EP2837890A2 - Method for operating a gas oven and gas oven - Google Patents

Abstract

In a method for operating a gas oven, the latter has a muffle with a lower gas burner and with an upper gas burner, an electronic controller being provided for the control thereof for controlling two gas valves and for igniting the gas burners and for monitoring the flame. For a combined operation with top heat and bottom heat in the muffle of the upper gas burner and the lower gas burner are operated in alternation with each other with heating phases, advantageously always only one of the two gas burners at a time, so not simultaneously.

Description

Field of application and state of the art

The invention relates to a method for operating a gas oven and a correspondingly designed gas oven.

There are known electronic controls for gas ovens that generate a spark via a spark plug to ignite the gas burner. It can also take over flame monitoring.

Task and solution

The invention has for its object to provide an aforementioned method and a gas oven suitable for its implementation, with which problems of the prior art can be avoided and it is particularly possible to operate a gas oven in a comfortable and diverse manner with a not too complicated control.

This object is achieved by a method having the features of claim 1 and by a gas oven with the features of claim 14 and 15. Advantageous and preferred embodiments of the invention are the subject of further claims and are explained in more detail below. Some of the features are described only for the process or only for the gas oven. However, they should be able to apply independently for both the process and for the gas oven independently. The wording of the claims is incorporated herein by express reference.

The gas oven has a muffle as an interior space, in which an upper gas burner and at the bottom a lower gas burner are arranged at the top. Furthermore, it is advantageous to provide a thermostat which is known per se for controlling the temperature in the muffle. The gas oven has any electronic control, for example with a DSI (Direct Spark Ignition) system, to control the gas burners and their gas valves. Thus, an associated gas valve can be controlled per gas burner. Furthermore, the electronic control can be designed to ignite the gas burners, in particular with a spark plug on the gas burner.

According to the invention for an operating mode with top heat and bottom heat, so a so-called combination operation, the upper gas burner and the lower gas burner in the muffle operated alternately, so advantageous with each heating phases, and particularly advantageous rest periods at each gas burner between the heating phases. This means that the upper gas burner and the lower gas burner are not in operation at the same time, as this could cause problems with the combustion conditions in the muffle or ignition problems or extinction of the flame at the upper gas burner could occur due to lack of fresh air supply and air turbulence on the upper gas burner by the combustion gases of the lower gas burner. Nevertheless, this combination operation with alternating operation of the upper and lower gas burner has the great advantage that a food can be supplied from above and from below heat. In particular, in such a combined operation, an upper heating device is operated in the manner of a grill or with the effect of a grill, since food to be cooked is usually not covered on its upper side. Due to the changing operation, a desired temperature for the food to be cooked in the muffle can be kept in all cases without any problems, which can be set and monitored by a thermostat or temperature controller. So it is thus ensured that a desired temperature in the muffle prevails for the cooking process. Furthermore, it is also possible, phase-wise and over a significant period of time or up to half of the duration of the entire cooking process to supply the food from above heat in the manner of an aforementioned grill.

Such controls for gas ovens are well known under the keyword Direct Spark Ignition. With these controls, single or double solenoid valves can be controlled, wherein advantageously the gas valves are not proportional valves, but are designed only for opening and closing. Thus, with such a DSI, one or two gas burners can be operated in one or two cavities of a gas oven. The DSI can open and close the solenoid valves to supply the gas burner with gas. Furthermore, the DSI advantageously generates a spark on the gas burner via an ignition plug to ignite the gas. Even a flame monitoring can be taken over by the controller or the DSI, and this can be done advantageously via a Ionisationsstrommessung. These latter two functions can also be taken over by a differently designed electronic control.

An advantageous electromechanical regulator may be a thermostat. It can be set mechanically to a specific preset temperature and then switches on when it is exceeded Fall below this preset temperature with a certain hysteresis. In any case, it does not provide any permanent signals that correspond to the measured temperature, but switches at a predetermined temperature or signal their exceeding or falling below. When using a so-called DSI, the use of such a thermostat is advantageous because it only switches the mains voltage to the corresponding input of the DSI. By contrast, when using a fully electronic control, the temperature in the muffle is measured by a thermistor, and the control derives the heating demand from the comparison of desired and actual temperature. However, the operation of the invention is conceivable in both versions.

