JP2009299970A - Refrigerating cycle device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress liquid back while suppressing a rise of discharged refrigerant temperature of a compressor. <P>SOLUTION: This refrigerating cycle device includes the compressor 1 for sucking and compressing a refrigerant, a radiator 2 radiating heat of a high-pressure refrigerant, an expansion valve 5 of which a valve opening is electrically adjusted and which decompresses and expands the refrigerant cooled by the radiator 2, an evaporator 6 absorbing heat by evaporating the refrigerant decompressed by the expansion valve 5, an internal heat exchanger 7 exchanging heat between the high-pressure refrigerant before decompressed by the expansion valve 5 and the low-pressure refrigerant sucked to the compressor 1, and a control means 10 for controlling the valve opening of the expansion valve 5, the control means 10 controls the valve opening with the first control characteristic to suppress a superheating degree of an outlet-side refrigerant of the evaporator 6 to be a prescribed quantity or less, when the outlet refrigerant temperature of the evaporator 6 is a first prescribed temperature or higher, and controls the valve opening with the second control characteristic to increase the superheating degree in comparison with that in the first control characteristic when the outlet refrigerant temperature is less than the first prescribed temperature. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a refrigeration cycle apparatus including an expansion valve and an internal heat exchanger.

  Conventionally, this type of refrigeration cycle apparatus is described in Patent Document 1. In this prior art, heat is exchanged between the high-pressure refrigerant before being decompressed by the expansion valve and the low-pressure refrigerant sucked into the compressor by an internal heat exchanger (double pipe).

  As a result, the high-pressure refrigerant before being depressurized by the expansion valve is cooled, and the enthalpy of the refrigerant at the inlet side of the evaporator is reduced. The capacity can be increased, and as a result, the cooling performance can be improved.

In this prior art, R134a is used as the refrigerant, and a temperature type expansion valve that adjusts the valve opening based on the refrigerant temperature and refrigerant pressure on the evaporator outlet side is used as the expansion valve. Then, as shown in FIG. 5 (a), the evaporator outlet refrigerant has almost no superheat by bringing the control characteristic line (solid line) of the expansion valve as close as possible to the saturation line (broken line) of the refrigerant. . As a result, the rise in the discharge refrigerant temperature of the compressor is suppressed, so that various resin parts on the discharge side of the compressor and the seal material in the compressor can be prevented from deteriorating at a high temperature. Can be protected.
JP 2007-71461 A

  By the way, in the above prior art, the control characteristic line of the expansion valve is made as close as possible to the saturation line of the refrigerant so that the evaporator outlet refrigerant has almost no superheat. Phenomenon (liquid back) that liquid phase refrigerant flows out of the vessel is likely to occur. As a result, there is a problem that a phenomenon (hunting) in which the evaporator outlet refrigerant pressure fluctuates easily occurs.

  This will be described in detail. First, when the liquid back occurs, the internal pressure loss of the evaporator decreases and the evaporator outlet refrigerant pressure rises as compared with the case where the liquid back does not occur, that is, when only the gas-phase refrigerant flows out of the evaporator.

  Then, since the expansion valve restricts the valve opening so as to reduce the evaporator outlet refrigerant pressure, the refrigerant flow rate decreases. When the refrigerant flow rate decreases, all of the refrigerant evaporates in the evaporator and the evaporator outlet refrigerant has a superheat degree (superheat), so the liquid back is eliminated.

  However, when the liquid back is eliminated, the internal pressure loss of the evaporator increases and the evaporator outlet refrigerant pressure decreases, so the expansion valve increases the valve opening so as to increase the evaporator outlet refrigerant pressure. Then, since the refrigerant flow rate increases, liquid back occurs again. In this way, hunting occurs when the liquid bag and the superheat are alternately repeated.

  If the refrigerant side load Qre is larger than the air side load Qae (Qae <Qre), the liquid back state is maintained, so that hunting does not occur. However, if the liquid back state is maintained, the compressor sucks the liquid-phase refrigerant, which causes a problem that the driving power of the compressor increases.

