GB2446347A - Cooking apparatus - Google Patents

Abstract

Conventional cooking devices for commercial use are more frequently used than those for domestic use. This results, in a commercial-use cooking device, in a short service life of a punched plate located at the bottom surface of a cooking chamber and shielding a microwave while allowing a magnetic flux to pass. In the cooking device of the invention, a circular opening is provided in a bottom plate (71) forming the bottom of a cooking chamber, and an annular bottom-plate fitting (73) to which a punched plate (72) is fused is removably attached to the opening. The bottom-plate fitting (73) is fixed to the bottom plate (71) by a combination of a fixation section (75) and a press-contact section (78). In the fixation section (75), welded bolts secured to the bottom plate (71) and nuts are screwed with each other for the fixation, and in the press-contact section (78), projections (73b) are simply pressed against the bottom plate (71). The construction sufficiently achieves improved replacement/repair work efficiency of the punched plate and strength required for the bottom surface of the cooking device.

Description

DESCRIPTION

COOKING APPARATUS

TECHNICAL FIELD

1] The present invention relates to a hybrid type cooking apparatus having both a radio-frequency heater and an induction heater for cooking food placed in a substantially sealable cooking chamber.

BACKGROUND ART

2] Microwave ovens are very effective in high-speed cooking, such as warming foods, because they directly heat food by radio-frequency waves (microwaves). However, they are incapable of, and therefore unsuitable for, browning food. Meanwhile, induction heating (IH) cooking apparatuses popular in recent years are most suitable for browning or boiling foods since they perform cooking by heating a magnetic-metallic pan or similar utensils by induction heating. Given this factor, in order to cover the shortcomings of cooking by radio-frequency heating as stated earlier, there have been known hybrid type cooking apparatuses using induction heating cooking.

rfvwvfl L'J'J'JJJ For example, in the cooking apparatus described in Patent Document 1, an induction heating coil is placed underneath the bottom surface of a substantially box-shaped cooking chamber and a cooking plate put on the bottom surface of the cooking chamber can be inductively heated by a magnetic flux generated from the coil. On the other hand, a magnetron is placed outside the cooking chamber, and the microwaves generated from the magnetron are supplied to the inside of the cooking chamber via a power feeding port formed on a side surface of the cooking chamber. The food placed on the cooking plate can thus be radio-frequency heated. The cooking apparatuses of this kind are preferable for browning, stewing or boiling fbod contained in an induction-heatable pan. frying pan, or other types of containers.

4] No doubt the aforementioned cooking apparatus is convenient for everyday household use, and is also very useful for industrial use in restaurants, convenience stores and other commercial facilities in which the reduction of cooking time is strongly demanded. With regard to use status of cooking apparatuses, there is a significant difference in the frequency of use between everyday household use and industrial use.

Specifically, when industrially used, cooking apparatuses are expected to be operated uninterruptedly, almost continuously, for a long period of time since it is demanded that the cooking apparatus be operated as efficiently as possible; that is, improvement in the operational efficiency is desired in industrial use.

5] In a case where the induction heating coil is disposed below the bottom surface portion of the cooking chamber as in the aforementioned configuration, the bottom surface portion of the cooking chamber is formed by a member allowing magnetic flux to penetrate therethrough, such as a punched plate in which a large number of small holes are formed.

Although this kind of punched plate is not easily heated by induction heating, it can be slightly heated due to the effect of part of magnetic flux penetrating through the member.

The temperature of the punched plate is further increased by conduction of the heat from the induction heating coil which increases its temperature. Accordingly, when induction heating is almost continuously carried out as described earlier, heat is accumulated in the punched plate to increase the temperature thereof, with a possible result that the temperature of the punched plate reaches a level that cannot take place in everyday household use. For the aforementioned reasons, in industrial use, the punched plate is rapidly consumed due to heating, and thus damages such as breakage easily occur.

6] Therefore, especially in a cooking apparatus for industrial use, a punched plate often needs to be replaced. On the other hand, since it is important to improve the operational efficiency of the apparatus as much as possible in industrial use as explained earlier, a time required for repairing or other maintenance tasks is desirably reduced to a minimum level. However, as for a conventional cooking apparatus, the punched plate-changing operation is highly troublesome. This is because, since in general a box-shaped cooking chamber is integrally formed by five faces (a ceiling surface portion, a bottom surface portion, a backside surface portion, and both right-and left-side surface portions) except for a front surface portion closable by a door, replacement of a punched plate in the bottom surface portion of the cooking chamber with the aforementioned configuration requires changing the entire body of the cooking chamber. Due to various components mounted on the outer faces of the cooking chamber, the cooking apparatus in its entirety first needs to be disassembled to change the cooking chamber, and then reassembled. Furthermore, after reassembly, various mechanical adjustments such as the adjustment of a door switch movement become necessary, making the repair work more troublesome. For those reasons, even a person in charge of service in a manufacturing company inevitably takes time for the repair work, and thus it is often the case that the apparatus itself is replaced by a new one to avoid the aforementioned burdens. Accordingly, repair or replacement of a damaged punched plate costs quite high in a conventional cooking apparatus.

7] In an apparatus disclosed in Patent Document 1, a bottom surface portion of a cooking chamber includes a thin plate-like member, such as a punched plate, which allows magnetic flux to penetrate therethrough while it reflects microwaves, and on which is mounted a mounting plate having a dielectric, heat-resistant, and non-magnetic body. Also, an induction heating coil is disposed below the bottom surface portion of the cooking chamber. A magnetic flux density of the alternating magnetic flux generated by the induction heating coil is decreased along with an increase of the distance from the induction heating coil, and thus it is preferable that, in consideration of the induction heating efficiency, the induction heating coil be provided at the smallest possible distance from a bottom surface of a container to be heated. However, since the plate-like members such as the mounting plate and the punched plate are interposed between the bottom surface of the container and the induction heating coil as mentioned earlier, and also heat of the container, that is possibly rising to 200 to 300 C depending on the content, has to be prevented from transmitting to the induction heating coil, it is in some cases necessary to provide an appropriate amount of space between them.

8] In light of these considerations, it is desirable that an appropriate amount of space be secured between the bottom surface of the container and the induction heating coil, while the induction heating efficiency is improved as much as possible. However, this knowledge has not conventionally been taken into consideration and a sufficiently high heating efficiency has not been achieved.

9] Patent Document 1: Japanese Unexamined Patent Application Publication No.

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DISCLOSURE OF THE [NVENTION

PROBLEM TO BE SOLVED BY THE INVENTION

0] To solve the aforementioned problems, a first objective of the present invention is to achieve an improved maintainability in a hybrid type cooking apparatus provided with a combination of a radio-frequency heater and an induction heater, by making it easier to replace a plate member for transmitting magnetic flux such as a punched plate designed to allow magnetic flux to pass therethrough while blocking microwaves.

1] A second object of the present invention is to improve induction heating efficiency in a hybrid type cooking apparatus provided with a combination of a radio-frequency heater and an induction heater as compared with conventional products so as to achieve a shorter cooking time and reduced electric power consumption.

MEANS FOR SOLViNG THE PROBLEMS [0012] A first aspect of the present invention to achieve the aforementioned objective is a cooking apparatus provided with: a substantially sealable, box-shaped cooking chamber; a radio-frequency heater including a rnagnetton to generate microwaves for radio-frequency heating of food contained in the cooking chamber and a waveguide to guide the microwaves into the cooking chamber; and an induction heater including an induction heating coil to generate an alternating magnetic flux for induction heating of a heating member housed in the cooking chamber. In the cooking apparatus, part of a wall surface of the cooking chamber is formed by a plate member for transmitting magnetic flux which allows magnetic flux generated by the induction heating coil to penetrate therethrough and prevents penetration of the microwaves, and the plate member for transmitting magnetic flux is removably secured to the other part of the wall surface of the cooking chamber.

