Rotary expansible chamber devices – Heat exchange or non-working fluid lubricating or sealing – Non-working and working fluids intermix in working chamber
Patent
1996-04-08
1997-10-21
Vrablik, John J.
Rotary expansible chamber devices
Heat exchange or non-working fluid lubricating or sealing
Non-working and working fluids intermix in working chamber
418203, 418DIG1, F04C 1816, F04C 2902
Patent
active
056789874
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a rotary screw compressor of a kind wherein the axial gas forces acting on the rotors are counterbalanced by a thrust balancing piston in order to reduce a load on the thrust bearings. Compressors of this kind are disclosed for example in GB 1 026 165, U.S. Pat. No. 3,932,073 and U.S. Pat. No. 4,185,949.
Through the known devices an in normal cases appropriate reduction of the thrust load is attained. A problem, however, arises when the outlet pressure varies and in particular when also the inlet pressure varies. Under such working conditions axial gas forces will vary with the result that the rotor might be under- or overbalanced, depending on how the balancing piston is dimensioned and on the various working conditions. The result will be a decrease in the running life of the thrust bearings.
This problem is recognized in the above mentioned U.S. Pat. No. 3,932,073. That disclosure, however, does not present a complete solution to the problem, neither contains any claim related thereto, but only suggests in passing some measures that could be taken in order to overcome it. These measures include providing an expansion valve, which connects the high pressure side of the balancing piston with a closed working chamber in the compressor. The valve should be automatically opened or closed, and when open it creates a pressure drop over a throttling device between an oil separator and the balancing piston in a way not further described. The use of a control valve makes such an arrangement relatively complicated, and additional means probably also are required in order to realize the idea. The disclosure mentions this problem when the compressor is used in an automotive air condition apparatus, i.e. in an application where the pressure levels are quite low, and it is questionable if the arrangement would function in applications where the pressures are much higher.
The object of the present invention is to attain simple and reliable automatic adaptation of the thrust balancing force to various working conditions in a compressor in question, in particular for operating with high inlet and outlet pressures.
SUMMARY OF THE INVENTION
According to the present invention, a rotary screw compressor (1) comprises a pair of rotors operating in a working space (16) connected to a low pressure inlet port (2) and to a high pressure outlet port (3); a liquid injector (4) which injects a liquid into the working space at an intermediate pressure level; a liquid separator (10) connected to the outlet port; and a first pipe (6) including the liquid injector (4), the first pipe (6) connecting the liquid separator (10) to the working space (16) at the intermediate pressure level. A hydraulic thrust balancing piston (11) acts on at least one of the rotors. First (5) and second (4) throttling devices are provided in the first pipe (6); and a second pipe (7) is provided for connecting a first pressure surface (12) of the piston (11) to the first pipe (6), the connection to the first pipe (6) being located between the first (5) and second (4) throttling devices.
Preferably, each of the first (5) and second (4) throttling devices comprises a non-variable throttling device.
An arrangement according to the present invention requires a minimum of modifications of the compressor in order to attain the adaptation of the balancing force and introduces no movable parts for that. The dimensioning of the parameters in the system such as the area of the balancing piston and the degree of throttling of the two throttles can be easily calculated for an expected pressure variation range, and due to the simplicity of the system the risk for failure is minimized.
Since the liquid injection means normally represents a throttling of the liquid when it is injected, the second throttling device advantageously is comprised by the liquid injection means itself.
There is no need to use variable throttling neither in the first nor in the second of the throttling devices so that fixed throttles c
REFERENCES:
patent: 3932073 (1976-01-01), Schibbye et al.
patent: 3947078 (1976-03-01), Olsaker
patent: 4185949 (1980-01-01), Lundberg
patent: 5135374 (1992-08-01), Yoshimura et al.
Svenska Rotor Maskiner AB
Vrablik John J.
LandOfFree
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