  Further, when the liquid back state is maintained, as shown in the ph diagram of FIG. 5B, the evaporator outlet side is reduced by the amount of enthalpy of the refrigerant at the inlet side of the evaporator in the internal heat exchanger. Since the refrigerant has a dryness and the enthalpy of the evaporator outlet side refrigerant becomes small, there is a problem that the effect of increasing the refrigerating capacity (the effect of improving the cooling performance) by the internal heat exchanger cannot be obtained.

  The present invention has been made in view of the above points, and an object of the present invention is to suppress a liquid back while protecting a high-pressure side component such as a compressor by suppressing an increase in the refrigerant temperature discharged from the compressor.

In order to achieve the above object, in the first aspect of the present invention, a compressor (1) for sucking and compressing refrigerant,
A radiator (2) for cooling the heat of the high-pressure refrigerant;
An expansion valve (5) for adjusting the valve opening electrically and decompressing and expanding the refrigerant cooled by the radiator (2);
An evaporator (6) for absorbing heat by evaporating the decompressed refrigerant on the expansion valve (5);
An internal heat exchanger (7) for exchanging heat between the high-pressure refrigerant before being depressurized by the expansion valve (5) and the low-pressure refrigerant sucked by the compressor (1);
Control means (10) for controlling the valve opening of the expansion valve (5),
When the outlet refrigerant temperature of the evaporator (6) is equal to or higher than a first predetermined temperature, the control means (10) opens the valve with a first control characteristic that suppresses the degree of superheat of the outlet side refrigerant of the evaporator (6) to a predetermined amount or less. And when the outlet refrigerant temperature is lower than a first predetermined temperature, the valve opening degree is controlled with a second control characteristic that makes the degree of superheat greater than the first control characteristic.

  According to this, when the outlet refrigerant temperature of the evaporator (6) is equal to or higher than the first predetermined temperature, the superheat degree of the outlet side refrigerant of the evaporator (6) is suppressed to a predetermined amount or less by the first control characteristic. (1) An increase in discharge refrigerant temperature can be suppressed. As a result, high pressure side components such as the compressor (1) can be protected.

  In addition, when the outlet refrigerant temperature of the evaporator (6) is lower than the first predetermined temperature, the degree of superheat of the outlet side refrigerant of the evaporator (6) is greater than the first control characteristic due to the second control characteristic. Can be suppressed.

In the invention according to claim 2, in the refrigeration cycle apparatus according to claim 1, the first control characteristic is indicated by a characteristic line parallel to the saturation line of the refrigerant,
The second control characteristic is indicated by a characteristic line farther from the refrigerant saturation line than the first control characteristic.
The characteristic line indicating the second control characteristic is bent with respect to the characteristic line indicating the first control characteristic.

  Thereby, a liquid back | bag can be suppressed effectively, suppressing the raise of the discharge refrigerant | coolant temperature of a compressor (1) effectively.

  The “characteristic line parallel to the refrigerant saturation line” in the present invention does not mean only a characteristic line strictly parallel to the refrigerant saturation line, but also a characteristic line substantially parallel to the refrigerant saturation line. It is meant to include.

  In addition, the code | symbol in the bracket | parenthesis of each means described in this column and the claim shows the correspondence with the specific means as described in embodiment mentioned later.

  In this embodiment, the refrigeration cycle apparatus of the present invention is applied to a vehicle air conditioner. FIG. 1 is an overall configuration diagram of the vehicle air conditioner, and FIG. 2 is a ph diagram of the refrigeration cycle apparatus. It is.

  The compressor 1 that sucks and compresses refrigerant (R134a in this example) is driven to rotate by a vehicle travel engine (not shown) via an electromagnetic clutch, a belt, and the like (not shown). In this example, a variable capacity compressor capable of adjusting the refrigerant discharge capacity by changing the discharge capacity is used as the compressor 1.

  As the compressor 1, a fixed capacity type compressor that adjusts the refrigerant discharge capacity by changing the operating rate of the compressor operation by switching the electromagnetic clutch, or an electric compressor that adjusts the refrigerant discharge capacity by adjusting the rotation speed of the electric motor. May be used.

