Patent Publication Number: US-9885137-B2

Title: Washing machine and method of controlling the washing machine

Description:
This application is a divisional of U.S. application Ser. No. 12/450,508 filed on Sep. 29, 2009; which is a 35 USC § 371 National Stage entry of International Application No. PCT/KR2008/001776, filed Mar. 29, 2008, and claims the benefit of Korean Application No. 10-2007-0032080 filed Mar. 31, 2007, all of which are incorporated by reference in their entirety herein. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a washing machine and a method of controlling the washing machine, and more particularly, to a washing machine which can automatically supply a liquid detergent into a washing tub while preventing the liquid detergent from remaining in a liquid detergent supply path, and a method of controlling the washing machine. 
     BACKGROUND ART 
     In general, washing machines remove dust and dirt from clothing by performing a mechanical operation using water and a detergent. In recent years, an increasing number of washing machines have been equipped with a drier function for drying wet laundry with the use of a mechanical operation and hot wind generated by a heater. 
     A typical washing machine includes a washing tub, which is rotatably installed in the typical washing machine and can contain water and laundry therein. The typical washing machine performs a washing operation on laundry contained in the washing tub by rotating the washing tub with the aid of a driving unit. The typical washing machine also includes a water supply unit which supplies water into the washing tub, and a drainage unit which drains water from the washing tub. A detergent supply unit, which supplies a detergent into the washing tub, is disposed on a water supply path of the water supply unit. The detergent supply unit includes a dispenser which is connected to the water supply path and a detergent box which is installed so as to be able to be inserted into or ejected from the dispenser. Therefore, in order to supply a powder detergent or a liquid detergent into the washing tub, the detergent box may be taken out from the dispenser, a powder detergent or a liquid detergent may be injected into the detergent box, and the detergent box may be put back in the disperser. Then, if the water supply unit begins to operate, the powder detergent or the liquid detergent contained in the detergent box may be supplied into the washing tub along with water that flows along the water supply path of the water supply unit. 
     Conventionally, however, users are required to put a liquid detergent into a detergent box whenever necessary for a washing operation, thereby causing inconvenience and reducing the convenience of the use of a washing machine. 
     DISCLOSURE OF INVENTION 
     Technical Problem 
     The present invention provides a washing machine which can automatically supply a liquid detergent into a washing tub while preventing the liquid detergent from remaining in a liquid detergent supply path, and a method of controlling the washing machine. 
     Technical Solution 
     According to an aspect of the present invention, there is provided a washing machine including a washing tub which contains laundry and water therein; a circulation unit which circulates the water in the washing tub; a liquid detergent container which contains a liquid detergent to be supplied into the washing tub; and a liquid detergent supply unit which supplies the liquid detergent into the circulation unit and injects a mixture of the liquid detergent and the water circulated by the circulation unit into the washing tub. 
     According to another aspect of the present invention, there is provided a washing machine including a washing tub which contains water therein; a water supply path along which water is supplied from an external water source into the washing tub; a liquid detergent container which contains a liquid detergent; a circulation unit which circulates the water in the washing tub; and a circulation path along which a mixture of the liquid detergent and the water circulated by the circulation unit is supplied into the washing tub. 
     According to another aspect of the present invention, there is provided a method of controlling a washing machine, the method including supplying water into a washing tub; and discharging the water from the washing tub, mixing the discharged water with a liquid detergent in a liquid detergent container and injected the mixture of the discharged water and the liquid detergent into the washing tub. 
     According to the present invention, it is possible to improve user convenience by automatically supplying a liquid detergent into a washing tub. In addition, it is possible to prevent a liquid detergent from remaining in a liquid detergent supply path and prevent the liquid detergent supply path from being blocked due to the solidification of a liquid detergent by supplying a liquid detergent into a washing tub with the use of water circulated by a circulation unit. 
     Moreover, according to the present invention, it is possible to prevent a waste of liquid detergent and the deterioration of the performance of a washing machine by precisely controlling the amount of liquid detergent supplied into a washing tub. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  illustrates a perspective view of a drum-type washing machine according to an embodiment of the present invention; 
         FIG. 2  illustrates a partially exploded perspective view of a main body of the drum-type washing machine illustrated in  FIG. 1 ; 
         FIG. 3  illustrates a cross-sectional view of the drum-type washing machine illustrated in  FIG. 1 ; 
         FIG. 4  illustrates a block diagram of the drum-type washing machine illustrated in  FIG. 1 ; 
         FIG. 5  illustrates a cross-sectional view of a drum-type washing machine according to another embodiment of the present invention; and 
         FIG. 6  illustrates a block diagram of the drum-type washing machine illustrated in  FIG. 5 . 
