Abstract:
An air conditioner according to an embodiment of the invention includes a refrigerator cycle unit having a variable speed compressor, an outdoor heat exchanger, a decompression device, an indoor heat exchanger, and an accumulator sequentially connected to one another, a bypass pipe that connects the discharge side of the compressor and an outlet of the accumulator and has a two-way valve in the middle thereof, a discharge temperature sensor that detects the temperature of the compressor, and a controller that opens or closes the two-way valve, and limits the number of rotations of the compressor to a predetermined value or less, on the basis of the temperature detected by the discharge temperature sensor when the compressor starts.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a Continuation Application of PCT Application No. PCT/JP2007/059102, filed Apr. 26, 2007, which was published under PCT Article 21(2) in Japanese. 
     
    
       [0002]    This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2006-122482, filed Apr. 26, 2006, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The present invention relates to an air conditioner, and more particularly, to an air conditioner capable of preventing the dilution of a refrigerator oil of a compressor provided in an outdoor unit. 
         [0005]    2. Description of the Related Art 
         [0006]    In order to prevent the discharge of a refrigerator oil during a flooding operation of a compressor and achieve a rapid operation corresponding to a load, an air conditioner has been proposed which is provided with a bypass pipe that connects the discharge side and the suction side of the compressor and has a two-way valve in the middle thereof (for example, see Jpn. Pat. Appln. KOKAI Publication No. 2005-61738). In such an air conditioner, after the air conditioner starts up, a low-frequency operation time during the first startup of a compressor is set to be longer than that of a normal operation. In addition, a two-way valve is opened for a predetermined amount of time during the first startup of the compressor, and the compressor is operated for a long time at a low frequency at the first startup. In this way, the discharge of a refrigerator oil is prevented during startup, and a portion of the discharged refrigerator oil returns to the compressor. At or after the second startup, the low-frequency operation time is shortened to rapidly perform a necessary operation. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    The above-mentioned air conditioner has the following problems. That is, after the startup of the air conditioner, when the stagnation of a refrigerant is dissolved and the two-way valve is closed, a large amount of refrigerant stored in the accumulator flows into the compressor and the dilution of the refrigerator oil is likely to occur. 
         [0008]    Accordingly, an object of the invention is to provide an air conditioner capable of preventing the dilution of a refrigerator oil due to the inflow of a large amount of refrigerant stored in an accumulator to a compressor. 
         [0009]    In order to achieve the object, an air conditioner according to an aspect of the invention has the following structure. 
         [0010]    It comprises: a variable speed compressor; a four-way valve; an outdoor heat exchanger; a decompression device; an indoor heat exchanger; an accumulator; a bypass pipe which connects a discharge side of the compressor and an outlet of the accumulator and has a two-way valve in the middle thereof; compressor temperature detecting means for detecting the temperature of the compressor; and control means for opening the two-way valve and limiting the number of rotations of the compressor to a predetermined value or less on the basis of the temperature detected by the compressor temperature detecting means, when the temperature detected by the compressor temperature detecting means is less than or equal to a first determination temperature at the time of the startup of the compressor after the air conditioner is operated, and closes the two-way valve, when the temperature detected by the compressor temperature detecting means is greater than or equal to a second determination temperature, wherein the variable speed compressor, the four-way valve, the outdoor heat exchanger, the decompression device, the indoor heat exchanger, and the accumulator are connected to one another in a ring shape. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0011]      FIG. 1  is a block diagram illustrating the structure of an air conditioner according to a first embodiment of the invention. 
           [0012]      FIG. 2  is a flowchart illustrating a control process of the air conditioner. 
           [0013]      FIG. 3  is a timing chart illustrating the operating frequency of a compressor, a compressor temperature, and the opening/closing timing of a two-way valve in a method of controlling the air conditioner. 
           [0014]      FIG. 4  is a timing chart illustrating the compressor temperature and the opening/closing timing of the two-way valve in the control method. 
