EP3863372B1 - Cooking hob and method for controlling a heating device of a cooking hob - Google Patents

Description

Area of application and state of the art

The invention relates to a method for controlling a heating device of a hob or a cooking appliance and a corresponding hob or cooking appliance. The hob has a radiant heating device as a heating device, a hob plate above it and a safety temperature limiter between the two. Such a safety temperature limiter is designed as a thermomechanical functional device in order to deactivate the radiant heating device when the temperature is too high or a switch-off temperature is reached. This serves in particular to protect the hob plate from damage caused by excessive temperatures due to the heating output of the radiant heating device. Such safety temperature limiters are known from the prior art, for example from EP 1 569 257 A1 .

From the DE 60 2004 005 105 T2 a method for controlling a heating device of a hob is known, which should be able to detect abnormal temperature increases and then react appropriately to them. For this purpose, a temperature-sensitive device is provided as a resistance temperature sensor made of platinum, with which the temperature above the heating device and under a hob plate can be recorded. A second similar temperature-sensitive device is also provided. If an unusual, particularly rapid, increase in temperature is detected at the temperature-sensitive devices, heating output can be reduced.

From the EP 2 472 999 A1 Another similar method for controlling a heating device of a hob is known. An energy supply is to be monitored by means of a protective device, which detects a temperature on the top side of a hob plate or a cookware standing on it using a temperature sensor. If the temperature is too high, energy supply to the heating device can be limited.

The disadvantage of such safety temperature limiters is that, on the one hand, they function very reliably in the event that they detect a switch-off temperature that is too high. On the other hand, their switching behavior is determined directly by the temperature they detect, and changing the activation state of the radiant heating device due to processes in a cooking vessel on the hob plate has not yet been possible.

Task and solution

The invention is based on the object of creating a method mentioned at the beginning and a hob or cooking device mentioned at the beginning, with which problems of the prior art can be solved and in particular it is possible to make such a hob or its radiant heating device advantageous, diverse and practical to use, in particular to ensure safe operation of the hob.

This object is achieved by a method with the features of claim 1 and by a hob or cooking appliance with the features of claim 11. Advantageous and preferred embodiments of the invention are the subject of the further claims and are explained in more detail below. Some of the features are only described for the process or only for the hob. However, they should be able to apply independently and independently of each other to both the process and the hob. The wording of the claims is incorporated into the content of the description by express reference.

It is intended that the hob is designed as explained at the beginning. The safety temperature limiter is advantageously attached to the radiant heating device or the latter has the safety temperature limiter, so that they can both form a prefabricated structural unit. For this purpose, the safety temperature limiter is particularly advantageously arranged in an upper region of the radiant heating device, so that it runs at least with an elongated temperature detection element or a temperature detection device between the radiant heating device or its heating conductors and the hob plate. This is the effective range of the radiant heating device or its heating conductors upwards through the hob plate into a cooking vessel placed on it. The hob can also have other conventional switching devices, in particular as a power supply for the radiant heating device. These options are explained in more detail below. The safety temperature limiter is designed to switch off or deactivate the radiant heating device when a predetermined switch-off temperature is reached.

The preceding step for the method is that a cooking vessel is placed on the hob plate above the radiant heating device, in particular where a so-called cooking area is formed by the radiant heating device. This hob is to be heated using the radiant heating device, for which this is activated. The power supply to the radiant heating device, for example through relays or electromechanical switches, is advantageously used for this activation. When the radiant heating device begins to be activated, an initial switch-on time is recorded or this begins to run, advantageously in a type of timer of a hob control. This initial switch-on time is the time or duration for which the radiant heating device is operated or activated for the first time after the hob is switched on, in particular at least when the hob plate is cool or has cooled down after previous operation.

The radiant heating device is then activated or supplied with power and heats the cooking vessel that has been set up. At the same time, the safety temperature limiter or at least its aforementioned temperature detection device is also heated up, so that the temperature recorded by it also increases. At some point, the aforementioned switch-off temperature is reached at the safety temperature limiter, which results in the radiant heating device being deactivated by the safety temperature limiter. In particular, this deactivation can take place through a direct switching process. At the same time, the initial switch-on time is stopped or its end is determined and it is recorded. The initial switch-on time therefore indicates the duration between the first activation and deactivation of the radiant heating device.

Finally, the recorded initial switch-on time is compared with a predefined limit switch-on time. In the event that the initial switch-on time is below the limit switch-on time, the power with which the radiant heating device is activated and operated or is operated during activation is reduced. A reduction can occur to varying degrees, as will be explained in more detail below.

