JP2011017345A - Oil-cooled screw compressor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem that, when an oil-cooled screw compressor is started after being stopped for a long period of time at a cooling environment, starting torque is increased due to a viscosity increase in oil stored in an operation chamber, and a drive means having a larger capacity than normal operation is required.SOLUTION: This oil-cooled screw compressor 1 includes: a casing 5; a pair of rotors 3, 4 housed in the casing and having threaded tooth grooves; an electric motor rotatively driving the rotors; a control device 11 controlling the electric motor; an oil supply mechanism supplying the oil to the operation chamber surrounded by the rotors and the casing by meshing the tooth grooves of the pair of the rotors; and an oil separating mechanism separating the oil from compressed gas delivered from the operating chamber. Only in a short time immediately after starting, drive is performed at low speed not increasing torque and the oil is discharged. After that, the speed is increased to the normal operation speed. Alternatively, residual pressure is released after stopping and the rotors are subsequently rotated for a short time, thereby the oil accumulated in the operation chamber is discharged and a succeeding start is easily performed.

Description

  The present invention relates to an oil-cooled screw compressor, and relates to a technique for avoiding an increased burden on an electric motor and a power supply circuit that drive the compressor.

  The oil-cooled screw compressor has a plurality of closed spaces called working chambers formed by meshing with the tooth spaces of the pair of rotors and reducing the gap between each rotor and the inner surface of the casing. Have.

  As the rotors rotate, the working chamber moves and its volume repeatedly expands and contracts. The working chamber communicates with the outside through the opening provided in the casing or becomes a sealed space depending on the rotational position of the rotor. During expansion of the volume of the working chamber, communication with an opening called a suction port continues, and compressed gas is sucked into the working chamber from the outside. When the working chamber has the maximum volume, the communication with the suction port is terminated, the compressed gas is confined, and the compressed gas is compressed by reducing the volume. When a predetermined pressure is reached, the compressed gas is discharged until the volume reaches zero after communicating with an opening called a discharge port.

Japanese Patent Laid-Open No. 2003-3976

  In the oil-cooled screw compressor, the compression operation proceeds while injecting oil into the working chamber in the compression process. The reason for injecting oil is to lubricate and cool the rotors, and fill the gaps between the rotors and between the rotor and the casing inner surface with oil to suppress leakage of compressed gas from the high pressure working chamber to the low pressure working chamber. It is to do.

In the case of an air compressor, the temperature of the oil during operation is 50 to 70 ° C., the viscosity (strictly kinematic viscosity, the same shall apply hereinafter) is as low as 40 mm / s ² or less, and the oil around the rotor obstructs rotation. do not become.

  As a mechanism for injecting oil into the working chamber, a differential pressure oil supply mechanism using a pressure difference between the suction side and the discharge side created by the compressor itself is common. This mechanism connects the oil reservoir under high pressure that separates and collects oil mixed in the compressed gas immediately after leaving the working chamber, and the working chamber close to the suction pressure immediately after the start of compression by piping. Oil is fed using differential pressure. In this mechanism, after the rotor of the compressor is stopped, oil supply to the compressor is continued with the remaining differential pressure for about 10 to 20 seconds. Therefore, a large amount of oil is accumulated in the working chamber, and the compressor is in that state. Will stop.

During operation, the compressor is at a high temperature of about 80 to 100 ° C. mainly in the vicinity of the discharge flow path due to the compression heat or the like. In winter in cold regions, the temperature may be below freezing, and the oil collected in the working chamber has a viscosity of 150 mm / s due to the low temperature.
Rise to ² or higher.

  For this reason, if it tries to start at low temperature, highly viscous oil will inhibit rotation of a rotor and will increase the torque required for starting. Particularly in a screw compressor, when the working chamber moves and reaches the discharge end face, the reaction force of the oil colliding with the end face acts on the tooth surface, and a large inertia force is generated in the form of torque.

