Gas Compressor

Abstract

To provide a gas compressor capable of suppressing a hunting phenomenon of a suction throttle valve without any harmful effects.SOLUTION: In a gas compressor (100), when a control unit (14) determines that after shifting from a no-load operation to a load operation, a rotational speed of an electric motor (1) is less than or equal to a speed threshold and a state in which a time change rate of the rotational speed of the electric motor (1) is less than or equal to a change rate change threshold continues for a certain period of time, the control unit determines that a hunting phenomenon occurs in which a valve plate (29) of a suction throttle valve (3) repeatedly opens and closes, and increases the rotation speed of the electric motor (1) at a constant time change rate.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a gas compressor. [Background technology]

[0002] There is known a gas compressor in which the driving speed of a driving source (e.g., an electric motor) is variably controlled using a rotation speed control device (e.g., a power conversion device or an inverter). In this gas compressor, control is performed to perform unloaded operation.

[0003] No-load operation is an operation in which, when the amount of compressed air used decreases and exceeds a specified pressure desired by the user of the compressor body, the rotational speed of the drive source that drives the compressor body is reduced to reduce the load.

[0004] For example, Patent Document 1 discloses a compressor that performs variable speed control using PID control according to the discharge pressure value of the compressor body using an electric motor controlled by a power conversion device and the temperature of the discharge compressed air corresponding to that pressure value.

[0005] In the technology described in Patent Document 1, when the amount of compressed air used decreases and the discharge pressure exceeds a preset pressure, the suction throttle valve is closed to reduce the amount of intake air. At the same time, compressed air is released from the compressor body to the atmosphere through a piping route downstream. This reduces the power load on the compressor body.

[0006] In this manner, by lowering the rotation speed of the drive source to a predetermined lower limit rotation speed, a no-load operation is performed to reduce power consumption.

[0007] On the other hand, there are two types of suction throttle valves installed in the suction portion of a gas compressor: a normally closed type and a normally open type.

[0008] Here, the normally closed type suction throttle valve has the characteristic that it can form a wide suction flow passage and can set the pressure loss low, which makes it possible to reduce power consumption.

[0009] A normally closed type suction throttle valve is equipped with a body that defines a suction passage, a control spring, a shaft, a valve plate, and a check spring. During load operation, the suction throttle valve pressurizes the piston chamber and contracts the control spring. This causes the shaft to operate in the opening direction, and the dynamic pressure of the suction air becomes a load higher than the check spring that acts in the direction to close the valve plate, causing the valve plate to open.

[0010] In a normally closed type suction throttle valve, the pressure applied to the piston is reduced when the drive source stops rotating. This causes the control spring to return to its original position, the shaft to move in the closing direction, the valve plate to close, and the control spring to return to its original position.

[0011] On the other hand, a gas compressor has a characteristic that when the rotation speed of the drive source stops, the pressure on the discharge side flows back to the suction side. This causes the cooling liquid sucked in for air cooling during the pressure process to flow back at the same time, and there is a possibility that the cooling liquid will spray out of the compressor body via the suction throttle valve. To prevent this, a check spring is provided between the valve plate and the shaft. This is configured so that the valve plate closes before the control spring and the shaft return to their original positions.

[0012] In particular, the higher the discharge pressure is at low loads, the more likely it is that the coolant will flow out at a high speed when the compressor is stopped. In addition, in gas compressors that use oil as the coolant, whose kinetic viscosity changes with temperature, the frictional force at the sliding part between the valve plate and the shaft increases at low temperatures, slowing down the speed at which the valve plate closes, making it more likely that oil will gush out.

[0013] Therefore, when a normally closed type suction throttle valve is used, it is necessary to set the check spring load as follows when the rotation speed of the drive source is stopped: In other words, the check spring load is set so that the speed at which the valve plate closes is faster than the speed at which the cooling liquid in the compressor body sprays out from the suction throttle valve at ambient temperature and discharge pressure within the operating range.

[0014] By increasing the load of the check spring, the speed at which the valve plate closes increases, which is advantageous for the ejection of coolant from the suction throttle valve. However, when the rotation speed of the drive source is reduced under low load, the valve plate tends to repeatedly open and close, which is known as hunting.

[0015] First, the dynamic pressure of the intake air acts on the valve plate of the intake throttle valve, and when the dynamic pressure exceeds the load of the check spring, the valve plate moves in the opening direction. The larger the amount of intake air, the wider the opening of the valve plate.

[0016] In contrast, when the air pressure on the usage side is high and the load is low, if the rotation speed of the drive source is reduced and the amount of suction air is reduced, the dynamic pressure acting on the suction throttle valve decreases and the opening of the valve plate becomes narrower. As a result, the valve plate stops at a position where it is balanced with the load of the check spring.

[0017] When the operation is stopped and the intake air flow rate becomes zero, the valve plate closes under the load of the check spring alone.

[0018] During no-load operation, the rotation speed of the drive source is kept at the minimum and the pressure on the piston is released to the atmosphere, which causes the shaft to be forcibly moved in the closing direction by the control spring, closing the valve plate.

[0019] Next, when switching from no-load operation to loaded operation, pressure is applied to the piston again, causing the shaft and valve plate to move in the opening direction. At the same time, the valve plate, which previously had a pressure difference close to vacuum pressure between the primary and secondary sides of the valve plate, initially maintains a state of close contact with the shaft. At this time, the check spring is at its most contracted during use, creating a reaction force.

