JP4259891B2 - Superheat control method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a superheat degree control method, and more particularly, to a superheat degree control method in which an expansion device controls an outlet temperature of an evaporator to a predetermined superheat degree in a refrigeration cycle such as an automobile air conditioner.
[0002]
[Prior art]
For example, in an automotive air conditioner, generally, a compressor that compresses a circulating refrigerant, a condenser that condenses the compressed refrigerant, a receiver that stores the refrigerant in the refrigeration cycle and separates the condensed refrigerant into gas and liquid, A refrigeration cycle is configured by an expansion valve that squeezes and expands the liquid refrigerant thus formed and an evaporator that evaporates the refrigerant expanded by the expansion valve. As the expansion valve, a temperature type expansion valve that senses the temperature and pressure of the refrigerant at the outlet of the evaporator and controls the flow rate of the refrigerant sent to the evaporator is used. In the temperature expansion valve, the refrigerant temperature at the outlet of the evaporator must be fed back to control the refrigerant flow rate, and the evaporator should completely evaporate the refrigerant so that no liquid is contained in the refrigerant returned to the compressor. For this reason, the refrigerant at the evaporator outlet is given a predetermined degree of superheat.
[0003]
A thermal expansion valve is composed of a temperature-sensitive part that is partitioned by a diaphragm and sealed with a working gas similar to that of a refrigerant, and a valve part that squeezes and expands the refrigerant. By exposing the diaphragm to the refrigerant at the evaporator outlet, A pressure difference corresponding to the degree of superheat occurs between the saturation pressure of the working gas corresponding to the refrigerant temperature at the evaporator outlet in the section and the saturation pressure of the refrigerant at the evaporator outlet, and the balance between the pressure difference and the spring force The opening degree is determined, and the flow rate of the refrigerant sent to the evaporator is controlled.
[0004]
A solenoid-operated electronic control valve is used as an expansion valve for such a temperature type expansion valve (see, for example, Patent Document 1). Such an electronic expansion valve can freely change the opening of the valve section by changing the current supplied to the solenoid, so that fine control is possible and the superheat degree of the refrigerant at the evaporator outlet can also be controlled. It becomes possible.
[0005]
In order to control the degree of superheat using an electronic expansion valve, it is necessary to know the degree of superheat. The degree of superheat is the difference between the refrigerant temperature at the evaporator outlet and the refrigerant temperature corresponding to the evaporation pressure of the evaporator, and can be obtained by measuring the refrigerant temperature at the evaporator outlet and the evaporation pressure of the evaporator.
[0006]
However, a pressure sensor that detects pressure is very expensive compared to a temperature sensor that detects temperature, which increases the cost of an air conditioner for automobiles. Therefore, conventionally, a method has been adopted in which the evaporation pressure of the evaporator is estimated from the temperature at the evaporator inlet.
[0007]
That is, by measuring the refrigerant temperature at the evaporator inlet and referring to the saturated vapor pressure-temperature characteristics of the refrigerant used, the pressure at the evaporator inlet corresponding to the temperature can be obtained. Further, a pressure loss occurs when the refrigerant passes through the evaporator, and the pressure difference is assumed to be substantially constant here. Since the evaporation pressure of the evaporator can be calculated by subtracting the pressure difference from the previously determined pressure at the evaporator inlet, the temperature corresponding to the calculated evaporation pressure is referred to the saturated vapor pressure-temperature characteristics of the refrigerant used. Can be obtained. The degree of superheat can be obtained by subtracting the refrigerant temperature corresponding to the evaporation pressure of the evaporator thus obtained from the refrigerant temperature at the evaporator inlet measured by the temperature sensor. In this way, the degree of superheat that is the control target value is estimated from the refrigerant temperature measured at the inlet and outlet of the evaporator.
[0008]
[Patent Document 1]
JP 2001-153495 A (paragraph numbers [0010] to [0022], FIG. 1 and FIG. 2)
[0009]
[Problems to be solved by the invention]
Conventionally, however, the approximate superheat degree is estimated from the measured two refrigerant temperatures under the assumption that the differential pressure due to the pressure loss of the evaporator is constant. Therefore, the exact degree of superheat is not required. Therefore, when the flow rate of the refrigerant flowing through the evaporator changes, there is a problem that the superheat degree cannot be accurately controlled due to a difference between the calculated superheat degree and the actual superheat degree.
[0010]
This invention is made | formed in view of such a point, and it aims at providing the superheat degree control method which calculates and controls a heating degree correctly.