  In a model that uses a large capacity motor and operates at a variable speed, if the power device represented by an inverter is strengthened, the compressor can be started by generating the required large starting torque in the motor. However, for the purpose of starting only in a low-temperature environment, it is wasteful to provide an electric motor or power device that is many times the capacity required during operation, and the efficiency during operation is inferior to that of an electric motor with an appropriate capacity.

  In some conventional motors such as induction type, even if the starting torque is excessive for a very short time, it has the capacity to withstand for a short time and can be started. However, in that case, the compressor instantaneously consumed a large current.

  In recent years, electric motors that have been used widely have many systems that are driven by controlling a current by a semiconductor element represented by an inverter or the like. In this method, an excessive current damages a semiconductor element even for a moment, so that a large starting torque cannot be received, and starting when there is an excessive torque is not good.

  There are several types of driving force transmission systems, such as those in which the output shaft of the motor and the rotating shaft of the rotor are integrated, coupling by shaft coupling, and rotation transmission through gears, belts, etc. . In the coupling via a flexible shaft coupling or belt, even if an excessive starting torque is momentarily generated, the shaft coupling or belt in the middle serves as a buffer material, which has an effect of reducing the burden on the motor. However, if the coupling is rigid, there is no effect, and especially if the rotor and the motor shaft are integrated, the excessive torque is transmitted directly and the burden on the motor remains large, which is severe for the motor. It is easy to become a condition.

  In a screw compressor, the problem of starting torque has been a problem for a long time, and various efforts have been made. For example, Patent Document 1 discloses a method of reducing a starting torque by providing a discharge port that opens only at the start-up in addition to a normal discharge port.

  In this method, it is necessary to newly add a valve device and its opening / closing means to the conventional compressor body, and there are problems in the complexity of the structure and the increase in manufacturing cost.

  In view of the above problems, the object of the present invention is to reduce the excessive starting torque generated by the oil, and to provide a reliable starting even in a low temperature environment while including an electric motor having an appropriate capacity during steady operation. The object is to provide an oil-cooled screw compressor.

  Another object of the present invention is to provide a motor drive system provided with a control device that gives a command to an inverter in accordance with the startup status of the electric motor.

  In order to achieve the above object, an oil-cooled screw compressor according to the present invention includes a casing, a pair of rotors built in the casing and having thread-like tooth grooves, an electric motor that rotationally drives these rotors, A control device that controls the electric motor, an oil supply mechanism that meshes the tooth gaps of the pair of rotors, and supplies oil into a working chamber surrounded by the rotor and the casing, and discharged from the working chamber In an oil-cooled screw compressor having an oil separation mechanism for separating oil from compressed gas, the rotor is brought into a rotation stop state from a normal operation state, and the electric motor is started from the rotation stop state so that the rotor is normally operated. During the state, the control unit discharges at least part of the oil supplied to the space in the casing that houses the pair of rotors outside the space. A.

  In order to achieve the above object, a motor drive system according to the present invention includes an electric motor connected to an object to be driven, an inverter that controls the rotation speed of the electric motor, and a setting device that sets operating conditions of the object to be driven. And a control device that gives a first rotation speed command to the inverter based on detection information from a detector that detects setting information from the detector and output information of the driving object, When starting the electric motor, a second rotational speed command that gives a lower rotational speed than the first rotational speed command is given to the inverter based on the starting torque estimation information of the driven object, and the electric motor After being driven based on the second rotational speed command, the first rotational speed command is given to the inverter.

  According to the present invention, the oil-cooled screw compressor can be started smoothly. In addition, since it can be sufficiently activated with a small and small output device, it can be reduced in size and weight and the manufacturing cost can be reduced, and an optimum motor can be selected during normal operation, and energy efficiency is improved.

It is a schematic diagram of the periphery of the main body of the oil-cooled screw compressor of the first and second embodiments and the oil system. It is a graph which shows the change of the rotational speed of the rotor before and behind starting. It is a graph of the change of the rotational speed of a rotor and the amount of lubrication during stop operation. It is a schematic diagram of the main body periphery and oil system | strain of the oil-cooled screw compressor of a 3rd Example.

