Abstract:
A cooking device ( 1 ) has a vapor generating device ( 5 ) for supplying vapor to a heating chamber ( 2 ), a heater ( 14 ) for changing saturated water vapor generated by the vapor generating device to superheated water vapor, and a circulation fan ( 14 ) for circulating gas in the heating comber ( 2 ) through a circulation duct ( 10 ). A control device ( 60 ) for controlling the entire cooking device ( 1 ) performs, according to selection by a user, a bacteria elimination mode such as a resin tableware mode, a ceramic mode, or a kitchenware mode, and the modes have different water vapor temperature settings for different categories of objects from which bacteria are to be eliminated. When a bacteria elimination key ( 70 ) provided at an operation section ( 3   b ) is pressed, the cooking device ( 1 ) enters an operation for selecting among the bacteria elimination modes.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a cooking device that can heat food inside a heating chamber by use of steam. 
       BACKGROUND ART 
       [0002]    Household cooking devices that can heat food with steam are increasingly common nowadays. An example is seen in Patent Document 1 listed below. 
         [0003]    Steam is also used for sterilization. Examples of devices for sterilization by steam are seen in Patent Documents 2 and 3 listed below. Patent Document 2 discloses a device that sterilizes kitchenware with steam, and Patent Document 3 discloses a device that sterilizes food with steam. 
       LIST OF CITATIONS 
     Patent Literature 
       [0000]    
       
         Patent Document 1: JP-2008-25894 
         Patent Document 2: JP-2004-222816 
         Patent Document 3: JP-2001-145568 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0007]    Household tableware and kitchenware needs proper sterilization. Different articles, however, have different levels of heat resistance, and should not be sterilized under uniform conditions. 
         [0008]    Under the background discussed above, an object of the present invention is to provide a cooking device that can properly sterilize differently heat-resistant articles of tableware and kitchenware used in households. 
       Solution to Problem 
       [0009]    To achieve the above object, according to the present invention, a cooking device that can heat food inside a heating chamber by use of steam is characterized in that a controller that governs overall control of the cooking device performs a plurality of sterilizing courses with varied steam temperature settings for different sterilization target categories according to a user&#39;s selection. 
         [0010]    With this configuration, by selecting a sterilization course according to what needs to be sterilized, it is possible to prevent the sterilization target from being hit by steam at an inappropriate temperature. 
         [0011]    In the cooking device described above, preferably, when the user presses a sterilization-dedicated key provided in an operation portion, the cooking device enters a mode for selection among the sterilizing courses. 
         [0012]    With this configuration, it is possible to select and perform a sterilizing course surely. 
       Advantageous Effects of the Invention 
       [0013]    According to the present invention, it is possible to properly sterilize differently heat-resistant various articles present in households. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0014]    [ FIG. 1 ] is a front sectional view showing a cooking device embodying the invention. 
           [0015]    [ FIG. 2 ] is a side sectional view showing the cooking device embodying the invention. 
           [0016]    [ FIG. 3 ] is a top sectional view showing the cooking device embodying the invention. 
           [0017]    [ FIG. 4 ] is a front sectional view showing the cooking device embodying the invention as cut on a plane through a first exhaust port. 
           [0018]    [ FIG. 5 ] is a top sectional view showing the cooking device embodying the invention in a state with an exhaust damper closed. 
           [0019]    [ FIG. 6 ] is a top sectional view showing the cooking device embodying the invention in a state with the exhaust damper opened. 
           [0020]    [ FIG. 7 ] is a top sectional view showing the cooking device embodying the invention in a state with a feed damper closed. 
           [0021]    [ FIG. 8 ] is a top sectional view showing the cooking device embodying the invention in a state with the feed damper opened. 
           [0022]    [ FIG. 9 ] is a top sectional view showing the cooking device embodying the invention during cooking by microwaves. 
           [0023]    [ FIG. 10 ] is a flow chart showing the operation of the cooking device embodying the invention during cooking by steam. 
           [0024]    [ FIG. 11 ] is a top sectional view showing the cooking device embodying the invention during cooling after cooking by steam. 
           [0025]    [ FIG. 12 ] is a block configuration diagram of the cooking device embodying the invention. 
           [0026]    [ FIG. 13 ] is a front view of the cooking device embodying the invention. 
           [0027]    [ FIG. 14 ] is an enlarged view of an operation portion of the cooking device embodying the invention. 
           [0028]    [ FIG. 15 ] shows a display screen for selection of a cooking course in the cooking device embodying the invention. 
           [0029]    [ FIG. 16 ] shows a display screen for selection of a sterilizing course in the cooking device embodying the invention. 
           [0030]    [ FIG. 17 ] is a flow chart of a resin tableware sterilization course in the cooking device embodying the invention. 
           [0031]    [ FIG. 18 ] is a flow chart of a china and porcelain tableware sterilization course in the cooking device embodying the invention. 
           [0032]    [ FIG. 19 ] is a flow chart of a kitchenware sterilization course in the cooking device embodying the invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0033]    An embodiment of the present invention will be described below with reference to the accompanying drawings. A cooking device  1  has, inside a cabinet  4 , a heating chamber  2  which is open frontward and openably closed with a door  3 . Inside the heating chamber  2 , a tray  9  is disposed, and food placed on the tray  9  is accommodated. 
