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AssigneeFrick Company
InventorsDavid A. Murphy, Peter C. Spellar
Estimating the term…
An axial flow helical screw type compressor has a slide valve member and slide stop member mounted end to end beneath the intermeshing rotors such that the slide valve member controls communication between the work chamber defined by the rotors and the casing to the outlet port and the slide stop member and the valve member together control the working fluid inlet to the bores of the rotors, the slide valve member and the slide stop being independently movable. Control means for the slide valve member and slide stop include position sensing means for these two members, inlet and outlet pressure sensing means, and means for feeding these inputs into programmable circuitry to control the positions of the slide member and slide stop. Additional control means senses the occurrence of full load operation and then causes the slide valve member and slide stop member to move as a closed unit in a given direction, or the reverse, as the compressor drive motor current is sensed, continuously seeking the position at which such current is at a minimum.
In an electric motor driven screw compressor having meshing helical rotors on parallel axes and mounted in a housing having intersecting cylindrical bores, a high pressure end wall at one end of said housing and a low pressure end wall at the other end thereof, the low pressure end wall having an inlet opening and the high pressure end wall having a discharge opening, an axially extending recess in the housing in open communication with said bores, a slide member mounted for axial movement in the recess, said slide member having interfacial sealing relationship with said rotors, said slide member having a discharge face at one end thereof which is adjacent to the high pressure end wall whereby movement of the slide member is operative to change the compression ratio, the improvement comprising, means sensing the magnitude of current to said electric motor, means for sensing when the compressor is operating at full load, means for incrementally moving the slide member in each direction, and means responsive to full load operation for causing the slide member to move in one direction while the motor current is decreasing, to change to the other direction upon an increase in the motor current, to continue to move in said other direction while the motor current is decreasing, and to change back to said one direction upon an increase in the motor current.
In an electric motor driven screw compressor having meshing helical rotors on parallel axes and mounted in a housing having intersecting cylindrical bores, a high pressure end wall at one end of said housing and a low pressure end wall at the other end thereof, the low pressure end wall having an inlet opening and the high pressure end wall having a discharge opening, and means for selectively and incrementally raising and lowering the internal compression ratio of said compressor, the improvement comprising, means sensing the magnitude of current to said electric motor, means for causing the compression ratio raising and lowering means to operate in one mode while the motor current is decreasing, to change to the other mode upon an increase in the motor current, to continue to operate in said other mode while the motor current is decreasing, and to change back to said one mode upon an increase in the motor current.
In an electric motor driven screw compressor having meshing helical rotors on parallel axis and mounted in a housing having intersected cylindrical bores, a high pressure end wall at one end of said housing and a low pressure end wall at the other end, the low pressure end wall having an inlet opening and the high pressure end wall having a discharge opening, an axially extending recess in the housing in open communication with said bores, the improvement comprising, a slide valve mounted for axial movement in the recess, said slide valve having interfacial sealing relationship with said rotors, said slide valve having a discharge face at one end thereof which is adjacent to the high pressure end wall and a rear face at its remote end, a slide stop having a front face which is adapted to engage the slide valve rear face to form a continuous composite member, said slide valve and slide stop being moveable apart to provide an opening therebetween of variable selected size and axial position in communication with the inlet opening in order to permit selective unloading of the compressor, first means sensing the pressure at the discharge opening, second means sensing the pressure at the inlet opening, third means sensing the position of said slide stop, fourth means sensing the position of said slide valve, fifth means sensing the magnitude of current to said motor, pressure transducer means responsive to the first and second means and operative to deliver electrical outputs proportional thereto, electrical circuit means responsive to set third, fourth and fifth means and operative to deliver electrical outputs proportional thereto, means delivering the outputs to a microcomputer, said microcomputer being programmed in accordance with predetermined parameters and operative to control the movement of said slide stop member and said slide valve member, said microcomputer control being operative to move incrementally the slide valve and slide stop in each direction, said microcomputer being programmed responsive to full load operation to cause the slide valve and slide stop to move as a composite member in one direction while the motor current is decreasing, to change to the other direction upon an increase in the motor current, to continue to move in said other direction while the motor current is decreasing, and to change back to said one direction upon an increase in the motor current.
Dependencies are inferred from the claim text.