GB2442830A - Screw Compressor with Axial thrust Balancing Device - Google Patents

Screw Compressor with Axial thrust Balancing Device Download PDF

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Publication number
GB2442830A
GB2442830A GB0717267A GB0717267A GB2442830A GB 2442830 A GB2442830 A GB 2442830A GB 0717267 A GB0717267 A GB 0717267A GB 0717267 A GB0717267 A GB 0717267A GB 2442830 A GB2442830 A GB 2442830A
Authority
GB
United Kingdom
Prior art keywords
pressure
screw compressor
balancing piston
compressor according
rotor
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB0717267A
Other versions
GB0717267D0 (en
Inventor
Dieter Mosemann
Dmytro Zaytsev
Ottomar Neuwirth
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
GEA Refrigeration Germany GmbH
Original Assignee
Grasso GmbH Refrigeration Technology
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Grasso GmbH Refrigeration Technology filed Critical Grasso GmbH Refrigeration Technology
Priority to GB0717267A priority Critical patent/GB2442830A/en
Publication of GB0717267D0 publication Critical patent/GB0717267D0/en
Publication of GB2442830A publication Critical patent/GB2442830A/en
Withdrawn legal-status Critical Current

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
    • F04C18/00—Rotary-piston pumps specially adapted for elastic fluids
    • F04C18/08—Rotary-piston pumps specially adapted for elastic fluids of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing
    • F04C18/12—Rotary-piston pumps specially adapted for elastic fluids of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing of other than internal-axis type
    • F04C18/14—Rotary-piston pumps specially adapted for elastic fluids of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing of other than internal-axis type with toothed rotary pistons
    • F04C18/16—Rotary-piston pumps specially adapted for elastic fluids of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing of other than internal-axis type with toothed rotary pistons with helical teeth, e.g. chevron-shaped, screw type
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01C—ROTARY-PISTON OR OSCILLATING-PISTON MACHINES OR ENGINES
    • F01C21/00—Component parts, details or accessories not provided for in groups F01C1/00 - F01C20/00
    • F01C21/02—Arrangements of bearings
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
    • F04C29/00—Component parts, details or accessories of pumps or pumping installations, not provided for in groups F04C18/00 - F04C28/00
    • F04C29/0021—Systems for the equilibration of forces acting on the pump

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Applications Or Details Of Rotary Compressors (AREA)

Abstract

A screw compressor comprising a male 2 and a female 3 rotor, one of which comprises an axial thrust balancing piston 11. A control means is provided to vary the pressure of a fluid acting on the balancing piston in response to varying operational parameters, such that the balancing piston exerts a force on the rotor substantially balancing the axial gas force acting on the rotor. Both rotors are enclosed in housing sections and the control means may comprise a processor 14 controlling a fluid pressure regulating valve 17 based on an algorithm relating rotor drive torque, and thus power, and suction side pressure with the balancing piston fluid pressure so that pressure increases with increasing torque and suction pressure. There may be fluid pressure measuring devices and a controllable pump may supply the balancing fluid e.g. an oil.

