Patent Description:
Generally, in a washing machine, a drum accommodating laundry is rotatably provided in a tub for providing a space for containing water. Through holes are formed in the drum, water in the tub flows into the drum, and the laundry is moved by the rotation of the drum to remove contamination.

Conventional washing machine may be provided with a heater for heating the water in the tub. The heater is, generally, operated in a state of being submerged inside the tub, and directly heats the water. However, such a heater should be operated in a state of being always submerged in the water for safety reasons. That is, the heater may be used for heating the water in the tub. However, the heater is not suitable for heating the air in the drum in the state where there is no water in the tub, or for heating the wet laundry.

As a washing machine which directly heats a drum in contact with laundry regardless of whether the tub is filled with water, <CIT> discloses a washing drying machine (or a washing machine having a drying function) provided with a non-contact type heating device using microwave, electromagnetic induction, infrared rays, and the like.

In addition, <CIT>discloses a washing machine in which a drum is heated by an induction heating system. In this washing machine, a heat sensor is disposed between the drum and a tank (or the tub) is configured to detect the temperature of water or the temperature of air in the tank, and control the induction heating system based on such detected value.

However, since the method of controlling the temperature using the heat sensor is based on the premise that the washing machine operates normally, when the heat sensor malfunctions or when a failure occurs in a controller for processing a signal of the heat sensor, the control over the induction heating system is also unreliable, which may cause a safety accident due to overheating.

<CIT> discloses for washing and/or drying laundry comprising at least a first electrical unit and at least a first electrical sensor element which is arranged to rotate together with the drum, wherein the first electrical unit and the first electrical sensor element are arranged and configured to allow a temperature dependent electrical interaction.

Additional background information can be found in documents <CIT>, <CIT>, <CIT>, <CIT> , and <CIT>.

The present invention has been made in view of the above problems, and provides a washing machine in which the operation of the induction heater is automatically stopped when the temperature of the drum using the temperature sensor is not normally controlled and the drum is overheated.

The present invention further provides a washing machine having a safety device for automatically blocking the power applied to the induction heater, not only when the drum is overheated, but also when the induction heater is overheated. In particular, the present invention further provides a washing machine in which a circuit for transmitting a control signal to a relay for applying a current of an input power to the induction heater is opened by the safety device.

The present invention further provides a washing machine capable of still driving the motor for rotating the drum even if the power applied to the induction heater is blocked by the safety device.

The present invention further provides a washing machine configured to include a first safety control means for reversibly opening a circuit for applying power to the induction heater, and a second safety control means for irreversibly opening the circuit when the overheating condition is not resolved despite the first safety control.

The present invention further provides a washing machine having a thermostat as the first safety control means, and a thermal fuse as the second safety control means.

The present invention further provides a washing machine in which the position of the thermostat is optimized so that the thermostat may be sensitive to temperature changes of the drum.

The present invention further provides a washing machine in which the position of the thermal fuse is optimized so that the thermal fuse may be sensitive not only to the heat of the drum but also to the heat of the induction heater.

The present invention further provides a washing machine having a thermostat which reversibly blocks the circuit by the heat of the induction heater before the thermal fuse is operated.

In accordance with an aspect of the present invention, there is provided a washing machine as defined by independent claim <NUM>.

In accordance with another aspect of the invention, the is provided a method of controlling a washing machine as defined by independent claim <NUM>.

The objects, features and advantages of the present invention will be more apparent from the following detailed description in conjunction with the accompanying drawings, in which:.

Exemplary embodiments of the present invention are described with reference to the accompanying drawings in detail. The same reference numbers are used throughout the drawings to refer to the same or like parts. Detailed descriptions of well-known functions and structures incorporated herein may be omitted to avoid obscuring the subject matter of the present invention.

<FIG> is a side sectional view of a washing machine according to an embodiment of the present invention. <FIG> is an exploded perspective view of a tub and an induction heater. <FIG> is a plan view of a heater base shown in <FIG>.

Referring to <FIG>, a casing <NUM>, <NUM>, <NUM>, <NUM> forms an outer shape of a washing machine <NUM> according to an embodiment of the present invention, and an input port into which laundry is inputted is formed on the front surface of the washing machine. The casing may include a cabinet <NUM> which has a front surface opened, a left surface, a right surface, and a rear surface, and a front panel <NUM> which is coupled to the open front surface of the cabinet <NUM> and has the input port formed therein. In addition, the casing <NUM>, <NUM>, <NUM>, <NUM> may further include a top plate <NUM> covering the opened upper surface of the cabinet <NUM> and a control panel <NUM> disposed above the front panel <NUM>.

In the casing <NUM>, <NUM>, <NUM>, <NUM>, a tub <NUM> for containing water is disposed. The tub <NUM> has an opening formed on the front surface thereof so as to allow laundry to be inputted, and the opening communicates with the input port formed in the casing <NUM>, <NUM>, <NUM>, <NUM> by a gasket <NUM>. The tub <NUM> may be configured in such a manner that a tub front portion <NUM> forming a front portion of the tub <NUM> and a tub rear portion <NUM> forming a rear portion of the tub <NUM> are coupled to each other.

The front panel <NUM> is rotatably provided with a door <NUM> for opening and closing the input port. The control panel <NUM> is provided with a display unit (not shown) for displaying various state information of the washing machine <NUM> and an input unit (not shown) for receiving various control commands such as a washing course, operating time for each process, reservation from a user.

A dispenser <NUM> for supplying an additive such as laundry detergent, fabric softener, or bleaching agent to the tub <NUM> is provided. The dispenser <NUM> includes a detergent box in which the additive is contained, and a dispenser housing in which the detergent box is removably stored. A water supply hose <NUM> connected to an external water source such as a faucet to receive raw water, and a water supply valve <NUM> for interrupting the water supply hose <NUM> may be provided. When the water supply valve <NUM> is opened and water is supplied through the water supply hose <NUM>, the detergent in the detergent box is mixed with water and flows into the tub <NUM>.

The tub <NUM> may be suspended from the top cover <NUM> by a spring <NUM>, and may be supported by a damper <NUM> disposed in a lower side. Therefore, the vibration of the tub <NUM> is buffered by the spring <NUM> and the damper <NUM>.

A drum <NUM> is rotatably disposed in the tub <NUM>. The drum <NUM> may be implemented of a material (or a material whose current is induced by a magnetic field (or a magnetic force) or a ferromagnetic body) heated in a non-contact type by a later-described induction heater <NUM>. Preferably, the drum <NUM> may be implemented of metal material, e.g., stainless steel. A plurality of through holes <NUM> may be formed in the drum <NUM> so that water can be exchanged between the tub <NUM> and the drum <NUM>.

The washing machine according to the present embodiment is a front loading type in which the drum <NUM> is rotated about a horizontal axis O. However, the present invention is also applicable to a washing machine of a top loading type. In this case, a drum rotated about a vertical axis is provided.

The drum <NUM> is rotated by a driving unit <NUM>, and a lifter <NUM> is provided inside the drum <NUM> so as to lift laundry. The driving unit <NUM> may include a motor capable of controlling a rotation direction and a speed. The motor is preferably a brushless direct current electric motor (BLDC), but it is not necessarily limited thereto.

A drainage bellows <NUM> for discharging the water in the tub <NUM> to the outside, and a pump <NUM> for pumping the water discharged through the drainage bellows <NUM> to a drainage hose <NUM> may be provided. The water pumped by the pump <NUM> is discharged to the outside of the washing machine through the drainage hose <NUM>.

An induction heater <NUM> for heating the drum <NUM> is provided. The induction heater <NUM> is a heater that uses an induction current generated by a magnetic field as a heat source. When a metal is placed in a magnetic field, an eddy current is generated in the metal due to electromagnetic induction and the metal is heated due to Joule heat.

