Title:
Method for controlling dishwasher
Kind Code:
A1


Abstract:
A method for controlling a dishwasher is disclosed. The control method basically includes a preliminary washing operation for spraying wash water required to hydrate waste adhered to dishes, a main washing operation implemented plural times for washing the dishes contaminated by the waste, a rinsing operation implemented after the preliminary washing operation and also, after the main washing operation for rinsing the dishes from which the waste is removed, and a drying operation for drying the dishes after completion of the washing and rinsing operations. The control method further comprises a steam supply operation implemented at least once before, after, or during the main washing operation for supplying steam to the dishes. With the control method, steam is supplied to a tub in which dishes are received, to enable not only easy removal of food waste adhered to the dishes, but also sterilization of the dishes and tub. The supply of steam is accomplished without requiring an additional steam supply heater, water supply device and nozzle, resulting in easy fabrication and reduced costs.



Inventors:
Kim, Min Chul (Changwon-Si, KR)
Application Number:
12/331188
Publication Date:
09/24/2009
Filing Date:
12/09/2008
Assignee:
LG Electronics Inc. (Seoul, KR)
Primary Class:
International Classes:
A47L15/46
View Patent Images:



Foreign References:
JP2007301188A2007-11-22
WO2006129963A22006-12-07
GB964954A1964-07-29
EP17386772007-01-03
Other References:
JP 2007-301188A abstract
JP 2007-301188A machine translation
Machine translation of EP1738677
Primary Examiner:
LEE, DOUGLAS
Attorney, Agent or Firm:
BIRCH, STEWART, KOLASCH & BIRCH, LLP (Falls Church, VA, US)
Claims:
What is claimed is:

1. A method for controlling a dishwasher comprising: a preliminary washing operation for spraying wash water required to hydrate waste adhered to dishes; a main washing operation implemented plural times for washing the dishes contaminated by the waste; a rinsing operation implemented after the preliminary washing operation and also, after the main washing operation for rinsing the dishes from which the waste is removed; and a drying operation for drying the dishes after completion of the washing and rinsing operations, wherein the method further comprises a steam supply operation implemented at least once before, after, or during the main washing operation for supplying steam to the dishes.

2. The method according to claim 1, wherein the steam supply operation is implemented to supply steam via operation of a heater having an adjustable heating capacity depending on the amount of wash water.

3. The method according to claim 2, wherein a hot-water supply operation for heating and supplying wash water is selectively implemented during the main washing operation upon stoppage of steam supply.

4. The method according to claim 3, wherein a heating value of the heater in the steam supply operation is controlled to be higher than a heating value of the heater in the hot-water supply operation.

5. The method according to claim 4, wherein a level of wash water in the steam supply operation is controlled to be lower than a level of wash water in the main washing operation.

6. The method according to claim 5, wherein a lowest level of wash water in the steam supply operation is controlled to be higher than an installation position of the heater.

7. The method according to claim 1, wherein the steam supply operation is implemented to supply steam by adjusting the amount of wash water when a heater having a constant heating value is used.

8. The method according to claim 7, wherein a hot-water supply operation for heating and supplying wash water is selectively implemented during the main washing operation upon stoppage of steam supply.

9. The method according to claim 8, wherein a level of wash water in the steam supply operation is controlled to be lower than a level of wash water in the hot-water supply operation.

10. The method according to claim 9, wherein a lowest level of wash water in the steam supply operation is controlled to be higher than an installation position of the heater.

11. The method according to claim 1, wherein the steam supply operation is controlled to discharge water residue and supply new water, prior to implementing the steam supply operation.

Description:

This application claims the benefit of the Korean Patent Application No. 10-2007-0127524, filed on Dec. 10 2007, which is hereby incorporated by reference as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for controlling a dishwasher, and more particularly, to a control method of a dishwasher, which can achieve an improvement in washing performance via supply of steam.

2. Discussion of the Related Art

Generally, a dishwasher is an apparatus in which high-pressure wash washer is sprayed to dishes received in the dishwasher, so as to wash the dishes contaminated by, for example, food waste attached to surfaces of the dishes.

