Heating device for a steering wheel of a vehicle with redundant temperature determination, heating and detection device, system and method

Abstract

One aspect of the invention relates to a heating device (6) for a steering wheel (3) of a vehicle (1), comprising an energy source (7) for generating heating energy, and at least one thermistor (8) with which the actual temperature of the steering wheel (3) can be detected during heating, wherein the heating device (6) has an evaluation unit (10) with which at least an actual heating power and / or an actual heating energy of the energy source (7) can be evaluated during heating of the steering wheel (3), wherein the evaluation unit (10) is configured to determine the actual temperature, in particular in addition to the thermistor (8), as a function of the actual heating power and / or the actual heating energy. Further aspects relate to a heating and detection device (16), a system (1), and a method.

Description

[0001] One aspect of the invention relates to a heating device for a steering wheel of a vehicle. The heating device has an energy source for generating heating energy for heating a steering wheel. The heating device has at least one thermistor with which an actual temperature can be detected during heating. Another aspect of the invention relates to a heating and detection device for heating a steering wheel and for detecting whether a hand is gripping the steering wheel. Another aspect of the invention relates to a system for a vehicle. Yet another aspect of the invention relates to a method for operating such a system.

[0002] US Pat. No. 6,664,517 B2 discloses a heating device for a vehicle steering wheel. A temperature sensor, in particular an NTC (Negative Temperature Coefficient), is provided for temperature monitoring.

[0003] Heated steering wheels are available in a wide variety of designs. Heating a steering wheel is comfortable for the driver, especially in cool outside temperatures. However, excessive heating of a steering wheel is not only technically disadvantageous, but also has disadvantages in terms of use, as touching the overheated areas of the steering wheel with a user's hand can be uncomfortable. This can also lead to the user removing their hand from the steering wheel or only touching it very lightly, thus possibly no longer fully gripping a heated area of ​​the steering wheel.

[0004] This not only affects the safe driving of a vehicle, but also the general usage behavior of a user.

[0005] It is an object of the present invention to provide a heating device, a heating and detection device, a system and a method in which operational reliability is increased.

[0006] This object is achieved by a heating device, a heating and detection device, a system and a method according to the independent claims.

[0007] One aspect of the invention relates to a heating device for a steering wheel of a vehicle. The heating device is thus designed and provided for heating the steering wheel. The heating device has an energy source for generating heating energy for heating a steering wheel. The heating device has at least one thermistor with which an actual temperature can be detected during heating. In particular, an actual temperature of a heating element of the heating device, which is arranged on the steering wheel, is thereby detected. In particular, in addition to or instead of this, the actual temperature of the steering wheel during heating can be detected with this thermistor.

[0008] The heating device in particular has an evaluation unit or an evaluation circuit. This can be a computer or have one. It can be a processor or a microprocessor. With this evaluation unit, at least an actual heating output and / or an actual heating energy of the energy source can be evaluated when heating the steering wheel or during active heating operation of the heating device. The evaluation unit is further configured to determine the actual temperature depending on the actual heating output and / or the actual heating energy. This heating device therefore makes it possible, in particular, to increase operational reliability. This is because a heating device is thus provided which enables the actual temperature to be determined in two different ways. This provides a redundant system with regard to determining the actual temperature.This not only increases accuracy, but also allows the plausibility of one actual temperature value to be checked against the other. It is therefore provided that, in addition to the thermistor, the actual temperature can also be determined based on this actual heating energy and / or the actual heating power, in addition to the thermistor, and in particular in a different way than with the thermistor. In particular, in this context the heating device has a heating element, such as a heating mat. This is intended to be attached to the steering wheel. In particular, the heating element is intended to be attached to an area of ​​the steering wheel that is intended to be gripped by a user's hand. In particular, the temperature of this heating element can also be determined in this context.

[0009] The heating device thus makes it possible, in particular, to record and determine the actual temperature virtually directly using the thermistor, and on the other hand to determine it indirectly on the basis of the aforementioned electrotechnical parameters, namely the actual heating power and / or the actual heating energy.