The induction heater <NUM> is fixed to the tub <NUM> while being spaced apart from the drum <NUM>. When the induction heater <NUM> is operated, the drum <NUM> of metal material is heated. The tub <NUM> is implemented of a material (preferably, synthetic resin) through which a magnetic field can pass, and the induction heater <NUM> is disposed outside the tub <NUM>. However, it is not limited thereto, and the induction heater <NUM> can be disposed inside the tub <NUM>.

The induction heater <NUM> may include a coil <NUM> to which a current is applied, a heater base <NUM> that fixes the coil <NUM>, and a heater cover <NUM> which is coupled to the heater base <NUM> and covers the coil <NUM> from the upper side of the coil <NUM>.

The heater base <NUM> may be fixed to the tub <NUM>. The heater base <NUM> may be disposed in the outer side of the tub <NUM>, preferably, in the upper side of the tub <NUM>. The heater base <NUM> has a first coupling tab <NUM> provided with a fastening hole. Four first coupling tabs <NUM> may be symmetrically disposed. A fastening boss <NUM> is formed, in the tub <NUM>, at a position corresponding to the first coupling tab <NUM>. The heater base <NUM> has a substantially flat shape, but preferably has a shape substantially corresponding to the curvature of the outer circumferential surface of the tub <NUM>. The heater base <NUM> is implemented of a material through which a magnetic field can pass, and is preferably a synthetic resin material.

The coil <NUM> is fixed to the upper surface of the heater base <NUM>. In an embodiment, the coil <NUM> is formed by winding a single conducting wire 71a several times based on homocentricity on the upper surface of the heater base <NUM>, but may be formed of a plurality of conducting wires in the form of a closed curve having homocentricity according to an embodiment.

A fixing rib <NUM> for fixing the coil <NUM> is protruded from an upper surface <NUM> of the heater base <NUM>. The fixing rib <NUM> is wound while maintaining a gap 74r corresponding to the diameter of the conducting wire 71a forming the coil <NUM>. The coil <NUM> may be formed by winding the conducting wire 71a along the gap 74r.

The heater cover <NUM> may be provided with a ferromagnetic body. The ferromagnetic body may include ferrite. The ferromagnetic body may be fixed to the bottom surface of the heater cover <NUM>. Since the high resistance of the ferrite prevents the generation of eddy current, a current is intensively induced in the drum <NUM> positioned in the lower side of the coil <NUM>, so that the drum <NUM> can be effectively heated.

The heater cover <NUM> may be provided with a cooling fan <NUM> for cooling the coil <NUM>. The heater cover <NUM> may be provided with a fan mount 72d that forms an air passage for ventilating a space in which the coil <NUM> is accommodated. The cooling fan <NUM> may be disposed in the air passage.

The heater cover <NUM> is provided with a second coupling tab 72b having a fastening hole at a position corresponding to the first coupling tab <NUM> of the heater base <NUM>. A screw (not shown) may pass through the second coupling tab 72b and the first coupling tab <NUM> sequentially, and then be fastened to the fastening boss <NUM>.

Meanwhile, in order to process the laundry in the drum <NUM> at a desired temperature, the temperature of the drum <NUM> should be accurately controlled. The temperature of the drum <NUM> is greatly affected by the output of the induction heater <NUM>. The amount of the laundry inputted in the drum <NUM>, the amount of water contained in the tub <NUM>, the rotation speed of the drum <NUM>, and the amount of water contained in the laundry are affected by various factors. Therefore, it is difficult to obtain an accurate value when estimating the temperature of the drum <NUM> by only the output (or input) of the induction heater <NUM>.

Furthermore, it is assumed that the processes such as washing, rinsing, dewatering, drying, are usually performed by rotating the drum <NUM>. Thus, it is difficult to use a contact type temperature sensor to measure the temperature of the rotating drum <NUM>.

For these reasons, the present invention includes two temperature sensors 80a and 80b configured to detect the temperatures of air of two points between the drum <NUM> and the tub <NUM>, and the temperature of the drum <NUM> is estimated based on the values detected by these temperature sensors 80a and 80b.

Since this method measures the temperature of the air and estimates the temperature of the drum <NUM> based on the temperature of the air, it does not directly measure the temperature of the drum <NUM>. However, by using the value detected by two temperature sensors 80a and 80b, it is possible to estimate the temperature of the drum <NUM> more accurately and to detect the temperature change of the drum <NUM> more sensitively than in the conventional case where the temperature is sensed through a single temperature sensor.

<FIG> schematically shows a position where a first temperature sensor and a second temperature sensor are installed. <FIG> shows a state where a first temperature sensor is installed in a tub, and <FIG> shows a cross section of a thermistor. <FIG> is a graph showing the changes over time of the actual temperature Td_p of a drum, the detection value T1 of a first temperature sensor, the detection value T2 of a second temperature sensor, and the estimated value Td of drum temperature, when the induction heater is controlled in a certain pattern. <FIG> is a block diagram showing a control relationship between main components of a washing machine according to an embodiment of the present invention. <FIG> shows the heat amount transferred between an induction heater, a drum, and a first temperature sensor, which are referred to in the process of obtaining the estimated value of drum temperature.

Referring to <FIG>, two temperature sensors 80a and 80b include a first temperature sensor 80a and a second temperature sensor 80b. The first temperature sensor 80a itself is heated by the induction heater <NUM>, and the temperature detected by the first temperature sensor 80a under the normal operating condition of the washing machine is higher than the temperature Ta of the air in the tub <NUM>. That is, in a state of being heated by the induction heater <NUM>, the first temperature sensor 80a is a heating element that transmits heat to the air in the tub <NUM>, and the heat amount transmitted to the air at this time is indicated by Q1 in <FIG>.

Referring to <FIG>, the first temperature sensor 80a may include a thermistor assembly <NUM> and a heat insulating cover <NUM>. The thermistor assembly <NUM> may include a tube <NUM> made of a material (preferably, metal) that is heated by the induction heater <NUM>, and a thermistor <NUM> disposed in the tube <NUM>. Here, at least a part of the outer surface of the tube <NUM> is exposed between the tub <NUM> and the drum <NUM> to sense the temperature of the air. The tube <NUM> is heated by the induction heater <NUM> while an induction current flows through the metal so that the temperature of the tube <NUM> is reflected in the temperature obtained through the thermistor <NUM> disposed in the tube <NUM>.

The upper end of the tube <NUM> is open so that the thermistor <NUM> can be inserted into the tube <NUM>. Two lead wires <NUM> and <NUM> for inputting and outputting a current are connected to the thermistor <NUM> and a filler for fixing the thermistor <NUM> and the lead wires <NUM> and <NUM> is filled in the tube <NUM>. The filler is made of a material that transmits heat but does not conduct electricity.

The open upper end of the tube <NUM> is closed by a cap <NUM>. The cap <NUM> is provided with a pair of terminals connected to two lead wires <NUM> and <NUM> respectively, and is connected to a certain circuit electrically connected to a controller <NUM>.

A sensor installation port <NUM> is formed in the tub <NUM>, and the tube <NUM> passes through the sensor installation port <NUM>. The first temperature sensor 80a may include a soft sealer <NUM> that seals hermetically between the tube <NUM> and the sensor installation port <NUM>. The sealer <NUM> has a cylindrical shape extended in the longitudinal direction of the tube <NUM>, and the tube <NUM> is disposed inside the sealer <NUM>. The tube <NUM> passes through a hollow formed in the sealer <NUM>. The sealer <NUM> may include an upper side portion <NUM> located outside the tub <NUM>, a lower side portion <NUM> located inside the tub <NUM>, and a connection portion <NUM> which connects the upper side portion <NUM> and the lower side portion <NUM> and is inserted into the sensor installation port <NUM>. The lower surface of the upper side portion <NUM> may be brought into close contact with the outer surface of the tub <NUM>, and the upper surface of the lower surface portion <NUM> may be brought into close contact with the inner surface of the tub <NUM>.

