JP2647579B2 - Screw compressor capacity control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacity control device for a screw compressor having an on / off control valve on a suction side.

[0002]

2. Description of the Related Art A capacity control device of a screw compressor having an on / off control valve is disclosed in, for example, Japanese Patent Publication No. 1-336.
No. 76, an on / off control valve is provided on the suction side, a discharge air release valve is provided on the discharge side, and the screw compressor is operated at full load to increase the discharge pressure. When the pressure exceeds a preset upper limit, the on / off control valve is closed, and the discharge air release valve is opened to switch the screw compressor to the no-load operation. When the pressure of the compressed air falls below a preset lower limit value due to the use of the compressed air on the load side, the discharge air release valve is closed, the on / off control valve is opened, and the screw compressor is operated at full load. To automatically control the capacity.

[0003]

The pressure set value for switching the operating state of the screw compressor between full-load operation and no-load operation is fixed at the initial setting.
For this reason, when the amount of compressed air in the air storage tank connected to the discharge side of the screw compressor is constant, the air storage tank and piping connecting the air storage tank to the discharge side of the screw compressor are connected. The larger the capacity of the battery, the longer the full-load operation time until the upper-limit set value is reached and the longer the no-load operation time from the upper-limit set value to the lower-limit set value.

That is, in the above case, the switching time (cycle), which is the sum of the full-load operation time and the no-load operation time, becomes longer, and the screw compressor is operated at a discharge pressure higher than the used air pressure. The time will be longer and the power consumption will increase.

[0005] When the amount of compressed air used increases, the pressure in the air storage tank during the no-load operation of the screw compressor decreases rapidly, so that the switching time between full-load operation and no-load operation is shortened. Because the full-load operation and the no-load operation are frequently repeated, the on / off control valve opens and closes frequently, and the on / off control valve's sliding parts, contact parts, etc., wear out, causing capacity control. The reliability of the device decreases.

In view of the above circumstances, an object of the present invention is to reduce the time for full load operation even when the amount of compressed air used is small or when the capacity of the storage tank discharge piping system is large. Power consumption can be reduced and the load side
While ensuring the pressure and air volume of the compressed air used in
Screw compressor capacity for improved reliability
It is to provide a control device .

[0007]

[0008]

According to the present invention , there is provided a screw compressor provided on a suction side of a screw compressor.
Gage ON / OFF control valve and discharge pressure of screw compressor
Discharge pressure setting means for setting force and detecting load side pressure
Pressure detecting means, and a negative pressure detected by the pressure detecting means.
Load side pressure value and discharge pressure set in the discharge pressure setting means
Difference amplifying means for calculating a pressure difference value from the force value;
To control the on / off control valve continuously,
Add the full-load operation time and the no-load operation time of the
Function generated with the switching interval time as the cycle
Generating means, and the periodic function value from the periodic function generating means and the
By comparing the pressure difference value from the difference amplifying means with the pressure difference value,
Comparison means for turning on / off the on / off control valve.
In the differential amplification means, the pressure on the load side is suddenly increased.
When it becomes higher, the pressure difference value is greatly corrected,
When the pressure on the load side suddenly decreases, the difference value is reduced.
Correction means for correcting the periodic function;
Generating means for controlling the load side pressure Pd of the screw compressor;
When the pressure difference value ΔPt from the discharge pressure set value Pt is 0,
When the discharge pressure set value Pt is
A circumference that is positive when the pressure is greater than Pd and negative when the pressure is less than Pd.
It consists of a triangular wave generator that generates a triangular wave with a fixed period.
Wherein the comparing means is applied from the difference amplifying means.
Pressure difference value ΔPt and triangle applied from triangle wave generating means
And the pressure difference value in the process of rising the triangular wave
When it matches ΔPt, an ON signal is output when the triangular wave falls.
Off signal is output when the pressure difference value ΔPt matches
It is configured to work .

