JP2013224754A - Air conditioner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air conditioner capable of suppressing that the pressure of a refrigerant compressed by a compressor exceeds a pressure reference value.SOLUTION: A compressor 10 has an electric motor M1 and compresses a refrigerant. A four-way switching valve 12 switches a warming connecting state H that an inlet port and a discharge port of the compressor 10 are connected to one end 11a of an outdoor heat exchanger 11 and one end 21a of an indoor heat exchanger 21, respectively, and a cooling connecting state C that the one end 21a and the one end 11a are connected to each other. A pressure detection part detects pressure at the discharge port side of the refrigerant. The four-way switching valve control part 41 has a function for controlling the four-way switching valve 12, and when pressure while the four-way switching valve 12 is made to select the warming connecting state H is higher than the pressure reference value, makes the four-way switching valve 12 selects the cooling connecting state C.

Description

  The present invention relates to an air conditioner, and more particularly to a technique for suppressing the pressure of a refrigerant on the discharge port side of a compressor.

  The air conditioner includes an indoor unit and an outdoor unit. The indoor unit includes an indoor heat exchanger and an expansion valve, and the outdoor unit includes an outdoor heat exchanger, a compressor, and a four-way switching valve. The indoor heat exchanger, the expansion valve, the outdoor heat exchanger, the compressor, and the four-way switching valve are appropriately connected by a refrigerant pipe to constitute a refrigerant circuit.

  The four-way switching valve switches its connection state to switch the connection state between the compressor, one end of the indoor heat exchanger, and one end of the outdoor heat exchanger. The compressor compresses the refrigerant flowing from the indoor heat exchanger and supplies it to the outdoor heat exchanger depending on the connection state of the four-way switching valve, or conversely compresses the refrigerant flowing from the outdoor heat exchanger to compress the refrigerant flowing from the outdoor heat exchanger. To supply. The expansion valve is provided between the other end of the indoor heat exchanger and the other end of the outdoor heat exchanger to squeeze and expand the refrigerant.

  For example, in the heating operation, the refrigerant evaporated in the outdoor heat exchanger is supplied to the compressor via the four-way switching valve, and the refrigerant compressed by the compressor is supplied to the indoor heat exchanger via the four-way switching valve. At this time, the refrigerant condenses in the indoor heat exchanger. Along with this, heat is given to the room to warm the room. On the other hand, in the cooling operation, the refrigerant evaporated in the indoor heat exchanger is supplied to the compressor via the four-way switching valve, and the refrigerant compressed by the compressor is supplied to the outdoor heat exchanger via the four-way switching valve. At this time, in the indoor heat exchanger, the amount of heat accompanying the evaporation of the refrigerant is absorbed from the room to cool the room.

  Patent Document 1 is disclosed as a technique related to the present invention.

JP 2003-222415 A

  In the air conditioner, if the pressure of the refrigerant compressed by the compressor exceeds a predetermined pressure reference value, a malfunction may occur in the compressor.

  Then, an object of this invention is to provide the air conditioner which can suppress that the pressure of the refrigerant | coolant compressed with a compressor exceeds a pressure reference value.

  A first aspect of an air conditioner according to the present invention includes a compressor (10) having an electric motor (M1) and compressing a refrigerant, an indoor heat exchanger (21), and an outdoor heat exchanger (11). A heating connection state (H) in which the suction port (10b) and the discharge port (10a) of the compressor are connected to one end (11a) of the outdoor heat exchanger and one end (21a) of the indoor heat exchanger, respectively. A four-way switching valve (12) for switching between a cooling connection state (C) for connecting the suction port and the discharge port to the one end of the indoor heat exchanger and the one end of the outdoor heat exchanger, respectively, and the indoor heat exchanger An expansion mechanism (22) provided between the other end (21b) of the outdoor heat exchanger and the other end (11b) of the outdoor heat exchanger, a refrigerant circuit (300) through which the refrigerant circulates, and the refrigerant A pressure detection unit (51, 33) for detecting pressure on the discharge port side, and a function of controlling the four-way switching valve, wherein the heating connection state is selected by the four-way switching valve Provided said pressure is four-way switching valve control unit for selecting the cooling connection state to the four-way switching valve when greater than the pressure reference value (41) at.