In an advantageous embodiment of the invention, the upper gas burner and the lower gas burner are always operated alternately or always successively. This means that after a certain period of operation of the upper gas burner the lower gas burner is operated and no other, and then again the upper gas burner. On the one hand, this can always take place in succession in the manner of a replacement continuous power generation. Alternatively and advantageously, between each heating phase of the gas burner, so either the upper gas burner or the lower gas burner, a resting phase without operation of the gas burner is inserted. This can be used especially when using an aforementioned thermostat or an electromechanical thermostat, for example, that the heating of the muffle is slow or again with short periods of rest between the heating phases to allow a more accurate temperature measurement through the thermostat. Likewise, after the operation of one of the gas burners, the conditions in the muffle can normalize and also create disturbing turbulences until the other gas burner is then ignited.

Advantageously, is changed during a heating phase after a certain time of a gas burner to the other gas burner. This can still be provided when heating the gas oven or the muffle. Although it can be provided a short break without heating between two so-called partial heating phases of the gas burner, but this need not be. Due to the alternating operation of the two gas burners even during the heating of the muffle a uniformly distributed heating is ensured.

In an embodiment of the invention, a thermostat for the temperature control have a cycle time. In the event that a heating phase of the gas burner, especially when heating the muffle, is shorter than the cycle time of the thermostat, even after a heating phase for heating in continuous operation of the gas burner, a change of the gas burner during a thermostatic cycle done. Thus, the special circumstances here can be taken into account.

In an advantageous embodiment of the invention, a change in the operating mode of the gas oven from a pure bottom heat operation with only the lower gas burner or a pure top heat operation with only the upper gas burner on a common operation or combined operation of both gas burners with change between the be made both gas burners. In this case, a currently operated gas burner can still be operated until the end of a cycle or the thermostatic cycle before, if necessary, after a short rest period, is changed to the other gas burner. Thus, the operation of the gas burner or a heating or an increase in the temperature in the muffle is interrupted as little as possible.

Alternatively, when changing the operating mode as previously explained for a change between the gas burners of previously operated gas burner can be switched off immediately. Either directly or advantageously after a certain waiting time then the other gas burner is ignited. This is for both a previous bottom heat operation and a previous top heat operation.

In one embodiment of the invention it can be provided that, in the event that a change of the operating mode of the gas oven takes place during a rest phase of the gas burner, the next time the thermostat is switched to the other gas burner used last. This is then seen again over a long period of time always made a change of the gas burner.

The variation of the cycle time is only advantageous up to a certain point. If a cycle time becomes too long, it can happen that a food is only heated from one side for a very long or even too long and thus unevenly. This in turn may be undesirable. Especially during a heating process, this can happen.

Due to an awkward ratio of the cycle time of the temperature control and the cycle time of the alternating operation, it can also happen that one burner is operated for the desired cycle time, but the other burner is interrupted after a few seconds by the end of the heating cycle. This would create an unevenness between the two types of heating. This can be counteracted by the fact that the open cycles of the alternating operation accordingly in the next heating cycle of the temperature control be continued or made up as compensation. Thus, an arbitrary distribution of change cycles within thermostat cycles may result.

These and other features will become apparent from the claims but also from the description and drawings, wherein the individual features each alone or more in the form of sub-combination in one embodiment of the invention and in other areas be realized and advantageous and protectable Represent embodiments for which protection is claimed here. The subdivision of the application into individual sections as well as intermediate headings does not restrict the general validity of the statements made thereunder.

Brief description of the drawings

Fig. 1

eine schematische Darstellung eines Gasbackofens,

Fig. 2

das Schaltbild eines Gasbackofens gemäß Fig. 1 mit einem DSI-System und

Fig. 3 bis 11

verschiedene mögliche Wechselbetriebe von Gasbrennern in dem Gasbackofen.

