This application claims priority to German Application No. 10 2020 201 610.0, filed Feb. 10, 2020, the contents of which are hereby incorporated herein in its entirety by reference.
The invention relates to a method for actuating a heating device of a hob or a cooking device, and to a corresponding hob or cooking device. Here, the hob has a radiant heating device as the heating device, a hob plate above said radiant heating device, and a safety temperature limiter between the two. A safety temperature limiter of this kind is designed as a thermomechanical functional device in order to deactivate the radiant heating device when an excessively high temperature or a switch-off temperature is reached. This serves in particular to protect the hob plate against damage due an excessively high temperature on the basis of the heating power of the radiant heating device. Safety temperature limiters of this kind are known from the prior art, for example from U.S. Pat. No. 7,345,572.
One disadvantage of safety temperature limiters of this kind is that although they function very reliably in the case of an excessively high switch-off temperature that is detected by them, their switching behavior is determined directly by the temperature that is detected by them and to date it has not been possible to change the activation state of the radiant heating device on the basis of processes in a cooking vessel on the hob plate.
The invention is based on the problem of providing a method mentioned at the outset and a hob or cooking device mentioned at the outset by way of which problems that arise in the prior art can be solved and in particular it is possible to use a such a hob or its radiant heating device in an advantageous, versatile and practical manner, in particular to ensure safe operation of the hob.
This problem is solved by a method having the features of the claims and by a hob or cooking device having the features of the claims. Advantageous and preferred refinements of the invention are the subject matter of the further claims and will be explained in greater detail below. In said explanation, some of the features will be described only for the method or only for the hob. However, irrespective of this, they are intended to be able to apply independently both to the method and also to the hob. The wording of the claims is incorporated in the description by express reference.
It is provided that the hob is designed as explained at the outset. Here, the safety temperature limiter is advantageously fastened to the radiant heating device or said radiant heating device comprises the safety temperature limiter, so that the two can form a prefabricated structural unit. To this end, the safety temperature limiter is particularly advantageously arranged in an upper region of the radiant heating device, so that it can run, at least by way of an elongate temperature detecting element or a temperature detecting device, between the radiant heating device or its heating conductors and the hob plate. This is the active region of the radiant heating device or its heating conductors upward through the hob plate into a cooking vessel that is placed on it. The hob can have yet further customary switching devices, in particular as a power supply for the radiant heating device. These possibilities will be explained in even greater detail below. The safety temperature limiter is designed to switch off or to deactivate the radiant heating device when a predetermined switch-off temperature is reached.
For the method, it is provided as a preceding step that a cooking vessel is placed on the hob plate above the radiant heating device, in particular where a so-called cooking point is formed by the radiant heating device. This hob is intended to be heated by means of the radiant heating device, for which purpose said radiant heating device is activated. The power supply to the radiant heating device, for example by relays or electromechanical switches, advantageously serves for this activation. When the activation of the radiant heating device starts, a first switch-on time is monitored or starts to run, advantageously in a type of timer of a hob controller. This first switch-on time is the time or period for which the radiant heating device is operated or is activated for the first time after the hob is switched on, in particular at least when the hob plate is cold or has cooled down after previous operation.
The radiant heating device is then activated or supplied with power and heats up the placed-on cooking vessel. At the same time, the safety temperature limiter or at least its abovementioned temperature detection device is also heated up as a result, so that the temperature that is detected by it likewise rises. At some point, the abovementioned switch-off temperature is reached on the safety temperature limiter, this leading to the radiant heating device being deactivated by the safety temperature limiter. In particular, this deactivation can take place by way of a direct switching process. At the same time, the first switch-on time is stopped or its end is established, and it is monitored or recorded. respectively. Therefore, the first switch-on time specifies the period between first activation and deactivation of the radiant heating device.
Finally, the monitored or recorded first switch-on time is compared with a predefined limit switch-on time. If the first switch-on time lies below the limit switch-on time, the power with which the radiant heating device is activated and is operated or is operated during the activation is reduced. A reduction can take place to different extents, as will be explained in even greater detail below.
This can cover the possibility of a placed-on cooking vessel becoming too hot too quickly during heating, so that for example grease or the like that is contained in said cooking vessel could catch fire. The resulting risk of an accident is very high, for which reason it should be avoided as far as possible; grease fires in the kitchen are very dangerous. However, if a placed-on cooking vessel contains a sufficient quantity of product being cooked, which reduces the heat that is generated by the radiant heating device through its mass or for example, because it consists largely of water, absorbs said heat by evaporation, the time taken until the radiant heating device is deactivated, that is to say is switched off, by the safety temperature limiter for the first time is therefore longer than the predefined limit switch-on time. However, the abovementioned possibility should be avoided.
