CRANKCASE OIL SEPARATOR

Abstract: In a refrigeration motor compressor of the hermetic type containing an electric motor compartment, and a crankcase compartment, an oil separator installed in the crankcase arranged to prevent oil splash from entering the system. The oil separator includes a generally nautilus shell-shaped structure, an elongated tubular structure, and a check valve assembly for controlling flow. The shell-shaped structure has cross baffles for controlling flow characteristics and a pin for centering the check valve assembly. The check valve assembly includes a helical spring with one end positioned in a retainer in the tubular structure. The other end of the spring fits around the pin and abuts an orifice disk in the shell-shaped structure.

Description: This invention relates to compressor systems, and more particularly to an oil separator for use in the crankcase of an accessible hermetic refrigerant compressor. In refrigerating systems using self-contained motor compressor units in which the returning refrigerant is used to cool the motor it is important that the crankcase pressure be maintained at a sufficiently low level relative to the rest of the system to permit return of lubricant collected in the motor compartment to the crankcase. During the starting period of the compressor, refrigerant mixed with the lubricant in the crankcase will foam and the foamed oil will tend to be drawn from the crankcase. Typically check valve passages have been provided for permitting pressure relief from the crankcase while preventing loss of lubricant. However, additional problems have occurred in that the refrigerant being supplied to the intake manifold may back up through such passages to maintain or even increase the crankcase pressure. Piston blow-by gas is another factor making it difficult to maintain crankcase pressure at a sufficiently low level. It is an object of the present invention to overcome the disadvantages of previously known means for obtaining crankcase pressure reduction in refrigerating units of this type and to provide a novel and improved construction for venting the crankcase and maintaining lubricant supply in an efficient and reliable manner. It is a further object of this invention to allow for the venting of piston blow-by gas while preventing the loss of entrained oil. During a flooded start transient the crankcase is filled with liquid refrigerant. The rotating crank generates a great deal of heat from drag loss and causes the liquid to flash. It is another object of the present invention to allow this gas to vent off at a metered rate while centrifugally separating the oil. GB-A-780 053 discloses a refrigerant motor compressor crankcase apparatus comprising an oil separator. In this prior proposal, a simple non-return valve is provided so as to open to allow the flow of gas from the crankcase when a sufficiently large pressure differential is provided across the valve, the valve normally being spring biased into its closed position. Accordingly, the greater the pressure differential, the smaller the restriction to flow which means that excessive gas flow could occur under high pressure differentials with the drawbacks as indicated previously, such that foamed oil will tend to be drawn from the crankcase during starting and generally lubricant and refrigerant can interfere with the maintenance of the required low pressure condition in the crankcase. With the present invention, as defined in claim 1, the valve tends to close upon increase in pressure differential so that while the valve is quite wide open under low pressure differential conditions, it will tend to close upon increase of pressure differential so as to serve as an additional restriction to the flow of gas whereby an additional oil separating function is carried out during this restricted discharge. During normal operation, the crankcase oil separator inlet of the present invention is oriented relative to the crank throw to prevent piston blow-by gas from carrying away entrained oil. This results in a lower system oil circulation rate and reduced compressor oil pump-out rate. During a flooded start or defrost condition, the crankcase oil separator provides a centrifugal oil separating capability to keep oil from being washed out when liquid refrigerant flashes. When a flooded start occurs, an orifice disk closes and metres flow at a rate that can be handled by the crankcase oil separator. The larger entrained oil droplets are removed from the flow and gravity drained back out the lower part of the inlet into the oil sump. There are several advantages to the present invention. First, the reliability of the compressor is improved by reducing the chance of a lubrication related failure due to oil loss. Second, the possibility of slugging during a flooded start is greatly reduced by oil retention. Third, the amount of running time spent at low oil pressure due to refrigerant in the lube system during flooded start is reduced. Fourth, the crankcase oil separator allows crankcase pressure to be vented off relatively quickly without major oil loss. The reduced oil pump-out rate is particularly important on systems with long piping lines where oil is slow to return. The foregoing and other objects and advantages will become more apparent when viewed in light of the accompanying drawings and the following description wherein: Figure 1 is a partial, front view of a conventional refrigerant compressor with a cutaway view showing the novel crankcase oil separator of the present invention installed in the crankcase; Figure 2 is an enlarged cross-sectional view of a portion of the crankcase oil separator of Figure 1; Figure 3 is a sectional view taken generally along line 3-3 in Figure 2; and Figure 4 is a partial perspective view of the oil separator orientation with respect to the