JP2002349467A - Oil-free screw compressor of rotation speed variable type - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce seizure of a rotor and a casing of an oil free screw compressor of rotation speed variable type having a low pressure stage compressor body and a high pressure stage compressor body. SOLUTION: This oil free screw compressor 100 of rotation speed variable type has the low pressure stage compressor body 1 and the high pressure stage compressor body. A pipe 20 branched from the midway of an air pipe 9 connecting the low pressure stage compressor body 1 to the high pressure stage compressor body 2 is provided with an orifice 30 and a low pressure stage exhaust two-way valve 21. A pipe 15 branched from an air discharging pipe 11 disposed on the discharge side of the high pressure stage compressor body is provided with an orifice 31 and a high pressure stage exhaust two-way valve 16. Exhaust pressure in no load operation is adjusted by providing the orifices 30 and 31, and an exhaust valve opening timing is controlled by a control device 18 so that the low pressure stage exhaust two-way valve 21 is opened simultaneously with or slower than the high pressure stage exhaust two-way valve 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable rotation speed oil-free screw compressor, and more particularly to a variable rotation speed oil-free screw compressor having a low pressure stage compressor main body and a high pressure stage compressor main body.

[0002]

2. Description of the Related Art A conventional variable-speed oil-free screw compressor includes a low-pressure stage screw compression section (hereinafter referred to as a low-pressure stage compressor body) and a high-pressure stage, as described in Japanese Patent Application Laid-Open No. 10-82391. A screw compressor (hereinafter, referred to as a high-pressure stage compressor body) was connected in series, and a cooler was connected to the two compressor bodies. Then, a motor is connected to each of the low-pressure stage compressor main body and the high-pressure stage compressor main body, and this motor is driven at a variable speed by an inverter. In the variable-speed screw compressor configured as described above, when the flow rate becomes low, both the low-pressure stage compressor body and the high-pressure stage compressor body become low-speed, and the amount of internal leakage cannot be ignored. And the low-pressure stage compressor body and the high-pressure stage compressor body were operated at the minimum rotation, and the air blowing was controlled.

[0003]

SUMMARY OF THE INVENTION In a variable speed oil-free screw compressor constructed by connecting two stages of compressor bodies, a low pressure stage and a high pressure stage, in series, a low pressure stage compressor main body has an outlet side. The inlet side of the high-pressure stage compressor body is connected via an intercooler, and the outlet side of the high-pressure stage compressor body and the aftercooler are connected via a check valve. A low-pressure stage air release means for discharging compressed air to the atmosphere from the middle of the pipe connecting the outlet side of the low-pressure stage compressor body and the intercooler, and a pipe connecting the high-pressure stage side compressor body and the check valve to the atmosphere. A high-pressure stage air discharging means for discharging the compressed air is provided.

FIG. 3 shows an example of changes in the compressor rotational speed during the no-load operation and the discharge pressure when the low-pressure stage and high-pressure stage compressor bodies 1 and 2 are directly ventilated. When considering the power consumption of an oil-free screw compressor, the lower the rotation speed, the lower the power consumption.During the no-load operation, that is, during the air discharge operation, the rotation speed is as low as possible from the viewpoint of power consumption. Should be lowered. However, as shown in FIG. 3, during the no-load operation, that is, during the air release operation, if the discharge air of the low-pressure stage compressor main body 1 and the high-pressure stage compressor main body 2 is directly discharged, the rotation speed decreases and the low-pressure stage and The discharge pressure of the high-pressure compressor bodies 1 and 2 decreases, and the differential pressure between the suction pressure and the discharge pressure in the high-pressure compressor body 2 decreases. At a certain rotational speed, the differential pressure becomes zero, but when the rotational speed is further reduced, the discharge pressure of the high-pressure stage compressor main body 2 is higher than the discharge pressure of the low-pressure stage compressor main body 1, that is, the suction pressure of the high-pressure stage compressor main body 2. Is reduced. For this reason, the load in the axial direction (the direction from the discharge side to the suction side) generated in the high-pressure stage compressor main body 2 decreases as the rotation speed decreases, and finally reverses.