         [0034]    Inside the cabinet  4 , a circulation duct  10  is provided which runs along the exterior walls of the heating chamber  2 . The circulation duct  10  is composed of a side portion  11  at the right side, a top portion  12  at the top, and a side portion  13  at the left side, and these are coupled together in this order. In the side portion  11 , approximately at the middle in the depth (front-rear) direction, an evacuation port  10   a  is formed which is open to the heating chamber  2 . In the top portion  12  and the side portion  13 , blowout ports  10   b  and  10   c  are formed which are open to the heating chamber  2 . 
         [0035]    In the right-side wall of the heating chamber  2 , there are formed, frontward of the evacuation port  10   a , a feed port  33  and, rearward of the evacuation port  10   a , a first exhaust port  34 . The feed port  33  is disposed near the door  3  so that a stream of air blown out via the feed port  33  passes along the door  3 . Rearward and downward of the first exhaust port  34 , a second exhaust port  35  is formed. The second exhaust port  35  has a smaller opening area than the first exhaust port  34 . 
         [0036]    In the side portion  11 , a circulation fan  14  is disposed which is driven by a circulation motor  14   a . As the circulation fan  14  is driven, steam and air inside the heating chamber  2  are sucked into the circulation duct  10  via the evacuation port  10   a , and are then blown out via the blowout ports  10   b  and  10   c . In the side portion  11 , a temperature sensor  16  is provided which monitors the temperature of the steam and air inside the heating chamber  2  as they enter the side portion  11 . 
         [0037]    In the top portion  12 , a heater  15 , such as a sheathed heater, is disposed. The heat radiated from the heater  15  heats the article to be cooked. The heater  15  also heats the steam and air passing through the circulation duct  10 , so that the heated steam and air are blown out via the blowout ports  10   b  and  10   c . This keeps the steam and air inside the heating chamber  2  at a predetermined temperature. The steam fed into the heating chamber  2  can also be further heated to produce superheated steam. 
         [0038]    On the right side of the heating chamber  2 , a removable water tank  7  is disposed. Behind the water tank  7 , a steam generator  5  is provided. The steam generator  5  is connected to the water tank  7 , and generates steam with heat from a heater (not shown). From the steam generator  5 , a steam duct  6  extends to be connected to the side portion  11  of the circulation duct  10 . The steam generated in the steam generator  5  passes through the steam duct  6 , and enters the side portion  11  of the circulation duct  10  via an inflow port  6   a.    
         [0039]    Under and on the right side of the heating chamber  2 , between the cabinet  4  and the heating chamber  2 , an outside air introduction duct  8  is formed. The outside air introduction duct  8  has a suction port  8   a  formed in the bottom face of the cabinet  4 . In a lower part of the outside air introduction duct  8 , there are disposed a cooling fan  17 , an electric unit  18 , and a magnetron  20 . In a side part of the outside air introduction duct  8 , an air blow duct  30  is disposed. Inside the air blow duct  30 , a dilution fan  31  is provided which is driven by a motor  31   a.    
         [0040]    The electric unit  18  includes driving circuits for driving relevant parts of the cooking device  1  and control circuits for controlling those circuits, and has many components mounted thereon that release heat. The magnetron  20  feeds microwaves into the heating chamber  2  through a wave guide  21 . The cooling fan  17  introduces outside air into the outside air introduction duct  8  via the suction port  8   a , so as to cool the electric unit  18  and the magnetron  20 , which release heat. The outside air introduced into the outside air introduction duct  8  by the cooling fan  17  is drawn by the dilution fan  31 . The outside air introduced into the outside air introduction duct  8  eventually passes out of the cabinet  4  via an opening (not shown) formed in the rear face thereof or elsewhere. 
         [0041]      FIG. 4  is a front sectional view of the cooking device  1  as cut on a plane through the first exhaust port  34 . In  FIGS. 1 to 4 , at the right-side wall of the heating chamber  2 , a first exhaust duct  36  (first exhaust passage) extends from the first exhaust port  34 . The first exhaust duct  36  is composed of a transverse passage  36   a , which extends horizontally, and an upright passage  36   b , which bends upward from the transverse passage  36   a . At the upper end of the upright passage  36   b , a top cap  40  is provided which is disposed on the top face of the cabinet  4 . 
         [0042]    In the rear side of the transverse passage  36   a , a suction port  38   a  is formed via which outside air is sucked in through a suction duct  38 . In the front side of the transverse passage  36   a , a humidity sensor  39  is disposed opposite the suction port  38   a . The humidity sensor  39  monitors the humidity of the exhaust air at the first exhaust port  34 . Moreover, in the transverse passage  36   a , a exhaust damper  37  is provided which selectively opens either the first exhaust port  34  or the suction port  38   a.    
         [0043]      FIG. 5  is a top sectional view showing the details of the exhaust damper  37 . The exhaust damper  37  has an arm  37   c  which is supported at a shaft portion  37   b  to be pivotable thereabout by a motor (not shown), and at the tip end of the arm  37   c , a flexible member  37   a  is disposed. The arm  37   c  is a slender solid bar, and is elastically deformable. As shown in  FIG. 5 , when the flexible member  37   a  is in close contact with the rim of the first exhaust port  34 , the first exhaust port  34  remains closed, and the suction port  38   a  remains open. In this state, the elasticity of the arm  37   c  (elastic member) urges the exhaust damper  37  in its closing direction. 
