Patent Publication Number: US-9897371-B2

Title: Refrigerator

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The application claims priority under 35 U.S.C. § 119 and 35 U.S.C. § 365 to Korean Patent Application No. 10-2016-0015032, filed Feb. 5, 2016, the entire contents of which is hereby incorporated by reference. 
     TECHNICAL FIELD 
     The present application generally relates to technologies about a refrigerator. 
     BACKGROUND 
     A refrigerator is an electric home appliance to store food in a refrigerated state or in a frozen state. 
     In recent years, the capacity of refrigerators has increased, and a home bar, an ice maker, a shelf, or a door box has been mounted on the rear of a door of the refrigerator. In this type of refrigerator, when the door is closed, the components mounted on the rear of the door may interfere with a shelf or a drawer mounted in a storage compartment of a main body of the refrigerator. 
     In order to prevent this interference, the front end of a drawer mounted in the storage compartment (e.g., a refrigerating compartment or a freezing compartment) is located at a place spaced apart from the front of the main body by a predetermined distance. 
     SUMMARY 
     In general, one innovative aspect of the subject matter described in this specification can be embodied in a refrigerator including: a cabinet that includes a storage compartment and an opening on a first surface of the storage compartment; a door that is coupled to the cabinet and that is configured to open or close the opening; a first drawer that is located in the storage compartment and that is configured to store food; a plurality of rollers, each of the plurality of rollers being coupled to a first side of the first drawer or a second side of the first drawer; a plurality of first support rails, each of the plurality of first support rails (i) being coupled to a first side of the storage compartment or a second side of the storage compartment and (ii) being configured to guide one or more of the plurality of rollers; a base that is located at a third side of the first drawer in the storage compartment and that is configured to move between a first position and a second position; and a withdrawal unit that is configured to move the base between the first position and the second position based on movement of the door, wherein each of the base or the first drawer respectively includes either a connection protrusion or a protrusion insertion groove, the connection protrusion being coupled to the protrusion insertion groove based on a distance between the first drawer and the base, wherein, based on coupling between the connection protrusion and the protrusion insertion groove, the base is configured to move together with the first drawer, wherein each of the plurality of first support rails includes an inclined section that is configured to (i) guide one or more of the plurality of rollers and (ii) gradually change a height of the first drawer as one or more rollers of the plurality of rollers move in the inclined section, and wherein, based on the height of the first drawer, the connection protrusion is separated from the protrusion insertion groove. 
     The foregoing and other embodiments can each optionally include one or more of the following features, alone or in combination. In particular, one embodiment includes all the following features in combination. Each of the plurality of first support rails further includes: a first section that extends from a first portion of the inclined section. Each of the plurality of first support rails further includes: a second section that extends from a second portion of the inclined section. The connection protrusion protrudes from a first surface of the base and the protrusion insertion groove is located on a first surface of the first drawer. A first end of the first drawer is located in the storage compartment based on each of the plurality of rollers being located in at least one inclined section of the plurality of first support rails. The connection protrusion protrudes from the first surface of the first drawer and the protrusion insertion groove is located on the first surface of the base. A first end of the first drawer is located in the storage compartment based on one or more of the plurality of rollers being located in at least one inclined section of the plurality of first support rails. The refrigerator further includes a second drawer that is located at a fourth side of the first drawer in the storage compartment and that is configured to store food; a plurality of second rollers, each of the plurality of second rollers being coupled to a first side of the second drawer or a second side of the second drawer; a plurality of second support rails, each of the plurality of second support rails (i) being coupled to the first side of the storage compartment or the second side of the storage compartment and (ii) being configured to guide one or more of the plurality of second rollers; and a first connection unit that is configured to couple the first drawer to the second drawer based on the height of the first drawer. The first connection unit includes: a first connection member that is coupled to the first drawer, and a second connection member that is coupled to the second drawer, wherein, based on the first connection member and the second connection member being in a coupled state, the first drawer is coupled to the second drawer, and wherein, based on the first connection member and the second connection member being in an uncoupled state, the first drawer is separate from the second drawer. The second connection member includes: a protrusion support part that is located at a third side of the second drawer, and a connection protrusion that protrudes from a surface of the protrusion support part, and
     wherein the first connection member includes a protrusion insertion hole (i) that is located at a first side of the protrusion support part and (ii) into which the connection protrusion of the second connection member is inserted. The connection protrusion of the second connection member is separated from the protrusion insertion hole based on movement of one or more rollers moving into the inclined section of at least one of the plurality of the first support rails. The second connection member further includes: a hinge that is configured to support the connection protrusion of the second connection member, and   wherein the connection protrusion is configured to elastically rotate with respect to the protrusion support part. In a first state, the connection protrusion of the second connection member is located in the protrusion insertion hole. In a second state, the connection protrusion of the second connection member is spaced apart from the protrusion insertion hole. The refrigerator further includes: a third drawer that is located at a fourth side of the second drawer in the storage compartment and that is configured to store food; a plurality of third rollers, each of the plurality of third rollers being coupled to a first side of the third drawer or a second side of the third drawer; a plurality of third support rails, each of the plurality of third support rails (i) being coupled to the first side of the storage compartment or the second side of the storage compartment and (ii) being configured to guide one or more of the plurality of third rollers, wherein each of the plurality of third support rails includes a third inclined section that is configured to (i) guide one or more of the plurality of third rollers and (ii) gradually change a third height of the third drawer as the third drawer moves in the third inclined section; and a second connection unit that is configured to couple the second drawer to the third drawer based on the third height of the third drawer. The withdrawal unit includes: a link that includes a first portion that is rotatably coupled to the door and a second portion that is rotatably coupled to the base.   

     In general, another innovative aspect of the subject matter described in this specification can be embodied in a refrigerator comprising: a cabinet that includes a storage compartment and an opening on a first surface of the storage compartment; a door that is coupled to the cabinet and that is configured to open or close the opening; a first drawer that is located in the storage compartment and that is configured to store food; a plurality of rollers, each of the plurality of rollers being coupled to a first side of the first drawer or a second side of the first drawer; a plurality of first support rails, each of the plurality of first support rails (i) being coupled to a first side of the storage compartment or a second side of the storage compartment and (ii) including an inclined section that is configured to: guide one or more of the plurality of rollers, and gradually change a height of the first drawer as one or more rollers of the plurality of rollers move in the inclined section; and a base that is located at a third side of the first drawer in the storage compartment and that is configured to, based on movement of the door, move between a first position and a second position, wherein each of the base or the first drawer respectively includes either a connection protrusion or a protrusion insertion groove, wherein, based on coupling between the connection protrusion and the protrusion insertion groove, the first drawer is configured to move together with the base, and wherein, based on the height of the first drawer, the connection protrusion is separated from the protrusion insertion groove. 