Such a dishwasher includes a water supply device to which wash water from an external source is supplied, and a drain device from which the used wash water is discharged to the outside. The dishwasher contains a tub defining a space in which dishes are received and washed. The tub is provided with spray nozzles capable of spraying wash water at a high pressure.

To collect the sprayed wash water, a sump is provided underneath the tub. The sump contains elements to filter and crush waste that is mixed with the wash water during washing of dishes. Then, under operation of a drive unit, the wash water is pumped upward so as to again be sprayed into the tub via a spray arm. In this way, the dishes received in the tub are washed via washing circulation of wash water.

Recently, a variety of measures have been proposed to improve washing performance of the above-described dishwasher. In particular, operations of the dishwasher may be classified into a preliminary washing operation and a main washing operation. In the preliminary washing operation, wash water is sprayed to dishes, to hydrate food waste attached to the dishes for easy washing of the dishes. The preliminary washing operation is followed by the main washing operation in which the dishes are washed in earnest.

To further improve the washing performance of the dishwasher, detergent is mixed into the wash water, so as to facilitate effective separation of food waste from the dishes. Some conventional dishwashers may also have a function to irradiate ultraviolet light to the washed dishes, for sterilization of the dishes.

However, conventional dishwashers have a problem in that, when used dishes are left for a long time and thus, food waste is dried and firmly adheres to the dishes, it is difficult to remove the food waste from the dishes via only spraying of high-pressure wash water.

To solve the above-described problem, although one might consider implementing the above-described preliminary washing operation having a hydrating function, it has been found that the preliminary washing operation cannot completely solve the above-described problem. Furthermore, implementation of the hydrating function requires a great time and thus, disadvantageously lengthens the entire washing operation.

Furthermore, even if the propagation of bacteria occurs as used dishes are left for a long time, conventional dishwashers have a difficulty to remove the bacteria. Although some conventional dishwashers have an ultraviolet sterilizing function, they exert sterilizing effects only on a local area to which ultraviolet light is irradiated, and cannot completely solve any problems, such as the propagation of bacteria, etc.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a method for controlling a dishwasher that substantially obviates one or more problems due to limitations and disadvantages of the related art.

Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a method for controlling a dishwasher comprises: a preliminary washing operation for spraying wash water required to hydrate waste adhered to dishes; a main washing operation implemented plural times for washing the dishes contaminated by the waste; a rinsing operation implemented after the preliminary washing operation and also, after the main washing operation for rinsing the dishes from which the waste is removed; and a drying operation for drying the dishes after completion of the washing and rinsing operations, wherein the method further comprises a steam supply operation implemented at least once before, after, or during the main washing operation for supplying steam to the dishes.

The steam supply operation may be implemented to supply steam via operation of a heater having an adjustable heating capacity depending on the amount of wash water.

A hot-water supply operation for heating and supplying wash water may be selectively implemented during the main washing operation upon stoppage of steam supply.

A heating value of the heater in the steam supply operation may be controlled to be higher than a heating value of the heater in the hot-water supply operation.

A level of wash water in the steam supply operation may be controlled to be lower than a level of wash water in the main washing operation.

A lowest level of wash water in the steam supply operation may be controlled to be higher than an installation position of the heater.

The steam supply operation may be implemented to supply steam by adjusting the amount of wash water when a heater having a constant heating value is used.

A hot-water supply operation for heating and supplying wash water may be selectively implemented during the main washing operation upon stoppage of steam supply.

A level of wash water in the steam supply operation may be controlled to be lower than a level of wash water in the hot-water supply operation.

A lowest level of wash water in the steam supply operation may be controlled to be higher than an installation position of the heater.

The steam supply operation may be controlled to discharge water residue and supply new water, prior to implementing the steam supply operation.

