Abstract:
High frequency microwaves and stem are supplied to a heating chamber ( 20 ) disposed inside the disclosed high frequency cooking device ( 1 ). On the floor of the heating chamber is formed a funnel-shaped slope ( 28 ), at the bottom of which is formed a condensate drain ( 27 ). A rotation shaft ( 31   d ) for transmitting rotation to a turn table ( 30 ) passes through the condensate drain. A cup-shaped support base ( 33 ) supporting a motor ( 32 ) for rotating the rotation shaft catches the condensate flowing out of the condensate drain. A drain pipe ( 36 ) forming part of the drain path ( 37 ) is connected to a drain ( 35 ) of the support base. A U-shaped bend ( 36   a ) formed in the drain pipe constitutes a water-sealing unit ( 39 ) where condensate accumulates.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to microwave cooking devices that are capable of cooking by steam. 
       BACKGROUND ART 
       [0002]    Microwave cooking devices heat food from within by oscillating the molecules of the food with microwaves (high frequency electromagnetic waves). These cooking devices are generally called “microwave ovens” and are today indispensable in households. Some microwave cooking devices are furnished with a mechanism to supply steam into the heating chamber so as to be capable of steam-cooking using steam and combined use of microwaves and steam. An example is seen in Patent Document 1 listed below. 
       LIST OF CITATIONS 
     Patent Literature 
       [0000]    
       
         Patent Document 1: JP-A-2008-32294 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0004]    When steam is used in a microwave cooking device, the steam condenses inside the heating chamber to produce condensate, of which the disposal poses a problem. One solution is to add a heater to heat the heating chamber to vaporize the condensate back into the gas phase. This approach, however, is not believed to be quite preferable because it increases the number of components and hence increases the manufacturing cost, and in addition increases the power consumption. Proper drainage of the condensate is the best approach to a feasible solution. 
         [0005]    The aim of using steam in cooking is to replace the air inside the heating chamber with steam to lower the oxygen concentration there, in order to lessen oxidation-induced degradation in taste. When a condensate drain port is formed in the heating chamber, it can be used as an exhaust port for air; as the replacement of air with steam progresses, however, it becomes necessary to prevent leakage of steam and entry of outside air through the condensate drain port. 
         [0006]    The present invention has been made against the above background, and a main object of the invention is to provide, for microwave cooking devices capable of cooking by steam, a mechanism that allows reliable drainage of condensate out of the heating chamber but that nevertheless is free from leakage of steam and entry of outside air during cooking. 
       Solution to Problem 
       [0007]    To achieve the above object, according to the invention, a microwave cooking device which is adapted to be capable of supplying steam into a heating chamber inside the device is characterized in that: a condensate drain port is formed in the bottom wall of the heating chamber, and a water-seal portion which keeps condensate is formed in a drain passage which starts at the condensate drain port. 
         [0008]    According to the invention, in the microwave cooking device constructed as described above, a funnel-shaped slope is formed in the bottom wall of the heating chamber, and the condensate drain port is arranged in the lowest part of the slope. 
         [0009]    According to the invention, in the microwave cooking device constructed as described above, a turntable on which an object to be heated is placed is arranged inside the heating chamber, and a rotary shaft which transmits rotation to the turntable penetrates the condensate drain port. 
         [0010]    According to the invention, in the microwave cooking device constructed as described above, a cup-shaped support base is fixed on the outer face of the bottom wall of the heating chamber, the support base supports a motor which gives rotation to the rotary shaft, and the support base collects condensate that flows out through the condensate drain port. 
         [0011]    According to the invention, in the microwave cooking device constructed as described above, a drain pipe which constitutes part of the drain passage is connected to a drain port which is formed in the support base, and a bend which is formed as a part of the drain pipe constitutes the water-seal portion. 
         [0012]    According to the invention, in the microwave cooking device constructed as described above, a drain pan is arranged where the drain passage ends. 
