"GAS BURNER FOR OVENS"

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FIELD OF THE INVENTION

The present invention refers to α gas burner for ovens, or grill, of the type comprising a Venturi tube for mixing fuel gas and primary air, a main chamber, longitudinally extended in the flow forwarding direction of the mixture, and located downstream the Venturi tube, as well at least one chamber outside such a main chamber, fluidically connected to the latter, and provided with flame holes for the outflow of the gas - primary air mixture. KNOWN PREVIOUS ART

It is known art realizing gas burners for domestic ovens, or grill, comprising a first extended chamber for distributing the gas - primary air fuel mixture, immediately placed downstream to the mixing tube having a Venturi effect, and a second delivery chamber, fluidically connected to the first one, provided with outflow holes outwardly for such a fuel mixture (flame holes). The shape and dimensions of the fuel mixture passageways from the distribution chamber to the delivery chamber, as well the shape of such a delivery chamber and of the corresponding outflow holes, determine the local thermodynamic conditions of the mixture inside the burner, particularly its point by point pressure and concentration, and thereby determine the flame shape, profile, and distribution outside the outflow holes of the second chamber. For example, the US Patent 3.156.292, in the name of ROSS, describes a similar gas burner for ovens, in which a tubular distribution chamber, longitudinally extended in the inflow direction of the fuel mixture, and situated downstream to the mixing tube, is fitted in an outer case provided with flame holes. The outer case defines, between its upper

wall and the distribution tubular chamber itself, a delivery chamber, that is fluidically connected to such a distribution chamber via some passageways, longitudinally extended, and obtained over the walls of the latter. Such a longitudinally extended passageways have the object to guarantee the homogeneous gas inflow from the distribution chamber to the mixing chamber and thereby to guarantee some homogeneity in the flame distribution and profile. Such a solution, although aiding a fairly burner operation, does not consider the pressure difference generating within the tubular distribution chamber because of the sudden stop of the mixture flow at the closed end, opposite to the mixing tube, of the distribution chamber itself.

Particularly, the mixture flow within the tubular distribution chamber, given by the gas outflow from the corresponding injector, longitudinally proceeds from the Venturi tube towards the closed end of the distribution chamber itself, where it encounters the ending closed wall of the latter, that will obstruct, divert and render the flow itself incoherent. Because of this, within the distribution chamber a non - null pressure gradient is generated, whereby the pressure is locally greater at the closed end of the distribution chamber and is locally smaller at the outlet section of the mixing tube.

Such a pressure gradient, as it will be evident to a person skilled in the art, will cause a non - homogeneous distribution of the mixture in the burner and then, even if in presence of an outer delivery chamber, separated from the afore said tubular distribution chamber, will generate an heterogeneous distribution of the flames, and consequently a non - constant geometrically distribution of the temperature and heat generated by the burner. There is an attempt to solve this problem in the International Patent

Application WO 2004/005799, in the name of CAST srl, that describes an extended burner for ovens of the type comprising a tubular extended distribution chamber of the fuel mixture situated downstream the gas and primary air mixing tube with a Venturi effect (Venturi tube). The mixture distribution chamber, for some length starting from the Venturi tube, is situated in fluidic communication, by some sort of longitudinal coil, with an outer delivery chamber provided with flame holes. The declared scope of such a coil, realized by two longitudinal ribs inside the burner, reciprocally transversally spaced, and of height lower than the burner chamber height, is to set up some walls disposed to carry part of the mixture flow to the delivery chamber, situated sideways to the tubular distribution chamber, thereby forming some sort of trap for the mixture, which would reach a higher pressure at the flame holes being present in the afore said delivery chamber. Such a higher pressure, that would occur, as said, only at those flame holes of the burner placed in the afore said delivery chamber in a length near the Venturi tube, would be sufficient to compensate the greater pressure occurred at the burner end opposite to the Venturi tube, wherein the flame holes are directly obtained into the distribution chamber and there is not any outer delivery chamber, thereby concurring in regulating the distribution of the burner flames. This solution described in the CAST application tried to solve the problem of the existence of a pressure gradient in the mixture within the distribution chamber of the burner, but, apart from resulting practically difficult to put into action, it does not allow to obtain, within the main distribution chamber or within the delivery chamber, a sufficient homogeneity in distributing the local pressure of the mixture, being able to make the flames regular and homogeneous along the

whole burner development.

