Refrigeration – Processes – Lubricant handling
Reexamination Certificate
1999-09-27
2001-04-17
Tapolcai, William E. (Department: 3744)
Refrigeration
Processes
Lubricant handling
C062S193000, C062S469000
Reexamination Certificate
active
06216474
ABSTRACT:
BACKGROUND OF THE INVENTION
Screw compressors used in water cooled chillers are of the oil flooded type. Oil provides a seal between adjacent trapped volumes during the compression process and an oil separator removes oil from the hot, compressed gas downstream of the compression process. At high speeds, the percentage of gas leakage between the rotor and housing and interlobes is small as compared to the inlet flow. This is partly due to the oil film formed between the rotor and housing. Additionally, to reduce drag loses, the amount of oil injected should be kept at a minimum. For screw compressors the loading or flow is directly proportional to speed. At low speeds the sealing at the tips and interlobes is poor which reduces the volumetric efficiency of the compressor.
SUMMARY OF THE INVENTION
Volumetric efficiency is increased at low speeds by increasing the oil flow at low loads to offset the poorer sealing at low speeds. Oil from the cooler or evaporator is injected at the rotor inlet for sealing. An oil-rich layer tends to form at the top of the cooler and an ejector is used to draw oil from the top surface of the cooler. The drive or motive fluid for the ejector is, preferably, taken from the last closed lobe, although the discharge pressure may be used. The last closed lobe pressure is preferred because it is determined by compressor operation whereas discharge pressure is determined by system conditions. The amount of oil injected is optimized for full load operation by proper selection of ejector size. Because, at low loads the oil supply should be increased for better volumetric efficiency, a supplemental oil supply is provided. One approach is to provide a parallel supply path from the ejector which is controlled by a solenoid valve responsive to motor speed. Another approach is to provide a second ejector and supply path to the rotors with a solenoid valve in the second path responsive to motor speed.
It is an object of this invention to improve part load performance of variable speed screw compressors.
It is another object of this invention to increase volumetric efficiency at low speeds by increasing oil flow to the rotors at low speeds. These objects, and others as will become apparent hereinafter, are accomplished by the present invention.
Basically, lubrication supply to the rotors of a variable speed screw compressor is optimized for full load and a supplemental supply path is provided which is opened during low speed operation.
REFERENCES:
patent: 4503685 (1985-03-01), DiCarlo et al.
patent: 4662190 (1987-05-01), Tischer
patent: 5603227 (1997-02-01), Holden et al.
patent: 5634345 (1997-06-01), Alsenz
patent: 5761914 (1998-06-01), Carey et al.
patent: 5970722 (1999-10-01), Shibata et al.
patent: 6010315 (2000-01-01), Kishimoto et al.
Carrier Corporation
Tapolcai William E.
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