WO2017022976A1

WO2017022976A1 - Steam generator and control method of steam generator

Info

Publication number: WO2017022976A1
Application number: PCT/KR2016/007780
Authority: WO
Inventors: Seunghun KIM; Sangwoo Woo
Original assignee: Lg Electronics Inc.
Priority date: 2015-08-04
Filing date: 2016-07-18
Publication date: 2017-02-09
Also published as: KR101741553B1; EP3331415A4; EP3331415A1; US20190010656A1; KR20170016661A

Abstract

A steam generator and a control method thereof are disclosed. The control method includes supplying water to a first chamber (C1), turning a heater (83) on, wherein power is supplied to the heater (83) to heat the heater (83) at a third temperature so as to generate steam, preventing overheating, wherein power supplied to the heater is cut at a first temperature so as to prevent overheating of the heater, and determining scale, wherein power supplied to the heater (83) is cut at a second temperature lower than the first temperature and then is resupplied after a predetermined time so as to prevent malfunction of the overheating prevention, wherein, when a time interval for the temperature of the heater to rise from the third temperature to the first temperature is within a predetermined time, determining scale is not performed.

Description

STEAM GENERATOR AND CONTROL METHOD OF STEAM GENERATOR

The present invention relates to a steam generator and a control method thereof, and more particularly to, a steam generator sensing abnormal scale of a heater mounted therein

A steam generator is a device for generating steam using supplied water.

A conventional steam generator includes a water tank storing water, a water supply line supplying water to the water tank, a heater heating stored water, a steam line supplying generated steam to an outside, and a thermal fuse preventing overheating of the heater.

Water hardness varies among localities. Degree of scale generated at the heater varies in accordance with water hardness.

Scale refers to impurities or metal oxide of a film attached to a metal surface. Since scale has low thermal conductivity, coefficient of the heat transfer of the entire heater is significantly decreased.

When water having high hardness is used in the steam generator for long, scale is generated at a surface of the heater. In this case, scale causes malfunction of the thermal fuse, which is mounted inside or outside of the heater and functions as a safety device for prevention of heater overheating.

In detail, when water is not stored in the water tank mounted in the steam generator, the thermal fuse is blown to prevent overheating of the heater. There is a problem in that the thermal fuse is blown by scale generated at the heater although water is stored in the water tank.

Particularly, scale is easily generated in heated alkali water, in which a water temperature is increased to approximately 100°C by the heater so as to generate steam and the heated water is mixed with detergent to be alkali.

An object of the present invention devised to solve the problem lies on an algorithm for sensing scale generated in a heating part of a heater.

Another object of the present invention devised to solve the problem lies on an algorithm for previously controlling scale as scale generated at the heater is sensed in advance.

A further object of the present invention devised to solve the problem lies on prevention of a thermal fuse from being blown due to accumulation of scale although water is stored and prevention of generation of costs due to blow the thermal fuse.

The object of the present invention can be achieved by providing a steam generator includes a first chamber storing water, a heater heated to a third temperature to generate steam, an overheating protector cutting power supplied to the heater at a first temperature to prevent overheating of the heater when water is not stored in the first chamber, a second temperature sensor cutting power supplied to the heater at a second temperature lower than the first temperature and resupplying power after a predetermined time to prevent malfunction of the overheating protector although water is stored in the first chamber, and a controller connected to the heater and second temperature sensor, wherein the second temperature sensor is inoperative when a time interval for the temperature of the heater to increase from the third temperature to the first temperature is within a predetermined time.

The overheating protector and second temperature sensor may be disposed at one of an inside of the heater, a surface of the heater, or a surface of a temperature bridge disposed at the surface of the heater.

The overheating protector may be disposed at a maximum temperature rise point of the heater and the second temperature sensor may be disposed at a minimum temperature rise point of the heater.

The overheating protector may include a thermal fuse and the second temperature sensor may include a thermostat.

When the second temperature sensor is operated, the controller may control the heater to be heated but not to generate steam.

The controller may control a water supply valve supplying water to the first chamber, and when the second temperature sensor is operated, the controller may control the water supply valve to supply water to the first chamber.

When the heater is heated to the first temperature, the overheating protector may be operated.

In another aspect of the present invention, provided herein is a control method of a steam generator including supplying water to a first chamber, turning a heater on, wherein power is supplied to the heater to heat the heater to a third temperature so as to generate steam, preventing overheating, wherein power supplied to the heater is cut at a first temperature so as to prevent overheating of the heater, and determining scale, wherein power supplied to the heater is cut at a second temperature lower than the first temperature and then is resupplied after a predetermined time so as to prevent malfunction of the overheating prevention, wherein, when a time interval for the temperature of the heater to rise from the third temperature to the first temperature is within a predetermined time, determining scale is not performed.

