JPH06193579A - Variable capacity compressor - Google Patents

Abstract

PURPOSE:To prevent the generation of vibration and noise through prevention of the occurrence of resonance owing to a specified rotation speed and cope with a low consumption amount of gas to be compressed by arranging a throttle means situated upper stream from the suction port of a compressor body when a delivery amount of gas to be compressed is varied through the change of the rotation speed of a rotor as a delivery pressure is kept at an approximately constant value. CONSTITUTION:In a compressor being of a volume type rotary type, such as a screw type, a compressor body 2 is driven with the aid of an induction motor 3. regulation of a delivery amount is controlled through control of the rotation speed of the induction motor 3 by controlling an inverter 4 according to a speed command value from a control device 5 in the compressor 1. In this case, a throttle valve 12 is located in the middle of a suction pipe connected to the suction port 8 of the compressor body 2. When a delivery amount equivalent to a rotation prohibition speed at which the compressor must avoid a rotation speed at which resonance is generated by the compressor is demanded, the suction passage is throttled by a throttle valve 12, and control is made so that the induction motor 3 is driven at a rotation speed higher than a proper rotation speed when the throttle valve 12 is fully opened.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to compressors, and in particular
In a variable displacement compressor that has the function of controlling the discharge pressure to a constant value even if the amount of compressed gas consumed increases or decreases, the resonance due to a specific rotation speed is avoided to reduce vibration and noise, The present invention relates to a compressor that can handle even a small amount of consumption.

[0002]

2. Description of the Related Art The basic function of a compressor is to inhale, compress, and discharge gas. It is desirable that the discharge pressure of a compressed gas (hereinafter, referred to as a compressed gas. It is often air, but other gas may be compressed for a chemical plant, etc.) is constant, and a compressor or It is adjusted by a regulator installed in the subsequent stage. When the compressor is operated at a constant rotation speed, the discharge pressure decreases when the amount of compressed gas consumed exceeds the amount discharged, and conversely, when the amount consumed is less than the amount discharged, the discharge pressure becomes excessive. Therefore, there are some methods for keeping the discharge pressure constant even if the consumption amount of the compressed gas changes. Among them, from the viewpoint of economic efficiency and ease of use, as a method suitable for the rotary positive displacement compressor, a method of controlling the discharge flow rate by feeding back the discharge pressure and increasing or decreasing the rotation speed of the rotor is special. Kaisho 55-1647
No. 92 publication.

In this known example, when the consumption amount increases, a phenomenon such as a decrease in the discharge pressure appears. Therefore, by detecting it, the rotor rotation is accelerated, the discharge amount is increased and the discharge pressure is kept constant. Therefore, it is stated that the rotation of the rotor can be continuously changed by the inverter. However, no mention is made of how to avoid the resonance of the structure, which may occur at a particular rotational speed. Further, it is difficult for current inverters and electric motors to realize a very slow drive frequency (usually about 5 Hz or less). This known example does not mention a driving method in the case where the required discharge amount that requires such a rotation speed is small.

[0004]

Since the compressor is composed of a large number of members such as an electric motor and a heat exchanger in addition to the main body of the compressor, a large number of vibration modes and natural vibrations corresponding thereto are taken from the viewpoint of vibration. Have a number. In the conventional compressor with a constant rotation speed, it was sufficient to design so that their natural frequencies did not match the rated rotation speed and its multiples, and it was easy to avoid resonance.

However, in a variable displacement compressor capable of continuously changing the rotation speed, since the rotation speed changes, the rotation frequency of the rotor or its multiple can take an infinite value. Therefore, there is a high possibility that it will resonate with the natural frequency determined by the structure at any rotation speed. Even if the natural frequency is changed by changing the rigidity of the structure or changing the mass of the member, the resonance frequency is changed, and this cannot be avoided. Resonance is a phenomenon that must be avoided, as vibration and noise become severe, and excessive force is applied to the resonating member to promote fatigue.

