AU750586B2 - Gas grill burner system - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT GAS GRILL BURNER SYSTEM The following statement is a full description of this invention, including the best method of performing it known to me: The invention relates to a grill burner system for a gas cooker.

Gas grill burner systems currently available in domestic cooking appliances in Australia typically utilise either a surface conrbustion burner or a fret burner, with the gas supply in •either case controlled by a throttling valve. The surface combustion burner with throttling o o: 10 valve gives good performance at high settings but tends to produce high levels of carbon monoxide if the flow of gas to the burner is too low. Therefore, for safety reasons grillers using surface combustion burners are manufactured so as to have only a limited ability to be turned down. The lowest settings of such grillers are generally too high to grill delicate foods such as those containing egg or cheese without burning, or for browning or gentle heating.

The fret burner and throttling valve combination is able to operate safely when the flow of gas to the burner is low but is a poor performing grill burner at high settings such as those required for grilling meat.

The invention aims to provide a gas grill burner system with a wider range of control.

The invention provides a grill burner arrangement for a gas cooker, including a surface combustion gas burner, control means which cycles gas flow to the burner on and off, means for varying the on/off cycle in response to a setting selection and ignition means and ignition means for igniting the gas each time the gas supply to the burner is turned on.

Further preferred embodiments will now be described with reference to the accompanying drawings, in which: Fig. 1 is a wiring schematic showing a first preferred control arrangement; Fig. 2 is a schematic of the gas supply arrangement for use in conjunction with Fig. 1; Figs. 3 and 4 illustrate the on/off cycling of the energy regulator and grill burner at two different griller settings; Fig. 5 is a wiring schematic showing a second preferred control arrangement; Fig. 6 is a schematic for the gas supply arrangement for use in conjunction with Fig. and Figs. 7 and 8 illustrate the on/off cycling of the electricity and burner at two different S.griller settings.

With reference to Fig. 1, the control of the griller is achieved by means of an energy regulator 10 which outputs pulses of current with a duty cycle which may be varied from 100% down to about 45%, depending on the griller setting selected by the user, and with °20 a cycle period of about 30 seconds.

Current from the energy regulator passes in series through a hot surface igniter 12 and a small resistance heater 14 in a thermally controlled gas valve 16.

The gas valve 16 contains a bimetallic strip (not shown) which responds to heating of the resistance heater 14 to open the gas valve. When the current from the energy regulator o ceases, during the pauses in the current cycle, the gas valve cools and the bimetallic strip responds by closing off the gas supply to the grill burner.

Fig. 2 is a schematic showing the gas supply system. A surface combustion burner 18, comprising a large number of low flow burner ports spread out over a relatively large surface of a thermally radiating body is positioned in an internal grilling chamber of a domestic gas cooker. The hot surface igniter 12, comprising a ceramic coil which glows red hot when current is applied, is located close to the surface combustion burner to be contacted by gas expelled from the burner.

Gas, for example natural gas, is supplied to the thermal valve, which is located remote from the burner so that operation of the valve is in response to heat from the resistance heater 14 rather than the heat generated by the surface combustion burner 18. A gas supply line 19 leads from the gas valve outlet to the burner.

When the gas valve 16 is open, the gas is expelled from the surface combustion burner and the burner is ignited by the hot surface igniter. The burning gas causes the thermally radiating body incorporated in the burner to radiate energy into the grilling chamber for grilling the food.

15 Figs. 3 and 4 show operation of the electrical and grill burner cycles at two different griller settings. Fig. 3 shows operation at two thirds of maximum gas consumption, while Fig.4 shows 41% of maximum gas consumption.

The electrical output of the energy regulator is shown by the solid lines. As can be seen, it consists of a regular series of pulses separated by pauses. The spacing and duration of the pauses will vary depending on the griller setting selected by the user. At maximum setting, the output of the energy regulator will be continuous.

