JPS6244187B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a refrigerant flow rate control device used in a refrigeration cycle, and more particularly to a refrigerant flow rate control device using an expansion valve having a mechanism whose opening degree can be adjusted by an electric signal. Regarding equipment.

A refrigeration cycle is usually configured as shown in FIG. 1, for example. 1 is a compressor, 2 is a condenser, 3 is an expansion valve,
4 is an evaporator. The expansion valve 3 has a control circuit 5 that controls the opening degree of the expansion valve 3 according to the difference in refrigerant temperature detected by first and second temperature sensors provided at the inlet and outlet of the evaporator 4. The temperature difference between the inlet and the outlet of the evaporator 4 is kept constant. Temperature sensors include those that convert temperature into a resistance value and those that convert temperature into voltage, but any sensor may be used as long as it can be converted into an electrical signal. As the expansion valve 3, for example, there is one having a configuration shown in FIG. Inside the valve frame 3A,
It has a valve 3A, a valve seat 3C, an inflow port 3D, and an outflow port 3E.
E and flows out through the outflow pipe 3G. The valve drive unit is housed in the case 3H, and is made of bimetal 3i,
Electric heater 3 for displacing bimetal 3i
j, Consists of spring 3K. The power supply line of the electric heater 3j is drawn out to the outside via the connection terminals 3L and 3M.

With this configuration, while the compressor 1 is operating, the first
If the difference T ₂ −T ₁ between the temperature T ₁ detected by the second temperature sensor and the temperature T ₂ detected by the second temperature sensor is lower than a predetermined temperature, the control circuit 5 controls the electric heater 3j.
A signal is output to reduce the energization amount, thereby reducing the opening degree of the expansion valve 3, thereby reducing the refrigerant flow rate, and thereby increasing T ₂ −T ₁ . Conversely, T ₂ −
If T ₁ is higher than the predetermined temperature, the control circuit 5 controls the expansion valve 3 in the direction of increasing the valve opening, the refrigerant flow rate increases, and T ₂ −T ₁ decreases. This operation keeps T ₂ −T ₁ at a substantially constant value, thereby keeping the degree of superheat at the evaporator outlet substantially constant.

However, in such a device, when the compressor 1 is started after being stopped for a long period of time, the following problem occurs. During stoppage, the inlet and outlet temperature of evaporator 4
T ₁ and T ₂ are almost equal, and T ₂ −T ₁ ≈0. For this reason, the control circuit 5 outputs an output in the direction of closing the valve opening of the expansion valve 3, so if the engine is started with the valve closed, the valve will not open forever. In other words, not only may the expansion valve 3 not open during startup, but even if the engine starts from an open state, the control circuit 5 will output an output in the direction of closing the valve, resulting in the valve being closed. . If this happens, it is obvious that the refrigeration cycle cannot operate normally.

The present invention aims to provide a refrigerant flow rate control device having a novel control circuit that eliminates the drawbacks of the conventional example described above. That is, in the control circuit 6,
By adding a starting control circuit that maintains the valve opening of the expansion valve 3 at a predetermined opening until the temperature difference T ₂ −T ₁ at the inlet and outlet of the evaporator 4 reaches a predetermined value after starting, the above-mentioned conventional method can be improved. This is an attempt to overcome the shortcomings of the example. The present invention will be explained below using the drawings.

