CN111902631A

CN111902631A - Gas compressor

Info

Publication number: CN111902631A
Application number: CN201880091281.2A
Authority: CN
Inventors: 森田谦次; 高野正彦; 田中英晴
Original assignee: Hitachi Industrial Equipment Systems Co Ltd
Current assignee: Hitachi Industrial Equipment Systems Co Ltd
Priority date: 2018-03-29
Filing date: 2018-03-29
Publication date: 2020-11-06
Anticipated expiration: 2038-03-29
Also published as: JP6940686B2; CN111902631B; WO2019186861A1; JPWO2019186861A1

Abstract

The invention provides a gas compressor, which can realize power reduction effect while keeping following performance to pressure change. The gas compressor includes: a compressor main body sucking gas and discharging compressed gas; a pressure detection device for detecting the discharge pressure of the compressed gas; a drive source of the compressor main body; and a control device for controlling the drive source in a variable speed manner based on a detection value of the pressure detection device and controlling the opening and closing of the suction regulator valve, wherein in the gas compressor, the control device drives the drive source at a rotation speed less than a full rotation speed and greater than a lower limit rotation speed of the drive source when the discharge pressure is greater than a set pressure P0 and less than an upper limit pressure P1 higher than the set pressure P0.

Description

Gas compressor

Technical Field

The present invention relates to a gas compressor, and more particularly, to a gas compressor which reduces a driving load.

Background

For example, various operation control methods for reducing a driving load have been known in a gas compressor that generates a high-pressure compressed gas by a compression mechanism such as a displacement type or a turbine type that sucks a gas such as air.

In a constant speed compressor in which the rotation speed of a drive source is kept constant, there is known no-load operation control in which, when a discharge pressure reaches a target pressure desired by a user, a suction regulating valve (suction throttle valve) provided in an intake passage of a compressor main body is closed to restrict an amount of gas flowing in, thereby reducing a power load. Such a no-load operation enables the required power consumption to be about 70% of the rated power.

In addition, in a gas compressor in which a variable speed control is performed to change the rotation speed of a motor by using an electric power conversion device such as an inverter, there is known a technique in which the gas compressor is operated at high speed (full speed) by the electric power conversion device until a target pressure is reached, and when a discharge pressure is higher than the target pressure, the rotation speed is reduced by the electric power conversion device to reduce power.

For example, when the amount of compressed gas used on the user (the user of the compressed gas) side is large and the user-side discharge pressure is lower than the target pressure, the engine is operated at the rated maximum rotational speed, and when the user-side discharge pressure is higher than the target pressure, the rotational speed is reduced to reduce the power. As such control for changing the rotation speed, a control method for changing the rotation speed in proportion to the discharge pressure, such as P, PI or PID, is generally known.

In addition, in a gas compressor with variable speed control, as a technique for achieving power reduction, there is also known a no-load operation method in which an intake regulating valve and an exhaust valve are used in combination in addition to rotation speed control by an electric energy conversion device. For example, patent document 1 discloses an air compressor that performs a PID control operation with a target pressure (P0) as a base, but performs a control of decreasing the rotation speed while maintaining a predetermined pressure range of P0 or more or greater than P0 when the user-side air usage is decreased and the user-side discharge pressure is increased from P0 to a predetermined pressure. More specifically, the following operation method: when the pressure rises to the upper limit pressure (P1) higher than P0, the suction modulation valve is closed, the rotation speed of the motor is reduced to the lower limit rotation speed to reduce the power, and the compressed air on the upstream side of the user-side discharge port is released to the atmosphere to reduce the load of the compressor main body (the load of the motor), thereby further reducing the power.

Further, patent document 1 also discloses such control: when the motor is operated at the lower limit speed after the upper limit pressure P1 is reached, the amount of air used on the user side gradually increases, and when the user-side discharge pressure reaches the lower limit pressure (P2), which is a pressure between P0 and P1, the exhaust valve is closed and/or the suction modulation valve is opened while the rotation speed is maintained at the lower limit speed, and the motor is operated at a boosted load until the motor reaches P1 again. A technique capable of reducing the power while keeping the pressure on the user side within a certain range. The power consumption required for such a no-load operation can be set to about 30% of the rated power.