     
    
    
     MODE FOR THE INVENTION 
     The present invention will hereinafter be described in detail with reference to the accompanying drawings in which exemplary embodiments of the invention are shown. 
       FIGS. 1 through 4  illustrate diagrams of a drum-type washing machine  100  according to an embodiment of the present invention. Referring to  FIG. 1 , the drum-type washing machine  100  includes a main body  102  which performs a washing operation on laundry; and a frame  104  which is disposed on one side of the main body  102  and contains various stuffs necessary for the use of the main body  102 . 
     A laundry inlet/outlet hole  2   a , through which laundry can be injected into or ejected from the main body  102 , is formed at the front of the main body  102 . A door  2   b  is rotatably installed so as to be able to open or close the laundry inlet/outlet hole  2   a . A plurality of legs  2   d , which support the main body  102 , are formed at the bottom of the main body  102 . A drawer-type container  106  is installed so as to be able to slide in and out of the frame  104 . The drawer-type container  105  may be ejected forward from the frame  104 . 
     The frame  104  may be selectively disposed on the top, the bottom, a left side, a right side, or a rear side of the main body  102 . In the embodiment of  FIGS. 1 through 4 , the frame  104  is disposed below the main body  102 . A plurality of leg settling units  108  respectively corresponding to the legs  2   d  are formed on the top of the frame  104 . Once the main body  102  is mounted on the frame  104 , the laundry inlet/outlet hole  2   a  is lifted up by as much as the height of the frame  104 , and thus a user can easily access the main body  102 . Therefore, the frame  104  not only contains various goods but also lifts up the main body  102  to the extent that the convenience of the use of the main body  102  can be improved. 
     Referring to  FIGS. 2 and 3 , the main body  102  includes a case  2  which forms the exterior of the main body  102 , a washing tub  4  which is rotatably installed in the case  2  and contains laundry, a detergent and water, and a driving unit  6  which drives the washing tub  4 . 
     The washing tub  4  may include a tub  8  which is installed so as to be able to be buffered by a spring  8   a  and a damper  8   c  and contains water and a detergent therein; a drum  10  which is rotatably installed in the tub  8 , contains laundry and includes a plurality of water holes  10   a  through which water and a detergent contained in the tub  8  can pass; and a lifter  12  which is disposed in the drum  10  and lifts up and drops laundry during the rotation of the drum  10 . 
     An opening  8   b  is formed at the front of the tub  8 , and an opening  10   b  is formed at the front of the drum  10 . The laundry inlet/outlet hole  2   a  is formed at the front of the case  2  and faces the openings  8   b  and  10   b . The door  2   b  is rotatably installed at the front of the case  2 . A gasket  14  is disposed between the opening  8   b  of the tub  8  and the laundry inlet/outlet hole  2   a . The gasket  14  alleviates shock caused by the rotation of the drum  10  and prevents a water spill. 
     Referring to  FIGS. 2 and 3 , the main body  102  also includes a water supply unit  16  which is disposed above the tub  8  and supplies water into the tub  8 ; and a detergent supply unit  18  which is disposed on a water supply path of the water supply unit  16  and supplies a detergent into the tub  8 . 
     The water supply unit  16  includes a plurality of water supply valves  20  which are disposed in the case  2  and are connected to an external water source, and the water supply path which connects the water supply valves  20  and the tub  8  and guides water into the tub  8 . The water supply path includes a plurality of first water supply hoses  22  which connect the respective water valves  20  to the detergent supply unit  18  and a second water supply hose  24  which connects the detergent supply unit  18  and the tub  8 . 
     The detergent supply unit  18  is provided with a detergent by a user before the operation of the drum-type washing machine  100  and supplies the detergent into the tub  8  during the operation of the drum-type washing machine  100 . The detergent supply unit  18  includes a dispenser  26  and a detergent box  28  which is installed in the dispenser  26  so as to be able to be inserted into or ejected from the dispenser  26  and includes a plurality of detergent containers  28   a  into which a detergent can be supplied by the user. The first water supply hoses  22  are connected to the top of the dispenser  26 , and the second water supply hose  24  is connected to the bottom of the dispenser  26 . The dispenser  26  has an open front and is connected to a hole  2   c , which is formed at the front of the case  2 . The detergent box  28  is disposed so as to be able to be inserted into or ejected from the dispenser  26  through the hole  2   c  of the case  2 . Therefore, the dispenser  26  selectively distributes water supplied thereto through the first water supply hoses  22  among the detergent containers  28   a  and then supplies water mixed with a detergent in the detergent containers  28   a  into the tub  8  through the second water supply hose  24 . A powder detergent, a liquid detergent or both may be supplied into the detergent supply unit  18 . 
