JP2004309081A - Expansion valve and its control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To sufficiently secure the circulation quantity of lubricating oil with a good coefficient of performance even at a prescribed flow rate or less. <P>SOLUTION: A solenoid valve 28 is provided in parallel with a high pressure lead-in chamber 12 into which a refrigerant is led from a receiver through a refrigerant piping connecting hole not shown in the figure, and with a refrigerant piping connecting hole 13 for supplying the throttled and expanded refrigerant to an evaporator. Normally, the solenoid valve 28 is closed to maximize the performance coefficient of a refrigerating cycle by controlling so that the refrigerant at an evaporator outlet has a prescribed degree of superheat. At the prescribed flow rate or less, the solenoid valve 28 is periodically opened for a prescribed time to allow the refrigerant to bypass a throttle passage. The flow of refrigerant is thereby increased temporarily to secure the sufficient circulation quantity of the lubricating oil, thus preventing the seizure of a variable displacement compressor. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an expansion valve and a method for controlling the expansion valve, and in particular, a high-temperature / high-pressure liquid refrigerant is throttled and expanded into a low-temperature / low-pressure refrigerant in a refrigeration cycle of an automotive air conditioner, and a state of evaporation of the refrigerant at an evaporator outlet is reduced. The present invention relates to a temperature-type expansion valve that controls a flow rate of a refrigerant supplied to an evaporator so as to have a predetermined degree of superheat, and a control method thereof.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in an automotive air conditioner, even when the engine speed fluctuates, the discharge capacity of the refrigerant continuously changes so that the flow rate of the refrigerant flowing through the refrigeration cycle can be maintained at a predetermined value corresponding to the cooling load. Variable displacement compressors that can be used are used.
[0003]
The variable displacement compressor has a swash plate provided at a variable inclination angle with respect to a rotation shaft through which the driving force of the engine is transmitted in a closed crank chamber. There is known a swash plate type in which the angle is changed, and thereby the stroke amount of a piston connected to the swash plate is changed to change the capacity of the discharged refrigerant. The pressure in the crankcase is controlled by a displacement control valve. The displacement control valve controls the pressure introduced from the discharge chamber to the crank chamber in response to the suction pressure of the variable displacement compressor. For example, when the cooling load decreases and the suction pressure drops below the set pressure, the capacity control valve senses the drop in the suction pressure and increases the opening, thereby increasing the pressure introduced from the discharge chamber into the crank chamber. Is controlled to increase. As the pressure difference between the pressure in the crank chamber and the suction pressure increases, the inclination angle of the swash plate decreases, the piston stroke decreases, and the capacity of the variable displacement compressor decreases. As a result, the suction pressure is controlled to the set pressure, and the outlet temperature of the evaporator can be kept constant.
[0004]
In a refrigeration cycle using a variable displacement compressor in which the suction pressure is controlled to be constant, a cross-charge type temperature expansion valve is used as an expansion valve. As shown by the characteristic A in FIG. 2 showing the characteristics of the temperature-type expansion valve, the cross-charge is based on the temperature-pressure characteristics in the temperature-sensitive cylinder of the expansion valve, and the saturated vapor pressure The slope is made gentler than the curve. When this cross charge is used, when the refrigerant temperature at the evaporator outlet is low and the load is low, the pressure in the temperature-sensitive cylinder becomes higher than the saturated vapor pressure curve of the refrigerant, so that the expansion valve is left open and the pressure at the evaporator outlet is reduced. Stop responding. Therefore, the control of the expansion valve does not compete with the control of the variable displacement compressor which controls the suction pressure almost equal to the pressure at the evaporator outlet in the variable displacement range of the variable displacement compressor, and the control is stable without hunting. Becomes possible.
[0005]
Further, when the load is low, the expansion valve is left open, so that the refrigerant at the outlet of the evaporator is returned to the variable displacement compressor while containing the liquid that has not completely evaporated. On the other hand, at the time of high load operation, since the flow rate of the refrigerant is large, the circulation amount of the lubricating oil of the variable displacement compressor included in the refrigerant is also large. When the variable capacity compressor is operating at a small capacity at low load, the refrigerant containing liquid is returned to the variable capacity compressor, so that sufficient oil circulation is ensured even if the refrigerant flow rate is small, and the variable capacity compressor due to lack of oil. Is prevented from burning.
