US 3777509 A
Apparatus for assuring return of oil separated from refrigerant in a vapor cycle refrigeration system. Means are provided for positively effecting flow of oil from a lower pressure reservoir into a crankcase of a compressor which is normally maintained at a higher pressure. Such means may take the form of an eductor powered by flow of lubricating oil in a closed circuit with respect to the compressor.
Description (OCR text may contain errors)
United States Patent 1 1 Muench 1 1 Dec. 11, 1973 1 41 OIL RETURN SYSTEM FOR 2,4 8, 4/1947 Zwiclrl 1. 62/470 REFRIGERATON APPARATUS 2,892,320 6/1959 Quick 62/471 2,975,613 3/1961 Heid0rr1.... 62/471 Inventor Paul Muench, Medford Lakes, 3,304,697 2/1967 Ramsey 62/471 NJ. 3,360,958 1/1968 Miner 62/470  Assignee: Borg-Warner Corporation, Chicago, 1
11L Primary Examiner-Meyer Perlin Attorney-Donald W. Banner et al.  Filed: Mar. 13, 1972  Appl. No.2 233,895  ABSTRACT Apparatus for assuring return of oil separated from re-  US. Cl. 62/470, 62/192 frigerant in a vapor cycle r geration system. Means  Int. Cl. F25b 43/02 are provided for p e y e fect ng flo of oil from a  Field of Search 62/84, 192, 193, lower pressure reservoir into a crankcase of a 62/194, 470, 471, 472, 473 pressor which is normally maintained at a higher pressure. Such means may take the form of an eductor  Refere Cit d powered by flow of lubricating oil in a closed circuit UNITED STATES PATENTS with respect to the compressor. 1,899,378 2/1933 Zouck 62/471 2 Claims, 1 Drawing Figure CONDENSER EVAPORATOR COMPRESSOR 52 on. STILL 5o SIGHT GLASS COM PR E550 Q BACKGROUND AND SUMMARY OF THE INVENTION Thisinvention relates to an oil return system for refrigeration apparatus.
In vapor cycle refrigeration systems, refrigerants pro cess considerable affinity for lubricant oil used in com- A pressors of such systems, so that mixtures of the oil and refrigerants occur. Since lubricating oil destroys the high operating efficiency of the evaporator, itis most desirable to recover the oil circulating with the refrigerant leaving the compressor and return it to the com- I pressor crankcase. Forthis purpose, an oil separator is used to protectthe compressor from liquidrefrigerant and/or oil returninginquantity through the suction line to the compressoriThe oil separator operates to separate refrigerant from the oil, the oil being transferred to an oil receiver, which may also be a still, for return to the compressor crankcase. Whenthe pressure of the oilinthe crankcase is higher than the pressure of the oil in the oil receiver, it is necessary to employ means to transfer the oil to the higher pressure chamber. While a mechanical pump can beused to perform this function, the pump has a multiplicity of moving parts subject to wear and deterioration, in addition to requiring an electrical or other source of motive power necessitating controls for its correct operation. While other liquid transfer means have been suggested, such means have been found to be incapable of transferring theoil if considerablepressure differences exist between the oil receiver and the compressor crankcase.
The present invention contemplates an oil return system featuring means, suchas an eductor, designed to be powered by main oil pressure from the compressor lubricating system and topositively effect flow of oil from a lower pressure reservoir into a compressor crankcase which is normally maintained at a higher pressure.
It is an object of the invention to provide an improved oil return system for refrigeration apparatus.
Another object of the invention is to provide an improved oil return system in which an eductor is disposed in a closed compressor lubricating oil circuit and powered by flow of oil therein to compel flow of oil from a reservoir into the circuit and thereby intothe compressor crankcase.
Additional objects and advantages will be apparent from the following detailed description taken in conjunction with the drawing.
