JP7650201B2 - Cooking equipment - Google Patents

Description

The present invention relates to a cooking device.

Patent Document 1 discloses an electric rice cooker (cooking appliance) that uses multiple coils to inductively heat a pot housed within the main body. Patent Document 2 discloses an induction heating cooker that uses multiple coils to inductively heat a pot placed on a flat heating surface. Patent Document 2 also discloses a cooking method in which two of multiple coils spaced apart in the circumferential direction are grouped together as a coil group, and the multiple coil groups are individually controlled.

JP 2004-242912 A JP 2013-149470 A

In the cookers of Patent Documents 1 and 2, coils of the same shape are simply arranged in a line around the periphery of the pot, so the flow direction of convection currents in the pot caused by induction heating is only in the radial direction of the pot. Furthermore, when two opposing coils are controlled as a set of coils as in Reference 2, the two convection currents caused by the two coils may cancel each other out, which may actually reduce the efficiency of stirring the food. Therefore, there is room for improvement in the cookers of References 1 and 2 in terms of the efficiency of stirring the food caused by the convection currents generated in the pot.

The objective of the present invention is to provide a cooking device that can improve the efficiency of stirring food by using convection currents generated in the pot through induction heating by a coil.

One aspect of the present invention provides a cooking utensil comprising a bottomed cylindrical pot having a bottom wall portion, a cylindrical peripheral wall portion, and a continuous portion that is connected to the bottom wall portion and the peripheral wall portion, and a heating portion disposed at a distance on the outer surface side of the pot, the heating portion having an inner coil disposed closer to the axis of the pot than the peripheral wall portion so as to inductively heat at least the bottom wall portion other than the peripheral wall portion, and an outer coil disposed outside the inner coil with respect to the axis so as to inductively heat at least the peripheral wall portion, the inner coil having a different shape from the outer coil.

It has an inner coil and an outer coil with different shapes and arrangements, and the inner coil inductively heats at least the bottom wall portion other than the peripheral wall portion, while the outer coil inductively heats at least the peripheral wall portion. The flow direction of the convection current generated by the induction heating by the inner coil is along the axis of the pot, and the flow direction of the convection current generated by the induction heating by the outer coil is along the radial direction of the pot. In this way, the two types of convection currents with different flow directions do not cancel each other out, but diverge after colliding. As a result, the efficiency of stirring the food cooked by the convection current generated in the pot by the induction heating by the coils can be improved.

The bottom wall portion has a central portion and an outer peripheral portion that is connected to the outside of the central portion, the inner coil is arranged to correspond to the area that spans from the central portion to the continuous portion, and the outer coil is arranged to correspond to the area that spans from the outer peripheral portion to the peripheral wall portion.

The inner coil extends from the center of the bottom wall to the continuous section, and the outer coil extends from the outer periphery of the bottom wall to the peripheral wall. This prevents unheated areas from occurring in the radial direction of the pot, and ensures that two types of convection with different flow directions are generated.

The shape of the pot when viewed from the direction in which the axis extends is circular, the inner coil when viewed from the direction in which the axis extends is non-circular with a long axis extending radially of the pot and a short axis extending circumferentially of the pot, and the outer coil when viewed from the direction in which the axis extends is non-circular with a long axis extending circumferentially of the pot and a short axis extending radially of the pot.

The inner coil is non-circular with a long axis extending radially of the pot and a short axis extending circumferentially of the pot, and the outer coil is non-circular with a long axis extending circumferentially of the pot and a short axis extending radially of the pot. In this way, the inner coil with a shorter circumferential dimension is placed inside the pot, and the outer coil with a longer circumferential dimension is placed outside the pot, so that the inner coil and outer coil can be arranged so as to be closely packed on the outer surface side of the pot. This makes it possible to prevent unheated areas from occurring in the pot.

The dimension of the outer coil in the direction along which the long axis extends is greater than the dimension of the inner coil in the direction along which the short axis extends.

The dimension of the long axis of the outer coil is larger than the dimension of the short axis of the inner coil. This allows the outer coil to be placed on a peripheral wall portion that has a larger diameter than the bottom wall portion, preventing unheated areas from occurring on the peripheral wall portion of the pot.

The inner coil has an inner portion that is disposed on the axial side and extends in the circumferential direction of the pot, and a pair of extension portions that extend radially outward from both ends of the inner portion and are inclined toward each other.

The inner coil has an inner portion that extends circumferentially around the pot, and a pair of extending portions that extend radially outward from both ends of the inner portion. In the case of the inner portion that extends circumferentially, the winding angle of the winding is gentler, making it possible to increase the wiring density per unit area. This improves the heating efficiency of the central portion of the pot by the inner coil.

The inner coil and the outer coil are arranged on opposite sides of the pot across the axis, and multiple coils are arranged side by side around the axis.

The inner coil and outer coil are placed on opposite sides of the pot, and multiple coils are arranged side by side around the axis. This allows the inner coils and outer coils to be arranged closely together on the outer surface of the pot, ensuring induction heating of the entire pot.

The inner coil and the outer coil, which are located in opposing positions on the pot, are grouped together as a set of coils, and a control unit is provided to individually control the multiple sets of coil groups.

The inner and outer coils, located on opposite sides of the pot, are grouped together, and the control unit controls the multiple groups of coils individually, allowing food to be cooked while being efficiently stirred by two types of convection.

The cooking device of the present invention can improve the efficiency of stirring the food by using convection currents generated in the pot through induction heating by the coil.

