The present invention relates to a method of operating a dual circuit gas burner. It further relates to a control unit for adjusting a gas flow to a dual circuit gas burner, to a dual circuit gas burner and to a gas stove.

In gas cooking appliances, it is common to use dual circuit gas burners including an inner and an outer burner ring. Such dual circuit gas burners generally possess a greater maximum burner power than gas burners with a single burner ring. Further, dual circuit gas burners can have an especially large spread between minimum burner power and maximum burner power.

US 2013/0056663 A1 shows an example of a dual circuit gas burner and of a corresponding gas valve unit, which allows first opening a gas outlet to the inner burner and subsequently opening a gas outlet to the outer burner while the flames of the inner burner are burning at their maximum size.

In dual circuit gas burners, there are cases in which the inner burner ring takes away the secondary air of the outer burner ring, leading to bad combustion and to flame disappearance at the outer burner ring.

It is one object of the present invention to provide an improved dual circuit gas burner.

According to a first aspect, a method of operating a dual circuit gas burner including an inner and an outer burner ring surrounding the inner burner ring is provided. The method includes: opening a gas flow to the outer burner ring while maintaining a gas flow to the inner burner ring closed during a predetermined period of time.

Opening a gas flow to the outer burner ring while maintaining a gas flow to the inner burner ring closed allows increasing the quantity of secondary air provided to the outer burner ring. This ensures that the outer burner receives enough secondary air for combustion and in particular prevents that the flame at the outer burner ring extinguishes. In detail, it can be prevented that the inner burner ring affects the flow of secondary air to the outer burner ring. Thereby, a balanced secondary aeration can be achieved at the outer burner ring. A combustion reliability of the outer burner ring can be improved. A safety of the dual circuit gas burner is increased because it can be ensured that the flame does not extinguish while gas is flowing.

As used herein, the gas (in particular, the gas provided in the gas flow) provided to the inner and/or outer burner ring comprises a fuel gas. In particular, the gas (in particular, the gas provided in the gas flow) can be a mixture of a fuel gas, such as acetylene, natural gas or propane, with an oxidizer, such as ambient air, supplied oxygen or the like. Such a gas mixture can be referred to as a combustible gas mixture. Preferably, the gas (in particular, the gas provided in the gas flow) is not solely made of ambient air.

As used herein, primary air is the air which is to be mixed with the gas for providing a combustible gas mixture before the combustion. In particular, such a mixing may be carried out below a plate, in particular top sheet, of a gas stove on which the dual circuit gas burner is arranged. The primary air and the gas may be mixed in a Venturi tube. As used herein, secondary air is the air which is provided during combustion for maintaining the combustion. A deficiency of secondary air may lead to a lapse of the flames.

The dual circuit gas burner is also referred to as "the gas burner" in the following. The dual circuit gas burner can be a double crown burner. The dual circuit gas burner can be construed as a gas burner configured to provide at least circularly arranged outer flames (with the outer burner ring) and circularly arranged inner flames (with the inner burner ring). Circularly arranged outer and inner burner rings can be construed as a double crown. The outer and inner burner rings can be circular, rectangular, hexagonal, octagonal, elliptical, kidney shaped and the like when looking from above. Preferably, the outer and inner burner rings are arranged concentrically. In particular, gas outlet openings of the outer burner ring and gas outlet openings of the inner burner ring are arranged concentrically. The term "outer" can also be referred to as a "external" and the term "inner" can also be referred to as "internal". The gas burner may include more than two rings. Opening a gas flow to the outer burner ring in particular means that a gas (preferably a combustible gas mixture) is provided to the outer burner ring. Upon reaching the outer burner ring, the gas may be ignited and form flames at the gas outlet openings of the outer burner ring.

During the predetermined period of time, the gas flow to the inner burner ring is closed. This in particular means that no gas is provided to the inner burner ring during the predetermined period of time. This means that no flames are formed at the gas outlet opening of the inner burner ring.

Expressed differently, during the predetermined time period, while the outer burner ring is provided with gas, the inner burner is not provided with gas. The outer burner ring provides a flame while the inner burner ring does not provide a flame. In particular, the state in which the gas flow to the outer burner ring is opened while the gas flow to the inner burner ring is maintained closed is a normal operating state of the gas burner and is not a state in which one of the burner rings is malfunctioning.

