JP2803238B2 - Compressor capacity control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a displacement control device for a compressor that controls an intake air amount by an intake blocker type unloader device provided at an intake port of a compressor body. About.

(Prior Art) Three types of methods are generally used to control the capacity of a rotary compressor. In the first method, as shown in Japanese Utility Model Laid-Open No. 1-78284, when the receiver tank pressure exceeds a prescribed pressure, the intake passage is closed by an intake closing type unloader device, while the pressure is reduced by the consumption of compressed air. The second method is to open the intake passage again when it falls below the lower limit and control the capacity. The second method is to use a pilot valve from a pressure regulating valve that operates according to the pressure in the receiver tank as shown in Japanese Utility Model Laid-Open No. 48-57704. Upon receiving the pressure, the suction gas control valve (unloader device) is closed, and at the same time, the internal pressure in the oil recovery unit is released to a predetermined pressure by the discharge valve to reduce the back pressure applied to the discharge port. As shown in JP-B-59-44514, the pressure of the receiver tank is detected by a pressure switch, and based on this signal, the solenoid valve in the control circuit for the unloader device is opened, and the intake port of the unloader valve is opened. So-called ON-, which collects the air and the gas-liquid mixed fluid of the oil remaining in the discharge chamber by the oil recovery pump in the receiver tank and removes the back pressure applied to the discharge port of the compressor.
This is a capacity control method in which the OFF control and the no-load discharge pressure removal method are combined.

(Problem to be Solved by the Invention) Among the above-mentioned capacity control methods, the first method is that the unloader device is steplessly controlled by the pressure regulator, so that when the compressed air is consumed on the consuming side, the corresponding compression is performed immediately. Since air is supplied, the fluctuation range of the pressure in the air pipe on the consuming side can be reduced as shown by the two-dot chain line (a) in FIG. 8, while the two-dot chain line (a ') in FIG.
As shown by, there is a disadvantage that the load power (power consumption ratio) during no-load operation can be reduced to only about 70% of the full load.
In the second method, as shown by the eighth thin broken line (b), the process until the suction gas control valve is closed is stepless capacity control similarly to the first method, but after the shift to the no-load operation. Discharges the pressure inside the oil recovery unit to the atmosphere.If there is a sudden consumption of compressed air during the no-load operation, the pressure in the consuming pipe will temporarily decrease until the operation returns to full-load operation. If this is repeated intermittently, the operation of the equipment used may become unstable. Since it has a useless process of discharging air to the atmosphere, there is a drawback that it does not lead to effective reduction of power consumption as shown by a thin broken line (b ') in FIG. In the third method, as shown by the thick broken line (c ') in FIG. 9, the power saving effect is far greater than in the first and second methods, but the unloader device is the fifth method.
Since the ON-OFF control is performed by the pilot pressure from the solenoid valve as shown by the line E in the figure, as shown by the thick broken line (c) in FIG. In addition, there is a problem that the pressure in the consuming side pipe fluctuates in a certain constant pressure range with the ON-OFF operation of the control device.
For this reason, particularly when the minimum driving pressure of the consuming device is high, when the fluctuating pressure reaches the lower limit value, problems such as slow operation of the device occur.

As a countermeasure against this, it is conceivable to narrow the pressure setting range in which the unloader device performs ON-OFF operation, or to set the operation setting pressure value higher as a whole, but in the former case, the no-load operation and the load operation operation are repeated. In addition to the increase in frequency, this may cause failure of the solenoid valve and other control devices and shorten the service life. In the latter case, the load power of the compressor increases due to the increase in the set pressure, and the compressor or the driving motor There is a high possibility of causing overheating.

The conventional capacity control methods described above are designed such that the unloader device is fully opened at a specified pressure (see P7 in FIG. 5), and the load power of the compressor substantially matches the rated output of the prime mover. The return pressure of the unloader device from no-load operation to full-load operation is determined in consideration of the minimum return pressure width of each control device such as a solenoid valve.
P6 (6 kgf / cm ² ), which is about 1 kgf / cm ² lower than (7 kgf / cm ² )
Is usually set as the lower limit (see FIG. 5, P6).

