Patent Publication Number: US-7904982-B2

Title: Washing machine having steam generator and method for controlling the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. 10-2006-0008523, filed Jan. 26, 2006, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a washing machine having a steam generator, which prevents the accumulation of scale in the steam generator due to the long-term use thereof, and a method for controlling the same. 
     2. Description of the Related Art 
     Korean Patent Laid-open Publication No. 2004-0085507 (dated Oct. 8, 2004) discloses a conventional washing machine, in which steam is supplied to the inside of a tub so as to increase washing capacity. 
     A steam generator of the washing machine disclosed in the above Patent, includes a pressure container having an inlet, into which washing water is supplied, and an outlet, from which steam is discharged, a heater installed in the pressure container for heating the washing water supplied to the pressure container, an inlet valve for controlling the supply of the washing water into the pressure container, and an outlet valve for controlling the discharge of the steam from the pressure container. 
     The steam generator further includes a water level sensor for sensing the amount of the washing water supplied to the pressure container, a temperature sensor for controlling the operation of the heater according to the temperature in the pressure container, a pressure sensor for sensing the pressure in the pressure container, and a thermostat for cutting the power supplied to the heater off when the temperature in the pressure container is excessively elevated. 
     Since such a steam generator employs a method in which a designated amount of water contained in the pressure container is heated by the heater so as to generate steam, scale caused by calcium and magnesium components contained in the water is easily accumulated on the internal surface of the pressure container or the external surface of the heater. Accordingly, the steam generator is required to be frequently cleaned. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an aspect of the present invention to provide a washing machine having a steam generator for generating steam of a high temperature, which prevents the accumulation of scale in the steam generator, and a method for controlling the same. 
     Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the invention. 
     The foregoing and/or other aspects of the present invention are achieved by providing a washing machine having a steam generatorincluding a water supply valve for supplying water to the inside of the steam generator therethrough, and a heater for heating the water supplied through the water supply valve, the washing machine including a controller to control operations of the water supply valve and the heater, to thereby cool the steam generator when an operating time of the steam generator exceeds a predetermined time. 
     The controller includes a counter to measure the operating time of the steam generator. 
     The counter measures the operating time of the heater, cumulatively. 
     The controller turns the heater off, to thereby cool the steam generator. 
     According to an aspect of the present invention, the controller simultaneously turns the heater off, and opens the water supply valve to supply the water, to thereby cool the steam generator. 
     According to an aspect of the present invention, the water supply valve supplies cold water. 
     The washing machine further includes a temperature sensor for sensing the temperature of the water heated by the heater, wherein the controller controls a cooling operation of the steam generator based on the temperature of the water sensed by the temperature sensor. 
     The temperature sensor is installed on a body of the steam generator. 
     The controller compares the temperature of the water sensed by the temperature sensor to a reference temperature, and performs the cooling operation at least once according to the comparison result. 
     The reference temperature is more than a predetermined temperature set by a user for performing a washing operation. 
     It is another aspect of the present invention to provide a method for controlling a washing machine having a steam generatorincluding a water supply valve for supplying water to the inside of the steam generator therethrough and a heater for heating the water supplied through the water supply valve, the method including measuring an operating time of the steam generator, determining whether the measured operating time of the steam generator exceeds a predetermined time, and controlling the water supply valve and the heater so as to cool the steam generator, when it is determined that the measured operating time of the steam generator exceeds the predetermined time. 
     The operating time of the steam generator is a cumulative operating time of the heater. 
     The cooling operation of the steam generator is performed by turning the heater off. 
     The cooling operation of the steam generator is performed by simultaneously turning the heater off and opening the water supply valve to supply the water. 
     The controlling of the water supply valve and the heater includes sensing the temperature of the water, heated by the heater, using a temperature sensor; comparing the temperature of the water sensed by the temperature sensor to a reference temperature; and controlling the cooling operation of the steam generator according to the comparison result. 
     The cooling operation of the steam generator may be repeated until the temperature of the water sensed by the temperature sensor is lowered less than the reference temperature. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a sectional view of a washing machine in accordance with an aspect of the present invention; 
         FIG. 2  is a perspective view of a steam generator of the washing machine in accordance with an aspect of the present invention; 
         FIG. 3  is a sectional view of the steam generator of the washing machine in accordance with an aspect of the present invention; 
         FIG. 4  is a block diagram of the washing machine in accordance with an aspect of the present invention; 
         FIG. 5  is a graph illustrating the control of the operation of a heater of the steam generator of the washing machine in accordance with an aspect of the present invention; 
         FIG. 6  is a flow chart illustrating a method for controlling a washing machine in accordance with one embodiment of the present invention; and 
         FIG. 7  is a flow chart illustrating a method for controlling a washing machine in accordance with another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the embodiments of the present invention, an example of which is illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. The embodiments are described below to explain the present invention by referring to the figures. 
