JP7812290B2 - rice cooker - Google Patents

Description

The present invention relates to a rice cooker.

Patent Document 1 describes a rice cooker that uses a steam temperature sensor and a lid temperature sensor as boiling temperature detection means. The steam temperature sensor is located in the gap between the inner lid and the lid underside member, and directly detects the temperature of steam that has flowed into the gap. The lid temperature sensor is located on the upper surface of the lid underside member, outside the gap, and indirectly detects the temperature within the gap via the lid underside member. The control unit determines whether the pot has boiled based on the detection results of only one of the steam temperature sensor and the lid temperature sensor, and performs the specified rice cooking process.

Japanese Patent Application Laid-Open No. 2000-14540

When determining whether the water in the pot is boiling based on the detection results of the steam temperature sensor, there is a delay in determining whether the water is boiling when the rice cooking capacity is large because it takes time for steam to be generated. When determining whether the water in the pot is boiling based on the detection results of the lid temperature sensor, there is a delay in determining whether the water is boiling when the rice cooking capacity is small because there is a lot of space inside the pot and heat transfer takes time. In other words, if the water is boiling based on the detection results of only one of the steam temperature sensor and the lid temperature sensor, there will be a delay in determining whether the water is boiling depending on the rice cooking capacity, and excessive heat will be applied to the rice. As a result, the rice will not be cooked properly.

The objective of the present invention is to provide a rice cooker that can accurately determine boiling in the pot regardless of the rice cooking capacity, and can cook rice in good condition.

During the heating process, the output from the heating unit is the same (full power) regardless of the rice cooking capacity. Therefore, the amount of heat per unit volume of rice and water in the rice cooker is greater when the rice cooking capacity is small than when it is large, and even at the same temperature, the amount of steam generated in the rice cooker is greater when the rice cooking capacity is small than when it is large. Also, the distance from the water surface to the lid in the rice cooker is shorter when the rice cooking capacity is large than when it is small. Therefore, heat transfer to the lid due to heating of the rice cooker is faster when the rice cooking capacity is large than when it is small. In other words, when the rice cooking capacity is small, more steam is generated in the rice cooker due to heating compared to when the rice cooking capacity is large, but heat transfer to the lid is slower. Also, when the rice cooking capacity is large, less steam is generated in the rice cooker due to heating compared to when the rice cooking capacity is small, but heat transfer to the lid is faster.

However, rice cookers are designed to automatically determine the rice cooking capacity while the rice cooking process is running, and the timing of this determination can be changed as needed. Therefore, when the step of quickly boiling the rice in the rice cooker is executed, the capacity determination may or may not have been completed.

Based on the above findings, the present invention makes it possible to accurately determine boiling in a rice cooker pot regardless of the rice cooking capacity, thereby enabling cooked rice to be cooked in good condition.

Specifically, one aspect of the present invention provides a rice cooker comprising: a cylindrical rice cooker pot with a bottom; a heating unit for heating the rice cooker pot; a lid for closing the opening of the rice cooker pot; an exhaust passage provided in the lid for exhausting steam from within the rice cooker pot to the outside; a steam temperature sensor having a first detection unit located within the exhaust passage for detecting the temperature of the steam within the exhaust passage; a lid temperature sensor having a second detection unit located outside the exhaust passage for detecting the temperature within the rice cooker pot through a partition wall closing the opening of the rice cooker pot; and a control unit that controls the heating unit to perform a rice cooking process including a heating step for raising the temperature inside the rice cooker pot to a boiling temperature, wherein the heating step includes a main heating step that ends when the temperature detected by either the steam temperature sensor or the lid temperature sensor reaches a predetermined transition temperature.

In this embodiment, when the rice cooking capacity is small, meaning that a large amount of steam is generated in the rice cooker pot and heat transfer to the lid is slow, the main heating step ends when the temperature detected by the steam temperature sensor reaches a specified transition temperature. On the other hand, when the rice cooking capacity is large, meaning that a small amount of steam is generated in the rice cooker pot and heat transfer to the lid is fast, the main heating step ends when the temperature detected by the lid temperature sensor reaches a specified transition temperature. In this way, this embodiment can accurately determine boiling in the rice cooker pot without delay, regardless of the rice cooking capacity, thereby optimizing the execution time of the heating step. This prevents excessive heat from being applied to the rice, allowing the rice to be cooked in good condition.

The transition temperatures include a first transition temperature for the steam temperature sensor and a second transition temperature for the lid temperature sensor, and the main heating step ends when either a first condition indicating that the temperature detected by the steam temperature sensor has reached the first transition temperature or a second condition indicating that the temperature detected by the lid temperature sensor has reached the second transition temperature is met.

With this configuration, when the rice cooking capacity is low, a large amount of steam is generated inside the rice cooker pot, but heat transfer to the lid is slow. Therefore, the temperature detected by the steam temperature sensor reaches the first transition temperature before the second condition is met, and the first condition is met, ending the main heating step. On the other hand, when the rice cooking capacity is high, a small amount of steam is generated inside the rice cooker pot, but heat transfer to the lid is fast. Therefore, the temperature detected by the lid temperature sensor reaches the second transition temperature before the first condition is met, and the second condition is met, ending the main heating step. In this way, boiling in the rice cooker pot can be determined with high accuracy and without delay regardless of the rice cooking capacity, and the execution time of the heating process can be optimized, allowing rice to be cooked in good condition.

The first transition temperature is higher than the second transition temperature.

The temperature detected by the steam temperature sensor, which directly detects the temperature of steam, becomes higher earlier than the temperature detected by the lid temperature sensor, which indirectly detects the temperature inside the rice cooker via a partition. Therefore, by setting the first transition temperature higher than the second transition temperature, boiling in the rice cooker can be determined with high accuracy from the detection results of either the steam temperature sensor or the lid temperature sensor.