The predetermined period of time may be any duration during which the gas flow to the outer burner ring is open while the gas flow to the inner burner ring is closed. The duration of the predetermined period of time can be preset, for example in accordance with experiments determining a duration of the predetermined period of time for which the best combustion at the outer burner ring and/or the best secondary air balance is achieved. Alternatively, the predetermined period of time may vary depending on an operation of the dual circuit gas burner by a user thereof. In particular, the predetermined period of time may have a minimum duration, which is for example preset. The predetermined period of time may be between 3 and 20 seconds, preferably between 5 and 10 seconds.

For example, the predetermined period of time is a duration between an outer burner opening time at which the gas flow to the outer burner ring is opened and an inner burner opening time at which the gas flow to the inner burner ring is opened.

According to an embodiment, the method further includes: opening a gas flow to the inner burner ring at an inner burner opening time which is the predetermined period of time later than an outer burner opening time at which the gas flow to the outer burner ring is opened.

Opening a gas flow to the inner burner ring in particular means that a gas (preferably a combustible gas mixture) is provided to the inner burner ring. Upon reaching the inner burner ring, the gas may be ignited and form flames at the gas outlet openings of the inner burner ring.

The gas flow to the inner burner ring is opened after a predetermined period of time has elapsed since the outer burner opening time, thereby ensuring a balanced secondary air flow. In particular, it can be ensured that the outer burner ring has had sufficient time to provide stable flames and that ignition of flames at the inner burner will not extinguish the flames at the outer burner.

According to a further embodiment, at the inner burner ring opening time, the outer burner ring is at a maximum opening state or at a predetermined intermediate opening state.

The maximum opening state of the outer burner ring can be a state at which a gas flow to the outer burner ring is maximum, leading to the largest possible flames on the outer burner ring. The predetermined intermediate opening state of the outer burner ring can be a state at which a gas flow to the outer burner ring is above minimum but below maximum, leading to flames of intermediate size on the outer burner ring. In particular, the larger the flames at the time of opening the inner burner ring, the more stable they are and the more unlikely they are to extinguish.

According to a further embodiment, the method according further includes: varying the gas flow to the outer burner ring during the predetermined period of time.

Preferably, during the predetermined period of time, the gas burner can be used normally for cooking purposes, but only with the outer burner ring. In particular, during the predetermined period of time, the gas flow to the outer burner ring is varied in accordance with a user's setting. According to a further embodiment, the step of varying the gas flow to the outer burner ring during the predetermined period of time includes: increasing the gas flow to the outer burner ring during a first portion of the predetermined period of time; and decreasing the gas flow to the outer burner ring during a second portion of the predetermined period of time which is subsequent to the first portion.

According to a second aspect, a control unit for adjusting a gas flow to a dual circuit burner including an inner and an outer burner ring is provided. The control unit includes a gas valve unit including: an adjustable outer burner outlet for adjustably providing the outer burner ring with gas; and an adjustable inner burner outlet for adjustably providing the inner burner ring with gas; wherein the gas valve unit is configured to open the adjustable outer burner outlet to provide the outer burner ring with a gas flow while maintaining the adjustable inner burner outlet closed during a predetermined period of time.

In particular, the gas valve unit can include one or two valves. The gas valve unit may be realized as an electromagnetic valve unit (with one or two electromagnetic valves). The valve(s) selectively open or close the adjustable outer burner outlet and the adjustable inner burner outlet to allow gas flowing out of the adjustable outer and inner burner outlets. The adjustable outer burner outlet can be connected to the outer burner ring, for example through a pipe, so that when gas flows out of the adjustable outer burner outlet, it is lead to the outer burner ring for combustion. Similarly, the adjustable inner burner outlet can be connected to the inner burner ring, for example through a pipe, so that when gas flows out of the adjustable inner burner outlet, it is lead to the inner burner ring for combustion.

Advantageously, the gas valve unit allows opening a gas flow to the outer burner ring while maintaining a gas flow to the inner burner ring closed, thereby increasing the quantity of secondary air provided to the outer burner ring. This ensures that the outer burner receives enough secondary air for combustion and in particular prevents that the flame at the outer burner ring extinguishes. In detail, it can be prevented that the inner burner ring affects the flow of secondary air to the outer burner ring. Thereby, a balanced secondary aeration can be achieved at the outer burner ring. A combustion reliability of the outer burner ring can be improved. This allows improving a safety of the dual circuit gas burner because it can be ensured that the flame does not extinguish while gas is flowing.

