JPS6058383B2 - Refrigerant flow control device - Google Patents

Description

Detailed Description of the Invention The present invention aims to maintain a highly 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 under conditions but also under transient conditions and wide-ranging 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 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 brought into contact with the refrigerant piping to detect the temperature of the refrigerant in that part for reasons such as maintenance and reliability. The output detection signal 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. Moreover, this time lag situation is caused by the time lag of 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 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, heat transfer to the refrigerant pipe is relatively fast, and the response speed detected by the temperature sensor is also relatively fast. However, in the latter case, the state of the refrigerant in the refrigerant piping is in the gas single-phase region during normal operation, and the heat transfer to the refrigerant piping is extremely slow.As a result, the response speed detected by the temperature sensor is extremely slow. It is becoming slower. 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 is
Approximately, the first-order delay has a time lag of about 3', 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 having 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.

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 for the control system to stabilize, and there was also a high probability that the control system would fall into an oscillation or vibration state. Therefore, the present invention achieves early stabilization of the refrigeration cycle by improving the responsiveness of the temperature sensor described above.
The objective is to expand the optimal control state and achieve improvements in the efficiency of refrigeration and air conditioning equipment, that is, the EER and SEER. In particular, the present invention compensates for the response characteristics of a temperature sensor provided at the outlet of the evaporator (or at the suction of the compressor).

The response is the same as or higher than that of the temperature sensor installed at the inlet (or middle) of the evaporator, and the temperature difference is determined from the results, and the control circuit is operated so that this temperature difference becomes a predetermined value. It attempts to control the refrigerant flow rate by adjusting the electrical signal to the expansion valve. 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 evaporation. This is a blower for the container 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 of the compressor 1, respectively; 9 is a temperature sensor 8;
10 is a response compensation circuit for compensating the responsiveness of the temperature signal detected by . A control circuit detects the difference between the temperature signals from the expansion valve 9 and the temperature sensor 7, and issues an electric signal to the expansion valve 4 to maintain the difference at a predetermined value.

The expansion valve 4, temperature sensors 7, 8, response compensation circuit 9, and control circuit 10 constitute a refrigerant flow rate control device.
In the above configuration, in this refrigerant cycle, due to the compression action of the refrigerant in the compressor 1, the refrigerant flows through the path of the condenser 2, the expansion valve 4, the evaporator 5, and the suction part of the compressor 1, and the evaporator 5 cools the refrigerant. Output ability. In this operation of the refrigerant cycle, when the refrigerant evaporated in the evaporator 5 becomes almost dry saturated vapor at its outlet, the most appropriate operating state is achieved. At this time, the temperatures of the refrigerant inside the evaporator 5 (in the middle) and at the outlet are 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, 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 gas-liquid multiphase region of It is preferable to always control the temperature at a predetermined value (for example, several degrees Celsius) to improve the efficiency of the refrigeration cycle and ensure stability. 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, the temperature sensors 7 and 8 often use temperature-sensitive resistance elements (thermistors), but this element itself has a response delay, and the refrigerant piping also has a response delay in the surface temperature relative to the internal refrigerant temperature. The detection signals output by the temperature 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, t indicates time, and θ. ,θEP,E
ES is the temperature of the refrigerant at the mounting part of the temperature sensor 7, the surface temperature of the refrigerant piping, and the temperature detected by the temperature sensor 7, respectively, and 0f3, 0SP, and θSs are the temperature of the refrigerant at the mounting part of the temperature sensor 8, and the refrigerant, respectively. There are the surface temperature of the pipe and the temperature detected by the temperature sensor 8. This Figure 2 shows the response characteristics of these temperature signals, θEP,
O,, is slightly delayed from θE,O,, and θE,,θ
, , are delayed with respect to θ5P, θ, p.

As a result, the temperature signals θE, , O detected by the temperature sensors 7 and 8 are delayed with respect to the refrigerant temperature θE, OP as shown in the figure. Also, θ$S 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 ratio of liquid is sufficiently large), whereas the refrigerant at the mounting part of the temperature sensor 8 The refrigerant in this section is a gas single-phase region, and differences occur depending on the heat transfer rate of the refrigerant piping, etc.
As described above, since the response of temperature sensors 7 and 8, especially temperature sensor 8, is slow, even if you attempt to control the expansion valve 4 by determining the temperature difference (degree of superheat) from these detection signals, the control characteristics may not be good. In many cases, this is not the case, and it is also disadvantageous in terms of early stabilization.

Therefore, the response compensation circuit 9 compensates the temperature signal θ, which is particularly poor in response, from the temperature sensor 8, so that the response characteristic is approximately the same as the true temperature θ, of the refrigerant.
Note that the detection signal output by the temperature sensor 7 is the same as that of the temperature sensor 8.
The response characteristic is better than that of θ, and under normal control conditions, θ is as high as shown in FIG. Since the variation range of 0s is usually not large and is sufficiently smaller than the variation range of 0s, compensation for the response to the detection signal of the temperature sensor 7 is omitted here. Due to the action of the response compensation circuit 9, the temperature signal input to the control circuit 11 becomes approximately equal to the temperature of the refrigerant, and the electric signal to the expansion valve 4 can be adjusted according to that value, and the degree of superheat can be quickly and stably adjusted. It becomes easier to control.

Now, FIG. 3 shows a block diagram related to the control of the degree of superheat, where SHd is the set value of the degree of superheat, SHO is the degree of superheat output, SHi is the degree of superheat based on the detection signals of temperature sensors 7 and 8, and GA (S) is the proportionality in the control circuit 10;
Transfer functions such as differential and integral operations, Gv(S) are the transfer functions of the expansion valve 4, and GEl(S) and Gs(S) are the output of the expansion valve 4 and the temperature θ, respectively.