[0020] When the amount of air used is small, the drive source may transition from unloaded to loaded operation while maintaining its minimum rotational speed through PID control. At this time, if the dynamic pressure acting on the valve plate is smaller than the load of the check spring, the valve plate may not be able to maintain close contact with the shaft, and the shaft may move in the closing direction.

[0021] When the drive source is rotating, the narrower the opening of the valve plate, the higher the pressure of the intake air on the valve plate, and the load acting in the direction to open the valve plate balances with the check spring, and the valve plate comes to rest at the balanced position. At the position where the check spring and pressure acting on the valve plate are balanced, the valve plate balances at a position where the opening of the valve plate becomes narrower as the amount of intake air decreases.

[0022] However, when the valve plate moves in the opening or closing direction, an inertial force is generated in the valve plate. Therefore, the faster the valve plate closes, the greater the inertial force becomes, and the valve plate overshoots instead of maintaining the balanced position. At this time, if the rotational speed of the drive source is maintained at the minimum rotational speed, the dynamic pressure acting on the valve plate is lower than when fully loaded. And when the balanced position of the valve plate is slightly open as described above, the valve plate overshoots as it closes, and may reach a position where the valve plate is completely closed.

[0023] When the valve plate is in the fully closed position, a negative pressure close to a vacuum pressure is generated on the suction side of the valve plate, which exerts a load on the valve plate that is significantly higher than the load acting in the closing direction of the check spring, causing the valve plate to open again.

[0024] Thereafter, the valve plate again overshoots the balanced position and opens to a position where it comes into close contact with the shaft, and the repulsive force of the check spring again reaches a maximum, causing the valve plate to move in the direction of completely closing.

[0025] In this way, when the inertial force of the valve plate is also added and the condition arises such that the valve plate moves to both ends of its operating range, the opening and closing operation of the valve plate does not converge, and the so-called hunting phenomenon occurs. [Prior art documents] [Patent documents]

[0026] [Patent Document 1] JP 2005-69100 A Summary of the Invention [Problem to be solved by the invention]

[0027] As a method for preventing the hunting phenomenon, the first measure is to increase the rotation speed of the drive source during no-load operation above the minimum rotation speed of the drive source during loaded operation, thereby increasing the dynamic pressure acting on the valve plate in advance, thereby suppressing the hunting phenomenon so that the valve plate does not close completely even when switching from no-load operation to loaded operation.

[0028] However, the first measure increases the power by increasing the rotation speed of the drive source during no-load operation, which is undesirable from the viewpoint of energy conservation and has a negative effect as a measure against the hunting phenomenon of the suction throttle valve.

[0029] As another method for preventing the hunting phenomenon, in which the valve plate is not completely closed, a second measure is to weaken the load of the check spring.

[0030] However, in the second measure, the load of the check spring is weak, and as described above, the oil return phenomenon specific to gas compressors causes the coolant to flow out of the suction throttle valve before the valve plate closes. This causes the liquid to adhere to the filter installed in the intake part of the suction throttle valve, which may impair the function of the filter, and is a detrimental measure to the hunting phenomenon of the suction throttle valve.

[0031] As described above, when taking measures against the hunting phenomenon of the suction throttle valve, there is a problem that some kind of adverse effect may occur.

[0032] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a gas compressor capable of suppressing the hunting phenomenon of the suction throttle valve without causing any adverse effects. [Means for solving the problem]

[0033] According to one aspect of the present invention, a gas compressor includes a compressor main body that compresses gas, a driving source that drives the compressor main body, a control unit that controls the rotational speed of the driving source in accordance with the discharge pressure of the compressor main body, and a suction throttle valve that closes the suction flow path by the elastic force of a check spring acting on a valve body when the rotation of the driving source stops, wherein the control unit performs unloaded operation in which the rotational speed of the driving source is controlled to a lower limit rotational speed when the discharge pressure reaches an upper limit pressure higher than a set pressure, and when the control unit determines that, after transitioning from unloaded operation to loaded operation, the rotational speed of the driving source is equal to or lower than a speed threshold and that a state in which the time rate of change of the rotational speed of the driving source is equal to or lower than a change rate threshold has continued for a certain period of time, it determines that a hunting phenomenon is occurring in which the valve body of the suction throttle valve repeats opening and closing movements, and increases the rotational speed of the driving source at a certain time rate of change. Effect of the Invention

[0034] According to the present invention, it is possible to provide a gas compressor in which the hunting phenomenon of the suction throttle valve can be suppressed without causing any adverse effects. [Brief description of the drawings]

[0035] [Figure 1] FIG. 1 is a block diagram illustrating a schematic configuration of a gas compressor according to a first embodiment. [Diagram 2] FIG. 2 is a vertical cross-sectional view showing a state in which the valve plate of the suction throttle valve is closed when the engine is stopped or in no-load operation according to the first embodiment. [Diagram 3] FIG. 3 is a vertical cross-sectional view showing a valve plate of the suction throttle valve according to the first embodiment in an open state. [Figure 4] FIG. 4 is a vertical cross-sectional view showing a state in which the valve plate of the suction throttle valve according to the first embodiment is slightly open. [Diagram 5] FIG. 5 is a vertical cross-sectional view showing a state in which the valve plate of the suction throttle valve is closed during load operation according to the first embodiment. [Figure 6]FIG. 6 is a chart showing a case where hunting phenomenon suppression control is performed when switching from no-load operation to full-load operation. [Figure 7] FIG. 7 is a flowchart showing a process flow of the hunting phenomenon suppression control according to the first embodiment. [Figure 8] FIG. 8 is a flowchart showing a process flow of hunting suppression control according to the second embodiment. [Figure 9] FIG. 9 is an explanatory diagram showing a table for correcting the rotation speed of the drive source in accordance with the intake air according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiment, and the technical idea of ​​the present invention may be realized by combining other known components. In each drawing, the same elements are denoted by the same reference numerals, and duplicated explanations are omitted. In each drawing, the U direction is the upward direction, the D direction is the downward direction, the R direction is the rightward direction, and the L direction is the leftward direction.

