The present invention relates to an improved gas burner for cooking appliances.

Gas burners are known with one or more rings of main flames, such as that described in U S 2001 /001 0897 , to be instal led on cooking hobs in general; these generally comprise a cup-shaped injector holder, at which the burner is installed on the cooking hob, a burner body, on which one or more venturi conduits are provided for mixing the gas with primary air to form the combustion m ixture, a f l a m e d iv i de r w ith o n e o r m o re ch a m be rs fo r distributing the combustion mixture to generate the flame rings, and with upper closure covers for the distribution chambers.

The market offers a vast range of burners with one or more main flame rings, with each user making individual choices based on certain burner aspects rather than others, according to requirements.

Gas burner manufacturers are often faced with a problem in that in the various countries or even in different regions of the same country, large differences can exist in the chemical gas composition, requiring burners with different characteristics.

As it has been found by research and experimentation that correct burner operation with a determ ined type of gas is l inked to the correct distance between the venturi conduit and the injector, and that as the gas com position varies this distance m ust be varied to obtain optimal burner operation, burners have also been proposed in which the axial position of the venturi conduit relative to the injector can be adjusted. These burners have however proved extremely complex and bulky and require the upper sheet metal of the cooking hob to be removed for their adjustment.

FR 2692014 describes a pipe burner, in which the injector is located a large distance from the burner head; this is not suitable for installation on a cooking hob and moreover is rather com pl icated to assem ble and hence costly, given that it comprises a large number of components, and in particular com prises a flame d ivider head , a curved first conduit, a second conduit internally housing a venturi conduit, two flanges and a U-shaped flange for supporting the injector.

Consequently, an object of the invention is to provide a gas burner which can be instal led in a cooking hob, and in which the position of the venturi condu it or of each venturi conduit can be adjusted relative to the injector, without having to disassemble the cooking hob.

Another object of the invention is to be able to make this adjustment easily and quickly.

Another object of the invention is to produce a burner in a very simple form and at low cost.

All these objects and others 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 .

The present invention is further clarified hereinafter in terms of some preferred embodiments thereof, with reference to the accompanying drawings, in which:

Figure 1 is an exploded perspective view showing a first em bodiment of a burner according to the invention, Figure 2 is a vertical diametrical section therethrough,

Figure 3 is a perspective view showi ng the cup-shaped support for the injector holder structure,

Figure 4 is a plan view thereof,

Figure 5 is a vertical section through a second embodiment of the burner according to the invention, and

Figure 6 is an exploded perspective view of its injector holder structure, Figure 7 is an exploded perspective view of a third embodiment of the lower support structure of the burner of Figure 1 , and

Figure 8 is an exploded perspective view showing a fourth embodiment of part of the structure of Figure 7.

As can be seen from Figures 1 -6, these show a particular multi-ring burner 2 to be applied to the upper sheet metal 3 of a traditional cooking hob, preferably of built-in type, in a position corresponding to an aperture provided therein.

The burner 2 has an inner circular distribution chamber 4 and an outer annular distribution chamber 6, to which mixtures of gas and primary air arrive originating from two separate venturi conduits 8, 8' fed with gas delivered by respective injectors 1 0, 1 0'. However, it is to be understood that the burner type, the number of flame rings, the number of injectors, and an entire series of characteristics recognizable in the burner illustrated in the drawings by way of example, could also be different, in the sense that, that which characterises the burner according to the invention is the manner of adjusting at least one venturi conduit 8, 8' relative to the injector 1 0, 1 0' wh ich l ies to the front thereof. The venturi conduit 8 is housed within a lower support structure 1 1 of the burner 2, and preferably within its lower cup 12.

In particular, the venturi conduit 8 is disposed approximately horizontal within the lower cup 12 and opens at its upstream end into a cavity 14, which is defined in said cup 12, is open lowerly, is closed upperly, and presents in a curved lateral wall thereof 16 an outer connector 1 8 for the gas and inner threaded seat for the injector 10.

In particular, the venturi conduit 8 is faced at its upstream end by the injector 10, it extends horizontally within the lower cup 12 of the support structure 1 1 and opens at its downstream end into an arched cavity 20, also provided in the lower cup 12, which is open upperly and is intended to feed at least one curved distribution chamber provided in at least one flame divider overlying said cup 12.

Preferably, the venturi conduit 8 is obtained from a piece of metal or non-metal tube which is externally cylindrical and internally shaped such as to define a first downwardly converging portion close to the injector 1 0, a second portion of constant cross-section, and a third downwardly diverging portion.

The venturi conduit 8 is inserted into and housed in a seat 9 provided in the lower cup 1 2. Correspondingly, the seat 9 also extends horizontally with in the lower cup 1 2 to connect together the cavity 1 4 and the arched cavity 20.