The upper surface of the upper side portion <NUM> may be opened to form a recessed space inside thereof. The hollow through which the tube <NUM> passes may pass the upper side portion <NUM>, the connection portion <NUM>, and the lower side portion <NUM> sequentially.

The connection portion <NUM> may have a radius smaller than the upper side portion <NUM> and the lower side portion <NUM>. The circumference of the sensor installation port <NUM> of the tub <NUM> may be inserted into a fixing groove 82r formed by a radial difference between the upper side portion <NUM> and the upper end of the connection portion <NUM> and a radial difference between the lower side portion <NUM> and the lower end of the connection portion <NUM>.

Meanwhile, the heat insulating cover <NUM> covers the portion of the first temperature sensor 80a protruded to the outside of the tub <NUM>. The heat insulating cover <NUM> may close the open upper surface of the upper side portion <NUM> of the sealer <NUM>. The heat insulating cover <NUM> is made of a material (e.g., synthetic resin or rubber) having good heat insulation property. Since the inside of the sealer <NUM> is insulated to a certain degree by the heat insulating cover <NUM>, the influence of the temperature outside the tub <NUM> on the detection value of the first temperature sensor 80a is reduced.

Similarly to the first temperature sensor 80a, the second temperature sensor 80b detects the temperature of the air between the tub <NUM> and the drum <NUM>, but is disposed in a position further away than the first temperature sensor 80a along the circumferential direction from the induction heater <NUM>.

Here, the second temperature sensor 80b is preferably configured not to be affected by the induction heater <NUM>. For example, the second temperature sensor 80b may be configured of a sensor that is not affected by the magnetic field generated by the induction heater <NUM>. For example, the second temperature sensor 80b may be configured with the exception of the metal part (e.g., tube <NUM>) that is heated by the induction heater <NUM>. However, in this case, since the second temperature sensor 80b should be configured differently from the first temperature sensor 80a, the commonality of parts is low. Thus, it is preferable to dispose the second temperature sensor 80b in a position where the influence of the induction heater <NUM> is substantially insufficient, while the second temperature sensor 80b has the same structure as the first temperature sensor 80a.

Referring to <FIG>, the second temperature sensor 80b may be disposed in a position of <NUM> degrees to <NUM> degrees from the first temperature sensor 80a with respect to the center O of the drum <NUM>. This section may be provided in both sides of the Y axis passing through the center of the drum <NUM>, and this section is indicated by S2(θ1=<NUM>°, θ2=<NUM>°) and S3 in <FIG>.

In <FIG>, S1 indicates an effective heating range in which the first temperature sensor 80a is disposed. The effective heating range S1 may include an area vertically downward from the induction heater <NUM>.

The tube <NUM> of the first temperature sensor 80a is positioned below the induction heater <NUM>, and is preferably positioned in an area overlapped with the induction heater <NUM> when viewed from the top in a vertical direction. The first temperature sensor 80a is preferably positioned at <NUM> o'clock (<NUM>) with reference to <FIG>, but is not necessarily limited thereto.

Meanwhile, on a side surface of the tub <NUM>, a cooling water port (not shown) may be provided to supply cooling water for condensing moisture in the air in the tub <NUM>. It is preferable that the first temperature sensor 80a and the second temperature sensor 80b are disposed above the cooling water port so that the influence of the condensed water is excluded when temperature is detected.

The controller <NUM> (e.g., a first processor 91a described later) may control the induction heater <NUM> based on a first detection value T1 of the first temperature sensor 80a and the second detection value T2 of the second temperature sensor 80b. Specifically, the controller <NUM> may obtain the temperature Td of the drum <NUM> based on the linear combination of the first detection value T1, and may control the induction heater <NUM> so that the temperature Td of the drum <NUM> is controlled within a preset range.

The controller <NUM> may obtain the temperature Td of the drum <NUM> based on the first detection value T1 and the second detection value T2, and may control the output of the induction heater <NUM> or the operation of the cooling fan <NUM> based on the obtained temperature Td (exactly, an estimated value of the actual temperature of the drum <NUM> (see <FIG>)) of the drum <NUM>. Hereinafter, a method of obtaining the temperature Td of the drum <NUM> will be described in more detail.

The temperature Td of the drum <NUM> may be obtained according to the following temperature equation (Equation <NUM>) obtained by linearly combining the first detection value T1 and the second detection value T2. The controller <NUM> may control the induction heater <NUM> based on the obtained temperature Td.

Here, Td=temperature of the drum, Z = correction coefficient, T1 = first detection value, T2 = second detection value.

The process of obtaining the above equations is explained in more detail.

The drum <NUM> and the first temperature sensor 80a heated by the induction heater <NUM> generate heat so that the temperature Ta of the air in the tub <NUM> is increased, which is expressed as follows. <MAT> <MAT> <MAT>.

Here, Qin is the heat amount outputted from the induction heater <NUM>, Qd is the heat value of the drum <NUM> heated by the induction heater <NUM>, Q1 is the heat value of the first temperature sensor 80a heated by the induction heater <NUM>, Ta is the temperature of the air between the tub <NUM> and the drum <NUM>, A1 is the heat generating area of the first temperature sensor 80a, Ad is the heat generating area of the drum <NUM>, h1 is the heat transfer coefficient of the first temperature sensor 80a, and hd is the heat transfer coefficient of the drum <NUM>.

It is assumed that the drum <NUM> has a uniform temperature Td, the temperature Ta of the air in the tub <NUM> is also uniform, and the second temperature sensor 80b is not influenced by the induction heater <NUM>.

Here, the shape coefficient p and the heat value coefficient q are defined as follows, <MAT> <MAT>.

Equation <NUM> is summarized using Equation <NUM> as follows.

Here, the following equations may be obtained by using Equation <NUM> and Equation <NUM> to summarize.

The following equation may be obtained by substituting Equation <NUM> into Equation <NUM>.

Equation <NUM> may be summarized by using the shape coefficient p and the heat value coefficient q, and the correction coefficient Z may be defined as follows. <MAT> <MAT>.

Here, since Ta is a value obtained by the second temperature sensor 80b, Ta = T2, and Equation <NUM> becomes the same as the temperature equation of Equation <NUM>. In this process, the second detection value T2 obtained by the second temperature sensor 80b is compensated by a difference between the first detection value T1 obtained by the first temperature sensor 80a and the second detection value T2, so that the temperature Td of the drum <NUM> can be obtained.

Meanwhile, in Equation <NUM>, the correction coefficient Z is obtained by taking the shape coefficient p and the heat value coefficient q as factors. The shape coefficient p is a coefficient whose value is determined according to the shape of the first temperature sensor 80a and the drum <NUM>, and the heat value coefficient q is a variable determined by the output (input from the viewpoint of control) of the induction heater <NUM> and the quantity of state.

Therefore, Z can be expressed as follows.

Here, Zconst is a constant, and Zpower is a variable according to the input of the induction heater <NUM>.

