Patent Publication Number: US-10775087-B2

Title: Ice-making tray and refrigerator comprising same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/029,703, filed Apr. 15, 2016, which is a U.S. national stage application of International Application No. PCT/KR2014/009684 filed Oct. 15, 2014, and claims the priority benefit of Korean Application No. 10-2013-0123551, filed Oct. 16, 2013, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a refrigerator having an ice-making tray which stores ice-making water, cools the ice-making water, and generates ice. 
     BACKGROUND ART 
     In general, a refrigerator is an appliance which includes storage compartments and cooling air supply units which supply cooling air to the storage compartments and thus maintains the freshness of stored food. The refrigerator may further include an ice-making chamber and an ice-making unit for generating ice. 
     An automatic ice-making unit includes an ice-making tray which stores ice-making water, an ejector which separates ice made by the ice-making tray, an ice-separating heater which heats the ice-making tray when the ice is separated from the ice-making tray, and an ice bucket which stores the ice separated from the ice-making tray. 
     Among ice-making methods for cooling ice-making water, a direct cooling method has a refrigerant pipe provided to extend into an ice-making chamber for cooling ice-making water and to be in contact with an ice-making tray. In such a direct cooling method, the ice-making tray receives cooling energy from the refrigerant pipe by thermal conduction. Accordingly, the direct cooling method has a merit in that a cooling speed of ice-making water is fast. However, when the cooling speed of ice-making water is excessively fast, ice which is not transparent and is turbid is generated. 
     DISCLOSURE 
     Technical Problem 
     The present invention is directed to providing an ice-making tray capable of generating ice of which transparency is improved by decreasing conductivity of cooling energy slightly, and a refrigerator having the same. Here, the ice-making tray is in contact with a refrigerant pipe, receives cooling energy from the refrigerant pipe by thermal conduction, and generates ice. At this time, the efficiency of a cooling function of an ice-making chamber by the ice-making tray, that is, the function in which the ice-making tray cools the ice-making chamber while exchanging heat with air in the ice-making chamber, does not decrease. 
     In addition, the present invention is also directed to providing an integrated ice-making tray in which the ice-making tray and related parts of the ice-making tray are integrated. 
     Technical Solution 
     One aspect of the present invention provides a refrigerator including: a main body; an ice-making chamber formed in the main body; a refrigerant pipe which is provided in the ice-making chamber and in which a refrigerant flows; and an ice-making tray which stores ice-making water and generates ice, wherein the ice-making tray includes: a first tray in contact with the refrigerant pipe to receive cooling energy from the refrigerant pipe; and a second tray having at least one ice-making cell which stores the ice-making water, coupled to overlap a top surface of the first tray to receive the cooling energy from the first tray, and formed of a material having a lower thermal conductivity than the first tray. 
     Here, the first tray may be formed of an aluminum material, and the second tray may be formed of a plastic material. 
     The cooling energy in the refrigerant pipe may sequentially pass through the first tray and the second tray, and may be transmitted to the ice-making water stored in the at least one ice-making cell. 
     At least one heat-transfer-area-reducing hole may be formed in the first tray to decrease a heat transfer area between the first tray and the refrigerant pipe such that a cooling speed of the ice-making water is delayed. 
     At least one auxiliary hole may be formed in the first tray to decrease a heat transfer area between the first tray and the second tray such that a cooling speed of the ice-making water is delayed. 
     At least one ice-making cell accommodating part which is provided to correspond to the at least one ice-making cell and accommodates the at least one ice-making cell may be formed in the first tray. 
     At least one heat exchanging rib may protrude at the first tray to expand an area through which heat transfers from the first tray to air in the ice-making chamber, and to facilitate cooling of the air in the ice-making chamber. 
     A refrigerant pipe accommodating part which accommodates the refrigerant pipe may be formed in the first tray. 
     An ice-separating heater accommodating part which accommodates an ice-separating heater configured to emit heat to separate the ice may be formed in the first tray. 
     Each of the first tray and the second tray may be integrally formed. 
     Another aspect of the present invention provides a refrigerator including: a main body; an ice-making chamber formed in the main body; a refrigerant pipe in which a refrigerant flows; an ice-making chamber fan configured to forcibly flow air in the ice-making chamber; and an ice-making tray which stores ice-making water and generates ice, wherein the ice-making tray includes: a first tray having a refrigerant pipe accommodating part which accommodates the refrigerant pipe; and a second tray having at least one ice-making cell which stores the ice-making water, and coupled to overlap a top surface of the first tray, and at least one heat-transfer-area-reducing hole is formed in the refrigerant pipe accommodating part of the first tray to decrease a heat transfer area between the first tray and the refrigerant pipe such that a cooling speed of the first tray is delayed. 
     Here, the second tray may be formed of a material having a lower thermal conductivity than the first tray. 
     Cooling energy in the refrigerant pipe may sequentially pass through the first tray and the second tray, and may be transmitted to the ice-making water stored in the at least one ice-making cell. 
     At least one ice-making cell accommodating part which is provided to correspond to the at least one ice-making cell and accommodates the at least one ice-making cell may be formed in the first tray. 
     At least one heat exchanging rib may protrude at the first tray to expand an area through which heat transfers from the first tray to air in the ice-making chamber, and to facilitate cooling of the air in the ice-making chamber. 
     Still another aspect of the present invention provides an ice-making tray which is in contact with a refrigerant pipe of a refrigerator, receives cooling energy, and generates ice, including: a first tray in which a refrigerant pipe accommodating part which accommodates the refrigerant pipe is formed at a lower portion thereof; and a second tray having at least one ice-making cell which stores ice-making water, coupled to overlap a top surface of the first tray, and formed of a material having a lower thermal conductivity than the first tray. 
     Here, at least one heat-transfer-area-reducing hole may be formed in the refrigerant pipe accommodating part of the first tray to decrease a heat transfer area between the first tray and the refrigerant pipe such that a cooling speed of ice-making water is delayed. 
     The second tray includes a fixing part which fixes the ice-making tray in the ice-making chamber. 
     The fixing part may include a groove part coupled to a hook part provided at a ceiling of an inner box of the ice-making chamber. 
     The fixing part may include a mounting part which is put on and supported by a supporting part provided in the ice-making chamber. 
     The fixing part may be formed at an upper outside of the ice-making cell of the second tray. 
