LU501680B1

LU501680B1 - Electric Heating Device and Method for Improved Heat-Up Performance

Info

Publication number: LU501680B1
Application number: LU501680A
Authority: LU
Inventors: Caroline Derieux; Frank Althaus; Driss Chabach; Thomas Meyers; Thomas Faber
Original assignee: Iee Sa
Priority date: 2022-03-17
Filing date: 2022-03-17
Publication date: 2023-09-22

Abstract

An electric heating device (10), comprising a resistive heating unit (12), a controllable electric power supply (14) and a heater control unit (16) for controlling a level of electric current supplied to the resistive heating unit (12) by the electric power supply (14). The heater control unit (16) is configured for adapting, at least in a portion of the potential range for the actual electric resistance ( ), the level of the electric current to be supplied to the resistive heating unit (12) in dependence of the actual electric resistance ( ).

Description

Electric Heating Device and Method for Improved Heat-Up Performance

Technical field

[0001] The invention relates to an electric heating device, a method of operating such electric heating device and a computer program for automatically carrying out such method.

Background of the Invention

[0002] Electric heating devices employing one or more electric resistive heating members are widely used particularly in the automotive industry for providing passenger comfort, for instance by heating a vehicle compartment in general, and/or passenger seats, and/or arm rests, and/or panels. Electric heating devices having flexible and/or stretchable heater members are known to be employed in vehicle steering wheels for heating right after start-up of a vehicle engine at cold ambient conditions.

[0003] However, the electric resistance of such electric resistive heating members is subject to production tolerances (part-to-part and/or process-related) and potentially to drifting due to effects such as aging, applied strain or compression and environmental influence, for instance temperature changes.

[0004] Tolerances in the electric resistance may result in - a less reproducible heat-up performance due to part-to-part variation - a reduced heat-up performance in the case of high electric resistance - a supply current potentially exceeding amperage specifications in the case of low resistance, and - a reduced average heat-up performance dependent of resistance tolerance range together with current limitations.

[0005] All of these effects impair the objective of an as fast as possible heating up to a desired temperature.

[0006] A conventional approach for solving this issue is to narrow tolerance margins for the electric resistance of the resistive heating members so as to have the electric resistance of the resistive heating members to match required design and/or process parameters of the intended electric heating device. Obviously, this approach leads to a rise of the costs of resistive electric heating devices.

Object of the invention

[0007] It is therefore an object of the invention to provide an economical electric heating device with lowered tolerance requirements for resistive heating members and an improved heat-up performance, i.e. an as short as possible time for reaching a desired temperature level, under the constraint of a predetermined maximum amperage.

General Description of the Invention

[0008] In one aspect of the present invention, the object is achieved by an electric heating device comprising a resistive heating unit, a controllable electric power supply and a heater control unit.

[0009] The resistive heating unit includes at least one resistive heating member and has a total nominal resistance value, wherein the resistive heating unit has an actual electric resistance.

[0010] The controllable electric power supply is configured for supplying electric power to the resistive heating unit. The phrase “being configured to”, as used in this application, shall in particular be understood as being specifically programmed, laid out, furnished or arranged.

[0011] The heater control unit is configured for controlling a level of electric current supplied to the resistive heating unit by the electric power supply.

[0012] It is proposed that the heater control unit is configured for adapting, at least in a portion of the potential range for the actual electric resistance, the level of the electric current to be supplied to the resistive heating unit in dependence of the actual electric resistance.

[0013] Forinstance, the adapting can be performed by using predefined adaptation factors that are stored in a look-up table.

[0014] In conventional electric heating devices, the level of a maximum electric power that can be provided to the resistive heating unit for transforming into heat is ruled by the minimum electric resistance, which is determined by a predefined specification for a maximum amperage, i.e. predefined limit for the electric current through the resistive heating unit. Since the maximum amperage must not be exceeded, the minimum electric resistance characterizes the lower end of the resistance range. Any actual electric resistance of the resistive heating unit that is larger than the minimum electric resistance will result in an electric power level provided for heating that is lower than the maximum electric power level. This is illustrated in Fig. 1 by the line marked with circle symbols.