  The radiator 2 is a high-pressure side heat exchanger that cools the high-pressure refrigerant by exchanging heat between the high-pressure refrigerant discharged from the compressor 1 and the outdoor air blown from the electric blower 2a. In this example, since the pressure of the high-pressure refrigerant is less than the critical pressure of the refrigerant, the refrigerant in the radiator 2 lowers its enthalpy while changing phase from a gas-phase refrigerant to a liquid-phase refrigerant.

  The receiver 3 is a gas-liquid separator that separates the refrigerant flowing out of the radiator 2 into a gas-phase refrigerant and a liquid-phase refrigerant and stores the excess refrigerant as a liquid-phase refrigerant. The subcooler 4 is a liquid supplied from the receiver 3. It is a subcooler which further cools the phase refrigerant and increases the degree of supercooling of the refrigerant.

  The expansion valve 5 serving as a decompression unit for decompressing the high-pressure refrigerant is an electric expansion valve whose valve opening degree is electrically adjusted. In this example, as the expansion valve 5, a solenoid-type electric expansion valve is used that displaces the position of the valve body that adjusts the opening of the throttle passage by the electromagnetic suction force generated by the electromagnetic coil. As the expansion valve 5, an actuator type electric expansion valve that displaces the position of the valve body by an electric actuator composed of a stepping motor may be used.

  The evaporator 6 is a low-pressure side heat exchanger that evaporates the liquid-phase refrigerant decompressed by the expansion valve 5. In the evaporator 6, the liquid refrigerant decompressed by the expansion valve 5 absorbs heat from the blown air (indoor air, outdoor air) blown from the electric blower 6a and evaporates.

  The internal heat exchanger 7 exchanges heat between the high-pressure refrigerant before being decompressed by the expansion valve 5 and the low-pressure refrigerant sucked by the compressor 1, and flows into the expansion valve 5 by the internal heat exchanger 7. As the refrigerant is cooled, the enthalpy of the refrigerant flowing into the evaporator 6 decreases, and conversely, the refrigerant flowing out of the evaporator 6 and sucked into the compressor 1 is heated to increase the degree of superheat.

  In this example, the internal heat exchanger 7 has a double tube structure including an inner tube through which high-pressure refrigerant flows and an outer tube through which low-pressure refrigerant flows.

  Next, an outline of the electric control unit in the present embodiment will be described. The valve opening degree of the expansion valve 5 is controlled by a control device (control means) 10. In this example, the control device 10 is composed of a well-known microcomputer including a CPU, a ROM, a RAM and the like and its peripheral circuits, and performs various calculations and processes based on a control program stored in the ROM. The operation of electric devices such as the compressor 1, the electric motors of the electric blowers 2a and 6a, and the expansion valve 5 is controlled.

  On the input side of the control device 10, a blown air temperature sensor 11 for detecting the blown air temperature Te of the evaporator 6, a refrigerant temperature sensor 12 for detecting the outlet refrigerant temperature of the evaporator 6, and an outlet refrigerant pressure of the evaporator 6 are detected. A refrigerant pressure sensor 13 or the like is connected.

  The control device 10 also receives detection signals from a group of sensors including a known outside air temperature sensor, inside air temperature sensor, solar radiation sensor, and the like. These various sensors constitute various detection means of the present embodiment. In addition, various air conditioning operation signals are input to the control device 10 from operation members of an air conditioning operation panel (not shown) arranged near the instrument panel (instrument panel) in the vehicle interior.

  Specifically, a set temperature signal in the passenger compartment by a temperature setting switch, a compressor operation command signal by an air conditioner switch, an air volume switching signal of the electric blower 6a by an air volume switching switch, and the like are input from the air conditioning operation panel.

  Next, the operation of this embodiment in the above configuration will be described. First, the basic operation of the refrigeration cycle apparatus will be described. When an operation command signal for the compressor 1 is generated by an operation member (air conditioner switch) of the air conditioning operation panel, the compressor 1 is driven.

  The refrigerant is compressed by the compressor 1 to be in a high temperature and high pressure state. This high-temperature and high-pressure refrigerant then flows into the radiator 2 where it exchanges heat with the outside air (outdoor air) blown by the electric blower 2a and radiates heat into the outside air.

  The outlet refrigerant of the radiator 2 is separated into a gas-phase refrigerant and a liquid-phase refrigerant by a receiver (gas-liquid separator) 3 and excess refrigerant is stored as a liquid-phase refrigerant. The liquid-phase refrigerant supplied from the receiver 3 is further cooled by the supercooler 4 to increase the degree of supercooling.