     The foregoing and other embodiments can each optionally include one or more of the following features, alone or in combination. In particular, one embodiment includes all the following features in combination. The refrigerator further includes: a withdrawal unit that is configured to move the base between the first position and the second position based on movement of the door. The refrigerator further includes: 
     a second drawer that is located at a fourth side of the first drawer in the storage compartment and that is configured to store food; a plurality of second rollers, each of the plurality of second rollers being coupled to a first side of the second drawer or a second side of the second drawer; a plurality of second support rails, each of the plurality of second support rails (i) being coupled to the first side of the storage compartment or the second side of the storage compartment and (ii) being configured to guide one or more of the plurality of second rollers; and a first connection unit that is configured to couple the first drawer to the second drawer based on the height of the first drawer. The refrigerator further includes: a third drawer that is located at a fourth side of the second drawer in the storage compartment and that is configured to store food; a plurality of third rollers, each of the plurality of third rollers being coupled to a first side of the third drawer or a second side of the third drawer; a plurality of third support rails, each of the plurality of third support rails (i) being coupled to the first side of the storage compartment or the second side of the storage compartment and (ii) being configured to guide one or more of the plurality of third rollers, wherein each of the plurality of third support rails includes a third inclined section that is configured to (i) guide one or more of the plurality of third rollers and (ii) gradually change a third height of the third drawer as the third drawer moves in the third inclined section; and a second connection unit that is configured to couple the second drawer to the third drawer based on the third height of the third drawer. 
     The subject matter described in this specification can be implemented in particular embodiments so as to realize one or more of the following advantages. Comparing to a conventional refrigerator, a refrigerator includes a drawer that is not withdrawn until a door of a refrigerator is completely opened. 
     In addition, based on movement of the door, multiple drawers of the refrigerator that are arranged at different heights in a storage compartment are simultaneously withdrawn or inserted. Thus, the refrigerator does not need to include an additional part such as a frame for holding multiple drawers. 
     The details of one or more examples of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other potential features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claim. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating an example refrigerator. 
         FIG. 2  is a diagram illustrating example doors of the refrigerator of  FIG. 1 . 
         FIG. 3  is a diagram illustrating example drawers of a refrigerator. 
         FIG. 4  is a diagram illustrating the example drawers of the refrigerator in  FIG. 3 . 
         FIG. 5  is a diagram illustrating an example assembly including an example base and an example base guide. 
         FIG. 6  is a diagram illustrating example drawers and example support rails. 
         FIG. 7  is a diagram illustrating an example first drawer and an example base when a door of a refrigerator is closed. 
         FIG. 8  is a diagram illustrating an example first drawer and an example base when a door of a refrigerator is being opened. 
         FIG. 9  is a diagram illustrating an example first drawer and an example base when a door of a refrigerator is being opened to a separation angle. 
         FIG. 10  is a diagram illustrating an example first drawer and an example base when a door of a refrigerator is fully open. 
         FIG. 11  is a diagram illustrating an example base. 
         FIG. 12  is a diagram illustrating an example first connection unit. 
         FIGS. 13( a ) and 13( b )  are diagrams illustrating an example first connection unit that couples a first drawer to a second drawer. 
         FIG. 14  is a diagram illustrating an example first drawer and an example second drawer when a door of a refrigerator is open to a separation angle. 
         FIG. 15  is a diagram illustrating an example first drawer and an example second drawer when a door of a refrigerator is closed. 
         FIGS. 16( a ) and 16( b )  are diagrams illustrating an example second drawer and an example third drawer. 
         FIG. 17  is a diagram illustrating an example second drawer and an example third drawer when a door of a refrigerator is open to a separation angle. 
         FIG. 18  is a diagram illustrating an example third drawer and an example second connection unit. 
     
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
       FIG. 1  illustrates an example refrigerator.  FIG. 2  illustrates example doors of the refrigerator of  FIG. 1 .  FIG. 3  illustrates example drawers of a refrigerator. In  FIG. 1 , directions including “forward”/“rearward”/“leftward”/“rightward”/“upward”/“downward” are illustrated as an example. 
     Referring to  FIGS. 1 to 3 , a refrigerator  1  may include a cabinet  10  having compartments RC and FC (or storage compartments S 1 , S 2 , S 3 , and S 4 ) defined therein and doors  3   a ,  3   b ,  3   c , and  3   d  for opening and closing the compartments RC and FC. The doors  3   a ,  3   b ,  3   c , and  3   d  may be hinged to the cabinet  10 . 
     The front surfaces of the compartments RC and FC are open such that food is introduced and removed through the front surfaces of the compartments RC and FC. The open front surfaces of the compartments RC and FC may be opened and closed by the doors  3   a ,  3   b ,  3   c , and  3   d . Cool air is supplied into the compartments RC and FC. The compartments RC and FC may be sealed by the doors  3   a ,  3   b ,  3   c , and  3   d  such that cool air does not leak from the compartments RC and FC. In some implementations, two or more compartments RC and FC may be provided. For a bottom freezer type refrigerator, the cabinet  10  is partitioned into the upper part and the lower part, and the compartments RC and FC are respectively provided in the upper part and the lower part of the cabinet  10 . For example, the lower compartment FC can be a freezing compartment and the interior temperature of which can be maintained below 0° C. The upper compartment RC can be a refrigerating compartment and the interior temperature of which can be maintained above 0° C. In this specification, a “compartment” can be a refrigerating compartment or a freezing compartment. 
     Each of the compartments RC and FC may be opened and closed by a pair of doors. For example, the refrigerating compartment RC may be opened and closed by a pair of refrigerating compartment doors  3   a  and  3   b , and the freezing compartment FC may be opened and closed by a pair of freezing compartment doors  3   c  and  3   d.    
     The storage compartments S 1 , S 2 , S 3 , and S 4  constitute all or portions of the compartments RC and FC. The storage compartments S 1 , S 2 , S 3 , and S 4  may be defined as regions that are opened and closed by the doors  3   a ,  3   b ,  3   c , and  3   d . The refrigerating compartment RC may include a storage compartment S 1 , the open front surface of which is opened and closed by a left refrigerating compartment door  3   a , and a storage compartment S 2 , the open front surface of which is opened and closed by a right refrigerating compartment door  3   b . Hereinafter, the storage compartment S 1  may be referred to as a left refrigerating storage compartment and the storage compartment S 2  may be referred to as a right refrigerating storage compartment as needed. 
     In the same manner, the freezing compartment FC may include a storage compartment S 3 , the open front surface of which is opened and closed by a left freezing compartment door  3   c , and a storage compartment S 4 , the open front surface of which is opened and closed by a right freezing compartment door  3   d . Hereinafter, the storage compartment S 3  may be referred to as a left freezing storage compartment and the storage compartment S 4  may be referred to as a right freezing storage compartment as needed. 