[0037] First Embodiment <Overall configuration of gas compressor 100> FIG. 1 shows a schematic configuration of a gas compressor 100 (hereinafter referred to as "compressor 100") according to a first embodiment to which the present invention is applied. In this example, air is used as compressed air, but this is not limited thereto and other gases may be used. Compressor 100 is a liquid-feed type positive displacement compressor that supplies liquid (e.g., oil) to a compression working chamber, and in this example, an oil-feed type screw compressor is applied. However, the present invention is not limited thereto and may be a turbo type.

[0038] The compressor 100 comprises an electric motor 1 as a driving source, an inverter 16 that changes the frequency of the power supplied to the electric motor, a compressor body 2 equipped with a screw rotor, an intake throttle valve 3 that controls the amount of intake air on the intake side, an intake filter 4 provided at the inlet of the intake section that takes in air into the intake flow path 22 in which the suction throttle valve 3 is located, and a gas-liquid separator 5 that separates the compressed air and lubricating oil discharged from the compressor body 2.

[0039] Compressor body 2 compresses gas. Electric motor 1, which serves as a drive source, drives compressor body 2. As shown in Fig. 2, suction throttle valve 3 closes suction flow path 22 by the elastic force of check spring 30 acting on valve plate 29, which serves as a valve body, when rotation of electric motor 1 stops.

[0040] The gas-liquid separator 5 separates the lubricating oil from the compressed air by centrifugal force and collision. The compressed air then passes through a pipe 7a and is subjected to a second gas-liquid separation by a filter 8, and flows to a heat exchanger 9 via a downstream pressure regulating check valve 6 and a discharge pipe 7b. The compressed air exchanges heat with cooling air in the heat exchanger 9, and is cooled from the temperature at which it is discharged from the compressor body 2 (for example, about 110°C) to a predetermined temperature (for example, about 70°C) lower than that, and is supplied to the user of the compressed air via a discharge pipe 7c.

[0041] On the other hand, the lubricating oil separated in the gas-liquid separator 5 flows through the oil piping 10a to the heat exchanger 11, where it is cooled by heat exchange with cooling air, and is returned to the compressor body 2 through the oil piping 10b and the oil filter 12.

[0042] A pressure detection device 13 is provided at the outlet of the heat exchanger 9, and a control unit 14 to which the pressure detection device 13 is connected opens and closes an air release valve 17, thereby pressing or depressurizing the suction throttle valve 3 to switch between no-load operation and loaded operation, i.e., to control the capacity.

[0043] The air release valve 17 is provided on a path of a control pipe 18 provided from the inlet side of the filter 8 to the suction throttle valve 3. The air release valve 17 performs capacity control by switching between pressurizing a pressurizing chamber 24 (see FIG. 2) provided in the suction throttle valve 3 or releasing to the atmosphere by opening and closing the air release valve 17.

[0044] The control unit 14 also constitutes a functional unit through cooperation between a program and a computing device, for example, and is configured to perform various controls of the compressor 100. In the first embodiment, the control unit 14 is configured to variably control the rotation speed of the electric motor 1 by PID control according to the discharge pressure.

[0045] More specifically, the control unit 14 monitors the detection value of the pressure detection device 13 and controls the rotation speed of the electric motor 1 so as to maintain a predetermined target pressure (e.g., 0.70 MPa) set via an input device (not shown).

[0046] For example, the control unit 14 rotates the electric motor 1 at full rated speed (full load operation) until the target pressure is reached, and then, after the target pressure is reached, reduces power by increasing or decreasing the rotation speed of the electric motor 1 in response to pressure fluctuations according to the amount of compressed air used.

[0047] Furthermore, when the amount of compressed air used decreases and the detected pressure of the pressure detection device 13 reaches a predetermined upper limit pressure (e.g., 0.78 MPa) that is higher than the target pressure, the control unit 14 performs no-load operation to further reduce power.

[0048] That is, when the discharge pressure reaches an upper limit pressure that is higher than the set pressure, the control unit 14 executes a no-load operation in which the rotation speed of the electric motor 1 is controlled to the lower limit rotation speed.

[0049] Here, in no-load operation, when the discharge pressure reaches the upper limit pressure, the rotation speed of the electric motor 1 is reduced to a predetermined lower limit rotation speed. Furthermore, the suction throttle valve 3 is closed to reduce the intake amount, and the air release valve 17 (e.g., a solenoid valve) is opened to release the compressed air to the atmosphere. This reduces the pressure in the gas-liquid separator 5 and the discharge pipe 7c, reducing the pressure load on the compressor body 2 and reducing the power of the electric motor 1.