  Examples of the present invention will be described below. The oil-cooled screw compressor in the present embodiment includes a casing, a pair of rotors built in the casing and having a thread-like tooth groove, an electric motor that rotationally drives these rotors, and a control device that controls the electric motor. And an oil supply mechanism that meshes the tooth spaces of the pair of rotors and supplies oil into the working chamber formed by being surrounded by the rotor and the casing, and an oil separation mechanism that separates the oil from the compressed gas discharged from the working chamber And having.

  In such an oil-cooled screw compressor, in order to ensure smooth start-up, the rotor changes from the normal operation state to the rotation stop state, and the electric motor is started from the rotation stop state to bring the rotor into the normal operation state. In the meantime, the control device discharges at least a part of the oil supplied to the space in the casing that houses the pair of rotors out of the space.

  In a conventional oil-cooled screw compressor, even if oil is accumulated in a space provided with a rotor provided in a casing, the oil is accelerated at a stroke and reaches a normal operation speed.

  On the other hand, in this embodiment, at the time of start-up, the rotor is rotated only for a certain period at a sufficiently low rotational speed compared to the normal operation speed, and then accelerated to the normal rotational speed. Specifically, for example, in a compressor having a rated operation speed of 3000 revolutions per minute, the rotor is rotated at a rotational speed of 300 revolutions per minute or less for about 3 seconds or about 5 revolutions of the rotor. is there.

  This compressor is started only after the temperature is detected by the temperature sensing means when the start-up temperature is lower than a predetermined temperature, after rotating for a certain period at a sufficiently low rotation speed compared to the normal operation speed. You may make it accelerate to a rotational speed.

  Further, at the time of stop, when the compressor receives a stop command during operation, an operation for stopping the electric motor is performed, and at the same time, an operation for releasing the high pressure remaining in the piping connected to the casing discharge side is performed. Therefore, the high pressure on the discharge side gradually decreases to the same level as the suction side pressure. Thereafter, the rotor is controlled to rotate at a low speed for a short time.

  In addition, a flow path that communicates with the oil reservoir located below the suction side space in which the rotor is housed is provided, and it is allowed to flow only in the oil storage direction from the rotor storage space in the middle of the flow path. A check valve may be provided.

  Next, specific examples will be described. A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a schematic view showing an oil-cooled screw compressor for air. FIG. 2 is a graph showing changes in the rotational speed of the rotor before and after startup.

  The air compressor 1 includes a compressor main body 2 therein, and male and female rotors 3 and 4 meshed with each other are rotatably provided therein. Each rotor 3, 4 has a thread-like tooth groove on its axial surface.

  The casing 5 that houses both rotors has an internal space that closes the outer circumference in the axial radial direction and the end face in the axial direction of the rotors 3 and 4. In this internal space, a suction port 6 that is an opening for sucking in the compressed gas and a discharge port 7 that is an opening for discharging the compressed gas are provided in the internal space.

  The flow path beyond the discharge port 7 once extends in the axial direction and then bends downward and makes a U-turn, is located at the lower part of the compressor body 2 and is provided with the casing 5 and an oil separator 8 provided integrally therewith. Connect with.

  The shaft that is a part of the male rotor 3 is connected to the rotating shaft of the electric motor 9. The electric motor 9 generates rotational power for rotating the male rotor 3 with electric power supplied from the inverter 10 which is a power supply device. The inverter 10 controls the frequency and voltage of power to be sent to the electric motor 9 based on a command from the control device 11 that is an attached motor control device.

  A temperature sensor 12 is provided on the downstream side of the discharge port 7 as temperature detection means, and its output is input to the control device 11. This temperature sensor 12 is for monitoring the discharge temperature of the compressor and determining the presence or absence of abnormality.