[0011]
[Means for Solving the Problems]
In the present invention, in order to solve the above problems, in the superheat degree control method for controlling the refrigerant state at the outlet of the evaporator to be a predetermined superheat degree by the expansion device in the refrigeration cycle, the inlet and outlet of the evaporator are connected to the expansion device. The flow rate control valve that controls the differential pressure before and after the pressure to be determined by the current supplied to the solenoid, the inlet refrigerant temperature and the outlet refrigerant temperature measured at the inlet and outlet of the evaporator, and the current value supplied to the solenoid The superheat degree is calculated from the pressure difference determined by the control value, and the current value is controlled so that the superheat degree becomes a predetermined value. The superheat degree refers to a saturated vapor pressure-temperature characteristic of the refrigerant. The inlet pressure corresponding to the measured inlet refrigerant temperature is obtained, and is lower from the inlet pressure by the differential pressure determined by the current value. Calculated force as an evaporation pressure in the evaporator, the saturated vapor pressure - with reference to the temperature characteristics calculated evaporation temperature corresponding to the evaporation pressure, was calculated by the measured the outlet refrigerant temperature subtracting the evaporation temperature, The superheat degree control method characterized by this is provided.
[0012]
According to such a superheat degree control method, the estimated differential pressure of the evaporator can be directly known from the current value supplied to the solenoid of the flow rate control valve that controls this differential pressure. Thus, the refrigeration cycle can be controlled more accurately.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a saturated vapor temperature-pressure diagram of a refrigerant for explaining a superheat control method according to the present invention.
[0014]
It is known that there is a certain relationship between the temperature and pressure of the refrigerant, and the relationship is shown in the saturated vapor temperature-pressure diagram of the refrigerant shown in FIG. In this figure, the horizontal axis represents the evaporator outlet temperature Te, and the vertical axis represents the evaporator outlet pressure Pe. A curve is a TP curve which shows the change of the pressure with respect to the temperature of a refrigerant | coolant. The change in the TP curve is determined by the type of refrigerant, and if the type and temperature of the refrigerant are known, the pressure at that time can be known.
[0015]
In the present invention, what is actually measured is the evaporator inlet temperature Tx and the outlet temperature Te as in the prior art. Since the superheat degree SH is the difference between the outlet temperature Te of the evaporator and the temperature T (Pe) corresponding to the evaporation pressure Pe of the evaporator,
[0016]
[Expression 1]
SH = Te-T (Pe) (1)
Can be expressed as Therefore, if the temperature T (Pe) corresponding to the evaporation pressure Pe can be obtained from these measured values, the superheat degree SH can be obtained.
[0017]
Since the temperature T (Pe) corresponding to the evaporation pressure Pe is a temperature corresponding to the pressure Pe lower by the difference pressure ΔP from this TP curve,
[0018]
[Expression 2]
T (Pe) = Tx−ΔT (ΔP, Tx) (2)
It is represented by That is, the temperature T (Pe) corresponding to the evaporation pressure Pe is obtained by subtracting the temperature difference ΔT (ΔP, Tx) as a function of the differential pressure ΔP and the inlet temperature Tx from the inlet temperature Tx.
[0019]
Here, the differential pressure ΔP is a differential pressure between the inlet pressure Px and the outlet pressure Pe of the evaporator, and if this can be accurately obtained, it is possible to finally obtain an accurate superheat degree SH.
[0020]
In the present invention, as the expansion valve, a differential pressure ΔP is supplied to the solenoid by using a flow rate control valve that controls the differential pressure between the inlet and outlet of the evaporator to a predetermined differential pressure determined by the current supplied to the solenoid. The current is read directly from the current value. Since this current value is a target value of the differential pressure to be controlled by the flow control valve, the differential pressure ΔP between the inlet pressure Px and the outlet pressure Pe of the evaporator can be directly and accurately known.
[0021]
Thus, since this differential pressure ΔP is a function of the current i supplied to the solenoid,
[0022]
[Equation 3]
ΔP = ΔP (i) (3)
Can be expressed by the, from equations 1 and 2 above, superheat degree SH is
[0023]
[Expression 4]
SH = Te−Tx + ΔT (ΔP (i), Tx) (4)
And can be obtained accurately.
[0024]
FIG. 2 is a diagram showing a refrigeration cycle to which the present invention is applied.