Advantageous ly, the seat 9 is a cy l i nd ri ca l th roug h seat and , preferably, the venturi conduit 8 has a length greater than the length of said seat 9, such as to project therefrom with both its ends into the two cavities 14 and 20. As represented for example in Figure 6, the lower support structure 1 1 can be formed from two parts, i.e. from the lower cup 1 2 and from a cover element 1 3, which can be joined together either permanently by rivets or removably by screws. In this embodiment, the seat 9 can be defined lowerly by an elongated cavity provided i n the lower cup 1 2 , and upperly by a complementary cavity provided in the cover element 13.

The venturi conduit 8 has an outer diameter slightly less than the inner diameter of its seat 9, such as to be able to be easily displaced axially within it.

The seat 9 housing the venturi conduit 8 communicates with the space overlying the lower support structure 1 1 of the burner via an internal ly threaded cylindrical hole housing a grub screw 22 for locking the venturi conduit 8 in its seat 9.

The head of th is g ru b screw 22 is preferab ly p rovi ded with a hexagonal recess into which a traditional Allen key can be inserted for its operation from above through the aperture provided in the sheet metal 3, without having to remove the burner 2 from the cooking hob to which it is applied.

In the embodiment shown in Figures 1 -4, the arched cavity 20 into which the downstream end of the venturi condu it 8 opens, presents, in a position facing said venturi conduit 8, an aperture which can be closed by a plug 24 applicable from the outside. Its purpose is to enable the venturi conduit 8 to be inserted into its seat through said aperture during burner assembly, and also to enable its possible substitution, should it be necessary to modify its characteristics and performance. In the embodiment shown in Figures 5 and 6, the plug 24 is applied to the lateral wall 16 of the cavity 14, and is provided with a threaded axial cavity fo r t h e i nj e cto r 1 0 a n d w i t h a n ext e rn a l co n n e ct o r fo r t h e g a s . Advantageously, the plug 24 is retained in its seat by an elastic fork 26.

Whereas the installation of the burner 2 on the cooking hob and its operation are traditional and do not form a subject matter of the invention, and for this reason can be varied in accordance with the burner characteristics, that which does in contrast constitute a characteristic of the invention is the adjustability of the axial position of the venturi conduit 8 relative to the injector 10.

If it does becomes necessary to vary this position to adapt the burner to the characteristics of the avai lable gas, and which can be done during installation or during use, the operation is extremely simple and can be carried out even with the burner installed on the cooking hob, and at the very most after removing that burner part defining the outer annular distribution chamber 6, and which rests on the lower support structure 1 1 .

Following this removal, the hexagonal cavity provided in the head of the locking grub screw 22 becomes accessible, so that it can be unscrewed, for example by a suitable Allen key.

After the grub screw 22 has been slackened, by which the venturi conduit 8 is able to be moved within its seat, it can be displaced along it such that its upstream end can be positioned at the correct distance from the injector 1 0. This operation can be facilitated not only by the mobility of the venturi conduit 8 within its seat, but also by the presence of both ends projecting into the respective cavities 14 and 20, and easily accessible from above through the opening made in the upper sheet metal of the cooking hob.

When the correct axial position of the venturi conduit 8 has been achieved in its seat, it can be securely locked therein by completely screwing down the grub screw 22.

It should also be noted that in the lower cup 12 of the lower support structure 1 1 , several seats 9 can be provided, each of which is intended to house a venturi conduit 8, 8', as described above. In this case, the described adjustment operation can be repeated independently for each venturi conduit.

In particular, the burner according to the invention could have two Venturis 8, 8' adjustable within their respective seats 9. In greater detail, a first seat 9 connects, as stated, an inlet cavity 14 of the lower support 1 1 to an outlet cavity 20 which is in flu idic com m unication with the outer annular distribution chamber 6; whereas the other seat 9' connects an inlet cavity 14' of the lower support 1 1 to an outlet cavity 20' which is in fluidic communication with the inner central distribution chamber 4 (see Figure 4).

In the embodiment illustrated in Figure 7, the lower support structure 1 1 consists of a single piece, and presents a shape which is irregular but preferably with it outer edge inscribable within a circumference.

I n particu lar, the lower support structure 1 1 is of cup shape and comprises:

- a first portion provided with a first cavity which is divided by a vertical baffle 34 into two chambers 33, 35 which are provided on their outer wall 31 with two circular apertures 30, 32, - a second portion provided with a second cavity 37 situated in a position diametrically opposite the first cavity,

- a third connection portion indicated overall by 39, which connects the two preceding portions together.