[0010] In one embodiment, a reference heating output is specified. This reference heating output characterizes a reference temperature. The evaluation unit is configured to determine the actual temperature by comparing the actual heating output with the reference heating output. In particular, the fixed assignment between the reference heating output and this reference temperature also makes it possible to determine the actual temperature based on this aforementioned comparison. In addition to or instead of this, it is possible to specify a reference heating energy. This characterizes a reference temperature. The evaluation unit is configured in particular to determine the actual temperature by comparing the actual heating energy with the reference heating energy.

[0011] In one embodiment, the reference heating power and / or the reference heating energy characterize a maximum temperature that the steering wheel and / or the heating element of the heating device may have. This reference temperature is therefore this maximum temperature. This advantageously ensures that, thanks to a very precise and reliable operation of the heating device, it is always detected when the temperature of the steering wheel and / or the heating element approaches or reaches this maximum temperature. This very reliably prevents the steering wheel from becoming too hot. This in particular enables a high level of operational reliability of the heating device. In particular for the aspects explained above and at the beginning, especially if a detection device is also provided which is intended to detect gripping of the area of ​​the steering wheel, this enables significantly increased safety.

[0012] By preventing a specific area of ​​the steering wheel from overheating, it is also possible to prevent a hand from being removed from that area, or to prevent the hand from being moved around the steering wheel as such, but rather only lightly touching that area. Especially when this movement around the steering wheel is linked to a vehicle assistance system, and the assistance system only operates or performs specific functions when the hand is detected grasping that area of ​​the steering wheel, the corresponding operation of the assistance system can be achieved very advantageously and safely.Especially when this detection of a gripping of the steering wheel area with one hand is linked, for example, to a change between different autonomy levels when driving a vehicle, operational safety is also significantly increased in this regard.

[0013] In one embodiment, the heating device has a control unit with which the energy source can be controlled at least depending on the determined actual temperature, in particular such that the actual temperature is less than or equal to the maximum temperature. The control unit can have the evaluation unit. It is also possible for the control unit and the evaluation unit to be separate units.

[0014] In one embodiment, the evaluation unit is configured to determine the actual heating power and / or the actual heating energy depending on the actual electrical current provided and the actual electrical voltage of the energy source. In this context, it is known that power is the product of current and voltage. In this regard, energy, in turn, is the product of power and a time or a time interval.

[0015] This means that the actual heating output and / or the actual heating energy can be determined easily, safely and quickly using simple and available electrical parameters.

[0016] In one embodiment, an electronic circuit of the heating device includes a semiconductor switch. This switch can be used, in particular, to measure the actual electrical current and the actual electrical voltage of the energy source. Such a semiconductor switch is preferably a so-called high-side switch.

[0017] The energy source is preferably a battery. It can be a vehicle battery. In particular, it is the battery of the vehicle in which the heating device and a steering wheel to be heated by the heating device are also located.

[0018] The proposed heating device also makes it possible to meet the ASIL-C safety standard. The required failure probability, which is met by the proposed heating device, therefore also allows this heating device to be used when highly complex and / or autonomous driving processes occur in a vehicle and these are linked to a corresponding device. Especially with such a specific electronic circuit design with such a high-side switch, the voltage and current can be detected or measured very quickly and accurately.Especially when the actual temperature, a target temperature, and thus the reference temperature, as well as the materials of the steering wheel, particularly the area to be heated, are known, the electrical heating energy or electrical heating power required to avoid exceeding this reference temperature, but especially to preferably achieve it, can be determined. The operational reliability of the heating device can be further improved by the reference heating power and / or reference heating energy then specified in this regard, which can also be determined and specified taking into account the materials of the steering wheel.

[0019] A further aspect of the invention relates to a heating and detection device for heating a steering wheel and for detecting whether a hand is gripping the steering wheel, in particular an area provided for this purpose, such as a steering wheel rim. This heating and detection device preferably comprises a heating device according to the above-mentioned aspect or an advantageous embodiment thereof. Furthermore, this heating and detection device also comprises a detection device for detecting whether a hand is gripping the steering wheel. It is precisely in this aspect of the invention that the above-mentioned advantage with the heating device, as explained, is to be emphasized.Especially when a hand is also required to grip the steering wheel area in order to perform or not perform certain functions of the vehicle, in particular an assistance system, it is also of particular importance that this area of ​​the steering wheel is reliably heated only to such an extent that it can also be reliably and permanently touched and gripped by a hand. Such a device in particular can then be used to better prevent a hand from no longer gripping this area, or from abruptly letting go, or from only lightly touching it, particularly due to overheating of this area of ​​the steering wheel. This also makes the associated operation of the assistance system particularly safe and reliable.

