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(11) | EP 2 741 575 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
| published in accordance with Art. 153(4) EPC |
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| (54) | MICROWAVE HEATING DEVICE |
| (57) In a microwave heating device according to the present invention, a feeding portion
(22) for radiating microwaves includes a vertical shaft element (22b) provided in
the vertical direction by penetrating through a coupling hole (25) formed in portions
at which a feeding chamber (24) and a waveguide (21) are bonded to each other, and
a flat-plate element (22a) having a radiation surface for radiating microwaves within
the heating chamber, wherein the flat-plate element (22a) is bonded to the vertical
shaft element. At least a partial radiation surface, out of the microwave radiation
surface of the flat-plate element, is placed to be inclined at a predetermined angle
θ with respect to a horizontal direction. |
Technical Field
[0001] The present invention relates to microwave heating devices for inductively heating objects to be heated through radiation of microwaves, and more particularly, relates to heating cookers for cooking food as objects to be heated through induction heating.
Background Art
[0002] Among microwave heating devices, heating cookers using microwaves, which are represented by microwave ovens, have basic structures including a heating chamber sealed in such a way as to prevent leakages of microwaves to the outside, a magnetron for generating microwaves, and a waveguide for propagating microwaves generated from the magnetron to the heating chamber.
[0003] Such heating cookers have employed various structures according to the system suitable for the aim, as components other than the heating chamber, the magnetron and the waveguide. For example, there have been lateral feeding systems, downward feeding systems, upward feeding systems and upward-and-downward feeding systems, depending on the direction in which microwaves should be incident to the heating chamber. According to these respective feeding systems, there have been provided different structures.
[0004] In cases of lateral feeding systems adapted to cause microwaves to be incident to a side surface of a heating chamber, there is a need for rotating food itself as an object to be heated within the heating chamber in order to prevent ununiformity of the microwave distribution. Such lateral feeding systems have employed so-called turn table systems. On the other hand, in cases of downward feeding systems adapted to cause microwaves to be incident to the bottom surface of the heating chamber, upward feeding systems adapted to cause microwaves to be incident to the ceiling wall surface of the heating chamber, and upward-and-downward feeding systems adapted to cause microwaves to be incident to both the bottom surface and the ceiling wall surface of the heating chamber, and the like, an antenna as a feeding portion provided in the portion which couples the waveguide and the heating chamber is rotated to stir and radiate microwaves, without moving food as an object to be heated. So-called rotational antenna systems for rotating an antenna as described above have been employed with downward feeding systems, upward feeding systems and upward-and-downward feeding systems.
[0005] Which feeding system should be employed in a microwave oven is determined in consideration of not only functions of the microwave oven but also other functions, such as oven functions, grill functions, steam functions and the like. In cases of employing functions of a microwave oven in combination with other functions, it is necessary to provide heaters, a water tank, a steam generating mechanism and the like, for example, in addition to a microwave feeding structure. Therefore, each of the components should be efficiently placed within the apparatus (refer to Patent Literature 1, for example).
[0006] Further, in cases of employing, for example, an oven, a grill and a superheated steam, which is water vapor at a temperature higher than 100°C, in a heating cooker, a plate made of a conductor having higher heat resistance may be used, as the material of the plate for placing food as objects to be heated thereon, since the inside of the heating chamber can be raised to higher temperatures. In cases of employing such a plate made of a conductor, the plate made of the conductor reflects microwaves, which changes the microwave distribution within the heating chamber from those in cases of employing plates made of dielectric members such as glasses, ceramics and the like which pass microwaves therethrough.
[0007] Also, instead of plates made of conductors, grids made of conductors may be employed. In cases of employing a grid made of a conductor, when its meshes have a size larger to some extent than the wavelength, microwaves may pass therethrough. Therefore, the microwave distribution within the heating chamber may be also changed depending on the shape of the meshes.
[0008] Further, recently, there have been increasingly needs for cooking using functions of a microwave oven in combination with other functions. For example, in cases of roasting larger food or in cases of roasting frozen food, and the like, the food can be heated only on its surface by using heaters, and thus, the food may not be cooked in its interior. Toaster ovens including only heaters as heating sources correspond to such cookers using only heaters. In order to heat food in its interior only with heaters, using the toaster oven, it is possible to employ only a method which includes a step of gradually heating the food through heat conduction for a long time period at a lower temperature, with reduced heating power (output), in order to prevent the food surfaces from being scorched.
[0009] On the other hand, by heating an object to be heated using a microwave oven for induction heating, it is possible to heat the food in its interior, since the food as the object to be heated is a dielectric member, and thus, microwaves can penetrate up to the interior of the food. By employing a microwave oven as described above, it is possible to cook food in its interior in a shorter time period. Accordingly, by employing functions of a microwave oven for heating the interior of food in combination with functions of heaters for roasting the surfaces of food, it is possible to deliciously roast larger food and frozen food in shorter time periods.
Citation List
Patent Literature
Summary of Invention
Technical Problem
[0011] However, in cases of performing high-frequency heating using microwaves in conventional heating devices, when microwaves are not efficiently absorbed by food as objects to be heated, microwaves reflected within the heating chamber are returned to the magnetron through the waveguide from the feeding portion, thereby inducing the problem of self-heat generation in the magnetron.
[0012] Further, in cases of performing heater heating using convection heat through hot air flows or using radiant heat for burning the surface of food, at the same time as high-frequency heating with microwaves, in conventional heating cookers, the magnetron, which is the microwave supply source, is influenced by the heating chamber being heated at higher temperatures, thereby inducing the problem of temperature rises therein during running and operations. In such cases, if the heating cookers are not structured in such a way as to inhibit reflected waves having been reflected by the food without having been absorbed by the food, out of microwaves radiated within the heating chamber, from returning to the feeding chamber, this induces the problem of more significant temperature rises in the magnetron due to self-heat generation in the magnetron, as described above.
[0013] Particularly, heating cookers adapted to be built in kitchens as equipment appliances have been made to have a largest possible heating chamber, and also, have been provided with a manipulation panel above the heating chamber, in order to enable users to easily manipulate the heating cookers. Therefore, there has been a need for compactly and collectively mounting the microwave feeding structure and other structures (for example, a heater driving circuit and a cooling structure), similarly, above the heating chamber. In the structure, since the microwave feeding structure is placed above the heating chamber, which is to be raised to higher temperatures, the magnetron is prone to receive heat from the heating chamber. Particularly, in cases where the magnetron itself is in contact with the wall surface of the heating chamber or in cases where the waveguide bonded to the magnetron is in contact with the outer wall surface of the heating chamber ceiling, and also, is extended along this outer wall surface, the waveguide is significantly influenced by heat from the heating chamber. Accordingly, in cases of employing both the microwave feeding structure and the heater electric power supply structure in such a way as to run them at the same time, there has been the problem of difficulty in attaining both prevention of temperature rises in the magnetron and size reduction of the apparatus.
[0014] Fig. 10 is a front cross-sectional view schematically illustrating the structure of a heating cooker having an ordinary microwave feeding structure provided above a heating chamber, wherein a heater electric power supply structure having heaters is further provided. The conventional heating cooker illustrated in Fig. 10 is provided with the heating chamber 101 for performing induction heating on food 107 as an object to be heated, within a casing 100 which forms the external appearance of the heating cooker. The heaters 102 are provided at upper and lower positions within the heating chamber 101. Further, above the upper heater 102 and also above the heating chamber 101, there is placed the microwave feeding structure constituted by a magnetron 103, a waveguide 104, a rotational antenna 105 and a motor 106 and the like. The conventional heating cooker having this structure is adapted to direct microwaves radiated from the rotational antenna 105 as a feeding portion, to the food 107 as the object to be heated. About 64% of the microwaves directed to the food 107 are reflected by the boundary surface between the food 107 and air, due to the permittivity difference between air and the food 107, based on the conversion of microwaves into electric power. The microwaves reflected thereby are directed toward the rotational antenna 105 vertically above the food 107 and thus, are received by the rotational antenna 105 having strong directivity in the vertical direction. As a result thereof, the reflected microwaves received by the rotational antenna 105 are returned to the magnetron 103 through the waveguide 104, thereby causing self-heat generation in the magnetron 103. When the food 107 has a smaller size, a larger amount of microwaves, out of the microwaves radiated from the rotational antenna 105, reach the bottom surface of the heating chamber 101 beyond the food 107. Accordingly, almost all the microwaves having reached the bottom surface of the heating chamber 101 are reflected toward the ceiling wall surface of the heating chamber 101, and these reflected waves are received by the rotational antenna 105 provided on the ceiling wall surface. The reflected waves having been received by the rotational antenna 105 are transmitted to the magnetron 103 through the waveguide 104, thereby causing self-heat generation in the magnetron 103.
[0015] Further, conventional heating cookers having structures as described above have been structured such that heat generated in the heating chamber 101 is conducted to the magnetron 103 by being conducted through the waveguide 104, so that the magnetron 103 is prone to be heated thereby. As a result thereof, such conventional heating cookers have been structured such that the magnetron 103 is prone to receive heat from the heating chamber 101, in addition to heat generated from the magnetron 103 itself during running, thereby inducing the problem of temperature rises in the magnetron 103. Accordingly, such conventional heating cookers have had the problem of failures of the magnetron 103 and reduction of the life of the magnetron 103. Further, such conventional heating cookers have had the problem of the necessity of setting the output to be lower, in order to overcome the problems.
[0016] Further, conventional heating cookers have had the problem of degradation of the microwave heating efficiency, due to temperature rises in the magnetron 103. Further, in such conventional heating cookers, the microwave feeding structure is placed in the space above the heating chamber 101, and, also the magnetron is vertically connected to the upper side of the heating chamber 101 as illustrated in Fig. 10, the magnetron 103 has been further prone to be heated by ascending air at higher temperatures, and also, there has been a need for a space with a significant height above the heating chamber 101. This has resulted in the problem that the casing 100 should have a larger size.
[0017] It is an object of the present invention to attain compaction of a microwave feeding structure placed above a heating chamber to provide a small-sized microwave heating device and also to suppress temperature rises in a magnetron due to its self-heat generation with a feeding structure less prone to receive reflected waves for elongating the life of the magnetron, thereby providing a microwave heating device which has higher reliability and improved heating efficiency while being capable of preventing degradation of the output.
Solution to Problem
[0018] A microwave heating device according to the present invention comprises:
a heating chamber which is adapted to house an object to be heated and to direct microwaves to the object to be heated for performing high-frequency heating;
a microwave feeding chamber formed to protrude upwardly from a ceiling wall surface of the heating chamber;
a microwave generating portion adapted to create microwaves for performing high-frequency heating on the object to be heated, within the heating chamber;
a waveguide adapted to couple the feeding chamber to the microwave generating portion for propagating microwaves; and
a feeding portion including a vertical shaft element provided in a vertical direction by penetrating through a coupling hole formed in portions at which the feeding chamber and the waveguide are bonded to each other, and a flat-plate element having a radiation surface for radiating microwaves within the heating chamber, the flat-plate element being bonded to the vertical shaft element,
wherein at least a partial radiation surface, out of the microwave radiation surface of the flat-plate element, is placed to be inclined at a predetermined angle θ with respect to a horizontal direction.
[0019] In the microwave heating device according to the present invention, the flat-plate element in the feeding portion is placed in such a way as to radiate microwaves downwardly at the predetermined angle θ through the coupling hole in the feeding chamber provided in the ceiling wall surface of the heating chamber. Therefore, even when the radiated microwaves are partially reflected by the boundary surface of the object to be heated, the reflected waves are reflected in directions deviated from the feeding portion, by an angle corresponding to θ with respect to the vertical direction. This largely inhibits waves reflected by the object to be heated and the like from being received by the feeding portion, which largely reduces the reflected-wave components which are returned to the microwave generating portion through the waveguide.