That is, the lower the rotation speed in the no-load operation, the smaller the amount of compressed air and the pressure at the time of discharge can be reduced, and the power consumption can be reduced by the decrease in the rotation speed. However, a decrease in the discharge pressure due to a decrease in the rotation speed causes a decrease or reverse rotation of the differential pressure between the suction pressure and the discharge pressure in the high-pressure compressor body, and pushes the rotor to the suction side in the compressor body. The load in the direction will be reduced or reversed.

In the compressor main body, as shown in FIG. 4, a rotor discharge side end face 40 and a casing discharge side end face 41 are provided.
In order to minimize the internal leakage of compressed air, a small gap is set, and the axial load generated during load operation and no-load operation is the direction in which the gap is larger than the set value, That is, it is applied in a direction to push the rotor toward the suction side. However, when the load in the axial direction decreases or reverses, the gap on the discharge end face side becomes smaller than the set value, and the compressor endlessness (sliding or intermittent contact) between the rotor end face and the casing discharge end face. There is a risk of failure. This can be said of the low-pressure stage compressor main body, and it is necessary to secure a certain discharge pressure in the low-pressure stage and high-pressure stage compressor main body.

[0007] Each of the compressor bodies has a pressure ratio (compression ratio).
However, if the time for discharging compressed air from the low pressure stage air release means to the atmosphere is earlier than the time for discharging compressed air from the high pressure stage air release means to the atmosphere, the pressure of the former decreases first. As a result, the pressure ratio of the high-pressure stage compressor body may exceed the set pressure ratio. In such a case, the temperature of the compressed air increases, and there is a possibility that the rotors or the rotor and the casing may become hard due to thermal expansion.

On the other hand, when the above-mentioned no-load operation is performed, since the compressed air is discharged from the low-pressure-stage discharge device and the high-pressure-stage discharge device to the atmosphere, a silencer must be provided for each of them. Is inevitable.

It is an object of the present invention to realize an oil-free screw compressor of a variable rotation speed which does not have the above-mentioned danger.

[0010]

Means for Solving the Problems In order to eliminate the fear of stiffness, the pressure ratio of the high-pressure stage compressor body exceeds the pressure ratio set in the high-pressure stage compressor body at the stage of air release. Or the time when the pressure ratio of the high-pressure stage compressor body exceeds the pressure ratio set in the high-pressure stage compressor body is such that the thermal expansion of the rotor does not exceed the plan. It needs to be time. Further, it is necessary to prevent the pressure on the discharge side of the compressor body from dropping below the pressure on the suction side during the no-load operation, that is, during the air release operation.

As means for this, the inventors control the timing of starting the discharge of compressed air from the low pressure stage discharge means to the atmosphere and the timing of starting the discharge of compressed air from the high pressure stage discharge means to the atmosphere. The method and the method of controlling the pressure drop when the compressed air is discharged from the low-pressure stage discharge means to the atmosphere and the pressure drop when the compressed air is discharged from the high-pressure stage discharge means to the atmosphere are studied. Invented the invention.

That is, a first means of the present invention for achieving the above object is a low-pressure stage compressor body for compressing air, and a high-pressure stage compressor for further compressing the air compressed by the low-pressure stage compressor body. A variable-speed oil-free screw compressor for controlling the capacity by changing the rotation speed of the low-pressure stage compressor body and the high-pressure stage compressor body, wherein the compression is performed by the low-pressure stage compressor body. A low-pressure stage air release means that is provided in the middle of a pipeline that guides the extracted air to the high-pressure stage compressor main body and discharges the air in the pipeline to the atmosphere; and the air compressed by the high-pressure stage compressor main body. A high-pressure-stage discharge device that is provided in the middle of the conduit leading to the check valve and discharges air in the conduit to the atmosphere; and a high-pressure stage discharge pressure higher than the low-pressure stage discharge pressure during the discharge operation. Discharge pressure setting means for setting.