[0020] In one embodiment, electrodes of the detection device of this heating and detection device, with which a gripping of the steering wheel by hand can be detected, are arranged adjacent to a heating element of the heating device. The evaluation unit is configured, in particular, to evaluate the electrical voltage profile of the energy source and, depending on this, to determine any influence on the detection accuracy of the detection device. In particular, the electrodes are intended to be arranged on an area of ​​the steering wheel to be heated. This is also provided for the heating element.

[0021] This approach also makes it particularly advantageous to detect relatively strong and / or undesirable fluctuations in the electrical voltage of the energy source. Since such fluctuations, which can also be referred to as noise, can potentially impair the accurate detection of a hand gripping the steering wheel area, this mode of the heating and detection device is advantageous. This is because it can essentially generate an advance warning if excessive noise and thus excessive fluctuations in the voltage of the energy source occur. As already mentioned above, this can then potentially lead to inaccuracies in the detection of whether or not a hand has been gripped in the steering wheel area.It is precisely through this proposed principle that this can be detected or anticipated that such inaccuracy may occur in the detection of a hand grasp.

[0022] In one embodiment, if a specific influence greater than a threshold influence occurs, a safety state of the detection device can be set or is adjustable. This also makes it possible to proactively prevent such incorrect assessments regarding a possible gripping of the hand in the area of ​​the steering wheel. In addition to or instead of this, if a specific influence greater than a threshold influence occurs, it is also possible that a measurement frequency of the detection device that is different from the current measurement frequency can be set or is set to determine whether the steering wheel has been gripped by the hand. This way, by changing the measurement frequencies in this way, the accuracy of detecting whether or not a hand has gripped the steering wheel can be improved.By changing the measuring frequency, it can be ensured that the electrical influences on the electrodes of the detection device caused by the voltage fluctuations of the energy source are not so significant with regard to the measurement inaccuracies or can generally be disregarded.

[0023] This is particularly advantageous if, when measuring the voltage and analyzing the course of the electrical voltage, the relevant frequency can also be determined, so that it is then possible to switch specifically to a measuring frequency that is not critical to this frequency of the fluctuating voltage.

[0024] A further aspect of the invention relates to a system for a vehicle. In one embodiment, the system comprises a heating device according to the above-mentioned aspect or an advantageous embodiment thereof. In addition or instead, the system may comprise a heating and detection device according to the above-mentioned aspect or an advantageous embodiment thereof. The system further comprises a steering wheel. The steering wheel has an area that is intended to be gripped by a hand when the steering wheel is to be operated. For example, this area can be a strand-like area. It can be, for example, a steering wheel rim.

[0025] A further aspect of the invention relates to a method for operating a system, in particular according to the above-mentioned aspect or an advantageous embodiment thereof. In particular, this method comprises the following steps: - activating at least the heating device for heating a gripping area of ​​the steering wheel; - Detecting the actual temperature of the area with a thermistor of the heating device; - Providing the actual electrical current and the actual electrical voltage of an energy source of the heating device to an evaluation unit of the heating device; - Determining an actual heating power and / or an actual heating energy of the energy source depending on the actual electrical current and the actual electrical voltage, in particular with the evaluation unit; - Additional determination of the actual temperature of the area depending on the actual heating power and / or the actual heating energy, in particular with the evaluation unit.

[0026] By this method, the above-mentioned advantages as explained for the heating device and / or the heating and detection device and / or the system are also achieved.

[0027] In one embodiment of the method, it is possible for the energy source to be operated as a function of the actual heating output and / or the actual heating energy. Provision can be made for a comparison of the actual heating output with a reference heating output and / or a comparison of an actual heating energy with a reference heating energy. In particular, an actual temperature can be determined, in particular estimated, on the basis of these comparisons. This is particularly true when a reference heating output and / or a reference heating energy is characterized by a reference temperature, in particular a maximum permissible temperature for the steering wheel and / or the heating element of the heating device.