         [0044]    As shown in  FIG. 6 , when the arm  37   c  swings so as to bring the flexible member  37   a  into close contact with the rim of the suction port  38   a , the suction port  38   a  is closed; at this time, the first exhaust port  34  is opened. Thus, the exhaust damper  37  serves as a suction damper that opens and closes the suction port  38   a . Opening and closing the first exhaust port  34  and the suction port  38   a  with a single exhaust damper  37  helps reduce the number of components. 
         [0045]    The upright passage  36   b  of the first exhaust duct  36  is, in an upper part thereof, given an increased passage cross-sectional area and coupled to the top cap  40 . The top cap  40  is, at the free end thereof, open frontward to form a discharge port  40   a . The discharge port  40   a  is disposed with the lower end thereof away from the top face of the cabinet  4 . The aim is to prevent entry of water into the first exhaust duct  36  in case water is spilt on top of the cabinet  4 . 
         [0046]    The upper and lower walls of the top cap  40  are inclined 20° or more upward relative to the horizontal line. Thus, the exhaust air discharged out via the discharge port  40   a  of the top cap  40  is blown out obliquely upward, at 20° or more relative to the horizontal line. Locating the lower end of the discharge port  40   a  away from the top face of the cabinet  4  and discharging the exhaust air obliquely upward via the discharge port  40   a  helps reduce steam that passes along the top face of the cabinet  4 . This reduces condensation on the top face of the cabinet  4 . 
         [0047]    At the lower end of the discharge port  40   a , a projection (not shown) may be provided that projects frontward. This helps cancel the Coanda effect, whereby steam from a lower part of the discharge port  40   a  passes along the top face of the cabinet  4 . This further reduces condensation on the top face of the cabinet  4 . Forming the tip end of the projection in an acute angle is further preferable, because that further cancels the Coanda effect. 
         [0048]    To the lower face of the transverse passage  36   a  of the first exhaust duct  36 , a second exhaust duct  41  (second exhaust passage) extending from the second exhaust port  35  is coupled at a coupling  41   a . Thus, the humidity sensor  39  disposed in the transverse passage  36   a  is disposed upstream of the coupling  41   a  provided in the upright passage  36   b . The second exhaust duct  41  may be formed of flexible tube. 
         [0049]    The second exhaust duct  41  is formed to have a smaller passage cross-sectional area than the first exhaust duct  36 . The exhaust air via the second exhaust port  35  passes through the second exhaust duct  41 , enters the first exhaust duct via the coupling  41   a , and is discharged out via the discharge port  40   a  of the top cap  40 . The lower face of the first exhaust duct  36  is inclined downward toward the coupling  41   a.    
         [0050]    In a lower part of the air blow duct  30  at the side of the heating chamber  2 , the dilution fan  31  is disposed, and in an upper part of the air blow duct  30 , an air blow passage of the dilution fan  31  is formed. The air blow duct  30  has an upright passage  30   a , a transverse passage  30   b , and a nozzle portion  30   c . The upright passage  30   a  extends upward from the dilution fan  31 . The transverse passage  30   b  bends rearward from the upright passage  30   a , and is disposed into the first exhaust duct  36 . 
         [0051]    The nozzle portion  30   c  further bends upward from the transverse passage  30   b , and has, at the end thereof, an opening  30   d  that is open upward. Thus, inside the first exhaust duct  36 , an ejector is formed, so that, as the dilution fan  31  is driven, a stream of air is produced that runs from the first exhaust port  34  to the open end (discharge port  40   a ). Here, the coupling  41   a  and the suction port  38   a  are disposed upstream of the opening  30   d . Thus, a negative pressure is applied to the second exhaust duct  41  and the suction duct  38 , and this prevents a backward stream of air. 
         [0052]    In the transverse passage  30   b , a lowered portion  30   g  is formed whose level is lower than the lower end of the part of the transverse passage  30   b  connecting to the upright passage  30   a . At one end of the lowered portion  30   g , a sub-nozzle portion  30   e  is formed which is open to the top cap  40 . The sub-nozzle portion  30   e  has the lower wall thereof inclined upward. Thus, as the dilution fan  31  is driven, the stream of air that passes from the sub-nozzle portion  30   e  into the first exhaust duct  36  runs upward, and this prevents a backward stream of air into the second exhaust duct  41 . 
         [0053]    The lower wall of the lowered portion  30   g  is inclined downward toward the sub-nozzle portion  30   e . Thus, even in case water is spilt on the top face of the cabinet  4  and enters the air blow duct  30  via the top cap  40 , the water is collected in the lowered portion  30   g  and is drained into the first exhaust duct  36  via the sub-nozzle portion  30   e . The water that has entered the first exhaust duct  36  runs down the inclined lower face, and is collected, through the second exhaust duct  41 , in the heating chamber  2 . In this way, the motor  31   a  of the dilution fan  31  is prevented from being soaked in water. 
         [0054]    The air blow duct  30  has, at the part thereof where the upright passage  30   a  connects to the transverse passage  30   b , a rib  30   f  that extends upward. The rib  30   f  is disposed inside the transverse passage  30   b , and lopsided toward the heating chamber  2 . The motor  31   a  of the dilution fan  31  is disposed inside the upright passage  30   a , and lopsided toward the heating chamber  2 . That is, the rib  30   f  is disposed lopsided in the same direction as the motor  31   a . Thus, in case water is spilt on the top face of the cabinet  4  and enters the air blow duct  30 , the motor  31   a  of the dilution fan  31  is more surely prevented from being soaked in water. 