Therefore, on the consuming side, it is necessary to select the equipment to be used according to the return pressure value of the unloader device. In other words, when viewed from the consumer side, the rated pressure of the compressor (specified pressure
Even if the equipment to be used is selected according to P7), when the compressor is in a medium load condition, the pressure in the piping may be lower than P6, so eventually select the equipment to use according to the return pressure. Therefore, there is a disadvantage that the compressor itself does not operate with sufficient performance.

Further, in the conventional capacity control method, the unloader device is operated only in response to an increase or decrease in the consumption-side pressure, so that there is a limit in improving the power saving effect.

To solve such a problem, Japanese Patent Application Laid-Open No.
Japanese Patent Application Laid-Open No. 159589 proposes a discharge pressure flow control device for a screw compressor. This discharge pressure flow control device has a first functional unit that outputs a signal in a direction to close the intake adjustment valve in accordance with a difference between the discharge pressure and the discharge pressure lower limit value, and when the discharge pressure exceeds the discharge pressure upper limit. A signal for fully closing the intake control valve and fully opening the blow-off valve is input, and outputting a signal for fully opening the intake control valve and fully closing the blow-off valve when the discharge pressure becomes equal to or lower than the discharge pressure lower limit value. A second functional unit that performs
A third function unit for selectively switching the second function unit, and a switching point between the first function unit and the second function unit in the third function unit is determined by the suction pressure and the discharge by the first function unit. A fourth function determined by a function of the pressure ratio of the pressure, the operation frequency of the intake adjustment valve and the air release valve by the second function unit, and the power difference between the first function unit and the second function unit. A discharge pressure flow control device for a screw compressor having a function unit and a capacity control device for a compressor that controls the amount of intake air by an intake closing type unloader device provided at an intake port of the compressor body.
The power consumed by the prime mover of the screw compressor is detected by a power detector, and control is performed based on the power.

However, even in such a control method, as in the second method, there is a wasteful process of consuming power and discharging compressed air compressed to a predetermined pressure to the atmosphere after shifting to the no-load operation. It does not lead to effective power savings.

Accordingly, the present invention has been made to solve the above-mentioned problems, and to provide a compressor capacity control device capable of always maintaining the consumption-side pressure at a specified pressure or higher and improving the power saving effect at a light load or a medium load. Aim.

[Constitution of the Invention] (Means for Solving the Problems) The present invention relates to a content control device for a compressor, which controls an intake air amount by an intake blocker type unloader device provided at an intake port of a compressor body. A pressure detecting means for detecting a consumption pressure of a piping system communicating with a discharge port of the main body; a power consumption detecting means for detecting power consumption of a motor; and an electropneumatic device for controlling a valve opening / closing operation of the unloader device based on an electric signal. A converter, and control means having determination means for determining whether the power consumption of the prime mover is within the rating of the prime mover during the load operation, and the control means includes the power consumption detection means and the power consumption during the load operation. Based on the signal from the pressure detecting means, the opening degree of the valve of the unloader device is steplessly controlled via an electropneumatic converter so as to regulate the consumption side pressure so that the power of the compressor body falls within the rating of the prime mover. When the pressure is raised above the pressure and when the consuming pressure reaches a predetermined pressure higher than the specified pressure, the unloader device is completely closed to shift to a no-load operation, and thereafter when the no-load operation release pressure is reached. The unloader device is controlled to open to shift to the load operation operation, and the determination means increases the opening degree of the valve of the unloader device when it is within the rated value, and increases the valve opening when the rated value is out of the rated value. The control is performed to reduce the opening.

(Operation) According to the above capacity control device, at the time of so-called light load or medium load in which the consumption of compressed air is small on the consuming side, the opening of the valve of the unloader device is stepless and the load power of the compressor is driven by the prime mover. The consumption pressure rises above the specified pressure by controlling the output within the range not exceeding the rated output of, and when the consumption pressure reaches the specified pressure equal to or higher than the specified pressure, the unloader device is completely closed and then the normal no-load operation When the consumption-side pressure reaches the no-load operation release pressure, the unloader device is opened to shift to the load operation.

(Embodiment) Hereinafter, an embodiment of the present invention will be described with reference to the drawings based on the third capacity control method described in the conventional example.