[0009]

[0010]

[0011]

[0012]

[0013]

[0014]

[0015]

[Function] Detects the pressure on the load side and sets it in advance.
Calculate the pressure difference value with the discharge pressure of the screw compressor,
For continuously controlling the on / off control valve and the discharge valve
The full-load operation time of the screw compressor and the no-load operation
The switching interval plus the switching time is given as the cycle.
Comparing the periodic function with the pressure difference value,
When the pressure on the side suddenly increases, the pressure difference value is increased.
When the pressure on the load side drops sharply,
The difference value is corrected to be small, and
The on / off control valve and the air release valve are turned on / off.
Caught.

[0016]

[0017]

[0018]

[0019]

[0020]

[0021]

[0022]

[0023]

[0024]

[0025]

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A description will now be given of FIGS. 1 to 7 showing a capacity control device for a screw compressor according to an embodiment of the present invention.

FIG. 1 is a block diagram showing the configuration of the control device of the screw compressor. In FIG. 1, 1 is a screw compressor. 2 is an on / off control valve also serving as a suction valve,
It is connected to the suction port of the screw compressor 1. Reference numeral 3 denotes a suction filter, which is connected to the on / off control valve 2.
Therefore, when the on / off control valve 2 is opened during the operation of the screw compressor 1, the air 4 is sucked into the screw compressor 1 through the suction filter 3 and the on / off control valve 2.

Reference numeral 5 denotes an air release valve which is connected to one end of a branch pipe 7 branched from a discharge pipe 6 connected to a discharge port of the screw compressor 1. When the air release valve 5 is opened, the compressed air flowing in the discharge pipe 6 is discharged into the atmosphere through the branch pipe 7, the air release valve 5, and the air release silencer 8.

An air storage tank 11 is connected to the discharge pipe 6 via a check valve 9 and an oil cooler 10, stores the compressed air discharged from the screw compressor 1, and supplies the compressed air to a load that requires it. I do.

Reference numeral 12 denotes a hydraulic cylinder, which has two suction and discharge ports 12.
a and 12b are formed. Reference numeral 13 denotes a piston, which is slidably fitted to the hydraulic cylinder 12, and has the suction / discharge port 12a,
The inside of the hydraulic cylinder 12 is slid up and down by the suction and discharge of the pressure oil from 12b. A piston rod 14 slidably penetrates the hydraulic cylinder 12, one end of which is fixed to the piston 13. The piston rod 14 has a central portion engaged with the on / off control valve 2, and the other end engaged with the air release valve 5. When the on / off control valve 2 is opened, the air release valve 5 is opened. When the air release valve 5 is opened, the on / off control valve 2 acts to close.

Numeral 15 denotes a four-way solenoid valve which supplies pressure oil pumped from an oil tank 16 by a pump 17 to one of the suction and discharge ports 12a and 12b of the hydraulic cylinder 12, and is discharged from the other suction and discharge ports 12a and 12b. Oil tank 1
6 is switched.

Reference numeral 18 denotes a pressure sensor,
The pressure sensor is disposed in a discharge pipe 6 connecting the storage tank 11 and the air storage tank 11, and detects the pressure of compressed air flowing through the discharge pipe 6. Reference numeral 19 denotes a control device that drives the four-way solenoid valve 15 based on the pressure of the compressed air applied from the pressure sensor to control the opening / closing of the on / off control valve 2 and the air release valve 5.

FIG. 2 is a block diagram showing the configuration of the control device 19. As shown in FIG. In FIG. 2, reference numeral 191 denotes a discharge pressure setting device. A difference amplifier 192 is connected to the pressure sensor 18 and the discharge pressure setting device 191, and compares the pressure Pd of the compressed air applied from the pressure sensor 18 with a preset discharge pressure Pt, and compares the pressure difference value ΔPt. Output. 193 is a triangular wave generator, which is the on / off control valve 2
Of the screw compressor 1 to generate a triangular wave corresponding to a periodic function value whose cycle is a switching time obtained by combining the full load operation time Ton and the no-load operation time Toff. A comparator 194 is connected to the difference amplifier 192 and the triangular wave generator 193, and generates a command signal (ON / OFF) for driving the four-way solenoid valve 15.