FIG. 3 is a diagram of a control circuit in an embodiment of the present invention. The same reference numerals as in FIGS. 1 and 2 indicate the same parts. 60A and 60B are DC power supplies for the circuit described below, and their middle point is grounded. 61 is a switch, which is a DC power supply 60A, 60 for the circuit described below.
Turn the power supply from B on and off. 5A and 5B are negative characteristic thermistors as first and second temperature sensors, which have the same characteristics in this embodiment. 62
is a resistance, which gives a predetermined temperature ΔT of the difference T ₂ −T ₁ between the evaporator inlet temperature T ₁ and the outlet temperature T ₂ . What if (T ₂
-T ₁ )=ΔT, the sum of the resistance value of thermistor 5B and the resistance value of resistor 62 is the thermistor 5
It becomes equal to the resistance value of point A, and becomes the voltage V _A at point A. If (T ₂ - T ₁ )>ΔT, the sum of the resistance value of thermistor 5B and the resistance value of resistor 62 will be smaller than the resistance value of thermistor 5A,
The voltage V _A at point A becomes a positive voltage. Conversely (T ₂ − _{T 1} )
<ΔT, the voltage V _A at point A becomes a negative voltage. That is, the temperature difference between the inlet and outlet temperatures T ₁ and T ₂ of the evaporator 4 is converted into a voltage V _A as an electrical signal. 6
3 is an amplifier that proportionally multiplies the voltage V _A at point A. The amplifier 63 includes resistors 63A, 63B, and an operational amplifier 63.
C, an operational amplifier 63C, and an output protection resistor 63D. Reference numeral 64 is a drive circuit for the electric heater 3j, which is a buffer that uses the output voltage of the amplifier 63 as an input voltage and makes the input voltage equal to the output voltage. Buffer 64 is operational amplifier 64A, current limiting resistor 64
B and a transistor 64C, the output of which is the collector voltage of the transistor 64C. Now, if the voltages of the DC power supplies 60A and 60B are +V _cc and -V _cc , the output voltage will be V _{iB with respect to the buffer input voltage V iB ,} and the applied voltage of the electric heater 3j will be V _H
becomes V _H =(2V _cc −V _iB ). That is, V _iB
As the voltage decreases, the voltage applied to the heater 3j increases, the amount of heat generated by the heater 3j increases, the amount of displacement of the bimetal 3i increases, and the valve opening increases. If V _iB becomes high,
The voltage applied to the heater 3j becomes small, and the valve opening degree decreases. 65 is the starting control circuit, operational amplifier 63C
An operational amplifier 65C serves as a comparison means, with the output V _AO of the amplifier as an inverting input, and a voltage V _R obtained by dividing the power supply voltage by resistors 65A and 65B as its non-inverting input. When the output of the operational amplifier 65C is Lo, the inverting of the operational amplifier 64A Diode 65D for pulling in the input, diode 65E for making the non-inverting input almost equal to its output voltage when the operational amplifier 65C output is Hi, and prohibiting its output from becoming Lo again, when the power is turned on V _AO >V So that _R
Capacitor 65 for short-term _VR to _-Vcc
The charging time of this capacitor 65F is approximately 2 to 3 seconds, for example.

After the compressor 1 has stopped for a long period of time, the switch 61 is closed at the same time as the compressor 1 is operated. Immediately after starting, the temperature difference T ₂ - T ₁ at the inlet and outlet of the evaporator 4 is almost zero, so the voltage V _A at point A becomes a negative voltage, so
The output voltage of the operational amplifier 63B is a positive voltage. Now suppose that the resistance values of resistors 65A and 65B are V _AO
When V becomes zero V, select V _R to be the voltage at which the output of the operational amplifier 65 is inverted. Therefore, V _AO > V _R and the output of the operational amplifier 65C is
The Lo voltage (≈-V _cc ) is applied, the inverting input of the operational amplifier 64A becomes approximately -V _cc , the voltage applied to the heater 3j becomes 2V _cc , and the valve opening of the expansion valve 3 operates in the fully open direction. The valve opening degree does not become fully open immediately even when 100% voltage is applied to the electric heater 3j, but moves toward the fully open direction as time passes. Due to refrigerant circulation after startup, a difference in evaporator inlet and outlet temperatures occurs,
When T ₂ −T ₁ reaches a predetermined temperature difference ΔT, the voltage at point A becomes zero volts, and the output voltage of the operational amplifier 63B also becomes zero volts. As a result, V _AO <V _R and the output of the operational amplifier 65C becomes Hi. This completes the operation of pulling in the inverting input of the operational amplifier 64A, and the output of the operational amplifier 63C is applied to the inverting input of the operational amplifier 64A, returning to normal control operation. Move. At the same time, the non-inverting input of operational amplifier 65C becomes equal to its output voltage (≈V _cc ), and is prohibited from going Lo again even if V _AO changes. Here, the resistance values of the resistors 65A and 65B are appropriately selected, and the inlet and outlet temperature difference T ₂ - T ₁ of the evaporator 4 is set to a predetermined temperature ΔT.
When the output of the fully open signal to the expansion valve 3 is completed, the temperature difference required to complete the output is completed.
T ₂ −T ₁ may be a value other than ΔT, and this can be achieved by appropriately selecting the values of the resistors 65A and 65B.

According to this embodiment, after starting, the temperature difference T ₂ −T ₁
The control circuit 6 outputs a signal to fully open the expansion valve 3, regardless of the temperature difference T ₂ -T ₁ , until the temperature difference reaches a predetermined temperature difference. The refrigerant flow rate can be stably controlled without moving in the closing direction.

FIG. 4 is a drawing showing another embodiment of the present invention. The embodiment shown in FIG. 3 outputs a fully open signal, but this embodiment outputs a signal to maintain a predetermined opening degree. This is a circuit in which a relay 66 and a DC power source 67 are added to the circuit shown in FIG. That is, during the period when the output of the operational amplifier 65C is Lo, the relay 66 is turned on, and the inverting input of the operational amplifier 64A receives the voltage V _C - which is the sum of the voltage V _C of the DC power supply 67 and -V _CC .
V _cc and the voltage applied to heater 3j is 2V _cc −V _C
becomes. As a result, the opening degree of the expansion valve 3 becomes an opening degree between fully closed and fully open. If V _C is set to zero, then
Similar to the circuit shown in FIG. 3, the valve opening is fully open. Also V
If _C is chosen as V _C =V _cc , the voltage applied to the heater becomes V _cc , which is 50% of the energization amount, and the valve opening is maintained at a corresponding valve opening.

In the above description, the first temperature sensor was provided at the inlet of the evaporator, but considering that the refrigerant temperature within the evaporator is substantially uniform, it is clear that it may be provided at the intermediate portion. In addition, although thermistors are used as the first and second temperature sensors, other sensors may be used, and if their nonlinearity becomes a problem, they may be used in series, in parallel, or in series-parallel with the thermistors. It can also be made straight by adding a resistor to it, and the thermistors 5A and 5B in FIG. 3 can be replaced with this. As the expansion valve 3, the one shown in Fig. 2 was used, but there are other ones that use a proportional solenoid valve or a reversible motor, but in any case, the valve opening can be adjusted by an electric signal. It is clear from the above explanation that this is the case.

As detailed above, according to the present invention, the control circuit outputs a signal that maintains the expansion valve opening at a predetermined opening until the temperature difference T ₂ −T ₁ after startup reaches a predetermined temperature. This provides an excellent effect of stably starting the refrigeration cycle.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram of a refrigeration cycle, Fig. 2 is a sectional view showing an example of an expansion valve, Fig. 3 is a control circuit diagram of an embodiment of the present invention, and Fig. 4 is a control circuit diagram of another embodiment of the present invention. It is a circuit diagram of the main part of a circuit. 3... Expansion valve, 4... Evaporator, 5A... First temperature sensor, 5B... Second temperature sensor, 6...
Control circuit, 65... Starting control circuit, 65C... Operational amplifier as comparison means.

Claims (1)

[Scope of Claims] 1. An expansion valve whose valve opening degree can be adjusted by an electric signal, a first temperature sensor provided at an inlet portion or an intermediate portion of the evaporator to convert refrigerant temperature into an electric signal, and an evaporator. a second temperature sensor provided at the outlet of the chamber; and a control circuit that outputs an electric signal to the expansion valve according to the difference between the electric signals of the first temperature sensor and the second temperature sensor, The control circuit compares the difference in the electrical signals with a predetermined value when the compressor is started, and when the difference in the electrical signals is smaller than the predetermined value, maintains the valve opening of the expansion valve at the predetermined opening. A refrigerant flow control device comprising a starting control circuit having a comparison means for outputting an electric signal. 2. The refrigerant flow rate control device according to claim 1, wherein the expansion valve has a valve drive consisting of an electric heater and a bimetal, and the predetermined valve opening degree is set to be fully open.