Embodiments of the invention are shown schematically in the drawings and are explained in more detail below. In the drawings show:

Fig. 1

a schematic representation of a gas oven,

Fig. 2

the diagram of a gas oven according to Fig. 1 with a DSI system and

Fig. 3 to 11

various possible change operations of gas burners in the gas oven.

Detailed description of the embodiments

In Fig. 1 schematically, a baking oven 11 is shown with a muffle 12, in which an upper gas burner 14 and a lower gas burner 16 are arranged. The gas burners 14 and 16 are formed as generally known in the art. The upper gas burner 14 is supplied via a gas valve 18 and the lower gas burner 16 via a gas valve 20, wherein the two gas valves can be physically or constructively integrated in a structural unit. In addition, two gas valves can be connected in series in a burner string in order to meet the operational safety requirements in the event of malfunction of a gas valve. The gas valves 18 and 20 are connected to a controller 22 of the gas oven 11, which can operate electromechanically or electronically and is designed accordingly or consists of one or more components. Furthermore, a temperature sensor is still provided in the muffle 12, which is advantageous as an electromechanical thermostat 24 or thermistor is trained. It is connected to the controller 22 and provides this in a known manner a signal.

In the Fig. 2 a circuit diagram for a gas oven 11 with DSI system is shown as a control. At the gas burners 14 and 16 here spark plugs 26 and 28 are shown for ignition. The spark plugs 26 and 28 are connected to a DSI 34. Thermocouples are not provided here because the flame is monitored by known ionization current measurement. Furthermore, the gas oven 11 and its controller 22 still a switch for selecting the baking mode, a thermostat 24 for temperature control via the temperature sensor, a timer 36, a door switch 38, a furnace lamp 40 and a power indicator 42.

In a lower heat mode, the output of the thermostat 24 is switched through the corresponding switching path of the selector switch on a so-called heat request channel of the DSI 34, which is associated with the lower gas burner 16. If mains voltage is present at the heat request channel, the gas valve of the corresponding burner is opened and the ignition is initiated. In the upper heat mode, the output of the thermostat is switched to the heat request channel of the DSI 34, which is assigned to the upper gas burner 14. In the combined mode with top heat and bottom heat the output of the thermostat 24 is switched to both heat request channels of the DSI 34. Then an alternating operation between the gas burners 14 and 16 is carried out, that is, when both heat request channels are simultaneously energized or switched delayed by fractions of a second. In this case, according to the invention, only one of the two gas burners ignited, since never both should be operated together. The selection of the gas burner can be arbitrary or according to predetermined programming. This can be, for example, based on the Fig. 3 seen.

In the Fig. 3 the temperature in the muffle 12 is plotted on the vertical axis, namely at a center of gravity. The line "Active burner" shows which of the two gas burners 14 or 16 is operated or is active. The middle row stands for Heat Request top heat and the bottom row stands for Heat Request bottom heat. Both signal the input to the respective gas burner 14 or 16 at the DSI 34.

According to Fig. 3 At first only the upper gas burner 14 is operated for a top heat OH. For this purpose, it is ignited by the spark plug 26 and supplied by the gas valve 18 with gas. Because the Gas valves 18 and 20 are advantageous generally not proportional valves, but only fully open or close completely, the gas burners can only work with a fixed predetermined instantaneous power, namely their full power or rated power. In the alternative procedure according to Fig. 4 It can be seen how to start with the lower gas burner 16 is started as a bottom heat UH, which is ignited by the spark plug 28 and supplied by the gas valve 20 with gas. Which of the two gas burners 14 or 16 is used first can be stored either deliberately in a software in the controller 22. Alternatively, it can be selected at random.