[0050] Thereafter, when the amount of compressed air used increases and the discharge pressure falls to a predetermined lower limit pressure that is lower than the upper limit pressure and equal to or higher than the target pressure, the control unit 14 leaves the lower limit rotation speed of the motor 1 unchanged and switches to load operation with the suction throttle valve 3 "open."

[0051] If the discharge pressure rises again to the upper limit pressure during the load operation due to the usage of compressed air, the control unit 14 closes the suction throttle valve 3 and performs no-load operation again. Conversely, if the discharge pressure falls below the lower limit pressure during the no-load operation, the control unit 14 transitions again to load operation and returns to PID control.

[0052] Figures 2, 3, 4, and 5 are longitudinal sectional views of the suction throttle valve 3 in various states according to the first embodiment of the present invention. In Figures 2, 3, 4, and 5, the rightward direction R and the leftward direction L in Figure 1 are shown in the opposite directions.

[0053] The suction throttle valve 3 comprises a body 25 which defines the suction passage 22, a spring chamber 23 and a pressurizing chamber 24. The suction throttle valve 3 comprises a control spring 26 which is provided in the spring chamber 23 and has an elastic force for transmitting a load to a piston 27. The suction throttle valve 3 comprises a piston 27 which is provided in the pressurizing chamber 24 and receives the pressure of compressed air and transmits it to a shaft 28, a shaft 28 which is fixed to the piston 27 and operates in the axial direction, and a valve plate 29 through which the shaft 28 is inserted into a hole and which opens and closes the suction passage 22 of the suction throttle valve 3. The suction throttle valve 3 comprises a check spring 30 which is wound around the shaft 28 and has an elastic force for opening and closing the valve plate 29. The suction throttle valve 3 comprises a one-way valve 31 which releases the pressure in the suction passage 22.

[0054] Fig. 2 shows the state of the suction throttle valve 3 when the compressor is stopped or is operating at no load. In Fig. 2, the control spring load Kca+check spring load Ka exceeds the pressure difference F1+valve plate load M between the suction passage 22 around the valve plate 29 and the compression chamber of the compressor body 2, so the valve plate 29 is closed. The control spring load Kca is the elastic force of the control spring 26 acting on the piston 27. The control spring 26 urges the piston 27 in the upward direction U. The check spring load Ka is the elastic force of the check spring 30 acting on the valve plate 20. The check spring 30 urges the valve body 29 in the upward direction U.

[0055] Figure 3 shows the state of the suction throttle 3 valve when it has shifted from the state shown in Figure 2 to load operation. In Figure 3, compressed air pressurizes piston 27 through control piping 18 connected from gas-liquid separator 5 to pressurizing chamber 24, generating a load on piston 27, and when this load exceeds the load of control spring 26, shaft 28 moves in the opening direction. When the compressor is operating, a load consisting of the dynamic pressure F1 of the suction air and the valve plate weight M acts on valve plate 29 supported by check spring 30, exceeding the load Ka of check spring 30, and valve plate 29 opens.

[0056] When the operation transitions again to no-load operation or to a stop, the pressure in the pressurizing chamber 24 is released to the atmosphere by the air release valve 17, and the piston 27 and shaft 28 are moved upward by the control spring 26, and the valve plate 29 is closed. During no-load operation, the compressor 100 is operating, so negative pressure F1 is generated, and the control spring load Kca of the control spring 26 is set so that the valve plate 29 does not open even if negative pressure F1 is generated.

[0057] When the compressor 100 is stopped or shifted to a loaded operation, the dynamic pressure F1 of the intake air acting on the valve plate 29 exceeds the load Ka of the check spring 30, thereby opening the valve plate 29. However, the dynamic pressure acting on the valve plate 29 is greater at the maximum rotation speed of the motor 1 than at the preset minimum rotation speed, and therefore the opening degree of the valve plate 29 also becomes greater.

[0058] When the pressure on the user side (the pressure of the pressure detection device 13) exceeds the target pressure, the rotational speed of the motor 1 is decreased by rotational speed control, the flow rate of the suction air is decreased, and the opening degree A of the valve plate 29 becomes narrower.

[0059] When the pressure on the user side exceeds the upper limit pressure, the pressure in the pressurizing chamber 24 is reduced while maintaining the lowest rotational speed, and the valve plate 29 is in a closed state.

[0060] Fig. 4 shows the state of the suction throttle valve 3 when the motor 1 is operating under load at the lowest rotational speed. In Fig. 4, the dynamic pressure F1 acting on the valve plate 29 downward + the valve plate weight M and the check spring load Ka acting on the valve plate 29 upward are in balance.

[0061] When shifting from no-load operation to load operation, if the amount of air used by the user is small, there may be a case of shifting to load operation while maintaining the same lowest rotational speed as in no-load operation. It is desirable that the valve plate 29 stops at the position shown in Fig. 4. Here, when the rotational speed of the motor 1 is such that the dynamic pressure F1 acts on the valve plate 29 in a state where the valve plate 29 does not contact the shaft 28 as shown in Fig. 4, the check spring load Ka shown in Fig. 3 is higher than the dynamic pressure F1 + the valve plate load M acting on the valve plate 29 (Ka > F1 + M). Therefore, the valve plate 29 moves in the closing direction shown in Fig. 4. At this time, due to the inertial force of the valve plate 29, the valve plate load M is directed in the closing direction. For this reason, the relationship of Ka + M = F1 shown in Fig. 4 does not hold, and the valve plate 29 moves to the position shown in Fig. 5.