  A second aspect of the air conditioner according to the present invention is the air conditioner according to the first aspect, wherein the pressure detector uses the temperature of the indoor heat exchanger (21) as the pressure of the refrigerant. A temperature detection unit (51) for detecting, the four-way switching valve control unit (41), the temperature in a state in which the four-way switching valve (12) has selected the heating connection state (H), When the temperature is larger than the temperature reference value corresponding to the pressure reference value, the cooling connection state (C) is selected by the four-way switching valve.

  A third aspect of the air conditioner according to the present invention is the air conditioner according to the first aspect, wherein the pressure detector detects a current of the electric motor (M1) as the pressure of the refrigerant. A detection unit (33), the four-way switching valve control unit (41), the current reference corresponding to the pressure reference value in the state where the four-way switching valve (12) has selected the heating connection state (H) When the current is larger than the value, the cooling connection state (C) is selected by the four-way switching valve.

  The 4th aspect of the air conditioner concerning this invention is an air conditioner concerning a 2nd aspect, Comprising: The said pressure detection part detects the electric current of the said motor (M1) as the said pressure of the said refrigerant | coolant The air conditioner further includes a detection unit (33), in which the four-way switching valve (12) adopts the cooling connection state (C), the current reference value corresponding to the pressure reference value. A compressor stop unit (35) for stopping the electric motor (M1) and stopping the compressor (10) when the current is large is further provided.

  According to the 1st aspect of the air conditioner concerning this invention, when the pressure (henceforth high pressure) by the side of the refrigerant | coolant discharge port is larger than a pressure reference value, a four-way switching valve is made to select a cooling connection state. As a result, the high pressure of the refrigerant can be reduced.

  According to the 2nd aspect of the air conditioner concerning this invention, since the temperature detection part is employ | adopted, cost can be reduced compared with the case where a pressure detection sensor is used.

  According to the 3rd aspect of the air conditioner concerning this invention, since the electric current detection part is employ | adopted, cost can be reduced compared with the case where a pressure detection sensor is used.

  According to the 4th aspect of the air conditioner concerning this invention, the detection accuracy of the pressure detected by the temperature detection part is lower than the detection accuracy of the pressure detected by the electric current. This is due to the following reason, for example. That is, the temperature detection unit detects the temperature of the indoor heat exchanger, and a deviation from the actual refrigerant saturation temperature occurs.

  On the other hand, the current reference value corresponding to the pressure reference value in the state where the cooling connection state is adopted is higher than the current reference value corresponding to the pressure reference value in the state where the heating connection state is adopted. This is because the high pressure of the refrigerant in the cooling operation is smaller than the high pressure of the refrigerant in the heating operation if the currents flowing to the motor of the compressor are the same.

  In the fourth aspect of the air conditioner, the pressure is detected at a temperature with lower accuracy in the heating connection state, the cooling connection state is adopted when the temperature is higher than the temperature reference value, and the accuracy is higher in the cooling connection state. The pressure is detected by current. Therefore, compared with the case where the current is detected in the heating connection state and the temperature is detected in the cooling connection state, it is possible to suppress the high pressure from exceeding the pressure reference value more accurately.

It is a figure which shows an example of a notional structure of an air conditioner. It is a figure which shows an example of the relationship between the pressure of a refrigerant | coolant, and saturation temperature. It is a figure which shows an example of the cycle of air_conditionaing | cooling operation and the cycle of heating operation in a Mollier diagram. It is a figure which shows an example of an equicurrent line. It is a figure which shows an example of a notional structure of an air conditioner. It is a figure which shows an example of a notional structure of an air conditioner.

First embodiment.
As illustrated in FIG. 1, the air conditioner includes a compressor 10, heat exchangers 11 and 21, a four-way switching valve 12, and an expansion mechanism 22, which form a refrigerant circuit 300.