It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings:

FIG. 1 is a schematic view illustrating the configuration of a dishwasher in accordance with an embodiment of the present invention;

FIG. 2 is an exploded perspective view illustrating components of a drive unit shown in FIG. 1;

FIG. 3 is a sectional view of the drive unit shown in FIG. 1;

FIG. 4 is a control block diagram of a control unit; and

FIG. 5 is a flow chart schematically illustrating a method for controlling the dishwasher shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

Hereinafter, a preferred first embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic view illustrating the configuration of a dishwasher in accordance with an embodiment of the present invention.

As shown in FIG. 1, the dishwasher includes a cabinet 1 defining an external appearance of the dishwasher, a tub 10 defining a space in which dishes are washed, and a drive unit 20 to pump wash water, used to wash the dishes, into the tub 10.

The tub 10 is provided therein with at least one rack 11 in which dishes are received, and at least one spray arm 12 to spray pumped wash water to the dishes. In this case, the spray arm 12 has a plurality of spray holes for spraying wash water. Preferably, the spray arm 12 is rotatably installed at a position corresponding to the rack 11, to uniformly spray wash water to all the dishes.

The drive unit 20 is coupled to a water supply device 55, through which wash water from an external tap water source is supplied. In addition, a drain device 50 is coupled to a sump 30, and is used to discharge wash water received in the sump 30.

The drive unit 20 is installed underneath the tub 10 and is configured such that wash water, sprayed and dropped from the spray arm 12, is received in the drive unit 20. Preferably, to pump the wash water upward from the drive unit 20, a connecting pipe 13 is further coupled to the drive unit 20 while being connected to the spray arm 12.

FIG. 2 is an exploded perspective view illustrating components of the drive unit shown in FIG. 1, and FIG. 3 is a sectional view of the drive unit shown in FIG. 1.

As shown in FIGS. 2 and 3, the drive unit 20 includes the sump 30 in which wash water is received, the water supply device 50 to supply wash water into the sump 30, the drain device 50 coupled to the sump 30, from which wash water is drained, a washing pump received in the sump 30 and used to pump the wash water received in the sump 30, and a filtering device to filter the pumped wash water remaining in the sump 30 after guiding some of the pumped wash water into the spray arm 12.

The sump 30 defines a space in which wash water is received and is provided, at a portion thereof, with a drain chamber 32 that communicates with the drain device 50. Preferably, a flow-path control device 35 is provided at the exterior of the sump 30 and in turn, a flow-path control valve 36 is axially coupled to the flow-path control device 35 via a shaft.

The water supply device 55 is connected with an external tap water source and serves to supply wash water into the tub 30. Preferably, the water supply device 55 is connected to a specific position of the sump 30. Of course, it will be appreciated that this installation of the water supply device 55 is provided only by way of example and wash water may be directly supplied into the tub 10. In the present embodiment, the water supply device 55 consists of a water supply pipe 56 to supply wash water, and a water supply valve 57 to selectively open or close the water supply pipe 56.

The drain device 50 may include a drain pump 53 provided in the drain chamber 32. The drain pump 53 consists of a drain motor 51 and an impeller 52.

The washing pump consists of a washing motor 41 provided underneath the sump 30 and used to generate a drive force, and an impeller 42 coupled to the filtering device and used to pump wash water. In addition, a disposer 43 is axially coupled to a shaft of the washing pump and functions to crush food waste via rotation thereof. Preferably, a screen 44 having a predetermined mesh size sufficient to filter a relatively large size of food waste is disposed above the disposer 43.

The filtering device includes a pump housing 60 defining a space for installation of the impeller 42, a filter housing 70 disposed to cover the top of the pump housing 60, and a cover 80 coupled to the top of the filter housing 70 and sump 30. Preferably, the pump housing 60 is disposed at a lower surface of the filter housing 70, and the cover 80 is disposed at an upper surface of the filter housing 70.

The filter housing 70 may contain, for example, a waste collecting chamber 71, and the waste collecting chamber 71 may be coupled to a drain pipe 72 that communicates with the drain chamber 32. For this, preferably, the drain pipe 72 is configured to protrude downward from the lower surface of the filter housing 70 by a predetermined length.