       Advantageous Effects of the Invention 
       [0013]    According to the present invention, the condensate produced inside the heating chamber during steam cooking is reliably drained through the condensate drain port formed in the bottom wall of the heating chamber. The drain passage which starts at the condensate drain port has a part of it formed into the water-seal portion in which the condensate keeps. Thus, when the air inside the heating chamber is replaced with steam and the oxygen concentration there lowers, and as a result the steam starts to condense, the flow of steam in the gas phase is blocked by the water-seal portion. Also if outside air tends to enter, it is blocked by the water-seal portion. Thus, during steam cooking, steam is enclosed inside the heating chamber so as to keep a low-oxygen condition and to continue to be used to heat food. In this way, it is possible to prevent oxidation-induced degradation in taste. Moreover, the energy used to generate steam is not wasted, and thus it is possible to perform cooking with improved energy efficiency. Drainage of condensate without passage of steam is achieved by means of a simple mechanism, that is, the water-seal portion, and thus no complicated mechanism needs to be adopted as would lead to increased cost. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0014]      FIG. 1  is a perspective view of a microwave cooking device embodying the invention; 
           [0015]      FIG. 2  is a vertical sectional view showing an outline of the construction inside the microwave cooking device; 
           [0016]      FIG. 3  is a side exterior view of a heating chamber inside the microwave cooking device; 
           [0017]      FIG. 4  is a partial vertical sectional view showing the structure of a bottom part of the heating chamber; 
           [0018]      FIG. 5  is a top view of the bottom part of the heating chamber; and 
           [0019]      FIG. 6  is a block configuration diagram of the microwave cooking device. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0020]    The construction of a microwave cooking device  1  embodying the invention will be described below with reference to the accompanying drawings. In  FIG. 1 , the top and bottom of the page coincide with the top and bottom of the microwave cooking device  1 ; moreover, it is assumed that the left and right sides of the page correspond to the left and right sides, respectively, of the microwave cooking device  1 . 
         [0021]    The microwave cooking device  1  has a cabinet  10  which is a structural member formed of sheet metal in the shape of a rectangular parallelepiped. Inside the cabinet  10 , a heating chamber  20  is provided which is a structural member formed of sheet metal in the shape of a rectangular parallelepiped smaller than the cabinet  10 . The heating chamber  20  has an opening at the front of the cabinet  10 . At the front of the cabinet  10 , a metal door  11  is provided by which the opening of the heating chamber  20  is opened and closed. The door  11  is, at its left end, coupled to the cabinet  10  via a hinge  12  so as to be swingable about the hinge  12  in the horizontal plane. 
         [0022]    The door  11  has a window  13  formed in it which permits a view inside the heating chamber  20 . The window  13  is fitted with a door screen  14  composed of a sheet of punched sheet metal held between two glass plates. This provides an inside view while preventing leakage of electromagnetic waves. The door  11  is provided with, in addition to the door screen  14 , further means for preventing leakage of electromagnetic waves, is fitted with a gasket for preventing leakage of steam, and is furnished with a locking device for keeping a closed state. These all belong to well-known technologies, and therefore will not be discussed in detail. 
         [0023]    In a part of the cabinet  10  to the right of the door  11 , an operation panel  15  is provided. On the operation panel  15  are arranged, as members constituting an operation interface, a set of membrane switches  15   a  and a dial  15   b . Over the membrane switches  15   a , a display device  15   c  is arranged which includes a liquid crystal panel. 
         [0024]    The cabinet  10  is supported on a table or a stand via a base  16 . The base  16  has front feet  16 F (see  FIG. 4 ) at two, left and right, places at the front and rear feet  16 R at two, left and right, places at the rear. The rear feet  16 R have a fixed height; by contrast, the front feet  16 F allow adjustment of their height by means of a screw-based mechanism. Adjusting the height of the front feet  16 F allows the cabinet  10  to be kept level. 