The control method may further include supplying steam when preventing overheating and determining scale are not performed.

The control method may further include resupplying water to the first chamber after determining scale is performed.

The control method may further include waiting a predetermined time to have a resting phase.

The control method may further include supplying heated washing water after determining scale is performed.

Preventing overheating may be performed by a thermal fuse and determining scale may be performed by a thermostat.

There are advantages as below.

First, an algorithm for sensing scale generated in the heating part of the heater is provided.

Secondly, an algorithm for previously controlling scale as scale generated at the heater is sensed in advance is provided.

Third, problems in that the thermal fuse is blown due to accumulation of scale although water is stored and the heater is damaged are prevented, and, as such, expenses due to the problems are prevented.

Fourth, scale generated at the heater is sensed using a thermostat.

The accompanying drawings, which are included to provide a further understanding of the invention, illustrate embodiments of the invention and together with the description serve to explain the principle of the invention.

In the drawings:

FIG. 1 is a view illustrating a steam generator mounted in a dishwasher according to an embodiment of the present invention;

FIG. 2 is a view illustrating a pump of the steam generator according to the illustrated embodiment of the present invention;

FIG. 3 is an exploded view illustrating a part of the steam generator according to the illustrated embodiment of the present invention;

FIG. 4 is a graph illustrating change in temperature of the heater over time according to the illustrated embodiment of the present invention;

FIG. 5 is a graph illustrating change in temperature of the heater according to number of usage of the heater to generate steam in the illustrated embodiment of the present invention;

FIG. 6 is a block diagram of the illustrated embodiment of the present invention;

FIG. 7 is a flowchart illustrating a control method of the dishwasher including the steam generator according to the illustrated embodiment of the present invention;

FIG. 8 is an algorithm for preventing overheating of the heater and for sensing scale of the heater according to the illustrated embodiment of the present invention; and

FIG. 9 is an algorithm for preventing overheating of the heater and sensing abnormality of a water supply valve according to the illustrated embodiment of the present invention.

Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Unless otherwise defined, all terms including technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

Meanwhile, the configuration of an apparatus or a control method of the apparatus, which will be described below, is merely given to describe the embodiments of the present invention, without being intended to limit the scope of the present invention. The same reference numerals used throughout the specification refer to the same constituent elements.

The present invention relates to a steam generator and a control method of the same. The steam generator is used to be included in household electric appliances such as a dishwasher, a washing machine, and so on. Hereinafter, the steam generator used to be included in the dishwasher will be explained.

FIG. 1 is a view illustrating a steam generator mounted in a dishwasher according to an embodiment of the present invention. FIG. 2 is a view illustrating a pump of the steam generator according to the illustrated embodiment of the present invention.

FIG. 3 is an exploded perspective view illustrating a part of the steam generator according to the illustrated embodiment of the present invention.

A dishwasher is a household electric appliance for spraying washing water to a washing target so as to remove foreign substances remaining at the washing target. The dishwasher is capable of washing the washing target using heated washing water (hot water), or washing or sterilizing the washing target by supplying stream to the washing target.

As illustrated in FIG. 1, the dishwasher 100 may include a cabinet 1, a tub 11 disposed in the cabinet 1 to provide a washing space, spray arms 3 and 5 for spraying washing water to the washing target, and a pump 8 for supplying washing water to the spray arms 3 and 5.

Racks for storing washing targets may be disposed in the tub 11. The racks may include an upper rack 191 disposed at an upper portion of the tub 11 and a lower rack 193 disposed below the upper rack 191.

The tub 11 may be opened/closed by a door 16 disposed at one side of the cabinet 1. After a user opens the tub 11 by the door 16, the

racks

191 and 193 may be withdrawn from the tub 11.

When the racks include the upper and

lower racks

191 and 193, the spray arms may include an upper spray arm 3 for spraying washing water to the upper rack 191, and a lower spray arm 5 for spraying washing water to the lower rack 193.

Washing water (washing water remaining in the tub 11) sprayed by the spray arms 3 and 5 to the washing targets may be recovered to a sump 13.

The sump 13 may be disposed below the tub 11 and may be a means for storing washing water. The sump 13 may be separated from the tub 11 by a sump cover 15. In this case, the sump cover 15 may include recovery holes 151 communicating an inside of the tub 11 with an inside of the sump 13.

Meanwhile, the sump 13 may be connected to a water source (not shown) through a water supply line 135. The water supply line 135 may be opened/closed by a water supply valve 136 controlled by a controller (not shown).

