Patent Publication Number: US-7708007-B2

Title: Door assembly for home appliance, electric oven using the same, and method for operating electric oven

Description:
This application claims the benefit of the Korean Patent Application No. 10-2005-0116836, filed on Dec. 2, 2005, which is hereby incorporated by reference for all purposes as if fully set forth herein. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a door assembly which opens and closes a heating chamber of home appliance, to an electric oven employing the door assembly, and to method for operating the electric oven. 
   2. Discussion of the Related Art 
   Electric oven is an apparatus which heats food deposited in a heating chamber thereof using heaters operable by electricity, such as, a ceramic heater, a sheath grill heater, and/or a halogen heater. 
   Electric oven can cook food quickly and has a high thermal efficiency. In addition, electric oven is relatively safe from a fire started by a flame compared to gas oven. Therefore, electric oven gets more popular nowadays. 
   Meanwhile, dirt including ingredient of food and oil sticks to inner walls of the heating chamber of the electric oven while cooking. It is hard for the user to clean the dirt stuck to the inner walls of the heating chamber. Therefore, some electric ovens provide a special function which automatically cleans the inner walls of the heating chamber. 
   During the operation of the electric oven in an automatic cleaning mode, heaters of the electric oven heats up the heating chamber to a very high temperature, for example, over 450 degree Celsius higher than a temperature from 100 to 300 degree Celsius at which food is cooked. Therefore, the dirt stuck to the inner walls of the heating chamber is pyrolyzed and carbonized during the automatic cleaning mode. After the electric oven finishes the automatic cleaning mode, the user can easily remove carbonized dirt from the inner walls of the heating chamber by sweeping it with a brush. 
   Heat in the heating chamber is transferred to a door which opens and closes the heating chamber when the heaters heat up the heating chamber to cook food or to clean the inner walls of the heating chamber. Because the door is also heated by the heaters during the operation of the electric oven, the user may get a burn in case he/she accidentally touches the door during the operation of the electric oven, especially in the automatic cleaning mode. 
   In order to solve this problem, some electric ovens automatically cool down the door during the operation of the electric oven. These electric ovens include a fan that forms air flows running through an inner space of the door during the operation of the electric oven. The air flow generated by the fan usually cools down an inner surface of the door as well as an outer surface of the door while running through the inner space of the door. Therefore, the heating chamber as well as the door is cooled down by the air flow running through the door. 
   Accordingly, thermal efficiency of electric oven decreases when the fan cools the door during the operation of the electric oven. In addition, food deposited in the heating chamber is not evenly cooked because an area in the heating chamber adjacent to the door is so cooled compared to another area in the heating chamber opposite to the side adjacent to the door. Further, cooking time of electric oven increases. 
   SUMMARY OF THE INVENTION 
   Accordingly, the present invention is directed to a door assembly for home appliance, an electric oven using the same, and a method for operating the electric oven that substantially obviate one or more of the problems due to limitations and disadvantages of the related art. 
   An object of the present invention is to minimize a loss of thermal efficiency of a home appliance. Further, a user may be prevented from burns caused by accidentally (or otherwise) touching the door of a home appliance, e.g., during the operation of an electric oven in a cooking or an automatic cleaning mode. 
   Another object of the present invention is to improve efficiency for cooling an electric outfit room of an electric oven. 
   Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out, by way of non-limiting embodiments, in the written description and claims hereof as well as the appended drawings. 
   To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a door assembly for a home appliance may include a door which opens and closes a heating chamber, the door may have a first plate and a second plate, the first and second plates may form a first air gap in the door for insulating heat in the heating chamber; and a valve may be provided in the door to selectively allow air outside the first air gap to communicate with the first air gap. 
   The door assembly may further include a third plate located proximate (or arranged next to) the first or second plate to form a second air gap between the third plate and the first or second plate, wherein the second air gap forms an air flow passage for cooling the door. 