[0062] Fig. 5 shows the state of the valve plate closed of the suction throttle valve 3 during load operation. When the state of Fig. 5 is reached, the relationship of Ka > F1 + M is reversed and Ka < F1 + M, then the valve plate 29 moves back to the position of Fig. 3. Eventually, without converging to the position of Fig. 4, a hunting phenomenon occurs where the valve plate 29 repeats the positions of Fig. 3 and Fig. 5.

[0063] The cause of the hunting phenomenon is due to the rotational speed of the motor 1 after shifting from no-load operation to load operation, and it occurs when a state below a predetermined rotational speed is maintained for a predetermined time.

[0064] Therefore, in the first embodiment, if the rotation speed is maintained for a certain period of time after the load operation at the same speed as that of the no-load operation or below a certain rotation speed, it is determined that the hunting phenomenon is occurring, and a method is provided in which the motor frequency is forcibly increased at a constant speed for a certain period of time.

[0065] In other words, when the control unit 14 determines that the rotational speed of the motor 1 is below the speed threshold and that the time rate of change of the rotational speed of the motor 1 remains below the change rate threshold for a certain period of time after the transition from unloaded operation to loaded operation, it determines that a hunting phenomenon is occurring in which the valve plate 29 of the suction throttle valve 3 repeatedly opens and closes, and increases the rotational speed of the motor 1 at a certain constant time rate of change.

[0066] Here, the speed threshold value is a rotation speed at which the hunting phenomenon of the suction throttle valve 3 occurs when transitioning from unloaded operation to loaded operation occurs at a rotation speed equal to or lower than the speed threshold value.

[0067] The change rate threshold is the rotation speed at which the hunting phenomenon of the suction throttle valve 3 occurs when the time rate of change of the rotation speed of the motor 1 is equal to or less than the change rate threshold, in the case of transition from unloaded operation to loaded operation at a rotation speed equal to or less than the speed threshold. Time rate of change of It is.

[0068] The certain time rate of change is a value that can suppress the hunting phenomenon of the suction throttle valve 3.

[0069] Then, after a predetermined time has elapsed since starting control to increase the rotation speed of the electric motor 1 at a certain time change rate, the control unit 14 returns to load operation in which the rotation speed of the electric motor 1 is controlled in accordance with the load.

[0070] Next, FIG. 6 shows a chart in which the rotation speed N of the motor 1 after switching from no-load operation to loaded operation, the check spring load Ka, the differential pressure F1 acting on the valve plate 29, the load difference between the check spring load Ka and the differential pressure F1, and the valve plate opening are shown on the vertical axis, and the horizontal axis is the time axis.

[0071] As shown in FIG. 6, the rotation speed of the electric motor 1 is a lower limit rotation speed N0 (min -1 ), and after the load operation is started, the lower limit rotation speed N0 (min -1 ) to upper limit rotation speed N2(min -1 ) is controlled between

[0072] During no-load operation, when the user pressure drops and reaches the return pressure, the system switches to load operation. During no-load operation, the air supply is cut off, so the rotation speed of the motor 1 is set to the minimum N0(min -1 The amount of air used after the load operation is switched to the rotation speed N0 (min -1 If the supply amount at the rotation speed N(min -1 ) remains the same even after load operation. -1 Since the rotation speed of the motor 1 cannot be set below this value, the pressure on the user side indicated by the pressure detector 13 rises again, and when it reaches the upper limit pressure, the motor again switches to no-load operation.

[0073] Under the above conditions, even if the load operation is switched to, the rotation speed of the motor 1 remains at the lower limit rotation speed N0 (min -1 ) will be used for driving.

[0074] Fig. 6 shows the state after shifting from no-load operation to loaded operation, starting from the state shown in Fig. 3. The opening degree of the valve plate 29, A (mm), shows the state shown in Fig. 3, and 0 (mm), shows the state shown in Fig. 5.

[0075] The rotation speed of motor 1 is N0min -1 Starting from the state of, during period C, no load operation N0min -1 Assume that the valve plate 29 is maintained in the state shown in FIG. 1. At this time, in the state of A mm, the check spring load Ka is greater than the pressure difference F1, so the valve plate 29 moves in the closing direction. On the other hand, in the state of 0 mm, the check spring load Ka is less than the pressure difference F1, so the valve plate 29 moves in the opening direction again.

[0076] Motor 1 rotation speed N1min -1 During PID control, if the rotation speed falls below this value, a hunting phenomenon like that in period C occurs. In the first embodiment, N1min -1 The following rotation speed conditions do not change (for example, 10 min per second) -1 If the control unit 14 determines that the hunting phenomenon suppression control for the period D is performed, the control unit 14 executes the hunting phenomenon suppression control for the period D.

[0077] In period D, the PID control is turned off for a predetermined period, for example, 10 minutes per second. -1 The rotation speed is forcibly increased step by step. This increases the pressure difference F1 when the valve plate 29 closes from the state of the opening degree Amm of the valve plate 29 shown in FIG. 6F, and the valve plate 29 opens slightly rather than to an opening degree of 0mm at which the valve plate 29 is completely closed. This makes it possible to reduce the pressure difference F1 when the valve plate 29 is next operated to open.