FIGS. 1 to 9 show an embodiment of the present invention. In FIGS. 1 and 2, an intake blockage type unloader device 3 is mounted on a suction port 2 of a compressor body 1 and a discharge port 4 is provided. Is connected to a receiver tank 7 via a check valve 5 and a discharge pipe 6. A consuming air pipe 11 is connected to the air outlet 8 of the receiver tank 7 via an opening / closing valve 9 and a check valve 10.
Is provided with a pressure sensor 12 as pressure detecting means for detecting the pressure in the air pipe on the consumption side. The air outlet 8 of the receiver tank 7 is connected to the inlet 15 of the electropneumatic converter 14 via the control pipe 13, and the outlet 16 is connected to the primary chamber 19 of the unloader device 3 by the control pipe 18. Have been. On the other hand, an oil reservoir 20 is provided below the receiver tank 7, and lubricating oil is supplied to the working space 24 of the compressor body 1 via an oil supply pipe 21, a cooler 22, and an oil amount adjustment valve 23. I have. Reference numeral 25 denotes an oil recovery pump which recovers the gas-liquid mixed fluid discharged from the discharge port 4 to a communication path with the discharge pipe 6 via a pipe 26. A piston 28 fixed to a diaphragm 27 and an unloader valve 29 are connected to the unloader device 3. A compressed air pressure from the control pipe 18 supplied to the primary chamber 19 and a return spring disposed on the opposite side are provided. The intake passage 31 is opened and closed according to the balance with the tension of 30.

The electropneumatic converter 14 is capable of freely adjusting the discharge air pressure by an electric signal and performs control for obtaining a capacity control characteristic of the unloader device 3 described later, and the characteristic is almost proportional to the control current. It is. FIG. 2 shows an example of the electropneumatic converter 14, in which the distance between the movable plate 34 and the nozzle 35 changes via the magnet 33 in accordance with the amount of current flowing through the coil 32. When the pressure in the pilot chamber 36 communicating with 35 rises, the main valve 37 opens, and the air pressure (control air pressure) on the discharge port 16 side increases, while the space between the movable plate 34 and the nozzle 35 increases, the pilot chamber 36 , The relief valve 38 opens and the discharge air pressure (control air pressure)
Is reduced, and the control characteristic thereof is such that a pressure on the outlet side substantially proportional to the control current is obtained. In FIG. 2, reference numeral 39 indicates an atmospheric pressure portion.

The power supply line 41 of the prime mover 40 is provided with a power consumption detector 42 as power consumption detection means such as a current transformer CT. The control circuit 43 is composed of a microcomputer,
A motor having an A / D converter 44, a D / A converter 45, an arithmetic processing circuit 46, and a data setting circuit 47, and a consuming side pressure detected by the pressure sensor 12 and a power consumption detected by the power consumption detector 42; The input current and voltage of 40 are power-converted by a power converter 48, then converted into digital signals by an A / D converter 44 and sent to an arithmetic processing circuit 46. Further, various data such as set pressure and allowable power set in advance according to the type and use of the compressor are sent from the data setting circuit 47 to the arithmetic processing circuit 46, and the arithmetic processing circuit 46 performs processing based on these data. D /
The control signal is output to the electropneumatic converter 14 via the A converter 45 to control the discharge pressure of the electropneumatic converter 14.

Next, the capacity control operation will be described with reference to the flowchart of FIG.