The refrigeration cycle includes a compressor 1 that compresses the circulating refrigerant, a condenser 2 that condenses the compressed refrigerant, a receiver 3 that stores the refrigerant in the refrigeration cycle and separates the condensed refrigerant into gas and liquid, and a liquid refrigerant. A flow control valve 4 for throttle expansion and an evaporator 5 for evaporating the refrigerant expanded by the flow control valve 4 and returning it to the compressor 1 are provided. The evaporator 5 is provided with a temperature sensor 6 for detecting the inlet temperature Tx of the refrigerant at the inlet and a temperature sensor 7 for detecting the outlet temperature Te of the refrigerant at the outlet. To the control device 8. The control device 8 outputs a current i that controls the flow control valve 4.
[0025]
FIG. 3 is a central longitudinal sectional view showing an example of the flow control valve.
The flow control valve 4 includes a high-pressure refrigerant inlet 12 through which a refrigerant having a pressure Po is sent from the receiver 3 to the main body block 11, a low-pressure refrigerant outlet 13 through which the refrigerant is sent to the evaporator 5 while expanding, and a refrigerant from the evaporator 5. Is provided with a return refrigerant inlet 14 and a return refrigerant outlet 15 for sending the returned refrigerant to the compressor 1. A strainer 16 is disposed at the high-pressure refrigerant inlet 12 so as to close the passage.
[0026]
A large-diameter hole is formed in the upper part of the body block 11, a cylinder concentric with the large-diameter hole is formed in the vertical direction in the figure, and the lower part communicates with the central cylinder. A hole is formed. The lower hole communicates with the return refrigerant inlet 14, the return refrigerant outlet 15 and the return passage 17, and further opens at the lower end surface of the main body block 11. The opening is closed by screwing a screw 19 into the main body block 11 via a packing and a packing presser 18.
[0027]
The upper end edge of the central cylinder constitutes a valve seat 20, and a valve body 21 is disposed on the valve seat 20 so as to face and separate from the upper side of the figure. The valve body 21 is integrally formed in a form connected to a piston 22 as a pressure-sensitive member arranged so as to be movable back and forth in the axial direction in the cylinder and a small-diameter shaft. In the cylinder, a refrigerant passage communicating with the high-pressure refrigerant inlet 12 is opened at a portion where the small-diameter shaft is located. The chamber in the upper part of the cylinder formed by a large-diameter hole formed in the upper part of the main body block 11 is also communicated with the low-pressure refrigerant outlet 13 through the refrigerant passage.
[0028]
A solenoid is disposed on the main body block 11. The solenoid includes a plunger 23 formed integrally with the valve body 21, a core 24 disposed concentrically with the plunger 23, an electromagnetic coil 25 disposed around them, and a plunger 23 and a core 24. A spring 26 disposed therebetween and a yoke 27 surrounding the electromagnetic coil 25 are provided. The core 24 has a hollow shape, and an adjustment screw 28 for adjusting the load of the spring 26 is screwed into the core 24. The adjustment screw 28 also has a hollow shape, and constitutes a bearing that supports a shaft 29 having a lower end portion fixed to the plunger 23 so as to be movable back and forth in the axial direction. The upper open end of the core 24 is hermetically closed by a ball 30 and a fixing screw 31. This solenoid is screwed into a large-diameter hole formed in the upper part of the main body block 11 by the connecting portion 32.
[0029]
Here, when the solenoid is not energized, the plunger 23 is energized in a direction away from the core 24 by the spring 26, so that the valve body 21 is seated on the valve seat 20, and the flow control valve 4 is Closed.
[0030]
When a predetermined current i is supplied to the electromagnetic coil 25 of the solenoid, the plunger 23 is attracted to the core 24 against the urging force of the spring 26, so that the valve body 21 is lifted from the valve seat 20 and the flow control valve. 4 is set to an opening determined by the balance between the solenoid force corresponding to the current i of the solenoid and the load of the spring 26. At this time, the refrigerant introduced into the high-pressure refrigerant inlet 12 is squeezed and expanded when passing through the gap between the valve body 21 and the valve seat 20, and is sent out from the low-pressure refrigerant outlet 13 to the evaporator 5.
[0031]
Since the effective diameter of the valve seat 20 and the effective diameter of the piston 22 are substantially equal, the pressure Po of the refrigerant supplied to the space between the valve body 21 and the piston 22 pushes the piston 22 in the direction in which the valve body 21 is pushed up. Since the forces acting in the directions are almost equal and cancelled, the pressure Po does not affect the movement of the valve body 21 and the piston 22.