  The oil separator 8 centrifuges the oil discharged from the compressor main body 2 by being mixed with the compressed air by the principle of the cyclone separator, and the oil drops and accumulates in the lower part inside. The oil is injected into the working chamber 14 immediately after the start of compression of the compressor body 2 and the bearing 15 supporting the rotors 3 and 4 from the pipe line drawn from below the oil separator 8 through the oil cooler 13. The oil separator 8 has a high pressure substantially equal to the discharge pressure, and the internal pressure of the working chamber 14 and the pressure around the bearing 15 are slightly higher than the suction pressure but lower than the internal pressure of the oil separator 8. Therefore, the oil supply mechanism in this embodiment forms a differential pressure oil supply mechanism that can supply oil with a differential pressure without providing an oil pump between the oil separator 8 and the working chamber 14 or the bearing 15. Yes. With these configurations, the oil injected into the working chamber 14 is mixed with the flow of compressed air, exits from the discharge port 7, and returns to the oil separator 8 and circulates again.

  There is an outlet for compressed air at the upper center of the oil separator 8, which is connected to a flow path of compressed air from which most of the oil has been separated. An air discharge channel branched from the flow channel is provided, and an electromagnetic valve 16 is provided immediately after branching. The electromagnetic valve 16 opens and closes according to instructions from the control device 11. The secondary (downstream) side of the solenoid valve 16 opens the compressed air to the atmosphere via a silencer. As will be described later, the electromagnetic valve 16 is controlled to be closed during operation and open when stopped.

  When the user performs a stop operation, such as turning off the switch, on the control device 11 of the compressor 1 in the operating state, the control device 11 instructs the inverter 10 to decelerate and stop. Immediately, the inverter 10 decreases the frequency of the power supplied to the electric motor 9 and stops. The rotation of the motor 9 and the male rotor 3 directly connected to the output shaft and the female rotor 4 meshed with the motor 9 are also stopped immediately after the supply power is stopped, although there is a slight delay due to inertia. The control device 11 issues an instruction to open the solenoid valve 16 almost simultaneously with the instruction to stop the electric motor 9. Compressed air in the high pressure pipe connected to the oil separator 8 and further downstream from the discharge port 7 of the compressor main body 2 is discharged to the atmosphere through the opened electromagnetic valve 16, and the internal pressure of the space is about 10-30. It gradually decreases over a period of seconds. During this time, since the differential pressure between the oil separator 8 and the working chamber 14 remains, the injection of oil into the stopped working chamber 14 continues for a while after the rotor stops. This oil remains in the working chamber 14 even after the pressure difference disappears, and gradually cools to the ambient temperature when the oil stops for a long time.

  Next, the starting process of the oil-cooled screw compressor of this embodiment will be described.

  When the start switch of the compressor is pressed, if the temperature sensor 12 senses that the temperature of the surrounding environment is a predetermined temperature, for example, 10 ° C. or less, the control device 11 judges and normal start is Adopt different low temperature mode. As shown in FIG. 2, in the normal mode, the rotor is accelerated immediately after the start at time T0 and accelerated to the rotational speed N during normal operation. By doing so, the compressed air which a user needs can be supplied quickly. In the low temperature mode, the motor is rotated at a low speed Ns for a certain period (T0 to T1) immediately after starting. As a specific example, it is assumed that the rotor is rotated at a speed of about 300 revolutions per minute for 3 seconds. After that, it accelerates at once to the rotational speed N (3,000 to 4000 revolutions per minute) during normal operation.

  The reason why the rotor is rotated at a low speed Ns for a certain period at low temperature is to discharge the oil accumulated in the working chamber 14. The torque required to discharge the oil has a correlation with the rotational speed of the rotor, and even if the oil has a high viscosity at a low temperature, the torque can be reduced if it is extruded at a low speed. In addition, since the amount of oil accumulated inside is limited, if the rotor is rotated, for example, about 5 rotations or for 1 to 2 seconds, most of the oil accumulated due to the nature of the screw rotor is discharged from the discharge port 7. Can do. After the oil is discharged, no oil discharge torque is generated, so that the motor 9 and the inverter 10 can be accelerated without imposing a burden.

