Patent Publication Number: US-9416978-B2

Title: Cooker and burner assembly thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Stage Application under 35 U.S.C. §371 of PCT Application No. filed May 14, 2009, which claims priority to Korean Patent Application No. 10-2008-0074136 filed in Korea on Jul. 29, 2008, which is hereby incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a cooking appliance and a burner assembly thereof. 
     2. Description of the Related Art 
     Cooking appliances are appliances that heat food, using gas or electricity. In general, a plurality of burner units are provided at the upper portion of cooking appliances using gas and food is directly heated by heating a vessel filled with food by the flame generated in the process of gas combustion in the burner unit. The flame generated by the appliance is exposed to the outside. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a cooking appliance manufactured to be safely used and a burner assembly of the cooking appliance. 
     It is another object of the present invention to provide a cooking assembly of which efficiency in cooking is provided and a burner assembly of the cooking appliance. 
     It is another object of the present invention to provide a cooking appliance having a simple structure and a burner assembly of the cooking appliance. 
     The burner assembly of a cooking appliance according to an aspect of the present invention includes: a first port where gas mixture of gas and air is supplied and a second port that is separated from the first port and where gas mixture of gas and air is supplied; a combustion mat where the gas mixture that is supplied to the first port or the second port is burned; and a tube assembly that guides gas and air to the ports. 
     A cooking appliance according to another aspect of the present invention includes: a burner assembly that includes a burner port having a first space where gas mixture of gas and air is supplied and a second space that is separated from the first space and where gas mixture is supplied, and a combustion mat where at least one gas mixture in the first space and the second space is burned; a tube assembly that guides the gas mixture to the spaces; and a nozzle assembly that injects gas to the tube assembly. 
     A cooking appliance according to another aspect of the present invention includes: a first space where gas mixture of gas and air is supplied; a second space that is separated from the first space and where gas mixture of gas and air is supplied; a first mixing channel and a second mixing channel that mix gas with air that will be supplied to the spaces; an intake channel into which external air that will flows into the mixing channels flows; and an exhaust channel that exhausts combustion gas generated when the gas mixture is burned in the first space and combustion gas generated when the gas mixture is burned in the second space. 
     According to the present invention, gas mixture is selectively burned in an outer port and an inner port in accordance with a vessel filled with food, such that it is possible to improve cooking efficiency according to the kinds of food. 
     Further, since whether to supply gas, the amount of supplied gas, operation of an ignition plug, and turning-on/off of light emitter are achieved by one valve assembly, it is possible to reduce the number of parts. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a cooking appliance according to an embodiment of the present invention. 
         FIG. 2  is an exploded perspective view of the cooking appliance according to an embodiment of the present invention. 
         FIG. 3  is an exploded perspective view of a burner assembly according to an embodiment of the present invention. 
         FIG. 4  is an exploded perspective view of a nozzle assembly according to an embodiment of the present invention. 
         FIG. 5  is a view illustrating gas flow when gas mixture is burned only in an inner port according to an embodiment of the present invention. 
         FIG. 6  is a view showing a knob that has been operated to burn gas mixture only in the inner port. 
         FIG. 7  is a view illustrating air flow when gas mixture is burned in an outer port and an inner port according to an embodiment of the present invention. 
         FIG. 8  is a view showing a knob that has been operated to burn gas mixture only in the outer port and the inner port. 
         FIG. 9  is a vertical cross-sectional view illustrating air flow in the cooking appliance according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment is described hereafter in detail with reference to the accompanying drawings. 
       FIG. 1  is a perspective view of a cooking appliance according to an embodiment of the present invention and  FIG. 2  is an exploded perspective view of the cooking appliance according to an embodiment of the present invention. 
     Referring to  FIGS. 1 and 2 , a cooking appliance  10  according to an embodiment of the present invention includes a cabinet  100  that defines the outer shape and a top cover  600 . 
     The cabinet  100  is formed in a hexahedral shape with the upper surface open. The top cover  600  covers the upper opening of the cabinet  100 . 
     A plurality of cooling holes  110  is formed in the bottom of the cabinet  100 . Air for cooling the parts disposed inside the cabinet  100  can flow inside and outside the cabinet  100  through the cooling holes  110 . Further, a cooling channel P 3  (see  FIG. 9 ) through which air passing through the cooling holes  110  is formed inside the cabinet  100 . 