The cover 80 is preferably provided with a filter 81 such that the filter 81 corresponds to the waste collecting chamber 71 of the filter housing 70. More preferably, the cover 80 is provided with a plurality of recovery holes 82 arranged around the filter 81, and the recovery holes 82 communicate with the sump 30.

The filter housing 70 is further provided with at least one main flow-path connected to the spray arm 12, and is also provided with a sampling flow-path penetrating through the waste collecting chamber 71. The flow-path control valve 36, which is axially coupled to the flow-path control device 35, is disposed in the filter housing 70 and is used to open or close the flow path(s) inside the filter housing 70.

Preferably, regardless of any one main flow-path being opened or closed by the flow-path control valve 36, some wash water is always introduced into the sampling flow-path. This serves to assure continuous filtering of wash water containing waste.

Once the wash water is introduced into the waste collecting chamber 71 through the sampling flow-path, the wash water flows through the filter 81 which is located above the waste collecting chamber 71. Preferably, the filter 81 is used to filter waste contained in the wash water.

As the wash water, which is filtered via the above-described overflow process, as well as the wash water, which is sprayed from the spray arm 12 to thereby drop into the cover 80, are introduced into the sump 30 through the recovery holes 82, washing circulation of wash water is accomplished.

Hereinafter, a heater 100 provided at the drive unit 20 will be described in detail with reference to FIGS. 2 and 3.

In the present embodiment, the heater 100 is preferably provided, to supply steam into the tub 10.

Steam is supplied because simply spraying high-pressure wash water to dishes may often fail to completely remove food waste adhered to surfaces of the dishes. Although one might consider providing a washing operation with a function for hydrating food waste adhered to surfaces of dishes, this still has a difficulty to completely remove dried food waste firmly adhered to dishes. Therefore, there is a risk of requiring an excessively long time to sufficiently hydrate food waste adhered to surfaces of dishes.

As will be appreciated, since steam has a considerably higher temperature than wash water and is able to be easily adsorbed into food waste adhered to dishes, the use of steam can accomplish sufficient hydration of food waste within a short time. Accordingly, when steam is supplied into the tub 10 as proposed in the present embodiment, food waste adhered to dishes may be easily removed by wash water, resulting in a remarkable improvement in washing performance of dishes.

Steam further has sterilizing effects since steam is a gas having a high-temperature of up to 100° C. and thus, provides the same effect as boiling of dishes. As compared to a conventional sterilizing device using ultraviolet light that is very expensive and exerts sterilizing effects only a local area to which ultraviolet light is irradiated, according to the present embodiment, steam is supplied to the entire inner surface of the tub 10 and surfaces of dishes, enabling sterilization of the entire dishwasher at low cost.

Preferably, steam is supplied before or after a main washing operation. This is advantageous to hydrate food waste adhered to dishes before the main washing operation, or to finally sterilize the dishes and tub after completion of the main washing operation. Of course, it will be appreciated that this supply of steam is given only by way of example and in the case where the main washing operation is implemented several times, steam may be supplied between the repeatedly implemented main washing operations, or may be supplied during the main washing operation.

Preferably, the heater 100 is installed to heat wash water received in the sump 30 for supply of steam. Of course, one might consider generating steam using water additionally supplied from the water supply device 55, rather than using the wash water received in the sump 30. However, when generating steam using the additionally supplied water, for example, a flow-path and valve connected to the water supply device 55, a steam generator in which a receiving space for storing and heating water is defined, and a nozzle to supply steam into the tub are additionally required, entailing a risk of causing complexity in configuration.

Therefore, in the present embodiment, the heater 100 is installed in a bottom region of the sump 30 and is used to heat the wash water received in the sump 30 so as to generate steam. In this case, the steam is supplied into the tub 10 through a water collecting path, through which the wash water used to wash the dishes is collected.

Specifically, the wash water, sprayed into the tub 10, drops downward, thereby being collected in the sump 30. For this, most dishwashers have a water collecting path, which is connected to the top of the sump 30 while communicating with the tub 10 (here, the water collecting path is not an additional line, but a movement path along which the wash water drops). Steam rises because it is less dense than air and therefore, tends to be supplied into the tub 10 through the water collecting path. Accordingly, in the present embodiment, steam is supplied into the tub 10 through, for example, the recovery holes 82 perforated in the cover 80.