Further, when the variable speed is realized by the inverter, there is a problem that the consumption amount of the compressed gas is small and the proper rotation speed is very slow and the driving is difficult. This is because a low frequency causes problems such as too much current flowing through the motor, so the inverter is equipped with a function to prevent this, and low frequencies are not output. The frequency for driving the electric motor is stopped or limited to a certain value (usually about 5 Hz) or higher, and no output can be made during that time.

In view of the above problems, the present invention, in a compressor in which the rotor rotation speed changes according to the load, avoids the occurrence of resonance while maintaining the discharge pressure at a constant value, and at the same time, compresses the gas to be compressed. It is an object of the present invention to realize a variable displacement compressor that can be used even if the consumption of the compressor is small.

[0008]

The first means for achieving the above-mentioned object is to provide throttling means upstream of the suction port of the compressor body so as to have the following functions. The throttle means is normally in the fully open state, but has a function of throttle the flow path by air pressure or electromagnetic force in response to a command from the control device. The control device has a function of making a judgment based on information from various sensors and controlling the rotor rotation speed of the compressor body and the opening of the throttle means.

A second means for achieving the above object is
An air discharging means is provided downstream of the discharge port of the compressor body to have the following functions. This air releasing means responds to a command from the control device,
It has a function of discharging the compressed gas to be compressed from the discharge path. The control device has a function of making a judgment based on information from various sensors and controlling the rotor rotation speed of the compressor body and the opening of the throttle means.

A third means for achieving the above object is
Install the software that performs the operation described in the next section "Operation" in the control device.

[0011]

The first means operates as follows. Normally, the throttle means is in a fully opened state, and the rotor rotates at a rotation speed matching the discharge amount. However, in order to avoid the operation at the resonating rotation speed, the following operation is performed when the discharge amount corresponding to the resonance rotation speed is required. The controller causes the rotor to rotate at a rotational speed higher than the resonant rotational speed.
As it is, the discharge amount of the compressed gas is larger than the required value. Therefore, the suction amount is limited by narrowing the suction passage by the throttle means, and the discharge amount is suppressed to the target value.

The second means operates as follows.
The discharge means is normally fully closed, and the rotor is rotated at a rotation speed matching the discharge amount. However, in order to avoid the operation at the resonating rotation speed, the following operation is performed when the discharge amount corresponding to the resonance rotation speed is required. The controller causes the rotor to rotate at a rotational speed higher than the resonant rotational speed. Since the discharge amount of the compressed gas is larger than the required value as it is, the discharge amount of the compressed gas is discharged to the target value by discharging the excess compressed gas.

The above-mentioned third means operates as follows.
When a discharge amount corresponding to the resonance rotation speed is required, the control device alternately selects a rotation speed higher than the resonance rotation speed and a rotation speed slower than the resonance rotation speed, and rotates the rotor in a time division manner. Then, when the time average is taken, the discharge amount becomes a target value. The average discharge amount can be changed by the ratio of the duration of the fast rotation speed to the slow rotation speed.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention based on claim 1 will be described below with reference to FIGS.

FIG. 1 is a system diagram of the variable capacity air compressor of this embodiment. The compressor 1 is composed of a compressor body 2 and some auxiliary machines. The compressor body 2 is a positive displacement rotary compressor such as a screw type or a scroll type, and the discharge amount can be increased or decreased in proportion to the rotation speed. The compressor main body 2 operates by being supplied with rotational power by the induction motor 3, sucks air from the suction port 8, compresses it, and then discharges it from the discharge port 9. The electric motor 3 is supplied with a three-phase alternating current from the inverter 4 and rotates. The inverter 4 has a capability of receiving a speed command value from the control device 5 inside the compressor 1, converting the commercial AC power 6 supplied from the outside into a commanded frequency and voltage, and outputting the commanded frequency and voltage.

The suction port 8 of the compressor body 2 sucks the atmosphere from the air cleaner 7 through the throttle valve 12. The throttle valve 12 is a solenoid valve that opens and closes electrically by a command from the control device 5. A discharge pipe 10 is connected from the discharge port 9 to the outside, and a pressure sensor 11 is provided on the way. The output information of the pressure sensor 11 is wired so as to be sent to the control device 5 as an electric signal. The wiring is also used to supply electric power from the control device 5 to the pressure sensor 11.