         [0055]    In an upper part of the upright passage  30   a  of the air blow duct  30 , a feed tube  32  is provided to branch off. The feed tube  32  is connected to a feed duct  50  which extends from the feed port  33  of the heating chamber  2 . The feed tube  32  and the feed duct  50  form an air feed passage through which, as the dilution fan  31  is driven, air is fed into the heating chamber  2  via the feed port  33 . The feed tube  32  may be formed as a duct. 
         [0056]    The feed duct  50  has a leak hole  50   a  formed therein opposite the feed port  33 , and is provided with a feed damper  51  which selectively opens, or closes, either the feed port  33  or the leak hole  50   a . The feed duct  50  forms the housing for the feed damper  51 . 
         [0057]      FIG. 7  is a side sectional view showing the details of the feed duct  50  and the feed damper  51 . The feed duct  50 , which forms the housing for the feed damper  51 , has, in a side face thereof, fitted with a ring-shaped gasket  52  formed as a flexible member, and is fitted in the feed port  33 . This keeps air-tightness between the feed port  33  and the feed duct  50 . 
         [0058]    The gasket  52  has a ring-shaped projection  52   a  formed around the inner circumference thereof. As shown in  FIG. 7 , when closed, the feed damper  51  is in close contact with the projection  52   a  so that no stream of air leaks through the feed port  33 . Thus, the gasket  52  that keeps air-tightness between the feed port  33  and the feed duct  50  keeps air-tightness between the feed port  33  and the feed damper  51 , and this helps reduce the number of components. 
         [0059]    The feed damper  51  is supported at a shaft portion  51   a  at the lower end thereof to be pivotable thereabout, and is urged in its opening direction by a tension spring  53  which is coupled to the feed duct  50 . Behind the feed damper  51 , a motor  54  is disposed. The shaft  54   a  of the motor  54  is fitted with a cam  55  which makes contact with the rear face of the feed damper  51 . 
         [0060]    In an upper part of the feed duct  50 , an inflow portion  50   b  is formed to which the feed tube  32  is connected. The inflow portion  50   b  is so inclined as to be increasingly low frontward, and through the inflow portion  50   b , a stream of air is blown out via the feed port  33  toward the door  3  (see  FIG. 3 ). The leak hole  50   a  is provided under the inflow portion  50   b . The wall face  50   c  around the leak hole  50   a  is inclined relative to the vertical line. 
         [0061]    As the motor  54  is driven, the feed damper  51  is pressed by the cam  55  so that, against the urging force of the tension spring  53 , the feed damper  51  is brought into close contact with the projection  52   a  of the gasket  52 . This allows the feed damper  51  to be kept closed by the pressing force of the cam  55  which is formed as an inelastic member. At this time, the leak hole  50   a  is opened. As the dilution fan  30  is driven, a stream of air that enters the feed duct  50  through the inflow portion  50   b  returns into the outside air introduction duct  8  via the leak hole  50   a.    
         [0062]    The exhaust damper  37  is urged in its closing direction by the arm  37   c  (see  FIG. 5 ), which is an elastic member, and the feed damper  51  is kept closed by the cam  55 , which is an inelastic member. Thus, when the exhaust damper  37  and the feed damper  51  are closed, if the pressure inside the heating chamber  2  becomes abnormally high, the exhaust damper  37  opens against the urging force of the arm  37   c  to exhaust air. This helps increase the safety of the cooking device  1 , and also prevents a backward stream of steam via the feed port  33 . 
         [0063]    As shown in  FIG. 8 , when the cam  55  rotates in the direction retreating from the feed damper  51 , the urging force of the tension spring  53  opens the feed damper  51 . The feed damper  51  is thus kept in contact with the inclined wall face  50   c  and hence open. At this time, the leak hole  50   a  is closed. Now, as the air dilution fan  30  is driven, a stream of air that enters the feed duct  50  through the inflow portion  50   b  is fed into the heating chamber  2  via the feed port  33 . 
         [0064]    On a lower part of the feed damper  51 , a rib serving as a gutter  51   b  is formed to project toward the heating chamber  2 . The gutter  51   b  is formed in the shape of a cornered C open at the top and toward the heating chamber  2 . When opened, the feed damper  51  is exposed to the hot gas inside the heating chamber  2 , and this causes condensation to form on its surface. The feed damper  51 , then resting on the wall face  50   c  and inclined, lets condensed water run down to collect in the gutter  51   b . When the feed damper  51  is closed, the condensed water is collected from the gutter  51   b  into the heating chamber  2 . This prevents water from leaking into the outside air introduction duct  8  (see  FIG. 1 ) in which the electric unit  18  is disposed. 
         [0065]    The elements involved in the control of the cooking device  1  are shown in  FIG. 12 . Overall control is governed by a controller  60 . Connected to the controller  60  are the circulation fan  14 , the heater  15 , the steam generator  5 , the cooling fan  17 , the magnetron  20 , the dilution fan  31 , the exhaust damper  37 , the feed damper  51 , the temperature sensor  16 , and the humidity sensor  39 , which have been mentioned above; additionally connected to the package can  60  are an operation portion  3   b , a display portion  3   c , a water level sensor  5   a , and a tank water level sensor  7   a . The operation portion  3   b  is provided on the front face of the door  3 , and includes means of operation such as push buttons, a dial, etc. The display portion  3   d  is provided within the operation portion  3   b , and includes a means of display such as a liquid crystal display panel. The water level sensor  5   a  is provided in the steam generator  5  to monitor the level of the water inside it; the tank water level sensor  7   a  is provided in the water tank  7  to monitor the level of water inside it. 