     Referring to  FIGS. 2, 3 and 4 , the main body  102  also includes a drainage unit  30 , which is disposed below the tub  8  and drains water and a detergent from the tub  8 . The drainage unit  30  includes a drain path which guides water in the tub  8  to the outside of the case  2 ; a drain filter  32  which is disposed on the drain path and removes foreign materials from drain water; and a drain pump  34  which is disposed in the drain filter  32  and flows water along the drain path. The drain path includes a first drain hose  36  which connects a lower portion of the tub  8  and the drain filter  32  and a second drain hose  38  which has one end connected to the drain filter  32  and the other end disposed outside the case  2 . 
     Referring to  FIGS. 3 and 4 , the main body  102  also includes a circulation unit  40  which is disposed on one side of the tub  8  and circulates water in the tub  8 . Due to the circulation unit  40 , laundry in the drum  10  can be evenly soaked with water within a relatively short time. The circulation unit  40  includes a circulation path which connects both end portions of the tub  8  at different heights; a circulation filter  42  which removes foreign materials from water that flows along the circulation path; a circulation pump  44  which is disposed in the circulation filter  42  and circulates water in the tub  8  so as to flow along the circulation path; and a circulation nozzle  46  which is disposed on one side of the circulation path, from which water is discharged, and injects water into the tub  8 . 
     The circulation pump  44  is driven when the tub  8  is filled with a certain amount of water by the water supply unit  16 , and forcefully circulates the water in the tub  8  from one end to the other end of the circulation path. The circulation nozzle  46  is formed through the top of the gasket  14  and thus sprinkles water supplied thereto from the circulation path on laundry. The circulation nozzle  46  may be optional. The circulation nozzle  46  may be installed directly at the tub  8 . The circulation path includes a first circulation hose  48  which connects the lower portion of the tub  8  and the circulation filter  42  and a second circulation hose  49  which has one end connected to the circulation filter  42  and the other end connected to the circulation nozzle  46 . 
     Referring to  FIGS. 1 and 3 , the frame  104  also includes at least one liquid detergent container  50  which contains at least one type of liquid detergent to be supplied into the tub  8 . The liquid detergent container  50  is disposed in the drawer-type container  106 . A number of liquid detergent containers  50  corresponding to the number of types of liquid detergents used in a washing operation may be provided in the drum-type washing machine  100 . In the embodiment of  FIGS. 1 through 4 , only one liquid detergent container  50  is provided in the drum-type washing machine  100 , and only one type of liquid detergent is used in a washing operation performed by the drum-type washing machine  100 . The liquid detergent container  50  includes an injection hole  52  which is formed on the top of the liquid detergent container  50  and through which a liquid detergent is injected into the liquid detergent container  50 . A cover  54  is formed so as to be able to open and close the injection hole  52 . When the drawer-type container  106  is ejected from the dispenser  108 , the injection hole  52  is completely exposed. 
     Referring to  FIGS. 3 and 4 , the drum-type washing machine  100  also includes a liquid detergent supply unit  60  which automatically supplies a liquid detergent contained in the liquid detergent container  50  into the tub  8 . The liquid detergent supply unit  60  automatically supplies an appropriate amount of liquid detergent into the tub  8  according to the amount of laundry in the drum  10 . Therefore, the supply of a detergent by the detergent supply unit  18  may not be performed. 
     Referring to  FIGS. 1, 3 and 4 , the liquid detergent supply unit  60  includes a liquid detergent supply path  62  which connects the liquid detergent container  50  and the circulation unit  40 ; and a liquid detergent supply pump  64  which is disposed on the liquid detergent supply path  62 . 
     The liquid detergent supply path  62  has a first end connected to the liquid detergent container  50  in the frame  104  and a second end connected to the circulation path of the circulation unit  40  in the main body  102 . The second end of the liquid detergent supply path  62  is connected to the first circulation hose  48 , which is less affected by pressure caused by the circulation pump  44  during the operation of the circulation unit  40 . Alternatively, the second end of the liquid detergent supply path  62  may be connected to the circulation pump  44  or the circulation nozzle  46 . 