This can cover the possibility that an installed cooking vessel becomes too hot too quickly when heating up, so that, for example, fat or the like contained in it. could ignite. The resulting risk of accidents is very high, which is why it should be avoided if possible; grease fires in the kitchen are very dangerous. However, if an installed cooking vessel contains a sufficient amount of food to be cooked, which absorbs the heat generated by the radiant heating device through its mass or, for example, because it consists largely of water, absorbs it through evaporation, then it takes longer than the predefined limit switch-on time for the radiant heating device to first switch on It is deactivated by the safety temperature limiter, i.e. switched off. However, the aforementioned possibility should be avoided.

Thus, in the aforementioned case, heating is carried out at the full set power during the first heating cycle of the radiant heating device or during its first activation, but no longer afterwards. In particular, if the radiant heating device is connected directly to a supply voltage or to a mains voltage and either works at full power in the connected state or is deactivated, the radiant heating device is activated at its full or maximum power during this initial switch-on time. Their output can then be reduced either in a very simple case by deactivating the radiant heating device for a certain time in the case mentioned that the initial switch-on time is below the limit switch-on time, i.e. the heating has taken place too quickly, which is longer than the time actually intended for the set operation or clocked operation when switched off. The entire hob is advantageously not switched off, since it can be assumed that there is no fatal or serious malfunction, but only a case of a possibly too high temperature or dangerously high temperature on this cooking vessel to be heated above the radiant heating device. Such deactivation of the radiant heating device or reduction of its power can be selected or predetermined, for example, for a period of 1 minute to 5 minutes.

Such very rapid heating and thus premature deactivation of the radiant heating device by the safety temperature limiter usually takes place when a cooking vessel that has been set up is empty or has very little content, for example only a small amount Amount of water or oil or fat. A small amount of water could have evaporated very quickly, and the subsequent further heating of the cooking vessel could damage it, for example by causing it to become severely deformed or bent. If there is a small amount of oil or fat, there is a risk that it will reach temperatures of almost 400°C or above and that it could ignite at these temperatures. This fire risk should be eliminated as far as possible with the invention.

In a further advantageous embodiment of the invention, a reduction in the power of the radiant heating device is visually and/or acoustically indicated to an operator in the case mentioned. In this way, an operator can be made aware of the possible danger involved and the cause of the reduction in performance.

Furthermore, it can be provided that an operator can reactivate the operation of the radiant heating device as intended by operating a control element. On the one hand, this necessarily conscious action shows that the operator is present and can therefore quickly recognize a dangerous situation and react accordingly. On the other hand, such very rapid heating may be desired, and if the operator is aware of this, a possible risk of an uncontrollable situation is also reduced or eliminated.

As explained above, the safety temperature limiter is advantageously arranged on the radiant heating device. It particularly advantageously has a temperature detection device, which can be designed as a thermomechanical temperature detection device. It can consist of two materials with different coefficients of thermal expansion, which leads to relative movement when heated. This temperature detection device acts on a switch to deactivate the radiant heating device by switching the switch, preferably due to the said relative movement. In particular, this switch can be looped directly into a power supply for the radiant heating device. For this purpose, the safety temperature limiter is advantageously arranged in the vicinity of electrical connections to the radiant heating device, so that connection is simplified. An example of such a radiant heating device is from the DE 42 29 375 A1 known, to which explicit reference is hereby made. An arrangement of a safety temperature limiter in the form of a so-called rod controller is also known from this. With regard to such a safety temperature limiter, the aforementioned is also explicitly mentioned EP 1 569 257 A1 referenced, which shows its exact design with both an elongated thermomechanical temperature detection device and with two switches.

In an embodiment of the invention it can be provided that only if the initial switch-on time is too short until the radiation heating device is deactivated by the safety temperature limiter is the power of the radiation heating device reduced or it is completely deactivated if it is to be activated with a power that is above a predefined one Limit performance is. Such a limit power can be an area output of more than 5 W/cm ² , in particular more than 7 W/cm ² , alternatively more than 70% of a maximum area output. In the case of a conventional hob, for example, these would be area outputs from a power level 7. The method can thus be limited to checking cases in which the danger mentioned at the beginning actually exists due to relatively high or very high power of the radiant heating device. On the other hand, it should be said that with lower outputs or area outputs, the initial switch-on time will probably be significantly longer than the predefined limit switch-on time. Although the method according to the invention would be started, the switch-on time would not be undercut. The procedure would therefore not intervene as a safety function because the case mentioned does not occur. A necessary or maximum area performance also depends on an adjustment of the safety temperature limiter. This means that the higher the adjustment, the higher the area performance is, otherwise the safety temperature limiter cannot switch quickly enough to detect and prevent an error. This can preferably also apply the other way around, the higher the area performance should be, the higher the adjustment should be.

In a further embodiment of the invention, it is possible for the predefined limit switch-on time to be adjustable. It can therefore not only be preset at the factory, but can also possibly be changed by an operator. For this purpose, it can be provided that it can only be set in a separate setting mode on the hob. For the safety function itself, it should be provided that it is always activated, at least from the aforementioned relatively high powers for the radiant heating device, and therefore cannot be deactivated. This ensures the desired safety function.