1 is a schematic cross-sectional view showing a cooking device according to a first embodiment of the present invention. FIG. 4 is a block diagram showing the arrangement of the coil relative to the pot and the configuration of the control unit. FIG. 3 is a front view of the inner coil of FIG. 2 . FIG. 3 is a front view of the outer coil of FIG. 2 . FIG. 4 is a schematic cross-sectional view showing convection when current is applied to the inner coil and the outer coil. FIG. 5B is a schematic diagram of the convection in FIG. 5A as viewed from above. FIG. 13 is a schematic cross-sectional view showing convection in a cooker in which the same coils are arranged in the circumferential direction. FIG. 6B is a schematic diagram of the convection in FIG. 6A as viewed from above. FIG. 11 is a bottom view showing the arrangement of coils in the second embodiment. FIG. 8 is a front view of the outer coil of FIG. FIG. 13 is a bottom view showing the arrangement of coils in the first modified example. FIG. 11 is a bottom view showing the arrangement of coils in a second modified example.

The following describes an embodiment of the present invention with reference to the drawings.

First Embodiment
1 shows a rice cooker 1, which is one of the cooking appliances according to the first embodiment of the present invention. The rice cooker 1 includes a rice cooker pot 10, a rice cooker body 20 that houses the rice cooker pot 10, and a lid body 30 that is attached to the rice cooker body 20 so as to be able to open and close. The rice cooker 1 is a multi-coil type in which multiple coils 51, 55 are arranged in the rice cooker body 20 as the heating section 50 of the rice cooker pot 10. In this embodiment, two types of coils 51, 55 with different shapes are arranged at different radial positions of the rice cooker pot 10, thereby improving the stirring efficiency of rice (cooked food) by convection generated in the rice cooker pot 10.

First, we will provide an overview of the rice cooker 1.

Referring to FIG. 1, the rice cooker pot 10 is cylindrical with a bottom, having a bottom wall portion 11, a cylindrical peripheral wall portion 12, and a continuous portion 13 that connects the bottom wall portion 11 and the peripheral wall portion 12, and is circular when viewed in the direction in which the axis A of the rice cooker pot 10 extends. This rice cooker pot 10 is made of a magnetic material and is formed by pressing or casting.

Referring to Figures 1 and 2, the bottom wall portion 11 has a central portion 11a and an outer peripheral portion 11b that is connected to the outside of the central portion 11a.

The central portion 11a is circular when viewed in the direction in which the axis A extends, has its center located on the axis A, and extends flat in the horizontal direction. The flat central portion 11a is not limited to a configuration that extends flat in the strict geometric sense, and may be somewhat curved as long as the convection currents generated by heating flow along the axis A.

The outer periphery 11b is annular when viewed from the direction in which the axis A extends, and is inclined upward from the inside to the outside in the radial direction. In this embodiment, the outer periphery 11b has a curved shape that bulges slightly downward, but it may have an inverted cone shape that extends linearly from the bottom end to the top end. The inclination angle of the outer periphery 11b with respect to the central portion 11a is 5 degrees or more and 30 degrees or less. The inclination angle of the curved outer periphery 11b is defined as the angle at which a virtual line (not shown) connecting the bottom end and the top end of the outer periphery 11b is inclined with respect to the central portion 11a. In addition, a slightly bulging curved shape means that the curvature is approximating a straight line.

The peripheral wall portion 12 is cylindrical in shape corresponding to the outer shape of the bottom wall portion 11, and has an expansion portion 12a and an upper portion 12b that is connected to the upper end of the expansion portion 12a.

The expanding portion 12a is cylindrical with a diameter that gradually increases from the bottom end to the top end. In this embodiment, the expanding portion 12a has a curved shape that bulges outward in the radial direction, but it may also be an inverted conical cylindrical shape that extends linearly from the bottom end to the top end. The inclination angle of the expanding portion 12a with respect to the central portion 11a is 60 degrees or more and 90 degrees or less. The inclination angle of the curved expanding portion 12a is defined as the angle at which a virtual line (not shown) connecting the bottom end and the top end of the expanding portion 12a is inclined with respect to the central portion 11a. The top end of the expanding portion 12a is higher than the maximum rice cooking capacity position 14a of the water level line 14 described later.

The upper portion 12b is cylindrical with a uniform diameter and has a flange portion at the upper end that protrudes radially outward. However, the upper portion 12b may be an inverted conical cylinder whose diameter gradually increases from the bottom to the top, or may be a curved surface that bulges slightly radially outward.

The continuous portion 13 is cylindrical with a diameter that gradually increases from the bottom to the top, with the inner periphery continuing to the outer periphery 11b of the bottom wall portion 11 and the outer periphery continuing to the expanding portion 12a. The cross-sectional shape of the continuous portion 13 is an arc that bulges downward and radially outward.

A water level line 14 is provided on the inner surface of the rice cooker pot 10 configured in this manner. The position 14a of the maximum rice cooking capacity (5 cups in this embodiment) is preferably set at a position between 50% (1/2) and 66% (2/3) of the total height of the rice cooker pot 10, and in this embodiment is set at a position of 60% (3/5).

Referring to FIG. 1, the rice cooker main body 20 has an exterior body 21 with a hinge connection shaft 22 on the back portion located on the right side in FIG. 1. A circular opening is formed on the top surface of the exterior body 21, and a storage section 23 that detachably stores the rice cooker pot 10 is formed below this opening. The storage section 23 is a bottomed tube that includes a cylindrical metal inner body 24 that corresponds to the shape of the rice cooker pot 10 in a plan view, and a saucer-shaped protective frame 25 made of resin (a non-conductive material) that covers the lower end of the inner body 24. By placing the rice cooker pot 10 in this storage section 23, the axis of the protective frame 25 and the axis A of the rice cooker pot 10 coincide with each other.