Advantageous Effects of Invention
[0020] According to the present invention, it is possible to provide a microwave heating device with higher reliability and with improved output efficiency which is capable of preventing temperature rises in the microwave generating portion for elongating the life of the microwave generating portion, without reducing the output.
Brief Description of Drawings
[0021]
Fig. 1 is a front cross-sectional view illustrating the internal structure of a main part of a heating cooker according to a first embodiment of the present invention.
Fig. 2 is a perspective view illustrating a waveguide and a feeding chamber, in the heating cooker according to the first embodiment of the present invention.
Fig. 3 is a main-part cross-sectional view illustrating the feeding portion and an object to be heated, in the heating cooker according to the first embodiment of the present invention.
Fig. 4 is a front cross-sectional view illustrating the internal structure of a main part of a heating cooker according to a second embodiment of the present invention.
Fig. 5 is a side cross-sectional view of the main part of the heating cooker according to the second embodiment of the present invention.
Fig. 6 is a perspective view illustrating a waveguide and a feeding chamber, in the heating cooker according to the second embodiment of the present invention.
Fig. 7 is a rear view illustrating a feeding portion, a heating portion and the like, which are provided on a ceiling wall surface in the heating cooker according to the second embodiment of the present invention.
Fig. 8 is a main-part cross-sectional view illustrating a feeding portion and an object to be heated, in the heating cooker according to a third embodiment of the present invention.
Fig. 9 is a main-part cross-sectional view illustrating a feeding portion having another structure, and an object to be heated, in the heating cooker according to the third embodiment of the present invention.
Fig. 10 is the front cross-sectional view illustrating an ordinary microwave feeding structure in a conventional heating cooker.
Description of Embodiments
[0022] A microwave heating device according to a first aspect of the present invention comprises:
a heating chamber which is adapted to house an object to be heated and to direct microwaves to the object to be heated for performing high-frequency heating;
a microwave feeding chamber formed to protrude upwardly from a ceiling wall surface of the heating chamber;
a microwave generating portion adapted to create microwaves for performing high-frequency heating on the object to be heated, within the heating chamber;
a waveguide adapted to couple the feeding chamber to the microwave generating portion for propagating microwaves; and
a feeding portion including a vertical shaft element provided in a vertical direction by penetrating through a coupling hole formed in portions at which the feeding chamber and the waveguide are bonded to each other, and a flat-plate element having a radiation surface for radiating microwaves within the heating chamber, the flat-plate element being bonded to the vertical shaft element,
wherein at least a partial radiation surface, out of the microwave radiation surface of the flat-plate element, is placed to be inclined at a predetermined angle θ with respect to a horizontal direction.
[0023] In the microwave heating device having the structure in the first aspect, the coupling hole for supplying microwaves is provided in portions at which the waveguide and the feeding chamber in the ceiling wall surface of the heating chamber are bonded to each other, and the flat-plate element in the feeding portion is placed in such a way as to radiate microwaves downwardly at the predetermined angle θ through the coupling hole. Therefore, even when microwaves radiated from the feeding portion are partially reflected by the boundary surface of the object to be heated, the reflected waves are reflected in directions deviated from the feeding portion by an angle corresponding to e with respect to the vertical direction. This inhibits the reflected waves from being received by the feeding portion, which reduces the reflected-wave components which are returned to the microwave generating portion through the waveguide. As a result thereof, with the microwave heating device in the first aspect, it is possible to prevent temperature rises in the microwave generating portion due to its self-heat generation. Further, in the microwave heating device in the first aspect, the waveguide is bonded to the heating chamber through the feeding chamber, and the waveguide is placed to be spaced apart from the heating chamber. Therefore, even when the heating chamber is at higher temperatures inside thereof, the microwave generating portion is less prone to receive heat from the ceiling wall surface of the heating chamber, thereby largely reducing heat conduced to the microwave generating portion through the waveguide from the heating chamber. Therefore, the microwave heating device in the first aspect is adapted to certainly prevent temperature rises in the microwave generating portion. With the microwave heating device in the first aspect, it is possible to suppress temperature rises in the microwave generating portion, which enables elongation of the life of the microwave generating portion, further enables maintaining higher outputs of the microwave generating portion without reducing the output of the microwave generating portion and, also, realizes higher reliability and improvement of the output efficiency, even with the compact structure having the microwave generating portion provided above the heating chamber.
[0024] A microwave heating device according to a second aspect of the present invention is configured that at least a partial radiation surface, out of the microwave radiation surface of the flat-plate element of the first aspect in particular, is folded at the predetermined angle θ with respect to the horizontal direction, and the radiation surface folded at the predetermined angle θ is made to have an area which occupies 1/2 or more of the entire radiation surface of the flat-plate element.
[0025] In the microwave heating device having this structure in the second aspect, microwaves radiated from the feeding portion have strong radiation directivity in the direction normal to the radiation surface of the flat-plate element, and the radiation surface folded to be set at the angle θ is made to occupy 1/2 or more of the entire radiation surface. Therefore, in the microwave heating device having this structure in the second aspect, a significant part of microwaves radiated from the feeding portion are radiated obliquely at the angle θ with respect to the vertical direction. The microwaves radiated obliquely from the radiation surface of the flat-plate element are reflected by the object to be heated, and the like, in directions deviated from the feeding portion, by an amount corresponding to the obliqueness. Therefore, the microwave heating device having this structure in the second aspect is adapted to inhibit reflected waves from being received by the feeding portion, which reduces the reflected-wave components which are returned to the microwave generating portion through the waveguide, thereby preventing temperature rises in the microwave generating portion due to its self-heat generation. As a result thereof, with the microwave heating device in the second aspect, it is possible to elongate the life of the microwave generating portion and, further, it is possible to eliminate the necessity of power down settings for the microwave generating portion, thereby improving the output efficiency.
[0026] A microwave heating device according to a third aspect of the present invention, particularly in the heating chamber of the first or second aspect, further comprises a high-temperature heating portion adapted to perform heating on the object to be heated, through at least one of radiant heat and convection heat, at the same time as high-frequency heating, the microwave generating portion and the waveguide being placed above the heating chamber,
wherein the waveguide includes a propagation path bent orthogonally to have a horizontal portion and a vertical portion, the microwave generating portion is horizontally connected to the vertical portion, the feeding chamber provided in the ceiling wall surface of the heating chamber is coupled to the horizontal portion through a coupling hole, and the waveguide and the microwave generating portion are both placed to be spaced apart from the heating chamber.
[0027] In the microwave heating device having this structure in the third aspect, even when the object to be heated is placed on a material having a radio-wave intercepting effect, such as a metal tray, in such a way as to utilize both high-frequency heating and another heating at the same time, it is possible to supply microwaves downwardly from the feeding chamber provided in the ceiling wall surface of the heating chamber. Therefore, the microwave heating device in the third aspect is enabled to certainly perform microwave heating on the object to be heated, without intercepting the microwaves. Further, the microwave heating device in the third aspect is adapted to radiate microwaves obliquely with respect to the vertical direction from the radiation surface of the flat-plate element in the feeding portion, it is possible to reduce the reflected wave components returned to the microwave generating portion, thereby preventing temperature rises due to its self-heat generation. Further, since the feeding chamber is provided in the ceiling wall surface of the heating chamber, the waveguide bent orthogonally is connected to the feeding chamber, and the waveguide and the microwave generating portion are both placed to be spaced apart from the ceiling wall surface of the heating chamber, the microwave heating device in the third aspect is adapted to inhibit the microwave generating portion from receiving heat from the ceiling wall surface of the heating chamber being heated at higher temperatures, and also, is adapted to reduce heat conduced to the microwave generating portion through the waveguide from the heating chamber. Therefore, with the microwave heating device in the third aspect, it is possible to certainly prevent temperature rises in the microwave generating portion. Therefore, the microwave heating device in the third aspect is adapted to reduce heat conduction from the heating chamber to the microwave generating portion, thereby enabling elongation of the life of the microwave generating portion, elimination of the necessity of power down settings for the microwave generating portion and improvement of the output efficiency, even with the compact structure having the microwave generating portion provided above the heating chamber. Further, in the microwave heating device in the third aspect, the microwave generating portion, which is constituted by a magnetron, for example, is horizontally connected to the vertical propagation path in the waveguide, which allows the entire apparatus to have a compact size in the heightwise direction.
[0028] In a microwave heating device according to a fourth aspect of the present invention, particularly, assuming that Ly is a total length of the radiation surface inclined at the predetermined angle θ with respect to a horizontal plane, in the direction of the inclination, out of the entire radiation surface of the flat-plate element in any one of the first to third aspect, and H is a height from the object to be heated within the heating chamber to a position in the radiation surface of the flat-plate element which is coincident with the position where the flat-plate element is bonded to the vertical shaft element, the inclination angle θrad of the inclined radiation surface is set to be an angle which is larger than Ly/2/H but is smaller than Ly/H.
[0029] In the microwave heating device having this structure in the fourth aspect, since the inclination angle θrad of the inclined radiation surface of the flat-plate element is larger than Ly/2/H, i.e., (ly/2/H<θ), the angle setting is made such that, even when microwaves having strong radiation directivity in the normal direction which are radiated from the radiation surface of the flat-plate element are reflected by the object to be heated or the wall surfaces near the bottom portion of the heating chamber, these microwaves are not returned to the feeding portion. Further, since the inclination angle θrad of the inclined radiation surface of the flat-plate element is smaller than Ly/H, i.e., (θ<ly/H), it is possible to prevent the inclination angle from being excessively larger, thereby preventing the formation of areas which can not be irradiated with microwaves in the vicinity of the center of the bottom surface of the heating chamber, which is beneath the vertical shaft element. This can set the radiation surface to be at a preferable radiation angle which can prevent the object to be heated from being heated in a donut shape (a ring shape), due to insufficient heating at the center portion of the object to be heated. Therefore, the microwave heating device in the fourth aspect is enabled to attain both realization of microwave heating without heating unevenness, and prevention of temperature rises in the microwave generating portion due to its self-heat generation, through reduction of reflected wave components returned to the microwave generating portion.
[0030] In a microwave heating device according to a fifth aspect of the present invention, particularly, the flat-plate element in any one of the first to fourth aspect is formed from a flat plate with a substantially circular shape with a diameter of about 62 mm.
[0031] The microwave heating device having this structure in the fifth aspect is adapted to realize the flat-plate element adaptable to the wavelengths to be used for microwave heating with microwave ovens and the like, which enables the flat-plate element to certainly resonate at the wavelengths of microwaves. In the microwave heating device in the fifth aspect, the radiation surface of the flat-plate element is adapted to generate a unidirectional radiation pattern with a beam center axis in the direction normal to the radiation surface, and therefore, microwaves from the radiation surface of the flat-plate element are radiated obliquely at an angle θ with respect to the vertical direction. As a result thereof, reflected waves propagate in directions deviated from the feeding portion by an amount corresponding to the angle θ of the obliqueness, and the microwave heating device in the fifth aspect is adapted to inhibit the reflected waves from being received by the feeding portion, thereby preventing temperature rises in the microwave generating portion due to its self-heat generation.
[0032] In a microwave heating device according to sixth aspect of the present invention, particularly, the feeding portion of the fifth aspect is adapted such that the vertical shaft element is bonded to the flat-plate element at a position deviated from a center of the disk plate, and the vertical shaft element is rotated.
[0033] The microwave heating device having this structure in the sixth aspect is enabled to stir and radiate microwaves uniformly within the heating chamber from the radiation surface of the flat-plate element.