     An upper side of the ice-making cell of the second tray may be open. 
     The second tray may include a water supply hole through which water is supplied to the ice-making chamber. 
     The first tray and the second tray may respectively include a first coupling part and a second coupling part which are respectively coupled to each other. 
     The first coupling part and the second coupling part may be respectively provided at sides of the first tray and the second tray, and may be elastically coupled to each other. 
     The refrigerator may further include: an ejector which rotates to separate ice in the ice-making cell; and an ice separating motor which supplies a rotational force to the ejector, wherein the second tray may include an air insulating part which insulates the ice-making tray from the ice separating motor. 
     The air insulating part may include an air accommodating part in which air is accommodated, and an air wall part protruding from the second tray such that the air accommodating part is formed. 
     The refrigerator may further include an ejector which rotates to separate ice in the ice-making cell, and has a rotating shaft and an ejector body protruding from the rotating shaft, wherein the second tray may include a plurality of rotating shaft supporting parts which rotatably support the rotating shaft. 
     The second tray may include a temperature sensor accommodating part in which a temperature sensor configured to measure a temperature of the ice-making cell is accommodated. 
     The second tray may include a separation preventing wall which extends upward from one end in a widthwise direction of the second tray to guide a movement of ice when the ice is separated from the ice-making cell, and a slit which blocks thermal conduction may be formed in the separation preventing wall. 
     The first tray may include at least one drain hole which drains defrosted water generated between contact parts of the first tray and the second tray. 
     The refrigerator may further include a drain duct provided under the ice-making tray to collect defrosted water of the ice-making tray, and to form a circulation flow path of cooling air, wherein the drain duct may include: a drain plate which collects defrosted water; a frost preventing cover which surrounds a lower portion of the drain plate to prevent frost from occurring in the drain plate; and an air insulating layer formed between the drain plate and the frost preventing cover. 
     Yet another aspect of the present invention provides a refrigerator including: a main body; an ice-making chamber formed in the main body; an ice-making tray which stores ice-making water, cools the ice-making water, and generates ice; an ejector rotatably provided to separate ice generated at the ice-making tray from the ice-making tray; and an ice separating motor which supplies a rotational force to the ejector, wherein the ice-making tray includes: an upper tray having an ice-making cell which stores ice-making water, and a rotating shaft accommodating part which rotatably accommodates a rotating shaft of the ejector; and a lower tray which is provided to overlap the upper tray at a lower side of the upper tray, and transmits cooling energy to the upper tray. 
     The lower tray may be provided to be in contact with a refrigerant pipe. 
     The upper tray may be formed of a material having a lower thermal conductivity than the lower tray. 
     The upper tray may be formed of a plastic material, and the lower tray may be formed of an aluminum material. 
     The upper tray may include a temperature sensor accommodating part in which a temperature sensor configured to measure a temperature of the ice-making cell is accommodated. 
     The upper tray may include an air insulating part which insulates the ice-making tray from the ice separating motor. 
     The upper tray may include a fixing part which fixes the ice-making tray in the ice-making chamber. 
     Advantageous Effects 
     According to the embodiments of the present invention, a direct cooling ice-making tray according to the present inventive concept can generate ice having improved transparency by decreasing a cooling speed of ice-making water slightly compared to a conventional direct cooling ice-making tray formed of only an aluminum material. In addition, the direct cooling ice-making tray according to the present inventive concept can still have a cooling speed faster than that of an indirect cooling method. 
     An ice-making tray according to the present inventive concept can be easily assembled using a method in which each of an aluminum tray and a plastic tray is integrally formed, and the plastic tray is simply disposed to overlap a top surface of the aluminum tray. 
     Since an aluminum tray having excellent thermal conductivity is disposed at a lower portion of a direct cooling ice-making tray according to the present inventive concept, and a heat exchanging rib which expands an area which transfers heat to air in an ice-making chamber is formed at the aluminum tray, the performance for cooling an inner portion of the ice-making chamber can be maintained the same as that of a conventional ice-making tray. 
     According to the present inventive concept, since related parts of an ice-making tray are integrally unified to the ice-making tray, and the number of the parts is decreased, assembly performance and productivity can be improved. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view illustrating an exterior of a refrigerator according to an embodiment of the present invention. 
         FIG. 2  is a schematic cross-sectional view illustrating an internal structure of the refrigerator of  FIG. 1 . 
         FIG. 3  is a schematic enlarged cross-sectional view illustrating a structure of an ice-making chamber of the refrigerator of  FIG. 1 . 
         FIG. 4  is an exploded view illustrating an ice-making tray of the refrigerator of  FIG. 1 . 
         FIG. 5  is a view illustrating an assembled ice-making tray of the refrigerator of  FIG. 1 . 
         FIG. 6  is a cross-sectional view illustrating a coupling relation among the ice-making tray, a refrigerant pipe, and an ice-separating heater of the refrigerator of  FIG. 1 . 
         FIG. 7  is a rear perspective view illustrating the coupling relation among the ice-making tray, the refrigerant pipe, and the ice-separating heater of the refrigerator of  FIG. 1 . 
         FIG. 8  is a rear view illustrating a first tray at a lower portion of the refrigerator of  FIG. 1 . 
         FIGS. 9 and 10  are views for describing a control method of an ice-making process of the refrigerator of  FIG. 1 . 
         FIG. 11  is a view illustrating an ice maker according to a second embodiment of the present invention. 
         FIG. 12  is an exploded view illustrating the ice maker of  FIG. 11 . 
         FIG. 13  is a cross-sectional view illustrating the ice maker of  FIG. 11 . 
         FIGS. 14 and 15  are top exploded perspective views illustrating an ice-making tray of the ice maker of  FIG. 11 . 
         FIG. 16  is a bottom exploded perspective view illustrating the ice-making tray of the ice maker of  FIG. 11 . 
         FIG. 17  is a view for describing a structure of an ice-making chamber for coupling the ice-making tray of  FIG. 11  to the ice-making chamber. 
         FIG. 18  is a cross-sectional view for describing an air insulating part of the ice-making tray of  FIG. 11 . 
         FIG. 19  is a plan view illustrating a lower portion tray of the ice-making tray of  FIG. 11 . 
         FIG. 20  is a view for describing an ice maker according to a third embodiment of the present invention. 