Moreover, two parallel cylindrical conduits 36, 38 are provided within the lower support structure 1 1 , and are axially aligned with the two apertures 30, 32. Advantageously, these two conduits 36, 38 can be easily formed by suitably boring through the lower support structure 1 1 from one side to the other.

An externally cylindrical respective tubular element 42, 44 internally shaped as a venturi (venturi condu it) is insertable into each of the two cylindrical conduits 36, 38, and has a convergent upstream portion followed by a cylindrical central portion, then by a divergent downstream portion.

The outer diameter of each venturi conduit 42, 44 is suitably slightly less both than the inner diameter of the respective apertures 30, 32, and than the inner diameter than the corresponding cylindrical conduits 36, 38, both to enable each venturi conduit 42, 44 to be i nserted i nto the respective cylindrical conduit through the respective aperture 30, 32, and to enable it to move axially therein.

Each venturi condu it 42 , 44 can be locked with in the respective cylindrical conduit 36, 38 in the desired axial position, by means of a grub screw 46 provided through the inner lateral wall of each of the two chambers 33, 35 and operable from above the cooking hob on wh ich the burner is installed. Advantageously, the length of each venturi conduit 42, 44 is greater than the length of the respective cyl indrical condu it 36, 38 in wh ich it is housed, so that it is able to project from both its ends.

An injector holder unit 52 can be inserted through the two circular apertures 30, 32 provided in the outer wall 31 to the cavity provided in the support structure 1 1 . This unit consists of two roughly cylindrical parts 54, 56 joined together by a connecting cross-piece 58. The injector holder unit can also be formed as two separate cylindrical parts 54, 56 insertable into the two ape rtu res 30 , 32 of the s u pport structu re 1 1 a nd f ixab l e to them by conventional systems.

Independently of the embodiment used, in each of these parts 54, 56 a threaded outer cylindrical cavity is provided for connecting a gas feed conduit, together with a threaded inner cylindrical cavity for connecting an injector 60, 62, which is coaxial with the venturi conduit 42, 44 housed in the respective cyl indrical conduit 36, 38 when the injector holder unit 52 is fixed to the support structure 1 1 .

The injector holder unit 52 is removably connected to the cup shaped structure 1 1 by a screw 64, which passes through the connection bar 58 and engages in the outer wall 31 of the cup structure 1 1 , after the two cylindrical parts 54, 56 of the i njector ho lder unit 52 have been inserted into the respective apertu res 30 , 32. To avoid assem bly errors, both the two cylindrical pieces 54, 56, and the respective apertures 30, 32 have different diameters.

I n contrast, in the case of an i njector holder un it form ed as two separate cylindrical parts 54, 56, one for each injector, these can be both fixed to the support structure 1 1 , for example by a traditional spring clip 66, as visible in Figure 8.

In assembling the burner according to the invention, the two venturi conduits 42, 44 are firstly inserted into the corresponding cylindrical conduits 36, 38 of the support structure 1 1 , after which the injector holder unit 52 is applied to the burner body and is fixed to it by the screw 64.

The burner assembled in this manner is ready to be installed in the cooking hob. For this purpose the gas feed conduits are fixed to the injector holder unit 52, and the support structure 1 1 is fixed by screws to the sheet metal of the cooking hob.

The operation of the burner 2 with the support structure 1 1 of Figure 7 is substantially traditional and will therefore not be further described.

Depend ing on the characteristics of the avai lable gas, it m ay be necessary to vary the d istance between the inlet aperture of the venturi conduit 42 , 44 and the respective injector 60, 62, which operation can be easily carried out by simply slackening the locking grub screw 46 of one or other venturi conduit 42, 44 or of both, to enable said venturi conduit 42, 44 to be axially adjusted before being re-locked in the correct position.

In a different embodiment, the injector holder unit 58 is formed as a single piece with the support structure 1 1 . In this case it is evidently not possible to insert the venturi conduits 42, 44 through the application apertures of the injector holder unit 58, and apertures have to be provided in the outer wall of the second cavity 37, which apertures, after insertion of the venturi conduits 42, 44, are closed by suitable threaded plugs, as already described with reference to Figure 1 . From the aforesaid it is apparent that the burner accord ing to the i nvention is particu larly advantageous com pared with traditional burners, in that:

- it is of compact construction and therefore also suitable for installation in built-in cooking hobs of small thickness,

- it is of simple, lightweight and low-cost production, by consisting of only a small number of components,

- the position of the venturi conduit/condu its can be easi ly and qu ickly adjusted, even with the burner installed on the cooking hob, and hence the burner can be adapted to different feed gas characteristics,

- it enables the upstream end of the venturi conduit to be positioned very close to the corresponding injector, if this is required for correct burner operation, while still enabling it to be withdrawn therefrom, for easy burner replacement when necessary.