JPS61184367A - Refrigerant flow controller - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a refrigerant flow rate control device for a refrigeration cycle equipped with a variable rotation speed compressor, and particularly relates to a refrigerant flow rate control device for maintaining the refrigerant superheat degree at a constant value at the outlet of an evaporator. Regarding a control device.

[Background of the invention]

A conventional refrigerant flow rate control device, as shown in Japanese Patent Application Laid-Open No. 56-44569, uses an electric signal corresponding to the temperature difference between the degree of superheating of the refrigerant at the evaporator outlet and a set value, multiplied by a first proportionality constant. 1 electric signal, a second electric signal obtained by multiplying the electric signal corresponding to the value obtained by integrating the temperature difference with respect to time by a second proportionality constant, and an electric signal corresponding to the value obtained by differentiating the temperature difference with respect to time. The electric expansion valve is configured to control the opening degree of the electric expansion valve according to the sum of the signal and a third electric signal obtained by multiplying the signal by a third proportionality constant.
A good degree of superheating can be achieved on the side legs.

However, when applied to a refrigeration cycle that is operated over a wide range such as a refrigeration air conditioner, no consideration was given to the influence of changes in operating conditions (load conditions).

[Purpose of the invention]

An object of the invention is to provide a refrigerant flow rate control device that can always appropriately control the degree of superheating of the refrigerant at the evaporator outlet even if the load conditions of the refrigeration cycle change significantly.

[Summary of the invention]

In the present invention, the degree of superheating of the refrigerant is appropriately controlled by adding to the control circuit a constant corrector that corrects all three proportionality constants in accordance with the rotational speed of the pressure IllI machine.

[Embodiments of the invention,]

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. FIG. 1 shows a refrigeration cycle system diagram provided in a refrigerant flow rate control device 11 according to the present invention, and FIG. 2 shows a block diagram of the control circuit in FIG. 1. In Figure 1, 1
2 is a condenser, 3 is an electric expansion valve whose opening degree is set by an electric signal (hereinafter simply referred to as an expansion valve), 4 is an evaporator, and 5 is an evaporator 40. Inlet temperature T
11 a first temperature sensor that detects; 6 a temperature L at the outlet of the evaporator 4;
A second temperature sensor that detects TZ, 7 a sensor that detects the rotation speed of the pressure m machine 1, and 8 a sensor that takes in all the signals from each sensor 5, 6.7 and generates an electric signal for controlling the opening of the expansion valve 3. This is a control circuit that outputs.

In FIG. 2, the control circuit includes an arithmetic unit 9, a comparator 10,
Multipliers 11, 12, 13 and equinox 14, minute molecule 2F
15, an adder 16, and a constant corrector 17.

In this control circuit, the expansion valve 3 controls the refrigerant flow tG.
is determined, and the evaporation temperature T1 of the refrigerant and the refrigerant temperature T2 at the outlet of the evaporator 4 at that time are determined by the first and second thermal storage sensors 5 and 5, respectively.
When the temperature signal is detected by 6, the temperature signal is input to a calculator 9. .

The calculator 9 outputs an electric signal corresponding to the temperature difference (T2-T1) from both temperature signals to the comparator 10. The comparator 10 compares the electrical signal from the calculator 9 with the set superheat degree ΔT0, and sends the electrical signal corresponding to the difference E=(Tz Tl)−ΔTo to the multiplier 11, the integrator 14, and the differentiator ← --÷humiliation 1
5, respectively. The electrical signal output to the multiplier 11 is multiplied by a constant by 1 and input to the adder 16. The electrical signal input to the integrator 14 is integrated with respect to time, multiplied by 2 by a constant in the multiplier 12, and input to the adder 16.

Further, the electrical signal input to the differentiator 15 is differentiated with respect to time, multiplied by 3 by a constant in the multiplier 13, and then added to the adder 16.
is input. The adder 16 takes the sum t of these three electric signals and once outputs a control electric signal to the expansion valve 3.

That is, this is P (proportional) action, ■ (integral) action, D (
This is a control method known as PID control in control engineering. These can be expressed as formulas as follows.

αE ■=1・E×2・/Bαt−1−−3. −・・・・
...(1) However, V: Valve opening degree of the expansion valve.

On the other hand, when the rotation speed of the compressor is detected by the sensor 7, the signal is input to the constant corrector 17. The constant corrector 17 adjusts the constants of each multiplier +1, 12, and 13 according to the signal from the sensor 7, that is, the rotation speed of the compressor, N2. Set N3.

