EP3307019B1 - Method for the operation of an induction hob and induction hob - Google Patents

Description

APPLICATION AREA AND PRIOR ART

The invention relates to a method for operating an induction hob in order to heat water or a similar liquid in a cooking vessel set up above at least one induction heating coil of the induction hob. Furthermore, the invention relates to an induction hob which is designed to carry out this method.

It is from the DE 102009047185 A1 It is known, when heating a cooking vessel by means of an induction heating coil from vibration parameters or operating parameters of the induction heating coil, to record a profile of the temperature on the heated cooking vessel or its cooking vessel base. Only a relative temperature profile of the temperature of the bottom of the cooking vessel can be recorded, but certain functions can be derived from this. These are for example in the DE 102011083397 A1 described, which is based on the same physical principle.

It is from the EP 2574143 A2 known to heat or heat liquid in a cooking vessel by means of an induction heating device. Operating parameters of the induction heating device are monitored and a change in temperature is determined therefrom. A boiling point of the liquid can be determined in this way.

From the WO 2008/148529 A1 an induction hob is known with a possibility of determining a temperature of the hob plate and thus of a cookware base. For this purpose, heat sensor units and a light source are arranged below the hob plate in order to evaluate a measuring spot above them with regard to a temperature.

From the EP 1492385 A2 it is known to recognize heating processes in an induction hob and to measure and evaluate temperature profiles. Here, a cooking vessel can be heated, a temperature profile being recorded and measured and evaluated. The heating can be suspended for a certain time, the temperature profile being evaluated after the end of the energy supply, and its gradient being determined in the process.

TASK AND SOLUTION

The invention has for its object to provide a method mentioned above and an induction hob designed to carry it out, with which problems of the prior art can be solved and in particular it is possible to create further comfort functions or operating functions for operating an induction hob.

This object is achieved by a method having the features of claim 1 and by an induction hob having the features of claim 14. 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 induction hob. However, regardless of this, they should be able to apply independently and independently of one another both for a method and for a corresponding induction hob. The wording of the claims is made the content of the description by express reference.

It is provided that the method has the following steps, in particular in order to be able to heat water or a corresponding liquid in the boiling vessel with different degrees of boiling.

A controller of the induction hob controls the at least one induction heating coil for inductively heating the cooking vessel which is set up above the induction heating coil. It is heated with a specified power density, i.e. a certain power per area. This is a high power density being higher than 4 W / cm ² to 6 W / cm ² , possibly also a maximum or boost power density of up to 12 W / cm ² . This power density can be specified by an operator. Alternatively, in a specific operating mode, for example "boiling water", which can be selected on the induction hob, the control of the induction hob can, so to speak, automatically and program-dependent.

During the heating of the cooking vessel, operating parameters of the at least one induction heating coil, advantageously all of the induction heating coils covered by the cooking vessel and operated to heat it, are recorded by the control. A vibration response of the induction heating coil is advantageously used as the operating parameter. This operating parameter or these operating parameters are evaluated by a relative temperature profile of the Detect or monitor the temperature of the bottom of the cooking vessel. This is also known from the prior art.

As soon as the detected or monitored relative temperature profile of the bottom of the cookware flattens out as a kind of curve, or the slope decreases or even falls below zero, the controller recognizes this. It then determines this as the case of a "light boiling" condition of the water or liquid in the cooking vessel. Furthermore, it is then determined that a temperature has been reached on the top of the cooking vessel base that is 5 ° C to 15 ° C below the boiling point of the water. It can be said here that this boiling point is based on a height above sea level that is usual in Germany, i.e. about 20m to 500m above sea level. This height range has only an insignificant effect on the boiling point and can therefore be neglected. In an embodiment of the invention, it can be provided that this height above sea level is entered into the induction hob, for example when installing for the first time or when starting up for the first time. The controller then takes into account its effects on the boiling point. The approximate relative temperature curve will always be somewhat the same regardless of the altitude. Only the absolute temperature at the start of the "light boiling" state will of course vary and be lower the higher the induction hob is operated above sea level. Usually, however, this only has a certain effect at altitudes above 1000m above sea level, namely around 5 ° C. An increase in the relative temperature profile of the bottom of the cooking vessel can take a certain time, in particular 10 seconds to 300 seconds or 400 Sec. Of course, this depends on the specified power density. If this is very high or maximum, in particular using a so-called boost power density for operating the at least one induction heating coil, the duration can also be in the range between 60 seconds and 150 seconds.