     Each part of the cooking appliance is described in detail hereafter. 
     Referring to  FIG. 2 , inside the cabinet  100 , a plurality of burner assemblies  200 ,  201 , and  202  that mix gas with air and burn the gas mixture, a plurality of tube assemblies  300  (see  FIG. 3 ) that guides gas and air into the plurality of burner assemblies  200 ,  201 , and  202 , a plurality of nozzle assemblies  400  that injects gas into the tube assemblies  300  (see  FIG. 3 ), respectively, and a plurality of control units  500  that controls the operation of the plurality of burner assemblies  200 ,  201 , and  202 . 
     The plurality of burner assemblies  200 ,  201 , and  202  burn gas mixture and guide combustion gas generated in a combustion process of air for making the gas mixture and gas mixture. 
     The tube assembly  300  guides the gas injected from the nozzle assembly  400  and the air introduced with the gas into the tube assembly in the gas injection process to the burner assemblies  200 ,  201 , and  202 . 
     The control units  500  control the operation of the cooking appliance, that is, the combustion of gas mixture in the burner assemblies  200 ,  201 , and  202 . 
     Three burner assemblies, that is, the first burner assembly  200 , the second burner assembly  201 , and the third burner assembly  202  are included in the plurality of burner assemblies  200 ,  201 , and  202 , respectively. 
     The first and second burner assemblies  200  and  201  are disposed at the right and left inside the cabinet  100  in the figure, respectively. The third burner assembly  202  is disposed between the first and second burner assemblies  200  and  201 , that is, at the center portion inside the cabinet  100 . The first to third burner assemblies  200 ,  201 , and  202  may be manufactured in different sizes. 
     Although it is described that three burner assemblies are provided in the cabinet  100  in this embodiment, it should be noted that the number of burner assemblies is not limited and at least one or more assemblies can be provided in the cabinet  100 . 
     Meanwhile, the first to third burner assemblies  200 ,  201 , and  202  are fixed in the cabinet  100 , with each rear end connected to a connection bracket  800 . 
     The connection bracket  800  has a fixing portion  810  (see  FIG. 9 ) that is long in the left-right direction and a flow guide  820  (see  FIG. 9 ) that vertically extends from the rear end of the fixing portion  810 . 
     The first to third burner assemblies  200 ,  201 , and  202  are fixed to the fixing portions  810  (see  FIG. 9 ). 
     The flow guide  820  (see  FIG. 9 ) divides a channel for air flowing through a flow guide unit  700 , which is described below, and a channel for combustion gas, and guides the air and the combustion gas. 
     A discharge guide  830  (see  FIG. 9 ) is provided at the end of the flow guide  820  (see  FIG. 9 ). The discharge guide  830  (see  FIG. 9 ) extends to be inclined upward to the front. 
     The discharge guide  830  (see  FIG. 9 ) prevents air discharged outside through an exhaust portion  720  (see  FIG. 9 ) from flowing to an intake port  710  (see  FIG. 9 ). 
     On the other hand, there are provided three tube assemblies and three nozzle assemblies  400 , the same as the number of burner assemblies. The nozzle assemblies  400  inject gas supplied from an external gas supplier to the tube assemblies  300 , respectively. 
     The control units  500  are positioned in front of the burner assemblies  200 ,  201 , and  202 , respectively, that is, at the front portion inside the cabinet  100 . The control units  500  include three valve assemblies  510  that adjust whether to supply gas and the amount of gas supplied to the burner assemblies  200 ,  201 , and  202 , and light emitters  530 . A knob  520  is combined with the valve assembly  510 . The knob  520  is a part that a user holds to operate the valve assembly  510 . 
     The light emitters  530  show whether the burner assemblies  200 ,  201 , and  202  are ignited to the outside while being turned on/off in accordance with the operation of the valve assemblies  510 . 
     On the other hand, the top cover  600  has a top frame  610  and a top plate  620 . 
     A plurality of knob-through holes  611  through which the valve assemblies  510  are disposed is formed at the front of the top frame  610 . Further, a plurality of light emitter-through holes  613  through which the light emitters  530  are disposed is formed at the front of the top frame  610 . 
     A plurality of openings  615  for sucking and exhausting air is formed at the rear of the top frame  610 . The openings  615  function as passages through which external air that will be supplied to the burner assemblies  200 ,  201 , and  202  is sucked and the combustion gas generated in the combustion process of the gas mixture is exhausted. 