As the discharge pressure setting means, there is provided a high-pressure step discharge means or a throttle means connected to the high-pressure step discharge means and the low-pressure step discharge means for restricting a flow path of air discharged. Can be. As the throttling means, an orifice or a pipe which reduces the diameter of the pipe so as to obtain the effect of the orifice is provided so that the discharge pressure of the high pressure stage discharge means is higher than the discharge pressure of the low pressure stage discharge means.

With this configuration, the force in the direction of separating the rotor discharge-side end face from the casing discharge-side end face is maintained even during the air discharge operation, so that the tightness between the rotor discharge-side end face and the casing discharge-side end face is avoided. In addition, it is possible to adjust power consumption.

A second means of the present invention for achieving the above object is a low-pressure stage compressor body for compressing air with a pair of male and female rotors, and a compressor compressed by the low-pressure stage compressor body with a pair of male and female rotors. A high-pressure stage compressor body for further compressing the compressed air, wherein the low-speed stage compressor body and the high-pressure stage compressor body change the rotation speed to control the displacement to perform a displacement control type oil-free screw compressor. A low-pressure stage air release means provided in the middle of a pipeline for guiding the air compressed by the low-pressure stage compressor main body to the high-pressure stage compressor main body and discharging the air in the pipeline to the atmosphere; A high-pressure stage discharge means provided in the middle of a pipe for guiding the air compressed by the compressor body to the check valve and discharging the air in the pipe to the atmosphere; Control means for controlling the timing of air release of the air means; The is characterized in that provided.

The control means may start the discharge from the high-pressure discharge means simultaneously with the discharge from the low-pressure discharge means or earlier than the discharge from the low-pressure discharge means. And, it is configured to control the timing of the air release so that the time from the start of the air release from the low pressure stage air release means to the start of the air release from the high pressure stage air release means becomes a predetermined time or less, The predetermined time is determined by the heat of the rotor accompanying an increase in the pressure ratio of the high-pressure stage compressor body due to the release of air from the low-pressure stage release device preceding the release from the high-pressure release device. The expansion amount may be set to a time that does not exceed the thermal expansion amount of the rotor during normal operation.

With this configuration, the pressure ratio of the high-pressure stage compressor body rises above the planned pressure ratio at the time of air release, causing a rise in the temperature of the compressed air and abnormal thermal expansion of the rotor. Can be prevented.

A third means of the present invention for achieving the above object is that the outlet side of the high-pressure stage air discharging means and the outlet side of the low-pressure stage air releasing means are joined and then discharged in one system. The piping system on the downstream side of each air discharging means is configured as described above. With this configuration, the number of required air release silencers is reduced, and the number of parts of the air release system is reduced.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a configuration of a variable rotation speed oil-free screw compressor according to the present embodiment, and FIG. 2 is a diagram showing the discharge air amount and the discharge air amount of the variable rotation speed oil-free screw compressor shown in FIG. 4 is a graph illustrating a relationship between rotation frequencies. Both the discharge air amount and the rotation frequency are shown in proportions with the rated value being 100%.

A variable-rotation speed oil-free screw compressor 100 shown in FIG. 1 includes a housing 40, a low-pressure stage compressor main body 1 and a high-pressure stage compressor main body 2 housed in the housing 40. I have. The low-pressure compressor body 1 holds a pair of male and female rotors in a casing having a cooling jacket formed on the outer periphery. The male and female rotors are
The rotors are configured to rotate synchronously when the timing gears attached to the shaft ends of the rotors mesh with each other. A pinion gear 6 is attached to the end of the rotation shaft 1A opposite to the timing gear attachment end of one of the rotors. Similarly, the high-pressure stage compressor main body 2 holds a pair of male and female rotors in a casing having a cooling jacket formed on the outer periphery. The male and female rotors are configured to rotate synchronously when a timing gear attached to a shaft end of each rotor meshes. A pinion gear 7 is attached to the end of the rotation shaft 2A opposite to the timing gear attachment end of one of the rotors.

