GB2121520A - Gas valve means - Google Patents

Abstract

Tandem shut-off valve (18, 22) and modulating valve (19, 27) are operated together by a solenoid (16). Movement of the valves is opposed by a spring (25) providing a resistance to movement of the valves which increases as the valves open. Power is supplied to the solenoid by an interface unit (11), which varies the power by a phase-clipping system or by voltage variation or by cyclic switching to vary the movement of the solenoid armature and thereby the valve opening. The valves supply gas to a cooker oven the temperature of which is sensed and fed back to the interface, whereby the valve opening is adjusted to attain and maintain a desired cooking temperature. <IMAGE>

Description

SPECIFICATION Gas valve means This invention relates to electrically-operated gas valve means particularly, though not exclusively, for use in gas cookers.

The invention provides gas valve means comprising an electrically-operated modulating gas valve and control meansforsupplying variable electrical power to operate said gas valve, said control means being adapted to respond to a temperature-representing signal and to vary its power outputto the gas valve accordingly, whereby the gas valve takes up modulated positions to allow variable gas flows related to the said temperatureto take place.

The control means may comprise an electrical interface unit supplying power to an electrical actuator forthe modulating valve, which actuatormaycom- prise a solenoid or a heat motor. The interface unit may operate to vary the power output by a phase clipping technique or by intermittent switching cycles.

Preferably said gas valve means comprises a shut-offvalve and a modulating valve secured to be operatedtogether by a common actuator. Said modulating valve may be adapted so that during initial opening movement from closed by the actuator only the shut-offvalve opens, and there may be a by-pass around the modulating valve so that a limited gas flow path is established.

A specific embodiment of the invention is shown in the accompanying diagrammatic drawing, which shows an automatic control system for a domestic cooking oven.

An electrical interface unit (11) receives an electrical signal on lines (12) when a cookertimer (not shown) commands a startforthe cooker oven. A selector knob (13) is manually operable to select a desired cooking temperature against an index. A temperature-sensing device (not shown) which may be a thermocouple is located in the oven and provides a signal on line (14) related to the actual temperature in the oven for comparison with the desired cooking temperature.

Circuits in the interface unit (11) then provide energization to a solenoid (16) in orderto open a gas valve means (17) and allow gas to reach burners of the oven, in the sense to bring the sensed oven temperature up to the desired cooking temperature and to maintain it there.

The gas valve means (17) comprise tandem valve plates (18, 19), secured together to be operated by an actuating rod (20) and armature (21) moveable by the solenoid. Valve plate (18) co-operates with a seat (22) toform ashut-offvalve,whilevalve plate (19) co-operates with a seat (23) to form a modulating valve in gas series with the shut-off valve. A by-pass (24) allows a selected by-passflowofgaswhenthe modulating valve is still closed. A spring (25) resists the opening of the two valve plates (18, 19).

The spring (25) is selected to have a higher rate of change of load with deflection than the rate of change of force applied from the solenoid to the armature (21 ) as the armature moves. In otherwords,the resistance to movement of the valves increases the furtherthe valves are opened. Theforce applied by the solenoid to open the valves also increases as the valves open due to the movement ofthe armature, but at a rate less than the increase in the spring resistance. Accordingly, the valves reach a floating position at which the axial spring resistance is equal to the electromagnetic opening force. By providing the solenoid with variable power it is therefore possible to alter the axial floating position at which the valves are in equilibrium.

Spring (25) is shown in the drawing as a helical spring, but it may also be a diaphragm spring, i.e. a slightly dished disc of spring steel, the periphery of which is radially slotted to achieve a crenellated shape ofthe desired spring rate.

Valve plate (19) is secured to a tapered plug (27) which moves in the opening in seat (23) so as to vary the gas flow thereth rough according to the floating position taken up by the valves. The plug immediately adjacent the plate (19) is cylindrical with straight sides which are a close sliding fit in the opening so thatfor the first part of the opening movement of the valves there is no gas flow th rough the valve opening in seat (23). In this same movementshut-offvalve plate (18) opens to the position shown in the drawing in which gas flow is allowed through seat (22) and by-pass (24).

This limited gas flow is sufficientto feed the oven burners at their lowest safe rate, thus maintaining the oven alight.

The circuits of the interface unit (11) compare the incoming signal on line (14) and the setting of temperature selecting knob (13). If the desired temperature is considerably higher than the actual oven temperature, as for instance when the oven is first lighted, then full wave power is applied to energize the solenoid, and the valves open to their maximum extent with the narrowest part of the plug in the opening in the seat.

