GB2073868A

GB2073868A - Improvements in or relating to gas hobs

Info

Publication number: GB2073868A
Application number: GB8108511A
Authority: GB
Original assignee: LINDMAYR F; NIBELLE P
Current assignee: LINDMAYR F; NIBELLE P
Priority date: 1980-04-08
Filing date: 1981-03-18
Publication date: 1981-10-21
Also published as: DE3104774A1; GB2073868B; DE3104774C2

Abstract

A gas hob comprises a cooking surface formed from a heat transmitting ceramic glass plate 1, a radiation gas burner consisting of a perforated ceramic burner plate 3 the gas-air mixture passing from a mixing compartment 18 to be burnt in the region of the surface thereof. A waste gas channel 6 is directly connected to the space 5 betweeen the burner plate and the heat transmitting plate, the gas-air mixture being fed in proportions in excess of stoichiometric through a venturi tube 20 to the mixing compartment. A damming element 7, 19 is disposed in the mixing compartment 18 in the flow path of the gas-air mixture flowing from the venturi tube 20. An ignite is disposed on the top of the burner plate 3 in the region of the gas-air mixture emerging from the damming area formed by the damming element 7, 19, and through the perforations 4. The damming element can for example be formed by a baffle plate or by a spark plug 7 projecting through the mixing compartment. <IMAGE>

Description

SPECIFICATION Improvements in or relating to gas hobs The invention relates to a gas hob of the type comprising at least one cooking surface formed by a heat transmitting plate, for example a ceramic glass plate, which is heated by means of a radiation gas burner comprising at least one heat-resistant perforated burner plate through which the gas-air mixture from a mixing compartment passes from below upwardly to be burnt in the region of the surface thereof, a waste gas channel being directly connected to the space between the burner plate and the heat transmitting plate, the gasair mixture being fed in proportions in excess of stoichiometric through a venturi tube to the mixing compartment, and an ignition device being provided for igniting the gas-air mixture emerging from the perforations in the burner plate.

In such a known gas hob, the gas-air mixture flows out substantially uniformly over the entire surface of the burner plate and into the combustion compartment. However, there is a certain time span until the mixture becomes enriched with gas in the position of the electrical ignition device to such an extent that it becomes ignited, and during this time span the gas-air mixture flows unburnt from the other positions of the surface of the burner plate and into the waste gas channel.

According to the invention there is provided a gas hob comprising at least one cooking surface formed by a heat transmitting plate which is arranged to be heated by means of a radiation gas burner comprising at least one heat-resistant perforated burner plate through which the gas-air mixture from a mixing compartment can pass from below upwardly to be burnt in the region of the surface thereof, a waste gas channel directly connected to the space between the burner plate and the heat transmitting plate, a venturi tube arranged to supply a gas-air mixture in proportions in excess of stoichiometric to the mixing compartment, an ignition device for igniting the gas-air mixture emerging from the perforations in the burner plate, and a damming element disposed in the mixing compartment in the flow path of the gas-air mixture from the venturi tube, the ignition device being disposed in the top of the burner plate in the region of the gas-air mixture emerging from the damming area formed by the damming element and through the perforations.

The gas-air mixture emerging from the perforations in the burner plate may thus be ignited at the earliest possible point in time and in the most favourable position.

In a preferred embodiment, the mixture flows through the venturi tube and tangentially into the mixing compartment. A circular flow takes place in the mixing compartment, and the damming element forms a damming space, from which the mixture flows preferably through the perforations of the burner plate under the action of the dynamic pressure. By this means, there is an enrichment of the gas in the gas-air mixture in the region of the ignition device. An ignitable mixture arises very early in this region, and ignition takes place without delay, so that unburnt gas is prevented from reaching the waste gas channel. The damming element is preferably in the form of a baffle plate.

The ignition device may be in the form of a spark plug, which projects through a through bore in the burner plate and is joined in a sealed manner thereto, for instance cemented, the spark plug projecting into the mixing compartment and at least partly forming the damming element. Thus, ignition takes place immediately above the surface of the burner plate, and in the most favourable position for igniting the mixture, the ignition position remaining unaltered even after removing and inserting the burner plate.