         [0025]    The construction inside the microwave cooking device  1  will now be described. On the outer face of the right side wall of the heating chamber  20 , there are mounted a microwave generating device (magnetron)  21  and a steam generating device  22 . The microwave generating device  21  supplies microwaves into the heating chamber  20 , and the steam generating device  22  supplies steam into the heating chamber  20 . The microwave generating device  21  and the steam generating device  22  are located in a space inside the cabinet  10  behind the operation panel  15 . In the same space, a circuit board (not shown) is also arranged which constitutes a control device, which will be described later. 
         [0026]    On the outer face of the right side wall of the heating chamber  20 , an illumination device  23  is also arranged which illuminates inside the heating chamber  20 . The illumination device  23  includes a light emitting diode (LED) as a light source. In the right side wall of the heating chamber  20 , a large number of light passing perforations  25  are formed in a rectangular array to let through the light from the LED  24 . The light passing perforations  25  are sized and arrayed like the perforations in the punched sheet metal of the door screen  14 , so that no radio waves leak through them. 
         [0027]    The array of light passing perforations  25  is covered, from outside the heating chamber  20 , with a cover  26  in the shape of a rectangular parallelepiped. The cover  26  encloses the LED  24 , and serves as a mounting base for the LED  24 . The cover  26  is formed of punched sheet metal to let through air to cool the LED  24 . 
         [0028]    In the right side face of the cabinet  10 , an exhaust port  17  is formed which is an array of small perforations, and inside the exhaust port  17 , a cooling fan  18  is arranged. When the cooling fan  18  is operated, the air inside the cabinet  10  is exhausted through the exhaust port  17 . As a result, through a suction port (not shown) provided somewhere else in the cabinet  10 , air outside the microwave cooking device  1  is sucked in. The air sucked in flows toward the cooling fan  18 . The flow of the air cools heat-generating components such as the microwave generating device  21 , the LED  24 , and the circuit board. 
         [0029]    In the bottom wall of the heating chamber  20 , a condensate drain port  27  is formed for draining condensate resulting from steam forming dew. In the bottom wall of the heating chamber  20 , a funnel-shaped slope  28  is formed which descends toward its center. In the lowest part of the slope  28 , the condensate drain port  27  is arranged. 
         [0030]    In the heating chamber  20 , a turntable  30  is arranged on which a food item as an object to be heated is placed. The turntable  30  is a glass member circular in shape as seen in a plan view, and has a slightly depressed top face like a dish. The turntable  30  is supported on the bottom wall of the heating chamber  20  via a roller stay  31 . As shown in  FIG. 5 , the roller stay  31  is composed of a hub  31   a  at the center, three arms  31   b  radially protruding from it at angular intervals of 120 degrees, and rollers  31   c  rotatably held at the tip end of them respectively. The rollers  31   c  make contact with, at one side, a ring-shaped track surface  29  surrounding the slope  28  and, at the other side, the bottom face of the turntable  30  to bear the weight of the turntable  30  and the food item. To prevent the turntable  30  from deviating from the roller stay  31 , on the bottom face of the turntable  30 , a ring-shaped rib  30   a  is formed so as to surround the three rollers  31   c.    
         [0031]    The roller stay  31  receives rotation via a rotary shaft  31   d . The rotary shaft  31   d  is molded integrally with the hub  31   a  so as to extend down from it. The rotary shaft  31   d  vertically penetrates the condensate drain port  27 . Between the outer face of the rotary shaft  31   d  and the inner face of the condensate drain port  27 , a gap is provided which allows passage of drips of water. The rotary shaft  31   d  protrudes down from the bottom wall of the heating chamber  20 , and is unrotatably coupled to an output shaft  32   a  of a motor  32 . 