  The compressor 10 includes a discharge port 10a, a suction port 10b, an electric motor M1, and a compression mechanism (not shown). The compression mechanism is driven by the electric motor M1, compresses the refrigerant sucked from the suction port 10b, and discharges it from the discharge port 10a. The four-way switching valve 12 includes a heating connection state H in which the discharge port 10a is connected to one end 21a of the heat exchanger 21 and the suction port 10b is connected to one end 11a of the heat exchanger 11, and the discharge port 10a is connected to one end of the heat exchanger 11. The cooling connection state C in which the suction port 10b is connected to the one end 21a of the heat exchanger 21 is selected.

  The heat exchangers 11 and 21 perform heat exchange between the refrigerant flowing inside and the outside air, respectively. The expansion mechanism 22 is provided between the other end 11 b of the heat exchanger 11 and the other end 21 b of the heat exchanger 21. The expansion mechanism 22 squeezes and expands the refrigerant. The expansion mechanism 22 may be, for example, an electric valve or may be realized by a pipe structure.

  In the illustration of FIG. 1, the compressor 10, the heat exchanger 11, and the four-way switching valve 12 are provided in the outdoor unit 100, and the heat exchanger 21 and the expansion mechanism 22 are provided in the indoor unit 200. A fan 13 that blows air to the heat exchanger (outdoor heat exchanger) 11 is provided in the outdoor unit 100, and a fan 23 that blows air to the heat exchanger (indoor heat exchanger) 21 is provided in the indoor unit 200. The fans 13 and 23 promote heat exchange in the heat exchangers 11 and 21, respectively.

  The outdoor unit 100 is provided with an outdoor control unit 4. The outdoor control unit 4 controls the outdoor unit 100 by controlling the compressor 10, the four-way switching valve 12 and the fan 13. In FIG. 1, a four-way switching valve control unit 41 belonging to the outdoor control unit 4 is illustrated. The four-way switching valve control unit 41 has a function of controlling the four-way switching valve 12. In the example of FIG. 1, the outdoor control unit 4 controls the compressor 10 by giving a command to the compressor control unit 3, which will be described later.

  The indoor unit 200 is provided with an indoor control unit 5. The indoor control unit 5 controls the fan 23. If the expansion mechanism 22 is a controlled expansion valve, the indoor control unit 5 also controls the expansion mechanism 22. The outdoor control unit 4 and the indoor control unit 5 are communicably connected to each other, and cooperate with each other to execute an air conditioning operation (such as a cooling operation / a heating operation).

  More specifically, in the present air conditioner, the four-way switching valve control unit 41 causes the four-way switching valve 12 to select the heating connection state H, and the outdoor control unit 4 appropriately controls the compressor 10 and the fan 13. The controller 5 appropriately controls the fan 23 and the expansion mechanism 22. At this time, the refrigerant compressed by the compressor 10 condenses in the heat exchanger 21 and gives heat to the indoor air. The refrigerant from the heat exchanger 21 expands by the expansion mechanism 22, and then evaporates in the heat exchanger 11 to absorb heat from the outdoor air and flows again to the compressor 10. In this way, the air conditioner can perform the heating operation.

  Further, the four-way switching valve control unit 41 causes the four-way switching valve 12 to select the cooling connection state C, the outdoor control unit 4 appropriately controls the compressor 10 and the fan 13, and the indoor control unit 5 appropriately controls the fan 23 and expansion. The mechanism 22 is controlled. At this time, the refrigerant from the compressor 10 condenses in the heat exchanger 11 and gives heat to the outdoor air. The refrigerant from the heat exchanger 11 expands by the expansion mechanism 22, and then evaporates in the heat exchanger 21 to absorb heat from the indoor air and flows to the compressor 10 again. In this way, the air conditioner can perform a cooling operation.

  In the illustration of FIG. 1, the power conversion unit 1 is connected to the electric motor M <b> 1 that drives the compression mechanism, and the power conversion unit 1 is connected to the power source E <b> 1. The power conversion unit 1 is controlled by the compressor control unit 3 to appropriately convert the voltage from the power source E1, and applies this to the motor M1. The electric motor M1 rotates according to the applied voltage and drives the compression mechanism.