The ignition device or spark plug is preferably disposed at the transition between a perforated and non-perforated surface of the burner plate. Preferably, no perforations are provided in the burner plate in the immediate region of the ignition device. By this means, the ignition is favoured because in this position a gasair mixture cloud is formed which can be easily ignited, and because the spark does not become cooled by the mixture stream flowing from the perforations.

The ignition device or spark plug may be disposed immediately upstream of the transition between the combustion compartment and the waste gas channel. By this means, it is ensured that the gas-air mixture to be ignited reaches the region of the already ignited mixture, and is not able to escape without burning into the waste gas channel, where an unburnt gas-air mixture can give rise to an explosion. The spark gap between the ignition electrode and the earth electrode is preferably disposed transversely to the flow direction of the gas-air mixture, so that the ignition spark makes better contact with the gas-air mixture. The outflow space for the gasair mixture can be narrowed behind the ignition device by means of a wedge in the form of a circular segment, so that the gas-air mixture is further dammed in the region of the ignition spark, and ignition is improved.The wedge may have a groove, which guides the escaping gas-air mixture over the region of the ignition device, so that the gas-air mixture becomes concentrated in the ignition region.

Preferably, the spark plug projects through the mixing compartment and is screwed in a gas-tight manner to the base thereof. The lower end of the spark plug then projects from the underside of the mixing compartment, and is accessible for connecting the electric lead.

In this respect, a connection lug of the ignition electrode may be disposed within a ceramic insulation of the spark plug, so that this connection position is protected, against damage. The primary concern here is to protect the connection position of the ignition cable to the ignition electrode so that no spark path can arise towards an earth part (e.g. the burner base).

The ignition device can also be in the form of an incandescent coil.

A pilot burner bounded by a pilot burner tube may be disposed in the burner plate, the damming element being at least partly form by the pilot burner tube projecting through the mixing compartment.

The invention will be further described, by way of example, with reference to the accm- panying drawings, in which: Figure 1 is a section through a burner plate, a mixing compartment, a combustion compartment and a heat transmitting plate on the line i-l of Fig. 2; Figure 2 is a plan view of the burner plate with the heat transmitting plate removed; Figure 3 is a part section on the line Ill-Ill of Fig. 1; and Figure 4 is a plan view of the burner plate, showing a modification.

In the embodiment shown in Figs. 1 to 3, a radiation burner 2 is covered by a heat transmitting plate 1, which forms a cooking surface. A burner plate 3 comprises perforations 4, through which a gas-air mixture flows from a mixing compartment 1 8 and into a combustion compartment 5. By partly covering the perforations 4, the burner plate 3 is divided into a part 3a which radiates during operation, and a part 3b which non-radiant during operation.On opening the gas feed, the gasair mixture flows through a venturi tube 20 into the circular mixing compartment 18, and a circular flow indicated by arrows a is formed in the mixing compartment 1 8. The mixture flows from the mixing compartment 18 through the perforations 4 in the burner plate 3, and into the combustion compartment 5. 6 represents a waste gas channel.

A spark plug 7 comprises an ignition electrode 8, insulation 9, an earth ring 10 and an earth electrode 24 connected thereto. The spark plug 7 is inserted through bore 11 in the burner plate 3, and is cemented in a gas tight manner thereto at 1 2. The earth ring 10 comprises a thread 1 3 at its lower end, and is screwed to the base 25 of the mixing compartment 1 8 in a gas- tight manner by means of nuts 14, with gaskets disposed therebetween. By means of such a construction, the ignition spark at the end of the radiant surface 3a is immediately above the surface of the burner plate 3. The ignition spark jumps from the ignition electrode 8 to the earth ring electrode 24 transversely to the direction of flow of the gas-air cloud, which flows from the combustion chamber 5 and towards the waste gas channel 6.Thus, the ignition spark is not located above a perforation 4 of the burner plate 3, and it is therefore not cooled by the mixture flow. The distance between the ignition electrode 8 and the earth electrode 24 is fixed and does not change on removing and assembling the burner.

The gas-air mixture flowing through the venturi tube 20 and into the mixing compartment 1 8 flows in the mixing compartment 1 8, which has a circular contour, in the direction of the arrows a. Thus, the mixing stream meets the spark plug 7, and thus becomes dammed. The damming effect is further improved by means of a baffle plate 1 9 inserted into the mixing compartment 18.