The temperature-raising process includes an adjustment heating step for adjusting the heating time after the main heating step, and the control unit determines the rice cooking capacity based on the time from the start to the end of the main heating step, and sets the temperature or time at which the adjustment heating step ends to differ depending on the determined rice cooking capacity.

This configuration optimizes the overall execution time of the heating process, improving the balance between the execution times of the heating process and the boiling maintenance process. This allows the rice to be cooked in excellent condition.

The partition wall has an inner lid that closes the opening of the rice cooker pot and a heat sink that covers the inner lid, and the exhaust passage has an inlet section that is a space defined by the inner lid, the heat sink, and an endless sealing member that seals between the inner lid and the heat sink, and the first detection unit is located within the sealing member, and the second detection unit is located outside the sealing member so as to contact the heat sink or the inner lid.

With this configuration, the steam temperature sensor can reliably detect the temperature of the steam in the exhaust passage, and the lid temperature sensor can reliably detect the temperature inside the rice cooker via the heat sink and inner lid.

The rice cooker of the present invention can accurately determine boiling in the pot regardless of the rice cooking capacity, allowing rice to be cooked in good condition.

1 is a schematic diagram of a rice cooker according to an embodiment of the present invention. A block diagram showing the arrangement of induction heating coils and the configuration of a rice cooker. 10 is a time chart showing an example of a rice cooking process for a small amount of rice. FIG. 4 is an enlarged view of part IV in FIG. 3 . 10 is a time chart showing an example of a rice cooking process for a medium amount. FIG. 6 is an enlarged view of part VI in FIG. 5 . 10 is a time chart showing an example of a rice cooking process for a large amount of rice. FIG. 8 is an enlarged view of part VIII of FIG. 7 . 10 is a flowchart of a rice cooking process. 10 is a flowchart of the middle-pumping process shown in FIG. 9 .

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

Referring to Figures 1 and 2, the rice cooker 10 according to an embodiment of the present invention is a multi-coil type rice cooker that includes a rice cooker pot 15, a rice cooker main body 20, and a lid 30, and has multiple coils (heating units) 26, 27 arranged within the rice cooker main body 20.

The rice cooker 10 further includes a pot temperature sensor 50, a lid temperature sensor 51, a steam temperature sensor 52, and a control unit 60. The control unit 60 performs a rice cooking process that includes a preheating step, a medium-heating step (heating step), a boiling maintenance step (power control), and a steaming step, according to a predetermined program and based on the temperatures Tp, Tc, and Ts detected by the temperature sensors 50-52 (see Figures 3, 5, and 7).

In this embodiment, boiling in the rice cooker pot 15, which marks the end of the intermediate cooking process, is determined based on the temperatures Tc and Ts detected by the temperature sensors 51 and 52 and the preset transition temperatures Ty1 and Ty2, thereby preventing excessive heat from being applied to the rice and allowing the rice to be cooked in good condition.

The configuration of the rice cooker pot 15, rice cooker body 20, and lid 30 will be explained in detail below with reference to Figures 1 and 2.

The rice cooker pot 15 is cylindrical with a bottom, having a bottom wall 16, a cylindrical peripheral wall 17, and a continuous portion 18 that connects the bottom wall 16 and the peripheral wall 17, and is circular when viewed in the direction of the axis A of the rice cooker pot 15. The rice cooker pot 15 is made of a magnetic material and is formed by pressing or casting. However, as long as rice cooking is not hindered, the rice cooker pot 15 may be polygonal or hemispherical when viewed in the direction of the axis A, and does not have to be cylindrical with a bottom in the strict geometric sense.

The rice cooker main body 20 includes an exterior body 21 with a hinge connection shaft 22 on the back, located on the right side in Figure 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 15 is formed below this opening. The storage section 23 is tubular with a bottom and is composed of a cylindrical metal inner body 24 that corresponds to the shape of the rice cooker pot 15 in a plan view, and a saucer-shaped protective frame 25 made of resin (a non-conductive material) that covers the bottom end of the inner body 24. By placing the rice cooker pot 15 inside the storage section 23, the axis of the protective frame 25 and the axis A of the rice cooker pot 15 are aligned.

Coils 26 and 27 are arranged on the outer surface of the protective frame 25, i.e., between the exterior body 21 and the housing 23, as heating sections. The coils 26 and 27 are shaped as multiple windings wound in an elliptical ring shape, and when a high-frequency current is passed through them, eddy currents are generated, which inductively heat the rice cooker pot 15. The inner coil 26 is arranged in the protective frame 25 so as to inductively heat the bottom wall 16 and the continuous section 18 of the rice cooker pot 15. The outer coil 27 is arranged in the protective frame 25 so as to inductively heat the peripheral wall 17 and the continuous section 18 of the rice cooker pot 15.

In this embodiment, three coils 26, 27 are used, arranged at intervals in the circumferential direction around the axis A of the rice cooker pot 15. The multiple inner coils 26 and outer coils 27 are arranged at different circumferential positions, with one of the multiple inner coils 26 and one of the multiple outer coils 27 facing each other in the radial direction. However, the arrangement, number, shape, etc. of the coils can be changed as needed. Furthermore, the heating unit is not limited to coils, and may be a heating plate with a heater arranged inside a metal plate.