Supplying steam through the recovery holes 82 of the cover 80 eliminates a need for an additional nozzle used to supply steam. When using the steam supply nozzle, there is a risk of steam being condensed at a surface of the nozzle. As compared to the use of the steam supply nozzle, the present embodiment can minimize condensation of steam during a steam supply operation, allowing a greater amount of steam to be supplied into the tub 10.

Some of the steam generated by the heater 100 may be supplied by use of a path, through which wash water is supplied from the sump 30 into the tub 10. Specifically, steam generated in the sump 30 has characteristics of diffusion and therefore, may be introduced into the filter housing 70 through an opening perforated in the bottom of the pump housing 60. Thereafter, the steam may be supplied into the tub 10 via operation of the spray arm 12 after having passed through the main flow-path of the filter housing 70. This has an advantage of sterilizing a flow path, along which the wash water is pumped from the sump 30 into the tub 10.

Meanwhile, during washing circulation of the wash water used to wash the dishes, the heater 100 may heat the wash water to a high temperature sufficient to enable washing of dishes using high-temperature wash water. The higher the temperature of wash water, the easier it is to hydrate and remove food waste adhered to dishes and a further improved washing performance of the dishwasher can be accomplished upon washing circulation of the high-temperature wash water.

For this reason, in the present embodiment, the heater 100 heats the wash water received in the sump 30 according to operating modes of the dishwasher, so as to supply steam into the tub 10, or to supply high-temperature wash water during the main washing operation.

For example, the heater 100 may heat wash water to more than 100° C., so as to generate steam. Otherwise, during the main washing operation, the heater 100 may heat wash water to less than 100° C., so as to generate high-temperature wash water.

In this case, to adjust the temperature of wash water heated by the heater 100, a variety of methods may be adopted.

As the background of the above steam generation, the heater 100 may be a variable heater in which heating capacity is adjustable to adjust the temperature of wash water. In this case, when it is desired to supply steam into the tub 10, it is preferable that the heater 100 heat wash water with an increased heating value sufficient to generate steam.

In addition, during washing circulation of wash water, it is preferable that the heater 100 heat wash water with a lower heating value than that required for the supply of steam, so as to supply a predetermined temperature of hot water.

If the heater 100 has no function of adjusting a heating value thereof, the temperature of wash water may be adjusted by adjusting the amount of wash water heated by the heater 100. This is because, assuming that the heater has a constant heating value, the smaller the amount of wash water, the higher the temperature of wash water.

Accordingly, it is preferable that the amount of wash water during the supply of steam be kept at a lower value than the amount of wash water during washing circulation, to allow the wash water to be heated to a high temperature sufficient to generate steam.

In the present embodiment, in addition to the heater 100 in which heating capacity is adjustable according to an operating mode of the dishwasher, a control unit 110 is preferably provided, to adjust the amount of wash water received in the sump 30.

As described above, it is preferable that the heater 100 heat the wash water during the supply of steam with a higher heating value than a heating value required during washing circulation of wash water.

In addition, the control unit 110 may control the amount of wash water such that a water level during the supply of steam is higher than a water level during washing circulation of wash water. This is because a steam generating time can be reduced according to the amount of wash water even though the heater 100 having an adjustable heating value is used.

FIG. 4 is a control block diagram of the control unit.

As shown in FIG. 4, in the present embodiment, the water supply device 55 and drain device 50 are preferably controlled, respectively, by the control unit 110. Accordingly, the control unit 110 is able to control the water supply device 55 so as to effectively supply wash water, or to control the drain device 50 so as to adjust the amount of wash water to be received in the sump 30.

In the present embodiment, a sensor unit 120 may be further provided, to measure a level of wash water received in the sump 30. In this case, preferably, the control unit 110 acts to adjust the amount of wash water received in the sump 30 in response to a signal corresponding to a sensed level of wash water from the sensor unit 120. The sensor unit 120 may consist of a high water level sensor 121 and a low water level sensor 122 (these sensors will be described hereinafter).

