JP2010203458A - Oil-free screw compressor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simplify structure and improve reliability of an oil-free screw compressor by commonly using parts on the compressor body side and parts on the electric motor side by eliminating the need for a step-up gear for output of an electric motor and a suction throttle valve. <P>SOLUTION: A compressor body 1 and a high speed motor 21 are directly coupled via a driving side gear 19 and a driven side gear 18 of the constant velocity ratio. High speed motor side bearings 29 and 30 respectively use the same size as compressor body side bearings 6 and 13. Visco-seals 41 and 42 arranged in both end parts of a motor shaft 25 use the same object as a visco-seal 11 arranged in both end parts of a male rotor 2 and a female rotor 3. The high speed motor 21 is driven by using a high frequency type inverter 20. The electric motor side and the compressor body side are formed as a pseudo symmetric rotary shaft structure with a constant velocity gear part as the center. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an oil-free screw compressor that rotates a pair of screw rotors synchronously without contact, and particularly to an oil-free screw compressor that is suitable for being driven by a high-speed motor.

  In a conventional oil-free screw compressor, for example, as described in JP-A-6-346881, the rotational speed of an electric motor is increased using a belt and gears, and the screw compressor body is rotated. Japanese Patent Laid-Open No. 3-151592 describes an example in which an increase gear device in which an increase gear is housed in a casing is connected via a coupling to a rotor shaft having a screw tooth profile. Yes.

  In addition, in the screw compressor, in addition to operation control such as loading and unloading, capacity control for controlling the opening and closing of the suction throttle valve is performed in accordance with the consumption request of the demand source. As an example of this capacity control, Japanese Patent Laid-Open No. 59-93989 discloses a suction throttle valve valve plate attached to the tip of an air cylinder that operates at the pressure of the compressor itself. The amount is adjusted in two steps.

JP-A-6-346881 Japanese Patent Laid-Open No. 3-151592 JP 59-93989 A

  By the way, the compressor described in the above-mentioned Japanese Patent Application Laid-Open No. 6-346881 includes, in addition to a gear case housing a speed increasing gear, a bearing for rotating and supporting the speed increasing gear, a rotating shaft for mounting the speed increasing gear, and a speed increasing power. Many parts such as a belt and a pulley for transmitting the power are necessary, which contributes to the high cost of the compressor. Further, in this compressor, the electric motor for driving the screw rotor is also increased in size, which is insufficient in terms of downsizing the entire compressor unit including a frame for fixing the electric motor.

  Further, in the compressor described in Japanese Patent Application Laid-Open No. 3-151592, the speed increase ratio of the speed increasing gear is increased because the speed is not increased by the belt, and the gear case that accommodates the speed increasing gear is enlarged. . And, when it is serialized as a general-purpose compressor, it is necessary to combine various compressor bodies and speed increasing gear devices, which has been a factor of high cost in terms of product lineup.

  Further, in the compressor described in Japanese Patent Application Laid-Open No. 59-93989, a three-way solenoid valve is connected to the air cylinder in order to supply the operation air of the suction throttle valve to the air cylinder every time the line pressure fluctuates. The air cylinder operating air supply hole is switched by a solenoid valve. Thus, it is necessary to provide a three-way solenoid valve, which is expensive and complicated in the configuration of the flow rate control system. Moreover, in order to cancel the unloading at the time of starting, a plurality of three-way solenoid valves are required, and the structure of the capacity control device becomes complicated.

  In any of the compressors described above, although some consideration has been given to downsizing the compressor, further downsizing is desired. An object of the present invention is to simplify the structure of the compressor unit, in view of the above-mentioned problems of the prior art. Another object of the present invention is to realize a compressor unit that is downsized and has a high degree of freedom in installation. Still another object of the present invention is to realize an inexpensive compressor unit with reduced cost. Still another object of the present invention is to realize a highly reliable compressor unit by sharing the components on the compressor body side and the components on the electric motor side.

