Micro-processor control of compression ratio at full load in a helical screw rotary compressor responsive to compressor drive motor current

Claim 2

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.

Claim 3

The invention of claim 1 in which said slide member comprises a slide valve and a slide stop, said slide valve having a rear face at its end remote from its discharge face, said 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 movable 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, means sensing the pressure at said inlet opening, and means operative to cause the slide valve and slide stop to move apart when the inlet pressure drops below a predetermined set point.

Claim 4

The invention of claim 1 in which said slide member comprises a slide valve and a slide stop, said slide valve having a rear face at its end remote from its discharge face, said 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 said slide stop being movable 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, means responsive to said first, second, third and fourth means and operative to deliver electrical outputs proportional thereto, means connecting said electrical outputs to a microcomputer, said microcomputer being programmed in accordance with predetermined parameters and operative to control the movement of said slide valve and said slide stop.

Claim 5

The invention of claim 2, and means continually urging said slide stop towards said slide valve.

Claim 6

The invention of claim 2, said slide stop being connected by first rod means to a first piston means, said slide valve being connected by second rod means to a second piston means, said first and second piston means being movable along the same axis, bulkhead means separating the piston means for movement within first and second isolated chamber means, means for introducing and removing fluid into and from said chamber means on each side of said first and second piston means for controlling the movement thereof, said first rod means having an axial bore, said second rod means extending through said slide stop, said bore, said first piston means and said bulkhead means, and compressible means in said bore around said second rod means and engaging said slide stop and said bulkhead means and tending to urge said slide stop towards said slide valve.

Claim 7

The invention of claim 5, in which said means for introducing and removing fluid into and from said chamber means on each side of said first and second piston means comprises first means operative to drive said first piston means in one direction, second means operative to permit fluid in said second piston means to bypass from one side of said second piston means to the other side thereof, third means operative to drive said second piston means in the other direction, and fourth means operative to permit fluid in said first chamber means to bypass from one side of said first piston means to the other side thereof.

Claim 8

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.

Claim 9

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.

Claim 10

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.

Claim 11

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.