JPH0260875B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a helical screw type compressor for axially flowing fluid, and means for controlling the internal compression ratio of the compressor at full load depending on the operating variables of the compressor. Relating to compressors that are equipped with.

Prior Art For a description of the prior art, see U.S. Patent Application No.
See the description of the prior art disclosed in No. 416768. Other known techniques are as follows.

In Haugsted's patent No. 2,418,835, the input current of the drive motor is sensed, the centrifugal compressor is tested for surges, and more gas is input or the discharge pressure is reduced as required to prevent such surges. .

No. 3,380,650 to Drummond discloses a means for preventing surges in a centrifugal compressor by sensing the pressure in the discharge line and reducing the discharge rate.

Jednacz's Patent No. 3,535,053 discloses a method for preventing overloading of a motor driving a centrifugal compressor by sensing the input current to the motor and activating a load removal means to reduce the input current to the motor. A method is disclosed.

Richardson's patent No. 3,648,479 teaches equalizing the input currents of two motors driving two centrifugal compressors connected to the same load, and detecting the input current of the motors to prevent overloading of the motors. A method for preventing this is disclosed.

Hutchins Patent No. 3,855,515 discloses means provided for minimizing peak current and reducing resonant effects in a stepper motor.

In the Szymaszek patent No. 4,080,110, motor current and gas inlet pressure or temperature or gas outlet pressure or temperature are sensed and a displacement controller is adjusted to maintain the motor input current at a predetermined value.

Further known techniques are disclosed in Shaw's patent no. 4,249,866 and Kountz's patent no. 4,351,160.

SUMMARY OF THE INVENTION The present invention relates to a control means for varying the internal compression ratio of a compressor while sensing the compressor drive motor current when the compressor is operating at full load. The compression ratio is varied by operating a compound valve that interfaces with the compressor rotor. The compound valve is moved in one direction as determined by the associated computer program as long as the sensed current decreases. When the current begins to increase, the direction is reversed. More specifically, the present invention relates to determining and maintaining an optimum compression ratio for an electric motor driven screw compressor when the compressor is operating under full load conditions. The optimum compression ratio occurs when there is neither maximum compression nor under-compression. If overcompressed, the gas will be compressed more than enough to be introduced into the pipeline. If undercompressed, the gas will be returned to the compressor. In either of these cases, the horsepower required to operate the compressor increases;
This is undesirable as it becomes inefficient. The present invention attempts to determine and maintain the optimum compression ratio by sensing the magnitude of the current in the electric motor driving the compressor under full load conditions. According to the invention, the slide valve member is moved in increments while the motor current is monitored. If the motor current increases, the direction of movement of the slide valve is reversed and the slide valve continues to be moved in the direction of decreasing the motor current until a position is reached where the motor current begins to increase again. Thus, the present invention relates to determining the optimum compression ratio during full load operation of the compressor.

However, in some cases it may be necessary to operate the compressor at a load condition other than full load. Therefore, if the suction pressure falls below a predetermined set point, this indicates that full load operation should be transitioned to part load operation. Such a transition is effected by separating the two parts of the compound valve so that a portion of the gas can be recirculated to the suction side. At this time, the electric motor current is not used as a basis for positioning the slide valve.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring in particular to FIGS. 1 to 4 of the accompanying drawings, a helical screw compressor 10 has a central rotor casing 11, an input casing 12, and an output casing 13 connected in sealing relation to each other. ing. The rotor casing has intersecting bores 15 and 16 which interlock male and female helical rotors or screws 18 and 19, which are mounted for rotation about parallel axes by suitable bearings. It creates a working space for people to work together.

The rotor 18 includes a bearing (not shown) in the output part casing 13 and an input part casing 1.
The shaft 20 is rotatably mounted on a shaft 20 supported by a bearing 22 within the shaft 20. Shaft 2
0 extends outwardly from the output casing for connection to a motor (not shown) via a suitable coupling (not shown).

The compressor has an input passage 25 in the input casing 12, which communicates with the working space through the port 2. The discharge channel 28 in the output casing 13 is connected to ports 29 (at least one of which
part (in the output casing 13) communicates with the working space.

