METHOD FOR OPERATING A HOB, AND HOB

Abstract

A method for operating a hob for maintaining a state, which exists at the time of activation of the maintaining operation, at a cooking point of the hob with a cooking vessel on it detects a change in temperature of the cooking vessel as a change in state, wherein supplied power and/or a change in temperature of the cooking vessel are evaluated. A maintaining function for maintaining the state, which is indicated at this time, at the cooking point with a cooking vessel placed on it can be triggered. In doing so, the current state at the cooking point is classified as a process at the boiling point of water on the one hand and as a process which is different therefrom or as a process which takes place at a different temperature without a phase transition of water on the other hand.

Claims

1. A method for operating a hob for maintaining a state at a cooking point of the hob with a cooking vessel on said cooking point, wherein said state exists at the time of activation of an operation for maintaining, the method comprising: placing a cooking vessel onto said cooking point of said hob and being heated by said cooking point or by an inductive heating device of said cooking point according to requirements; detecting a change in temperature of said cooking vessel as a change in state; detecting a heating process of said cooking vessel and evaluation of supplied power and/or a temperature of said cooking vessel and/or a profile thereof with respect to time; triggering of a maintaining function by an operator for maintaining said state, which is indicated at said time, at said cooking point with said cooking vessel placed on it; and dividing a current state at said cooking point firstly into a process at a boiling point of water and secondly into a process which is different therefrom or into a process which takes place at a different temperature without a phase transition of water, wherein, in a case of a decision in favor of a process at said boiling point of water, said power supply at said point is then kept largely constant or a customary power supply for continued boiling is set, and wherein, in a case of a decision in favor of a process not at said boiling point of water, said process is regulated at a constant temperature of said cooking vessel by adapting said power supply.

2. The method according to claim 1, wherein a size of said cooking vessel is determined, which size has been put into place, on a basis of a size, which is known in said hob, of said cooking point which is operated for said cooking vessel or a heating device of said cooking point.

3. The method according to claim 1, wherein said hob comprises an induction hob with an inductively heated heating device, wherein a change in temperature of said cooking vessel is detected from operating parameters for said inductively heated heating device.

4. The method according to claim 1, wherein, in an event of a sudden drop in temperature after triggering of said maintaining function, a temperature is again brought to said previous temperature before said sudden drop in temperature and a time taken until said temperature is again at the previous temperature before said sudden drop in temperature or until said change in temperature is compensated for again is detected.

5. The method according to claim 4, wherein said previously used control variable temperature or power supply is used again directly after detection of said sudden drop in temperature until compensation.

6. The method according to claim 4, wherein said sudden drop in temperature in a case of a time of less than 10 seconds until compensation is evaluated as an introduction of a product to be fried into said cooking vessel, wherein said cooking vessel then continues to be heated with said previous temperature or said temperature which has been reached again being maintained.

7. The method according to claim 4, wherein a sudden, sharp drop in said temperature is evaluated as introduction of water into said cooking vessel, wherein said cooking vessel then continues to be heated with said previous power supply or power or is heated at a customary power for continued boiling of water.

8. The method according to claim 7, wherein said sudden, sharp drop in temperature has a subsequent temperature limiting.

9. The method according to claim 4, wherein, in an event of a sudden change in signal or change in temperature with a change time of less than 5 seconds, a displacement of said cooking vessel is identified, wherein a signal deviation, which is caused by said displacement and not by an actual change in temperature, is not considered to be a control deviation.

10. The method according to claim 9, wherein, in an instance in which a displacement of said cooking vessel is identified, said signal deviation, which is caused by the displacement and not by an actual change in temperature, is not considered to be a control deviation.

11. The method according to claim 1, wherein, in a case of a process with a temperature at said boiling point of water having been identified, said heating device is supplied with a constant power of between 0.5 W/cm.sup.2 and 7 W/cm.sup.2.

12. The method according to claim 1, wherein, in processes at said boiling point, boiling-dry is identified in an instance in which water no longer covers a pot base and as a result said pot base is warmer than an instance in which it is covered with water and this is suitably indicated to an operator and/or said power output is reduced or stopped.

13. The method according to claim 1, wherein, during said maintaining process, an operator has an option of adapting or finely adjusting an actual maintaining level once again, wherein, in an instance in which said fine adaptation is performed, said setpoint temperature is adapted in an event of a temperature control operation and/or a set power density per unit area is adapted in a case of water at said boiling point.