To achieve the above object, the present invention provides a motor shaft to which a motor rotor is attached, a motor casing that holds a motor stator disposed facing the motor rotor, a male rotor in which a screw-shaped male tooth shape is formed, A high-speed motor driven by a high-frequency inverter in an oil-free screw compressor provided with a female rotor having a screw-shaped female tooth shape and a casing for housing the male rotor and the female rotor. The high-speed motor is connected to a motor shaft on which a motor rotor is formed, and a load provided on the compressor side that rotatably supports the motor shaft. A shaft having the same size as the suction-side bearing of the rotor, and a load-side bearing of the high-speed motor. Each of the bearings supporting the rotor of the compressor, and the bearings supporting the motor shaft. The shaft seal device is configured with a screw seal so as to prevent the lubricating oil that lubricates each bearing supporting the compressor rotor from entering the compression chamber, and further, the load on the motor shaft Provided with a shaft seal device that prevents the lubricating oil that lubricates the side bearing and the anti-load side bearing from entering the inside of the high-speed motor, and the shaft seal device of this motor and the shaft seal device of the compressor are screw seals of the same size The rotational speed of the high-frequency motor and the rotational speed of at least one of the male rotor and female rotor are the same, and a first gear is provided on one end of the shaft of the male rotor or female rotor. Wherein one end side of the high frequency motor is provided a second gear meshed with the first gear, the gear ratio of the first and second gears of the gear was set to 1: 1.

  Further, according to the present invention for achieving the above object, in the oil-free screw compressor, the first gear is engaged with the shaft end of the male rotor and the first gear is engaged with the load side shaft end of the high-frequency motor. The second gear was fitted, and the gear ratio between the first gear and the second gear was in the range of 2: 1 to 1: 2.

  Furthermore, the present invention for achieving the above object includes an inverter, an electric motor driven by the inverter, and a compressor main body driven by the electric motor, and the rotation speed of the compressor main body is controlled by the inverter. In the oil-free screw compressor, heat radiating fins are formed on the outer periphery of the casing housing the male rotor and the female rotor and the motor casing housing the high-speed motor.

As described above, the present invention has the following effects.
(1) A speed increasing device such as a speed increasing gear or a belt is not required, and the oil-free screw compressor unit can be reduced in size, weight, and cost.
(2) A capacity control device such as a suction throttle valve or a three-way solenoid valve is not required, and the structure of the oil-free screw compressor unit can be simplified and the cost can be reduced.
(3) Since the vibration-mechanical configuration of the motor system and the compressor main body system is shared, a highly reliable rotating system can be adopted for these motor system and compressor main body system. A possible oil-free screw compressor unit can be provided.
(4) By sharing the parts of the electric motor system and the compressor main body system, it is possible to reduce the cost and improve the reliability of the oil-free screw compressor.

It is a figure which shows one Example of the oil free screw compressor which concerns on this invention, and the longitudinal cross-sectional view seen from the upper surface. The longitudinal cross-sectional view seen from the front of the oil free screw compressor shown in FIG. The detailed longitudinal cross-sectional view of the load side bearing part vicinity of the oil-free screw compressor shown in FIG. The detailed longitudinal cross-sectional view of the non-load side bearing part vicinity of the oil-free screw compressor shown in FIG. The longitudinal cross-sectional view seen from the upper surface of the other Example of the oil free screw compressor which concerns on this invention. The front view when the oil-free screw compressor which concerns on this invention is packaged. It is the side view of the Example shown in FIG. 6, and the figure which showed a part in cross section. The system diagram of the compressed air of the oil free screw compressor which concerns on this invention.

  An embodiment of the present invention will be described with reference to FIGS. 1 is a cross-sectional view of an oil-free screw compressor driven by a high-speed motor according to the present invention, FIG. 2 is a cross-sectional view of a front view, and FIGS. 3 and 4 are motor shaft supports. It is a longitudinal cross-sectional view which shows the detail of a part. In the compressor main body 1, a pair of male rotor 2 and a tooth groove portion of a female rotor that are meshed with each other are housed in a casing 4, and a driving side is housed in a suction-side casing 5. The male rotor 2 and the female rotor 3 are rotatably supported by a suction side bearing 6 and a discharge side bearing 7 to which lubricating oil is forcibly lubricated. The suction side bearing 6 is a cylindrical roller bearing, and the discharge side bearing 7 is an angular ball bearing combined with a cylindrical roller bearing.

  A pair of timing gears 8 and 9 are fitted to the discharge side shaft ends of the male rotor 2 and the female rotor 3, and the tooth groove portions of the male rotor 2 and the female rotor 3 are rotated synchronously. A shaft seal device is provided between the suction side bearing 6 and the discharge side bearing 7 and the tooth groove portions of the male rotor 2 and the female rotor 3. This shaft seal device includes an air seal 10 that reduces leakage of air from the compression chamber formed by the tooth groove portions of the male rotor 2 and the female rotor 3 and the casing 4 as much as possible, and lubricating oil supplied to the bearing portion to the compression chamber. A screw seal 11 called a visco seal that prevents intrusion is provided.

