Abstract:
An improved gas burner for cooking appliances, with an inner central portion ( 40 ) defining an inner chamber ( 52 ) provided with a central flame ring ( 72 ) and with an outer portion ( 42 ) concentric with said central portion ( 40 ) defining an outer chamber ( 47 ) provided with at least one outer flame ring ( 78 ), characterised by comprising a pair of first injectors ( 14 ) of substantially horizontal axis, symmetrically disposed about a diametrical vertical plane of said burner, said first injectors ( 14 ) being associated with respective adjacent venturi conduits ( 24 ) with substantially horizontal parallel axes, feeding said outer portion ( 42 ) with a gas/primary air mixture to generate said outer flame ring ( 78 ), said adjacent conduits ( 24 ) being spaced apart to define a space within which a second injector ( 16 ) of vertical axis is disposed facing a venturi conduit ( 50 ) of vertical axis feeding said inner central portion ( 40 ) with a gas/primary air mixture to generate said central flame ring ( 72 ).

Description:
The present invention relates to an improved gas burner for cooking appliances. 
     BACKGROUND OF THE INVENTION 
     Standard gas burners are known comprising a single flame ring of various dimensions and developable powers. 
     Special gas burners are also known comprising several concentric flame rings. They are commonly known as wok burners, from the name of the convex-based pans which are widespread in Asiatic countries, and require burners with several concentric rings. 
     Dual wok burners are also known, provided with special two-way valves for separately feeding the central flame ring and the annular ring or rings with gas, to hence generate either only the inner central flame ring or the central ring and the outer annular ring or rings, in order to vary the cooking intensity within wide limits, from just the inner flame ring fed at minimum level to all the flame rings fed at maximum level for high temperature cooking. 
     In order for a wok burner to completely cover market needs, it must simultaneously satisfy a large number of requirements, often of a contrasting nature. In particular:
         it must be of small vertical height, to be positioned either on cookers or on built-in hobs,   it must be insensitive to the streaming effect, i.e. it must be able to remain always ignited, even under minimum flow conditions, in the case of a reduction in pressure accidentally caused by the effect of opening a door in the kitchen cabinet below the hob,   it must be able to develop high power,   its injectors must be accessible from above for easy replacement if the burner has to be adapted to gas types different from that for which the burner was factory set,   it must be able to operate both as a dual burner, i.e. fed via a two-exit valve, and as a three ring burner, i.e. fed via a normal single-exit valve.   it must comprise just a fed easily assembled parts of low cost,   all its parts must be easily accessible for simple cleaning.       

     Various burner types have been proposed to satisfy most of the aforelisted requirements, however they all represent compromise solutions aimed at enhancing certain requirements at the necessary sacrifice of others. 
     IT 1,232,887 describes a dual burner provided with three injectors associated with three venturis of radial type, i.e. comprising a first vertical frusto-conical section followed by a radial horizontal section. This is of small vertical size, is able to provide reasonable power and uses primary air and secondary air withdrawn from above the hob, hence being substantially insensitive to the streaming effect. 
     The drawback of this known burner is that the two radial venturis which feed mixture to the outer portion of the burner determine its shape: in this respect, to obtain a radial portion the two venturis are made to extend towards the burner interior, so giving the outer burner portion a shape which is not annular, as is normally required for a wok burner, but presenting a circular outer perimeter and an elliptical inner perimeter. This gives the burner a strange shape and also subtracts secondary air from the central inner part of the burner; consequently the flames at the second ring and at the central burner are very small, hence hardly satisfying the concept of a wok burner, which instead requires considerable flame at the pan centre. 
     Moreover the three venturis are of small radial extension, with consequent limitation on the maximum power which the burner is able to develop. 
     U.S. Pat No. 5,401,164 describes a burner of type substantially similar to the preceding and with its venturi too short to develop sufficient power. Moreover this burner withdraws primary air exclusively from below the hob and is hence sensitive to the streaming effect. 
     U.S. Pat. No. 5,842,849 describes a burner with a cup support closed at its base, on which the injectors associated with the vertical venturis are positioned. The burner withdraws primary air from above the hob, however as the burner is of reduced height in order to be able to be housed within the hobs, its venturis are too short and hence of low efficiency. 
     EP 1 120 603 describes a burner with a vertical venturi feeding an inner central burner and a diametrical venturi feeding an outer annular burner. 
     The power developed by this burner is fairly limited; moreover the burner is formed from a very large number of parts and finally, as the two gas inlets feeding the two separate nozzles cannot be connected together, the burner operates only as a dual burner and is unable to function as a single-command burner. 
     U.S. Pat No. 5,704,778 describes a burner with three horizontal venturis, which is able to develop moderate power, but withdraws the primary air from below the hob and is hence sensitive to the streaming effect. 
