GB2292630A

GB2292630A - Ignition system for gaseous fuel burner assemblies

Info

Publication number: GB2292630A
Application number: GB9516009A
Authority: GB
Inventors: Geoffrey John Edmond Brown
Original assignee: Stoves PLC
Current assignee: Stoves PLC
Priority date: 1994-08-11
Filing date: 1995-08-04
Publication date: 1996-02-28
Anticipated expiration: 2015-08-04
Also published as: GB9516009D0; GB9416205D0; GB2292630B

Abstract

A cooker having an oven and grill heated by gaseous fuel burner assemblies 1 and 4, includes a burner ignition system for the burners which, when a burner is to be brought into use, initiates an ignition cycle comprising the steps of allowing fuel to flow to the burner, bringing into use an ignition device associated with the burner, and checking that ignition has taken place. In the event that ignition is found not to have taken place, fuel flow to the burner is stopped for a predetermined time interval after which the ignition cycle is repeated. If ignition still does not take place, the cycle is repeated for five times after which the system is shut down if ignition still has not occurred. <IMAGE>

Description

Improvements in and relating to Gaseous Fuel Burner Assemblies This invention relates to gaseous fuel burner assemblies and has particular but not exclusive reference to such assemblies for use in gas-fired cooking apparatus for domestic use.

Many forms of gas-fired cooking apparatus have an oven with a gas burner for heating the oven and its contents.

The burner is usually of a relatively high thermal output and, when the oven is required for use, is ignited by a user.

For reasons of safety, it is usual to limit the heat output of the oven burner during the ignition process when the latter is effected with the oven door closed. That limitation ensures that there is only a small escape of gas into the oven should ignition not take place. Such limitation creates difficulties in cases where the oven burner requires a high thermal output for satisfactory performance and the user is not able to open the oven door to effect ignition.

Other forms of gas-fired apparatus in which gaseous fuel burners are used intermittently are provided with an ignition device for igniting gas emerging from the burner ports. One form of ignition device is a continuouslyburning pilot burner situated close to the burner ports and which ignites gas emerging from those ports when the burner is brought into use. However, such continuously-burning pilot burners have drawbacks, for example, they consume gas and also they can be a fire hazard.

An alternative form of ignition device that has been proposed is the electrical device comprising either a device that emits a stream of sparks when energised or an electrically-energised heater coil that is raised to incandescence when the burner is to be brought into use.

Such electrical devices are usually energised automatically when the burner is brought into use and are then de-energises after a short period of time. However, if the ignition device fails to ignite gas emerging from the burner ports the continued supply of gas thereto can give rise to dangerous situations.

Accordingly, it is an object of the present invention to provide a gaseous fuel burner assembly in which the risks just referred to are eliminated.

According to one aspect of the present invention a gaseous fuel burner assembly includes a burner ignition system in which the burner is supplied with gaseous fuel at full rate for a short period during which ignition means associated with the burner are energised, and in which, in the event that ignition does not take place during the short period, the input of fuel to the burner is terminated for a controlled time interval after the expiry of which the supply of fuel to the burner is resumed and the ignition means re-energised.

If ignition still does not take place, the cycle is repeated for a predetermined number of times after which, in the event that ignition has still not taken place, the system locks out and cannot be re-used until it has been reset.

Preferably, a reset control is provided for manual operation by a user. Alternatively, the system may be reset by appropriate actuation of a burner control.

In one particular embodiment of the invention, the system is such that the mean heat input to the burner over the total cycle time does not exceed a predetermined value.

The short period during which fuel is initially supplied to the burner may be about four seconds whilst the controlled time interval that must elapse before a second attempt at ignition may be about sixteen seconds.

The ignition system may be electronically operated and be part of a control system that also controls other functions of the gas-fired apparatus.

In the case of a gas-fired cooker oven it is preferable that the cooker has door cooling and this may be effected by means of an air flow through the door. The air flow may be supplied from a plenum chamber maintained at an air pressure above atmospheric. In that case, the control system will bring into operation a fan that supplies air to the plenum chamber and will check that air is flowing into the chamber before the oven burner can be brought into use.