In yet another embodiment of the invention, it can be provided that after a certain cooling time, which can advantageously be predefined, after reducing the power on the radiant heating device or deactivating it, the previously set power is at least partially restored, in particular completely restored. Such a cooling time can be between 2 minutes and 5 minutes. This ensures that the cooking vessel is heated again to at least a certain temperature, which at the same time can be viewed as non-critical. So it doesn't cool down completely again. However, similar to what was explained at the beginning, it should be ensured that the security function is activated again. So if the radiant heating device is activated again after the cooling time has elapsed the initial switch-on time should again start running again, and if it is again below the limit switch-on time, i.e. the safety temperature limiter should deactivate the radiant heating device again relatively quickly, the power with which the radiant heating device is activated should be reduced again or switched off . In this way, any further risk can be ruled out.

In a further embodiment of the invention, it is possible for the switching behavior of the safety temperature limiter to be monitored throughout the entire operation of the radiant heating device, in particular by a hob control. In the event that a time of less than 90 seconds, in particular less than 60 seconds, elapses between the safety temperature limiter being triggered twice in succession, it can be concluded that the cooking vessel heated by the radiant heating device is boiling empty. A similar safety function is then also achieved during the continuous heating of the cooking vessel, i.e. not just at the beginning. If it is concluded that the cooking vessel is boiling empty or that the cooking vessel is being heated too quickly, the power for this radiant heating device is reduced again, as explained at the beginning, and in particular it is deactivated. Such deactivation or reduction of power should take place at least for the aforementioned cooling down time.

It is also possible to store a ratio of an active time of the operation of the radiant heating device to the sum of this active time and a deactive time during which the radiant heating device is not operated in a control device or the hob control. This can also be done in connection with a power level set for the radiant heating device. The control device or hob control can also monitor and store the power generated by the radiant heating device over time, so that this is known. In a further embodiment, it can be provided that the aforementioned ratio of an active time to the sum of active time and deactivation time for an energy controller with which the radiant heating device is supplied with power is greater than the corresponding ratio for the safety temperature limiter. This ensures that at least at the relatively high or maximum powers for the radiant heating device to be considered here, the safety temperature limiter switches or switches off for the first time in front of the energy regulator. This can be important for detecting the switching process on the safety temperature limiter. Such an energy regulator is, for example, from DE 36 39 186 A1 known, to which explicit reference is made in this regard.

In one possibility of the invention it is provided that a switching state of the safety temperature limiter, which is connected to an aforementioned energy regulator for power supply, is detected for the radiant heating device is connected in series, only takes place on this energy controller. Since such an energy regulator is usually arranged away from the radiant heating device and close to other control devices or the other energy regulators, an electrical connection is easier here. Based on the current flow through the energy controller, the switching state on the safety temperature limiter can then be deduced, since when current flows, the safety temperature limiter must be switched on and the radiant heating device must therefore be activated.

According to an alternative second possibility, only the switching state of the energy regulator can be detected and the switching state of the safety temperature limiter can also be detected. Then the current flow does not have to be monitored directly. This is possible by detecting a voltage across the radiant heating device, since current only flows through the radiant heating device or a voltage lies above it when the safety temperature limiter is closed.

In a further embodiment of the invention, it is possible to detect that the cooking vessel is boiling empty in the further course of the cooking process, i.e. after a few minutes, by detecting during this entire cooking process when the safety temperature limiter activates and deactivates the radiant heating device. If, after a time of more than 5 minutes and/or after deactivating the radiant heating device more than ten times by the safety temperature limiter, it is determined that the period of time for activating the radiant heating device is shortened, in particular shortened by at least 10% to 50%, this means that The usual switching pattern or clock pattern of the safety temperature limiter has changed. If the power setting for the radiant heating device has not been changed, shortening the activation time can only mean that the cooking vessel now becomes significantly hotter compared to before or can no longer absorb as much heat. This is very often the case when the cooking vessel is boiled empty. If such empty boiling of the cooking vessel is detected or evaluated as detected, the power with which the radiant heating device is activated and operated is reduced or it is deactivated as described above in the event that heating up too quickly is detected at the beginning.

In an advantageous embodiment of the invention, an electronic control device of the hob can have switching elements as a hob control, preferably relays or power semiconductors, with which the radiant heating device is activated or deactivated. Such activation or deactivation of the radiant heating device is advantageously carried out by connecting it to a mains voltage, in particular directly to the mains voltage, or completely Disconnect from the mains voltage. There is no intermediate conversion of a supply voltage for the radiant heating device, as is known, for example, for induction heating devices. Relays here are understood to mean other switching devices such as those in the aforementioned energy regulator. Such an energy controller is a thermally controlled electromechanical switching device, which does not require or contain any so-called intelligence. In this case, a specific cycle ratio for the radiant heating device is set on the energy controller and thus its long-term generated power. The hob then has an additional control to record the switching state of the safety temperature limiter, record the initial switch-on time and carry out the procedure. Advantageously, only a single additional control is provided for all hotplates or all radiant heating devices and electromechanical control devices of the hob. This additional control then has appropriate recording means for the time and, for example, a microcontroller.

