Patent Document

CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims the benefit of Korean Patent Application No. 2004-21494, filed on Mar. 30, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a refrigerator and a defrosting method thereof, and, more particularly, to a refrigerator and a defrosting method thereof which are capable of achieving an appropriate defrosting operation even when a part of constituent elements included in a defrosting system fails. 
   2. Description of the Related Art 
   Generally, in a refrigerator, lowering of a temperature around a heat exchanger is generated due to heat absorption caused by evaporation of a liquid-state refrigerant passing through the heat exchanger. When the temperature around the heat exchanger is lowered, moisture around the heat exchanger is cooled, so that frost accumulates on the surface of the heat exchanger. The accumulated frost should be removed because it may degrade the cooling efficiency of the heat exchanger. 
   In order to remove frost accumulated on such a heat exchanger, conventional refrigerators are provided with a defrost heater arranged around the heat exchanger, and adapted to generate heat, and a heat exchanger temperature sensor (or defrost sensor) adapted to measure a temperature of the heat exchanger. 
   In such a refrigerator, a defrosting mode is periodically carried out. When the defrosting mode is to be performed, the defrost heater is turned on to generate heat. The heat generation of the defrost heater is continued until a temperature sensed by the heat exchanger temperature sensor reaches a predetermined temperature. However, where the heat exchanger temperature sensor operates erroneously due to, for example, a failure thereof, it is impossible to appropriately determine the point of time at which the defrost heater is to be turned off. In this case, the defrosting mode is not carried out, in order to prevent overheat caused by an uncontrolled operation of the defrost heater. 
   However, the above mentioned conventional refrigerator takes a measure to stop driving of a compressor thereof when the heat exchanger temperature sensor, in addition to the measure to prevent the defrosting mode from being carried out. For this reason, there is a problem in that food stored in the refrigerator may go bad. 
   SUMMARY OF THE INVENTION 
   Therefore, it is an aspect of the invention to provide a refrigerator and a defrosting method thereof which are capable of achieving an appropriate defrosting operation even when a part of constituent elements included in a defrosting system fails. 
   In accordance with one aspect, the present invention provides a defrosting method of a refrigerator comprising the steps of: determining whether or not a predetermined first defrosting completion condition is usable; if the predetermined first defrosting completion condition is usable, executing a first defrosting mode, which uses the predetermined first defrosting completion condition; and if the predetermined first defrosting completion condition is not usable, executing a second defrosting mode, which uses a predetermined second defrosting completion condition different from the predetermined first defrosting completion condition, and a defrosting execution determination condition different from that of the first defrosting mode. 
   The determination of whether or not the predetermined first defrosting completion condition is usable may be made, based on whether a heat exchanger temperature sensor adapted to measure a temperature of a heat exchanger, to be defrosted, is in a normal state or in a failure state. 
   The first defrosting mode may be executed when it is determined that the heat exchanger temperature sensor is in the normal state. The second defrosting mode may be executed when it is determined that the heat exchanger temperature sensor is in the failure state. 
   The step of executing the second defrosting mode may comprise the steps of, comparing a temperature of a storage compartment, to be cooled in accordance with an operation of the heat exchanger, with a reference temperature, and if the temperature of the storage compartment is lower than the reference temperature, turning on a defrost heater adapted to defrost the heat exchanger for a predetermined time. 
   The step of executing the second defrosting mode may further comprise the step of, if the temperature of the storage compartment is not lower than the reference temperature, preventing the defrost heater from being driven. 
   The second defrosting completion condition may be satisfied when a predetermined time has elapsed after the turning-on of the defrost heater. 
   The first defrosting completion condition may be satisfied when the temperature measured by the heat exchanger temperature sensor reaches a reference temperature. 