         [0066]    In the cooking device  1  configured as described above, when cooking by microwaves is started, the magnetron  20  is driven. Moreover, as shown in  FIG. 9 , the feed damper  51  and the exhaust damper  37  open the feed port  33  and the first exhaust port  34 , and the cooling fan  17  and the dilution fan  31  are driven. The magnetron  20  feeds microwaves into the heating chamber  2  through the wave guide  21 , and an article to be cooked is heated by microwaves. 
         [0067]    The cooling fan  17  introduces outside air into the outside air introduction duct  8  via the suction port  8   a  as indicated by arrow A 1  (see  FIG. 1 ). The outside air that has entered the outside air introduction duct  8  cools the electric unit  18  and the magnetron  20  as indicated by arrow A 2  (see  FIG. 1 ). The outside air that has cooled the electric unit  18  and the magnetron  20  and has thereby been heated is drawn by the dilution fan  31  as indicated by arrow A 3  (see  FIG. 1 ). 
         [0068]    The dilution fan  31  sends the outside air out, so that the outside air passes through the air blow duct  30 , the feed tube  32 , and the feed duct  50  as indicated by arrows A 4  and A 5  (see  FIG. 2 ). The outside air that has entered the feed duct  50  is fed into the heating chamber  2  via the feed port  33  as indicated by arrow A 6  (see  FIG. 9 ). 
         [0069]    Here, the stream of air blown out via the feed port  33  disposed near the door  3  passes along the door  3 . Thus, the air heated as a result of cooling the electric unit  18  and the magnetron  20  prevents condensation on the door  3 . Moreover, the inflow portion  50   b  of the feed duct  50  blows the stream of air out toward the door  3 . This ensures that the stream of air blown out via the feed port  33  reaches the door  3 , and thereby helps further prevent condensation. 
         [0070]    In addition, as indicated by arrows A 7  and A 8  (see  FIG. 2 ), the outside air is fed into the first exhaust duct  36  via the nozzle portion  30   c  and the sub-nozzle portion  30   e  of the air blow duct  30 . 
         [0071]    The air inside the heating chamber  2  is exhausted via the first and second exhaust ports  34  and  35  as indicated by arrows A 9  and A 11  (see  FIG. 9 ). The exhaust air via the second exhaust port  35  passes through the second exhaust duct  41 , and enters the first exhaust duct  36  via the coupling  41   a  as indicated by arrow A 10  (see  FIG. 2 ). 
         [0072]    The exhaust air via the first exhaust port  34  makes contact with the humidity sensor  39  in the transverse passage  36   a  of the first exhaust duct  36 . Thus, the humidity inside the heating chamber  2  is detected. The exhaust air through the transverse passage  36   a  passes through the upright passage  36   b  to join the exhaust air through the second exhaust duct  41  and goes up, so as to be discharged out via the discharge port  40   a  of the top cap  40  as indicated by arrow A 12  (see  FIG. 2 ). Here, since the nozzle portion  30   c  and the sub-nozzle portion  30   e  of the air blow duct  30  form an ejector, a negative pressure is applied to the second exhaust duct  41  and the feed port  33 . This prevents a backward stream of exhaust air. 
         [0073]    Heated by microwaves, the article being cooked gives off steam. When the humidity inside the heating chamber  2  becomes equal to a predetermined level, the humidity sensor  39  detects it, and thereby the time to end cooking is recognized. Thus, cooking by microwaves is ended. 
         [0074]      FIG. 10  is a flow chart showing how cooking by steam proceeds. When cooking by steam is started, at step # 11 , as shown in  FIG. 3  described previously, the feed damper  51  and the exhaust damper  37  close the feed port  33  and the first exhaust port  34 . At step # 12 , the steam generator  5  and the heater  15  are driven. As a result, steam is fed into the circulation duct  10  and is heated by the heater  15  to produce superheated steam. 
         [0075]    At step # 13 , the cooling fan  17 , the dilution fan  31 , and the circulation fan  14  are driven. In a similar manner as described previously, as the cooling fan  17  and the dilution fan  31  are driven, outside air enters the outside air introduction duct  8  via the suction port  8   a . The outside air is then fed into the first exhaust duct  36  via the nozzle portion  30   c  and sub-nozzle portion  30   e  of the air blow duct  30 . 
         [0076]    As the circulation fan  14  is driven, the steam inside the heating chamber  2  enters the circulation duct  10  via the suction port  8   a  as indicated by arrow C 1  (see  FIG. 1 ). The steam that has entered the circulation duct  10  is blown out into the heating chamber  2  via the blowout ports  10   b  and  10   c  as indicated by arrows C 2  and C 3  (see  FIG. 1 ). As a result, the steam inside the heating chamber  2  circulates through the circulation duct  10 . The steam passing through the circulation duct  10  is heated by the heater  15 , so that the steam is kept at a required temperature to perform cooking. The temperature and driving duration of the heater  15  may be adjusted so as to perform cooking with saturated steam. 