  A cooling jacket 12 is provided on the outer peripheral portion of the casing 4 and liquid coolant such as cooling water or coolant is supplied. A part of the heat generated inside the compressor body 1 exchanges heat with the supplied cooling water or liquid refrigerant, and is heated to be discharged to the outside.

  The high-speed motor 21 includes a motor shaft 25 having a rotor core 26 attached at the center, and a load side bearing 29 and an anti-load side bearing 30 that rotatably support the vicinity of both ends of the motor shaft. Further, a stator core 27 around which a stator coil 28 is wound is held by a motor casing 23 so as to face the rotor core 26. A load side bearing 29 that supports the motor shaft 25 is held, and a load side bearing cover 22 that forms a casing together with the motor casing 23 is provided at the end of the load side shaft. Similarly, an anti-load side bearing cover 24 that holds the anti-load side bearing 30 that supports the motor shaft 25 and constitutes a casing together with the motor casing 23 is provided at the end portion of the anti-load side shaft. The non-load side bearing cover 24 is formed with an outlet portion (not shown) for taking out the lead wire 31 of the stator coil 28.

  A cylindrical roller bearing that bears a radial load is used as the load side bearing 29, and a combined angular ball bearing that can bear both a radial load and a thrust load is used as the anti-load side bearing 30. The size of each of these bearings is the same as, for example, the compressor body side. Further, the load side bearing 29 and the anti-load side bearing 30 are fixed to the bearing retainers 32 and 33 after being fitted to the covers 22 and 24 on the outer peripheral surface. Oil supply holes 34 and 35 are formed in the bearing retainers 32 and 33.

  Between the load side bearing 29 and the rotor core 26, and between the anti-load side bearing 30 and the rotor core 26, a shaft seal device is provided to prevent the lubricating oil from entering the stator coil side. As shown in detail in FIGS. 3 and 4, the shaft seal device includes visco seals 41 and 42, wave springs 44 that press the bisco seals 41 and 42, and bisco seals 41 and 42 via a retaining ring 45. And a seal presser 43 that holds the cover 22 and 24 on the cover. The visco seals 41 and 42 have a minute gap between the inner diameter side and the motor shaft 25. Further, on the inner diameter side of the Bisco seals 41 and 42, a screw seal having a square thread groove is formed. A motor-side cooling jacket 47 is provided on the outer periphery of the motor casing 23 in order to dissipate heat generated by the high-speed motor, and liquid coolant such as cooling water or coolant is supplied to the cooling jacket. The

  A motor-side flange 46 is formed at the end of the load-side bearing cover 22 on the compressor main body side, and is coupled to the flange 16 formed on the casing 4 with a bolt. A drive side gear 19 is fitted to the load side shaft end of the motor shaft 25, and a driven side gear 18 is fitted to the suction side shaft end of the male rotor 2. The gears 18 and 19 have the same number of teeth, and the speed increasing ratio is 1: 1. The lead wire 31 of the high speed motor is connected to the high frequency inverter 20.

  When the high-frequency inverter 20 is energized, power is supplied to the high-speed motor 21 side. As a result, the rotational force generated in the motor shaft 25 is transmitted to the male rotor 2 via the pair of gears 18 and 19, and the air is compressed by the engagement of the rotor tooth groove portions of each rotor.

  Lubricating oil is guided from an oil pump (not shown) to oil supply holes 34 and 35 via oil supply nozzles 36 and 37, and jetted from the oil supply holes 34 and 35 into the bearing. The lubricating oil that has lubricated and cooled the bearings is discharged out of the machine through the oil discharge holes 38 and 39, and is finally collected by the oil sump device. The lubricating oil passes between the bearing inner ring and the outer ring when lubricating the bearing. Thereafter, the lubricating oil discharged from the bearing flows into the visco seals 41 and 42, but when the motor shaft 25 rotates, pressure is generated in the groove portion on the inner diameter side of the visco seal, and the lubricating oil is returned to the bearing side. As a result, oil can be prevented from entering the motor coil 28 side.