It is an object of the present invention to realize a burner for domestic ovens or grill that-would not have the drawbacks of the oven burners known in the art and thereby exhibiting a regular flame distribution for the whole longitudinal extension of the burner itself. It is therefore an object of the present invention to realize a burner for ovens of the type comprising a Venturi tube for mixing fuel gas and primary air and a longitudinally extended distribution chamber, located downstream the Venturi tube, exhibiting on its own inside a regular distribution of the mixture pressure for the whole burner extension, at least at the corresponding flame holes. It is another object of the present invention to provide an oven or grill burner of the afore mentioned type, that allows to have regular and homogeneously distributed flames for the whole development of the burner itself.

SUMMARY OF THE INVENTION

These and other objects are obtained by the oven or grill burner according the first independent claim and the following dependent claims. The gas burner for ovens, or grill, according to the present invention comprises a Venturi tube for mixing fuel gas and primary air, a main distribution chamber, longitudinally extended in the flow forwarding direction of the mixture, and located downstream to the Venturi tube, as well as at least one delivery chamber placed outside such a main chamber and provided with flame holes for the outflow of the gas - primary air mixture. The main distribution chamber and the outer delivery chamber are mutually fluidically connected, at least for a longitudinal length of the main chamber, by at least one through opening that, advantageously, has, relative to the longitudinal

forwarding direction of the mixture flow, a greater cross section in the upstream portion and a smaller cross section in the downstream portion of such a longitudinal length.

Preferably, although not necessarily in a continued way along the whole longitudinal extension of the aforesaid main chamber, the through opening between the main chamber and the outer chamber, develops for the whole extension of the main chamber, from the outlet section of the Venturi tube to substantially the ending wall, opposite to the Venturi tube, of such a main chamber. Such a solution allows an effective regulation of the local pressure in the aforesaid outer delivery chamber, forcing the mixture to outflow through passageways having differently shaped sections, to produce dissimilar load losses on the mixture flow. In practice, thanks to the solution claimed herein, the load losses will be greater at that through opening between the two chambers having smaller section, placed in proximity of the closed burner end, and will be on the contrary smaller where the through opening will show a greater section, that is in proximity of the outlet section of the Venturi tube. In such a way, the fuel mixture pressure and distribution in the outer delivery chamber will be practically homogeneous for the whole development of the burner, allowing a similar homogeneous and regular distribution of the burner flames.

In addition, according to a preferred aspect of the present invention, the burner comprises two outer delivery chambers having longitudinal development along the axes parallel to the axis of the main distribution chamber, and disposed at the sides of the latter. In a preferred embodiment of the present invention, the burner comprises an upper shell, an intermediate diaphragm and a lower shell, reciprocally coupled so as to define both the Venturi tube and

the αfore said main chamber and the outer chambers, and a further compensation chamber, placed at the bottom. In such an embodiment, the particular shape of the intermediate diaphragm, with a concave portion and at least one convex portion, allows to easily and precisely determine the cross section of the afore said through openings between the main chamber and the outer chamber, or the outer chambers, of the burner.

In such an embodiment of the burner according to the present invention, the Venturi tube is preferably a Venturi tube with an axial development.