In the case of an electronic control device mentioned, after the power has been adjusted by an operator, it specifies switching or a clock for relays or other switching means for the radiant heating device. The aforementioned options for influencing via a control are fulfilled by this electronic control device. No additional control is necessary.

In a further development of the invention, it is possible for a switching state of the safety temperature limiter to be detected by at least one of the options mentioned below. According to a first possibility, a voltage across the radiant heating device can be measured. A corresponding voltage measurement can be contained, for example, in an aforementioned electronic control device or an additional control.

According to a second possibility, a current that flows through the radiant heating device can be measured. A corresponding current measuring device can also be included in the aforementioned electronic control device or additional control.

According to a third possibility, a current can be measured that flows in parallel to a series connection of a safety temperature limiter and a radiant heating device, advantageously in front of an energy regulator or switching means towards the mains connection. This option is also advantageously integrated directly into an electronic control device or additional control.

A mains power supply can advantageously be provided for the hob, which has a connection to a so-called neutral conductor of a power network. For all radiant heating devices, either a single common isolating relay can be provided in this connection to the neutral conductor. Alternatively, each radiant heating device can have its own isolating relay on the neutral conductor. This means that, for example as a safety function, either an individual radiant heating device or the entire hob can be switched off using the cut-off relay.

The division of the application into individual sections and subheadings does not limit the general validity of the statements made under them.

Brief description of the drawings

Fig. 1

eine Schnittdarstellung durch ein erfindungsgemäßes Kochfeld mit einer Strahlungsheizeinrichtung und aufgestelltem Kochgeschirr,

Fig. 2

eine vereinfachte Darstellung eines Stabreglers als Sicherheitstemperaturbegrenzer,

Fig. 3

eine Darstellung eines normalen zeitlichen Verlaufs für Leistung und Temperatur mit taktendem Betrieb einer Strahlungsheizeinrichtung des Kochfelds aus Fig. 1,

Fig. 4

der zeitliche Verlauf entsprechend Fig. 3 mit Einbeziehung der Erfindung durch Deaktivieren der Strahlungsheizeinrichtung, weil das erste Abschalten durch den Stabregler zu früh erfolgt ist,

Fig. 5

eine mögliche Verschaltung von vier Strahlungsheizeinrichtungen eines Kochfelds, deren Leistung durch Energieregler eingestellt wird, mit einer Zusatz-Steuerung zur Realisierung der Erfindung,

Fig. 6

eine Darstellung des Innenaufbaus eines Energiereglers und

Fig. 7 bis 9

verschiedene vereinfachte Verschaltungen als Möglichkeiten, um ein Deaktivieren der Strahlungsheizeinrichtung durch den Stabregler zu erkennen.

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

Fig. 1

a sectional view through a hob according to the invention with a radiant heating device and set-up cookware,

Fig. 2

a simplified representation of a rod controller as a safety temperature limiter,

Fig. 3

a representation of a normal time course for power and temperature with clocked operation of a radiant heating device of the hob Fig. 1 ,

Fig. 4

the time course accordingly Fig. 3 incorporating the invention by deactivating the radiant heating device because the first switch-off by the rod controller occurred too early,

Fig. 5

a possible connection of four radiant heating devices of a hob, the output of which is adjusted by energy regulators, with an additional control to implement the invention,

Fig. 6

a representation of the internal structure of an energy regulator and

Fig. 7 to 9

various simplified circuits as ways to detect deactivation of the radiant heating device by the rod controller.

Detailed description of the exemplary embodiments

In the Fig. 1 A hob 11 according to the invention is shown in section with a hob plate 12. A hob 14 is formed thereon, on which a cookware 13, here a pan, is placed. The hotplate 14 is essentially defined by a radiant heating device 16 of the usual type arranged under the hob plate, for example according to the one mentioned above DE 42 29 375 A1 . The radiant heating device 16 has a metal receiving shell 17, within which a type of thick thermal insulation 18 is arranged, which is electrically insulating. A heating conductor 20 is laid on the top, which glows in the visible range when operated with mains voltage and thus generates radiant heat. This goes up through the hob plate into the bottom of the cookware 13.