[0078] After that, the valve plate 29 moves again in the closing direction after the valve plate opening reaches an opening lower than Amm, but the check spring load Ka has further decreased. Therefore, the valve plate 29 moves in the closing direction from a state more open than the previous time, thereby ending the hunting phenomenon of the valve plate 29 as shown in G in Figure 6, and the valve plate 29 can be held in the position shown in Figure 4.

[0079] After the period D has elapsed, the period moves to period E, and the PID control is turned ON to perform rotation speed control based on the pressure value of the pressure detection device 13.

[0080] Here, the lower limit rotation speed N0min of the motor 1 is -1 Rotation speed N1min -1 It is possible to suppress the hunting phenomenon by setting it to a higher value. However, in the first embodiment, the rotation speed N1min -1 This suppresses the hunting phenomenon without increasing the rotation speed to a high level, ensuring energy savings.

[0081] Fig. 7 is a flowchart showing the process flow of the hunting phenomenon suppression control according to the first embodiment. Fig. 7 shows an example of the process flow of the hunting phenomenon suppression control of the control unit 14 that performs the above operations.

[0082] In S1, the control unit 14 determines whether or not the operation has shifted from no-load operation to loaded operation. If it is determined in S1 that the operation has shifted from no-load operation to loaded operation, the process proceeds to S2. In S2, the timer T1 (seconds) starts to count up, and the process proceeds to S3. Note that if it is not determined in S1 that the operation has shifted from no-load operation to loaded operation, the hunting phenomenon suppression control process is temporarily terminated.

[0083] In S3, the control unit 14 judges whether the motor frequency is equal to or lower than F2Hz (the lower limit of the motor frequency at which hunting occurs when switching from no-load operation to loaded operation during PID control). F2Hz is the rotation speed N1min of the motor 1 shown in FIG. -1 is converted into a motor frequency. If it is determined in S3 that the frequency is F2 Hz or less, the process proceeds to S4. If it is not determined in S3 that the frequency is F2 Hz or less, the hunting phenomenon suppression control process is temporarily terminated.

[0084] In S4, the control unit 14 judges whether the change in the motor frequency is equal to or less than V1 Hz / sec. V1 Hz / sec is a value for judging that the hunting phenomenon occurs when the rate of change in the rotation speed is equal to or less than V1 Hz / sec after the transition from unloaded operation to loaded operation during PID control. V1 Hz / sec is the time rate of change of the rotation speed of the electric motor 1 described above converted into the motor frequency. In other words, V1 Hz / sec is the value obtained by dividing the number of rotation circumferences (2πR: wavelength) of the electric motor 1 repeated in one second by the number of seconds (time), and is the acceleration that is the amount of change in the rotation speed per unit time.

[0085] If it is determined in S4 that the rate of change in rotation speed is equal to or lower than V1 Hz / sec, the process proceeds to S5. Note that if it is not determined in S4 that the rate of change in rotation speed is equal to or lower than V1 Hz / sec, the hunting phenomenon suppression control process is temporarily terminated.

[0086] In S5, it is determined whether or not T2 seconds have elapsed on the timer T1 (seconds). If it is determined in S5 that T2 seconds have elapsed on the timer T1 (seconds), the process proceeds to S7. Note that if it is not determined in S5 that T2 seconds have elapsed on the timer T1 (seconds), the process of the hunting phenomenon suppression control is temporarily terminated.

[0087] That is, when the frequency is F2Hz or less in S3, the rate of change in rotation speed is V1Hz / sec or less in S4, and T2 seconds have elapsed on timer T1 (seconds) in S5, control unit 14 executes processing to turn off PID control, which is processing in S6. When PID control is turned off in S6, control unit 14 executes processing 1 to increase the motor frequency at a predetermined rate V2Hz / sec in S7. The predetermined rate V2Hz / sec is a value obtained by dividing the number of rotation circumferences (2πR: wavelength) of motor 1 repeated in one second by seconds (time), and is an acceleration that is the amount of change in rotation speed per unit time, and is the above-mentioned certain time change rate.

[0088] In S8, the control unit 14 starts counting up the timer T3 (seconds). Here, the processes of S6, S7, and S8 can be performed simultaneously or in the order shown in the figure.

[0089] In S9, if the control unit 14 determines that the timer T3 (seconds) has reached T4 seconds, the process proceeds to S10. If it is not determined in S9 that the timer T3 (seconds) has reached T4 seconds, the process of the hunting phenomenon suppression control is temporarily terminated.

[0090] In S10, the control unit 14 executes the stop of the process 1. When the stop of the process 1 is executed in S10, the process proceeds to S11.

[0091] In S11, the control unit 14 executes the PID-ON process.

[0092] That is, the flow of processing by the control unit 14 is as follows.

[0093] After the transition from unloaded operation to loaded operation, the control unit 14 determines whether the rotation speed of the motor 1 reaches the speed threshold (N1min -1 ) and it is determined that the fluctuation in rotation speed below a predetermined value has continued for a certain period of time, it is determined that this is a hunting phenomenon in which the valve plate 29 of the suction throttle valve 3 is repeatedly opening and closing, and the rotation speed of the motor 1 is increased at a certain rate.

[0094] Speed ​​threshold (N1min -1 ) is the speed threshold (N1min -1 When the engine is operated under load at a speed below the speed threshold (N1min), the hunting phenomenon of the suction throttle valve 3 occurs. -1 ) is the speed threshold (N1min -1 When the load is operated at a rotation speed below a predetermined value, the speed threshold (N1min) at which the suction throttle valve 3 hunting phenomenon occurs is reached when the rotation speed fluctuates due to the rate of change in the rotation speed being below a predetermined value. -1 ) rotation speed becomes clear.