As the two temperatures approach one another, then the interface unit (11) reduces its power output by phase clipping the electrical waveform. This technique uses a thyristor switch biased to switch ON when a selected positive or negative voltage is reached in each cycle of an alternating waveform, so that only a proportion of the available power is conducted. The proportion is altered by changing the biasing of the thyristor switch so that it switches at a different selected positive or negative voltage level . Since the reduced power is applied to the solenoid,the field produced by the solenoid is likewise reduced and the force equilibrium position between spring (25) and the solenoid changes.The valve plate (19) therefore takes up a new floating position, the plug (27) changes its postition and a different gas flow is allowed through the valve means. Therefore by appropriate biasing of the thyristor switch different gas flows can be achieved. As the desired and actual temperatures approach one another, the plug (27) moves to reduce the gas flow so that when the temperatures are substantially equal the gas flow through the valve opening in seat (23) ceases, and only the by-pass (24) allows gas through. The energization ofthe solenoid is controlled, however, so that the shut-offvalve plate (18) never closes during a cooking operation whereby a minimum oven burner setting is always maintained.

The solenoid is only cut offfrom power completely when the cooker timer commands a finish to the cooking operation.

Alternatively, instead of a phase clipping technique to alterthe power output, the interface unit may employ a voltage variation technique changing the applied voltage to achieve different valve settings.

Downstream ofthegasvalve means (17) maybe a flame-fa.surevalve (29) controlled bya sealedthermal system comprising a phial (30) bellows (31), a capillaryjoining the two, and an expansible liquid filling the system. The phial (30) is located to be heated bya pilot lightforthe main oven burners. A by-pass (33) allowsjust sufficient gas to pass to supply the pilotwhen the valve (29) is closed.

An ignition system (not shown) is operated bythe cookertimer on start-up of the cooker and is disabled eitherastheflame4ailurevalve opens indicating that the pilot is alight, or when a flame sensing device detects flame.

It will be noted that in the above embodiment, the shut-offvalve and the thermostatically controlled valve are coupled to be operated bya single solenoid actuator. The only othervalve required bythe automatic cooking system is the flame-failure valve, and in the embodiment described this is a nonelectrical valve operating independently of the cooker timer.

In a variation (not shown) of the illustrated embodiment, the solenoid actuator is replaced by a heat motor.This comprises a bimetal strip heated by an electrical winding or other heater sothatthe bimetal strip moves and operates the rod (20). The power supply to the winding determines the temperature reached and the degree of movement of the bimetal strip and thereforethe position taken up by the valves.

The power supply may be altered by the phaseclipping orvoltage variation means described above.

Alternatively, it may be altered by a slower switching device providing ON and OFF periods of the order of a fewseconds,the lengths ofthe ON and OFF periods determining the temperature reached by the bimetal strip.

The interface unit (11) may be mounted in the same casing as the cooker timer.

Claims (14)

1. Gas valve means comprising an electricallyoperated modulating gas valve and control means for supplying variable electrical powerto operate said gas valve, said control means being adapted to respond to a temperatu re-representing signal and to vary its power output to the gas valve accordingly, wherebythegasvalvetakesup modulated positions to allow variable gas flows related to the said temperature to take place.

2. Gas valve means as claimed in claim 1, wherein said control means includes an electrical interface unit adapted to provide a poweroutputvaried by a phase-clipping technique or by intermittent switching cycles or by changing the voltage.

3. Gas valve means as claimed in claim 2, wherein said control means includes atimerforprogramming the operation of the valve.

4. Gas valve means as claimed in claim2 orclaim 3;wherein said control means includes a temperature selector operable to select a desired temperature and said interface unit operates to comparethe selected temperature with the temperature-representing signal and to adjustthe said power output in the sense to cause the temperature represented by said signal to arriveatand be maintained atsaidselectedtempera- ture.

5. Gasvalve means as claimed in claim 4,wherein said interface unit,timer and temperature selector are all mounted in one casing.

6. Gas valve means as claimed in any of claims 1 to 5, wherein said valve comprises a combined shut-off valve and modulating valve operated in tandem by a common actuator and connected in gas series.

7. Gas valve means as claimed in claim 6, wherein said shut-offvalve comprises a valve plate cooperating with a seat and said modulating valve comprises a tapered plug movable in an opening to modulate the gas flow.

8. Gas valve means as claimed in claim 6 or claim 7, wherein a permanent by-pass allows a selected by-pass flow of gas around the modulating valve, the valve and its control means being adapted so that in use the shut-offvalve remains open while the modulating valve varies its opening.

9. Gas valve means as claimed in any of claims 1 to 8, wherein said valve is operated by a solenoid or by a heat motor.

10. Gas valve means as claimed in any of claims 6 to 9, wherein the resistance to movement of the valves is arranged to increase the furtherthe valves are opened by means of a spring selected to have an appropriate rate of change of load with deflection, whereby the valves take up different positions for different opening forces.

11. Gas valve means as claimed in claim 10, wherein said spring is a helical spring or a diaphragm spring.

12. Gas valve means as claimed in any of claims 7 or claims 8to 10 as appendantto claim 7, wherein said tapered plug has an initial straight portion forming a close sliding fit in the said opening whereby initial opening movement of the valves opens the shut-off valvealone,furthermovementopeningthe modulat ingvalve.

13. Gas valve means substantially as described hereinbefore with reference to the accompanying drawing.

14. A gas-fired cooker having burners controlled by gas valve means as claimed in any of claims 1 to 13.