The normal load operation is performed by the operation of the compressor body 1, and the air flowing into the suction port 2 from the unloader device 3 is compressed through the working space 24, and then is discharged together with the lubricating oil injected into the working space 24. And is fed to the receiver tank 7 via the check valve 5 and the discharge pipe 6, and is sent from the outlet 8 after being separated from the lubricating oil to the consumption-side air pipe 11. When the consumption air consumption decreases, the pressure in the receiver tank 7 gradually increases. In this case, the control circuit 43 determines whether or not the operation is in the no-load operation (step 1). Since the operation is in the load operation, the control circuit 43 determines whether or not the power consumption of the prime mover 40 is within the rating based on the signal of the power consumption detector 42. (Step 2), and when the pressure on the consuming side is within the rating after exceeding the specified pressure, the electropneumatic converter 14 is controlled so that the discharged air pressure becomes small, and the unloader valve 29 is slightly opened ( In step 3), when it is out of the rating, the unloader valve 29 is closed slightly (step 4). By repeating such control and controlling the discharge air pressure of the electropneumatic converter 14 so that the power consumption of the prime mover 40 is within the rated range within the range shown by the hatched area in FIG. An amount of control air corresponding to the increase in the consumption pressure is pumped to the next chamber 19. In this way, as shown in FIG. 6, the lift L of the unloader valve 29 is continuously narrowed to limit the amount of intake air. And the control circuit
43, the air consumption is further reduced, the intake air amount is continuously reduced to a level corresponding to approximately 80% of the full load, and the consumption pressure is reduced to the no-load operation start pressure P8 (8 kgf / cm ² ) (No. (See Fig. 5)
(Step 5), the unloader valve 29 is completely closed and the operation shifts to the no-load operation (step 6) (step 5).
(See point B in the figure and point B 'in FIG. 6). Thereafter, it is determined whether or not the consumption pressure has reached the no-load operation release pressure P7 (7 kgf / cm ² ) (Step 7). When the consumption pressure reaches the no-load operation release pressure, the unloader valve 29 is opened. The operation is fully opened and the operation shifts to the load operation (step 8), and thereafter, the same control is repeated in the order described first. The change in the pressure on the consumption side at this time is, as shown by the line H in FIG.
And no-load operation start pressure P8. As shown in FIG. 4, the control circuit 43 sends a valve closing control signal for the unloader valve 29 when the power consumption of the drive motor 40 is at the rated value, and when the power consumption of the unloader valve 29 is rated at -α (α is about 95% of the rated value). A valve opening control signal for the valve 29 is sent, and has a dead zone indicated by oblique lines in FIG. This prevents an excessive response of the unloader valve 29 and prevents hunting and deterioration of the life of the unloader valve 29. Further, when comparing the relationship between the receiver tank pressure and the power consumption based on the capacity control method of the present invention described above with the conventional capacity control method,
A solid line (d) in FIG. 8 and a solid line (d ′) in FIG. 9 are obtained. That is, in FIG. 8, the conventional method (a),
The pressure in the consuming air piping is the specified pressure compared to (b) and (c).
Regarding the relationship between the load factor and the power consumption ratio shown in FIG. 9 even though it is held at P7 or higher, the power consumption ratio is almost within 100% up to a load factor of about 80%. Of course,
The range of the load factor can be changed to 70% or 60% depending on the adjustment of the discharge air pressure of the electropneumatic converter 14. The setting of the no-load operation start pressure P8 may be determined as appropriate according to the repetition frequency of the full-load and no-load operation operations. If the difference between the specified pressure P7 and the no-load operation start pressure P8 is small, the compressor The repetition frequency of the full-load and no-load operation increases, which leads to shortening of the life of each control device, but at the same time, the energy saving effect increases. On the other hand, as the difference between the specified pressure P7 and the no-load operation start pressure P8 increases, the frequency of repetition of full-load and no-load operation decreases, so that the operation frequency of each control device also decreases, and the life of the control device also increases. , The energy saving effect decreases.

As described above, the magnitude of the pressure difference between the specified pressure P7 and the no-load operation start pressure P8 has a relationship that is inconsistent with the life of the control device and the energy saving effect. It is appropriate to set the pressure range to about 1 kgf / cm ² .

If this is shown in the case where the first to third capacity control methods explained in the conventional example are set to the same set pressure as in the embodiment of the present invention, the power consumption ratio becomes as shown by the two-dot chain line K in FIG.
The result is much larger than 100%, in which case the various problems described above are caused.

In FIG. 9, the load factor L and the power consumption ratio W are expressed by the following equations.

Load factor = (air consumption (m ³ / min) / rated air amount of compressor (m ³ / min)) × 100 Power consumption ratio = (power consumption (kw / Hr) / rated power of driving motor (kw / Hr)) × 100 Note that the present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the present invention. For example, an intake blockage type unloader device and an electropneumatic converter are various types. Is applicable. Further, in the present embodiment, the description has been made that the control is performed by detecting the power consumption of the prime mover 40, but this may be replaced with the current consumption. Also, the electropneumatic converter can be changed to a flow control type.