If the water has reached a temperature of 100 ° C, a further temperature increase cannot take place. In this respect, the top of the bottom of the cooking vessel, which is in direct contact with the water, cannot reach a higher temperature. So it goes into a kind of saturation or reaches a kind of stop. However, a flattening of an increase in the temperature of the bottom of the cooking vessel occurs beforehand, which is exploited.

After recognizing the "light boiling" state, the power density is automatically reduced for a predetermined holding time. In this way it should be possible to avoid, under certain circumstances, excessive boiling or excessive bubbling of the boiling of the water or the liquid. The power density can advantageously be reduced to a value between 1 W / cm ² and 3.5 W / cm ² . Relatively speaking, the power can be reduced by 10% to 50% or even by 75%, depending on the previously used power density.

An operator is then offered a hold option. This hold option consists in that by operating an operating element, advantageously a single operating element, which can be particularly advantageously a touch switch, the temperature is regulated by means of automatic adjustment of the power density to the value that prevailed at the time of the start of the holding time . Alternatively, the power density that was used at the time the "light boiling" condition began could be adjusted and maintained constant. This can be the power density that has been automatically reduced to for the predetermined hold time. Thus, when the operator actuates the control element, this "light boiling" state can be maintained or set even for a long time. By using the possibility according to the invention, she does not have to set this state herself in a complex manner by means of a power density which in the long run leads to this state "light boiling".

The hold time can be in the range of a few seconds, advantageously a maximum of 20 seconds, particularly advantageously a maximum of 10 seconds. If the hold time has expired without the operator having selected the hold option or performing an actuation process for the hold option has or another actuation process for this induction heating coil, with which, for example, a completely different power density is set manually, the default will be again Power density set. This is a power density that is in all probability higher than the power density that was automatically reduced during the hold time. A further heating of the bottom of the cooking vessel and thus also of the water or the liquid therein will thus take place again. This can be of advantage in this case if the operator wants to use the water not only in the "light boiling" state, but as "strong boiling" or bubbling boiling. This is advantageous for cooking pasta, for example, or is often used.

Such "light boiling" is used, for example, more for boiling potatoes or eggs and has the advantage that disruptive splashing out of hot water during boiling boiling can be avoided. Furthermore, some foods can be undesirably mechanically moved or impaired during preparation by the strong water movements in the cooking vessel or also by the strong movements of the resulting steam bubbles. For this reason too, a "light boiling" condition may be more desirable.

In simple terms, the invention provides an operator with the possibility, for a certain holding time, of holding a "light boiling" state that has been achieved, so to speak, in a stable manner. This has been recognized according to the invention. If the operator lets this option or this holding option pass unused, for example because he wants to bring the water or the liquid to a boiling point, this takes place automatically after the holding time has expired. Another actuation process is not necessary.

In an advantageous embodiment of the invention, it can be provided that the operator is signaled when the "light boiling" state has been reached, ie when a temperature of almost 100 ° C. or a temperature between 85 ° C. and 100 ° C. has been reached for the water at which the hold time for the hold option begins. Signaling can take place optically and / or acoustically according to various possibilities which are known to the person skilled in the art. Such signaling can differ particularly advantageously from other signaling, so that the operator can clearly see that this stop option is now offered according to the invention and the stop time has started to run.

In the invention, it is provided that after the holding time has elapsed without an actuation process for this induction heating coil, this induction heating coil is operated with a higher power density in order to further heat the cooking vessel or to increase the water therein Bring temperature. This will be a even higher power density set, for example also a maximum power density. In this way, the water in the cooking vessel can be heated to a higher temperature for a "strong boiling". In this way, the water can actually be brought up to 100 ° C or the maximum temperature so that it boils gently.