         [0032]    The motor  32  is of a vertical-shaft type, and is supported on the heating chamber  20  via a cup-shaped support base  33  fixed on the outer face of the bottom wall of the heating chamber  20 . The motor  32  incorporates a reduction mechanism, and rotates the output shaft  32   a  at reduced speed. Where the output shaft  32   a  penetrates the support base  33 , a sealing member  34  is arranged which prevents leakage of water out of the support base  33  toward the motor. The support base  33  is at its top end welded to the bottom wall of the heating chamber  20  with intimate contact between them, so that no water or steam leaks there. 
         [0033]    The support base  33  serves to collect water that flows out through the condensate drain port  27 . As shown in  FIG. 4 , the bottom face of the support base  33  is lowest in its part facing the door  11 , and there a drain port  35  is formed. 
         [0034]    To the drain port  35 , the inlet of a drain pipe  36  is connected. The support base  33  and the drain pipe  36  together constitute a drain passage  37  which starts at the condensate drain port  27  and ends at the outlet of the drain pipe  36 . Where the drain passage  37  ends, a drain pan  38  is arranged. The drain pan  38  is removably supported on the cabinet  10 , and can be detached and attached through under the door  11 . 
         [0035]    The drain pipe  36  gradually descends from inlet to outlet, and a part of it near the inlet is formed into a U-shaped bend  36   a . The bend  36   a  constitutes a water-seal portion  39  that keeps condensate. The drain pipe  36  may be a pipe of a hard synthetic resin, or a tube or hose of a soft material. 
         [0036]    The controlling components of the microwave cooking device  1  are shown in  FIG. 6 . The overall control is assumed by a control device  40 . To the control device  40  are connected, among the components already mentioned, the operation panel  15 , the cooling fan  18 , the LED  24 , and the motor  32 . In addition, the following components are also connected to the control device  40 : a microwave drive power supply  21   a  which enables the microwave generating device  21  to perform microwave oscillation; a steam generation heater  22   a  incorporated in the steam generating device  22 ; a water feed pump  22   b  appended to the steam generating device  22 ; a water level sensor  22   c  incorporated in the steam generating device  22 ; a tank water level sensor  22   d  incorporated in a water tank (not shown) appended to the steam generating device  22 ; a humidity sensor  20   a  and a temperature sensor  20   b  provided in the heating chamber  20 ; and a door state sensor  11   a  provided for the door  11  to check whether it is open or closed. 
         [0037]    The microwave cooking device  1  operates as follows. To perform heating by microwaves, the user puts a food item as an object to be heated on the turntable  30 , closes the door  11 , and presses, among the membrane switches  15   a  on the operation panel  15 , one for “microwave cooking.” If secure closure of the door  11  is detected by the door state sensor  11   a , the microwave drive power supply  21   a  is energized, and the microwave generating device  21  starts microwave oscillation. Thus, the food item in the heating chamber  20  is heated by microwaves. 
         [0038]    When the microwave generating device  21  is energized, the cooling fan  18 , the LED  24 , and the motor  32  are also energized. The cooling fan  18  produces a stream of air, and with it cools the heat-generating components in the cabinet  10 . The LED  24  illuminates inside the heating chamber  20 . The motor  32  rotates the output shaft  32   a , which rotates the roller stay  31 . 
         [0039]    As the roller stay  31  rotates, the rollers  31   c  with the turntable  30  supported on them roll on the track surface  29 . The rolling rollers  31   c  further thrust the turntable  30  placed on them in the rotating direction. Thus, the turntable  30  rotates at twice the angular velocity of the rollers  31   c.    
         [0040]    On passage of a predetermined length of time, or in response to an operation by the user, or on detection of the food temperature having reached a predetermined level by a sensor specially provided for that purpose, the control device  40  stops energizing the microwave drive power supply  21   a , the cooling fan  18 , the LED  24 , and the motor  32  to end cooking by microwave heating. The user opens the door  11 , and takes the food item out. It is also possible to adopt a configuration in which for a predetermined length of time after the end of cooking by microwave heating, the cooling fan  18  continues to operate to keep cooling the heated components. 