The two pinion gears 6 and 7 mesh with a bull gear 5 attached to a bull shaft coupled to a rotary shaft 4A of the motor 4 also housed in the housing 40. The motor 4 is a variable speed motor driven by an inverter 8. Note that the pinion gears 6 and 7 and the bull gear 5 are housed in the gear casing 3. The lower portion of the gear casing is an oil reservoir for lubricating oil that lubricates the bearings of the compressor bodies 1 and 2 and the bull gear 5 and the pinions 6 and 7.

An air intake 40A for taking in outside air is formed in the inside of the casing 40 in the shape of a rectangular tube. The inside of the air intake 40A is for filtering ambient air and supplying it to the low-pressure stage compressor body 1. Are mounted. Downstream of the filter 14, a suction port 14A
This suction port 14A is connected to the low-pressure stage compressor main body 1.
Are connected to the suction channel of

The discharge side of the low-pressure stage compressor body 1 is connected to an air pipe 9
Is connected to the air inlet side of the intercooler 10, and the air outlet side of the intercooler 10 is connected to the suction side of the high-pressure stage compressor main body 2 by an air pipe 9A. The discharge side of the high-pressure stage compressor body 2 is connected to an air inlet of an aftercooler 13 via a check valve 12 via an air pipe 11. The air outlet of the aftercooler 13 has a discharge air pipe 23 for supplying the compressed air cooled by the aftercooler 13 to the use side.
Is connected.

The low-pressure stage compressor body 1 and the intercooler 10
From the middle of the air pipe 9 connecting the low pressure stage
0 branches. An orifice 30 that constitutes a discharge pressure setting means and a low-pressure step discharge two-way valve 21 that is a low-pressure step discharge means are connected to the low-pressure step discharge pipe 20 in this order. Outlet 21 is air release silencer 5
0 is open to the atmosphere in the housing 40. Similarly,
A high-pressure stage air discharge pipe 15 branches off from the middle of the air pipe 11 connecting the discharge side of the high-pressure stage compressor body 2 and the check valve 12. The high-pressure stage discharge pipe 15 is provided with an orifice 31 which constitutes a discharge pressure setting means and a high-pressure step discharge two-way valve 16 which is a high-pressure step discharge means.
The outlet side of 6 is open to the atmosphere in the housing 40 via the air release silencer 50. Both the low-pressure stage discharge two-way valve 21 and the high-pressure stage discharge two-way valve 16 are solenoid valves. Instead of the orifices, pipes 30 and 31 each having a small inner diameter for obtaining the effect of the orifice may be attached.

A cooling water pipe for sequentially cooling the intercooler 10, the cooling jacket of the low-pressure stage compressor main body 1, the cooling jacket of the high-pressure stage compressor main body 2, and the aftercooler 13 is provided.

A pressure detector 17 for measuring the pressure of the compressed air in the discharge air pipe 23 and outputting it as an electric signal is mounted in the middle of the discharge air pipe 23.
7 is connected to a control device 18 which is a control means also housed in the housing 40. The output side of the control device 18 is connected to a low-pressure stage discharge two-way valve 21, a high-pressure stage discharge two-way valve 16 and an inverter 8, which are electromagnetic valves. The control device 18 controls the opening and closing of the low-pressure stage discharge two-way valve 21 and the high-pressure stage discharge two-way valve 16 using the signal of the pressure detector 17 as an input, and the signal of the pressure detector 17 as an input.
A signal indicating the number of revolutions is output to inverter 8.

As described above, the variable-rotation-speed oil-free screw compressor 100 shown in the drawing is provided with a compressor body, an intercooler 10, an aftercooler 13, a motor 4, a control device 18, a gas release silencer 50, etc. It is a package type with interior.