A rod controller 23 is arranged on the radiant heating device 16 as a safety temperature limiter according to the invention. The rod controller 23 is in Fig. 2 shown in enlargement and has a housing 25, from which an elongated sensor 27 extends, according to Fig. 1 over the entire surface of the heating conductor 20 or between this or the radiant heating device 16 and the hob plate 12. Thus, the rod controller 23 with the elongated sensor 27 as the aforementioned temperature detection element detects the temperature near the underside of the hob plate 12, which usually consists of glass ceramic. As in the aforementioned EP 1 569 257 A1 As explained, this rod regulator 23 thus protects the hob plate 12 from excessive heating or excessive temperatures, as this could otherwise be mechanically damaged. Due to the properties of the glass ceramic material often used for this purpose, an excessive increase in electrical conductivity could otherwise occur, which the safety regulations do not allow.

The elongated sensor 27 has a sensor tube 28 made of metal, in particular made of steel. An elongated rod 29 made of ceramic material runs in the sensor tube 28 and strikes the inside of the end of the sensor tube 28 with its one free end. When heated, the metallic sensor tube 28 expands and thus becomes longer, while the rod 29 is made of ceramic, which does not expand. As a result, the rod 29, pushed away by a coil spring in the housing 25, moves slightly with its other end. This other end rests on a switch 31, which is designed here as a simple switching spring, but in practice is advantageously designed as a so-called snap spring, see also the aforementioned prior art. From a certain movement distance, the rod 29 no longer presses against the switch 31 so strongly that the two switching contacts still touch each other, but rather they open. Then there is no longer any current flow between the switch connection 33 on the left and the counter connection 34 on the right, with which it is switched into the current flow to the radiant heating device 16 is. The rod controller 23 is therefore open and thus interrupts the current flow to the radiant heating device 16, whereby it is deactivated as described at the beginning. The temperature at which the switch 31 is opened can be precisely adjusted with such a rod regulator 23 and can therefore, for example, be set according to the invention so that the hob plate 12 of the hob 11 does not become too hot due to the aforementioned aspects.

In the Fig. 3 is the time course for the average temperature T on the cookware 13, namely on its base, as well as the power of the radiant heating device 16 shown during a heating or a cooking process according to the prior art. At time t=0, the radiant heating device 16 is switched on or activated, with full mains voltage, i.e. 230 V. Its power P increases very quickly and remains almost constant for a certain time, here at around 2700 W. During this time, it increases the temperature T increases significantly to around 275°C. If the rod controller 23 is adjusted to a temperature of, for example, 500 ° C to 600 ° C for switching, it switches off after a time t = 2.2 min as the initial switch-on time t _E or deactivates the radiant heating device 16. The rod controller therefore has its Switch-off temperature reached by operating the radiant heating device 16 for a period of t _E =2.2 min. After a short time, for example 0.2 min, the temperature on the rod controller 23 has dropped so far that it closes again and thus the radiant heating device 16 again activated, so it heats again with the previously used power P. As a result, the temperature T on the cookware 13 continues to rise. The next switch-off by the rod controller 23, because it has reached its switch-off temperature again, takes place significantly faster, for example after about 0.5 minutes. From then on, a kind of cycle takes place with slightly shortened durations until an almost constant temperature is reached approximately T=460°C from t=10 min with a then regular cycle pattern.

A power supply for the radiant heating device 16 is set here so that it should work at maximum power and thus the power supply itself does not switch off the radiant heating device 16 at all. The radiant heating device is deactivated or the clocking is done solely with the rod controller 23. Here it can be seen that the temperature T would be so high in the long term at around 460 ° C that, as explained at the beginning, either the cookware 13 would be damaged by warping or but small amounts of oil or fat could ignite. A possible situation may be that an operator has placed the cookware 13 with some fat in it on the hotplate 14, set the radiant heater 16 to maximum power and started operation. Then the operator may have left the room. Based on Fig. 3 It can be seen that from the time t=5 min the temperature T is above 400°C and there is therefore a risk that the fat could ignite. Although this smokes before ignition when the operator but is not present, she would not notice it and the great potential for danger mentioned above would therefore exist.

