Control means for a variable capacity rotary screw compressor

• US 3,924,972 A
• Filed: 10/29/1974
• Issued: 12/09/1975
• Est. Priority Date: 10/29/1974
• Status: Expired due to Term

• Current Assignee: Paul G. Szymaszek
• Original Assignee: Paul G. Szymaszek
• Inventors: Szymaszek, Paul G.
• Primary Examiner(s): Cohan, Alan
• Application Number:
  US05/518,267
• Time in Patent Office: 406 Days
• Field of Search: 417/310 251/131,130,30 137/487.5 91/363R
• US Class Current: 417/310
• CPC Class Codes: F04B 49/002 Hydraulic systems to change the pump delivery
• CPC Class Codes: F04B 49/06 Control using electricity regulating by means of floats actuating electric switches F04B49/04
• CPC Class Codes: F04C 28/125 with sliding valves controlled by the use of fluid other than the working fluid

Abstract

A variable capacity rotary screw compressor has a pair of helical rotors mounted within a housing for compressing fluid and an axially movable slide valve in the housing to control the capacity of the compressor. Control means are provided for moving the slide valve to regulate or adjust compressor capacity and comprise an hydraulic actuator including a movable piston connected to the slide valve and a pair of solenoid valves for controlling hydraulic fluid flow between a pump and the actuator to effect piston and slide valve movement. The control means also comprises a bridge balancing relay which receives input control signals from either an automatic control unit or a manually operable control unit and compares the control signals with feedback signals indicative of valve spool position and provides output signals for operating the solenoid valves accordingly. The automatic control unit provides a control signal indicative, for example, of a system condition to operate the compressor at a capacity necessary to maintain the system condition constant. The manual control unit provides a control signal to move the slide valve to a desired fixed position and to maintain the slide valve in that position. The feedback signal is indicative of slide valve position and is compared in the bridge balancing relay with the control signal from either the automatic or manual control units, whichever is operating, to effect proper positioning of the slide valve.

Claims

1. In combination:

a variable capacity compressor having an adjustable control valve for regulating the capacity of said compressor;

an actuator for adjusting said control valve;

electro-responsive means for operating said actuator;

control means for providing a control signal to establish an initial control valve adjustment, said control means including an automatic control unit and a manual control unit which are alternatively and selectively operable, said automatic control unit being responsive to a variable condition to provide a control signal to regulate compressor capacity, said manual control unit being selectively operable to provide a control signal to maintain said control valve in a fixed position;

feedback means operable in response to control valve adjustment to provide a feedback signal related thereto; and

balancing means for receiving and comparing said control signal and said feedback signal and for providing an output signal related thereto to control said electro-responsive means.

2. A combination according to claim 1 including means responsive to control valve adjustment to provide a visual indication of the capacity at which said compressor is operating.

3. In combination:

a variable capacity compressor having an adjustable control valve for regulating the capacity of said compressor;

a fluid actuator for adjusting said control valve;

solenoid valve means operable to control fluid flow for said actuator to thereby operate said actuator;

control means for providing an electric control signal to establish an initial control valve adjustment, said control means including an automatic control unit and a manual control unit which are alternatively and selectively operable, said automatic control unit being responsive to a variable condition to provide a control signal to regulate compressor capacity, said manual control unit being selectively operable to provide a control signal to maintain said control valve in a fixed position;

feedback means operable in response to control valve adjustment to provide an electric feedback signal related thereto; and

balancing means for comparing said electric control signal and said electric feedback signal and for providing an electric output signal related thereto to control said solenoid valve means.

4. A combination according to claim 3 including means responsive to the adjustment of said adjustable valve to provide a visual indication of the capacity at which said compressor is operating.

5. In combination:

a variable capacity compressor having a movable slide valve for regulating the capacity of said compressor;

a fluid actuator operable to move said slide valve;

solenoid valve means including a pair of solenoid valves operable to control fluid flow to and from said actuator to operate said actuator;

control means for providing an electric control signal to establish slide valve position, said control means including an automatic control unit and a manual control unit which are alternatively and selectively operable, said automatic control unit being responsive to a variable condition to provide a control signal to regulate compressor capacity, said manual control unit being selectively operable to provide a control signal to maintain said slide valve in a fixed position;

feedback means responsive to slide valve position for providing an electric feedback signal related to slide valve position; and

balancing means for comparing said electric control signal and said electric feedback signal and for providing an electric output signal related thereto to operate said solenoid valve means to effect positioning of said slide valve.

6. A combination according to claim 5 including means responsive to the position of said slide valve to provide a visual indication of the capacity at which said compressor is operating.

7. In combination:

a variable capacity compressor having a movable slide valve for regulating the capacity of said compressor;

a fluid actuator operable to move said slide valve;

solenoid valve means including a pair of solenoid valves operable to control fluid flow to and from said actuator to operate said actuator;

control means for providing an electric control signal to effect slide valve positioning, said control means comprising an automatic control unit and a manual control unit which are alternatively and selectively operable, said automatic control unit being responsive to a variable condition to provide a control signal to regulate compressor capacity, said manual control unit being selectively operable to provide a control signal to maintain said slide valve in a fixed position;

feedback means responsive to slide valve position for providing an electric feeDback signal related to slide valve position; and

balancing means for comparing said electric control signal and said electric feedback signal and for providing an electric output signal related thereto to operate said solenoid valve means to position said slide valve.

8. A combination according to claim 7 wherein said automatic control unit includes sensing means for sensing said condition and a first potentiometer adjustable in response to said sensing means for providing an electric control signal related to said condition;

wherein said manual control unit includes a second potentiometer selectively adjustable to provide a control signal to position said movable slide valve in a fised position; and

wherein said feedback means includes a third potentiometer adjustable in response to slide valve position.

9. A combination according to claim 8 wherein said sensing means is temperature responsive.

10. A combination according to claim 8 wherein said sensing means is pressure responsive.

11. A combination according to claim 8 including indicator means responsive to the position of said slide valve to provide a visual indication of the capacity at which said compressor is operating.

12. A combination according to claim 11 wherein said indicator means includes a fourth potentiometer adjustable in response to slide valve position and a meter connected to receive a signal from said fourth potentiometer and calibrated to show compressor capacity.

13. A variable capacity rotary compressor having a control valve adjustable to control the capacity of the compressor;

and control means operable in either an automatic mode or a manual mode to adjust said control valve, said control means including feedback means operable in both said modes, said control means being operable in the manual mode to adjust said control valve to maintain said slide valve in a fixed position, said control means being operable in the automatic mode to adjust said control valve to regulate compressor capacity, said control means including condition sensing means operable in the automatic mode to sense a system condition and being responsive to a departure of the system condition from said predetermined level to effect adjustment of said control valve to vary the compressor capacity to maintain said system condition at said predetermined level.

14. Control means according to claim 13 wherein said system condition is pressure and wherein said condition sensing means includes pressure responsive control means.

15. Control means according to claim 13 wherein said system condition is temperature and said condition sensing means includes temperature responsive control means.