         [0041]    To perform cooking by combined use of microwaves and steam, the user puts a food item as an object to be heated on the turntable  30 , closes the door  11 , and presses, among the membrane switches  15   a  on the operation panel  15 , one for “microwave-and-steam cooking.” If secure closure of the door  11  is detected by the door state sensor  11   a , the water feed pump  22   b  is energized, and water is fed from a water tank to the steam generating device  22 . When the water level inside the steam generating device  22  is found to have reached a predetermined level by the water level sensor  22   c , the water feed pump  22   b  stops operating. When, through evaporation, the water level inside the steam generating device  22  becomes so low as to require a new supply of water, the water feed pump  22   b  starts to operate again. 
         [0042]    When the steam generating device  22  is supplied with so much water that the water level inside it reaches a predetermined level, the steam generation heater  22   a  is energized, and the water inside the steam generating device  22  is heated. When the water boils and steam starts to be supplied to the heating chamber  20 , the control device  40  starts microwave heating. The control device  40  recognizes the start of the supply of steam to the heating chamber  20  on passage of a predetermined length of time after the start of the energizing of the steam generation heater  22   a , or on detection of the humidity inside the heating chamber  20  having raised to a predetermined level by the humidity sensor  20   a , or on detection of the temperature inside the heating chamber  20  having raised to a predetermined level by the temperature sensor  20   b . When microwave heating starts, the microwave drive power supply  21   a , the cooling fan  18 , the LED  24 , and the motor  32  are energized. The LED  24  may be lit at an earlier stage. 
         [0043]    As steam fills the heating chamber  20 , the air inside the heating chamber  20  is removed out of the heating chamber  20 . The condensate drain port  27  serves as one exhaust port for air. As air is replaced with steam, the oxygen concentration inside the heating chamber  20  lowers. Cooked in such a low-oxygen atmosphere, food suffers less from oxidation-induced degradation in taste, and thus the user can have satisfactory cooking results. 
         [0044]    On passage of a predetermined length of time, or in response to an operation by the user, or on detection of the food temperature having reached a predetermined level by a sensor specially provided for that purpose, the control device  40  stops energizing the microwave drive power supply  21   a , the cooling fan  18 , the LED  24 , the motor  32 , and the steam generation heater  22   a  to end cooking by combined use of microwaves and stream. The user opens the door  11 , and takes the food item out. 
         [0045]    The steam from the steam generating device  22  alone, without microwaves, may be used to perform steam-cooking. In that case, there is little need to rotate the turntable  30 , and accordingly the control device  40  keeps the motor  32  at a standstill. The cooling fan  18 , on the other hand, needs to cool the LED  24  and also to prevent the interior of the cabinet  10  from becoming too hot from the heat generated by the steam generating device  22 ; thus, the control device  40  operates the cooling fan  18  as usual. 
         [0046]    Irrespective of whether cooking is performed by combined use of microwaves and steam or steam-cooking is performed by steam alone, when cooking proceeds by use of steam with the air inside the heating chamber  20  replaced with steam and thus under low-oxygen-concentration condition, steam in contact with the inner wall faces of the heating chamber  20 , the turntable  30 , and the roller stay  31  condenses to form condensate. The condensate drips onto the bottom wall of the heating chamber  20 . The condensate that has dripped onto the bottom wall moves along the slope  28  to a central part of the heating chamber  20 , and flows out through the condensate drain port  27 . The condensate will then flow down the drain passage  37 . 
         [0047]    The condensate that has flowed down through the condensate drain port  27  is collected in the support base  33 , and is drained through the drain port  35 . The condensate that has flowed out through the drain port  35  proceeds to flow through the drain pipe  36 , where the bend  36   a  keeps condensate and thereby seals the drain pipe  36 . Thus, the water-seal portion  39  is formed here. The flow of steam in the gas phase is blocked by the water-seal portion  39 ; also if outside air tends to enter, it is blocked by the water-seal portion  39 . 