In the example considered here, in a horizontally oriented machine, the input ports 26 are primarily above the horizontal plane passing through the axis of the rotor, and the output ports 29 are primarily below this horizontal plane.

Centrally located below the bores 15 and 16 and having parallel axes is a longitudinally extending cylindrical recess 30 that communicates with both the input and output ports. ing.

Mounted for sliding movement within recess 30 is a composite valve member including a slide valve 32 and its cooperating member or slide stop 33. The inner surface 35 of the slide valve and the inner surface 36 of the slide stop face the outer periphery of the rotors 18 and 19 within the rotor casing 11.

The right end (as viewed in FIG. 1) of the slide valve has an opening 38 in its upper surface which forms a radial port communicating with the output port 29. The left end 39 of the slide valve is flattened or shaped as desired to fit the right end 40 of the slide stop and the recess 30 is formed into bores 15 and 16 by engagement of the two adjacent ends of the slide valve and the slide stop. It has become sealed since then.

The slide valve has an internal bore 42 and a head 43 at one end thereof. rod 4
4, one end of which is fixed to the head 43 by the fixing means 45.
A rod 44 extends through the head and is connected at its other end to a piston 46. The piston is mounted for reciprocating movement within a copper section 47 of a cylinder 48, which is connected to the input casing 12 and extends axially therefrom. A cover or end plate 50 is attached to the outer end of cylinder 48. Input part casing 12
is connected to the cylinder 48 by an input section cover 51 that receives the reduced diameter end 52 of the cylinder 48 .

Mounted inside the input section cover 51 is a sleeve 54 having a partition wall portion 55 at one end.
, which extends longitudinally towards the rotor casing. The slide stop 33 has a head 56 terminating in the end 40, which head has an inclined slot 57 on its underside, which slopes upwardly from left to right as viewed in the drawing. . The axial length of the slot is sufficient to provide the desired maximum movement of the slide stop.
The slide stopper extends from its head to the main portion 58.
, which is slidably received within sleeve 54. At the other end of the slide stop, a piston 60 is fixed by suitable fixing means 61.

A fixed partition 62 is fixed to the cylinder 48 centrally between its ends, which divides the interior of the cylinder into an outer compartment 64 in which the piston 46 moves and an inner compartment 66 in which the piston 60 moves. Cylinder 48 has fluid ports 67 and 68 in close proximity to each side of septum 62, which each have fluid ports 67 and 68 in compartment 64.
and 66. A fluid port 70 is provided at the outer end of the cylinder 48, which
It communicates with the compartment 64 on the opposite side of the piston 46. At the inner end of the cylinder 48 is a port 72 which communicates with a recess 73 provided in the outer end surface of the bulkhead portion 55 of the sleeve 54 .
Fluid is introduced into and removed from the compartment 66 on the opposite side of the piston 60.

The internal bore 74 of the slide stop matches the diameter of the bore 42 of the slide valve 32 and communicates therewith. At the outer end of the slide stop there is a head 75 on which the piston 60 is mounted.

A self-load release coil spring 76 is connected to the coaxial bore 7
4 and 42 about the rod 44, the spring forces the slide valve 32 into the closed position and the slide stop into an abutting relationship with the bulkhead 62. In such a position, the slide valve and slide stop are separated by a maximum distance.

In operation, a working fluid, such as refrigerant gas, is admitted to the group of compressor rotors 18 and 19 by input 25 and port 26. The rotation of the rotor forms a chevron-shaped compression chamber that receives gas and whose volume gradually decreases as it moves toward the inner surface of the output casing 13. A port 38 where the peak of the rotor island defining the tip of the compression chamber communicates with the discharge path 28
Fluid is released as it passes the edge of the When the slide valve 32 is located further away from the output casing 13, the compression ratio is reduced by enlarging the final compression chamber. On the other hand, if the slide valve is positioned toward the output casing when the slide valve and slide stopper are together,
The opposite effect is obtained. Therefore, movement of the slide valve changes the compression ratio and changes the pressure of the gas discharged from the compressor.