[0006]
In addition to the variable displacement compressor of the constant suction pressure control, a flow control variable displacement compressor for controlling the discharge flow rate of the refrigerant at a constant level is also known. Even in a refrigeration cycle using a variable displacement compressor with such a flow rate control, a cross-charge type temperature expansion valve is used from the viewpoints of stable control and ensuring oil circulation at a low load. However, the use of a cross-charge type temperature expansion valve as the expansion valve requires variable evaporation of the liquid contained in the refrigerant instead of the evaporator because the liquid returns from the evaporator to the variable capacity compressor during low load operation. As a result, the displacement coefficient is reduced, and the performance coefficient of the refrigeration cycle is deteriorated.
[0007]
On the other hand, there is also known a refrigeration cycle using a variable displacement compressor for flow control and a temperature-type expansion valve of a normal charge type as shown by a characteristic B in FIG. 2 (for example, see Patent Document 1). . Since the normal charge has the refrigerant temperature at the evaporator outlet always higher than the saturated vapor pressure curve of the refrigerant used in the refrigeration cycle, that is, the degree of superheat SH, the coefficient of performance can be improved. As for the point that the lubricating oil circulation amount is reduced by using the normal charge type thermal expansion valve, make sure that the variable displacement compressor for flow control does not fall below the minimum flow rate to secure the required oil return amount. By controlling the flow rate of the refrigerant, seizure of the variable capacity compressor due to insufficient oil is avoided.
[0008]
[Patent Document 1]
JP 2001-133053 A (paragraph numbers [0015] to [0017], FIG. 2)
[0009]
[Problems to be solved by the invention]
However, in order to keep the coefficient of performance of the refrigeration cycle at a maximum, the conventional thermal expansion valve employs a normal charge method and controls the refrigerant at the evaporator outlet so that the refrigerant always has a predetermined degree of superheater than the evaporation temperature and has a predetermined flow rate. In order to ensure the amount of lubricating oil circulated below, it is necessary to control the refrigerant flow rate so that the lubricating oil does not fall below the minimum flow rate. Thus, there was a problem that the coefficient of performance of the refrigeration cycle could not be maximized.
[0010]
The present invention has been made in view of such a point, and an object of the present invention is to provide an expansion valve which has a good coefficient of performance even at a predetermined flow rate or less and can sufficiently secure a circulation amount of lubricating oil, and a control method thereof. And
[0011]
[Means for Solving the Problems]
In the present invention, in order to solve the above problem, in an expansion valve for restricting and expanding a refrigerant circulating in a refrigeration cycle while ensuring circulation of lubricating oil to a variable capacity compressor, an oil circulation is performed in parallel with a valve for restricting and expanding the refrigerant. An expansion valve is provided, which is provided with a bypass passage for securing and a solenoid valve for opening and closing the bypass passage.
[0012]
According to such an expansion valve, usually, the solenoid valve is closed, and the refrigerant at the evaporator outlet is controlled so as to have a predetermined degree of superheat, thereby maximizing the coefficient of performance of the refrigeration cycle. By periodically opening the solenoid valve for a predetermined period of time to bypass the throttle passage, the flow rate of the refrigerant can be temporarily increased and a sufficient circulation amount of the lubricating oil can be secured.
[0013]
According to the present invention, in the control method of the expansion valve for restricting and expanding the refrigerant circulating in the refrigeration cycle, when the refrigerant flow rate is large, the refrigerant at the evaporator outlet is controlled so as to have a predetermined degree of superheat, and the refrigerant is At a predetermined flow rate or less, the refrigerant at the evaporator outlet is controlled so as to have a predetermined degree of superheat, and a solenoid valve for bypass provided in parallel with a valve for restricting and expanding the refrigerant is periodically forcibly opened for a predetermined time. And controlling the expansion valve.
