The present invention relates to an improved gas burner.

Currently, market requirements are increasingly aimed at producing burners with several flame rings, combined with the ever increasing requirement of reducing production costs of such burners.

Burners with several flame rings of the so-called multi-ring type are known, provided with a single gas inlet controlled by a standard single-exit valve. In particular, the valve enables the gas to be fed to the burner inlet and from there simultaneously to all the flame rings, of both maximum and minimum capacity.

Burners with several flame rings of the so-called dual type are also known, which present two gas inlets, one associated with the burner outer portion, usually of annular shape, and the other associated with its central inner portion of circular shape. In particular, this type of burner uses a special two-way valve, enabling two operative conditions: one of maximum power, in which both the burner portions are fed, and one in which the outer annular portion is not fed, so enabling more modular use and allowing a very low minimum power to be delivered.

In particular, from IT 1232887 a multi-ring burner is known which uses primary air and secondary air both originating from above the cooking hob. In particular, it presents three cup-shaped closed chambers, each of which houses an injector; in greater detail, the injector positioned in the central cup feeds the circular central portion with gas, while the two lateral injectors each feed an outer portion of substantially half-moon shape. In the central portion, mixing takes place by virtue of a venturi conduit of essentially radial type, i.e. with a gas and primary air feed conduit which open into a radially extending mixing chamber.

The two outer portions are instead fed by venturi conduits, each of which is formed by a vertical conduit which widens from the bottom upwards and creates a venturi effect by interaction with a dome-shaped projection provided in the lower face of the flame divider. In greater detail, this projection is inserted in the top of the vertical conduit such that the lower face of this projection and the upper terminal part of this conduit define a narrow passage causing the mixture to accelerate, giving rise to the venturi effect. Consequently, the two venturi conduits which feed the outer portions are also of substantially radial type, mixture acceleration taking place by virtue of the combination of a vertical conduit merging into a horizontal half-moon shaped chamber.

A first drawback of this solution is its particularly high production cost; in particular the dome projection provided in the lower face of the flame divider cannot be formed by the normal sheet metal cold-pressing process used for producing nearly all burners, but instead requires cast-iron casting or steel sintering processes, which are much more costly.

Another drawback derives from the half-moon shape of the outer chamber portions. In particular, the chambers internally present a portion which re-enters to define a substantially elliptical space between them and the central portion. However, this shape does not enable the outer annular portion to generate an inwardly-directed annular ring of flames. The result is that this type of burner has only two flame rings, one on the outer annular portion and one on the central portion, whereas the market mainly requires burners with three flame rings, one on the central portion and two on the annular portion, one directed outward and one directed inward.

WO2004/044490 describes a multi-ring burner fed with primary air and secondary air both totally drawn from above the cooking hob.

In particular, it presents three separate cup-shaped chambers, each of which houses an injector. In greater detail, the central injector feeds the central portion of the burner via a radial venturi, while the other two lateral injectors feed the outer annular portion of the burner via two Venturis of radial type such as those described in IT 1232887. As already stated, this type of venturi requires its horizontal chamber to have rather large dimensions, and presents an internal diameter widening in that zone into which said radial Venturis flow; in other words, the annular portion is of unusual and irregular shape.

Moreover the vertical conduits of this burner are cylindrical, do not present any converging and/or diverging portions and do not cause any vertical venturi effect. In greater detail, at their outlet, the vertical lateral conduits present a constriction which then passes into a zone having a significant radial extension; the combination of these characteristics defines a venturi of radial effect.

This type of burner presents a third ring of flames which emerge from the annular portion and are directed inward; however said flames are distributed along an irregular annular profile. Because of this, traditional inexpensive closure covers of regular annular shape cannot be used to upperly close the chamber defined by the irregular annular portion. Consequently, this solution is particularly costly and characterised by a particular non-traditional appearance little liked by cooking hob manufacturers.

WO2005/078342 describes a multi-ring burner also fed with primary and secondary air both drawn from above the cooking hob. It is composed of a single cup closed at its bottom and housing three injectors, in which the central injector is disposed vertically and feeds the central portion with gas, while the other two lateral injectors are inclined outward. The flame divider body is formed in two parts which when connected together define two inclined conduits of venturi effect facing said lateral injectors.