   The door assembly may further include a lock which selectively locks the door. Further, the valve may be operatively coupled to the lock (i.e., operable by the lock). The lock may include an actuator; and a rod operatively couple to the actuator (i.e., coupled to and operable by the actuator), the rod moving the valve to open a portion of the first air gap while locking the door. The valve may include a first member which opens and closes a portion of the first air gap; a second member movable along with the first member by the lock; a pivot about which the first and second members rotate together when the lock touches (or engages) the second member; and an elastic member which allows the first and second members to return to an initial position of the first and second members. 
   In another aspect of the present invention, an electric oven includes a case; a heating chamber in the case; a door which opens and closes the heating chamber. Further, the door may include a first glass facing the heating chamber and a second glass located in the door, the first and second glasses may form a first air gap in the door; and a valve may be provided in the door, the valve permitting air to enter the first air gap to cool the door or preventing air from entering the first air gap to insulate heat in the heating chamber. 
   The electric oven may further include: a third glass proximate (or arranged next to) the second glass to form a second air gap between the second and third glasses; and a supporter which supports the first, second, and third glasses thereon, the supporter permitting air to flow into the second air gap while preventing air from flowing into the first air gap. 
   The electric oven may further include a lock which selectively locks the door, wherein the valve is operable by the lock. The lock may include an actuator; and a rod coupled to and operable by the actuator, the rod moving the valve to open the first air gap while locking the door. The actuator may be mounted in the case so that it swings the rod to hook the door and pushes the valve. Alternatively, the actuator may be mounted in the case so that it pushes out the rod to hook the door and pushes the valve. Of course, it should be appreciated that any suitable mounting arrangements can be employed. 
   The valve may include a first member which opens and closes a portion of the first air gap; and a second member movable along with the first member by the lock; a pivot about which the first and second members rotate together when the lock touches the second member; and an elastic member which allows the first and second members to return to an initial position of the first and second members. 
   The valve may permit the air to flow into the first air gap to cool the door when a temperature of the heating chamber reaches a preset value. Alternatively, the valve may permit the air to flow into the first air gap to cool the door when the electric oven performs a preset operation mode. 
   The electric oven may further include a fan which introduces air outside the case into the case to cool a circumference of the heating chamber and into the door to cool the door. The electric oven may further include a first vent hole on the case, which introduces air outside the case to a proximity (or vicinity) of a control panel to cool the control panel. The electric oven may further include a second vent hole provided on the case, which introduces air outside the case to a vicinity of a motor of the fan to cool the motor. 
   In still another aspect of the present invention, an electric oven include a case; a heating chamber in the case; a door which opens and closes the heating chamber, the door including a first air gap therein and a second air gap therein; a fan provided in the case, the fan allowing air to flow through the second air gap to cool the door; a valve provided in the door, the valve permits air to enter the first air gap to either cool the door or prevent air from entering the first air gap to insulate heat in the heating chamber, selectively. 
   In still another aspect of the present invention, a method for operating an electric oven includes heating a heating chamber of the electric oven; and either flowing air through an air gap provided in a door of the heating chamber to cool the door or preventing air from entering the air gap to insulate heat in the chamber, selectively. 
   It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is further described in the detail description which follows, in reference to the noted plurality of drawings, by way of non-limiting examples of preferred embodiments of the present invention, in which like characters represent like elements throughout the several views of the drawings, and wherein: 
       FIG. 1  is a cross sectional view schematically illustrating an electric oven including a door assembly according to the present invention; 
       FIG. 2  is an exploded perspective view of the door assembly according to the present invention; 
       FIG. 3  is a partial sectional view schematically illustrating the lock and the valve of the door assembly according to the first embodiment of the present invention when the door of the electric oven is unlocked; 
       FIG. 4  is a partial sectional view schematically illustrating the lock and the valve of the door assembly according to the first embodiment of the present invention when the door of the electric oven is locked; 
       FIG. 5  is a partial plan view schematically illustrating working mechanism of the lock shown in  FIGS. 3 and 4 ; 
       FIG. 6  is a partial sectional view schematically illustrating the lock and the valve of the door assembly according to the second embodiment of the present invention when the door of the electric oven is unlocked; and 
       FIG. 7  is a partial sectional view schematically illustrating the lock and the valve of the door assembly according to the first embodiment of the present invention when the door of the electric oven is locked. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the present invention may be embodied in practice. 