center line of the crankshaft. Referring now to the drawings, there is illustrated a hermetic motor compressor generally indicated at 10 and of a type widely known in the refrigeration trade. Threadably engaged into the upper side wall of crankcase 12 of the compressor 10 is the crankcase oil separator 14 of the present invention. In the preferred embodiment of the invention, an elongated first body portion 16 is secured to a second body portion 18. Following the preferred procedure, the first body portion 16 and second body portion 18 are plastic injection molded and ultrasonically welded together. Of course, other materials and methods of joining may work as well. The first and second body portions 16, 18 may even be formed from the same piece, eliminating the need for later joining both portions 16, 18. The two body portions 16, 18 are welded together at a bottom face 20 of the first body portion 16 and an upper lip 22 of the second body portion 18. The bottom face 20 and upper lip 22 have matching shapes in the preferred embodiment. The first body portion 16 is substantially tubular in shape but has a stepped down region 24 formed approximately one-third of the way up the tube from the bottom face 20. This results in the first body portion 16 having two concentric tubular portions 26 and 28 formed from one piece. A purpose of the stepped down region 24 is to provide a shoulder 30 for one end 40 of a check valve spring 32. The tube of the first body portion 16 extends into a high velocity passage 50 through which suction gas movably flows from the crankcase to the suction gas manifold and valve plate (not shown). This produces a relatively lower pressure in the crankcase 12 for oil transfer/return. The check valve spring 32 is part of a check valve assembly 34 which includes the helical spring 32 and an annular orifice disk 36. One end 40 of the spring 32 resides in a retainer 38. The retainer 38 is sized to fit onto the shoulder 30. The other end 42 of the spring 32 may be wound to a small inside radius so that it fits around a metal pin 44. The pin 44 has one end 46 molded into the second body portion 18 and the other end 48 is positioned axially inside the first body portion 16. End 42 of the spring 32 abuts an orifice disk 36 which is annularly positioned around the pin 44. As the pressure inside the second body portion 18 increases the orifice disk 36 will rise up the pin 44 and at the same time will be resisted by the spring 32. The greater the pressure inside the second body portion 18 the more the disk 36 will compress the spring 42 and the farther it will rise up the pin 44. The disk 36 can rise until it contacts the bottom face 20 of the first body portion 16. This bottom face 20 may have a rounded seat 52 to prevent the disk 36 from sticking to the bottom face 20 due to trapped oil between the surface of the disk 36 and the bottom face 20. The second body portion 18 is shaped much like the spiral section of a nautilus shell. The second body portion 18 has an inlet passage 54 which at its lower end is also an exit passage 56. The second body portion 18 also has an opening 58 which matches the hole in the bottom face 20 of the first body portion 16 when both body portions 16 and 18 are assembled together. In addition the second body portion 18 has a raised island portion 60 which holds one end 46 of the pin 44. In the preferred embodiment, the raised island portion 60 is circular in shape and has cross baffles 62 molded on the top surface thereof. The cross baffles 62 serve as a bottom seat for the disk 36 when it is in the lowermost position, as shown in Figure 2. While the disk 36 is in its uppermost position seated against the bottom face 20 of the first body portion 16, the baffles 62 prevent the flow next to the raised island portion 60 from swirling and the only gas flow through the separator is through the clearance space 63 between pin 44 and the center opening in disk 36. This prevents the creation of low pressure in the center which could suck oil up into the gas flow. A hex nut 64 may also be cast into the bottom of the second body portion 18 to assist in installation of the crankcase oil separator 14. The first body portion 16 may be threaded for installation into a hole in the wall of the crankcase 12. Oil separation is accomplished in two principal ways. First, the oil separator inlet 54 orientation to the crank throw is positioned close to the rotating crank throw and located so that oil splash cannot enter directly. Additionally, the swirling draft induced by the rotating throw is at right angles to the oil separator inlet 54 so that the momentum of larger oil droplets resists the entry turn. The oil separator 14 may be oriented by means of a washer 66 with two tabs. One tab 68 may be bent upward into a suitable recess in the wall of the crankcase 12 and the other tab 70 may be bent down into a slot 72 formed in the bottom face 20 of the first body portion 16 and the upper lip 22 of the second body portion 18. Secondly, during a flooded start, or whenever the pressure drop across the oil separator 14 exceeds a predetermined pressure, the orifice disk 36 closes. The pressure continues to increase and the gas velocity through clearance opening 63, becomes high enough for centrifugal separation to occur. The opening 63 is sized to meter the flow at a rate which the oil separator 14 can handle without being plugged with liquid. When the entrained oil is removed from the gas and settles out it flows by gravity back to the exit 56. However, for the oil to leave the oil separator through the exit 56 the pressure differential of the entire separator must be less than the head of oil necessary to drain. The opening 63 is sized for high pressure differential and the exit 56 area is large and radiused for low pressure differential in the preferred embodiment.

