn by said motor for controlling said valve.

2. The combination with a motor compressor unit including a compressor and an electric motor for driving the same, of an unloader mechanism' for the compressor, an oil pump driven by the unit and developing an oil pressure varying as a function of the speed of the unit, means responsive to said oil pressure for actuating said unloader mechanism to load said compressor, and means responsive to a predetermined maximum value a of the electric current flowing through said motor for releasing oil from said pressure-responsive meansto' prevent loading of the compressor until the motor current has decreased to a value indicating substantially normal running speed. 7

' 3. The combination with a motor compressor unit including a compressor and an electric motor for driving the same, of a pressure-operated unloader mechanism adapted to load the compressor upon application of suflicient fluid pressure thereto, an oil pumpdriven by the unit at a speed proportional to that of the unit and developing an oil pressure which is sufiicient, at normal operating speed of the unit, to actuate the unloader mechanism to' load the compressor, means including a valve and adapted in the closed position of the valve to apply the oil pressure de-- veloped by the oil pump to the unloader mecha-. nism and adapted in the open position of the valve to permit the oil to return to the inlet of the pump and thereby avoid application of oil pressure to the unloader mechanism, and means operable automatically to open said valve during starting periods of theunit and to close said valve at a time when the unit has attained substantially normal operating speed.

4. The combination with a motor compressor anism, and operating mechanism for said valve, said mechanism being automatically operable to release said oil pressure fromthe unloader mechanism during the starting period oi. the unit and to position said valve for applying said oil pressure to the unloader mechanism at a time when the unit has attained substantially normal operating speed.

5. The combination with a motor compressor unit including a compressor and an electric mofor for driving the same, of a pressure-operated unloader mechanism adapted to load the compressor upon application of sufficient fluid pressure thereto, an oil pump driven by the unit and developing afroil pressure which is suflicient, at normal operating speed of the compressor, to actuate the unloader mechanism to loadthe compressor, means for conveying oil from said pump to a bearing of the compressor for lubricating the same, means including and controlled by a valve for imposing said oil pressure on the unloader mechanism, and means responsive to a predetermined maximum value of the electric current flowing through said motor for controlling said valve to cut ofithe supply or oil pressure to said unloader mechanism. I

6. The combination with a motor compressor unit including a compressor and an electric motor for driving the same, of a pressure-operated unloader mechanism adapted to load the compressor upon application ofsufllcient fluid pressure'thereto, a pump driven by the unit and developing a fluid pressure which is sufficient, at normal operating speed of the compressor, to actuate the unloader mechanism to load the com-' pressor, means including and controlled by a valve for imposing said fluid pressure on the unloader mechanism, a solenoid'electrically con-- nected in a circuit supplying electric current to said motor and mechanically connected directly to saidvalve, said solenoidbeing adapted to control said valve so as to unload said. compressor in response to starting current and to load said compressor in response to running current.

JOHN G. RI'IIER.

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