   In accordance with another aspect, the present invention provides a defrosting method of a refrigerator comprising the steps of: determining whether or not a heat exchanger temperature sensor adapted to measure a temperature of a heat exchanger, to be defrosted, is in a failure state; if the heat exchanger temperature sensor is in a failure state, comparing a temperature of a storage compartment, to be cooled in accordance with an operation of the heat exchanger, with a reference temperature; and if the temperature of the storage compartment is lower than the reference temperature, turning on a defrost heater adapted to defrost the heat exchanger for a predetermined time. 
   The defrosting method may further comprise the step of, if the temperature of the storage compartment is not lower than the reference temperature, preventing the defrost heater from being driven. 
   The failure state of the heat exchanger temperature sensor may correspond to an open-circuited or short-circuited state. 
   In accordance with another aspect, the present invention provides a refrigerator comprising: a heat exchanger adapted to exchange heat with air in a storage compartment; a heat exchanger temperature sensor adapted to measure a temperature of the heat exchanger; a defrost heater adapted to perform a defrosting operation for the heat exchanger; and a control unit adapted to execute a first defrosting mode when the heat exchanger temperature sensor is in a normal state, while executing a second defrosting mode, which uses a defrosting completion condition and a defrosting execution determination condition different from those of the first defrosting mode, when the heat exchanger temperature sensor is in a failure state. 
   The first defrosting mode may be executed to drive the defrost heater until the temperature measured by the heat exchanger temperature sensor reaches a first reference temperature. The second defrosting mode may be executed to drive the defrost heater for a predetermined time when a temperature of the storage compartment is not higher than a second reference temperature. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above objects, and other features and advantages of the present invention will become more apparent after reading the following detailed description when taken in conjunction with the drawings, in which: 
       FIG. 1  is a sectional view illustrating a refrigerator according to an exemplary embodiment of the present invention; 
       FIG. 2  is a block diagram illustrating a configuration of the refrigerator illustrated in  FIG. 1 ; 
       FIG. 3  is a circuit diagram illustrating a first heat exchanger temperature sensor and a first defrost heater included in the refrigerator of  FIG. 2 ; and 
       FIG. 4  is a flow chart illustrating an operation of the refrigerator illustrated in  FIG. 2 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Preferred embodiments of the present invention will now be described in detail with reference to the annexed drawings. Referring to  FIG. 1 , a refrigerator according to an exemplary embodiment of the present invention is illustrated. As shown in  FIG. 1 , the refrigerator includes a refrigerator body  10 , a freezing compartment  12  defined in the refrigerator body  10  over a partition wall  11  constituting a part of the refrigerator body  10 , while being opened at a front side thereof, and a freezing compartment door  13  adapted to open and close the opened front side of the freezing compartment  12 . The refrigerator also includes a refrigerating compartment  14  defined in the refrigerator body  10  beneath the partition wall  11 , while being opened at a front side thereof, a refrigerating compartment door  15  adapted to open and close the opened front side of the refrigerating compartment  14 , and a compressor  16  arranged at a lower rear portion of the refrigerator body  10 . 
   A freezing compartment heat exchanging device  30  is arranged between a rear wall of the freezing compartment  12  and a wall portion of the refrigerator body  10  facing the rear wall of the freezing compartment  12 , in order to perform a heat exchanging operation for the freezing compartment  12 . Similarly, a refrigerating compartment heat exchanging device  40  is arranged between a rear wall of the refrigerating compartment  14  and a wall portion of the refrigerator body  10  facing the rear wall of the refrigerating compartment  14 , in order to perform a heat exchanging operation for the refrigerating compartment  14 . A freezing compartment temperature sensor  17  and a refrigerating compartment temperature sensor  18  are provided at desired wall portions of the freezing and refrigerating compartments  12  and  14 , respectively. Shelves  19  and storage containers  20  are arranged in the freezing and refrigerating compartments  12  and  14  to store food. 