         FIG. 21  is a view for describing an ice maker according to a fourth embodiment of the present invention. 
     
    
    
     MODES OF THE INVENTION 
     Hereinafter, exemplary embodiments of the present invention will be described in detail. 
       FIG. 1  is a view illustrating an exterior of a refrigerator according to an embodiment of the present invention,  FIG. 2  is a schematic cross-sectional view illustrating an internal structure of the refrigerator of  FIG. 1 , and  FIG. 3  is a schematic enlarged cross-sectional view illustrating a structure of an ice-making chamber of the refrigerator of  FIG. 1 . 
     Referring to  FIGS. 1 to 3 , a refrigerator  1  according to an embodiment of the present invention may include a main body  2 , storage compartments  10  and  11  capable of keeping food refrigerated or frozen, an ice-making chamber  60  formed to be partitioned off from the storage compartments  10  and  11  by an ice-making chamber wall  61 , and a cooling unit  50  for supplying cold air to the storage compartments  10  and  11  and the ice-making chamber  60 . 
     The main body  2  may include an inner box  3  forming the storage compartments  10  and  11 , an outer box  4  coupled to an outside of the inner box  3  and forming the exterior, and an insulating material  5  foamed between the inner box  3  and the outer box  4 . 
     The storage compartments  10  and  11  may be formed such that a front surface thereof is open, and may be partitioned into a refrigerator compartment  10  at an upper side thereof and a freezer compartment  11  at a lower side thereof by a horizontal partition  6 . The horizontal partition  6  may include an insulation material for blocking heat exchange between the refrigerator compartment  10  and the freezer compartment  11 . 
     Shelves  9  on which food is put and which vertically divide a storage space of the refrigerator compartment  10  may be disposed in the refrigerator compartment  10 . The open front surface of the refrigerator compartment  10  may be hinge-coupled to the main body  2 , and be opened and closed by a pair of doors  12  and  13  which are rotatable. Handles  16  and  17  configured to open and close the doors  12  and  13  may be respectively provided at the doors  12  and  13 . 
     A dispenser  20  capable of dispensing ice from the ice-making chamber  60  to an outside thereof without opening a door  12  may be provided at the door  12 . The dispenser  20  may include an dispensing space  25  through which ice is dispensed, a lever  25  by which ice is determined whether to be dispensed or not, and a chute  22  which guides the ice discharged through an ice discharge hole  93  to the dispensing space  25 . 
     An open front surface of the freezer compartment  11  may be opened and closed by a sliding door  14  capable of sliding in the freezer compartment  11 . A storage box  19  capable of accommodating food may be provided at a rear surface of the sliding door  14 . A handle  18  configured to open and close the sliding door  14  may be provided at the sliding door  14 . 
     The cooling unit  50  may include a compressor  51  which compresses a refrigerant using high pressure, a condenser  52  which condenses the compressed refrigerant, expansion units  54  and  55  which expand the refrigerant to low pressure, evaporators  34  and  44  which evaporate the refrigerant and generate cold air, and a refrigerant pipe  56  which guides the refrigerant. 
     The compressor  51  and the condenser  52  may be disposed in a machine compartment  70  provided at a rear lower portion of the main body  2 . In addition, the evaporators  34  and  44  may be respectively disposed at a refrigerator compartment cold air supply duct  30  which is provided at the refrigerator compartment  10 , and a freezer compartment cold air supply duct  40  which is provided at the freezer compartment  11 . 
     The refrigerator compartment cold air supply duct  30  may include an inlet  33 , a cold air discharge hole  32 , and a blower fan  31 , and may circulate cold air in the refrigerator compartment  10 . In addition, the freezer compartment cold air supply duct  40  may include an inlet  43 , a cold air discharge hole  42 , and a blower fan  41 , and may circulate cold air in the freezer compartment  11 . 
     The refrigerant pipe  56  may be divided at one dividing position such that a refrigerant flows to the freezer compartment  11  or the refrigerant flows to the refrigerator compartment  10  and the ice-making chamber  60 , and a switching valve  53  which switches a flow path of the refrigerant may be installed at the dividing position. 
     A part  57  of the refrigerant pipe  56  may be disposed in the ice-making chamber  60  to cool the ice-making chamber  60 . The refrigerant pipe  57  disposed in the ice-making chamber  60  may be in contact with an ice-making tray  81 , and may directly supply cooling energy to the ice-making tray  81  by thermal conduction. 
     Hereinafter, the part  57  of the refrigerant pipe disposed in the ice-making chamber  60  to be in contact with the ice-making tray  81  is referred to as an ice-making chamber refrigerant pipe  57 . A refrigerant in a liquid state may pass through the expansion unit  55  to become a low temperature and low pressure state, flow in the ice-making chamber refrigerant pipe  57  to absorb heat in the ice-making tray  81  and the ice-making chamber  60 , and evaporate in a gas state. Accordingly, the ice-making chamber refrigerant pipe  57  and the ice-making tray  81  may serve as an evaporator in the ice-making chamber  60 . 
     An ice maker includes the ice-making tray  81  which stores ice-making water, an ejector  84  which separates ice from the ice-making tray  81 , an ice separating motor  82  which rotates the ejector  84 , an ice-separating heater  87  which heats the ice-making tray  81  to separate ice easily when the ice is separated from the ice-making tray  81 , an ice bucket  90  which stores ice generated by the ice-making tray  81 , a drain duct  83  which collects defrosted water of the ice-making tray  81  and simultaneously guides an air flow in the ice-making chamber  60 , and an ice-making chamber fan  97  which circulates air in the ice-making chamber  60 . 
     The ice bucket  90  is disposed under the ice-making tray  81  to collect ice which falls from the ice-making tray  81 . The ice bucket  90  is provided with an auger  91  which transfers stored ice to the ice discharge hole  93 , an auger motor  95  which drives the auger  91 , and a grinding unit  94  capable of grinding ice. 
     The auger motor  95  may be disposed at a rear of the ice-making chamber  60 , and the ice-making chamber fan  97  may be disposed above the auger motor  95 . A guiding path  96  which guides air discharged from the ice-making chamber fan  97  toward a front side of the ice-making chamber  60  may be provided above the ice-making chamber fan  97 . 