[0095] When the rotation speed fluctuation state is below a certain level and continues for a certain period of time, it is determined that the speed threshold (N1min -1 ) or less, and the rate of change in the rotation speed is below a predetermined value for a certain period of time. -1 ) or less, and the fluctuation in the rotation speed continues for a certain period of time. This causes the hunting phenomenon of the suction throttle valve 3. With this configuration, the criterion for determining whether the hunting phenomenon of the suction throttle valve 3 occurs becomes clear.

[0096] "Increasing the rotation speed of the electric motor 1 at a certain constant speed" means increasing the rotation speed at a stable speed below a predetermined speed at which the hunting phenomenon of the suction throttle valve 3 subsides, since the faster the rotation speed of the electric motor 1 increases, the more difficult it is for the hunting phenomenon of the suction throttle valve 3 to subside. The certain constant speed corresponds to a predetermined speed V2 Hz / sec. In this configuration, the rotation speed of the electric motor 1 can be increased at a stable speed below a predetermined speed at which the hunting phenomenon of the suction throttle valve 3 subsides.

[0097] The control unit 14 increases the rotation speed of the motor 1 at a certain constant speed, and after a predetermined time has elapsed, returns the motor 1 to a loaded operation in which the rotation speed is controlled according to the load. This allows the control of the compressor 100 to quickly return to a loaded operation from a no-load operation.

[0098] <Advantages of the First Embodiment> According to the first embodiment, when it is determined that the hunting phenomenon of the suction throttle valve 3 is occurring, the rotation speed of the electric motor 1 is increased at a certain time rate of change (speed). The hunting phenomenon of the suction throttle valve 3 tends to persist as the increase in the rotation speed of the electric motor 1 increases. In the first embodiment, the rotation speed of the electric motor 1 is increased at a certain time rate of change, so that the hunting phenomenon can be suppressed during the increase in the rotation speed of the electric motor 1, while the rotation speed of the electric motor 1 can be increased to a sufficiently high rotation speed at which the hunting phenomenon is unlikely to occur.

[0099] In the first measure described above, the rotation speed of the drive source is increased during no-load operation, which results in a drawback that energy is wasted. In contrast, in the first embodiment, the rotation speed of the electric motor 1 can be kept low during no-load operation, so there is no drawback in that energy is wasted.

[0100] In the second measure described above, the load of the check spring 30 is weak, and the coolant flows out of the suction throttle valve 3 before the valve plate 29 closes due to the coolant return phenomenon specific to liquid-cooled compressors, and the coolant adheres to the intake filter 4 provided in the intake part of the suction throttle valve 3, causing a problem that the function of the intake filter 4 is impaired. In contrast, in the first embodiment, the load of the check spring 30 is appropriately set and the hunting phenomenon can be suppressed. As a result, the occurrence of the coolant return phenomenon can be prevented, the coolant is prevented from flowing out to the outside, and the coolant is prevented from adhering to the intake filter 4.

[0101] As described above, according to the first embodiment, it is possible to provide the compressor 100 capable of suppressing the hunting phenomenon of the suction throttle valve 3 without causing any adverse effects.

[0102] <Second embodiment> In the second embodiment, the same explanation as in the above embodiment will be omitted by assigning the same reference numerals. Fig. 8 is a flowchart showing the process flow of the hunting suppression control according to the second embodiment. Fig. 9 is an explanatory diagram showing a table for correcting the rotation speed of the electric motor 1 according to the intake air according to the second embodiment.

[0103] As shown in Fig. 1, the compressor 100 includes a temperature detector 15 that detects the temperature of the intake section that takes in air into the intake passage 22 and outputs the detection result to the control section 14. The control section 14 according to the second embodiment determines the speed threshold N1min of the electric motor 1 according to the detection result of the temperature detector 15 installed near the intake filter 4 in Fig. 1. -1 The value of is varied.

[0104] As the temperature of the intake air decreases, the amount of air decreases, so the value of the differential pressure F1 acting in the direction to push down the valve plate 29 becomes smaller, and the hunting phenomenon tends to occur more easily than when the temperature is high. In order to suppress the hunting phenomenon, the speed threshold N1min of the electric motor 1 in the first embodiment is set to 0.5. -1 For example, when the temperature detection device 15 changes from 20° C. (T0° C.) to 15° C. (T1° C.), the speed threshold N10min of the motor 1 is -1 The upper speed threshold N11min -1 The method shown in the second embodiment corrects the above.

[0105] Speed ​​threshold N1min used to judge the hunting phenomenon of the suction throttle valve 3 -1 is configured to be changeable according to the temperature of the intake section detected by the temperature detection device 15. As shown in the correction table of FIG. 9, when the temperature of the intake section detected by the temperature detection device 15 falls from T0 to T1, the control unit 14 changes the speed threshold to N10min. -1 From N11min -1That is, when the temperature of the intake part becomes low, the control unit 14 increases the speed threshold N1min -1 In addition, when the temperature of the intake part detected by the temperature detection device 15 rises from T0 to T2, the control unit 14 increases the speed threshold N1min. -1 N10min -1 From N12min -1 That is, when the temperature of the intake part becomes high, the control unit 14 reduces the speed threshold N1min -1 Reduces.

