JP2001082345A - Oilless type variable displacement compressor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a speed control at approximately a constant pressure irrespective of the amount gas in service by providing a blow-off valve having a plurality of ON-OFF control valves installed thereon in parallel with each other, reducing the amount of each blow air more than a specified amount of gas, and increasing the sum of the amounts of blow air from all ON-OFF control valves over a specified amount of gas. SOLUTION: A blow-off valve 8 is formed of a plurality of ON-OFF control valves arranged in parallel with each other blowing compressed air when the amount of air in service Qc is smaller than a specified amount of air qc0. The amount of blow air from solenoid valves (a) and (b) is set at approximately 1/3 of qc0, and that from a solenoid valve (c) is set at a value slightly larger than 1/3 of qc0. Thus, when the solenoid valves (a) to (c) are opened, the total of qc0 can be blown off and, even if Qc becomes zero, a compressor 2 can perform a constant pressure control continuously, and the amount of delivery air Qs from the compressor 2 becomes slightly larger than qc0. Thus, because the amount of air Qs delivered from the compressor 2 is larger than the specified amount of air qc0, the compressor 2 can always perform the constant pressure control.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to an oilless type variable displacement compressor using a blow-off valve, and more particularly to an oilless type variable displacement compressor capable of controlling the number of revolutions even in a low use gas amount region below a temperature limit revolution number.

[0002]

2. Description of the Related Art As an example of a conventional oilless compressor, an oilless screw compressor will be described. The capacity control method is disclosed in, for example, JP-A-59-79094.
According to the upper limit pressure and lower limit pressure set in the discharge pressure switch, the unload operation with the suction valve closed and the air release valve opened, and the full load operation with the suction valve opened and the air release valve closed, perform Operate while repeating unload operation time and full load operation time according to the amount.

[0003] Disadvantages of this control method are that a relatively large tank capacity for storing the discharge gas is required and that the discharge pressure fluctuates. In addition, the suction valve and the blow-off valve have an integral structure as shown in JP-A-59-79094, JP-A-59-93988, and the like, in order to reliably link the opening and closing operations. It is a valve.

[0004] In recent years, oil-filled screw compressors that inject a large amount of oil into a compression chamber have been driven by an inverter as disclosed in JP-A-7-286584 and have a constant discharge pressure control. Many have been proposed.

However, an oilless screw compressor has a temperature limit point as described in Japanese Patent Application Laid-Open No. 9-119379, and a used gas amount corresponding to this temperature limit point (hereinafter referred to as a predetermined gas). When the used gas amount is less than the above, the rotation speed cannot be controlled by the inverter, and it is necessary to blow off the discharged gas by the blow-off valve.

In this control method, when the used gas amount is equal to or less than the predetermined gas amount, the full load operation described in JP-A-59-79094 is changed to the operation at the predetermined gas amount, and the unload operation is performed. It is necessary to repeat the operation at the predetermined gas amount, which also requires a certain amount of tank capacity, and also requires the expensive interlocking valve.

Japanese Patent Application Laid-Open No. Hei 6-193579 proposes that when a gas amount is required in a non-operable region, unnecessary gas is blown off while operating at a rotation speed higher than this region. I have.

[0008]

SUMMARY OF THE INVENTION In view of the foregoing, it is an object of the present invention to control the number of revolutions even when the amount of gas used is equal to or less than a predetermined gas amount, and to reduce the tank capacity.
It is another object of the present invention to provide an oilless variable displacement compressor driven by an inverter which does not require an expensive intake-air discharge interlocking valve.

[0009]

In order to achieve the above object, according to the present invention, the number of revolutions is controlled so that the discharge pressure becomes constant, and when the amount of gas used becomes equal to or less than a predetermined gas amount, the blow-off valve is set. In an oilless variable displacement compressor that opens and discharges a discharge gas, a plurality of ON-type compressors in which the discharge valves are installed in parallel are provided.
It has an OFF control valve, and when the used gas amount becomes equal to or less than the predetermined gas amount, the ON-OFF control valve is sequentially opened and closed to maintain the discharge pressure substantially constant.

Further, the amount of each air blown from the ON-OFF control valve is made smaller than the predetermined gas amount so that all the ON-OF
The sum of the amount of air discharged from the F control valve is larger than the predetermined gas amount.

That is, by configuring the oilless variable displacement compressor as described above, the ON-OFF control valve is sequentially opened or closed according to the used gas amount even when the used gas amount becomes less than the predetermined gas amount. In addition, it is possible to control the rotation speed of the compressor by the inverter while blowing air.

Accordingly, it is possible to provide an inverter-driven oilless variable displacement compressor which requires only a small tank capacity and does not require a suction-air discharge interlocking valve.