[0034] In a microwave heating device according to seventh aspect of the present invention, particularly, the flat-plate element of the fifth or sixth aspect is formed by folding one radiation surface with respect to the other radiation surface, by the predetermined angle θ, at a folding line on a straight line including a center line of the disk plate.
[0035] The microwave heating device having this structure in the seventh aspect is enabled to radiate a larger amount of microwaves, within the heating chamber, obliquely at an angle θ with respect to the vertical direction, from the radiation surface of the flat-plate element
[0036] Hereinafter, with reference to the accompanying drawings, there will be described preferred embodiments of a microwave heating device according to the present invention. Further, in the following embodiments, the microwave heating device will be described with respect to a heating cooker. However, the heating cooker is merely illustrative, and the microwave heating device according to the present invention is not limited to heating cookers and is intended to include heating devices utilizing induction heating as high-frequency heating, and heating devices such as drying apparatuses, ceramic-art heating devices, garbage disposers, semiconductor fabrication apparatuses, and the like. Accordingly, the present invention is not limited to the concrete structures in the following embodiments and is intended to include structures based on equivalent technical concepts.
(First Embodiment)
[0037] In a first embodiment of the present invention, a heating cooker as a microwave heating device will be described. Further, hereinafter, each of embodiments will be described by exemplifying a microwave oven including at least a single heater as heating means in the heating cooker.
[0038] Fig. 1 is a front cross-sectional view illustrating the internal structure of a main part of the heating cooker as the microwave heating device according to the first embodiment of the present invention. The heating cooker illustrated in Fig. 1 is provided with a heating chamber 11 for performing induction heating (higher-frequency heating) on food 15 as an object to be heated, within a cabinet 10 which forms the external appearance of the heating cooker. Namely, the food 15 as an object to be heated is housed in the heating chamber 11, and microwaves are radiated toward this food 15, thereby performing high-frequency heating thereon. Inside the heating chamber 11 which is formed from steel plates having enamel-coated surfaces, there are provided two heaters, which are an upper heater 12 and a lower heater 13, as a radiative heating portion which forms a high-temperature heating portion for raising the inside of the heating chamber to higher temperatures. The upper heater 12, which is one of the heaters, is placed near the ceiling wall surface of the heating chamber 11 (in the upper side), while the lower heater 13, which is the other heater, is placed near the bottom surface wall of the heating chamber 11 (in the lower side). Inside the heating chamber 11, there is detacheably provided a roasting grid 14 formed from stainless-steel rod members which are longitudinally and laterally coupled and welded to one another. The roasting grid 14 can be mounted at desired positions in a plurality of stages in the heating chamber 11. The food 15 as the object to be heated, which is placed on the roasting grid 14, is sandwiched between the upper heater 12 and the lower heater 13 and is radiatively heated thereby in upper and lower directions. The corners of the bonding portions between the respective wall surfaces forming the heating chamber 11 are formed to have curved surfaces. Further, the bottom surface wall of the heating chamber 11 is formed to have a curved-surface shape having a larger radius of curvature, in its entirety.
[0039] Further, the heating cooker according to the first embodiment will be described with respect to an example where the wall surfaces of the heating chamber 11 are formed from enamel-coated steel plates, but they can be also formed from steel plates provided with other thermal-resistant coating. Also, the material of the wall surfaces can be PCM (Pre-coated metal) steel plates. While, in the first embodiment, the roasting grid 14 is formed from stainless-steel rod members coupled to one another, the roasting grid 14 can be also formed from plated steel members and the like.
[0040] As illustrated in Fig. 1, a feeding chamber 24 is provided near the center of the ceiling wall surface of the heating chamber 11. Inside the feeding chamber 24, there is placed a feeding portion 22 which forms a rotational antenna, as a radio-wave stirring portion. The wall surface of the feeding chamber 24 is made of a material which reflects microwaves radiated from the feeding portion 22, and further, has a shielding structure for preventing microwaves from being leaked to the outside of the feeding chamber 24. The feeding portion 22 forming the rotational antenna is provided such that the feeding portion 22 protrudes through a feeding port 25 which is formed, as a coupling hole, in a waveguide 21. The waveguide 21 is adapted to propagate, to the feeding portion 22, microwaves from a magnetron 16 as a microwave creating portion. The magnetron 16 creates microwaves for performing high-frequency heating on the food 15 as the object to be heated, within the heating chamber 11. The microwaves propagated to the feeding portion 22 are radiated within the heating chamber 11. The magnetron 16 is placed on the right end portion (see Fig. 1) of the waveguide 21 placed on the upper side of the heating chamber 11, and a magnetron output portion 44, which forms an oscillation antenna of the magnetron 16, is inserted, in a lateral orientation (horizontal direction), into the waveguide 21.
[0041] The heating cooker having the structure according to the first embodiment has an induction heating portion which utilizes microwaves as a single heating means, and further, has a radiative heating portion as a high-temperature heating portion which utilizes radiation through the upper heater 12 and the lower heater 13, as another heating means. Thus, the heating cooker according to the first embodiment utilizes both the induction heating portion and the radiative heating portion, and therefore, is enabled to perform desired heating cooking to the food 15 as the object to be heated, within the heating chamber 11.
[0042] Further, although the heating cooker according to the first embodiment will be described as being structured to have the induction heating portion which utilizes microwaves as a single heating means, and the radiative heating portion which utilizes the upper heater 12 and the lower heater 13 as the other heating means, the heating cooker can be also provided with a convection heating portion adapted to circulate hot air flows within the heating chamber for performing heating cooking, instead of a high-temperature heating portion such as a radiative heating portion. Such a convection heating portion is structured to heat air within the heating chamber to a higher temperature and to circulate it, with a circulation fan and a circulation heater which are provided near the back surface of the heating chamber. As a matter of course, the heating cooker can be also provided with three heating portions, which are an induction heating portion, a radiative heating portion and a convection heating portion, for performing heating cooking.
[0043] In the heating cooker according to the first embodiment, the upper heater 12 and the lower heater 13 which form the radiative heating portion are constituted by electrical heating wires and a filler material which are enclosed in a metal pipe. Within the heating chamber 11, an upper-heater thermocouple 17 is provided in contact with the surface of the upper heater 12. The upper-heater thermocouple 17 is covered with a metal pipe, in order to prevent it from being influenced by microwaves radiated from the feeding portion 22, and further, the upper-heater thermocouple 17 functions as means for detecting the temperature of the upper heater 12. Further, within the heating chamber 11, a lower-heater thermocouple 18 is provided in contact with the surface of the lower heater 13, wherein the lower-heating thermocouple 18 has the same structure as that of the upper-heater thermocouple 17. The lower-heater thermocouple 18 functions as means for detecting the temperature of the lower heater 13. A thermistor 19 is fixed to a wall surface of the heating chamber 11, as means for detecting the temperature within the heating chamber. The upper-heater thermocouple 17, the lower-heater thermocouple 18 and the thermistor 19 are electrically connected to a control portion 20 as control means. The control portion 20 is adapted to control the amounts of electricity supplied to the upper heater 12 and the lower heater 13, based on respective detection signals from the upper-heater thermocouple 17, the lower-heater thermocouple 18 and the thermistor 19. As described above, in the heating cooker according to the first embodiment, the amount of heating for the heating chamber 11 is accurately controlled to be increased and decreased, in such a way as to realize a set temperature.
[0044] Within the heating chamber 11, the upper heater 12 in the radiative heating portion, which is adapted to heat the food 15 as the object to be heated, through radiant heat from thereabove, is placed in an area which is not beneath the feeding chamber 24. Namely, the food 15 as the object to be heated is directly irradiated with microwaves radiated from the feeding portion 22 as the rotational antenna within the feeding chamber 24, while the upper heater 12 is not directly irradiated therewith.
[0045] The waveguide 21 provided on the upper side of the heating chamber 11 is constituted by a horizontal portion 42 extended in the horizontal direction, and a vertical portion 43 extended in the vertical direction. Namely, the waveguide 21 includes an internal passage (propagation path) having an orthogonally-folded L-shape which is constituted by a horizontal propagation path (42) formed by the horizontal portion 42, and a vertical propagation path (43) formed by the vertical portion 43. The magnetron 16 which forms the microwave generating portion is connected to the vertical portion 43 of the waveguide 21 such that its magnetron output portion 44 as an oscillation antenna is horizontally introduced and inserted therein. Accordingly, the magnetron 16 is coupled in a lateral orientation (coupled horizontally) to the waveguide 21, so that its heightwise size in the vertical direction is smaller than that in the case where the magnetron 16 is coupled longitudinally (coupled vertically, see Fig. 10) to the waveguide 21.
[0046] In the feeding port 25 formed in the horizontal portion 42 (the horizontal propagation path) in the waveguide 21 having the L-shaped internal passage (the propagation path) as described above, the feeding portion 22 as the rotational antenna is provided. The feeding portion 22 is constituted by a flat-plate element 22a and a vertical shaft element 22b. The vertical shaft element 22b in the feeding portion 22 is connected to a motor 23. By driving the motor 23, the vertical shaft element 22b is rotated, thereby rotating the flat-plate element 22a. The feeding portion 22 is coupled to the horizontal propagation path (42) of the waveguide 21, so that microwaves having propagated through the waveguide 21 are radiated and stirred within the heating chamber 11, through the flat-plate element 22a of the feeding portion 22.
[0047] Substantially at the center of the ceiling wall surface of the heating chamber 11, there is provided the dome-shaped antenna room 24 which houses the flat-plate element 22a adapted to rotate. The feeding chamber 24 is shaped to extend in a circular shape at its lower end portion and thus has a circular truncated cone shape. The feeding chamber 24 is formed to have such a circular truncated cone shape, by outwardly protruding the ceiling wall surface of the heating chamber 11 through drawing processing. The feeding port 25 formed in the lower surface of the horizontal portion 42 of the waveguide 21 is connected to an opening formed in the upper end portion of the feeding chamber 24 and is caused to function as a coupling hole integrally therewith, which secures a feeding port with a predetermined diameter, around the portions of the waveguide 21 and the feeding portion 22 which are coupled to each other. As described above, the feeding chamber 24 is provided in the ceiling wall surface of the heating chamber 11, and further, is structured to reflect microwaves radiated laterally (substantially horizontally) from the flat-plate element 22a. The flat-plate element 22a is adapted to resonate at the wavelength of microwaves being used, and further, to generate an unidirectional radiation pattern having a beam center axis in the direction normal to the radiation surface of the flat-plate element 22a. If even a small amount of microwaves are radiated in the horizontal direction from the flat-plate element 22a, the feeding chamber 24 reflects them at its wail surface. Further, the feeding chamber 24 is opened in its lower end portion, such that microwaves from the flat-plate element 22a are radiated to the inside of the heating chamber 11.
[0048] As illustrated in Fig. 1, a cover 27 is provided on the ceiling wall surface of the heating chamber 11, over the opening portion at the lower end of the feeding chamber 24. The cover 27, which is made of mica, is provided, in order to prevent contaminations and the like which have scattered from the food within the heating chamber 11 from being adhered to the flat-plate element 22a of the feeding portion 22, and the like. The cover 27 is detacheably mounted on an insulation hook 26 provided on the ceiling wall surface of the heating chamber 11. Further, although there has been described an example where the cover 27 is made of mica, which is a low dielectric-loss material, the material thereof is not limited to mica, and it is also possible to employ ceramics, glasses or other materials, which can offer the same effects.