     In the case in which two storage compartments are provided in one compartment in the horizontal direction, as described above, the storage compartments may communicate with each other. For example, when the refrigerating compartment RC is viewed from the front, the left refrigerating storage compartment S 1  and the right refrigerating storage compartment S 2  are not partitioned from each other. Consequently, cool air may freely flow between the left refrigerating storage compartment S 1  and the right refrigerating storage compartment S 2 . 
     In some implementations, a vertical partition  9  is provided between the left freezing storage compartment S 3  and the right freezing storage compartment S 4  of the freezing compartment FC, unlike the refrigerating compartment RC. As a result, the storage compartments S 3  and S 4  are partitioned from each other. Even in this case, however, the flow of cool air between the storage compartments S 3  and S 4  may not be completely blocked by the vertical partition  9 . For example, the vertical partition  9  may be provided with through holes, through which the storage compartments S 3  and S 4  communicate with each other. 
     In the case in which one space is partitioned into two parts by the vertical partition  9  to form two storage compartments S 3  and S 4  in the horizontal direction, as in the freezing compartment FC, the bottom surface of each of the storage compartments S 3  and S 4  may be defined by the inner bottom surface  11  of the cabinet  10 . The upper surface of each of the storage compartments S 3  and S 4  may be defined by the bottom surface of a horizontal partition  7 , which partitions the refrigerating compartment RC and the freezing compartment FC from each other. One of the side surfaces of each of the storage compartments S 3  and S 4  may be defined by an inner surface  12  of the cabinet  10 , and the other side surface of each of the storage compartments S 3  and S 4  may be defined by one surface of the vertical partition  9  that faces the inner surface  12  of the cabinet  10 . 
     In some implementations, the refrigerating compartment RC can be partitioned into a pair of storage compartments by the vertical partition. For example, one of the side surfaces of each of the storage compartments S 1  and S 2  constituting the refrigerating compartment RC may be defined by the inner surface  12  of the cabinet  10 , and the other side surface of each of the storage compartments S 1  and S 2  may be defined by one surface of the vertical partition  9  that faces the inner surface  12  of the cabinet  10 . 
     Referring to  FIG. 2 , the doors  3   a ,  3   b ,  3   c , and  3   d  may be provided corresponding to the storage compartments S 1 , S 2 , S 3 , and S 4 , respectively. A door storage unit for storing food may be formed in the rear parts of the doors  3   a ,  3   b ,  3   c , and  3   d , i.e., the parts of the doors  3   a ,  3   b ,  3   c , and  3   d  that face the open front surfaces of the storage compartments S 1 , S 2 , S 3 , and S 4 . The door storage unit may include storage chambers  8   a  for storing food that is frequently taken out of the refrigerator, such as dairy products, beverages, vegetables, etc., a tray  8   b  for storing ice, and baskets  8   c  for storing small-sized frozen food. In the state in which the doors  3   a ,  3   b ,  3   c , and  3   d  are closed, at least a portion of the door storage unit  8   a ,  8   b , and  8   c  may be located in the storage compartments S 1 , S 2 , S 3 , and S 4 . 
     Referring to  FIGS. 2 and 3 , at least one drawer may be disposed in the compartments RC and FC or the storage compartments S 1 , S 2 , S 3 , and S 4 . The drawer is provided to store or hold food. A plurality of drawers  21 ,  22 , and  23  may be arranged in the upward-downward direction. Each of the drawers  21 ,  22 , and  23  has therein a predetermined sized space for storing food. Rollers  61 ,  62  and  63  may be provided at opposite sides of the drawers  21 ,  22 , and  23 . The rollers  61 ,  62  and  63  are rotated about rotation shafts protruding from the drawers  21 ,  22 , and  23  in the lateral direction of the storage compartments S 1 , S 2 , S 3 , and S 4 . In addition, the rollers  61 ,  62  and  63  are supported and guided such that the rollers  61 ,  62  and  63  are movable along support rails  31 ,  32 , and  33 , a description of which will follow, in the forward-rearward direction. 
     At least one drawer may be provided in the storage compartments S 1 , S 2 , S 3 , and S 4 . Hereinafter, three drawers  21 ,  22 , and  23  will be described as being disposed in the right freezing storage compartment S 4  so as to be arranged at different heights in the upward-downward direction, which, however, is merely illustrative. The following description is also applicable to the other storage compartments S 1 , S 2 , and S 3 . 
       FIG. 4  illustrates example drawers of the refrigerator in  FIG. 3 .  FIG. 5  illustrates an example assembly including an example base and an example base guide. Referring to  FIGS. 4 and 5 , the first drawer  21 , the second drawer  22 , and the third drawer  23  are sequentially arranged from below in the storage compartment S 4 . In the storage compartment S 4 , pairs of support rails  31 ,  32 , and  33  are provided so as to respectively correspond to the drawers  21 ,  22 , and  23 . The support rails  31 ,  32 , and  33  may include a pair of first support rails  31  for supporting opposite sides of the first drawer  21 , a pair of second support rails  32  for supporting opposite sides of the second drawer  22 , and a pair of third support rails  33  for supporting opposite sides of the third drawer  23 . 
     The drawers  21 ,  22 , and  23  are respectively supported by the support rails  31 ,  32 , and  33 , which are fixed in the storage compartment S 4 . Specifically, rollers  61 ,  62 , and  63 , provided at the opposite sides of the drawers  21 ,  22 , and  23 , are respectively supported by the support rails  31 ,  32 , and  33  provided at the opposite sides of the drawers  21 ,  22 , and  23 . 
     In addition, the support rails  31 ,  32 , and  33  may be respectively provided with rollers  311 ,  321 , and  331 . The drawers  21 ,  22 , and  23  may be respectively provided at the opposite sides thereof with guide ribs  217 ,  227 , and  237 , which extend in the forward-rearward direction so as to be respectively supported by the rollers  311 ,  321 , and  331 . The rollers  311 ,  321 , and  331  are respectively provided to balance the drawers  21 ,  22 , and  23 . The rollers  311 ,  321 , and  331  may be disposed before the rollers  61 ,  62 , and  63  so as to respectively support the guide ribs  217 ,  227 , and  237 . The rollers  61 ,  62 , and  63 , provided at the drawers  21 ,  22 , and  23 , are respectively supported by the support rails  31 ,  32 , and  33 , and the guide ribs  217 ,  227 , and  237 , provided at the drawers  21 ,  22 , and  23 , are respectively supported by the rollers  311 ,  321 , and  331 , provided at the support rails  31 ,  32 , and  33 , whereby the drawers  21 ,  22 , and  23  are balanced. In particular, each of the guide ribs  217  and  237 , provided at the drawers  21  and  23 , may be configured to have an appropriate shape such that the drawers  21  and  23  are balanced even when the heights of the rollers  61  and  63 , provided at the drawers  21  and  23 , are changed after the rollers  61  and  63  respectively pass inclined sections S 12  and S 13 , a description of which will follow, while the rollers  61  and  63  respectively move along the first support rails  31  and the third support rails  33 . For example, the guide ribs  217  may be provided with inclined parts corresponding to the inclined sections S 12  (i.e., parts that are gradually inclined upward from the rear to the front). While the rollers  61 , provided at the first drawer  21 , move upward along the inclined sections S 12 , therefore, the inclined parts of the guide ribs  217  pass the rollers  311 , whereby not only the rear part of the drawer  21 , supported by the rollers  61  but also the front part of the drawer  31 , at which the guide ribs  217  are supported, move upward. As a result, the drawer  21  may be balanced. This structure may be applied to the guide ribs  237  formed at the third drawer  23 . 