It can be provided that after the state of "strong boiling" of the water in the cooking vessel has been recognized, the operator is offered a cooking option for a predetermined cooking option time, which can be a maximum of 20 seconds, possibly also a maximum of only 10 seconds Rise in the relative temperature of the bottom of the cooking vessel stopped by reducing the power density. If, during this cooking option, an operating element is actuated accordingly by the operator, the control adjusts the power density on the at least one induction heating coil in such a way that this “strong boiling” state is maintained in the cooking vessel. Thus, the previously used power density with which this "heavy boiling" condition has been achieved is not necessarily maintained. A lower power density may also be sufficient to maintain the state, although it should still be a high power density. For this purpose, it can advantageously be provided that control is carried out to precisely that relative temperature which was present at the time the temperature rise stopped, which is therefore the target temperature or which must then also be at 100.degree. Alternatively, the power density that has been used at that time can be maintained.

The operator can also be generally or specifically signaled when the water in the cooking vessel has reached the "boiling point" state. In principle, signaling is suitable in a manner similar to that previously explained.

In a further embodiment of the invention, it can be provided that a reduction in the power density on the at least one induction heating coil for the cooking vessel after the detection of the "light boiling" state is used to detect a first temperature difference between the temperature at the time of the detection of the "light boiling" state "and to determine a temperature that was present 3 seconds to 20 seconds after the start of the reduction in the power density, in particular during the hold option. After this time of 3 seconds to 20 seconds, the power density on the at least one induction heating coil can increase again or the controller can increase it. In particular, it can adjust to the specified power density during the first heating of the water in the cooking vessel increase. This can be a previously described increase in performance from light boiling to heavy boiling.

The power density can then be reduced again and a second difference between a temperature at the time the power density is reduced again and a temperature after a time between 3 seconds and 20 seconds after the power density has been reduced can be determined. This second difference is then compared to the first difference. In the event that the second difference is less than the first difference, it is assumed that the relative temperature of the cooking vessel at the time of the first reduction in the power density does not yet correspond to the "heavy boiling" state, but only to the "light boiling" state . If this state of "light boiling" is desired, the temperature is suitable. Then can be settled on it. If the condition "strong boiling" is desired, the power density should be increased again to heat up even more.

In a further embodiment of the invention, it can be provided that the control switches off the at least one induction heating coil when the cooking vessel is heated with a power density for maintaining the “light boiling” state after a maximum of 2 hours. This time can be a maximum of 1 hour, alternatively also 5 minutes to 30 minutes, so that this state does not last so long that it is obvious that there is an error or that the operator no longer monitors or keeps an eye on the cooking process .

In a similar form as mentioned above, it can be provided that the at least one induction heating coil is operated at a power density when the cooking vessel is heated, which is sufficient to maintain the "high boiling" state. Then you can switch off after a maximum of 30 minutes. This can only be a maximum of 20 minutes. Finally, a significantly higher power density is set than previously described, and thus there is a certain higher risk of malfunction. As an alternative to switching off, the power density can be reduced by at least 30% to 60%.

In yet another embodiment of the invention it can be provided that the control unit sets a medium or rather low power density for the at least one induction heating coil in order to maintain the state of "light boiling" or the state of "strong boiling". Here, a power density of less than 4 W / cm ^{2 may be} sufficient, advantageously less than 3 W / cm ² , in order to maintain the "light boiling" state. It can be provided that an operator on an operating device of the induction hob, which is of course connected to the control, either has a corresponding predetermined power density selects and then additionally a special function that causes the hold option to be reached. Alternatively, a certain program sequence can be started immediately, in which the operator does not directly specify the power density as a cooking level, but only this type of heating, in which the hold option is offered in the "light boiling" state and after its expiration without appropriate actuation, heating continues until the boiling is strong.

In a further embodiment of the invention it can be provided that the control is designed for the hold option, possibly after basic user-dependent programming, when a set-up cooking vessel heats up and the temperature reaches almost 100 ° C. or a temperature slightly below the boiling point offer automatically. It is therefore always available to an operator without having to be selected beforehand with a certain amount of adjustment. The aforementioned time delay of a maximum of 20 seconds for the hold option seems acceptable, even if an operator does not specifically want this hold option at all.