Washing water stored in the sump 13 is discharged from the dishwasher by a drain line 137 and a drain pump 139.

Washing water stored in the sump 13 may be supplied to the spray arms 3 and 5 through a pump 8 and a supply line 7. The supply line 7 may include a connection line 77 connected to the pump 8, a first supply line 71 connected between the connection line 77 and upper spray arm 3, and a second supply line 73 connected between the connection line 77 and lower spray arm 5.

The upper spray arm 3 may be rotatably coupled to the first supply line 71. The lower spray arm 5 may be rotatably coupled to the second supply line 73.

The first and

second supply lines

71 and 73 may branch off the connection line 77. In this case, a switching valve 75 for controlling opening/closing the first and

second lines

71 and 73 may be disposed at a branch point of the first and

second supply lines

71 and 73.

The pump 8 may include a body 82 fixed in the cabinet 1, a partition 84 separating an inner space of the body 82 to define a first chamber C1 and a second chamber C2 in the body 82, a communication hole 86 disposed at the partition 84 to communicate the first chamber C1 with the second chamber C2, an inlet 841 connecting the sump 13 to the first chamber C1, an outlet 849 connecting the second chamber C2 to the connection line 77, an impeller disposed in the second chamber C2, and a heater assembly H disposed at a bottom surface of the first chamber C1.

As illustrated in FIG. 2, the body 82 may be disposed to have a cylinder shape having an open top surface 821 and an open bottom surface 825. A cover 823 is mounted at the open top surface 821 (a top surface of the second chamber C2) disposed at an upper part of the body 82. The heater assembly H is detachably coupled to the open bottom surface 825 (a bottom surface of the first chamber C1) disposed at a lower part of the body 82.

According to the illustrated embodiment of the present invention, as the heater assembly H is formed at the bottom surface 825 of the first chamber C1, the pump 8 capable of both heating and circulating washing water may be provided. In addition, as the heater assembly H is detachable at an outside of the pump 8. Thus, the pump 8 including the heater assembly H which is easily assembled or disassembled may be provided.

The impeller 85 may be a means for transferring washing water introduced from the first chamber C1 to the second chamber C2 through the communication hole 86. The impeller 85 may be rotated by a driving part 87 disposed at the outside of the body 82.

The driving part 87 may include a motor 871 fixed at the cover 823. A rotation axis 873 of the motor 871 may be fixed at the impeller 85 while passing through the cover 823.

As illustrated in FIG. 3, the heater assembly H may include a housing 81 forming the bottom surface 825 of the first chamber C1 and a heater 83 disposed at the outside of the first chamber C1 to heat the housing 81. Accordingly, the heater 83, the housing 81, the first chamber C1 and the second chamber C2 are sequentially stacked in a height direction to have a vertical mutual arrangement.

To efficiently supply thermal energy supplied by the heater 83 to washing water in the first chamber C1, the housing 81 may be formed of a highly thermally conductive material such as metal.

The housing 81 may include an accommodating groove 811 disposed at an outside of the first chamber C1 so as to accommodate the heater 83, and a coupler 812 for fixing the housing 81 at the body 82.

The accommodating groove 811 may have a shape capable of maximizing a surface area of the housing 81 to exchange heat with washing water. As illustrated in FIG. 3, the accommodating groove 811 protrudes toward an inside of the first chamber C1 as an example.

According to the illustrated embodiment of the present invention, to prevent the heater inserted into the accommodating groove 811 from being exposed to the outside of the accommodating groove 811, a heater cover 815 fixed to the housing 81 may be further provided.

The heater cover 815 is a means for preventing washing water or foreign substances from being supplied to the heater 83 as well as for preventing other components of the dishwasher around the pump 8 from directly contacting the heater 83.

The heater 83 may include a heater body 831 for generating thermal energy upon supply of current, and first and

second terminals

833 and 835 for supplying current to the heater body 831.

According to the illustrated embodiment of the present invention, since the heater 83 is disposed at the outside of the first chamber C1, the heater 83 does not contact washing water. Thus, decrease of heat exchange efficiency between washing water and the heater 83 due to attachment of foreign materials to a surface of the heater 83, or decrease of durability due to corrosion of the surface of the heater 83 may be prevented. However, in another embodiment of the present invention, the heater 83 does not exclude a structure, in which washing water is in contact with the heater 83 to heat the washing water.

To easily assemble the heater assembly H and the body 82, position fixers 89 may be further provided at the pump 8.

Each position fixer 89 may include a coupling protrusion 891 disposed at the body 82 and a protrusion accommodating groove 893 disposed at the housing 81 to accommodate the coupling protrusion 891.