[0049] The upper heater 12 provided at an upper portion within the heating chamber 11 is placed so as not to be beneath the opening portion at the lower end of the feeding chamber 24, in order that the upper heater 12 is not directly heated by microwaves from the feeding portion 22. Thus, the upper heater 12 is placed in such a way as to evade the opening portion in the feeding chamber 24, thereby forming a vacant portion 28 at the center portion of the upper heater 12. Accordingly, microwaves M (see Fig. 1) radiated directly toward the food 15 from the feeding portion 22 are not obstructed by the upper heater 12. As described above, the heating cooker according to the first embodiment is adapted to prevent the upper heater 12 from being directly heated by microwaves M radiated from the feeding portion 22, which prevents occurrences of losses, thereby improving the heating efficiency.
[0050] Fig. 2 is a perspective view illustrating the waveguide 21 and the feeding chamber 24 in the heating cooker according to the first embodiment. As illustrated in Fig. 2, the waveguide 21 includes the horizontal portion 42 forming the horizontal propagation path, and the vertical portion 43 forming the vertical propagation path, wherein the internal passage forming the propagation path has a folded shape which is folded orthogonally in an L shape. Namely, the direction in which the horizontal propagation path (42) extends (the horizontal direction) is orthogonal to the direction in which the vertical propagation path (43) extends (the vertical direction). As described above, the waveguide 21 includes the horizontal propagation path (42) and the vertical propagation path (43) which are orthogonal to each other, wherein the magnetron 16 as the microwave creating portion is horizontally coupled to the vertical propagation path (43), so that microwaves from the magnetron 16 are propagated to the horizontal propagation path (42).
[0051] In the first embodiment, assuming that the horizontal propagation distance to the center of the feeding port 25 from the folding position C (see Fig. 2) at the portion at which the horizontal portion 42 and the vertical portion 43 are coupled to each other is Lh (see Fig. 2), the distance Lh is set to be about 135 mm in the first embodiment. Further, the horizontal propagation distance Lh refers to the horizontal distance from the folding position C to the center of the feeding port 25 in the propagation path in the waveguide 21, along the direction in which the horizontal propagation path extends (the rightward and leftward direction in Fig. 1).
[0052] The width a of the internal passage, which is the propagation path in the waveguide 21, is about 80 mm, and the height b of the internal passage in the horizontal portion 42 in the waveguide 21 is about 16 mm. The width "a" of the internal passage and the height "b" of the internal passage in the horizontal portion 42 indicate the sizes of the propagation path in the inner-surface side of the waveguide 21.
[0053] As described above, the magnetron 16 is secured to the vertical portion 43 of the waveguide 21, by being horizontally coupled thereto in a lateral orientation. Namely, the magnetron output portion 44 as the oscillation antenna in the magnetron 16 is inserted and mounted, in a lateral orientation, in an opening portion 29 formed in the side surface wall (the right side surface wall) of the vertical portion 43 in the waveguide 21. Assuming that the vertical propagation distance (the length in the vertical direction) from the folding position C to the center of the magnetron output portion 44 in the magnetron 16 is Lv (see Fig. 2), the vertical propagation distance Lv is set to be about 15 mm in the first embodiment.
[0054] The heating cooker according to the first embodiment employs, as the magnetron 16, one having an oscillation frequency of about 2450 MHz. Therefore, assuming that the in-tube wavelength within the waveguide 21 is λg in the case where the waveguide 21 is adapted such that the width "a" of the internal passage is about 80 mm, λg is about 190 mm, and the length of half the wavelength (λg/2) is about 95 mm (λg/2 = 95 mm). Accordingly, in the heating cooker according to the first embodiment, the waveguide 21 is structured such that the horizontal propagation distance Lh (about 135 mm), which is substantially the length of the propagation path in the horizontal portion 42, is larger than half the wavelength (λg/2 = 95 mm), i.e., (Lh > λg/2). Further, the vertical propagation distance Lv (about 15 mm), which is substantially the length of the propagation path in the vertical portion 43, is smaller than 1/4 the wavelength (λg/4=47.5 mm), i.e., (Lv < λg/4).
[0055] Fig. 3 is a main-part cross-sectional view illustrating the feeding portion 22 and the object to be heated 15, in the heating cooker according to the first embodiment. As illustrated in Fig. 3, the flat-plate element 22a in the feeding portion 22, which is adapted to rotate for radiating and stirring microwaves having been propagated through the waveguide 21, is made of a metal and is shaped by folding, by an angle of 10 degrees, a disk plate with a thickness of 1 mm and a diameter of 62 mm, along a folding line including a center line of the disk plate (a line including the center point of the disk plate). The vertical shaft element 22b, which is adapted to transmit the rotation of the motor 23 to the flat-plate element 22a, is connected to the flat-plate element 22a at a position deviated by about 12 mm from the disk-plate center. Accordingly, one of half-circular portions of the flat-plate element 22a is connected, in its radiation surface, to the vertical shaft element 22b and is placed in the horizontal direction, while the remaining half-circular portion is folded in its radiation surface with respect to the horizontal direction and is placed to be oriented downwardly at a predetermined angle θ (θ=10 degrees). Further, although the flat-plate element 22a according to the first embodiment will be described as being folded at a folding line on a straight line including a disk-plate center line, regarding the position of the folding line, the present invention is not limited to this structure, and the folding line is not necessarily required to include a disk-plate center line. Accordingly, in the microwave heating device according to the present invention, the flat-plate element is required to be structured only such that at least a partial radiation surface, out of the microwave radiation surface of the flat-plate element, is folded at a predetermined angle θ with respect to the horizontal direction, and the the radiation surface folded at the predetermined angle θ is made to have an area which occupies 1/2 or more of the entire radiation surface of the flat-plate element.
[0056] As described above, the flat-plate element 22a is divided, by the folding line, into two areas, which are a horizontal surface portion Ah placed in the horizontal direction, and an oblique surface portion As which is downwardly oblique from the folding line by the predetermined angle θ with respect to a horizontal plane. Further, the oblique surface portion As is adapted such that its radiation surface is equal to the radiation surface of the horizontal surface portion Ah or larger than the radiation surface of the horizontal surface portion Ah (As ≥ Ah). In the heating cooker according to the first embodiment, a line (Y) orthogonal to the folding line, which is included in the oblique surface portion As of the flat-plate element 22a, is oriented downwardly from a horizontal plane (X), by the folding angle (θ=10 degrees), with respect to the horizontal surface portion Ah. The folding angle (θ=10 degrees), which is the predetermined angle, can be expressed as θ ≈ 0.175 rad, according to circular measure (radian). In this case, sin θ (≈ 0.174) is substantially equal to θrad, since the angle (θ=10 degrees) is smaller. Accordingly, it can be considered that the length (Ly) of the flat-plate element 22a, which is a disk plate with a diameter of 62 mm, in the direction Y orthogonal to the holding line is about 62 mm.
[0057] Further, assuming that the height from the surface of the food 15 to a position in the radiation surface of the horizontal surface portion Ah of the flat-plate element 22a which is opposed to the position where the flat-plate element 22a is bonded to the vertical shaft element 22b is H, within the heating chamber 11, H is about 330 mm, in the heating cooker according to the first embodiment. Accordingly, since the angle of obliqueness θrad of the oblique surface portion As of the flat-plate element 22a is about 0.175, this angle of obliqueness is set to be an angle which is larger than Ly/2/H ≈ 0.094 but is smaller than Ly/H ≈ 0.188, i.e., (Ly/2/H<θrad<Ly/H).
[0058] The vertical shaft element 22b includes a portion made of a fluorocarbon resin which is closer to the motor 23, and further, includes a portion made of a metal which is closer to the flat-plate element 22a. The metal portion of the vertical shaft element 22b has a portion inserted in the waveguide 21, and further, has a portion protruded into the feeding chamber 24 through the feeding port 25 in the waveguide 21. Further, it is ensured that the gap between the feeding port 25 and the metal portion of the vertical shaft element 22b has a length equal to or more than 5 mm.
[0059] Next, the heating cooker having the structure according to the first embodiment will be described, with respect to operations and effects thereof.
[0060] It has been known that, in cases of a flat-plate element with a circular shape as in the first embodiment, the resonance frequency excited in the fundamental mode can be determined by using the formula c = 0.58 × (wavelength), assuming that the diameter of the flat-plate element is c. However, the resonance frequency of the flat-plate element including the vertical shaft element 22b is varied depending on the length and the diameter of the vertical shaft element 22b, and depending on the position in the flat-plate element 22a where the vertical shaft element 22b is bonded thereto. Therefore, the accurate resonance frequency is finally determined depending on these dimensions and shapes.
[0061] Accordingly, in the heating cooker having the structure according to the first embodiment, the flat-plate element 22a having the circular shape with a diameter of about 62 mm is caused to resonate, and the resonance current generates a unidirectional radiation pattern having a beam center axis in the direction normal to the respective radiation surfaces of the oblique surface portion As and the horizontal surface portion Ah which are folded with respect to each other, in the flat-plate element 22a. Microwaves having strong radiation directivity which are radiated from the radiation surface of the oblique surface portion As, which is inclined downwardly by the predetermined angle θ with respect to the horizontal direction, are radiated obliquely at an angle θ with respect to the vertical direction.
[0062] Generally, the food 15 has a higher water content, and thus, can be considered to be substantially equivalent to water, for microwaves. Since water has a relative dielectric constant of about 80, the proportion of microwaves which penetrate the food to be absorbed thereby to microwaves incident vertically to the food 15 is about 36 %, based on conversion of microwaves into electric power in view of the permittivity difference between water and air. The remaining proportion of about 64 % is reflected at the boundary between the food 15 and air.
[0063] As described above, microwaves radiated obliquely at an angle of θ with respect to the vertical direction from the flat-plate element 22a are partially reflected by the boundary surface of the food 15. These reflected waves are reflected in directions deviated from the antenna formed by the feeding portion 22, by an amount corresponding to the angle θ with respect to the vertical direction. The inclination angle θrad is larger than Ly/2/H (Ly/2/H<θrad). Therefore, ideally, while microwaves propagates by a distance H, the microwaves are reflected by the food 15 at a point deviated by a distance of Ly/2 from the radiation surface of the flat-plate element 22a. Further, while the reflected waves propagate upwardly by the distance H again, the reflected waves are deviated by a distance of Ly/2. Accordingly, the reflected waves reach positions where the flat-plate element 22a does not exist, which prevents the reflected waves from the food 15 from being received by the antenna, in the heating cooker according to the first embodiment.
[0064] As described above, in the heating cooker according to the first embodiment, there is provided the feeding port 25 as a coupling hole for connecting the waveguide 21 to the ceiling wall surface of the heating chamber 11 and for supplying microwaves therethrough, and further, the flat-plate element 22a is placed in such a way as to radiate microwaves downwardly at the predetermined angle θ through the coupling hole portion. Therefore, the radiated microwaves are partially reflected by the boundary surface of the food 15 which is the object to be heated, and the reflected waves are reflected in directions deviated from the feeding portion 22 forming the antenna, by an amount corresponding to the angle θ with respect to the vertical direction. This largely inhibits the waves reflected by the object to be heated from being received by the antenna formed by the feeding portion, which reduces the reflected-wave components which are returned to the magnetron 16 through the waveguide 21. As a result thereof, the heating cooker according to the first embodiment is adapted to prevent temperature rises in the magnetron 16 due to its self-heat generation, which elongates the life of the magnetron 16, and also, eliminates the necessity of power down settings for the magnetron 16, thereby enabling improvement of the output efficiency.