  Further, if the engine is rotated several times at a low speed before accelerating at once, the load is increased after the oil is distributed to mechanical elements such as bearings and shaft seals that require oil lubrication. This has the effect of improving the lubrication conditions, and can enjoy the effect of preventing wear of these machine elements and thus extending their life.

  The described startup process is particularly effective when starting after a long stop. When it is desired to accelerate at a low temperature even at low temperatures, there is a method including a large capacity electric motor 9 and an inverter 10 with a margin. However, providing a large-capacity device that is not necessary during steady operation is wasteful in terms of both energy efficiency and manufacturing cost. Therefore, according to the configuration of the present embodiment, the oil-cooled screw compressor can be started smoothly even in a low temperature environment without sacrificing cost increase and energy efficiency during steady operation.

  Further, when the ambient temperature is sufficiently high, it is possible to supply compressed air quickly by acceleration as usual. Since oil is accumulated in the working chamber 14 during the stop period, an antirust effect inside the compressor can be expected. Further, in this embodiment, it is not necessary to add expensive parts to the conventional air compressor, and the design can be easily changed.

  The motor drive system of the present embodiment is an example of a model that performs variable speed operation with an inverter that is highly necessary due to semiconductor current limitation. However, a model that operates at a constant speed without an inverter has similar effects and effects. The same effect can be obtained even in a model in which the output shaft of the electric motor 9 and the input shaft of the male rotor 3 are not directly connected and a power transmission means such as a shaft coupling, a gear, or a belt is interposed therebetween. However, in the method of driving with an induction motor via a belt, the instantaneous starting torque peak is alleviated by a soft belt, and an induction motor that does not go through an inverter using a semiconductor also generates excessive torque if it is instantaneous. Therefore, the configuration of this embodiment is not necessarily required. In this embodiment, the air compressor is taken as an example, but the same effect can be obtained even in an oil-cooled screw compressor for the purpose of compressing other gases such as refrigerant gas and fuel gas.

  In this embodiment, the rotor is rotated at a low speed Ns for a certain period, but the low speed Ns is not necessarily a constant speed. For example, if the rotational speed N is sufficiently low during normal operation, the same effect can be obtained even if the vehicle is gradually accelerated.

  Another embodiment of the present invention will be described with reference to FIG. FIG. 3 is a graph showing the time variation of the rotational speed of the rotor, the discharge side pressure, the amount of injected oil, and the amount of oil accumulated in the working chamber in the air oil-cooled screw compressor. is there. In this embodiment, the description of the structure, operation and effect common to the first embodiment and the applicable range will be omitted.

The device configuration of the air compressor in the present embodiment is the same as that of the first embodiment shown in FIG. 1, but the software built in the control device 11 is different, and the stopping operation is different from the conventional procedure.
Further, the temperature sensor 12 is not necessarily required.

  The present embodiment is characterized by a stop operation, and its operation will be described with reference to FIG.

  The stop operation is performed at time T5, for example, when the user turns off the operation switch of the screw compressor 1 that is in the operating state and supplies compressed air at the rotational speed N and the discharge pressure Pd. Immediately, the control device 11 instructs the inverter 10 to stop, the inverter 10 decreases the frequency of the power supplied to the electric motor 9, and stops the power supply at time T6 (as a specific example, after 2 to 5 seconds). At the same time, the rotational speeds of the electric motor 9 and the rotors 3 and 4 are gradually decreased, and the operation is stopped at about time T6.

