GB2314925A - A gas cooker and a control system therefor - Google Patents

Abstract

A gas fired twin burner cooker (1) has a cooking section (22) and a boiler (35) thermally insulated from one another. The cooking section has at least one oven (22) and a hotplate. A gas burner (40) heats the cooking section (22) and a gas burner (30) heats the boiler (35). Each burner (30, 40) has a separate fan and separate flue passages to lead the combustion by-products to a common outlet flue (18). Circuitry is provided to operate continuously the fan of the idle burner during the operation of the cooker burner (40) or the boiler burner (30) thereby maintaining air pressure in the flue passageway of the idle burner.

Description

A GAS COOKER AND A CONTROL SYSTEM THEREFOR The present invention relates to a gas fired twin series cooker which is a multi-functional domestic heat and cooking appliance. It can be used as a domestic boiler capable of producing up to 100,000 Btu/hour and as a domestic cooker with oven and hotplate facilities while also providing space heating. The appliance utilises two independent forced draught burners, one for heating the boiler and the other providing heat for cooking. The boiler and oven are thermostatically controlled with the boiler also having a fully programmable facility.

As of the 1st January 1996 every gas appliance sold in the EU must be manufactured in accordance with the Gas Appliance Directive. In order to attain this "CE" approval every gas appliance must undergo type testing carried out by a notified body. This type testing is mainly concerned with issues such as combustion emissions under various conditions, surface temperatures, operation of safety devices and general safety, including a blocked flue test.

A blocked flue test for a forced draught appliance involves running the appliance at nominal input until it reaches thermal equilibrium. The flue is then gradually blocked until the pressure switch on the appliance senses a build up of pressure in the appliance and shuts off the burner. As the back pressure increases the level of C02 in the combustion chamber increases, which increases the flame length. As a result the flame starts to impinge on the walls of the combustion chamber and CO starts to form.

The CO level at shutoff must not exceed 0.2 ppm in an air free sample. The back pressure at which the pressure switch is set to shut off the appliance is very important.

If the pressure switch is set too low the appliance may be subjected to nuisance shut-down in the field by minor pressure fluctuations. These may be caused by gusts of wind for example. The pressure switch must be set high enough to overcome these pressure fluctuations but low enough to shut off the appliance in a blocked flue situation before CO reaches unacceptable levels. On previous single burner appliances shutoff at 0.8 mbar has proven to work well.

During pre-testing of our twin burner gas cooker it was discovered that if the flue was gradually blocked while operating on a single burner, sufficient pressure did not build up inside the appliance to actuate the pressure switch. This was due to the combustion gases travelling back down the flue passage of the opposite burner and venting out to the room through the idle burner.

The present invention provide a gas fired twin burner cooker having a cooking section and a boiler thermally insulated from one another, the cooking section having at least one oven and a hotplate, the cooker comprising a gas burner to heat the cooking section and a gas burner to heat the boiler, each burner having a separate fan and separate flue passages to lead the combustion by-products from the cooker burner and the boiler burner to a common outlet flue characterised in that means are provided to operate continuously the fan of the idle burner during the operation of the cooker burner or the boiler burner thereby maintaining air pressure in the flue passageway of the idle burner.

To allow this continuous idle fan to run a control system has been specially designed around the burner's own sequential control box. When operating one burner alone this special control system is capable of: - Allowing the control box to go through it's start up sequence without interrupting unnecessarily.

- Running the idle fan when one burner is operating.

- Recognising a loss in burner pressure or a build up of combustion chamber pressure sending the burner to lockout.

- Recognising a loss in pressure in the idle fan sending the burner to lockout.

The system must also allow both burners to operate together. The operation of turning on or off either burner at any time should not in itself send either burner to lockout. If both burners are operating and either pressure switch actuates then this should lead to lockout of both burners.

Other features of the invention will be apparent from the claims appended hereto.

The invention will be more clearly understood from the following drawings which illustrate by way of example only the main features of the cooker. In the drawings: Figure 1 is a perspective view of the assembled cooker; Figure 2 is a perspective view of the cooker with a portion of the front cut away to show the internal workings of the cooker; Figure 3 is a perspective view which is further cut-away to show the location of the two burners and their relative positions to one another within the cooker; Figure 4 is a further perspective cut away drawing with the burners removed and showing the boiler and the sheets of ceramic insulation used; Figure 5 is a front elevation view of the cooker as shown in Figure 4; Figure 6 is a cross sectional plan view of the cooker as shown in Figure 4; Figure 7 is a view similar to Figure 4 but without the ceramic insulation panels being shown; Figure 8 is a perspective view of the base unit of the cooker; Figure 9 is an exploded perspective view of the latch mechanism used on each of the four doors; and Figure 10 is a wiring installation diagram showing the circuitry required to operate a twin gas burner cooker according to the invention.