The order in which the gas valve unit opens and closes the adjustable burner outlets can be preprogrammed and/or controlled in line with a stored curve or table, or mechanically predefined by the manner the gas valve unit functions.

According to an embodiment, the control unit is configured to operate according to the method of the first aspect or of any embodiment thereof.

The embodiments and features described with reference to the method of the first aspect apply mutatis mutandis to the control unit of the second aspect.

According to a further embodiment, the control unit further includes: a control knob which is rotatable by a user; wherein the adjustable outer burner outlet and the adjustable inner burner outlet are configured to adjust their gas outlets to the outer and inner burner rings as a function of the position of the control knob.

Preferably, the quantity of gas output to the inner and outer burner rings depends on the position of the control knob. In particular, the quantity of gas output to the inner and outer burner rings depends solely on the position of the control knob. For example, each position of the control knob (discrete position or not) corresponds to a particular opening state of the adjustable outer burner outlet and to a particular opening state of the adjustable inner burner outlet.

According to a further embodiment, the gas valve unit is configured to vary a total gas flow to the inner burner ring and the outer burner ring smoothly upon rotation of the control knob. Smoothly in particular means that there are no sudden jumps in the quantity of gas output to the inner and outer burner rings upon rotation of the control know. Preferably, when the control knob is rotated in one direction, the total gas flow increases smoothly while when the control knob is rotated in the opposite direction, the total gas flow decreases smoothly.

According to a further embodiment, the predetermined period of time is defined by a duration at which the control knob is maintained in a position corresponding to opening the adjustable outer burner outlet while maintaining the adjustable inner burner outlet closed.

According to a third aspect, a dual circuit gas burner for a gas stove is provided. The dual circuit gas burner includes: the control unit according to the second aspect or any embodiment thereof; an inner burner ring connected to the adjustable inner burner outlet and configured to receive gas in accordance with an opening state of the adjustable inner burner outlet; and an outer burner ring connected to the adjustable outer burner outlet and configured to receive gas in accordance with an opening state of the adjustable inner burner outlet.

The embodiments and features described with reference to the control unit of the second aspect or any embodiment thereof apply mutatis mutandis to the dual circuit gas burner of the third aspect.

According to a fourth aspect, a gas stove having a dual circuit gas burner according to the third aspect, and a plate having an upper surface on which the dual circuit gas burner is mounted is provided.

The embodiments and features described with reference to the dual circuit gas burner of the third aspect or any embodiment thereof apply mutatis mutandis to the gas stove of the fourth aspect.

Further possible implementations or alternative solutions of the invention also encompass combinations - that are not explicitly mentioned herein - of features described above or below with regard to the embodiments. The person skilled in the art may also add individual or isolated aspects and features to the most basic form of the invention. Further embodiments, features and advantages of the present invention will become apparent from the subsequent description and dependent claims, taken in conjunction with the accompanying drawings, in which:

Fig. 1 shows a gas stove according to an embodiment;

Fig. 2 shows a dual circuit gas burner according to an embodiment;

Fig. 3 shows a control unit according to an embodiment;

Fig. 4 shows an operation of a gas burner known from the prior art;

Fig. 5 shows a method of operating a dual circuit gas burner according to an embodiment;

Fig. 6 shows an operation of a gas burner according to a first example;

Fig. 7 shows an operation of a gas burner according to a second example; and

Fig. 8 shows an operation of a gas burner according to a third example.

In the Figures, like reference numerals designate like or functionally equivalent elements, unless otherwise indicated.

Fig. 1 shows a gas stove 100 viewed from above. The gas stove 100 includes a plate 101 with an upper surface 102. Four dual circuit gas burners 1 are arranged on the upper surface 102. The gas burners 1 are different in size but their operation is identical. The upper surface 102 further has four control knobs 103 arranged thereon, which can be rotated by a user to adjust the gas flow to the respective gas burners 1 , as will be explained further below.

Fig. 2 shows an example of a dual circuit gas burner 1 for the gas stove 100 of Fig. 1. The gas burner 1 shown in Fig. 2 includes an outer burner ring 2 having a circular shape.

Outer gas outlet openings 3 are arranged along an outer perimeter of the outer burner ring 2 such as to emit flames radially outwards. The gas burner 1 of Fig. 2 further includes an inner burner ring 4 having a circular shape. Inner gas outlet openings 5 are arranged along an outer perimeter of the inner burner ring 4 such as to emit flames radially outwards.

