JP3346208B2 - Load control device for multi-stage compressor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load control device for a multi-stage compressor, and more particularly to a load control device that suppresses the influence of voltage fluctuation.

[0002]

2. Description of the Related Art
A vent that opens and closes with an electromagnetic valve is provided in the relay line connecting the former and latter compressors of the multi-stage compressor, and when the drive current of the motor exceeds the preset current upper limit, the electromagnetic valve is opened. There is known a load control device that reduces a driving load of a motor to prevent overload of a power supply and heat generation of the motor.

[0003] This type of load control device includes a device that closes the solenoid valve to release load control after a certain period of time has elapsed after the solenoid valve is opened, and a device that performs electromagnetic control when the motor drive current falls below a set control release current value. Some valves release the load control by closing the valve.

However, in the case of controlling the solenoid valve with time, the solenoid valve is closed after a certain period of time regardless of the driving load of the motor. Therefore, if the tank pressure does not decrease at the time of closing the solenoid valve, the solenoid valve is controlled. However, there is a drawback that it frequently opens and closes.

[0005] Further, in the device which detects the motor drive current and cancels the control, the above-mentioned disadvantage in the time control is solved, but the load-current characteristics change due to the change of the power supply voltage, and the solenoid valve opens and closes. There is a problem that the tank pressure level varies. For example, if the power supply voltage is lower than the specified voltage, the solenoid valve does not close until the tank pressure drops significantly below the reference control release pressure, so the return to the multi-stage compression operation is delayed, and the compressed air discharge performance decreases. Problem arises. In particular, at the construction site, voltage drop is likely to occur due to wiring routing and the use of other electric devices,
Load control tends to be unstable.

Therefore, there arises a technical problem to be solved in order to eliminate the influence of the voltage fluctuation and to stabilize the discharge capability of the multi-stage compressor, and the present invention has an object to solve the above problem. I do.

[0007]

SUMMARY OF THE INVENTION The present invention is proposed to achieve the above object, and is provided at a vent of a pipe connecting a discharge port of a first-stage compressor and an intake port of a second-stage compressor. A load control device for a multi-stage compressor that controls opening and closing of a valve, comprising a motor drive current detection circuit, a setting unit for a current upper limit value and a load control release current value, and a comparison unit for comparing the detected current value with the set current value. Control means for controlling the opening and closing of the valve according to the comparison result, the valve is opened when the detected current value exceeds the current upper limit value, and the detected current value has decreased below the load control release current value. Sometimes in a load control device for a multi-stage compressor that closes the valve, the current immediately after opening the valve
Is detected and stored, and the detected value is
There is provided a load control device for multi-stage compressor comprising providing a control means for the flow data.

A load control apparatus for a multi-stage compressor, further comprising control means for detecting and storing a current immediately after the valve is opened, and using the detected value as the next load control release current data. Is provided.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a circuit of the two-stage compressor 1, in which a pre-stage compressor 2, a post-stage compressor 3, and an air tank 4 are connected in series, and a relay connecting the discharge port of the pre-stage compressor 2 and the intake port of the post-stage compressor 3 is connected. A vent 6 is provided in the pipe 5, and a solenoid valve 7 is attached to the vent 6. The phases of the crank mechanisms of the first-stage compressor 2 and the second-stage compressor 3 are shifted by 180 degrees, and are driven by the electric motor 8 to alternately perform the suction and compression operations.

A normally closed pressure switch 9 installed in the air tank 4 is inserted in series into an AC power supply line connecting the main switch 10 and the electric motor 8, and shuts off the power supply when the tank pressure reaches the maximum pressure. The electric motor 8 is stopped.

A current switch 11 for switching the upper limit of the current of the electric motor 8 between 17.5 A and 14.5 A in accordance with the power supply capacity is provided, and is used at a construction site where a large-capacity switchboard is installed. In this case, 17.5A is selected to obtain a large discharge capacity, and when a lower capacity general household power supply is used, the power supply load is switched to 14.5A to limit the power supply load.

The current changeover switch 11 and the voltage-current detection circuit 12 provided on the AC power supply line are connected to a load control device 13 for controlling the solenoid valve 7. Load control device 1
Reference numeral 3 includes a control unit 14 and a storage unit 15, and the storage unit 15 stores two-step current upper limit data and voltage-control release current data in a data table format.

The data table is shown in FIG.
As shown in the flow characteristics graph, load control at 14A / 100V
Tank pressure P to release control_CR1For example, 85
Load control release tank pressure is constant pressure in the range of V to 105V
P_CR1Individually for multiple levels of voltage.
FIG. 2 shows a high voltage data table in which the release current value is set.
As shown in (b), the load control is released at 13A / 100V.
Tank pressure P to be removed_CR2Load control release
Pressure is constant pressure P in the same voltage range as in FIG. _CR2When
Control release current individually for multiple levels of voltage
Two types of low-voltage data tables with set values
There is a bull.

[0014] By setting the current upper limit value by the current change-over switch 11 to 17.5A, the control unit 14 selects the high data table of the load control release tank pressure P _CR1, if you set the current limit to 14.5A Select and refer to the low pressure data table of the load control release tank pressure _PCR2 .