     That is, in this embodiment, external air is sucked inside and the combustion gas inside is exhausted outside through one opening  615 . In this configuration, the intake channel P 1  (see  FIG. 9 ) for external air and the exhaust channel P 2  (see  FIG. 9 ) for combustion gas are divided by the flow guide  830  in the cabinet  100 , as described above. 
     The top plate  620  is disposed on the top frame  610 . The top plate  620  transfers heat generated in the combustion process of the gas mixture in the burners  200 ,  201 , and  202  to food (vessels filled with food). 
     The top plate  620 , for example, may be made of glass, such as ceramic. Vessels filled with food are placed on the top plate  620 . Vessel seats (not shown) for showing the seating positions of vessels may be formed on the top plate  620 . 
     A flow guide unit  700  is disposed at the rear portion of the upper surface of the top frame  610 . The flow guide unit  700  guides the external air that is sucked inside to be supplied to the burner assemblies  200 ,  201 , and  202  and the combustion gas that is discharged from the burner assemblies  200 ,  201 , and  202 . 
     The structure of the burner assembly is described in detail hereafter. 
       FIG. 3  is an exploded perspective view of a burner assembly according to an embodiment of the present invention and  FIG. 4  is an exploded perspective view of a nozzle assembly according to an embodiment of the present invention. 
     Since the first to third burner assemblies  200 ,  201 , and  202  have the same configuration, except for the size, only the first burner assembly  200  (hereafter, referred to as ‘burner assembly’ for the convenience of description) in the first to third burner assemblies  200 ,  201 , and  202  is described. 
     Referring to  FIGS. 3 and 4 , the burner assembly  200  according to this embodiment includes a combustion unit, an igniting unit, and an exhaust guide unit. 
     The combustion unit is where gas mixture is burned and includes a burner port and a combustion mat  230 . The burner port includes an outer port  210  (also called “first port”) and an inner port  220  (also called second port). 
     The igniting unit generates a spark for burning gas mixture in the combustion unit. The igniting unit includes a plug assembly  240 . 
     The mixing unit mixes gas with air and supplies it to the combustion unit. The mixing unit includes a tube assembly  300 . 
     The exhaust guide unit guides combustion gas that is generated in the combustion process of the gas mixture in the combustion unit to be exhausted. The exhaust guide unit includes a burner frame  250  and a barrier  260 . 
     In detail, the outer port  210  and the inner port  220  are parts where the gas mixture is burned. The gas mixture can be independently burned in the outer port  210  and the inner port  220 . That is, as a user operates the valve assembly  510 , the gas mixture is burned in the outer port  210  and the inner port  220 , or only in the inner port  220 . 
     The outer port  210  can be formed, for example, in a flat cylinder shape. Further, a fixing portion  211  is formed at the rear of the outer port  210 . The tube assembly  300  is fixed to the fixing portion  211 . 
     Further, a mat seat  215  is formed on the inner circumference of the outer port  215 . The bottom edge of the combustion mat  230  is seated on the mat seat  215 . 
     Further, a support flange  217  is formed along the upper edge of the outer port  215 . The support flange  217  radially extends from the upper edge of the outer port  210 . The lower portion of the burner frame  250  is placed on the support flange  217 . Further, a plurality of fastening holes  218  where fasteners are inserted is formed through the support flange  217  to be fastened to the burner frame. 
     On the other hand, at least a portion of the inner port  220  is positioned inside the outer port  210 . The burner port is divided into a first space  212  defined between the outside of the inner port  220  and the inside of the outer port  210  and a second space  222  defined inside the inner port  220 , by the inner port  220 . 
     The outer port  210  has a plurality of first supply holes  213  and a second supply hole  214  formed between the plurality of first supply holes  213 . The first supply holes  213  allow gas mixture to flow into the first space  212  and the second supply hole  214  allows gas mixture to flow into the second space  220 . 
     At least a portion of the inner port  220  is formed in a cylindrical shape coaxially arranged with the outer port  210  and having a diameter relatively smaller than that of the outer port  210 . In this structure, the height of the inner port  220  is a value obtained by subtracting the thickness of the combustion mat  230  from the height of the outer port  210 . 
     The upper end of the inner port  220  is positioned at the same level as the upper end of the mat seat  215 . 