  The stator core 27 and the stator coil 28 in the high-speed motor 21 generate heat due to electrical losses such as iron loss and copper loss. The motor 21 can be cooled by heat-exchanging liquid refrigerant such as cooling water to the motor 21 whose temperature has been increased by this heat generation and the cooling jacket 47 provided in the motor casing 23.

The oil-free screw compressor has a single-stage output of 55 kW class and a discharge pressure of 7 kgf / cm ² , the male rotor diameter is about 90 mm and the rotational speed is about 20000 rpm. If the gear ratio between the driving gear and the driven gear is 1: 1, if the number of poles of the high-speed motor is two, the set frequency of the high-frequency inverter is about 330 Hz.

  By the way, in the present embodiment, in order to realize common parts and stable high-speed rotation, the compressor main body side and the high-speed motor side have substantially the same structure in terms of vibration mechanics. In other words, the compressor main body and the electric motor are connected by a gear provided at the shaft end of their rotating shafts. Considering the shaft divided at this part, the motor shaft, female rotor shaft, male rotor shaft support section The structure is similar. Specifically, the bearings 13 and 30 that support the shafts are the same model number, and the bearings 6, 7, and 29 are the same model number. Further, the visco seals 11 and 24 have the same shape. Further, the lubrication method for the bearing is also spray lubrication, which is the same in that a cooling jacket is provided on the outer peripheral side of the motor and the outer peripheral side of the compressor body.

  Since the compressor body is connected to the high-speed motor with a gear ratio of 1: 1, that is, constant speed gears, if the high-speed motor is increased to the specified rotational speed of the compressor with a high-frequency inverter, the compressor specifications The rotational speed can be obtained as it is. Therefore, according to the present invention, all the speed increasing devices are unnecessary. Since the high-speed motor is used in a high rotation speed range, the required motor torque is reduced. Therefore, the stator core and the stator coil can be reduced in size. Thus, if the compressor body is connected to the high-speed motor at a speed increase ratio of 1: 1, the size of the entire drive system for driving the compressor can be reduced, and the compressor unit can be reduced in size and cost. .

  In this embodiment, the high-speed motor and the compressor body are connected by a gear having a 1: 1 speed increase ratio, but the speed increase ratio is not limited to this, and the speed reduction ratio is reduced from 2: 1 to 2: 1. If it is up to about 1: 2, it is not necessary to increase the size of the motor and the size of the gear used for deceleration or speedup, so the effect of the present invention can be obtained. However, if the speed increasing ratio is increased, the motor can be reduced in size, but the size of the speed increasing device and the cost required for this speed increasing device are undesirably increased. On the other hand, the speed reduction device is used by further increasing the motor rotation speed. However, it is difficult to increase the speed of the motor, which is not practical. Further, in this embodiment, the motor shaft and the rotating shaft of the male rotor are connected using a gear, but a constant velocity coupling such as a gear coupling or a diaphragm coupling, or a combination of a spline and a spline coupling, etc. Needless to say, it may be a quick coupling means.

  Next, another embodiment of the present invention will be described with reference to FIG. When the parts shown in FIG. 5 and the parts shown in the above embodiment are the same, the same reference numerals are given. This embodiment is different from the embodiment shown in FIG. 1 in that the shaft of the male rotor 2 of the compressor body 1 and the motor shaft of the high-speed motor 21 are integrally formed. In other words, the compressor body 1a and the individual components on the high-speed motor side are basically the same as those in the upper air embodiment except that the male rotor shaft and the rotary shaft of the high-speed motor are connected.

  A stator core 27 and a stator coil 28 are attached to the motor casing 23a. A rotor core 26 of a high-speed motor is attached to the suction side shaft portion 2b of the male rotor 2a having a male tooth shape formed in the middle. The male rotor 2a is rotatably supported by the discharge-side bearings 7 and 13 at the shaft end side from the male tooth-shaped portion and by the anti-load side bearing 30a at the end portion side from the rotor core 26. Similarly to the male rotor 2a, the female rotor 3a is supported on the discharge side by the discharge side bearings 7 and 13 and on the suction side by the suction side bearing 6a. However, unlike the above embodiment, no gear is attached to the suction side end. Cylindrical roller bearings and combined angular bearings are used as the suction side bearings 7 and 13 of the male rotor and the female rotor, and grease lubricated roller bearings 6a are used as the suction side bearing 6a on the female rotor side. As cooling structures for dissipating heat generated by the compressor main body and the restraining motor, radiating fins 48 and 49 are formed on the outer peripheral portion of the casing 2 and the outer peripheral portion of the motor casing 23, respectively.