The operation of the embodiment constructed as described above will be described below. When the motor 4 is operated, the rotational force of the motor 4 is transmitted to the low-pressure stage compressor body 1 and the high-pressure stage compressor body 2 via the bull gear 5 and the pinion gears 6 and 7. As a result, a pair of rotors provided in the low-pressure stage compressor main body 1 and the high-pressure stage compressor main body 2 respectively rotate synchronously. First, the low-pressure stage compressor main body 1 passes through the air as the working gas, that is, the suction port 14A through the filter 14. Compresses the ambient air sucked from.

The air compressed by the low-pressure stage compressor body 1 is
The temperature rises with increasing pressure. This high-temperature compressed air is guided to the intercooler 10 via the air pipe 9,
Cooled by the intercooler 10. Intercooler 10
The compressed air cooled in step (1) is guided to the high-pressure compressor body 2 via the air pipe 9A, and is further compressed to increase the temperature to a predetermined discharge pressure and increase the temperature. The compressed air whose temperature has risen is guided to the aftercooler 13 via the air pipe 11 and the check valve 12, cooled by the aftercooler 13, and then supplied from the discharge air pipe 23 to the use side.

When the amount of consumed air on the user side decreases, the discharge pressure detected by the pressure detector 17 increases. The discharge pressure detected by the pressure detector 17 is input to the control device 18. When the input discharge pressure increases, the control device 18 outputs a command signal to decrease the rotation speed of the motor 4 to the inverter 8. When the rotation speed of the motor 4 decreases, the rotation speeds of the rotors provided in the low-pressure stage compressor main body 1 and the high-pressure stage compressor main body 2 decrease, and the discharge air amount of the oil-free screw compressor 100 decreases.

That is, when the amount of consumed air decreases and the amount of air discharged from the oil-free screw compressor can be 100% to about 50% of the specified discharge air amount, the control device 18 keeps the discharge pressure constant. Therefore, the rotation speed of the motor 4 is controlled in proportion to the discharge air amount ratio as shown in an operation range D of FIG. In the present embodiment, the minimum rotation frequency ratio in the displacement control of the compressor is 50%. On the other hand, when the discharge air amount may be about 50% or less of the specification discharge air amount, the control device 18 instructs the discharge air reduction operation. Specifically, if the discharge pressure detected by the pressure detector 17 exceeds the set upper limit pressure preset in the controller 18 while the compressor speed is the set lower limit speed, the controller 18
Sends a command to the inverter 8 to maintain the set lower limit rotation speed, and outputs an open command signal to the low-pressure stage discharge two-way valve 21 and the high-pressure stage discharge two-way valve 16. Low pressure stage discharge two-way valve 21
When the high-pressure stage discharge two-way valve 16 is opened, the low-pressure stage compressor body 1 is opened.
The compressed air compressed by the high-pressure stage compressor main body 2 is released to the atmosphere without being guided to the intercooler 10 and the aftercooler 13.

In this embodiment, the low-pressure stage air discharge pipe 2
0 is connected to the low pressure stage discharge two-way valve 21 via the orifice 30, and the downstream end of the high pressure stage discharge pipe 15 is connected to the high pressure stage discharge two-way valve 16 via the orifice 31. I have. It is for the following reasons.

At the time of no-load operation in which the consumption of compressed air on the use side is reduced and the supply of compressed air to the use side is no longer required, the control device 18 controls the low-pressure stage compressor body 1 and the high-pressure stage compressor body 2 A command is issued to the inverter 8 so that the rotation speed becomes the set lower limit value, and an open command is output to the low-pressure stage discharge two-way valve 21 and the high-pressure stage discharge two-way valve 16. A part of the compressed air and the compressed air compressed by the high-pressure compressor body 2 are released to the atmosphere in the housing 40. As described above, when considering the power consumption of the compressor, the rotational speed of the compressor during no-load operation decreases as the power consumption decreases, and the rotational speed decreases as much as possible from the viewpoint of power consumption. You should lower it. However, as shown in FIG. 3, when the discharge air from the low-pressure stage compressor main body 1 and the high-pressure stage compressor main body 2 is directly discharged, the rotation speed is reduced and the low-pressure stage and high-pressure stage compressor main bodies 1, 2 are discharged. The pressure decreases, and the differential pressure between the suction pressure and the discharge pressure in the high-pressure compressor body 2 decreases or reverses, so that the axial load generated in the low-pressure and high-pressure compressor bodies 1 and 2 is reduced. Or reverse.