Therefore, in the abovementioned case, heating is performed during the first heating cycle of the radiant heating device or during its first activation with the full, set power but this is no longer done afterward. In particular when the radiant heating device is connected directly to a supply voltage or to a mains voltage and either operates in the connected state with full power or else is deactivated, the radiant heating device is therefore activated with its full or maximum power during this first switch-on time. A reduction of its power can then take place either in a very simple case by way of, for said case of the first switch-on time lying below the limit switch-on time, that is to say the heating having taken place too quickly, the radiant heating device being deactivated for a certain time which lies above the time for the switched-off state that is actually provided for the set operation or cyclical operation, that is to say lasts longer. In this case, the entire hob is advantageously not switched off since it can be assumed that there is no fatal or serious fault but rather only a situation of a possibly excessively high temperature or dangerously high temperature at this cooking vessel, that is to be heated, above the radiant heating device. Such a deactivation of the radiant heating device or reduction of its power can be selected or prespecified for example for a time period of from 1 min to 5 min.
Such very quick heating and therefore premature deactivation of the radiant heating device by the safety temperature limiter usually takes place when a placed-on cooking vessel is empty or has only very little contents, for example only a very small amount of water or oil or grease. A small amount of water could be evaporated very quickly and, due to the further heating of the cooking vessel that then takes place, said cooking vessel could be damaged, for example by way of said cooking vessel deforming or bending to a great extent. When there is a small amount of oil or grease, there is a risk of this reaching temperatures of almost 400° C. or above and it could catch fire starting from these temperatures. This risk of fire is intended to be precluded as far as possible by the invention.
In a further advantageous refinement of the invention, a reduction of the power of the radiant heating device is optically and/or acoustically indicated to an operator in said situation. Therefore, an operator can be informed of the possibly associated danger and of the cause of the reduction of power.
Furthermore, it can be provided that an operator can reactivate the operation of the radiant heating device as intended by operating an operator control element. However, this necessarily deliberate action firstly shows that the operator is present and therefore can quickly identify a dangerous situation and can accordingly respond to it. Secondly, such very quick heating may possibly be specifically desired, and if the operator is aware of this, a possible risk of an uncontrollable situation is also reduced or precluded.
As explained above, the safety temperature limiter is advantageously arranged on the radiant heating device. Said safety temperature limiter particularly advantageously has a temperature detection device which can be designed as a thermomechanical temperature detection device. Said temperature detection device can consist of two materials with different coefficients of thermal expansion, this leading to a relative movement in the event of heating. This temperature detection device acts on a switch for deactivating the radiant heating device by switching the switch, preferably on the basis of 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 known from U.S. Pat. No. 5,498,853, to which reference is explicitly made hereby. Said document also discloses an arrangement of a safety temperature limiter in the form of a so-called rod-type thermostat. Reference is also explicitly made to abovementioned document U.S. Pat. No. 7,345,572 in respect of such a safety temperature limiter, said document showing the exact design of said safety temperature limiter both with an elongate thermomechanical temperature detection device and with two switches.
In a refinement of the invention, it can be provided that, in the case of an excessively short first switch-on time until the deactivation of the radiant heating device by the safety temperature limiter, the power of the radiant heating device is reduced or said radiant heating device is completely deactivated only when said radiant heating device is intended to be activated with a power which lies above a predefined limit power. Such a limit power can be a power per unit area of more than 5 W/cm2, in particular more than 7 W/cm2, alternatively more than 70% of a maximum power per unit area. In a conventional hob, these would be, for example, powers per unit area starting from a power level of 7. Therefore, the method can be restricted to checking of situations in which the danger mentioned at the outset actually exists on account of a relatively high or very high power of the radiant heating device. On the other hand, it should be stated that, at lower powers or powers per unit area, the first switch-on time will presumably be considerably longer than the predefined limit switch-on time in any case. The method according to the invention would be started, but the limit switch-on time would not be undershot. Therefore, the method would not intervene as a safety function because said situation does not occur. A required or maximum power per unit area also depends on a calibration of the safety temperature limiter. This should mean that the higher the calibration, advantageously the higher the power per unit area is too, otherwise the safety temperature limiter cannot switch quickly enough to identify and to prevent a fault. This can preferably also apply conversely; the higher the power per unit area is intended to be, the higher the calibration should advantageously also be.