As shown in the temperature equation (Equation <NUM>), if the detection value T1 of the first temperature sensor 80a and the detection value T2 of the second temperature sensor 80b are known, the estimated value Td of the temperature of the drum <NUM> may be approximated to the current temperature Td_p of the drum <NUM> by appropriately setting the Zpower value. In particular, in the temperature equation (Equation <NUM>), the first term of the right side is a value used to compensate so that the second detection value T2 of the second temperature sensor 80b follows the actual temperature of the drum <NUM>, and is influenced by the Z value. Here, Z is a value that varies depending on the variable Zpower. If Zpower is properly set, the estimated value Td approximating the actual temperature Td_p of the drum <NUM> may be obtained. The Zpower value according to the input of the induction heater <NUM> may be previously set through an experiment that the estimated value Td of the drum <NUM> obtained while varying the input of the induction heater <NUM> follows the actual temperature Td_p of the drum <NUM>.

Meanwhile, in <FIG>, the input of the induction heater <NUM> is gradually decreased so that the actual temperature Td_p of the drum <NUM> does not exceed about <NUM> degrees Celsius. Here, examining a section (i.e., a section in which the detection value of the first temperature sensor 80a is gradually decreased) in which the input of the induction heater <NUM> is gradually decreased, the actual temperature Td_p of the drum <NUM> is maintained within a certain range even though the output (input) of the induction heater <NUM> is reduced. However, the first detection value T1 of the first temperature sensor 80a is gradually decreased and the second detection value T2 of the second temperature sensor 80b does not vary greatly. Accordingly, it can be seen that the difference between the first detection value T1 and the second detection value T2 is gradually reduced.

This means that the value of (T1-T2) is decreased in the first term (i.e., the term compensating T2 so that the estimated value Td of the temperature of the drum <NUM> may be approximated to the actual temperature Td_p of the drum <NUM>) in the left side of the temperature equation (Equation <NUM>). Therefore, in order for the estimated value Td of the temperature of the drum <NUM> in the temperature equation to approximate the actual temperature Td_p of the drum, Z should be increased. That is, by compensating T2 by setting Zpower inversely proportional to (T1-T2) (or by setting inversely proportional to the input of the induction heater <NUM>), the estimated value Td of a value approximate to the actual temperature Td_p of the drum <NUM> can be finally obtained.

Meanwhile, as shown in the temperature equation (Equation <NUM>), the temperature Td of the drum takes T1 as a variable. Since T1 is a value which is changed sensitively to the output of the induction heater <NUM>, the temperature Td of the drum <NUM> obtained by the temperature equation reflects the output change of the induction heater <NUM>. This means that the variation of the temperature of the drum <NUM> due to the output change of the induction heater <NUM> can be detected quickly.

Particularly, when the output of the induction heater <NUM> is changed, the temperature change of the air in the tub <NUM> is accomplished slower than the temperature change of the drum <NUM>. Therefore, in the conventional method of detecting the temperature of the air by using only a single temperature sensor, the temperature change of the drum <NUM> due to the output change of the induction heater <NUM> cannot be detected sensitively. However, in the case of the present invention, since the heat value Q1 of the first temperature sensor 80a that sensitively reflects the output of the induction heater <NUM> is considered in the process of obtaining the temperature Td of the drum <NUM>. Accordingly, the change in the temperature of the drum <NUM> can be detected more sensitively and quickly than in the conventional method.

Meanwhile, when the second temperature sensor 80b is also heated by the induction heater <NUM> like the first temperature sensor 80a (e.g., when the second temperature sensor 80b has the same structure as the first temperature sensor 80a), the first temperature sensor 80a is disposed within an effective heating range (See S1 in <FIG>) in which the temperature of the tube <NUM> of the first temperature sensor 80a is raised by the magnetic flux (or a magnetic field generated by the induction heater <NUM>) radiated from the induction heater <NUM>, and the second temperature sensor 80b is disposed outside the effective heating range (see S2 and S3 in <FIG>).

Here, the effective heating range is set such that, when the output of the induction heater <NUM> is changed, a temperature change of the first temperature sensor 80a positioned within the effective heating range has a phase (i.e., a large phase) that precedes the second temperature sensor 80b positioned outside the effective heating range. For example, when the output of the induction heater <NUM> is raised, the temperature of the first temperature sensor 80a positioned within the effective heating range first rises to a peak due to the influence of the induction heater <NUM>, and the temperature of the second temperature sensor 80b positioned outside the effective heating range reaches the peak only after the heat is transferred to the air from the drum <NUM> and the first temperature sensor 80a which are heating element. Thus, the temperature T2 detected by the second temperature sensor 80b has a smaller phase value than the temperature T1 detected by the first temperature sensor 80a (i.e., the variation of T2 follows the variation of T1).

Meanwhile, according to an embodiment, even when the second temperature sensor 80b is implemented of a sensor which is not influenced by the induction heater <NUM> and disposed in the effective heating range S1, the second temperature sensor 80b is preferably disposed in a position further away than the first temperature sensor 80a in the circumferential direction from the induction heater <NUM>.

The present invention compensates the measured temperature T2 of the air by using the correction values Z(T1-T2) obtained based on two temperature sensors 80a and 80b and obtains the estimated value Td which approximates to the actual temperature of the drum <NUM>. Therefore, a deviation of more than a certain level should exists between the first detection value T1 detected by the first temperature sensor 80a and the second detection value T2 detected by the second temperature sensor 80b. For this reason, even if the second temperature sensor 80b is not influenced by the induction heater <NUM>, it is preferable that the second temperature sensor 80b is configured to detect the temperature of an area spaced by a certain distance from the first temperature sensor 80a in the circumferential direction instead of detecting the temperature of the circumference of the first temperature sensor 80a.

Preferably, the second temperature sensor 80b is spaced farther away than the first temperature sensor 80a from the induction heater <NUM> in the direction of rotation of the drum <NUM>. Since the drum <NUM> is cooled during the rotation of a portion heated by the induction heater <NUM>, the heated portion is cooled when reaching a position corresponding to the second temperature sensor 80b, so that the detection value T2 of the second temperature sensor 80b can be distinguished from the detection value T1 of the first temperature sensor 80a.

<FIG> is a conceptual diagram of active temperature control and safety control applied to a washing machine according to an embodiment of the present invention. <FIG> is a perspective view of a thermostat. <FIG> is a front view of a thermostat. <FIG> is a block diagram showing magnetic flow, heat flow, control signal, and current between main components of a washing machine according to an embodiment of the present invention. <FIG> is a circuit diagram of a washing machine according to an embodiment of the present invention.

Referring to <FIG>, the washing machine according to an embodiment of the present invention basically performs an active temperature control for controlling the operation of the induction heater <NUM> based on the temperatures detected by the first temperature sensor 80a and the second temperature sensor 80b. However, the washing machine is provided with a safety control system (or a power-off system) to prepare a case where the above control is not normally performed. The active temperature control is performed by the controller <NUM>, and corresponds to a control performed based on the temperature Td of the drum <NUM> described above.

The safety control is performed in such a manner that the thermostat 60a, 60b and the thermal fuse <NUM> electrically connected to a circuit for supplying power to the induction heater <NUM> mechanically operate according to the ambient temperature and open the circuit to interrupt the power supply to the induction heater <NUM>. That is, in order to prevent a safety accident due to overheating even when the active temperature control fails, the safety control system based on the thermostats 60a, 60b and the thermal fuse <NUM> which are mechanically operated by the ambient temperature are provided.

The thermostat 60a, 60b is, as well known, an automatic temperature regulator or a constant-temperature device, and serves as an automatic switch that opens when the temperature increases and closes when the temperature decreases. Usually, the thermostat 60a, 60b uses a bimetal having two alloy plates having different linear expansion coefficients, and opens and closes a switch by using a phenomenon of changing the bow-bent degree of the bimetal depending on temperature.

The alloys used for the bimetal may include an alloy of iron and nickel that has a small expansion coefficient, and alloys of copper and zinc, nickel-manganese-iron, nickel-molybdenum-iron, and the like that have a large expansion coefficient.