  The power converter 1 is, for example, a three-phase inverter, and the motor M1 is also a three-phase motor. The power conversion unit 1 is controlled by the compressor control unit 3 to convert the DC voltage from the power source E1 into a three-phase AC voltage and apply it to the motor M1. For example, the compressor control unit 3 receives a command value (for example, a command value such as the rotation speed, torque, or current of the electric motor M1) from the outdoor control unit 4, and controls the power conversion unit 1 based on the command. Therefore, the outdoor control unit 4 can control the compressor 10 via the compressor control unit 3. Note that the power conversion unit 1 may be a single-phase inverter or an inverter having three or more phases. At this time, the number of phases of the electric motor M1 is adjusted to the inverter.

  Here, the compressor control unit 3, the outdoor control unit 4, and the indoor control unit 5 include a microcomputer and a storage device. The microcomputer executes each processing step (in other words, a procedure) described in the program. The storage device is, for example, a ROM (Read-Only-Memory), a RAM (Random-Access-Memory), a rewritable nonvolatile memory (EPROM (Erasable-Programmable-ROM), etc.), and various storage devices such as a hard disk device. One or more can be configured. The storage device stores various information, data, and the like, stores a program executed by the microcomputer, and provides a work area for executing the program. It can be understood that the microcomputer functions as various means corresponding to each processing step described in the program, or can realize that various functions corresponding to each processing step are realized. The compressor control unit 3, the outdoor control unit 4 and the indoor control unit 5 are not limited to this, and various procedures executed by these control units, various means to be realized, or some or all of various functions are hardware. It may be realized by hardware.

  As shown in FIG. 1, a temperature detection unit 51, which is an example of a pressure detection unit, is connected to the indoor control unit 5. The temperature detector 51 is provided in the indoor heat exchanger 21 and detects the saturation temperature T of the refrigerant. Since the saturation temperature T of the refrigerant has a positive correlation with the pressure of the refrigerant as shown in FIG. 2, the saturation temperature T of the refrigerant can be associated with the pressure. In the illustration of FIG. 2, pressure-saturation temperature curves for a plurality of types of refrigerants are shown.

  Referring to FIG. 1, the indoor control unit 5 that has received the saturation temperature T of the refrigerant from the temperature detection unit 51 transmits this to the outdoor control unit 4. Accordingly, the outdoor control unit 4 can recognize the refrigerant saturation temperature T in the indoor heat exchanger 21. Here, it is assumed that the pressure of the refrigerant at the discharge port 10a of the compressor 10 (hereinafter also referred to as high pressure) is detected. That is, it is assumed that the pressure of the refrigerant after being compressed by the compressor 10 is detected. The compressed refrigerant is supplied to the indoor heat exchanger 21 when the heating connection state H is adopted. Therefore, the saturation temperature T when the heating connection state H is employed is associated with a high pressure.

  Here, as described above, the temperature detection unit 51 is employed as an example of the pressure detection unit, but not limited thereto, a pressure detection sensor that detects the pressure of the refrigerant at the discharge port 10a of the compressor 10 may be employed. However, since the pressure detection sensor is relatively expensive, if the temperature detection unit 51 is employed, the cost can be reduced.

  In such an air conditioner, the four-way switching valve control unit 41 operates as follows. That is, when the high pressure is larger than the pressure reference value Pref in the heating operation, the four-way switching valve control unit 41 causes the four-way switching valve 12 to select the cooling connection state C. In other words, the four-way switching valve control unit 41 selects the cooling connection state C for the four-way switching valve 12 when the high pressure in the state where the heating connection state H is selected by the four-way switching valve 12 is greater than the pressure reference value Pref. Let

  As an example of a more specific operation, the outdoor control unit 4 stores, for example, the connection state of the four-way switching valve 12 in a storage medium (not shown). The outdoor control unit 4 determines whether the saturation temperature T is higher than the temperature reference value Tref. This temperature reference value Tref corresponds to the pressure reference value Pref. More specifically, the temperature reference value Tref is a value equal to the saturation temperature T when the high pressure takes the pressure reference value Pref. When the four-way switching valve 12 selects the heating connection state H and the saturation temperature T is larger than the temperature reference value Tref, the outdoor control unit 4 notifies the four-way switching valve control unit 41 to that effect. The four-way switching valve control unit 41 that has received the notification causes the four-way switching valve 12 to select the cooling connection state C.