As shown in FIG. 4, a small gap is provided between the rotor end face 40 and the casing discharge end face 41 in order to minimize internal leakage of compressed air. During the load operation and the no-load operation, the rotor is caused to move in a direction in which the gap becomes larger than a set value by an axial load generated by a pressure difference between the pressure on the rotor suction side and the pressure on the discharge side. However, if the differential pressure decreases or reverses, the gap on the discharge end face side becomes smaller than the set value, and there is a possibility that the compressor may fail due to the tightness between the rotor end face 40 and the casing discharge end face 41. In the present embodiment, the orifice 31 is connected to the high-pressure stage
And the discharge pressure of the high-pressure stage compressor body 2 at the time of air release is made larger than the suction pressure, and the axial direction of the load applied to the rotor is maintained in the direction in which the gap becomes larger than a set value. . As a result, it is possible to avoid the tightness between the rotor end face and the casing end face during the no-load operation. The consumption of compressed air during the load operation and the no-load operation is determined by the pressure detector 17 provided in the discharge air pipe 23.
Is determined based on the detected pressure.

The orifice 30 provided on the upstream side of the low-pressure stage discharge two-way valve 21 is provided for adjusting the differential pressure between the discharge pressure and the suction pressure for the rotor of the low-pressure stage compressor body 1. If a sufficient differential pressure is obtained, it may be omitted.

In the present embodiment, a pressure detector 17 for detecting the pressure of the high-pressure air discharged from the high-pressure compressor main body 2 is provided on the discharge side of the high-pressure compressor main body 2, A control device 18 is provided which outputs a control signal for controlling the opening / closing timing of the high-pressure stage discharge two-way valve 16 and the low-pressure stage discharge two-way valve 21 using the detected discharge pressure signal as input. It is for the following reasons.

When the operation is switched to the no-load operation in which the consumed air amount is almost zero, the opening timing of the low-pressure stage discharge two-way valve 21 is controlled to be simultaneous or delayed with the opening timing of the high-pressure stage discharge two-way valve 16. To do that. A pressure ratio (discharge pressure / suction pressure) is set for each of the compressor bodies.
However, the opening timing of the low-pressure stage discharge two-way valve 21 that discharges compressed air from the upstream side of the intercooler to the atmosphere in the middle of the pipe connecting the low-pressure stage compressor body and the high-pressure stage compressor body, If the timing is earlier than the opening timing of the high-pressure stage discharge two-way valve 16 that discharges compressed air from the upstream side of the check valve to the atmosphere in the middle of the air pipe connecting the high-pressure stage side compressor body and the aftercooler. The pressure of the air pipes 9 and 9A connecting the low-pressure stage compressor main body and the high-pressure stage compressor main body to the air pipe 1 connecting the high-pressure stage side compressor main body and the aftercooler
It will drop before the pressure of 1.

In this case, the pressure ratio actually generated in the high-pressure stage compressor main body 2 exceeds the set pressure ratio, the discharge air temperature rises, and the rotors or the rotor and the casing may become tight. There is. In order to avoid such a state, the control device 18 controls the low-pressure stage discharge two-way valve 21.
Is controlled so as to be simultaneous or delayed with the opening timing of the high-pressure stage discharge two-way valve 16. When the low-pressure stage discharge two-way valve 21 opens at the same time or after the opening timing of the high-pressure stage discharge two-way valve 16, the pressure ratio generated in the high-pressure stage compressor body 2 exceeds the set pressure ratio. Therefore, the temperature of the compressed air discharged from the high-pressure compressor body 2 does not rise above the planned temperature. In other words, the thermal expansion of the rotor does not increase and the end face of the rotor and the casing end face are not tight.