   The freezing compartment heat exchanging device  30  includes a freezing compartment heat exchanger  31  adapted to cool air in the freezing compartment  12  in accordance with a heat exchanging operation thereof, a freezing compartment fan  32  arranged over the freezing compartment heat exchanger  31  to circulate, through the freezing compartment  12 , air cooled while passing the freezing compartment heat exchanger  31 , and a freezing compartment fan motor  33  adapted to drive the freezing compartment fan  32 . A suction hole  34  is formed at the rear wall of the freezing compartment  12  beneath the freezing compartment heat exchanger  31  to suck air from the freezing compartment  12  toward the freezing compartment heat exchanger  31  in accordance with operation of the freezing compartment fan  32 . At the rear wall of the freezing compartment  12 , a plurality of discharge holes  35  are formed to uniformly discharge cold air blown by the freezing compartment fan  32  into the freezing compartment  12 . 
   A first heat exchanger temperature sensor  36  is arranged above the freezing compartment heat exchanger  31  to measure a temperature of the freezing compartment heat exchanger  31 . For the first heat exchanger temperature sensor  36 , a negative temperature coefficient (NTC) themistor may be used. 
   The NTC thermistor, which has a negative temperature coefficient, exhibits a decreased resistance when the temperature of a space where the NTC thermistor is installed increases, while exhibiting an increased resistance when the temperature of the space decreases. Accordingly, after the resistance of the NTC thermistor is measured, it is possible to identify the temperature of the space where the NTC thermistor is installed, using a relation between the resistance of the NTC thermistor and the temperature of the space. 
   A first defrost heater  37  is provided at the freezing compartment heat exchanger  31  such that it extends along the bottom and one side of the freezing compartment heat exchanger  31 . The first defrost heater  37  comprises an electric heating wire adapted to generate heat when current is supplied thereto. 
   The refrigerating compartment heat exchanging device  40  has a configuration similar to that of the freezing compartment heat exchanging device  30 . That is, the refrigerating compartment heat exchanging device  40  includes a refrigerating compartment heat exchanger  41  adapted to cool air in the refrigerating compartment  14  in accordance with a heat exchanging operation thereof, a refrigerating compartment fan  42  arranged over the refrigerating compartment heat exchanger  41  to circulate, through the refrigerating compartment  14 , air cooled while passing the refrigerating compartment heat exchanger  41 , and a refrigerating compartment fan motor  43  adapted to drive the refrigerating compartment fan  42 . A suction hole  44  is formed at the rear wall of the refrigerating compartment  14  beneath the refrigerating compartment heat exchanger  41  to suck air from the refrigerating compartment  14  toward the refrigerating compartment heat exchanger  41  in accordance with operation of the refrigerating compartment fan  42 . At the rear wall of the refrigerating compartment  14 , a plurality of discharge holes  45  are formed to uniformly discharge cold air blown by the refrigerating compartment fan  42  into the refrigerating compartment  14 . 
   A second heat exchanger temperature sensor  46  is arranged above the refrigerating compartment heat exchanger  41  to measure a temperature of the refrigerating compartment heat exchanger  41 . For the second heat exchanger temperature sensor  46 , an NTC themistor may be used, as in the case of the first heat exchanger temperature sensor  36 . 
   A second defrost heater  47  is provided at the refrigerating compartment heat exchanger  41  such that it extends along the bottom and one side of the refrigerating compartment heat exchanger  41 . The second defrost heater  47  comprises an electric heating wire adapted to generate heat when current is supplied thereto. 
   As shown in  FIG. 2 , the refrigerator, which has the configuration shown in  FIG. 1 , also includes a compressor driving unit  51  adapted to drive the compressor  16 , a first defrost heater driving unit  52  adapted to drive the first defrost heater  37 , a second defrost heater driving unit  53  adapted to drive the second defrost heater  47 , and a microcomputer  50  adapted to control the entire operation of the refrigerator. 