     Air which forcibly flows by the ice-making chamber fan  97  may circulate in the ice-making chamber  60  in an arrow direction denoted in  FIG. 3 . That is, the air discharged upward from the ice-making chamber fan  97  may flow through the guiding path  96  and may flow between the ice-making tray  81  and the drain duct  83 . At this time, the air may exchange heat with the ice-making tray  81  and the ice-making chamber refrigerant pipe  57 , and the cooled air may flow to a side of the ice discharge hole  93  of the ice bucket  90  and may be suctioned by the ice-making chamber fan  97 . 
     A lower portion of the ice-making tray  81  according to an embodiment of the present invention may include a first tray  100  (see  FIG. 4 ) formed of an aluminum material, which will be described below. Since a heat exchanging rib  180  (see  FIG. 6 ), which expands an area which transfers heat to air in the ice-making chamber  60 , is provided at the first tray  100 , the efficiency of exchanging heat of internal air between the ice-making tray  81  and the ice-making chamber  60  is increased, and accordingly, an inner portion of the ice-making chamber  60  may be efficiently maintained to be cooled and chilled. 
       FIG. 4  is an exploded view illustrating an ice-making tray of the refrigerator of  FIG. 1 ,  FIG. 5  is a view illustrating an assembled ice-making tray of the refrigerator of  FIG. 1 ,  FIG. 6  is a cross-sectional view illustrating a coupling relation among the ice-making tray, a refrigerant pipe, and an ice-separating heater of the refrigerator of  FIG. 1 ,  FIG. 7  is a rear perspective view illustrating the coupling relation among the ice-making tray, the refrigerant pipe, and the ice-separating heater of the refrigerator of  FIG. 1 , and  FIG. 8  is a rear view illustrating a first tray at a lower portion of the refrigerator of  FIG. 1 . 
     Referring to  FIGS. 4 to 8 , the ice-making tray  81  according to an embodiment of the present invention includes the first tray  100  which is in contact with the refrigerant pipe  57 , receives cooling energy from the refrigerant pipe  57  by thermal conduction, and is positioned at a lower portion thereof, and a second tray  200  which is coupled to overlap a top surface of the first tray  100  to receive the cooling energy from the first tray  100 , and includes at least one ice-making cell  210  which stores ice-making water. 
     In the above-described structure, cooling energy is sequentially transferred from the refrigerant pipe  57  through the first tray  100  to the second tray  200 , ice-making water stored in the ice-making cell  210  of the second tray  200  may be cooled, and ice may be generated. 
     The first tray  100  includes an ice-making cell accommodating part  110  concavely formed to accommodate the ice-making cell  210  of the second tray  200 , a first base part  120  forming the ice-making cell accommodating part  110 , a separation preventing wall  140  which extends upward from one end in a widthwise direction of the first base part  120  and guides a movement of ice when the ice is separated from the ice-making cells  210 , a cutting rib  132  capable of cutting links between ice pieces generated in the ice-making cells  210  when the ice pieces are separated from the ice-making cells  210 , a water supply hole  160  provided at one end in a lengthwise direction to receive water, and an excessively supplied water discharge hole  150  which discharges excessively supplied water to the drain duct  83  when the ice-making cell  210  is supplied with water more than a predetermined amount of water. 
     The ice-making cell accommodating part  110  has a shape corresponding to the ice-making cell  210  to accommodate the ice-making cell  210 . The number of ice-making cell accommodating parts  110  are equal to that of the ice-making cells  210 . The ice-making cell accommodating parts  110  are partitioned each other by first partition parts  130 . First communication parts  131  which enable the ice-making cells  210  to communicate with each other are provided at the first partition parts  130 . 
     At least one heat exchanging rib  180  which expands an area which transfers heat to air in the ice-making chamber  60 , and facilitates heat exchange of internal air between the first tray  100  and the ice-making chamber  60  may protrude at a lower portion of the first tray  100 . 
     In addition, a refrigerant pipe accommodating part  190  (see  FIG. 6 ) which accommodates the ice-making chamber refrigerant pipe  57 , and an ice-separating heater accommodating part  191  (see  FIG. 6 ) which accommodates the ice-separating heater  87  may be formed at an outside of the lower portion of the first tray  100 . Each of the refrigerant pipe accommodating part  190  and the ice-separating heater accommodating part  191  may have a concave shape. The refrigerant pipe accommodating part  190  and the ice-separating heater accommodating part  191  may be formed between the heat exchanging ribs  180 . 
     Each of the ice-making chamber refrigerant pipe  57  and the ice-separating heater  87  may be provided in an approximately U shape, and the refrigerant pipe accommodating part  190  and the ice-separating heater accommodating part  191  of the first tray  100  may also have an approximately U shape to correspond thereto. The refrigerant pipe accommodating part  190  may be provided in the ice-separating heater accommodating part  191 . 
     The refrigerant pipe  57  may be accommodated in the refrigerant pipe accommodating part  190  to be in contact therewith, and the ice-separating heater  87  may be accommodated in the ice-separating heater accommodating part  191  to be in contact therewith. 
     Such a first tray  100  may be formed of a material having high thermal conductivity to accelerate thermal conduction of cooling energy. For example, the first tray  100  may be formed of an aluminum material. The first tray  100  may be integrally formed. 
     The second tray  200  may be coupled to be pressed against a top surface of the first tray  100 . As the second tray  200  is simply put on the top surface of the first tray  100 , the second tray  200  may be coupled to the first tray  100 . 
     The second tray  200  may include the at least one ice-making cell  210  which stores ice-making water, a second base part  220  forming the at least one ice-making cell  210 , second partition parts  230  which partition the ice-making cells  210  from each other, and second communication parts  231  which enable the ice-making cells  210  to communicate with each other to supply water to all of the ice-making cells  210  when the water is supplied. 
     When the ice-making speed of ice-making water is excessively high, a gas such as oxygen or carbon dioxide and other impurities melted in the ice-making water are not discharged, and a turbidity phenomenon in which ice is turbid may occur. 
     In order to solve the above-described turbidity phenomenon, the second tray  200  of the ice-making tray  81  according to an embodiment of the present invention is formed of a material having low thermal conductivity. For example, the second tray  200  may be formed of a plastic material. As a result, as the speed of thermal conduction of cooling energy decreases, the cooling speed of ice-making water may decrease, and accordingly, transparency of ice may be improved. 