  By adopting the cooling connection state C in this way, the high pressure is reduced. This is considered for the following reasons. FIG. 3 shows a cycle during cooling operation and a cycle during heating operation in the Mollier diagram. In FIG. 3, the cycle during the cooling operation is indicated by a solid line and a thick line, and the cycle during the heating operation is indicated by a broken line and a thick line. Here, the work of the compressor 10 in the cooling operation and the work 10 of the compressor in the heating operation will first be considered with reference to FIG. In order to explain the difference in work amount as illustrated in FIG. 3 in an easy-to-understand manner, the case where the high pressure is equal is considered here. When the high pressure takes the same value, the refrigerant pressure (hereinafter referred to as low pressure) on the suction port 10b side of the compressor 10 is higher during the cooling operation than during the heating operation. This is because the low pressure is higher as the temperature of the air exchanging heat with the evaporator is higher, and the outdoor temperature in the cooling operation is higher than the indoor temperature in the heating operation. Therefore, the enthalpy that increases in the compressor 10 is smaller in the cooling operation than in the heating operation. In the illustration of FIG. 3, the enthalpy Δh1 in the cooling operation is about 15 kJ / kg, and the enthalpy Δh2 in the heating operation is about 20 kJ / kg. Therefore, at this time, the enthalpy Δh1 is about 3/4 times the enthalpy Δh2.

On the other hand, the flow rate of the refrigerant flowing through the compressor 10 is proportional to the low pressure. Since the low pressure PL1 in the cooling operation is larger than the low pressure PL2 in the heating operation, the refrigerant flow rate G1 in the cooling operation is larger than the flow rate G2 in the heating operation. In the illustration of FIG. 3, the low pressure PL1 is about 12 kgf / cm ² and the low pressure PL2 is about 5 kgf / cm ² . Therefore, at this time, the low pressure PL1 is about 2.4 times the low pressure PL2, and the flow rate G1 is also about 2.4 times the flow rate G2.

  The work of the compressor 10 is represented by the product of enthalpy and flow rate. As described above, the flow rate G1, G2 ratio (G1 / G2) is higher than the enthalpy Δh1, Δh2 ratio (Δh1 / Δh2). As a result, the work amount W1 of the compressor 10 in the cooling operation is the heating operation. It becomes larger than the work amount W2 of the compressor 10 at. For example, in the illustration of FIG. 3, the work amount W1 in the cooling operation is approximately 1.8 times (= 2.4 × 3/4) the work amount W2 in the heating operation.

  If the four-way switching valve 12 is switched from the heating connection state H to the cooling connection state C in the heating operation, the function of the indoor heat exchanger 21 is switched from the function of the evaporator to the function of the condenser, and the function of the outdoor heat exchanger 11 is changed. The function switches from the condenser function to the evaporator function. The low pressure of the refrigerant depends on the temperature of the air that exchanges heat with the evaporator as described above. However, the temperature of the indoor heat exchanger 11 that functions as an evaporator (for example, 20 ° C.) evaporates before switching. The temperature is higher than the indoor temperature (for example, 7 ° C.) for exchanging heat with the outdoor heat exchanger 21 functioning as a heat exchanger. Therefore, the low pressure increases due to the switching. As a result, the flow rate of the refrigerant increases while the heat exchange rate of the heat exchangers 11 and 21 decreases. This is because the target temperature in the room remains at the time of heating operation, and the room cannot be warmed by cooling operation, so the work amount of the compressor 10 is also reduced in the temperature control performed for the target temperature. . Therefore, the high pressure of the refrigerant also decreases. That is, since the cooling operation is performed under the temperature conditions (room temperature, outdoor temperature and target temperature) where the heating operation is originally performed, the high pressure decreases due to this. In addition, as long as the target temperature used by air_conditionaing | cooling operation is more than the target temperature employ | adopted by heating operation, you may employ | adopt the target temperature used by air_conditionaing | cooling operation with the said switching. Since the work amount of the compressor 10 is also reduced by the temperature control with respect to the target temperature, the high pressure is reduced.