     Further, a communication hole  221  is formed in the inner port  220 . The communication hole  221  allows the gas mixture that is supplied through the second supply hole  214  to be supplied inside (the second space) the inner port  220 . 
     The inner port  220  is provided with a connection tube  223 . The connection tube  223  guides the gas mixture supplied through the second supply hole  214  to the inner port  220 . One end of the connection tube  223  communicates with the communication hole  221  and the other end of the connection tube  223  is positioned close to the second supply hole  214 . 
     An ignition guide  225  is formed at one side of the inner port  220  which is opposite to the communication hole  221 . The ignition guide  225  is formed in order that the gas mixture supplied to the combustion mat  230  is ignited by the plug assembly  240 . The ignition guide  225  extends toward the inner circumference of the outer port  210 . 
     The outer port  210 , inner port,  220 , and connection tube  223  may be substantially integrally formed. For example, the outer port  210 , inner port  220 , and connection tube  223  can be integrally formed by die-casting a metal member, such as aluminum. Alternatively, it is also possible to manufacture individually the outer port  210 , inner port  220 , and connection tube  223 , and then weld them or fasten them with fasteners. 
     On the other hand, the combustion mat  230  is where combustion gas is substantially burned. The combustion mat  230 , for example, may be made of glass, such as ceramic. The bottom edge of the combustion mat  230  is seated on the mat seat  215  and the bottom center portion of the combustion mat  230  is seated on the inner port  220 . In this structure, the upper surface of the combustion mat  230  is positioned higher than the upper surface of the support flange  217 . 
     Further, the edge of the combustion mat  230  has a step  231 . The step  231  is formed by depressing a portion of the edge of the combustion mat  230 . 
     In this structure, the upper surface of the step  231  is positioned at the same level as the upper surface of the support flange  217 . 
     On the other hand, the plug assemble  240  includes an ignition plug  241  and a plug target  243 . The ignition plug  241  and the plug target  243  generate a spark for igniting gas mixture. 
     The plug target  243  is made of metal and spaced apart from the ignition plug  241 . When power is supplied to the ignition plug  241 , a spark is generated between the ignition plug  241  and the plug target  243 . 
     The plug assembly  240  is disposed through the burner frame  250 . 
     Further, ends of the ignition plug  241  and the plug target  243  which generate a spark are positioned over the ignition guide  225 . In more detail, the ends of the ignition plug  241  and the plug target  243  are positioned over the interface (right over the inner port) of the first space  212  and the second space  222 . 
     On the other hand, the burner frame  250  is disposed above the burner port and the combustion mat  230 . The burner frame  250  includes a first burner frame  251  and a second burner frame  256 . The first burner frame  251  guides the combustion gas generated when gas mixture is burned in the combustion mat  230  to the second burner frame  256 . The second burner frame  256  guides the combustion gas to the flow guide unit  700 . 
     The first and second burner frames  251  and  256  may be integrally formed, or individually formed and then welded or fastened by fasteners. 
     The first burner frame  251  fixes the position of the combustion mate by being fixed to the outer port  210 . 
     A heat transfer hole  252  that allows the heat generated when gas mixture is burned in the combustion mat  230  to be easily transferred to the top plate  620  is formed at the center portion of the first burner frame  251 . The heat transfer hole  252  can by formed in a shape corresponding to the upper surface of the combustion mat  230 . 
     The upper surface of the combustion mat  230  is inserted into the heat transfer hole  252 , when the first burner frame  251  is fixed to the outer port  210 . 
     The first burner frame  251  has a guide rib  253  and a plate support rib  254 . The guide rib  253  allows the combustion gas generated when gas mixture is burned in the combustion mat  230  to flow to the second burner frame  256 , without being dispersed. 
     The guide rib  253  guides the heat generated when combustion gas is burned in the combustion mat  230  to be concentrated to the top plate  620 , without being dispersed. 
     The guide rib  253  extends upward from the bottom edge of the first burner frame  251 , except for the rear end of the first burner frame  251 . 
     The plate support rib  254  supports the bottom of the top plate  620 . The plate support rib  254  extends outside the first burner frame  251  from the guide rib  253 . 
     Further, a plurality of through-holes  255  is formed at the bottom of the first burner frame  251  adjacent to the heat transfer hole  252 . Fasteners that are inserted in the outer port  210  pass through the through-holes  255 . 