Referring to the drawings, the cooker 1 is of cast iron construction with a fabricated metal base 2 and is of the appropriate dimensions to be accommodated in a modern kitchen. As shown in Figure 1, the cooker has four doors 11, 12, 13 and 14, each of which has a slam-shut facility in that the user simply slams the door to close it and lifts the handle 15 to release the latch and open the door. Further details regarding the latch and handle are given later in this description. The cooker has a hot plate 16 which is of standard construction. The only other feature shown in Figure 1 is the air inlet 17 at the base 2 through which air is introduced into the base for the operation of the gas burners.

As can be seen from Figure 2, behind the door 11 is a control panel 21 for operation of the cooker and behind the door 12 is the main roasting oven 22. The door 13 provides access to a port 23 for getting access to the two burners 30 and 40 which operate the cooker. The warming oven 24 is behind door 14. The air inlet 17 is shown in Figure 2 as is the electrical and fuel supply circuitry 26 which controls the operation of the cooker.

From Figure 3 onwards, the front of the cooker and doors are all removed so it is easier to see the main roasting oven 22, the warming oven 24, the boiler burner 30 and the cooker burner 40.

The boiler burner 30 is located at the base of the boiler 35 and is arranged so that it fires horizontally into the chamber 36 at the base of the boiler 35. The chamber portion 36 of the boiler extends from the front of the boiler to the rear. The construction of the boiler is more clearly shown in Figure 4. The boiler 35 is generally of U-shaped construction and is shown in cross section. It has a left hand water jacket 51, bottom water jacket 52 and right hand water jacket 53 which is adjacent the chamber 41 for the cooker burner 40. Inside the boiler 35 is a central panel 55 and a number of baffles 56 for the distribution of heat through the boiler. The boiler burner 30 is mounted on a front plate which has a ceramic lining 57 and the blast tube 32 of the burner 30 projects horizontally into the chamber 36 so that the burner 30, when operated, fires horizontally directly into the boiler to heat the water in the panels or water jackets 51, 52, 53 and 55.

The chamber 41 for the cooker burner 40 can be seen in Figures 3, 4, 5, 6 and 7. There are a number of significant differences between the chamber 41 for the cooker burner 40 and the chamber 36 for the boiler burner 30. Firstly, the chamber 41 is arranged so that the burner 40 fires vertically upwardly towards the hot plate 61, thus causing greater heating of the hot plate. The flue gases also go between the ovens 22 and 24 and around the oven to the flue exit 18.

As well as the burners 30 and 40 firing in different directions, the chamber 41 is above the chamber 36, therefore the chambers do not coincide and are not located side by side. The shape of the chamber 41 as shown in Figure 6 is generally trapezium shaped so as to reduce the contact area between the chamber 41 and the boiler 35.

The base and walls of the chamber are insulated with ceramic insulation panels, namely four side panels 42, 44, 45 and 46 and base panel 43. It will be seen in Figure 4 that the top edge of ceramic lining 57 is approximately in line with the top surface of insulation panel 43 of the cooker burner chamber 41. The main function of the ceramic side panel 42 is to insulate the chamber 41 from the boiler 35 so that the heat generated in the chamber 41 will not transfer, to an appreciable extent, to the boiler 35. There is no insulation between the chamber 36 and the burner 40 other than that achieved by the cooling effect of water flowing through the lower section of the right hand water jacket 53.

The flue gases from the boiler burner 30 and the cooker burner 40 are diverted through separate channels and do not mix until they reach the flue exit 18.

Referring to Figures 7 and 8, it can be seen that behind the air inlet 17 are conduits 61 and 62 which channel the air around the circuitry 26 into a plenum space 63 beneath the burners 30 and 40 from which they can draw air as required for combustion purposes. The conduits which are rectangular in shape are of wire mesh construction and are insulated with rock wool over all surfaces so as to reduce noise levels. An alternative air intake into the conduit 61 can be provided at the rear of the base if the inlet 17 is not suitable.