The lid 30 comprises a resin lid body 31 and lid cover 32, each rotatably attached to the hinge connection shaft 22 of the exterior body 21. It releasably covers the top of the rice cooker body 20 as well as the opening of the rice cooker pot 15. A heat sink 33 is attached to the inner surface of the lid body 31 facing the rice cooker pot 15 (the lower side in Figure 1), covering the opening of the rice cooker pot 15. A metal inner lid 34 is attached to the underside of the heat sink 33, and is equipped with a sealing member 35 that forms a seal with the inner periphery of the rice cooker pot 15. The inner lid 34 may be detachable from the lid 30, or may be permanently attached. A lid heater 36 is located on the upper surface of the heat sink 33, heating the inner lid 34 via the heat sink 33 and evaporating any dew adhering to the inner lid 34.

The lid 30 is formed with an exhaust passage 40 for discharging steam generated within the rice cooker 15 due to the pressure inside the rice cooker 15 that increases when heated. The exhaust passage 40 is composed of an inlet 41 that is spatially connected to the inside of the rice cooker 15, and a steam vent set 47 that is an outlet that is spatially connected to the inlet 41.

The inlet section 41 is defined by the heat sink 33, the inner lid 34, and an endless sealing member 44 that seals the space between the heat sink 33 and the inner lid 34. A vent hole 42 that forms the entrance to the exhaust passage 40 is provided approximately in the center of the inner lid 34. The heat sink 33 has a through opening 43 that includes the vent hole 42 when viewed from the direction of axis A. The sealing member 44 is attached to the edge of the opening 43 of the heat sink 33 and is pressed against the inner lid 34, surrounding the vent hole 42. This sealing member 44 divides the gap between the heat sink 33 and the inner lid 34 into the inlet section 41, through which steam can flow, and a closed space 45, through which steam cannot flow.

The steam vent set 47 is a duct located between the lid body 31 and the lid cover 32. The steam vent set 47 has a cylindrical connection portion 47a for connecting to the inlet portion 41, and this connection portion 47a is connected via a seal to the communication port 46 formed in the lid body 31. The steam vent set 47 has a cylindrical exhaust portion 47b that forms the outlet of the exhaust passage 40, and this exhaust portion 47b is located in the opening of the lid cover 32 and is open to the outside.

Steam generated inside the rice cooker pot 15 flows out through the vent 42, inlet 41, communication port 46, and steam port set 47. Steam does not flow into the closed space 45 located outside the seal member 44 in the gap between the heat sink 33 and the inner lid 34. This prevents the heat sink 33 from becoming soiled by steam.

The rice cooker 10 configured in this manner is equipped with a pot temperature sensor 50, a lid temperature sensor 51, and a steam temperature sensor 52 to detect the temperature inside the rice cooker pot 15. Also, a liquid crystal panel (display unit) 55 and multiple switches (input unit) 56 are attached to the front side, located on the left side in Figure 1.

The pot temperature sensor 50 is provided to detect the temperature inside the rice cooker pot 15 through the peripheral wall 17 of the rice cooker pot 15. The pot temperature sensor 50 is located on the outer surface of the protective frame 25 and has a detection part 50a that is positioned to penetrate the protective frame 25 and contact the outer surface of the rice cooker pot 15. In this embodiment, the pot temperature sensor 50 is a side sensor that detects the temperature of the lower part of the peripheral wall 17, but it may also be a center sensor that detects the temperature of the bottom wall 16 of the rice cooker pot 15.

The lid temperature sensor 51 is provided to detect the temperature inside the rice cooker pot 15 through the heat sink 33, which is a partition of the lid body 30 that closes the opening of the rice cooker pot 15, and the inner lid 34. The lid temperature sensor 51 is located on the upper surface of the heat sink 33 and has a detection unit (second detection unit) 51a that contacts the heat sink 33. The detection unit 51a is located outside the sealing member 44, which is outside the exhaust passage 40, i.e., above the closed space 45. However, the lid temperature sensor 33 may be located on the upper surface of the lid main body 31, and the detection unit 51a may be positioned so that it penetrates the lid main body 31 and contacts the upper surface of the heat sink 33, or it may be positioned so that it penetrates the lid main body 31 and contacts the upper surface of the heat sink 33 and contacts the upper surface of the inner lid 34.

The steam temperature sensor 52 is provided to detect the temperature of steam passing through the exhaust passage 40. The steam temperature sensor 52 is located on the upper surface of the lid body 31 and has a detection unit (first detection unit) 52a that penetrates the lid body 31 and is located within the inlet section 41. The detection unit 52a is located inside the seal member 44 within the exhaust passage 40. However, the detection unit 52a may also be located within the steam port set 47, as long as it is configured to directly detect the steam temperature within the exhaust passage 40.

The LCD panel 55 is provided to display the selected rice cooking menu and the current operating status. In this embodiment, the LCD panel 55 is located at the top front of the rice cooker body 20, but it may also be formed on the top surface of the lid 30, and its location can be changed as needed. Rice cooking menus include "white rice," "quick white rice," "mixed rice," "porridge," "brown rice," and "multigrain rice." White rice also includes "soft," "normal," and "firm," among others.

The multiple switches 56 are each, for example, tactile switches, and are arranged around the LCD panel 55. The multiple switches 56 include a menu switch for selecting a rice cooking menu, a rice cooking switch for executing the rice cooking process, a keep-warm switch for executing the keep-warm process, a timer switch for cooking rice at a desired time, and a cancel switch for canceling (ending) the rice cooking process, keep-warm process, and selected state.

A control board 59 is mounted via a holder 58 on the front side of the rice cooker main body 20, which is located on the left side in Figure 1. The control board 59 is equipped with a control unit 60 that controls the electrical components, as well as an inverter circuit 63 and a switching unit 64 for supplying power to the coils 26 and 27. However, the control unit 60, inverter circuit 63, and switching unit 64 may be separated into two or three control boards, and their placement between the rice cooker main body 20 and the protective frame 25 may also be changed as needed.