Description

1 2442830 Screw Compressor with Axial-Thrust Balancing Device The
invention relates to screw compressors, and particularly, but not exclusively, relates to an arrangement of an oil-flooded screw compressor for balancing axial thrust, which allows the gas force on a rotor of the compressor to be counteracted in the axial direction. In a conventional screw compressor a working space designated also as working chamber is formed by the interlobe spaces of male and female rotors, adjacent housing sections and other adjacent components such as a control slide. Depending on the position of the control slide circumferential wall portions of the cylindrical sections enclosing the rotors are opened.
Working fluid already sucked in is shunted back via a channel system in the housing to the suction side through the opened circumferential wall portions out of the interlobe spaces as these spaces are reduced in size due to rotation of the rotors. This has an influence on the compressor displacement and on the axial force on the bearings.
Depending on the suction pressure, discharge pressure, size of the discharge port and the position of the control slide, the resultant force from the difference of the gas force acting on the rotor and from the unloading force acting on the balancing piston will change. The resultant force will act in one or the other direction depending on the operational condition of the compressor.
As a result, the axial bearings will be loaded more or less in one or the other direction. In this case, due to the elastic deformation of the bearing, there will be a change of the axial bearing gap and of the distance between the male rotor and the end faces of the housing walls on both the suction-and discharge sides of the rotor profile. During part-load operation, the unloading force can also considerably exceed the gas force on the male rotor. For this reason, the unloading action of the balancing piston during part-load operation of the compressor Is cut off in a previously-proposed technical solution.A disadvantage is that in this case the entire gas force in a part-load region will act on the axial bearings, thus shortening impermissibly the service life of the axial bearings.
The object of the invention is to prevent the disadvantages mentioned and to create an arrangement on a screw compressor enabling the bearing loads to be held at a constant low level.
According to a first aspect of the invention there is provided a screw compressor comprising two rotors, a male rotor and a female rotor, wherein the male rotor or female rotor comprise a balancing piston, the balancing piston being fixed to the male rotor or female rotor, wherein a control means is provided, the control means being arranged to vary the pressure of a fluid acting on the balancing piston In response to varying operational parameters, such that the balancing piston exerts a force on the male rotor or female rotor substantially balancing the axial fluid force acting on the male rotor or female rotor.
The control means may comprise a pressure-regulating valve arranged to regulate the pressure of the fluid acting on the balancing piston, the control means may also comprise a processing means and there may be a control interconnection between the processing means and the pressure-regulating valve.
The processing means may carry out an algorithm containing a relationship between the torque driving the male rotor, the pressure on a suction side of the compressor and the pressure of the fluid acting on the balancing piston required to balance the axial fluid force acting on the male rotor or female rotor.
The relationship of the control algorithm may be such that the pressure of the fluid acting on the balancing piston will increase when the torque driving the male rotor increases. The relationship of the control algorithm may be such that the pressure or the fluid acting on the balancing piston will increase when the pressure on the compressor suction side increases.
The relationship of the control algorithm may be such that the pressure of the fluid acting on the balancing piston will decrease when the torque driving the male rotor decreases. The relationship of the control algorithm may be such that the pressure of the fluid acting on the balancing piston will decrease when the pressure on the compressor suction side decreases.
At least one output of the processing means may have a control interconnection to the pressure-regulating valve. The output signal of the processing means may modulate the pressure acting on the balancing piston.
A pressure-measuring point may be located in a supply line between the pressure-regulating valve and a connection for admission or pressunsed fluid to the balancing piston.
an output signal of the pressure-measuring point may be connected to a three-position controller forming part of the processing means.
The output signal of the processing means may be a set value and the output signal of the pressure-measuring point may be an actual value, where both values may be inputs to the three-position controller, and an output of the three-position controller may have a control interconnection to the pressure-regulating valve.
The output signal of the processing means may comprise the output of the three-position controller. A controllable pump may be arranged in the supply line for admission of pressure to the balancing piston, wherein the speed of the pump depends on the result of comparison of the three-position controller.
The male rotor may have essentially convex lobe flanks. The female rotor may have essentially concave flank portions. The male rotor and female rotor may be enclosed in housing sections.
The balancing piston may be positioned at a discharge end of the compressor. The balancing piston may be positioned at a suction end of the compressor. The fluid acting on the balancing piston may be an oil. The balancing piston may be an oil-pressure loaded balancing piston and may be supplied with oil via a pressure line.
There may be provided a regulating device arranged either on or in the compressor, the inputs of which may be at least connected to measuring means for the pressure on a suction side of the compressor and measuring means for determination of the input power to the compressor.
There may be provided means for changing the pressure in a pressure line to the balancing piston, said means having a control interconnection to a regulating device, with the latter having an algorithm between operating parameters representing input variables for the regulating device and the pressure in the pressure line to the balancing piston.
The control means may comprise a regulating device. The pressure-regulating valve may be a proportional pressure-regulating valve.
According to a second aspect of the invention there is provided an arrangement on an oil-flooded screw compressor with two rotors, a male rotor having essentially convex lobe flanks and a female rotor having essentially concave flank portions, with the male rotor having a drive-shaft end and an oil-pressure loaded balancing piston supplied with oil via a pressure line, both rotors are enclosed in housing sections, with a regulating device arranged either on or in the compressor the inputs of which are at least connected to measuring means for the pressure on the suction side and measuring means for determination of the input power, wherein means for changing the pressure in the pressure line to the balancing piston are arranged with said means having a control interconnection to the regulating device, with the latter having an algorithm between operating parameters representing input variables for the regulating device and the pressure in the pressure line to the balancing piston.