The inner and outer shapes of the protective frame 25 correspond to the shape of the rice cooker pot 10. Specifically, the protective frame 25 has a bottom portion 25a shaped to fit the bottom wall portion 11 of the rice cooker pot 10, an outer peripheral portion 25b shaped to fit the expansion portion 12a of the rice cooker pot 10, and a continuous portion 25c shaped to fit the continuous portion 13 of the rice cooker pot 10.

Continuing to refer to FIG. 1, a heating section 50 for induction heating the rice cooker pot 10 is provided inside the exterior body 21. The heating section 50 consists of two types of coils 51, 55. These coils 51, 55 are attached to the outer surface of the protective frame 25 on the exterior body 21 side so that they are spaced apart from each other on the outer surface side of the rice cooker pot 10. Specifically, a holder (not shown) holding a ferrite core is disposed on the outside of the coils 51, 55, and the coils 51, 55 are held between this holder and the protective frame 25. The specific configuration of the coils 51, 55 will be described in detail later.

The lid body 30 is rotatably attached to the hinge connection shaft 22 of the exterior body 21. The lid body 30 has a heat sink 31 on the inner side (lower side in FIG. 1) facing the rice cooker pot 10. An inner lid 32 that closes the upper end opening of the rice cooker pot 10 is attached to the lower surface of the heat sink 31. A lid heater 33 is disposed on the upper surface of the heat sink 31, which heats the inner lid 32 via the heat sink 31 and evaporates dew adhering to the inner lid 32. The lid body 30 also has an exhaust passage 34 formed therein for discharging steam from within the rice cooker pot 10 to the outside.

A control board 41 is disposed via a holder 40 on the front side of the rice cooker main body 20, which is located on the left side in FIG. 1. Referring to FIG. 2, the control board 41 is provided with a control unit 42 that controls the electrical components, and an inverter circuit 43 and a switching unit 44 for supplying power to the heating unit 50. However, the control unit 42, inverter circuit 43, and switching unit 44 may be provided separately on two or three control boards.

The control unit 42 is composed of a single or multiple microcomputers and other electronic devices. The control unit 42 has a storage unit (memory) 42a and a timing unit (timer) 42b. The storage unit 42a stores programs for executing the rice cooking process and the warming process, as well as settings (temperature and time) used in the programs. The timing unit 42b measures the time for the rice cooking process and the warming process.

In the rice cooking process, the control unit 42 executes the preheating process, the middle-heating process (heating process), the boiling maintenance process, the cooking process, and the steaming process in this order based on the detection results of the two temperature sensors 45A and 45B (see Figure 1), and cooks the rice in the rice cooker pot 10. In the warming process, the control unit 42 adjusts the temperature of the cooked rice (rice cooker pot 10) to a set temperature based on the detection results of the two temperature sensors 45A and 45B. The temperature sensor 45A is a pot sensor that detects the temperature of the rice cooker pot 10, and in this embodiment is a side sensor that detects the temperature of the peripheral wall portion 12 (expanded portion 12a). The temperature sensor 45B is a lid sensor that detects the temperature inside the rice cooker pot 10 via the heat sink 31.

The inverter circuit 43 is electrically connected to the control unit 42 and supplies power to the coils 51 and 55. The inverter circuit 43 includes a number of power transistors (e.g., IGBTs) provided in accordance with the number of coils 51 and 55.

The switching unit 44 is electrically connected to the control unit 42 and the inverter circuit 43. The switching unit 44 is composed of a number of switches (e.g., relays) provided according to the number of coils 51, 55, and switches the connection state between the inverter circuit 43 and the multiple coils 51, 55 according to a command from the control unit 42. Specifically, the switching unit 44 switches the connection state so that a high-frequency current is applied to one or more predetermined coils among the multiple coils 51, 55, and current is cut off to the remaining coils.

Next, we will explain in detail the coils 51 and 55 that make up the heating unit 50.

Referring to Figures 1 and 2, the heating unit 50 has an inner coil 51 and an outer coil 55 that are different in shape, and when a high-frequency current is passed through them, eddy currents are generated, which inductively heats the rice cooker pot 10.

The inner coils 51 and the outer coils 55 are each arranged in multiples around the axis A. In this embodiment, three of each of the inner coils 51 and the outer coils 55 are arranged. The inner coils 51 adjacent to each other in the circumferential direction are arranged at intervals, and the outer coils 55 adjacent to each other in the circumferential direction are arranged at intervals. Furthermore, the inner coils 51 and the outer coils 55 adjacent to each other in the radial direction are arranged at intervals. These intervals are the distance at which the heating areas of the rice cooker 10 by the adjacent coils 51, 55 partially overlap.

The inner coil 51 and the outer coil 55 are formed by winding multiple windings. In this embodiment, they are formed so that the density of the windings per unit area is uniform. As a result, as shown in FIG. 3, when viewed from the front of the inner coil 51, the inner circumference 51a and the outer circumference 51b extend parallel to each other, and the width of the inner coil 51 is generally uniform around the entire circumference. Also, as shown in FIG. 4, when viewed from the front of the outer coil 55, the inner circumference 55a and the outer circumference 55b extend parallel to each other, and the width of the outer coil 55 is generally uniform around the entire circumference.

Referring to Figures 1 and 2, the inner coil 51 is arranged on the axis A side of the peripheral wall portion 12 so as to inductively heat the bottom wall portion 11 and the continuous portion 13 of the rice cooker pot 10 other than the peripheral wall portion 12. More specifically, the inner coil 51 is arranged on the outer surface of the bottom portion 25a and the continuous portion 25c of the protective frame 25 so as to correspond to the area spanning from the central portion 11a of the bottom wall portion 11 to the continuous portion 13 of the rice cooker pot 10.