When the detected pressure Pd on the discharge side of the screw compressor 1 fluctuates in a short time, the difference amplifier 19
2 also changes in a short time,
The opening / closing of the on / off control valve 2 is repeatedly performed in a short time. In order to prevent such a phenomenon, a first-order lag element is provided in the difference amplifier 192 to delay the fluctuation of the pressure difference value ΔPt applied to the comparator 194,
Hunting of the discharge side pressure is prevented.

FIG. 3 shows the fluid system on the load side of the screw compressor replaced by a similar circuit of an electric system.
In FIG. 3, Q is the amount of compressed air. 20 is a switch SW
By turning on / off, the screw compressor is switched between full-load operation and no-load operation. Reference numeral 21 denotes inertance (Inertance) L, and the larger the size, the more difficult it is for compressed air to flow. 22 is a capacitance (Capa)
C), the larger the pressure, the smaller the pressure fluctuation on the storage tank side when the compressed air is discharged to the load.
13 is a diode. These constants are:
It is expressed by two equations.

Inertance L = P / (dQ / dt) (1) Capacitance C = Q / (dP / dt) (2) where dQ / dt and dP / dt are the compressed air amount Q
And the pressure difference (storage tank pressure PD-screw compressor discharge pressure PS) with time. In addition, inertance L
And the capacitance C is equivalent to an air tank.

FIG. 4 is a characteristic diagram showing changes in pressure and amount of compressed air during full load operation and no load operation of the screw compressor. In FIG. 4, (a) shows a change in the pressure P of the compressed air when the vertical axis represents pressure and the horizontal axis represents time,
(B) shows the change of the compressed air amount Q when the vertical axis is the compressed air amount and the horizontal axis is the time.

As shown in FIGS. 3 and 4, the switch S
When W20 is turned on and the screw compressor is operated at full load, the air compressed by the screw compressor flows into the air storage tank, and the compressed air amount Q in the air storage tank gradually increases, and The pressure in the tank gradually increases. The compressed air amount Q at this time
Is assumed to be a, the increase ΔQ of the compressed air amount Q in the case of the slope a can be expressed by Equation 3.

ΔQ = (ΔP · t) / L ΔP = PS−PD is expressed as ΔQ = (PS−PD) · Ton / L (3) In addition, when the pressure of the compressed air in the air storage tank reaches a predetermined pressure and the switch SW20 is turned off, the screw compressor enters a no-load operation, and the supply of the compressed air into the air storage tank is stopped.

When compressed air is supplied to the load in such a state, the compressed air amount Q in the air storage tank gradually decreases. Assuming that the slope of the decrease in the compressed air amount Q at this time is b, the slope b
In the case of (1), the decrease amount ΔQ of the compressed air amount Q can be expressed by the following equation (4).

ΔQ = (Pd−0) · Toff / L = Pd · Toff / L (4) Since the compressed air amounts ΔQ of the above formulas 3 and 4 are equal, Pd = PS · Ton / ( (Ton + Toff) = PS · Ton / T (5) where T is a cycle of a switching time obtained by adding the full-load operation time Ton and the no-load operation time Toff. In the above formula 5, since the discharge pressure PS of the screw compressor is constant, a cycle T obtained by adding the full load operation time Ton and the no-load operation time Toff of the screw compressor.
Is constant, it is possible to control the pressure Pd of the compressed air in the air storage tank in proportion to the time Ton of the full load operation. The amount of compressed air used is the average value T1 of the gradients a and b.

FIG. 5 is an explanatory diagram of the operation of the comparator 194 in FIG. 5A is a characteristic diagram illustrating a relationship between a discharge pressure Pt set in the discharge pressure setting device 191 in FIG. 2 and a detection pressure Pd detected by the pressure sensor in FIG. (B) shows the triangular wave generator 19 in FIG.
FIG. 3 is a characteristic diagram of a triangular wave output at a constant period from the waveform 3; (C)
FIG. 3 is a characteristic diagram of a control signal output from a comparator 194 in FIG. 2.

As shown in FIG. 5A, the discharge pressure Pt set in the discharge pressure setting device 191 in FIG.
Are compared with the detected pressure Pd detected by the pressure sensor 18 in the step (a), and the difference is used as a pressure difference value ΔPt as the difference
Output from 2. At this time, the pressure difference value ΔPt output from the difference amplifier 192 is become.