In such a configuration of the heater assembly H, since the housing 81 forms the bottom surface of the first chamber C1, the impeller 85 may be rotated and hot water (heated washing water) may be supplied to the spray arms 3 and 5 during operation of the heater 83 (during supply current to the heater 83).

In the illustrated pump 8, since the heater assembly H is disposed at the bottom surface of the first chamber C1, the pump 8 may also function as a steam generator when only the heater 83 is operated after a certain amount of washing water is supplied to the first chamber C1. That is, according to the illustrated embodiment of the present invention, it may regard that a steam generator including the first chamber C1 storing water and the heater 83 heating water to generate steam are provided.

However, when the pump 8 functions to generate steam, a steam outlet 843 for discharging steam generated in the first chamber C1 to the outside of the first chamber C1 may be further provided at the pump 8.

As illustrated in FIG. 1, a steam supplier 6 may communicate with the tub 11 through the steam outlet 843. The steam supplier 6 may include a nozzle 61 fixed at the tub 11 and a supply pipe 63 connected between the nozzle 61 and the steam outlet 843. The steam outlet 843 may be disposed to be lower than the partition 84 and to be higher than the inlet 841.

Meanwhile, when the steam outlet 843 is disposed at the first chamber C1, a valve 844 for preventing inflow of outside air may be further provided at one of the steam outlet 843 and the supply pipe 63.

When outside air is introduced to the first chamber C1 through the steam outlet 843, water pressure of washing water sprayed from the spray arms 3 and 5 may be decreased or washing water may not be supplied to the spray arms 3 and 5. During rotation of the impeller 85, when there is no valve 844 at the steam outlet 843, outside air may be introduced to the first chamber C1.

The valve 844 may be disposed to discharge fluid in the first chamber C1 to the outside of the first chamber C1 and to prevent introduction of outside fluid to the first chamber C1. That is, the valve 844 may include a check valve, which opens the steam outlet 843 (or the steam supplier 6) only when internal pressure of the first chamber C1 is equal to or greater than a predetermined reference pressure.

FIG. 4 is a graph illustrating change in temperature of the heater over time when an overheating protector is operated according to the illustrated embodiment of the present invention. FIG. 5 is a graph illustrating change in temperature according to number of repetition of steam generation according to the illustrated embodiment of the present invention.

Meanwhile, as illustrated in FIG. 3, the heater assembly H may further include the overheating protector 90 for preventing overheating of the heater 83 and a second temperature sensor 93 for preventing malfunction of the overheating protector 90.

When water is not stored in the first chamber C1, in order to prevent damage of the heater 83 due to overheating of the heater 83 and fire risk, the overheating protector 90 functions to cut current supplied to the heater 83 at a first temperature T1.

The overheating protector 90 is disposed to be in contact with the inside of the heater 83, the surface of the heater 83, or a thermal bridge 91 disposed at the surface of the heater 93.

The overheating protector 90 includes an electric circuit. The electric circuit and the heater 83 are disposed in series and, as such, overheating of the heater 83 is prevented when excessive current is supplied to the heater 83.

The overheating protector 90 may include a thermal fuse. The thermal fuse is a kind of switch for preventing overheating of electric appliances, and is deformed or melts at a certain temperature to open an electric circuit. For example, a low melting point alloy line or a ribbon which melts at a certain temperature to cut itself may be used. A plastic which is deformed to soften at a certain temperature to open an electric contact may be used.

Meanwhile, when a thermal fuse is provided as the overheating protector 90, the overheating protector 90 may include a first thermal fuse 90a connected to the first terminal 933 and a second thermal fuse 90b connected to the second terminal 835. Since there are at least two thermal fuses, although one of the thermal fuses malfunctions, fire risk may be prevented in advance.

The overheating protector 90 is mounted at a point where temperature maximally rises when the heater body 82 of the heater 83 is heated. For example, the overheating protector 90 may be disposed at a central part of the heater body 82 between the first and

second terminals

833 and 835. It is because the temperature of the central part of the heater body 82 is likely to maximally increase. The overheating protector 90 needs to be mounted at a maximum temperature rise point so as to prevent fire and overheating of the heater 83.

Water is heated to 100°C or more to generate steam. To this end, as illustrated in FIG. 4, the heater 83 is heated to a third temperature T3 of 100°C or more. However, when there is no water in the first chamber C1, temperature of the heater 83 rapidly increases and, as such, fire may occur. The overheating protector 90 is operated at the first temperature T1 to cut power supplied to the heater 83 and, as such, temperature of the heater 83 rapidly falls.