3] In the cooking apparatus according to the first aspect of the present invention, a heating member which is an object member to be inductively heated may be a single body.

However, as a typical embodiment, the heating member may be a container made of an induction-heatable material such as metals. Food stored in the container is cooked upon induction-heating the container.

4] Namely, a second aspect of the present invention according to the embodiment is a cooking apparatus provided with: a substantially sealable, box-shaped cooking chamber for storing food to be cooked; a radio-frequency heater including a magnetron to generate microwaves for radio-frequency heating of the food and a waveguide to guide the microwaves into the cooking chamber; and an induction heater including an induction heating coil to generate an alternating magnetic flux for induction heating of a container containing the food. In the cooking apparatus, part of a wall surface of the cooking chamber is formed by a plate member for transmitting magnetic flux which allows magnetic flux generated by the induction heating coil to penetrate therethrough and prevents penetration of the microwaves, and the plate member for transmitting magnetic flux is removably secured to another wall surface member forming the wall surface of the cooking chamber.

5] The induction heating coil may be disposed outside of any of wall surfaces of the cooking chamber and part or the entire wall surface at which the induction heating coil is disposed may be fonned by the aforementioned plate member for transmitting magnetic flux, Taking the efficiency of the induction heating into consideration, the closer the induction heating coil to the object to be heated, the better.

6] According to the cooking apparatus of the first and second aspects of the present invention, only the plate member for transmitting magnetic flux which tends to incur breakage or damage is removably secured to another wall surface member, e.g. the wall surface member forn-iing the bottom surface portion of the cooking chamber. Therefore, for example, a person in charge of service in a manufacturing company can replace the plate member for transmitting magnetic flux for a new one in a short period of time. As a result of this, it is possible to reduce the time in which the apparatus is not usable due to the maintenance work, leading to a higher operation rate of induction heating devices, especially in industrial use. Moreover, it is not necessary to change the entire cooking chamber upon changing the plate member for transmitting magnetic flux, nor is it necessary to replace the cooking apparatus itself for a new one. Accordingly, the cost for repair or replacement can be reduced.

7] An example of the embodiment of the cooking apparatus according to the first and second aspects of the present invention is a configuration in which the plate member for transmitting magnetic flux includes a circular frame plate and a punched plate having therein a large number of small holes, which is fixed so as to obstruct a central opening of the frame plate, and the frame plate is removably secured to the wall surface member.

8] In general, a smaller thickness is desirable for the punched plate to increase the

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transmission efficiency of magnetic flux. According to the aforementioned configuration, the punched plate is able to be fixed to the wall surface member with a high degree of strength when the punched plate with a reduced thickness and a frame plate having a thickness larger than that of the punched plate are used. On the other hand, when the plate member is fixed to the wall surface member by, for example, a nut and bolt or a similar fastener, a slight size allowance is usually needed. According to the aforementioned configuration, such allowance can be secured between the frame plate and the wall surface member, and therefore the punched plate can be stretched over the plate member in a desired state, irrelevantly to the allowance.

9] Furthermore, in the aforementioned configuration, the plate member for transmitting magnetic flux may be attached to the wall surface member by inserting a threaded rod of a weld bolt anchored to the wall surface member through the hole formed in the frame plate, and screwing a nut onto the threaded rod.

0] In this configuration, one end of the weld bolt is firmly fixed to the wall surface member by, for example, welding. Accordingly, it is not necessary to hold the threaded rod side, i.e. the weld bolt side, to prevent it from revolving while screwing the nut, and thus attachment of the plate member for transmitting magnetic flux can be efficiently carried out.

1] Since, even in the aforementioned case, a large number of portions to be clamped by nuts and weld bolts make the assembling operation complicated, the number of fixing points is desirably reduced. However, mere reduction of the fixing points may cause formation of a space between the plate member for transmitting magnetic flux and the wall

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surface member, possibly leading to a leakage of microwaves or other problems. In light of this, in a preferable configuration, a convex portion is formed on at least either one of the contact faces of the wall surface member and the frame plate, and a part of the portions each clamped by the weld bolt and the nut is substituted with pressure welding utilizing the pressing force of the convex portion.

2] For example, upon providing a plurality of clamping portions on the circumferences, the clamping portions may be substituted with pressure welding utilizing the pressing force of the convex portion, alternately or at every third portion. Although, the pressure-welded portions do not contribute to the clamping strength, it is sufficiently effective for preventing the leakage of microwaves from the space between the wall surface member and the frame plate. Further, the operation of screwing a weld bolt (threaded rod) into a nut is reduced so that the working efficiency can be improved.

3] In a desirable configuration of the cooking apparatus according to the first and second aspects of the present invention, the induction heating coil and a fan for cooling at least the induction heating coil are assembled into a unit, and the unit is disposed outside the wall surface formed by the plate member for transmitting magnetic flux in the cooking chamber.

4] Since the heating coil and the cooling fan are unitized in this configuration, the operation of attaching the cooking chamber to the wall surface can be easily, or in other [0025] It is desirable that the plate member for transmitting magnetic flux has a size large enough to reach an area which is practically beyond the influence of the magnetic flux generated by the induction heating coil. For example, when the plate member for transmitting magnetic flux consists of the punched plate and the frame plate as described earlier, the punched plate is preferably made large enough to reach an area which is practically beyond the influence of the magnetic flux generated by the induction heating coil.

6] This configuration allows the magnetic flux generated by the induction heating coil to efficiently penetrate into the cooking chamber without having influences on the wall surface members in the vicinity of the plate member for transmitting magnetic flux, with the result that the magnetic flux more frequently acts on the container to be heated (heating member) housed in the cooking chamber so as to inductively heat the container.

[00271 Moreover, not only does the induction heating coil generate heat by itself due to the ohmic loss when the coil is supplied with radio-frequency current along with the induction heating, but the plate member for transmitting magnetic flux generates heat due to the eddy current loss caused by penetration of a part of the magnetic flux. Therefore, it is preferable that the coafiguration includes a fan to cool both the induction heating coil and the plate member for transmitting magnetic flux.

8] More specifically, in the configuration in which an insulation board is disposed between the induction heating coil and the plate member for transmitting magnetic flux, preferably a space for air ventilation is secured between the induction heating coil and the insulation board and between the plate member for transmitting magnetic flux and the insulation board in such a manner that airflow from the fan is allowed to pass through both of the aforementioned spaces. In this configuration, since both the induction heating coil and the plate member for transmitting magnetic flux can be cooled by the airflow generated by one fan, the cost for the apparatus can be saved as compared with the case where fans are separately provided, and also unwanted temperature rise can be assuredly avoided.

9] Furthermore, in another configuration, another plate member made of a heat-resistant, low-loss dielectric material may be disposed at an inner side of the wall surface formed by the plate member for transmitting magnetic flux in the cooking chamber so as to provide a gap between the plate member and the plate member for transmitting magnetic flux. In the case where the wall surface forms the bottom wall portion of the cooking chamber, the plate member can function as a mounting table for mounting a container. In this configuration, since air flows between the plate member for transmitting magnetic flux and the plate member, temperature rise of the plate member for transmitting magnetic flux is more easily suppressed.

0] It is also possible to secure the aforementioned gap between the plate member for transmitting magnetic flux and the plate member by interposing an insulator which tends not to be inductively heated. This arrangement makes it possible to assuredly secure the gap of a predetermined distance between the plate member for transmitting magnetic flux and the plate member.

1] Moreover, while the plate member for transmitting magnetic flux generates heat by itself as explained earlier, when the plate thickness thereof is reduced for easy passage of magnetic flux, deformation due to heat easily occurs and, when the plate member for transmitting magnetic flux inwardly warps in the cooking chamber to come in contact with the plate member, this may cause red heat. In order to avoid this, the plate member for transmitting magnetic flux may be previously configured in a bent shape to be expanded out of the cooking chamber.