     The liquid detergent supply path  62  passes through the top of the frame  104  and the bottom of the main body  102 . Therefore, the liquid detergent supply path  62  may be divided into more than one portion that can be selectively connected to or disconnected from each other, thereby facilitating the installation of the liquid detergent supply path  62  in the drum-type washing machine  100 . The liquid detergent supply path  62  may be formed as a hose having a sufficient length to not interfere with the ejection of the drawer-type container  106 . 
     The liquid detergent supply pump  64  pumps a liquid detergent out of the liquid detergent container  50 , which is disposed below the tub  8 , and thus forcefully flows the liquid detergent into the circulation unit  40  through the liquid detergent supply path  62 . The liquid detergent supply pump  64  is disposed in the frame  104 . The liquid detergent supply pump  64  may be disposed in the main body  102 . 
     The amount of liquid detergent supplied by the liquid detergent supply unit  60  is controlled according to the number of revolutions per minute of the liquid detergent supply pump  64  and the duration of the operation of the liquid detergent supply pump  64 . In the embodiment of  FIGS. 1 through 4 , the number of revolutions per minute of the liquid detergent supply pump  64  is uniformly maintained, and thus, the amount of liquid detergent supplied by the liquid detergent supply pump  64  is determined according to the duration of the operation of the liquid detergent supply pump  64 . That is, once the amount of liquid detergent to be supplied is set according to the amount of laundry injected into the drum  10  and a washing course, the liquid detergent supply pump  64  is continuously driven for an amount of time corresponding to the set amount of liquid detergent, and thus, the set amount of liquid detergent can be supplied into the tub  8 . 
     Referring to  FIGS. 3 and 4 , the liquid detergent supply unit  60  also includes a check valve  66 , which is disposed on the liquid detergent supply path  62  and limits the direction of the flow of a liquid detergent from the liquid detergent container  50  to the circulation unit  40 . That is, the check valve  66  prevents water and foreign materials in the first circulation hose  48  from flowing into the liquid detergent container  50  along the liquid detergent supply path  62  during the operation of the circulation unit  40 . The check valve  66  is disposed between the liquid detergent supply pump  64  and the circulation unit  40  in order to prevent the operating pressure of the circulation unit  40  from affecting the liquid detergent supply pump  64 . Thus, it is possible to reduce damage to the liquid detergent supply pump  64 , caused by pressure generated during the operation of the circulation unit  40 . 
     Referring to  FIGS. 3 and 4 , the liquid detergent supply unit  60  also includes a liquid detergent mixer  68 , which is connected to the connection between the liquid detergent supply path  62  and the circulation unit  40  and mixes a liquid detergent with water. The liquid detergent mixer  68  is formed as a cylinder having an empty space therein. The liquid detergent mixer  68  is connected to the liquid detergent supply path  62 , and thus, a liquid detergent that flows along the liquid detergent supply path  62  can be injected into the liquid detergent mixer  68 . In addition, the liquid detergent mixer  68  is connected to a middle portion of the first circulation hose  48 , and thus, water that flows along the first circulation hose  48  can be injected into the liquid detergent mixer  68  and mixed with the liquid detergent injected into the liquid detergent mixer  68 . Then, the liquid detergent mixer  68  supplies a liquid detergent completely dissolved in water into the drum  10  through the circulation nozzle  46 . 
     As the difference between the height of the liquid detergent mixer  68  and the height of the liquid detergent container  50  increases, the pump head of the liquid detergent supply pump  64  increases. Accordingly, the required capacity of the liquid detergent supply pump  64  increases, and the manufacturing cost of the liquid detergent supply pump  64  increases. Therefore, the liquid detergent mixer  68  may be disposed between the tub  8  and the liquid detergent container  8  so as to be as close as possible to the liquid detergent container  50 . 
     The operation of the drum-type washing machine  100  will hereinafter be described in detail. Assume that the detergent supply unit  18  supplies no detergent, and that the liquid detergent supply unit  60  supplies a liquid detergent instead. 
     Laundry is injected into the drum  10  through the laundry inlet/outlet hole  2   a  of the main body  102 , and the door  2   b  is closed so that the laundry inlet/outlet hole  2   a  can be sealed. Then, the main body  102  is driven. The main body  102  detects the amount of laundry injected into the drum  10 , and sets a feed-water level, an amount of detergent to be supplied, and a washing time. 