DESCRIPTION OF THE DRAWING The single FIGURE is a schematic diagram of a refrigeration system utilizing the oil return system of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the FIGURE, there is shown a refrigeration system employing a pair of compressors op erating in parallel to feed a single condenser and single evaporator, although various combinations of multiple condenser and evaporator systems, which are familiar to thoseskilled in the art, may be employed. Compressors and 12 dischargehot gas into respective outlet lines 14 and 16 which are connected to a common hot gas discharge line 18. The gas passes through an oil separator 20 of any common type and is delivered through line 22 to condenser 24. Gas then flows through a re-..
striction, such as provided by a thermostatic valve or an orifice 26, into an evaporator 30, which iscommonly of the flooded type. The suction gas, leaving the evaporator, is delivered to what is referred to as a dead-end trap 32 which is adapted to eliminate any trace of oil carried in the suction gas to prevent the same from flowing into the suction side of the compressors. The suction gas passes through line 38 which is joined to suction lines 40 and 42 of compressors 10 and 12, respectively.
Oil, separated from the discharge gas, is delivered by a line 44 to a still and receiver 50 where the refrigerant is boiled off and returned to the suction side of the system preferably to trap 32 through line 54. At the same time, the oil, separated from the suction gas, is deliv ered to the still through line 56.
The refrigerant-free oil, which is collected in the still, is available for use in the compressors in the event the oil level in either one of them drops below a predetermined point.
The oil makeup system includes eductor 58 which, in effect, operates as a pump driven by oil circulating in line 60 and is responsive to the pressure generated by the oil circulating system in the compressor 10. In this way, the relatively low pressure oil in the still 50 and flowing in lines 62 and 64 is positively driven into the oil return system by being aspirated into the return stream by the eductor 58. In practice, the oil is continuously circulating through a pressure-responsive valve 65 (sensing oil pressure through line 61) which has a minimum setting of about 100 psi and a maximum setting of 150 psi. When the oil level in the compressor crankcase drops to a dangerous level, the oil level float switch 66 completes an electric circuit to activate a solenoid valve 68 in line 64 to permit the oil in still 50 to enter the suction side of the eductor. When the oil level is brought up to the proper point, the switch 66 will open to deenergize the solenoid of the valve 68 and valve 68 closes to discontinue oil flow from still 50 to the eductor. The same manner of operation applies to oil circulating line 71, pressure sensing line 73, eductor 70, pressure-responsive valve 72, oil level switch 76, and solenoid valve 74 on compressor 12. Check valves 69 and 75 are employed to prevent back flow of oil from the compressor to the oil still.
A feature of the invention resides in the use of oilsampling line directly connected to the evaporator 30 and to line 56which permits oil to flow into the still 50 via line '56 when an electric heater element 82 and solenoid 84 of valve 86 are energized, valve 86 being opened by activating solenoid 84. Solenoid 84 and electric heater element 82 may be operatively interconnected by control line 90 so that they are energized simultaneously by suitable means (not shown). This will assure that the heater will be in operation to boil off refrigerant flowing from evaporator 30 through valve 86 to the oil still 50.
In the preferred embodiment of the invention, the oil return system can operate with unequal compressor loadings or crankcase pressures; a minimumquantity of oil is in circulation through the oil still and receiver; there is more positive draining of the dead-end trap 32; simplicity of piping and equalizing of the oil still isrealized; and the system is in operation at all times that the compressor is operating.
It will be apparent that, while this invention has been described in connection with a refrigeration system employing dual compressors operating in parallel to supply a single condenser and evaporator, it is believed obvious the invention can be used in a refrigeration system employing a single compressor. Also, the use of an oil still or oil receiver is optional. Accordingly, it is to be understood that the described preferred embodiment of the invention is by way of illustration and not by way of limitation; and the scope of the appended claims should be construed as broadly as the prior art will permit.
What is claimed is: I
1. In a refrigeration system including a compressor having an oil-carrying crankcase; an oil separator connected to the high pressure side of said compressor to effect separation of oil from the refrigerant; means pro viding a closed lubricant oil circuit in fluid communication with said crankcase of said compressor; an oil receiver connected to the oil discharge side of said oil separator and to said circuit, said receiver containing oil under pressure lower than the pressure of the oil in said crankcase; and eductor means in said circuit and operative, in response to the pressure generated by the oil circulating in said circuit, to effect flow of oil from said receiver into said circuit.
2. A refrigeration system as defined in claim 1 including a conduit connecting said receiver to said closed lubricant oil circuit; means for sensing the oil level in'said crankcase; and valve means associated with said con duit and responsive to said oil level sensing means for permitting oil in said receiver to flow through said conduit into said circuit by the operation of said eductor whenever said oil level is less than a predetermined value.