     However, materials of the first tray  100  and the second tray  200  are not respectively limited to an aluminum material and a plastic material, and as long as the second tray  200  is formed of a material which has a lower thermal conductivity than that of the first tray  100 , it may be consistent with the scope of the present invention. 
     That is, materials of the first tray  100  and the second tray  200  may be properly selected as long as the first tray  100  positioned thereunder is formed with a comparatively high thermal conductivity and effectively serves as a heat exchanger which cools the ice-making chamber  60 , the second tray  200  positioned thereabove decreases a speed of thermal conduction of cooling energy slightly, and thus ice whose transparency is improved is generated. 
     The second tray  200  may be integrally formed. Accordingly, since each of the above-described first tray  100  and second tray  200  are formed, and the second tray  200  is simply coupled to overlap the top surface of the first tray  100 , the ice-making tray  81  may be easily assembled, and thus all objectives of maintaining cooling performance in the ice-making chamber  60  and improving transparency of ice may be achieved. 
     In the above description, as the second tray  200  is formed of a material having a lower thermal conductivity than that of the first tray  100 , a speed of thermal conduction of cooling energy and a speed of cooling ice-making water may be delayed, but, alternatively or additionally, as a heat transfer area of the ice-making chamber refrigerant pipe  57  and the first tray  100  is decreased, a speed of thermal conduction of cooling energy and a speed of cooling ice-making water may be delayed. 
     To this end, a heat-transfer-area-reducing hole  170  (see  FIGS. 6 and 8 ) which reduces a heat transfer area of the refrigerant pipe  57  may be formed at a portion in contact with the refrigerant pipe  57  of the first tray  100 . That is, the heat-transfer-area-reducing hole  170  may be formed at the refrigerant pipe accommodating part  190  of the first tray  100 . 
     The heat-transfer-area-reducing hole  170  may be formed to penetrate the first base part  120  of the first tray  100 . Accordingly, not only a heat transfer area of the refrigerant pipe  57  and the first tray  100  may be decreased but also a heat transfer area of the first tray  100  and the second tray  200  may also be decreased by the heat-transfer-area-reducing hole  170 . 
     At least two or more of the heat-transfer-area-reducing holes  170  may be formed at the refrigerant pipe accommodating part  190  to be spaced apart from each other, or one of the heat-transfer-area-reducing hole  170  may also be continuously formed unlike the present embodiment. 
     At least one auxiliary hole  171  which decreases the heat transfer area of the first tray  100  and the second tray  200  may be additionally provided at the first base part  120  of the first tray  100  excluding the refrigerant pipe accommodating part  190 . As the heat transfer area of the first tray  100  and the second tray  200  is decreased, a speed of thermal conduction of cooling energy from the second tray  200  to the first tray  100  may be delayed, and thus, an ice-making speed of ice-making water may also be delayed. 
     In addition, the auxiliary hole  171  may drain defrosted water of frost frosted between the first tray  100  and the second tray  200 . 
     With the above-described structure, the ice-making tray  81  may receive cooling energy from the ice-making chamber refrigerant pipe  57  by the direct cooling method, and may quickly generate ice, and ice having improved transparency may be obtained compared to a conventional ice-making tray. In addition, the same cooling performance of the ice-making chamber  60  of the ice-making tray  81  as that of a conventional ice-making tray may be maintained. 
       FIGS. 9 and 10  are views for describing a control method of an ice-making process of the refrigerator of  FIG. 1 . 
     A control method of an ice-making process of the refrigerator of  FIG. 1  will be described with reference to  FIGS. 9 and 10 . Hereinafter, a control method illustrated in  FIG. 9  is referred to as a first control method, and a control method illustrated in  FIG. 10  is referred to as a second control method. 
     As illustrated in  FIG. 9 , an entire ice-making process of the ice maker may include a first operation (cooling and water supply delay operation), a second operation (cooling and ice-making operation), and a third operation (heating and ice-separating operation). 
     In the first operation (cooling and water supply delay operation), a refrigerant may be supplied to the ice-making chamber refrigerant pipe  57 , and the ice-making chamber fan  97  may be operated. Accordingly, cooling air generated from the ice-making chamber refrigerant pipe  57  may forcibly flow by the ice-making chamber fan  97  to cool the ice-making chamber  60 . 
     When a predetermined water supply delay time is passed, the second operation (cooling and ice-making operation) may start. 
     Water may be supplied to the ice-making tray  81  at an initial stage of the second operation (cooling and ice-making operation). In the second operation (cooling and ice-making operation), a refrigerant may be supplied to the ice-making chamber refrigerant pipe  57 , and the ice-making chamber fan  97  may be operated. Accordingly, a part of cooling air generated in the ice-making chamber refrigerant pipe  57  may be transferred to the ice-making tray  81 , and make ice with the water supplied to the ice-making tray  81 , and the remaining part may cool the inner portion of the ice-making chamber  60 . 
     When the ice making is completed with the water supplied to the ice-making tray  81 , the third operation (heating and ice-separating operation) may start. 
     In the third operation (heating and ice-separating operation), supply of the refrigerant to the ice-making chamber refrigerant pipe  57  may stop, the operation of the ice-making chamber fan  97  may stop, and the ice-separating heater  87  may generate heat. When ice adhered to the ice-making tray  81  is slightly melt by heat generated from the ice-separating heater  87 , the ice separating motor  82  may be operated and the ejector  84  may rotate. As the ejector  84  rotates, the ice in the ice-making tray  81  may be separated from the ice-making tray  81  to fall into the ice bucket  90 . 
     A cycle of the entire ice-making process (ice-separating cycle T) of the ice maker may correspond to a sum of a first operation operating time T 1 , a second operation operating time T 2 , and a third operation operating time T 3 . 
     Although an operating time S 2  of a second operation (cooling and ice-making operation) of the second control method illustrated in  FIG. 10  may be greater than that of the first control method illustrated in  FIG. 9 , a cycle of the entire ice-making process (ice-separating cycle S) may be the same as that of the first control method (S 2 &gt;T 2 , S=T). 
     The reason is that an operating time S 1  of a first operation (cooling and water supply delay operation) of the second control method is less than the operating time T 1  of the first operation (cooling and water supply delay operation) of the first control method (S 1 &lt;T 1 ). Operating times of third operations (heating and ice-separating operation) in the first control method and the second control method are assumed to be the same (S 3 =T 3 ). 