In a further refinement of the invention, it is possible for the predefined limit switch-on time to be settable. Therefore, it can be fixedly prespecified not only at the factory, but rather possibly can be changed by an operator. For this purpose, it can be provided that said limit switch-on time is settable only in a separate setting mode on the hob. For the safety function itself, it should be provided that said safety function is always activated, that is to say cannot be deactivated, at least starting from abovementioned relatively high powers for the radiant heating device. The desired safety function is ensured in this way.
In yet a further refinement of the invention, it can be provided that, after a specific cool-down time, which can advantageously be predefined, after reduction of the power at the radiant heating device or the deactivation of said radiant heating device, the previously set power is at least partially re-established, in particular is fully established again. Such a cool-down time can be between 2 min and 5 min. This ensures that the cooking vessel is again heated at least to a specific temperature which at the same time can be considered non-critical. That is to say it does not completely cool down again. However, similarly to the manner explained at the outset, it should be ensured here that the safety function is reactivated. That is to say when the radiant heating device is reactivated after the cool-down time has elapsed, the first switch-on time should in turn begin to run again, and if it once again lies below the limit switch-on time, the safety temperature limiter should therefore once again deactivate the radiant heating device relatively quickly and the power with which the radiant heating device is activated should be reduced or switched off again. Therefore, renewed danger can be precluded.
In a further refinement of the invention, it is possible for the switching behavior of the safety temperature limiter to be monitored, in particular by a hob controller, throughout operation of the radiant heating device. If a time of less than 90 sec, in particular less than 60 sec, elapses between two responses of the safety temperature limiter one after the other or in succession, it can be concluded that the cooking vessel that is heated by the radiant heating device has boiled-dry. A similar safety function is then also achieved during continuous heating of the cooking vessel, that is to say not only at the start. If it is concluded that the cooking vessel has boiled-dry in this way or that the cooking vessel is being heated too quickly, the power for this radiant heating device is once again reduced as explained at the outset, in particular said radiant heating device is deactivated. Such a deactivation or a reduction of the power should take place at least for the abovementioned cool-down time.
Furthermore, it is possible for a ratio of an active time of operation of the radiant heating device to the sum of this active time and a non-active time, during which the radiant heating device is not operated, to be stored in a control device or the hob controller. This can also take place in conjunction with a power level that is set for the radiant heating device. In this case, the control device or hob controller can also monitor and store the power that is generated by the radiant heating device over time, so that this is known. In a further embodiment, it can be provided that the abovementioned ratio of an active time to the sum of the active time and the non-active 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 for the relatively high or maximum powers for the radiant heating device to be considered here, the safety temperature limiter is switched or switched off for the first time before the energy controller. This may be of importance for detecting the switching process at the safety temperature limiter. Such an energy controller is known, for example, from U.S. Pat. No. 4,829,279 to which reference is explicitly made in this respect.
In one possibility of the invention, it is provided that detection of a switching state of the safety temperature limiter, which is connected in series with an abovementioned energy controller for supplying power for the radiant heating device, takes place only at this energy controller. Since such an energy controller is usually arranged remote from the radiant heating device and close to further control devices or the other energy controllers, an electrical connection is more readily possible here. On the basis of the current flow through the energy controller, a conclusion can then be drawn about the switching state at the safety temperature limiter since, in the event of current flow, the safety temperature limiter has to be switched on and therefore the radiant heating device has to be activated.
According to an alternative second possibility, only detection of the switching state of the energy controller can take place and the switching state at the safety temperature limiter can additionally also be detected at the energy controller. The current flow then does not have to be directly monitored. This is possible by detecting a voltage across the radiant heating device since current flows through the radiant heating device or a voltage is dropped across said radiant heating device only when the safety temperature limiter is closed.