         [0077]    Feeding steam from the steam generator  5  into the heating chamber  2  causes steam to pass out of the heating chamber  2  via the second exhaust port  35  as indicated by arrow A 9  (see  FIG. 1 ). This keeps the pressure inside the heating chamber  2  constant. The second exhaust duct  41  has a smaller passage cross-sectional area than the first exhaust duct  36 , and thus allows less steam to pass out. This contributes to increased heating efficiency. 
         [0078]    The exhaust air via the second exhaust port  35  passes through the second exhaust duct  41 , and enters the first exhaust duct  36  via the coupling  41   a . Since the dilution fan  31  feeds outside air into the first exhaust duct  36 , the exhaust via the second exhaust port  35  is diluted before being discharged out. This allows steam to be discharged after being cooled down, and thus helps increase the safety of the cooking device  1 . 
         [0079]    At this time, the outside air passing through the outside air introduction duct  8  exchanges heat with the electric unit  18  and the magnetron  20  and is thereby heated. Thus, the exhaust air via the second exhaust port  35  is mixed with heated outside air, and this lowers the relative humidity of the exhaust air. It is thus possible to reduce condensation inside the first and second exhaust ducts  36  and  41 . 
         [0080]    Disposing the humidity sensor  39  upstream of the coupling  41   a  of the second exhaust duct  41  helps reduce contact between the steam passing from the second exhaust duct  41  into the first exhaust duct  36  and the humidity sensor  39 . This helps reduce condensation on the humidity sensor  39 , and makes it possible to perform cooking by microwaves satisfactorily the next time. 
         [0081]    As a result of outside air entering the first exhaust duct  36  via the nozzle portion  30   c  and the sub-nozzle portion  30   e , a negative pressure produced by an ejector is applied to the suction duct  38 . As a result, as indicated by arrow B 1  (see  FIGS. 2 and 3 ), outside air is sucked into the first exhaust duct  36  via the suction port  38   a . This helps further dilute the exhaust air via the second exhaust port  35 . In addition, since the humidity sensor  39  is disposed between the suction port  38   a  and the coupling  41   a , the humidity sensor  39  makes contact with the outside air from the suction port  38   a . This allows the humidity sensor  39  to be dried, and helps further prevent condensation on the humidity sensor  39 . 
         [0082]    The negative pressure produced by the ejector is also applied to the second exhaust duct  41 , and this prevents a backward stream through the second exhaust duct  41 . Since the second exhaust duct  41  has a small passage cross-sectional area, when condensation forms, the second exhaust duct  41  may become closed airtight, causing the pressure inside the heating chamber  2  to rise instead of being sucked up by the negative pressure by the ejector. To avoid this, it is preferable to drive the dilution fan  31  in an intermittent operation in which driven periods and halted periods alternate. In this way, while the dilution fan  31  is halted, the condensation inside the second exhaust duct  41  runs down and collects in the heating chamber  2 , and this helps maintain the pressure inside the heating chamber  2 . 
         [0083]    At step # 14 , passage of a predetermined cooking time is waited for. When the predetermined time passes and cooking ends, then, at step # 15 , the steam generator  5  and the heater  15  are stopped. At step # 16 , the circulation fan  14  is stopped. 
         [0084]    At step # 17 , as shown in  FIG. 11 , the feed damper  51  is opened. Now, outside air is fed through the feed tube  32  and the air blow duct  30  into the heating chamber  2  via the feed port  33  (arrow A 6 ), and is exhausted via the second exhaust port  35 . As a result, the inside of the heating chamber  2  is cooled. At this time, the exhaust damper  37  remains closed, and this prevents contact between the steam inside the heating chamber  2  and the humidity sensor  39 . 
         [0085]    At step # 18 , passage of a predetermined cooling time is waited for. When the predetermined time passes, an advance is made to step # 19 . It is also possible to monitor the temperature inside the heating chamber  2  so that, when it reaches a predetermined temperature, an advance is made to step # 19 . At step # 19 , the cooling fan  17  and the dilution fan  31  are stopped. At step # 20 , completion of cooking is indicated. 
         [0086]    It is also possible to stop the feeding of steam while driving the heater  15  and the circulation fan  14  to perform cooking with hot air. In that case also, through operation similar to cooking by steam, cooking is achieved. Since no steam is used then, the exhaust damper  37  may be opened during cooling after cooking. This increases the exhaustion rate, and thus allows quick cooling of the inside of the heating chamber  2 . 
         [0087]    It is also possible to open, during cooling, the feed damper  51  that has been closed during cooking by steam or hot air and, a predetermined period thereafter, open the exhaust damper  37 . This makes it possible to first cool to a certain degree by exhausting a small amount of gas via the second exhaust port  35  and then further cool by exhausting a large amount of gas via the first exhaust port  34 . In this way, it is possible to secure safety and achieve quick cooling. 
         [0088]    Instead of cooling the heating chamber  2  by opening, after cooking, the feed damper  51  that has been closed during cooking by steam or hot air, it is also possible to open the feed damper  51   a  predetermined period (for example, one minute) before completion of cooling. This permits the heating chamber  2  to have been cooled, and hence the door  3  to be opened, on completion of cooling, and thus makes the cooking device  1  more convenient to use. 
         [0089]    The cooking device  1  can sterilize articles put inside it by use of steam. The mechanism will now be described with reference to  FIGS. 13 to 19 . 