[0065] In the heating cooker according to the first embodiment, since the flat-plate element 22a is adapted such that its downwardly-facing surface functions as a radiation surface, microwaves radiated from the antenna have strong radiation directivity in the direction normal to the downwardly-facing surface, Further, the flat-plate element 22a is folded along a disk-plate center line, and the oblieque surface portion As set to be at the folding angle θ is adapted such that its radiation surface occupies 1/2 or more of the entire radiation surface. Therefore, most of waves radiated from the flat-plate element 22a are radiated obliquely at the angle θ with respect to the vertical direction. Microwaves radiated obliquely from the radiation surface of the oblique surface portion As of the flat-plate element 22a are obliquely incident to the object to be heated, and the like, and the microwaves are reflected in directions deviated by an amount corresponding to the obliqueness, from the position of the antenna formed by the feeding portion 22. Accordingly, in the heating cooker according to the first embodiment, it is possible to largely reduce reflected waves received by the antenna, which can largely reduce reflected-wave components returned to the magnetron 16. Therefore, the heating cooker according to the first embodiment is adapted to prevent temperature rises in the magnetron 16 due to its self-heat generation.
[0066] In the heating cooker according to the first embodiment, the waveguide 21 is orthogonally folded to have an L shape, and the magnetron 16 is coupled, in a lateral orientation, to the waveguide 21. Namely, the magnetron output portion 44 in the magnetron 16 is mounted to the vertical wall surface of the waveguide 21, such that its protruded portion is orthogonal thereto. Therefore, the waveguide 21 to which the magnetron 16 is bonded is placed in a space having a smaller size (height) in the vertical direction, which is the upward and downward direction. For example, the waveguide 21 to which the magnetron 16 is bonded according to the first embodiment is placed in a space having a smaller height, in comparison with the height of a space in which there is placed a waveguide 104 to which a magnetron 103 is bonded in the vertical direction as in the conventional structure illustrated in Fig. 10. Further, since the magnetron 16 is bonded laterally to the waveguide 21, there is leeway in the space above the magnetron 16, which enables placing other structural members therein.
[0067] Accordingly, in the heating cooker according to the first embodiment, it is possible to compactly form the microwave feeding structure constituted by the magnetron 16, the waveguide 21, the feeding chamber 24 and the like. Further, in cases where the heating cooker is structured to be built in a kitchen, it is possible to provide a manipulation panel above the heating chamber, and also, it is possible to provide a space for collectively and compactly mounting electric circuits, the microwave feeding structure, a cooling structure and other structures, above the heating chamber.
[0068] In the heating cooker according to the first embodiment, the horizontal portion 42 of the waveguide 21 is connected to the feeding port 25 in the protruding end portion of the feeding chamber 24 protruded upwardly from the ceiling wall surface of the heating chamber 11, and the vertical portion 43 of the waveguide 21 is extended upwardly from the bending position C. Therefore, the waveguide 21 is placed such that it gradually gets further away from the ceiling wall surface of the heating chamber 11. Further, in the heating cooker according to the first embodiment, the feeding chamber 24 is formed in the ceiling wall surface of the heating chamber 11, and the waveguide 21 is connected to the upper end portion of the feeding chamber 24. Therefore, the waveguide 21 is coupled to the heating chamber 11 through the feeding chamber 24. This allows the waveguide 21 and the feeding chamber 24 to be in contact with each other over their portions with smaller areas, in comparison with cases where the waveguide is directly in contact with the ceiling wall surface of the heating chamber. This can prevent half or more of the horizontal portion 42 from coming in contact with other members. Further, the waveguide 21 is structured in such a way as to be spaced apart from the heating chamber 11, thereby forming a space therebetween. Therefore, the heating cooker according to the first embodiment is structured to prevent direct heat conduction to the waveguide 21 from the ceiling wall surface of the heating chamber 11 being heated at higher temperatures.
[0069] Further, the heating cooker according to the first embodiment is structured to largely reduce the amount of heat which is conducted from the heating chamber 11 to the magnetron 16 through the feeding chamber 24 and the waveguide 21. Further, since the magnetron 16 is placed in such a way as to be spaced apart from the heating chamber 11, it is possible to prevent direct heat conduction to the magnetron 16 from the ceiling wall surface of the heating chamber 11, in the heating cooker according to the first embodiment.
[0070] The heating cooker having the structure according to the first embodiment is adapted to inhibit the magnetron 16 from receiving heat from the ceiling wall surface of the heating chamber 11 being heated at higher temperatures, which prevents heat conducted to the magnetron 16 from the heating chamber 11 through the waveguide 21, thereby preventing temperature rises in the magnetron 16. As a result thereof, even with the compact structure having the magnetron 16 provided above the heating chamber 11, it is possible to suppress heat conduction from the heating chamber 11 to the magnetron 16, which enables elongating the life of the magnetron 16, elimination of the necessity of power down settings for the magnetron 16, and improvement of the output efficiency.
[0071] Further, in the heating cooker according to the first embodiment, the magnetron 16 which forms the microwave generating portion is laterally and horizontally connected to the vertical propagation path (43) of the waveguide 21, which can make the entire apparatus have a compact size in the heightwise direction.
[0072] In the heating cooker according to the first embodiment, the horizontal propagation distance Lh (see Fig. 2) in the horizontal portion 42 of the waveguide 21 can be set to be longer, which can further reduce the amount of heat conducted to the magnetron 16 from the heating chamber 11 through the feeding chamber 24 and the waveguide 21. The magnetron 16 generally exhibits higher efficiency at lower temperatures, and therefore, the heating cooker according to the first embodiment is structured to improve the output efficiency of the magnetron 16.
[0073] In the heating cooker according to the first embodiment, even when the food 15 is placed on a material having a radio-wave intercepting effect, such as a metal tray, in such a way as to utilize both radio waves and another heating function at the same time, it is possible to supply microwaves downwardly from the feeding chamber 24 in the ceiling wall surface portion, which enables certainly performing microwave heating on the food 15 without intercepting the microwaves.
[0074] Further, since microwaves are radiated obliquely with respect to the vertical direction from the radiation surface of the oblique surface portion As of the flat-plate element 22a, it is possible to largely reduce the reflected wave components returned to the magnetron 16 which forms the microwave generating portion, thereby preventing temperature rises in the magnetron 16 due to its self-heat generation.
[0075] Further, since both the waveguide 21 and the magnetron 16 are spaced apart from the ceiling wall surface of the heating chamber 11, it is possible to largely reduce the amount of heat which is conducted to the magnetron 16 through the waveguide 21 from the heating chamber 11 being heated at higher temperatures, which can further prevent temperature rises in the magnetron 16.
[0076] In the heating cooker according to the first embodiment, since the inclination angle θrad is larger than Ly/2/H, i.e., (Ly/2/H<θrad), the angle setting is made such that, even when microwaves having strong radiation directivity which are radiated obliquely with respect to the vertical direction from the radiation surface of the oblique surface portion As of the flat-plate element 22a are reflected by the food 15 or the wall surfaces near the bottom portion of the heating chamber 11, these microwaves are not returned to the antenna. Further, since the inclination angle θrad of the radiation surface of the oblique surface portion As is smaller than Ly/H, i.e., (θrad<Ly/H), it is possible to prevent the inclination angle of the radiation surface from being excessively larger, thereby preventing impossibility of radiation of microwaves to the vicinity of the center of the bottom surface of the heating chamber 11 in the vertical direction, which is beneath the antenna. In the heating cooker according to the first embodiment, the radiation surface of the flat-plate element 22a is set to be at a preferable radiation angle, in order to certainly prevent the food 15 from being heated in a donut shape (a ring shape), due to insufficient heating at the center portion of the food 15. Therefore, the heating cooker according to the first embodiment is enabled to attain both realization of microwave heating without heating unevenness, and prevention of temperature rises in the magnetron 16 due to its self-heat generation, through significant suppression of reflected wave components returned to the magnetron 16. Therefore, the heating cooker according to the first embodiment is capable of elongating the life of the magnetron 16, and further, is capable of eliminating the necessity of power down settings for the magnetron 16, thereby improving the output efficiency.
[0077] In the heating cooker according to the first embodiment, the flat-plate element 22a adaptable to the wavelengths of microwaves to be used in a 2450-MHz microwave oven is realized, and the flat-plate element 22a is constituted by a flat plate with a substantially circular shape with a diameter of about 62 mm. Therefore, the heating cooker according to the first embodiment is enabled to cause resonation at a microwave wavelength of 2450 MHz, thereby generating a unidirectional radiation pattern with a beam center axis in the direction normal to the radiation surface of the flat-plate element 22a. Further, the heating cooker according to the first embodiment is adapted to cause radiated waves from the radiation surface of the oblique surface portion AS of the flat-plate element 22a to be radiated obliquely at an angle θ with respect to the vertical direction. Therefore, the radiated waves are reflected in directions deviated from the antenna by an amount corresponding to the obliqueness (θ), which inhibits the reflected waves from being received by the antenna, thereby preventing temperature rises in the magnetron 16 due to its self-heat generation. This enables elongation of the life of the magnetron 16, elimination of the necessity of power down settings for the magnetron 16 and improvement of the output efficiency.
[0078] In the heating cooker according to the first embodiment, the waveguide 21 is provided, in its E surfaces which are its opposite wall surfaces facing each other, with ventilation areas 21a having a considerable number of through holes 36a and 36b. Although, in Fig. 2, there is illustrated only the ventilation area 21a formed from the plurality of through holes 36a in one wall surface, there is also formed the ventilation area 21a formed from the plurality of through holes 36b similarly in the other wall surface opposed to this one wall surface, although it is behind this one wall surface. The ventilation areas 21a are areas in the wall surfaces in which there are arranged the considerable number of small through holes 36a and 36b with a diameter of about 2 to 5 mm, in order to prevent leakages of microwaves to the outside of the waveguide 21. Due to the provision of the ventilation areas 21a including the pluralities of the through holes 36a and 36b in the wall surfaces of the waveguide 21, it is possible to increase the heat transfer resistance in the wall surfaces of the waveguide 21, and further, it is possible to allow air to move through the through holes 36a and 36b in the ventilation areas 21a. This results in movement of air through the waveguide 21, which exerts a cooling effect thereon, thereby reducing heat conducted from the heating chamber 11 to the magnetron 16 through the waveguide 21. Accordingly, even with the compact structure having the magnetron 16 provided above the heating chamber 11, it is possible to suppress heat conduction to the magnetron 16 from the heating chamber 11 being heated at higher temperatures, which prevents temperature rises in the magnetron 16, thereby elongating the life of the magnetron 16. The magnetron 16 generally exhibits higher efficiency at lower temperatures, and therefore, the heating cooker according to the first embodiment is structured to improve the output efficiency of the magnetron 16.
[0079] Further, in the structure according to the first embodiment, the horizontal propagation distance Lh in the horizontal portion 42 of the waveguide 21 is set to be larger than half the wavelength (λg/2), which can stabilize the state of coupling between the magnetron 16 and the feeding portion 22, thereby realizing a structure capable of maintaining higher efficiency, even in cases of changes of operating states, such as load changes.
[0080] Further, the waveguide 21 having the longer horizontal propagation path can suppress heat conduction from the heating chamber 11 to the magnetron 16, and thus, even with the compact structure having the magnetron 16 provided above the heating chamber 11, it is possible to prevent temperature rises in the magnetron 16.
[0081] Further, in the heating cooker according to the first embodiment, by setting the vertical propagation distance Lv to the folding position C from the center of the magnetron output portion 44 in the waveguide 21 to be shorter than 1/4 the wavelength (λg/4), it is possible to improve the propagation efficiency. Further, by setting the vertical propagation distance Lv to be equal to or less than 1/4 the wavelength corresponding to the oscillation frequency, it is possible to prevent occurrences of electric fields in the opposite direction within the area from the magnetron output portion 44 to the folding portion including the folding position C, which can prevent occurrences of complicated reflections within the propagation path in the waveguide 21. As a result thereof, the heating cooker according to the first embodiment has higher oscillation efficiency, and thus, forms an apparatus with higher heating efficiency.
