JPS6058384B2 - Refrigerant flow control device - Google Patents

Description

Detailed Description of the Invention The present invention aims to maintain an efficient refrigeration cycle at all times in a refrigeration system or air conditioner using an electric expansion valve such as a thermoelectric expansion valve. The present invention relates to a refrigerant flow rate control device for optimizing a refrigeration cycle not only in a stable state but also in a transient state and a wide range of load fluctuations.

Conventionally, in this type of control device, temperature sensors are installed at the inlet and outlet of the evaporator, and the difference between the temperatures detected by these temperature sensors is determined. A control device controlled the 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 placed in contact with the refrigerant piping for reasons such as maintenance and reliability, and are designed to detect the temperature of the refrigerant in that part. The detection signal output by the sensor has a time delay with respect to the actual change in the refrigerant in the refrigerant pipe.

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. Furthermore, this time delay situation is caused by a delay in the temperature sensor installed at the evaporator outlet (or the compressor suction) compared to the time lag of the temperature sensor installed at the evaporator's inlet (or the middle). The time delays are different, with the latter having a larger value. In other words, in the former case, the state of the refrigerant inside the refrigerant pipe is in a gas/liquid multiphase region, and the heat transfer to the refrigerant pipe is relatively fast, and the response speed detected by the temperature sensor is also relatively fast. There are, but
In the latter case, the state of the refrigerant in the refrigerant piping is in the gas single-phase region during normal operation, and heat transfer to the refrigerant piping is extremely slow, resulting in a very slow detection response speed of the temperature sensor. It has become a thing. In this way, the detection signals of the two temperature sensors are slower than the actual change in refrigerant temperature, and the two temperature sensors have different time delays.

For example, the temperature sensor at the evaporator inlet has a time lag of about 308 when approximated to the first-order lag, and the temperature sensor at the evaporator outlet has a time lag of about 6@. Therefore, in the past, the temperature difference was simply determined from two detection signals with a large time lag and different degrees of lag as described above, and control was performed to maintain the temperature difference at a predetermined value. Ta.

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 temperature of the refrigerant. Therefore, it took time to stabilize the control system, and there was also a high risk of oscillation or vibration. Therefore, the present invention aims to improve the efficiency of refrigeration and air conditioning equipment, so-called EER and SEER, by improving the responsiveness of the temperature sensor described above to achieve early stabilization of the refrigeration cycle and expansion of the optimal control state. It is something. In particular, the present invention provides a temperature sensor provided at the inlet portion (or intermediate portion) of the evaporator, and a temperature sensor provided at the evaporator outlet portion (or intermediate portion).
The response characteristics of the temperature sensors installed in the compressor suction section are compensated for, so that they almost correspond to the refrigerant, and the temperature difference is determined from the results, and the refrigerant flow rate is adjusted to maintain this temperature difference at a predetermined value. It is an attempt to control the

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

FIG. 1 is a circuit 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, 7 is a temperature sensor provided at the inlet of the evaporator 5, 8 is a temperature sensor provided at the suction portion of the compressor 1, 9
10 is a response compensation circuit that compensates for the responsiveness of the temperature signal detected by temperature sensor 8; 11 is an output from response compensation circuits 9 and 10; input the signal, detect the difference in temperature of the refrigerant at the mounting part of the temperature sensors 7 and 9,
This is a control circuit that outputs an electric signal (DC voltage) to the expansion valve 4 to maintain the difference at a predetermined value.

The expansion valve 4, temperature sensors 7, 8, response compensation circuits 9, 10, and control circuit 11 constitute a refrigerant flow rate control device. In the above configuration, in this refrigerant cycle, the refrigerant flows through the condenser 2, the expansion valve 4, the evaporator 5, and the suction section of the compressor 1 due to the compression action of the refrigerant by the compressor 1, and the evaporator 5 has a cooling capacity. Output.

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 reached. At this time, the temperature of the refrigerant inside (middle part) and the outlet part of the evaporator 5 is equal.
Therefore, it is appropriate to detect these temperatures and adjust the opening degree of the expansion valve 4 so that the temperature difference becomes approximately zero.
However, due to 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 inhalation and liquid compression in the multiphase region,
Normally, the temperature at the inlet or intermediate part of the evaporator 5 and the temperature at the inlet or intermediate part of the evaporator 5
The temperature difference between the outlet part of the compressor 1 and the suction part of the compressor 1 (usually referred to as the degree of superheating) is always controlled to a predetermined value (for example, several degrees Celsius), improving the efficiency and safety of the refrigeration cycle. It is preferable to secure it. Therefore, as shown in FIG. 1, temperature sensors 7 and 9 are installed 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 of the refrigerant at those positions. There is.