These and further features emerge from the claims and also from the description and the drawings, the individual features being implemented individually or in groups in the form of sub-combinations in one embodiment of the invention and in other fields, and being advantageous and protectable per se Can represent versions for which protection is claimed here. The division of the application into individual sections and sub-headings do not limit the general validity of the statements made under these.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1

eine schematische Darstellung eines Induktionskochfelds mit Induktionsheizspule zur Durchführung des erfindungsgemäßen Verfahrens und

Fig. 2

verschiedene Verläufe von Temperaturen sowie ein Verlauf eines Betriebsparameters einer Induktionsheizspule des Induktionskochfelds aus Fig. 1 als relativer Temperaturverlauf über der Zeit.

Exemplary embodiments of the invention are shown schematically in the drawings and are explained in more detail below. The drawings show:

Fig. 1

a schematic representation of an induction hob with induction heating coil for performing the method according to the invention and

Fig. 2

different courses of temperatures and a course of an operating parameter of an induction heating coil of the induction hob Fig. 1 as a relative temperature curve over time.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the Fig. 1 is shown very schematically a part of an induction hob 11 with a hob 13 and an induction heating coil 15 arranged underneath, as are known from the prior art, in particular also from the aforementioned. A pot 18 with water is placed on a hotplate 16 formed above the induction heating coil 15 in order to be heated or brought to a boil.

Furthermore, the induction hob 11 has a controller 20 which is connected to the induction heating coil 15 in order to detect the operating parameter of the induction heating coil 15 described at the outset, in particular an oscillation response in order to thus detect a relative temperature profile of the temperature of the bottom of the pot 18. In this regard, the above mentioned DE 102009047185 A1 and DE 102011083397 A1 referred. Furthermore, the controller 20 is also connected to an optical or acoustic display 22 and at least one operating element 23. In addition, the controller 20 is advantageously connected to all control elements of the induction hob 11 and forms the only controller of the induction hob 11.

In the Fig. 2 is shown in a diagram over time t, how the temperature T _{B of} the bottom of the pot 18, namely at the top of the bottom, as well as the temperature T _{W of} the water in the pot 18. These values are not recorded during the method according to the invention and are shown here by way of example in accordance with measurements that were carried out within the scope of the invention. The temperature T _{W of} the water is an average temperature, since the water directly above the bottom of the pot will be slightly hotter than in the upper area. Such an inhomogeneous temperature distribution is common during heating. The temperature differences are a maximum of about 10 ° C to 20 ° C apart. Furthermore, the relative temperature profile S of the bottom of the pot 18 is plotted over time, as can be determined from the above-described operating parameters of the induction heating coil 15.

At time t = 0, a pot 18 placed on the induction hob 11 or the hotplate 16 is heated with water by the induction heating coil 15. For this purpose, the controller 20 specifies a high power density, for example a maximum boost power density of 10 W / cm ² . During the first approx. 20 seconds to 40 seconds, the relative temperature profile S rises sharply, the pot bottom temperature T _{B also} rises, albeit weaker. In contrast, the temperature T _{W of} the water rises only slowly. In this phase, the bottom of the pot is especially important heated up, because only this can couple the heat into the water, which is naturally slower.

Between a time of approximately 50 seconds to 250 seconds, the temperatures T _B and T _{W run} with an almost constant gradient and also almost parallel, the water temperature T _W approaches the temperature curve T _B somewhat. At the time of approximately t = 300 seconds, the averaged water temperature T _{W reaches} a value of approximately 85 ° C. The bottom of the pot may already have reached a temperature of 100 ° C. a few seconds beforehand, which means that, as can be seen, this temperature cannot be exceeded while there is still water in the pot 18. Here the course S flattens or its slope becomes smaller, from t = 300 seconds the course S is approximately horizontal. This is where the invention begins, as described above. Before going into this in more detail, a further cooking process will be described as an example. Up to the point in time t = 370 seconds, the water temperature T _W still rises, but only weaker at the end. At this point, the water is then continuously heated to about 100 ° C., so all the water in the pot 18 boils, so to speak, as a state of "strong boiling".

At the time t = 300 seconds, the water in the pot 18 has just reached the "light boiling" state. Even if an average water temperature T _{W is} only about 85 ° C, there is already a clear formation and detachment of steam bubbles at the bottom of the pot, so that an operator can already see a certain boiling or light boiling. This is also sufficient for processes such as boiling pasta, potatoes or the like, but not yet, for example, to usually start cooking pasta.