FIG . 3 is a flowchart of load control.
When the power supply is connected (step 101), the state of the current changeover switch 11 is read, the current upper limit (17.5A or 14.5A) is set (step 102), and the voltage-current measurement is performed via the voltage-current detection circuit. Is started (step 103).

When the main switch 10 is turned on with the pressure switch 9 turned on, the electric motor 8 is started and the air tank 4 is filled with compressed air. When the pressure of the air tank 4 rises to some extent and the drive current reaches the set upper limit,
Proceeding from step 104 to step 105, the control unit 14
Outputs the solenoid valve opening signal to reduce the driving load of the multi-stage compressor, and measures the voltage-current after the control is started (step 1).
06).

Subsequently, control release current data corresponding to the measured voltage is read from the high-voltage or low-voltage control release current data table corresponding to the current upper limit value setting (step 10).
7) Compare the current value with the control release current value (step 108).

When the measured current value drops below the control release current value, a solenoid valve closing signal is output (step 1).
09), the vent is closed to return to the multi-stage compression operation, and the above routine is repeated.

As described above, the load control release current value is varied in accordance with the power supply voltage, and the load control is released at a substantially constant tank pressure regardless of the power supply voltage to maintain the tank pressure at or above a certain value.

When the tank pressure reaches the maximum pressure by repeating the multi-stage compression and the load control, the pressure switch 9 is turned off and the electric motor 8 is stopped, similarly to the conventional multi-stage compressor.
Load control is forcibly reset. Then, when the tank pressure falls below the maximum pressure and the pressure switch 9 is turned on, the load control is restarted.

Next, the load control device of the present invention will be described.
This load control device updates the control release current data in the storage unit 15 based on the measured current value and converts the control release current data to the power supply voltage instead of the control means for performing load control with reference to the control release current data corresponding to the power supply voltage described above. This is to perform the corresponding load control.

The storage unit 15 stores two types of high and low current upper limit values.
Data set of control release current value (for example, 17.5A-
14.5A and 14.5A-13.5A) are stored, and one of the current value data sets is selected according to the switching position of the current switch 11. The initial value of the control release current combined with the current upper limit data (14.5 A and 13.5 A)
A) is 100V each to correspond to low voltage
It is set higher than the control release current value (14A and 13A) at the time.

FIG. 4 shows the procedure of the above load control, in which the current switch 11 is connected to the power supply (step 201).
Is read and the current upper limit value-control release current value data is set (step 202). If the number of times of opening of the solenoid valve 7 is 0 immediately after the start, the steps 203 to 205 are performed.
Go to and measure the current. When the drive current reaches the upper limit value due to the increase in the pressure of the air tank 4, step 20 is executed.
The process proceeds from step 6 to step 207 to output an electromagnetic valve opening signal to reduce the driving load of the multi-stage compressor.

Subsequently, the number of times the solenoid valve 7 is opened is set to n = n + 1 (step 208), and the current after the start of control is measured (step 209). When the measured current value falls below the initial value of the control release current, steps 210 to 211 are performed.
Then, a solenoid valve closing signal is output, the operation returns to the multi-stage compression operation, and the process returns to step 201.

After the second cycle, in step 204, the control release current value data is updated by rewriting the current value measured after the solenoid valve was opened in the previous step 209, and the process proceeds to step 205 to execute load control.

As described above, the current value that changes in accordance with the power supply voltage is measured after the solenoid valve is opened, and the current value is used as the next control release current value to control the closing of the solenoid valve. Also, the pressure level of the control release does not decrease from the reference control release pressure level, the load control is released at a substantially constant tank pressure, and the tank pressure can be maintained at a fixed value or more.

It should be noted that the present invention is not limited to the above-described embodiment, and various modifications are possible within the technical scope of the present invention, and it goes without saying that the present invention extends to those modifications. is there.

[0028]

As described above, the load control device for a multi-stage compressor according to the present invention cancels the load control at a constant tank pressure regardless of the fluctuation of the power supply voltage. However, the return to the multi-stage compression operation is not delayed, and the influence of the voltage fluctuation on the compressed air discharge performance can be eliminated, and the discharge performance is stabilized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a two-stage compressor, showing an embodiment of the present invention.

FIGS. 2A and 2B are load-current characteristic graphs of 85 V to 105 V, respectively.

FIG. 3 is a control flowchart of a known load control device related to the present invention .

FIG. 4 is a control flowchart of the load control device of the present invention .

Claims (1)

(57) [Claims] 1. A load control device for a multi-stage compressor for controlling the opening and closing of a valve provided in a vent of a pipe connecting a discharge port of a first-stage compressor and an intake port of a second-stage compressor, comprising: a motor drive current detection circuit; Setting means for setting a current upper limit value and a load control release current value; comparing means for comparing a detected current value with the set current value; and control means for controlling opening and closing of the valve according to a result of the comparison. In a load control device for a multi-stage compressor, the valve is opened when the value exceeds the current upper limit value, and the valve is closed when the detected current value drops below the load control release current value . Detects and stores the current immediately after
A load control device for a multi-stage compressor , further comprising control means for setting an output value as next load control release current data .