BRIEF DESCRIPTION OF THE DRAWINGS

For purposes of illustrations only and not limitative a preferred embodiment of the burner for ovens or grill of the present invention will be described with reference to the accompanying figures, in which: Figure 1 is a top perspective view of a burner according to a particular aspect of the present invention;

Figure 2 is a partial side section view of the burner of figure 1 ; Figure 3 is another partial side section view of the burner of preceding figures; Figure 4 is a top perspective view of an intermediate diaphragm within the two outer shells composing the burner body of figure 1 ;

Figure 5 is a frontal section view of the burner of figure 1 , according to the cut line A - A represented in the same figure 1 ; and Figure 6 is a front section view of the burner of figure 1 , according to the cut line B - B.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE PRESENT

INVENTION

Referring first to figure 1 , the oven or grill burner 1 , according to an aspect of the present invention, is constituted by an upper shell 5 and

α lower shell 6, reciprocally coupled and attached in a known way, which define the outer body, or casing, of the burner 1 comprising a coupling section 7 for joining, directly or indirectly, the burner 1 to an inner wall 101 of the oven, or grill, a longitudinally extended body that is laterally provided with a plurality of flame holes 4, and a closed ending section 8, opposite to the afore said coupling section 7, eventually provided with means for fixing, directly or indirectly, the casing to another inner wall of the oven, or grill. The shells 5 and 6, reciprocally coupled with the interposition of a intermediate diaphragm 13 (see for example figure 4), at least partially define the inner geometry of the burner 1 , that comprises, starting from its coupling end 7 to the closed section 8, a Venturi tube 2 of the type having an axial development, a main chamber 3, placed downstream to the Venturi tube 2 and longitudinally coaxially extended with it, as well as two side outer chambers 16, 17 (figures 2 and 3), longitudinally extended along parallel axes that extend laterally to the main chamber 2 axis, and provided with the afore mentioned flame holes 4. Now referring also to figure 2, showing a side section of part of burner 1 in proximity of its coupling section 7, the connection between the burner 1 and an inner wall 101 of an oven, or grill, could be obtained by an apposite bracket 100, provided with means - known in the art - to constrain the burner 1 at its coupling section 7, and disposed as well to hold an injector 9 of the fuel gas in the burner itself 1 , when the latter is just connected to such a bracket 100.

More in detail, as shown in figure 2, the inner geometry of the burner 1 provides a first tubular zone 10, immediately placed downstream the coupling section 7, presenting a truncated cone shape with a converging section, until it encounters a zone 1 1 , having a cylindrical

profile with α reduced section, that leads to a further zone 12, gradually widening relative to the zone 1 1 , or presenting a diverging section, substantially in a plane orthogonal to the section of figure 2, as visible in figure 1. The zones 10, 1 1 and 12 extend along an unique axis and constitute the afore said Venturi tube 2 having an axial development, adapted to allow the mixing of the fuel gas, injected by the injector 9, with the (primary) air drawn in by the Venturi tube 2 itself from the environment outside the burner 1. As can be seen in figure 2, such a Venturi tube 2 is partially defined by the lower shell 6, partially by the intermediate diaphragm 13, this latter being conveniently shaped such as to overlap the same lower shell 6 starting from a predefined position, and by the upper shell 5. Considering the forwarding direction of the fuel gas, and then of the mixture, within the burner 1 , immediately downstream to the outlet section 14 of the Venturi tube 2, a main chamber 3 is obtained intended to supply the mixture into the burner 1 itself. The main chamber 3 develops longitudinally and coaxially to the Venturi tube 2 and it is defined by the intermediate diaphragm 13 and the upper shell 5. Between the intermediate diaphragm 13 and the lower shell 6 is as well obtained a lower compensation chamber 15, fluidically connected with the main chamber 3 thanks to some holes 20 (figure 4), conveniently obtained along the lower wall of the intermediate diaphragm 13, intended not only for regulating the mixture outflow towards the outside, thanks to some passageways 23a, 23b opened outwardly, and realized between such a diaphragm 13 and the lower shell 6, but also to allow the optimal propagation of the flame to the several flame holes 4 during the ignition of the burner 1. Now referring to figure 3, showing a side section of a portion of the

burner 1 , herein described, at its closed ending section 8, it might be noted that the main chamber 3 is tapered in proximity of the same ending section 8. .