[0013]

1 and 2 show a first embodiment in which the present invention is applied to a single-stage oilless screw air compressor. FIG. 1 shows the structure of the compressor. FIG. 2 is a diagram for explaining the operation and characteristics of the capacity control method.

In FIG. 1, 1 is a suction filter, 2
Is a single-stage oilless screw compressor having no suction valve (suction throttle valve) conventionally used between 1 and 2. Three
Is a precooler as a first-stage cooler of compressed air, 4 is a check valve, 5 is an aftercooler of a second-stage cooler of compressed air, and 7 is a pressure sensor. In this embodiment, no tank is provided, and the pressure sensor 7 detects the outlet pressure of the aftercooler 5.

The air is sucked into the compressor 2 from the atmosphere through the filter 1 and is compressed to a discharge pressure (usually about 7 kg / cm ² gauge pressure) and becomes high temperature (300 ° C. or higher). This high-temperature air is cooled by the pre-cooler 3 (up to one hundred and several tens of degrees Celsius), flows through the check valve 4 to the after-cooler 5, and is cooled to near room temperature before use. 8 is used air volume Q
When c is smaller than the predetermined air amount qc0, the air discharge valve blows compressed air from between the precooler 3 and the check valve 4, and is constituted by a plurality of ON-OFF control valves arranged in parallel. In this embodiment, the solenoid valve is constituted by three solenoid valves a, b and c. Solenoid valves have the advantage of being cheaper and more reliable than needle valves and the like. Reference numeral 9 denotes a control device which calculates a difference between a pressure output value from the pressure sensor 7 and a pressure instruction value given from the outside, and outputs an instruction value of a power supply frequency of the motor 11 to the inverter 10 so as to reduce the difference. It has a function of outputting and performing constant pressure control, and a function of controlling the opening and closing of the solenoid valves a, b and c of the blow-off valve 8 when Qc is smaller than qc0.

In FIG. 2, the horizontal axis represents the amount of used air Qc,
The vertical axis indicates the power of the compressor, both of which are shown as a ratio to the value during full load operation. A indicates a full load operation, C indicates an operation at the predetermined air amount qc0, a constant pressure control by the inverter 10 is performed between A and C, and the power is substantially a straight line connecting A and C. Can be expressed.

In this embodiment, the amount of air discharged from the solenoid valves a and b is, for example, approximately one third of qc0, and the amount of air discharged from the solenoid valve c is slightly larger than one third of qc0. Therefore, if the solenoid valves a, b, and c are opened, the entire amount of qc0 can be blown off, and even if Qc becomes zero (point I), the compressor continues to operate at C 'on the constant pressure control (AC) line. The operation at the point can be continued, and the discharge air amount Qs of the compressor at this time is q
It is slightly more than c0.

Qc1 where the used air amount Qc is smaller than qc0
, The electromagnetic valve a or b
Is released, the air amount of about 1/3 of qc0 is blown off, and the capacity control characteristic shifts to the straight line DE. Straight line DE is straight line B
−C is a straight line that is translated to the left, and the discharge air amount Qs of the compressor 2 is Qc obtained by adding the air discharge amount of the solenoid valve a or b to Qc1.
c2. The used air amount qc1 at the point E is a value obtained by subtracting approximately 1/3 of the air discharge amount of the solenoid valve a or b, that is, qc0 from qc0. The compressor has a B on the constant pressure control (AC) line.
The rotation speed is controlled on -C.

When the amount of air used further decreases, both the solenoid valves a and b are opened by a command from the control device 9, and the displacement control characteristic shifts to a straight line FG, but the discharge air amount of the compressor is qc
More than 0, pressure constant control is continued on BC.

When the amount of air used further decreases, all of the solenoid valves a, b and c are opened according to a command from the control device 9, and the displacement control characteristic shifts on a straight line HI. Is also larger than qc0, and the pressure constant control is continued on B′-C ′ on the AC line.

Conversely, when the amount of air used increases, the solenoid valves are closed one after another, and the capacity control characteristic changes from the line IH to the line GF.
The line moves on a straight line E-D, and when the amount of used air further increases, the line moves on a straight line C-A constant pressure control line. However, since the discharge air amount Qs of the compressor 2 is always larger than the predetermined air amount qc0, the compressor 2 is always operated on the constant pressure control line on AC.

FIGS. 3 and 4 are views showing a second embodiment in which the present invention is applied to a single-stage oilless screw air compressor. FIG. 3 is a view showing the structure of a blow-off valve. FIG. 4 illustrates the operation and characteristics of the capacity control method.