Claims: A crankcase oil separator for installation in a refrigerant motor compressor crankcase to vent gas from the crankcase while returning oil to the crankcase, said oil separator comprising a passageway (54,58,63) for the venting of gas from the crankcase, means (18,36) at the inlet of the passage for separating oil from the venting gas, and a check valve (34) following said means (18,36) in said passageway for controlling the flow of gas therethrough, said check valve (34) being operable to close the passage to restrict the flow of gas upon an increase in pressure differential thereacross. A separator according to claim 1, wherein said check valve (34) is designed to close when the pressure drop across the valve exceeds 0.69 bar (10 psi). A separator according to claim 1 or 2, wherein said check valve (34) includes an annular disk (36) movable between open and closed positions and means (32) for biasing said disk (36) to its open position. A separator according to claim 3, wherein said disk (36) includes a small orifice (63) to permit a reduced flow of said gas through said passageway when said disk (36) is in its closed position. A separator according to any preceding claim, wherein said means for separating oil from the venting gas includes a body portion (18) shaped similar to a nautilus shell section and wherein said oil is centrifugally separated from said gas. A separator according to claim 5, wherein said body portion (18) includes an interior raised island portion (62) having cross baffles (62) formed on a top surface thereof for preventing the swirling flow of said gas over said raised island portion. A separator according to any preceding claim, which comprises a first body portion (16) and a second body portion (18) depending from one end of said first body portion, said second body portion having an opening in relationship with an opening in said first body portion, the check valve (14) being positioned within said first and said second body portions (16,18) and passing through said openings for controlling gas flow through said openings. A separator according to claim 7, when appendant to claim 3, wherein said check valve (14) includes a helical compression spring (32), said spring (32) having a first end (40) which abuts a retainer (38) within said first body portion (16) and a second end (42) which abuts an annular disk (36), said disk (36) and said second end (42) of said spring (32) being axially movable along a pin (44) in said second body portion (42). A separator according to claim 8, wherein a rounded set (52) is formed on a bottom face (20) of said first body (16) portion for preventing said disk (32) from sticking to said bottom face (20) when said disk (32) rises as the pressure in said second body portion increases. A separator according to claim 7, 8 or 9, wherein said first body portion (16) is at least partially threaded to engage within a hole in said crankcase (12). A separator according to any one of claims 7 to 10, wherein a hex nut (64) is formed in said second body portion (16) to facilitate installation. A separator according to any one of claims 7 to 11, wherein said first and said second body portions (16,18) are made from a polymeric material. A separator according to any preceding claim, which comprises a washer (66) with tabs (68,70) for orienting said separator (14) in said crankcase to prevent oil splash from directly entering said passageway, at least one tab (68) to engage said crankcase (12) and at least one other tab (70) to engage said separator (14). A separator according to any preceding claim, mounted in combination with a refrigerant motor compressor crankcase apparatus. A separator according to claim 14, wherein the inlet of said passageway (54) is so orientated in said crankcase (12) as to prevent oil splash from directly entering said passageway. A separator according to claim 15, wherein said inlet (54) is so orientated as to be normal to a swirling draft induced by the rotating crank throw. A separator according to claim 14, 15 or 16, further comprising means (56) for returning separated oil to said crankcase (12).

Inventors: FAIN, GARY KENT
Applicants: COPELAND CORPORATION
Application year: 1990
Main classification: F25B43
IPC codes: F01M13, F04B39, F25B31