     In some implementations, the guide ribs  217  and  237  can be different from the example described above. For example, the guide ribs  217  and  237  may be entirely horizontal. In this example, at least portions of the drawers  21  and  23  may ascend while the rollers  61  and  63  move along the inclined sections S 12  and S 32 , even though the guide ribs  217  and  237  are always move horizontally. The connection and disconnection between the drawers  21 ,  22 , and  23  may be performed by partial ascent of the drawers  21  and  23 , even though the drawers  21  and  23  are slightly inclined. 
     In some implementations, the second support rails  32  are substantially entirely horizontal (see  FIG. 6 ). In response thereto, the guide ribs  227 , provided at the second drawer  22 , may be substantially entirely horizontal. 
     In some implementations, one of each pair of the support rails  31 ,  32 , and  33 , which respectively correspond to the drawers  21 ,  22 , and  23 , is fixed to the inner surface  12  of the cabinet  10 , and the other is fixed to the vertical partition  9 , which faces the inner surface  12  of the cabinet  10 . For a refrigerator configured such that a single compartment is opened and closed by a single door, the support rails may be fixed to opposite inner surfaces of the cabinet. In some implementations, in  FIG. 3 , one of each pair of the support rails  31 ,  32 , and  33 , which respectively correspond to the drawers  21 ,  22 , and  23 , is shown as being disposed at the inner surface  12  of the cabinet  10 . Of course, the other of each pair of the support rails  31 ,  32 , and  33  is disposed at one surface of the vertical partition  9 , which faces the inner surface  12  of the cabinet  10 . 
     In the storage compartment S 4 , a base  40  may be provided at the lower side of the first drawer  21 . The base  40  is configured to move in response to the opening and closing operation of the door  3   d . When the door  3   d  is opened, the base  40  moves forward. When the door  3   d  is closed, the base  40  moves rearward. 
     The base  40  may include a plate  41  (see  FIG. 5 ) having a top surface, which faces the bottom surface of the first drawer  21 , and a pair of legs  42  and  43  protruding downward from the plate  41  and extending in the forward-rearward direction. 
     In some implementations, the plate  41  can be flat. A protrusion insertion groove  45 , into which a connection protrusion  215  formed on the first drawer  21  is inserted, may be formed in the top surface of the plate  41 . The protrusion insertion groove  45  may extend in the lateral direction of the plate  41 . The protrusion insertion groove  45  may be provided so as to be adjacent to the front end of the plate  41 . 
     As shown in  FIGS. 4 and 5 , the legs  42  and  43  may be spaced apart from each other by a predetermined distance in the lateral direction of the plate  41  so as to be parallel to each other. A pair of base guides  50   a  and  50   b , which are spaced apart from each other in the lateral direction of the storage compartment S 4 , may be disposed at the bottom surface  11  of the storage compartment S 4  so as to be parallel to each other. The first leg  42  may be disposed between the vertical partition  9  and the first base guide  50   a , and the second leg  43  may be disposed between the inner surface  12  of the cabinet  10  and the second base guide  50   b.    
     Each of the base guides  50   a  and  50   b  may include a guide body  51  extending in the forward-rearward direction and at least one roller  52  rotatably provided at the guide body  51 . The guide body  51  is provided with a plurality of roller installation recesses  51   a , which are arranged in the forward-rearward direction. The rollers  52  may be rotatably connected to a rotation shaft  53 , which extend through opposite sidewalls  51   b  and  51   c  of the roller installation recesses  51   a  in the state of being inserted into the roller installation recesses  51   a . The rollers  52  may be installed in the respective roller installation recesses  51   a  such that the plate  41  is supported by the rollers  52 . 
     A withdrawal unit may be provided to move the base  40  in response to the operation of the door  3   d . That is, the withdrawal unit may be configured to move the base  40  depending on the opening angle of the door  3   d . When the door  3   d  is opened, the withdrawal unit may move the base  40  forward. When the door  3   d  is closed, the withdrawal unit may move the base  40  rearward. The opening angle of the door  3   d  is measured on the basis of the state in which the door  3   d  is completely closed. As the opening angle of the door  3   d  is increased (i.e., as the door  3   d  is turned in the direction in which the door  3   d  is opened), the base  40  moves forward. As the opening angle of the door  3   d  is decreased (i.e., as the door  3   d  is turned in the direction in which the door  3   d  is closed), the base  40  moves rearward. 
     In some implementations, the withdrawal unit may include a link  70 , the front end of which is rotatably connected to the door  3   d  and the rear end of which is rotatably connected to the base  40 . In  FIG. 11 , reference numerals  72  and  73  respectively indicate a front-end rotation shaft and a rear-end rotation shaft of the link  70 . 
     Referring to  FIG. 11 , the front end of the link  70  is coupled to the door  3   d  at a position spaced apart from a rotation shaft C of the door  3   d  with respect to the cabinet  10  by a predetermined distance r. When the door  3   d  is turned, therefore, the front-end rotation shaft  72  of the link  70  moves along a circle having the rotation shaft C of the door  3   d  as the center and the distance r as the radius. At this time, the rear-end rotation shaft  73  is also displaced. Consequently, the base  40 , which is connected to the rear-end rotation shaft  73 , also moves. 
     In other implementations, the withdrawal unit may include a driving unit, such as an electric motor or an electric actuator, and a power conversion unit for transferring power generated from the driving unit to the base  40  to move the base  40  in the forward-rearward direction. For example, in the case in which a rotary motor is provided as the driving unit, the power conversion unit may include a rack and pinion or a crank, which converts the rotational force of the motor into a rectilinear motion. 
       FIG. 6  illustrates example drawers and example support rails.  FIG. 7  illustrates an example first drawer and an example base when a door of a refrigerator is closed.  FIG. 8  illustrates an example first drawer and an example base when a door of a refrigerator is being opened.  FIG. 9  illustrates an example first drawer and an example base when a door of a refrigerator is being opened to a separation angle θe.  FIG. 10  illustrates an example first drawer and an example base when a door of a refrigerator is fully open.  FIG. 11  illustrates an example base. 
     In  FIG. 11 , P(θi) indicates the position of the rear-end rotation shaft  73  of the link  70  in the state in which the door  3   d  is closed, P(θe) indicates the position of the rear-end rotation shaft  73  of the link  70  in the state in which the door  3   d  is open to the separation angle θe, and P(θf) indicates the position of the rear-end rotation shaft  73  of the link  70  in the state in which the door  3   d  is fully open. 