The control unit 60 is composed of one or more microcomputers and other electronic devices. The control unit 60 is electrically connected to the lid heater 36, three temperature sensors 50-52, LCD panel 55, multiple switches 56, inverter circuit 63, and switching unit 64, and is electrically connected to multiple coils 26, 27 via switching unit 64. The control unit 60 is equipped with a memory 61 and a timer 62. The memory 61 stores programs for executing the rice cooking process and the keep-warm process, as well as setting values (temperature, time, etc.) used in the program. The timer 62 measures the execution time of specified processes (steps) in the rice cooking process and the keep-warm process.

During the rice cooking process, the control unit 60 executes the preheating process, medium-heating process, boiling maintenance process, and steaming process in this order based on the detected temperatures Tp, Tc, and Ts obtained from the detection results of the three temperature sensors 50-52, and cooks the rice in the rice cooker pot 15. During the keep-warm process, the control unit 60 adjusts the temperature of the cooked rice to a predetermined temperature based on the detected temperatures Tp, Tc, and Ts by the three temperature sensors 50-52.

In this embodiment, the inverter circuit 63 includes a pair of opposing inner and outer coils 26 and 27, and three power transistors (e.g., IGBTs) connected to each of the three coil pairs via a switching unit 64. In other words, multiple inverter circuits 63 are provided, corresponding to the number of pairs of coils 26 and 27. The power supplied to the coils 26 and 27 by the inverter circuit 63, which corresponds to the heating power used to heat the rice cooker 15, is duty-controlled by the control unit 60.

The switching unit 64 is electrically connected to the control unit 60 and the inverter circuit 63. The switching unit 64 is composed of multiple switches (e.g., relays) provided according to the number of coils 26, 27. The switching unit 64 switches between a first energized state in which the first set of coils 26, 27 is electrically connected and the second and third sets of coils 26, 27 are de-energized; a second energized state in which the second set of coils 26, 27 is electrically connected and the third set of coils 26, 27 is de-energized; and a third energized state in which the third set of coils 26, 27 is electrically connected and the first and second sets of coils 26, 27 are de-energized. This switching operation is repeated. In other words, the switching unit 64 switches the energized states in a predetermined order so that one of the three sets of coils 26, 27 is energized and the remaining two sets are de-energized.

Next, we will explain in detail the rice cooking process performed by the control unit 60.

Figures 3, 5, and 7 are time charts showing examples of rice cooking processes. Of these, Figure 3 shows rice cooking process 1 when cooking a small amount of white rice, Figure 5 shows rice cooking process 2 when cooking a medium amount of white rice, and Figure 7 shows rice cooking process 3 when cooking a large amount of white rice. For example, in the case of a rice cooker 10 with a maximum rice cooking capacity of 10 cups, small amount cooking is generally in the range of 1 cup to 3 cups, medium amount cooking is in the range of more than 3 cups to 7 cups, and large amount cooking is in the range of more than 7 cups to 10 cups.

In Figures 3, 5, and 7, the vertical axis represents temperature (°C) and power (W), and the horizontal axis represents time (minutes). In Figures 3, 5, and 7, the thick solid line represents the temperature Tp detected by the pot temperature sensor 50, the thick dashed line represents the temperature Tc detected by the lid temperature sensor 51, the thick dashed line represents the temperature Ts detected by the steam temperature sensor 52, and the thin solid line represents the actual temperature of the inner lid 34 detected by a thermocouple. Transition temperatures Ty1, Ty2, Tz1, and Tz2, which will be described in detail later, are set based on the actual measured temperatures.

Referring to Figures 3, 5, and 7 in addition to Figure 9, the rice cooking process includes a preheating step (step S1), a medium-heating step (step S2), a boiling maintenance step (step S3), and a steaming step (step S4), and these steps are carried out in this order. Once the rice cooking process is complete, a keep-warm process is then carried out.

In the preheating process, the rice cooker pot 15 is heated (temperature controlled) to maintain a set preheat temperature (e.g., 40°C), causing the rice to absorb water. During this preheating process, multiple sets of coils 26, 27 are duty-controlled in sequence and are turned on and off based on the temperature Tp detected by the pot temperature sensor 50. The preheating process ends when a set time has passed (when the transition condition is met). For example, the transition time is 20 minutes for regular cooking and 10 minutes for scheduled cooking. In other words, the preheating process comprises a first step, in which the temperature is raised to the preheat temperature, and a second and third step, in which the temperature is maintained at the preheat temperature. The third step is performed in regular cooking but not in scheduled cooking.

In the intermediate boiling process, the rice cooker pot 15 is heated at high power until the water reaches a boiling temperature higher than the preheating temperature, quickly boiling the water inside. During this intermediate boiling process, multiple sets of coils 26, 27 are controlled in sequence to maintain an on state at 100% of the rated power (full power). The intermediate boiling process is powered at full power from start to finish, but with reference to Figures 4, 6, and 8, it is subdivided and controlled into a warm-up heating step, a main heating step, and an adjustment heating step. The rice cooking capacity is determined by the execution time of the main heating step in this intermediate boiling process. The warm-up heating step, main heating step, and adjustment heating step will be described in detail below.

The boiling maintenance process includes an initial pause step whose execution is determined by the rice cooking capacity, and steps 1 through 3 which are executed regardless of the rice cooking capacity.

Referring to Figures 3, 5, and 7, the pause step is skipped (not executed) when the rice cooking capacity is small, and is executed when the rice cooking capacity is medium or large. In the pause step, power supply to coils 26 and 27 is stopped, preventing the occurrence of "overflow," which occurs when the residual heat of rice cooker pot 15 from heating during the intermediate cooking process causes viscous liquid material in rice cooker pot 15 to flow out through exhaust passage 40.