The resultant gas supply to the burner is shown by the dashed lines. As can be seen, the cycling of the gas supply lags behind the cycling of the energy regulator due to the time required for the thermal valve to heat up when current is provided from the energy 25 regulator. For safe operation of the griller, the characteristics of the energy regulator, igniter and gas valve combination are tailored to ensure that the hot surface igniter reaches a sufficient temperature for ignition before the gas valve opens. There is also a lag in closing of the gas valve, due to the time required for the thermal valve to cool and the bimetallic strip respond by closing the gas valve after current from the energy regulator ceases. For this reason the period of the intrinsic duty cycle of the energy regulator must be made sufficiently long for the valve and igniter to stay in phase with the energy regulator.

As can be seen by a comparison of Figs.3 and 4, by varying the length and spacing of the current pulses from the energy regulator, the gas consumption, and therefore the setting, of the griller may be varied. This is achieved without throttling of the gas supply, thereby obviating the problems encountered by surface combustion burners at low gas rates and allowing a wider range of control.

The arrangement of Figs. 5 and 6 differs from Figs. 1 and 2 by replacement of the energy regulator with a thermostat switch 20 with a sensing bulb 22 located in close proximity to the burner. The thermostat controls cycling of the electrical power to the thermal gas valve 16 as the sensed temperature attains and drops below that corresponding to the e selected griller setting. The thermostat also has a setting with 100% duty cycle, for continuous operation of the burner.

S" As can be seen in Figs. 7 and 8, the electricity and gas cycles operate in a similar manner to those of Figs. 3 and 4. However, since the thermostat receives feedback from the o burner, it 'waits' for the valve and igniter and the system always remains in phase. The difference in time lag in opening and closing the gas valve in Figs. 7 and 8, compared to Figs. 3 and 4, is a function of the lag characteristics of the igniter and gas valve rather S""than being inherent in the use ofa thermostat-controlled system.

In an unillustrated, and less preferred, embodiment a spark igniter, flash tube or 25 interrupted pilot can be used in place of the hot surface igniter and a solenoid operated gas valve may be used. Such a system would not display lags between current pulses and gas flow to the burner.

While particular embodiments of this invention have been described, it will be evident to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiments and examples are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

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Claims (12)

1. A grill burner arrangement for a gas cooker, including a surface combustion gas burner, control means which cycles gas flow to the burner on and off, means for varying the on/off cycle in response to a setting selection and ignition means for igniting the gas each time the gas supply to the burner is turned on.

2. A grill burner arrangement according to claim 1 wherein the control means includes a gas valve and an igniter both actuated by electric current, means for providing pulses of 10 said current to the gas valve and igniter and means for varying a duty cycle of said pulsed i current in response to setting selection. .o•

3. A grill burner arrangement according to claim 2 wherein the control means provides continuous current to the valve and igniter when a maximum setting is selected. i

4. A grill burner arrangement according to claim 3 wherein the duty cycle may be varied in the range of about 45% to 100%.

5. A grill burner arrangement according to claim 2 or 3 wherein the gas valve opens in 20 response to heating by an electric heater.

6. A grill burner arrangement according to claim 5 wherein there is a time lag between commencement of a current pulse and opening of the gas valve, the time lag being sufficient for the igniter to reach an ignition temperature before the gas valve opens.

7. A grill burner arrangement according to claim 6 wherein the igniter comprises a hot surface igniter heated by the current.

8. A grill burner arrangement according to any of claims 2 to 7 wherein the gas valve and igniter are located in series in an electric circuit.

9. A grill burner arrangement according to any of claims 2 to 8 wherein the current is provided to the gas valve and igniter by an energy regulator with a constant peak current output and variable duty cycle.

A grill burner arrangement according to any of claims 2 to. 8 wherein the current is controlled by a thermostat sensing heat output from the burner.

11. A grill burner arrangement for a domestic gas cooker substantially as herein described with reference to Figs. 1 and 2.

12. A grill burner arrangement for a domestic gas cooker substantially as herein described with reference to Figs. 5 and 6. DATED this 26th day of August 1998. EMAIL LIMITED By their Patent Attorneys 20 HALFORD CO .i*