As shown most clearly in FIG. 2, when viewed from the direction of axis A of the rice cooker pot 10, the inner coil 51 has a non-circular shape with a long axis La1 extending radially of the rice cooker pot 10 and a short axis Sa1 extending circumferentially of the rice cooker pot 10. The inner coil 51 of this embodiment has a roughly kite shape with the short axis Sa1 positioned closer to the axis A than the center of the long axis La1.

Referring to FIG. 3, the dimension of the inner coil 51 in the direction in which the major axis La1 extends is SL1, and the dimension in the direction in which the minor axis Sa1 extends is SS1. Also referring to FIG. 2, the dimension SL1 on the major axis La1 side is larger than the radius r1 of the bottom wall portion 11 of the rice cooker pot 10, and smaller than the outer radius r2 of the continuous portion 13. For example, if the radius r1 of the bottom wall portion 11 is 65 mm and the radius r2 of the continuous portion 13 is 85 mm, the dimension SL1 on the major axis La1 side of the inner coil 51 is set to 75 mm. Also, the dimension SS1 on the minor axis Sa1 side of the inner coil 51 is set to 65 mm.

More specifically, as shown in Figures 2 and 3, the inner coil 51 has an inner portion 52 that is disposed on the axis A side of the rice cooker pot 10, and an outer portion 53 that extends from the inner portion 52 radially outward of the rice cooker pot 10. The inner portion 52 and the outer portion 53 are connected via a pair of curved portions 54 that are curved at a predetermined curvature.

The inner portion 52 is composed of a pair of extending portions 52a and one curved portion 52b, and extends in the circumferential direction of the rice cooker pot 10 as a whole. The outer portion 53 is composed of a pair of extending portions 53a and one curved portion 53b, and extends in the radial direction of the rice cooker pot 10 as a whole. The extending portion 52a of the inner portion 52 is shorter than the extending portion 53a of the outer portion 53. The pair of extending portions 52a of the inner portion 52 are connected to the outer portion 53 via the curved portions 54, and are inclined in a direction approaching each other. The pair of extending portions 53a of the outer portion 53 are connected to the inner portion 52 via the curved portions 54, and are inclined in a direction approaching each other.

As shown most clearly in FIG. 3, the angle α between the pair of extensions 52a of the inner part 52 is greater than the angle β between the pair of extensions 53a of the outer part 53. The angle between the extensions 52a of the inner part 52 and the extensions 53a of the outer part 53 is smaller than the angle α and larger than the angle β. These angles depend on the shape of the jig that forms the inner coil 51. The jig has an outer periphery that is the same shape as the inner periphery 51a of the inner coil 51, and the inner coil 51 is formed by winding the wire around this jig.

In the case of the inner part 52 extending in the circumferential direction of the rice cooker pot 10, the winding angle of the winding is gentle, making it easy to ensure the winding density per unit area constituting the inner coil 51. Furthermore, in the rice cooker 1 of this embodiment, since a side sensor 45A is used to detect the temperature of the rice cooker pot 10, the inner coil 51 can be brought as close as possible to the axis A. This improves the heating efficiency of the central part of the rice cooker pot 10 by the inner coil 51.

When three inner coils 51 are arranged as in this embodiment, the angle α of the inner portion 52 is preferably set to 100 degrees or more and 140 degrees or less. If the angle α is made too small, the interval between adjacent inner coils 51 will be wide, making it easier for non-heated areas to occur in the bottom wall portion 11 of the rice cooker pot 10. If the angle α is made too large, and the adjacent inner coils 51 are arranged so as not to overlap, the curved portion 52b will move away from the axis A, making it easier for non-heated areas to occur in the center of the bottom wall portion 11 of the rice cooker pot 10. To prevent these inconveniences, it is preferable to set the angle α of the inner portion 52 within the above-specified range, and in this embodiment it is set to 120 degrees.

When three coils 51, 55 are arranged as in this embodiment, the angle β of the outer portion 53 is preferably set to 30 degrees or more and 70 degrees or less. If the angle β is made too small, the interval between the inner coil 51 and the outer coil 55 adjacent to each other in the circumferential direction of the rice cooker pot 10 becomes wider, and non-heated areas are likely to occur on the bottom wall portion 11 (outer peripheral portion 11b) of the rice cooker pot 10. If the angle β is made too large, if the adjacent inner coil 51 and the outer coil 55 are arranged so as not to overlap, the dimension on the long axis La1 side must be shortened, and non-heated areas are likely to occur on the bottom wall portion 11 of the rice cooker pot 10. To prevent these inconveniences, the angle β of the outer portion 53 is preferably set within the above-specified range, and is set to 60 degrees in this embodiment.

Referring to Figures 1 and 2, the outer coil 55 is positioned radially outward of the inner coil 51 with respect to the axis A so as to inductively heat the entire rice cooker pot 10 except for the central portion 11a of the bottom wall portion 11. More specifically, the outer coil 55 is positioned on the outer surface of the protective frame 25 from the bottom portion 25a to the outer peripheral portion 25b so as to correspond to the area of the rice cooker pot 10 that spans from the outer peripheral portion 11b of the bottom wall portion 11 to the expanded portion 12a of the peripheral wall portion 12.

As shown most clearly in FIG. 2, when viewed from the direction of axis A of the rice cooker pot 10, the outer coil 55 has a non-circular shape with a major axis La2 extending circumferentially of the rice cooker pot 10 and a minor axis Sa2 extending radially of the rice cooker pot 10. Referring to FIG. 4, the outer coil 55 of this embodiment has an elliptical shape with the minor axis Sa2 located in the center of the major axis La2. The shape of this outer coil 55, like the inner coil 51, depends on the shape of the jig that forms the outer coil 55.