   Reference will now be made in detail to an embodiment of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
     FIG. 1  is a cross sectional view schematically illustrating an electric oven including a door assembly according to the present invention. As shown in  FIG. 1 , the electric oven includes a case  100 , a heating chamber  110  provided in the case  100 , a door assembly including a door  200  provided at a front of the case  100  for opening and closing the heating chamber  110 , and an electric outfit room  150  provided in an upper portion of the case  100 , i.e., above the heating chamber  110 . 
   The case  100  may have a hexahedral shape and includes a back plate (or rear plate)  101  which forms a rear of the case  100 , a top plate which forms a top of the case  100 , side plates (not shown) that form both sides of the case  100 , and a bottom plate that forms a bottom of the case  100 . 
   A cooktop or a hob (not shown) may be provided above the electric oven. In this case, a space for electric wiring and piping to be arranged is necessary between the case  100  and the cooktop or the hob. For this, the top plate of the case  100  may have a stepped portion which divides the top plate into a front portion  102  and a rear portion  103  lower than the front portion  103 , as shown in  FIG. 1 . The front and the rear portions ( 102  and  103 , respectively) may be formed as one body, but may be formed as a separate body as shown in  FIG. 1 . In  FIG. 1 , the rear portion  103  of the top plate and the rear plate  101  are formed as one body and the rear portion  103  of the top plate is extended from a top of the rear plate  101  towards the stepped portion of the top plate after being bent. 
   A plurality of heaters  301  and  302  are provided with the electric oven for heating the heating chamber  110  so that food deposited in the heating chamber  110  is cooked or dirt stuck to inner walls of the heating chamber  110  is pyrolyzed and carbonated. In  FIG. 1 , the heater  301  is provided under a bottom of the heating chamber  110  and the heater  302  is provided at an upper portion of the heating chamber  110 . The heathers  301  and  302  may include a ceramic heater, a halogen heater, and/or a sheath grill heater. A convection fan may blow air into the heating chamber  110  to form convention currents in the heating chamber  110  during operation of the electric oven in a cooking mode or an automatic cleaning mode. 
   A control panel  140  is provided at an upper portion of the front of the case  100 , above the door  200  as shown in  FIG. 1 . The control panel  140  has a plurality of buttons (not shown) at a front thereof for the user to press to control the electric oven. A rear of the control panel  140  faces the electric outfit room  150  as shown in  FIG. 1 . 
   The electric outfit room  150  accommodates a plurality of electric parts, for example, a printed circuit board. A fan  400  operable by a motor (not shown) and a second duct  130  are provided in the electric outfit room  150  for cooling the case  100  surrounding the heating chamber  110  as well as the electric outfit room  150 . 
   More particularly, a first opening (not shown) is provided at a lower portion of the case  100 , and an air flow passage in communication with the first opening and the electric outfit room  150  is provided between the case  100  and the heating chamber  110  to surround a part of an outer circumference of the heating chamber  110 , as shown in  FIG. 1 . The second duct  130  is in communication with an outlet of the fan  400  and a second opening provided at the upper portion of the case  100 , for example, between the door  200  and the control panel  140 . 
   The air outside the electric oven ( FIG. 1 ) is introduced into the case  100  through the first opening provided at the lower portion of the case  100  and flows through the air flow passage between the case  100  and the heating chamber  110  when the fan  400  operates, and thereby the case  100  and the outer circumference of the heating chamber  110  are cooled down. Therefore, the case  100  is prevented from being heated enough to hurt the user and the heating chamber  110  is also prevented from being overheated. After cooling the case  100  and the heating chamber  110 , the air enters the electric outfit room  150  and is eventually discharged toward the outside of the case  100  by the fan  400  via the second duct  130  and the second opening, and thereby the electric outfit room  150  is cooled down. 