     EP 1 042 634 describes a burner with two injectors feeding a vertical venturi for an inner central flame ring and a horizontal venturi for an outer annular flame ring. The primary air for the vertical venturi is withdrawn from above the hob, whereas the primary air for the horizontal venturi is withdrawn from below the hob. 
     As the injector holder for the vertical venturi is positioned above the horizontal venturi, the axial length of the vertical venturi is too small and does not enable the burner to develop the required power. 
     BRIEF SUMMARY OF THE INVENTION 
     An object of the invention is to overcome all the limitations which are recognizable conjointly or separately in burners pertaining to the state of the art, by providing a burner which satisfies all the aforelisted requirements. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       This and other objects which will be apparent from the ensuing description are attained, according to the invention, by an improved gas burner for cooking appliances, as described in claim  1 . 
       A preferred embodiment of the present invention together with some variants thereof are described in detail hereinafter with reference to the accompanying drawings, in which: 
         FIG. 1  is a partly interrupted perspective view of the cup-shaped support of the burner of the invention in its dual version, 
         FIG. 2  is a perspective view of a burner of the invention in its dual version, shown partly sectioned on two vertical planes forming an angle therebetween, 
         FIG. 3  is a plan view of the cup-shaped support, 
         FIG. 4  is a plan view of the flame divider, 
         FIG. 5  is a perspective view of the burner shown sectioned on a diametrical vertical plane, 
         FIG. 6  shows the cup-shaped support in the same view as  FIG. 1  but in the three ring version with a single gas inlet. 
         FIG. 7  shows a variant of the burner in the same view as  FIG. 1 , but with the primary air intake for the two injectors of horizontal axis positioned below the hob, 
         FIG. 8  shows a variant of the burner in the same view as  FIG. 6 , but with the primary air intake for the two injectors of horizontal axis positioned partly below and partly above the hob. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 to 5  show the burner of the invention in the dual version, comprising a cup-shaped support  3  formed from two superposed parts  2  and  4 , which are coupled together and fixed to the upper sheet metal  6  of the hob by screws  8 . 
     Two gas inlets  10  and  12  are provided at a vertical wall of the upper part  4  of the cup-shaped support  3 . 
     The inlet  10  communicates with a pair of spaced-apart nozzles  14  of horizontal axis, whereas the inlet  12  communicates with a nozzle of vertical axis positioned at the centre of the cup-shaped support  3 . 
     The two horizontal nozzles  14  terminate at an upperly open cavity  18  defined by a rim emerging from the sheet metal  6  of the cooking hob. 
     Specifically this rim, which forms all the side walls of the cavity  18 , comprises a lesser projecting portion  20  of the cavity wall, to which the nozzles  14  are applied, and a greater projecting portion  22  involving the other three walls. 
     Two parallel venturi conduits  24  of horizontal axis extend from that wall of the cavity  18  opposite the wall to which the nozzles  14  are applied. These venturis extend from the cavity  18 , they are spaced apart and, after passing through virtually the entire cup-shaped support  3 , open into an arcuate channel  26  which extends as two branches, themselves extending upperly into two vertical channels  28  which pass through the sheet metal  6  of the hob and are each provided with a rim  30  projecting upwards to an extent equal to the rim  22  of the cavity  18 . 
     The two horizontal venturis  24  extend spaced apart to define a space within which the nozzle  16  of vertical axis is positioned. It is housed in a cavity  32  defined by side walls which emerge via their upper rim from the sheet metal  6  of the hob. 
     This upper rim comprises a portion  34  joined to the greater projecting rim  22  of the cavity  18  and having the same height thereas, and a portion  36  more distant from the cavity  18  and depressed to an extent substantially equal to the rim  20  thereof. 
     The burner body  38  is positioned on the top portion  4  of the cup-shaped support  3 . It comprises an inner cylindrical portion  40  and an outer annular portion  42  joined together by a substantially horizontal flange  44 . 
     The outer annular portion  42  is provided with a base  46  in which two apertures are provided in positions corresponding with the vertical channels  28  of the cup-shaped support  3 , so that when the burner body  38  is positioned on said cup-shaped support, there is communication continuity between the channel  26  and the annular cavity  47  of the portion  42 . 
     The outer wall of the annular cavity  47  of the portion  42  is provided with a plurality of ports  48  for emergence of the gas-primary air mixture. 
     A vertical venturi conduit  50  is provided in the inner cylindrical portion  40  of the burner  38  and upperly faces the nozzle  16  of vertical axis. It opens upperly into a circular chamber  52 , the outer wall of which comprises a plurality of ports  54 . 
     The annular chamber  47  is closed upperly by a removable annular cover  56 , while the circular chamber  52  is closed upperly by a circular cover  58 . 