         [0090]    The door  3  is provided with, in an upper part, a handle  3   a  and, in a right-side part, an operation portion  3   b . The operation portion  3   b  includes a display portion  3   c . On the left side of the operation portion  3   b , a sight window  3   d  is provided which allows visual inspection inside the heating chamber  2 . The sight window  3   d  has a pane of heat-resistant glass set therein. 
         [0091]    The display portion  3   c  is built around a liquid crystal display panel. Under the display portion  3   c , three rectangular keys are arranged in a horizontal row. These are, from left, a “sterilize” key  70 , a “cancel” key  71 , and a “return” key  72 . The “sterilize” key  70  is a key dedicated to sterilization, and pressing it invokes a mode for selection among a plurality of sterilizing courses. The “cancel” key  71  is used to cancel an operation. The “return” key  72  is used to return to the stage one operation before. 
         [0092]    Closely under the “return” key  72 , a circular “start” key  73  is provided. On the lower left side of the “start” key  73 , that is, right under the “cancel” key  71 , a selection dial  74  is provided. At the center of the selection dial  74 , an “enter” key  75  is provided. While the selection dial  74  is rotary, the “enter” key  75  is not. 
         [0093]    The “start” key  73  is used to turn the power on and off, and to start the selected course. The selection dial  74  is used to select among different courses and different preferences displayed on the display portion  3   c . The “enter” key  75  is used to fix a selection. 
         [0094]    During ordinary cooking, displayed on the display portion  3   c  are, as shown in  FIG. 15 , tabs for different cooking courses, such as “microwave cooking,” “steam cooking,” “drink warming/thawing,” “automatic menus,” and “manual.” When the user turns the selection dial  74  and selects one of the tabs, the selected tab becomes bigger than the other, and a message showing an outline of that cooking course is displayed. When the user confirms his selection correct and presses the “enter” key  75 , a screen for selection of preferences to be specified for execution of the cooking course is displayed. When the user makes necessary selections and presses the “start” key  73 , the cooking course is executed. 
         [0095]    Pressing the “sterilize” key  70  invokes a mode for selection among a plurality of sterilizing courses, and the screen on the display portion  3   c  switches to a sterilizing course selection screen as shown in  FIG. 16 . Displayed on the sterilizing course selection screen are tabs for three sterilizing courses, namely “resin tableware course,” “china and porcelain course,” and “kitchenware course.” When the user turns the selection dial  74  and selects one of the tabs, the selected tab becomes bigger than the other, and a message showing an outline of that sterilizing course is displayed. When the user confirms his selection correct and presses the “enter” key  75 , a screen for selection of preferences to be specified for execution of the sterilization course is displayed. When the user makes necessary selections and presses the “start” key  73 , the sterilization course is executed. Now, with reference to  FIGS. 17 to 19 , how each sterilizing course proceeds will be described. 
         [0096]    [Resin Tableware Course] 
         [0097]    The procedure shown in a flow chart in  FIG. 17  starts when the user puts a sterilization target—suppose here, for example, a piece of plastic tableware heat-resistant to 120° C. (degrees Celsius) or more—in the heating chamber  2  and presses the “start” key  73 . At step # 101 , the feed damper  51  and the exhaust damper  37  are closed. At step # 102 , a pre-heating process is started. In the resin tableware course, the temperature of the steam used for sterilization is low; therefore, if the heating chamber  2  is cold, condensation forms on the interior surface of the heating chamber  2 . To prevent this, the heating chamber is pre-heated to about a temperature at which condensation does not form. The temperature inside the heating chamber during pre-heating is set for 100° C. 
         [0098]    At step # 103 , the circulation fan  14  and the heater  15  are turned on, so that the heating chamber  2  is pre-heated. The cooling fan  17  and the dilution fan  31  are also turned on. At step # 104 , the time that has passed since the pre-heating process was started is checked so that, if a predetermined time (t 13 ) has passed, an advance is made to step # 105 . 
         [0099]    At step # 105 , a superheated steam heating process is started. The temperature inside the heating chamber  2  is set for 105° C. At step # 106 , the steam generator  5 , the circulation fan  14 , and the heater  15  are all turned on, so that superheated steam is blown out into the heating chamber  2 , and the superheated steam inside the heating chamber  2  circulates. The cooling fan  17  and the dilution fan  31  are also turned on. 
         [0100]    At step # 107 , the time (t 23 ) that has passed since the superheated steam heating process was started is checked so that, if a predetermined time has passed, an advance is made to step # 108 . At step # 108 , the steam generator  5  and the heater  15  are turned off, but the circulation fan  14  is kept on, so that the gas inside the heating chamber  2  continues to circulate. The cooling fan  17  and the dilution fan  31  are also kept on. 
         [0101]    At step # 109 , a cooling process is started. At this time, the feed damper  51  and the exhaust damper  37  are opened. The hot gas inside the heating chamber  2  is exhausted through the first exhaust duct  36  out via the discharge port  40   a.    
         [0102]    At step # 110 , the time (t 33 ) that has passed since the cooling process was started is checked so that, if a predetermined time has passed, an advance is made to step # 111 . At step # 111 , the circulation fan  14  is turned off. The cooling fan  17  and the dilution fan  31  are also turned off. Then, an advance is made to step # 112 , where completion of the process is indicated. Completion of the process is indicated visibly on the display portion  3   c  and audibly, with an audible signal, from a sound generator (not shown). This ends the resin tableware sterilizing course. 