[0082] Further, although the heating cooker according to the first embodiment has been described as being structured to have the induction heating portion which utilizes microwaves as a single heating means, and the high-temperature heating portion which utilizes radiations through the upper heater 12 and the lower heater 13 as the other heating means, in combination with each other, the present invention is not limited to this structure, and it is also possible to provide a convection heating portion adapted to circulate hot air flows within the heating chamber for performing heating cooking, as another high-temperature heating portion.
[0083] Also, the microwave heating device according to the present invention can be also provided with both the radiative heating portion and the convection heating portion, as the high-temperature heating portion, in addition to the induction heating portion employing the magnetron. The microwave heating device having this structure according to the present invention is capable of largely reducing the amount of heat conducted from the heating chamber to the magnetron through the feeding chamber and the waveguide, in the structure of the induction heating portion. Therefore, even when the microwave heating device according to the present invention employs other heating means, it is possible to prevent temperature rises in the magnetron, thereby elongating the life thereof.
[0084] Further, although the heating cooker according to the first embodiment has been described with respect to the case where the flat-plate element 22a has a circular shape, a circle is a type of ellipse, and therefore, the flat-plate element can be also made to have an elliptical shape, such that a horizontal surface portion Ah and an oblique surface portion As are formed therein, by forming a folding line in the direction orthogonal to the longer axis of the ellipse. Provided that the total length (Ly) of the oblique surface of the flat-plate element having this structure, in the direction of the longer axis, is substantially coincident with 1 / 2 the wavelength, even when the total length of the horizontal surface of the flat-plate element in the direction of the longer axis is different, to some degree, from the length (Ly) of the oblique surface in the direction of the longer axis, it is possible to cause excitation in a resonation mode similar to that of the flat-plate element 22a in the heating cooker according to the first embodiment, while inducing only slight changes in the resonation frequency. Therefore, provided that the total length of the horizontal surface of the flat-plate element in the direction of the longer axis falls within the range of about 1/4 the wavelength to 3/4 the wavelength, it is possible to form the flat-plate element such that it exhibits characteristics of sufficiently exerting the functions of the present invention.
[0085] Further, although the flat-plate element has been described as having only a circular shape or an elliptical shape, the flat-plate element can be also made to have a rectangular shape in order to be brought into a resonance state, and further, the flat-plate element is not necessarily required to have a perfect rectangular shape or a perfect elliptical shape. For example, it goes without saying that the flat-plate element can be possibly made to have various shapes, such as rectangular shapes which are largely cut or rounded at their corners, or shapes intermediate therebetween. Namely, basically, the flat-plate element is only required to be a flat plate having an oblique surface with a maximum width coincident with about 1/2 the wavelength and having a horizontal surface with a maximum width falling within the range of about 1/4 the wavelength to 3/4 the wavelength.
(Second Embodiment)
[0086] Hereinafter, a heating cooker according to a second embodiment of the present invention will be described as one example of the microwave heating device of the present invention. The heating cooker according to the second embodiment is different from the heating cooker according to the first embodiment, in terms of the structure for supplying microwaves to a heating chamber.
[0087] The heating cooker according to the second embodiment will be described, hereinafter, by designating components having the same functions and structures as those of the components of the heating cooker according to the first embodiment by the same reference characters, and by substituting the description about the first embodiment for detailed descriptions thereof. Fig. 4 is a front cross-sectional view illustrating the internal structure of a main part of the heating cooker according to the second embodiment. Fig. 5 is a side cross-sectional view of the heating cooker illustrated in Fig. 4.
[0088] As illustrated in Fig. 4 and Fig. 5, in the heating cooker according to the second embodiment, a waveguide 21 for propagating microwaves from a magnetron 16 is structured to include a horizontal portion 42 and a vertical portion 43 and, thus, is folded in an L shape, similarly to the waveguide 21 according to the first embodiment. Namely, the waveguide 21 includes an internal passage constituted by a horizontal propagation path and a vertical propagation path which are orthogonal to each other. The magnetron 16 is coupled in a lateral orientation (horizontally coupled) to the waveguide 21, such that a magnetron output portion 44 is horizontally inserted in the waveguide 21. Namely, the magnetron output portion 44 is provided such that its protruding portion is orthogonal to the vertical side surface of the vertical portion 43 of the waveguide 21. Accordingly, in the state where the magnetron 16 is coupled to the waveguide 21, the heightwise size in the vertical direction, which is the upward and downward direction, is made smaller, similarly to in the structure according to the first embodiment.
[0089] A feeding portion 22 which forms an antenna having a flat-plate element 22a and a vertical shaft element 22b is connected to the horizontal portion 42 of the waveguide 21 having the L-shaped internal passage (the propagation path), as described above. A feeding chamber 49 housing the flat-plate element 22a is formed substantially at the center portion of the ceiling wall surface of the heating chamber 11. The feeding chamber 49 is shaped to extend in a circular shape at its lower end portion, and thus, has a circular truncated cone shape. The feeding chamber 49 is formed by performing drawing processing on the ceiling wall surface of the heating chamber 11. Further, in the second embodiment, there is not provided a cover covering the lower end portion of the feeding chamber 49, which prevents the occurrence of slight dielectric losses in such a cover, thereby further improving the heating efficiency.
[0090] Fig. 6 is a perspective view illustrating the waveguide 21 and the feeding chamber 49 in the heating cooker according to the second embodiment. As illustrated in Fig. 6, in the waveguide 21 according to the second embodiment, similarly to in the waveguide 21 according to the first embodiment, the horizontal propagation distance Lh in the horizontal portion 42 is about 135 mm and, thus, is set to be longer than half the wavelength (λg/2), i.e., (Lh > λg/2). Further, the vertical propagation distance Lv (see Fig. 2) in the vertical portion 43 of the waveguide 21 is about 15 mm and, thus, is set to be shorter than 1/4 the wavelength (λg/4), i.e., (Lv < λg/4), Further, in the second embodiment, the width "a" of the internal passage which forms the propagation path in the waveguide 21 is 80 mm, similarly to in the first embodiment. Accordingly, the magnetron 16 used therein has an oscillation frequency of about 2450 MHz, and therefore, the in-tube wavelength λg within the waveguide 21 is about 190 mm in the case where the waveguide 21 is adapted such that the width "a" of the internal passage is about 80 mm, and the length of half the wavelength (λg/2) is 95 mm (λg/2 = 95 mm).
[0091] As illustrated in Fig. 4, the feeding chamber 49 is protruded into the heating chamber 11, at its bottom portion at the lower end portion, to form a shield wall protruding downwardly from the ceiling surface of the heating chamber. On the other hand, the feeding chamber 49 is protruded upwardly, at its upper end portion, from the ceiling wall surface of the heating chamber 11. A feeding port 25 formed in the horizontal portion 42 of the waveguide 21 is connected to an opening formed in the upper end portion of the feeding chamber 49 and is caused to function as a coupling hole integrally therewith. Therefore, the waveguide 21 is connected to the heating chamber 11 through the feeding chamber 49. This allows the waveguide 21 and the feeding chamber 49 to be in contact with each other over their portions with smaller areas, in comparison with cases where the waveguide is directly in contact with the ceiling wall surface of the heating chamber. This can prevent half or more of the horizontal portion 42 from coming in contact with other members. Further, the waveguide 21 is structured in such a way as to be spaced apart from the heating chamber 11, thereby forming a space therebetween. This prevents direct heat conduction to the waveguide 21 from the ceiling wall surface of the heating chamber 11 being heated at higher temperatures. Further, on the upper surface in the ceiling wall surface of the heating chamber 11, a heat insulation portion 50 made of a heat insulation material is provided in such a way as to surround the periphery of the feeding chamber 49. Since the heat insulation portion 50 is provided as described above, it is possible to suppress heat dissipation in the upward direction from the ceiling wall surface of the heating chamber 11. The heat insulation portion 50 is placed in the space between the waveguide 21 and the ceiling wall surface of the heating chamber 11, which prevents the waveguide 21 from being directly heated by heat dissipated through the ceiling wall surface of the heating chamber 11. This can largely reduce the amount of heat conducted to the magnetron 16 through the waveguide 21 from the heating chamber 11 being heated at higher temperatures. Further, since the magnetron 16 is adapted to be spaced apart from the heating chamber 11, it is possible to prevent direct heat conduction to the magnetron 16 from the ceiling wall surface of the heating chamber 11.
[0092] Further, as illustrated in Figs. 4 and 5, within the feeding chamber 49, there is provided the flat-plate element 22a which is shaped by folding, by a predetermined angle θ (for example, 10 degrees), a disk plate with a diameter of 62 mm, along a folding line including a center line thereof (a line including the center point of the disk plate). The flat-plate element 22a is adapted to resonate at the wavelength of used microwaves, thereby generating a unidirectional radiation pattern having a beam center axis in the direction normal to the radiation surface of the flat-plate element 22a. Therefore, microwaves are radiated downwardly from the radiation surface of the flat-plate element 22a of the feeding portion 22, which is provided in the coupling hole portion in the ceiling wall surface of the heating chamber 11, and the microwaves are partially radiated at a predetermined angle θ with respect to the vertical direction. The radiated microwaves are partially reflected by the boundary surface of the food 15 which is the object to be heated, and these reflected waves are reflected in directions deviated from the feeding portion 22 forming the antenna, by an amount corresponding to the angle θ with respect to the vertical direction. This largely inhibits the reflected waves from being received by the antenna, which reduces the reflected-wave components which are returned to the magnetron 16 through the antenna. As a result thereof, the heating cooker according to the second embodiment is adapted to prevent temperature rises in the magnetron 16 due to its self-heat generation, as well as temperature rises due to heat conduction from the heating chamber 11 as described above.
[0093] Therefore, the heating cooker according to the second embodiment is adapted to enable elongation of the life of the magnetron 16, elimination of the necessity of power down settings for the magnetron 16 and improvement of the output efficiency, even with the compact structure having the magnetron 16 provided above the heating chamber 11.
[0094] Further, the horizontal propagation distance Lh in the horizontal portion 42 of the waveguide 21 can be set to be larger than half the wavelength (λg/2), which can stabilize the state of coupling between the magnetron 16 and the feeding portion 22, thereby realizing a structure capable of maintaining higher heating efficiency, even in cases of changes of running states, such as load changes. Further, the waveguide 21 having the longer horizontal propagation path can suppress heat conduction from the heating chamber 11 to the magnetron 16, and thus, even with the compact structure having the magnetron 16 provided above the heating chamber 11, it is possible to prevent temperature rises in the magnetron 16.
[0095] Further, in the heating cooker according to the second embodiment, by setting the vertical propagation distance Lv to the folding position C from the center of the magnetron output portion 44 in the waveguide 21 to be shorter than 1/4 the wavelength (λg/4), it is possible to improve the oscillation efficiency. Further, by setting the vertical propagation distance Lv to be equal to or less than 1/4 the wavelength corresponding to the oscillation frequency, in the waveguide 21, it is possible to prevent occurrences of electric fields in the opposite direction within the area from the magnetron output portion 44 to the folding portion including the folding position C, which can prevent occurrences of complicated reflections within the propagation path in the waveguide 21. As a result thereof, the heating cooker according to the second embodiment can have largely improved oscillation efficiency.