Further, the opening/closing control of the regulator valve and the exhaust gas are not necessarily used in combination, and even either of them has a power reduction effect.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2001-280275

Disclosure of Invention

Technical problem to be solved by the invention

However, in patent document 1, the rotation speed of the motor is set to the lower limit rotation speed in the no-load and no-load operation to achieve energy saving, but the compressor varies in pressure according to a change in the usage state of the compressed air. Even if the amount of discharged air is constant, the pressure fluctuates when the amount of compressed air used varies. In the case where the compressed air pressure requires a specific pressure (or higher), if the amount of the compressed air used is too large, the compressed air is not generated in time, and may be lower than the specific pressure. I.e., the following to the change in the amount of use is reduced.

For such pressure fluctuations, the gas compressor generally adopts a structure in which: a downstream pipe of the customer-side discharge port is connected to a gas tank (also referred to as a storage tank) for storing compressed gas, and the gas is supplied from the gas tank to each customer-side terminal device via a pipe. That is, the various operation controls for achieving the power reduction as described above can be said to be controls that can be efficiently achieved by making the gas tank have a certain volume.

The gas tank functions as a buffer device for keeping constant the pressure fluctuation with respect to the change in the amount of compressed gas used at the user-side terminal when the capacity is large, and the rate of the differential pressure fluctuation required for the compressor main body can be set within a relatively small range. This reduces the frequency of the change in the rotational speed of the compressor, and contributes to a reduction in power. In addition, it is also helpful to prevent speed deviation (hunting) and trip protection (trip) of a driving source such as a motor in order to reduce a sudden pressure variation.

As described above, the gas tank required to function as a pressure fluctuation damper has a large volume, and even if the compressor is downsized, it is necessary to secure an installation space in an actual use environment.

A technique capable of achieving a power reduction effect while maintaining the followability to pressure fluctuations is desired. Techniques for making compressor equipment space efficient are also desired.

Means for solving the problems

In order to solve the above-described problems, for example, a configuration described in the scope of claims can be used. Namely, a gas compressor, comprising: a compressor main body sucking gas and discharging compressed gas; a pressure detection device for detecting the discharge pressure of the compressed gas; a drive source of the compressor main body; and a control device for controlling the drive source in a variable speed manner based on a detection value of the pressure detection device and controlling opening and closing of the suction adjustment valve (suction throttle valve), wherein the control device drives the drive source at a rotation speed less than a full-speed rotation speed and greater than a lower-limit rotation speed of the drive source when the discharge pressure is greater than a set pressure P0 and less than an upper-limit pressure P1 higher than the set pressure P0.

Effects of the invention

According to the present invention, it is possible to improve the following performance of the gas compressor to pressure fluctuations and to reduce the power load. Moreover, it also contributes to space saving and the like of the compressor installation comprising the gas tank.

Drawings

Fig. 1 is a block diagram schematically showing the structure of an air compressor using embodiment 1 of the present invention.

Fig. 2 is a change diagram schematically showing changes in pressure, rotation speed, and the like of the air compressor of example 1.

Fig. 3 is a block diagram schematically showing the structure of an air compressor using embodiment 2 of the present invention.

Fig. 4 is a change diagram schematically showing changes in pressure, rotation speed, and the like of the air compressor of example 2.

Detailed Description

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

Example 1

Fig. 1 schematically shows a configuration of an air compressor 50 (hereinafter, also referred to as "compressor 50") as an example using an embodiment of the present invention.

The compressor 50 mainly includes a compressor main body 1, a motor 2, an electric power conversion device 3, a control device 4, a gas-liquid separator 12, an air cooler 16, a pressure sensor 17, an oil cooler 21, and a fan device 25, and has a structure of a hermetic compressor in which the front, rear, left, right, and upper surfaces are surrounded by a panel 40 from the base.