   The air entered the electric outfit room  150  from the air flow passage does not circulate within the electric outfit room  150  because the air entered the electric outfit room  150  is inhaled by the fan  400  as soon as the air enters the electric outfit room  150 . Therefore, the control panel  140 , the motor of the fan  400 , and other electric/electronic parts placed within the electric outfit room  150  are not sufficiently cooled down by the air introduced into the electric outfit room  150  from the air flow passage by the fan  400 . 
   In order to solve this problem, a first vent hole  106  may be provided on the case  100 , for example at a proximity (or vicinity) of the control panel  140 , as shown in  FIG. 1 . Then, air introduced into the electric outfit room  150  via the first vent hole  106  can cool down the rear of the control panel  140  and other electric/electronic parts while circulating within the electric outfit room  150  before being sucked by the fan  400 . 
   In addition, a second vent hole  105  may be provided on the case  100 , e.g., at a proximity (or vicinity) of the motor of the fan  400 . Then, the air introduced into the electric outfit room  150  via the second vent hole  105  can cool down the motor of the fan  400  before being sucked by the fan  400  while flowing around the motor of the fan  400 . Accordingly, the first and the second vent holes  106  and  105  provided on the case  100  notably improve efficiency for cooling the electric outfit room  150  of electric oven. 
   As explained above, the fan  400  cools the case  100 , the heating chamber  110 , and the electric outfit room  150 . In addition, according to the present invention, the fan  400  may further cool the door  200  down as well. 
   For this, the door  200  may be constituted such that the air outside the case  100  is able to be introduced therein, and a first duct  120  may be provided to guide the air introduced in the door  200  to the fan  400 . As the fan  400  cools the door  200  down, the user is prevented from getting a burn even if he/she accidentally touches the door  200  when the electric oven cooks food or pyrolyzes dirt stuck to the inner walls of the heating chamber  110 . In addition, the heating chamber  110  is also prevented from being overheated. 
   In addition, the door  200 , according to the present invention, may isolate the heat in the heating chamber  110  in order to increase the thermal efficiency of the electric oven when the electric oven cooks food. 
   An embodiment of the door  200  is shown in  FIGS. 1 and 2 . Therefore, more detailed explanation about the door  200  will be described, referring to  FIGS. 1 and 2 .  FIG. 2  is an exploded perspective view of the door assembly according to the present invention. 
   The door  200  may include a frame  280  forming a circumference of the door  200 , a handle  205  provided at a front of the door  200  for the user to grip when opening and closing the door  200 , and a plurality of plates forming an inner and an outer surfaces of the door  200  and also forming air gaps within the door  200  in order to prevent the heat in the heating chamber  110  from being transmitted to the outside of the door  200  through the door  200 . The plurality of plates may be constituted as a plurality of glasses so that the user can see the heating chamber  110  and can easily clean the inner surface of the door  200  facing the heating chamber  110 . 
   As shown in  FIG. 1 , the plurality of plates may include a first glass  210 , a second glass  220 , a third glass  230 , and a fourth glass  240 . The first glass  210  forms the inner surface of the door  200  and faces and seals the heating chamber  110  when the door  200  is closed. The forth glass  240  forms the outer surface of the door  200  and supports the handle  205  thereon. The second glass  220  is arranged within the door  200 , e.g., next to the first glass  220  and the third glass  230  is arranged between the second glass  220  and the fourth glass  240 . 
   The four glasses  210 ,  220 ,  230 , and  240  are arranged with a gap therebetween, and thereby a first air gap  201  is provided between the first glass  210  and the second glass  220 , a second air gap  202  is provided between the second glass  220  and the third glass  230 , and a third air gap  203  is provided between the third glass  230  and the fourth glass  240 . 
   The number of plates or glasses, however, is not limited to the above mentioned example. Alternatively, only one glass may be provided between the first glass  210  and the fourth glass  240 . In this case, two air gaps may be provided within the door  200 . Alternatively, only two glasses from the inner and the outer surfaces of the door  200  may be provided with the door  200 . In this case, only one air gap may be provided within the door  200 . Alternatively, a plurality of glasses over five may be provided with the door  200 . In the followings, however, one example which has four glasses mentioned above and shown in the drawings will be described in detail for convenience. 