  The liquid-phase refrigerant supplied from the subcooler 4 is cooled by exchanging heat with the low-pressure refrigerant sucked into the compressor 1 by the internal heat exchanger 7 and then cooled by the expansion valve 5. It becomes a liquid two-phase state. This low-temperature and low-pressure gas-liquid two-phase refrigerant then flows into the evaporator 6, where it absorbs heat from the blown air of the electric blower 6a and evaporates. Thereby, the blowing air of the electric blower 6a can be cooled by the evaporator 6, and cold air can be blown out indoors.

  The low-pressure refrigerant that has passed through the evaporator 6 is heated by exchanging heat with the high-pressure refrigerant before being depressurized by the expansion valve 5 in the internal heat exchanger 7, and is sucked into the compressor 1 after the degree of superheat increases. It is compressed again.

  Next, basic control processing executed by the control device 10 of the present embodiment will be described. This control process starts when the air conditioner switch is turned on while the start switch (not shown) of the vehicle is turned on.

  First, flags, timers, etc. are initialized, and detection signals from various sensors and operation signals from the air conditioning operation panel are read. And the control state of electric devices, such as the compressor 1, the electric motor of the electric blowers 2a and 6a, and the expansion valve 5, is determined.

  Specifically, a target blowing temperature TAO to be blown into the vehicle interior is calculated based on the target temperature of the blown air into the room, the inside air temperature, and the outside air temperature. Based on the target blowing temperature TAO and the like, the target rotational speed (applied voltage to the electric motor) of the electric blowers 2a and 6a is calculated.

  Furthermore, based on the target blowing temperature TAO, a target evaporator blowing temperature TEO that is a target value of the degree of cooling of the evaporator 6 is determined, so that the blowing air temperature Te of the evaporator 6 approaches the target evaporator blowing temperature TEO. Then, the refrigerant discharge capacity of the compressor 1 is calculated.

  Then, an output signal is output from the control device 10 to the electric devices such as the compressor 1, the electric motors of the electric blowers 2a and 6a, and the expansion valve 5 so that the determined control state is obtained.

  Next, the operation control of the expansion valve 5, which is a feature of this embodiment, will be described with reference to FIG. In FIG. 2, the solid line indicates the operating characteristics of the expansion valve 5 in the present embodiment. In FIG. 2, the broken line shows the saturation line of the refrigerant (R134a in this example). Further, in FIG. 2, a two-dot chain line indicates an operation characteristic of the expansion valve in the conventional technique (Patent Document 1).

  The control device 10 controls the expansion valve 5 based on the outlet refrigerant temperature of the evaporator 6 detected by the refrigerant temperature sensor 12 and the outlet refrigerant pressure of the evaporator 6 detected by the refrigerant pressure sensor 13 with the solid lines L1 to L1 in FIG. Control is performed with the operating characteristic indicated by L3.

  As can be seen from FIG. 2, a region where the outlet refrigerant temperature of the evaporator 6 is equal to or higher than the first predetermined temperature T1 is set as a compressor protection region, and protection control of the compressor 1 is performed in this compressor protection region. A region where the outlet refrigerant temperature of the evaporator 6 is equal to or higher than the second predetermined temperature T2 and lower than the first predetermined temperature T1 is defined as a superheat region, and superheat control is performed in this superheat region.

  A region where the outlet refrigerant temperature of the evaporator 6 is lower than the second predetermined temperature T2 is defined as a cross charge region, and the expansion valve 5 is controlled by the cross charge method in this cross charge region. It is not always necessary to provide a cross charge area. That is, all the regions where the outlet refrigerant temperature of the evaporator 6 is lower than the first predetermined temperature T1 may be set as the superheat region.

  In this example, the characteristic lines L1 to L3 indicating the control characteristics of the expansion valve 5 are folded in three. That is, the characteristic line L2 indicating the control characteristic (second control characteristic) of the expansion valve 5 in the superheat area is bent with respect to the characteristic line L1 indicating the control characteristic (first control characteristic) of the expansion valve 5 in the compressor protection area. The characteristic line L3 indicating the control characteristic of the expansion valve 5 in the cross charge region is bent with respect to the characteristic line L2 indicating the control characteristic of the expansion valve 5 in the superheat region.