     The burner  38  rests on the cup-shaped support  3  at the greater projecting rims  22 ,  30  and  34  thereof, and remains centered in the correct mutual position by the engagement of its appendices  38 , projecting downwards from the central portion  40  of the burner  38  and cooperating with the cavity  32  of the cup-shaped support  3 . At the peripheral edge of its annular portion  42  it remains spaced from the sheet metal of the cooking hob, to hence define a passage for entry of the primary air which has to reach the two cavities  18  and  32 . 
     Because of the lesser height of the rim  20  of the cavity  18  and of the rim  36  of the cavity  32 , when the burner  38  is positioned on the cup-shaped support  3 , two passages form between them to serve, as described hereinafter, to allow entry of primary air into the cavities  18  and  32  respectively, from above the hob. 
     in a position facing the depressed rim  36  of the cavity  32 , the annular portion  42  of the burner  38  presents a channel  62 , the side walls  64  of which present small slits  66 . 
     The aforedescribed burner operates in the following manner. 
     Gas leaving through the vertical nozzle  16  and through the two spaced-apart horizontal nozzles  14  can be regulated in the required manner by a two-exit dual valve. 
     The gas flow leaving the vertical nozzle  16  entrains into the cavity  32  a flow of primary air originating from the top of the hob  6  via a first passage defined lowerly by this latter and upperly by the outer edge of the burner  38 , and then via a second passage defined lowerly by the depressed rim  36  of the cavity  32  and upperly by the burner  38 . 
     The path of the primary air is indicated by the arrow  68  in  FIG. 5 . 
     Within the vertical venturi  50  the gas mixes with the primary air, the formed mixture then reaching the circular cavity  52 , from which it can leave towards the ports  54 . 
     A suitable spark plug  70  positioned in proximity to the inner burner  40  ignites the flame ring  72 , which remains fed with secondary air originating from above the sheet metal  6  of the hob, via the annular passage defined by this latter and by the burner  38 . 
     The secondary air flow path for the central burner  40  is indicated by the arrow  74  in  FIG. 5 . 
     The gas flow leaving the two nozzles  14  entrains into the cavity  18  another flow of primary air originating from the top of the hob  6  via a first passage defined lowerly by this latter and upperly by the outer edge of the burner  38 , and then via a second passage defined lowerly by the depressed rim  20  of the cavity  18  and upperly by the burner  38 . 
     This flow of primary air is indicated by the arrow  76  in  FIG. 2 . 
     Within the two horizontal venturis  24  the gas mixes with the primary air, the formed mixture passing through the two branches of the arcuate channel  26  and the two vertical channels  28  to reach the annular cavity  42 , from which it can leave towards the ports  48 , to give rise to the outer flame ring  78 , fed by secondary air originating from above the hob  6 , as indicate by the arrow  80  in  FIG. 2 . 
     If the dual valve is arranged to feed only the central nozzle  16  with gas, only the inner flame ring  72  will be fed. If the valve is then made to also feed the horizontal nozzles  14 , the slits  66  give rise to flames which enable mixture ignition to be transmitted by the flames  72  to the flames  78 . 
     In the embodiment shown in  FIG. 6  one of the two gas inlets is closed by a plug  88 , while the other, fed by a single-exit valve, feeds both the two horizontal nozzles  14  and the vertical nozzle  16 . 
     In this case the burner operates with the flame rings fed simultaneously, as in the case of traditional burners. 
     In the embodiment shown in  FIG. 7 , the chamber  18  comprises apertures  82  in its base and is closed upperly by a cover  84  fixed by screws. 
     In this manner the primary air flow entrained by the nozzles  14  is withdrawn from below the hob via the apertures  82 , as indicated by the arrow  86 . 
     This solution is more advantageous than the preceding one because of the presence of the cover  84 , which prevents spilled liquids from entering the chamber  18 , while at the same time enabling said cover  84  to be easily removed if the nozzles  14  need to be replaced. 
     This solution is also more advantageous than the preceding one with regard to the primary air volume which can be drawn in, and hence the greater power which the burner can develop. At the same time it is insensitive to the streaming effect in that, even if on opening and/or closing the ports below the hob the outer portion is extinguished, the inner portion, being fed by primary air originating from above the hob, continues to operate and is able to immediately re-ignite said outer portion. 
     In contrast, if this embodiment were applied to a cooker provided with a tangential fan for cooling the cavity, the burner could be disturbed and would require the installed fan to be suitably repositioned in order not to disturb the primary air flow. 
     In the embodiment shown in  FIG. 8  that wall of the chamber  18  to which the nozzles  14  are applied is provided with an aperture positioned below the sheet metal  6  of the hob. 
     In this case there are two primary air flows, which are entrained by the gas leaving the nozzles  14 ; one of these, the path of which is indicated by the arrow  76 , is drawn from above the hob, while the other, the path of which is indicated by the arrow  86 , is drawn from below the hob.