   The four glasses  210 ,  220 ,  230 , and  240  are secured to the frame  280 . The frame  280  may cover both sides and a top of the door  200  but may not cover a bottom of the door  200  so that the air outside the case  100  may be introduced into the door  200  through the bottom of the door  200 . A space is secured between the second and the third glasses ( 220  and  230 , respectively) and a portion of the frame  280  forming the top of the door  200 . An opening  204  is provided at the frame  280  to allow the first duct  120  to be in communication with the space within the door  200 . 
   A supporter  250  may be provided at the bottom of the door  200  to support the first, the second, and the third glasses  210 ,  220 , and  230 , as shown in  FIGS. 1 and 2 . The supporter  250  secures the bottoms of the first, the second, and the third glasses  210 ,  220 , and  230 . The supporter  250  however does not secure the fourth glass  240 , and thereby a lower portion of the third air gap  204  is open, as shown in  FIG. 1 . The supporter  250  may include a ridge  251  located between two adjacent glasses when the supporter  250  secures the glasses. The ridge  251  of the supporter  251  secures the first air gap  201  between the first glass  210  and the second glass  220  and the second air gap  202  between the second glass  220  and the third glass  230 . 
   The ridge located between the second glass  220  and the third glass  230  may include a plurality of slots  255  which permits the air outside the case  100  to enter the second air gap  202  through the slots  255 , as shown in  FIG. 2 . On the contrary, the ridge located between the first glass  210  and the second glass  230  may have no slot so that the air outside the case is prevented from entering the first air gap  201  through the bottom of the door  200 . 
   When the fan  400  operates, the air outside the case  100  flows into the door  200  through the bottom of the door  200 . The air introduced into the door  200  through the bottom of the door  200  goes to the space within the door  200  after flowing through the second air gap  202  and the third air gap  203 . However, the air introduced into the door  200  through the bottom of the door  200  does not flow through the first air gap  201  because the supporter  250  covers a lower portion of the first air gap  201 . Nevertheless, the air moved to the space may enter the first air gap  201  because an upper portion of the air gap  201  is open. 
   The air moved to the space within the door  200  moves towards an inlet of the fan  400  via the opening  204  and the first duct  120 . Then, the fan  400  discharges the air toward outside of the case through the second duct  130  whose outlet is located between the control panel  140  and the top of the door  200  as shown in  FIG. 1 . Accordingly, the door  200  and the electric outfit room  150  are cooled down. 
   During the operation of the electric oven in the automatic cleaning mode for pyrolyzing dirt stuck to the inner walls of the heating chamber  110 , the heating chamber  110  is heated up to a high temperature, for example, over 450 degree Celsius. Accordingly, the door  200  is also heated and thereby it is dangerous for the user to touch the door  200 . In order to protect the user, it is preferable that the door  200  is cooled down by the fan  400  during the operation of the electric oven in the automatic cleaning mode. When the fan  400  operates, the heating chamber  110  is also protected from being overheated. 
   During the operation of the electric oven in the cooking mode for cooking food, the heating chamber  110  is heated up to a temperature in a range from about 100 to about 300 degree Celsius. In this case, the door  200  is not heated up to a high temperature and thereby the user does not get a burn even if he/she accidentally touches the door  200 . Accordingly, it is preferable that the door  200  isolates the heat in the heating chamber  110  in order to improve the thermal efficiency of the electric oven while the electric oven cooks food. 
   A valve  260  may be provided in the door  200 . The valve  260  is able to selectively open and close any one of the air gaps  201 ,  202 , and  203  in order to selectively allow the air outside the air gap closable by the valve  260  to communicate with the air gap closable by the valve  260 . In the embodiment shown in  FIGS. 1 and 2 , the valve  260  is provided to selectively open and close the first air gap  201  in order to selectively allow the air outside the first air gap  201  to communicate with the first air gap  201 . 