However, although temperature sensitive resistance elements (thermistors) or the like are used as the temperature sensors 7 and 9, these temperature sensors 7 and 9 themselves have a delay in response, and the refrigerant piping also has a delay in response of the surface temperature to the temperature of the refrigerant inside. As a result, the detection signals output from the temperature sensors 7 and 9 have a lag in response to the temperature of the refrigerant. FIG. 2 shows an example of its temperature response characteristics. In the figure, 0 indicates temperature, t indicates time,
θ8・JOGP, θ. 3 are the refrigerant temperature at the mounting part of the temperature sensor 7, the surface temperature of the refrigerant pipe, and the temperature detected by the temperature sensor 7, and θ,,0sp,0,,
are the temperature of the refrigerant at the attachment part of the temperature sensor 8, the surface temperature of the refrigerant pipe, and the temperature detected by the temperature sensor 8, respectively.

This FIG. 2 shows the response characteristics of these temperature signals. θEP and θSp are slightly delayed from θE and θ2, and 0E,, θ,, is θ. There is a delay with respect to P and θSp. As a result, the temperature signals θ detected by the temperature sensors 7 and 9 with respect to the refrigerant temperatures θE and θs. ,,θ,, have characteristics that cause a delay as shown in the figure. Also, 0ss has a large delay compared to θES, but this is because the refrigerant at the mounting part of the temperature sensor 7 is in the gas-liquid multiphase region (the proportion of liquid is sufficiently large), whereas the refrigerant at the mounting part of the temperature sensor 9 is This is a gas single-phase region, and differences occur depending on the heat transfer rate of refrigerant piping, etc. As described above, since the response characteristics of the temperature sensors 7 and 8, especially the temperature sensor 8, are slow, even if you try to control the expansion valve 4 by determining the temperature difference (degree of superheat) from these detection signals, the stability of the control will be poor. It is often not good, and it is also disadvantageous for early stabilization.

Therefore, the response compensation circuits 9 and 10 shown in FIG. 1 compensate for the temperature signals θ111 . ,,θ, , is the true temperature change θE, θ of the refrigerant
The response characteristics are compensated to the same extent as s, and the output thereof is input to the control circuit 11. As a result, the control circuit 11
The input temperature signal is approximately equal to the true temperature of the refrigerant, and the electric signal to the expansion valve 4 can be adjusted according to that value, making it easy to quickly and stably maintain the degree of superheat at a predetermined value. . Now, FIG. 3 shows a block diagram related to superheat degree control, where SHd is the superheat degree setting value, SHO is the superheat degree output, and SHl is the temperature sensor 7.
, 8, the degree of superheat obtained from the signal detected by GA(S
) is the transfer function of proportional, differential, and integral operations in the control circuit 11, Gv(S) is the transfer function of the expansion valve 4, and GE(S)
G and (S) are the output of the expansion valve 4 and the temperatures θE and θ, respectively.
GEP(S) and G0(S) are the transfer functions of the refrigerant pipes, G5, (S) and G8(S) are the transfer functions of the temperature sensors 7 and 8, respectively, GEc(S),
Gsc(S) is the transfer function of the response compensation circuits 9 and 10, respectively.

Here, due to the action of response compensation circuits 9 and 10, if the respective output signals become equal to 0E and 0, GE
Since p(S)・GIcs(S)・GEO(S)=1, the transfer function G(S) of SHO to SHd is expressed as can.

That is, the superheat degree SHO of the controlled object in this control system
If the response compensation circuits 9 and 10 are appropriately configured to detect the true value of , the control system regarding the degree of superheating can be expressed by a simple block diagram as shown in FIG.

So Gv(S), and [G,(S)-GO(S)]
or Gv(S) [Gs(S)-GE
(S)], it becomes possible to relatively easily determine the transfer function GA(S) based on proportional, differential, and integral operations in the control circuit 11 to obtain stability of the control system. This will greatly contribute to improving the analysis, design, and characteristics of control systems. Next, one embodiment of the response compensation circuit 9 is shown in FIG.

Note that the same applies to the response compensation circuit 10.

In FIG. 5, Vcc is a DC power supply, and 7 is a temperature sensor, in which a negative temperature sensitive resistance element is used. 12 is a resistor, and 13 is a capacitor for noise absorption.