Alternatively, the thermostat 60a, 60b may utilize the vaporization pressure of a liquid which is easy to vaporize. For example, toluene, or the like is sealed in a pipe, and is used for a purpose like bimetal by using expansion or contraction due to temperature.

The thermostat 60a, 60b opens the circuit when the temperature increases and the bimetal is bent (or when the liquid is vaporized) to block the power supply to the induction heater <NUM>. In this state, when time elapses and the temperature is increased again, the bimetal is restored to its original state and the circuit is closed. That is, the thermostat 60a, 60b serves as a switch for reversibly opening and closing the circuit depending on time.

On the other hand, as is well known, the thermal fuse <NUM> is a kind of overheat protection switch which is deformed or melted to open an electric circuit at a specific temperature, and is used for the purpose of preventing overheating of an electric device. The thermal fuse <NUM> may be made of a low melting point alloy wire or a ribbon that is fused (i.e., melted and broken) at a certain temperature and may be configured in such a manner that a plastic is softened and deformed at a specific temperature to open an electrical contact.

The safety control is performed firstly by the thermostat 60a, 60b, but is performed again (second safety control) by the thermal fuse <NUM> when the first safety control fails. The first safety control by the thermostat 60a, 60b is suitable when it is required to block the power due to temporary overheating of the induction heater <NUM> or the drum <NUM> in a situation where a serious problem does not occur in a circuit or the devices constituting the circuit.

The second safety control by the thermal fuse <NUM> is accomplished to permanently open the circuit when the thermostat 60a, 60b cannot be operated normally, i.e., when the thermostat 60a, 60b cannot be switched in spite of being heated above a specified temperature so that the overheated state continues.

Since the operation of the thermostat 60a, 60b or the thermal fuse <NUM> is caused not by the current flowing in the circuit but by the change of ambient temperature, the operation is achieved regardless of the cause of the overheating of the induction heater <NUM> or the drum <NUM>, so that the operation of the induction heater <NUM> which is a controllable heat source can be stopped preferentially.

Hereinafter, such safety control will be described in more detail.

The first thermostat 60a is disposed between the drum <NUM> and the tub <NUM> and is operated (or switched) according to the temperature of a first air (i.e., air around the first thermostat 60a). The first thermostat 60a is operated (switched) at a first safety control temperature to open a circuit for supplying power to the induction heater <NUM>. The first safety control temperature is a temperature of the first air set to correspond to a case where the temperature of the drum <NUM> is in a first safety temperature range. Here, the first safety temperature range and the first safety control temperature are values previously determined based on an operation condition of the washing machine according to a preset standard.

When the circuit is opened by the first thermostat 60a, the temperature of the drum <NUM> falls within the first safe temperature range. At this time, the circuit is opened by the first thermostat 60a so that the temperature of the drum <NUM> is controlled so as not to exceed the upper limit of the first safety temperature range.

Since the first safety control temperature is the temperature of the air outside the drum <NUM>, it differs from the temperature of the drum <NUM>. Since the heat flows from the heated drum <NUM> to the air, the first safety control temperature is lower than the first safety temperature range. Preferably, the first safety control temperature is a value smaller than a lower limit of the first safety temperature range. The first safety temperature range may be between <NUM> degrees and <NUM> degrees Celsius, and the first safety control temperature may be <NUM> degrees Celsius. Particularly, since the tub <NUM> may be deformed or burned by heat as the material of the tub <NUM> is a synthetic resin, the maximum temperature should preferably be controlled to be equal to or less than <NUM> degrees Celsius, and when the first safety control temperature is <NUM> degrees Celsius, such condition can be satisfied.

Meanwhile, the tub <NUM> may be provided with an installation port in which the first thermostat 60a is installed, and the first thermostat 60a may be inserted into the installation port. Referring to <FIG>, in a state in which the first thermostat 60a is positioned in the installation port, a sealing mount <NUM> for supporting the first thermostat 60a and sealing a gap between the first thermostat 60a and the installation port may be further provided.

The sealing mount <NUM> is, as a whole, in the form of a cylindrical shape having a hollow to which the first thermostat 60a is inserted. An annular concave groove 57r is formed on the outer circumferential surface of the sealing mount <NUM> so that the circumference of the installation port is press-fitted into the groove 57r. The sealing mount <NUM> may be made of a soft material.

The upper end of the sealing mount <NUM> is positioned in the outer side of the tub <NUM> and the lower end is positioned in the inner side of the tub <NUM>. In the first thermostat 60a, a portion <NUM> protruding further downward than the lower end of the sealing mount <NUM> comes into contact with the air in the tub <NUM>, so that the heat is transferred from the air in the tub <NUM> to the first thermostat 60a. The pair of terminals <NUM> and <NUM> of the first thermostat 60a are positioned in the upper end side of the sealing mount <NUM>, and connected to the circuit in the outside of the tub <NUM>.

The thermal fuse <NUM> is disposed outside the tub <NUM> and operated according to the temperature of a second air (i.e., the air around the thermal fuse <NUM>). The thermal fuse <NUM> operates at a second safety control temperature to open a circuit for supplying power to the induction heater <NUM>. Here, the second safety control temperature is a temperature of the second air set to correspond to a case where the temperature of the drum <NUM> is in a second safety temperature range. In particular, the second safety temperature range has a larger value than the first safety temperature range. The middle value of the second safety temperature range may be larger than the middle value of the first safety temperature range. The lower limit of the second safety temperature range may be larger than the upper limit of the first safety temperature range. Here, the second safety temperature range and the second safety control temperature are values previously determined by experiment based on operating condition of the washing machine according to a preset standard.

Since the thermal fuse <NUM> is disposed outside the tub <NUM>, the thermal fuse <NUM> is less affected by the heat generated by the heated drum <NUM> than the first thermostat 60a. Therefore, even if the second safety temperature range is higher than the first safety temperature range, the second safety control temperature may be lower than the first safety control temperature. That is, even if the thermal fuse <NUM> is configured to operate at a lower temperature than the first thermostat 60a, the temperature of the drum <NUM> at the time of operation of the thermal fuse <NUM> may be higher than the temperature of the drum <NUM> at the time of operation of the first thermostat 60a. The second safety temperature range is from <NUM> degrees Celsius to <NUM> degrees Celsius (at this time, the temperature of the coil <NUM> ranges from <NUM> degrees Celsius to <NUM> degrees Celsius), and the second safety control temperature may be <NUM> degrees Celsius, but it is not limited thereto.

A second thermostat 60b that operates by the heat of the induction heater <NUM> may be further provided. The second thermostat 60b opens a circuit at a third safety control temperature. Here, the third safety control temperature is a temperature of the second thermostat 60b set to correspond to a case where the heat temperature of the induction heater <NUM> is in a third safety temperature range. The second thermostat 60b may be disposed outside the tub <NUM>, and the third safety control temperature may be lower than the second safety control temperature.

It is preferable that the second thermostat 60b is disposed at a position close to the induction heater <NUM>, particularly, at a position closer to the induction heater <NUM> than the thermostat 60a so that the heat amount generated from the induction heater <NUM> can be sufficiently transmitted to the second thermostat 60b.

Meanwhile, assuming that the temperature of the coil <NUM> is Tc at the time when the induction heater <NUM> normally operates in a preset standard and that, at this time, the temperature of the second thermostat 60b (or the temperature of the ambient air) is Ts2, the third safety temperature range is from <NUM>. 18Tc to <NUM>. 32Tc, and the third safety control temperature ranges from <NUM>. 2Ts2 to <NUM>. 3Ts2 (preferably, <NUM>. The third safety temperature range may be from <NUM> degrees Celsius to <NUM> degrees Celsius, and the third safety control temperature may be <NUM> degrees Celsius, but is not limited thereto.