14. The method according to claim 1, wherein an operator can interrupt said maintaining process and can later restart said maintaining process or can select other, power-controlled power densities in the meantime.

15. The method according to claim 1, wherein said measurement variable which is correlated to said cooking vessel temperature is a period duration of said resonant circuit of said cooking point and/or another variable is derived from this.

16. A hob wherein a control means is provided, which is designed to carry out the method according to claim 1.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0034] Exemplary embodiments of the invention are schematically illustrated in the drawings and are explained in more detail in the text which follows. In the drawings:

[0035] FIG. 1 shows a highly schematic illustration of a hob with which the method according to the invention can be carried out;

[0036] FIG. 2 shows a possible functional sequence for illustrating the method according to the invention; and

[0037] FIGS. 3 and 4 show different profiles for temperature and power supply per unit area in the case of different heating processes or states at the hob in accordance with FIG. 1.

DETAILED DESCRIPTION

[0038] FIG. 1 highly schematically illustrates a hob 11 in the form of an induction hob which is designed to carry out the method according to the invention. The hob 11 has a hob plate 12 and an induction coil 14 which is arranged beneath the hob plate. A power electronics system 16 for the induction coil 14 is driven by a control means 17 for the purpose of setting a power supply or power supply per unit area. The control means 17 is further connected to an operator control element 18 of the hob 11, illustrated here by a capacitive sensor element beneath the hob plate 12.

[0039] The induction coil 14 defines, as it were, a cooking point 20 on the hob 11, on which cooking point a cooking vessel 22 is positioned. Here, the cooking vessel is illustrated as a cooking pot, wherein frying can also be performed in a cooking pot. It goes without saying that, as an alternative, the cooking vessel can be a considerably taller cooking pot or a considerably shorter pan. Items which may be added to the cooking vessel 22 are also illustrated. A piece of meat 24 which may be intended to be seared in the cooking vessel is illustrated on the right-hand side. The addition of water 25 into the cooking vessel 22 using a vessel 26 is illustrated on the left-hand side.

[0040] Instead of a single induction coil 14, a cooking point 20 can also be formed from a plurality of induction coils, for example two to four or even more, depending on the size of the cooking vessel 22. Induction coils of this kind are disclosed, for example, in EP 2945463 A1 and WO 2009/016124 A1. However, a plurality of these induction coils are then operated as a single common induction coil, advantageously with a uniform power density per unit area for the base of the cooking vessel 22, so that they can be considered to be a single induction coil here. All of the induction coils of a cooking point, and not just a single induction coil, are then simply taken into consideration for the abovementioned temperature control operation.

[0041] According to US 2011/120989 A1 mentioned above, the control means 17 can, owing to the connection to the power electronics system 16 and the induction coil 14, identify a change in temperature from operating parameters of the induction coil 14. Express reference is made to US 2011/120989 A1 for the details.

[0042] The functional diagram in FIG. 2 schematically illustrates how the method according to the invention can proceed. At the beginning of a process of placing the cooking vessel 22 with unknown contents onto the cooking point 20 and beginning the heating operation, the power supply or power supply per unit area at the induction coil 14 are already detected by the control means 17 by means of the power electronics system 16. The power supply per unit area can be calculated from a power supply, which flows across the power electronics system 16, from a geometric size, which is known to the control means 17, of the induction coil 14. If the maintaining function is then activated as function activation at a specific time, an attempt has to be made to classify the current state depending on the process at the boiling point of water on the one hand and the process at a different temperature on the other hand, that is to say a kind of characterization. This leads simply to case analysis.

[0043] In the case of function activation of the maintaining function on account of the presence of a state in which a largely constant temperature can be identified at the cooking vessel 22 without much control having to be performed, it can be concluded during the characterization that a process at the boiling point of water is present. To this end, the control means 17 can, for example, also evaluate different additional factors, which are not illustrated here, such as the level of the current power supply per unit area for example. In order to maintain a process at the boiling point of water, that is to say in order to bring water to the boil and to maintain boiling, a power supply per unit area of between 0.5 W/cm.sup.2 and 6 W/cm.sup.2 is usually required. If the current power supply per unit area is considerably above the range or considerably below the range, there may be a fault and the maintaining function may then no longer be activated under certain circumstances. If, however, a plausibility check of this kind reveals that a process at the boiling point can by all means be present, a state with a constant boil-off rate is present, specifically boiling of the water. The further steps are explained in more detail below.