According to the object of the invention, the oil pressure on the balancing piston, and hence the unloading force of the balancing piston, is controlled depending on operating parameters. The output signal of a regulating device preferably controls the pressure on the balancing piston depending on the driving torque at the compressor drive shaft and depending on the pressure on the compressor suction side. For this purpose, the output signal of the regulating device in a first arrangement according to the invention acts on a pressure-regulating valve located in an oil-supply line from a pressure source to the balancing piston. The control algorithm is designed so that the pressure on the balancing piston will increase when the driving torque rises or when the pressure on the suction side rises or when in combination of rising driving torque and rising pressure on the suction.
Preferably, there exists a control algorithm considering these parameters and calculating the required pressure on the balancing piston.
In a technically preferable embodiment according to the invention the means for realization of this control task represent a regulating device into which the speed of rotation to be expected, e.g. 49 Hz (us), the electric voltage of a three-phase asynchronous motor, e.g. 380 V, the cos p, e.g. 0,93, and the electrical efficiency of the electric motor, e.g. 0,95, have been entered manually, or are metrologically registered during operation, analogue inputs for registration of the motor current, for registration of the pressure on the compressor suction side, as well as an output with an analogue signal representing the desired pressure on the balancing piston. Voltage, cos p, efficiency and motor current serve in the algorithm of the regulating device first to determine the power at the compressor drive shaft, and in connection with the speed of rotation the torque will be calculated. In addition, the control algorithm considers the pressure on the compressor suction side during calculation of the output signal.
The output in a preferable arrangement according to the invention has a control interconnection to a pressure-regulating valve, e.g. a proportional pressure-regulating valve, with the flow rate being modulated by changing the output signal of the regulating device.
Depending on the flow rate, the pressure on the balancing piston will change. The regulating device incorporates the control algorithm for calculation of the required pressure on the balancing piston and the presentation of this value in the range of a standard signal, e.g. from 4 to 20 mA, or directly as control current for a proportional pressure-regulating valve.
In another embodiment according to the invention, a pressure-measuring point is located in the supply line between the pressure-regulating valve and the connection for admission of pressure to the balancing piston. The output signal of the regulating device and the output signal of the pressure-measuring point are led to a three-position controller and compared.
Depending on the result of the comparison, the proportional pressure-regulating valve will be opened more, when the pressure at the pressure-measuring point lies below the calculated value of the regulating device, or will be closed more, when the pressure at the pressure-measuring point exceeds the calculated value of the regulating device.
In another embodiment according to the invention, a speed controlled oil pump is located in the supply line for admission of pressure to the balancing piston. Depending on the result of comparison of the three-position controller, the speed of the oil pump will be increased.
when the pressure at the pressure-measuring point lies below the calculated value of the regulating device, or will be decreased further, when the pressure at the pressure-measuring point exceeds the calculated value of the regulating device.
For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the following drawings, in which: Figure 1 is an arrangement according to the invention with a pressure-regulating valve controllable by an input signal Figure 2 is another arrangement according to the invention with a pressure-regulating valve controllable by a three-position controller.
The screw compressor according Figure 1 is driven at the drive-shaft end 5 forming a fixed part of the male rotor 2 via a coupling not shown. The interlobe spaces of the male rotor 2 and of the female rotor 3 form working chambers to which on the suction side adjoin inlet ports 6. Due to rotation of the rotors at the drive-shaft end 5, the volume of an interlobe space changes. Radial bearings I are arranged on the suction side of the shaft shoulders, while radial bearings 9 and axial bearings 10 are arranged on the discharge side of the shaft shoulders. For compensation of the axial thrust on the male rotor 2 exerted by the gas force due to compression of the working fluid, a rotating disk, the balancing piston 11. is arranged sealing hydraulically and contactiessly at its external diameter. On one side, it is loaded with pressurized oil directly coming from the oil separator arranged on the discharge side, or the oil is brought up to a higher pressure by an oil pump. The pressurized oil is drained to areas of lower pressure after passing the sealing gap of the balancing piston. On the other side of the balancing piston, there is nearly suction pressure. Thus, the force of the balancing piston 11 counteracts the gas force on the male rotor 2 in axial direction. As a result, the axial bearings 10 are unloaded. The gas force acting in axial direction of the rotors is comparatively high at the male rotor compared to the female rotor. For this reason, the male rotor features the balancing piston. The force on the axial bearing of the male rotor is a resultant from the difference of the gas force acting on the rotor and from the unloading force acting on the balancing piston.
According to the embodiment of the invention shown, the regulating device 12 is arranged as part of a controlled system. A control algorithm calculates the pressure on the balancing piston 11 depending on the pressure on the compressor suction side and on the torque at the drive-shaft end 5 (essentially from motor current in connection with both motor voltage and speed). Pressure and motor current are passed over to the control at the interfaces 13.
14. The regulating device 12 delivers the output signal 16 for the proportional pressure- regulating valve 17. According to the control characteristics of the proportional pressure-regulating valve 17, there is a proportional relationship between the input signal and the pressure at the outlet of the proportional pressure-regulating valve 17. It increases the pressure on the balancing piston 11 in case the regulating device 12 has calculated this from the algorithm and given a corresponding output signal. It decreases the pressure on the balancing piston 11 when the regulating device 12 calculates a lower pressure for the balancing piston.
In the arrangement shown in Figure 2, a pressure-measuring point 18 is located in the supply line between the proportional pressure-regulating valve 17 and the connection for admission of pressure to the balancing piston. The output signal of the regulating device 12 and the output signal 19 of the pressure-measuring point 18 are led to a three-position controller preferably arranged in the regulating device 12 and compared. Depending on the result of the comparison, the proportional pressure-regulating valve 17 will be opened more, when the pressure at the pressure-measuring point 18 lies below the calculated value of the regulating device 12, or will be closed more, when the pressure at the pressure-measuring point 18 exceeds the calculated value of the regulating device 12.