         [0048]    Thus, during steam cooking, steam is enclosed inside the heating chamber  20  so as to keep a low-oxygen condition and to continue to be used to heat food. In this way, it is possible to prevent oxidation-induced degradation in taste. Moreover, the energy used to generate steam is not wasted, and thus it is possible to perform cooking with improved energy efficiency. Drainage of condensate without passage of steam is achieved by means of a simple mechanism, that is, the water-seal portion  39 , and thus no complicated mechanism needs to be adopted as would lead to increased cost. 
         [0049]    When condensate overflows out of the bend  36   a , it flows down the drain pipe  36  and, where it ends, flows out of the drain passage  37  into the drain pan  38 . Taking notice of the condensate collecting in the drain pan  38 , the user, as necessary, pulls out the drain pan  38  and clears it of its contents while the microwave cooking device  1  is out of operation. The user then puts the drain pan  38  back in position in preparation for steam cooking next time. 
         [0050]    In the construction according to the embodiment, in the bottom wall of the heating chamber  20 , the funnel-shaped slope  28  is formed and, in the lowest part of the funnel-shaped slope  28 , the condensate drain port  27  is arranged. Thus, the condensate left after steam-cooking using steam can be collected from over a wide area and be disposed of reliably. This facilitates the cleaning after steam-cooking. The rotary shaft  31   d  which transmits rotation to the turntable  30  on which an object to be heated is placed penetrates the drain port  27 , and thus there is no need to separately provide a through hole in the bottom wall of the heating chamber  20  to put the rotary shaft  31   d  through. This helps simplify the construction and reduce the manufacturing cost. Condensate left collected under the turntable  30  leads to hygienic problems; the construction according to the embodiment, however, is free from such concerns. 
         [0051]    On the outer face of the bottom wall of the heating chamber  20 , the cup-shaped support base  33  is fixed, and this support base  33  supports the motor  32  which gives rotation to the rotary shaft  31   d , and in addition collects the condensate flowing out through the condensate drain port  27 . Thus, it is possible to reliably prevent energized parts of electric components from becoming wet with condensate, and thus to achieve enhanced safety. Moreover, the support base  33  serving both to support the motor  32  and to collect condensate helps reduce the number of components needed and hence reduce the manufacturing cost. 
         [0052]    To the drain port  35  formed in the support base  33 , the drain pipe  36  which constitutes part of the drain passage  37  is connected, and the bend  36   a  formed as a part of the drain pipe  36  constitutes the water-seal portion  39 . Thus, it is possible to form the water-seal portion  39  easily. Moreover, where the drain passage  37  ends, the drain pan  38  is arranged. Thus, it is possible to dispose of condensate easily so as not to incur an unhygienic condition. 
         [0053]    The water-seal portion  39  may be formed by any other means than the bend  36   a  formed in the drain pipe  36 ; any structure may instead be used so long as it acts as a water-seal portion that keeps water somewhere within it in such a way that the water stops the drain pipe  36 . 
         [0054]    The embodiment by way of which the invention has been specifically described above is in no way meant to limit the scope of the invention; in implementing the invention, many modifications and variations are possible within the spirit of the invention. 
       INDUSTRIAL APPLICABILITY 
       [0055]    The present invention finds wide application in microwave cooking devices that are capable of cooking by steam. 
       LIST OF REFERENCE SIGNS 
       [0000]    
       
         
           
               1  microwave cooking device 
               10  cabinet 
               11  door 
               15  operation panel 
               20  heating chamber 
               21  microwave generating device 
               22  steam generating device 
               27  condensate drain port 
               28  slope 
               30  turntable 
               31  roller stay 
               31   d  rotary shaft 
               32  motor 
               33  support base 
               35  drain port 
               36  drain pipe 
               36   a  bend 
               37  drain passage 
               38  drain pan 
               39  water-seal portion