In a further refinement of the invention, it is possible to detect that the cooking vessel has boiled-dry in the further course of the cooking process, that is to say after a few minutes, by way of the time at which the safety temperature limiter respectively activates and deactivates the radiant heating device being detected throughout a cooking process. If it is established after a time of more than 5 min and/or after more than ten deactivations of the radiant heating device by the safety temperature limiter that the duration of the activation of the radiant heating device has shortened, in particular has shortened by at least 10% to 50%, this means that the usual switching pattern or cycle pattern of the safety temperature limiter has changed. If there is no change in the power setting for the radiant heating device, shortening of the duration of the activation can only mean that the cooking vessel has now become considerably hotter than before or can no longer absorb as much heat. This is very often the case in the event of the cooking vessel boiling-dry as mentioned above. If such boiling-dry of the cooking vessel is identified or evaluated as being identified, the power with which the radiant heating device is activated and is operated is reduced or said radiant heating device is deactivated as described above in the case of excessively quick heating at the start being identified.
In an advantageous refinement of the invention, an electronic control device of the hob can have switching elements, preferably relays or power semiconductors, with which the radiant heating device is activated or is deactivated, as the hob controller. Such an activation or deactivation of the radiant heating device advantageously takes place by connection to a mains voltage, in particular directly to the mains voltage, or complete disconnection from the mains voltage. There is no intermediate conversion of a supply voltage for the radiant heating device, as is known for induction heating devices for example. Here, relays are understood to mean other switching devices as comprised by an abovementioned energy controller. Such an energy controller is in fact a thermally actuated electromechanical switching device which, however, does not require or contain any so-called intelligence. Here, a specific duty ratio for the radiant heating device is set at the energy controller and therefore its permanently generated power is set. The hob then has an additional controller in order to detect the switching state of the safety temperature limiter, to monitor the first switch-on time and to carry out the method. Only one single additional controller for all cooking points or all radiant heating devices and electromechanical control devices of the hob is advantageously provided in this case. This additional controller then has corresponding detection means for time and, for example, a microcontroller.
In an abovementioned electronic control device, this prespecifies switching or cycling for relays or other switching means for the radiant heating device after power setting by an operator. The abovementioned possibilities for influencing by means of a controller are met by this electronic control device. An additional controller is not required.
In a further embodiment, it is possible for a switching state of the safety temperature limiter to be detected by at least one of the possibilities 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 abovementioned electronic control device or an additional controller.
According to a second possibility, a current which flows through the radiant heating device can be measured. A corresponding current measuring device can likewise be contained in the abovementioned electronic control device or additional controller.
According to a third possibility, a current which flows parallel to a series circuit comprising the safety temperature limiter and the radiant heating device can be measured, advantageously upstream of an energy controller or switching means in the direction of the mains connection. This possibility is also advantageously directly integrated into an electronic control device or additional controller.
A mains power supply, which has a connection to a so-called neutral conductor of a power supply system, can advantageously be provided for the hob. Either a single common disconnector relay can be provided in this connection to the neutral conductor for all radiant heating devices or, alternatively, a dedicated disconnector relay can be provided in the connection to the neutral conductor for each radiant heating device. Therefore, for example as a safety function, either an individual radiant heating device or the entire hob can be switched off by means of the disconnector relay.
These and further features are apparent not only from the claims but also from the description and the drawings, where the individual features can in each case be realized on their own or jointly in the form of subcombinations in an embodiment of the invention and in other fields and can constitute advantageous and inherently protectable embodiments for which protection is claimed here. The subdivision of the application into individual sections and sub-headings does not restrict the general validity of the statements made thereunder.
Exemplary embodiments of the invention are schematically illustrated in the drawings and will be explained in greater detail below.
A rod-type thermostat 23 is arranged on the radiant heating device 16 as the safety temperature limiter according to the invention. The rod-type thermostat 23 is illustrated on an enlarged scale in
A sensor tube 28 composed of metal, in particular composed of steel, is provided in the elongate sensor 27. An elongate rod 29 composed of ceramic material which, by way of its one free end stops on the inside against the end of the sensor tube 28, runs in the sensor tube 28. When heated, the metal sensor tube 28 expands and therefore becomes longer, while the rod 29 consists of ceramic which does not expand. As a result, the rod 29, in a manner pushed away by a helical spring in the housing 25, moves to a certain extent by way of its other end. This other end bears against a switch 31 which is designed as a simple switching spring here but in practice is advantageously designed as a so-called snap-action spring, also see the abovementioned prior art in this respect. Starting from a specific movement path, the rod 29 no longer presses so strongly against the switch 31 that the two switching contacts still bear against one another, but rather they open. There is then no longer any current flow between the switch connection 33 on the left and the mating connection 34 on the right with which said current flow is switched to the current flow to the radiant heating device 16. The rod-type thermostat 23 is therefore opened and therefore interrupts the current flow to the radiant heating device 16, as a result of which said radiant heating device is deactivated as described at the outset. The temperature at which the switch 31 is opened can be precisely adjusted in the case of such a rod-type thermostat 23 and therefore, for example, can also be set according to the invention such that, in the case of the hob 11, the hob plate 12 does not become too hot on account of the abovementioned aspects.