[0014]
According to the control method of the expansion valve, when the flow rate of the refrigerant is controlled to be equal to or less than the predetermined flow rate, the circulation amount of the lubricating oil of the variable capacity compressor dissolved in the refrigerant also decreases, but periodically. By opening the solenoid valve for a predetermined period of time, the circulation amount of the refrigerant is temporarily increased, whereby the seizure of the variable displacement compressor can be prevented.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a longitudinal sectional view showing a configuration example of an expansion valve according to the present invention, and FIG. 2 is a view showing characteristics of a thermal expansion valve. In FIG. 1, in order to simultaneously show a state in which the solenoid valve is open and a state in which the solenoid valve is closed, the upper part of the valve body and the movable part of the solenoid are closed when power is not supplied. The valve state is shown, and the lower side shows the valve open state when energized. Further, in FIG. 1, in order to simultaneously show the configuration of the same refrigerant passage in different cross-sections, a cross-section viewed in a plane passing through the axis of the refrigerant passage is shown on the left side from the center of the figure, and the right-hand side of the refrigerant passage is 2 shows a cross section viewed from a plane perpendicular to the vertical axis.
[0016]
The expansion valve according to the present invention is provided with a refrigerant pipe connection hole (not shown) in the body 11 in relation to a cut surface, and the refrigerant pipe connection hole is connected to a refrigerant pipe extending from the receiver and communicates with the high-pressure introduction chamber 12. ing. The body 11 also has a refrigerant pipe connection hole 13 connected to the inlet of the evaporator, a refrigerant pipe connection hole 14 connected to the outlet of the evaporator, and a refrigerant pipe connection hole 15 connected to the variable capacity compressor.
[0017]
The high-pressure introduction chamber 12 communicates with the refrigerant pipe connection hole 13 through a fluid passage, and a valve seat 16 is formed integrally with the body 11 at an open end thereof. A ball-shaped valve body 17 facing the valve seat 16 and a compression coil spring 18 for urging the valve body 17 in a direction to seat the valve body 16 on the valve seat 16 are arranged in the high-pressure introduction chamber 12. The coil spring 18 is received by an adjusting screw 19. The adjusting screw 19 is screwed to the lower end of the body 11, and has a function of adjusting the screwing amount and changing the load of the compression coil spring 18 to adjust a set value at which the valve element 17 starts to open. I have.
[0018]
This expansion valve is further provided with a power element at the upper end of the body 11. The power element includes an upper housing 20, a lower housing 21, a diaphragm 22 arranged to partition a space surrounded by the upper housing 20, a lower housing 21, and a disk 23 arranged on a lower surface of the diaphragm 22. The same refrigerant as the refrigerant of the refrigeration cycle is filled in a gas-liquid mixed state in a temperature sensing chamber surrounded by the upper housing 20 and the diaphragm 22 of the power element, and a normal charge system shown by a characteristic B in FIG. 2 is employed.
[0019]
Below the disk 23, a shaft 24 for transmitting the displacement of the diaphragm 22 to the valve body 17 is arranged. The upper portion of the shaft 24 is held by a holder 25 arranged across a fluid passage communicating with the refrigerant pipe connection holes 14 and 15. A compression coil spring 26 that applies a lateral load to the upper end of the shaft 24 is disposed in the holder 25 so as to suppress the longitudinal vibration of the shaft 24 due to the pressure fluctuation of the refrigerant.
[0020]
Further, the body 11 is provided with a bypass passage 27 that bypasses a fluid passage that connects the high-pressure introduction chamber 12 and the refrigerant pipe connection hole 13, and a solenoid valve 28 that opens and closes the bypass passage 27. The bypass passage 27 is large enough to flow a flow rate that is sufficiently larger than the minimum flow rate required for securing the oil return amount necessary for the variable displacement compressor when the expansion valve is almost closed by the throttle control. The expansion valve is set to a size capable of flowing a refrigerant flow rate of 50% or less of the maximum flow rate width in which the expansion control can be performed, and preferably, the maximum flow rate that the expansion valve can flow is 25%. % Refrigerant flow is set to be bypassable.
[0021]
The solenoid valve 28 has a core 29 fixed to the body 11, a plunger 30 arranged to be able to freely contact and separate from the core 29, and a solenoid valve 28 arranged so as to penetrate the core 29, one end of which is fixed to the plunger 30. A valve body 31 having an end tapered so as to open and close the bypass passage 27, a compression coil spring 32 for urging the valve body 31 in a direction to open the bypass passage 27, and a peripheral member provided around the core 29 and the plunger 30. Electromagnetic coil 33 provided.