           [0015]      FIG. 5  is a timing chart illustrating the compressor temperature and the opening/closing timing of the two-way valve in the control method. 
           [0016]      FIG. 6  is a timing chart illustrating the relationship between a compressor temperature, a temperature difference ΔT (compressor temperature−saturated vapor temperature corresponding to discharge pressure), and the opening/closing of a two-way valve in another method of controlling the air conditioner. 
           [0017]      FIG. 7  is a flowchart illustrating a control process of an air conditioner according to a second embodiment of the invention. 
           [0018]      FIG. 8  is a timing chart illustrating a compressor temperature and the opening/closing timing of a two-way valve in a method of controlling the air conditioner. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]      FIG. 1  is a block diagram illustrating the structure of an air conditioner  10  according to a first embodiment of the invention.  FIG. 2  is a flowchart illustrating a control process of the air conditioner.  FIG. 3  is a timing chart illustrating the operating frequency of a compressor  21 , a compressor temperature, and the opening/closing timing of a two-way valve  4 . 
         [0020]    The air conditioner  10  includes an outdoor unit  20 , an indoor unit  50 , and connection pipes  60  and  61  that connect the indoor and outdoor units. 
         [0021]    The outdoor unit  20  includes the compressor  21  of a high-pressure and variable speed type, an outdoor heat exchanger  23  that is connected to a discharge pipe  21   a  of the compressor  21  through a four-way valve  22 , and a decompression device  24  that is connected to an outlet of the outdoor heat exchanger  23  in a case. An outlet of the decompression device  24  is connected to an inlet of an indoor heat exchanger  51  of the indoor unit  50  through the connection pipe  60 . 
         [0022]    An accumulator  25  is connected to a suction pipe  21   b  of the compressor  21 . A blower fan  23   a  is provided adjacent to the outdoor heat exchanger  23 . 
         [0023]    A discharge pressure sensor  27 , which is discharge pressure detecting means, and a discharge temperature sensor  28 , which is compressor temperature detecting means, are attached to the discharge pipe  21   a  of the compressor  21 . 
         [0024]    The connection pipe  61  is connected to an inlet of the accumulator  25  through the four-way valve  22 . The connection pipe  61  is connected to an outlet of the indoor heat exchanger  51  of the indoor unit  50 . 
         [0025]    The suction pipe  21   b  and the discharge pipe  21   a  are connected to each other by a bypass pipe  30 , and the bypass pipe is opened or closed by the two-way valve  31 . 
         [0026]    A controller  40 , which is control means, is provided in the outdoor unit  20 . The controller  40  controls the driving of the compressor  21 , the driving of the blower fan  23   a , the switching of the four-way valve  22 , and the opening/closing of the two-way valve  31 , on the basis of, for example, the output values of the discharge pressure sensor  27  and the discharge temperature sensor  28 . 
         [0027]    The indoor unit  50  includes the indoor heat exchanger  51  and a blower fan  51   a . The connection pipe  60  is connected to an inlet of the indoor heat exchanger  51 , and the connection pipe  61  is connected to an outlet thereof. 
         [0028]    The compressor  21 , the outdoor heat exchanger  23 , the decompression device  24 , the indoor heat exchanger  51 , and the accumulator  25  are connected to each other in a ring shape to form a heat-pump-type refrigerator cycle. 
         [0029]    The air conditioner  10  having the above-mentioned structure is operated as follows. As shown in  FIG. 2 , when the compressor  21  starts (ST 1 ), the output value of the discharge temperature sensor  28  is input to the controller  40 , and the controller  40  determines whether a compressor temperature is less than or equal to a first determination temperature (hereinafter, referred to as an initial determination temperature which is, for example, 10° C.) (ST 2 ). If it is determined that the compressor temperature is less than or equal to an initial determination temperature of 10° C., the two-way valve  31  is opened (ST 3 ). If it is determined that the compressor temperature is greater than 10° C., the process proceeds to Step ST 8 . 