A power supply for the radiant heating device 16 is set here such that it is intended to operate with maximum power and therefore the power supply itself does not switch off the radiant heating device 16 at all. The deactivation of the radiant heating device or the cycling takes place solely with the rod-type thermostat 23. It can be seen here that the temperature T permanently at approximately 460° C. would be so high that, as explained at the outset, either the item of cookware 13 will be damaged by warping or else a small amount of oil or grease could catch fire. A possible situation can be that of an operator having placed the item of cookware 13 containing some fat onto the cooking point 14, set the radiant heating device 16 at maximum power and started operation. The operator may then have possibly left the room. On the basis of
It is obviously not possible to use the rod-type thermostat 23 to detect the temperature at the item of cookware 13 or at its base itself. However, it can be seen from the temperature profile according to
With reference to
An additional controller 36 is provided since no switches, normally even no controller or controller intelligence at all, apart from the energy controllers 42, are provided or have to be provided in such a hob. The additional controller 36 has a microcontroller 38 and a disconnector relay 40 of the heating conductors 20 to the neutral conductor N. The energy controllers 42 and the rod-type thermostats 23 operate as it were autonomously, the energy controllers 42 in the same way as when they are set by an operator. This will be explained in greater detail below. The rod-type thermostats 23 operate, as explained above, at the switch-off temperatures calibrated for them at the factory, specifically likewise autonomously.
The microcontroller 38 is connected to the current paths in front of and behind the rod-type thermostats 23, but a connection can also be designed in another way. As a result, as will be explained further below, the switching state or the current flowing is detected. Therefore, the microcontroller 38 knows when the rod-type thermostat 23 switches off or deactivates the radiant heating device 16 or the heating conductor 20, and it can therefore detect the first switch-off time in the manner described at the outset. Therefore, said rod-type thermostat detects the period starting from the first switch-on or activation of the radiant heating device 16 with the heating conductors 20 until its first switch-off or deactivation. This monitored first switch-on time is then compared with a limit switch-on time that is stored in the microcontroller 38, as has been explained above. If said monitored first switch-on time lies below said limit switch-on time, the power of the radiant heating device which has as it were heated up too quickly has to be reduced. Since the additional controller 36 or the microcontroller 38 cannot directly actuate the energy controller 42 for the corresponding radiant heating device, likewise cannot actuate the rod-type thermostat 23, and otherwise only a single disconnector relay 41 is jointly provided in the current path to each radiant heating device 16, the additional controller 36 can open only the disconnector relay 40. Therefore, not only the radiant heating device 16 in question, but rather all radiant heating devices 16, are switched off. However, this is not possible in a different way here, and the safety function is therefore ensured in all cases. As an alternative, a disconnector relay to the neutral conductor could also be provided separately for each of the radiant heating devices 16 or their heating conductors 20. However, the complexity would then be considerably higher. The disconnector relay 40 does not necessarily have to be installed in the additional controller 36 either; it may be a disconnector relay that is possibly present in any case with an additional connection to the additional controller 36.
Precise possibilities for detecting the activation state of the rod-type thermostat 23 are not illustrated in
Voltage measurement by means of a voltage measuring device 58 is provided here for detecting the switching state of the rod-type thermostat 23. Said voltage measuring device is connected parallel to the heating conductor 20. If the relay 57 is closed and a voltage is detected at the voltage measuring device 58, the rod-type thermostat 23 also has to be closed. If the relay 57 is closed, but the voltage measuring device 58 does not establish a voltage at the heating conductor 20, the rod-type thermostat 23 has opened or deactivated the heating conductor 20. Therefore, the first switch-on time can be monitored or recorded and then, as explained above in relation to
In the yet further exemplary embodiment of
The optical or acoustic signaling to an operator mentioned at the outset when the power for the radiant heating device 16 has been reduced or has been deactivated, that is to say has been switched off, is not illustrated here. However, such signaling can be easily generated by the microcontroller 38 in each case; this does not present any problems in respect of implementation.
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