From the representations of 3 and 4 It can be seen that first only the first started gas burner is active for a time. Then it is switched off for a rest phase, in particular when the temperature has reached a value detected by the thermostat 24 and predetermined by a control element according to the request of an operator. Then there is a phase or resting phase without heating, as is generally known in two-point controllers. This is followed by an operating phase with heating of the muffle 12, but of course with the other gas burner.

From the two bottom lines along the X-axis can be seen that during the operating phases in each case for both gas burners 14 and 16, a heat request is present. The controller 22 or the DSI 34 then turns on the gas burners but alternately.

Furthermore, it is known that a cycle time or cycle time t _{T, T} or _{T, from} the thermostat of its hysteresis, a position of the thermostat sensor in the muffle 12, the thermal insulation of the furnace 11 and the muffle 12, the heating power and the given temperature depends. Thus, a cycle time of the thermostat can vary, as from the Fig. 5 can be seen with a relatively long cycle time. In comparison, lie in the 3 and 4 short cycle times and thus also a smaller fluctuation of the temperature. With such long cycle times, however, there is the danger that a food to be cooked will only heat from one side and thus unevenly for a relatively long time. This should be avoided. This is not only the case with relatively long cycle times according to the Fig. 5 the case, but of course also when heating, especially if according to the Fig. 3 and 5 the heating is started with the upper gas burner 14 or upper heat, since the risk of burns is particularly great here.

In order to avoid such a long uneven heat input, in a further embodiment of the invention may be just provided that the gas burner after a set or predetermined time to be changed. This is in the Fig. 6 shown for a thermostat with a relatively long cycle time. Here is either controlled or arbitrarily started with one of the gas burner 14 or 16, in the Fig. 6 just with the lower gas burner 16 as bottom heat UH. This is operated for a stored in the program flow of the controller 22 time t _{UH, a} . This can be, for example, 30 seconds to 120 seconds. Thereafter, the lower gas burner 16 is cleared and followed by a short waiting time t _UH, as a resting phase. During this time, the atmosphere normalizes in the muffle 12, so that the upper gas burner 14 can easily ignite and operate, for a time t _{OH, a} . This is in turn followed by a rest period as a waiting time t _{OH, off} . These four times are selected according to the conditions in the gas oven 11 and the muffle 12 and a desired ratio between top heat OH and bottom heat UH. In the case that the time t _{UH, one} shorter than the cycle time t _{T, one of} the thermostat, as in the Fig. 6 is shown, takes place not only during heating, but also in the steady state, a change of the gas burner. This is just in the Fig. 6 to recognize with a change from the lower gas burner 16 to the upper gas burner 14 during the cycle time t _{T, a} . This is thus a relatively long thermostatic cycle as previously described. However, if the time t _{UH, one} or the time t _{OH, one} greater than the cycle time t _{T, a} , so there is no change within a Thermostatsyklus, but until the next cycle. This is in the Fig. 7 can be seen in the after the heating phase during a relatively short Thermostatzyklus t _{T, a} respective only one of the two gas burners 14 or 16 is operated.

Alternatively, however, it is also possible that a change cycle of a gas burner, which was interrupted before its completion by the cycle of the thermostat, is made up in the next cycle. This results in an arbitrary distribution of the cycles within the thermostat cycles, see Fig. 11 ,

In the Fig. 8 is shown how a change of the operating mode of the gas oven 11 takes place. At the beginning, there is a bottom heat operation only with the lower gas burner 16. If, during a cycle time t _{T, a} transition from the operating mode of lower heat to a combined operation to a dashed vertical drawn time, so in a first alternative, the currently operated burner can continue to operate until the end of the clock. In the Fig. 8 namely, it can be seen that during the second switching on of the lower gas burner 16 there is already a heat request for top heat OH. Alternatively, it is also possible that the previously operated gas burner, here the lower gas burner 16, is switched off immediately. Then the other gas burner, here the upper gas burner 14, after a waiting or rest phase be ignited to calm the conditions in the muffle 12. This is in the Fig. 9 to see.