It can thus be seen that after the "light boiling" state has been reached, when the base of the pot has already reached a temperature of T _B = 100 ° C., over 60 seconds pass until the water in the pot 18 actually boils gently and thus has a temperature of T _W = 100 ° C continuously or averaged. Furthermore, it can be seen from the relative temperature profile S that there are changes in the profile S or the gradient at these two points in time, which can be evaluated by the controller 20.

In the method according to the invention, the controller 20 recognizes from the relative temperature profile S at time t = 300 seconds that the state “light boiling” begins, since here the relative temperature profile S flattens out or even becomes horizontal, that is, its slope is zero becomes. From the first derivation of the relative temperature profile S, this point in time can be roughly recognized. During the cooking process from the controller 20 If a high or maximum power density has just been started, after the "light boiling" state has been recognized at time t = 300 seconds, the above-mentioned hold option for the hold time TH shown above of approximately 20 seconds is offered. The power density is greatly reduced to about 2 W / cm ² to 3 W / cm ² , so it is only 20% to 25%. On the display 22, the controller 20 outputs a corresponding signal to an operator and the above-mentioned hold time TH is started. Due to the reduced power density, the state of "light boiling" is then maintained as far as possible and the water temperature T _W takes the course shown in broken lines, ie remains at about 85 ° C. This holding option offered to the operator can then be accepted by actuating the operating element 23 if this takes place within the holding time T _H. The actuation of the operating element 23 or the acceptance of the hold option then leads to the fact that this reduced power density is approximately maintained or that a temperature control by means of the relative temperature profile S regulates to the temperature T _W at the time t = 300 seconds. This is in the Fig. 2 represented by the constant dash-dot line of the water temperature T _W at 85 ° C.

However, if the operator lets the hold time T _H pass and thus does not use the hold option, the previous high power density can be set again after the hold time has expired, in this case the maximum boost power density. Then according to the in Fig. 2 solid course for the water temperature T _W again an increase take place up to 100 ° C. Alternatively, after an unsuccessful elapse of the hold option or the hold time, the power density can be increased again by the controller 20, but not to the maximum boost power density used at the beginning, but to a high power density, for example at 4 W / cm ² to 6 W / cm ² . Then the water in the pot is reheated to a final temperature of 100 ° C throughout, but this takes a little longer.

Dash-dotted lines show the curve for the pot bottom temperature T _B from the point in time of 300 seconds when the control 20 has reduced the power during the hold option. As a result of this reduction in output, the pot bottom temperature T _B also drops somewhat, as shown in dotted lines. If the holding option is used, the power density remains low, so that in the long term, here for example from about 370 seconds, the pot bottom temperature T _B has approached and is equal to the water temperature T _W.

Claims (14)

1. Method for operating an induction hob (11) in order to heat water in a cooking vessel (18) which is placed above at least one induction heating coil (15) of the induction hob, comprising the following steps:

   - a controller (20) of the induction hob drives the at least one induction heating coil (15) for a first inductive heating of the placed-on cooking vessel (18) with a prespecified power density,

   - during the heating of the cooking vessel (18), operating parameters of the at least one induction heating coil (15) are detected and evaluated by the controller (20) in order to monitor a relative temperature profile of the temperature of a cooking vessel base,

   - as soon as the relative temperature profile of the cooking vessel base levels off to a significant extent or a gradient of the relative temperature profile decreases, the controller (20) identifies this and determines this as the situation of a "lightly boiling" state and of a temperature of a top side of the cooking vessel base which is 5°C to 15°C below the boiling point being reached,

   - the power density is then automatically reduced for a predetermined hold time,

   characterized in that

   - an operator is offered a hold option in such a way that, by operating an operator control element (23), the temperature is regulated to the value at the time of the start of the hold time by means of automatic setting of the power density, or the power density at the time of the start of the "lightly boiling" state is kept constant,