         [0030]    When the two-way valve  31  is opened, the control unit determines whether a temperature difference ΔT between the compressor temperature and the saturated temperature of a refrigerant corresponding to the output of the discharge pressure sensor  27  is greater than or equal to a predetermined value (for example, 20K) (ST 4 ). If it is determined that the temperature difference ΔT is greater than or equal to 20K, the two-way valve  31  is closed (ST 6 ). If it is determined that the temperature difference ΔT is less than 20K, it is determined whether the compressor temperature is greater than or equal to a second determination temperature (hereinafter, referred to as an end determination temperature which is, for example, 50° C.) (ST 5 ). If it is determined that the compressor temperature is greater than or equal to an end determination temperature of 50° C., the two-way valve  31  is closed (ST 6 ). If it is determined that the compressor temperature is less than the end determination temperature of 50° C., the two-way valve  31  is kept open. 
         [0031]    When the two-way valve  31  is closed in Step ST 6 , it is determined whether the amount of reduction in compressor temperature after a predetermined time (for example, 3 minutes) has elapsed since the closing of the two-way valve is greater than or equal to a predetermined value (for example, 25K) (ST 7 ). If it is determined that the amount of reduction in compressor temperature is greater than or equal to 25K, the process returns to Step ST 3  to open the two-way valve  31  again. If it is determined that the amount of reduction in compressor temperature is less than 25K, it is determined whether the compressor temperature is greater than or equal to a third determination temperature (hereinafter, referred to as a re-determination temperature which is, for example, 20° C.) (ST 8 ). If it is determined that the compressor temperature is greater than or equal to a re-determination temperature of 20° C., the two-way valve  31  is kept closed. If it is determined that the compressor temperature is less than the re-determination temperature of 20° C., it is determined whether the temperature difference ΔT is greater than or equal to a predetermined value (for example, 20K) (ST 9 ). If it is determined that the temperature difference ΔT is greater than or equal to 20K, the two-way valve  31  is closed. If it is determined that the temperature difference ΔT is less than 20K, the process returns to Step ST 3  to open the two-way valve  31  again. 
         [0032]    Next, the opening/closing operations of the two-way valve  31  and the driving of the compressor  21  will be described.  FIG. 3  is a timing chart illustrating the operating frequency and the temperature of the compressor, and the opening/closing timing of the two-way valve when the operating frequency of the compressor  21  and the opening/closing operations of the two-way valve  31  are controlled on the basis of the compressor temperature.  FIG. 4  is a timing chart illustrating the compressor temperature and the opening/closing timing of the two-way valve when the compressor temperature is reduced after the two-way valve  31  is closed.  FIG. 6  is a timing chart illustrating the compressor temperature and the opening/closing timing of the two-way valve when the amount of reduction in compressor temperature is greater than or equal to a predetermined value. 
         [0033]    As shown in  FIG. 3 , at the time of the startup of the compressor  21 , the two-way valve  31  is opened since the compressor temperature is less than or equal to 10° C. Therefore, while the two-way valve  31  is being opened, a liquid refrigerant stored in the accumulator  25  does not return to the compressor. 
         [0034]    When an oil temperature is gradually increased by compression, the operating frequency of the compressor is increased, and an increase in the oil temperature is accelerated. That is, if the compressor temperature is less than or equal to 20° C., the compressor is operated at a maximum frequency of 25 Hz. If the compressor temperature is less than or equal to 40° C., the compressor is operated at a maximum frequency of 40 Hz. If the compressor temperature is less than or equal to 50° C., the compressor is operated at a maximum frequency of 55 Hz. 
         [0035]    When the compressor temperature reaches a second determination temperature of 50° C., the dilution of a refrigerator oil is less likely to occur even when the liquid refrigerant stored in the accumulator  25  returns to the compressor  21 . Therefore, the two-way valve  31  is closed, and the compressor  21  is operated at a predetermined frequency corresponding to a necessary indoor load (normal operation). 
