GAS BURNER WITH IMPROVED PRIMARY AIR DUCT DESCRIPTION

The present invention relates to a gas burner, preferably of the type generally used in the household cooking gas appliances and in particular gas built-in hobs, provided with improved means to convey the primary air into the Venturi pipe. In the following of this description it will be referred to a gas burner provided with both a central body with a peripheral flame crown, and a perimetral body provided with two flame crowns, oriented inwards and outwards, but it will be intended that what explained may be identically applied and therefore valid also for gas burners provided with only a peripheral body, that is without the central flame body.

It is known that in such kind of cooking gas appliance two main requirements are present:

- a constructional and assembly requirement, i.e. the cooking gas appliance, particularly when it is a gas hob, has to show a minimum height, due to constraints which are well known to the man skilled in the art, and therefore will not be repeated, and

- a functional requirement, consisting in that the burner, specially those burners with limited diameter, are requested to provide in any case a suitable thermal power, and in any case the maximum possible power. These two requirements are however in apparent contradiction to each other, as the need to keep down the total gas appliance height obliges to also keep down the same height of the Venturi pipes providing the gas to the burners; however such limitation operates also as a limitation for the amount of gas/air mixture which can be produced, and therefore determines the limit of the burner thermal power. In order to overcome such reciprocal conditioning, some cooking appliances have been proposed and divulged, which are provided with one ore more Venturi pipes which are horizontally extended as for instance in the patents WO 2005/078342 and WO 2007/012766.

It is apparent that by horizontally placing the Venturi pipes, it is automatically void the problem of their height which conditions the overall height of the cooking appliance.

Moreover the two cited patents show respective solutions wherein the Venturi pipes leave from the burner central zone and branch out radially; therefore their

total length is limited by the radius, that is by the horizontal size of the burner itself.

In order to eliminate such condition it was proposed, for instance in EP Publication 1 120603 and in EP Application n. 071 19078.9 a type of burner wherein the Venturi pipe is placed into horizontal for the whole width, that is basically for the diameter of the burner body itself.

However the showed solutions suffer from a quite common drawback in such type of burners, that is from the fact that the primary air is sucked and sent to the inlet of the Venturi pipe from one access way only, i.e. either from the inner box body of the cooking appliance, or from the outer room, that is from the zone over the cooking hob itself.

Of course such circumstance does limit the total amount of the available primary air, and therefore limits the available thermal power.

In order to increase the primary air inlet flow, it was proposed to intake and convey the primary air flow through a coaxial and preferably tubular conduit, the final portion of which ending with the gas injection nozzle.

Such solution is for instance divulged in the patents:

a) US 2006/01991 19, b) US 6,951 ,454, c) JP 3-244906, d) JP 3-244905, e) US 2005/0279862.

However no one of said patents suggest, and even less divulgates, the solution which shows that the primary air flow, bound to the Venturi pipe, is taken from two distinct access ways, that is from a conduit which is coaxial to the gas conduit, and also from an opening which is independent of said coaxial conduit.

It would therefore be desirable, and is actually a main purpose of the present invention, to implement a kind of burner provided with two different and distinct inlet ways for the primary air flows to the Venturi pipe made up by a conduit which is coaxial to the gas conduit, and by an opening or gate placed just after the gas injection nozzle, wherein said access ways are independently flown with air taken from the inside of the box body of the cooking appliance, and from the outer room over it.

However such purpose turns to be profitable not only with gas conduits and related Venturi pipes when horizontally oriented, where the benefits are more apparent, but also with cooking appliances provided with gas conduits and Venturi pipes which are vertically oriented, even if some drawbacks may be experienced

caused by the height of the cooking appliance, yet the same the same benefits due to a double primary air suction are achieved, i.e. from the inside of the cooking appliance body, and from the outer room over it.

According to the present invention, this and further aims are reached in a kind of burner provided with a Venturi pipe which can be either horizontally or vertically extended, which is provided with connecting and inlet conduits for the primary air flow incorporating the characteristics as recited in the appended claims and including such operating means as described below by mere way of non-limiting example with reference to the accompanying drawings, in which:

- Fig. 1 is a perspective outer view of a burner body and of the relevant cooking gas appliance, here represented by a gas hob, according to a first embodiment of the invention,

- Fig. 2 is an exploded view of the cooking burner shown in fig. 1 , - Fig. 3 shows a vertical and side section view according to the section A - A of the assembly of fig. 1 ,

- Fig. 3A shows a section view, which is orthogonal to the "X" axis of the gas conduit, of a detail of the burner assembly of fig. 3,

- Fig. 4 shows a vertical and side section view according to the section A - A of a different embodiment of the assembly of fig. 1 ,

- Fig. 4A shows a section view, which is orthogonal to the "X" axis of the gas conduit, of a detail of the burner assembly of fig. 4,

- Figures 5 and 6 do show perspective views of the details respectively shown in figures 3A and 4A, - Fig. 7 shows a view which is equivalent to fig. 3, but referred to a cooking appliance provided with a gas conduit and a Venturi pipe which are vertically oriented.

With reference to figures 1 to 4, a cooking appliance according to the invention comprises:

- a gas supply conduit 1 horizontally oriented,

- a burner body 2 on which one or more flame crowns 3B, 3C... are mounted,

- a Venturi pipe 4 which is also extended into horizontal, and is substantially aligned with the final portion of said conduit 1 , - an gas injection nozzle 5 at the end of said conduit 1 towards said Venturi pipe 4.