More specifically, the outer coil 55 has a pair of large diameter sections 56 with a small curvature and a pair of small diameter sections 57 with a large curvature. The pair of large diameter sections 56 face each other in the direction in which the minor axis Sa2 extends. The pair of small diameter sections 57 face each other in the direction in which the major axis La2 extends and are connected to each of the pair of large diameter sections 56.

Continuing to refer to FIG. 4, the dimension of the outer coil 55 in the direction in which the major axis La2 extends is SL2. Referring to both FIG. 2 and FIG. 3, the dimension SL2 on the major axis La2 side is greater than the dimension SS1 on the minor axis Sa1 side of the inner coil 51. For example, as described above, if the dimension SS1 on the minor axis Sa1 side of the inner coil 51 is 65 mm, the dimension SL2 on the major axis La2 side of the outer coil 55 is set to 130 mm.

More specifically, the dimension SL2 on the long axis La2 side of the outer coil 55 is set based on the angle range around the axis A for induction heating the rice cooker pot 10. Considering the productivity of the outer coil 55, it is preferable to form the outer coil 55 with a dimension SL2 that creates an angle range of 90 degrees relative to the rice cooker pot 10. Considering the heating properties of the rice cooker pot 10, it is preferable to form the outer coil 55 with a dimension SL2 that creates an angle range of 120 degrees relative to the rice cooker pot 10. In this embodiment, the productivity of the outer coil 55 is prioritized, and the outer coil 55 is formed with a dimension SL2 that creates an angle range of 90 degrees relative to the rice cooker pot 10.

The dimension of the outer coil 55 in the direction in which the minor axis Sa2 extends is SS2. With reference to Figures 2 and 4, the dimension SS2 on the minor axis Sa2 side is set based on the radial creepage distance to the rice cooker pot 10. For example, in the case of a rice cooker pot 10 in which the radius r3 of the central portion 11a of the bottom wall portion 11 is 45 mm and the outer radius r3 of the expanded portion 12a of the peripheral wall portion 12 is 97.5 mm, the dimension SS2 on the minor axis Sa2 side is set to 60 mm.

More specifically, as shown in FIG. 1, the dimension SS2 of the outer coil 55 is set by first determining the highest position of the outer coil 55 relative to the rice cooker pot 10, and then based on the required distance to the lowest position. The highest position of the outer coil 55 is preferably set at a position between 20% (1/5) and 33% (1/3) of the total height of the rice cooker pot 10, and in this embodiment, it is set at a position of 25% (1/4). Here, a height position of 25% of the total height of the rice cooker pot 10 corresponds to a position of 40% of the maximum rice cooking capacity (i.e., the height of the maximum water level 14a). On the other hand, the lowest position of the outer coil 55 is located within the outer periphery 11b of the bottom wall portion 11. This prevents the gap between the outer coil 55 and the inner coil 51 from becoming excessively wide, ensuring a heating area.

The inner coil 51 and the outer coil 55 thus configured are arranged in groups of three around the axis A of the rice cooker pot 10, as shown in FIG. 2. In the following description, the three inner coils may be referred to as 51A, 51B, and 51C, and the three outer coils may be referred to as 55A, 55B, and 55C.

Continuing to refer to FIG. 2, the control unit 42 uses the inverter circuit 43 and the switching unit 44 to individually control the three coil groups, which are the inner coil 51A and the outer coil 55A, the inner coil 51B and the outer coil 55B, and the inner coil 51C and the outer coil 55C, located at opposing positions on the rice cooker pot 10. The pair of inner coil 51 and outer coil 55 is attached to the outer surface of the protective frame 25 so that they are positioned at opposing positions on the rice cooker pot 10 with the axis A in between. The centroids of each pair of inner coil 51 and outer coil 55 are located on a reference line (not shown) extending radially of the rice cooker pot 10.

The control unit 42 repeatedly performs a current mode in which a high-frequency current is applied to one of the multiple coil groups and current is cut off to the remaining coils. Specifically, the control unit 42 repeatedly performs a first current mode in which a high-frequency current is applied to coils 51A and 55A and current is cut off to coils 51B, 51C, 55B, and 55C, a second current mode in which a high-frequency current is applied to coils 51B and 55B and current is cut off to coils 51A, 51C, 55A, and 55C, and a third current mode in which a high-frequency current is applied to coils 51C and 55C and current is cut off to coils 51A, 51B, 55A, and 55B.

Figures 5A and 5B show convection when the rice cooker pot 10 is induction heated by the inner coil 51 and outer coil 55 of this embodiment. Figures 6A and 6B show convection when the rice cooker pot 10 is induction heated by a different type of coil 60 from the present invention.

The coil 60 of the comparative example in Figure 6 has an elliptical shape when viewed from the opposite direction, and is arranged in the protective frame 25 so as to heat the area from the center 11a of the bottom wall 11 to the expanded portion 12a of the peripheral wall 12.

First, as shown in Figs. 6A and 6B, when high-frequency current is applied to the coil 60 of the comparative example, a portion of the circumference from the bottom wall 11 to the peripheral wall 12 of the rice cooker pot 10, more specifically, the angular range in which the coil 60 is arranged, is locally inductively heated. In the rice cooker pot 10, the water located near the area heated by the coil 60 is indirectly heated, and the water away from the heated area is not heated. Convection occurs in the rice cooker pot 10 due to the temperature difference between the heated water and the non-heated water, and when the temperature approaches the boiling temperature, the convection speed increases due to the air bubbles generated from the heated area. The convection generated by the heating by the coil 60 flows upward along the peripheral wall 12, then flows radially toward the center of the rice cooker pot 10 on the water surface and converges. The water then flows radially toward the position opposite the coil 60.