[0032]
In addition, the valve body 21 and the piston 22 are subjected to the outlet pressure of the flow rate control valve 4, that is, the inlet pressure Px of the evaporator 5, which is the pressure on the downstream side of the valve body 21. The outlet pressure Pe of the evaporator 5 is applied via the passage 17. Therefore, the valve body 21 and the piston 22 receive a differential pressure between the inlet pressure Px and the outlet pressure Pe of the evaporator 5, and the axis line according to the change in the differential pressure from the position corresponding to the differential pressure ΔP set by the solenoid current i. Will move in the direction. For example, when the differential pressure between the inlet pressure Px and the outlet pressure Pe of the evaporator 5 increases, the outlet pressure Pe of the evaporator 5 tries to push down the piston 22, so that the valve body 21 moves in the closing direction, thereby causing the flow rate of the refrigerant. Acts to reduce the differential pressure. On the other hand, when the differential pressure is reduced, the differential pressure is increased. Therefore, this flow control valve 4 functions as a constant differential pressure valve that regards the evaporator 5 as a fixed orifice and controls the differential pressure between the inlet pressure Tx and the outlet pressure Pe of the evaporator 5 to be a predetermined differential pressure ΔP almost constant. As a result, the refrigerant sent to the evaporator 5 is controlled to a substantially constant flow rate determined by the energization current i of the solenoid. Such an expansion valve with flow control is useful in the case of differential pressure control in which the compressor 1 controls the differential pressure between the discharge pressure and the suction pressure to be substantially constant, and competes with the two controls performed in the refrigeration cycle. Can be done without.
[0033]
The flow control valve 4 has a temperature sensor 6 for detecting the refrigerant temperature at the evaporator inlet disposed at the low-pressure refrigerant outlet 13 and a temperature sensor 7 for detecting the refrigerant temperature at the evaporator outlet disposed at the return refrigerant inlet 14. May be configured integrally.
[0034]
Moreover, the superheat degree control by this invention is not limited to the refrigerating cycle of a motor vehicle air conditioner, It can apply also in the other refrigerating cycle used for household use, industrial use, etc.
[0035]
【The invention's effect】
As described above, in the present invention, the superheat degree of the refrigerant at the evaporator outlet is calculated from two inexpensive temperature sensors and the control current of the flow rate control valve that controls the differential pressure across the evaporator substantially constant. . Thereby, since there is no estimation item in the calculation of the degree of superheat, it is possible to provide a low-cost automobile air conditioner that can accurately calculate the degree of superheat and that can be accurately controlled.
[Brief description of the drawings]
FIG. 1 is a saturated vapor temperature-pressure diagram of a refrigerant for explaining a superheat control method according to the present invention.
FIG. 2 is a diagram showing a refrigeration cycle to which the present invention is applied.
FIG. 3 is a central longitudinal sectional view showing an example of a flow control valve.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Compressor 2 Capacitor 3 Receiver 4 Flow control valve 5 Evaporator 6, 7 Temperature sensor 8 Control device 11 Main body block 12 High pressure refrigerant inlet 13 Low pressure refrigerant outlet 14 Return refrigerant inlet 15 Return refrigerant outlet 16 Strainer 17 Return passage 18 Packing retainer 19 Screw 20 Valve seat 21 Valve body 22 Piston 23 Plunger 24 Core 25 Electromagnetic coil 26 Spring 27 Yoke 28 Adjust screw 29 Shaft 30 Ball 31 Fixing screw 32 Connecting portion Pe Evaporator outlet pressure (evaporation pressure)
Px evaporator inlet pressure SH Superheat

Claims (1)

In the superheat degree control method for controlling the refrigerant state at the outlet of the evaporator to be a predetermined superheat degree by the expansion device in the refrigeration cycle,
Using a flow rate control valve that controls the expansion device so that the differential pressure between the inlet and the outlet of the evaporator becomes a differential pressure determined by the current supplied to the solenoid,
Calculating the degree of superheat from the inlet refrigerant temperature and the outlet refrigerant temperature measured at the inlet and outlet of the evaporator and the pressure difference determined by the current value supplied to the solenoid;
Controlling the current value so that the degree of superheat becomes a predetermined value;
The degree of superheat is
Obtaining an inlet pressure corresponding to the inlet refrigerant temperature measured with reference to a saturated vapor pressure-temperature characteristic of the refrigerant;
The pressure lower than the inlet pressure by the differential pressure determined by the current value is determined as the evaporation pressure in the evaporator,
Determine the evaporation temperature corresponding to the evaporation pressure with reference to the saturated vapor pressure-temperature characteristics,
Calculated by subtracting the evaporation temperature from the measured outlet refrigerant temperature,
A superheat degree control method characterized by the above.

Images