As previously mentioned, the main purpose of the present invention is to maintain an optimum compression ratio to avoid inefficient operation, and the present invention does not monitor the suction and discharge pressures, but rather The optimal compression ratio is maintained by monitoring the magnitude of the motor current. This is accomplished according to the invention by continuously nudging the compound slide valve while sensing the current magnitude during full load operation. As long as the current is decreasing, the slide valve is moved in the same direction. However, when the current starts to increase, the direction of movement of the slide valve is reversed, thus
The point where there is no increase or decrease in current is continually sought as an indication of the optimum position of the compound slide valve. Therefore, as discussed below, the slide valve and slide stop are controlled as a combined unit to vary the internal compression ratio of the compressor when motor current is sensed to find a position that minimizes the current. be done. When it becomes necessary to reduce the load, the slide valve and slide stop are separated from each other, as shown in FIG. The space between them therefore communicates with the intermeshed rotors 18 and 19 and allows the working fluid at the input pressure present in the compression chamber between the rotors to flow through the slot 78 and the casing 1.
The compressor can be maintained in communication with the input via one flow path (not shown), thereby reducing the amount of fluid being compressed and allowing the compressor to operate at less than full load.

Control System The compressor of the present invention is equipped with a control system that moves the slide valve and slide stopper according to a predetermined program to achieve the above object. To do this, four variables from the compressor are constantly sensed and sent to the electrical network. Thus, the output casing 13 is connected to the discharge pressure transducer 82 by the conduit 81.
It has a plug opening 80 connected to. Input casing 12 has a plug opening 84 connected by a conduit 85 to a suction pressure transducer 86 . The potentiometer 90 is
It has a movable element 91 which extends through the wall of the rotor casing 11 and which engages the inclined slot 57 of the slide stop 33 and serves as P1 to control the voltage divider network 92. Potentiometer 94 has a movable element 95 that extends through cylinder cover 50 and engages rod 44 of slide valve 32 and is connected to voltage divider network 95.
Acts as P2 that controls 6. Voltage divider network 9
2 includes calibration resistors R1 and R2, and line 1
Analog input module 9 via 00 and 101
8 to provide a 1-5 volt DC signal. Similarly,
Voltage divider network 96 includes calibration resistors R3 and R4.
provides a 1-5 volt DC signal to analog input module 98 via lines 102 and 103.

The discharge pressure transducer 82 and the suction pressure transducer 86 each transmit the received signal to one
-Convert to 5V D signal and connect line 104-10
7 to an analog input module 98.

The module 98 converts the signal it receives into a digital signal and sends it to the microcomputer 110.
supply to The microcomputer 110 has a program 112 with predetermined characteristics so that the output of the microcomputer achieves desired control of the slide valve 32 and slide stopper 33. A suitable readout unit, i.e. display device 114
is connected to the microcomputer 110, and the feedback potentiometers 90 and 9 are connected to the microcomputer 110.
The positions of the slide valve and slide stopper are indicated based on the signals received from 4.

Four control signals are sent from the microcomputer 110 via outputs 116, 117, 118 and 119. Therefore, the two signals sent from voltage divider networks 92 and 96 and the two signals sent from discharge pressure and suction pressure transducers 82 and 86 in response to slide stop and slide valve positions are analog The signals are passed through the input module to the microcomputer 110 where they are processed and provide the appropriate outputs 116-119. Outputs 116 and 117 are connected to solenoids 120 and 121 via lines 122 and 123, respectively. Outputs 118 and 119
are connected to solenoids 125 and 126 via lines 127 and 128, respectively.

Solenoids 120 and 121 are control valve 130
via which a hydraulic circuit for positioning the slide stop 33 is controlled. Solenoids 125 and 12
6 controls a hydraulic circuit that positions the slide valve 32 via a control valve 131.

Control valve 130 is connected by line 134 to a source of pressurized oil or other suitable pressurized liquid from the compressor's pressurized lubrication system. Conduit 135 connects valve 130 to fluid port 72 and conduit 136
connects valve 130 to fluid port 68. The oil drain line 137 is connected to the input area of the compressor.