  The control device 11 issues an instruction to open the valve to the electromagnetic valve 16 at approximately the same time T5 as the stop instruction of the electric motor 9. Compressed air is discharged to the atmosphere from the discharge port 7 of the compressor body 2 through the oil separator 8 and further through the high-pressure pipe line connected downstream to the electromagnetic valve 16, and the pressure in the pipe line is the discharge pressure during operation. The temperature gradually decreases from Pd over a period of about 10 to 30 seconds, and reaches approximately atmospheric pressure Pa at time T6. Since there is a time difference from time T6 to time T7, the pressure difference remains for a while after the rotor stops rotating, and oil injection into the stopped working chamber 14 continues. As shown in FIG. 3, during operation, the oil that has been discharged one after another due to the rotation of the rotor suddenly accumulates in the working chamber 14 from time T6 when the rotor is stopped and stops increasing until time T7.

  In the conventional oil-cooled screw compressor, the next start-up is performed with this oil accumulated. This embodiment is characterized by the subsequent operation.

  At time T8 when the residual pressure becomes sufficiently low, the control device 11 instructs rotation at a low speed Ns for only a short time (T8 to T9), and the inverter 10 drives the motor 9 at a low frequency to drive both rotors 3, 4 Rotates at a low speed Ns of about 100 revolutions per minute, and the oil accumulated in the working chamber 14 is discharged from the discharge port 7. At this time, the compressor body 2 as a whole is not so much lowered from the temperature during operation and the viscosity of the oil is low, so that the torque required for discharging is light and the rotors 3 and 4 can be rotated easily. Further, since the rotation is low speed and short time and the solenoid valve 16 is kept open, the pressure on the discharge side does not increase, and no oil is sent from the oil separator 8 to the working chamber 14.

  Therefore, most of the oil accumulated in the compressor body 2 due to the rotation of the rotors 3 and 4 is discharged at time T9 when the low-speed operation ends. In this state, the stop operation is completed and the system waits for the next activation. Note that the time T8 at which the low speed operation is started and the time T9 at which the low speed operation is started are determined based on T5 that is stopped by the timer function built in the control device 11.

  In the next start after the above stop operation, a large amount of oil is not collected around the rotor even in a low temperature environment, and the torque required for oil discharge is not a problem level. Therefore, smooth and reliable start-up is possible without increasing the capacity of the electric motor 9 and the inverter 10.

  The rotation of the rotor at a low speed in a short time in the process of the stop operation is controlled by setting of software built in the control device 11. The amount of this rotation may be controlled by a time such as 2 to 3 seconds, or may be controlled by the total number of rotations such as 5 to 10 rotations. In any case, a sensor for detecting the amount of oil and torque is unnecessary, and no major design change is required other than the software change compared to the conventional model.

  According to the present embodiment, the object of the present invention can be achieved without making a major design change to the conventional model. Moreover, since it can accelerate immediately after starting even at low temperatures, compressed air can be supplied in a short time after the switch is turned on.

  The following embodiment of the present invention will be described with reference to FIG. FIG. 3 is a graph showing the time variation of the rotational speed of the rotor, the discharge side pressure, the amount of injected oil, and the amount of oil accumulated in the working chamber in the air oil-cooled screw compressor. is there. In this embodiment, the description of the structure, operation and effect common to the first embodiment and the applicable range will be omitted.

  The equipment configuration of the air compressor in this embodiment is the same as that of the first embodiment shown in FIG. 1, but no special control device and control software are required. Further, the temperature sensor 12 is not necessarily required.

Instead, of the space inside the casing 5 in which the male and female rotors 3 and 4 are housed, a communication passage 21 is provided that communicates from the lower portion of the suction chamber 25 on the suction side to the upper space 26 of the oil separator.
A valve chamber 22 having a wide cross-sectional area is provided in the middle of the communication passage 21, and a spherical valve body 23 that can move freely is housed therein. Below the valve chamber, a plurality of projections 24 are provided inward from the wall surface of the valve chamber to prevent the valve body 23 from passing through, thereby preventing the drop. On the other hand, the part connected to the communication path 21 at the upper part of the valve chamber 22 is configured to be closed by the valve body 23.