  In the compressor protection area, the control characteristic line L1 is substantially parallel to the R134a saturation line and as close as possible to the R134a saturation line. For this reason, the superheat degree of a refrigerant | coolant is suppressed below to predetermined amount, and the raise of the compressor 1 discharge refrigerant | coolant temperature is suppressed. As a result, the high pressure side parts such as the compressor 1 can be protected.

  In the superheat region, the inclination of the control characteristic line L2 is increased so that the control characteristic line L2 is farther from the R134a saturation line than the compressor protection region. For this reason, the superheat degree of a refrigerant | coolant becomes large and a liquid back is prevented. For this reason, hunting can be prevented and cooling performance can be improved by the subcooling by the internal heat exchanger 7.

  In the cross charge region, the slope of the control characteristic line L3 is smaller than that in the superheat region, and the control characteristic line L3 intersects the R134a saturation line. Therefore, the outlet of the evaporator 6 in the low temperature region where the refrigerant flow rate decreases. It is possible to increase the refrigerant pressure and thus prevent the oil return amount to the compressor 1 from being insufficient.

  FIG. 3A is a flowchart illustrating an example of control processing of the expansion valve 5 by the control device 10 of the present embodiment. Steps S100 and S110 are for controlling the expansion valve 5 to the initial opening. First, in step S100, the blown air temperature Te of the evaporator 6 detected by the blown air temperature sensor 11 and the target blown temperature described above. The difference from TeO (Te-TAO) is calculated.

  In step S110, based on the difference (Te−TAO) between the blown air temperature Te of the evaporator 6 calculated in step S100 and the target blown temperature TAO (Te−TAO), the initial opening of the expansion valve 5 is controlled to be fully opened or intermediate. .

  Specifically, when the difference (Te−TAO) between the blown air temperature Te of the evaporator 6 and the target blown temperature TAO is larger than a predetermined threshold value, it is considered that the air conditioning load is large, and the initial opening degree of the expansion valve 5 To fully open.

  On the other hand, when the difference (Te−TAO) between the blown air temperature Te of the evaporator 6 and the target blown temperature TAO is equal to or smaller than a predetermined threshold value, it is considered that the air conditioning load is small, and the initial opening degree of the expansion valve 5 is set to an intermediate value. Control the opening.

  After the expansion valve 5 is controlled to the initial opening degree in step S110, the opening degree control of the expansion valve 5 shown in step S120 is performed. Specifically, in step S120, the outlet refrigerant temperature of the evaporator 6 detected by the refrigerant temperature sensor 12 and the control characteristic lines L1 to L3 in FIG. And the opening degree of the expansion valve 6 is controlled so that the outlet refrigerant pressure of the evaporator 6 detected by the refrigerant pressure sensor 13 becomes the target pressure. And the opening degree of the expansion valve 5 is controlled like the control characteristic lines L1-L3 of FIG. 2 by performing step S120 repeatedly.

  FIG. 3B shows an example of the operation according to the flowchart of FIG. In the example of FIG. 3B, as a result of controlling the expansion valve 5 to the initial opening degree in steps S100 and S110, the compressor protection area is reached, and thereafter the opening degree control of the expansion valve 5 is performed in step S120. As a result, the state transitions to the superheat range and the cross charge range.

  Incidentally, the first and second predetermined temperatures T1 and T2 can be set as appropriate. Therefore, a setting example of the first predetermined temperature T1 will be described. FIG. 4 shows the refrigerant flow rate (or refrigerant performance) and the compressor 1 when the cooling capacity is maintained at 100% in the refrigeration cycle apparatus of the present embodiment. It is a graph which shows the relationship with discharge refrigerant temperature. Since this relationship varies depending on the outlet refrigerant temperature of the evaporator 6, FIG. 4 shows the case where the outlet refrigerant temperature of the evaporator 6 is 25 ° C., 30 ° C., 35 ° C., 40 ° C., and 45 ° C.