Fig. 3 shows a control unit 20 for adjusting a gas flow to the gas burner 1. The control unit 20 includes a gas valve unit 14. The gas valve unit 14 comprises a main gas line 6 providing gas or a gas mixture to the gas burner 1. A main gas valve 7 is arranged in the main gas line 6. A branch line 8 to the outer burner ring 2 and a branch line 9 to the inner burner ring 4 branch off from the main gas line 6 downstream of the main gas valve 7. In each of the branch lines 8, 9 there is an on/off valve 10, which can be designed as a solenoid valve, for example, as well as a control valve 11. With the control valve 11, the opening cross-section of the respective branch line 8, 9 and thus the size of the gas flow to the external burner 2 or to the internal burner 4 can be adjusted steplessly or in several stages.

The control valves 11 can, for example, each be driven by a stepper motor. In addition to adjusting the opening cross-section in each of the branch lines 8, 9, it is also possible to clock the gas flow in the branch lines 8 and/or 9. This means that the gas flow to the outer burner ring 2 or to the inner burner ring 4 is completely interrupted and reopened at predetermined times. This can be done, for example, by opening and closing the on/off valve 10 or by opening and closing the control valve 11 in the corresponding branch line 8, 9.

Accordingly, the valves 10, 11 of the branch line 8 to the outer burner ring 2 allow to adjustably provide the outer burner ring 2 with gas. This gas is provided through an adjustable outer burner outlet 16 located on the branch line 8 downstream of the valve 11. Further, the valves 10, 11 of the branch line 9 to the inner burner ring 4 allow to adjustably provide the inner burner ring 4 with gas. This gas is provided through an adjustable inner burner outlet 15 located on the branch line 9 downstream of the valve 11.

The main gas valve 7 as well as the on/off valves 10 and the control valves 11 are controlled by means of a preferably electronic control unit 12, which is connected to the valves 7, 10, 11 via control lines 13. The electronic control unit 12 can be coupled to the control knob 103 and send a control signal through the control lines 13 as a function of the position of the control knob 103 set by the user, thereby selecting the gas flow to the outer and inner burner 2, 4.

Fig. 4 shows an example of an operation of a gas burner 1 in the prior art. Fig. 4 comprises three parts: (a), (b) and (c), wherein part (a) represents the power (in kW) of the outer burner ring 2, part (b) represents the power (in kW) of the inner burner ring 4, and part (c) represents the total power (in kW) of the gas burner 1 , namely an addition of the power of both burner rings 2, 4. The power output by the burner 1 and the burner rings 2, 4 is proportional to the gas flow provided to the burner 1 and burner rings 2, 4.

The horizontal axis of Fig. 4 shows an evolution of the operation of the gas burner 1 as the control knob 103 is rotated. On the leftmost point of Fig. 4, the gas burner 1 is "OFF", which indicates that no gas is reaching the inner or outer burner 2, 4. Upon rotating the control knob 103, the gas burner 1 is turned on. Upon turning on the gas burner 1 , the inner burner ring 4 is provided with gas and continuously maintained with gas while the outer burner ring 2 is provided with gas. In other words, a gas flow to the inner burner ring 4 is open at all times while the gas flow to the outer burner ring 2 is open. When the gas flow to the outer burner ring 2 is open, the gas flow to the inner burner ring 4 is at its maximum Max(b).

In zone Z1 of Fig. 4, through rotation of the control knob 103, the gas flow to the outer gas burner 2 is increased until the outer burner ring 2 reaches its maximum Max(a). The total power of the gas burner 1 is maximum Max(c) when the outer burner ring 2 reaches its maximum Max(a).

In zone Z2 of Fig. 4, rotating the control knob 103 further will decrease the gas flow to the outer burner ring 2 until the outer burner ring 2 is turned off. The gas burner 1 is then at its intermediate operation state "Int". To decrease the power of the gas burner 1 even further, in zone Z3, the outer burner ring 2 is kept off, while the power to the inner burner ring 4 is reduced until the gas burner 1 reaches its minimum power "Min".

In the operation of the gas burner 1 known from the prior art and shown in Fig. 4, the gas flow to the inner burner ring 4 is always open when the gas flow to the outer burner ring 2 is open. The inner burner ring 4 can however disturb the secondary air flow to the outer burner ring 2. As a result, there is a risk that the flame at the outer burner ring 2 is extinguished due to the lack of secondary air.

To overcome this problem, the gas burner 1 is advantageously operated according to the operation method shown in Fig. 5.

In detail, according to step S1 of Fig. 5, a gas flow to the outer burner ring 2 is opened while maintaining a gas flow to the inner burner ring 4 closed during a predetermined period of time. This is achieved by keeping the valves 10, 11 of the branch line 9 to the inner burner ring 4 closed while opening the valves 10, 11 of the branch line 8 to the outer burner ring 2. Advantageously, it is prevented that the inner burner ring 4 interferes with the secondary air to the outer burner ring 2.

Optionally, in a step S2 shown in Fig. 6, the gas flow to the inner burner ring 4 is opened after the predetermined period of time has elapsed since the gas flow to the outer gas burner ring 2 was opened. This is achieved by opening the valves 10, 11 of the branch line 9 to the inner burner ring 4 while keeping the valves 10, 11 of the branch line 8 to the outer burner ring 2 open.

The control of the operation of the valves 10, 11 is performed by the control unit 12 in response to a position of the control knob 103.

Fig. 6 shows an example of an operation and power output of the gas burner 1. The structure of Fig. 6 is similar to that of Fig. 4, and in particular also includes three parts (a), (b) and (c) corresponding to the outer burner ring 2, the inner burner ring 4 and the entire gas burner 1. Fig. 6 further shows a time axis showing labels at which particular events occur, as will be detailed below.

As can be seen in Fig. 6, when the gas burner 1 is turned on at an outer burner opening time ti , only the gas flow to the outer gas ring 2 is opened, while the gas flow to the inner gas ring 4 remains closed. For a predetermined period of time T after the outer burner opening time ti , only the gas flow to the outer gas ring 2 is opened while the gas flow to the inner gas ring 4 remains closed. This corresponds to the state achieved through step S1 of Fig. 5 described above. During this predetermined period of time T, the gas flow to the outer burner ring 2 is varied: during a first portion T1, it is increased until it reaches its maximum Max(a), and during a second portion T2, it is decreased again.

At a time t ₂ , the predetermined period of time T has elapsed, which corresponds to a user rotating the control knob 103 beyond a predetermined position. The time t ₂ marks the opening of the gas flow to the inner burner ring 4 and can be designated as the inner burner opening time t ₂ . As a result, at and shortly after the inner burner opening time t ₂ , the total power to the gas burner 1 increases again. Upon rotating the control knob 103 further, the gas flow to the outer burner ring 2 is decreased further while the gas flow to the inner burner ring 4 remains constant. This results in a decreasing power of the gas burner 1. The gas flow to the outer burner ring 2 decreases until it is entirely off ("Int" state in Fig. 6). Then, upon rotating the control knob 103 further, the gas flow to the inner burner ring 4 is reduced further until it reaches its minimum Min.

The operation of the gas burner 1 shown in Fig. 6 is a mere example and different operations are possible, as shown in Fig. 7 and 8, for example.

In the example of Fig. 7, the inner burner ring 4 is opened at the time at which the gas flow to the outer burner ring 2 is maximum Max(a). As a result, the total maximum Max(c) output of the gas burner 1 is higher than in the example of Fig. 6, because the addition of the power of the inner burner ring 4 to power of the outer burner ring 2 occurs before the power of the outer burner ring 2 is decreased again. This results in a smoother operation curve as compared to the curve of Fig. 6.

The example of Fig. 8 is similar to the example of Fig. 6, wherein the power through the outer burner ring 2 is set such as to be the same as the power of opening the inner burner ring 4. This results in a smoother operation curve as compared to the curve of Fig. 6.

Although the present invention has been described in accordance with preferred embodiments, it is obvious for the person skilled in the art that modifications are possible in all embodiments. For example, the control unit 20 can be different from the control unit shown in Fig. 3. In particular, the control unit 20 may include only the valves 11 but not the valves 10. Reference Numerals:

1 dual circuit gas burner

2 outer burner ring

3 outer gas outlet opening

4 inner burner ring

5 inner gas outlet opening

6 main gas line

7 main gas valve

8, 9 branch line

10 on/off valve

11 control valve

12 control unit

13 control line

14 gas valve unit

15 adjustable inner burner outlet

16 adjustable outer burner outlet

20 control unit

100 gas stove

101 plate

102 upper surface

103 control knob ti outer burner opening time tz inner burner opening time

T predetermined period of time

T 1 first portion

T2 second portion

S1 , S2 method steps