Referring to FIG. 6B, when two opposing coils 60 are energized at the same time, the two convection currents from the two coils 60 cancel each other out. Also, referring to FIG. 6A, the rice located in the center of the bottom of the rice cooker pot 10 is pushed against the bottom wall 11 by the convection currents from above to below, so no stirring action is achieved.

On the other hand, when coils 51 and 55 with different shapes and arrangements are used as in this embodiment, the convection currents generated within the rice cooker pot 10 are as follows.

As shown in Figures 5A and 5B, when high-frequency current is applied to the inner coil 51A, the angle range in which the inner coil 51A is arranged among the bottom wall portion 11 and the continuous portion 13 of the rice cooker pot 10 is locally inductively heated. Also, when high-frequency current is applied to the outer coil 55A, the angle range in which the outer coil 55A is arranged among the ridge portion of the rice cooker pot 10, that is, the outer peripheral portion 11b, the continuous portion 13, and the expanded portion 12a, is locally inductively heated. In the rice cooker pot 10, water located near the inner heating area by the inner coil 51A is heated, and water away from the inner heating area is not heated. Also, water located near the outer heating area by the outer coil 55A is heated, and water away from the outer heating area is not heated. The same applies when current is applied to the coils 51B and 55B, and when current is applied to the coils 51C and 55C.

In the rice cooker pot 10, convection occurs due to the temperature difference between the heated water and the unheated water, and when the water approaches the boiling temperature, the convection flow speed increases with the generation of bubbles from the heated area. Referring to FIG. 5A, the flow direction of the convection current caused by heating by the inner coil 51 is along the axis A of the rice cooker pot 10 because the inner coil 51 is located inside the peripheral wall portion 12. The convection current caused by heating by the outer coil 55 flows upward along the peripheral wall portion 12, and then flows radially toward the center of the rice cooker pot 10 on the water surface and converges. It then flows radially toward a position opposite the outer coil 55. In this way, two types of coils 51 and 55 with different shapes and arrangements can be used to generate two types of convection currents with different flow directions.

Therefore, when a pair of inner coil 51 and outer coil 55 are energized at the same time, two types of convection currents with different flow directions are generated simultaneously inside rice cooker 10, as described above. As shown most clearly in Figure 5B, the two types of convection currents do not cancel each other out, but are separated after colliding.

By the convection current from the bottom to the top caused by the inner coil 51, the rice accumulated in the center of the bottom wall 11 of the rice cooker pot 10 is lifted toward the water surface. In addition, by the convection current along the peripheral wall 12 caused by the outer coil 55, the rice accumulated on the outer periphery 11b of the rice cooker pot 10 is lifted toward the water surface, and then it is swept sideways by the convection current toward the opposite position in the radial direction. After the two types of convection collide, the rice lifted by the convection current caused by the inner coil 51 is pushed toward the peripheral wall 12 by the convection current caused by the outer coil 55, and then flows along the peripheral wall 12 toward the outer coil 55.

As described above, in the rice cooker 1 of this embodiment, the rice at the bottom of the rice cooker pot 10 is lifted toward the water surface by convection caused by the inner coil 51, and then the rice is moved radially and circumferentially by convection caused by the outer coil 55. This dramatically improves the stirring efficiency of the rice.

The rice cooker 1 configured in this way has the following features:

It has an inner coil 51 and an outer coil 55 with different shapes and arrangements, and the inner coil 51 inductively heats at least the bottom wall 11 other than the peripheral wall 12, and the outer coil 55 inductively heats at least the peripheral wall 12. The flow direction of the convection current caused by heating by the inner coil 51 and the flow direction of the convection current caused by heating by the outer coil 55 are different, and these convection currents are diverged after colliding without canceling each other out. As a result, the stirring efficiency of rice (cooked food) by the convection generated in the rice cooker 10 can be improved.

The inner coil 51 extends from the central portion 11a of the bottom wall portion 11 to the continuous portion 13, and the outer coil 55 extends from the outer peripheral portion 11b of the bottom wall portion 11 to the peripheral wall portion 12. This prevents non-heated areas from occurring in the radial direction of the rice cooker pot 10, and ensures that two types of convection with different flow directions are generated.

The inner coil 51 is non-circular with a long axis La1 extending radially of the rice cooker pot 10 and a short axis Sa1 extending circumferentially of the rice cooker pot 10, and the outer coil 55 is non-circular with a long axis La2 extending circumferentially of the rice cooker pot 10 and a short axis Sa2 extending radially of the rice cooker pot 10. In this way, the inner coil 51 with the short circumferential dimension SS1 is arranged inside the rice cooker pot 10, and the outer coil 55 with the long circumferential dimension SL2 is arranged outside the rice cooker pot 10, so that the inner coil 51 and the outer coil 55 can be arranged so as to be spread out on the outer surface side of the rice cooker pot 10. This prevents unheated areas from being created in the rice cooker pot 10.

The dimension SL2 of the outer coil 55 on the long axis La2 side is greater than the dimension SS1 of the inner coil 51 on the short axis Sa1 side. This ensures a sufficient area for the outer coil 55 to be placed on the peripheral wall 12, which has a larger diameter than the bottom wall 11, preventing unheated areas from occurring on the peripheral wall 12 of the rice cooker pot 10.