The first temperature T1 allowing the overheating protector 90 to be cut off may be approximately 260°C. However, according to present invention, the first temperature T1 is not limited to the above description. In addition, the first temperature T1 may have an optimized value based on specifications of the overheating protector 90 and specifications of the electric appliance including the steam generator.

Furthermore, a time interval ΔT for temperature of the heater 83 to rapidly rise from the third temperature T3 to the first temperature T1 is within a predetermined time ΔTd. The predetermined time ΔTd, in which temperature of the heater 83 rapidly rises to the first temperature, is about 20 to 30 seconds.

Meanwhile, the second temperature sensor 93 functions to prevent malfunction of the overheating protector 90 although there is water in the first chamber C1.

Generally, the steam generator includes a first sensor 92 to measure the temperature of water in the first chamber C1. The first temperature sensor 92 may include a thermistor. Temperature of the heater 83 may be controlled by temperature of water sensed at the thermistor and, as such heated washing water and steam may be generated.

However, when water supplied to the first chamber C1 has high hardness and water is heated to 100°C or more to generate steam, scale is generated at a part (the heater 83 or a part receiving heat transmission from the heater 83) for heating water mixed with alkali. When scale is generated, thermal conductivity of the part for heating water may be decreased.

As illustrated in FIG. 5, as number of usage of the heater 83 for generating steam is increased, thermal conductivity of the part for heating water, and as such, the heater 83 should be heated to higher temperature to generate steam. Accordingly, when a temperature of the heater 83 rises to the first temperature T1, the overheating protector 90 is operated (blowing the thermal fuse) and then is replaced.

To this end, in the illustrated embodiment of the present invention, the second temperature sensor 93 is provided to prevent malfunction of the overheating protector 90. To prevent operation of the overheating protector 90 although water is stored in the first chamber C1, the second temperature sensor 93 cuts current supplied to the heater 83 at the second temperature T2 lower than the first temperate T1 and then resupplies current after a predetermined time.

The second temperature sensor 93 may be connected to the heater 83 in series. The second temperature sensor 93 may be disposed between the first terminal 833 and the first thermal fuse 90a or between the second terminal 835 and the second thermal fuse 90b.

The second temperature sensor 93 may be disposed at a minimum temperature rise point of the heater 83. In detail, the second temperature sensor 93 may be disposed at a part (an end of the heater body 82) of the heater body 82 in contact with the first terminal 833 of the heater 83 because the end of the heater body 82 has a temperature lower than the central part of the heater body 82.

The second temperature sensor 93 includes a thermostat. The thermostat is an auto temperature controller, that is, a device automatically maintaining constant temperature using expansion or contraction thereof based on temperature. Generally, a bimetal type thermostat may be mostly used. The bimetal type thermostat is formed by attaching two kinds of metal materials having different coefficients of thermal expansion. In this case, as temperature increases, the bimetal type thermostat bends toward one metal material having low coefficient of thermal expansion and, as such, the point of contact is opened to cut current. After a predetermined time, the metal materials are cooled to be restored and, as such, current flows again.

Meanwhile, when the time interval ΔT for temperature of the heater 83 to increase from the third temperature T3 to the first temperature T1 is within a predetermined time ΔTd, the second temperature sensor 93 is not operated. The predetermined time ΔTd is about 20 to 30 seconds.

That is, although the second temperature sensor 93 opens the electric circuit at the second temperature T2 and closes the same after a predetermined time, the second temperature sensor 93 does not respond to rapid temperature change.

When predetermined thermal energy is supplied to the second temperature sensor 93, the second temperature sensor 93 opens and closes the electric circuit at the second temperature T2. Conversely, when predetermined thermal energy is not supplied to the second temperature sensor 93, the second temperature sensor 93 does not open and close the electric circuit although temperature of the heater 83 is greater than the second temperature T2.

Namely, when temperature of the heater 83 increases to the second temperature T2 or more, the second temperature sensor 93 cuts power supplied to the heater 83, and then resupplies power to the heater 83 after a predetermined time. However, when the heater 83 is heated and then the time interval ΔT for temperature of the heater 83 to rapidly rise from the third temperature T3 to the first temperature T1 (temperature for operation of the overheating protector 90) is within the predetermined time ΔTd, the overheating protector 90 operates earlier than the second temperature sensor 93.

The second temperature T2 for operation of the second temperature sensor 93 may be within about 120°C. However, temperature to be determined by tests is not limited to the above temperature.

