GB2176910A

GB2176910A - Electrical control means for gas flow to a burner

Info

Publication number: GB2176910A
Application number: GB08613634A
Authority: GB
Inventors: Rudolf Begero; Walter Gramlich; Werner Haberl
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-06-24
Filing date: 1986-06-05
Publication date: 1987-01-07
Also published as: FR2583856B1; IT8620773A0; GB2176910B; IT8622260V0; DE3522545C1; FR2583856A1; ATA152586A; AT398242B; GB8613634D0; IT8620773A1; IT1189545B

Abstract

Electrical control means for a gas burner serves to terminate the gas supply to the burner, and thereby a cooking process, by means of an automatic time switch (8), the burner having a thermal safety element (6, 7). For this purpose, the automatic time switch (8) connects a previously charged capacitor (10) to the winding of a relay (13) which in its turn by way of a switch contact (14) influences the current circuit of the thermal safety element (6, 7) in such a manner that the gas supply to the burner is interrupted. <IMAGE>

Description

SPECIFICATION Electrical control means for gas flow to a burner The present invention reiates to control means for gas flow to a burner.

Automatic time switches have for a long time been used in various applications in electric cookers, for example in the case of cookers with electrical heating systems. In this connection, the time switch equipment is limited to controlling electrical power switches. The application of automatic time switches to gas cookers is substantially more expensive. In this case, in place of an electrical power switch, it is necessary to control a gas valve capable of securely interrupting a gas flow which is additionally controlled in throughflow rate. On the other hand, the possibility of normal burner operation without automatic time switching is also to be provided. It is known, and in different countries prescribed, to provide a corresponding gas valve in gas fittings, namely as so-called thermal safety element.This thermal safety element contains a thermal element, such as a thermocouple, which is heated by the flame of the gas burner and supplies a current which excites an electro-magnet in the gas fitting, whereby in turn a shut-off valve for the gas flow is kept open. On extinction of the flame in the gas burner, excitation of the electromagnet is terminated and the gas valve closes.

It is possible for an automatic time switch to act on this current circuit and to interrupt the gas flow through the gas fitting with the aid of an automatic time switch which terminates the excitation of the electromagnet. The control must, however, be such that the normal function of the thermal safety element is not impaired.

There is thus scope for a control arrangement by which an automatic time switch for a gas burner can be brought into application in conjunction with thermal safety equipment. A circuit arrangement of that kind should satisfy safety regulations for the gas operation and afford favourable conditions for gas burner operation without utilisation of automatic time switching.

According to the present invention there is provided electrical control means for gas flow to a burner, comprising a thermal element heatable by a gas flame of such burner to generate electrical current, a gas flow control device operable by such current to permit gas flow to the burner to continue, influencing means operable, subject to prior charging of chargeable means thereof, for a predetermined period of time to so influence current supply to the gas flow control device as to cause such operation of the device to be terminated and timing means to initiate operation of the influencing means at a selectable point in time.

In a preferred embodiment, the control means provides time-controlled switching-off of a gas burner with the aid of an automatic time switch through disturbance of the current flow from the thermal element heated by the gas flame to a gas safety element in the gas fitting. A time control unit is arranged with a time constant in the range of seconds and during its active phase effects a disturbance of the current flow from the thermal element to the gas safety element, this active phase being dependent on an initiating operation by the automatic time switch unit and on a charging operation for the time control unit preceding this initiating operation.

Such a circuit arrangement may provide high functional reliability with relatively low effort.

Through switching-on of the automatic time switch unit, a charging operation of the time control unit takes place, i.e. this time control unit is set into functional readiness. On rundown of a preselected time period, the operation of the time control unit is initiated by the automatic time switch, i.e. the time control unit is for a brief time - a few seconds - subject to an active phase, during which the current flow from the thermal element heated by the flame of the gas burner to the gas safety element in the gas fitting is disturbed. This disturbance can be a simple interruption of the electrical current feed. The consequence is that an electromagnet in the gas fitting is no longer excited and the gas safety valve closes during this phase. This phase must be of sufficient length to secure the interruption of the burner operation.After the relatively rapid cooling-down of the thermal element in the region of the gas burner, no excitation of the electromagnet in the gas fitting takes place. It is, however, readily possible to restart the heating operation by the gas burner manually in a conventional mode and manner. Equally, it is possible again to switch on the automatic time switch.

For preference, the time control unit comprises a series connection of a capacitance means such as a capacitor, a relay winding, a switch controllable by the automatic time switch unit, and a charging path for the capacitor, wherein the charging path is switched on in the state of the switch interrupting the series connection at the capacitor and that the disturbance of the current path from the thermal element to the gas safety element takes place by way of the relay switch contact. The switch is preferably a change-over switch which is actuable by the automatic time switch unit and by way of which the capacitor is connectible in series alternatively with the charging path and the relay winding. Such a circuit arrangement is simple in construction and thereby economic to manufacture.By putting the automatic time switch unit into operation, the capacitor is charged with direct current by way of the charging path. When the automatic time switch unit triggers in the case of a preset intended termination of a period of operation of the burner, for example for cooking in a gas stove, the capacitor element is disconnected from the charging path and connected to the relay winding. The capacitor is discharged by way of the relay winding through this series connection and the current flowing through the relay winding excites the relay, the relay switch contact of which controls the disturbance of the current path from the thermal element to the gas safety element. Since the capacitor element has assumed its highest state of charge before connection of the capacitor to the relay winding, the highest excitation current is available for attraction of the relay.This current decays according to an exponential function, but the relay is, however, held in its attracted state for a certain time. This time span is determined by the capacitance value of the capacitor and the resistance value of the relay winding.