When the pause step is completed or skipped, the rice cooker pot 15 is heated (temperature controlled) to maintain the boiling temperature and remove any water inside (Step 1). In Step 1, the multiple coils 26, 27 are duty-controlled in sequence and are on/off controlled based on the temperature Tp detected by the pot temperature sensor 50. When the temperature Tp detected by the pot temperature sensor 50 indicates a predetermined dry-up temperature (e.g., 110°C), the output is reduced and the rice cooker pot 15 is heated over low heat (Step 2). In Step 2, the multiple coils 26, 27 are duty-controlled in sequence and are on/off controlled based on the temperature Tc detected by the lid temperature sensor 51. After Step 2 has been executed for a predetermined time (e.g., 5 minutes), the output is increased and the rice cooker pot 15 is heated over medium heat (Step 3). In Step 3, the multiple coils 26, 27 are duty-controlled in sequence at 75% of the rated power and are on/off controlled based on the temperature Tc detected by the lid temperature sensor 51. Then, when the temperature Tp detected by the pan temperature sensor 50 again indicates the set dry-up temperature (e.g., 110°C), the boiling maintenance process ends.

During the soaking process, the temperature of the rice cooker pot 15 is adjusted at low output to steam the cooked rice. During this soaking process, the lid heater 36 is controlled based on the temperature Tc detected by the lid temperature sensor 51, and power to the coils 26, 27 is stopped (cut off). Furthermore, if a copper heater is provided on the radially outer side of the inner body 24, the copper heater is duty controlled. The soaking process ends when the soaking time set based on the rice cooking capacity determined in the middle-steaming process has elapsed. In other words, the execution time of the soaking process varies depending on the rice cooking capacity.

Next, we will explain in more detail how the control unit 60 controls the inner filling process.

First, during the intermediate cooking process, the power input to coils 26 and 27 is the same and at full power, regardless of the rice cooking capacity. Therefore, the amount of heat per unit volume of rice and water in rice cooker pot 15 is greater when the rice cooking capacity is small than when it is large. Even at the same temperature, the amount of steam generated in rice cooker pot 15 is greater when the rice cooking capacity is small than when it is large. Furthermore, the distance from the water surface in rice cooker pot 15 to lid 30 is shorter when the rice cooking capacity is large than when it is small. Therefore, heat transfer to lid 30 due to heating of rice cooker pot 15 is faster when the rice cooking capacity is large than when it is small. In other words, when the rice cooking capacity is small, the amount of steam generated in rice cooker pot 15 due to heating is greater than when the rice cooking capacity is large, but heat transfer to lid 30 is slower. Furthermore, when the rice cooking capacity is large, the amount of steam generated in rice cooker pot 15 due to heating is less than when the rice cooking capacity is small, but heat transfer to lid 30 is faster.

For this reason, when the rice cooking capacity is small, boiling in the rice cooker pot 15 can be determined with less delay and more accuracy by using the temperature Ts detected by the steam temperature sensor 52, which directly detects the steam temperature, rather than using the temperature Tc detected by the lid temperature sensor 51, which indirectly detects the temperature inside the rice cooker pot 15. On the other hand, when the rice cooking capacity is large, boiling in the rice cooker pot 15 can be determined with less delay and more accuracy by using the temperature Tc detected by the lid temperature sensor 51, which indirectly detects the temperature inside the rice cooker pot 15, rather than using the temperature Ts detected by the steam temperature sensor 52, which directly detects the steam temperature.

However, when the middle-water-pumping process begins, the rice cooking capacity is not determined. Therefore, in this embodiment, when either the temperature Tc detected by the lid temperature sensor 51 or the temperature Ts detected by the steam temperature sensor 52 reaches the specified transition temperatures Ty1 and Ty2, it is determined that the rice inside the rice cooker pot 15 has boiled, and the transition temperatures and execution times for the subsequent steps and processes are set (adjusted).

Specifically, referring to Figures 4, 6, and 8, the intermediate heating process includes a warm-up heating step, a main heating step, and an adjustment heating step, which are performed in this order.

The warm-up step is provided to eliminate the influence of factors such as room temperature on the temperature sensors 50-52 and allow the temperatures of the temperature sensors 50-52 to adapt to the temperature inside the oven, thereby enabling accurate temperature detection. The warm-up step ends when the temperature Tp detected by the pan temperature sensor 50 indicates that it has reached the specified transition temperature Tx.

The main heating step is the main intermediate heating process for boiling the rice inside the rice cooker pot 15. The main heating step ends when either the first condition is met: that the temperature Ts detected by the steam temperature sensor 52 has reached the first transition temperature Ty1; or the second condition is met: that the temperature Tc detected by the lid temperature sensor 51 has reached the second transition temperature Ty2. In this embodiment, the cooking capacity of the rice inside the rice cooker pot 15 is determined based on the time from the start to the end of this main heating step.

The temperature Ts detected by the steam temperature sensor 52, which directly detects the temperature of steam, becomes higher earlier than the temperature Tc detected by the lid temperature sensor 51, which indirectly detects the temperature inside the rice cooker pot 15 via the inner lid 34 and heat sink 33. Therefore, the first transition temperature Ty1 for the steam temperature sensor 52 is set higher than the second transition temperature Ty2 for the lid temperature sensor 51.

The adjusted heating step is performed after the main heating step and is provided to adjust the heating time for the entire middle-pumping process. This adjusted heating step ends when either the first condition is met: that the temperature Ts detected by the steam temperature sensor 52 has reached the first transition temperature Tz1; or the second condition is met: that the temperature Tc detected by the lid temperature sensor 51 has reached the second transition temperature Tz2. As with the main heating step, the first transition temperature Tz1 for the steam temperature sensor 52 is set higher than the second transition temperature Tz2 for the lid temperature sensor 51.