This solution enables the annular portion to be of regular shape; however, the fact that the flame divider body is made in two parts to form the two inclined venturi conduits makes the burner production cost particularly high.

Moreover, the fact that the outer injectors are inclined creates a problem both during production, assembly and burner leakage control, and along the production line where the burner is mounting on the cooking hob, as specific suitable equipment is required.

US 2011/151385 describes a burner comprising a support body to be fixed to the lower surface of the cooking hob sheet metal; it is provided with three injectors facing three conduits defined in the flame divider. Inside the flame divider at the exit of the vertical venturi, barriers are provided to prevent flame separation phenomena. The outer edges of the flame divider body rest on the cooking hob sheet metal. In the light of all these characteristics, it is particularly complicated both to produce and to mount. US 2010/279238 describes a burner comprising a support body provided with three injectors facing three vertical venturi conduits defined in the flame divider. In particular, the lateral vertical venturi conduits are rather lengthy, hence the burner is particularly tall and bulky in height. Moreover, in the light of the numerous components required, it is particularly complicated constructionally and hence costly.

An object of the invention is to eliminate the drawbacks of the known solutions by providing an improved three flame-ring gas burner which can operate both as a multi-ring and as a dual burner.

Another object of the invention is to provide an improved gas burner, the flames of which are not disturbed by sudden opening of an oven or unit door positioned below the cooking hob.

Another object of the invention is to provide an improved gas burner of reduced overall height.

Another object of the invention is to provide an improved gas burner of simple, rapid and low-cost construction.

All these objects which will be apparent from the ensuing description are attained according to the invention by an improved gas burner with the characteristics indicated in claim 1.

Two preferred embodiments of the invention are further clarified hereinafter with reference to the accompanying drawings, in which:

Figure 1 is a vertical section through a first embodiment of the improved gas burner according to the invention,

Figure 2 is a vertical section therethrough perpendicular to that of Figure 1 , Figure 3 shows it in plan view under maximum flow conditions,

Figure 4 is a plan view of the injector holder of the burner of Figure 1 ,

Figure 5 is a vertical section through a first embodiment of the improved gas burner according to the invention,

Figure 6 is a vertical section therethrough perpendicular to that of Figure 5.

As can be seen from Figures from 1 to 4, the improved gas burner 2, according to the invention, comprises an injector holder 4 provided with a gas inlet 6 associated with a standard single-exit valve, not shown. In particular, these figures show a burner according to the invention in the multi-ring version, i.e. in which all the flame rings are fed by a single gas source and are regulated altogether in the same manner.

On the base of the injector holder 4 a conduit 8 is provided which faces the gas inlet 6 and extends along the diameter of said injector holder 4. In this latter, cup-shaped depressed zones are also provided, i.e. closed both on their base and laterally, and open upwards; in particular, a central cup 10 and two lateral cups 12 and 12' are provided.

On the base of the central cup 10 a first injector 14 is provided, which is disposed vertically and is in communication via the conduit 8 with the gas inlet 6. Instead, on the base of the lateral cups 12 and 12' a second injector 16 and a third injector 18 are provided respectively, which are also disposed vertically and are in communication via the conduit 8 with the gas inlet 6.

On its circumferential surface, the injector holder 4 presents a flange 20 provided with widened zones in which seats 22 are provided, required to fix the injector holder 4 by screws to the upper sheet metal of a cooking hob, not shown. On the injector holder 4 a flame divider 24 rests provided with appendices 26, which facilitate positioning and centring of this latter relative to the injector holder.