2] Since it is normal and effective for heating a container containing food to heat at the bottom surface portion of the container, one typical example of the first and second aspects of the present invention may include a configuration in which the plate member for transmitting magnetic flux is removably secured to the wall surface member forming the bottom surface portion of the cooking chamber, and the induction heating coil is disposed below the bottom surface portion.

3] A third aspect of the present invention to achieve the second objective is a cooking apparatus provided with: a substantially sealable, box-shaped cooking chamber; a radio-frequency heater including a magnetron to generate microwaves for radio-frequency heating of food contained in the cooking chamber and a waveguide to guide the microwaves into the cooking chamber; and an induction heater including an induction heating coil to generate an alternating magnetic flux for induction heating of a heating member housed in the cooking chamber. In this cooking apparatus, the induction heating coil is disposed outside of one of the wall surfaces of the cooking chamber; at least part of the aforementioned one wall surface has a portion for transmitting magnetic flux which allows magnetic flux generated by the induction heating coil to penetrate therethrough and prevents penetration of the microwaves; a plate member made of a heat-resistant, low-loss dielectric material is disposed at an inner side of the portion for transmitting magnetic flux in the aforementioned one wall surface, and provided that a distance from the inner surface of the plate member to the portion for transmitting magnetic flux in the thickness direction is 1, and a distance from the inner surface of the plate member to the inner surface of the induction heating coil in the thickness direction is L, I and L are set to satisf' the inequalities of! = L/2 and L-l = 3 mm.

4] In a typical embodiment of the cooking apparatus according to the third aspect of the present invention, the heating member is a container capable of holding food, and the wall surface including a portion for transmitting magnetic flux in the cooking chamber is a bottom wall surface. Accordingly, a fourth aspect of the present invention based on the aforementioned embodiment is a cooking apparatus provided with: a substantially sealable, box-shaped cooking chamber for storing food to be cooked; a radio-frequency heater including a magnetron to generate microwaves for radio-frequency heating of the food and a waveguide to guide the microwaves into the cooking chamber; and an induction heater including an induction heating coil to generate an alternating magnetic flux for induction heating of a container containing the food. In this cooking apparatus, the induction heating coil is disposed below the bottom surface portion of the cooking chamber, the bottom surface portion includes a bottom plate which prevents penetration of the microwaves and a portion for transmitting magnetic flux which allows magnetic flux generated by the induction heating coil to penetrate therethrough and prevents penetration of the microwaves, the bottom plate having thereon the portion for transmitting magnetic flux, a mounting table made of a hcat-resistant, low-loss dielectric material is disposed above the bottom surface portion, and provided that a distance from the upper side of the mounting table to the portion for transmitting magnetic flux in the thickness direction is 1, and a distance from the upper side of the mounting table to the upper surface of the induction heating coil in the thickness direction is L, I and L are set to satisfy the inequalities of I =

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L/2 and L-1 = 3 mm.

5] In the cooking apparatus according the fourth aspect of the present invention, since the container to be heated such as a pan is directly placed on the mounting table, the upper surface of the mounting table can be considered to correspond to the bottom surface of the container. Even in the case where the distance between the bottom surface of the container and the upper surface of the induction heating coil is the same, the heating efficiency is different depending upon the position of the portion for transmitting magnetic flux. The heating efficiency becomes relatively higher when the portion for transmitting magnetic flux is provided at a position closer to the container from a center between the bottom surface of the container and the upper surface of the induction heating coil.

6] Therefore, according to the cooking apparatus of the third and fourth aspects of the present invention, leakage of microwaves from the cooking chamber can be assuredly prevented from occurring by the portion for transmitting magnetic flux during radio-frequency heating, and at the same time a reduction in heating efficiency of the induction heating due to insertion of the portion for transmitting magnetic flux can be suppressed. Although, the portion for transmitting magnetic flux itself slightly generates heat due to the induction heating, transmission of the heat to the induction heating coil can be suppressed by placing the portion for transmitting magnetic flux away from the induction heating coil. Furthermore, the larger space between the induction heating coil and the portion for transmitting magnetic flux brings about a better airflow, with the result that an improved efficiency of cooling both the induction heating coil and the portion for transmitting magnetic flux can be achieved.

7] Moreover, according to the cooking apparatus of the third and fourth aspects of the present invention, the distance between the portion for transmitting magnetic flux and the inner surface of the induction heating coil is set at 3 rum or more, and as a result it is possible to efficiently prevent leakage of microwaves from inside the cooking chamber at the time of radio-frequency heating.

[0038) Furthermore, the cooking chamber of the third and fourth aspects of the present invention desirably has a configuration in which the induction heating coil is housed in a flat box-shaped case made of a resin, one side of the case opening on the side facing a wall surface of the cooking chamber; a metal layer is formed on the outer surface of the case and the circumferential edge of the opening; and the case is disposed in such a manner that the circumferential edge makes contact with the outside of the metallic wall surface of the cooking chamber.

9] This configuration makes it possible to reduce the leakage of magnetic flux from the gap between the circumferential edge of the opening of the case and the wall surface of the cooking chamber. Therefore, it is possible to avoid unnecessary heating of members made of magnetic metals disposed outside the case.

0] One embodiment of the cooking apparatus according to the third and fourth aspects of the present invention may havc a configuration including: a temperdture detector to detect the temperature of the portion for transmitting magnetic flux; and a controller to control electric power to be supplied to the induction heating coil based on the temperature detected by the temperature detector.

1] In this configuration, for example, when the temperature detected by the temperature detector exceeds a predetermined value, the controller reduces or stops the power supply to the induction heating coil. For example, in the case of dry boiling or abnormally long heating time of a pan, the temperature of the portion for transmitting magnetic flux may abnormally increase. In such a situation, magnetic force generated by the induction heating coil is reduced or eliminated, and thus the temperature rise of the portion for transmitting n1agnetic flux due to the induction heating can be suppressed. As a result, it is possible to prevent occurrence of abnormal heating of the portion for transmitting magnetic flux itself as well as the abnormal temperature rise of the induction heating coil caused by conduction of heat from the portion for transmitting magnetic flux, or abnormal temperature rise of other peripheral electrical equipment.

EFFECT OF THE INVENTION

2] As described thus far, in the cooking apparatus according to the first and second aspects of the present invention, since the plate member for transmitting magnetic flux, which is secondary heated along with induction heating, can be easily and independently detached from the other wall surface member forming the cooking chamber, it is possible to save time and labor for repair or replacement of the plate member for transmitting magnetic flux when damaged. As a result of this, it becomes possible to reduce a non-working period of the apparatus, and thus forexample the apparatus can bc efficiently operated in industrial use. Further, it becomes possible to reduce cost for repairing and replacing the plate member for transmitting magnetic flux, namely, cost for the components itself and cost for repair or replacement work.

3] Further, use of the cooking apparatus according to the third and fourth aspects of the present invention makes it possible to superbly heat an object to be heated such as a pan located in a cooking chamber by allowing magnetic flux to efficiently pass through the object, while effectively preventing leakage of microwaves to the outside of the cooking chamber during radio-frequency heating. As a result, cooking time can be saved, and electric power consumption can also be suppressed, thus contributing to a reduction in cooking cost.

BRIEF EXPLANATION OF THE DRAWINGS

4] Fig. 1 is an external perspective view showing a cooking apparatus with its door open according to one embodiment of the present invention.

Fig. 2(a) and Fig. 2(b) are a top plan view and a front plan view, respectively, of the cooking apparatus according to the embodiment.

Fig. 3 is a cross-sectional view taken along line A-A' of Fig. 2(a).

Fig. 4 is a block diagram showing an electrical system of the cooking apparatus according to the embodiment.

Fig. 5 is a perspective view showing the cooking apparatus of the embodiment after removing the housing.

Fig. 6 is a perspective view showing the electric system of Fig. 4 with a ventilation duct cover removed.