The compressor body 1 has a compression mechanism such as a positive displacement type or a turbine type, and compresses air sucked from the suction filter 8. In the compression working chamber of the compressor body 1, lubricating oil is supplied through the oil pipe 20, and compressed gas mixed with air and liquid can be discharged together with air.

In the present embodiment, a compressor in which a rotary-type screw rotor is provided as a compression mechanism is explained.

The motor 2 is a driving source of the compressor main body 1. As the drive source, an internal combustion engine can also be used. The motor 2 supplies a rotational force generated by electric power to the screw rotor of the compressor body 1 coaxially or via a belt or a gear. The electric energy conversion means converts the frequency of the electric energy supplied to the electric motor 2 based on a command from the control means 4, changing the rotation speed of the electric motor 2.

The control device 4 includes a semiconductor arithmetic device such as an MPU or a CPU and a storage device, and realizes a functional unit for performing overall control of the compressor 1 in cooperation with a program. The control device 4 may be configured by an analog circuit configuration or a combination thereof. The control device 4 can receive input of detection values from a temperature sensor 11 that detects the temperature of the exhaust gas and a pressure sensor 17 that detects the pressure of the exhaust gas, and output a frequency command to the electric power conversion device 3, an opening/closing command to various valve bodies, and the like. The details are described later.

The gas-liquid separator 12 is a separator for primarily separating oil from a compressed gas mixed with the gas and liquid discharged from the compressor main body 1. In the present embodiment, a rotating separation type separator is used in which oil and air are separated by centrifugal force by rotating compressed gas in an inner cylinder, but an impact separation type separator may be used. The separated oil is stored in the bottom of the gas-liquid separator 12, is sent to an oil cooler 21 by the air pressure in the gas-liquid separator 12 or the pump 10 via an oil pipe 20, is cooled to a predetermined temperature, and is returned to the compressor body 1.

The secondary filter 13 is made of, for example, a nonwoven fabric, and performs secondary separation of the compressed air from which the oil is primarily separated by the gas-liquid separator 12. The compressed air after the secondary separation flows to a discharge pipe on the downstream side and further flows through an air cooler 16 via a check valve 15 that allows the flow to the downstream side.

The air cooler 16 is a heat exchanger, and is driven by the fan device 25, and can suck outside air as cooling air from the air inlet 30 into the compressor 50 and discharge the air to the outside from the air outlet 32. The fan device 25 can perform variable speed control based on the detection value of the temperature sensor 11. Further, an electromagnetic three-way valve and a bypass pipe 24 are disposed upstream of the oil cooler 21, and the control device 4 can control switching of the flow path of the lubricating oil returned from the gas-liquid separator 12 and the driving state of the pump 23 based on the detection value of the temperature sensor 11. The air cooler 16 cools the compressed air to a predetermined temperature (for example, 70 degrees) by exchanging heat between the compressed air having a high temperature due to the compression action and the cooling air generated by the fan device 25.

With such a cooling system, the cooling air cools the motor 2 and the compressor body 1, and then flows to the air cooler 16 and the oil cooler 21 on the downstream side to exchange heat with the respective coolers.

The pressure sensor 17 is disposed on a pipe from the outlet of the air cooler 16 to the external pipe 59 (or may be disposed on the external pipe 59). The pressure sensor 17 is connected in controllable communication with the control device 4, and is capable of outputting a pressure value of the compressed air discharged from the compressor 50 to the control device 4. The control device 4 can monitor the input value from the pressure sensor 17 and output a frequency command corresponding to a set pressure, an upper limit pressure, and the like, which will be described later, and an opening/closing command of the valve body.

The compressed air cooled to a predetermined temperature by the air cooler 16 is then discharged from the compressor 1 through the external pipe 59. The external pipe 59 is connected to the gas tank 60. The gas tank 60 is a pressure vessel for storing compressed gas at a predetermined pressure. The compressed air is supplied from the gas tank 60 to a terminal device using the compressed air via a terminal pipe (not shown).