Referring to <FIG>, the controller <NUM> may include a first processor 91a that controls the driving unit <NUM> and controls the overall operation of the washing machine, and a second processor 91b that controls the induction heater <NUM>. The first processor 91a and the second processor 91b may be electrically connected to each other to communicate with each other. Particularly, the second processor 91b may control the heat of the induction heater <NUM> according to an instruction applied from the first processor 91a.

Meanwhile, in <FIG>, a first PCB 92a is a circuit board on which the first processor 91a is mounted, and a second PCB 92b is a circuit board on which the second processor 91b is mounted and is connected to the first PCB 92a.

The magnetic force generated in the coil <NUM> of the induction heater <NUM> may heat not only the drum <NUM> and the first temperature sensor 80a but also heat in some degree the first thermostat 60a positioned within the effective heating range, but the heating amount is not so large.

Referring to <FIG>, the flow of heat at the time when the induction heater <NUM> is operated is divided into the heat exchange between the heated coil <NUM> and the tub <NUM>, the heat amount transferred from the drum <NUM> to the first temperature sensor 80a and the second temperature sensor 80b through the air as medium, the heat amount transferred to the thermal fuse <NUM> from the tub <NUM> heated by the heat of the drum <NUM>, and the heat amount transferred to the thermal fuse <NUM> and the second thermostat 60b due to the heat of the coil <NUM>.

Particularly, since the first thermostat 60a is directly affected by the heat of the drum <NUM>, the temperature of the first thermostat 60a has a close correlation with the temperature of the drum <NUM>. Therefore, the safety control of the present invention is achieved in such a manner that the temperature in the drum <NUM> is controlled not to exceed the first safety temperature range, based on the first thermostat 60a which is primarily sensitive to the temperature change of the drum <NUM>.

In addition, the thermal fuse <NUM> is affected by both the heat of the drum <NUM> transferred through the tub <NUM> and the heat of the coil <NUM>. Therefore, even if the temperature of the drum <NUM> is controlled in a range lower than the first safe temperature range (i.e., even if the circuit is not opened by the first thermostat 60a as the temperature of the drum <NUM> falls within a normal range), the power supplied to the coil <NUM> is blocked by the thermal fuse <NUM> when the coil <NUM> is abnormally overheated as in the case where the coil <NUM> is short-circuited.

Since the thermal fuse <NUM> is controlled in an irreversible manner, it needs to be replaced once it operates. Therefore, it is preferable to provide a device that can attempt to control the abnormal heating of the coil <NUM> in a reversible manner before the thermal fuse <NUM> operates. In this respect, the second thermostat 60b which is operated in response to the heat of the coil <NUM> like the thermal fuse <NUM> is further provided.

Hereinafter, it is illustrated that the safety device <NUM> includes the first thermostat 60a, the second thermostat 60b, and the thermal fuse <NUM>.

As described above, the safety device <NUM> is configured such that the first thermostat 60a, the second thermostat 60b, and the thermal fuse <NUM> operate at respective safety control temperatures, thereby opening a circuit for supplying power to the induction heater <NUM>. That is, when a heater power supply circuit HPSC is opened by the safety device <NUM>, the current applied to the coil <NUM> is blocked. This will be described in more detail below.

Referring to <FIG>, the washing machine according to an embodiment of the present invention may include a power supply circuit PSC, a heater power supply circuit HPSC, a heater driving circuit HDC, and a drum driving circuit DDC.

The power supply circuit PSC may include an input power <NUM> and a noise filter <NUM>. The input power <NUM> may be an AC power. The alternating current applied from the input power <NUM> is applied to the heater power supply circuit HPSC and used as the driving source of the induction heater <NUM> or is applied to the drum driving circuit DDC and used as the driving source of the motor 35a.

A relay <NUM> for interrupting the current applied from the input power <NUM> to the coil <NUM> of the induction heater <NUM> is provided. The heater power supply circuit HPSC includes a relay <NUM>, a noise filter <NUM>, and a switching mode power supply (SMPS).

The relay <NUM> is electrically connected to the first processor 91a. The relay <NUM> electrically connects (or circuit connects) or disconnects the input power <NUM> to the heater power supply circuit HPSC under the control of the first processor 91a. The relay <NUM> includes an electromagnetic relay for physically moving a contact by the electromagnet to open and close the contact, a reed relay having a structure in which a metal reed of a ferromagnetic material is enclosed in a container together with an inert gas and a coil is wound around the container and the reed opens and closes a contact according to a magnetic field generated when a current flows through the coil, a semiconductor relay (e.g., a solid state relay (SSR)) that opens and closes a large output voltage with a small input power by using a semiconductor element such as a thyristor or a photocoupler, and the like, but the present invention is not limited thereto, and may be implemented by other known ones.

The relay <NUM> is operated in accordance with a control command (or instruction) applied from the first processor 91a. That is, in response to the control command received via a line in a state of being electrically connected to the first processor 91a, the relay <NUM> supplies the current output from the input power <NUM> to the heater power supply circuit HPSC do.

The safety device <NUM> is connected to a circuit connecting the first processor 91a and the relay <NUM>. Thus, when the safety device <NUM> operates and the circuit is opened, the electrical connection between the relay <NUM> and the processor 91a is released and the control command can no longer be transmitted, so that the relay <NUM> is opened and power can no longer be supplied from the input power <NUM> to the heater power supply circuit HPSC.

The drum driving circuit DDC includes a rectifier <NUM> for converting an alternating current (AC) passed through the noise filter <NUM> into a direct current (DC), a smoothing circuit <NUM> for reducing a pulsating current included in the output voltage of the rectifier <NUM>, a SMPS <NUM> for converting the current outputted from the smoothing circuit <NUM> and driving the first processor 91a, and an intelligent power module (IPM) <NUM> for switching the current outputted from the smoothing circuit <NUM> and driving the motor 35a.

The heater driving circuit HDC includes a rectifier <NUM> for rectifying the AC that passed through the noise filter <NUM>, a switching element <NUM> for switching the current outputted from the rectifier <NUM> and applying to the coil <NUM>, and a driving driver <NUM> for driving the switching element <NUM> under the control of the second processor 91b. In an embodiment, the switching element <NUM> is configured of an insulated gate bipolar transistor (IGBT), but is not necessarily limited thereto.

Even if the power of the induction heater <NUM> is blocked by the operation of the safety device <NUM>, the power supply to the drum driving circuit (DDC) is continuously performed, so that the driving of the drum <NUM> can be normally performed. Particularly, even if the thermal fuse <NUM> is fused, the drum <NUM> is driven normally. Therefore, a simple washing (or rinsing) or dewatering may be performed until the thermal fuse <NUM> is replaced.

Meanwhile, according to an embodiment, even when the controller <NUM> determines that the active temperature control is not performed normally, the operation of the induction heater <NUM> is not stopped immediately, but more alternatives can be provided to control the temperature of the drum <NUM>.

Specifically, the controller <NUM> may select a temperature sensor which operates abnormally among two temperature sensors 80a and 80b, based on the temperature change of the first temperature sensor 80a or the second temperature sensor 80b. In this case, it can be determined that the active temperature control is not normally performed.

For example, when a temperature increase amount of the first temperature sensor 80a (or the second temperature sensor 80b) is below a first reference increase amount (a second reference increase amount in case of the second temperature sensor 80b) until a set time elapses after the operation of the induction heater <NUM> is started, the controller <NUM> may determine that the first temperature sensor (or the second temperature sensor 80b) is failed. In this case, the controller <NUM> (e.g., the first processor 91a) does not immediately block the power applied to the induction heater <NUM>, but may control the heat of the induction heater <NUM> based on the detection value (or the detection value of the first temperature sensor 80a) of the second temperature sensor 80b that normally operates.