It is obviously not possible with the rod controller 23 to record the temperature on the cookware 13 or on its base itself. According to the temperature curve Fig. 3 However, it can be seen that the very strong increase is due to the fact that the measured cookware 13 alone does not have very much heat capacity or gets hot very quickly, otherwise the increase in temperature T would be flatter and would not be so rapid at correspondingly high temperatures end or not reach them at all. The temperature curve would hardly be different if there was a small amount of fat in it. That's why the invention follows the path that is in Fig. 4 is shown. A limit switch-on time of 2.3 min is predefined for the initial switch-on time t _E. The operation of the hob 11 with the radiant heating device 16 now proceeds as in Fig. 3 , their operation starts at time t=0 with full power, here again a power of P=2700 W. The temperature T on the rod controller 23 rises quickly and reaches the set switch-off temperature at time t _E as an initial switch-on time of 2, 2 min. The rod controller 23 switches or deactivates the radiant heating device 16 for the first time. This first switching off or deactivation is recorded at time t _E as the first switch-on time, which is a period of time. Since this is below the limit switch-on time of 2.3 minutes, it can be seen that the cookware 13 heats up too quickly. From this it can be concluded that it is empty or contains only very small amounts of food to be cooked, possibly potentially dangerous food to be cooked such as some fat or oil with the aforementioned risk of ignition if temperatures are too high. For this reason, the radiant heating device 16 is reduced in its output, namely completely switched off here. As a result, the temperature T rises slightly further to a value of slightly above 300 ° C, which is not critical, and then falls again. At the same time, the aforementioned signaling should be given to an operator, which can be visual and/or acoustic, drawing attention to this shutdown. As an alternative to the shutdown shown here, the power of the radiant heating device could also be reduced, for example halved, whereby the aforementioned critical temperatures are also no longer reached. In any case, it is safer to deactivate the radiant heating device, which can be reversed by an operator through appropriate operation or actuation of a control element. Then the operator must be present and can recognize and eliminate a dangerous situation.

Based on Fig. 4 It is also easy to imagine how, with a slower increase in temperature T, which is shown in dashed lines, a temperature on the cookware 13 of approximately 280 ° C would only be reached after well over 3 minutes. This can be due to a larger amount of food being cooked in the cookware 13. It can be concluded from this that the switch-off temperature on the rod controller 23 is only reached later than previously explained, for example only after significantly more than 2.5 minutes corresponding to the limit switch-on time. The safety function would therefore not intervene here, but at the same time it can be assumed that with the temperature curve shown in dashed lines, as indicated, a maximum temperature of 330 ° C will be achieved in the long term. No danger can arise and therefore the safety function according to the invention is not required. Furthermore, it can happen that, for example, when water boils, the power is usually reset by the user in practice and the device or the hob is therefore out of operation. This means that normal cooking processes with the presence of the user are advantageously not disrupted.

In the Fig. 5 a simplified circuit for a hob 11 is shown in order to operate four radiant heating devices or their heating conductors 20 shown. The circuit is connected to two phases L1 and L2 as well as a neutral conductor of a power network. Two current paths to the heating conductors 20 are provided for the conductors L1 and L2, with an aforementioned energy regulator 42 being connected in each current path, which determines the level of continuous power of the heating conductors 20. Furthermore, rod controllers 23 are provided for each heating conductor 20.

An additional control 36 is provided, since in such a hob, apart from the energy regulators 42, no switches are or need to be provided, and normally no control or control intelligence whatsoever. The additional control 36 has a microcontroller 38 and an isolating relay 40 of the heating conductor 20 to the neutral conductor N. The energy regulators 42 and the rod regulators 23 work, so to speak, autonomously, the energy regulators 42 as they are set by an operator. This will be explained below. As explained above, the rod controllers 23 work with the switch-off temperatures adjusted for them at the factory, and also independently.

The microcontroller 38 is connected to the current paths in front of and behind the rod controllers 23; a connection can also be designed differently. As a result, as will be explained below, the switching state or the current flow is recorded. The microcontroller 38 thus knows when the rod controller 23 switches off or deactivates the radiant heating device 16 or the heating conductor 20, so it can detect the initial switch-on time in the manner described above. It thus records the duration from the first switching on or activation of the radiant heating device 16 with the heating conductors 20 until they are first switched off or deactivated. This recorded initial switch-on time is then stored in the microcontroller 38 Limit switch-on time compared, as explained previously. If it is below this, the output of the radiant heating device, which has heated up too quickly, so to speak, must be reduced. Since the additional control 36 or the microcontroller 38 cannot directly control the energy controller 42 for the corresponding radiant heating device, nor can they control the rod controller 23, and otherwise only a single isolating relay 41 is provided in the current path to each radiant heating device 16 the additional control 36 only opens the isolating relay 40. This means that not only the relevant radiant heating device 16 is switched off, but all radiant heating devices 16 are switched off. However, there is no other way to do this here, and the safety function is guaranteed in any case. Alternatively, an isolation relay for the neutral conductor could also be provided separately for each of the radiant heating devices 16 or their heating conductors 20. However, the effort would then be considerably higher. The isolating relay 40 does not necessarily have to be installed in the additional control 36; it can be an isolating relay that may already be present with an additional connection to the additional control 36.

Not shown here in the Fig. 5 are precise ways of detecting the activation state of the rod controller 23, but these are easy to imagine since they have already been described previously. Furthermore, in the Fig. 7 to 9 Possibilities are described that can also be used here.