     If the base  40  and the first drawer  21  are connected to each other via a predetermined connection unit, the first drawer  21  may move forward together with the base  40  when the door  3   d  is opened. However, the base  40  continuously move forward until the door  3   d  is completely open. Therefore, the first drawer  21  also continuously moves forward until the door  3   d  is completely open. As a result, a portion of the first drawer  21  may unnecessarily protrude out of the cabinet  10  beyond the front surface of the storage compartment S 4 . 
     A user does not always open the door  3   d  in order to put food in the first drawer  21  or to take food out of the first drawer  21 . For example, the door  3   d  may be opened to take food out of the door storage unit  8   c  or to withdraw other drawers  22  and  23 . Consequently, it is necessary to restrict a moving distance of the first drawer  21  when the door  3   d  is opened. 
     For this reason, it is necessary to configure the connection unit such that, when the base  40  is withdrawn by the link  70  and reaches a predetermined position, the first drawer  21  cannot be withdrawn any further, whereby the base  40  and the first drawer  21  are separated from each other. In the refrigerator  1 , the connection unit includes a connection protrusion  215  formed on one of the first drawer  21  and the base  40  and a protrusion insertion groove  45  formed in the other of the first drawer  21  and the base  40 . The connection protrusion  215  is engaged with or inserted into the protrusion insertion groove  45 , and the coupling between the connection protrusion  215  and the protrusion insertion groove  45  is released when the first drawer  21  moves higher than a predetermined height. In the following description, the connection protrusion  215  and the protrusion insertion groove  45  are arranged in the upward-downward direction. In addition, the protrusion insertion groove  45  is formed in a top surface of the plate  41 , and the connection protrusion  215  protrudes downward from the bottom surface of the first drawer  21 . Alternatively, the protrusion insertion groove  45  may be formed in the first drawer  21 , and the connection protrusion  215  may be formed on the plate  41 . 
     In the state in which the door  3   d  is closed, the connection protrusion  215  of the first drawer  21  is located in the protrusion insertion groove  45 . As will be described hereinafter in more detail, the first drawer  21  may be located at a certain position in the state in which the door  3   d  is open, but the connection protrusion  215  is engaged with or inserted into the protrusion insertion groove  45  while the door  3   d  is closed, with the result that the base  40  and the first drawer  21  simultaneously return to the original positions thereof. In the state in which the door  3   d  is closed, therefore, the coupling between the connection protrusion  215  and the protrusion insertion groove  45  is maintained. 
     In some implementations, the first support rails  31  are configured such that, when the rollers  61  pass specific sections while the first drawer  21  moves forward, the rollers  61  ascend by at least a predetermined height ΔP (see  FIG. 9 ). Each of the first support rails  31  may include a rear horizontal section S 11 , an inclined section S 12 , and a front horizontal section S 13 , which are sequentially arranged from the rear to the front. 
     Each of the first support rails  31  may include a roller guide groove  310  formed in the surface thereof that faces the first drawer  21  so as to extend in the forward-rearward direction. A corresponding one of the rollers  61  is inserted into the roller guide groove  310 . The sections S 11 , S 12 , and S 13  may define support surfaces for supporting the lower side of the roller  61  in the roller guide groove  310 . That is, the support surfaces of the rear horizontal section S 11  and the front horizontal section S 13 , which support the lower side of the roller  61 , may horizontally extend in the forward-rearward direction, and the support surface of the inclined section S 12  may be gradually inclined upward from the rear to the front. 
     When the door  3   d  starts to be opened from the closed state, the base  40  is moved forward by the link  70 . At this time, the base  40  and the first drawer  21  are interlocked, since the connection protrusion  215  is located in the protrusion insertion groove  45 . Consequently, the roller  61  of the first drawer  21  rolls forward along the rear horizontal section S 11  (from  FIG. 7  to  FIG. 8 ). The height of the first drawer  21  at this time is denoted by P 0  in  FIGS. 7 to 9 . 
     When the door  3   d  is continuously turned and the opening angle of the door  3   d  reaches a predetermined angle (hereinafter, referred to as an “ascent start angle”), the roller  61  enters the inclined section S 12  (see  FIG. 8 ). From this time, the roller  61  rolls along the inclined section S 12 , with the result that the height of the first drawer  21  is increased. For example, the ascent start angle may be 50 degrees or more. In some other implementations, the ascent start angle can be set differently. 
     Subsequently, as shown in  FIG. 9 , the door  3   d  is opened further, and the roller  61  of the first drawer  21  continuously rolls along the inclined section S 12 . As the height of the first drawer  21  is increased, the height of the connection protrusion  215  is increased. When the first drawer  21  ascends to a predetermined height P 1  (hereinafter, referred to as a “separation height”), the connection protrusion  215  is completely separated from the protrusion insertion groove  45 . For reference, in the drawings, “L” indicates the position of the roller  61  when the roller  61  enters the inclined section S 12  (i.e., the position of the rear end of the inclined section S 12 ), and “H” indicates the position of the roller  61 , having ascended to the maximum height along the inclined section S 12  (i.e., the position of the front end of the inclined section S 12 ). 
     In some implementations, when the connection protrusion  215  is completely separated from the protrusion insertion groove  45 , the opening angle θe (hereinafter, referred to a “separation angle”) of the door  3   d  does not exceed 90 degrees. In some other implementations, the opening angle θe can be set more than 90 degrees. 
     The distance d 1  (see  FIG. 11 ) that the roller  61  moves forward until the door  3   d  is opened to the separation angle θe from the closed state is set within a range in which the front end of the first drawer  21  does not pass beyond the front surface of the storage compartment S 4 . Here, the distance dl is the distance that the first drawer  21  is automatically withdrawn by the base  40  when the door  3   d  is opened even when the user does not directly pull the drawer  21 . 
     When the door  3   d  is opened to the separation angle θe, i.e., when the connection protrusion  215  is separated from the protrusion insertion groove  45 , the roller  61  may be located within the inclined section S 12 . When the door  3   d  is continuously opened even after the connection protrusion  215  is separated from the protrusion insertion groove  45 , the base  40  moves further forward. Since the first drawer  21  is disconnected from the base  40 , however, the roller  61  descends rearward along the inclined section S 12  by a predetermined distance, with the result that the connection protrusion  215  remains in contact with the top surface of the plate  41 . When the door  3   d  is closed from the state in which the door  3   d  is open to the separation angle θe or more (see  FIGS. 10 and 11 ( c )), therefore, the protrusion insertion groove  45  is arranged at the lower side of the connection protrusion  215  while the base  40  is moved rearward by the link  70 , and then the connection protrusion  215  is inserted again into the protrusion insertion groove  45 . From this time, the first drawer  21  moves rearward together with the base  40  and returns to the original position thereof until the door  3   d  is completely closed. 