The air compressor of this embodiment operates as follows. FIG. 2 is a graph illustrating the operation of the variable displacement air compressor of the present embodiment, showing the rotor rotation speed and the throttle valve opening with respect to the required discharge amount.

The present compressor basically operates as follows. The commercial AC power 6 is converted into voltage and frequency by the inverter 4 and drives the electric motor 3. The compressor main body 2 which receives power from the electric motor 3 and rotates rotates in and sucks air from the suction port 8, compresses the air, and discharges the air from the discharge port 9. The air passes through the air cleaner 7, removes dust, passes through the suction throttle valve 12, and is sucked into the suction port 8. On the other hand, the compressed air discharged from the discharge port 9 is discharged to the outside from the discharge pipe 10. The discharge pressure at that time is constantly monitored by the pressure sensor 11, and the obtained discharge pressure data is sent to the control device 5.

The control system for keeping the discharge pressure constant operates as follows. When the amount of compressed air consumed increases and the pressure inside the discharge pipe 10 decreases, the pressure sensor 11 senses it, and the controller 5 commands the acceleration of the rotor rotation speed. In response to this, the inverter 4 raises the output frequency to accelerate the electric motor 3, and the rotor of the compressor body 2 is accelerated. Since it is a positive displacement compressor, the amount of discharge increases as the rotation speed increases, and the discharge pressure recovers to a specified value. When the amount of compressed air used decreases, it works in reverse and the rotor rotation speed is decelerated to respond. Therefore, the discharge pressure that has risen once decreases and approaches the set value. In this way, the discharge pressure becomes constant regardless of the amount of compressed air consumed.

From the principle of the compressor, it is possible to continuously select an arbitrary value for the rotor rotation speed from the stop to the maximum rotation speed defined by the motor output. However, in reality, the resonance caused by the structure of the compressor must be avoided, and there can be a rotation speed that cannot be selected.

In FIG. 2, the rotational speed at which resonance occurs is indicated by Fc. Even if the rotation speed is not strictly Fc, if it is a close value, vibration noise is severe.
From F2 to F2, the rotation prohibited speed cannot be selected. Also,
Due to the nature of the inverter 4 and the electric motor 3, it cannot rotate at a speed lower than F0 for the reason described in the above "Problem".

Q1 which is the discharge amount corresponding to the rotation inhibition speed
When a discharge amount in the range from to Q2 is required, the upper limit F2 of the rotation inhibition speed is selected as the rotation speed of the rotor as shown in FIG. At that time, the suction throttle valve 12 receives a command from the control device 5 and throttles the suction passage. When the required discharge amount is smaller and closer to Q1, the throttle valve 12 is throttled to limit the flow amount, and when the required discharge amount is closer to Q2, the throttle valve 12 is opened to control the discharge amount.

Even when the compressed air consumption amount is smaller than the discharge amount Q0 at the minimum rotation speed F0, the rotation speed is kept constant at F0. Then, the intake throttle valve 12 is opened and closed according to the required discharge amount to control the discharge amount.

In the case of the required discharge amount other than the above, the suction throttle valve 12
Is always open so there is no obstacle. Further, in order to ensure the operation of the compressor 1 even when the suction throttle valve 12 fails, a fail-safe function having the open side as a basic position is provided.

According to this embodiment, there is little wasteful compression,
A variable capacity compressor with good energy efficiency can be realized. Further, since the suction throttle valve is a technology that has been used for a long time in the conventional fixed rotation speed type compressor, it has high reliability. In addition, the accuracy and stability of the discharge pressure are high.

Incidentally, in the present embodiment, explanations are omitted by omitting a separating device for the lubricating oil injected into the compressed air and a heat exchanger for cooling the air whose temperature has risen due to compression, which are not directly related to the present theory. .