Claims (25)

  1. Claims: 1. A screw compressor comprising two rotors, a male rotor and a
    female rotor, wherein the male rotor or female rotor comprise a balancing piston, the balancing piston being fixed to the male rotor or female rotor, wherein a control means is provided, the control means being arranged to vary the pressure of a fluid acting on the balancing piston in response to varying operational parameters, such that the balancing piston exerts a force on the male rotor or female rotor substantially balancing the axial gas force acting on the male rotor or female rotor.
  2. 2. A screw compressor according to claim I wherein the control means comprises a pressure-regulating valve arranged to regulate the pressure of the fluid acting on the balancing piston, the control means also comprising a processing means with a control interconnection between the processing means and the pressure-regulating valve.
  3. 3. A screw compressor according to claim 2, wherein the processing means cames out an algorithm containing a relationship between the torque driving the male rotor, the pressure on a suction side of the compressor and the pressure of the fluid acting on the balancing piston required to balance the axial gas force acting on the male rotor or female rotor.
  4. 4. A screw compressor according to claim 3, wherein the relationship of the control algorithm is such that the pressure of the fluid acting on the balancing piston will increase when the torque driving the male rotor increases.
  5. 5. A screw compressor according to claim 3 or 4, wherein the relationship of the control algorithm is such that the pressure of the fluid acting on the balancing piston will increase when the pressure on the compressor suction side increases.
  6. 6. A screw compressor according to any one of claims 3 to 5, wherein the relationship of the control algorithm is such that the pressure of the fluid acting on the balancing piston will decrease when the torque driving the male rotor decreases.
  7. 7. A screw compressor according to any one of claims 3 to 6, wherein the relationship of the control algorithm is such that the pressure of the fluid acting on the balancing piston will decrease when the pressure on the compressor suction side decreases.
  8. 8. A screw compressor according to any one of claims 2 to 7, wherein at least one output of the processing means has a control interconnection to the pressure-regulating valve.
  9. 9. A screw compressor according to claim 8, wherein the output signal of the processing means modulates the pressure acting on the balancing piston.
  10. 10. A screw compressor according to any one of claims 2 to 9, wherein a pressure-measuring point is located in a supply line between the pressure-regulating valve and a connection for admission of pressurised fluid to the balancing piston, an output signal of the pressure-measuring point being connected to a three-position controller forming part of the processing means.
  11. 11. A screw compressor according to claim 10, wherein the output signal of the processing means is a set value and the output signal of the pressure-measuring point is an actual value, with both values being inputs to the three-position controller, and an output of the three-position controller has a control interconnection to the pressure-regulating valve.
  12. 12. A screw compressor according to claim 11, wherein the output signal of the processing means comprises the output of the three-position controller.
  13. 13. A screw compressor according to any one of claims 10 to 12, wherein a controllable pump is arranged in the supply line for admission of pressure to the balancing piston.
    wherein the speed of the pump depends on the result of comparison of the three-position controller.
  14. 14. A screw compressor according to any previous claim, wherein the male rotor has essentially convex lobe flanks.
  15. 15. A screw compressor according to any previous claim, wherein the female rotor has essentially concave flank portions.
  16. 16. A screw compressor according to any previous claim, wherein the fluid acting on the balancing piston is an oil.
  17. IT. A screw compressor according to any previous claim, wherein the balancing piston is an oil-pressure loaded balancing piston and is supplied with oil via a pressure line.
  18. 18. A screw compressor according to any previous claim, wherein the male rotor and female rotor are enclosed in housing sections.
  19. 19. A screw compressor according to claim 1, wherein there is provided a regulating device arranged either on or in the compressor, the inputs of which are at least connected to measuring means for the pressure on a suction side of the compressor and measuring means for determination of the input power to the compressor.
  20. 20. A screw compressor according to claim 1, wherein there Is provided means for changing the pressure in a pressure line to the balancing piston, said means having a control interconnection to a regulating device, with the tatter having an algorithm between operating parameters representing input variables for the regulating device and the pressure In the pressure line to the balancing piston.
  21. 21. A screw compressor according to claim 1, wherein the balancing piston is positioned at a discharge end of the compressor.
  22. 22. A screw compressor according to claim 1, wherein the balancing piston is positioned at a suction end of the compressor.
  23. 23. A screw compressor according to claim 1, wherein the control means comprises a regulating device.
  24. 24. A screw compressor according to any one of claims 2 to 23, wherein the pressure-regulating valve is a proportional pressure-regulating valve.
  25. 25. A screw compressor substantially as described herein, with reference to and as shown in the accompanying drawings.
GB0717267A 2007-09-05 2007-09-05 Screw Compressor with Axial thrust Balancing Device Withdrawn GB2442830A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB0717267A GB2442830A (en) 2007-09-05 2007-09-05 Screw Compressor with Axial thrust Balancing Device