The first and second temperatures T1 and T2 are determined corresponding to the surface temperature of the heater 83. For example, when temperature for cutting power is the first temperature T1 to prevent overheating of the heater 83 at the maximum temperature rise point of the heater 83, the temperature of the maximum temperature rise point may be determined to be lower than the first temperature T1 and the temperature of the minimum temperature rise point may be determined to be the second temperature T2.

Thus, although water is stored in the first chamber C1, when the heater 83 is overheated and temperature of the heater 83 is increased, a surface temperature of a part, at which the second temperature sensor 93 is mounted, is around the second temperature T2, and a surface temperature of a part, at which the overheating protector 90 is mounted, is below the first temperature T1. As a result, the overheating protector 90 is not operated.

However, when there is no water in the first chamber C1, the heater 83 is overheated, and temperature of the heater 83 is increased, the surface temperature of the part, at which the overheating protector 90 is mounted, reaches the second temperature T2 before the second temperature sensor 93 is operated. Thus, the overheating protector 90 is operated to cut power supplied to the heater 83.

FIG. 6 is a block diagram illustrating a controller and the components according to the illustrated embodiment of the present invention.

Referring to FIG. 6, according to the illustrated embodiment of the present invention, the dishwasher 100 may further include the controller 94 for controlling the heater 83 and the water supply valve 136, and a display part 95 connected to the controller 94 to display information to a user.

When the second temperature sensor 93 includes a thermostat and current supplied to the heater 83 is cut off by the thermostat, the controller 94 recognizes change of current of a DC link device 941, thereby counting whether the second temperature sensor 93 is operated or not.

When the controller 94 senses change of current of the DC link device 941 at least once, the controller 94 recognizes that scale is generated at the heater 83.

When the second sensor 89 is operated, the controller 94 controls the heater 83 to be heated but not to generate steam. For example, when temperature of the heater 83 is the third temperature T3 to generate steam and the second temperature sensor 93 is operated, the controller 94 may control the heater 83 to have temperature lower than the third temperature T3. Thus, reoperation of the second temperature sensor 93 may be prevented.

Then, the controller 94 commands stoppage of steam supply and supply of heated washing water (hot water).

When the first temperature sensor 92 is operated, the controller 94 controls the water supply valve 136 to resupply water to the first chamber C1. Thus, the overheated heater 83 is cooled.

Meanwhile, when the first temperature sensor 92 is operated, the controller 94 informs a user of scale generated at the heater 83 through the display part 95.

The display part 95 may include a display device to visually display information. Alternatively, the display part 95 may include an alarm device to acoustically transfer information.

FIG. 7 illustrates a control method of the dishwasher mounted with the stream generator according to the illustrated embodiment of the present invention.

The control method includes selecting course/option S10, in which the user selects a course or an option, washing/rinsing the washing target S20, and drying the washing target S30, in which rinsing is completed.

In selecting the course/option S10, the user may select a course using steam or a course without steam. Additionally, options such as spraying steam or not, steam spraying time, spraying amount of steam, and so on may be selected.

Washing/rinsing S20 includes spraying a cleansing solution S22 including a detergent, and spraying washing water S23 mixed with the cleaning solution, which rinses the washing target. In addition, spraying final washing water S23 which is finally rinsing the washing target may be further conducted after spraying washing water S23.

Furthermore, pre-washing S21 which is spraying a small quantity of washing water or stream in order to sock foreign substances of the washing target may be further provided before spraying cleaning solution step S22.

Drying S30 may include drying using steam S31, wherein steam is supplied to the washing target, the temperature of the washing target is increased and water in the washing target is vaporized, and as such, the washing target is dried. In addition, after drying using steam S31, the control method of the dishwasher may further include cooling the heater 83 S32, in which water is resupplied to the first chamber C1 to cool the heated heater 83, and draining remaining water from the first chamber C1 S33.

FIG. 8 is an algorithm to prevent overheating of the heater or to sense scale of the heater according to the illustrated embodiment of the present invention. FIG. 9 is an algorithm to prevent overheating of the heater or to sense malfunction of the water supply valve.

Hereinafter, when the user selects the course using steam or the option using steam, a control algorithm for sensing scale generated in the heater 83 will be explained. Namely, in pre-washing S21 or drying using steam S31, when steam is sprayed to the washing target stored in the tub 11, a control algorithm for preventing overheating of the heater 83 and sensing scale generated in the heater 83 is used.

According to the illustrated embodiment of the present invention, the control method of the steam generator includes supplying stream S100, wherein water is supplied to the first chamber C1, turning the heater 83 on S130, wherein power is supplied to the heater 83 to heat the heater 83 to the third temperature T3, preventing overheating S200, wherein power supplied to the heater 83 is cut off to prevent overheating of the heater 83, and determining scale S300, in which power supplied to the heater 83 is cut off at the second temperature T2 lower than the first temperature and then is resupplied after a predetermined time so as to prevent malfunction of preventing overheating S200.