     The front horizontal section S 13  may extend forward from the front end of the inclined section S 12 . Since the first drawer  21  is disconnected from the base  40  while the roller  61  passes the inclined section S 12 , the first drawer  21  does not move any further, but only the base  40  continuously advances when the door  3   d  is further turned beyond the separation angle θe. In order to further withdraw the first drawer  21 , therefore, it is necessary for the user to directly pull the first drawer  21 . In this case, the roller  61  moves along the front horizontal section S 13 , whereby the first drawer  21  is further withdrawn. 
       FIG. 12  illustrates an example first connection unit.  FIGS. 13( a ) and 13( b )  illustrate an example first connection unit that couples a first drawer to a second drawer.  FIG. 14  illustrates an example first drawer and an example second drawer when a door of a refrigerator is open to a separation angle θe. 
     The second drawer  22  is supported and guided by the second support rails  32 . Each of the second support rails  32  may include a roller guide groove  320 , into which a corresponding one of the rollers  62  of the second drawer  22  is inserted (see  FIG. 6 ). The roller guide groove  320  may include a horizontal guide section S 21 , which horizontally extends in the forward-rearward direction. The horizontal guide section S 21 , which horizontally extends in the forward-rearward direction, is defined by a support surface for supporting the lower side of the roller  62  in the roller guide groove  320 . Each of the first support rails  31  includes an inclined section S 12 , whereas each of the second support rails  32  includes only a horizontal guide section S 21 , which includes a portion corresponding to the inclined section S 12 . 
     The first connection unit  500  is provided to interlock the first drawer  21  and the second drawer  22 . The first connection unit  500  may include a lower connection member  510  fixed to the first drawer  21  and an upper connection member  520  fixed to the second drawer  22 . Depending on the height of the first drawer  21 , the lower connection member  510  and the upper connection member  520  may be connected to or disconnected from each other. Particularly, in the state in which the lower connection member  510  and the upper connection member  520  are connected to each other (i.e., in the state in which the first drawer  21  and the second drawer  22  are interlocked), the roller  61  of the first drawer  21  moves along the inclined section S 12  of the first support rail  31 . When the lower connection member  510  fixed to the first drawer  21  ascends to a predetermined height or higher, therefore, the lower connection member  510  and the upper connection member  520  may be disconnected from each other. 
     More specifically, in the state in which the door  3   d  is closed, the lower connection member  510  and the upper connection member  520  are connected to each other. As a result, the base  40 , the first drawer  21 , and the second drawer  22  simultaneously move until the door  3   d  is opened to the separation angle θe. When the opening angle of the door  3   d  reaches the separation angle θe (i.e., when the roller  61  ascends along the inclined section S 12  of the first support rail  31 , whereby the lower connection member  510  fixed to the first drawer  21  ascends to a predetermined height ΔP (see  FIG. 9 ) or higher), the connection (or the coupling) between the lower connection member  510  and the upper connection member  520  is released. 
     Since the second drawer  22  is horizontally guided along the second support rail  32 , the upper connection member  520  is continuously located at a constant height. Since the first drawer  21  ascends in the inclined section S 12 , however, the lower connection member  510  also ascends. That is, the first connection unit  500  may be configured such that the lower connection member  510  moves in the state of being connected with the upper connection member  520 , and when the lower connection member  510  ascends to a predetermined height or higher, the lower connection member  510  is disconnected from the upper connection member  520 . 
     More specifically, the upper connection member  520  may include a protrusion support part  521  located at the lower side of the second drawer  22  and a connection protrusion  522  protruding upward from the top surface of the protrusion support part  521 . The lower connection member  510  may include a protrusion connection part  511 , located at the upper side of the protrusion support part  521  and having therein a protrusion insertion hole  511   h , into which the connection protrusion  522  is inserted upward. 
     The lower connection member  510  may include a first coupling part  512 , which is coupled to the upper end of the rear surface  211  of the first drawer  21 , and a first sidewall part  513 , which extends upward from the side end of the first coupling part  512  and from the upper end of which the protrusion connection part  511  extends in the lateral direction. The protrusion connection part  511  is located at the upper side of the first coupling part  512  by the length of the first sidewall part  513  in the upward-downward direction, whereby a recess  510   h , through which the protrusion support part  521  may extend in the forward-rearward direction, is formed between the protrusion connection part  511  and the first coupling part  512 . 
     The upper connection member  520  may include a second coupling part  523 , which is coupled to the bottom surface of the second drawer  22 , a front protrusion  524 , which extends forward from the second coupling part  523 , and a second sidewall part  525 , which extends from the front protrusion  524  and from the lower end of which the protrusion support part  521  extends in the lateral direction. 
     When the second drawer  22  is longer than the first drawer  21  in the forward-rearward direction and the front ends of the first drawer  21  and the second drawer  22  are arranged at predetermined positions, the rear end of the second drawer  22  is located further rearward than the first drawer  21 . Even when the second coupling part  523  is coupled to the rear of the second drawer  22 , therefore, the connection protrusion  522  may be inserted into the protrusion insertion hole  511   h , which is located at the rear of the first drawer  21 , since the connection protrusion  522  is located further forward than the second coupling part  523  by the length of the front protrusion  524  in the forward-rearward direction. 
       FIG. 12  is a view showing the first connection unit  500  in the state in which the door  3   d  is closed. The protrusion support part  521  is located in the recess  510   h , and the connection protrusion  522  is inserted into the protrusion insertion hole  511   h . The distance between the front end and the rear end of the protrusion insertion hole  511   h  (i.e., the length of the protrusion insertion hole  511   h  in the forward-rearward direction) may be set such that the connection protrusion  522  and the protrusion insertion hole  511   h  can move relative to each other by a predetermined distance ds in the forward-rearward direction. As shown in  FIG. 12 , the connection protrusion  522  is spaced apart from the rear end of the protrusion insertion hole  511   h  by the distance ds in the state in which the door  3   d  is closed. Preferably, the connection protrusion  522  is in contact with the front end of the protrusion insertion hole  511   h . When the door  3   d  is opened in this state, the first drawer  21 , which is interlocked with the base  40 , moves forward by the distance ds, with the result that the second drawer  22  does not move until the rear end of the protrusion insertion hole  511   h  comes into contact with the connection protrusion  522 . 