Preferably, an alternating current feed is connectible in parallel with the terminals of the thermal element by way of the relay switch contact, Since relatively low voltages, but a relatively high current flow, is attainable by way of the thermal element, mains voltage can be applied by way of a repeater (transformer) to the terminals of the thermal element. In principle, it would be feasible for the conductor path from the thermal element to the gas safety element to be merely interrupted by way of a switching element through the time control unit.

Due to the very low voltages and relatively very high current in this region, the utilisation of such a switching element in this location may give rise to difficulties. For this reason, it is expedient to apply alternating current, for an appropriate short time, in superimposition to the electromagnet winding of the gas safety element. Preferably, the primary winding of the repeater is to be controlled through the relay switch contact of the time control unit.

An embodiment of the present invention will now be more particularly described by way of example with reference to the accompanying drawing, the single figure of which is a schematic circuit diagram of control means embodying the invention in conjunction with a gas fitting.

Referring now to the drawing, there is shown a gas fitting 1 to which combustible gas is fed in the inlet arrow direction by way of a supply duct 2.

The gas throughflow rate can be manually regulated by way of an operating knob 3 through rotary setting thereof. By pressing axially on the knob 3, a gas safety valve is opened so that the gas leaving the gas fitting in the outlet arrow direction by way of the duct 5 can flow to a burner and is ignited there. The ignition flame heats a thermal element 6, for example a thermocouple, disposed in its path. The resulting electrical voltage generates an electrical current which, through excitation of an electromagnet 7 in the gas fitting 1, keeps the gas safety valve 4 open.

In manual operation, the gas burning operation, for example a cooking process, is terminated by turning the knob 3 to its zero setting, whereby the gas supply to the burner is interrupted. The extinction of the flame also has the effect that the gas safety valve is no longer attracted by the electromagnet 7 and closes the gas duct.

If the termination of the burning operation is to take place automatically after a selected time span, then this can be effected by appropriate presetting of an automatic time switch unit 8. As a result, a change-over switch 9 is switched over from the position shown in the figure. This causes a capacitor 10 to be appiied, by way of a rectifier 11 and a charging resistor 12, to voltage so that the capacitor is charged correspondingly. When the switching instant to be performed by the automatic time switch unit 8 is reached, i.e. at the conclusion of the selected time span, then the switch 9 is switched over into the position illustrated in the figure. The capacitor element 10 is thereby directly connected in series with the winding of a relay 13.

The discharge current now flowing excites the relay 13 and an associated relay contact 14 is closed.

By way of a repeater (transformer) 15, alternating current thereby stepped down is fed to the connecting lines from the thermal element 6 to the electromagnet 7. The superposition of the transformed alternating current on the direct current supplied by the thermal element 6 effects a dropping-off of the gas safety valve 4 from the electromagnet 7 so that the gas flow through the fitting 1 to the burner is interrupted. The relay contact 14 remains closed until the charging voltage at the capacitor 10 has fallen so far that the discharge current flowing through the relay winding 13 is no longer capable of holding the relay in the attracted position. This time span, in the range of seconds, must through appropriate dimensioning of the capacitor 10 and of the resistance value of the relay winding 13 be so determined that the closing of the gas safety valve and thereby the termination of the burning process is ensured. Thereafter, the relay 13 drops off and the relay contact 14 is again opened. The entire installation is disposed in a neutral state, which means that a new burning process can be started at once and can be terminated either by hand or by way of the automatic time switch equipment 8.

Claims

1. Electrical control means for gas flow to a burner, comprising a thermal element heatable by a gas flame of such burner to generate electrical current, a gas flow control device operable by such current to permit gas flow to the burner to continue, influencing means operable, subject to prior charging of chargeable means thereof, for a predetermined period of time to so influence current supply to the gas flow control device as to cause such operation of the device to be terminated and timing means to initiate operation of the influencing means at a selectable point in time.

2. Control means as claimed in claim 1, the influencing means comprising capacitance means as the chargeable means, a relay connectible in series with the capacitance means to be actuable by current discharge therefrom to cause said influencing of the current supply to the control device to take place, switching means arranged between the capacitance means and the relay to control the series connection thereof and actuable by the timing means to interrupt such connection and current supply means arranged to permit supply of charging current to the capacitance means when connection thereof with the relay is interrupted.

3. Control means as claimed in claim 2, the switching means comprising a change-over switch controllable by the timing means to connect the capacitance means in series alternatively with the relay and the current supply means.

4. Control means as claimed in either claim 2 or claim 3, comprising alternating current feed means arranged to be connected to the control device in parallel with the thermal element on actuation of the relay.

5. Control means as claimed in claim 4, the alternating current feed means being caused by said actuation of the relay to apply mains voltage to terminals of the thermal element by way of a repeater.

6. Control means as claimed in claim 5, wherein the relay comprises electrical contact means arranged to control current flow through a primary winding of the repeater.

7. Control means substantially as hereinbefore described with reference to the accompanying drawing.