Next, the operation of this embodiment will be explained with reference to FIGS. 3 to 6. Figure 3 shows the refrigerant flow rate G passing through the expansion valve on the vertical axis, and the expansion valve opening degree v on the horizontal axis, and the differential pressure ΔP before and after the expansion valve, Δ
P2. ΔPa (ΔP1>ΔP2>ΔP3) and compressor rotation speed Nl + N2 + N3 (N1>N2>N
3) is used as a parameter to show the flow rate of refrigerant passing through the expansion valve. When the rotational speed of the compressor 1 is N1, the differential pressure before and after the expansion valve is ΔP1, and the flow rate change is ΔG1 for a change in the valve opening of Δ■. Similarly, when the rotation speed is N2, the differential pressure is ΔP2, and for a change in valve opening of ΔV, the flow rate change is ΔG2, and when the rotation speed is N3, the differential pressure is ΔP.
3, the flow rate change is ΔG3 for the valve opening of Δ■.

That is, when the rotation speed of the pressure f1i1 machine 1 is high for a constant change in the valve opening degree, the flow rate change range is large. now,
If the proportional constant Kt + N2 + N3 in the above equation (1) is constant and the rated operation is when the compressor 10 rotation speed is N2, a larger flow rate change width will be given as the rotation speed increases, and the control The system becomes more responsive but less stable. Furthermore, when the rotational speed is lower, a smaller flow rate variation range is given, which improves the stability of the control system, but reduces responsiveness. However, in this embodiment, the constant corrector 17 has characteristics as shown in FIG. 4, and when the rotation speed of the compressor 1 is high, the constant is adjusted by 1°K2. If the rotation speed is low, set the constant 11. 2. Since 3 is made small, the opening degree of the expansion valve is maintained appropriately, and the degree of superheating of the refrigerant in the evaporator can always be stably controlled.

FIGS. 5 and 6 are characteristic diagrams showing the effects of this embodiment.

Figure 5 shows the change in the degree of refrigerant superheating ΔT when the rotation speed N of the pressure m machine increases in a stepwise manner. is large, so the refrigerant superheat degree ΔT becomes unstable as shown by the broken line. However, in this embodiment, the refrigerant superheat degree ΔT fluctuates slightly as shown by the solid line, but is quickly controlled to the original value.

Figure 6 shows the change in the degree of superheating ΔT of the refrigerant when the rotational speed N of the compressor decreases in a stepwise manner. Therefore, as shown by the broken line, it will take a considerable amount of time for the refrigerant superheat degree ΔT to return to its original value, but in this example,
As shown by the solid line, the refrigerant superheat degree ΔT is controlled to the original value in a short time.

〔Effect of the invention〕

According to the present invention, even if the load conditions of the refrigeration cycle change, the degree of superheating of the refrigerant in the evaporator can always be stably controlled. As a result, it is possible to prevent the liquid from returning to the compressor and improve the reliability of the refrigeration cycle.
The evaporator can be used effectively and energy can be saved.

[Brief explanation of the drawing]

Fig. 1 is a refrigeration cycle system diagram equipped with a refrigerant flow rate control device according to the present invention, Fig. 2 is a block diagram of the control circuit in Fig. 1, Fig. 3 is a characteristic diagram of the electric expansion valve, and Fig. 4 is a diagram of the control circuit in Fig. 1. The characteristic diagrams of the constant corrector, FIGS. 5 and 6, are diagrams illustrating the state of control of the refrigerant superheat degree with respect to changes in the rotational speed of the compressor. 1... Compressor 3... Electric expansion valve 5...
First temperature sensor 6...Second temperature sensor 7...
- Sensor for detecting the rotation speed of the compressor 8...Control circuit 17...Constant corrector.

Claims (1)

[Claims] In a refrigeration cycle consisting of a compressor with a variable rotation speed, a condenser, an evaporator, and an expansion valve whose valve opening degree is variable according to an electric signal, a first temperature sensor detects the evaporation temperature of the refrigerant, and a refrigerant at the outlet of the evaporator. The control circuit includes a second temperature sensor that detects temperature, and a control circuit that outputs an electric signal that controls the opening degree of the expansion valve, and the control circuit detects the temperatures detected by the first temperature sensor and the second temperature sensor. an electric signal corresponding to a value obtained by integrating the temperature difference over time by multiplying an electric signal corresponding to the temperature difference between the difference and the set superheat degree of the evaporator outlet refrigerant by a first proportionality constant; A second electrical signal is generated by multiplying the temperature difference by a second proportionality constant, and a third electrical signal is generated by multiplying the electrical signal corresponding to the value obtained by differentiating the temperature difference with respect to time by a third proportionality constant. , a refrigerant flow rate control device configured to output an electric signal for controlling an expansion valve according to the sum of the first, second, and third electric signals. A refrigerant flow rate control device characterized in that a constant corrector for correcting the first, second, and third proportionality constants is added to the control circuit.