By way of example only a domestic gas-fired cooker having a burner assembly system embodying the invention and a control system therefor will now be described in greater detail with reference to the accompanying drawing that shows the embodiment in block schematic form only.

The cooker is one having an oven and a grill chamber whose burners are controlled by the system.

An oven burner indicated by block 1 is supplied with gaseous fuel from a main fuel supply line 2 via a solenoidoperated fuel flow control valve 3. A grill burner shown as block 4 is also supplied from line 2 via a second solenoidoperated fuel flow control valve 5. The operation of valves 3 and 5 is under the control of a micro-computer shown as block 6 which effects operation of the solenoids via a power switch shown as block 7.

The oven and grill burners each have associated with them a combined ignition/flame detector (not shown) which are also controlled by the micro-computer 6 via a flame detection means indicated as block 8. Flame detection is effected by means of flame rectification.

The oven and grill burners 1, 4 are user operated by means of rotary controls 9 and 10 respectively. The controls 9, 10 incorporate ON/OFF switches 11, 12 and potentiometers 13, 14, respectively. The switches are operated by rotation of the control 9, 10 to a first position which turns the switch 10, 12 to its ON condition, the potentiometers coming into use on continued rotation of the control and providing means for setting the oven/grill temperature to a required value. Sensors 15, 16, for example, thermistors, associated with the oven and grill burners, respectively, are responsive to the temperature within the oven and grill chamber respectively, and they input directly to the micro-computer 6.

Switches 18 and 19 operated by the oven and grill doors, respectively, also input to the micro-computer. Such switches operate to ensure that the relevant door must be correctly positioned before the associated burner can be brought into use. In the present example, the oven door must be shut before the oven burner can be brought into use, and the door of the grill chamber must be open before a grilling operation can take place.

Preferably, the cooker has provision for cooling the oven door and, desirably, the grill door also. Cooling is effected by an air flow supplied from a plenum chamber that may be located behind the oven. Examples of cookers with air cooled doors are found in UK Patent No. 2255632B. The chamber, which is not shown may be used to accommodate components of the cooker control system, is supplied with air by a fan indicated by circle 20 in the drawing. The fan is driven by an electric motor (not shown) controlled by the micro-computer via the power switch 7. The motor has an indicator lamp 21 that is energised with the motor. The existence of air under pressure in the plenum chamber is sensed by a sensor 22 that is responsive to the flow of air into the chamber and which inputs to the micro-computer via the analogue-to-digital convertor 17. The sensor 22 is a heated PTC device. A compensating sensor 23 whose function is to compensate for changes in ambient temperature also inputs to the micro-computer via the convertor 17.

The cooker is provided with a programmer shown in the drawing as block 24 that allows a user to programme the start time, the duration and/or the finish time of cooking operations. The programmer may also include a timer. As shown the programmer inputs directly to the micro-computer 6.

Power for the system is obtained from the domestic mains supply via an isolating transformer 25 whose secondary provides a suitable low voltage output, for example 24 volts, from which the various switches and the solenoids are powered. The use of low voltage supplies is less hazardous than the use of full mains voltage.

Other indicating lamps are provided as required, for example, lamps 26 and 27 which may be light emitting diodes indicate, respectively, when the grill and oven burners are in use. The indicating lamps may be adapted to display two colours each of which represents a different condition.

For example, red to indicate that a burner is in use and green to show that the burner is ready for use.

The micro-computer is programmed to control the various stages of a cooking or grilling operation in the following manner.