         [0036]    As described above, since the compressor is operated at a frequency corresponding to the compressor temperature, the refrigerant dissolved in the refrigerator oil is slowly discharged, and the refrigerator oil is slowly foamed. In addition, it is possible to rapidly increase the compressor temperature up to a sufficient temperature to remove the stagnation of the refrigerant. 
         [0037]    As shown in  FIG. 4 , after the closing of the two-way valve  31 , during the normal operation, when the refrigerant stored in the accumulator  25  flows into the compressor  21  and the compressor temperature is less than the re-determination temperature (20° C.), the two-way valve  31  is opened again and the compressor  21  is operated at a frequency corresponding to the compressor temperature. 
         [0038]    As described above, even though an excessively large amount of refrigerant flows into the compressor  21  and the compressor temperature is reduced while the compressor is operated with the two-way valve  31  closed, it is possible to prevent the dilution of a refrigerator oil due to the inflow of the refrigerant and prevent the discharge of the refrigerator oil from the compressor  21  due to foaming by opening the two-way valve  31  and operating the compressor  31  at a frequency corresponding to the compressor temperature. In this embodiment, the re-determination temperature (20° C.) is set to be greater than the initial determination temperature (10° C.), thereby improving reliability. However, the re-determination temperature may be set to be equal to the initial determination temperature. 
         [0039]    As shown in  FIG. 5 , when the compressor temperature is reduced by a predetermined value or more after a predetermined amount of time has elapsed since the closing of the two-way valve  31 , it is estimated that a large amount of refrigerant is stored in the accumulator  25 , and the two-way valve  31  is opened again before the compressor temperature is less than the re-determination temperature (20° C.). Specifically, when the compressor temperature is reduced by 25K or more three minutes after the two-way valve  31  is closed, the two-way valve  31  is opened again, and the compressor  21  is operated at a frequency corresponding to the compressor temperature. 
         [0040]    In this way, even when the two-way valve  31  is closed with a large amount of refrigerant stored in the accumulator  25 , it is possible to prevent rapid dilution of the refrigerator oil or the discharge of the refrigerator oil from the compressor  31  due to foaming. 
         [0041]    Next, another method of controlling the opening/closing operations of the two-way valve and the driving of the compressor will be described.  FIG. 6  is a timing chart illustrating the relationship between a compressor temperature, a temperature difference ΔT (compressor temperature−saturated vapor temperature corresponding to discharge pressure), and the opening/closing of the two-way valve in another method of controlling the opening/closing operations of the two-way valve and the driving of the compressor. 
         [0042]    If a difference between the saturated temperature of a refrigerant corresponding to the output of the discharge pressure sensor  27  provided on the discharge side of the compressor  21  and the output value of the discharge temperature sensor  28  is greater than or equal to a predetermined value, the two-way valve  31  is closed. That is, if the degree of superheat of a discharge gas refrigerant is sufficiently high, the stagnation of the refrigerant has already been removed, and the dilution of a refrigerator oil does not occur even when the liquid refrigerant stored in the accumulator  25  flows into the compressor  21 . Therefore, it is preferable to immediately close the two-way valve to perform the normal operation. 
         [0043]    Specifically, if the temperature difference ΔT is more than 20K, it can be determined that the stagnation of the refrigerant is sufficiently removed and the stagnation does not occur even when the refrigerant stored in the accumulator  25  flows into the compressor  21 . Therefore, the two-way valve is closed even though the compressor temperature does not reach an end determination temperature of 50° C. 
         [0044]    According to the above-mentioned control method, it is possible to rapidly perform a normal operation while preventing the dilution of a refrigerator oil. 
         [0045]    As shown in  FIG. 6 , even though the compressor temperature is less than or equal to the re-determination temperature after the two-way valve  31  is closed, the two-way valve  31  is kept closed if the temperature difference ΔT is greater than or equal to a predetermined value. That is, in the case in which the compressor temperature is reduced, but the degree of superheat of a discharge gas refrigerant is sufficient high, the dilution of the refrigerator oil does not occur even when the liquid refrigerant stored in the accumulator  25  flows into the compressor  21 . Therefore, the normal operation is performed with the two-way valve closed. 