  Further, as described above, the work of the compressor in the cooling operation is smaller than the work of the compressor in the heating operation. This also contributes to a decrease in high pressure. As described above, when the high pressure in the heating connection state H is larger than the pressure reference value Pref, the four-way switching valve 12 selects the cooling connection state C, whereby the high pressure can be reduced. Therefore, it is possible to suppress the high pressure from exceeding the pressure reference value Pref.

<Pressure detector>
In the above description, the temperature detector 51 is employed as an example of the pressure detector. However, you may employ | adopt the electric current detection part 33 illustrated in FIG. 1 as a pressure detection part. In this case, the temperature detector 51 is not an essential requirement.

  The current detection unit 33 detects a current flowing to the electric motor M1. However, in the illustration of FIG. 1, the current detection unit 33 detects a direct current (hereinafter also referred to as current I) input to the power conversion unit 1. This is because the direct current is converted into a three-phase alternating current by the power converter 1 and flows through the motor M1, so that the direct current can also be grasped as a current flowing through the motor M1. Unlike the example of FIG. 1, the current detection unit 33 may detect at least one of the three-phase AC currents (line currents) flowing through the electric motor M <b> 1.

  FIG. 4 illustrates an equicurrent line of the current (current I or the amplitude of the line current) flowing through the motor M1 on the coordinates where the rotation speed of the motor M1 is taken on the horizontal axis and the high voltage is taken on the vertical axis. . In the illustration of FIG. 4, equicurrent lines with squares, triangles, inverted triangles, rhombuses, circles, stars, pentagons, and trapezoids are shown as current values 10A, 12A, 14A, 16A, 17A, 18A, 20A and 22A, respectively. Indicates. As illustrated in FIG. 4, if the rotation speed of the electric motor M1 is equal, the higher the refrigerant pressure, the higher the current flowing through the electric motor M1.

The current flowing through the motor M1 is compared with the current reference value IrefH. The current reference value IrefH corresponds to the pressure reference value Pref. More specifically, the current reference value IrefH is a value equal to the current flowing through the electric motor M1 when the high pressure takes the pressure reference value Pref in the heating operation (the amplitude of the alternating current). In addition, when there are a plurality of these values according to the rotation speed, it is preferable to adopt the minimum value among these values. For example, if the pressure reference value Pref is 45 kgf / cm ² in FIG. 4, the current reference value IrefH is about 15.8 A, for example. If, for example, 16 A is adopted as the current reference value IrefH, it can be considered that the pressure reference value Pref is about 46.2 kgf / cm ² . As a result, no matter what value the rotation speed takes in the heating operation, if the current flowing through the motor M1 is smaller than the current reference value IrefH, the high pressure is smaller than the pressure reference value Pref.

  The four-way switching valve control unit 41 causes the four-way switching valve 12 to select the cooling connection state C when the current I when the heating connection state H is adopted is larger than the current reference value IrefH. An example of a more specific operation will be described. In the example of FIG. 1, the current detection unit 33 is connected to the compressor control unit 3, and the compressor control unit 3 compares the current I detected by the current detection unit 33 with the current reference value IrefH. When the current I is larger than the current reference value IrefH in the heating operation, the compressor control unit 3 notifies the outdoor control unit 4 to that effect. The outdoor control unit 4 that has received the notification notifies the four-way switching valve control unit 41 when the four-way switching valve 12 selects the heating connection state H, and the four-way switching valve control unit 41 notifies the four-way switching valve 12. Allows the cooling connection state C to be selected.

  Therefore, high pressure can be reduced. Moreover, since the current detection unit 33 is employed as a pressure detection unit for detecting pressure, the cost can be reduced as compared with the case where a pressure detection sensor is used.

Second embodiment.
The conceptual configuration of the air conditioner illustrated in FIG. 5 is the same as the air conditioner of FIG. 1 except for the internal configuration of the compressor control unit 3. In the second embodiment, both the current detection unit 33 and the temperature detection unit 51 are provided.