     As shown in  FIG. 1 , a washing machine in accordance with an embodiment of the present invention comprises a cylindrical tub  11  installed in a main body  10  for containing washing water, and a rotary drum  12  rotatably installed in the tub  11 . 
     The tub  11  in the main body  10  is inclined against the installation plane of the washing machine at a designated angle a so that the front surface of the tub  11  provided with an inlet  11  a formed therethrough is higher than the rear surface of the tub  11 . The rotary drum  12  in the tub  11  is inclined in the same manner as the tub  11 . Since a rotary shaft  13  connected to the central portion of the rear surface of the rotary drum  12  is rotatably supported by the central portion of the rear surface of the tub  11 , the rotary drum  12  is rotatable. A plurality of through holes  12   b  for passing the washing water are formed thorough the cylindrical surface of the rotary drum  12 , and a plurality of lifters  14  for lifting and dropping laundry are installed on the inner surface of the rotary drum  12 . 
     A washing motor  15  for rotating the rotary drum  12  is installed on the rear surface of the tub  11 . The washing motor  15  comprises a stator  15   a  fixed to the rear surface of the tub  11 , a rotor  15   b  rotatably disposed around the circumference of the stator  15   a , and a rotating plate  15   c  for connecting the rotor  15   b  to the rotary shaft  13 . 
     An opening  16  is formed through the front surface of the main body  10  at a position corresponding to an opening  12   a  of the rotary drum  12  and an opening  11   a  of the tub  11  so that a user can insert or take laundry into or out of the rotary drum  12 , and a door  17  for opening and closing the opening  16  is installed around the opening  16 . 
     A detergent supply device  18  for supplying a detergent to the inside of the tub  11  and a steam generator  30  for supplying steam to the inside of the tub  11  are installed above the tub  11 . A drain device  19  comprising a drain pipe  19   a , a drain valve  19   b  and a drain motor  19   c  for discharging water from the inside of the tub  11  to the outside of the washing machine is installed below the tub  11 . 
     A first electric heater  20  (hereinafter, referred to as “a first heater”) for heating the washing water is installed on the bottom of the tub  11 . 
     Although now shown in  FIG. 1 , the washing machine of the present invention further comprises a water level sensor  42  installed in the tub  11  for sensing the level of the washing water, and a first temperature sensor  44  for measuring the temperature of the washing water. 
     The detergent supply device  18  has a space formed therein for containing the detergent, and is installed in the front surface of the main body  10  so that a user can easily insert the detergent into the detergent supply device  18 . A first water supply pipe  21  branching off from a pipe connected to an external water supply source is connected to the detergent supply device  18 , and a first water supply valve  22  for controlling the supply of the water to the detergent supply device  18  is installed in the first water supply pipe  21 . A connection pipe  23  for supplying the water from the detergent supply device  18  to the tub  11  is connected between the detergent supply device  18  and the tub  11 . The connection pipe  23  supplies the water from the outside to the tub  11  through the detergent supply device  18 , thereby supplying the detergent contained in the detergent supply device  18  to the tub  11  under the condition that the detergent dissolves in the water. 
     A second water supply pipe  24  branching off from the pipe connected to the external water supply source (not shown) is connected to the steam generator  30 , and a second water supply valve  25  for controlling the supply of the water to the steam generator  30  is installed in the second water supply pipe  24 . Further, a steam supply pipe  26  for guiding steam generated from the steam generator  30  to the inside of the tub  11  is connected to the steam generator  30 . 
     As shown in  FIGS. 2 and 3 , the steam generator  30  comprises a body  31  made of a mold obtained by die-casting aluminum, a steam generating channel  32  formed in the body  31  and provided with an inlet connected to second water supply pipe  24  and an outlet connected to the steam supply pipe  26 , a second electric heater (hereinafter, referred to as “a second heater”) buried in the body  31  for heating the water passing through the steam generating channel  32  to generate steam, and a second temperature sensor  34  installed on the outer surface of the body  31  for sensing the temperature of the body  31  to control the heater  33 . 