         [0046]    Specifically, if the temperature difference ΔT is more than 20K, it can be determined that the stagnation of the refrigerant is sufficiently removed and the dilution of the refrigerator oil does not occur even when the liquid refrigerant stored in the accumulator  25  flows into the compressor  21 . Therefore, the two-way valve is kept closed even when the compressor temperature reaches the re-determination temperature (20° C. or less). In this way, it is possible to continuously perform the normal operation while preventing the dilution of the refrigerator oil without closing the two-way valve. 
         [0047]    Next, a second embodiment of the invention will be described. 
         [0048]      FIG. 7  is a flowchart illustrating a control process according to this embodiment, and  FIG. 8  is a timing chart illustrating the relationship between time, a compressor temperature, and the opening/closing operations of a two-way valve in a method of controlling the opening/closing operations of the two-way valve and the driving of a compressor according to the second embodiment. The second embodiment is similar to the first embodiment except that, in Step ST 3  of  FIG. 3 , instead of opening the two-way valve  31 , the two-way valve  31  is alternately opened and closed at a predetermined time interval. In the second embodiment, a description of the same components as those in the first embodiment will be omitted. 
         [0049]    In this embodiment, the air conditioner  10  is operated as follows. As shown in  FIG. 7 , when the compressor  21  starts (ST 1 ), the output value of the discharge temperature sensor  28  is input to the controller  40 , and the controller  40  determines whether a compressor temperature is less than or equal to an initial determination temperature of 10° C. (ST 2 ). If it is determined that the compressor temperature is less than or equal to 10° C., the two-way valve  31  is opened and closed (ST 3 ). For example, the opening/closing operations of the two-way valve  31  are alternately performed at a time interval of 3 minutes and 20 seconds, and the two-way valve is closed for, for example, 5 seconds. If it is determined that the compressor temperature is greater than 10° C., the process proceeds to Step ST 8 . 
         [0050]    When the opening/closing operations of the two-way valve are performed in Step ST 3 , the control unit determines whether a temperature difference ΔT between the compressor temperature and the saturated temperature of a refrigerant corresponding to the output of the discharge pressure sensor  27  is greater than or equal to 20K (ST 4 ). If it is determined that the temperature difference ΔT is greater than or equal to 20K, the two-way valve  31  is closed (ST 6 ). If it is determined that the temperature difference ΔT is less than 20K, it is determined whether the compressor temperature is greater than or equal to an end determination temperature of 50° C. (ST 5 ). If it is determined that the compressor temperature is greater than or equal to 50° C., the two-way valve  31  is closed (ST 6 ). If it is determined that the compressor temperature is less than 50° C., the opening/closing operations of the two-way valve  31  are continuously performed. 
         [0051]    When the two-way valve  31  is closed in Step ST 6 , it is determined whether the amount of reduction in compressor temperature after 3 minutes have elapsed since the closing of the two-way valve is greater than or equal to 25K (ST 7 ). If it is determined that the amount of reduction in compressor temperature is greater than or equal to 25K, the process returns to Step ST 3  to perform the opening/closing operations of the two-way valve  31  again. If it is determined that the amount of reduction in compressor temperature is less than 25K, it is determined whether the compressor temperature is greater than or equal to a re-determination temperature of 20° C. (ST 8 ). If it is determined that the compressor temperature is greater than or equal to 20° C., the two-way valve  31  is kept closed. If it is determined that the compressor temperature is less than 20° C., it is determined whether the temperature difference ΔT is greater than or equal to 20K (ST 9 ). If it is determined that the temperature difference ΔT is greater than or equal to 20K, the two-way valve  31  remains closed. If it is determined that the temperature difference ΔT is less than 20K, the process returns to Step ST 3  to perform the opening/closing operations of the two-way valve  31  again. 