  The compressor control unit 3 includes a switching signal generation unit 31, a current reference value setting unit 34, and a compressor stop unit 35. The switching signal generator 31 generates a switching signal to be given to the power converter 1. For example, the switching signal generation unit 31 receives a command value (for example, a command value such as the rotation speed, torque, or current of the electric motor M1) from the outdoor control unit 4, and generates a switching signal based on the command value.

  The current reference value setting unit 34 sets a current reference value IrefC for the current flowing through the motor M1 and outputs this to the compressor stop unit 35. This current reference value IrefC corresponds to the pressure reference value Pref. More specifically, the current reference value IrefC is a value equal to the current flowing through the electric motor M1 when the high pressure takes the pressure reference value Pref in the cooling operation (the amplitude of the alternating current). In addition, when there are a plurality of these values according to the rotation speed, it is preferable to adopt the minimum value among these values. In this case, no matter what value the rotation speed takes in the cooling operation, if the current flowing through the motor M1 is smaller than the current reference value IrefC, the high pressure is smaller than the pressure reference value Pref.

  The current reference value IrefC is larger than the current reference value IrefH. This is due to the following reason. That is, as described with reference to FIG. 3, if the high pressure is the same, the work amount W1 in the cooling operation is higher than the work amount W2 in the heating operation. In other words, if the high pressure is the same, the current in the cooling operation is higher than the current in the heating operation.

  The current I detected by the current detection unit 33 is input to the compressor stop unit 35. The compressor stop unit 35 includes a comparator 351. The comparator 351 compares the current I with the current reference value IrefC. The comparator 351 is formed by an operational amplifier, for example. The compressor stop unit 35 controls the power conversion unit 1 to stop the motor M1 when the current I is larger than the current reference value IrefC. As a result, the compressor 10 is stopped.

  In the example of FIG. 5, for example, the compressor stop unit 35 includes a logic circuit 352. The logic circuit 352 receives the output of the comparator 351 and the output of the switching signal generator 31. The logic circuit 352 outputs a switching signal that stops the power conversion unit 1 when the current I is larger than the current reference value IrefC, and performs switching from the switching signal generation unit 31 when the current I is smaller than the current reference value IrefC. The signal is output to the power converter 1. For example, the comparator 351 outputs an active signal when the current I is larger than the current reference value IrefC. Further, for example, a switching element (not shown) belonging to the power converter 1 is turned on when an active switching signal is input. In this case, the logic circuit 352 is, for example, an AND circuit. As a result, the logic circuit 352 outputs the switching signal from the switching signal generation unit 31 to the power conversion unit 1 while receiving the activated signal from the comparator 351, and receives the inactivated signal from the comparator 351. Sometimes, an inactive switching signal is output to the power converter 1. Accordingly, the motor M1 can be stopped when the current I is larger than the current reference value IrefC.

  As described above, the current reference value IrefC is larger than the current reference value IrefH. When the high pressure is smaller than the pressure reference value Pref in the heating operation, the current I does not exceed the current reference value IrefC because it is smaller than the current reference value IrefH. Therefore, the stop of the compressor 10 by the compressor stop unit 35 is not executed in the heating operation but executed in the cooling operation.

  As described in the first embodiment, the four-way switching valve control unit 41 has a four-way switching valve control unit 41 when the saturation temperature T detected by the temperature detection unit 51 in the heating operation exceeds the temperature reference value Tref. Causes the four-way switching valve 12 to select the cooling connection state C. Therefore, it can be avoided that the high pressure exceeds the pressure reference value Pref in the state where the heating connection state H is adopted.

  As described above, when the heating connection state H is adopted, it is possible to avoid the pressure from exceeding the pressure reference value Pref by adopting the cooling connection state C based on the saturation temperature T, and the cooling connection state C is adopted. In order to prevent the pressure from exceeding the pressure reference value Pref, the compressor 10 is stopped based on the current I.

  The pressure detection accuracy detected by the temperature detection unit 51 is lower than the pressure detection accuracy detected by the current detection unit 33. This is considered, for example, for the following reason. That is, the temperature detector 51 detects the temperature of the indoor heat exchanger 21, and a deviation from the actual refrigerant saturation temperature T occurs.