In this embodiment, the revolving rotor rotation speed Fc is used.
However, there may be some displacement depending on individual differences and usage conditions. In that case, there is a method of measuring the natural frequency of each product at the time of completion and storing it in the storage means inside the control device. In addition, if a vibration sensor is installed inside the compressor and the compressor itself has the function of searching for the rotational speed at which resonance occurs by monitoring vibration, the natural frequency may change due to changes in conditions such as aging and temperature. However, it is possible to drive without resonance without influence.

In the present embodiment, the throttle valve 12 is an electromagnetic valve and has a structure in which an arbitrary opening can be selected, but it may be operated by air pressure or hydraulic pressure. In addition, the valve with a structure that allows you to select only open or closed state is simple and durable, and the price is low. When an intermediate opening is required, opening and closing may be repeated in a time-sharing manner.

Next, a second embodiment of the present invention based on claim 2 will be described with reference to FIGS. 3 and 4. The description of the same parts as those in the first embodiment will be omitted.

FIG. 3 is a system diagram of the variable capacity air compressor of this embodiment. A discharge valve 21 is provided downstream of the discharge port 9 and branched from the discharge pipe 10. The outlet of the discharge valve 21 is connected to the middle of a suction pipe 23 via a discharge pipe 22.

The air compressor of this embodiment operates as follows. FIG. 4 illustrates the operation of the variable displacement air compressor of the present embodiment. The rotor rotation speed with respect to the discharge amount and the discharge rate of the discharge valve 21 (from the discharge valve 21 with respect to the discharge amount of the compressor body 1). It is a graph which shows the ratio of the flow volume discharged | emitted) opening degree.

When a discharge amount in the range of Q1 to Q2, which is the discharge amount corresponding to the rotation prohibition speeds F1 to F2, is requested, as shown in FIG. 4, the rotation speed of the rotor is F2 which is the upper limit of the rotation prohibition speed. Select. At that time, the discharge valve 21 receives a command from the control device 5 and discharges part of the compressed air. The smaller the required discharge amount, the more the air discharge amount is limited, and the larger the required discharge amount, the more the valve is opened to control the discharge amount. The discharged air passes through the discharge pipe 22 and enters the suction pipe 23, and is sucked into the compressor body 2 again.

Even when the required discharge amount is smaller than the discharge amount Q0 at the minimum rotation speed F0, the rotation speed is kept constant at F0. Then, the discharge valve 21 is opened and closed according to the required discharge amount to control the discharge amount.

Since the discharge valve 21 is always closed at the required discharge amount other than the above, the compressed air is not wasted.

According to this embodiment, since the flow rate is controlled on the discharge side, the followability with respect to the change in the consumption of compressed air and the pressure accuracy are good. Further, since the air is discharged in a closed system, the generation of air noise can be prevented, and in the case of an oil-cooled compressor, the lubricating oil can be prevented from being taken away.

In this embodiment, the air discharged from the discharge valve 21 is compressed again, but it may be discharged into the atmosphere depending on the case. In that case, the temperature of the compressor body 1 can be lowered by sucking in the atmosphere having a temperature lower than that of the discharged air.

Next, a third embodiment of the present invention will be described with reference to FIGS. The description of the parts common to the first and second embodiments will be omitted.

FIG. 5 is a system diagram of the variable capacity air compressor of this embodiment. The constituent elements are less than those in the first and second embodiments, and only common elements are provided. However, the control device 5 incorporates software for performing the operation described below.

The operation of this embodiment will be described with reference to FIG.
FIG. 6 is a graph showing the change over time of the rotation speed in this embodiment. It is assumed that the compressed air consumption gradually increases for easy explanation. Resonant rotation speed is Fc,
The rotation prohibition speed before and after that is from F1 to F2.

When the required discharge amount gradually increases, the rotation speed also increases, and at time T1, the rotation prohibition speed lower limit F is reached.
Reach 1. Although the rotation speed changes to F1 for a short time, the discharge amount is insufficient, so the rotation speed rises to the upper limit F2 of the rotation inhibition speed for a short time and then returns to F1 again.
Subsequently, the rotation speed repeats F1 and F2 at a certain time interval, but as the required discharge amount increases, the rotation time at F1 becomes shorter and the rotation speed at F2 becomes longer. At time T2, the rotation speed corresponding to the required discharge amount exceeds F2, and therefore the normal rotation speed control is resumed.