To bring the control system into use, a user first switches on the power supply, the "POWER ON" being proved by the energisation of signal lamp (not shown). The computer powers up and proceeds to check the status of the sensor 22 and the flame sensors. If no air movement and flames are detected, the system is allowed to move to start up. If the oven is to be used, the user first ensures that the oven door is shut, that action resulting in operation of switch 18 and the appropriate input to the microcomputer. Control 9 is then operated to its first position after which the control 9 is set to a desired oven temperature. The micro-computer responds to movement of the control to its first position by energising the motor driving fan 20.Sensor 22 checks for movement of air into the plenum chamber and if satisfactory air movement is found, the computer then commences an ignition cycle and first energises solenoid 3 to open fully the valve 5 controlling fuel supply to the oven burner. The flame igniter associated with the oven burner 4 is then energised after a short delay of 0.5 seconds. If the igniter is of the sparking type, sparking commences at the rate of one spark every 1.1 seconds and continues for 4 seconds. If the flame detector proves the existence of a flame, sparking is terminated and the solenoid valve 3 is left open and the oven and its contents are heated thereby commencing the cooking operation.When the oven reaches the temperature to which the oven control has been set, the input from the sensor 15 to the computer results in the latter deenergising the solenoid valve 3 which closes and terminates the supply of fuel to the oven burner. When the oven temperature has fallen below the set value by a predetermined amount , the computer initiates the ignition cycle and re-energises the solenoid and the supply of fuel to the burner 4 is restarted and the ignition cycle described above is repeated. In that way, the oven temperature is maintained at the set value.

If, however, during the initial start-up, the flame detector fails to detect the existence of a flame after 4 seconds, the computer closes the fuel supply valve and stops the sparking for a period of 15 seconds. At the end of the 15 second period, the computer repeats the ignition cycle and shuts down the system if no flame is detected after the ignition cycle has been repeated five times.

Alternatively, the shut down may be timed to take place after the expiry of say 90 second. The user is thus warned and the system has to be reset by operation of the oven control to "OFF" and then to its first position.

At the end of a cooking operation, the user returns the control 9 to its "OFF" position and the micro-computer responds by de-energising the solenoid valve 3 so terminating the supply of fuel to the burner 1. The motor driving the fan 20 is also de-energised.

If the grill burner is required to be brought into use, the user switches on the power supply as explained above and then, having ensured that the door of the grill chamber is open, the grill switch is moved to its ON position. That action drives the micro-computer to energise the motor driving fan 20. Sensor 22 checks for movement of air into the plenum chamber and if satisfactory air movement is found, the valve 5 is opened thereby establishing full flow of fuel to the grill burner 4. At the same time the igniter associated with the grill burner is energised. If the igniter is of the sparking type, the sparking commences at the rate of one spark every 1.1 seconds and continues for 4 seconds. When the existence of a flame at the grill burner is proved, sparking is stopped and the valve 5 is left open.Grilling then commences and continues until the user operates the grill control to its OFF position at the end of the grilling operation. That results in the turning off of the solenoid valve 5 and the cessation of fuel flow to the grill burner.

If during the grilling operation, sensor 16 indicates that the temperature in the grill chamber exceeds the value to which it has been set by the grill control then valve 5 is closed and will be re-opened when the temperature in the grill chamber drops below the preset temperature when the valve 5 will be re-opened and the ignition cycle re-started.

Alternatively, control of the ignition cycle of the grill burner may be such that if no flame is detected within a preset time, for example 15 seconds, after the ignition device is energised then the grill burner will be shut down, the fuel supply to the burner is stopped and the ignition device is also turned off. The system then requires to be reset before the grill burner can be used again. Resetting may be effected by turning the grill switch 20 to its OFF position.

The procedure followed when one of the burners is already in use and it is required to bring the other burner into use is generally similar to that just described except that the fan 22 will already be energised. Before operation of the control of the other burner, the user will ensure that the relevant door is correctly positioned.

During the start, the periods of fuel on and fuel off are so selected that the mean heat input to he burner over the period of ignition is not greater than a specified value, for example 600 watts.

The programmer is of a conventional form and is used when it is desired to carry out an automatic cooking operation. The relevant information is keyed into the programmer and the user then sets the burner control to the desired temperature at which cooking is to be carried out.

The cooking operation is then started at the "start" time set into the programmer and terminates at the "finish" time that is also set into the programmer.

It will be appreciated that both oven and grill compartments may have compartment lights and that these may be brought into use either by operation of switches or automatically when the solenoid valve are energised.

Furthermore, in cookers having ovens with fans for circulating hot air within the oven during a cooking operation, the control system will ensure that such fans are brought into use at the commencement of an ignition cycle. Ovens with circulating fans are described in UK Patent Application No. 9402566.5.

The system is such that short interruptions of the main power supply are ignored but longer interruptions that are sufficient to risk closure of the fuel supply valves result in the control system shutting down and the user will then have to reset it by turning the controls 9 and 10 to "Off" before restarting a cooking or grilling operation.