  In this embodiment configured as described above, the suction side bearing and shaft seal device on the male rotor side, the load side bearing and shaft seal device on the high speed motor side, and the gear for transmitting the power of the high speed motor are compared with the previous embodiment. This eliminates the need to reduce the size and cost of the drive system including the compressor body. In this embodiment, the shaft of the male rotor is shared with the motor shaft, but it goes without saying that the shaft of the female rotor may be shared with the motor shaft.

  Next, a state in which the oil-free screw compressor in which the compression main body and the electric motor described in any of the above-described embodiments are integrally formed will be described with reference to FIGS. 6 and 7. After the compressor main body and the high-speed motor are integrated, this integrated assembly is arranged on the upper part of the main body frame 51 that also serves as a cooler. The main body mount 51 is divided to form two rooms. The first chamber 51a is a room for storing a cooler for compressed air, and includes a precooler 52 that primarily cools the air, an aftercooler 53 that cools the air secondarily, and a discharge cooler 54 that cools the discharged air during unloading. Is housed. The second chamber 51b is a chamber used as an oil sump, and stores an oil cooler 55 that cools the lubricating oil.

  The precooler 52, the aftercooler 53, and the discharge cooler 54 are each provided with a U-shaped cooling pipe, and cooling water is passed to the outside of the pipe. On the other hand, the oil cooler 55 is also provided with a U-shaped cooling pipe, and the lubricating oil is guided to the outside of the pipe. A header 57a to which a check valve 56 is attached is provided on the side surface of the first chamber 51a of the main frame, and a cooling water header 57b having a cooling water inlet / outlet is provided on the side surface of the second chamber 51b. . The compressor body 1 and the precooler 52 are connected by a discharge pipe 58, and the oil discharge ports 35 and 36 of the high-speed motor 21 and the oil cooler 55 are connected by oil discharge pipes 59 and 60. A suction filter 90 is attached to the suction side of the compressor body 1, and an air discharge pipe 93 with an air discharge valve 91 interposed is attached to the discharge side. An air release silencer 83 is attached to the tip of the air discharge pipe. The main body base 51, the compressor main body 1, the high-speed motor 21, the suction and outlet piping systems are housed in a housing 95 to constitute a package type oil-free screw compressor.

  The length of the pipe that connects the integrated assembly and each cooler by assembling the compressor body and high-speed motor together and placing this integrated assembly directly above the main body frame that houses the precooler, aftercooler, etc. In addition, by making the longitudinal dimensions of the main body frame approximately the same as the longitudinal dimensions of the integrated assembly, the wasteful space in the compressor package can be reduced, and the compressor unit can be made smaller and lighter. can do.

  Next, the case of controlling the rotational speed of the oil-free screw compressor described in the embodiment shown in FIG. 1 or FIG. 5 using an inverter will be described with reference to FIG. In a conventional oil-free compressor, an unloader assembly is disposed on the suction side of the compressor body. The unloader assembly includes an air cylinder, a suction throttle valve, an air release valve, an unloader body, and the like.

  On the other hand, in this invention, the capacity | capacitance control apparatus is not provided in the suction side of a compressor, but the suction filter 90 is arrange | positioned directly. Further, the compressor main body 1, a precooler 52 that primarily cools high-temperature compressed air, a check valve 56, and an aftercooler 53 that secondarily cools high-temperature compressed air are connected in order by a discharge pipe 58. An air discharge pipe 93 is disposed on the primary side of the check valve 56 and on the secondary side of the precooler, and the air discharge electromagnetic valve 91 is provided in the air discharge pipe 93. The operation of the air release valve 91 is changed according to the operating state of the compressor and the rotational speed of the compressor body. This operating state is shown in Table 1.

なお、ここでは圧縮機本体の最高使用回転数を２００００rpmとし、その半分の１００００rpmをアンロード時回転数、すなわち下限の回転数としている。

Here, the maximum use rotation speed of the compressor main body is 20000 rpm, and half of the rotation speed is 10,000 rpm, that is, the lower limit rotation speed.