In the Fig. 6 is an energy regulator 42 shown in detail according to DE 36 39 186 A1 , to which explicit reference is made in this regard. The energy regulator 42 has a device switch 43, which is designed as a so-called snap switch. A non-round cam disk 45 sits on a rotary shaft 44, which can be rotated by an operator using a control knob. A projection 48 of a support lever 47 rests on its outer edge in a spring-loaded manner, whereby an adjusting device 49 for the device switch 43 is formed. The device switch 43 is attached to the support lever 47. It has a snap spring 51 with a switching contact 52 at the left end. The switching contact 52 is connected to a mating contact 53, so the energy regulator 42 conducts current because the device switch 43 is closed. A switching element 55 made of a bimetal is provided, which presses on the right free end of the snap spring 51. A heating element 56 is provided above this, which is heated when the device switch 43 is closed. As a result, the switching element 55 bends clockwise, i.e. with the right free end downwards, and thus presses on the right free end of the switching spring 51. At a certain distance, the snap spring 51 snaps and opens the device switch 43, so the current flow is interrupted . The heating element 56 is then no longer heated and cools down again, as does the switching element 55, which bends back again and thus enables the device switch 43 to be closed again. This is how timing is achieved.

The respective durations can be adjusted by turning the cam 45 using the rotating shaft 44. This is an electromechanical or electro-thermomechanical power setting for a radiant heating device 16.

In the Fig. 7 is shown in simplified form, as in an electronic hob control for the hob 11 a microcontroller 38 is provided alone without an energy regulator or the like, so the corresponding hob has its own intelligence. The microcontroller 38 is supplied with information by operating elements, for example conventional touch switches, for example a power setting by an operator, which in the aforementioned example was done via the energy regulator 42. The hob control 35 with the microcontroller 38 has a relay 57 in order to also operate the heating conductor 20 of the radiant heating device 16 in a clocking manner, similar to that shown in FIG Fig. 3 and 4 is shown and how the energy regulator 42 does. For this purpose, the relay 57 is connected to the microcontroller 38 and thus replaces an energy regulator. Furthermore, for safety reasons, an isolating relay 40 is provided towards the neutral conductor N, for example a single isolating relay for all radiant heating devices 16.

To detect the switching state of the rod regulator 23, a voltage measurement using a voltmeter 58 is provided here. This is connected in parallel to the heating conductor 20. If the relay 57 is closed and a voltage is detected on the voltmeter 58, the rod regulator 23 must also be closed. If the relay 57 is closed, but the voltage measuring device 58 does not detect any voltage on the heating conductor 20, the rod controller 23 has opened or the heating conductor 20 has been deactivated. In this way, the initial switch-on time can be recorded and then, as before Fig. 5 explained, the microcontroller 38 can carry out the comparison with a stored predetermined limit switch-on time. The further measures correspond to those explained above.

In the Fig. 8 An alternative embodiment of the hob control 35 is shown with an ammeter 60, which is looped into the current path to the heating conductor 20 behind the relay 57 and thus still within the hob control 35. The current measuring device 60 can only detect a current flow if both the relay 57 of the microcontroller 38 is closed and the rod controller 23 is closed. When the relay 57 is closed, interrupting the current flow necessarily means that if the isolating relay 40 is also closed, the rod regulator 23 has opened. The first deactivation of the heating conductor 20 or the radiant heating device 16 after the initial switch-on time can also be detected by the rod controller 23.

In the yet further exemplary embodiment Fig. 9 an ammeter 60 is provided from the connection of the relay 57 to the phase L to the connection of the heating conductor 20 to the isolating relay 40. If relay 57 and isolating relay 40 are closed, it can also be determined by monitoring the current flow whether the rod controller 23 is closed or open. The microcontroller 38 can also record the initial switch-on time or its duration.

Not shown here are the aforementioned optical or acoustic signals to an operator when the power for the radiant heating device 16 has been reduced or it has been deactivated, i.e. switched off. Such signaling can easily be generated by the microcontroller 38, but this does not pose any problem in implementation.

Claims (15)

1. Method for controlling a heating device (16) of a hob (11), the hob (11) having:

   - at least one radiation heating device (16) as heating device,

   - a hob plate (12) under which the radiation heating device (16) is arranged,

   - a safety temperature limiter (23) which is designed as a thermomechanical functional device and which is arranged between the radiation heating device (16) and the hob plate (12), the safety temperature limiter (23) being designed to deactivate the radiation heating device (16) when a switch-off temperature is reached,

   comprising the steps:

   - placing a cooking vessel (13) on the hob plate (12) above the radiation heating device (16),

   - activating the radiation heating device (16) and simultaneously beginning to detect an initial turn-on time,

   - detecting deactivation of the radiation heating device (16) by the safety temperature limiter (23) when a switch-off temperature is reached at the safety temperature limiter (23), and detecting the initial switch-on time which has elapsed up to that point between activation and deactivation of the radiation heating device (16),