Further, a suction adjustment valve (suction throttle valve) 5 is disposed on the suction side of the compressor body 1 (downstream of the suction filter 8). The suction modulation valve 5 is a valve body that allows or restricts the inflow of suction gas from the suction port into the compression chamber of the compressor main body 1 according to the operating state of the compressor 50. In the present embodiment, the suction adjustment valve 5 describes a configuration in which the discharge pressure of the compressor body 1 is used as the power source and the piston of the valve body is opened and closed. The opening and closing of the suction modulation valve 5 is performed by the control device 4.

One of the features of the present embodiment is that the suction modulation valve 5 is closed when reaching an upper limit pressure P1 described later. More specifically, the suction modulation valve 5 is fully opened until the upper limit pressure P1 is reached, and is closed when the upper limit pressure P1 is reached.

Next, the control of the control device 4 will be described in detail.

In fig. 2, the discharge pressure, the rotation speed of the motor 2 (the frequency of the power conversion device 3), and the state change of the suction modulation valve 5 of the present embodiment are shown in time series. In the figure, the pressure P0 and the upper limit pressure P1 are set, and 0.70MPa and 0.80MPa are taken as examples. The set pressure is a pressure input from a user or a pressure initially set, and is a pressure value to be a discharge target of the compressor 50. The upper limit pressure is a maximum discharge pressure determined according to a rated specification of the equipment, and is a pressure value determined according to equipment maintenance or various safety standards. In the present embodiment, a pressure smaller than the safety pressure determined based on the safety reference is set as the upper limit pressure P1, and the description will be given.

The full speed rotation speed of the motor 2 is 6000rpm/min, and the lower limit rotation speed is 800rpm/min as an example. The full-speed rotation speed is a rated maximum rotation speed of the motor 2, and the lower limit rotation speed is a predetermined rotation speed smaller than the full-speed rotation speed. For example, the minimum rotation speed that can be used when driving the compressor, such as the driving load operation and the no-load operation disclosed in patent document 1.

In the figure, changes in pressure and rotation speed are schematically shown for the sake of simplicity, and the present invention is not necessarily limited to the numerical values shown in the figure.

First, the control device 4 can perform PID control with a predetermined set pressure P0 input by a user or the like as a target. Namely, it is the control: the frequency value output from the electric power conversion device 3 is changed in accordance with the fluctuation of the discharge pressure, and the discharge air amount of the compressor body 1 is increased or decreased. In addition, P or PI control may also be used.

When the compressor 1 starts to operate at time t0 to t1 in fig. 2, the controller 4 outputs a frequency command value to the electric power converter 3 so that the motor 2 operates at a rated full speed at a predetermined acceleration rate, and performs operation under PID control so that the input value from the pressure sensor 17 becomes P0. Further, the suction modulation valve 5 at this time is Open (Open).

Next, at time t1 to t2, when the amount of air used by the compressed air on the user side decreases (for example, about 20% of the amount of air used) and the discharge pressure rises to be higher than the set pressure P0, the control device 4 outputs a command having a predetermined frequency between the full-speed rotation speed and the lower-limit rotation speed to the electric power conversion device 3 (full-speed rotation frequency > predetermined frequency > lower-limit rotation). More specifically, the predetermined frequency is gradually decreased to decrease the rotation speed of the motor in response to the increase in the discharge pressure from P0. In the present embodiment, in the pressure region which is greater than the set pressure P0 and less than the upper limit pressure P1, the corresponding rotation speed and pressure value have a proportional relationship, but the discharge pressure may be varied in accordance with the corresponding rotation speed such as by increasing the reduction rate of the rotation speed as the discharge pressure becomes larger, or by increasing the reduction rate of the rotation speed as the discharge pressure becomes lower. The pressure region may be changed in a stepwise manner such that a predetermined rotation speed amount is increased or decreased at a predetermined pressure amplitude.