     That is, when an ice-making speed is delayed, the operating time of the second operation (cooling and ice-making operation) is increased, and at this time, by decreasing the operating time of the first operation (cooling and water supply delay operation), the same cycle of the entire ice-making process may be maintained. 
     In addition, although the operating time of the first operation (cooling and water supply delay operation) in the second control method is decreased as described above, cooling performance of the ice-making chamber  60  is not lowered compared to that of the first control method. The reason is that cooling of the ice-making chamber  60  is performed at both of the first operation (cooling and water supply delay operation) and the second operation (cooling and ice-making operation), and sums of the operating times of the first operations (cooling and water supply delay operation) and the operating times of the second operations (cooling and ice-making operation) in the first control method and the second control method are the same (S 1 +S 2 =T 1 +T 2 ). 
     That is, in the first control method and the second control method, cooling energy generated from the ice-making chamber refrigerant pipe  57  during the entire operating times of the first operation and the second operation may be the same, cooling energy, among the cooling energy, which is used for ice making with water of the ice-making tray  81  may be the same, and as a result, cooling energy used for cooling the ice-making chamber  60  may also be the same. 
     As a result, since the ice-making tray  81  according to an embodiment of the present invention is provided to decrease an ice-making speed to improve the transparency of ice, the cycle of the entire ice-making process (ice-separating cycle) may be maintained in the same extent compared to a conventional process as well as the transparency of ice is improved through a control method which decreases the operating time of the first operation (cooling and water supply delay operation) compared to the conventional process. 
       FIG. 11  is a view illustrating an ice maker according to a second embodiment of the present invention,  FIG. 12  is an exploded view illustrating the ice maker of  FIG. 11 ,  FIG. 13  is a cross-sectional view illustrating the ice maker of  FIG. 11 ,  FIGS. 14 and 15  are top exploded perspective views illustrating an ice-making tray of the ice maker of  FIG. 11 ,  FIG. 16  is a bottom exploded perspective view illustrating the ice-making tray of the ice maker of  FIG. 11 ,  FIG. 17  is a view for describing a structure of an ice-making chamber for coupling the ice-making tray of  FIG. 11  to the ice-making chamber,  FIG. 18  is a cross-sectional view for describing an air insulating part of the ice-making tray of  FIG. 11 , and  FIG. 19  is a plan view illustrating a lower portion tray of the ice-making tray of  FIG. 11 . 
     An ice maker according to a second embodiment of the present invention will be described with reference to  FIGS. 11 to 19 . The same reference number as the first embodiment refers to the same component in the drawings and the detail description may be omitted. 
     An ice maker may include an ice-making tray  281  which stores and cools ice-making water to generate ice, an ejector  84  which separates ice from the ice-making tray  281 , an ice separating motor part  540  which rotates the ejector  84 , a slider  88  having a guide  89  formed to be inclined to guide ice separated by the ejector  84  to one side in a widthwise direction of the ice-making tray  281 , an ice-separating heater  87  which heats the ice-making tray  281  to easily separate ice when the ice is separated from the ice-making tray  281 , an ice bucket  90  which stores ice generated from the ice-making tray  281 , and a drain duct  500  which collects defrosted water of the ice-making tray  281  and simultaneously guides an air flow in an ice-making chamber  60 . 
     The ice-making tray  281  includes a first tray  300  which is in contact with a refrigerant pipe  57 , receives cooling energy from the refrigerant pipe  57  by thermal conduction, and is positioned at a lower portion thereof, and a second tray  400  which is coupled to overlap a top surface of the first tray  300  to receive cooling energy from the first tray  300 , and includes at least one ice-making cell  410  which stores ice-making water. 
     Since the first tray  300  is provided under the second tray  400 , the first tray  300  may be referred to as a lower tray, and the second tray  400  may be referred to as an upper tray. 
     Cooling energy generated from the refrigerant pipe  57  is transferred through the first tray  300  to the second tray  400 , ice-making water stored in the ice-making cell  410  of the second tray  400  may be cooled, and ice may be generated. 
     The first tray  300  may include an ice-making cell accommodating part  310  concavely formed to accommodate the ice-making cell  410  of the second tray  400 , and a first base part  320  forming the ice-making cell accommodating part  310 . 
     The ice-making cell accommodating part  310  of the first tray  300  may have a shape corresponding to the ice-making cell  410  to accommodate the ice-making cell  410  of the second tray  400 . The number of ice-making cell accommodating parts  310  may be equal to that of the ice-making cells  410 . The ice-making cell accommodating parts  310  may be partitioned from each other by first partition parts  330 . First communication parts  331  which enable the ice-making cells  410  to communicate with each other may be provided at the first partition parts  330 . Ice-making water may be sequentially supplied to the adjacent ice-making cells  410  through the first communication parts  331 . 
     At least one heat exchanging rib  380  which expands an area which transfers heat to air in the ice-making chamber  60 , and facilitates heat exchange of internal air between the first tray  300  and the ice-making chamber  60  may protrude at a lower portion of the first tray  300 . 
     A refrigerant pipe accommodating part  390  (see  FIG. 13 ) which accommodates the ice-making chamber refrigerant pipe  57 , and an ice-separating heater accommodating part  391  (see  FIG. 13 ) which accommodates the ice-separating heater  87  may be formed at an outside of the lower portion of the first tray  300 . Each of the refrigerant pipe accommodating part  390  and the ice-separating heater accommodating part  391  may have a concave shape. The refrigerant pipe accommodating part  390  and the ice-separating heater accommodating part  391  may be formed between the heat exchanging ribs  380 . 
     Each of the ice-making chamber refrigerant pipe  57  and the ice-separating heater  87  may be provided in an approximately U shape (see  FIG. 12 ), and the refrigerant pipe accommodating part  390  and the ice-separating heater accommodating part  391  of the first tray  300  may also have an approximately U shape to correspond thereto. The refrigerant pipe accommodating part  390  may be provided in the ice-separating heater accommodating part  391 . 
     The refrigerant pipe  57  may be accommodated in the refrigerant pipe accommodating part  390  to be in contact with the first tray  300 , and the ice-separating heater  87  may be accommodated in the ice-separating heater accommodating part  391  to be in contact with the first tray  300 . 