When the course using steam or the addition option using steam is selected in selecting the course/option S10, supplying steam S100 includes supplying a small quantity of water to the first chamber C1 so as to use steam in pre-washing S21 or dying using steam S31. In detail, water is supplied to the sump 13 through the water supply line 135. Water is supplied to the first chamber C1 through the inlet 841.

Meanwhile, after supplying steam S100, the control method may further include sensing a water level in the first chamber C1 S110 and resupplying water S120 when the sensed water level is lower than a predetermined water level according to the course or option.

In sensing the water level S110, the water level is sensed by a water level sensor 96 disposed in the first chamber C1 and the water level sensor 96 is connected to the controller 94. In this case, when the water level sensor 96 senses that the water level is lower than the predetermined water level, the water supply valve 136 is opened to supply water to the first chamber C1.

In turning the heater 83 on S130, power is supplied to the heater 83 and the heater 83 is heated to a temperature for generation of steam.

In preventing overheating S200, when water is not supplied to the first chamber C1 or water is evaporated, fire due to overheating of the heater 83 may be prevented.

Preventing overheating S200 is performed by the overheating protector 90. The overheating protector 90 includes a thermal fuse. Accordingly, when temperature of the heater 83 reaches to the first temperature T1, the thermal fuse is blown to cut power supplied to the heater 83.

In determining scale S300, although the temperature reaches to the first temperature T1, blowing the thermal fuse is prevented because, as thermal conductivity is decreased due to scale generated at the heater 83, the heater 83 is heated to a higher temperature than before generating scale. Namely, although water is stored in the first chamber C1, the thermal fuse may be blown, and, as such, determining scale S300 prevents operation of the thermal fuse.

Determining scale S300 is not performed S310 when the time interval ΔT for temperature of the heater 83 to rise from the third temperature T3 to the first temperature T1 is within a predetermined time ΔTd. That is, when the first chamber C1 has no water, temperature of the heater 83 is rapidly increased. Thus, determining scale S300 is not performed, but preventing overheating S200 is performed.

Determining scale S300 is performed by the second temperature sensor 83. The second temperature sensor 83 includes a thermostat. As explained above, the second temperature sensor 83 cuts power of the heater 83 at the second temperature T2. However, when temperature of the heater 83 is rapidly increased from the third temperature T3 to the first temperature T1, the thermostat is supplied insufficient thermal energy to be operated, thereby not being operated. When the temperature of the hater 83 reaches the first temperature T1, the thermal fuse is blown.

The predetermined time ΔTd is about 20 to 30 seconds. The predetermined time ΔTd refers to as a minimum time for driving the second temperature sensor 93.

Meanwhile, according to the illustrated embodiment of the present invention, after determining scale S300, resupplying water S340 to the first chamber C1 may be further performed.

This is when the heater 83 is overheated by scale of the heater 83 and, as such, the controller 94 controls the water supply valve 136 to supply water to the first chamber C1. Accordingly, damage of the heater 83 is prevented and blowing the thermal fuse, as the overheating protector 90, is prevented.

Meanwhile, according to the illustrated embodiment of the present invention, after determining scale S300, waiting S330 a predetermined time to have a resting phase is further performed.

Here, a reason for waiting S330 will be explained. When the first temperature sensor 92 includes a thermostat and is operated at the second temperature T2, the thermostat needs a predetermined time for reconnection thereof to supply power the heater 83.

Meanwhile, according to the illustrated embodiment of the present invention, when determining scale S300 is performed, a user may be acoustically or visually informed of scale generation using the display part 96.

Meanwhile, according to the illustrated embodiment of the present invention, after determining scale S300, supplying hot water S350, which is supplying heated washing water, is further performed.

That is, steam is generated to perform supplying steam but the sequential operation changes from supplying steam to supplying heated washing water (hot water) in case of determining that scale is generated at the heater 83 so as to prevent overheating of the heater 83.

In detail, the heater 83 is heated to spray steam during pre-washing S21 or drying using steam S31 of drying S30. In this case, when determining scale S300 is performed, the sequential operation changes to a general operation, such as, pre-washing using hot water or drying using hot water S30.

Meanwhile, according to the illustrated embodiment of the present invention, when preventing overheating S200 and determining scale S300 are not performed, supplying steam S160 is performed.