As described above, when the discharge pressure is higher than the set pressure P0, the controller 4 operates the compressor body 1 under frequency control such that the compressor body does not have the lower limit rotation speed, but has a rotation speed higher than the lower limit rotation speed and lower than the full speed. Further, during the period from t1 to t2, the suction modulation valve 5 is fully opened.

Then, during the period from time t2 to time t, when the amount of compressed air used is further reduced, the discharge pressure is further increased, and the discharge pressure quickly reaches the upper limit pressure (P1). When the discharge pressure reaches the upper limit pressure P1, the control device 4 outputs a frequency command value that becomes the lower limit rotation speed to the electric power conversion device 3 and outputs a control command to close the suction regulator valve 5 (OClose). This stops the pressure rise of the pressure sensor 17.

That is, as one of the features of the present embodiment, there can be mentioned: during the period from the set pressure P0 to the upper limit pressure P1, the compressor body 1 is operated at a rotational speed less than the full rotational speed and greater than the lower limit rotational speed. That is, when the discharge pressure is in a pressure region larger than P0 and smaller than P1, the engine is operated at a rotation speed larger than the lower limit rotation speed, and therefore, there is an effect of improving the follow-up property to the fluctuation of the discharge pressure as compared with the case of operating at the lower limit rotation speed in the pressure region.

For example, a case may be considered in which the discharge pressure is higher than P0 by decreasing the usage amount of compressed air, the discharge air amount of the compressor body 1 is decreased by setting the rotation speed to the lower limit rotation speed, and then the usage amount of compressed air is increased again.

Since the amount of air used increases again, the pressure of the gas tank 60 decreases, but even if the operation is increased again from the lower limit rotation speed to the full speed to increase the amount of air discharged from the compressor body 1 with the decrease, a time deviation occurs until the rotation speed reaches the full speed. That is, in order to avoid the trip protection by the inertia of the motor 2 and the compressor body 1 or to protect the power conversion device 3 from outputting a severe overcurrent, it is difficult to operate at a speed exceeding the acceleration rate. Therefore, a time lag occurs until the compressor body 1 discharges an air amount equal to or larger than the re-increased used air amount, and when the increased amount of used air is larger, the compressed air pressure on the user side may become lower than the set pressure P0.

In contrast, in the present embodiment, when the discharge pressure is higher than the set pressure P0 and lower than the upper limit pressure P1, the compressor body 1 is operated at a rotation speed lower than the full rotation speed and higher than the lower limit rotation speed. Thus, when the amount of used air is increased again as described above, the time until the full-speed operation rotation speed of the compressor body 1 is restored can be relatively shortened.

Further, since the period from the set pressure P0 to the upper limit pressure P1 is a rotation state slower than the full-speed rotation, the effect of reducing the power consumption corresponding to the rotation state can be expected, and the energy saving effect of reducing the power required for boosting can be expected.

For example, in the conventional suction modulation valve control, the suction modulation valve is gradually closed during a period from the set pressure P0 to the upper limit pressure P1 (the used air amount ratio is decreased), and therefore the suction pressure of the compressor is also gradually decreased. Thus, the vacuum pressure is substantially reduced when fully closed. That is, the compressor body 1 is driven under a pressure difference such that the suction side is a vacuum pressure and the discharge side is an upper limit pressure P1.

In contrast, in the present embodiment, even if the used air amount ratio is reduced, the intake regulating valve 5 is kept in the fully opened state. The suction pressure of the compressor body 1 is maintained substantially at atmospheric pressure. That is, in the case of the present embodiment in which the suction pressure of the compressor main body 1 decreases as going toward the upper limit pressure, and therefore the pressure increase amount increases, it is maintained at the pressure increase amount for reaching the upper limit pressure, and therefore the energy saving effect greatly increases accordingly.