More specifically, the transition temperature Tx in the warm-up heating step is set to the same temperature regardless of the rice cooking capacity and rice cooking menu. The transition temperatures Ty1 and Ty2 in the main heating step are set to the same temperature regardless of the rice cooking capacity, but may be set to different temperatures depending on the rice cooking menu. The transition temperatures Tz1 and Tz2 in the adjustment heating step are set to different temperatures depending on the rice cooking capacity and also depending on the rice cooking menu.

For example, if the rice cooking menu is "white rice" and the hardness is "normal," the transition temperatures Tx, Ty1, Ty2, Tz1, and Tz2 are set as follows. Note that the specific transition temperatures Tx, Ty1, Ty2, Tz1, and Tz2 below were discovered by the inventors of the present application through experiments, and may be changed depending on the placement of temperature sensors 52 and 51.

The transition temperature Tx in the warm-up step is set to 60°C. In the main heating step, the first transition temperature Ty1 for the steam temperature sensor 52 is set to 80°C, and the second transition temperature Ty2 for the lid temperature sensor 51 is set to 60°C.

The transition temperatures Tz1 and Tz2 in the adjustment heating step are set as follows: If the result of the determination is small-volume cooking, which generates a lot of steam in the rice cooker pot 15, the first transition temperature Tz1 is set to 110°C and the second transition temperature Tz2 is set to 60°C. If the result of the determination is medium-volume cooking, which generates less steam than small-volume cooking but has faster heat transfer within the rice cooker pot 15, the first transition temperature Tz1 is set to 110°C and the second transition temperature Tz2 is set to 63°C. If the result of the determination is large-volume cooking, which generates the least amount of steam but has the fastest heat transfer within the rice cooker pot 15, the first transition temperature Tz1 is set to 80°C and the second transition temperature Tz2 is set to 63°C. If the transition temperatures Tz1 and Tz2 that end the adjustment heating step are set as the execution time, the execution time is set to shorten as the rice cooking volume increases. Note that in the adjustment heating step, the transition time, instead of the transition temperatures Tz1 and Tz2, may be set differently depending on the determined rice cooking volume.

In this way, in the adjusted heating step, the first transition temperature Tz1 for the steam temperature sensor 52 is set to be equal to or higher than the first transition temperature Ty1 in the main heating step, and the second transition temperature Tz2 for the lid temperature sensor 51 is also set to be equal to or higher than the second transition temperature Ty2 in the main heating step. In other words, depending on the rice cooking capacity and cooking menu, the first transition temperature Ty1 in the main heating step and the first transition temperature Tz1 in the adjusted heating step may be set to the same temperature, and the second transition temperature Ty2 in the main heating step may be set to the same temperature as the second transition temperature Tz2 in the adjusted heating step. Setting the transition temperatures Ty1, T2 in the main heating step and the transition temperatures Tz1, Tz2 in the adjusted heating step to the same temperature means that, depending on the rice cooking capacity and cooking menu, the middle-heating process may skip (not execute) the adjusted heating step and execute only the warm-up heating step and main heating step.

With this configuration, the rice cooker 10 can accurately and without delay determine whether the rice has boiled in the rice cooker pot 15 during the intermediate boiling process.

Specifically, when cooking a small amount of rice as shown in Figure 4, a large amount of steam is generated within the rice cooker pot 15, but heat transfer from the rice cooker pot 15 to the lid 30 is slow. Therefore, before the second condition is met, that is, the temperature Ts detected by the steam temperature sensor 52 reaches the first transition temperature Ty1, the first condition is met. This ends the main heating step.

When cooking a large amount of rice as shown in Figure 8, the amount of steam generated within the rice cooker pot 15 is small, but heat transfer from the rice cooker pot 15 to the lid 30 is rapid. Therefore, before the first condition is met, that is, the temperature Ts detected by the steam temperature sensor 52 reaches the first transition temperature Ty1, the temperature Tc detected by the lid temperature sensor 51 reaches the second transition temperature Ty2, and the second condition is met. This ends the main heating step.

On the other hand, in the case of medium-volume cooking shown in Figure 6, the amount of steam generated within the rice cooker pot 15 is less than in small-volume cooking but more than in large-volume cooking, and heat transfer from the rice cooker pot 15 to the lid 30 is slower than in large-volume cooking but faster than in small-volume cooking. Therefore, the first condition, that the temperature Ts detected by the steam temperature sensor 52 reaches the first transition temperature Ty1, and the second condition, that the temperature Tc detected by the lid temperature sensor 51 reaches the second transition temperature Ty2, are met roughly at the same time, and there are cases where the first condition is met first and cases where the second condition is met first. In the example shown in Figure 6, the first condition, that the temperature Ts detected by the steam temperature sensor 52 reaches the first transition temperature Ty1, is met first. This ends the main heating step.

In this way, the main heating step ends when either the first condition, that the temperature Ts detected by the steam temperature sensor 52 reaches the first transition temperature Ty1, or the second condition, that the temperature Tc detected by the lid temperature sensor 51 reaches the second transition temperature Ty2, is met. This allows for highly accurate determination of boiling in the rice cooker pot 15 without delay in determining whether the rice has boiled. As a result, excessive heat can be prevented from being applied to the rice, allowing the rice to be cooked in good condition.

Furthermore, the adjusted heating step following the main heating step also ends when either the first condition that the temperature Ts detected by the steam temperature sensor 52 reaches the first transition temperature Tz1 or the second condition that the temperature Tc detected by the lid temperature sensor 51 reaches the second transition temperature Tz2 is met. This allows the execution time of the middle-pumping step to be optimized, enabling the rice to be cooked in good condition.