, 0, and the transfer function, GEp(S), G,p(S)
are the transfer functions of the refrigerant piping, GO, (S), and Gss, respectively.
(S) are the transfer functions of temperature sensors 7 and 8, G and O, respectively.
(S) is a transfer function of the response compensation circuit 9. Here, if the response compensation circuit 9 makes its output signal equal to θs, then G,p(S) ・Gss(S) ・G,.

(S)=1 Also, the temperature signal 00 output by the temperature sensor 7
, is approximated as θES″−θs for the reasons mentioned above.
Since GE, (S)・GO, (S)...1, the transfer function G(S) of SHO to SHd is G(s):GAS-
GVSCG3S-GOS〕 1+GA(S)・G
v(S) [G, (S) - G8(S)], and the fourth
It can be shown in a block diagram as shown in the figure.

In other words, if the response compensation circuit 9 can be appropriately configured or approximated so as to detect a value almost equivalent to the superheat degree SHO, which is the control target of this control system, the control system regarding the superheat degree will be as shown in the figure. Can be expressed in a simple form.

Therefore, Gv(S) and [G,(S)-GO(S)]
or Gv(S) [Gs(S)-GO
(S)], it is possible to relatively easily obtain the transfer function GA(S) by proportional, differential, and integral operations in the control circuit 10 to obtain stability of the control system.
It has a great effect on the analysis, design, and improvement of characteristics of control systems.

Next, one embodiment of the response compensation circuit 9 is shown in FIG. Fifth
In the figure, 11 is a DC power supply, which supplies power supply voltage Vcc to the following circuits. 8 is a temperature sensor, in which a negative characteristic temperature-sensitive resistance element is used.

12 is a resistor, and 13 is a capacitor for noise absorption.

The above constitutes the temperature detection section. Here, the output signal voltage Vτ is determined by the temperature sensor 8 depending on the selection of the resistor 12.
An almost linear relationship is obtained with the temperature θSs detected by .
9 is a response compensation circuit, 14 is an operational amplifier, R1 and C1
are the resistance and capacitor for response compensation. 15 and 16 are small-capacity capacitors and low-resistance resistors for noise control.

This response compensation circuit 9 is a so-called proportional differentiator, with a time constant T1=R1・C1 and a transfer function G1(S)=1+Tl.
It has the property of Sl. Here, when the signal voltage ■τ has a first-order delay/response characteristic with a time constant τ, if R1 and C1 are selected such that T1=τ, the output voltage VO
As shown in FIG. 6, regardless of the first-order lag response of the signal voltage ■T, a step-like output is obtained.

In other words, from this, when the temperature signal θSs output by the temperature sensor 8 is a first-order lag response with respect to the refrigerant temperature 0, its transfer function is Gsp(S)・G9(S)=±, so the output voltage VO has the same change characteristic of 1+τS as the temperature θ3.

Furthermore, FIG. 7 shows another embodiment of the response compensation circuit, in which the response compensation circuit 9 provides response compensation characteristics using resistors, R2, and capacitors Cl, C2 to compensate for quadratic lag response characteristics.
Configure ″.

When Gsp(S)/Gss(S) is a second-order lag response or a higher-order lag response, this circuit generates an output voltage ■0 that has almost the same change characteristics as the temperature 03 as shown in Figure 5 above. It is something that can be output. The present invention has been described above based on embodiments, and a case has been described in which the response compensation circuit 9 is configured to emit an output signal having the same characteristics when the temperature of the refrigerant is 011:, θ.
In relation to the transfer function GA(S), it is also possible to have a tendency toward overcompensation or undercompensation. For example, the delay in detecting temperature θε is compensated for to the same extent as GA(S
) can also be determined. 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 inevitably occurs, including the response of the refrigerant piping, if the compensation operation is made to be slightly overcompensated, it is usually possible to generate a substantially good output signal. Also, the temperature sensor 7,
8 may be other than a temperature sensitive resistance element. Although the embodiment shown in FIG. 1 is used in a cooling device, it 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 based on the present invention optimizes the refrigeration cycle by controlling the refrigerant flow rate using an expansion valve whose valve opening degree can be adjusted by an electric signal, and particularly improves response. By compensating for the temperature signal from the temperature sensor provided at the evaporator outlet or the compressor suction, which has slow characteristics, it is possible to speed up the control operation and achieve early stabilization.

This can be expected to contribute to an improvement in so-called SEER, and the effect is significant.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram showing an implementation of the refrigerant flow rate control device based on the present invention, FIG. 2 is an explanatory diagram of the operation in FIG. 1, FIGS. 3 and 4 are block diagrams of the control system, and FIG. 6 is a circuit configuration diagram of a 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, and 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... Response compensation circuit, 10...
...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 of the evaporator or an intermediate portion; a second temperature sensor provided at the outlet of the evaporator or the suction portion of the compressor; and a detection output from the second temperature sensor. A response compensation circuit that compensates for the response characteristics of the signal, and a temperature difference signal obtained from the difference between the detection signal outputted by the first temperature sensor and the output signal of the response compensation circuit, and the value thereof is maintained at a predetermined value. A refrigerant flow rate control device comprising: a control circuit that issues an electric signal to the expansion valve; 2. The refrigerant flow rate control device according to claim 1, wherein the response compensation circuit is constituted by a proportional differential circuit mainly composed of an operational amplifier, a resistor, and a capacitor.