Control valve 131 is connected to a source of pressurized oil by line 134 and drained by line 137. Conduit 138 connects valve 131 to fluid port 6
7 and conduit 139 connects valve 131 to fluid port 70 .

In operation, energizing the solenoid 120 of the valve 130 causes fluid to flow according to the diagram on the left side of the valve, i.e. from "P" to "B" and thus through the conduit 136 to the piston 60. Valve 130 is positioned so that while applying hydraulic pressure to the left side, oil is sent from the opposite side of the piston through conduit 135 and from "A" to "T" at valve 130, and drained into the oil drain pipe. be done. This forces the piston and its associated slide stop to the right in the drawing.

When the solenoid 121 of the valve 130 is energized, fluid will flow according to the diagram shown on the right side of the valve, i.e. from "P" to "A", through the conduit 135 to the right side of the piston 60. Apply hydraulic pressure and push it to the left, and at the same time send oil from the other side of the piston through conduit 136 and from "B" to "T" at the valve, and drain the oil to the oil drain pipe. , the valve 130 is positioned.

Similarly, energizing the solenoid 125 of valve 131 causes fluid to flow from "P" to "B" through fluid port 70 and to apply pressure to fluid port 67.
Drain the oil from "A" to "T" through
31 is located. Solenoid 1 of valve 131
When 26 is energized, fluid flows from "P" to "A", applying pressure through fluid port 67, and draining oil from "B" to "T" through fluid port 70, causing the slide valve to open. valve 1 to move it to the left.
31 is located.

When the compressor is used in a refrigeration system, it is usually desired to operate the slide valve to maintain a certain suction pressure, commonly referred to as a "set point." Optionally, other parameters such as the temperature of the product being processed in the refrigeration system associated with the compressor may be used as a factor influencing the position of the slide valve and thus the capacity of the compressor. good. In the system of the present invention, the desired set point is entered into microcomputer 110 by a suitable switch connected to a control panel (not shown) associated with display 114. The control panel may also include structures for controlling the mode of operation, such as automatic or manual, and the operation of the slide stop, slide valve, and compressor. A readout or display device 114 from the microcomputer 110 operates based on the signals it receives. The necessary electrical connections are made between the control panel and microcomputer 110 to perform the desired functions by means well known in the art.

To achieve the objectives of the invention, another variable, namely the compressor motor current, is also sensed and sent to the network. Accordingly, a motor current transducer 140 is connected to the motor (not shown). This transducer 140 is connected to the line 14
Analog input module 9 by 1 and 142
8 and this module is connected to a microcomputer 110 as described above. The microcomputer is programmed to unload the compressor if the motor current exceeds a predetermined value. This is achieved by appropriate separation of the slide valve and slide stop.

When the microcomputer detects a full load operating condition, the program causes the slide valve and slide stopper to move together as a unit an incremental distance in one direction determined by the program. If this movement causes the sensed current of the motor to drop during full load operation, the microcomputer programs another incremental movement in the same direction. This continues until the current reaches its lowest level and begins to increase. The program then reverses the direction of movement described above and finds the position where the current is at a minimum. If the current increases due to the initial movement of the compound valve, the program causes it to reverse direction and continue in this direction until the minimum current condition is met.

Feedback from both the slide stop and slide valve potentiometers determines whether a conflict or overlap condition exists between the desired mechanical position of the slide stop and the actual mechanical position of the slide valve. It is used to judge. If a conflict condition exists, the slide valve is temporarily repositioned to favor the position of the slide stop.

The system also includes arrangement to allow manual positioning of both the slide valve and the slide stop by operating appropriate controls indicated on the control panel.

Although hydraulic means for moving the slide stop and slide valve have been described above, it will be apparent that other means known to those skilled in the art may also be used.
If desired, for example, electric step motors or hydraulic means guided by step motors can also be used.