     The second burner frame  256  has guide ribs  257  and plate support ribs  258 . The guide rib  257  extends upward from both side of the second burner frame  256 , at the same height as the guide rib  253  of the first burner frame  251 . 
     The plate support rib  258  extends to both sides from the upper ends of the guide ribs  257 . Further, the plate support rib  258  supports the top plate  620 . 
     Through-holes  259  through which fasteners that are inserted in the barrier  260  are formed at the guide ribs  257 . 
     On the other hand, the intake channel P 1  (see  FIG. 9 ) is formed under the burner frame  250  inside the cabinet  210 . Air that is supplied to the burner assemblies  200 ,  201 , and  202  flows through the intake channel P 1 . 
     In this embodiment, the intake channel P 1  is substantially defined by the bottom of the cabinet  100  and the bottom of the second burner frame  265 . 
     The barrier  260  is fastened to the upper portion of the second burner frame  256  and substantially positioned between the top plate  620  and the second burner frame  256 . The barrier  260  is formed in a U-shape. 
     In this structure, the rear end of the barrier  260  is spaced apart from the rear end of the second burner frame  256 . Therefore, the exhaust channel P 2  through which the combustion gas flow is defined by the second burner frame  256  and the barrier  260 . The combustion gas flowing through the exhaust channel P 2  is discharged through a gap between the second burner frame  256  and the barrier  260 . However, the exhaust channel P 2  may be defined by the second burner frame  256  and the top plate  620 , with the barrier  260  removed. 
     A plurality of fastening holes  261  through which fasteners that are inserted in the second burner frame  256  is formed at both sides of the barrier  260 . 
     A guide rib  263  that guides the combustion gas flowing through the exhaust channel p 2  to the flow guide unit  700  is formed at the rear end of the barrier  260 . The guide rib  263  extends upward from the rear end of the upper surface of the barrier  260   
     The barrier  260  is provided with dividing ribs  265 . The dividing ribs  265  of the barrier  260  are provided to prevent the combustion gases that are guided to the flow guide unit  700  through the exhaust channel P 2  of each other burner assemblies  200 ,  201 , and  202  from being mixed with each other. The dividing ribs  265  extend rearward from the ends of both sides of the guide rib  263 . 
     The barrier  260  allows some of the heat of the combustion gas flowing through the exhaust channel P 2 , in more detail, only the heat to warm up food to be transferred to the top plate  620 . 
     Accordingly, warm zones where food can be warmed by the heat of the combustion gas flowing through the exhaust channels P 2  are formed over the exhaust channels P 2  in the top plate  620 . 
     On the other hand, a thermo couple  290  is combined with the first burner frame  251 . A portion of the thermo couple  290  is positioned inside the first burner frame  251  through the first burner frame  251  and the other portion is disposed outside the first burner frame  251 . 
     The thermo couple  290  generates an electromotive force, using a difference in temperature between the portion inside the first burner frame  251  and the portion outside the first burner frame  251  while combustion gas is burned in the combustion mat  230 . 
     The valve assembly  510  that supplies gas is kept open or the open valve assembly  510  is closed, in accordance with whether the thermo couple  290  generates the electromotive force. 
     On the other hand, the tube assembly  300  includes a plurality of first mixing tubes  310 , a second mixing tube  320  disposed between the plurality of first mixing tubes  310 , a close contact portion  330  connected with the mixing tubes, and connectors  340  for connection with the nozzle assembly. 
     The first and second mixing tubes  310  and  320  provide first and second mixing channels where gas and air are substantially mixed. Further, the plurality of first mixing tubes  310  and the second mixing tube  320  are arranged in parallel. 
     The first mixing tubes  310  communicate with the first supply holes  213 , respectively. The second mixing tube  320  is inserted in the connection tube  223  through the second supply hole  214 . Accordingly, the length of the second mixing tube  220  is larger than that of the first mixing tube  210 . 
     The close contact portion  330  is fixed to the fixing portion  211 . Though not shown, a gasket for preventing leakage of gas mixture may be provided between the fixing portion  211  and the close contact portion  330 . 
     The connectors  340  substantially connect the first mixing tubes  310  with the second mixing tube  320 . 
     A fastening protrusion  350  and a fastening hole  360  for fastening the nozzle assembly  400  are formed in the connector  340 . 
     Referring to  FIG. 4 , the nozzle assembly  400  includes a nozzle body  410 , a nozzle cover  420 , and a plurality of injection nozzles  431  and  433 . 