[0044] If, however, the characterization and the case analysis reveal that a process at the boiling point of water is not taking place, but rather a so-called temperature control process because the temperature control therefore has to intervene in order to compensate for slightly fluctuating temperatures, a temperature controller will commence operation after activation of the maintaining function. This means that the control means 17 then simply attempts to control the power supply or power supply per unit area by means of the power electronics system 16 such that the temperature prevailing at the time of function activation of the maintaining function is further maintained. Therefore, temperature deviations are regulated out. In both cases, this can then be continued as a maintained state for a relatively long time or an unspecified duration. Certain maximum durations after which the method is stopped can be provided as a safety function since ultimately a kind of automatic cooking programme takes place and therefore an operator could possibly forget that the hob 11 is switched on. For example, a considerable reduction in the power supply per unit area, for example to 10% to 30% or 50%, can take place after 30, 60 or 90 minutes. As an alternative, the power supply per unit area can be completely switched off after this time has elapsed. Before a reduction or switch-off, an operator can be provided with optical and/or acoustic notification, but this does not necessarily have to be the case.

[0045] In FIG. 3, for the first case, the behavior with respect to time for the temperature T is illustrated on the left-hand side Y axis and the power supply per unit area P is illustrated on the right-hand side Y axis, wherein primarily the power supply per unit area P is not illustrated in a linear manner. The temperature T increases, specifically relatively slowly, because water is heated in the cooking vessel 22 and therefore initially a large amount of energy has to be introduced for an increase in temperature. At a temperature of 100° C., the water in the cooking vessel 22 boils, in response to which the temperature T becomes constant. The maintaining function is activated at a specific time t*, that is to say when the operator takes the view that precisely this state with boiling water and also this degree of boiling should be continued. The temperature T remains constant starting from this point. A power supply per unit area may first have been somewhat higher at the start, as is illustrated by the thick line, at for example 10 W/cm.sup.2. It may then have been somewhat reduced by an operator before the time t*, for example because the water in the cooking vessel 22 had boiled excessively, for example at 4 W/cm.sup.2. If a desired cooking impression has then been established in the case of the second somewhat lower power supply per unit area, the maintaining function is activated. Further continued cooking is performed at the power supply per unit area of the time t*. This is also illustrated in FIG. 3.

[0046] If the case of a sudden drop in temperature as mentioned at the outset now occurs, for example to a temperature of approximately 60° C. here, the temperature T falls and the power supply per unit area is initially maintained. Since the control means 17 then sees that the temperature T is increasing only slowly, it is clear that a relatively large quantity of additional product to be cooked, in particular additional water 25 according to FIG. 1, has been introduced into the cooking vessel 22. The process can then either continue to be heated with the power supply per unit area P as at time t* until the water in the cooking vessel 22 comes to the boil again and the temperature T=100° C. is reached again with a cooking impression which will then have again largely approximated the previous one from time t*. This constant power supply per unit area is illustrated at 4 W/cm.sup.2. As an alternative, the power supply per unit area can be increased at least until a constant temperature T has been established again, for example increased to the power supply per unit area used at the beginning of the heating process, here 10 W/cm.sup.2. This is illustrated using dashed lines. If a constant temperature T is then established, a change can again be made to the previous power supply per unit area at time t*. The brief increase in the power supply per unit area is then used to more rapidly reach the temperature T=100° C. again. This is illustrated at the bottom right in FIG. 2 with the case of cooling as a sudden drop in temperature and reheating until the boiling point has been reached again.

[0047] If the control means 17 establishes that a signal drop takes place suddenly and possibly even in steps, for example within a few seconds, it can be concluded that the cooking vessel 22 on the hob 11 has been displaced, for example by 0.5 cm to 3 cm. As an alternative, the cooking vessel can also have been briefly removed from the cooking point 20 and then placed on it again. In this case, the control means 17 can advantageously maintain the power supply per unit area from time t* and a brief increase is not required.