In addition, in the case of having the gas box 60 as in the present embodiment, the volume of the gas box 60 can be reduced. Generally, the gas tank 60 has a function of mitigating pressure fluctuations caused by an increase or decrease in the amount of air used. In other words, the gas tank 60 can function as a buffer device, and since the pressure fluctuates due to the fluctuation of the air amount in many cases, the gas tank can store a certain volume of compressed air in advance according to the usage amount, thereby reducing the fluctuation range of the pressure accompanying the usage. In the present embodiment, since the following property to the pressure fluctuation becomes high, the volume of the gas tank 60 can be reduced accordingly.

Next, the following improvement effect of the present embodiment and the effect of reducing the volume of the gas box 60 will be described by using examples.

For example, the air volume is 6m when the air volume is 100%³(cubic meter)/min, the volume of the gas-liquid separator 12 was set to 30L, the temperature of the discharged air was set to 80 ℃, the set pressure P0 was set to 0.7MPa, and the upper limit pressure P1 was set to 0.8 MPa. The compressor body 1 needs to be operated as follows: when the used air amount ratio is about 0%, the pressure in the gas-liquid separator 12 becomesThe upper limit pressure P1(0.8 MPa). Then, the set pressure (0.7MPa) can be secured even if the air amount ratio used on the user side becomes 100%.

Here, the time t at which the pressure in the gas-liquid separator 12 (the detection value of the pressure sensor 17) decreases to 0.80Mpa → 0.70Mpa is calculated by the following equation 1, and is about 0.3 seconds.

t＝C/Qs×(Ts/Ps)×{(Pf/Tf)-(Pi/Ti)}[s]

Formula (1)

Here, the number of the first and second electrodes,

t: pressure drop time (min)

C: volume of gas box (m3) 0.03m3

And Qs: average discharge air amount of compressor 50 (m 3/min): (6+ (6 × 0.65))/2 ═ 4.95m3

Ts: absolute temperature (K) of exhaust air: 30+273 ═ 303K

Ps: absolute pressure of exhaust air (MPa): 0.1013MPa

Pf: final absolute pressure (MPa) in gas-liquid separator: 0.7+ 0.1013-0.8013 MPa

Tf: final absolute temperature (K) in gas-liquid separator: 80+273 ═ 353K

Pi: initial absolute pressure (MPa) in gas-liquid separator: 0.8+ 0.1013-0.9013 MPa

Ti: initial absolute temperature (K) in the gas-liquid separator: 80+273 ═ 353K.

If the time until the full-speed rotation is restored is not set to 0.3 seconds or less, the target pressure P0 cannot be ensured. In the case where the acceleration time of the motor 2 from the stop to the full speed is required to be 6 seconds, when the consumed power ratio at the upper limit pressure P1 is set to 65%, the time required to reach the full speed is about 2 seconds, and the period of 1.7 seconds is less than the target pressure P0. Therefore, in the present embodiment, in order to maintain the target pressure P0, an air tank of about 0.2m3 is required downstream of the compressor 50.

In contrast, in the compressor having the discharge air amount of 6m3/min, the gas tank required for the fixed speed machine and the transmission, in which the rotation speed is set to the lower limit rotation speed and the suction adjustment valve is gradually closed during the period from the target pressure P0 to the upper limit pressure P1, is as follows.

Speed setter approximately 0.7m3 (3.5 times of the embodiment)

The transmission approximately equal to 0.4m3 (2 times of the embodiment)

As described above, the present embodiment is found to have a significant effect in terms of improvement in followability to pressure fluctuations and downsizing of the gas box.

Example 2

Next, example 2 using the present invention will be described.

Fig. 3 schematically shows the structure of the compressor 100 of embodiment 2. Note that the same reference numerals are used for the same components as in embodiment 1, and detailed description thereof may be omitted.

The compressor 100 of embodiment 2 is mainly different from the compressor 50 of embodiment 1 in that the suction modulation valve 5 is not provided. In the compressor 100, a discharge valve 14 is provided between the check valve 15 and the secondary filter 13 in the discharge pipe 10.