   When the valve  260  closes the upper portion of the first air gap  201  as shown in  FIG. 1 , the air introduced into the door  200  cannot enter the first air gap  201 , and thereby the first air gap  201  plays a role as an insulating air gap. The first air gap  201  therefore can isolate the heat in the heating chamber  110  during the operation of the electric oven in the cooking mode and thereby the thermal efficiency of the electric oven increases. 
   The second air gap  202  and the third air gap  203  can work as an air flow passage, respectively, when the fan  400  operates during the operation of the electric oven in the cooking mode, while the first air gap  201  works as the insulating air gap. In this case, the air running through the second air gap  202  and the third air gap  203  cools down the fourth glass  240  forming the outer surface of the door  200 , and thereby the user is prevented from getting a burn even if he/she touches the door  200 . Meanwhile, the valve  260  may be operable by an independent actuator (not shown) provided within the case  100 . 
   A lock  270  may be provided in the electric oven according to the present invention. The lock  270  may selectively lock the door  200  in order to prevent the door  200  from being open during the operation of the electric oven, especially in the automatic cleaning mode. The lock  270  may operate the valve  260  when locking the door  260 , different from the above. 
   The valve  260  and the lock  270  may be embodied as several embodiments.  FIGS. 3 and 4  show the valve  260  and the lock  270  according to the first embodiment of the present invention. Therefore, more detailed explanation about the valve  260  and the lock  270  will be described referring to  FIGS. 3 and 4 .  FIG. 3  is a partial sectional view schematically illustrating the lock and the valve of the door assembly according to the first embodiment of the present invention when the door of the electric oven is unlocked, and  FIG. 4  is a partial sectional view schematically illustrating the lock and the valve of the door assembly according to the first embodiment of the present invention when the door of the electric oven is locked. 
   The valve  260  may include a first member  261  which opens and closes a portion, especially the upper portion, of the first air gap  201  and a second member  263  extended from the first member  261  and movable along with the first member  261 . The first and the second members  261  and  263  have an angled shape, for example, having a generally “L” shape, as shown in  FIGS. 1 to 4 . 
   The valve  260  may further include a pivot  265  provided at a portion at which the first member  261  and the second member  262  are connected with each other. The pivot  265  is coupled to the frame  280  of the door  280  so that the first member  261  and the second member  263  can rotates together about the pivot  265 . The valve  260  may further include an elastic member (not shown) which allows the first member  261  and the second member  263  to return to an initial position thereof. The elastic member may be formed as a spring which is installed between the frame  280  and the second member  263  or the pivot  265 . 
   The first member  261  of the valve  260  seals the upper portion of the first air gap  201  when the valve  260  is at the initial position thereof. At this time, the elastic member (not shown) pushes the first member  261  of the valve  260  toward the upper portion of the first air gap  201  and thereby a secure sealing of the first air gap  201  is guaranteed. The elastic member  265 , on the other hand, urges the first member  261  to return to the initial position when the valve  260  opens the first air gap  201 . 
   The lock  270  may include an actuator  271  and a rod  273  as shown in  FIGS. 3 and 4 . The actuator  271  may be located within the electric outfit room  150  provided above the heating chamber  110 . The rod  273  is coupled to the actuator  271  and is operable by the actuator  271 . In the first embodiment of the lock  270 , the rod  273  includes a hook provided at an end of the rod  273 , and the actuator  271  swings the rod  273  in order to lock/unlock the door  200 , as shown in  FIG. 5 . 
   An opening  281  is provided at a portion of the frame  280  which is located between the lock  270  and the valve  260  so that the rod  273  is able to pass through the opening  281  when swinging. When the rod  273  is at an initial position thereof, the rod  273  is located within the electric outfit room  150  and therefore the rod  273  does not project from the case  100  as illustrated by a solid line in  FIG. 5 . In this case, the door  200  is openable because the rod  273  does not hook the door  200 . 
   When the actuator  271  operates the rod  273  to lock the door  200 , the rod  273  swings counterclockwise as illustrated by a dotted line in  FIG. 5 . In this case, the rod  273  projects from the case  100 , passes through the opening  281  at the frame  280 , and eventually hooks the door  200  by the hook. Accordingly, the door  200  is locked. 
