GB2202583A - Electronic flame ignition spark generator - Google Patents

Abstract

A low voltage DC source 2, e.g. a battery, supplies a DC to AC converter 1 for generating a high voltage AC supply 3. A spark generating circuit 4 is operable from the AC supply 3 and is effective for causing a succession of sparks to be generated at spark electrodes 5. An arrangement C2, R2 applies the AC supply 3 to the spark electrodes 5 for generating a DC signal only when the spark electrodes 5 are disposed in a flame, the DC signal being used to inhibit the operation of the spark generating circuit 4 to thereby inhibit the generation of sparks whilst the flame is present. <IMAGE>

Description

Electronic Ignition Generators This invention relates to electronic ignition generators. It is especially applicable to electronic ignition generators for use in gas cooking appliances.

Ignition generators operated from batteries are known. Ignition generators are also known which make use of the rectification effect of a flame in order to detect flame presence but these operate from an alternating current (AC) source, such as a mains supply. Access to an AC supply is not always possible, and it is an object of the present invention to provide an electronic ignition generator which makes use of the rectification effect but which operates from a low voltage direct current (DC) source, such as a battery.

According to the present invention there is provided an electronic ignition generator comprising a DC to AC converter for affording an alternating current signal, a spark generating circuit operable from said alternating current signal for generating a succession of sparks between spark electrodes thereof for igniting burner means to be associated with said spark electrodes, means for applying said alternating current signal to said spark electrodes for generating a DC voltage only when said spark electrodes are disposed in a flame of said burner means, said DC voltage being applied to said spark generating circuit for inhibiting the generation of said sparks whilst said flame is present.

In carrying out the invention it may be arranged that the spark generating means comprises capacitor means which is charged by said alternating current signal, means for causing said capacitor means to be discharged through the primary winding of transformer means thereof, a secondary winding of said transformer means being connected in series with said spark electrodes, a free-running oscillator for causing said capacitor means to be successively discharged through said primary winding for causing a succession of sparks to be generated at said spark electrodes, and means responsive to said DC voltage for inhibiting the operation of said oscillator when said flame is present.

Conveniently, a sparkgap may be provided connected in series with said secondary winding and said spark electrodes for DC isolating said secondary winding, and a DC generator may also be provided operable from said alternating current signal for affording a DC supply to said spark generating means.

An exemplary embodiment of the invention will now be described with reference to the accompanying single figure drawing which is a circuit diagram of an electronic ignition generator in accordance with the present invention.

The electronic ignition generator shown in the drawing comprises a DC to AC converter shown in dashed lines 1 of conventional known form, which operates from a low voltage DC source, typically a battery, which is connected to input terminals 2, and which affords a high voltage AC supply on line 3. The AC supply on line 3 is applied to a spark generating circuit shown in dashed lines 4, again of conventional known form.

The spark generating circuit 4 comprises a transformer T2, the primary winding P2 of which is connected via a thyristor T across a capacitor C3 which is arranged to be continuously charged from the AC supply line 3. The secondary winding S2 (shown in the bottom right-hand corner of the drawing) of the transformer T is connected in series with a pair of spark electrodes 5 and also a sparkgap 6, which is used for isolating purposes as will later be described.

The spark generating circuit 4 also includes a pair of logic gates G1 and G2 which are connected in a free-running flip-flop circuit which is used to fire the thyristor T at the required spark generation rate.

When the thyristor T is fired, the charge on the capacitor C3 is discharged through the primary winding of the transformer T2 and the voltage induced in the secondary winding S2 of the transformer T2 causes a spark to be generated across the spark electrodes 5. A spark is also generated across the sparkgap 6, but because this is physically smaller than the distance between the spark electrodes 6 (typically 0.8 mm compared to 3-4 mm), the main spark appears across the spark electrodes 5.

In use of the electronic ignition generator thus far described, the spark electrodes 5 would be disposed in the vicinity of a gas burner, say of a gas cooking appliance, such that the spark electrodes 5 are actually in the flame of the burner when it is lit.

When the gas to the gas burner is initially turned on, it is arranged that the electronic ignition generator is actuated to cause a succession of sparks to be generated at the spark electrodes 5. When the gas burner ignites, it is necessary to inhibit the generation of any further sparks.

This is achieved in the electronic ignition generator shown in the drawing by applying the AC supply on line 3, to the spark electrodes 5 via a capacitor C1, a resistor R2 and the secondary winding S2. When the spark electrodes 5 are not disposed in a flame, i.e. when the associated gas burner is not ignited, they act simply as an open-circuit so that only an alternating current signal is present at the junction of capacitor C1 and resistor R2, and this alternating current signal, which is applied across resistor R1 and capacitor C2, is filtered by capacitor C2 so that zero voltage appears across it.

However, when a flame is present, current is caused to be conducted across the electrodes 5, in one direction only, so that a DC signal is generated at the junction of capacitor C1 and resistor R2. This DC signal is applied, via the resistor R1 and capacitor C2, and via further resistors R3 and R4 to the input of a further gate G3, the gate G3 being connected to the gates G1 and G2 (which operate as a free-running flip-flop) such that when it is operated it disables the flip-flop, thus inhibiting the spark generation.

It will be appreciated that without the sparkgap 6, the AC signal applied to the spark electrodes 5 would be short-circuited.

One advantage of the use of this rectification effect is that resistive losses in the spark electrodes or in the wiring thereto, such as may be caused by condensation on the spark electrodes 5, result in an AC signal being produced across resistor R1 and capacitor C2, this being filtered by capacitor C2 so that it has no affect on the operation of the flip-flop formed by the gates G1 and G2 and thus has no affect on spark generation.

Because of the polarity of the DC signal generated in the presence of a flame, it is necessary to supply the gates G1, G2 and G3 with a negative supply voltage, and this is generated on line 7 by a DC generator shown in dashed lines 8, of conventional known form, which operates from the AC supply on line 3.

One proposed use of the electronic ignition generator described is in cooking appliances for use in recreational vehicles, e.g. caravans.

Claims (5)

1. An electronic ignition generator comprising a DC to AC converter for affording an alternating current signal, a spark generating circuit operable from said alternating current signal for generating a succession of sparks between spark electrodes thereof, for igniting burner means to be associated with said spark electrodes, means for applying said alternating current signal to said spark electrodes for generating a DC voltage only when said spark electrodes are disposed in a flame of said burner means, said DC voltage being applied to said spark generating circuit for inhibiting the generation of said sparks whilst said flame is present.

2. A generator as claimed in claim 1, in which the spark generating means comprises capacitor means which is charged by said alternating current signal, means for causing said capacitor means to be discharged through the primary winding of transformer means thereof, a secondary winding of said transformer means being connected in series with said spark electrodes, a free-running oscillator for causing said capacitor to be successively discharged through said primary winding for causing a succession of sparks to be generated at said spark electrodes, and means responsive to said DC voltage for inhibiting the operation of said oscillator when said flame is present.

3. A generator as claimed in claim 2, comprising a sparkgap connected in series with said secondary winding and said spark electrodes for DC isolating said secondary winding.

4. A generator as claimed in any preceding claim, comprising a DC generator operable from said alternating current signal for affording a DC supply to said spark generating means.

5. An electronic ignition generator substantially as hereinbefore described with reference to the accompanying drawings.