     As shown in  FIGS. 2 and 3 , the body  31  of the steam generator  30  is molded by die-casting aluminum, and a pipe  35  for forming the steam generating channel  32  and the heater  33  are buried in the steam generator  30  during the molding of the body  31 . Since the body  31  of the steam generator  30  is made of a metal having high thermal conductivity and the heater  33  is buried in the body  31 , the body  31  is heated to a high temperature by the heater  33 . Further, water flowing along the steam generating channel  32  is heated by the heat of the body  31 , thus being changed to steam. That is, a small amount of water is supplied to the steam generating channel  32  under the condition that the body  31  is heated to a high temperature. Thus, while the water passes through the steam generating channel  32 , the water is heated and changed to steam of a high temperature in a short period of time. In order to smoothly perform the above procedure, as shown in  FIG. 2 , the body  31  has a rod shape having a designated length and the steam generating channel  32  is formed in the longitudinal direction of the body  31 . In this embodiment, as shown in  FIG. 2 , the U-shaped heater  33  is buried in the body  31 . 
     As shown in  FIG. 3 , the outlet of the steam generating channel  32  connected to the steam supply pipe  26  is always opened, and the inner diameter of the outlet of the steam generating channel  32  is smaller than the inner diameter of the inlet of the steam generating channel  32 . The relatively smaller inner diameter of the outlet of the steam generating channel  32  generates channel resistance at the outlet, and increases a stay time of the steam in the steam generating channel  32 , thereby effectively generating the steam of a high temperature. Further, the opened structure of the outlet of the steam generating channel  32  prevents the excessive increase of a pressure in the steam generating channel  32 , thereby assuring the safety of the steam generator  30 . A spiral coil member  37  for delaying the flow of the water in the steam generating channel  32  so that the generation of the steam is facilitated is installed in the steam generating channel  32 , as shown in  FIG. 3 . 
     When water is supplied to the steam generator  30 , the water supply and the suspension of the water supply are repeated through the second water supply valve  25  or a small amount of the water flows along the steam generating channel  32  by opening the steam generating channel  32  to a small degree so that the all amount of the water supplied to the steam generator  30  can be heated through the steam generating channel  32  and be evaporated to steam. For this reason, it is preferable that a motor operated valve opened and closed by electric motion or a flow control valve controlling a flow rate is used as the second water supply valve  25 . 
     The washing machine of the present invention further comprises a controller  46  for controlling the overall washing operations of the washing machine including the operation of the steam generator  30 . Hereinafter, the controller will be described with reference to  FIG. 4 . 
     An input unit  60  for inputting user&#39;s instructions to the controller  46 , the water level sensor  42  for sensing the level of the washing water, the first temperature sensor  44  for sensing the temperature of the washing water, and the second temperature sensor  34  for sensing the temperature of the body  31  of the steam generator  30  are electrically connected to an input side of the controller  46 . 
     A valve driving unit  48  for controlling the operations of the first water supply valve  22 , the second water supply valve  25  and the drain valve  19   b , a heater driving unit  50  for controlling the operations of the first heater  20  and the second heater  33 , and a motor driving unit  52  for controlling the operations of the washing motor  15  and the drain motor  19   c  are electrically connected to an output side of the controller  46 . 
     The controller  46  comprises a counter  46 - 1  for measuring the operating time of the second heater  33 . 
     The controller  46  controls the operations of the second heater  33  of the steam generator  30  and the second water supply valve  25 . The controller  46  controls the supply of water to the steam generator  30  by adjusting the opening and closing or the opening degree of the second water supply valve  25  using a program, which was set in advance, or based on data sensed by the second temperature sensor  34  installed in the body  31  of the steam generator  30 . In the case that the controller  46  controls the supply of water based on the data sensed by the second temperature sensor  34 , when the temperature of the body  31  is excessively lowered, the controller  46  decreases the supply amount of the water or stops the supply of the water, and when the temperature of the body  31  is excessively elevated, the controller  46  increases the supply amount of the water. As shown in  FIG. 5 , when the temperature of the body  31  sensed by the second temperature sensor  34  is elevated to a temperature T 2  (for example, 180° C.), the second heater  33  is turned off, and when the temperature of the body  31  sensed by the second temperature sensor  34  is lowered to a temperature T 1  (for example, 160° C.), the second heater  33  is turned on. 