   When the rod  273  swings by the actuator  271  in order to lock the door  200 , the rod  273  also operates the valve  260  as shown in  FIG. 4 . More particularly, the rod  273  touches and pushes the second member  263  of the valve  260  when swinging in order to lock the door  200 , and thereby the second member  263  is urged to rotate about the pivot  265 , When the second member  263  rotates, the first member  261  also rotates because the first and second members  261  and  263  of the valve  260  are movable together. Therefore, the first air gap  201  is opened when the door  200  is locked by the lock  270 . Meanwhile, the first air gap  201  is automatically closed by an elastic force of the elastic member (not shown) when the door  200  is unlocked. Of course, it should be appreciated that any suitable arrangement capable of locking and unlocking the door can be employed. 
     FIGS. 6 and 7  show a valve  260   a  and a lock  270   a  according to the second embodiment of the present invention. Therefore, more detailed explanation about the valve  260   a  and the lock  270   a  will be described referring to  FIGS. 6 and 7 .  FIG. 6  is a partial sectional view schematically illustrating the lock and the valve of the door assembly according to the second embodiment of the present invention when the door of the electric oven is unlocked, and  FIG. 7  is a partial sectional view schematically illustrating the lock and the valve of the door assembly according to the first embodiment of the present invention when the door of the electric oven is locked. 
   The valve  260   a  may include a first member  261   a , a second member  263   a , and a pivot  265   a . The first member  261   a  covers a portion, for example, the upper portion, of the first air gap  201  to seal the first air gap  201 . The second member  263   a  extends from the first member  261   a  toward a side opposite to the first member  261   a  and the pivot  265   a  is provided at a connection portion of the first and the second members  261   a  and  263   a.    
   The valve  260   a  may further include a fourth member  267   a  that extends from the connection portion of the first and the second members ( 261   a  and  263   a , respectively) toward a top of the second glass  220  in case there is a gap between the first member  261   a  and the top of the second glass  220  in order to cover the gap between the first member  261   a  and the top of the second glass  220  so that the first air gap  201  is securely sealed by the valve  260   a . The valve  260   a  may further include an elastic member (not shown) which allows the first member  261   a  and the second member  263   a  to return to an initial position thereof. The elastic member may be formed as a spring which is installed between the frame  280  and the second member  263   a  or the pivot  265   a.    
   The lock  270  may include an actuator  271   a  and a rod  273   a . The actuator  271   a  may be located within the electric outfit room  150 , e.g., above the door  200 , as shown in  FIGS. 6 and 7 . The rod  273   a  is coupled to and operable by the actuator  271 . More particularly, the rod  273   a  pushes the rod  273   a  out of the case  100  to lock the door  200 . The rod  273   a  operates the valve  260   a  while being pushed by the actuator  270   a.    
   An opening  281   a  is provided at the top of the door  200  so that the rod  273   a  can face the second member  263   a  of the valve  260   a  through the opening  281   a . When the rod  273   a  is at an initial position thereof, the rod  273   a  is located within the electric outfit room  150  and therefore the rod  273   a  does not project from the case  100  as shown in  FIG. 6 . In this case, the door  200  is openable because the rod  273   a  does not hook the door  200 . 
   When the actuator  271   a  of the lock  270   a  operates the rod  273   a  to lock the door  200 , the rod  273   a  projects downward as shown in  FIG. 7 . In this case, the rod  273   a  projects from the case  100 , passes through the opening  281   a  at the frame  280 , and eventually hooks the door  200 . Thereby, the door  200  is locked. 
   When the rod  273   a  projects downward by the actuator  271   a  in order to lock the door  200 , the rod  273   a  also operates the valve  260   a  as shown in  FIG. 7 . More particularly, the rod  273   a  pushes down the second member  263   a  of the valve  260   a , and thereby the second member  263   a  is urged to rotate about the pivot  265   a . When the second member  263   a  rotates, the first member  261   a  also rotates because the first and second members  261   a  and  263   a  of the valve  260   a  are movable together. Therefore, the first air gap  201  is opened when the door  200  is locked by the lock  270   a . Meanwhile, the first air gap  201  is automatically closed by an elastic force of the elastic member (not shown) when the door  200  is unlocked. 