Fig. 7 is an exploded view showing a bottom surface portion of the cooking chamber and an induction heating unit.

Fig. 8 is an assembly structural view of the bottom portion of the cooking chamber.

Fig. 9 is an assembly structural view of the induction heating unit.

Fig. 10 is a vertical cross-structural view showing the induction heating unit and the bottom surface portion of the cooking chamber.

Fig. 11(a) and Fig. 11(b) each is a longitudinal cross-sectional view of a fixing portion in an attachment structure of the bottom plate fitting and the bottom plate.

Fig. 12(a) and Fig. 12(b) each is a longitudinal cross-sectional view of a welding portion in an attachment structure of the bottom plate fitting and the bottom plate.

Fig. 1 3 is a graph showing results of actual measurements of relations between the distance of L-1 between the induction heating coil and the punched plate, and the heating efficiency.

EXPLANATION OF NUMERALS

5] I... Housing 2...Door 3... Cooking Chamber 3a... Backside Surface Portion 3b... Ceiling Surface Portion 3c... Bottom Surface Portion 3d... Left Side Surface Portion 3e... Right Side Surface Portion . (-* * in 11i..uITuiei1L1a1 [OLLIUII UL 4...Air Inlet 5... Magnetron 6... Waveguide 7... Microwave Diffusion Chamber 8... Antenna Drive Motor 9... Radiation Antenna 16... EM-Cooling Fan Motor 17... IH-Cooling Fan Motor 1 8... Induction Heating Drive Unit 19... Radio-Frequency Heating Drive Unit 20... Main Control Unit 21... Load Drive Unit 22... Commercial Power Supply 23... Power Supply Circuit 231... Power Switch 232... Noise Filter 233, 234... Rectifier Circuit 24. . . induction Heating Inverter Circuit 25. . . Radio-Frequency Heating Inverter Circuit 26... Direct Current Power Supply Circuit 30... FirstFanUnit 31... Second Fan Unit 32... ThirdFanunit 33, 35... Ventilation Duct Cover 34, 36... Exhaust Duct 60... Mounting Plate 70... Bottom Portion of the Cooking Chamber 71... Bottom Plate 72... Punched Plate

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73... Bottom Plate Fitting 73a... Threaded Hole 73b... Convex Portion 74... Mica Plate 75... Fixing Portion 76... Weld Bolt 76a... Threaded Rod 77... Nut 78... Pressure-Welded Portion 79... Punched Plate-Cooling Air Path 80... Induction Heating Unit 81... Case 82... Induction Heating Coil 83... Heat Insulation Board 84... Coil-Cooling Fan Motor 85... Mica Plate 86... Temperature Sensor 87... Spring 88... Coil-Cooling Air Path 90... Container 90a... Handle 90b... Protection Cover

BEST MODE FOR CARRYING OUT THE INVENTION

6] The following description will discuss one embodiment of the cooking apparatus according to the first through fourth aspects of the present invention with reference to drawings.

7] Fig. I is an external perspective view showing a cooking apparatus with its door open according to the present embodiment, Fig. 2(a) and Fig. 2(b) are a top plain view and a front plain view, respectively, of the cooking apparatus, and Fig. 3 is a schematic cross-sectional view taken along line A-A' shown in Fig. 2(a).

8] As shown in Figs. 1, 2(a) and 2(b), the cooking apparatus includes a housing 1 having a substantially rectangular-parallelepiped shape, and a cooking chamber 3, with its front surface opened, is formed in the housing 1. The front opening of the cooking chamber 3 is opened and closed by a side-opening door 2. A punched plate for preventing microwave leakage, and a heat-resistance glass to see through the inner portion of the cooking chamber 3 are disposed at the center portion 2a of the door 2. In the vicinity of the door 2, a microwave leakage prevention structure is provided to prevent the door 2, when closed, from contacting to a circumferential portion 3f of the front opening of the cooking chamber 3 so that microwaves in the cooking chamber 3 are prevented from leaking.

Moreover, an operation panel including a key-input unit II on which a plurality of operation keys are arranged, and a display unit 12 using, for example, a segment LCD is disposed at an upper front portion of the housing 1 where the operation panel is not covered by the door 2 being closed. The key-input unit ii is manipulated by a user (i.e. the person who is cooking) to enter instructions concerning various cooking conditions or start/stop modes of operation, and the display unit 12 displays those cooking conditions or remaining time of the operation, and so forth. Furthermore, an air inlet 4 having a long horizontal shape for taking in fresh air to cool each portion inside the housing I to be mentioned later is formed at a front lower portion of the housing I as well as a lower side of the door 2.

9] As shown in Fig. 3, the cooking chamber 3 has a substantially rectangular parallelepiped shape formed by a backside surface portion 3a, a ceiling surface portion 3b, a bottom surface portion 3c, a left side surface portion 3d and a right side surface portion 3e, each forming a wall surface of the cooking chamber. When the front opening is closed by the door 2 as mentioned earlier, the cooking chamber is practically hermetically sealed.

The wall surface of the cooking chamber 3 may consist of separate members, or an integrated member (for example, an integrated plate member formed in a U-shape) formed by combining a plurality of wall surface members portions. However, in any case, the wall surfaces are formed into one box-shaped body in which each of the wall surfaces, except the front surface portion, are fixed together by spot welding. The integrated member constituting the cooking chamber 3 corresponds to the wall surface member according to the present invention. As shown in Figure, for example, a container 90 containing food 91 to be cooked is located in the cooking chamber 3. With regard to the cooking apparatus of the present invention, a radio-frequency (microwave) heater for microwave-oven-cooking and an induction heater to indirectly cook the food 91 by heating the container 90 serving as the heating member in the first and third aspects of the present invention are provided in combination for cooking the food 91.

0] More specifically, as the radio-frequency heater, a magnetron 5 which generates microwaves is disposed at an upper rear of the backside surface portion 3a of the cooking chamber 3, and the microwaves generated by the magnetron 5 are propagated through a waveguide 6 extending through an upper portion of the housing I to be introduced to a microwave diffusion chamber 7 provided at the ceiling surface portion 3b of the cooking chamber 3. A radiation antenna 9 driven to rotate within substantially a horizontal plane by an antenna drive motor 8 is provided in the microwave diffusion chamber 7. Microwaves are radiated while diffused by the radiation antenna 9 from a power feeding port in the ceiling surface portion 3b of the cooking chamber 3 into the cooking chamber 3 as shown by dashed arrows in Fig. 3. The microwaves contribute to cooking the food 91 in the container 90.

1] Meanwhile, the ceiling surface portion 3b of the cooking chamber 3 is not horizontal, but downwardly inclined toward the backside of the cooking chamber. This arrangement enables, when steam generated in the cooking chamber 3 forms condensation on the ceiling surface portion 3b, the condensed water to flow on the ceiling surface portion 3b towards the backside. Therefore, the drops of water tend not to fall on the hand of the user upon putting in or taking out the container 90 or food.

2] On the other hand, as the induction heater, a heating coil 82 housed in the case 81, the heating coil being used for direct induction heating the container 90, is almost horizontally disposed below the bottom surface portion 3c of the cooking chamber. When radio- frequency current is supplied to the induction heating coil 82 from an inverter circuit to be mentioned later, alternating magnetic flux is generated, and the magnetic flux enters into the cooking chamber 3 through the bottom surface portion 3c, and passes over the bottom portion of the container 90 formed of, for example, magnetic metals. Due to the induction effect of the alternating magnetic flux, an eddy current is induced in the bottom portion of the container 90 so that the container 90 is heated by Joule heat, and accordingly the food 91 contained in the container is cooked. The structure of the induction heating unit including the induction heating coil 82 and the bottom surface portion 3c of the cooking chamber 3 will be later detailed.