[0022]
Next, the operation of the expansion valve having the above configuration will be described.
First, when the automotive air conditioner is stopped, the solenoid valve 28 is in a non-energized state. At this time, the plunger 30 is urged by the compression coil spring 32 in a direction away from the core 29, and the bypass passage 27 is open. By configuring the solenoid valve 28 to be normally open, the bypass passage 27 is opened when a connector of a harness for supplying power to the solenoid valve 28 is disconnected or a disconnection of the harness occurs. Since the state is maintained, for example, when the expansion valve is controlled to the throttled state, even if the variable capacity compressor is continuously operated without knowing the malfunction of the solenoid valve 28, the variable capacity Can be prevented from burning.
[0023]
During operation of the automotive air conditioner, basically, the solenoid valve 28 is in an energized state. At this time, the plunger 30 is attracted to the core 29 against the urging force of the compression coil spring 32, The bypass passage 27 is in a closed state, and thus the expansion valve operates as a normal thermal expansion valve. That is, the power element senses the pressure and temperature of the refrigerant returning from the evaporator to the refrigerant pipe connection hole 14, and when the temperature of the refrigerant is high or low, the power element pushes the valve 17 in the valve opening direction, Conversely, when the temperature is low or the pressure is high, the flow rate of the refrigerant supplied to the evaporator is controlled by moving the valve element 17 in the valve closing direction. At this time, the expansion valve controls the refrigerant at the outlet of the evaporator so that the refrigerant always has a predetermined degree of superheat SH higher than the evaporation temperature. Therefore, the refrigeration cycle is controlled so that the coefficient of performance is maximized.
[0024]
In the control for maximizing the coefficient of performance, the cooling load is large, for example, when the power supply of the air conditioner for a vehicle is turned on, or when the outlet temperature of the air passing through the evaporator is sufficiently higher than the set room temperature. In this case, the expansion valve controls the refrigerant flow rate to increase. Therefore, at this time, since the circulation amount of the lubricating oil dissolved in the refrigerant is also large, a sufficient amount of the lubricating oil is supplied to the variable displacement compressor. At this time, the solenoid valve 28 is energized to close the bypass passage 27.
[0025]
However, as the cooling load decreases, the flow rate of the controlled refrigerant also decreases. If the superheat degree control operation in which the coefficient of performance is maximized at this small flow rate is continued, the lubricating oil of the variable displacement compressor runs short. In this case, the solenoid valve 28 is temporarily opened to forcibly. Increase the refrigerant flow rate. Next, an oil circulation mode in which the solenoid valve 28 is opened will be described.
[0026]
In this oil circulation mode, the flow rate of the refrigerant controlled by the expansion valve is estimated from the capacity of the variable capacity compressor, and when the capacity of the variable capacity compressor falls below a predetermined capacity, the solenoid valve 28 is temporarily opened. . Specifically, the setting value of the control valve that controls the capacity of the variable displacement compressor (here, the condition that the control valve starts controlling the capacity of the variable displacement compressor is determined by the current flowing through the control valve. When the evaporation temperature of the evaporator estimated from the above expression becomes lower than the outlet air temperature of the evaporator (or the pressure of the refrigerant of the evaporator or the temperature of the refrigerant at the entrance of the evaporator), the solenoid is adjusted according to the value. The valve 28 is opened in a time sharing manner.
[0027]
Here, the timing at which the solenoid valve 28 is turned on / off will be described, taking as an example a case where the evaporation temperature of the evaporator is set to 3 ° C. For example, if the outlet air temperature of the evaporator becomes 5 ° C., if 50 seconds have elapsed since the closing of the solenoid valve 28, the solenoid valve 28 is opened for 10 seconds, and if the outlet air temperature of the evaporator drops to 3 ° C. When 40 seconds have passed since the solenoid valve 28 was closed, the solenoid valve 28 was opened for 20 seconds. Further, when the outlet air temperature of the evaporator dropped to 2 ° C., 30 seconds passed after the solenoid valve 28 was closed. For example, the solenoid valve 28 is opened for 30 seconds, so that the lower the outlet air temperature of the evaporator, the longer the energization time of the solenoid valve 28 and the shorter the non-energization time, so that the opening and closing of the solenoid valve 28 is time-divisionally controlled. .