Modifications FIGS. 5 and 6 show modifications of the above embodiment. Rather than providing a spring 76 to move the slide valve and slide stop apart from each other as in FIGS. 1-4, a spring is provided around the shaft 44 only within the bore 74' of the slide stop. 76' is mounted with its left end extending through the slide stop into abutting relationship with bulkhead 62, and its right end abutting the right end of bore 74'. This spring therefore assists the movement of the slide stop to the right as viewed in FIG. 5 and opposes movement to the left. The large bore 42 in the slide valve shown in FIG. 1 has been omitted in FIG.

A further modification is the addition of outputs 5 and 6, indicated by reference numerals 148 and 143, which are connected to the microcomputer 110. Output 5 is connected by line 144 to a solenoid 145 which controls flow in bypass line 146 between lines 136 and 135. This conduit 146 is also provided with a one-way valve 147. Output 6 is connected by line 150 to a solenoid 151 which is connected to a bypass flow path 152 between lines 139 and 138.
One-way valve 1 is installed in this bypass flow path.
53 are provided.

To explain the operation of the variant shown in FIGS. 5 and 6, when the full load condition of the machine is detected,
The program causes the slide valve and slide stop to move together a predetermined incremental distance determined by the program. The slide valve and the slide stopper move together to the right in FIGS. 5 and 6 by energizing solenoid A 120, which applies hydraulic pressure to the piston 60, causing the piston to move to the right. be moved to Similarly, solenoids 151 in bypass lines 139-138 allow oil to bypass from the right side of piston 46 to the left side.

If the valve and stopper combination moves to the right while maintaining full load conditions, the program will cause the combination to move to the right another increment. This continues until the current reaches its lowest value and begins to rise. Then, the program causes the slide valve and the slide stopper to return to the current decreasing direction in search of a current value of zero.

The slide valve and slide stopper are moved together to the left when solenoid B 126 is energized, allowing hydraulic pressure to be applied to the right side of piston 46 and energizing bypass solenoid 145 . Therefore, the oil on the left side of the piston 60 can flow to the right side.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a screw-type compressor according to the present invention, with one part cut away for clarity of illustration, and FIG. 3 is the same as FIG. 1, but shows the slide valve and slide stopper in a different position from FIG. 1; FIG. 4 is a schematic diagram including the control circuit; FIG. 5 is a diagram showing a modified version of the compressor of the same type as FIG. 1, and FIG. 6 is a schematic diagram including a control circuit of the modified version of FIG. 10... Spiral screw type compressor, 11...
Rotor casing, 12...Input section casing, 1
3... Output part casing, 15, 16... Bore, 1
8, 19...Spiral rotor (screw), 20...Shaft, 25...Input channel, 26...Port, 28...
discharge channel, 29...port, 30...recess, 32...
Slide valve, 33... Slide stopper, 42... Bore, 43... Head, 44... Rod, 45... Fixing means, 46... Piston, 47... Body, 48... Cylinder, 50... Cover, 54... Sleeve, 55... Partition part, 57... Slot, 58... Main part, 60... Piston, 62... Fixed partition, 64... External compartment, 66
...Internal compartment, 67, 68...Port, 70, 72...
Port, 73... recess, 74... bore, 75... head, 76... coil spring, 78... slot, 80,
84...Plug opening, 82...Discharge pressure transducer, 86...Suction pressure transducer, 90,
94... Potentiometer, 92, 96... Voltage divider network, 98... Analog input module, 110
...Microcomputer, 112...Program,
114...Display device, 120, 121, 125, 1
26...Solenoid.

Claims (1)