The flame divider 24 presents a central portion 28 surrounded by an outer annular portion 30; in particular, the bases of said portions are connected together by a flange 32 forming the bottom of an annular cavity 34. In greater detail, the flame divider 24 is supported by raised portions 36 and 38 defined on the injector holder 4 and consisting of the upper prolongations of the lateral walls respectively of the two outer cups 12 and 12' and of the central cup 10. In this manner, between the flame divider 24 and the injector holder 4, passages are defined for the air drawn from above the cooking hob. In particular, first slots 40 are provided for entry of primary air 41 into the two outer cups 12 and 12', and second slots 42 for entry of primary air 43 into the central cup 10; in addition, between the bottom of the flame divider 24 and the injector holder 4, openings 44 are provided for entry of secondary air 45 into the annular cavity 34 for the central flame ring 80 and for the inner annular flame ring 82. In particular, the openings 44 define connection passages between the annular cavity 34 of the flame divider and the space surrounding the burner, above the cooking hob.

The central portion 28 of the flame divider 24 is provided centrally with a through vertical conduit 46 facing the injector 14 positioned in the central cup 10 and of upwardly converging frusto-conical shape. It opens into a cylindrical distribution chamber 48 of reduced height. The outer annular portion 30 of the flame divider 24 is instead provided with two conduits 50 which face the injectors 16 and 18 and enter an annular distribution chamber 52 provided in the annular portion itself.

The central portion 28 of the flame divider 24 is provided on its upper edge with a plurality of first radial recesses 64, while the annular portion 30 is provided with a plurality of second radial recesses 66 and 68, defined respectively at the outer upper edge 70 and at the inner upper edge 72 of the annular distribution chamber 52.

A circular closure cover 74 is rested on the central portion 28 of the flame divider 24 and upperly defines the recesses 64, while an annular closure cover 76 is rested on the annular portion 30 and upperly defines the recesses 66 and 68.

The upper end of the venturi conduits 50 projects and emerges from the base 53 of the annular distribution chamber 52. This is particularly advantageous in that it enables particularly lengthy vertical venturi conduits to be provided, in order to achieve optimal mixing of gas and primary air, while at the same time enabling a reduced overall height of the burner to be maintained. In addition to this aspect, it is also advantageous in that the fact that the upper end of the venturi conduits 50 is positioned at a level above the base 53 of the annular chamber 52 prevents any water which might spill over from a pan during cooking from entering the annular chamber 52 and from there arriving to obstruct the injector and/or enter the inner cavity of the cooking hob, where it could damage electrical circuits or other components. The lower end 60 of each conduit 50 is at a slightly higher level than the upper edge 62 of the injector holder 4, this facilitating draw-in of primary air for mixing.

The two lateral conduits 50 are configured such that air and gas flow which leaves them and enters the annular distribution chamber 52 is substantially already completely mixed. In particular, at the outlet of each lateral conduit 50, the height of the annular chamber 52 is greater than one half the radius of the lateral conduit 50 at its upper end.

In greater detail, each conduit 50 presents in sequence a convergent lower frusto-conical portion 54 of diameter at its lower end substantially between 11 and 12 mm and serves to convey the air and gas into a substantially cylindrical intermediate portion 56. This has a diameter substantially between 8 and 9 mm and defines a constriction which serves to accelerate the air/gas mixture; this mixture then opens into the divergent upper frusto-conical portion 58, having an upper diameter substantially between 10 and 11 mm, which causes the mixture to expand.

Moreover, the distance between the upper end of the venturi conduits 50 and the lower face of the annular cover 76 is substantially between 3 and 4 mm, preferably about 3.5 mm; essentially the passage between the outlet section of the venturi conduit 50 and the inlet section of the annular chamber 52 increases such that the mixture continues to expand, without hindrance, within the annular chamber itself. Advantageously, the flame divider 24 is provided with centring fins 78 in order to enable unique positioning of the annular cover 76 relative to the annular portion 30 of the flame divider.

The operation of the burner according to the invention derives from the aforegoing description.

When in its operative state, the burner single-exit control valve, not shown, is open and consequently the gas reaches the three injectors 14, 16 and 18.

The gas leaving the injector 14 draws in, from the top of the cooking hob, a flow of primary air 43 which passes through the slots 42 to enter the central cup 10 and from there is drawn along the frusto-conical vertical conduit 46 causing the air and gas to mix. In particular, when the air and gas flow reaches the distribution chamber 48 their mixing is already complete; the mixture thus formed then leaves the central portion 28 through the radial recesses 64 to generate a central flame ring 80.