The discharge valve 14 is a discharge mechanism for discharging compressed air from the compressor body 1 to the check valve 15 to the atmosphere, and includes a valve body. For example, the valve is constituted by an electromagnetic valve or the like and can be opened and closed in accordance with a control command from the control device 4. Further, the valve may be a mechanical valve body that opens at a predetermined pressure by a biasing force of a spring or the like. In the present embodiment, the prescribed pressure refers to the upper limit pressure P1.

Although not shown, the discharge valve 14 is connected to the suction side of the compressor body 1 (between the suction filter 8 and the suction port) and can discharge compressed air. The present invention is not limited to this, and may be directly discharged to any space inside the package or to the outside.

In the present embodiment, the control device 4 opens the exhaust valve (Open) when the detection value of the pressure sensor 17 is detected as the upper limit pressure P1. That is, the same thing as in embodiment 1 is that the control device 4 drives the motor 2 at a frequency in a range from the set pressure P0 to the upper limit pressure P1, which is smaller than the full speed and greater than the lower limit rotation speed. One of the features is that the exhaust valve 14 is opened to reduce the power load when the upper limit pressure P1 or higher is reached.

Fig. 4 shows the discharge pressure, the rotation speed of the motor 2 (the frequency of the electric power conversion device 3), and the state change of the exhaust valve 4 in time series in example 2. The set pressure P0, the upper limit pressure P1, and the like are the same in value as in fig. 2 of embodiment 1.

At time t0 to t1 in fig. 4, the controller 4 drives the motor 2 so that the motor 2 operates at a predetermined acceleration rate at a rated full speed, and performs operation under PID control so that the input value from the pressure sensor 17 becomes P0. Also, at this time, the exhaust valve 14 is closed (Close).

Next, at time t1 to t2, when the amount of air used by the compressed air on the user side decreases (for example, about 20% of the amount of air used) and the discharge pressure rises to be higher than the set pressure P0, the control device 4 outputs a command to the electric power conversion device 3 to achieve a predetermined frequency between the full-speed rotation speed and the lower-limit rotation speed (full-speed rotation frequency > predetermined frequency > lower-limit rotation).

Then, in time t2 to time t, when the amount of compressed air used is further reduced, the discharge pressure further rises, and the discharge pressure reaches the upper limit pressure (P1) immediately. When the discharge pressure reaches the upper limit pressure P1, the control device 4 outputs a frequency command value that becomes the lower limit rotation speed to the electric power conversion device 3 and outputs a control command to Open (Open) the exhaust valve 14. This stops the pressure rise of the pressure sensor 17, and the pressure upstream from the check valve 15 decreases.

Although not shown, a pressure retaining valve is disposed in the discharge pipe 10, and has a valve body that is vented for safety when the discharge pressure becomes a safety pressure higher than the upper limit pressure P1.

According to example 2, as in example 1, the effects of improving the follow-up property to the pressure fluctuation and downsizing the gas box can be expected. In addition, as described above, in the period from t1 to t2, the power consumption can be reduced in accordance with the rotation at the rotation speed less than the full rotation speed.

The present invention is not limited to the above-described examples, and various changes and substitutions can be made without departing from the scope of the present invention.

For example, in embodiment 1 described above, the suction modulation valve 5 is closed when the upper limit pressure P1 is reached, and the exhaust valve 14 is opened in embodiment 2, but both may be provided and controlled. When the upper limit pressure P1 or higher, the energy saving effect by both can be further expected.

In embodiments 1 and 2, the suction modulation valve 5 may be opened or the exhaust valve 14 may be closed when the pressure becomes lower than P1 after the suction modulation valve 5 is closed or the exhaust valve 14 is opened under the upper pressure limiting force P1 and the usage amount of the compressed air increases. When the upper limit pressure P1 continues for a predetermined time, the driving of the compressors 50 and 100 may be automatically stopped. Examples of the predetermined time include: the duration of the upper limit pressure P1, and the load factor (the ratio of the duration of operation at full speed to the operation time at less than full speed, etc.) for a predetermined time until the upper limit pressure P1 is immediately terminated. For these times, the compressor may be stopped from being driven by taking into account the minimum operation time (guard driving time) after the start of the compressors 50 and 100.