[0028]
Next, another control method of the oil circulation mode will be described. In this control method, the opening time and the closing time of the solenoid valve 28 are controlled based on a change in the degree of superheat SH that changes by time-sharing control of opening and closing of the solenoid valve 28.
[0029]
FIG. 3 is a diagram showing the ratio of the opening time of the solenoid valve to the change in the degree of superheat.
In the control method of the oil circulation mode, the solenoid valve 28 is forcibly opened periodically for a predetermined time, and a change in the degree of superheat SH that is changed by opening the solenoid valve is obtained. Control is performed so as to extend the open time of the solenoid valve 28. For example, one cycle, which is the sum of the opening time and the closing time of the solenoid valve 28, is 1 minute, and the opening time of the solenoid valve 28 is, for example, 6%, which is 10% of one cycle. At this time, it is assumed that the expansion valve controls the refrigerant at the evaporator outlet so that the degree of superheat SH is, for example, 7 degrees.
[0030]
Here, when the cooling load is large, the expansion valve controls the refrigerant flow rate to be large, and the superheat degree SH of the refrigerant at the evaporator outlet at that time is approximately 7 degrees. In such a state, if the solenoid valve 28 is opened for only 10% of the time and an excessive amount of refrigerant flows, the superheat degree SH becomes small. Therefore, the expansion valve reduces the flow rate and returns the superheat degree SH to 7 degrees. Control. When the flow rate of the refrigerant controlled by the expansion valve is large, the rate of change in the flow rate of the refrigerant that increases when the solenoid valve 28 is opened is small, and the rate at which the degree of superheat SH decreases is also small. In this control, when the difference in the change in the superheat degree SH, which is reduced by opening the solenoid valve 28 for a short time, is small, the refrigerant flow rate is large, and the amount of the lubricating oil of the variable displacement compressor circulates sufficiently in the refrigeration cycle. Presumed to be.
[0031]
Therefore, in the example shown in FIG. 3, when the difference in the change in the degree of superheat SH due to the opening of the solenoid valve 28 is in the range of 0 to 2 degrees, the refrigerant flow rate is large, and the variable displacement compressor has a shortage of lubricating oil. It is estimated that this is a safety region where there is no risk of seizure. In this safety region, the ratio of the open time is set to 10%, that is, the solenoid valve is opened by 10% of one cycle only to know the change in the superheat degree SH. 28 is controlled to open and close.
[0032]
From the above state, as the cooling load decreases, the flow rate of the refrigerant flowing through the expansion valve decreases. In the opening / closing control of the solenoid valve 28 that is periodically performed in order to know the change in the superheat degree SH, the opening time and the valve opening degree are the same, so that the cooling load is reduced, and the refrigerant flowing through the expansion valve is reduced. As the flow rate decreases, the rate of increase in the flow rate of the refrigerant flowing through the solenoid valve 28 during the open time relatively increases. In other words, while the expansion valve is controlling the small flow rate so as to output the predetermined degree of superheat SH, a relatively large flow rate of the refrigerant flows during the opening time of the solenoid valve 28. As a result, the flow rate of the refrigerant that can be evaporated by the evaporator decreases, and the degree of superheat SH decreases. The expansion valve is controlled so as to reduce the flow rate of the refrigerant in order to maintain the predetermined degree of superheat SH. However, when the flow rate of the refrigerant exceeds the flow rate that can be evaporated by the evaporator, the degree of superheat SH decreases to 0 degrees.
[0033]
In this control, when the degree of decrease in the degree of superheat SH due to the opening of the solenoid valve 28 increases, the flow rate of the refrigerant circulating in the refrigeration cycle decreases, and the variable displacement compressor is in a danger region where there is a risk of seizure due to depletion of lubricating oil. Presumed to be approaching.
[0034]
Accordingly, in the example shown in FIG. 3, when the difference in the change in the degree of superheat SH caused by opening the solenoid valve 28 exceeds 2 degrees, the flow rate of the refrigerant decreases, and the variable displacement compressor approaches its dangerous area. The opening time of the solenoid valve 28, which is periodically controlled to open as the difference in the degree of superheat SH increases, is controlled so as to increase the opening time. The ratio of the open time is set to about 0.9.