In addition, figure 3 illustrates two openings 16b and 17b, obtained between the inner ribs of the intermediate diaphragm 13 and the upper shell 5 of the burner 1 , defining a through section that is calibrated for the inflow of the fuel mixture towards one of the side delivery chambers 22b (see figures 5 and 6) on which the aforesaid flame holes 4 are opened. More in detail, generally referring also to figures 4 - 6, the particular shape of the intermediate diaphragm 13 and of the upper shell 5 allows the definition of the outer chambers 22a, 22b, which extend laterally having regard to the main distribution chamber 3, along axes parallel to the axis of the latter, and which are in fluidic communication with such a main chamber 3, thanks to the corresponding through openings 16a, 16b, 17a, 17b, having a cross section, relatively to the forwarding direction of the fuel mixture flow, with conveniently calibrated dimensions. Advantageously, according to a preferred aspect of the present invention, the through openings 16a, 16b closest to the outlet section 14 of the Venturi tube 2, have a cross section greater than the cross section of the through openings 17a, 17b obtained at the closed ending section 8 of the burner 1. Such a solution, as before mentioned, determines that the portion of the fluidic flow transiting across the through openings 17a, 17b, having cross section of smaller area, is subjected to greater load losses (that is it will encounter greater difficulties in reaching the corresponding side delivery chambers 22a, 22b), relative to those load losses that the fluidic flow crossing the through openings 16a, 16b, having a cross

section with α greater area, undergoes.

Such a different section of the through openings 16a, 16b and 17a, 17b, causing load losses mutually different, substantially compensates the local pressure difference occurring in the inner zone of the burner 1 placed next to the closed ending section 8, relative to the inner zone placed immediately downstream to the Venturi tube 2, making the fuel mixture concentration and pressure substantially homogeneous within the side delivery chambers 22a, 22b, with the consequent obtaining of regular and homogeneous flames along the whole burner 1.

Figures 4, 5, and 6 allow to investigate more in detail the whole inner profile of the herein described burner, and particularly the distinctive shape of the intermediate diaphragm 13, placed between the two upper 5 and lower 6 shells of the burner 1. Such an intermediate diaphragm 13, being just well visible in figures, might be realized by forging of a metallic plate, and comprises a lower wall shaped to define the lower zone of the Venturi tube 2 and of the main chamber 3 for distributing the mixture, respectively, as well as the upper wall of the afore said lower compensation chamber 15. Such a lower wall, starting from a zone downstream to the Venturi tube 2, is substantially concave and conveniently provided with a plurality of holes 20, that allow the fluidic exchange between the main chamber 3, placed in the top, and the compensation chamber 15, placed in the bottom. At the side ends of such a concave lower wall of the intermediate diaphragm 13, in some lengths downstream to the Venturi tube 2 only, according to the forwarding direction of the fuel mixture flow, some upwardly extending longitudinal ribs 18a, 18b and 19a, 19b are present, which are realized by convex protruding portions of the plate

composing such an intermediate diaphragm 13, and which aid to define, respectively, the aforesaid calibrated through openings 16a, 16b and 17a, 17b for the mixture from the main chamber 2 to the outer chamber 22a, 22b. Such ribs 18a, 18b and 19a, 19b project with different heights starting from the lower wall of the intermediate diaphragm 13, to thereby define some first through openings 16a, 16b for the mixture having cross section greater than the cross section of some second through openings 17a, 17b placed upstream to the former. It has to be mentioned that, in the particular embodiment herein illustrated, the through openings 16a, 16b, defined by the ribs 18a and 18b, as well as the through openings 17a, 17b defined by the ribs 19a, 19b, have a uniform cross section. About that, since the burner 1 presents at its own closed section of the ending section 8 a tapering, the ribs 19a, 19b too, disposed to functionally couple with the upper shell 5 of the burner 1 in proximity of such a closed ending section 8, have a decreasing height relative to the lower wall of the intermediate diaphragm 15, such that the through openings 19a, 19b result in having a substantially uniform cross section.