     A hose connecting portion  411  is formed at the rear of the nozzle body  410 . Two supply holes (not shown are formed in the hose connecting portion  411 . Gas hoses  471  and  473  are connected to the supply holes, respectively. The gas hoses  471  and  473  are composed of a first gas hose  471  through which gas that will be supplied to the first space  212  flaws and a second gas hose  472  through which gas that will be supplied to the second space  222  flows. 
     A plurality of injection holes  413  and  415  where the injection nozzles  431  and  433  are connected, respectively, are formed through the front of the nozzle body  410 . 
     The plurality of injection nozzles  431  and  433  are composed of a first injection nozzle  431  that injects gas to the first mixing tube  310  and a second injection nozzle  433  that injects gas to the second mixing tube  320 . The plurality of injection holes  413  and  415  are composed of a first injection hole  413  where the first injection nozzle  431  is connected and a second injection hole  415  where the second injection nozzle  433  is connected. 
     A thread is formed on the inner circumference of the plurality of injection holes  413  and  415  to combine the injection nozzle  413  and  415 , respectively. 
     Two gas channels divided by a dividing member (not shown) is formed in the nozzle body  410 . Any one of the gas channel communicates with the first gas hose  471  and the other communicates with the second gas hose  472 . 
     The nozzle body  410  is manufactured by die-casting aluminum and the injection hole  412  is formed by tapping to minimize the amount of material and effort for manufacturing the nozzle body  410 . 
     The top cover  420  covers the upper opening of the nozzle body  410 . Therefore, two channels are formed between the nozzle body  410  and the nozzle cover  420 . 
     The injection nozzles  431  and  433  inject gas at high pressure to the mixing tubes  310  and  320 , respectively. The injection nozzles  413  and  415  are connected to the injection holes  413  and  415 , respectively. The injection nozzles  431  and  433  connected to the injection holes  413  and  415  are spaced apart from the rear end of the mixing tubes  310  and  430  in order that air around the mixing tubes  310  and  330  flows into the mixing tubes  310  and  330  while the gas injected from the injection nozzles  431  and  433  flows into the mixing tube  310  and  330 . 
     A thread corresponding to the thread of the injection holes  413  and  415  are formed on the outer circumference of the injection nozzles  431  and  433 . 
     A plurality of fastening ribs  440  is formed at the nozzle body  410 . The fastening ribs  440  extend forward from the front of the nozzle body  410 , that is, toward the tube assembly  300 . A through-hole  460  through which a fastener passes and a guide groove  450  in which the guide protrusion  350  of the tube assembly  300  is inserted are formed at the fastening rib  440 . 
     Therefore, the tube assembly  300  and the nozzle assembly  400  are combined by the fastening members passing through the through-holes  460  are inserted in the fastening holes  360  of the tube assembly  300 , with the guide protrusions  350  inserted in the guide hole  450 . 
     Though not shown, a nozzle gasket may be provided between the nozzle body  410  and the nozzle cover  420 . The nozzle gasket blocks the gap between the nozzle body  410  and the nozzle cover  420 . The nozzle gasket prevents gas from leaking through the gap between the nozzle body  410  and the nozzle cover  420 . 
       FIG. 5  is a view illustrating gas flow when gas mixture is burned only in an inner port according to an embodiment of the present invention,  FIG. 6  is a view showing a knob that has been operated to burn gas mixture only in the inner port,  FIG. 7  is a view illustrating air flow when gas mixture is burned in an outer port and an inner port according to an embodiment of the present invention,  FIG. 8  is a view showing a knob that has been operated to burn gas mixture only in the outer port and the inner port, and  FIG. 9  is a vertical cross-sectional view illustrating air flow in the cooking appliance according to an embodiment of the present invention. 
     Referring first to  FIGS. 5 and 6 , in order to burn gas mixture only in the inner port  220 , that is, when the size of a vessel filled with food corresponds to the size of the inner port  220 , the valve assembly  510  is operated by the knob  520  such that gas mixture is supplied only to the inner port  220 . 
     Accordingly, gas flows only to the second gas hose  473 . Further, the gas is injected from the second injection nozzle  433 . 
     The gas injected from the second injection nozzle  433  is supplied together with air to the inner port  220  through the second mixing tube  320 . 