[0035]
Next, how to measure the degree of superheat SH at the evaporator outlet will be described. The superheat degree SH can be calculated from the difference between the evaporation temperature calculated from the pressure at the evaporator outlet and the actual refrigerant temperature at the evaporator outlet. For this purpose, a pressure sensor for measuring pressure and a temperature sensor for detecting temperature are provided at the evaporator outlet, the evaporation temperature of the refrigerant is calculated from the pressure at the evaporator outlet measured by the pressure sensor, and the evaporation temperature and the temperature sensor are used. The superheat degree SH can be calculated from the difference from the measured refrigerant temperature at the evaporator outlet.
[0036]
By the way, the pressure sensor is very expensive compared to the thermistor constituting the temperature sensor, and thus becomes a factor for increasing the cost of the automotive air conditioner. Therefore, the refrigerant temperature Te at the evaporator outlet and the refrigerant temperature Tx at the evaporator inlet can be measured, and the difference between them can be used as a substitute value of the superheat degree SH. In this simple calculation method, since the pressure loss of the evaporator is not known, the refrigerant temperature Tx at the inlet of the evaporator does not exactly correspond to the evaporation pressure of the evaporator, and an accurate degree of superheat SH is not obtained. . However, since the refrigerant temperature Tx at the evaporator inlet substantially corresponds to the evaporating pressure of the evaporator, the difference between the refrigerant temperature Te at the evaporator outlet and the refrigerant temperature Tx at the evaporator inlet can be regarded as the degree of superheat SH. In the example shown in FIG. 3, when the change in the temperature difference (Te-Tx) between the refrigerant temperature Te at the evaporator outlet and the refrigerant temperature Tx at the evaporator inlet is in the range of 2 to 7 degrees, the open time of the solenoid valve 28 is set to 10 % To 90%.
[0037]
In the case of a method in which the ratio of the open time of the solenoid valve 28 is changed in accordance with the change in the temperature difference (Te-Tx) between the evaporator outlet and the evaporator inlet, inexpensive temperature sensors are provided at the evaporator inlet and the evaporator outlet. Can calculate the substitute value of the superheat degree SH, so that the cost of the automotive air conditioner does not need to be increased much.
[0038]
Further, the refrigerant temperature Tx at the evaporator inlet is substantially equal to the outlet temperature of the expansion valve, and the outlet temperature of the expansion valve generally does not change much. Alternatively, the refrigerant temperature Tx may be regarded as a constant, and the change in the superheat degree SH may be obtained only by the change in the refrigerant temperature Te at the evaporator outlet. In this case, the refrigerant temperature Te at the evaporator outlet is measured by a temperature sensor provided at the evaporator outlet, and the difference between the changes is regarded as a change in the superheat degree SH.
[0039]
Although the expansion valve of the present invention has been described using a mechanical temperature expansion valve as an example, the refrigerant at the evaporator outlet is controlled so as to have a predetermined degree of superheat, and the coefficient of performance of the refrigeration cycle is always maximized. The present invention is also applicable to the electronic expansion valve described above. In this case, if an electronic expansion valve that controls the differential pressure (pressure loss) between the inlet and the outlet of the evaporator so as to be a differential pressure determined by the current supplied to the solenoid is used, the pressure of the evaporator can be reduced from the current supplied to the solenoid. Since the loss can be known, an accurate degree of superheat SH can be calculated from the temperature sensors provided at the inlet and the outlet of the evaporator.
[0040]
In addition, the opening time of opening the solenoid and the length of one cycle when obtaining the superheat degree SH exemplified above are adjusted to the optimum values according to the configuration of the refrigeration cycle. However, the present invention is not limited to this.
[0041]
【The invention's effect】
As described above, in the present invention, the bypass solenoid valve is provided in parallel with the valve for restricting and expanding the refrigerant. Thereby, while controlling the expansion valve so that the coefficient of performance of the refrigeration cycle always becomes the maximum, that is, while controlling the refrigerant at the evaporator outlet to have the predetermined degree of superheat, when the refrigerant flow rate becomes equal to or less than the predetermined value, Since the solenoid valve can be periodically opened for a predetermined time to forcibly circulate the refrigerant at a predetermined flow rate, it is possible to prevent the depletion of the lubricating oil in the variable displacement compressor during efficient operation at a small flow rate. .