         [0103]    [China and Porcelain Course] 
         [0104]    The procedure shown in a flow chart in  FIG. 18  starts when the user puts a sterilization target—suppose here, for example, a china or porcelain heat-resistant to 160° C. or more—in the heating chamber  2  and presses the “start” key  73 . At step # 121 , the feed damper  51  and the exhaust damper  37  are closed. At step # 122 , a superheated steam heating process is started. In the china and porcelain course, the steam used for sterilization is superheated steam at a high temperature; therefore, no condensation forms even without pre-heating. Accordingly, no pre-heating process is involved here. 
         [0105]    In the superheated steam heating process, the temperature inside the heating chamber  2  is set for 140° C. At step # 123 , the steam generator  5 , the circulation fan  14 , and the heater  15  are all turned on, so that superheated steam is blown out into the heating chamber  2 , and the superheated steam inside the heating chamber  2  circulates. The cooling fan  17  and the dilution fan  31  are also turned on. 
         [0106]    At step # 124 , the time (t 21 ) that has passed since the superheated steam heating process was started is checked so that, if a predetermined time has passed, an advance is made to step # 125 . At step # 125 , the steam generator  5  and the heater  15  are turned off, but the circulation fan  14  is kept on, so that the gas inside the heating chamber  2  continues to circulate. The cooling fan  17  and the dilution fan  31  are also kept on. 
         [0107]    At step # 126 , a cooling process is started. At this time, the feed damper  51  and the exhaust damper  37  are opened. The hot gas inside the heating chamber  2  is exhausted through the first exhaust duct  36  out via the discharge port  40   a.    
         [0108]    At step # 127 , the time (t 31 ) that has passed since the cooling process was started is checked so that, if a predetermined time has passed, an advance is made to step # 128 . At step # 128 , the circulation fan  14  is turned off. The cooling fan  17  and the dilution fan  31  are also turned off. Then, an advance is made to step # 129 , where completion of the process is indicated. Completion of the process is indicated visibly on the display portion  3   c  and audibly, with an audible signal, from a sound generator (not shown). This ends the china and porcelain sterilizing course. 
         [0109]    [Kitchenware Course] 
         [0110]    The procedure shown in a flow chart in  FIG. 19  starts when the user puts a sterilization target—suppose here, for example, a damp hand towel or a cutting board heat-resistant to 90° C. or more—in the heating chamber  2  and presses the “start” key  73 . At step # 131 , the feed damper  51  and the exhaust damper  37  are closed. At step # 132 , a saturated steam heating process is started. In the kitchenware course, the steam used for sterilization is saturated steam; accordingly, condensation on the heating chamber  2  and the sterilization target is taken as a matter of course, and no pre-heating process is involved here. 
         [0111]    In the saturated steam heating process, the temperature inside the heating chamber  2  is set for 80° C. At step # 133 , the steam generator  5  and the circulation fan  14  are turned on, whereas the heater  15  is turned off, so that saturated steam is blown out into the heating chamber  2 , and the saturated steam inside the heating chamber  2  circulates. The cooling fan  17  and the dilution fan  31  are also turned on. 
         [0112]    At step # 134 , the time (t 12 ) that has passed since the superheated steam heating process was started is checked so that, if a predetermined time has passed, an advance is made to step # 135 . At step # 135 , in addition to the heater  15 , the steam generator  5  is turned off, but the circulation fan  14  is kept on, so that the gas inside the heating chamber  2  continues to circulate. The cooling fan  17  and the dilution fan  31  are also kept on. 
         [0113]    At step # 136 , a cooling process is started. At this time, the feed damper  51  and the exhaust damper  37  are opened. The hot gas inside the heating chamber  2  is exhausted through the first exhaust duct  36  out via the discharge port  40   a.    
         [0114]    At step # 137 , the time (t 22 ) that has passed since the cooling process was started is checked so that, if a predetermined time has passed, an advance is made to step # 138 . At step # 138 , the circulation fan  14  is turned off. The cooling fan  17  and the dilution fan  31  are also turned off. Then, an advance is made to step # 139 , where completion of the process is indicated. Completion of the process is indicated visibly on the display portion  3   c  and audibly, with an audible signal, from a sound generator (not shown). This ends the kitchenware sterilizing course. 
         [0115]    In this way, by selecting a sterilizing course according to what needs to be sterilized, it is possible to prevent the sterilization target from being hit by steam at an inappropriate temperature. 
         [0116]    The embodiment described specifically above is in no way meant to limit the scope of the present invention; the invention may be carried out with many variations and modifications made without departing from the spirit of the invention. For example, it is possible to provide a course for sterilizing foods as well as those for sterilizing tableware and kitchenware. 
       INDUSTRIAL APPLICABILITY 
       [0117]    The present invention finds wide application in cooking devices provided with a function of heating food inside a heating chamber by use of steam. 
       LIST OF REFERENCE SIGNS 
       [0000]    
       
         
           
               1  cooking device 
               2  heating chamber 
               3  door 
               3   b  operation portion 
               3   c  display portion 
               5  steam generator 
               9  tray 
               10  circulation duct 
               14  circulation fan 
               15  heater 
               16  temperature sensor 
               17  cooling fan 
               18  electric unit 
               20  magnetron 
               31  dilution fan 
               37  exhaust damper 
               39  humidity sensor 
               51  feed damper 
               60  controller 
               70  “sterilize” key 
               74  selection dial 
               75  “enter” key