[0106] 8 shows an example of the process flow of the hunting phenomenon suppression control of the control unit 14 in the second embodiment. In comparison with the process flow in the first embodiment shown in FIG. 7, after S2, the speed threshold N1min is set according to the value of the temperature detection device 15. -1 The process of S12 is executed to correct the speed threshold N1min. -1 The control unit 14 performs the correction by using a correction table shown in FIG.

[0107] That is, the flow of processing by the control unit 14 differs from that of the first embodiment in the following points. In S12, the control unit 14 determines the speed threshold N1min of the rotation speed for determining the hunting phenomenon of the intake throttle valve 3. -1 is configured to be changeable according to the temperature of the intake section detected by the temperature detection device 15. When the temperature of the intake section drops from T0 to T1, the amount of intake air decreases, and the hunting phenomenon of the intake throttle valve 3 becomes more likely to occur. Therefore, the control unit 14 sets the speed threshold value N1min of the rotation speed for determining the hunting phenomenon of the intake throttle valve 3. -1 N10min -1 From N11min -1 When the temperature of the intake part rises from T0 to T2, the amount of intake air increases, making it difficult for the intake throttle valve 3 to experience a hunting phenomenon. Therefore, the control unit 14 increases the speed threshold value N1min of the rotation speed for determining the hunting phenomenon of the intake throttle valve 3. -1 N10min -1 From N12min -1 In this configuration, the optimum speed threshold N1min is set according to the intake temperature. -1 can be set.

[0108] <Effects of the second embodiment> In the second embodiment, the speed threshold N1min is set according to the detection result of the temperature detection device 15. -1 9, the hunting phenomenon can be appropriately prevented according to the change in the temperature of the intake part. In the first embodiment, for example, the speed threshold value N1min is set based on the lower limit value of the operating condition temperature of the compressor 100. -1 On the other hand, in the second embodiment, when the temperature is higher than the lower limit of the temperature of the use condition, the speed threshold value N1min is set, and the hunting phenomenon can be reliably prevented. -1 It is possible to set the temperature low, thereby ensuring energy conservation.

[0109] Although the embodiments of the present invention have been described above, the above-mentioned embodiments merely show some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above-mentioned embodiments. [Explanation of symbols]

[0110] DESCRIPTION OF SYMBOLS 1...electric motor (driving source), 2...compressor body, 3...suction throttle valve, 4...intake filter, 5...gas-liquid separator, 6...pressure regulating check valve, 7a...piping, 7b...discharge piping, 7c...discharge piping, 8...filter, 9...heat exchanger, 10a...oil piping, 10b...oil piping, 11...heat exchanger, 12...oil filter, 13...pressure detection device, 14...control unit, 15...temperature detection device, 16...inverter, 17...air release valve, 18...control piping, 22...suction flow path, 23...spring chamber, 24...pressurization chamber, 25...body, 26...control spring, 27...piston, 28...shaft, 29...valve plate (valve body), 30...check spring, 31...one-way valve, 100...gas compressor.

Claims

1. A compressor body that compresses gas; A drive source that drives the compressor body; a control unit that controls a rotation speed of the driving source in response to a discharge pressure of the compressor body; a suction throttle valve that closes the suction flow passage by the elastic force of a check spring acting on a valve body when the rotation of the drive source stops; Equipped with the control unit performs a no-load operation in which a rotation speed of the driving source is controlled to a lower limit rotation speed when the discharge pressure reaches an upper limit pressure higher than a set pressure, When the control unit determines that the rotation speed of the driving source is equal to or lower than a speed threshold and that a time rate of change of the rotation speed of the driving source is equal to or lower than a change rate threshold for a certain period of time, the control unit determines that a hunting phenomenon is occurring in which the valve body of the suction throttle valve repeats opening and closing movements, and increases the rotation speed of the driving source at a certain time rate of change. Gas compressor.

2. 2. The gas compressor according to claim 1, The speed threshold is a rotation speed at which a hunting phenomenon of the suction throttle valve occurs when transitioning from unloaded operation to loaded operation occurs at a rotation speed equal to or lower than the speed threshold. Gas compressor.

3. 3. A gas compressor according to claim 2, The change rate threshold is a time rate of change of the rotation speed at which a hunting phenomenon of the suction throttle valve occurs when the rotation speed of the driving source transitions from unloaded operation to loaded operation at a rotation speed equal to or lower than the speed threshold and the time rate of change of the rotation speed of the driving source is equal to or lower than the change rate threshold. Gas compressor.

4. 2. The gas compressor according to claim 1, a temperature detection device for detecting a temperature of an intake section that takes in gas into the intake passage, The speed threshold value used to determine the hunting phenomenon of the intake throttle valve is configured to be changeable according to the temperature of the intake section detected by the temperature detection device. Gas compressor.

5. 5. A gas compressor according to claim 4, The control unit increases the speed threshold when the temperature of the intake part detected by the temperature detection device decreases, and decreases the speed threshold when the temperature of the intake part detected by the temperature detection device increases. Gas compressor.

6. 2. The gas compressor according to claim 1, The certain time rate of change is a value that can suppress the hunting phenomenon of the suction throttle valve. Gas compressor.

7. 2. The gas compressor according to claim 1, The control unit returns to a load operation in which the rotation speed of the drive source is controlled in accordance with a load after a predetermined time has elapsed since starting control to increase the rotation speed of the drive source at a certain time change rate. Gas compressor.

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