[0042]
Further, in the present invention, the solenoid valve for bypass is periodically opened for a short time to check the change in the degree of superheat, and as the change in the degree of superheat increases, the ratio of the open time of the solenoid valve is increased, thereby reducing the flow rate at a small flow rate. It is possible to prevent exhaustion of lubricating oil in the variable displacement compressor while operating efficiently.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing a configuration example of an expansion valve according to the present invention.
FIG. 2 is a diagram showing characteristics of a thermal expansion valve.
FIG. 3 is a diagram illustrating a ratio of an opening time of a solenoid valve to a change in a degree of superheat.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 Body 12 High-pressure introduction chambers 13, 14, 15 Refrigerant piping connection hole 16 Valve seat 17 Valve element 18 Compression coil spring 19 Adjust screw 20 Upper housing 21 Lower housing 22 Diaphragm 23 Disk 24 Shaft 25 Holder 26 Compression coil spring 27 Bypass passage 28 Solenoid valve 29 Core 30 Plunger 31 Valve 32 Compression coil spring 33 Electromagnetic coil

Claims (12)

An expansion valve that restricts and expands the refrigerant circulating in the refrigeration cycle while ensuring the circulation of lubricating oil to the variable capacity compressor,
An expansion valve, comprising: a bypass passage for ensuring oil circulation provided in parallel with the valve for restricting and expanding the refrigerant; and a solenoid valve for opening and closing the bypass passage. 2. The expansion valve according to claim 1, wherein the bypass passage has a size that allows a flow rate of the refrigerant of 50% or less of a maximum flow rate that can be controlled by a valve that restricts and expands the refrigerant. 3. The expansion valve according to claim 1, wherein the valve that throttles and expands the refrigerant is a normally-charged temperature-type expansion valve. The expansion valve according to any one of claims 1 to 3, wherein the solenoid valve opens when power is not supplied. In a control method of an expansion valve for restricting and expanding a refrigerant circulating in a refrigeration cycle,
When the refrigerant flow rate is large, the refrigerant at the evaporator outlet is controlled so as to have a predetermined degree of superheat,
When the refrigerant is equal to or less than a predetermined flow rate, a bypass solenoid valve provided in parallel with a valve for restricting and expanding the refrigerant is periodically forcibly for a predetermined time while controlling the refrigerant at the evaporator outlet to have a predetermined degree of superheat. Control to open,
A method for controlling an expansion valve. 6. The expansion valve control method according to claim 5, wherein the predetermined flow rate is a refrigerant flow rate near a position where the variable capacity compressor starts capacity control. 6. The expansion valve control method according to claim 5, wherein the flow rate of the refrigerant is estimated from a capacity of a variable capacity compressor. The solenoid valve controls the solenoid valve to be closed and open for a longer time as the outlet air temperature of the evaporator approaches the evaporation temperature of the evaporator estimated from the capacity of the variable capacity compressor. The method for controlling an expansion valve according to claim 5, wherein In a control method of an expansion valve for restricting and expanding a refrigerant circulating in a refrigeration cycle,
While the refrigerant at the evaporator outlet is controlled to have a predetermined degree of superheat, a solenoid valve for bypass provided in parallel with a valve for restricting and expanding the refrigerant is periodically forcibly opened for a predetermined time,
Control to increase the open time of the solenoid valve as the difference in the degree of superheat that changes by opening the solenoid valve increases,
A method for controlling an expansion valve. 10. The expansion valve control method according to claim 9, wherein the degree of superheat is calculated from a difference between an evaporation temperature calculated from a pressure at the evaporator outlet and an actual refrigerant temperature at the evaporator outlet. 10. The expansion valve control method according to claim 9, wherein the degree of superheat is simply calculated from a difference between a refrigerant temperature at the evaporator outlet and a refrigerant temperature at the evaporator inlet. The expansion valve control method according to claim 9, wherein the degree of superheat is simply calculated from a refrigerant temperature at the evaporator outlet.

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