That is, if the amount of compressed air discharged from the screw compressor is larger than the amount of compressed air used on the load side, the detected pressure Pd will be higher than the set pressure Pt, and the compressed air used on the load side will be higher. Is equal to the amount of compressed air discharged from the screw compressor, the detected pressure Pd is equal to the set pressure Pt, and the amount of compressed air discharged from the screw compressor is equal to the amount of compressed air used on the load side. If the amount of compressed air decreases, the detected pressure Pd becomes lower than the set pressure Pt.

As shown in FIG. 5B, the pressure difference value ΔPt is superimposed on the zero position of the triangular wave. And
An intersection between the pressure difference value ΔPt and the triangular wave is obtained.

As shown in FIG. 5C, the comparator 194
Generates a command signal at the intersection of the pressure difference value ΔPt and the triangular wave. This command signal has a triangular wave as a pressure difference value ΔPt.
When going upward (+ side) from the intersection of the triangle wave and
The hydraulic cylinder 12 in FIG. 1 operates in the direction in which the hydraulic cylinder 12 operates and the on / off control valve 2 opens, and when the triangular wave goes downward (−) from the intersection of the pressure difference value ΔPt and the triangular wave. Then, the ON / OFF control valve 2 is generated in the closing direction.

That is, when the triangular wave is above the pressure difference value ΔPt, the screw compressor 1 is operated at full load, and when the triangular wave is below the pressure difference value ΔPt,
The screw compressor 1 is operated without load.

By performing such control, as is apparent from FIG. 5, when the detected pressure Pd is higher than the set pressure Pt, the full-load operation time Ton is shortened as compared with the no-load operation time Toff, and the compression is performed. Reduce air supply and reduce pressure. When the detected pressure Pd is lower than the set pressure Pt, the full-load operation time Ton is made longer than the no-load operation time Toff to increase the supply amount of the compressed air and increase the pressure. The supply amount can be secured.

FIG. 6 is an explanatory diagram of the operation of the comparator 194 in FIG. 2 when the amount of compressed air used on the load side fluctuates. FIG. 6A shows the comparator 19 shown in FIG.
FIG. 4 is a characteristic diagram of a control signal output from a control signal 4; FIG.
FIG. 6 is a characteristic diagram showing a change in a triangular wave output from the triangular wave generator 193 and a compressed air amount Q discharged from the screw compressor in FIG. For the sake of simplicity, the rising time of the triangular wave is shown as the full load operation time of the screw compressor, and the falling time is shown as the no-load operation time.

As shown on the left side of FIG. 6B, when the amount of compressed air Q used on the load side increases, the amount of compressed air in the air storage tank 11 in FIG. 1 decreases, and the pressure in the discharge pipe 6 also decreases. descend. Then, as described with reference to FIG. 5, the full load operation time (on time) of the screw compressor becomes longer, and the compressed air amount Q discharged from the screw compressor per unit time is increased.
It gradually increases, and as shown in the center of FIG.
It becomes equal to the amount of compressed air used on the load side.

As shown on the right side of FIG. 6B, when the amount of compressed air Q used on the load side decreases, the air storage tank 11
Since the compressed air amount Q discharged from the screw compressor is larger than the reduced amount of the compressed air inside, the pressure in the discharge pipe 6 also increases. Then, as described with reference to FIG. 5, the full load operation time (ON time) of the screw compressor is shortened, and the compressed air amount Q discharged from the screw compressor per unit time is gradually reduced.

In this manner, a fixed period (on time +
In the off time), by controlling the operation of the screw compressor by changing the ratio of the on time and the off time, it is possible to perform a full load operation according to the amount of compressed air used,
Energy efficiency can be improved.

FIG. 7 shows the discharge pressure setting device 19 in FIG.
3 shows an example of a pressure pattern set to 1. In this example, a temporal change in the amount of compressed air used per day over time is set as a change in the discharge pressure of the screw compressor. By setting the variation over time in this way, even when the variation in the amount of compressed air used on the load side is large, adjustment every time is unnecessary, and usability can be improved.

[0054]

As described above, according to the present invention, the following effects can be obtained.