For example, if the sensor unit 120 senses, during an operation for washing dishes using wash water, that a level of wash water is lowered, thus making it impossible for the drive unit 20 to pump the wash water, the control unit 110 controls the water supply device 55, so as to command supply of wash water.

Otherwise, if the sensor unit 110 senses, during an operation for supplying steam, that the amount of wash water is excessively increased to make it difficult to generate steam with a heating value of the heater 100, the control unit 110 controls the drain device 50, so as to command discharge of a predetermined amount of wash water.

The sensor 120 may include the high water level sensor 121, to maintain an appropriate amount of wash water during generation of steam. Here, the high water level sensor 121 is preferably installed at a height corresponding to a position of the bottom opening of the pump housing 60.

Preferably, the control unit 110 maintains a higher level of wash water received in the sump 30 than an installation position of the heater 100 during operation of the heater 100.

Generally, the heater 100 used in the dishwasher is adapted to heat wash water by transmitting heat, generated by a heating element inside the heater 100, to wash water in contact with an outer surface of the heater 100. Therefore, when a level of wash water is not maintained to be higher than the installation position of the heater 100, there is a risk of damage to the surface of the heater 100 due to overheating. In addition, this may cause remarkable deterioration in heating efficiency of the heater 100.

For this reason, in the present embodiment as shown in the drawing, the heater 100 is disposed in the bottom region of the sump 30 and under control operation of the control unit 110, a level of wash water is always maintained to be higher than the installation position of the heater 100. In this case, the control unit 110 may sense a level of wash water using the sensor unit 120. In addition, the sensor unit 120 may further include the low water level sensor 122 provided at the installation position of the heater 100 to sense a lowest level of wash water.

The control unit 110 is able to control the supply of wash water in such a manner that the wash water remaining in the sump 30 is discharged and new wash water is supplied, prior to generating steam via heating operation of the heater 100.

In the case where the wash water contains waste separated from dishes during washing, heating the wash water containing waste entails a risk of generating serious foul odors. In particular, if the resulting steam is supplied for sterilization of dishes in a final step, such foul odors may cause a user discomfort.

Therefore, in the present embodiment, the control unit 110 preferably controls the water supply device 55 and drain device 50, to selectively discharge the wash water remaining in the sump 30 and supply steam using newly supplied wash water, prior to generating steam.

FIG. 5 is a flow chart schematically illustrating a method for controlling the dishwasher shown in FIG. 1.

Hereinafter, a preferred control method of the dishwasher in accordance with the present invention will be described with reference to FIG. 5.

The dishwasher may be controlled such that washing of dishes is implemented using high-temperature wash water heated by the heater 100. In addition, the dishwasher may be controlled to supply steam into the tub 10 via heating of wash water. That is, the dishwasher may be controlled to supply high-temperature wash water., or to supply steam into the tub 10 at a predetermined time when no washing of dishes is implemented, under operation of the single heater 100.

As shown in FIG. 5, the dishwasher according to the present embodiment is basically controlled by the control unit 110 to implement a preliminary washing operation, a main washing operation, a rinsing operation, and a drying operation in this sequence. Additionally, before, after, or during the main washing operation, a steam supply operation is implemented at least once.

During the main washing operation, a hot-water supply operation for heating and supplying wash water may be selectively implemented when it is unnecessary to supply steam. Advantageously, prior to implementing the steam supply operation, the wash water remaining in the sump 30 is discharged and new wash water is supplied into the sump 30.

The preliminary washing operation serves to preliminarily spray wash water to dishes, so as to hydrate, for example, food waste adhered to the dishes. The preliminary washing operation is followed by the rinsing operation and main washing operation in sequence.

The main washing operation is controlled in such a manner that wash water is sprayed plural times to wash the dishes and is followed by the rinsing operation. The washing and rinsing operations are selectively repeated,

The steam supply operation may be selectively implemented at least once before or during the main washing operation under control operation of the control unit 110.