   As shown in  FIG. 3 , the NTC thermistor used as the first heat exchanger temperature sensor  36  is connected to a voltage dividing resistor R 1  adapted to divide a voltage supplied from a 5V constant voltage source. The NTC thermistor is also connected to a current limit resistor R 2  adapted to limit current supplied to the microcomputer  50 . A capacitor C is coupled between the current limit resistor R 2  and the microcomputer  50  to remove noise components from a voltage signal inputted to the microcomputer  50 . 
   Meanwhile, the first defrost heater  37 , which comprises an electric heating wire, is connected to a thermal fuse  54 . The thermal fuse  54  is connected between a voltage source AC and the first defrost heater  37  to prevent the first defrost heater  37  from being damaged due to overcurrent from the voltage source AC. The first defrost heater  37  is also connected to a relay  55 . The relay  55  connects or disconnects the first defrost heater  37  to or from the voltage source AC in accordance with a control signal from the microcomputer  50 . 
   In this defrosting system, the temperature of the freezing compartment heat exchanger  31  may vary during an operation of the refrigerator. Such a variation in the temperature of the freezing compartment heat exchanger  31  causes a variation in the resistance of the first heat exchanger temperature sensor  36 . Accordingly, where the first heat exchanger temperature sensor  36  operates normally, it must output voltages of diverse levels to the microcomputer  50 . 
   However, where the first heat exchanger temperature sensor  36  is in an open-circuited state, 5V is always inputted to an input port of the microcomputer  50  connected to the first heat exchanger temperature sensor  36 , irrespective of the actual temperature of the freezing compartment heat exchanger  31 . On the other hand, where the first heat exchanger temperature sensor  36  is in a short-circuited state, 0V is always inputted to the input port of the microcomputer  50  connected to the first heat exchanger temperature sensor  36 , irrespective of the actual temperature of the freezing compartment heat exchanger  31 . Accordingly, the microcomputer  50  can determine, based on the level of the voltage inputted thereto from the first heat exchanger temperature sensor  36 , whether the first heat exchanger temperature sensor  36  operates normally or fails due to open-circuit or short-circuit thereof. 
   Although only the first defrost heater  37  and first heat exchanger temperature sensor  36  associated with a defrosting operation for the freezing compartment heat exchanger  31  have been described with reference to  FIG. 3 , the same description may be given of the second defrost heater  47  and second heat exchanger temperature sensor  46  associated with a defrosting operation for the refrigerating compartment heat exchanger  41 . 
   Now, the operation of the refrigerator shown in  FIG. 2  will be described with reference to  FIG. 4 . In accordance with the present invention, the microcomputer  50  first determines whether or not the current operation mode of the refrigerator is a defrosting mode for the freezing compartment heat exchanger  31  (Step  60 ). Here, the defrosting mode is a mode for removing frost accumulated on the heat exchanger. In accordance with the illustrated embodiment of the present invention, the defrosting mode is executed at intervals of a predetermined time (for example, at intervals of 3 hours during the operation of the refrigerator). 
   When it is determined that the current operation mode of the refrigerator is not the defrosting mode, the microcomputer  50  completes a control cycle for the defrosting mode. On the other hand, where the current operation mode is the defrosting mode, the microcomputer  50  determines, based on an input voltage from the first heat exchanger temperature sensor  36 , whether the first heat exchanger temperature sensor  36  is in a normal state or a failure or abnormal state, for example, an open-circuited or short-circuited state (Step  62 ). The reason why it is determined whether or not the first heat exchanger temperature sensor  36  is in a normal state is that it is necessary to determine whether a desired defrosting operation is to be carried out in a first defrosting mode, to be described hereinafter, or in a second defrosting mode. If there is an abnormality in the first heat exchanger temperature sensor  36 , it is impossible to appropriately determine the point of time, at which the defrosting operation is to be completed, in association with the first defrosting mode. In this case, accordingly, it is undesirable to use the first defrosting mode. The second defrosting mode is proper in this case. 