   - comparing the detected first switch-on time with a predefined limit switch-on time, wherein in the event that the first switch-on time is below the limit switch-on time, the power with which the radiation heating device (16) is activated and operated is reduced.
2. Method according to claim 1, characterized in that, in the event that the initial switch-on time is below the limit switch-on time, the radiation heating device (16) is deactivated, preferably not the entire cooking field (11) being switched off.
3. Method according to one of the preceding claims, characterized in that the radiation heating device (16) is deactivated or its power is reduced only if a power with which the radiation heating device (16) is to be activated is above a predefined limit power, preferably with an area power of more than 5 W/cm², in particular more than 7 W/cm².
4. Method according to one of the preceding claims, characterized in that after a certain cooling time, which is preferably predefined, after reducing the power at the radiation heating device (16) or deactivating it, the previously set power is at least partially restored, this cooling time preferably being between 2 min and 5 min.
5. Method according to one of the preceding claims, characterized in that during an entire operation of the radiation heating device (16) the switching behavior of the safety temperature limiter (23) is monitored, wherein in the case that a time of less than 90 sec. elapses between two successive responses of the safety temperature limiter (23), in particular less than 60 sec, it is concluded that the cooking vessel (13) heated by the radiation heating device (16) is boiling empty and thereupon the power for this radiation heating device (16) is reduced, in particular this radiation heating device (16) is deactivated.
6. Method according to claim 4 or 5, characterized in that a ratio of an active time to the sum of active time and deactive time for the radiation heating device (16) is stored in a control device (38), in particular in connection with a set power level, the control device (38) preferably also monitoring and storing the power generated over time by the radiation heating device (16).
7. Method according to one of the preceding claims, characterized in that a detection of a switching state and a current flow only takes place at an energy controller (42) for the power supply of the radiation heating device (16).
8. Method according to one of the claims 1 to 6, characterized in that a switching state is detected at an energy controller (42) for the power supply of the radiation heating device (16) and additionally at the safety temperature limiter (23).
9. Method according to one of the preceding claims, characterized in that a switching state of the safety temperature limiter (23) is detected by at least one of the following possibilities:

   - measuring a voltage across the radiation heating device (16),

   - measuring a current flowing through the radiation heating device (16),

   - measuring a current flowing in parallel with a series connection of the safety temperature limiter (23) and the radiation heating device (16).
10. Method according to any one of the preceding claims, characterized in that during an entire cooking process with the cooking vessel (13) on the cooktop plate (12) above the radiation heating device (16), it is detected when the safety temperature limiter (23) activates and deactivates the radiation heating device (16), after a time of more than 5 minutes and/or after deactivation of the radiation heating device (16) by the safety temperature limiter (23) more than ten times, a shortening of the duration of the activation of the radiation heating device (16), in particular a shortening by at least 10% to 50% of the time duration, is evaluated as an empty boiling of the cooking vessel (13) and thereupon the power with which the radiation heating device (16) is activated and operated is reduced or the radiation heating device (16) is deactivated.
11. A hob (11) configured for carrying out the method according to any one of the preceding claims, the hob (11) comprising:

    - a radiation heating device (16),

    - a hob plate (12) under which the radiation heating device (16) is arranged,

    - a safety temperature limiter (23) which is designed as a thermomechanical functional device and which is arranged between the radiation heating device (16) and the hob plate (12), the safety temperature limiter (23) being designed to deactivate the radiation heating device (16),

    characterized in that the radiation heating device (16) has the safety temperature limiter (23), preferably in its upper region or between a heating conductor (20) of the radiation heating device (16) and the hob plate (12).
12. Hob according to claim 11, characterized in that it has an electronic control device (38), in particular with touch switches as operating elements, the control device (38) activating or deactivating the radiation heating device (16) via switching elements, in particular via relays (40, 41, 57) or power semiconductors, in particular by connecting to a mains voltage or completely disconnecting from the mains voltage.
13. Hob according to claim 12, characterized in that the power for the radiation heating device (16) is set by means of an electromechanical control device (38), the hob (11) having an additional control (36) for determining the switching state of the safety temperature limiter (23), preferably only a single additional control (36) being provided for all cooking zones (14) or radiation heating devices (16) of the hob (11).
14. Hob according to one of the claims 11 to 13, characterized in that it has a mains power supply with a connection to a neutral conductor (N), wherein for all radiation heating devices (16) either a single common isolating relay (40) is provided in the connection to the neutral conductor or that for each radiation heating device (16) a separate isolating relay is provided in the connection to the neutral conductor (N).
15. Hob according to one of claims 11 to 14, characterized in that the safety temperature limiter (23) is arranged on the radiation heating device (16), wherein the safety temperature limiter (23) comprises a temperature detection device (27), in particular a thermo-mechanically designed temperature detection device (27), which acts on a switch (31) for deactivating the radiation heating device (16) for switching, wherein in particular the safety temperature limiter is designed as a rod controller (23).

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