That is, the controller <NUM> may control the heat of the induction heater <NUM> so that the detection value of the second temperature sensor 80b is maintained in a preset second safety control temperature range (or the detection value of the first temperature sensor 80a is maintained in a preset first safety control temperature range).

<FIG> shows the positions where the first thermostat 60a can be installed based on an induction heater <NUM>, and <FIG> shows the state where the first thermostat is installed in respective positions when viewed from the front of the tub <NUM>.

The first thermostat 60a is installed in the tub <NUM> and disposed below the induction heater <NUM>. The temperature of a corresponding portion of the drum <NUM> is varied depending on a position of the corresponding portion of the drum <NUM> with respect to the induction heater <NUM>. Thus, the temperature of the first thermostat 60a, which is mainly influenced by the temperature of the drum <NUM>, will also vary depending on the position.

<FIG> is graphs showing a temperature of a first thermostat detected in each position shown in <FIG> while heating a drum by operating an induction heater. <FIG> shows detected temperatures when the first thermostat 60a is positioned in an outer position (hereinafter, referred to as "outer position (P_out)") of the induction heater <NUM>, <FIG> shows detected temperatures when the first thermostat 60a is positioned in an outer boundary position (hereinafter, referred to as "boundary position (P_ half)") of the induction heater <NUM>, and <FIG> shows detected temperatures when the first thermostat 60a is positioned in an inner position (hereinafter, referred to as "inner position (P_in)") of the induction heater <NUM>. In addition, the "large amount of wet cloth" means a state in which <NUM> of a wet cloth (or a laundry wet with water) is put into the drum <NUM>, the "small amount of wet cloth" means a state in which a certain amount of wet cloth not exceeding <NUM> is put into the drum <NUM>, and the "empty" means a state in which laundry is not put into the drum <NUM>. "Td" is the temperature of the drum <NUM>, "TS1" is the temperature of the first thermostat 60a, and "@" indicates that the temperature is measured at a position followed by "@", for example, TS1@P_out is the temperature of the first thermostat 60a disposed in the outer position P_out.

In the graphs, it can be seen that when the first thermostat 60a is positioned in the outer position (P_out), the temperature TS1@P_out is relatively slowly achieved in comparison with other cases.

When the first thermostat 60a is positioned in the inner position P_in, the temperature itself TS1@P_in of the first thermostat 60a is higher more than needs (even in the case of large amount of wet cloth, it goes up to <NUM> degrees Celsius or more), so that damage (or thermal deformation) of the tub <NUM> may occur.

Therefore, the first thermostat 60a is preferably disposed in the boundary position P_half, though it is not necessarily limited thereto.

Meanwhile, when viewed from above, the boundary position P_half is a position where the first thermostat 60a is partially overlapped with the induction heater <NUM>, preferably, a position where the first thermostat 60a is positioned in the outer edge of the coil <NUM> or in the outer edge of the heater base <NUM>, when the first thermostat 60a is spaced from the center of the coil <NUM> by a certain distance in the circumferential direction of the drum <NUM>. Here, the outer edge of the coil <NUM> is an outer edge of a portion spaced from the center of the coil <NUM> in the circumferential direction of the drum <NUM> and, as in the embodiment, corresponds to a side extended in the forward and backward directions when the overall shape of the coil <NUM> is in the form of a long plate in the front-back direction than in the left-right direction.

In addition, in the embodiment, the first thermostat 60a is positioned in the left side of the induction heater <NUM> when viewed from the front, but it is not limited thereto, and may be disposed in the right side. Further, in the embodiment, the first thermostat 60a is positioned in the front side based on a midpoint M of the length of the tub <NUM>, but can be positioned in the rear side.

The midpoint M may be defined as a portion where the tub front portion <NUM> and the tub rear portion <NUM> are coupled to each other, and the position is not necessarily the half of the length of the tub <NUM> in the front-rear direction.

Referring to the graphs, the first thermostat 60a is disposed in the boundary position P_half, and in order to prevent the temperature of the drum <NUM> from exceeding <NUM> degrees Celsius (i.e., when the first safety temperature range is set to <NUM> degrees Celsius or less), under the condition of small amount of wet cloth, the first safety control temperature may be set to <NUM> degrees Celsius. Assuming that the laundry is not put into the drum <NUM> under the same conditions (in this case, the temperature of the drum <NUM> has substantially the same change as the case in which the input wet cloth is completely dried). When the temperature (TS1@ P_half(empty)) of the first thermostat 60a reaches <NUM> degrees Celsius, the temperature of the drum <NUM> is raised to approximately <NUM> degrees Celsius.

That is, assuming that the first thermostat 60a is disposed in the boundary position P_half, when small amount of wet cloth is put into the drum <NUM>, the temperature of the drum <NUM> can be controlled by the first thermostat 60a so as not to exceed <NUM> degrees Celsius. Even if the laundry in the drum <NUM> is completely dried (corresponding to the case where there is no laundry in the drum <NUM>), the temperature of the drum <NUM> can be controlled so as not to exceed <NUM> degrees Celsius. Meanwhile, in the case of large amount of wet cloth under the same condition, the temperature of the drum <NUM> is controlled not to exceed <NUM> degrees Celsius.

Meanwhile, when the first thermostat 60a is disposed in the outer position P_out, the temperature of the drum <NUM> is raised up to <NUM> degrees Celsius under the condition of small amount of wet cloth when the first safety control temperature is <NUM> degrees Celsius, and the temperature of the drum <NUM> is raised up to <NUM> degrees Celsius in the dry (fully dried) state, so that there is a risk of over-heating and denaturalization of the clothes.

In addition, when the first thermostat 60a is disposed in the inner position P_in, the temperature of the drum <NUM> is raised up to <NUM> degrees Celsius under the condition of small amount of wet cloth when the first safety control temperature is <NUM> degrees Celsius, and the temperature of the drum <NUM> is raised up to <NUM> degrees Celsius in the dry (fully dried) state. In this case, there is no risk of over-heating and denaturalization of the clothes, but there is a risk of damaging the tub <NUM> as the first safety control temperature is high.

<FIG> shows the positions on a heater base <NUM> and <FIG> shows a temperature change in respective positions. Particularly, <FIG> shows the temperature measured at each point shown in <FIG> while operating the induction heater <NUM> and the cooling fan <NUM>, and the operation of the cooling fan <NUM> is stopped after the time t(off). As can be seen from the graphs, the temperature suddenly rises at any position after the operation of the cooling fan <NUM> is stopped. (for reference, the temperature falls again from approximately <NUM> minutes, because the operation of the induction heater <NUM> is stopped from this point.

Particularly, it can be seen that the temperature rise is large in a position (e.g., Coil_Left_2 position) near a central portion of the heater base <NUM> (or a central portion of the coil <NUM>). Therefore, when the second thermostat 60b is disposed in the center of the heater base <NUM>, it is possible to quickly cope with the overheating of the induction heater <NUM> due to the failure of the cooling fan <NUM>. Preferably, the second thermostat 60b is disposed in an area (i.e., the inner area according to the above definition) that is completely overlapped with the heater base <NUM> (or the coil <NUM>) when viewed from above, but the present invention is not limited thereto.

Meanwhile, when the second thermostat 60b is disposed in contact with the coil <NUM>, there is a risk of the short circuit of the coil <NUM>, thereby further requiring insulation means. Therefore, the second thermostat 60b should preferably be spaced apart from the coil <NUM>, and, due to this condition, the installation position thereof is restricted to the lower side of the heater cover <NUM> or the heater base <NUM>.