When the course for spraying steam or the option for spraying steam is selected by a user, the heater 83 is heated to generate steam. In this case, when preventing overheating S200 is performed, the power supplied to the heater 83 is cut off and thus washing is finished in an instant. Whereas, when determining scale S300 is performed, the course or option for spraying steam is not performed but the course or option for spraying hot water (heated washing water) is performed. Thus, supplying steam S160 may be performed only when the preventing overheating S200 and determining scale S300 are not performed.

Meanwhile, referring to FIG. 9, when a temperature T sensed by the first temperature sensor 92 is greater than a predetermined temperature Td, resupplying water S460 to the first chamber C1 is further performed according to the illustrated embodiment of the present invention. When the temperature T is less than the predetermined temperature Td, the control algorithm illustrated in FIG. 8 is performed to generate steam.

The first temperature sensor 92 is disposed in the first chamber C1 to measure temperature of water stored in the first chamber C1. The first temperature sensor 92 includes a thermistor.

When the first temperature sensor 92 is submerged in water stored in the first chamber C1, temperature of water heated by the heater 83 is not far above 100°C. However, when water in the first chamber C1 is evaporated, the first temperature sensor 92 measures temperature of air in the first chamber C1. In this case, temperature measured by the first temperature sensor 92 is rapidly increased. Additionally, when the heater 83 is heated without water, there may be a risk of fire. To this end, resupplying water S460 is used.

Meanwhile, according to the illustrated embodiment of the present invention, the temperature T sensed at the first temperature sensor 92 is greater than the predetermined temperature Td so that resupplying water S460 is performed. A number of times of performing resupplying water S460 is counted. In this case, comparing the number N of repetition with a predetermined number Nd to determine whether the number N is greater or less than the predetermined number Nd S440 is further provided. When the number N is less than the predetermined number Nd, resupplying water S460 is performed. Whereas, the number N is greater than the predetermined number Nd, a water supply error is displayed S450 using the display part 95.

It will be apparent to those skilled in the art that the present invention described above is not limited to the embodiments described above and the accompanying drawings, and various substitutions, modifications, and alterations may be devised within the spirit and scope of the present invention.

Various embodiments have been described in the best mode for carrying out the invention.

Claims

A steam generator comprising:

a first chamber storing water;

a heater heated to a third temperature to generate steam;

an overheating protector cutting power supplied to the heater at a first temperature to prevent overheating of the heater when water is not stored in the first chamber;

a second temperature sensor cutting power supplied to the heater at a second temperature lower than the first temperature and resupplying power after a predetermined time to prevent malfunction of the overheating protector although water is stored in the first chamber; and

a controller connected to the heater and second temperature sensor,

wherein the second temperature sensor is inoperative when a time interval for the temperature of the heater to be increased from the third temperature to the first temperature is within a predetermined time.
The steam generator according to claim 1, wherein the overheating protector and second temperature sensor are disposed at one of an inside of the heater, a surface of the heater, or a surface of a temperature bridge disposed at the surface of the heater.
The steam generator according to claim 1, wherein the overheating protector is disposed at a maximum temperature rise point of the heater and the second temperature sensor is disposed at a minimum temperature rise point of the heater.
The steam generator according to claim 1, wherein the overheating protector includes a thermal fuse and the second temperature sensor includes a thermostat.
The steam generator according to claim 1, wherein, when the second temperature sensor is operated, the controller controls the heater to be heated but not to generate steam.
The steam generator according to claim 1, wherein the controller controls a water supply valve supplying water to the first chamber, and

when the second temperature sensor is operated, the controller controls the water supply valve to supply water to the first chamber.
The steam generator according to 1, wherein, when the heater is heated to the first temperature, the overheating protector is operated.
A control method of a steam generator comprising:

supplying water to a first chamber;

turning a heater on, wherein power is supplied to the heater to heat the heater at a third temperature so as to generate steam;

preventing overheating, wherein power supplied to the heater is cut at a first temperature so as to prevent overheating of the heater; and

determining scale, wherein power supplied to the heater is cut at a second temperature lower than the first temperature and then is resupplied after a predetermined time so as to prevent malfunction of the overheating prevention,

wherein, when a time interval for the temperature of the heater to rise from the third temperature to the first temperature is within a predetermined time, determining scale is not performed.
The control method according to 8, further comprising supplying steam when preventing overheating and determining scale are not performed.
The control method according to 8, further comprising resupplying water to the first chamber after determining scale is performed.
The control method according to 8, further comprising waiting a predetermined time to have a resting phase.
The control method according to 8, further comprising supplying heated washing water after determining scale is performed.
The control method according to 8, wherein preventing overheating is performed by a thermal fuse and determining scale is performed by a thermostat.