[0028] In a further exemplary embodiment, it can be provided that a detection device of the system, which can be part of a heating and detection device of the system, can be used to detect a gripping of an area of ​​the steering wheel with a hand. For this procedure, in an advantageous exemplary embodiment, it can be provided that a safety assessment is carried out. In one exemplary embodiment, this safety assessment is intended to provide information as to whether sufficiently accurate detection is possible as to whether or not a hand is gripping this area. In particular, it is possible for a curve of an electrical voltage of the energy source with which energy is provided for the heating device to lead or could lead to the detection of a gripping of the area with a hand occurring with an accuracy less than a threshold value.In particular, it is possible if such a degree of accuracy less than a threshold degree of accuracy is detected, a warning is issued and / or a safety state of the detection device is set and / or a change is made from a current measuring frequency to a different measuring frequency, on the basis of which a more precise detection can then be made as to whether or not the area is being encompassed by a hand.

[0029] Another aspect relates to a vehicle with a system and / or a heating device and / or a heating and detection device.

[0030] Embodiments of the invention are explained in more detail below with reference to schematic drawings. They show: Fig. 1 a schematic representation of an embodiment of a heating device according to the invention as well as a schematic representation of an embodiment of a heating and detection device according to the invention, as well as an embodiment of a system according to the invention; and Fig. 2 diagrams in which heating intervals of the heating device are shown schematically and, on the other hand, the courses of the temperature of a steering wheel and / or a heating element of the heating device as well as a course of an actual heating power and / or an actual heating energy are shown as a function of the above-mentioned heating intervals.

[0031] In the figures, identical or functionally identical elements are provided with the same reference symbols.

[0032] In Fig. Figure 1 shows a schematic representation of a system 1. This can also be referred to as a vehicle system. System 1 can, for example, be part of a vehicle 2. Vehicle 2 can, for example, be a passenger car or a truck.

[0033] The system 1 comprises a steering wheel 3. A steering wheel can be formed with a circumferentially closed ring. However, a steering wheel can also be designed differently and, for example, have one or more handlebars, in particular cantilevered, curved, or straight, which are gripped with one hand or each with one hand.

[0034] The steering wheel 3 has at least one region 4 intended to be gripped by a hand of a vehicle driver. For example, the region 4 can be rope-like. It can be curved in this regard. In particular, the region 4 can be a circumferential steering wheel rim. Furthermore, the steering wheel 3 has a steering wheel spoke 5, to which the region 4 is connected.

[0035] The system 1 further comprises a heating device 6. The heating device 6 is designed to heat the steering wheel 3, in particular the area 4. The heating device 6 preferably comprises at least one energy source 7. This can be a battery. The energy source 7 can be, for example, a vehicle battery.

[0036] The energy source 7 is designed to generate energy for heating the steering wheel 3. In addition, the heating device has at least one thermistor 8. This can be an NTC element, for example. With this thermistor 8, an actual temperature of the steering wheel 3, in particular of the area 4, can be detected. In particular, in this context, an actual temperature of a heating element 9 of the heating device 6 can also be detected. The heating element 9 is intended for installation on the steering wheel 3, in particular of the area 4. The heating element 9 can be a heating mat, for example.

[0037] In the exemplary embodiment, the heating device 6 has an evaluation unit 10. This can be part of a control unit 11. In one exemplary embodiment, the evaluation unit 10 can also be referred to as an evaluation circuit. With this evaluation unit 10, at least an actual heating power and / or an actual heating energy can be evaluated during active operation of the heating device 6 and thus during heating. In particular, the actual heating power and / or the actual heating energy of the energy source 7 can be evaluated here. The evaluation unit 10 is also designed, in particular, to determine the actual temperature depending on this actual heating power and / or depending on this actual heating energy, in addition to measuring with the thermistor 8. In particular, this actual temperature can be determined indirectly with this evaluation unit 10.

[0038] The heating device 6 further comprises an electronic circuit 12. This circuit comprises a semiconductor switch, in this case, in particular a high-side switch 13. Furthermore, this electronic circuit 12 also comprises a low-side switch 14. As can be seen, in the exemplary embodiment, these two switches 13 and 14 are connected to the external load, in this case, the heating element 9.

[0039] As also shown schematically, the information of the thermistor 8 is transmitted in particular via a corresponding measuring unit 15, preferably also to the evaluation unit 10.