In this embodiment, the blow-off valves 8 are a, b, c and d.
And four solenoid valves. The amount of air discharged from the solenoid valves a, b, and c in this embodiment is approximately 1/3 of qc0, and the amount of air discharged from the solenoid valve d is approximately 1/6 of qc0, ie, the amount of air discharged from the solenoid valves a, b, and c. Is almost の of the above.
Therefore, if the solenoid valves a, b, c, and d are opened, the entire amount of qc0 can be blown off, and even if Qc becomes zero (point O), the compressor is kept on the constant pressure control (AC) line. The operation at the point C can be continued, and the discharge air amount Q
s is slightly more than qc0.

When the used air amount Qc becomes smaller than qc0, the solenoid valve d is opened according to a command from the control device 9, and qc
Almost 1/6 of the air amount is blown off, and the capacity control characteristic shifts to the straight line DE. The straight line DE is a straight line obtained by translating the straight line BC to the left, and the used air amount at the point E is a value obtained by subtracting approximately 1/6 of the air discharge amount of the solenoid valve d, that is, qc0 from qc0. At this time, the compressor operates on the B-
The number of rotations is controlled on C.

When the amount of air used further decreases, one of the solenoid valves a, b and c is opened and the solenoid valve d is closed according to a command from the control device 9, and the displacement control characteristic shifts to a straight line FG. The discharge air amount of the compressor is larger than qc0, and the constant pressure control is continued on B-C.

When the used air amount Qc becomes smaller than qc1, the solenoid valve d is opened by a command from the control device 9, and qc
Almost half of the amount of air is blown off, and the capacity control characteristic shifts to the straight line HI.

When the amount of air used further decreases, one of the solenoid valves a, b and c is opened and the solenoid valve d is closed according to a command from the control device 9.

When the used air amount Qc becomes smaller than qc2, the solenoid valve d is opened by a command from the control device 9, and qc
About 5/6 of the air amount is blown off, and the capacity control characteristic shifts to the straight line LM.

When the amount of air used further decreases, all of the solenoid valves a, b and c are opened according to a command from the control device 9 and the solenoid valve d is opened.
Is closed.

As described above, the power fluctuation can be reduced to almost half as compared with FIG. 2 only by adding one solenoid valve.

FIG. 5 shows a third embodiment in which the present invention is applied to a two-stage oilless screw air compressor driven by a single motor as disclosed in Japanese Patent Application Laid-Open No. 64-15484. FIG.

In FIG. 5, reference numeral 1 denotes a suction filter,
Reference numeral 2 denotes a low-pressure stage compressor which does not have a suction valve (suction throttle valve) conventionally used between 1 and 2. 13 is a high-pressure stage compressor, 14 is an intercooler for cooling the high-temperature air compressed by the low-pressure stage compressor 12, 4 is a check valve, 5 is an aftercooler for cooling the high-temperature air compressed by the high-pressure stage compression, 7 Is a pressure sensor. In this embodiment, no tank is provided, and the pressure sensor 7 detects the outlet pressure of the aftercooler 5.

Air is sucked from the atmosphere into the low-pressure compressor 12 through the filter 1 and discharged at a pressure (usually 2 kg / cm ^2).
(About a gauge pressure) and become high temperature (about one hundred and several tens of degrees Celsius). This high-temperature air is cooled by the intercooler 14,
It is sucked into the high-pressure stage compressor 13 and discharged at a pressure (usually 7 kg /
cm ² gauge圧程degree) is compressed to a high temperature (one hundred and several tens ℃ about). This high-temperature air flows through the check valve 4 to the aftercooler 5, where it is cooled to near room temperature before use.

8 is a graph showing that the used air amount Qc is equal to the predetermined air amount q.
When it is less than c0, it is a blow-off valve that discharges compressed air from between the high-pressure stage compressor 13 and the check valve 4, and is composed of a plurality of ON-OFF control valves arranged in parallel.
It is composed of three solenoid valves of 2, b2 and c2. Reference numeral 15 denotes a blow-off valve for blowing out the compressed air of the low-pressure stage compressor 12 from between the low-pressure stage compressor 12 and the intercooler 14, and is constituted by a plurality of ON-OFF control valves arranged in parallel. In the embodiment, it is constituted by three solenoid valves a1, b1 and c1.

Reference numeral 9 denotes a control device which calculates a difference between a pressure output value from the pressure sensor 7 and a pressure instruction value given from the outside, and controls a power supply frequency of the motor 11 to the inverter 10 so as to reduce the difference. A function of outputting an indicated value and performing a constant pressure control; a solenoid valve of a2, b2 and c2 of the blow-off valve 8 when the used air amount Qc is smaller than qc0;
5 to control the opening and closing of the solenoid valves a1, b1 and c1.

The amount of air blown off by the solenoid valves a2 and b2 in this embodiment is, for example, approximately one-third of qc0.
It is assumed that the blowing amount of 2 is slightly larger than 1/3 of qc0. In addition, the amount of air blown by the solenoid valves a1, b1 and c1 is approximately equal to the amount of air blown by the solenoid valves a2, b2 and c2 with respect to the amount of air flowing through the intercooler 14 at full load. Also, solenoid valves a1 and a2, b1 and b
2 and c1 and c2 are wired so as to open and close at the same time according to a command from the control device 9.