Water connections 64 and 65 are provided on the boiler 35 for connection to the domestic hot water and central heating systems of a house.

The main benefit of the cooker is that the user can select that either one or both burners 30 or 40 be turned on as required. The burners 30, 40 may be programmed by means of an electronic control panel 21 and can be turned on and off at specified times. While the boiler burner 30 is in operation, all its output is transferred to the water in the panels and jackets of the boiler and there is very little heat transferred to the hot plate 16 and none at all to the ovens. While the burner 40 is in operation, its main output is directed at heating the hot plate and oven and there is only a small amount of heat transferred to the boiler 35, of the order of 3,000 - 4,000 Btu's from 40,000 output from the cooker burner 40. This amount of heat is sufficient to supply domestic hot water requirements of a standard house and the hot water can be transferred to a domestic hot water cylinder. There is no requirement to operate the central heating system while the cooker burner is in operation which is what is currently required in cookers having a single burner which is used for heating the boiler and the cooker components.

The slam-shut mechanism will now be described in relation to the components as shown in Figure 9 which shows the oven door 12 and the handle 15 with the individual components exploded. The latch mechanism comprises a keeper 70 which is fixed to the body of the cooker, a latch member 81 fixed to a bracket 82 which is pivotally mounted in bearing elements 83 formed on the door 12. The latch member is pivoted in bearing elements 83 on pivot pin 84 which engages with pivot pin 85 which pivotally secures the handle cover 88 to the frame 82. The torsion spring 86 is provided so as to bias the latching member 81 into the closing position so that the cooker can be slammed shut and the latch member automatically engages with the keeper 70. To open the door, the user lifts the handle cover 88 vertically upwards, to pivot the latch member on the pin 84 to allow the latch to be disengaged from the keeper 70. This opening movement is a very simple movement for the user and can be accomplished even if the user is holding something in her hands. The closing action is even simpler in that the user just has to close the door with sufficient force to enable the latch member 81 to engage with the keeper 70.

Referring now to Figure 10 the control system the cooker is designed around the sequence of the burner control box.

The start up sequence of the LANDIS AND GRY (Trade Mark) LGB21.A34027 will now be explained in conjunction with Figure 10 which is a wiring installation diagram.

When power is sent to the control box it's first step is to wait for a time during which the air pressure switch and flame relays are tested for their correct contact position. This waiting time lasts approximately 8 seconds. When this time has elapsed a signal is sent from pin three (3) to start the motor. The control box then waits for five (5) seconds before checking the air pressure switch. After this time the set value of air pressure must have built up or else a lockout is initiated. If the correct pressure signal has been received then the control box will run through it's pre-purge cycle. This pre-purge of air will last at least thirty (30) seconds. When the pre-purge is completed the control box sends a signal to the transformer to provide an ignition spark. Two (2) seconds later the gas valve is opened and a low-load of gas is admitted to the burner head. After a maximum of five (5) seconds the control box checks that a flame has been established. To achieve this the ionisation current into pin one (1) of the control box must be a minimum of 7 Amps. This signal will continue uninterruptedly until controlled shut-down occurs or else the control box will initiate lockout. If a flame has been established the burner will continue to run on low-load for another four (4) seconds before opening the gas valve to full load. The burner will then continue to operate until a controlled shutdown occurs or a fault condition is recognised resulting in lockout.

Two PCB mounted relay safety systems are specially provided to allow an idle fan to operate without interfering unnecessarily with the sequence of the control box. In the diagram BRT and ORT are time delayed relays whose contacts make 1.5 seconds after they are energised.

The relays PSO and PSB are energised from the normally open (NO) contact of the oven and boiler air pressure switches respectively. When the oven thermostat is closed OR is energised instantly and ORT 1.5 seconds later. This results in the boiler fan starting which subsequently energises PSB. The control box checks that the relay PSO is in it's correct position by testing the continuity between pin three (3) and pin six (6). When satisfied a signal is sent from pin three (3) to start the oven motor.

After the oven motor starts the PSO is energised and when the control box checks for air it finds PSO in it's correct position. The control box will then go through the remainder of it's start sequence as described earlier.

The boiler burner will operate in a similar manner.