   Meanwhile, the lock  270 ,  270   a  and the valve  260 ,  260   a  may be operable according to the operation mode of the electric oven. For example, the lock  270 ,  270   a  may lock the door  200  during the operation of the electric oven in the automatic cleaning mode while the lock  270 ,  270   a  unlocks the door  200  during the operation of the electric oven in the cooking mode. In this case, the valve  260 ,  260   a  permits the air to enter the first air gap  201  to cool down the door  200  when the electric oven performs the automatic cleaning mode while the valve  260 ,  260   a  prevents the air from entering the first air gap  201  to insulate the heat in the heating chamber  110  in order to improve the thermal efficiency of the electric oven when the electric oven performs the cooking mode. 
   Alternatively, the lock  270 ,  270   a  and the valve  260 ,  260   a  may be operable according to a temperature of the heating chamber  110 . For example, the lock  270 ,  270   a  locks the door  200  when the temperature of the heating chamber  110  reaches a preset value while the lock  270 ,  270   a  unlocks the door  200  when the temperature of the heating chamber  110  is under the preset value. In this case, the valve  260 ,  260   a  allows the air to enter the first air gap  201  to cool the door  200  down when the temperature of the heating chamber  110  is at or above the preset value while preventing the air from entering the first air gap  201  to isolate the heat in the heating chamber  110  in order to improve the thermal efficiency when the temperature of the heating chamber  110  is under the preset value. 
   In operation of the electric oven, the heating chamber  110  is heated by the heaters  301  and  302  upon the user&#39;s request. 
   When the electric oven performs the cooking mode or the temperature of the heating chamber  110  does not reach the preset value, the lock  270 ,  270   a  unlocks the door  200  and the valve  260 ,  260   a  closes the first air gap  201  within the door  200  to insulate the heat in the heating chamber  110 , and thereby the thermal efficiency of the electric oven increases. In case additional air gaps  202  and  203  are provided, within the door  200 , next to the first air gap  201 , the fan  400  may urge the air outside the case  100  to flow through the air gaps next to the first air gap  201  to cool down the outer surface of the door  200 , and thereby the door  200  is prevented from hurting the user even if the user accidentally touches the door  200 . 
   When the electric oven performs the automatic cleaning mode or the temperature of the heating chamber  110  reaches the preset value, the lock  270 ,  270   a  locks the door  200  and the valve  260 ,  260   a  opens the first air gap  201  within the door  200  to allow the air outside the case  100  to enter the first air gap  201  and the fan  400  flows the air through the first air gap  201  to cool the door  200  down so that the electric oven guarantees the user&#39;s safety. Of course, in case the additional air gaps  202  and  203  are provided within the door  200 , the fan  400  may urge the air outside the case  100  to flow through the air gaps next to the first air gap  201  to cool down the door  200 . Accordingly, the heating chamber  100  and the case  100  are prevented from being overheated. 
   As explained above, the present invention has the following advantages. The electric oven according to the present invention minimizes a loss of the thermal efficiency by isolating the heat in the heating chamber during an operation of the electric oven and also guarantees the user&#39;s safety by cooling the door during another operation of the electric oven. In addition, the electric oven according to the present invention also guarantees a reliability of the product by preventing the heating chamber and the case from being overheated. Further, food deposited in the heating chamber is evenly cooked and the cooking time decreases because the door isolates the heat in the heating chamber while cooking. Furthermore, the present invention improves efficiency for cooling an electric outfit room of the electric oven because the first and the second vent holes provided the vicinities of the control panel and the motor guide the air outside the case to a control panel and a motor of the fan. 
   It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents. 
   It is further noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to a preferred embodiment, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the present invention has been described herein with reference to particular means, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims.