JPS6251386B2 - - Google Patents

Description

Detailed Description of the Invention The present invention relates to a refrigerant flow control device used in refrigeration equipment, air conditioning equipment, etc. that uses an electric expansion valve such as a thermoelectric expansion valve. In addition to responding to load conditions, the refrigeration cycle is quickly optimized for transient conditions during load fluctuations.

Conventionally, in this type of control device, for example, temperature sensors are provided at the inlet and outlet of the evaporator, the difference in temperature detected by these temperature sensors is determined, and this temperature difference (corresponding to the so-called degree of superheating) is determined to reach a predetermined value. A controller controlled an electrical signal to the expansion valve so that the expansion valve was maintained.

However, the two temperature sensors used to determine the temperature difference are usually brought into contact with the refrigerant piping for reasons such as maintenance and reliability, and detect the temperature of the refrigerant in that part. The signal has a time delay relative to the actual change in refrigerant in the refrigerant piping. Furthermore, a time delay occurs with respect to the surface temperature of the refrigerant pipe due to heat transfer at the contact portion and the thermal time constant of the temperature sensor itself. In this way, although the temperature sensor has a large time lag (for example, several tens of seconds), the configuration is such that the expansion valve is simply controlled according to the temperature difference. In addition to this temperature detection, the response of the refrigeration cycle itself, including the response of the expansion valve, is extremely slow, so it takes an extremely long time (for example, several minutes) for the temperature sensor to output a value approximately equal to the refrigerant temperature. ), it took time for the control system to stabilize, and there was also a high probability that it would fall into an oscillation or vibration state.

Therefore, the present invention aims to improve the response of control operations to the above-mentioned temperature sensor and refrigeration cycle time delays, to achieve early stabilization of the refrigeration cycle and expand the optimal control state, thereby improving the efficiency of refrigeration and air conditioning equipment. The aim is to achieve improvement.

In particular, in view of the responsiveness of the temperature signals from the two temperature sensors, the present invention detects the difference between the two temperature signals using a temperature detection circuit, electrically compensates for the response characteristics, and uses the operation of the control circuit to detect the difference between the two temperature signals. This attempts to control the refrigerant flow rate by adjusting the electrical signal to the expansion valve so that the degree of superheat is always maintained at a predetermined value.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The refrigerant flow rate control device of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an embodiment of a refrigerant flow rate control device according to the present invention, and the figure particularly shows the case where the refrigerant flow rate control device is used in a cooling device. In the figure, 1 is a compressor, 2 is a condenser, 3 is a blower for the condenser 2, 4 is an expansion valve whose opening degree can be adjusted by an electric signal (in this case, it is a thermoelectric expansion valve), and 5 is an evaporator. , 6 is a blower for the evaporator 5, and the above constitutes a refrigeration cycle. 7 and 8 are temperature sensors provided at the inlet of the evaporator 5 and the suction section of the compressor 1, respectively;
is a temperature detection circuit that detects the difference between the temperature signals detected by the temperature sensors 7 and 8, and compensates for the responsiveness of the difference signal. Reference numeral 10 denotes a control circuit that issues an electric signal to the expansion valve 4 in order to maintain the degree of superheat at a predetermined value based on a signal from the temperature detection circuit 9.

Expansion valve 4, temperature sensors 7, 8, temperature detection circuit 9
and the control circuit 10 constitute a refrigerant flow rate control device.

In the above configuration, in this refrigeration cycle, due to the compression action of the refrigerant in the compressor 1, the refrigerant flows through the condenser 2, the expansion valve 4, the evaporator 5, and the suction section of the compressor 1, and the evaporator 5 cools the refrigerant. Output ability. In this operation of the refrigeration cycle, when the refrigerant evaporated in the evaporator 5 becomes almost dry saturated vapor at its outlet, the most appropriate operating state is achieved.

However, in the actual configuration, there is a temperature drop due to the resistance inside the evaporator 5 and the refrigerant piping from the evaporator 5 to the suction part of the compressor 1, and in the process of adjusting the expansion valve 4, the compressor 1 In order to prevent suction and liquid compression in the liquid multiphase region, the evaporator 5 is usually used.
The difference between the temperature at the inlet or intermediate part of the evaporator 5 and the temperature at the outlet of the evaporator 5 or the suction part of the compressor 1 (usually referred to as the degree of superheat) is always controlled to a predetermined value (for example, several degrees Celsius). , improving the efficiency of the refrigeration cycle,
It is preferable to ensure safety.

Therefore, as shown in FIG. 1, temperature sensors 7 and 8 are provided on the surfaces of the refrigerant pipes at the inlet of the evaporator 5 and the suction section of the compressor 1, respectively, to detect the temperature at those positions. Here, temperature sensors 7 and 8 often use temperature-sensitive resistance elements (thermistors), but this element itself has a delay in response, and refrigeration pipes also have a delay in surface temperature response to the internal refrigerant temperature. The detection signals output by the sensors 7 and 8 have a response delay with respect to the temperature of the refrigerant. FIG. 2 shows an example of its temperature response characteristics. In the figure, θ indicates temperature and t indicates time.

Further, θ _E and θ _ES are the temperature of the refrigerant at the mounting part of the temperature sensor 7 and the temperature signal output from the temperature sensor 7, respectively, and θ _S and θ _SS are the temperature of the refrigerant at the mounting part of the temperature sensor 8 and the temperature, respectively. A temperature signal output by the sensor 8 is shown. This second
The characteristics shown in the figure are obtained by changing the throttling amount by slightly changing the electric signal, that is, the DC applied voltage, to the expansion valve 4 at time t= _t0 . After the DC applied voltage of the expansion valve 4 changes, the amount of expansion gradually changes due to the response delay, but at time _t1 , the temperature θ _E of the refrigerant at the mounting part of the temperature sensor 7 starts to change. do. The temperature θ _ES output by the temperature sensor 7 changes with a slight delay compared to θ _E due to the response of the piping and the response of the temperature sensor 7 itself. time t ₂
Then, the temperature of the refrigerant at the mounting part of the temperature sensor 8 θ _S
starts to change, and the temperature θ output by the temperature sensor 8
_SS changes later. Here, as shown in the figure,
Compared to θ _S , θ _E starts changing and becomes stable faster, and the range of temperature change is smaller.
Furthermore, θ _ES is also similar to θ _SS . θ
The reason why the change in _E and θ _ES starts earlier is because it is closer to the expansion valve 4, and the reason why the response speed is faster is because the refrigerant is in a liquid phase more than the refrigerant at the mounting part of the temperature sensor 8, and the refrigerant is in a liquid phase. This is because the temperature change is given almost in agreement with the pressure change.

Temperature sensors 7 and 8 having the above characteristics
The temperature signals θ _ES , θ _SS are expressed as the refrigerant temperatures θ _E , θ _S
It can be seen that the control characteristics can be improved by compensating so that the response is the same as or more than that, and by quickly applying the signal to the control circuit 10.

Therefore, temperature detection circuit 9 to achieve this
An example of this is shown in FIG.

In Figure 3, Vcc is the DC power supply voltage,
The temperature sensors 7 and 8 are connected in series with the DC power supply voltage, and output a detection voltage V _T from their connection point. 11 is a capacitor that absorbs noise in the detection voltage V _T , 12 is an operational amplifier, R ₁ is a resistor, and C ₁ is a capacitor. operational amplifier 12,
Proportional differentiation circuit 13 with resistor R ₁ and capacitor C ₁
and generates its output voltage V _O. Here, the detected voltage V _T has a substantially proportional relationship with the difference between the temperatures θ _E and θ _S detected by the temperature sensors 7 and 8, that is, the degree of superheat SH=θ _S −θ _E. Figure 4 shows the relationship between the degree of superheating SH, the detection voltage V _T and the output voltage V _O. In the figure, if θ _E = θ _S , temperature sensors 7 and 8 with the same specifications are used. Therefore, V _T =Vcc/2. Further, the output voltage V ₀ in FIG. 4 is a case where the detection voltage V _T is stable, and in this case, V _O =V _T .

Here, in the configuration shown in FIG. 3, the detection voltage V _T and the output voltage V _O when the changes shown in FIG. 2 occur
Figure 5 shows the change characteristics of . In the figure, the detected voltage V _T exhibits almost the same change characteristics as the difference between θ _SS and θ _ES shown in FIG. 2. On the other hand, the output voltage V _O is obtained by proportionally differentiating the detected voltage V _T , and its responsiveness is extremely improved, and the change characteristics from time t ₁ are rapid and the time to reach a stable value is shortened. ing.

Here, the resistor R ₁ configuring the proportional differentiation circuit 13
and capacitor C ₁ give a differential time T ₁ =R ₁ ·C ₁ , and this differential time T ₁ is relative to θ _S in FIG. Choose it equal to the time constant τ _S (for example, 30 seconds) of θ _SS . That is, if T ₁ = τ _S , θ _SS becomes θ
It is compensated to have almost the same characteristics as _S. on the other hand,
Since the time constant τ _E with respect to θ _E is τ _E <τ _S , θ _ES is compensated to give a more rapid change than θ _E by the differentiation _time T ₁ of the proportional differentiation circuit 13. Ru. Therefore, as shown in FIG. 5, the output voltage V _O of the temperature detection circuit 9 has a characteristic that first compensates for θ _ES , which has a small amount of change but has a fast response speed, and then (near time t ₂ ), the response It is a characteristic that compensates for θ _SS, which is slow but has a large variation, and the superheat degree
This makes it possible to quickly detect changes in SH. As is clear from the above explanation, θ _SS is compensated to be approximately equal to θ _S , and θ _ES is compensated to be approximately equal to θ _E
The configuration of one proportional differentiation circuit 13 can appropriately improve the responsiveness of the detected superheat degree.

Due to the function of the temperature detection circuit 9, the output voltage V _O corresponding to the superheat degree SH input to the control circuit 10 has improved response of the temperature sensors 7, 8, etc. Since the electric signal can be adjusted quickly, it becomes easy to quickly and stably control the degree of superheating.

Next, another embodiment of the temperature detection circuit 9 is shown in FIG. In FIG. 6, 14, 16 are resistors, 15,
17 is a capacitor for noise absorption, 18 is a differential amplifier circuit, and 19 and 20 are operational amplifiers forming the differential amplifier circuit 18.

13' is a proportional differential circuit, 23 and 24
are a capacitor and a resistor for preventing malfunction of the proportional differentiation circuit 13'. Further, V _TE and V _TS are temperature detection voltages output by the temperature sensors 7 and 8, and are approximately proportional to the detected temperatures of the temperature sensors 7 and 8, respectively, within the actual operating temperature range. V _R is a reference voltage of the differential amplifier circuit 18, and V _T is a detection voltage outputted from the differential amplifier circuit 18. Other details are the same as in FIG. 3.

In the figure, the temperatures detected by temperature sensors 7 and 8 are each independently determined by the temperature detection voltage V _T
Give _E and _VTS . This temperature detection voltage V _TE and V
_TS is input to the differential amplifier circuit 18, and the detected voltage V _T outputted from the differential amplifier circuit 18 has a relationship of V _T =k(V _TS −V _TE )+V _R . However, k is the differential amplifier circuit 18
is the degree of amplification. That is, the detection voltage V _T gives the difference (degree of superheat) between the temperatures detected by the temperature sensors 7 and 8.

Next, the proportional differentiation circuit 13' inputs the detection voltage V _T output from the differential amplifier circuit 18, improves the superheat response characteristic through its proportional differentiation operation, and generates an output voltage V _O. Since the capacitor 23 and resistor 24 for preventing malfunction are usually selected to have a sufficiently small capacitance or resistance value compared to the capacitor C ₁ and resistor R ₁ , their proportional and differential operation will be almost the same as that in Figure 3. .

Since the temperature detection circuit 9 of FIG. 6 obtains independent temperature signals from the temperature sensors 7 and 8, it is possible to use these temperature signals for other purposes. Furthermore, in the method of obtaining the difference between these two temperature signals (temperature detection voltages V _TE and V _TS ) using the differential amplifier circuit 18, the proportional relationship between the detection voltage _VT and the degree of superheating is generally more accurate than that shown in FIG. It will be expensive. Furthermore, by appropriately providing the value of the reference voltage V _R shown in FIG. 6, the detected voltage V _T can be provided not as the degree of superheat itself but as the difference between the degree of superheat and its set value, that is, as a deviation.

Although the present invention has been described above based on the embodiments, it is also possible that the compensation operation of the temperature detection circuit 9 corresponds to a quadratic lag response instead of simply a proportional differential operation, and the degree of the compensation operation can also be changed. It is desirable to slightly overcompensate depending on the purpose of use. Further, although the embodiment shown in FIG. 1 is used in an air conditioner, it can be used in a wide range of other applications such as refrigeration equipment and heat pump equipment.

As described above, the present invention includes an expansion valve whose opening degree can be adjusted by an electric signal, a first temperature sensor provided at the inlet or intermediate portion of the evaporator, and a first temperature sensor provided at the output of the evaporator or the suction portion of the compressor. a second temperature sensor, a temperature detection circuit that detects the difference between the respective detection signals output from the first and second temperature sensors, and compensates for the response characteristics; and a signal from this temperature detection circuit. Emit an electrical signal to the expansion valve,
Since it is equipped with a control circuit that maintains the difference between the detection signals at a predetermined value, it can compensate for the response delay caused by each temperature sensor, and can quickly and stably control the expansion valve, thereby stabilizing the refrigeration cycle early and increasing its duration. It can be expected to contribute to improving energy consumption efficiency.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a cooling device that employs a refrigerant flow rate control device according to an embodiment of the present invention, FIG. 2 is a diagram explaining the operation in FIG. 1, and FIG. 3 is a temperature detection circuit diagram of the same;
4 and 5 are explanatory diagrams of the operation in FIG. 3, and FIG. 6 is a circuit diagram of another embodiment of the same temperature detection circuit. 1... Compressor, 4... Expansion valve, 5... Evaporator,
7, 8...first and second temperature sensors, 9...
Temperature detection circuit, 10...control circuit, 13...proportional differential circuit.

Claims (1)

[Claims] 1. An expansion valve whose opening degree can be adjusted by an electric signal;
a second temperature sensor provided at the outlet of the evaporator or the suction part of the compressor, and a difference between detection signals output from the first and second temperature sensors; A refrigerant flow control device comprising: a temperature detection circuit that compensates for response characteristics; and a control circuit that issues an electric signal to the expansion valve based on a signal from the temperature detection circuit to maintain a difference between the detection signals at a predetermined value. 2. The refrigerant flow rate control device according to claim 1, wherein the temperature detection circuit includes a proportional differential circuit mainly composed of an operational amplifier, a resistor, and a capacitor.