If the boiler burner thermostat is turned on while the oven burner is running BR and BRT are energised. The boiler motor will stop and PSB will de-energise. The oven burner will continue to run however as BR is bridged across the PSB contact connected to pin eleven (11) on the oven control box. With PSB in it's correct starting position and PSO and OR closed the boiler control box will go through it's starting sequence as normal. If one burner is operating alone and there is a fault with either the burner's own fan or the idle fan, PSO or PSB will de-energise and the burner goes to lockout the OR2 or BR2 is energised and power is cut off to the opposite burner.

It is seen that relays BR2 and BR3 are energised from the boiler pressure switch and OR2 and OR3 from the oven pressure switch. When the oven thermostat is closed both oven and boiler fans start. BR3 and OR3 are energised.

The oven control box checks and finds continuity between pin three (3) and pin six (6). It then sends a signal from pin three (3) which energises relay OR1. This in turn energises OR2 giving continuity between pin three (3) and pin eleven (11) which satisfies the control box when it checks for air. The control box will then continue through it's start sequence as described earlier. The boiler burner will operate in a similar manner.

If the boiler thermostat is turned on while the oven burner is operating, relay R1 is energised. Power continues to be supplied to pin twelve (12) of the oven control box and both motors continue to run with power supplied from the normally open contact of R1. As a result the oven burner continues to operate. The boiler burner will go through it's sequence as described above with BR2 remaining de-energised until BR1 is energised by a signal from pin three (3) of the boiler control box. If either pressure switch is actuated due to a pressure build up in the combustion chamber of fan failure BR2 and BR3 or OR2 and OR3 will de-energise and the control box go to lockout.

It will of course be understood that the invention is not limited to the specific details described herein, which are given by way of example only, and that various modifications and alterations are possible within the scope of the invention as defined in the appended claims.

Claims (10)

CLAIMS:

1. A gas fired twin burner cooker having a cooking section and a boiler thermally insulated from one another, the cooking section having at least one oven and a hotplate, the cooker comprising a gas burner to heat the cooking section and a gas burner to heat the boiler, each burner having a separate fan and separate flue passages to lead the combustion by-products from the cooker burner and the boiler burner to a common outlet flue characterised in that means are provided to operate continuously the fan of the idle burner during the operation of the cooker burner or the boiler burner thereby maintaining air pressure in the flue passageway of the idle burner.

2. A gas fired twin burner cooker as claimed in Claim 1, including a first control apparatus for overriding burner control means provided on each burner, the first control apparatus having means for allowing the burner control means to go through its start-up sequence, and means for running the fan of the idle burner when the other burner is operating.

3. A gas fired twin burner cooker as claimed in Claim 2, in which the first control apparatus includes means for detecting a loss of pressure in the operating burner or for detecting a build up of combustion chamber pressure and means for disabling the operation burner on detection of a loss or build-up of pressure.

4. A gas fired twin burner cooker as claimed in Claim 2 or Claim 3 in which the first control apparatus includes means for detecting a loss of pressure in the fan of the idle burner and means for disabling the operational burner on detection of such a loss of pressure.

5. A gas fired twin burner cooker as claimed in any one of Claims 2 to 4, in which the first control apparatus includes means for operating both burners together and disabling both burners on detection of a change of pressure in relation to either one of the burners.

6. A gas fired twin burner cooker as claimed in any one of the preceding claims in which the boiler burner is located at the base of the boiler and is operable to fire horizontally into a chamber located at the base of the boiler, the chamber extending from the front of the boiler to the rear, and the cooker burner is located and operable to fire vertically upwards into a separate chamber towards the hot plate.

7. A gas fired twin burner cooker as claimed in Claim 6, in which the boiler burner is of generally U-shaped construction and has a left hand water jacket, a right hand water jacket, a bottom water jacket bridging the left hand and right hand jackets, a central panel parallel to the left hand and right hand jackets and a plurality of baffles for the distribution of heat through the boiler.

8. A gas fired twin burner cooker as claimed in Claim 6 or Claim 7 in which the cooker burner chamber is generally trapezium shaped in horizontal cross section, and the base and walls of the chamber are insulated with ceramic insulation panels whereby heat transfer between the chamber and the boiler is substantially minimized.

9. A gas fired twin burner cooker as claimed in any one of the preceding claims, in which an air inlet is provided at the base of the cooker for supplying air to the burners, with a conduit being provided to channel air from the inlet to a plenum space beneath the burners from which they draw air as required for combustion purposes, the conduit being constructed from wire meshing and being insulated over all surfaces so as to reduce noise levels.

10. A gas fired twin burner cooker substantially as herein described with reference to and as shown in the accompanying drawings.