     The first tray  300  may be formed of a material having high thermal conductivity to accelerate thermal conduction of cooling energy. For example, the first tray  300  may be formed of an aluminum material. The first tray  300  may be integrally formed. 
     Drain holes  392  (see  FIGS. 13 and 19 ) which drain defrosted water of frost frosted between the first tray  300  and the second tray  400  may be formed at the first tray  300 . The drain hole  392  may be formed at each of the ice-making cell accommodating parts  310  of the first tray  300 . 
     The above-described drain hole  392  may decrease a heat transfer area of the first tray  300  and the second tray  400 , and may serve as a function which decreases an ice-making speed similar to the auxiliary hole  171  (see  FIG. 8 ). 
     The second tray  400  may be coupled to be pressed against the top surface of the first tray  300 . As the second tray  400  is simply put on the top surface of the first tray  300 , the second tray  400  may be coupled to the first tray  300 . 
     However, a first coupling part  370  may be provided at the first tray  300  and a second coupling part  480  may be provided at the second tray  400  to increase a coupling force between the first tray  300  and the second tray  400 . 
     The first coupling part  370  and the second coupling part  480  may be respectively provided at a side surface of the first tray  300  and a side surface of the second tray  400 . The first coupling part  370  and the second coupling part  480  may be elastically coupled to each other. The first coupling part  370  may include a coupling protrusion  371  (see  FIG. 15 ) and the second coupling part  470  may include a coupling groove  481  (see  FIG. 15 ) to which the coupling protrusion  371  is coupled. 
     The second tray  400  may include the at least one ice-making cell  410  which stores ice-making water, a second base part  420  forming the at least one ice-making cell  410 , second partition parts  430  which partition the ice-making cells  410  from each other, and second communication parts  431  which enable the ice-making cells  410  to communicate with each other to supply water to all of the ice-making cells  410  when the water is supplied. 
     The second tray  400  may include a separation preventing wall  440  which extends upward from one end of a side surface in a widthwise direction of the second base part  420  to guide a movement of ice when the ice is separated from the ice-making cell  410 . When the ejector  84  rotates and lifts ice of the ice-making cell  410 , the separation preventing wall  440  may prevent the ice from falling to the other side opposite to one side in which the slider  88  is provided (see  FIG. 13 ). A slit  441  which prevents heat from vertically transferring through the separation preventing wall  440  may be formed at the separation preventing wall  440 . The slit  441  may be formed long in a horizontal direction at the separation preventing wall  440 . 
     The second tray  400  may include cutting ribs  432  which cut links between ice pieces generated in the ice-making cells  410  when the ice pieces are separated from the ice-making cell  410 . 
     The second tray  400  may include a water supplying hole  460  provided at one end in a lengthwise direction to supply water to the ice-making cell  410 . As the second tray  400  is provided to be inclined, water introduced through the water supplying hole  460  may be sequentially supplied from the ice-making cell  410  most adjacent to the water supplying hole  460  to the ice-making cell  410  farthest therefrom. 
     The second tray  400  may include an excessively supplied water discharge hole  450  (see  FIG. 15 ) which discharges excessively supplied water through the drain duct  500  when the ice-making cell  410  is supplied with water more than a predetermined amount of water. The excessively supplied water discharge hole  450  may be formed at one position of the separation preventing wall  440 . 
     The second tray  400  may include a structure which supports the ejector  84 , which separates ice generated in the ice-making cell  410 . The second tray  400  may include rotating shaft accommodating parts  401  and  402  which rotatably accommodate a rotating shaft  85  of the ejector  84 . The rotating shaft accommodating parts  401  and  402  may be respectively formed at a front end and a rear end of the second tray  400  in a lengthwise direction. 
     The second tray  400  may include a temperature sensor accommodating part  403  which accommodates a temperature sensor  600  which measures temperature of water or ice accommodated in the ice-making cell  410 . The temperature sensor accommodating part  403  may be formed at one end of the second tray  400  in a lengthwise direction, and accordingly, the temperature sensor  600  may measure temperature of water or ice accommodated in the ice-making cell  410  most adjacent to the one end of the second tray  400  in a lengthwise direction. 
     The second tray  400  may include an air insulating part  490  which insulates the ice-making tray  281  from an ice separating motor  541  (see  FIGS. 16 and 18 ). Since the air insulating part  490  insulates the ice-making tray  281  from the ice separating motor  541 , malfunction of the ice separating motor  541  and unnecessary heat loss may be prevented. 
     The air insulating part  490  may include an air wall part  492  which protrudes from a front end of the second tray  400  in a lengthwise direction, and an air accommodating part  491  formed in the air wall part  492 . A side surface of the air wall part  492  may be formed in a closed loop shape, and a front surface of the air wall part  492  may be open. The open front surface of the air wall part  492  may be closed by an ice separating motor case  541  which accommodates the ice separating motor  541 . Accordingly, an inner portion of the air accommodating part  491  may be a closed space. As the air accommodating part  491  is filled with air, the air accommodating part  491  may insulate the ice-making tray  281  from the ice separating motor  541 . 
     The ice separating motor case  542  may be formed by coupling a front case  544  and a rear case  543 , and the air wall part  492  may be provided to be pressed against the rear case  543 . An ice separating motor part  540  may include the ice separating motor  541  and the ice separating motor case  541 . 
     The second tray  400  may include a fixing part which fixes the ice-making tray  281  in the ice-making chamber  60 . That is, the ice-making tray  281  may be directly fixed in the ice-making chamber  60  without an additional fixing member. 
     The fixing part may couple the second tray  400  to a ceiling of an inner box  3  (see  FIG. 17 ) of the ice-making chamber  60 . To this end, the fixing part may include a groove part  471  coupled to a hook part  3   a  provided at the ceiling of the inner box  3  of the ice-making chamber  60 . 
     The groove part  471  may include a large diameter part  472  which is comparatively large, and a small diameter part  473  which is comparatively small. The large diameter part  472  may have a size through which the hook part  3   a  may enter, and the small diameter part  473  may have a size through which the hook part  3   a , which passed through the large diameter part  472 , may not move out. 
     When the ice-making tray  281  is inserted into the ice-making chamber  60 , the hook part  3   a  may be inserted into the large diameter part  472  of the second tray  400 , and may move toward the small diameter part  473 . Since the hook part  3   a  which moves toward the small diameter part  473  is not separated from the small diameter part  473 , the ice-making tray  281  may be fixed to the ice-making chamber  60 . 