  The discharge refrigerant temperature Tcmax shown in FIG. 4 is an upper limit value of the discharge refrigerant temperature that does not require protection of the high-pressure side parts such as the compressor 1 and is a temperature determined by the high-pressure side parts such as the compressor 1. For example, when the discharged refrigerant temperature Tcmax is 150 ° C., it means that protection of the high-pressure side parts such as the compressor 1 is necessary when the discharged refrigerant temperature exceeds 150 ° C.

  And the exit refrigerant | coolant temperature of the evaporator 6 in the point P in FIG. 4 is set to 1st predetermined temperature T1. Thereby, the compressor protection area shown in FIG. 2 can be set.

(Other embodiments)
In the above-described embodiment, the control characteristic line L1 in the compressor protection area is substantially parallel to the R134a saturation line, but is not necessarily parallel. Moreover, in the above-mentioned embodiment, although the control characteristic line L2 in the superheat region is curved, it is not always necessary to be a curve. For example, the control characteristic line L2 may be a straight line.

  Moreover, in the above-mentioned embodiment, although the control characteristic line L2 in the superheat region is bent with respect to the control characteristic line L1 in the compressor protection region, it is not always necessary to bend, and both control characteristic lines L1 and L2 are You may make it connect with a smooth curve. Similarly, the control characteristic lines L2 and L3 may be connected by a smooth curve in the superheat region and the cross charge region.

  In the above-described embodiment, the present invention is applied to the vehicle air conditioner. However, the application of the present invention is not limited to this, and for example, the present invention can be applied to a stationary air conditioner.

  Moreover, although the above-mentioned embodiment demonstrated the example which employ | adopted R134a as a refrigerant | coolant, the kind of refrigerant | coolant is not limited to this. For example, hydrocarbon refrigerant, carbon dioxide, etc. may be employed. Furthermore, the refrigeration cycle apparatus of the present invention may be configured as a supercritical refrigeration cycle apparatus in which the high-pressure side refrigerant pressure exceeds the critical pressure of the refrigerant.

1 is an overall configuration diagram of a refrigeration cycle apparatus according to an embodiment of the present invention. It is a graph which shows the operating characteristic of the expansion valve in the refrigeration cycle apparatus of FIG. (A) is a flowchart of expansion valve control in the refrigeration cycle apparatus of FIG. 1, (b) is a ph diagram showing an example of the operation according to the flowchart of (a). It is a graph which shows the relationship between the refrigerant | coolant flow volume and discharge refrigerant | coolant temperature in the refrigeration cycle apparatus of FIG. (A) is a graph which shows the operating characteristic of the expansion valve of a prior art, (b) is a ph diagram of a prior art.

Explanation of symbols

L1 Compressor protection zone control characteristics (first control characteristics)
L2 Superheat range control characteristics (second control characteristics)

Claims (2)

A compressor (1) for sucking and compressing refrigerant;
A radiator (2) for cooling the heat of the high-pressure refrigerant;
An expansion valve (5) whose valve opening is electrically adjusted and decompresses and expands the refrigerant cooled by the radiator (2);
An evaporator (6) for absorbing heat by evaporating the decompressed refrigerant in the expansion valve (5);
An internal heat exchanger (7) for exchanging heat between the high-pressure refrigerant before being depressurized by the expansion valve (5) and the low-pressure refrigerant sucked into the compressor (1);
Control means (10) for controlling the valve opening of the expansion valve (5),
The control means (10) has a first control characteristic that suppresses the degree of superheat of the outlet side refrigerant of the evaporator (6) to a predetermined amount or less when the outlet refrigerant temperature of the evaporator (6) is equal to or higher than a first predetermined temperature. The valve opening degree is controlled, and when the outlet refrigerant temperature is lower than the first predetermined temperature, the valve opening degree is controlled with a second control characteristic that makes the superheat degree larger than the first control characteristic. Refrigeration cycle equipment. The first control characteristic is indicated by a characteristic line parallel to a saturation line of the refrigerant,
The second control characteristic is indicated by a characteristic line farther from the saturation line of the refrigerant than the first control characteristic,
The refrigeration cycle apparatus according to claim 1, wherein a characteristic line indicating the second control characteristic is bent with respect to a characteristic line indicating the first control characteristic.

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