The primary air is being conveyed towards said nozzle 5 and into said Venturi

pipe through two different flowing paths, i.e.:

- the first path consists of a suction air flow beginning from inside the body of the cooking appliance, and which in its end portion takes the form of a conduit 6 coaxial with said first gas conduit 1 , having a preferably tubular shape, and which surrounds it at least in the end portion; therefore between said gas conduit 1 and said coaxial conduit 6 a prolonged annular interspace 7 is formed, in which flows a share of the primary air, sucked by the Venturi pipe.

As clearly shown in the figures, said coaxial conduit 6 stretches towards said

Venturi pipe 4, to which it joins through a suitable prolongation 9; as a matter of facts, it may be observed that the Venturi pipe is merely the properly shaped continuation of said prolongation 9, which to its time stretches ahead beyond said injector 5;

- the second path consists of a channel 13 whose suction mouth opens over of the upper plane 12, and in its end portion a through opening 8 is arranged, preferably placed on a side of said prolongation 9, just downstream of said injector

5 and upstream of said Venturi pipe 4.

Said through opening 8 then allows the primary air flow to pass from the outer room towards said Venturi pipe 4, so achieving the first invention goal, i.e. to make the primary air to intake by splitting the whole flow into two separate flows, one of which being arranged over said upper plane 12, and the other being conveyed from the inside of the cooking appliance and which in its end path enters into a conduit which is coaxial to the gas conduit.

The just described solution allows some profitable improvements; the first improvement consists in that, as shown in figures 3 and 4, said coaxial conduit 6 draws the relevant primary air flow directly from the inner volume delimited by the box body 34 of the cooking appliance, while instead said opening 8 is connected to the outer room, and exactly from over its top surface.

This circumstance favors a better air flowing in the case that the cooking appliance is undesirably lodged in such a way that the air circulation is obstructed or slowed down; moreover the two primary air flows, so conveyed, do not interfere in any working condition.

Also it is preferred that said opening 8 is placed upwards in said prolongation

9, so as to shorten and to make straighter the path of that share of primary air flow coming from over the cooking appliance. Such solution is suitable to match the temperature increase; since the heating from the burner reduces the density of the primary air, it is important to improve

the primary air flow, in order to avoid compromising the burner functionality (combustion performances, yellow tipping and soot).

In order to improve the mixing of the gas with the primary air, it was experienced as an useful improvement to arrange some means able of causing a turbulence in gas flow when coming out from the conduit 1 , so that the gas flow itself is being broken and therefore it is easier mixed with the primary air flow.

It was then found profitable to arrange some suitable means able of creating a turbulence in the air passing through said interspace 7, so that the air going out from it, and basically from said coaxial conduit 6, is soon mixed both to the gas exiting from the conduit 1 , and to the primary air flow entering from said opening 8.

Such complete and prompt mixing effect both with the gas and with the primary air flow obviously causes the mixture itself to become optimized, what improves the combustion performances.

To this purpose, inside said interspace 7 and on the outer surface 1 1 of said gas conduit some stirring wings 10 are arranged; according to the turbulence effect which is wanted, and also to the diameter of the coaxial conduit 6 itself, the two following embodiments are proposed:

- in the first embodiment and with ref. to the figures 4 and 4A, said wings 10 are flat, are preferably passing on the "X" axis of said gas conduit 1 , are radially oriented on the outer surface of the gas conduit 1 , are regularly distributed at the same angular distance to each other, and preferably are quite prolonged so as to be extended for the whole length of said coaxial conduit 6.

- in the second embodiment and with ref. to figure 5 and 5A, said wings 10A are bent and specifically are placed in an helical arrangement, as a screw thread, whose inner edge is still attached on the outer surface of the gas conduit 1 ; said wings 10A too are regularly distributed with the same angular distance, and preferably are quite prolonged so as to be extended for the whole length of said coaxial conduit 6.

The two just described improved embodiments are obviously helpful to make up a cooking appliance which is particularly effective not only from the point of view of the thermal power supply, but also which is compact and especially cheap and simple in the construction; moreover the invention may be highly appreciated also due to the advantage that the nozzle replacement may be carried out without any need to open the appliance, as this operation may be performed across said opening 8.

As just described, the shown embodiments may be implemented by a gas

conduit and a Venturi pipe which are horizontally oriented, as represented in the figures 2, 3 and 4; however, as previously remembered, it is also possible to make up the invention by placing the gas conduit and the relevant Venturi pipe vertically oriented, as schematically shown in fig. 7. In said case it has been proved that the most suitable embodiment, both from a functional and a constructive point of view is offered by the fig. 7 itself, wherein said Venturi pipe is substantially separated from the coaxial conduit 6 (differently from fig. 3, wherein said devices are interconnected by said prolongation 9).

Therefore the outlet mouth of the conduit 6 is completely opened, and so the air path, coming from the outside and sucked into the channel 13, crosses an opening 20 showing a substantially cylindrical or frustum-conical shape, extended on the horizontal plane for 360°, and connecting the outlet mouth 6A of the coaxial conduit to the inlet mouth 4B of the Venturi pipe 4.

Furthermore, and preferably, said same upper plane 12 makes also the lower side of the channel 13 through which the primary air is sucked into said second path and is conveyed into said opening 8.

So the inlet 14 of said channel 13 is then opened just over said upper plane 12; moreover, in correspondence of said mouth 14 said surface 12 takes a profile in relief 15, so as the incidental liquids and cooking remnants are prevented from entering said channel 13; advantageously said relief profile 15 may easily be obtained by a proper pressing /bending operation of this same upper plane 12.