When the amount of compressed air used is small,
Operate at full load even when the capacity of the outlet piping system is large.
Time and power consumption,
In addition, the pressure and air volume of the compressed air used on the load side are secured
And the reliability can be improved. Ma
In addition, the control follows the sudden pressure fluctuation on the load side.
Hunting of the screw compressor
And minimize the time for full load operation.
Minimal, energy efficiency can be improved
You.

[0056]

[0057]

[0058]

[0059]

[0060]

[0061]

[0062]

[0063]

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a configuration of a capacity control device of a screw compressor according to the present invention.

FIG. 2 is a block diagram showing a configuration of a control device in FIG. 1;

FIG. 3 is a circuit diagram similar to an electric system of a fluid system on a load side.

FIG. 4 is a characteristic diagram showing a relationship between a pressure and a compressed air amount during operation of the screw compressor.

FIG. 5 is an operation explanatory diagram showing operations of a triangular wave generator and a comparator.

FIG. 6 is a diagram illustrating the operation of the comparator when the amount of compressed air used on the load side fluctuates.

FIG. 7 is a characteristic diagram showing an example of a pressure pattern set in a discharge pressure setting device.

[Explanation of symbols]

1. Screw compressor, 2. On / off control valve, 3.
Suction filter, 5 ... Air release valve 6 ... Discharge pipe, 7 ... Branch pipe, 8
... Blower silencer, 9 ... Check valve, 10 ... Oil cooler,
11 ... air storage tank, 12 ... hydraulic cylinder, 13 ... piston,
14 piston rod, 15 four-way solenoid valve, 16 oil tank, 17 pump, 18 pressure sensor, 19 control device, 20 switch SW, 22 inertance L,
23: capacitance C, 191: discharge pressure setting device, 1
92: difference amplifier, 193: triangular wave generator, 194: comparator.

Continuation of the front page (56) References JP-A-56-124699 (JP, A) JP-A-54-76792 (JP, A) JP-A-57-60416 (JP, A) JP-A-63-56711 (JP) , A) Tokiko Hei 1-333676 (JP, B2) Suzuki, Higuchi "Patent pulse circuit technology dictionary" (Showa 55-5-20) Ohmsha, P. 562-564 The Society of Instrument and Control Engineers, "Automatic control hand" Book: Apparatus and Applications ”(58-10-30), Ohmsha, p. 241-243, 430-434

Claims (1)

(57) [Claims] 1. An on-board provided on a suction side of a screw compressor 1.
/ Off type control valve 2 and discharge pressure of screw compressor 1
The discharge pressure setting means 191 to be set and the pressure on the load side are detected.
Output pressure detecting means 18 and the pressure detecting means 18
The output load side pressure value and the discharge pressure setting means 191
Increase the difference to calculate the pressure difference value with the set discharge pressure value
The width means 192 and the on / off control valve 2 are continuously connected.
In order to control the screw compressor 1 at full load operation
Switching interval time, which is the sum of
A periodic function generating means 193 given as
The periodic function value from the function generating means 193 and the difference amplification value
Compare the pressure difference value from stage 192 with the on / off
And comparison means for turning on / off the control valve 2
The pressure on the load side is rapidly applied to the differential amplifying means 192.
When it becomes higher, the pressure difference value is greatly corrected,
When the pressure on the load side suddenly decreases, the difference value is reduced.
Correction means for correcting the periodic function;
The generating means 193 generates the load side pressure of the screw compressor 1.
Pressure difference value ΔPt between force Pd and discharge pressure set value Pt
Is set at 0, the discharge pressure set value Pt is
Positive when the pressure is higher than the load side pressure Pd, negative when the pressure is lower
Triangular wave generating means for generating a triangular wave with a constant period
And the comparing means 194 is provided with the differential amplifying means.
Pressure difference value ΔPt applied from 192 and the triangular wave generating means
Compare with the triangular wave applied from stage 193,
Turns on when the pressure difference value ΔPt coincides with the pressure difference value during the rising process
The signal is converted into the pressure difference value ΔPt while the triangular wave descends.
Output an off signal when the
Clew compressor capacity control device.