     The pipe  35  for forming the steam generating channel  32  is made of stainless steel having low surface roughness so as to prevent the accumulation of scale in the steam generating channel due to the long-term use of the steam generator, and the inner surface of the pipe  35  is smoothened by electrolytic polishing. The smooth inner surface of the pipe  35  minimizes the attachment of impurities thereonto, thereby preventing the accumulation of scale in the steam generating channel  32 . 
     An outlet nozzle  38  having a tapered inner surface  39  so that the inner diameter of the outlet nozzle  38  is decreased from one end thereof close to an outlet of the steam generating channel  32  to the other end distant from the outlet, is installed at the outlet of the steam generating channel  32 . This structure of the outlet nozzle  38  generates channel resistance at the outlet, and prevents the accumulation of scale in the steam generating channel  32 . That is, the outlet nozzle  38  has the tapered inner surface  39  so that the inner diameter of the end of the outlet nozzle  38  close to the outlet is the same as the inner diameter of the pipe  35  and the inner diameter of the outlet nozzle  38  is gradually decreased from the end thereof close to the outlet to the end thereof distant from the outlet. The above structure of the outlet nozzle  39  allows impurities in the steam generating channel  32  to be smoothly discharged to the outlet, thereby preventing the accumulation of scale in the steam generating channel  32 . 
     Although the steam generator  30  has such a structure for preventing the accumulation of scale in the steam generating channel  32 , when the steam generator  30  is used for a long period of time, a small amount of scale may be accumulated in the steam generating channel  32 . Accordingly, for example, when the operation for increasing the temperature of the washing water using steam is performed for a long period of time, an operation for cooling the steam generator  30  is required so as to prevent the accumulation of a small amount of scale. 
     That is, as shown in  FIG. 5 , the controller  46  controls the operations of the second heater  33  and the second water supply valve  25  so that the steam generator  30  is cooled so as to prevent the accumulation of scale in the steam generator  30  when the operating time of the steam generator  30  reaches a reference time Hr, and then controls the operations of the second heater  33  and the second water supply valve  25  so that the steam generator  30  generates steam when the temperature of the body  31  is lowered to a reference temperature Tr after a designated time Ha has elapsed. 
     In accordance with the first embodiment of the present invention, only the second heater  33  is turned off under the condition that the supply of the water through the second water supply valve  25  is stopped, as shown in  FIG. 6 , thereby performing a cooling operation of the steam generator  30 . Hereinafter, the cooling operation of the steam generator  30  will be described with reference to  FIGS. 1 and 6 . 
     In operation  100 , a user sets washing conditions, such as a washing course, a washing temperature, the number of a rinsing operation, and a dehydrating speed, through the input unit  40  under the condition that laundry is placed into the rotary drum  12 , the controller  46  starts the washing of the laundry according to the washing conditions. 
     At this time, the controller  46  opens the first water supply valve  22  so that water is supplied to the detergent supply device  18 , and the detergent contained in the detergent supply device  18  is dissolved in the supplied water and is supplied to the tub  11 . This water supply operation is continued until a designated amount of washing water is supplied to the inside of the tub  11 . 
     Then from operation  100 , the process moves to operation  102  where the controller  46  turns the first heater  20  on so that the washing water contained in the tub  11  is heated by the first heater  20 . 
     During heating the washing water, when a washing function using steam of a high temperature is required, in operation  104 , the controller  46  preheats the second heater  33  for a designated time. Such a preheating operation is performed under the condition that the second water supply valve  25  is closed. The preheating operation serves to generate steam immediately when the water is supplied to the steam generator  30 . The preheating operation is performed only when the preheating of the second heater  33  is required based on the temperature of the body  31 . 
     After the second heater  33  is preheated in operation  104 , the process moves to operation  106 , where the steam is supplied to the inside of the tub  11  in order to elevate the temperature of the washing water heated by the first heater  20 . Here, the controller  46  opens the second water supply valve  25  so as to supply water and turns the second heater  33  on simultaneously. Then, the controller  46  controls the operation of the second heater  33  so that the temperature of the body  31  sensed by the second temperature sensor  34  is changed in a predetermined temperature range (between temperatures T 1  and T 2 ). 
     From operation  106 , the process moves to operation  108  where the counter  46 - 1  measures the operating time of the second heater  33  cumulatively. 