[0040] Furthermore, the exemplary embodiment provides for system 1 to have a heating and detection device 16. This device comprises the heating device 6 and a detection device 17. The detection device 17 is intended to detect a vehicle driver grasping the area 4 with at least one hand, in particular both hands. In one exemplary embodiment, this detection device 17 has an evaluation unit 18. It is also possible for the evaluation units 10 and 18 to be combined into a common evaluation unit.

[0041] In one embodiment, the detection device 17 has at least two electrodes 19 and 20 arranged in the region 4. As can be seen, the heating element 9 is arranged adjacent to these two electrodes 19 and 20 in this region 4.

[0042] It is possible for a reference heating power to be specified, which characterizes a reference temperature, in particular a maximum permissible temperature for the area 4. In addition to or instead of this, it is possible for a reference heating energy to be specified, which characterizes the corresponding reference temperature. The evaluation unit 10 is preferably configured to determine the actual temperature by comparing the actual heating energy with the reference heating energy and / or the actual heating power with the reference heating power. In particular, the evaluation unit 10 is configured to determine the actual heating power and / or the actual heating energy depending on the actual electrical current provided and the actual electrical voltage of the energy source 7. The actual electrical current and the actual electrical voltage are preferably detected or measured using the high-side switch 13.In particular, the control unit 11 can be used to control the energy output of the energy source 7 for the heating device 6 depending on the determined actual temperature. In particular, this occurs such that the actual temperature is less than or equal to this maximum possible temperature. This prevents overheating of the area 4. Thus, a heat state is always set at the area 4 that allows a vehicle user to reach around the area 4 at any time, even permanently and thus for a longer period of time.

[0043] In Fig. 2, various scenarios are illustrated in schematic diagrams. The upper diagram, in which time t is plotted on the horizontal axis and voltage U and / or current I on the vertical axis, shows exemplary heating intervals. These extend from times t1 to t2 and from t3 to t4.

[0044] As can be seen, the actual voltage and / or current can be measured and / or determined at discrete time intervals during these time intervals. This is symbolized by the arrows. It is possible for the time intervals at which the respective measurements and / or determinations are carried out to remain the same. However, it is also possible for these time intervals to be changed during such a time interval between t1 and t2 and / or between t3 and t4. This can be advantageous, for example, if a fluctuation in the course of the electrical voltage, in particular of the energy source 7, occurs. It is possible for these time intervals, between which corresponding time-discrete measurements and / or determinations of the actual electrical voltage and / or the actual electrical current are carried out, to be shortened if, for example, stronger increases in these electrical parameters were to occur at the energy source 7 in this context.

[0045] However, it is also possible for such measurement and / or determination of the actual electrical current and / or the actual electrical voltage to occur, for example, only at the beginning of such a heating interval and / or only towards the end of such a heating interval. It is then possible for one and / or more measurements and / or determinations to be performed at each time.

[0046] As furthermore in Fig. 2 As can be seen in the lower diagram, the horizontal axis again shows the time period t and the vertical axis shows the temperature T at the steering wheel 3, in particular in area 4, and / or the heating element 9. The heating energy H is also shown there as an example. In this context, the heating energy H0 characterizes the reference heating energy. This is the maximum heating energy that can be set in order to reach or not exceed the maximum temperature. The diagram shows that as heating progresses, the provided heating energy and thus the actual heating energy to be generated is reduced because, as can also be seen, the temperature T increases starting from the initial value T0.

[0047] It is advantageous, as also mentioned, that based on the evaluation of an electrical parameter, in particular the actual voltage of the energy source 7, a fluctuation can be detected, which may be detrimental to the detection device 17. Therefore, it is particularly advantageous to be able to predict, based on the evaluation of the course of this electrical voltage of the energy source 7, whether this could or even does influence the detection accuracy of the detection device 17. In this context, corresponding fluctuations, in particular in the voltage of the energy source 7, can also influence the measurement accuracy of the electrodes 19 and 20, so that the detection accuracy, whether or not a hand is grasping the area 4, can fall below an accuracy threshold.In particular, it can then also be detected whether, in the case of a specific influence greater than a threshold value influence, a state exists in which a safety state of the detection device 17 is set and / or a measuring frequency different from the current measuring frequency is set for determining whether the steering wheel 3, in particular the area 4, is grasped with one hand.

[0048] A high-side switch is a transistor that connects or disconnects the high-voltage supply rail to the load. This type of arrangement is typically designed with an n-channel FET operating in the saturation region.