The above constitutes a temperature detection section based on the temperature sensor 7. Here, the output signal voltage ■T has a substantially linear relationship with the temperature θES detected by the temperature sensor 7 by selecting the resistor 12. 9 is a response compensation circuit, 14 is an operational amplifier, and R1 and C1 are a response compensation resistor and a capacitor.

15 and 16 are a small capacitor and a low resistance value resistor for noise suppression, respectively.

This response compensation circuit 9 is a so-called proportional differentiator with a resistor R
1 and the time constant T1 given by capacitor C1 = T1
- Due to C1, it has the characteristic that the transfer function G(S)=1+TlS. Here, when the signal voltage (I) has a first-order delay response characteristic with a time constant τ, if R1 and C1 are selected so that T1=τ, the output voltage (I).

As shown in FIG. 6, regardless of the first-order lag response of the signal voltage Vτ, the output is stepped. That is, from this, when the temperature signal θES output by the temperature sensor 7 is a first-order lag response with respect to the refrigerant temperature θE, the transfer function is GO, (S)・G6, (S)=±,
Output voltage V. has a change characteristic of 1+τ, which is the same as the temperature θ8.

Furthermore, FIG. 7 shows another embodiment of the response compensation circuit, in which a response compensation characteristic is provided by resistors R2, .

In this circuit, when GEp(S) ・GE3(S) is a second-order delay response or a higher-order delay response, the output voltage VO has almost the same change characteristics as the temperature 0E11 as shown in FIG. It is possible to output . The present invention has been described above based on the embodiments, and the case where the response compensation circuits 9 and 10 are configured to emit an output signal having the same characteristics as the refrigerant temperature 06, θ has been described.
In relation to the transfer function GA(S) of the control circuit 11,
It is also possible to slightly overcompensate or undercompensate.

Further, as the temperature sensors 7 and 8, it is preferable to use ones with a fast response speed, as long as there is no problem in terms of reliability and cost, since the degree of compensation can be small. Further, in this compensation operation, it is not possible to compensate for dead time, so it is necessary to select temperature sensors 7 and 8 that have as little dead time as possible. However, if some dead time unavoidably occurs, including the response of the refrigerant piping, it is usually possible to generate a substantially good output signal, even if the compensation operation is slightly overcompensated. Further, the temperature sensors 7 and 8 may be other than temperature-sensitive resistance elements. Although the embodiment shown in FIG. 1 is used in a cooling device, it is clear that the device can be used in a wide range of other applications such as refrigeration devices and heat pump devices.

As described above, the refrigerant flow rate control device of the present invention maintains the refrigeration cycle in an optimal state by controlling the refrigerant flow rate using an expansion valve whose valve opening degree can be adjusted by an electric signal. It compensates for the response characteristics of the signals output from the two temperature sensors that detect the temperature of the refrigerant, speeding up the control operation and achieving early stabilization, and particularly contributing to the improvement of so-called SEER. This is something to be expected.

Further, the device configuration, particularly the response compensation circuit configuration, can be realized with an extremely simple configuration, and other effects can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an implementation of a refrigerant flow rate control device in an embodiment of the present invention, FIG. 2 is an explanatory diagram of the operation in FIG. 1, and FIGS. 3 and 4 are block diagrams of a control system. FIG. 5 is a circuit configuration diagram showing an embodiment of the response compensation circuit in the refrigerant flow rate control device of the present invention, FIG. 6 is an explanatory diagram of the operation of FIG. 5,
FIG. 7 is a circuit diagram of another embodiment of the response compensation circuit. 1... Compressor, 4... Expansion valve, 5...
... Evaporator, 7, 8... First and second temperature sensors, 9, 10... First and second response compensation circuits, 11... Control circuit.

Claims (1)

[Claims] 1. An expansion valve whose opening degree can be adjusted by an electric signal;
a first temperature sensor provided at the inlet to the intermediate portion of the evaporator; a second temperature sensor provided at the outlet of the evaporator to the suction portion of the compressor; and a detection output from the first temperature sensor. a first response compensation circuit that compensates for response characteristics of the signal;
a second response compensation circuit that compensates for a response characteristic of a detection signal output by the second temperature sensor; 1. A refrigerant flow rate control device comprising: a control circuit that issues an electric signal to an expansion valve; 2. The first and second response compensation circuits are configured such that the lead compensation operation of the second response compensation circuit is selected to be larger than the lead compensation operation of the first response compensation circuit. Refrigerant flow control device. 3. The refrigerant flow rate control device according to claim 1, wherein the first and second response compensation circuits are constituted by proportional differential circuits mainly consisting of an operational amplifier, a resistor, and a capacitor.