     From operation  108 , the process moves to operation  110  where the controller  46  determines whether the measured operating time of the second heater  33  reaches the reference time Hr. When it is determined that the measured operating time of the second heater  33  does not reach the reference time Hr in operation  110 , the process moves to operation  120 . On the other hand, when it is determined that the measured operating time of the second heater  33  reaches the reference time Hr in operation  110 , the process moves to operation  112 , where the controller  46  turns the second heater  33  off so as to cool the steam generator  30 . From operation  112 , the process moves to operation  114 , where the second water supply valve  25  is turned off so that the supply of the water is stopped. 
     From operation  114 , the process moves to operation  116 , where the controller  46  senses the temperature of the body  31  through the second temperature sensor  34  during cooling of the steam generator, and from operation  116 , the process moves to operation  118  where the controller determines whether the sensed temperature of the body  31  is lowered less than the reference temperature Tr. When it is determined that the sensed temperature of the body  31  is not less than the reference temperature Tr in operation  118 , the process returns back to operation  112  to continue the cooling of the steam generator  30 . 
     When it is determined that the sensed temperature of the body  31  is less than the reference temperature Tr in operation  118 , the process moves to operation  120 , where the controller  46  determines whether the temperature of the washing water sensed by the first temperature sensor  44  exceeds a predetermined temperature set by a user. When it is determined that the sensed temperature of the washing water does not exceed the predetermined temperature in operation  120 , the process returns back to operation  102  to elevate the temperature of the washing water. 
     When it is determined that the sensed temperature of the washing water exceeds the predetermined temperature in operation  120 , the process moves to operation  122 , where the controller  46  turns the first and second heaters  20  and  33  off, thus stopping the elevating of the temperature of the washing water. From operation  122 , the process moves to operation  124 , where the controller  46  drives the washing motor  15  to rotate the rotary drum  12  at a low speed, thus performing a washing operation of the laundry. 
     After the washing operation has been terminated, a rinsing operation, which is carried out by supplying water to the tub  11  and discharging the water from the tub  11 , and a dehydrating operation are performed. The drain of the tub  11  is performed by opening the drain valve  19   b  and operating the drain pump  19   c . The dehydrating operation is performed by operating the drain pump  19   c  under the condition that the drain valve  19   b  is opened and rotating the rotary drum  12  at a high speed for a designated time. 
     The first embodiment of the present invention applies a method, in which the second heater  33  is turned off so as to naturally cool the steam generator  30  when the operating time of the second heater  33  reaches the reference time during generating steam and supplying the steam to the tub  11 . Thereby, it is possible to prevent the accumulation of a small amount of scale in the steam generating channel  32 . 
     When the reference temperature Tr to be compared to the temperature of the body  31  in the first embodiment is set to a low value, a cooling effect is increased but a cooling time is increased. Accordingly, it is preferable that the reference temperature Tr is set in consideration of the above relation. 
     Further, in accordance with a second embodiment of the present invention, in addition to turning the second heater  33  off, the second water supply valve  25  is opened so as to supply cold water to the steam generating channel  32 . Here, the supplied cold water is not heated and is introduced into the tub  11  through the steam supply pipe  26 . Preferably, the level of the washing water in the tub  11  is considered when the cold water for cooling the steam generator  30  is supplied to the steam generator  30 . Accordingly, before the cold water is supplied to the steam generating channel  32 , the level of the washing water in the tub  11  is compared to a predetermined water level, and whether or not the cold water is supplied to the steam generating channel  32  is determined based on the obtained comparison result. 
     As shown  FIG. 7 , in operation  200 , when a user sets washing conditions through the input unit  40  under the condition that laundry is placed into the rotary drum  12 , the controller  46  starts the washing of the laundry according to the washing conditions. 
     At this time, the controller  46  opens the first water supply valve  22  so that water is supplied to the detergent supply device  18 , and the detergent contained in the detergent supply device  18  is dissolved in the supplied water and is supplied to the tub  11 . This water supply operation is continued until a designated amount of washing water is supplied to the inside of the tub  11 . Then from operation  200 , the process moves to operation  202 , where the controller  46  turns the first heater  20  on so that the washing water contained in the tub  11  is heated by the first heater  20 . 
     During heating the washing water in operation  202 , when a washing function using steam of a high temperature is required, the process moves to operation  204 , where the controller  46  preheats the second heater  33  for a designated time. Such a preheating operation is performed under the condition that the second water supply valve  25  is closed. The preheating operation serves to generate steam immediately when the water is supplied to the steam generator  30 . The preheating operation is performed only when the preheating of the second heater  33  is required based on the temperature of the body  31 . 