[0096] As described above, in the heating cooker according to the second embodiment, the waveguide 21 is shaped to be folded in an L shape, and the antenna room 49 is protruded upwardly from the ceiling wall surface of the heating chamber 11. This enables provision of the heat insulation portion 50 in the space between the horizontal portion 42 of the waveguide 21 and the ceiling wall surface of the heating chamber 11. Thus, it is possible to couple the heating chamber 11 and the waveguide 21 to each other through the feeding chamber 49 and, further, it is possible to provide the heat insulation portion 50 for preventing heat conduction in the space between the heating chamber 11 and the waveguide 21, which enables forming the heating cooker with excellent heating efficiency and with a compact structure.
[0097] Further, in the heating cooker according to the second embodiment, the waveguide 21 folded upwardly is provided on the upper end portion of the feeding chamber 49 which is protruded from the ceiling wall surface of the heating chamber 11, which can secure a space for providing the heat insulation portion 50 on the ceiling wall surface of the heating chamber 11, thereby enabling placing the heat insulation portion 50 with a larger thickness therein. Note that the heating cooker according to the second embodiment is provided with a ventilation fan 61 for exhausting air within the heating chamber, and a lamp 62 adapted to provide illumination within the heating chamber.
[0098] With the heating cooker having the structure according to the second embodiment, it is possible to interrupt heat dissipated upwardly from the heating chamber 11 due to the heat insulation effect of the heat insulation portion 50, in cooking processing using heating portions such as heaters as the high-temperature heating portion. Therefore, the heating cooker according to the second embodiment is structured to largely improve the heating efficiency.
[0099] Further, the heating cooker according to the second embodiment is structured to largely reduce the amount of heat conducted from the heating chamber 11 to the magnetron 16 in cases of cooking using induction heating in combination with convection heating and radiative heating through heaters. Therefore, the heating cooker according to the second embodiment forms a compact cooker having excellent heating efficiency.
[0100] Further, the heating cooker according to the second embodiment is structured such that an upper heater 12 is provided at an upper side within the heating chamber 11, and a lower heater 13 is provided under the bottom surface wall of the heating chamber 11 as illustrated in Fig. 4 and Fig. 5. Further, the heating cooker according to the second embodiment is structured to heat the bottom surface wall of the heating chamber 11 through the lower heater 13. Further, the heating cooker according to the second embodiment includes a back-surface heater 30 and a circulation fan 31 for circulating hot air flows for oven cooking, near the back surface of the heating chamber 11 (see Fig. 5). As described above, the heating cooker according to the second embodiment is enabled to directly heat food through radiant heat and convective heat, in addition to heating through induction heating. Accordingly, the heating cooker according to the second embodiment forms a sophisticated cooker capable of coping with a plurality of cooking menus.
[0101] The upper heater 12 provided at an upper side in the heating chamber 11 is fixed, at its one end (near the terminal), to the back surface of the heating chamber 11, and further, the upper heater 12 is held at its front-surface side by upper heater supporting tools 51 (see Fig. 5). The upper-heater supporting tools 51 are structured to hold the upper heater 12 with degrees of freedom enough to cope with the thermal expansion of the upper heater 12. Further, as the material of the upper-heater supporting tools 51, the upper-heater supporting tools 51 are formed from ceramic members such as insulators according to the required heat-resistant temperature, and further, are made of a material which exerts smaller influences on microwaves than those of metal tools.
[0102] As illustrated in Fig. 4 and Fig. 5, the lower end portion of the feeding chamber 49 is protruded into the heating chamber 11 from the ceiling surface, and the upper heater 12 is placed around the lower end portion of the feeding chamber 49. Namely, the upper heater 12 is provided so as not to be beneath the opening portion at the lower end portion of the feeding chamber 49. Thus, the upper heater 12 is provided outside the shield wall formed by the lower end portion of the feeding chamber 49 protruded into the heating chamber. Therefore, the upper heater 12 is prevented from being directly heated by microwaves from the feeding portion 22. This can prevent occurrences of losses in microwave heating.
[0103] Fig. 7 is a placement view illustrating the lower surface side of the ceiling wall surface of the heating chamber 11, illustrating the feeding portion 22 provided in the ceiling wall surface, the feeding chamber 49, the upper-heater supporting tools 51, the upper heater 12, and the like. In Fig. 7, the front surface side of the apparatus is in the upper side. As illustrated in Fig. 7, the upper heater 12 is placed so as to avoid the opening portion at the lower end portion of the feeding chamber 49, and further, the upper heater 12 is held by the upper-heater supporting tools 51 at a plurality of positions so as to be movable.
[0104] In the heating cooker according to the second embodiment, the lower heater 13 provided under the bottom surface wall of the heating chamber 11 is adapted to heat the bottom surface wall of the heating chamber 11. The lower heater 13 is adapted to heat the bottom surface wall of the heating chamber 11, in order to generate radiant heat and convective heat within the heating chamber 11.
[0105] Further, the heating cooker according to the second embodiment is structured to include the back-surface heater 30 and the circulation fan 31 for circulating hot air flows for oven cooking, which are provided near the back surface of the heating chamber 11, thereby forming a convection heating portion. The convection heating portion is structured to heat air within the heating chamber 11 and to circulate hot air flows within the heating chamber 11, through heat generation from the back surface heater 30 and through the rotation of the circulation fan 31. The heating cooker according to the second embodiment is structured to circulate hot air flows within the heating chamber 11 for performing heating cooking on food 15 as an object to be heated, with the convection heating portion having the aforementioned structure.
[0106] Further, as illustrated in Fig. 5, the heating cooker according to the second embodiment is provided, at its front surface side, with a door 32 for opening and closing it, which enables taking in and out the object to be heated into and from the heating chamber 11 by opening and closing the door 32. Above the door 32, there is provided a manipulation portion 33 for making settings of various conditions and the like for heating cooking.
[0107] As illustrated in Fig. 5, in the heating cooker according to the second embodiment, a gap 34 is formed between the door 32 and the manipulation portion 33. The gap 34 constitutes a cooling passage for exhausting cooling air flows from a cooling fan 35, which is provided at a back position in the space above the heating chamber 11. Cooled air flows from the cooking fan 35 flow while coming in contact with the upper surface of the heat insulation portion 50, further pass through small through holes 36a and 36b formed in the opposite wall surfaces of the waveguide 21 which are faced to each other, and further, are exhausted in the forward direction through the gap 34. In this case, the small through holes 36a and 36b are holes having a size which prevents leakages of microwaves therethrough, such as a diameter of 2 to 5 mm, for example. Although ventilation areas 21c having the through holes 36a and 36b (see Fig. 5) are provided near the feeding port 25 in the waveguide 21, other ventilation areas 21a having a considerable number of through holes 36a and 36b are also formed in the E surfaces of the vertical portion 43 of the waveguide 21, similarly to in the structure according to the first embodiment, as illustrated in Fig. 6. Accordingly, cooling air flows from the cooling fan 35 are caused to cool the heat insulation portion 50, and further, caused to flow through the waveguide 21 to cool the waveguide 21.
[0108] As described above, the heating cooker according to the second embodiment is provided with the cooling fan 35 and the cooling passage, and therefore, is capable of cooling the ceiling wall surface of the heating chamber 11 from the outside, by driving the cooling fan 35, even when the inside of the heating chamber has been raised to higher temperatures during oven cooking, for example. Therefore, the heating cooker according to the second embodiment is capable of preventing temperature rises in various types of components which constitute the control portion 20 and the like, which are placed above the ceiling wall surface of the heating chamber 11. Further, the heating cooker according to the second embodiment is adapted to suppress temperature rises therein, even in cases of densely mounting and placing components above the ceiling wall surface of the heating chamber 11. Therefore, the heating cooker according to the second embodiment can be structured compactly, in the entirety of the apparatus.
[0109] Further, in the heating cooker according to the second embodiment, it is possible to force, by the cooling fan 35, cooling air to flow through a cooling path which causes the through holes 36a and 36b in the waveguide 21 to communicate with each other. Therefore, the heating cooker according to the second embodiment is adapted to have an improved effect of cooling the magnetron 16 and the waveguide 21, which prevents temperature rises in the magnetron 16, thereby enabling elongation of the life of the magnetron 16, elimination of the necessity of power down settings for the magnetron 16 and improvement of the output efficiency, even with the compact structure having the magnetron 16 provided above the heating chamber 11. Further, the magnetron generally exhibits higher efficiency at lower temperatures, and therefore, the heating cooker according to the second embodiment is structured to improve the heating efficiency of the magnetron 16.
[0110] In the heating cooker according to the second embodiment, the feeding chamber 49 is structured to protrude into the heating chamber 11 at its lower end portion, and the upper heater 12 is placed around the outer periphery of the lower end portion of the feeding chamber 49. Since the upper heater 12 is placed as described above, microwaves radiated from the feeding portion 22 are radiated directly to the food 15, and thus, are not interrupted by the upper heater 12. Thus, with the structure according to the second embodiment, the upper heater 12 is prevented from interrupting microwaves from the feeding portion 22, which can prevent microwaves from the feeding portion 22 from heating the upper heater 12 to induce losses therein. This can improve the heating efficiency.
[0111] Further, in the heating cooker according to the second embodiment, the portion of the feeding chamber 49 which protrudes into the heating chamber 11 functions as a microwave shield wall. This shield wall is made of a material which interrupts microwaves radiated from the flat-plate element 22a. Therefore, microwaves radiated in substantially-horizontal directions from the feeding portion 22 as the rotational antenna are certainly interrupted by the shield wall, which prevents the upper heater 12 and the upper-heater supporting tools 51 provided around the feeding chamber 49 from being directly heated by microwaves from the feeding portion 22. Namely, the shield wall reflects microwaves from the antenna portion, which prevents these microwaves from directly heating the high temperature heating portion in the upper heater 12 placed around the outer peripheral portion of the feeding chamber 49. As a result thereof, the heating cooker according to the second embodiment is adapted to largely suppress microwave losses, and thus, is enabled to perform heating cooking on food as objects to be heated, with higher heating efficiency.
(Third Embodiment)
[0112] Hereinafter, a heating cooker according to a third embodiment of the present invention will be described as one example of the microwave heating device. The heating cooker according to the third embodiment is largely different from the heating cookers according to the first and second embodiments, in terms of the structure for supplying microwaves to a heating chamber. The structures according to the first and second embodiments are applied to the other structures in the heating cooker according to the third embodiment.
[0113] The heating cooker according to the third embodiment will be described, hereinafter, by designating components having the same functions and structures as those of the components of the heating cookers according to the first and second embodiments by the same reference characters, and by substituting the descriptions about the first and second embodiments for detailed descriptions thereof.
[0114] Figs. 8 and 9 are main-part cross-sectional views illustrating a feeding portion and an object to be heated, in the heating cooker according to the third embodiment. As illustrated in Fig. 8, the feeding portion 22, which is adapted to radiate and stir microwaves having been propagated through a waveguide 21, has a flat-plate element 22a which is made of a metal and has a disk shape with a thickness of 1 mm and a diameter of 62 mm. A vertical shaft element 22b, which is adapted to transmit the rotation of a motor 23 to the flat-plate element 22a, is connected to the flat-plate element 22a at a position deviated by about 12 mm from the disk-plate center, and also, the flat-plate element 22a is obliquely connected to the vertical shaft element 22b in such a way as to be oriented downwardly at a predetermined angle θ (θ=10 degrees) with respect to the horizontal direction. As described above, in the third embodiment, the flat-plate element 22a illustrated in Fig. 8 is provided such that its radiation surface is entirely inclined by a predetermined angle θ (θ=10 degrees) with respect to a horizontal plane. In the flat-plate element 22a illustrated in Fig. 8, it is assumed that the downward direction at the predetermined angle θ=10 degrees with respect to the horizontal direction is a direction Y, while the direction coincident with the direction Y in a horizontal plane is a direction X. Namely, the angle θ between the direction X and the direction Y is 10 degrees. Assuming that Ly is the length of the entire radiation surface, in the direction Y, of the flat-plate element 22a, which is formed from a disk plate with a diameter of 62 mm, Ly is 62 mm.