     Thereafter, the water supply unit  16  is driven and thus supplies water into the tub  8  until reaching the set feed-water level. More specifically, the water supply valve  20  of the water supply unit  16  is opened so that water can be injected from an external water source into the drum-type washing machine  100  through the water supply valve  20  and then supplied into the tub  8  through the first water supply hose  22 , the detergent supply unit  18 , and the second water supply hose  24 . And at the same time, the liquid detergent supply unit  60  supplies the set amount of detergent into the tub  8 . More specifically, when the liquid detergent supply pump  64  of the liquid detergent supply unit  60  is driven, the liquid detergent supply pump  64  pumps a liquid detergent out of the liquid detergent container  50  so that the liquid detergent can be injected into the liquid detergent mixer  68  along the liquid detergent supply path  62 . 
     Thereafter, the circulation unit  40  is driven so that the water injected into the tub  8  can circulate, and that the liquid detergent in the liquid detergent mixer  68  can be supplied into the tub  8 . 
     Thereafter, the driving unit  6  is driven so that the drum  10  can rotate for a predefined amount of time. Accordingly, a washing operation is performed while repeatedly lifting up and dropping the laundry with the use of the rotation of the drum  10  and the lifter  12 . 
     Once the washing operation is complete, the operation of the driving unit  6  is terminated, and the drainage unit  30  is driven and thus drains water from the tub  8 . Thereafter, the water supply unit  16  is driven and thus supplies water into the tub  8  until reaching the set feed-water level. Thereafter, the driving unit  6  is driven and thus rotates the drum  10  again, thereby performing a rinsing operation. 
     Once the rinsing operation is complete, the operation of the driving unit  6  is terminated, and the drainage unit  30  is driven and thus drains water from the tub  8 . Thereafter, if the tub  8  is completely drained, the driving unit  6  is driven and thus rotates the drum  10  at high speed, and then, the operation of the drum-type washing machine  100  is terminated. When the drum  10  is rotated at high speed, water drains from the laundry, and water collected in the tub  8  is discharged by the drainage unit  30 . 
     The supply of a liquid detergent as performed in the drum-type washing machine  100  will hereinafter be described in detail with reference to  FIG. 4 . Referring to  FIG. 4 , solid-line arrows indicate water flow caused by the circulation unit  40 , and dotted-line arrows indicate water flow caused by the liquid detergent supply unit  60 . 
     Referring to  FIG. 4 , the liquid detergent supply pump  64  is driven and thus pumps a liquid detergent out of the liquid detergent container  50 . Then, the liquid detergent flows along the liquid detergent supply path, and thus, a predefined amount of liquid detergent is supplied into the liquid detergent mixer  68 . 
     The amount of liquid detergent supplied by the liquid detergent supply pump  64  may be determined indirectly based on the duration of the operation of the liquid detergent supply pump  64 . Therefore, if the duration of the operation of the liquid detergent supply pump  64  is more than a predefined amount of time, the operation of the liquid detergent supply pump  64  is terminated. The predefined amount of time may be set according to the amount of laundry, a washing course and the type of liquid detergent used in the drum-type washing machine  100 . Alternatively, the amount of liquid detergent supplied by the liquid detergent supply pump  64  may be measured by installing a water level sensor or a weight sensor in the liquid detergent container  50 . If an appropriate amount of liquid detergent is injected into the liquid detergent mixer  68 , it is determined whether a current water level in the tub  8  is appropriate for a circulation operation. If the current water level in the tub  8  is appropriate for a circulation operation, the circulation unit  40  may be driven. 
     When the circulation unit  40  is driven, the water in the tub  8  is injected into the circulation pump  44  through the first circulation hose  48 . Then, the water injected into the circulation pump  44  is injected into the liquid detergent mixer  68  through the first circulation hose  48 . The liquid detergent contained in the liquid detergent mixer  68  dissolves in and mixes with the water injected into the liquid detergent mixer  68 , and then the mixture is injected into the circulation pump  44 . The mixture flows to the circulation nozzle  46  along the second circulation hose  49  and then is injected into the drum  10 . 