     After the second heater  33  is preheated, the steam is supplied to the inside of the tub  11  in order to elevate the temperature of the washing water heated by the first heater  20 . Here, the controller  46  opens the second water supply valve  25  so as to supply water and turns the second heater  33  on simultaneously. Then, from operation  204 , the process moves to operation  206 , where the controller  46  controls the operation of the second heater  33  so that the temperature of the body  31  sensed by the second temperature sensor  34  is changed in a predetermined temperature range (between temperatures T 1  and T 2 ). 
     From operation  206 , the process moves to operation  208 , where the counter  46 - 1  measures the operating time of the second heater  33  cumulatively. 
     From operation  208 , the process moves to operation  210 , where the controller  46  determines whether the measured operating time of the second heater  33  reaches the reference time Hr. When it is determined that the measured operating time of the second heater  33  does not reach the reference time Hr in operation  210 , the process moves to operation  224 . On the other hand, when it is determined that the measured operating time of the second heater  33  reaches the reference time Hr in operation  210 , the process moves to operation  212  where the controller  46  turns the second heater  33  off so as to cool the steam generator  30 . Then from operation  212 , the process moves to operation  216 , where the controller  46  determines whether the level of the washing water sensed by the water level sensor  42  exceeds the predetermined water level, and from operation  216 , the process moves to operation  217 , where the controller turns the second water supply valve  25  off when it is determined in operation  216 , that the sensed washing water level exceeds the predetermined water level. 
     On the other hand, when it is determined that the sensed washing water level does not exceed the predetermined water level in operation  216 , the process moves to operation  218 , where the second water supply valve  25  is opened so as to rapidly cool the steam generator  30 , thereby supplying cold water to the steam generator  30  through the steam generating channel  32 . 
     From operation  218 , the process moves to operation  220 , where the controller  46  senses the temperature of the body  31  through the second temperature sensor  34  during cooling of the steam generator, and from operation  220 , the process moves to operation  222 , where the controller determines whether the sensed temperature of the body  31  is less than the reference temperature Tr. When it is determined that the sensed temperature of the body  31  is not less than the reference temperature Tr in operation  222 , the process returns back to operation  212  to continue the cooling of the steam generator  30 . 
     When it is determined that the sensed temperature of the body  31  is less than the reference temperature Tr in operation  222 , the process moves to operation  224 , where the controller  46  determines whether the temperature of the washing water sensed by the first temperature sensor  44  exceeds a predetermined temperature set by a user. When it is determined that the sensed temperature of the washing water does not exceed the predetermined temperature in operation  224 , the process returns back to operation  202  to elevate the temperature of the washing water. 
     When it is determined that the sensed temperature of the washing water exceeds the predetermined temperature in operation  224 , the process moves to operation  226 , where the controller  46  turns the first and second heaters  20  and  33  off, thus stopping the elevating of the temperature of the washing water. From operation  226 , the process moves to operation  228 , where the controller  46  drives the washing motor  15  to rotate the rotary drum  12  at a low speed, thus performing a washing operation of the laundry. 
     After the washing operation has been terminated, a rinsing operation, which is carried out by supplying water to the tub  11  and discharging the water from the tub  11 , and a dehydrating operation are performed. 
     In the second embodiment, the second heater  33  is turned off and the second water supply valve  25  is opened simultaneously so as to supply cold water, when the operating time of the second heater  33  reaches the reference time during generating steam and supplying the generated steam to the tub  11 , thus cooling the steam generator  30  in a short time. Thereby, it is possible to prevent the accumulation of a small amount of scale in the steam generating channel  32 . 
     The reference temperature Tr to be compared to the temperature of the body  31  in the second embodiment is set to a value sufficient to cool the steam generator  30 . Accordingly, it is preferable that the reference temperature Tr is set to be equal to the predetermined temperature in order to prevent the lowering of the temperature of the washing water in consideration of the supply of the cold water to the tub  11  through the steam generating channel  32 . 
     As apparent from the above description, the present invention provides a washing machine having a steam generator for generating steam of a high temperature, in which an operation for cooling the steam generator is performed so as to prevent the accumulation of scale in the steam generator due to the long-term use thereof, and a method for controlling the same. 
     Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.