[0015] The proposed adapting of the level of electric current to be supplied to the electric heating unit can adjust the electric power level provided for heating and, at the same time, keep the electric current level below a specified maximum amperage. By that, a larger average electric power can be provided to the electric heating unit, resulting in an improved heat-up performance with a shortened time for achieving a desired temperature level. Moreover, wider tolerance margins for the electric resistance of the resistive heating members can be allowed. Further, a larger design flexibility for the electric heating device with respect to the electric resistance of the resistive heating members can be accomplished.

[0016] The electric heating device in accordance with the invention is particularly advantageous for automotive applications. The term “automotive”, as used in this patent application, shall particularly be understood as being suitable for use in vehicles including passenger cars, trucks, semi-trailer trucks and buses. Typical automotive applications are, without being limited to, steering wheel heaters, dashboard heaters, window heaters and vehicle seat heaters. However, it is conceived within the scope of the invention to employ electric heating devices in accordance with the invention also in other technical fields, such as clothing.

[0017] The term “resistive heating member”, as used in this patent application, shall particularly encompass, without being limited to, wire heaters, mesh heaters and printed heaters.

[0018] In preferred embodiments of the electric heating device, the resistive heating unit has an actual electric resistance lying in a resistance range around the nominal resistance value between a minimum electric resistance and a maximum electric resistance. The heater control unit is configured for adapting, at least in a portion of the potential range for the actual electric resistance, the level of the electric current to be supplied to the resistive heating unit in dependence of a relation between the actual electric resistance and at least one out of the maximum electric resistance and a predefined typical electric resistance of the resistive heating unit.

In this way, the proposed adapting of the level of electric current to be supplied to the electric heating unit can be individually arranged in dependence of production- specific tolerance margins with respect to the actual electric resistance.

[0019] For instance and without being limited to, the predefined typical electrical resistance value R,, can be selected to be the electric resistance value having the highest probability in a specific production line for producing the resistive heating unit.

[0020] In preferred embodiments of the electric heating device, the relation is given by the rule that the level of the electric current to be supplied to the resistive heating unit can be expressed by kp‘ Lyre , With kp = [A (1)

Here, L,.. denotes a predetermined electric current level, Ray denotes the maximum electric resistance and R denotes the actual electric resistance. Hence, the pre-determined electric current level I, is adapted by multiplication with the factor kp, which can take values between 0 and 1.

[0021] The electric power P converted into heat by the resistive heating unit is given by

P = lévg ’ R, wherein denotes an average electric current flowing through the resistive heating unit. In conventional electric heating devices, it is quite common to provide the electric power employing a pulse width modulation (PWM) technique. However, any other method of providing the electric power to the resistive heating unit that appears suitable to the skilled person can be employed.

[0022] With avg = Er‘ Ipre ANd kg from (1), one obtains for the electric power P

R? v?

P = (kg Ipre)“ R = — lore — Ror with V being the available supply voltage and

Lyre = =

[0023] In other words, the electric power that is provided to the resistive heating unit is independent of the actual electric resistance of the resistive heating unit. This is illustrated in Fig. 1 by the line marked with diamond symbols, showing a flat power characteristic across the resistance range. For this reason, this strategy of adapting the level of electric current may be referred to as the ‘Matched Power strategy, which can enable the use of resistive heating members with larger tolerances.

[0024] In preferred embodiments of the electric heating device, the relation is given by the rule that the level of the electric current to be supplied to the resistive heating unit can, if the actual electric resistance is smaller than a predefined typical electric resistance value R,,, be expressed by kp‘ Lyre, With kp = ie. (2) yr

Herein, R denotes the actual electric resistance.