Instead, the gas that leaves the injectors 16 and 18 draws in, from the top of the cooking hob, a flow of primary air 41 which passes through the passages 40 to enter the respective cups 12 and 12' and from there is drawn along the conduits 50, to mix with the gas. Again in this case, when the gas and primary air flow leaves the upper end of the venturi conduits 50 and enters the annular distribution chamber 52, their mixing is already substantially complete; the mixture formed in this manner then leaves the annular portion 30 both through the internal radial recesses 72, to generate an annular ring of inwardly directed flames 82, and through the outer radial recesses 70, to generate an annular ring of outwardly directed flames 84. The secondary air 45 for igniting and maintaining the flames which form the central ring 80 and the inner annular ring 82 originates from the top of the cooking hob and enters the annular cavity 34 through the openings 44, while the secondary air for igniting and maintaining the flames which form the outer annular ring 84 originates from the environment surrounding the burner 2.

The embodiment shown in Figures 5 and 6 represents an improved gas burner 86 according to the invention in the dual version, i.e. in the version with the flame rings fed separately by two gas sources which are regulated independently.

It comprises all the characteristics previously described with reference to the embodiment shown in Figures from 1 to 4, with the exception of the fact that an injector holder 88 is provided comprising two gas inlets 90, 92 with which a traditional two-exit valve is associated (dual).

In particular, in the burner 86 illustrated in the embodiment of Figures 5 and 6, the upper end of the venturi conduits 50 projects and emerges from the base 53 of the annular distribution chamber 52. Moreover, again in the burner 86 the two lateral conduits 50 are configured such that the air and gas flow, which emerges therefrom and enters the annular distribution chamber 52, is substantially already completely mixed. In particular, again in the burner 86, at the outlet of the lateral conduit 50, the height of the annular chamber 52 is greater than one half the radius of the lateral conduit 50 at its upper end.

Essentially, that already stated relative to the configuration and to the dimensions of the lateral conduit 50, and for the distance between the upper end of these and for the lower surface of the outer annular cover 76 is also valid for the burner 86. The burner 86 presents a first gas inlet 90 facing a first conduit 94 communicating with the lateral injectors 16 and 18, and a second gas inlet 92 facing a second conduit 96 communicating with the central injector 14. In greater detail, the first conduit 94 extends along the diameter of said injector holder 88, while the second conduit 96 has a length substantially equal to one half of said diameter and is disposed perpendicularly to and at a level slightly above the first conduit 94.

The operation of the burner shown in Figures 5 and 6 is identical to that already described, with the difference that this burner when in its operative configuration can assume two conditions. In particular, when the two-exit valve causes gas to flow to both the inlets 90 and 92 there is a condition of maximum flow in which all three injectors 14, 16 and 18 are fed in order to generate simultaneously all three flame rings 82, 84 and 86. In contrast, when the inlet valve causes the gas to flow to just the inlet 92 there is a minimum flow condition in which only the central injector 6 of the central cup 10 is fed in order to generate only the central flame ring 80.

In a variant valid for both the aforedescribed and illustrated embodiments, the annular portion 30 could also not present inner radial recesses 72; in that case there would be no annular ring of inwardly direct flames 82, and there would be only two flame rings, namely the central flame ring 80 and the annular flame ring 84 with flames directed outward.

From that stated it is apparent that the improved gas burner according to the invention is more advantageous than traditional burners, in that: - as it is composed of only four parts (injector holder, flame divider and two closure covers) it is quick and particularly cheap to produce; in particular, the fact that the flame divider is formed in a single piece, and the fact that the closure cover of the annular portion is produced by cold pressing sheet metal, contribute to reducing the overall burner production costs,

- the primary air is totally drawn from the top of the cooking hob,

- between the central portion and the outer annular portion an annular cavity is defined such as to enable an annular ring of inner flames of regular shaped to be generated,

- the upper prolongation of the venturi conduits beyond the base of the annular chamber increases the length and hence the efficiency of the venturi conduits, without increasing the overall vertical height of the burner, and in addition eliminates the possible negative effects on the injectors and on the space below the cooking hob, due to possibly liquid spillage from a pan during cooking.