3] Fig. 4 is a structure diagram showing an electrical system of the cooking apparatus according to the present embodiment. As shown in Fig. 4, a main control unit 20 serving as a control center is configured with a Cpu (central control unit) at its center. The main control unit 20 receives a key-input signal from a key-input unit 11, a door open detection signal to detect an open/closed state of the door 2 from a door switch 14, and a temperature detection signal of the punched plate constituting a part of the bottom surface portion 3c from a temperature sensor 86. Moreover, the main control unit 20 drives an induction heating inverter circuit (IH inverter circuit) 24 via an induction heating (IH) drive unit 18 so as to supply radio-frequency current to the induction heating coil 82 constituting a part of the inverter circuit 24. Further, the main control unit 20 drives a radio-frequency heating inverter circuit (EM inverter circuit) 25 via a radio-frequency heating (EM) drive unit 19, and drive power is supplied to the magnetron 5 to generate microwaves.

4] The power supply circuit 23 includes a power switch 231, a noise filter 232 which is commonly used for radio-frequency heating and induction heating, and a rectifier circuit 233 and 234 which are independently used for induction heating and radio-frequency heating, respectively. The power Supply circuit 23 supplies a direct-current power converted from an alternating-current power of, for example, 200V supplied from a commercial alternating-current power supply 22 to the inverter circuit 24 for induction heating and the inverter heating 25 for radio-frequency heating. The main control unit 20, which receives the drive power from the power supply circuit 23 via a direct-current power supply circuit 26, controls via a load drive unit 21 the operations of each the antenna drive motor 8 as well as three fan motors for cooling, i.e. an EM-cooling fan motor 1 6, an IH-cooling fan motor 17, and a coil-cooling fan motor 84. Moreover, the main control unit outputs a display controlling signal concerning the determined cooking course information and an operation condition to the display unit 12 so as to make the display unit 12 perform a display and sound a buzzer 13, if necessary.

As will be later explained, the EM-cooling fan motor 16 is mainly used to cool the inverter circuit 25 for radio-frequency heating; the IH-cooling fan motor 17 is mainly used to cool the induction heating inverter circuit 24; and the coil-cooling fan motor 84 is mainly used to cool the induction heating coil 82.

5] The main control unit 20 is equipped with a RUM (read-only memory) storing an operation program, and in a process of running the operation program on the CPU, the main control unit 20 controls each of the aforementioned portions while monitoring the operation of the user and the performance status of the present device based on the aforementioned various signals.

6] Next, the structure of the induction heating unit which is one feature of the cooking apparatus of the present embodiment, and the structure of the bottom surface portion 3c of the cooking chamber 3 are described with reference to Figs. 7 through 13. Fig. 7 is an vr1ni1d view hnwina flip btitfim iirf'e r,rtitn. t-f' th il'inc t-hITrlhir nl th --* - t&b4tSfl.##4.#, t4S%S L&L.

induction heating unit 80 located below the bottom surface portion 3c; Fig. 8 is an assembly structural view of the bottom portion 70 of the cooking chamber; Fig. 9 is an assembly structural view of the induction heating unit 80; and Fig. 10 is a vertical cross-structural view of the induction heating unit 80.

7] As shown in Fig. 7, an integrated form of the induction heating unit 80 is disposed below the bottom portion 70 of the cooking chamber, the bottom portion 70 forming the bottom surface portion 3c of the cooking chamber 3. On the other hand, a mounting plate 60 for mounting a container containing food is placed on the bottom portion 70 of the cooking chamber. The mounting plate 60 needs to be made of a material allowing magnetic flux to pass therethrough for induction heating, and the material further needs to be a low-loss, dielectric material so as to not be easily heated by radio-frequency heating.

Moreover, the mounting plate 60 must be heat-resistant since it will have direct contact with a high temperature container. For those reasons, the mounting plate 60 may be made of, for example, crystal glass. The mounting plate 60 has a concave portion 61 of a substantially circle shape in which a position for mounting an object to be heated is caved in, with the concaved portion 61 coaxially located with the induction heating coil 82.

8] As shown in Fig. 8, the bottom portion 70 of the cooking chamber has a configuration in which a punched plate 72 (which corresponds to the plate member for transmitting magnetic flux and the portion for transmitting magnetic flux of the present invention) and a bottom plate fitting 73 are removably mounted on a bottom plate 71 made of stainless steel (SUS3O4) having a large circular opening constituting the bottom portion of the cooking chamber 3. More specifically, the bottom plate fitting 73 made of stainless steel (SUS3O4), corresponding to the frame plate of the present invention, has an annular shape, and the punched plate 72 made also of stainless steel in which a large number of punched holes with a predetermined diameter are formed has a circular shape, and those two members are formed into one body by a strong joining method such as spot welding.

The bottom plate 71 and the bottom plate fitting 73 have a thickness of 0.5 mm, and high rigidity, whereas the punched plate 72 is arranged to have a thickness of 0.1 mm to improve the magnetic flux passing efficiency. In this manner, although the punched plate is thin and has a low rigidity, since the thick bottom plate fitting 73 has a high rigidity, fixing of the bottom plate fitting 73 to the bottom plate 71 enables to achieve a sufficiently high degree of strength at the fixing portion between the bottom plate fitting 73 and the bottom plate 71. Meanwhile, although the bottom plate 71 constitutes the bottom surface portion 3c of the cooking chamber 3, and those members are depicted as one member in Figs. 7 and 8, actually as explained earlier, the bottom plate 71 and the bottom surface portion 3c are fixed by spot-welding to the backside surface portion 3a and the side surface portions 3d and 3e so as to as a whole form a single wall surface member constituting the cooking chamber 3.

9] As explained earlier, the punched plate 72 functions to allow magnetic flux generated by the induction heating coil 82 to pass through the punched plate, and at the same time flmctions to block microwaves supplied into the cooking chamber 3 as will be later described. The condition for a passing efficiency of the magnetic flux depends mainly on the aperture ratio and the plate thickness of the punched plate 72. On the other hand, the conditions for blocking passage of the microwaves depend mainly on the diameter of the holes and the plate thickness of the punched plate 72. Therefore, appropriate settings of those elements are required. in this embodiment, small holes with a diameter of 1.4 mm are formed at regular intervals of 1.7 mm. Under a condition where the plate thickness is thin, magnetic flux can pass through the plate even if small holes are not formed therein.

0] The punched plate 72 has a larger diameter than that of the induction heating coil 82 disposed therebelow. Actually, the punched plate 72 is formed to be larger than necessary with an appropriate margin. This arrangement makes it possible to avoid unnecessary heating of the bottom plate 71 and the bottom plate fitting 73 due to magnetic flux generated by the induction heating coil 82.

[006 1] The present cooking apparatus employs an installation configuration in which only the punched plate 72 (more exactly, the plate member for transmitting magnetic flux formed by integrating the punched plate 72 and the bottom plate fitting 73) can be easily replaced without replacing the bottom plate 71 in the case where damage such as a crack occurs in the punched plate 72. This feature will be described later with reference to Figs. 11(a), 11(b), 12(a) and 12(b). Figs. 11(a), 11(b), 12(a) and 12(b) are longitudinal cross-sectional views each showing the installation configuration of the bottom plate fitting 73 and the bottom plate 71. Each of Figs. 11(a) and 11(b) illustrates a fixing portion 75, and each of Figs. 12(a) and 12(b) illustrates a pressure welding portion 78. The installation configuration is provided on the bottom plate fitting 73 at each of 36 points located at approximately equal angular intervals in the circumferential direction, with the fixing portion 75 and the pressure welding portion 78 alternately provided. The distance between the installation configurations needs to be less than one fourth of the wavelength of microwaves in order to prevent microwaves from leaking. Since the wavelength of generally used microwaves is approximately 120 mm, the distance between the installation configurations is set at 30 mm or less.