The inner coil 51 has an inner portion 52 that extends circumferentially around the rice cooker pot 10, and a pair of extension portions 53a that extend radially outward from both ends of the inner portion 52. In the case of the inner portion 52 that extends circumferentially, the winding angle of the winding is gentler, making it possible to increase the wiring density per unit area. This improves the heating efficiency of the central portion of the rice cooker pot 10 by the inner coil 51.

The inner coil 51 and the outer coil 55 are arranged in opposing positions on the rice cooker pot 10, and multiple coils are arranged side by side around the axis A. This allows the inner coils 51 and the outer coils 55 to be arranged in a line on the outer surface of the rice cooker pot 10, so that the entire rice cooker pot 10 can be reliably induction heated.

The inner coil 51 and the outer coil 55, which are located in opposing positions on the rice cooker pot 10, are grouped together, and the control unit 42 controls the multiple groups of coils individually, so rice (food) can be cooked while being efficiently stirred by two types of convection.

Other embodiments and various modified examples of the present invention will be described below, but in these descriptions, points that are not specifically mentioned are the same as those in the first embodiment. In the drawings referred to below, elements that are the same as those in the first embodiment are given the same reference numerals.

Second Embodiment
7 shows the inner coil 51 and the outer coil 55 of the rice cooker 1 of the second embodiment. The rice cooker 1 of the second embodiment differs from the rice cooker 1 of the first embodiment in that one of a pair of large diameter portions 56 constituting the outer coil 55 (hereinafter referred to as large diameter portion 56A) is provided with a protruding portion 56a that protrudes toward the axis A of the rice cooker pot 10.

Referring to Figures 7 and 8, the protrusions 56a are provided to arrange the large diameter portions 56A along the extension portions 53a of each of the pair of inner coils 51 located radially inside the rice cooker pot 10, so as to make the gap between the outer coil 55 and the inner coil 51 uniform. Specifically, the large diameter portions 56A are connected to the pair of small diameter portions 57, respectively, and have a pair of extension portions 56b that are inclined so as to approach each other. The pair of extension portions 56b extend along the extension portions 53a of the inner coil 51, and are connected via the protrusions 56a that are curved at a predetermined curvature.

The angle γ between the pair of extensions 56b is set based on the angle between the extensions 53a of the inner coils 51 adjacent in the circumferential direction. In other words, the angle γ of the outer coil 55 is set based on the angle β of the inner coil 51. When three coils 51, 55 are arranged as in this embodiment, it is preferable to set the angle γ to 120 degrees or more and 180 degrees or less. If the angle γ is made too small, the interval between the inner coil 51 and the outer coil 55 adjacent in the circumferential direction of the rice cooker pot 10 becomes wider, making it easier for a non-heated area to occur on the bottom wall 11 of the rice cooker pot 10. If the angle γ is made too large, if the adjacent inner coil 51 and the outer coil 55 are arranged so as not to overlap, it is necessary to shorten the dimension on the short axis Sa2 side of the outer coil 55, making it easier for a non-heated area to occur on the bottom wall 11 of the rice cooker pot 10. To prevent these problems, it is preferable to set the angle γ of the outer coil 55 within the range specified above, and in this embodiment it is set to 170 degrees.

The rice cooker 1 of the second embodiment configured in this way can achieve the same effects and advantages as the first embodiment, and can also effectively prevent unheated areas from appearing in the rice cooker pot 1.

(Experimental Example)
In order to confirm the stirring efficiency by induction heating using coils 51, 55 with different shapes and arrangements, the inventors conducted experiments by preparing a rice cooker using the coils 51, 55 of the first embodiment shown in FIG. 5B and a rice cooker using the coil 60 of the comparative example shown in FIG. 6B.

In the first experiment, 1.5 cups of red colored cooked rice was placed in the rice cooker 10, and 0.5 cups of blue colored cooked rice was placed on top of it and cooked. The top surface of the cooked rice was photographed and the ratio of red and blue rice was analyzed using image processing, and the proportion of red rice was calculated as the stirring rate. As a result, the stirring rate was 43% when the coil 60 of the comparative example was used, while the stirring rate was 57% when the coils 51 and 55 of the first embodiment were used.

In the second experiment, normal rice was cooked and the Brix value (concentration of sweet components) of the cooked rice was measured. As a result, the Brix value when the coils 51 and 55 of the first embodiment were used was 24% higher than the Brix value when the coil 60 of the comparative example was used.

The above experimental results confirmed that the rice cooker 1 of this embodiment can cook rice with no unevenness and with an overall sweet and uniform finish, compared to the rice cooker of the comparative example.

The present invention is not limited to the configuration of the above embodiment, and various modifications are possible.

For example, the number of each of the inner coils 51 and the outer coils 55 is not limited to three, and four of each may be arranged as shown in Figures 9 and 10. Also, two of each of the inner coils 51 and the outer coils 55 may be arranged, or five or more of each may be arranged.

Referring to FIG. 9, in the first modified example, when viewed from the direction in which the axis A of the rice cooker pot 10 extends, four inner coils 51 each are shaped like a roughly right-angled isosceles triangle, and four outer coils 55 are shaped like an ellipse, and are arranged at intervals around the circumference of the rice cooker pot 10. The inner coil 51 has three apexes (corners), with the right-angled apex located on the axis A side of the rice cooker pot 10. The outer coils 55A to 55D are arranged in positions facing the inner coils 51A to 51D, respectively. With the rice cooker of the first modified example configured in this way, it is possible to obtain the same actions and effects as the first embodiment.