[0049] A semiconductor switch placed in the upper circuit with respect to an external load is called a high-side (power side) drive. If mounted in the lower circuit, it is called a low-side (ground side) drive.

[0050] A low-side driver is placed between the load and ground, while a high-side driver, as in Fig. 1, is placed between the load, here the heating element 9, and the supply voltage.

[0051] The low-side switch operates preferentially by applying an input voltage to the gate and grounding the MOSFET source. This control is the same as for single MOSFETs, so individual MOSFETs can be easily replaced.

[0052] In a vehicle where the battery voltage is fixed and the body is grounded, the output is susceptible to ground faults. A high-side switch is then better suited to detecting abnormal conditions such as ground faults. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] US 6 664 517 B2

[0002]

Claims

[1] Heating device (6) for a steering wheel (3) of a vehicle (1), with an energy source (7) for generating heating energy, and with at least one thermistor (8) with which the actual temperature of the steering wheel (3) can be detected during heating, characterized by that the heating device (6) has an evaluation unit (10) with which at least an actual heating power and / or an actual heating energy of the energy source (7) can be evaluated when heating the steering wheel (3), wherein the evaluation unit (10) is designed to determine the actual temperature, in particular in addition to the thermistor (8), depending on the actual heating power and / or the actual heating energy. [2] Heating device (6) according to claim 1, characterized bythat a reference heating power is specified which characterizes a reference temperature and the evaluation unit (10) is set up to determine the actual temperature by comparing the actual heating power with the reference heating power and / or a reference heating energy is specified which characterizes a reference temperature and the evaluation unit (10) is set up to determine the actual temperature by comparing the actual heating energy with the reference heating energy. [3] Heating device (6) according to claim 2, characterized by that the reference heating power and / or the reference heating energy characterize a maximum temperature that the steering wheel (3) may have. [4] Heating device (6) according to claims 2 and 3, characterized bythat the heating device (6) has a control unit (11) with which the energy source (7) can be controlled at least as a function of the determined actual temperature, in particular such that the actual temperature is less than or equal to the maximum temperature. [5] Heating device (6) according to one of the preceding claims, characterized by that the evaluation unit (10) is designed to determine the actual heating power and / or the actual heating energy depending on the actual electrical current provided and the actual electrical voltage of the energy source (7). [6] Heating device (6) according to claim 5, characterized by that an electronic circuit (12) of the heating device (6) has a semiconductor switch, in particular a high-side switch (13), with which the actual electrical current and the actual electrical voltage of the energy source (7) can be measured. [7] Heating device (6) according to one of the preceding claims, characterized bythat the energy source (7) is a battery, in particular a vehicle battery. [8] Heating and detection device (16) for heating a steering wheel (3) and for detecting whether a hand is gripping the steering wheel (3), with a heating device (6) according to one of the preceding claims. [9] Heating and detection device (16) according to claim 8, wherein electrodes (19, 20) of the detection device (17), with which a gripping of the steering wheel (3) with the hand can be detected, are arranged adjacent to a heating element (9) of the heating device (6), wherein the evaluation unit (10) is designed to evaluate the course of the electrical voltage of the energy source (7) and, depending thereon, to determine an influence on a detection accuracy of the detection device (17). [10] Heating and detection device (16) according to claim 9, wherein in the case of a certain influence greater than a threshold value influence, a safety state of the detection device (17) can be set and / or a measuring frequency different from the current measuring frequency can be set for determining whether the steering wheel (3) has been gripped by the hand. [11] System (1) for a vehicle (2), comprising a heating device (6) according to one of the preceding claims 1 to 7 and / or a heating and detection device (16) according to one of the preceding claims 8 to 10, and comprising a steering wheel (3). [12] Method for operating a system (1) according to claim 11, comprising the following steps: - activating at least the heating device (6) for heating a gripping area (4) of the steering wheel (3); - detecting the actual temperature of the area (4) with a thermistor (8) of the heating device (6); - Providing the actual electrical current and the actual electrical voltage of an energy source (7) of the heating device (6) to an evaluation unit (10) of the heating device (6); - determining an actual heating power and / or an actual heating energy of the energy source (7) depending on the actual electrical current and the actual electrical voltage; - Additional determination of the actual temperature of the area (4) depending on the actual heating output and / or the actual heating energy.

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