     As shown in  FIG. 13 , the front ends of the first drawer  21  and the second drawer  22  are arranged at the same position in the state in which the door  3   d  is closed (see  FIG. 13( a ) ). When the door  3   d  is opened, however, only the first drawer  21  is withdrawn by the distance ds until the opening angle of the door  3   d  reaches a predetermined angle. As shown in  FIG. 13( b ) , therefore, the front end of the first drawer  21  is located further forward than the second drawer  22  (i.e., the front end of the first drawer  21  is located at Pi). Consequently, the front ends of the first drawer  21  and the second drawer  22  are arranged in a stepped form. That is, the front end of the first drawer  21  protrudes further than the front end of the second drawer  22 . Subsequently, when the door  3   d  is opened further, the drawers  21  and  22  are withdrawn in the state in which the first drawer  21  and the second drawer  22  are arranged in a stepped form. In the case in which the first drawer  21  and the second drawer  22  are arranged in such a stepped form, it is possible for the user to easily check food stored in the first drawer  21 , since the portion of the open top surface of the first drawer  21  corresponding to the distance ds is not covered by the second drawer  22  but is exposed. 
     In some implementations, while the first drawer  21  and the second drawer  22  simultaneously move in the state in which the lower connection member  510  and the upper connection member  520  are coupled (or connected) to each other, the first drawer  21  is guided upward along the inclined section S 12  of the first support rail  31 , with the result that the first drawer  21  ascends by the predetermined height ΔP (see  FIG. 9 ). At this time, the protrusion connection part  511  of the lower connection member  510 , which is coupled to the first drawer  21 , also ascends, with the result that the connection protrusion  522  is separated from the protrusion insertion hole  511   h  (see  FIG. 14 ). The separation between the connection protrusion  522  and the protrusion connection part  511  is achieved when the door  3   d  is opened to the separation angle θe. At this time, the roller  61 , provided at the first drawer  21 , may be located within the inclined section S 12  of the first support rail  31 . 
       FIG. 15  illustrates an example first drawer and an example second drawer when a door of a refrigerator is closed 
     Referring to  FIG. 15 , the connection protrusion  522  may be connected the protrusion support part  521  via a hinge  526  so as to pivot in the forward-rearward direction. The pivoting operation of the connection protrusion  522  is elastically performed. To this end, the hinge  526  may include an elastic member configured to be deformed in response to the pivoting operation of the connection protrusion  522 . The elastic member may be a coil spring or a spiral spring. 
       FIG. 15( a )  shows the state in which, after the second drawer  22  is separated from the first drawer  21  (i.e., the connection protrusion  522  is separated from the protrusion insertion hole  511   h ), the second drawer  22  is pushed rearward by the user such that the second drawer  22  returns to the original position thereof. In this case, when the door  3   d  is closed again, the first drawer  21  moves rearward together with the base  40 , as described above. At this time, the first drawer  21  descends along the inclined section S 12  of the first support rail  31 , with the result that the protrusion connection part  511  also descends. When the door  3   d  is continuously turned to be closed, the first drawer is guided along the rear guide section S 11  of the first support rail  31 . At this time, the rear end of the protrusion connection part  511  comes into contact with the connection protrusion  522  (see  FIG. 15( b ) ), and the connection protrusion  522  is rotated rearward by the pushing force applied by the rear end of the protrusion connection part  511  (see  FIG. 15( c ) , showing the state in which the connection protrusion  522  is rotated in the clockwise direction). When the first drawer  21  continuously moves rearward, the contact between the protrusion connection part  511  and the connection protrusion  522  is released. When the protrusion insertion hole  511   h  reaches an appropriate position at the upper side of the connection protrusion  522 , the connection protrusion  522  is returned to the original position thereof by the restoring force of the elastic member, with the result that the connection protrusion  522  is inserted into the protrusion insertion hole  511   h  (see  FIG. 15( d ) ). 
     Depending on the position at which the rear end of the protrusion connection part  511  contacts the connection protrusion  522  (e.g. the position at which the roller  62  of the second drawer  22  is spaced apart from the end of the horizontal guide section S 21  of the second support rail  32 ) and the coefficient of elasticity of the elastic member, the connection protrusion  522  may be pushed to the rear of the second drawer  22  in the state of being in contact with the rear end of the protrusion connection part  511 . In this case, when the roller  62  reaches the end of the horizontal guide section S 21  of the second support rail  32 , the second drawer  22  does not move any further rearward. That is, the position of the second drawer  22  is fixed. When the door  3   d  is continuously turned so as to be closed in this state, the connection protrusion  522  is rotated rearward by the pushing force applied by the protrusion connection part  511 , with the result that the connection protrusion  522  is inserted into the protrusion insertion hole  511   h . In the state in which the door  3   d  is completely closed, therefore, the connection protrusion  522  may be continuously located in the protrusion insertion hole  511   h.    
     In some implementations, when the door  3   d  is opened, the first drawer  21  moves forward, with the result that the rear end of the protrusion insertion hole  511   h  pushes the connection protrusion  522  forward. At this time, it is necessary to prevent the connection protrusion  522  from being rotated by the pushing force applied by the rear end of the protrusion insertion hole  511   h , and therefore it is preferable to design the hinge  526  in order to satisfy the above-mentioned conditions. For example, the hinge  526  may be configured to allow the connection protrusion  522  to be rotated rearward, as shown in  FIG. 15( c ) , but to prevent the connection protrusion  522  from being rotated forward in the state in which the connection protrusion  522  returns to the original position thereof (see  FIG. 15( d ) ). Alternatively, the hinge  526  may be configured to allow the connection protrusion  522  to be rotated forward only when forward rotational force greater than rearward rotational force is applied to the connection protrusion  522 . 
       FIGS. 16( a ) and 16( b )  illustrate an example second drawer and an example third drawer. In  FIG. 16( a ) , the second drawer  22  is connected to the third drawer  23  when the door  3   d  is closed. In  FIG. 16( b ) , the door  3   d  is open to a predetermined angle and the front ends of the second drawer  22  and the third drawer  23  are arranged in a stepped form.  FIG. 17  is a diagram illustrating an example second drawer and an example third drawer when a door of a refrigerator is open to a separation angle θe. 
     Referring to  FIGS. 16 and 17 , each of the third support rails  33  may include a roller guide groove  330 , which includes a rear horizontal section S 31 , an inclined section S 32 , and a front horizontal section S 33 , in the same manner as in each of the first support rails  31 . 
     A second connection unit  600  is provided to interlock the second drawer  22  with the third drawer  23 . The second connection unit  600  may include a lower connection member  610  fixed to the second drawer  22  and an upper connection member  620  fixed to the third drawer  23 . Depending on the height of the third drawer  23 , the lower connection member  610  and the upper connection member  620  may be connected to or disconnected from each other. Particularly, in the state in which the lower connection member  610  and the upper connection member  620  are connected to each other (i.e., in the state in which the second drawer  22  and the third drawer  23  are interlocked), the roller  63  of the third drawer  23  moves along the inclined section S 32  of the third support rail  33 . When the upper connection member  620 , which is fixed to the third drawer  23 , ascends to a predetermined height or higher, therefore, the lower connection member  610  and the upper connection member  620  may be disconnected from each other. 