Referring to Figure 10, in the second modified example, when viewed from the direction in which the axis A of the rice cooker pot 10 extends, four of each of the roughly square inner coils 51 and the elliptical outer coils 55 are arranged at intervals around the circumference of the rice cooker pot 10. One of the four apexes (corners) of the inner coil 51 is arranged on the axis A side of the rice cooker pot 10. In the radial direction of the rice cooker pot 10, the outer coil 55A is arranged outside the inner coils 51C and 51D, the outer coil 55B is arranged outside the inner coils 51A and 51D, the outer coil 55C is arranged outside the inner coils 51A and 51B, and the outer coil 55D is arranged outside the inner coils 51B and 51C. In other words, coils 51A and 55A, 51B and 55B, 51C and 55C, and 51D and 55D are all arranged in opposing positions on the rice cooker pot 10, but the centroids of none of the pairs are located on the same reference line (not shown) that extends in the radial direction of the rice cooker pot 10. The rice cooker of the second modified example configured in this way can also achieve roughly the same actions and effects as the first embodiment.

The rice cooker 1 of the present invention may also be configured as follows:

For example, the inner coil 51 may be arranged in the protective frame 25 so as to inductively heat only the bottom wall portion 11 of the rice cooker pot 10, and the outer coil 55 may be arranged in the protective frame 25 so as to inductively heat only the peripheral wall portion 12 of the rice cooker pot 10.

The control unit 42 is not limited to a configuration in which the opposing inner coil 51 and outer coil 55 are controlled as a set of coil groups, but may control a plurality of inner coils 51 as a set of coil groups and a plurality of outer coils 55 as a set of coil groups individually. Also, the plurality of inner coils 51 and the plurality of outer coils 55 may each be controlled individually.

The temperature sensor 45A that detects the temperature of the rice cooker pot 10 is not limited to a side sensor, but may be a center sensor located in the center of the protective frame 25.

In the above embodiment, a rice cooker 1 has been used as an example, but it may also be a multi-cooker capable of various cooking methods such as baking, steaming, and deep-frying, and the present invention can be applied to any cooker that has multiple coils arranged on the outer surface of a cylindrical pot with a bottom, and similar functions and effects can be obtained.

1. Rice cooker (cooking appliance)
10 Rice cooker (pot)
11 Bottom wall portion 11a Central portion 11b Outer peripheral portion 12 Peripheral wall portion 12a Expanded portion 12b Upper portion 13 Continuous portion 14 Water level line 14a Maximum rice cooking capacity position 20 Rice cooker body 21 Exterior body 22 Hinge connection shaft 23 Storage portion 24 Inner body 25 Protective frame 25a Bottom portion 25b Outer peripheral portion 25c Continuous portion 30 Lid body 31 Heat sink 32 Inner lid 33 Lid heater 34 Exhaust passage 40 Holder 41 Control board 42 Control unit 42a Memory unit 42b Timer unit 43 Inverter circuit 44 Switching unit 45A, 45B Temperature sensor 50 Heating unit 51, 51A to 51C Inner coil 51a Inner peripheral portion 51b Outer periphery 52 Inner portion 52a Extension portion 52b Curved portion 53 Outer portion 53a Extension portion 53b Curved portion 54 Continuous portion 55, 55A to 55C Outer coil 55a Inner periphery 55b Outer periphery 56, 56A Large diameter portion 56a Protruding portion 56b Extension portion 57 Small diameter portion 60 Coil of comparative example La1 Long axis of inner coil Sa1 Short axis of inner coil La2 Long axis of outer coil Sa2 Short axis of outer coil A Axis of pot

Claims (4)

A bottomed cylindrical pot having a bottom wall portion, a cylindrical peripheral wall portion, and a continuous portion connecting the bottom wall portion and the peripheral wall portion;
and a heating portion disposed on an outer surface side of the pot at an interval.
The heating unit includes:
an inner coil disposed closer to the axis of the pot than the peripheral wall portion so as to induction heat at least the bottom wall portion other than the peripheral wall portion;
an outer coil disposed outside the inner coil with respect to the axis so as to inductively heat at least the peripheral wall portion,
The inner coil and the outer coil have different shapes ,
The bottom wall portion has a central portion and an outer periphery portion connected to an outer side of the central portion,
the inner coil is disposed to correspond to a region spanning from the central portion to the continuous portion,
The outer coil is disposed so as to correspond to a region spanning from the outer periphery to the peripheral wall . A bottomed cylindrical pot having a bottom wall portion, a cylindrical peripheral wall portion, and a continuous portion connecting the bottom wall portion and the peripheral wall portion;
and a heating portion disposed on an outer surface side of the pot at an interval.
The heating unit includes:
an inner coil disposed closer to the axis of the pot than the peripheral wall portion so as to induction heat at least the bottom wall portion other than the peripheral wall portion;
an outer coil disposed outside the inner coil with respect to the axis so as to inductively heat at least the peripheral wall portion,
The inner coil and the outer coil have different shapes ,
The shape of the pot as viewed in the direction in which the axis extends is circular,
When viewed from the direction in which the axis extends, the inner coil has a non-circular shape having a major axis extending in a radial direction of the pot and a minor axis extending in a circumferential direction of the pot,
A cooking appliance , wherein when viewed from the direction in which the axis extends, the outer coil has a non-circular shape having a major axis extending circumferentially of the pot and a minor axis extending radially of the pot . The cooking device according to claim 2 , wherein a dimension of the outer coil in a direction in which the major axis extends is greater than a dimension of the inner coil in a direction in which the minor axis extends. The inner coil is
an inner portion disposed on the axis line side and extending in a circumferential direction of the pot;
The cooking device according to claim 2 or 3 , further comprising a pair of extending portions extending radially outward from both ends of the inner portion of the pot and inclined toward each other.

Images