In the above-described embodiment, an air compressor is taken as an example, but the present invention can be applied to compressors of other gases without departing from the scope of the present invention.

In the above embodiment, the enclosed air compressor is taken as an example, and the gas tank 60 is disposed separately from the compressors 50 and 100, but a structure in which the gas tank is integrated with a compressor of a tank-mounted type or the like may be employed, or a structure in which the gas tank is built in the enclosure may be employed.

In the above embodiment, the oil supply type compressor is taken as an example, but a liquid supply type compressor that supplies other liquid such as water to the compression operation chamber may be used. Further, the present invention can also be applied to a gas compressor not supplied with liquid. In the case where the compressor body is configured by a plurality of stages, the location of the exhaust valve 14 is not limited to the high-pressure stage side, and may be a position for discharging air at an intermediate stage.

Description of the reference numerals

1 … … compressor body, 2 … motor, 3 … electric energy conversion device, 4 … control device, 5 … suction adjusting valve, 7 … suction inlet, 8 … suction filter, 10 … discharge piping, 11 … temperature sensor, 12 … gas-liquid separator, 13 … secondary filter, 14 … exhaust valve (air release valve), 15 … check valve, 16 … air cooler, 17 … pressure sensor, 20 … oil piping, 21 … oil cooler, 22 … three-way valve, 23 … pump, 24 … bypass piping, 25 … fan device, 30 … suction inlet, 32 … exhaust outlet, 40 … panel, 50 · 100 … compressor, 59 … external piping, 60 … gas tank.

Claims

1. A gas compressor, comprising:

a compressor main body sucking gas and discharging compressed gas;

a pressure detection device that detects a discharge pressure of the compressed gas;

a drive source of the compressor main body; and

a control device that controls the drive source in a variable speed manner based on a detection value of the pressure detection device and controls opening and closing of the suction regulator valve,

the gas compressor is characterized in that:

the control device drives the drive source at a rotation speed less than a full rotation speed and greater than a lower limit rotation speed of the drive source when the discharge pressure is greater than a set pressure P0 and less than a pressure higher than a set pressure P0 by an upper limit pressure P1.

2. The gas compressor as set forth in claim 1, wherein:

the control device drives at a rotation speed close to the lower limit rotation speed as the discharge pressure increases from the set pressure P0 to the upper limit pressure P1.

3. The gas compressor as set forth in claim 1, wherein:

the control device drives at the lower limit rotation speed when the discharge pressure is equal to or higher than the upper limit pressure P1.

4. The gas compressor as set forth in claim 1, wherein:

a suction regulating valve for controlling the amount of suction gas is arranged on the suction side of the compressor body,

the control device closes the suction modulation valve when the discharge pressure is equal to or higher than the upper limit pressure P1.

5. The gas compressor as set forth in claim 1, wherein:

the control means fully opens the suction regulator valve when the discharge pressure is greater than the set pressure P0 and less than the upper limit pressure P1.

6. The gas compressor as set forth in claim 1, wherein:

a discharge mechanism for discharging the compressed gas at a pressure equal to or lower than a safe pressure is provided on a downstream side of the compressor main body,

when the discharge pressure is higher than the upper limit pressure P1, the discharge mechanism discharges the compressed gas.

7. The gas compressor as set forth in claim 1, wherein:

an exhaust mechanism for discharging the compressor gas is provided on the downstream side of the compressor main body,

the control device opens the exhaust mechanism when the discharge pressure is equal to or higher than the upper limit pressure.

8. The gas compressor as set forth in claim 1, wherein:

the gas is air.

9. The gas compressor as set forth in claim 1, wherein:

the gas compressor is in liquid supply type.

10. The gas compressor as set forth in claim 1, wherein:

the compressor body is of a positive displacement type or a turbine type.