[00621 As shown in Fig. 1 l(a) in the fixing portion 75, the weld bolt 76 is fixed to the bottom plate 71 by welding or other fixing methods in such a manner that a threaded rod 76a protrudes downwardly. The bottom plate fitting 73 facing the threaded rod has a threaded hole 73a formed by punching. The threaded rod 76a is installed into the threaded

S

hole 73a, and then a nut 77 is screwed onto the threaded rod 76a from below and tightened so that the bottom plate fitting 73 integrated with the punched plate 72 is attached to the bottom plate 71 as shown in Fig. 11(b). Since the weld bolt 76 is fixed to the bottom plate 71, it is not necessary to hold the bolt to keep it from turning upon tightening the nut, thereby achieving a higher working efficiency in the operation of tightening the nut 77.

3] On the other hand, as shown in Fig. 12(a), the undersurface of the bottom plate 71 is flat in the pressure welding portion 78, whereas a dowel-like convex portion 73b is formed on the bottom plate fitting 73. In a state of being fixed at the adjacent fixing portions 75 in the circumferential direction as described above, the undersurface of the bottom plate 71 makes contact with the upper surface of the bottom plate fitting 73, and thus upper surfaces of the convex portions 73b of the bottom plate fitting 73 are strongly clamped against the undersurface of the bottom plate 71 at the pressure welding portion 78 as shown in Fig. 12(b). As a result of this, a high degree of contact is secured between the contacting surfaces of the two members.

4] Although troublesome operations of fixing the weld bolt 76 to the bottom plate 71 and tightening the nut 77 are required in the aforementioned fixing portion 75, no operations are required at the pressure welding portion 78. In other words, by allocating the fixing portions 75 at one half of the 36 points of the installation configuration and allocating the pressure welding portions 78 at the other haif it becomes possible to secure the contact between the bottom plate 71 and the bottom plate fitting 73 at such intervals that should prevent the leakage of microwaves while reducing operational labor and the cost for components. Therefore, leakage of microwaves can be assuredly prevented.

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As shown in Fig. 9, the induction heating unit 80 has a configuration in which a coil-cooling fan unit including a coil-cooling fan motor 84 and a fan rotationally driven by the fan motor 84, and the induction heating coil 82 which is spirally formed into a flat coil and mounted on the heat insulating board 83, and the like arc housed in a case 81 with the upper surface opened, and a thin mica plate 85 serving as an insulator is fixed over the induction heating coil 82. Namely, the aforementioned members are integrated in the case 81. The case 81 is formed by a resin such as a polypropylene (PP) resin, an acrylonitri le-butadiene-styrene (AB S) resin, a polycarbonate acrylonitrile-butadiene-styrene (PC/ABS) resin, polyethylene terephthalate (PET) resin, and a phenol resin, and has its outer surface and upper circumferential portion 8la plated with metal.

6] As shown in Fig. 3, upon placing the induction heating unit 80 below the bottom surface portion 3c, the upper circumferential portion 81a is placed in contact with the undersurface of the bottom plate 71. Here, since a metal layer is formed on the upper circumferential portion 81 a of the case 81 as mentioned previously, electrical conductivity is secured between the bottom plate 71 and the case 81, thereby preventing the leakage of microwaves through a space between them. In other words, even though a portion of microwaves radiated in the cooking chamber 3 pass through the punched plate 72, the microwaves are not permitted to leak out of the induction heating unit 80, making it possible to further alleviate unnecessary radiation to the surrounding area.

7] Moreover, a temperature sensor 86 is provided on a mica plate 85 with a spring 87 between them as shown in Fig. 9. Therefore, upon placing the induction heating unit 80 below the bottom surface portion 3c, the bias of the spring 87 presses and fixes the temperature sensor 86 against the undersurface of the punched plate 72 disposed thereabove. As a result, the temperature sensor 86 can accurately detect the temperature of the punched plate 72.

8] Meanwhile, as shown in Figs. 7 and 10, a mica plate 74 which is an insulator is disposed as a spacer on the punched plate 72 so as to keep a uniform distance between the punched plate 72 and the mounting plate 60. This arrangement is provided in consideration of the influence of variation in the distance between the punched plate 72 and the mounting plate 60 on the heating efficiency during induction heating.

9] As shown in Fig. 10, since a container 90 to be heated is placed on the mounting plate 60, it is possible to consider that an upper surface of the mounting plate 60 corresponds to the bottom surface of the container 90. Here, let a distance between an upper surface of the induction heating coil 82 functioning as a heat source and an upper surface of the mounting plate 60 be denoted by L (distance in a thickness direction) and a distance between the punched plate 72 and the upper surface of the mounting plate 60 denoted by 1. Since a plate thickness of the punched plate 72 is as small as 0.1 mm, measuring of the distance I from the upper surface or from the undersurface (or from the middle) makes no major difference. In Fig. 10, however, the distance 1 is measured from the upper surface of the punched plate 72.

Fflfl7fll The container 90 is heated by passage of alternating magnetic flux generated by the induction heating coil 82 through the container 90, and magnetic force of the alternating magnetic flux is stronger at a position closer to the induction heating coil 82. Therefore, from the viewpoint of only heating efficiency, the closer the induction heating coil 82 to the container 90, the better. However, the induction heating coil 82 generates heat by itself due to ohmic loss against radio-frequency current, and the punched plate 72 also generates heat by itself due to eddy-current loss caused by penetration of partial magnetic flux through the plate portion. Therefore, since the release of heat needs to be taken into consideration, it is necessary to provide an appropriate void (coil-cooling air path 88) between the induction heating coil 82 and the mica plate 85, and another appropriate void (punched plate-cooling air path 79) between the mica plate 85 and the punched plate 72.

For this reason, the distance L between the upper surface of the induction heating coil 82 and the upper surface of the mounting plate 60 needs to be secured at a certain level or more. Accordingly, the cooking apparatus of the present embodiment employs the configuration in which a highest possible heating efficiency can be achieved under a condition of the distance L being set at a certain value.

1] Fig. 13 is a graph showing a result of actual measurement of relationships between the distance L-1 from the induction heating coil 82 to the punched plate 72 and the heating efficiency when the distance L is set 8.5 mm and 11.7 mm. It is a matter of course that the heating efficiency is reduced when the punched plate is inserted than in the case without insertion of the punched plate, and it is further understood that a larger distance 1 between the punched plate 72 and the upper surface of the mounting plate 60 with the same distance L results in a greater reduction in the heating efficiency. This is supposedly because disposing the punched plate 72 at an area with a strong magnetic force of magnetic flux generated by the induction heating coil 82 causes a greater loss in the punched plate in proportion to the strength of the magnetic force, thus resulting in a reduction of the heating efficiency as a whole. Therefore, in this embodiment, the punched plate 72 is disposed at a position closer to the mounting plate 60 from the middle point between the upper surface of the induction heating coil 82 and the upper surface of the mounting plate 60, namely at a position where distance / is L/2 or less. This arrangement makes it possible to reduce as much as possible an influence of reduction in the induction heating efficiency due to the punched plate 72 provided to block microwaves.

2] It is to be noted that a distance between the punched plate 72 and the induction heating coil 82 is relatively increased by placing the punched plate 72 at a side closer to the mounting plate 60 within the space between the mounting plate 60 and the induction heating coil 82 so that the aforementioned punched plate-cooling air path 79 is more easily secured. This is advantageous for promoting heat release of the induction heating coil 82 and the punched plate 72.

3] On the other hand, under a condition of 1 = L/2, a smaller Lprovides a smaller value of L-l. Investigation by the inventors of the present invention has revealed that the value of L-1 has an influence on a microwave leakage ratio from inside the cooking chamber 3. This is because placing the induction heating coil 82 too close to the punched plate 72 causes an easy passage of microwaves. Therefore, in order to avoid the increase of microwave leakage, L-l is set at 3 mm or more.