         [0052]    As shown in  FIG. 8 , at the time of the startup of the compressor  21 , since the compressor temperature is less than or equal to an initial determination temperature of 10° C., the opening/closing operations of the two-way valve  31  are performed. The liquid refrigerant stored in the accumulator  25  flows into the compressor  21  in five seconds during which the two-way valve  31  is closed. However, the dilution of a refrigerator oil does not occur due to the liquid refrigerant flowing into the compressor  21  in a short time. 
         [0053]    When an oil temperature is gradually increased by compression, the stagnation of the refrigerant is removed. If the compressor temperature is less than or equal to 20° C., the compressor is operated at a maximum frequency of 25 Hz. If the compressor temperature is less than or equal to 40° C., the compressor is operated at a maximum frequency of 40 Hz. If the compressor temperature is less than or equal to 50° C., the compressor is operated at a maximum frequency of 55 Hz In this way, an increase in the oil temperature is accelerated. Therefore, an appropriate amount of liquid refrigerant flows into the compressor in a short time when the two-way valve  31  is closed to reduce the liquid refrigerant stored in the accumulator  25 . 
         [0054]    When the compressor temperature reaches an end determination temperature of 50° C., the dilution of the refrigerator oil is less likely to occur even when the liquid refrigerant stored in the accumulator  25  flows into the compressor  21 . Therefore, the two-way valve  31  is closed, and then the compressor  21  is operated at a predetermined frequency corresponding to a necessary indoor load (normal operation). 
         [0055]    As described above, since the compressor is operated at a frequency corresponding to the compressor temperature, the refrigerant dissolved in the refrigerator oil is slowly discharged, and the refrigerator oil is slowly foamed. In addition, it is possible to rapidly increase the compressor temperature up to a sufficient temperature to remove the stagnation of the refrigerant. 
         [0056]    In addition, when the two-way valve  31  is opened, the compressor temperature is increased while preventing the inflow of the liquid refrigerant from the accumulator  25  to the compressor  21 . When the two-way valve  31  is closed, an appropriate amount of liquid refrigerant flows into the compressor. In this way, it is possible to reduce the liquid level of the refrigerant in the accumulator  25 . As a result, it is possible to prevent a decrease in the compressor temperature and the dilution of a refrigerator oil due to the inflow of a large amount of liquid refrigerant when the opening or closing operation of the two-way valve ends. 
         [0057]    While the two-way valve  31  is repeatedly opened and closed, the controller  40  may determine the opening and closing times of the two-way valve  31  such that the temperature detected by the discharge temperature sensor  28  is increased. While the two-way valve  31  is opened, the compressor temperature is increased by compression since the inflow of the liquid refrigerant from the accumulator  25  is prevented. While the two-way valve  31  is closed, the compressor temperature is decreased due to the inflow of the liquid refrigerant from the accumulator  25 . However, the opening and closing times of the two-way valve are set such that the compressor temperature is generally increased. 
         [0058]    As such, during the opening/closing operations of the two-way valve, it is possible to reduce the amount of liquid refrigerant in the accumulator  25  while increasing the compressor temperature. In addition, when the stagnation of the refrigerant is removed and the two-way valve  31  is closed after the opening/closing operations, it is possible to prevent the inflow of a large amount of liquid refrigerant to the compressor. 
         [0059]    The invention is not limited to the above-described embodiments. For example, in the above-described embodiments, the discharge temperature sensor  28  attached to the compressor discharge pipe  21   a  is used as a compressor temperature detecting device to detect the compressor temperature, thereby reducing manufacturing costs. However, the compressor temperature sensor  26  that is directly mounted on the compressor may be used as the compressor temperature detecting device. It should be understood by those skilled in the art that various modifications and changes of the invention can be made without departing from the scope and spirit of the invention. 
         [0060]    According to the above-described embodiments of the invention, it is possible to prevent the dilution of a refrigerator oil due to the inflow of a large amount of liquid refrigerant from an accumulator to a compressor.