The invention may also be embodied in other forms of gaseous fuel fired apparatus, for example, gas-fired boilers or water heaters that may be used in central heating systems.

Claims

CLAIMS.

1. A gaseous fuel burner assembly comprising a main gaseous fuel burner, gaseous fuel flow control means for controlling the supply of fuel to the main burner, an ignition device for igniting fuel from the main burner and a control system which, when the main burner is to be brought into use, initiates an ignition cycle comprising the steps of operating the flow control means to allow the flow of fuel at a predetermined rate to the main burner, bringing the ignition device into use to ignite fuel emerging from the main burner, checking that ignition of fuel from the main burner has taken place, and in which, in the event that ignition of the fuel emerging from the main burner does not take place within a set time period, the system causes the flow control means to terminate the flow of fuel to the main burner for a predetermined time interval after which the ignition cycle is repeated.

2. An assembly as claimed in claim 1 in which, in the event that fuel emerging from the main burner is not ignited after the ignition device is again brought into use, the system repeats the ignition cycle for a preset number of times after which, if fuel emerging from the main burner is not ignited, the system is shut down and the supply of gaseous fuel to the main burner is terminated.

3. An assembly as claimed in claim 3 in which means are provided for resetting the control system after shut down.

4. An assembly as claimed in claim 3 in which the resetting means comprise a manually-operable control.

5. An assembly as claimed in any one of the preceding claims in which the mean heat input to the main burner over the total cycle time does not exceed a preset value.

6. An assembly as claimed in any one of the preceding claims in which the set time period is four seconds.

7. An assembly as claimed in claim 6 in which the predetermined time period is sixteen seconds.

8. A assembly as claimed in any one of the preceding claims in which the flow control valve is a solenoid operated valve.

9. Cooking apparatus comprising a cooking oven with a gaseous fuel burner assembly as claimed in any one of the preceding claims.

10. Cooking apparatus as claimed in claim 9 in which the ignition cycle is brought into use by operation of an oven switch.

11. Cooking apparatus as claimed in claim 10 in which the oven switch incorporates means for setting the temperature to which the oven is to be heated.

12. Cooking apparatus as claimed in claim 11 in which the oven temperature is sensed by sensing means which input to the control system to allow the latter to terminate the supply of fuel to the oven burner in the event that the oven temperature reaches the set value, the system repeating the ignition cycle when the oven temperature drops below the set value.

13. Cooking apparatus as claimed in any one of claims 9 to 12 in which the oven has a door with a arrangement for sensing whether the door is open or shut, the arrangement inputting to the control system to inhibit the latter should the oven door be in an incorrect position when the oven burner is to be brought into use.

13. Cooking apparatus as claimed in any one of claims 9 to 12 and further comprising a grill chamber with a gaseous fuel grill burner, a fuel flow control valve controlling the supply of fuel to the grill burner, ignition means for igniting fuel issuing from the grill burner and in which the operation of the grill burner is also controlled by the control system in the manner claimed in claim 1.

15. Cooking apparatus as claimed in claim 13 in which the grill chamber has a chamber door and in which means are provided for sensing the position of the door and inhibiting the operation of the control system in the event that the door is not in the correct position for carrying out a grilling operation.

16. Cooking apparatus as claimed in any one of claims 9 to 15 which further includes a plenum chamber, fan means for drawing air into the plenum chamber and air flow sensing means for sensing air flow into the plenum chamber and in which the control system, at the start of an ignition cycle, first energises the fan means and then checks that air is flowing into the plenum chamber, the ignition cycle being inhibited in the event that air flow into the plenum chamber is not detected.

17. Cooking apparatus as claimed in claim 16 in which air from the plenum chamber is used to cool the oven door and/or the grill chamber door.

18. Cooking apparatus as claimed din any one of claims 9 to 17 in which the oven chamber has fan means for circulating air within the oven.

19. Cooking apparatus as claimed in claim 18 in which the fan means for circulating air within the oven is bought into use by the control system at the commencement of an ignition cycle.

20. Cooking apparatus substantially as herein described with reference to and as illustrated by the accompanying drawing.