  At the time of start-up, the compressor body is accelerated to the maximum number of rotations by a control device (not shown). At this time, when the air release valve 91 is opened, the compressed air is released, and the discharge pressure is further lowered, so that the load on the inverter side can be reduced. During loading, the pressure sensor 92 detects an increase or decrease in the amount of air used on the demand side line, and the inverter rotates the compressor body so that the pressure at the compressor unit outlet detected by the pressure sensor 92 is constant. The number is controlled, thereby controlling the amount of discharge air.

  When the amount of air used decreases in the load state, the control device decreases the compressor rotation speed. As the amount of air used decreases, the compressor speed reaches the lower limit of 10000 rpm. In this state, when the pressure sensor 92 further detects a pressure increase, the control device determines that the compressor is in the unload operation normal state, and the control device issues a command to open the air release valve 91. When the release valve 91 is opened and compressed air is discharged, the operating speed of the compressor is at the lower limit, the discharge pressure is low, and the compressor power is also low. In the present embodiment, an electromagnetic valve that can be electrically opened and closed by the pressure detected by the pressure sensor 92 is used as the air release valve 91, but the present invention is not limited thereto.

  In the present embodiment configured as described above, since the inverter and the air release valve are combined, the conventionally used unloader device becomes unnecessary.

DESCRIPTION OF SYMBOLS 1 ... Compressor main body, 2 ... Male rotor, 3 ... Female rotor, 4 ... Casing, 6, 7 ... Bearing, 11 ... Bisco seal, 12 ... Cooling jacket, 18 ... Driven side gear, 19 ... Drive side gear, 20 DESCRIPTION OF SYMBOLS ... High frequency inverter, 21 ... High-speed motor, 23 ... Motor casing, 25 ... Motor shaft, 26 ... Rotor core, 27 ... Stator core, 29 ... Load side bearing, 30 ... Anti-load side bearing, 41, 42 ... Bisco seal, 47 ... Cooling Jacket, 51 ... Main body frame, 52 ... Precooler, 53 ... After cooler, 54 ... Air discharge cooler, 55 ... Oil cooler, 90 ... Suction filter, 91 ... Air release valve, 92 ... Pressure sensor, 93 ... Air release piping.

Claims (3)

A motor shaft to which a motor rotor is attached, a motor casing for holding a motor stator disposed opposite the motor rotor, a male rotor having a screw-shaped male tooth shape, and a female rotor having a screw-shaped female tooth shape And an oil-free screw compressor provided with a casing for housing these male and female rotors,
A high-speed motor driven by a high-frequency inverter is connected to the suction side of the compressor body via a pair of gears consisting of a driving gear and a driven gear,
The high-speed motor has a motor shaft on which a motor rotor is formed, a load-side bearing provided on the compressor side that rotatably supports the motor shaft, and an anti-load side bearing provided on the anti-compressor side,
The load side bearing of the high speed motor is composed of a bearing of the same size as the suction side bearing of the rotor,
The anti-load side bearing of the high speed motor is composed of a bearing of the same size as the discharge side bearing of the rotor,
The bearings for supporting the rotor of the compressor and the bearings for supporting the motor shaft are forcibly lubricated, and lubricating oil for lubricating the bearings supporting the compressor rotor enters the compression chamber. The shaft seal device is configured with a screw seal so as to prevent the motor shaft, and a shaft seal device for preventing the lubricating oil that lubricates the load side bearing and the anti-load side bearing of the motor shaft from entering the high speed motor is provided. The motor shaft seal device and the compressor shaft seal device are composed of screw seals of the same size,
The rotational speed of the high-frequency motor and the rotational speed of at least one of the male rotor and female rotor are the same,
A first gear is provided on one end side of the shaft of either the male rotor or the female rotor, and a second gear meshing with the first gear is provided on one end side of the high-frequency motor, and the first gear and the second gear are provided. An oil-free screw compressor characterized in that the gear ratio of the gears of the gear is 1: 1. The oil-free screw compressor according to claim 1,
A first gear is fitted to the shaft end of the male rotor, and a second gear meshing with the first gear is fitted to the load side shaft end of the high frequency motor, and the teeth of the first gear and the second gear are fitted. An oil-free screw compressor characterized in that the number ratio is in the range of 2: 1 to 1: 2. The oil-free screw compressor according to claim 1 or 2,
An oil-free screw compressor, wherein heat dissipating fins are formed on the outer periphery of a casing housing the male rotor and female rotor and a motor casing housing the high-speed motor.

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