Next, the control of the inner filling process by the control unit 60 will be explained with reference to Figure 10.

In Figure 10, steps S10 and S11 are warm-up heating steps, steps S12 to S17 are main heating steps including capacity determination, and steps S18 to S20 are adjustment heating steps. Of steps S12 to S17, steps S12 and S15 to S17 determine capacity and set the transition conditions for each step based on the determination results; steps S13 and S14 are essentially the main heating steps.

Specifically, in the middle filling process, in step S10, the control unit 60 controls the inverter circuit 63 and the switching unit 64 to output high-frequency current at 100% of the rated power to the coils 26 and 27. Next, in step S11, the control unit 60 waits until the temperature Tp detected by the pan temperature sensor 50 reaches the transition temperature Tx, and when this indicates that the detected temperature Tp has reached the transition temperature Tx, the control unit 60 proceeds to step S12.

In step S12, the timer 62 is reset and started. Then, in step S13, it is determined whether the temperature Ts detected by the steam temperature sensor 52 has reached the first transition temperature Ty1. If the detected temperature Ts indicates that it has reached the first transition temperature Ty1, the process proceeds to step S15. If the detected temperature Ts does not indicate that it has reached the first transition temperature Ty1, the process proceeds to step S14. In step S14, it is determined whether the temperature Tc detected by the lid temperature sensor 51 has reached the second transition temperature Ty2. If the detected temperature Tc indicates that it has reached the second transition temperature Ty2, the process proceeds to step S15. If the detected temperature Tc does not indicate that it has reached the second transition temperature Ty2, the process returns to step S13. In other words, if either the first condition (that the temperature Ts detected by the steam temperature sensor 52 has reached the first transition temperature Ty1) or the second condition (that the temperature Tc detected by the lid temperature sensor 51 has reached the second transition temperature Ty2) is met, the process proceeds to step S15, essentially terminating the main heating step.

In step S15, the timer 62 is stopped, and then in step S16, the rice cooking capacity is determined based on the time measured by the timer 62. Then, in step S17, based on the determined rice cooking capacity, the transition temperatures Tz1 and Tz2 in the adjustment heating step, whether to execute a pause step in the boiling maintenance step, and the execution time of the soaking step are set, and the process proceeds to step S18.

In step S18, it is determined whether the temperature Ts detected by the steam temperature sensor 52 has reached the first transition temperature Tz1. If the detected temperature Ts indicates that it has reached the first transition temperature Tz1, the process proceeds to step S20. If the detected temperature Ts does not indicate that it has reached the first transition temperature Tz1, the process proceeds to step S19. In step S19, it is determined whether the temperature Tc detected by the lid temperature sensor 51 has reached the second transition temperature Tz2. If the detected temperature Tc indicates that it has reached the second transition temperature Tz2, the process proceeds to step S20. If the detected temperature Tc does not indicate that it has reached the second transition temperature Tz2, the process returns to step S18. In other words, if either the first condition, that the temperature Ts detected by the steam temperature sensor 52 indicates that it has reached the first transition temperature Tz1, or the second condition, that the temperature Tc detected by the lid temperature sensor 51 indicates that it has reached the second transition temperature Tz2, is met, the process proceeds to step S20.

In step S20, output to coils 26 and 27 is stopped, i.e., heating of the rice cooker pot 15 is stopped, the adjusted heating step (medium heating process) is completed, and the process returns.

The rice cooker 10 configured in this manner has the following features:

The rice cooker is equipped with a steam temperature sensor 52 for detecting the steam temperature within the exhaust passage 40, and a lid temperature sensor 51 for detecting the temperature within the rice cooker pot 15 via the heat sink 33 and inner lid 34. When the rice cooking capacity is low—that is, when a large amount of steam is generated within the rice cooker pot 15 and heat transfer to the lid 30 is slow—the main heating step ends when the temperature Ts detected by the steam temperature sensor 52 reaches the specified transition temperature Ty1. On the other hand, when the rice cooking capacity is high—that is, when a small amount of steam is generated within the rice cooker pot 15 and heat transfer to the lid 30 is fast—the main heating step ends when the temperature Tc detected by the lid temperature sensor 51 reaches the specified transition temperature Ty2. In this way, boiling within the rice cooker pot 15 can be determined with high accuracy and without delay regardless of the rice cooking capacity, optimizing the execution time of the middle-heating process. This prevents excessive heat from being applied to the rice, ensuring the rice is cooked in good condition.

Specifically, the main heating step ends when either the first condition, indicating that the temperature Ts detected by the steam temperature sensor 52 has reached the first transition temperature Ty1, or the second condition, indicating that the temperature Tc detected by the lid temperature sensor 51 has reached the second transition temperature Ty2, is met. When the rice cooking capacity is low, the amount of steam generated in the rice cooker pot 15 is high but heat transfer to the lid 30 is slow. Therefore, the temperature Ts detected by the steam temperature sensor 52 reaches the first transition temperature Ty1 before the second condition is met, and the first condition is met, thereby ending the main heating step. On the other hand, when the rice cooking capacity is high, the amount of steam generated in the rice cooker pot 15 is low but heat transfer to the lid 30 is fast. Therefore, the temperature Tc detected by the lid temperature sensor 51 reaches the second transition temperature Ty2 before the first condition is met, and the second condition is met, thereby ending the main heating step. In this way, regardless of the rice cooking capacity, boiling in the rice cooker pot 15 can be determined accurately and without delay, and the execution time of the middle-heating process can be optimized, resulting in excellent cooked rice.