Furthermore, at the outer sides of the ribs 18a, 18b, 19a, 19b, the intermediate diaphragm presents two substantially flat side walls defining, respectively, with the upper shell 5, the outer chambers 22a, 22b for delivering the fuel mixture, with the corresponding flame holes A ₁ 4a, 4b, 4c, 4d, and, with the lower shell 6, the lower compensation chamber 15, with the corresponding calibrated passageways 23a, 23b.

Finally, at the ending section 8 of the burner 1 , the intermediate diaphragm further presents a final wall 21 , protruded upstreamly as the

ribs 18α, 18b and 19a, 19b, and intended for fluidically closing the main distribution chamber 2 of the burner 1.

It has to be herein observed that, although it has been so far described an oven or grill burner, provided with a main distribution chamber, two delivery side outer chambers and a lower compensation chamber, realized by coupling an upper shell with a lower shell and interposing a shaped intermediate diaphragm, any different oven or grill burner structure, presenting at least one main chamber and at least one outer delivery chamber, connected to the main chamber by calibrated through openings for the fuel mixture having greater section upstream and smaller section downstream, relative to the forwarding direction of the mixture flow, is part of the present invention. Similarly, although it has been described above an embodiment of the present invention proving substantially the presence of two longitudinal lengths in every sides of the main distribution chamber along which the two calibrated through openings with different sections open, respectively, although being uniform in every lengths, every other configuration, by a continuous reduction of the cross through section too, allowing to obtain the afore described effect, that is a smaller cross through section for the fluid from the main chamber to each delivery chamber at the closed ending section of the burner, is part of the group of possible embodiments of the present invention. The oven or grill burner 1 operation, above described, is as follows. Once the burner 1 is connected to the injector 9, and then to the burner 1 having been attached, at its coupling section 7, to the bracket 100 constrained to the oven or grill wall 101 , the fuel gas outflow through the injector 9, driven by a user thanks to a tap known

in the art, generates a gas flow passing through the Venturi tube 2, first in the zone having a converging section 10, then in the zone with a reduced section 1 1 and finally in the zone with a diverging section 12 of such a Venturi tube 2. As well known, the converging - diverging shape of the Venturi tube 2 causes in its turn, by the fuel gas flow passing, a depression in proximity of the zone with reduced section 1 1 , such a depression drawing (primary) air from the surroundings and generating the mixing, that ends in the zone with a diverging section 12, of the fuel gas with such a primary air. Then the fuel mixture thus formed passes into the main distribution chamber 3 and from here it reaches partially the lower delivery chamber 15, thanks to the holes 20 obtained on the concave lower wall of the intermediate diaphragm 13, and partially the side outer chambers 22a, 22b, passing through the calibrated openings 16a, 16b and 17a, 17b, respectively defined, as we could see, by the ribs, or convexities, 18a, 18b and 19a, 19b of the intermediate diaphragm 13 itself.

The different crossing through section of such a calibrated openings 16a, 16b and 17a, 17b, greater in proximity of the Venturi tube 2 and smaller in proximity of the closed ending section 8 of the main chamber 3, determines a different "easiness" for the fuel mixture flow to reach such a side chambers 22a, 22b (i.e. the flow is subjected to different load losses), that causes a substantially homogeneous distribution of the fuel mixture, and of its local pressure, inside the outer chamber 22a, 22b, in spite of the tendency, due to the closure of the ending section 8 of the main chamber 3, in settling a greater pressure of the fuel mixture in proximity of such an ending section 8 of the burner 1. From the inside of the outer delivery chambers 22a, 22b, as well as

from the compensation chamber 15, the fuel mixture outflows through the flame holes 4a, 4b, 4c, 4d, respectively, and through the calibrated passageways 23a, 23b, providing flames, once the burner 1 has been ignited, appearing homogeneously and regularly distributed along the whole outside development of the burner 1 itself.