  According to the second embodiment, in the heating connection state H, the pressure is detected by the saturation temperature T with lower accuracy, and in the cooling connection state C, the pressure is detected by the current I with higher accuracy. Therefore, compared with the case where the current I is detected in the heating connection state H and the saturation temperature T is detected in the cooling connection state C, it is possible to suppress the high pressure from exceeding the pressure reference value Pref more accurately.

  In addition, in the illustration of FIG. 5, the compressor stop unit 35 includes a comparator 351 and a logic circuit 352. Therefore, it is possible to realize the maintenance of the high pressure below the pressure reference value Pref by hardware. Therefore, the reliability is higher than that realized by software. Of course, it may be realized by software.

  Further, as illustrated in FIG. 6, the power conversion unit 1 may include a switch S1. The switch S1 is provided between the power supply E1 and the power conversion unit 1a, and selects supply / cutoff of power from the power supply E1 to the power conversion unit 1a. The power conversion unit 1a is the same as the power conversion unit 1 in FIG. 1 and converts, for example, a DC voltage from the power source E1 into an AC voltage. In the illustration of FIG. 6, two switches S1 are provided between the power source E1 and the power conversion unit 1a, but only one of them may be provided.

  The comparator 351 compares the current I with the current reference value IrefC, and gives a signal to the switch S1 to cut off the switch S1 when the current I is larger than the current reference value IrefC. As a result, the electric motor M1 stops, and as a result, the compressor 10 stops. Even in such a configuration, the compressor stop unit 35 can be realized by hardware, so that the reliability is high.

DESCRIPTION OF SYMBOLS 3 Compressor control part 10 Compressor 11, 21 Heat exchanger 12 Four-way switching valve 22 Expansion mechanism 33 Current detection part 41 Four-way switching valve control part 51 Temperature detection part 300 Refrigerant circuit

Claims (4)

A compressor (10) having an electric motor (M1) for compressing refrigerant, an indoor heat exchanger (21), an outdoor heat exchanger (11), and an intake port (10b) and a discharge port ( 10a) is connected to one end (11a) of the outdoor heat exchanger and one end (21a) of the indoor heat exchanger, respectively, in a heating connection state (H), and the suction port and the discharge port are respectively connected to the indoor heat exchanger. The one-way switching valve (12) for switching between the one end and the cooling connection state (C) connected to the one end of the outdoor heat exchanger, the other end (21b) of the indoor heat exchanger, and the other of the outdoor heat exchanger An expansion mechanism (22) provided between the end (11b), and a refrigerant circuit (300) through which the refrigerant circulates,
A pressure detector (51, 33) for detecting the pressure of the refrigerant on the outlet side;
Having the function of controlling the four-way switching valve, and selecting the cooling connection state for the four-way switching valve when the pressure is larger than a pressure reference value when the heating connection state is selected by the four-way switching valve. An air conditioner comprising a four-way switching valve control unit (41). The pressure detection unit has a temperature detection unit (51) for detecting the temperature of the indoor heat exchanger (21) as the pressure of the refrigerant,
The four-way switching valve controller (41) is configured such that the temperature in a state where the heating connection state (H) is selected by the four-way switching valve (12) is larger than a temperature reference value corresponding to the pressure reference value. The air conditioner according to claim 1, wherein the four-way switching valve is caused to select the cooling connection state (C). The pressure detection unit includes a current detection unit (33) that detects a current of the electric motor (M1) as the pressure of the refrigerant,
The four-way switching valve control unit (41), when the current is larger than the current reference value corresponding to the pressure reference value in the state where the heating connection state (H) is selected by the four-way switching valve (12). The air conditioner according to claim 1, wherein the four-way switching valve is caused to select the cooling connection state (C). The pressure detection unit further includes a current detection unit (33) that detects a current of the electric motor (M1) as the pressure of the refrigerant,
When the current is larger than the current reference value corresponding to the pressure reference value in a state where the four-way switching valve (12) adopts the cooling connection state (C), the air conditioner has the electric motor (M1 The air conditioner according to claim 2, further comprising a compressor stop section (35) for stopping the compressor (10) by stopping the compressor.

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