The temperature Ts detected by the steam temperature sensor 52, which directly detects the temperature of steam, becomes higher earlier than the temperature Tc detected by the lid temperature sensor 51, which indirectly detects the temperature inside the rice cooker pot 15 via the heat sink 33 and inner lid 34. Therefore, by setting the first transition temperature Ty1 higher than the second transition temperature Ty2, boiling in the rice cooker pot 15 can be determined with high accuracy and without delay from the detection results of either the steam temperature sensor 52 or the lid temperature sensor 51.

The control unit 60 determines the rice cooking capacity based on the time from the start to the end of the main heating step, and sets the transition temperatures Tz1, Tz2 or time for ending the adjustment heating step after the main heating step to differ depending on the determined rice cooking capacity. This configuration optimizes the overall execution time of the intermediate-heating step, improving the balance between the execution times of the intermediate-heating step and the boil maintenance step. This allows the rice to be cooked in good condition.

The detection unit 52a of the steam temperature sensor 52 is located within the seal member 44, while the detection unit 51a of the lid temperature sensor 51 is located outside the seal member 44 so as to contact the heat sink 33 or the inner lid 34. With this configuration, the steam temperature sensor 52 can reliably detect the temperature of the steam in the exhaust passage 40, and the lid temperature sensor 51 can reliably detect the temperature inside the rice cooker pot 15 via the heat sink 33 and inner lid 34.

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

For example, the rice cooking capacity may be determined during the warm-up heating step of the intermediate rice-pumping process, during the preheating process, or at the start of cooking using a weight sensor. In these cases, since the rice cooking capacity has already been determined during the main heating step of the intermediate rice-pumping process, in the case of a small amount of rice, only the temperature Ts detected by the steam temperature sensor 52 may be used to detect boiling; in the case of a medium amount, both the temperatures Ts and Tc detected by the steam temperature sensor 52 and the lid temperature sensor 51 may be used to detect boiling; and in the case of a large amount, only the temperature Tc detected by the lid temperature sensor 51 may be used to detect boiling. Furthermore, in the case of a medium amount of rice, boiling detection based on the detection results of the steam temperature sensor 52 and the lid temperature sensor 51 can be determined almost simultaneously, so only the temperature Ts detected by the steam temperature sensor 52 may be used to detect boiling.

The rice cooker 10 may be a pressure rice cooker in which a movable valve is placed midway through the exhaust passage 40, allowing the pressure inside the rice cooker pot 15 to be increased to a level higher than atmospheric pressure.

REFERENCE SIGNS LIST 10 Rice cooker 15 Rice cooker pot 16 Bottom wall portion 17 Peripheral wall portion 18 Continuous portion 20 Rice cooker main body 21 Exterior body 22 Hinge connection shaft 23 Storage portion 24 Inner body 25 Protective frame 26 Inner coil (heating portion)
27 outer coil (heating part)
30 Lid body 31 Lid body 32 Lid cover 33 Heat sink (partition wall)
34 Inner lid (partition)
35 Sealing member 36 Lid heater 40 Exhaust passage 41 Inlet portion 42 Vent 43 Opening 44 Sealing member 45 Closed space portion 46 Communication port 47 Steam port set 47a Connection portion 47b Exhaust portion 50 Pot temperature sensor 50a Detection portion 51 Lid temperature sensor 51a Detection portion (second detection portion)
52 Steam temperature sensor 52a Detector (first detector)
55 Liquid crystal panel 56 Switch 58 Holder 59 Control board 60 Control unit 61 Memory 62 Timer 63 Inverter circuit 64 Switching unit

Claims (5)

A cylindrical rice cooker with a bottom,
A heating unit that heats the rice cooker pot;
A lid that closes the opening of the rice cooker;
An exhaust passage provided in the lid for discharging steam from the rice cooker pot to the outside;
a steam temperature sensor having a first detection portion disposed in the exhaust passage and configured to detect the temperature of steam in the exhaust passage;
a lid temperature sensor having a second detection unit disposed outside the exhaust passage and configured to detect the temperature inside the rice cooker pot through a partition wall that closes the opening of the rice cooker pot;
and a control unit that controls the heating unit to perform a rice cooking process including a temperature raising step of raising the temperature inside the rice cooker pot to a boiling temperature,
The rice cooker includes a main heating step in which the temperature rising process detects temperature using the steam temperature sensor and the lid temperature sensor, and ends when either of the detected temperatures reaches a predetermined transition temperature. the transition temperatures include a first transition temperature for the steam temperature sensor and a second transition temperature for the lid temperature sensor;
The main heating step is terminated when either a first condition indicating that the temperature detected by the steam temperature sensor has reached the first transition temperature or a second condition indicating that the temperature detected by the lid temperature sensor has reached the second transition temperature is satisfied.
The rice cooker according to claim 1. The rice cooker of claim 2, wherein the first transition temperature is higher than the second transition temperature. the temperature increasing step includes an adjusting heating step for adjusting a heating time after the main heating step,
The control unit determines the rice cooking capacity based on the time from the start to the end of the main heating step, and sets the temperature or time to end the adjusted heating step so as to differ depending on the determined rice cooking capacity.
The rice cooker according to any one of claims 1 to 3. The partition wall has an inner lid that closes the opening of the rice cooker pot and a heat sink that covers the inner lid,
the exhaust passage has an inlet portion which is a space defined by the inner lid, the heat dissipation plate, and an endless sealing member which seals between the inner lid and the heat dissipation plate,
the first detection unit is disposed within the seal member,
the second detection unit is disposed outside the seal member so as to be in contact with the heat sink or the inner lid.
The rice cooker according to any one of claims 1 to 3.