     In the embodiment of  FIGS. 1 through 4 , the liquid detergent supply unit  60  and the circulation unit  40  supply a liquid detergent mixed with water into the tub  8  and thus prevent laundry in the drum  10  from directly contacting a liquid detergent. Therefore, it is possible to prevent laundry from being damaged or decolorized due to directly contacting a liquid detergent. In addition, in the embodiment of  FIGS. 1 through 4 , a liquid detergent is supplied into the tub  8  along with water circulated by the circulation unit  40 , and thus, no liquid detergent remains in the liquid detergent supply unit  50  and the circulation unit  40 . Therefore, since a liquid detergent only remains in the tub  8 , it is possible to supply an appropriate amount of liquid detergent into the tub  8 , to prevent the liquid detergent supply path  62  of the liquid detergent supply unit  60  and the circulation path of the circulation unit  40  from being blocked due to the solidification of a liquid detergent remained therein. 
       FIG. 5  illustrates a cross-sectional view of a drum-type washing machine  200  according to another embodiment of the present invention, and  FIG. 6  illustrates a block diagram of the drum-type washing machine  200 . In  FIGS. 1 through 6 , like reference numerals indicate like elements, and thus detailed descriptions thereof will be skipped. The drum-type washing machine  200  will hereinafter be described, mainly focusing on the differences with the drum-type washing machine  100 . 
     Referring to  FIGS. 5 and 6 , the drum-type washing machine  200  is different from the drum-type washing machine  100  in that the drum-type washing machine  200  does not include a frame, that a circulation unit  240  and a drainage unit  30  share some elements, and that a liquid detergent container  250  is disposed in a case  2  of the drum-type washing machine  200 . Referring to  FIG. 6 , solid-line arrows indicate water flow caused by the circulation unit  240 , and dotted-line arrows indicate water flow caused by a liquid detergent supply unit  260 . 
     The drainage unit  30 , like the drainage unit  30  of the drum-type washing machine  100 , includes a drain pump  34 , a drain filter  32 , a first drain hose  36 , and a second drain hose  38 . The circulation unit  240 , like the circulation unit  40  of the drum-type washing machine  100 , includes a circulation pump  44 , a second circulation hose  49 , and a circulation nozzle  46 . However, the circulation unit  240 , unlike the circulation unit  40  of the drum-type washing machine  100 , uses the drain filter and the first drain hose  36  of the drainage unit  30  as a circulation filter and a first circulation hose. That is, the drain filter  32  performs the functions of the circulation filter  42  of the circulation unit  40  of the drum-type washing machine  100 , and the first drain hose  36  performs the functions of the first circulation hose  48  of the circulation unit  40  of the drum-type washing machine  100 . By sharing the drain filter  32  and the first drain hose  36  between the drainage unit  30  and the circulation unit  240 , it is possible to simplify the structure of the drum-type washing machine  200 , to reduce the number of elements of the drum-type washing machine  200  and thus to reduce the manufacturing cost of the drum-type washing machine  200 . 
     At least one liquid detergent container  250  may be disposed in the case  2  of the drum-type washing machine  200 . In the embodiment of  FIGS. 5 and 6 , only one liquid detergent container  250  is disposed in the case  2 . The liquid detergent supply unit  260  includes a liquid detergent mixer  268  which is disposed at a middle portion of the first drain hose  36 , a liquid detergent supply path  62  which is connected to the liquid detergent mixer  268  and the liquid detergent container  250 , and a liquid detergent supply pump  64  which is disposed on the liquid detergent supply path  62 . 
     An appropriate amount of liquid detergent may be supplied into the liquid detergent mixer  268  by the liquid detergent supply unit  260 , and then, the liquid detergent contained in the liquid detergent mixer  268  may be supplied into the drum  10  by the circulation unit  240 . Since a liquid detergent is supplied into the tub  8  along with water circulated by the circulation unit  240 , no liquid detergent remains in the liquid detergent mixer  268 . Even if a liquid detergent is not completely washed out from the liquid detergent mixer  268  by the water circulated by the circulation unit  240  and thus remains in the liquid detergent mixer  268 , the liquid detergent remained in the liquid detergent mixer  268  may be discharged during a drainage operation performed by the drainage unit  30 . 
     The present invention is not restricted to the embodiments set forth herein. In addition, the present invention is not restricted to a drum-type washing machine. That is, the present invention can be applied to a water stream-type washing machine. 
     In the present invention, if a liquid detergent container is disposed above a tub, a liquid detergent supply pump may be optional because a liquid detergent can be automatically supplied into the tub due to gravity. In addition, in the present invention, a liquid detergent mixer may not be provided. Then, a liquid detergent may be directly supplied into a circulation path of a circulation unit. 
     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.