If a change takes place between the gas burners 14 and 16 during the time t _T, then the next time the thermostat is switched on, not the last used gas burner is operated, but the other one. This is at the time of the vertical dashed line in the Fig. 10 clearly visible. Then there is a heat request for the top heat OH and it is operated directly or fired the upper gas burner 14 as an active burner.

In a further further development of the invention, it is also conceivable that during the program run t _{T, on} and t _T, measured _from and calculated from the optimal values for the other four times described. In addition, even in the best case, the times t _{OH, off} and t _{UH, a} near zero, so as not to interrupt a heat supply unnecessarily long.

If, instead of the electromechanical thermostat together with the thermostat sensor 24, an electronic control is used, that is to say without DSI, with a temperature-dependent resistance as the temperature sensor, it is possible to continuously access measured values of the temperature sensor. It is not dependent on the signals "on" or "off" as supplied by a thermostatic thermostat.

Claims (15)

Method for operating a gas oven, wherein the gas oven has a muffle with a lower gas burner and with an upper gas burner, wherein for controlling the gas burner, an electronic control is provided for controlling gas valves and for igniting the gas burner and for flame monitoring, characterized in that for a mode with top heat and bottom heat in the muffle of the upper gas burner and the lower gas burner are operated in alternation. A method according to claim 1, characterized in that a temperature control takes place in the gas oven via an electromechanical thermostat or temperature controller. A method according to claim 1 or 2, characterized in that the upper gas burner and the lower gas burner are always operated alternately and always successively. Method according to one of the preceding claims, characterized in that always only the upper gas burner is operated or only the lower gas burner is operated without simultaneous operation of the two gas burners. Method according to one of the preceding claims, characterized in that between each heating phase of either the upper gas burner or the lower gas burner, a resting phase without operation of a gas burner is inserted. Method according to one of the preceding claims, characterized in that is changed during a heating phase after a certain time from one gas burner to the other gas burner. A method according to claim 6, characterized in that this takes place during heating of the gas oven or the muffle, in particular with a short rest phase without heating between two heating phases of the gas burner. Method according to one of the preceding claims, characterized in that a thermostat for the temperature control has a cycle time and in the event that a heating phase of the gas burner is shorter than the cycle time of the thermostat, even after a heating phase for heating in continuous operation of the gas burner, a change of the gas burner takes place during a thermostatic cycle. A method according to claim 8, characterized in that this takes place during heating of the muffle. Method according to one of the preceding claims, characterized in that a thermostat for the temperature control has a cycle time and in the event that a heating phase of the gas burner takes place in the change of the gas burner during a Thermostatzyklus, remaining after the interruption of the Thermostatzyklus remaining time of a burner the next cycle of thermostats. Method according to one of the preceding claims, characterized in that when changing the operating mode of the gas oven from a bottom heat operation only the lower gas burner or a top heat operation only the upper gas burner on a common operation of both gas burner with the change between the gas burners currently operated gas burner continues to operate until the end of a cycle or the thermostatic cycle. Method according to one of claims 1 to 10, characterized in that when changing the operating mode of the gas oven from a bottom heat operation only the lower gas burner or a top heat operation only the upper gas burner on a common operation of both gas burner with the change between the gas burners the previously operated gas burner is switched off immediately and ignited after a certain waiting time of the other gas burner. A method according to claim 11 or 12, characterized in that in the event that a change of the operating mode of the gas oven takes place during a rest phase of the gas burner, the next time the thermostat is operated the other than the last used gas burner. Gas oven for carrying out the method according to one of the preceding claims, comprising a muffle, in which an upper gas burner and a lower gas burner are arranged at the bottom and a temperature sensor is provided for temperature control in the muffle, wherein the gas oven has an electronic control. Gas oven for carrying out the method according to one of claims 1 to 13, with a muffle, in which an upper gas burner and a lower gas burner are arranged below and a thermostat is provided for controlling the temperature in the muffle, wherein the gas oven has a control, in particular a electronic control that activates the lighting of the corresponding gas burner after wiring the corresponding input with mains potential.

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