Claims: 1. Intermeshing helical rotors are mounted on parallel axes in a housing with intersecting cylindrical bores, a high pressure end wall at one end and a high pressure end wall at the other end. has a low pressure end wall, the low pressure end wall has an input opening and the high pressure end wall has a discharge opening, and an axially extending recess is provided in the housing in open communication with the bore. and a sliding member is mounted for axial movement within the recess, the sliding member being in an interfacial sealing relationship with the rotor, and the sliding member adjacent the high pressure end wall. An electric motor-driven screw compressor having a discharge surface at one end and having a compression ratio varied by movement of the slide member, comprising: means for sensing the magnitude of current to the electric motor; means for sensing when the motor is operating at full load; means for incrementally moving the slide member in each direction; and means for sensing when the motor is operating at full load; moving a member in one direction, changing the direction of movement of the sliding member to the other direction when motor current increases, and continuing to move the sliding member in the other direction while motor current decreases; and means for returning the moving direction of the slide member to the one direction when motor current increases. 2. The slide member comprises a slide valve and a slide stop, the slide valve having a rear surface at the end remote from the discharge surface, and the slide stop having a rear surface of the slide valve so as to form a continuous composite member. the slide valve and the slide stopper are arranged to form an opening between them that is variable in size and axial position and communicates with the input opening; means for sensing the pressure at said input opening, and a means for sensing the pressure at said input opening and said means for sensing the pressure at said input opening, said slide valve and said slide being able to move apart from each other when said input pressure falls below a predetermined set point. 2. A compressor according to claim 1, further comprising means for moving the stoppers apart from each other. 3. The slide member comprises a slide valve and a slide stop, the slide valve having a rear surface at the end remote from the discharge surface, and the slide stop having a rear surface of the slide valve so as to form a continuous composite member. The slide valve and the slide stopper are configured to form an opening between them that is variable in size and axial position and communicates with the input opening. first means for sensing the pressure of the discharge opening, second means for sensing the pressure of the input opening, and the slide; third means for sensing the position of the stopper; fourth means for sensing the position of the slide valve; and responsive to and providing an electrical output proportional to the first, second, third and fourth means. and means for connecting said electrical output to a microcomputer;
2. The compressor of claim 1, wherein said microcomputer is programmed based on predetermined parameters and operates to control the movement of said slide valve and slide stop. 4. The compressor according to claim 2, further comprising means for constantly pushing the slide stopper toward the slide valve. 5. said slide stopper is connected to first piston means by first rod means, said slide valve is connected to second piston means by second rod means, said first and second piston means are movable along the same axis, partition means separating said piston means for moving said piston means within first and second separated chamber means, said first and second pistons Means are further provided for controlling movement of said piston means by introducing or removing fluid from said chamber means on each side of said means, said first rod means having an axial bore and said first rod means having an axial bore; A second rod means extends through the slide stop, the bore, the first piston means and the bulkhead means, and further includes compressible means within the bore and around the second rod means. 3. A compressor according to claim 2, wherein said means engages said slide stopper and said partition means to urge said slide stopper toward said slide valve. 6. said means for introducing or removing fluid from said chamber means on each side of said first and second piston means, said first means operative to drive said first piston means in one direction; second means operable to bypass fluid within the second piston means from one side of the second piston means to the other side; and third means operable to drive the second piston means in the other direction. and fourth means operable to bypass fluid in said first chamber means from one side of said first piston means to the other side. 7. The slide member includes a slide valve and a slide stop, the slide valve having a rear surface, and the slide stop engaging the rear surface of the slide valve to form a continuous composite member. the slide valve and the slide stop having mating front surfaces, the slide valve and the slide stop being spaced apart from each other to form an opening therebetween of variable size and axial position, the opening communicating with the inlet opening; and selectively reducing the load on the compressor, and further comprising first means for sensing pressure at the discharge opening, second means for sensing pressure at the input opening, and a first means for sensing pressure at the input opening; fourth means for sensing the position of said slide valve; and means operative to provide an electrical output proportional thereto in response to said first and second means; third and fourth means and electrical circuit means operative to provide an electrical output proportional thereto in response to the means for sensing the magnitude of the current to the electric motor, and transmitting the electrical output to a microcomputer. the microcomputer is programmed based on predetermined parameters to control the movement of the slide stopper member and the slide valve member; and a slide stop in each direction, the microcomputer being operable to move the slide valve and the slide stop incrementally in each direction while motor current is decreasing in response to full load operation. When the motor current increases, the slide valve and the slide stopper are moved as a composite member in the direction of 2. The compressor of claim 1, wherein the compressor is programmed to continue moving in the other direction, and to return the direction of movement of said slide valve and slide stop to said one direction upon increase in motor current.