[Effects of the Invention] As described above in detail, according to the capacity control device of the present invention, the power consumption of the prime mover is detected, and the opening degree of the unloader valve is controlled based on this detection signal, thereby consuming the air piping on the consumption side. Since the capacity of the intake air is controlled so that the internal pressure is always at or above the specified pressure and the load power of the compressor does not exceed the rated output of the prime mover, there is a possibility that the operation of the equipment used on the consumer side may be defective. It can be operated economically without increasing power consumption, and is particularly effective when the usage time in a so-called light load or medium load state where the air consumption is small is long.

In addition, according to the conventional capacity control method, the size of the compressor is determined so that the load power of the compressor matches the rated output of the prime mover at the specified pressure P7. The capacity control method of the present invention can set the pressure of the lower limit pressure P6 to a specified pressure, as compared to a compressor having a pressure specification of pressure P6 having only the same performance. Therefore, the result obtained by the conventional control method remains unchanged and the discharge pressure further increases
→ A large energy-saving effect can be exhibited by the amount reduced to P6.

In addition, the present invention can be applied to a conventional machine currently in use and can be implemented by adding a simple configuration, so that the present invention is inexpensive.

Moreover, in the present invention, even when compressed air is used in the vicinity of the specified pressure P7, the compressed air can be stably supplied to the consuming side, and the time required to start the no-load operation up to the predetermined pressure P8 is longer than that of the conventional art. It becomes shorter, and the no-load operation time can be extended. More specifically, the specified pressure P7
In the above pressure range, the unloader device can be operated within a range where the power of the compressor does not exceed the rated output of the prime mover, so that the pressure above the specified pressure P7 can be maintained, and the predetermined pressure P8 higher than the specified pressure can be maintained. When the pressure reaches, the electropneumatic converter operates and supplies the consumption side pressure (internal pressure of the receiver tank) to the unloader device to close the valve of the unloader device. The valve lift immediately before the closing of the valve becomes large, thereby increasing the amount of air and increasing the pressure of the consuming side pressure (the internal pressure of the receiver tank). As a result, power consumption can be suppressed.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing an embodiment of the present invention, FIG. 2 is a sectional view of an electropneumatic converter, FIG. 3 is a flowchart, and FIG. FIG. 5 is a graph showing the pressure state during displacement control, FIG. 6 is a graph showing the opening / closing operation characteristics of the unloader valve in relation to the air amount ratio, and FIG. 7 is a consumption side pressure and air amount. FIG. 8 is a graph showing the relationship between the consumption-side pressure and the air amount ratio during the capacity control, and FIG. 9 is a graph showing the load characteristics. DESCRIPTION OF SYMBOLS 1 ... Compressor main body 3 ... Intake blockage type unloader device 12 ... Pressure sensor (pressure detection means) 14 ... Electro-pneumatic converter 42 ... Power consumption detector (power consumption detection means) 43 ... Control circuit ( Control means)

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F04C 29/10 321 F04C 29/10 331 F04C 29/10 311

Claims (1)

(57) [Claims] In a capacity control device for a compressor, wherein an intake air amount is controlled by an intake blocker type unloader device provided at an intake port of a compressor body, a consumption pressure of a piping system communicating with a discharge port of the compressor body. , A power consumption detecting means for detecting power consumption of the prime mover, an electropneumatic converter for controlling a valve opening / closing operation of the unloader device based on an electric signal, and a power consumption of the prime mover during a load operation. Control means having a determination means for determining whether or not the power consumption is within the rating of the prime mover. The control means operates the load of the compressor body based on signals from the power consumption detection means and the pressure detection means during a load operation. Through an electro-pneumatic converter to continuously control the opening of the valve of the unloader device to raise the consuming pressure from a specified pressure, and to reduce the consuming pressure to the specified value. When a predetermined pressure higher than the specified pressure is reached, the unloader device is completely closed and the operation shifts to a no-load operation operation. Thereafter, when the pressure reaches the no-load operation release pressure, the unloader device is opened to perform a load operation operation. And the determination means controls to increase the opening of the valve of the unloader device when the value is within the rating, and to decrease the opening of the valve when the value is out of the rating. Characteristic compressor capacity control device.