However, as it progresses to the center of the heater cover <NUM>, the distance from the tub <NUM> positioned in the lower side thereof is reduced. In the case where the second thermostat 60b is installed below the heater cover <NUM>, the installation is restricted due to the narrow space. Therefore, the second thermostat 60b is preferably disposed in the heater cover <NUM>. However, the present invention is not limited thereto.

<FIG> shows positions where a second thermostat 60b can be installed based on a heater base <NUM>, and <FIG> is a graph showing a temperature change of the second thermostat in respective positions. Here, "C_center" is a position in contact with the coil <NUM> at the middle portion of the heater base <NUM>, "C_front" is a position in contact with the coil <NUM> at the front portion of the heater base <NUM>, "D_center" is a position on the heater cover <NUM> corresponding to the middle portion of the heater base <NUM>, and "D_rear" is a position on the heater cover <NUM> corresponding to the rear portion of the heater base <NUM>.

As can be seen from <FIG>, no matter where the second thermostat 60b is installed, it can be known that the temperature rises sharply after the time t(off) at which the cooling fan <NUM> is stopped. Therefore, even if the second thermostat 60b is placed at any position on the heater cover <NUM>, when the coil <NUM> is overheated due to the failure of the cooling fan <NUM>, the second thermostat 60b may be operated at a preset third safety control temperature. However, as shown in the graphs, when the second thermostat 60b is positioned in the middle portion of the heater base <NUM> (e.g., the position C_center), the temperature of the second thermostat 60b is relatively low, thereby reducing the third safety control temperature.

For example, in <FIG>, the third safety control temperature may be set to about <NUM> degrees, when the circuit is opened so that the temperature at the C_front position does not exceed <NUM> degrees Celsius. Thus, the second safety control temperature may be set to be lower by <NUM> degrees corresponding to a difference between <NUM> degrees Celsius and <NUM> degrees Celsius.

<FIG> shows positions where a thermal fuse can be installed based on a heater base, and <FIG> is a graph showing a temperature change of the thermal fuse in respective positions. <FIG> is a graph showing the temperature change of the thermal fuse in each point shown in <FIG> when the operation of a cooling fan is stopped after t(off) after an induction heater and the cooling fan are operated.

As described above with reference to <FIG>, the thermal fuse <NUM> is positioned in a position where the temperature of thermal fuse is influenced not only by the heat of the coil <NUM>, but also by the heat transmitted from the drum <NUM> through the tub <NUM>. Therefore, the position of the thermal fuse <NUM> may be selected based on the condition i) that the temperature rise of the thermal fuse <NUM> is correlated with the temperature rise of the tub <NUM> (or the temperature rise of the drum <NUM>), and the condition ii) that there is also a correlation with the temperature rise of the coil <NUM>.

With respect to the condition i), when the drum <NUM> is overheated, the tub <NUM> has the highest temperature at the lower portion of the induction heater <NUM>, and has a high temperature at a portion (approximately, in the vicinity of the middle point M of the tub <NUM>) corresponding to the intermediate length of the coil <NUM> in the front-rear direction. Thus, the thermal fuse <NUM> is positioned outside the tub <NUM> (i.e., between the heater base <NUM> and the curve <NUM>), and, when viewed from above, it is preferable that at least a portion of the thermal fuse <NUM> is disposed in an area overlapped with the heater base <NUM> (or the coil <NUM>). Further, it should be spaced apart from the coil <NUM> for insulation.

Preferably, the thermal fuse <NUM> is in contact with the tub <NUM>, in contact with the bottom surface of the heater base <NUM>, and positioned in the midpoint M of the tub <NUM> in the front and rear direction.

Meanwhile, as can be seen from the comparison between <FIG> and <FIG>, even when the thermal fuse <NUM> is positioned in a position closer to the outer boundary than to the center as well as in a position (TF _center_side) close to the center of the heater base <NUM>, the temperature rises abruptly after the time point t(off) at which the cooling fan <NUM> is stopped, which is a pattern corresponding to the temperature change of the coil <NUM>. That is, if at least a portion of the thermal fuse <NUM>, when viewed from above, is positioned in an area overlapped with the heater base <NUM> (or coil <NUM>), the condition ii) seems to be relatively easily satisfied.

Taking all the above into consideration, the thermal fuse <NUM> is disposed in a position, outside the tub <NUM>, where the thermal fuse <NUM> is in contact with the tub <NUM> or in contact with the bottom surface of the heater base <NUM>, and it is preferable that the thermal fuse <NUM> is disposed approximately the middle point of the heater base <NUM> (or the coil <NUM>) in the front-rear direction. Therefore, not only the inner central position (TF_center_inside) shown in <FIG> but also the inner edge position (TF_center_side) are suitable positions for installing the thermal fuse <NUM>.

However, as shown in <FIG>, the inner central position (TF_center_inside) has a lower temperature than the inner edge position (TF_center_side), which is advantageous in that the second safety control temperature can be set relatively low.

As described above, in the washing machine of the present invention, firstly, when the temperature of the drum using the temperature sensor is not normally controlled and is overheated, the operation of the induction heater is automatically stopped to prevent a safety accident.

Secondly, in the washing machine of the present invention, a circuit for transmitting a control signal to a relay for applying a current of the input power to the induction heater is configured to be opened by the safety device. Here, only a small amount of current for transmitting the control signal flows in the circuit for transmitting the control signal. That is, the present invention does not open the power line for transmitting the electric power for driving the induction heater by using the safety device, but is configured to open the control line constituting the circuit, so that there is no risk that an accident due to the unexpected disconnection or short circuit of the power line in the safety control process occurs.

Third, there is an effect that the power applied to the induction heater is automatically blocked not only when the drum is overheated, but also when the induction heater is overheated.

Fourth, since the safety device is configured to include a first safety control means for reversibly opening the circuit for applying power to the induction heater, the circuit can be normally operated again when the cause of overheating is removed. Further, a second safety control means for irreversibly opening the circuit when the overheated state is not resolved despite a first safety control is provided, thereby more reliably preventing a safety accident.

Claim 1:
A washing machine (<NUM>) comprising:
a tub (<NUM>) configured to contain water;
a drum (<NUM>) of metal material configured to be rotated in the tub (<NUM>);
an induction heater (<NUM>) fixed to the tub (<NUM>) in a state of being separated from the drum (<NUM>), and configured to heat the drum (<NUM>);
a first temperature sensor (80a);
a second temperature sensor (80b); and
a controller (<NUM>);
characterized in that:
the first temperature sensor (80a) includes a tube (<NUM>) of metal material heated by the induction heater (<NUM>) and disposed in an effective heating range in which a temperature of the first temperature sensor (80a) is raised by a magnetic flux radiated from the induction heater (<NUM>), and a thermistor (<NUM>) disposed in the tube (<NUM>), wherein at least part of the tube (<NUM>) is exposed between the tub (<NUM>) and the drum (<NUM>); and
the second temperature sensor (80b) is disposed in a position further away than the first temperature sensor (80a) from the induction heater (<NUM>) in a circumferential direction of the tub (<NUM>) and configured to be outside the effective heating range and configured to detect a temperature of air between the tub (<NUM>) and the drum (<NUM>) such that the second temperature sensor (80b) is configured not to be affected by the induction heater (<NUM>); and
the controller (<NUM>) is configured to determine a temperature of the drum (<NUM>) based on a first detection value of the first temperature sensor (80a) and a second detection value of the second temperature sensor (80b) and control the induction heater (<NUM>) based on the temperature of the drum (<NUM>).