In the steam supply operation, preferably, the amount of wash water received in the sump 30 is adjusted before the wash water is heated by the heater 100 so as to generate steam. In this case, more preferably, a level of wash water received in the sump 30 during the steam supply operation is maintained to be lower than a level of wash water received in the sump 30 during the main washing operation or the hot-water supply operation.

The above washing operation requires more than a predetermined level of wash water required to pump the wash water using the drive unit 20. Furthermore, in view of an improvement in washing efficiency, it is necessary to maintain more than a predetermined amount of wash water.

On the other hand, the steam supply operation has no need to pump the wash water using the drive unit 20. This is because, assuming the heater 100 having a constant heating value, the smaller the amount of wash water, it is easier to generate steam via heating of the wash water.

Of course, under the assumption that the heater 100 is a variable heater in which heating capacity is adjustable, the steam supply operation may be controlled to generate steam with an increased heating value of the heater 100.

That is, a heating value of the heater 100 in the steam supply operation is preferably higher than a heating value in the hot-water supply operation. In this case, note that heating a reduced amount of wash water is advantageous in view of a reduction in steam generating time.

Accordingly, in the use of a variable heater, a level of wash water received in the sump 30 during the steam supply operation is preferably maintained to be lower than a level of wash water during the hot-water supply operation.

That is, regardless of whether the heater 100 has a constant heating value or a variable heating value, it is preferable that a level of wash water received in the sump 30 be maintained at a lowest level for the purpose of an improvement in steam generation efficiency.

In the steam supply operation, after the amount of wash water is adjusted, the wash water is heated by the heater 100 until the wash water reaches a boiling point thereof, so as to generate and supply steam into the tub 10. In this case, the supply of steam is continued for a predetermined time, so as to hydrate waste adhered to dishes for easy removal of the waste, or to sterilize the tub 10 and dishes.

Preferably, during implementation of the steam supply operation, a level of wash water is maintained to be higher than the installation position of the heater 100, under control operation.

In the case where a steam supply time is excessively long, the wash water received in the sump 30 may evaporate, lowering a level of wash water to a level close to the bottom of the heater 100. This may damage the surface of the heater 100 due to overheating and also, may cause remarkable deterioration in the heating efficiency of the heater 100. For this reason, during implementation of the steam supply operation, it is preferable to sense a level of wash water received in the sump 30, so as to keep the level of wash water above the installation position of the heater 100.

In the present embodiment, preferably, a lowest level of wash water is set to be slightly higher than the installation position of the heater 100. When the level of wash water received in the sump 30 reaches the lowest level in the steam supply operation, the steam supply operation can be controlled such that a predetermined amount of wash water is newly supplied into the sump 30.

In this case, the newly supplied amount of wash water is preferably set in consideration of the capacity and heating efficiency of the heater 100. Note that a level of wash water received in the sump 30 during the steam supply operation is preferably maintained to be lower than a level of wash water during the main washing operation. This is to assure effective generation of steam as described above.

In the case where the steam supply operation is followed by the main washing operation, it is preferable to additionally supply wash water prior to pumping the wash water received in the sump 30 for washing circulation of wash water. This serves to supplement wash water as much as a reduced amount of wash water received in the sump 30 during the steam supply operation, for the purpose of effective washing circulation of wash water.

In the case where the main washing operation is followed by the steam supply operation, it is preferable to implement an operation for discharging the wash water remaining in the sump 30 prior to implementing the steam supply operation.

This is because the wash water may contain waste separated from the dishes at the end of the main washing operation. Heating the wash water containing waste to generate steam may have a risk of causing, for example, serious foul odors.

Accordingly, when the steam supply operation is finally implemented for the purpose of sterilization, etc., it is preferable to discharge the wash water remaining in the sump 30 and supply new wash water, prior to implementing the steam supply operation.

In addition, even in the case where the steam supply operation is implemented during the main washing operation, it is preferable to discharge the wash water remaining in the sump 30 and supply new wash water, prior to implementing the steam supply operation.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.