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB0717267A GB2442830A (en) 2007-09-05 2007-09-05 Screw Compressor with Axial thrust Balancing Device

Publications (2)

Publication Number Publication Date
GB0717267D0 GB0717267D0 (en) 2007-10-17
GB2442830A true GB2442830A (en) 2008-04-16

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ID=38640280

Family Applications (1)

Application Number Title Priority Date Filing Date
GB0717267A Withdrawn GB2442830A (en) 2007-09-05 2007-09-05 Screw Compressor with Axial thrust Balancing Device

Country Status (1)

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Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6223590A (en) * 1985-07-24 1987-01-31 Kobe Steel Ltd Reverse thrust preventing apparatus for screw expansion machine
US4964790A (en) * 1989-10-10 1990-10-23 Sundstrand Corporation Automatic regulation of balancing pressure in a screw compressor
SE502631C2 (en) * 1994-04-19 1995-11-27 Svenska Rotor Maskiner Ab Screw rotor compressor with axial balancing component
US5707223A (en) * 1994-02-28 1998-01-13 Svenska Rotor Maskiner Ab Rotary screw compressor having a thrust balancing piston device and a method of operation thereof
GB2318617A (en) * 1996-10-25 1998-04-29 Kobe Steel Ltd Oil injected screw compressor
US6050797A (en) * 1998-05-18 2000-04-18 Carrier Corporation Screw compressor with balanced thrust
JP2004339994A (en) * 2003-05-14 2004-12-02 Mayekawa Mfg Co Ltd Screw compressor with balance piston device

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6223590A (en) * 1985-07-24 1987-01-31 Kobe Steel Ltd Reverse thrust preventing apparatus for screw expansion machine
US4964790A (en) * 1989-10-10 1990-10-23 Sundstrand Corporation Automatic regulation of balancing pressure in a screw compressor
US5707223A (en) * 1994-02-28 1998-01-13 Svenska Rotor Maskiner Ab Rotary screw compressor having a thrust balancing piston device and a method of operation thereof
SE502631C2 (en) * 1994-04-19 1995-11-27 Svenska Rotor Maskiner Ab Screw rotor compressor with axial balancing component
GB2318617A (en) * 1996-10-25 1998-04-29 Kobe Steel Ltd Oil injected screw compressor
US6050797A (en) * 1998-05-18 2000-04-18 Carrier Corporation Screw compressor with balanced thrust
JP2004339994A (en) * 2003-05-14 2004-12-02 Mayekawa Mfg Co Ltd Screw compressor with balance piston device

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