   Where the first heat exchanger temperature sensor  36  is normal, the microcomputer  50  performs a control operation associated with a defrosting operation in the first defrosting mode. That is, the microcomputer  50  sends a control signal to the first defrost heater driving unit  52  to turn on the first defrost heater  37  (Step  74 ). The microcomputer  50  then determines whether or not a temperature of the freezing compartment heat exchanger  31  measured by the first heat exchanger temperature sensor  36  is higher than a first reference temperature (Step  76 ). The first reference temperature is a temperature at which frost accumulated on the freezing compartment heat exchanger  31  is sufficiently removable. This temperature may be experimentally determined. 
   When it is determined that the measured temperature of the freezing compartment heat exchanger  31  is not higher than the first reference temperature, the microcomputer  50  determines that the sufficient defrosting has not been achieved yet. Accordingly, the microcomputer  50  controls the first defrost heater  37  to be continuously driven. On the other hand, when it is determined that the measured temperature of the freezing compartment heat exchanger  31  is higher than the first reference temperature, the microcomputer  50  sends a control signal to the first defrost heater driving unit  52  to turn off the first defrost heater  37  (Step  78 ). 
   On the other hand, where it is determined at step  62  that the first heat exchanger temperature sensor  36  is abnormal, the microcomputer  50  performs a control operation associated with a defrosting operation in the second defrosting mode. In this case, the microcomputer  50  first determines whether or not a temperature of the freezing compartment  12  measured by the freezing compartment temperature sensor  17  is lower than a second reference temperature (Step  64 ). 
   The second reference temperature is a reference temperature for determining whether or not the compressor  16  and freezing compartment fan  32  operate normally. This temperature is set by a maximum temperature of the freezing compartment  12  available when both the compressor  16  and the freezing compartment fan  32  operate normally. For example, where it is assumed that the maximum temperature of the freezing compartment  12  available when both the compressor  16  and the freezing compartment fan  32  operate normally is −2° C., the second reference temperature corresponds to −2° C. The second reference temperature may be experimentally determined. 
   When it is determined that the measured freezing compartment temperature is higher than the second reference temperature, the microcomputer  50  determines that there is an abnormality in the compressor  16  or freezing compartment fan  32 . In this case, accordingly, the microcomputer  50  prevents the first defrost heater  37  from being driven (Step  72 ). When the defrosting mode is executed in the case in which the temperature of the freezing compartment heat exchanger  32  has already been increased due to an abnormal operation of the compressor  16  or freezing compartment fan  32 , the freezing compartment heat exchanger  32  and peripheral devices may be damaged due to heat generated from the first defrost heater  37 . In this case, accordingly, the microcomputer  50  prevents the first defrost heater  37  from being driven. 
   On the other hand, where the measured freezing compartment temperature is not higher than the second reference temperature, the microcomputer  50  sends a control signal to the first defrost heater driving unit  52  to turn on the first defrost heater  37  (Step  66 ). Thereafter, the microcomputer  50  determines whether or not a predetermined time has elapsed (Step  68 ). The predetermined time is a time for which the first defrost heater  37  is to be driven. This time is set by a time capable of achieving sufficient defrosting. 
   When it is determined that the driving time of the first defrost heater  37  has not reached the predetermined time yet, the microcomputer  50  returns the control operation thereof to step  68 . On the other hand, where the driving time of the first defrost heater  37  has reached the predetermined time, the microcomputer  50  sends a control signal to the first defrost heater driving unit  52  to turn off the first defrost heater  37  (Step  70 ). 
   The operations of the second defrost heater  47  and second heat exchanger temperature sensor  46  associated with a defrosting operation for the refrigerating compartment heat exchanger  41  are carried out in the same manner as described above. 
   As apparent from the above description, in accordance with the present invention, it is possible to achieve an appropriate defrosting operation even when a part of constituent elements included in the defrosting system fails. 
   Although the preferred embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Technology Category: 2