When the rotational speed accelerates or decelerates between F1 and F2, it passes through the rotational speed Fc that resonates, but since it passes in a short time, resonance does not develop and a large vibration noise does not occur.

According to this embodiment, it is not necessary to increase the mechanical structure, and the manufacturing cost can be reduced. Moreover, since there is no useless compression, energy efficiency is good.

The discharge pressure pulsates for switching the rotation speed. However, if the switching time is shortened and a certain volume is provided in the middle of the discharge pipe, the problem does not occur.

[0044]

According to the present invention, in the compressor in which the rotor rotation speed changes according to the load, resonance is prevented while maintaining the discharge pressure at a constant value, and the required discharge amount is small. However, it is possible to realize a variable capacity compressor that is compatible with the above.

[Brief description of drawings]

FIG. 1 is a system diagram of a first embodiment of the present invention.

FIG. 2 is a graph showing a rotor rotation speed and a throttle valve opening with respect to a required discharge amount in the first embodiment of the present invention.

FIG. 3 is a system diagram of a second embodiment of the present invention.

FIG. 4 is a graph showing a rotor rotation speed and a discharge valve opening with respect to a required discharge amount in the second embodiment of the present invention.

FIG. 5 is a system diagram of a third embodiment of the present invention.

FIG. 6 is a graph showing a temporal transition of the rotation speed in the third embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Compressor, 2 ... Compressor main body, 3 ... Electric motor, 4 ... Inverter, 5 ... Control circuit, 6 ... Commercial AC power, 7 ... Air cleaner, 8 ... Suction port, 9 ... Discharge port, 10 ... Discharge pipe, 11 ...
Pressure sensor, 12 ... Intake throttle valve, 21 ... Exhaust valve, 22 ...
Air tube.

Claims (6)

[Claims] 1. A roller while keeping the discharge pressure substantially constant.
In a positive displacement rotary compressor having the function of varying the discharge rate of the compressed gas per unit time by changing the rotation speed of the compressor, a throttle means is provided upstream of the compressor body inlet port When the discharge amount is required depending on the number of rotations, the rotor is rotated at a higher rotation speed than the proper rotation speed when the throttle means is fully opened, and at the same time the discharge means is throttled to control the discharge amount. Variable capacity compressor characterized in that. 2. A low pressure roller while keeping the discharge pressure substantially constant.
In a positive displacement rotary compressor that has the function of varying the discharge rate of the compressed gas per unit time by changing the rotation speed of the compressor, a discharge device is provided downstream of the discharge port of the compressor body to specify When the amount of discharge is required depending on the number of rotations in the range, the rotor is rotated at a higher rotation speed than the proper rotation speed when no gas is released, and at the same time, excess compressed gas is discharged by the discharge means. Variable capacity compressor. 3. The variable capacity compressor according to claim 2, wherein the excess compressed gas discharged by the air discharge means is returned to the suction side of the compressor. 4. A low pressure roller while keeping the discharge pressure substantially constant.
In a positive displacement rotary compressor that has the function of changing the discharge rate of the compressed gas per unit time by changing the rotation speed of the compressor, when the discharge rate at a specific range of rotation speed is required, the appropriate rotation speed A variable displacement compressor characterized by alternately rotating at a higher rotation speed and a lower rotation speed in a time division manner. 5. A low pressure roller while maintaining the discharge pressure substantially constant.
In a positive displacement rotary compressor having a function of varying the discharge amount of the compressed gas per unit time by changing the rotation speed of the compressor, when a discharge amount at a specific range of rotation speed is required, according to claim 1. At least two of the operation, the operation according to claim 2, and the operation according to claim 4 are selectable, and a variable displacement compressor. 6. The compressor according to claim 1, wherein the compressor is a screw type air compressor having a screw rotor which is rotated by an induction motor which is supplied with electric power of variable frequency by an inverter. Variable capacity compressor characterized in that.