Even if the low-pressure stage discharge two-way valve 21 is opened before the high-pressure stage discharge two-way valve 16, even if the high-pressure stage discharge two-way valve
When 6 is opened, the temperature of the discharged air that has once risen again falls. Therefore, the time from when the low-pressure stage discharge two-way valve 21 is opened to when the high-pressure stage discharge two-way valve 16 is opened is such that the thermal expansion of the rotor caused by the temperature rise of the discharge air due to the increase in the pressure ratio can be ignored. , The low pressure stage discharge two-way valve 21
Is opened prior to the high-pressure stage discharge two-way valve 16, there is no fear that the rotor end face and the casing end face may be tight, and the control device 18 may perform such control.

Another embodiment of the present invention will be described with reference to FIG. FIG. 5 is an overall configuration diagram of a variable rotation speed oil-free screw compressor according to the present embodiment. This embodiment is different from the embodiment shown in FIG. 1 in that the outlet pipe of the low-pressure stage discharge two-way valve 21 (upstream of the discharge silencer 50) is provided with the high-pressure stage discharge two-way valve 16. The outlet side is connected, and one air release silencer 50 is used. That is, in the present embodiment, the air discharged from the high-pressure stage discharge two-way valve 16 and the air discharged from the low-pressure stage discharge two-way valve 21 are combined into one, and one air release silencer is provided. From the air to the atmosphere.

In the present embodiment configured as described above, during no-load operation in which compressed air is not supplied to the use side, the control device 18 instructs the inverter 8 to set the rotation speed of the motor 4 to the set lower limit rotation speed. I do. Further, the control device 1
8 instructs the low-pressure stage discharge two-way valve 21 and the high-pressure stage discharge two-way valve 16 to open simultaneously or quickly so that the high-pressure stage discharge two-way valve 16 opens. The compressed air during the no-load operation is supplied to an air pipe 9 connecting the low-pressure stage compressor body 1 and the intercooler 10,
A system that passes through the low-pressure stage discharge pipe 20, the orifice 30, and the low-pressure stage discharge two-way valve 21, and the air pipe 11 that connects the high-pressure stage compressor main body 2 and the aftercooler 13 and is connected to the check valve 12 After the air pipe 15 branched from the upstream side, the orifice 31, and the system passing through the high-pressure stage discharge two-way valve 16 merge, the air is discharged through the discharge silencer 50. As a result, the number of the air release silencers 50 can be reduced to one, which simplifies the air discharge piping system and is advantageous in terms of noise reduction.

According to the present embodiment, in addition to the effect of the embodiment shown in FIG. 1, the number of parts is reduced, and an advantageous effect in terms of noise reduction is obtained.

[0043]

As described in detail above, according to the present invention,
In the variable-rotation-speed oil-free screw compressor, it is possible to reduce the possibility that the rotor and the casing discharge end side face firmness.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a variable rotation speed oil-free screw compressor according to an embodiment of the present invention.

FIG. 2 is a graph illustrating a relationship between a rotation frequency ratio and a discharge air amount ratio of the variable rotation speed oil-free screw compressor shown in FIG.

FIG. 3 shows a portion of the discharge air of the low-pressure stage compressor main body and a portion of the high-pressure stage compressor main body when the variable-speed oil-free screw compressor having the low-pressure stage compressor main body and the high-pressure stage compressor main body has no load. It is a conceptual diagram explaining an example of the discharge pressure characteristic at the time of discharging air directly.

FIG. 4 is an enlarged view of a discharge end face side of a high-pressure stage compressor main body in the oil-free screw compressor.