     Meanwhile, the valve assembly  510  operates the plug assembly when the gas is supplied to the inner port  220 . Accordingly, the gas mixture supplied to the inner port is ignited. Further, substantial combustion of the gas mixture occurs at a portion of the combustion mat  230  which corresponds to the inner port  220 . 
     Further, the valve assembly  510  turns on the indication lamp  530 , when the gas is supplied to the inner port  220 . Accordingly, a user can easily recognize that the gas mixture is being burned in the burner assembly  200 . 
     Next, referring to  FIGS. 7 and 8 , when the size of a vessel filled with food corresponds to the size of the outer port  210  including the inner port  220 , the valve assembly  510  is operated by the knob  520  such that gas mixture is supplied to the outer port  210  and the inner port  220 . 
     Accordingly, gas flows into the first gas hose  471  and the second gas hose  473 , such that the gas is injected from the first injection nozzle  431  and the second injection nozzle  433   
     Further, the gas injected from the first injection nozzle  431  and the second injection nozzle  433  is supplied to the outer port  210  and the inner port  220  through the first mixing tube  310  and the second mixing tube  320 , respectively. 
     Further, since the plug assembly  240  is operated by the valve assembly  510 , the gas mixture supplied to the outer port  210  and the inner port  220  is ignited and burned. Further, substantial combustion of the gas mixture occurs throughout the combustion mat  230  which corresponds to the outer port  210  and the inner port  220 . Further, the indication lamp  530  is turned on by the valve assembly  510 . 
     Meanwhile, referring to  FIG. 9 , the heat generated while the gas mixture is burned in the combustion mate  230  is transferred to the vessel placed on the top plate through the top plate  620 . Therefore, the vessel is substantially heated and the food in the vessel is cooked. 
     The high-temperature combustion gas generated while the gas mixture is burned in the combustion mat  230  flows to the exhaust channel P 2 . Further, the combustion gas is exhausted to the outside through the exhaust portion  720  of the flow guide unit  700  communicating with the exhaust channel P 2 . The guide  820  of the connection bracket  800  guides forward the combustion gas discharged through the exhaust portion  720 . Therefore, the combustion gas discharged through the exhaust portion  720  is prevented from staining the rear wall, that is, the wall of a kitchen. 
     In this process, since the combustion gas is at higher temperature and pressure than the air outside the cooking appliance, it is discharged to the outside of the cooking appliance at low pressure (substantially atmospheric pressure, through the exhaust portion  720  by convection. 
     In contrast, the gas injected from the injection nozzle  431  and  433  flows at high speed into the tube assembly  300 . Since the gas passes through the mixing tubes  301  and  320  of the tube assembly  300  at high speed, the pressure around the inlet of the mixing tubes  310  and  320  is lower than the atmospheric pressure (the pressure outside the cooking appliance), by Bernoulli&#39;s theorem. Therefore, the air outside the cooking appliance  10  flows into the intake channel P 1  through the sucking port  710 . 
     The intake channel P 1  extends in parallel with the exhaust channel P 2 . Further, a portion of the exhaust channel P 2  is positioned over the intake channel P 1 . 
     Further, as shown in  FIG. 9 , since combustion gas flows inside and outside through the flow guide unit  700 , the flow direction of the air in the intake channel is opposite to the flow direction of the combustion gas in the exhaust channel. 
     The barrier  620  transfers some of the heat of the combustion gas flowing through the exhaust channel P 2  to the top plate  620 . Therefore, food can be warmed in the warm zone of the top plate  620  over the exhaust channel P 2 . 
     The air outside the cooking appliance is sucked inside the cabinet  100  through the cooling hole  110  of the cabinet  100  and flows through a cooling channel Pc. 
     As described above, the air flowing through the cooling channel cools the parts constituting the control unit  400  and then is discharged through the cooling hole  110 . 
     In this process, the air in the intake channel flows toward the nozzle assembly and some of the air in the cooling channel flows away from the nozzle assembly. 
     Further, in the embodiment described above, a cooling fan for cooling the electrical parts in the cabinet, including the control unit, is not provided. However, a cooling fan may be provided to efficiently cooling the electrical parts. 
     Although a single combustion mat  230  is disposed over the outer port  210  and the inner port  220  in the above embodiment, a combustion mat may be composed of an outer mat and an inner pat, the outer mat is disposed over the outer port and the inner mat is disposed over the inner port. The outer mat and the inner mat may be separate or connected by a frame.