When the used air amount Qc becomes smaller than qc0, the solenoid valves a1 and a2 or b1 and b2 are opened by a command from the control device 9.

When the amount of air used further decreases, the four solenoid valves a1, a2, b1 and b2 are opened in accordance with a command from the control unit 9.

When the amount of air used further decreases, all of the solenoid valves are opened according to a command from the control device 9.

The capacity control characteristic of this embodiment is almost the same as that of FIG.

According to this embodiment, the discharge valve 8 and the discharge valve 15
The ratio of the amount of air discharged from the compressor to the amount of air discharged from the high-pressure compressor 13 and the low-pressure compressor 12 at full load can be made substantially equal, so that the intermediate-stage pressure (for example, the suction pressure of the high-pressure compressor) becomes almost constant. Therefore, the discharge air temperature of the high-pressure stage compressor 13 and the low-pressure stage compressor 12 can be kept below the limit temperature.

In the embodiment of the present invention, an inexpensive solenoid valve is used as a blow-off valve. However, a small-sized manifold-type solenoid valve can be used.
Any -OFF control valve can be used.

In the embodiment of the present invention, air is used as the gas to be handled. However, when the present invention is applied to a general gas compressor, it is necessary to cool the gas blown from the blow-off valve and then return to the suction of the compressor. Good.

[0044]

According to the present invention, even in an oilless type variable displacement compressor having a temperature limit point, it is possible to control the rotational speed at a substantially constant pressure regardless of the amount of gas used. It is possible to realize an oilless type variable displacement compressor that requires a small capacity and does not require an expensive suction-blowing interlocking valve.

[Brief description of the drawings]

FIG. 1 is a view showing an oilless variable displacement compressor according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a relationship between the power of the compressor of FIG. 1 and the amount of air.

FIG. 3 is a configuration diagram of an oilless screw air compressor according to an embodiment of the present invention.

FIG. 4 is a characteristic diagram showing a relationship between power and air amount by the compressor of FIG. 3;

FIG. 5 is a configuration diagram of an oilless screw air compressor according to an embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Suction filter, 2 ... Oilless screw compressor, 3 ... Precooler, 4 ... Check valve, 5 ... Aftercooler, 7 ... Pressure sensor, 8 ... Blowoff valve, 9 ... Control device, 10
... Inverter, 11 ... Motor, Qc ... Gas consumption, Qs
... Amount of gas discharged from the compressor, qc0 ... A predetermined amount of gas.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Jin Nishimura 390 Muramatsu, Shimizu-shi, Shizuoka Prefecture F-term in Industrial Machinery Group, Hitachi, Ltd. 3H029 AA03 AB02 BB53 CC15 CC54 CC62 CC86 3H045 AA05 AA09 AA15 AA26 BA23 CA03 DA07 DA18 EA13 EA26

Claims (5)

[Claims] An oil-free type variable displacement compressor that controls the number of revolutions so that the discharge pressure is constant, and opens the blow-off valve to discharge the gas when the amount of gas used becomes equal to or less than a predetermined gas amount. A plurality of ON-Os in which the blow-off valves are installed in parallel
An FF control valve, wherein each of the ON-OFF control valves has a smaller amount of blown gas than the predetermined gas amount, and the sum of the blown air amounts of all the ON-OFF control valves is larger than the predetermined gas amount. Refueling type variable displacement compressor. 2. A non-lubricated variable displacement compressor that controls the number of revolutions so that the discharge pressure is constant, and opens the discharge valve to discharge the gas when the amount of gas used becomes equal to or less than a predetermined gas amount. A plurality of ON-Os in which the blow-off valves are installed in parallel
The FF control valve is a FF control valve, and when the used gas amount becomes equal to or less than the predetermined gas amount, the ON-OFF control valve is sequentially opened and closed to blow off the air, and is operated at a rotation speed higher than the minimum rotation speed corresponding to the predetermined gas amount. A non-lubricated variable displacement compressor characterized in that the discharge pressure is kept substantially constant. 3. The oilless variable displacement compressor according to claim 1, wherein the oilless variable displacement compressor is a two-stage compressor having a low-pressure stage compressor and a high-pressure stage compressor. A non-lubricated variable displacement compressor characterized in that a blow-off valve is also provided in the low-pressure stage compressor. 4. An oilless variable displacement compressor according to claim 1, wherein said blow-off valve is provided between said compressor and a gas cooler for cooling gas from said compressor. Oil-free variable displacement compressor characterized by being made. 5. The oilless variable displacement compressor according to claim 1, wherein said ON-OFF control valve is a solenoid valve. .