4] In the induction heating unit having the aforementioned configuration, alternating magnetic flUX is generated when radiofrequency current is introduced froiii the inverter circuit 24 to the induction heating coil 82 by the induction heating drive unit 18 which operates under the control of the main control unit 20, and the magnetic flux penetrates into the cooking chamber 3 through the punched plate 72 and the mounting plate 60, and then passes across the bottom portion of the container 90 in which at least the bottom portion is made of a magnetic metal. The induction action induces an eddy current in the bottom portion of the container 90 to heat the container 90 by Joule heat so that food 91 to be cooked in the container 90 is heated. Since the relationships among the induction heating coil 82, the punched plate 72, and the mounting plate 60 are appropriately determined as mentioned above, it is possible to achieve an efficient cooking by the efficient induction heating of the container 90. Moreover, since the bottom plate fitting 73 integrated with the punched plate 72 is removably attached to the bottom plate 71 as described earlier, a person in charge of service in the manufacturing company can easily replace the punched plate 72 by removing the nut 77 when the punched plate 72 is damaged.

5] Moreover, since the inverter circuits 24 and 25, which drive the induction heating coil 82 and the magnetron 5, respectively, are separately installed in the cooking apparatus of the present embodiment, it is possible to simultaneously perform an induction-heating operation and a radio-frequency-heating operation, and further, those operations may be performed alternately or independently. Each of the inverter circuits 24 and 25, which has a power switching element (e.g. power PET), generates a large amount of heat during operation, and thus requires a proper heat release. Moreover, temperature of the induction heating coil 82 for generating magnetic flux is increased due to the ohmic loss and the radiation heat from the heating member caused by induction heating, and thus a proper heat release from the induction heating coil 82 is also required. Furthermore, the induction heating coil 82 and the punched plate 72 themselves generate a considerable amount of heat as explainer earlier. Additionally, since the cooking chamber 3 is in some cases filled with steam or the like during the cooking process, discharge of the air in the cooking chamber 3 is also required.

6] Therefore, for the purpose of cooling or air-discharging, the cooking apparatus of the present embodiment is equipped with three fan units, which are a first fan unit 30 including an EM-cooling fan motor 16, a second fan unit 31 including Il-I-cooling fan motor 17, and a third fan unit 32 including a coil-cooling fan motor 84. As an air introduction inlet for those three fan units 30, 31 and 32, an air inlet 4 is disposed at a lower part of the front surface of the housing 1. As already described, the third fan unit 32 is integrated with the induction heating coil 82 in the previously described manner in the case 81.

7] Upon driving the coil-cooling fan motor 84, the fan in the third fan unit 32 starts rotating so that outdoor air taken in from the air inlet 4 is sent to the aforementioned coil-cooling air path 88 and the punched plate-cooling air path 79. As a result, temperature increase of the induction heating coil 82 and the punched plate 72 can be suppressed.

8] The following description will discuss configurations and operations of the first fan unit 30 and the second fan unit 31 with reference to Figs. 4 and 5. Fig. 4 is a perspective view showing the backside of the cooking apparatus with the housing removed. Fig. 5 is a perspective view shown in Fig. 4 in a state where the ventilation duct cover is further removed.

rnnioi LJ,J The space between the left side surface portion 3d of the cooking chamber 3 and a left side surface portion of the housing 1, and the space between the right side surface portion 3e of the cooking chamber 3 and a right side surface portion of the housing I respectively form a ventilation duct. Ventilation duct covers 33 and 35 vertically extending are provided at right and left sides of the backend in the housing 1, respectively. The radio-frequency heating inverter circuit 25 is installed inside the ventilation duct cover 33, and the first fan unit 30 is disposed below the cover 33. Namely, when the EM-cooling fan motor 16 of the first fan unit 30 is driven to rotate the fan, outside air taken in by the rotating fan via the air inlet 4 moves upward in the ventilation duct cover 33 while cooling the radio-frequency heating inverter circuit 25. The warmed air is transferred to the backside through the exhaust duct 34 disposed at the upper portion so as to be emitted outside the apparatus from an exhaust port formed on the backside of the housing 1.

0] The induction heating inverter circuit 24 is installed inside the ventilation duct cover 35, and the second fan unit 31 is disposed below the cover 35. Namely, when the IH-cooling fan motor 17 of the second fan unit 31 is driven to rotate the fan, outside air taken in by the rotating fan via the air inlet 4 moves upward in the ventilation duct cover while cooling the induction heating inverter circuit 24. The air is transferred to the front portion through the exhaust duct 36 disposed at the upper portion, and is supplied inside the cooking chamber 3 via an opening not shown in the figures. In other words, the first fan unit 30 is mainly used to cool the circuit 25, whereas the second fan unit 31 is used to discharge the impure air from the cooking chamber 3 as well as to cool the circuit 24. It is to be noted that a large number of exhaust openings are formed in the left side surface portion 3d of the cooking chamber 3. The air in the cooking chamber 3 is forced through the exhaust openings to be discharged outside the apparatus via an exhaust duct, not shown in the figures, which is disposed outside the left side surface portion 3d.

1] As mentioned previously, since the cooking apparatus of the present embodiment has the independently operable fans to cool the inverter circuit for the induction heater and the inverter circuit for the radio-frequency heater, heat release in each of the inverter circuits is sufficiently promoted, thereby making continuous use possible.

2] Meanwhile, although heat release from the punched plate 72 and the induction heating coil 82 is promoted by the air flow generated by the third fan unit 32 as described earlier, the punched plate 72 may be abnormally heated when, for example, the container is boiled dry, or such an item as an iron plate covering almost all the surface of the mounting plate 60 is contained and then continuously heated for a long period of time. The abnormal heating of the punched plate 72 may be accompanied by abnormal heating of the induction heating coil 82 and other peripheral members, possibly causing failure or other trouble. In light of this, the main control unit 20 performs the following controls to avoid the aforementioned abnormal heating situations.

3] That is, during the induction heating, the main control unit 20 periodically or randomly reads a temperature detected by the temperature sensor 86, and determines whether or not the temperature exceeds the predetermined uppermost temperature level.

When the temperature does not exceed the uppermost temperature level, the operation is continued, whereas when the temperature exceeds the uppermost temperature level, the main control unit 20 controls the inverter circuit 24 to reduce the amount of alternating electric current supplied to the induction heating coil 82 via the induction heating drive t 1 Q A if ic cch1 tr fn1nrtrQrIl, hrli1 t1 ciirrl'i, tf fhp c1ti-viitr,n L&LLS LU * *&gsL ZIttLI V dLJ, LI 10 fflJU0LJL SJ l.LLLjJIL S&L *1) *SIfl%& 111# 0LJJJJLJ fl LA%# .LLLSAL&LLA.Ab electric current to the induction heating coil 82. This arrangement reduces or stops magnetic flux generated by the induction heating coil 82 so as to suppress the temperature increase of the punched plate 72. It is also possible to enhance the cooling efficiency by increasing the rotational speed of the coil-cooling fan motor 84, instead of reducing the drive power by controlling the inverter circuit 24.

4] It is to be noted that, upon cooking using the cooking apparatus of the present embodiment, the placement of food in the cooking chamber 3 is sufficient for cooking by radio-frequency heating only, whereas in the case of cooking by induction heating, the container 90 needs to be positioned right above the induction heating coil 82, otherwise a preferable cooking operation cannot be performed. This is why the concave portion 61 is formed on the mounting plate 60 in the aforementioned embodiment. For the same purpose, applicable configurations include a configuration in which protrusions to disturb the mounting of the container are provided on the mounting plate 60 at a position undesirable for mounting the container, or a configuration in which the container itself has a convex portion or a concave portion to fit with the shape of the mounting plate 60. Moreover, a container-position-direction guard prepared as a separate member from the mounting plate may be provided on the mounting plate 60 so that the container 90 is placed in accordance with the guard.