FIG. 5 is a cross-sectional view illustrating a configuration of a variable rotation speed oil-free screw compressor according to another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Low-pressure stage compressor main body 2 High-pressure stage compressor main body 4 Motor 8 Inverter 9, 9A Air piping 10 Intercooler 11 Air piping 12 Check valve 13 Aftercooler 15 High-pressure stage discharge piping 16 High-pressure stage discharge two-way valve 17 Pressure Detector 18 Control device 20 Low pressure stage air release pipe 21 Low pressure stage air release two-way valve 30, 31 Orifice 40 Housing 100 Variable rotation speed oil-free screw compressor

 ──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Hiroshi Ota 390 Muramatsu, Shimizu-shi, Shizuoka F-term in the Industrial Equipment Group, Hitachi, Ltd. (Reference) 3H029 AA03 AA17 AA24 AB02 AB08 BB16 BB47 BB53 CC06 CC13 CC22 CC54 CC58 CC62 CC86

Claims (6)

[Claims] 1. A low-pressure stage compressor body for compressing air, and a high-pressure stage compressor body for further compressing the air compressed by the low-pressure stage compressor body. In a variable-speed oil-free screw compressor that performs displacement control by changing the rotation speed of a stage compressor main body, in the middle of a pipeline that guides air compressed by the low-pressure stage compressor main body to the high-pressure stage compressor main body. A low-pressure stage air releasing means for releasing air in the pipeline to the atmosphere, and a pipeline provided in the middle of a pipeline for guiding the air compressed by the high-pressure compressor body to a check valve. High-pressure stage air discharge means for discharging air to the atmosphere, and discharge pressure setting means for setting the high-pressure stage discharge pressure during the discharge operation higher than the low-pressure stage discharge pressure, Variable speed oil-free screw compressor. 2. The variable rotation speed oil-free screw compressor according to claim 1, wherein the discharge pressure setting means is connected to the high pressure discharge means or the high pressure discharge means and the low pressure discharge means. An oil-free screw compressor having a variable rotational speed, comprising a throttle means for restricting a flow path of the air discharged and discharged. 3. A low-pressure compressor body for compressing air with a pair of male and female rotors, and a high-pressure compressor body for further compressing the air compressed by the low-pressure compressor body with a pair of male and female rotors. In the variable-speed oil-free screw compressor, which performs capacity control by changing the rotation speed of the low-pressure stage compressor body and the high-pressure stage compressor body,
A low-pressure stage air release means provided in the middle of a pipeline for guiding the air compressed by the low-pressure stage compressor main body to the high-pressure stage compressor main body and discharging the air in the pipeline to the atmosphere; High-pressure stage air release means that is provided in the middle of a pipeline that guides air compressed by the machine body to the check valve and that releases air in the pipeline to the atmosphere;
A variable rotation speed oil-free screw compressor, further comprising control means for controlling the timing of air release of the high-pressure stage air release unit and the low-pressure stage air release unit. 4. The variable rotation speed oil-free screw compressor according to claim 3, wherein the control means controls the discharge of the air from the high pressure stage discharge means simultaneously with the discharge from the low pressure stage discharge means. A variable rotation speed oil-free screw compressor, wherein the compressor is started earlier than the discharge from the low-pressure stage discharge means. 5. The variable rotation speed oil-free screw compressor according to claim 3, wherein said control means starts air release from the low pressure stage air release means, and then starts air release from the high pressure stage air release means. It is configured to control the timing of air release so that the time until the start is equal to or less than a predetermined time, and the predetermined time is a time when the air release from the low pressure stage gas release unit is the air release from the high pressure stage gas release unit. That the amount of thermal expansion of the rotor accompanying an increase in the pressure ratio of the high-pressure stage compressor body due to the preceding is set to a time that does not exceed the amount of thermal expansion of the rotor during normal operation. Characteristic variable-speed oil-free screw compressor. 6. The variable-speed oil-free screw compressor according to claim 1, wherein an outlet of the high-pressure stage air discharging means and an outlet of the low-pressure stage air discharging means are connected to each other. A variable rotation speed oil-free screw compressor, wherein a piping system on the downstream side of each air release means is configured to be discharged by one system after being merged.