  In the operating state of the compressor, the pressure in the oil separator upper space 26 becomes higher than the pressure in the suction chamber lower portion 25 due to the action of compression. Therefore, the valve body 23 is pushed up to the upper end of the valve chamber 22 and closes the communication path 21. Therefore, the high-pressure gas that has been compressed does not return to the lower portion 25 of the suction chamber.

  When the compressor is stopped, the internal pressure becomes uniform, and the valve body 23 falls downward due to gravity and is caught by the protrusion 24. The outer diameter of the valve body 23 is smaller than the inner diameter of the valve chamber 22, and a gap is also opened around the protrusion 24. Therefore, the oil that passes from the lower portion of the suction chamber 25 to the oil separator upper space 26 through the communication passage 21 and accumulates in the suction chamber falls through the communication passage 21 to the oil separator 8 by gravity. Therefore, there is little oil around the rotors 3 and 4 at the next restart, which does not hinder the start.

  According to the present embodiment, the object can be achieved without adding a special electrical or control function. Therefore, it is possible to adopt a model that does not have a variable speed function, such as an inverter, assuming that it operates at a constant speed.

  In this embodiment, as a check valve, a circular hole is closed with a sphere, and gravity is used when opening. Of course, other types of check valves may be used as long as they have the same function, and a plate-like valve body that opens and closes by a hinge or a system that opens by the action of a spring may be used.

DESCRIPTION OF SYMBOLS 1 Air compressor 2 Compressor main body 3 Male rotor 4 Female rotor 5 Casing 6 Suction port 7 Discharge port 8 Oil separator 9 Electric motor 10 Inverter 11 Controller 12 Temperature sensor 13 Oil cooler 14 Working chamber 15 Bearing 16 Solenoid valve 21 Station Passage 22 Valve chamber 23 Valve body 24 Projection 25 Lower suction chamber 26 Upper space of oil separator

Claims (4)

A casing, a pair of rotors built in the casing and having thread-like tooth grooves, an electric motor that rotationally drives these rotors, a control device that controls the electric motor, and the tooth grooves of the pair of rotors An oil-cooled screw having an oil supply mechanism that supplies oil into a working chamber formed by being surrounded by the rotor and the casing, and an oil separation mechanism that separates oil from the compressed gas discharged from the working chamber In the compressor,
While the rotor is in a rotation stop state from the normal operation state, and the motor is started from the rotation stop state and the rotor is in a normal operation state, the control device is a space in a casing that houses the pair of rotors. Discharging at least part of the oil supplied to the outside of the space,
When a stop command is received, the motor is stopped to stop the rotation of the rotor, and high pressure compressed air remaining in the discharge pipe connected to the casing and communicating with the discharge port of the working chamber is removed. An oil-cooled screw compressor, wherein the rotor is rotated for a predetermined time after the pressure in the discharge port is reduced to the pressure of the suction port that opens to the atmosphere and communicates with the working chamber. The oil-cooled screw compressor according to claim 1,
The oil supply mechanism supplies oil into the working chamber using a differential pressure between the gas pressure of the gas separated by the oil separation mechanism and the gas pressure before discharge in the working chamber, and the oil separation An oil sump for storing oil separated by the mechanism; and a flow path for connecting the space supplied with the gas separated by the oil separation mechanism and the working chamber in a pressure state before discharge. Oil-cooled screw compressor. The oil-cooled screw compressor according to claim 1,
The electric motor is driven by a current passing through the control device, and an output shaft of the electric motor and a rotary shaft of the rotor are connected to each other. The oil-cooled screw compressor according to claim 1,
An oil sump for storing the oil separated by the oil separation mechanism below the space in which the rotor is accommodated, a flow path communicating with the oil sump, and the oil sump direction from the space in which the rotor is accommodated in the middle of the flow path An oil-cooled screw compressor, characterized by having a check valve that allows flow only into the valve.

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