5] Further, as the container 90 to be used for cooking, a container having a configuration in which a handle 90a is covered with a protection cover 90b made of a silicon rubber as shown in Fig. 10 may be preferably used. This is because the silicon rubber has a high heat resistance, and is less susceptible to the influence of microwaves.

Also, elethic discharge barely occurs when it comes close to a wall surface of the metal cooking chamber 3.

6] It is to be noted that each of the aforementioned embodiments is merely one example of the present invention, and thus those embodiments with a proper modification, amendment or addition within the scope of the present invention are naturally included in the scope of the claims of the present invention.

[00871 For example, a container containing food is heated by induction heating in the aforementioned embodiment, however a configuration in which a heating member such as a metal plate is disposed in place of the container and the heating member is heated by induction heating to increase the temperature inside the cooking chamber, or a configuration in which water is dropped or supplied to the heating member to generate steam, may be applicable. Further, although it is generally appropriate to employ a configuration in which the induction heating coil is disposed below the bottom wall surface of the cooking chamber for induction heating of the container as mentioned earlier, it is possible, for induction heating of a heating member other than the container as mentioned previously, to employ a modified configuration in which the induction heating coil is disposed outside of the other surfaces of the cooking chamber such as the wall surfaces, the ceiling surface, the backside surface, and the side surfaces, and the punched plate for transmitting magnetic flux is disposed so as to correspond to the location of the induction heating coil.

Claims (16)

1. CLAiMS 1. A cooking apparatus comprising: a substantially sealable,

   box-shaped cooking chamber; a radio-frequency heater including a magnetron to generate microwaves for radio-frequency heating of food contained in the cooking chamber and a waveguide to guide the microwaves into the cooking chamber; and an induction heater including an induction heating coil to generate an alternating magnetic flux for induction heating of a heating member housed in the cooking chamber, wherein part of a wall surface of the cooking chamber is formed by a plate member for transmitting magnetic flux which allows magnetic flux generated by the induction heating coil to penetrate therethrough and prevents penetration of the microwaves, and the plate member for transmitting magnetic flux is removably secured to the other part of the wall surface forming the wall surface of the cooking chamber.
2. 2. A cooking apparatus comprising: a substantially sealable, box-shaped cooking chamber for storing food to be cooked; a radio-frequency heater including a magnetron to generate microwaves for radio-frequency heating of the food and a waveguide to guide the microwaves into the cooking chamber; and an induction heater including an induction heating coil to generate an alternating magnetic flux for induction heating of a container containing the food, wherein part of a wall surface of the cooking chamber is formed by a plate member for transmitting magnetic flux which allows magnetic flux generated by the induction heating coil to penetrate therethrough and prevents penetration of the microwaves, and the plate member for transmitting magnetic flux is removably secured to another wall surface member forming the wall surface of the cooking chamber.
3. 3. The cooking apparatus according to claim 1 or 2, wherein: the plate member for transmitting magnetic flux includes a circular frame plate and a punched plate having therein a large number of small holes, which is fixed to the frame plate so as to obstruct a central opening of the frame plate; and the frame plate is removably secured to the wall surface member.
4. 4. The cooking apparatus according to claim 3, wherein the plate member for transmitting magnetic flux is attached to the wall surface member by: a threaded rod of a weld bolt anchored to the wall surface member, the threaded rod being inserted through a hole formed in the frame plate; and a nut screwed onto the threaded rod.
5. 5. The cooking apparatus according to claim 4, wherein: a convex portion is formed on at least either one of contact faces of the wall surface member and the frame plate; and a part of portions each clamped by the weld bolt and the nut is substituted with pressure welding utilizing a pressing force of the convex portion.
6. 6. The cooking apparatus according to any of claims 1 to 5, wherein: the induction heating coil and a fan cooling at least the induction heating coil are assembled into a unit; and the unit is disposed outside the wall surface formed by the plate member for transmitting magnetic flux in the cooking chamber.
7. 7. The cooking apparatus according to any of claims I to 6, wherein: the plate member for transmitting magnetic flux has a size large enough to reach an area which is practically beyond influence of the magnetic flux generated by the induction heating coil.
8. 8. The cooking apparatus according to any of claims 1 to 7, further comprising a fan that cools both the induction heating coil and the plate member for transmitting magnetic flux.
9. 9. The cooking apparatus according to any of claims I to 8, further comprising a plate member made of a heat resistant, low-loss dielectric material, which is disposed at an inner side of the wall surface formed with the plate member for transmitting magnetic flux in the cooking chamber so as to provide a gap between the plate member and the plate member for transmitting magnetic flux.
10. 10. Th ennkin annaratiis accordinh to claim 9. wherein -.-an insulator which tends not to be inductively heated is interposed between the plate member for transmitting magnetic flux and the plate member to secure the aforementioned gap.
11. 11. The cooking apparatus according to claim 9, wherein: the member for transmitting magnetic flux is configured in a bent shape to be expanded out of the cooking chamber.
12. 12. The cooking apparatus according to any of claims I to 11, wherein: the plate member for transmitting magnetic flux is removably secured to the wall surface member forming a bottom surface portion of the cooking chamber; and the induction heating coil is disposed below the bottom surface portion.
13. 13. A cooking apparatus comprising: a substantially sealable, box-shaped cooking chamber; a radio-frequency heater including a magnetron to generate microwaves for radio-frequency heating of food contained in the cooking chamber and a waveguide to guide the microwaves into the cooking chamber; and an induction heater including an induction heating coil to generate an alternating magnetic flux for induction heating of a heating member housed in the cooking chamber, wherein the induction heating coil is disposed outside of one of the wall surfaces of the cooking chamber, at least part of the aforementioned one wall surface has a portion for transmitting magnetic flux which allows magnetic flux generated by the induction heating coil to penetrate therethrough and prevents penetration of the microwaves, a plate member made of a heat-resistant, low-loss dielectric material is disposed at an inner side of the portion for transmitting magnetic flux in the aforementioned one wall surface, and provided that a distance from an inner surface of the plate member to the portion for transmitting magnetic flux in a thickness direction is 1, and a distance from the inner surface of the plate member to an inner surface of the induction heating coil in the thickness direction is L, /and L are set to satisfy inequalities of/ = L/2 and L-l = 3 mm.
14. 14. A cooking apparatus comprising: a substantially sealable, box-shaped cooking chamber for storing food to be cooked; a radio-frequency heater including a magnetron to generate microwaves for radio-frequency heating of the food and a waveguide to guide the microwaves into the cooking chamber; and an induction heater including an induction heating coil to generate an alternating magnetic flux for induction heating of a container containing the food, wherein the induction heating coil is disposed below a bottom surface portion of the cooking chamber, the bottom surface portion includes a bottom plate which prevents penetration of the microwaves and a portion for transmitting magnetic flux which allows magnetic flux generated by the induction heating coil to penetrate therethrough and prevents penetration of the microwaves, the bottom plate having thereon the portion for transmitting magnetic flux, a mounting table made of a heat-resistant, low-loss dielectric material is disposed above the bottom surface portion, and provided that a distance from an upper side of the mounting table to the portion for transmitting magnetic flux in a thickness direction is 1, and a distance from the upper side of the mounting table to an upper surface of the induction heating coil in the thickness direction is L, 1 and L are set to satisfy inequalities of! = L/2 and L-1 = 3 mm.
15. 15. The cooking apparatus according to claim 13 or 14, wherein: the induction heating coil is housed in a flat box-shaped case made of a resin, one side of the case opening on a side facing a wall surface of the cooking chamber; a metal layer is formed on an outer surface of the case and a circumferential edge of the opening; and the case is disposed in such a manner that the circumferential edge makes contact with an outside of the metallic wall surface of the cooking chamber.
16. 16. The cooking apparatus according to claim 13 or 14, further comprising: a temperature detector to detect a temperature of the portion for transmitting magnetic flux; and a controller to control electric power to be supplied to the induction heating coil based on the temperature detected by the temperature detector.