[0115] Further, assuming that the height to the surface of food 15 from a position in the radiation surface of the flat-plate element 22a which is opposed to the position where the vertical shaft element 22b is connected to the flat-plate element 22a is H, within the heating chamber 11 illustrated in Fig. 8, H is about 330 mm, in the heating cooker according to the third embodiment. Accordingly, since the inclination angle θrad of the flat-plate element 22a is about 0.175, this inclination angle is set to be an angle which is larger than Ly/2/H≈0.094 but is smaller than Ly/H ≈0.188, i.e., (Ly/2/H<θrad<Ly/H).
[0116] The vertical shaft element 22b includes a portion made of a fluorocarbon resin which is closer to the motor 23, and further, includes a portion made of a metal which is closer to the flat-plate element 22a. The metal portion of the vertical shaft element 22b has a portion inserted in the waveguide 21 and further, has a portion protruded into a feeding chamber 24 through a feeding port 25 in the waveguide 21. Further, it is ensured that the gap between the feeding port 25 and the metal portion of the vertical shaft element 22b has a length equal to or more than 5 mm.
[0117] In the heating cooker having the structure illustrated in Fig. 8 as described, the flat-plate element 22a is placed in such a way as to radiate microwaves downwardly at the predetermined angle θ and, therefore, the radiated microwaves are partially reflected by the boundary surface of the food 15 which is the object to be heated, and these reflected waves are reflected in directions deviated from the feeding portion 22 forming the antenna, by an amount corresponding to the angle θ with respect to the vertical direction. This largely inhibits waves reflected by the object to be heated from being received by the antenna formed by the feeding portion, which reduces the reflected-wave components which are returned to the magnetron 16 through the waveguide 21. As a result thereof, with the heating cooker having the structure illustrated in Fig. 8, it is possible to prevent temperature rises in the magnetron 16 due to its self-heat generation, which enables elongation of the life of the magnetron 16, elimination of the necessity of power down settings for the magnetron 16 and improvement of the output efficiency.
[0118] Fig. 9 illustrates yet another structure of the heating cooker according to the third embodiment. In the structure of the heating cooker illustrated in Fig. 9, a flat-plate element 22a in a feeding portion 22 is adapted to have a folding line having a curved surface which is warped.
[0119] In the structure of the heating cooker illustrated in Fig. 9, the flat-plate element 22a in the feeding portion 22, which is adapted to radiate and stir microwaves having been propagated through a waveguide 21, is made of a metal and has a disk shape with a thickness of 1 mm and a diameter of 62 mm. The flat-plate element 22a is formed to have a warped shape, from a disk plate which is bent, at a disk-plate center line portion, to have a curved surface, symmetrically about the disk-plate center line. Namely, the flat-plate element 22a illustrated in Fig. 9 is divided into two areas at the disk plate center line portion, such that these two areas are coupled to each other through a curved surface.
[0120] In the structure of the heating cooker illustrated in Fig. 9, a vertical shaft element 22b, which is adapted to transmit the rotation of a motor 23 to the flat-plate element 22a, is connected to the flat-plate element 22a at a position deviated by about 12 mm from the disk-plate center. Accordingly, one of the areas in the flat-plate element 22a is connected to the vertical shaft element 22b and is placed in the horizontal direction. Further, the other area in the flat-plate element 22a is coupled through the curved surface to the one area connected to the vertical shaft element 22b and is placed in such a way as to be oriented downwardly at a predetermined angle θ (θ=10 degrees) with respect to the one curved surface. In the flat-plate element 22a illustrated in Fig. 9, it is assumed that the direction of the diameter which is coincident with the ridge line of the curved surface is in the horizontal direction, and the direction which is orthogonal to the ridge line of the curved surface in the horizontal direction and is downward from the horizontal direction is a direction Y. Accordingly, substantially half of the area in the flat-plate element 22a is placed in the direction Y which is downward by the predetermined angle θ=10 degrees with respect to the horizontal direction. Assuming that Ly is the length of the entire radiation surface, in the direction Y, of the flat-plate element 22a, which is formed from a disk plate with a diameter of 62 mm, the length Ly in the direction Y can be considered to be about 62 mm, since the angle θ is smaller.
[0121] Accordingly, in the shape illustrated in Fig. 9, similarly, since the inclination angle θrad of the flat-plate element 22a is about 0.175, this inclination angle is set to be an angle which is larger than Ly/2/H≈0.094 but is smaller than Ly/H≈0.188, i.e., (Ly/2/H<θrad<Ly/H).
[0122] The vertical shaft element 22b illustrated in Fig. 9 includes a portion made of a fluorocarbon resin which is closer to the motor 23 and, further, includes a portion made of a metal which is closer to the flat-plate element 22a, similarly. The metal portion of the vertical shaft element 22b has a portion inserted in a waveguide 21 and, further, has a portion protruded into a feeding chamber 24 through a feeding port 25 in the waveguide 21. Further, it is ensured that the gap between the feeding port 25 and the metal portion of the vertical shaft element 22b has a length equal to or more than 5 mm.
[0123] In the heating cooker having the structure illustrated in Fig. 9, the flat-plate element 22a is placed in such a way as to radiate microwaves downwardly at the predetermined angle θ and, therefore, the radiated microwaves are partially reflected by the boundary surface of food 15 which is an object to be heated, and these reflected waves are reflected in directions deviated from the antenna, by an amount corresponding to the angle θ with respect to the vertical direction. This largely inhibits waves reflected by the object to be heated from being received by the antenna formed by the feeding portion, which reduces the reflected-wave components which are returned to the magnetron 16 through the waveguide 21. As a result thereof, with the heating cooker having the structure illustrated in Fig. 9, it is possible to prevent temperature rises in the magnetron 16 due to its self-heat generation, which enables elongation of the life of the magnetron 16, elimination of the necessity of power down settings for the magnetron 16, and improvement of the output efficiency.
[0124] As described above, in the heating cooker according to the third embodiment, the feeding portion 22 is provided with the flat-plate element 22a adapted to radiate microwaves downwardly at the predetermined angle θ, which can largely reduce reflected-wave components returned to the magnetron 16, due to the reception of the reflected waves by the antenna. As a result thereof, the heating cooker according to the third embodiment is capable of preventing temperature rises in the magnetron 16 due to its self-heat generation and thus is capable of exerting substantially the same characteristics and functions as those of the structure of the first embodiment, thereby enabling elongation of the life of the magnetron 16, elimination of the necessity of power down settings for the magnetron 16, and improvement of the output efficiency.
[0125] As described above, in the microwave heating device according to the present invention, the flat-plate element is placed in such a way as to radiate microwaves downwardly at the predetermined angle θ through the coupling hole portion in the ceiling wall surface of the heating chamber, as described in each of the embodiments. Therefore, waves reflected by the boundary surface of the object to be heated, out of the radiated microwaves, are reflected in directions deviated from the antenna by an amount corresponding to the angle θ with respect to the vertical direction. This inhibits the reflected waves from being received by the antenna, again, which largely reduces the reflected-wave components which are returned to the microwave generating portion. As a result thereof, the microwave heating device according to the present invention is enabled to prevent temperature rises in the microwave generating portion due to its self-heat generation. Further, the microwave heating device according to the present invention enables elongation of the life of the microwave generating portion, elimination of the necessity of power down settings for the microwave generating portion, and significant improvement of the output efficiency, even with the compact structure having the microwave generating portion provided above the heating chamber.
Industrial Applicability
[0126] The present invention is effective in heating cookers for inductively heating food through radiation of microwaves, particularly heating cookers using other heating through ovens, grills, superheated steams and the like. Furthermore, the present invention is also effective in microwave heating devices for various industrial applications, such as drying apparatuses, ceramic-art heating devices, garbage disposers, semiconductor fabrication apparatuses, and the like.
Reference Signs List
1. A microwave heating device comprising:
a heating chamber which is adapted to house an object to be heated and to direct microwaves to the object to be heated for performing high-frequency heating;
a microwave feeding chamber formed to protrude upwardly from a ceiling wall surface of the heating chamber;
a microwave generating portion adapted to create microwaves for performing high-frequency heating on the object to be heated, within the heating chamber;
a waveguide adapted to couple the feeding chamber to the microwave generating portion for propagating microwaves; and
a feeding portion including a vertical shaft element provided in a vertical direction by penetrating through a coupling hole formed in portions at which the feeding chamber and the waveguide are bonded to each other, and a flat-plate element having a radiation surface for radiating microwaves within the heating chamber, the flat-plate element being bonded to the vertical shaft element,
wherein at least a partial radiation surface, out of the microwave radiation surface of the flat-plate element, is placed to be inclined at a predetermined angle θ with respect to a horizontal direction.
2. The microwave heating device according to Claim 1, wherein
at least a partial radiation surface, out of the microwave radiation surface of the flat-plate element, is folded at the predetermined angle θ with respect to the horizontal direction, and the radiation surface folded at the predetermined angle θ is made to have an area which occupies 1/2 or more of the entire radiation surface of the flat-plate element.
at least a partial radiation surface, out of the microwave radiation surface of the flat-plate element, is folded at the predetermined angle θ with respect to the horizontal direction, and the radiation surface folded at the predetermined angle θ is made to have an area which occupies 1/2 or more of the entire radiation surface of the flat-plate element.
3. The microwave heating device according to Claim 1 or 2, further comprising a high-temperature
heating portion adapted to perform heating on the object to be heated, through at
least one of radiant heat and convection heat, at the same time as high-frequency
heating, the microwave generating portion and the waveguide being placed above the
heating chamber,
wherein the waveguide includes a propagation path bent orthogonally to have a horizontal portion and a vertical portion, the microwave generating portion is horizontally connected to the vertical portion, the feeding chamber provided in the ceiling wall surface of the heating chamber is coupled to the horizontal portion through a coupling hole, and the waveguide and the microwave generating portion are both placed to be spaced apart from the heating chamber.
wherein the waveguide includes a propagation path bent orthogonally to have a horizontal portion and a vertical portion, the microwave generating portion is horizontally connected to the vertical portion, the feeding chamber provided in the ceiling wall surface of the heating chamber is coupled to the horizontal portion through a coupling hole, and the waveguide and the microwave generating portion are both placed to be spaced apart from the heating chamber.
4. The microwave heating device according to any one of Claims 1 to 3, wherein, assuming
that Ly is a total length of the radiation surface inclined at the predetermined angle
θ with respect to a horizontal plane, in the direction of the inclination, out of
the entire radiation surface of the flat-plate element, and H is a height from the
object to be heated within the heating chamber to a position in the radiation surface
of the flat-plate element which is coincident with the position where the flat-plate
element is bonded to the vertical shaft element, the inclination angle θrad of the
inclined radiation surface is set to be an angle which is larger than Ly/2/H but is
smaller than Ly/ H.
5. The microwave heating device according to any one of Claims 1 to 4, wherein the flat-plate
element is formed from a flat plate with a substantially circular shape with a diameter
of about 62 mm.
6. The microwave heating device according to Claim 5, wherein the feeding portion is
adapted such that the vertical shaft element is bonded to the flat-plate element at
a position deviated from a center of the disk plate, and the vertical shaft element
is rotated.
7. The microwave heating device according to Claim 5 or 6, wherein the flat-plate element
is formed by folding one radiation surface with respect to the other radiation surface,
by the predetermined angle θ, at a folding line on a straight line including a center
line of the disk plate.
REFERENCES CITED IN THE DESCRIPTION
This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.
Patent documents cited in the description