     More specifically, in the state in which the door  3   d  is closed, the lower connection member  610  and the upper connection member  620  are connected to each other (see  FIG. 16( a ) ). As a result, the base  40 , the first drawer  21 , the second drawer  22 , and the third drawer  23  simultaneously move until the door  3   d  is opened to the separation angle θe. The structure in which the base  40 , the first drawer  21 , and the second drawer  22  are interlocked has been previously described. Hereinafter, the structure in which the second drawer  22  and the third drawer  23  are interlocked will be described. 
     When the door  3   d  is opened to the separation angle θe in the closed state (i.e., when the roller  63  ascends along the inclined section S 32  of the third support rail  33 , whereby the upper connection member  620 , which is fixed to the third drawer  23 , ascends to a predetermined height ΔP or higher), the connection (or the coupling) between the lower connection member  610  and the upper connection member  620  is released. From this time, the third drawer  23  does not advance any further even when the door  3   d  is further opened. 
     Since the second drawer  22  is horizontally guided along the second support rail  32 , the upper connection member  520  is continuously located at a constant height. Since the third drawer  23  ascends in the inclined section S 32 , however, the upper connection member  620  also ascends. That is, the second connection unit  600  may be configured such that the upper connection member  620  moves in the state of being connected with the lower connection member  610 , and when upper connection member  620  ascends to a predetermined height or higher, the upper connection member  620  is disconnected from the lower connection member  610 . 
     More specifically, the upper connection member  620  may include a coupling mount  621  coupled to the bottom surface of the third drawer  23  and a connection protrusion  622  protruding downward from the coupling mount  621 . 
     The lower connection member  610  may be coupled to the rear surface of the second drawer  22 , and may be located lower than the coupling mount  621 . A protrusion insertion recess  611 , which is open upward, may be formed in the top surface of the lower connection member  610 . 
     As shown in  FIG. 16( a ) , the connection protrusion  622  may be located in the protrusion insertion recess  611  in the state in which the door  3   d  is closed. At this time, the roller  63  of the third drawer  23  is located within the rear horizontal section S 31 . 
     The connection protrusion  622  is spaced apart from the rear end of the protrusion insertion recess  611  by the distance ds in the state in which the door  3   d  is closed. Preferably, the connection protrusion  622  is in contact with the front end of the protrusion insertion recess  611  (see  FIG. 16( a ) ). When the door  3   d  is opened in this state, the second drawer  22  moves, whereby the rear end of the protrusion insertion recess  611  advances by the distance ds, with the result that the third drawer  23  does not move until the rear end of the protrusion insertion recess  611  comes into contact with the connection protrusion  622 . That is, the second drawer  22  and the third drawer  23  may be withdrawn in the state of being arranged in a stepped form, in the same manner as in the case in which the first drawer  21  and the second drawer  22  are withdrawn in the state of being arranged in a stepped form (see  FIG. 16( b ) ). 
     Referring to  FIG. 17 , while the second drawer  22  and the third drawer  23  simultaneously move in the state in which the lower connection member  610  and the upper connection member  620  are coupled to each other, the third drawer  23  is guided upward along the inclined section S 32  of the third support rail  33 , with the result that the third drawer  23  ascends by the predetermined height. At this time, the upper connection member  620 , which is coupled to the third drawer  23 , also ascends, with the result that the connection protrusion  622  is separated from the protrusion insertion recess  611 . The separation between the connection protrusion  622  and the protrusion insertion recess  611  is achieved when the opening angle of the door  3   d  reaches the separation angle θe. At this time, the roller  63 , provided at the third drawer  23 , may be located within the inclined section S 32  of the third support rail  33 . 
       FIG. 18  illustrates an example third drawer and an example second connection unit. Referring to  FIG. 18 , the connection protrusion  622  may pivot in the forward-rearward direction, like the connection protrusion  522  of the first connection unit  500 . The pivoting operation of the connection protrusion  622  is elastically performed. To this end, the upper connection member  620  may include a hinge  625  for pivotally connecting the connection protrusion  622  to the coupling mount  621 . The hinge  625  may include an elastic member configured to be deformed in response to the pivoting operation of the connection protrusion  622 , in the same manner as in the hinge  526  of the first connection unit  500 . The elastic member may be a coil spring or a spiral spring. 
     In  FIG. 18( a ) , the door  3   d  is closed when the third drawer  23  is pushed rearward by the user such that the third drawer  23  returns to the original position and the second drawer  32  is inserted rearward together with the base  40  and the first drawer  21 . In this example, the roller  63  of the third drawer  23  is located within the rear horizontal section S 31  of the third support rail  33 . 
     As previously described, the second drawer  22  may move rearward in the state of being connected to the first drawer  21 . For example, when the door  3   d  is completely opened from the closed state, the connection protrusion  215  of the first drawer  21  is separated from the protrusion insertion groove  45  of the base  40 , and the lower connection member  510  and the upper connection member  520  of the first connection unit  500  are separated from each other. When the door  3   d  is closed again, the connection protrusion  215  of the first drawer  21  is inserted into the protrusion insertion groove  45  of the base  40  while the base  40  is moved rearward by the link  70 , whereby the base  40  and the first drawer  21  are interlocked. In addition, the roller  61  of the first drawer  22  descends along the inclined section S 12  of the first support rail  31 , with the result that the lower connection member  510  and the upper connection member  520  of the first connection unit  500  are connected to each other. 
     When the door  3   d  is closed, as described above, the second drawer  22  is interlocked with the first drawer  21 , and the lower connection member  610  of the second connection unit  600  comes into contact with the connection protrusion  622  (at this time, the roller  63  of the third drawer  23  may be located within the rear horizontal section S 31 ). When the second drawer  22  moves further rearward along the second support rail  32 , the connection protrusion  622  is rotated rearward by the pushing force applied by the lower connection member  610  (see  FIG. 18( a ) , in which the connection protrusion  622  is rotated in the counterclockwise direction). When the second drawer  22  continuously moves rearward, the connection protrusion  622  is returned to the original position thereof by the restoring force of the elastic member, with the result that the connection protrusion  622  is inserted into the protrusion insertion recess  611  (see  FIG. 18( b ) ). 
     When the door  3   d  is opened, the second drawer  22  moves forward, with the result that the rear end of the protrusion insertion recess  611  pushes the connection protrusion  622  forward. At this time, it is necessary to prevent the connection protrusion  622  from being rotated by the pushing force applied by the rear end of the protrusion insertion recess  611 , and therefore it is preferable to design the hinge  625  in order to satisfy the above-mentioned conditions. 
     For example, the hinge  625  may be configured to allow the connection protrusion  622  to be rotated rearward, as shown in  FIG. 18( a ) , but to prevent the connection protrusion  622  from being rotated forward in the state in which the connection protrusion  622  returns to the original position thereof (see  FIG. 18( b ) ). Alternatively, the hinge  625  may be configured to allow the connection protrusion  622  to be rotated forward only when forward rotational force greater than rearward rotational force is applied to the connection protrusion  622 .