     The fixing part may include a mounting part  474  in which the second tray  400  is put on a supporting part  98  provided at the ice-making chamber  60  and is supported thereby. The supporting part  98  may also be integrally formed with the inner box  3  of the ice-making chamber  60 , and may also be formed in a separate structure provided in the ice-making chamber  60 . 
     The above-described fixing part may be formed at a front outside or a rear outside of an upper portion of the ice-making cell  410  of the second tray  400 . That is, the upper portion of the ice-making cell  410  of the second tray  400  may be open. The reason is that injection molding of the second tray  400  in which the fixing part is integrally formed is performed easily. When the fixing part is not positioned at an outside of the upper portion of the ice-making cell  410  of the second tray  400  but is positioned at a direct upper portion thereof, it may not be easy to inject the second tray  400  using a general mold. 
     In the above-described structure, according to an embodiment of the present invention, an ice-making speed of the ice-making tray  281  is delayed and transparency of ice is improved. In addition, components of related parts of the ice-making tray  281  are integrally formed with the ice-making tray  281 , the number of components is decreased, and thus performance of assembly and productivity may be improved. 
     The drain duct  500  may be provided under the ice-making tray  281  and collect defrosted water fallen from the ice-making tray  281  or the ice-making chamber refrigerant pipe  57 . A flow path for cold air may be formed between the ice-making tray  281  and the drain duct  500 . 
     The drain duct  500  may include a drain plate  510  which collects defrosted water, and a frost preventing cover  520  which surrounds a lower portion of the drain plate  510  to prevent freezing of the drain plate  510 . 
     The drain plate  510  may be disposed to be inclined such that collected water flows toward a drain hole. 
     The drain plate  510  may include a refrigerant pipe fixing part  515  which presses the ice-making chamber refrigerant pipe  57  and presses and fixes the ice-making chamber refrigerant pipe  57  against and to the bottom surface of the first tray  300 . The refrigerant pipe fixing part  515  may include a protrusion  515   a  which protrudes upward from the drain plate  510 , and an elastic part  515   b  provided at an end portion of the protrusion  515   a . The elastic part  515   b  may be formed of a rubber material. Since the elastic part  515   b  has an elastic force, the elastic part  515   b  smoothly presses the ice-making chamber refrigerant pipe  57 , and accordingly, prevents damage of the ice-making chamber refrigerant pipe  57  from impact. In addition, the elastic part  515   b  may prevent cold air from being directly transferred from the ice-making chamber refrigerant pipe  57  to the drain plate  510 , and may prevent frost from occurring at the drain plate  510 . 
     The drain plate  510  may include an ice-separating heater contact part  516  which is in contact with the ice-separating heater  87 , fixes the ice-separating heater  87 , and receives heat from the ice-separating heater  87 . Since heat of the ice-separating heater  87  is transferred through the ice-separating heater contact part  516  to the drain plate  510 , frost is prevented from occurring at the drain plate  510 , and, even when frost occurs, the frost may be easily defrosted. 
     The frost preventing cover  520  may be formed of a plastic material having a low thermal conductivity. 
     An air insulating layer  530  which insulates the drain plate  510  from the frost preventing cover  520  may be formed between the drain plate  510  and the frost preventing cover  520 . That is, the drain plate  510  and the frost preventing cover  520  are provided to be spaced a predetermined gap from each other, and air may be filled therebetween. 
       FIG. 20  is a view for describing an ice maker according to a third embodiment of the present invention, and  FIG. 21  is a view for describing an ice maker according to a fourth embodiment of the present invention. 
     An ice maker according to third and fourth embodiments of the present invention will be described with reference to  FIGS. 20 and 21 . Structures which are the same as those of the previously described embodiments may be omitted. 
     Although the fixing part which fixes the ice-making tray  281  in the ice-making chamber  60 , the air insulating part  490  which insulates the ice-making tray  281  from the ice separating motor part  540 , the rotating shaft accommodating parts  401  and  402  which rotatably accommodate the rotating shaft  85  of the ejector  84 , and the temperature sensor accommodating part  403  which accommodates the temperature sensor  600  are integrally formed in the second tray  400  according to the second embodiment, unlike the above-description, an air insulating part  690  which insulates an ice-making tray from an ice separating motor, rotating shaft accommodating parts  601  and  602  which rotatably accommodate a rotating shaft  85  of an ejector  84 , and a temperature sensor accommodating part which accommodates a temperature sensor may be integrally formed in an second tray  600 , and a fixing part  700  which fixes the ice-making tray in an ice-making chamber  60  may be separately formed from the second tray  400 . 
     An ice-making cell  610  in which water is stored, and a water supply hole  660  which supplies the water to the ice-making cell  610  may be formed in the second tray  600 . The air insulating part  690  may include an air accommodating part  691  which accommodates air, and an air wall part  692  protruding such that the air accommodating part  691  is formed. 
     A non-described reference character  500  means a first tray coupled to overlap a lower portion of the second tray  600  and transfers cooling energy. 
     Unlike the above-description, rotating shaft accommodating parts  901  and  902  which rotatably accommodate a rotating shaft  85  of an ejector  84 , and a temperature sensor accommodating part which accommodates a temperature sensor may be integrally formed in a second tray  900 , and a fixing part  1000  which fixes an ice-making tray in an ice-making chamber  60 , an air insulating part  1100  which insulates the ice-making tray from an ice separating motor may also be separately formed from the second tray  900 . 
     An ice-making cell  910  in which water is stored, and a water supply hole  960  which supplies the water to the ice-making cell  910  may be formed in the second tray  900 . The air insulating part  1100  may include an air accommodating part  1101  which accommodates air, and an air wall part  1102  protruding such that the air accommodating part  1101  is formed. 
     A non-described reference character  800  means a first tray which is coupled to overlap a lower portion of the second tray  800 , and transfers cooling energy to the second tray  800 . 
     Although the technological scope of the above-described present invention is described with specific embodiments, the scope of the present invention is not limited to the above-described specific embodiments. Various other embodiments that may be changed or modified by those skilled in the art without departing from the scope and spirit of the present invention defined by the appended claims fall within the scope of the present invention.