[0048] FIG. 4 illustrates what the profiles for the temperature T and the power supply per unit area P with respect to time look like in a second case with desired searing of meat 24 in the cooking vessel 22. An operator will highly heat the cooking vessel 22 with a customarily high power supply per unit area if searing of, for example, steak is required. In this case, only a small amount of oil or fat is expected to be contained in a pan as cooking vessel 22, and therefore the cooking vessel does not have to be heated to a great extent. The temperature T increases continuously to a certain extent. A temperature which is considered by an operator to be good and sufficient to fry a steak as required, usually somewhat above 220° C., is reached at time t′. Therefore, the maintaining function is operated at time t′ here. Since the control means 17 has established a further change in temperature of the cooking vessel 22 by means of the power electronics system 16 at this time, the control means therefore knows that a process at the boiling point of water cannot take place, as has been explained previously. Therefore, temperature control is performed in accordance with the case analysis at this time and the temperature of time t′ is kept constant from now on. Even though, at first glance, the process appears to be very similar to that from FIG. 3 with the constant power supply per unit area of the first case, the cause is different in each case. In FIG. 3, the temperature is, owing to the boiling of water in the cooking vessel 22, necessarily kept at 100° C. as long as no quenching or the like takes place. In the case of FIG. 4, a first temperature control operation to the value established at time t′ is actually carried out.

[0049] If a sudden drop in temperature is established at time t″, the temperature control operation which is just carried out in any case attempts to compensate for this drop in temperature again and to return to the temperature of time t′ as quickly as possible. Whereas a very high or, under certain circumstances, even the maximum power density per unit area, for example 7 W/cm.sup.2, was selected at the beginning of the heating process, a lower power density per unit area has been used after t′, which lower power density per unit area is simply selected so as to maintain this temperature. The lower power density per unit area is, for example, 3 W/cm.sup.2. In order to compensate for the sudden drop in temperature at time t″, the power density per unit area can once again be increased and, in particular, be set at the maximum again. As soon as the sudden drop in temperature is then regulated-out again and the temperature at time t′ has been reached again, the temperature control means also reduces the power density per unit area again, as is illustrated here. The control behavior of the temperature controller can be designed, for example, as illustrated here, as a two-point controller. However, in an advantageous refinement, a continuous controller is used which sets the power requirement proportional to the temperature deviation from the controller setpoint value, or even can additionally be set depending on the derivative and/or integral thereof. Controllers of this kind, for example P, PI, PD or PID controllers, are known to a person skilled in the art.

[0050] If the temperature controller or the control means 17 establishes that the sudden drop in temperature takes place to a considerably lower temperature than that at time t′ and possibly a temperature increase takes place very quickly, for example within 15 seconds, a process of an abovementioned quenching of a seared piece of meat or steak can be identified. This is illustrated by the dotted temperature profile. A certain quantity of liquid is therefore added to the seared meat. The operation of the control means 17, as is also shown in FIG. 2, then changes from the case of constant temperature control to the case of a constant power density per unit area. Usually, specifically after quenching of seared meat in order to produce a sauce for example, the sauce is brought to a light boil or simmer. However, it should certainly not be bubbling hot. For this reason, a temperature of T=100° C. can then not be exceeded after reheating, the introduced liquid prevents this. Therefore, a change should now be made to a constant boil-off rate or a constant power density per unit area. However, this is not actually known to the control means 17 since the power density per unit area at time t′ was too high and has led to a temperature of 220° C. or has maintained this. Here, after a constant temperature is reached, in the present case specifically of approximately 100° C., a change can then be made to a freely selected fixed value for the power supply per unit area. The value can lie between 0.5 W/cm.sup.2 and 5 W/cm.sup.2, as mentioned at the outset, for example at 2 W/cm.sup.2 or 3 W/cm.sup.2, here at 2 W/cm.sup.2 illustrated with a dotted line. Here, the control means 17 can also further incorporate the size of the power density per unit area at time t′ in order to be able to approximately estimate therefrom whether a process is proceeding at rather high temperatures or rather relatively low temperatures. The starting gradient of the temperature after time t″ can also be taken into account.

[0051] Finally, FIG. 2 further illustrates that, starting from a case of a constant power density per unit area, the water in the cooking vessel 22 has boiled away, that is to say a case of boiling-dry is present. When the temperature then begins to rise again, specifically a safety switch-off can intervene in order to prevent damage to or burning of the rest of the products being cooked or food in the cooking vessel 22.

[0052] In the second case of regulation at a constant temperature, this case cannot be as easily identified since it is simply regulated at a constant temperature. However, it is possible to identify whether a lower or considerably lower power density per unit area is required in order to reach the constant temperature starting from a specific time. This could also be identified as a case of boiling-dry with a resulting safety switch-off.