   - after the hold time has elapsed without an operating process, the controller (20) operates the at least one induction heating coil (15) with a higher power density than the prespecified power density during the first heating of the cooking vessel (18) for further heating the cooking vessel (18) or the water contained therein to a higher temperature.
2. Method according to claim 1, characterized in that the controller (20) operates the at least one induction heating coil (15) for the first inductive heating of the placed-on cooking vessel (18) with a prespecified relatively high power density of 4 W/cm² to 12 W/cm².
3. Method according to claim 1 or 2, characterized in that the controller (20) automatically reduces the power density to a value of between 1 W/cm² and 3.5 W/cm² or by 10% to 50% for the predetermined hold time.
4. Method according to any one of the preceding claims, characterized in that the controller (20) signals, in particular visually and/or acoustically signals, to the operator that the temperature of almost 100°C or between 85°C and 100°C as a "lightly boiling" state of the water in the cooking vessel (18) has been reached.
5. Method according to any one of the preceding claims, characterized in that the controller (20) provides the operator with the hold option for a hold time of a maximum of 20 seconds, preferably a maximum of 10 seconds.
6. Method according to any one of the preceding claims, characterized in that, after the hold time has elapsed without an operating process, a higher power density is set in order to heat the water in the cooking vessel (18) to a greater extent to a higher temperature for a "vigorous boiling" state, preferably to 100°C.
7. Method according to claim 6, characterized in that, after the "vigorous boiling" state of the water in the cooking vessel (18) has been identified by an increase in the relative temperature of the cooking vessel base being stopped, the operator is offered a boil option for a predetermined boil option time of a maximum of 20 seconds, preferably a maximum of 10 seconds, in which boil option operation of an operator control element (23) has the effect that the controller (20) sets the power density on the at least one induction heating coil (15) such that this "vigorous boiling" state is maintained on the at least one induction heating coil (15) or in the cooking vessel (18), preferably by regulation to precisely this relative temperature at the time of the increase in the said temperature being stopped or by maintaining the power density set at this time.
8. Method according to claim 6 or 7, characterized in that the controller signals, in particular visually and/or acoustically signals, to the operator that the "vigorous boiling" state of the water in the cooking vessel (18) has been reached.
9. Method according to any of the claims 6 to 8, characterized in that a reduction in the power density on the at least one induction heating coil (15) after the "lightly boiling" state has been identified is used to ascertain a first temperature difference between the temperature at the time of identification of the "lightly boiling" state and a temperature 3 seconds to 10 seconds after the start of the reduction in the power density, wherein, after this time of 3 seconds to 10 seconds has elapsed, the controller increases the power density on the at least one induction heating coil (15) again, wherein the power density is then reduced again and a second difference between a temperature at the time of the renewed reduction in the power density and a temperature after a time of between 3 seconds and 10 seconds thereafter is ascertained, wherein this second difference is then compared with the first difference, wherein, in the case that the second difference is lower than the first difference, the relative temperature of the cooking vessel (18) at the time of the initial reduction in the power density is not yet classified as a "vigorous boiling" state, but rather as a "lightly boiling" state.
10. Method according to claim 9, characterized in that, after this time of 3 seconds to 10 seconds has elapsed, the controller increases the power density on the at least one induction heating coil (15) again to the prespecified power density during the initial heating of the water in the cooking vessel (18).
11. Method according to any one of the preceding claims, characterized in that the controller switches off the at least one induction heating coil (15) after a time of a maximum of 2 hours, in particular a maximum of 1 hour, when the cooking vessel (18) is heated with a power density for maintaining the "lightly boiling" state.
12. Method according to any one of the preceding claims, characterized in that the controller switches off the at least one induction heating coil (15) after a time of a maximum of 30 minutes, in particular a maximum of 20 minutes, or reduces the power density by at least 30% to 60%, when the cooking vessel (18) is heated with a power density for maintaining the "vigorous boiling" state.
13. Method according to any one of the preceding claims, characterized in that the controller (20) sets a low power density for the at least one induction heating coil (15) to a power density of less than 3 W/cm² for operating the induction heating coil (15) in order to maintain the "lightly boiling" state.
14. Induction hob characterized by:

    - at least one induction heating coil (15),

    - a controller (20),

    - an operator control element (23),

    wherein the controller (20) is designed to carry out the method according to any one of the preceding claims.

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