By this means, a damming area is formed, which is indicated by the dashed and dotted lines 26. By virtue of the dynamic pressure, the mixture flows preferentially through the perforations 4 located in the region of the damming area, and into the region of the ignition spark, where it is rapidly ignited.

In order also to exert a damming effect on the gas-air cloud, a wedge 1 5 in the form of a circular segment and likewise consisting of a heat-resistant substance is disposed at the non-radiant part 3b of the burner plate 3.

Behind the spark plug 7, the wedge 1 5 comprises a groove 1 6 through which the gas-air mixture encounters a small resistance when flowing out towards the waste channel 6. By this means, an easily inflammable gasair mixture is reliably present above the sparkling position of the spark plug 7 immediately after the outflow of the gas-air mixture from the burner plate 3a.

In order to ensure reliable insulation between a connection lug 1 7 and the casing base 2, this lug is disposed with the insulation 9.

Fig. 4 shows an embodiment in which a pilot burner 27 is inserted in the burner plate 3 by way of a pilot burner tube 21. The pilot burner 27 is supplied with mixture by way of a second venturi tube, and burns continuously, even on temporary extinguishing of the main burner, of which the burner plate is indicated by 3.

The pilot burner tube 21 projects through the mixing compartment 18, and therefore acts as a damming element. The damming area indicated by the dashed and dotted boundary line 26 is again formed. The ignition device is disposed above this damming area, and can be in the form either of an incandescant coil 22 or electrodes 8, 24 as diagrammatically indicated.

Claims

1. A gas hob comprising at least one cooking surface formed by a heat transmitting plate which is arranged to be heated by means of a radiation gas burner comprising at least one heat-resistant perforated burner plate through which the gas-air mixture from a mixing compartment can pass from below upwardly to be burnt in the region of the surface thereof, a waste gas channel directly connected to the space between the burner plate and the heat transmitting plate, a venturi tube arranged to supply a gas-air mixture in proportions in excess of stoichiometric to the mixing compartment, an ignition device for igniting the gas-air mixture emerging from the perforations in the burner plate, and a damming element disposed in the mixing compartment in the flow path of the gas-air mixture from the venturi tube, the ignition device being disposed on the top of the burner plate in the region of the gas-air mixture emerging from the damming area formed by the damming element and through the perforations.

2. A gas hob as claimed in claim 1, in which the damming element is in the form of a baffle plate.

3. A gas hob as claimed in claim 1 or 2, in which the ignition device comprises a spark plug, which projects through a through bore in the burner plate and is sealed thereto, the spark plug projecting into the mixing compartment and at least forming the damming element.

4. A gas hob as claimed in claim 3, in which the through bore for the spark plug lies at the transition between a perforated surface portion and a non-perforated surface portion of the burner plate.

5. A gas hob as claimed in any one of claims 1 to 4, in which the ignition device is disposed immediately upstream of the transition between the combustion compartment and the waste gas channel.

6. A gas hob as claimed in any one of claims 1 to 5, in which no perforations are provided in the burner plate in the immediate region of the ignition device.

7. A gas hob as claimed in claim 3 or 4, or in claim 5 or 6 when dependent on claim 3, in which the spark gap between an ignitiion electrode and earth electrode of the spark plug is disposed transversely to the flow direction of the gas-air mixture.

8. A gas hob as claimed in any one of claims 1 to 7, in which an outflow space for the gas-air mixture is narrowed immediately downstream of the ignition device by means of a wedge in the form of a circular segment.

9. A gas hob as claimed in claim 8, in which the wedge has a groove arranged to guide the escaping gas-air mixture over the region of the ignition device.

10. A gas hob as claimed in claim 3, 4 or 7, or in claim 5, 6, 8 or 9 when dependent on claim 3, in which the spark plug projects through the mixing compartment and is screwed in a gas-tight manner to the base thereof.

11. A gas hob as claimed in claim 10, in which a connection lug of an ignition electrode of the spark plug is disposed within a ceramic insulation of the spark plug.

12. A gas hob as claimed in claim 1 or 2, in which the ignition device comprises an incandescant coil.

13. A gas hob as claimed in claim 1, in which a pilot burner bounded by a pilot burner tube is disposed in the burner plate, the damming element being at least partly formed by the pilot burner tube projecting through the mixing compartment.

1 4. A gas hob substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.