[0025] If the actual electric resistance is equal to or larger than the predefined typical electric resistance value R,,p, ky is selected to have a value of 1, leaving the electric current to be supplied to the resistive heating unit unadapted as the predetermined electric current I)... kg = 1.

[0026] In dependence of the size of the actual electric resistance, the pre- determined electric current level I, is adapted by multiplication with the factor kg as defined in (2). By this strategy, the highest heating power can be achieved with resistive heating units having an actual electric resistance that is equal to the predefined typical electric resistance value R,,,. This is illustrated in Fig. 1 by the line marked with square symbols. For this reason, this strategy of adapting the level of electric current may be referred to as the ‘Maximized Power’ strategy, which can enable an improved heat-up performance. The size of the area below the characteristic in Fig. 1 can be taken as a measure showing the improvement in comparison to the conventional electric heating device (line marked with circle symbols).

[0027] Preferably, the predefined typical electrical resistance value R,,, is selected to be the electric resistance value having the highest probability in the production line. In this way, an almost identical, improved heat-up performance can be accomplished for the vast majority of produced electric heating devices.

[0028] In preferred embodiments of the electric heating device, for which the resistive heating unit has a predefined typical electric resistance R,,, that lies within the resistance range, the relation is given by the rule that the level of the electric current to be supplied to the resistive heating unit can, if the actual electric resistance lies within a predefined range around the typical electric resistance, be expressed by . | R

Kr ' Lyre, with Kr — Roman’ wherein L,.. denotes a predetermined electric current level, Ryax denotes the maximum electric resistance and R denotes the actual electric resistance.

[0029] Further, the level of the electric current to be supplied to the resistive heating unit can be expressed by ki Lyre, With kp = ——

R ‘pre R Reyp wherein R denotes the actual electric resistance, if the actual electric resistance is smaller than or equal to a lower limit of the predefined range around the typical electric resistance R,,,, and by

Kr = 1, if the actual electric resistance is equal to or larger than an upper limit of the predefined range around the predefined typical electric resistance value R,,,.

[0030] By this adaption strategy, an undesired large range of electric power to be provided to the resistive heating unit can be avoided, which would otherwise result in a high part-to-part variation.

[0031] As shown in Fig. 1, the conventional electric heating device shows the largest range of electric power, and the part-to-part variation is undesirably large.

[0032] The effect of the above-proposed strategy is illustrated in Fig. 1 by the line marked with triangle symbols and square symbols, respectively, for a non-limiting example of a predefined range around the predefined typical electric resistance value R;,, of + 3%. This strategy of adapting the level of electric current may be referred to as the ‘Balanced Power with Current Alignment’ strategy, which besides the lowered range of electric power, and thus low part-to-part variation, can also enable an improved heat-up performance. Again, the improvement in heat-up performance in comparison to the conventional electric heating device (line marked with circle symbols) can be taken from the measure given by the size of the area below the characteristic in Fig. 1. The lowered part-to-part variation can be taken from the reduced range or span of electric power in the field of operation.

[0033] Preferably, the heater control unit includes a digital data memory unit, a processor unit with data access to the digital data memory unit, and a control interface that is operatively connected to the controllable electric power supply for controlling the electric current that is to be supplied to the resistive heating unit.

Such controller units are nowadays readily available in many variations and can allow for a flexible and reliable execution of tasks that are related to the adaptation of the level of the electric current to be supplied to the resistive heating unit as described herein.

[0034] In preferred embodiments, the electric heating device further comprises electric current measurement means that are configured to provide data on an electric current flowing through the resistive heating unit to the heater control unit in support of determining the actual electric resistance. In this way, the adaptation of the level of electric current to be supplied to the resistive heating unit can be based on a current actual electric resistance, which can enable to consider effects of aging, strain, compression and/or environment on the actual electric resistance of the resistive heating unit. In this way, the benefits of the proposed electric heating device in accordance with the invention can be maintained throughout its lifetime.

[0035] In another aspect of the present invention, a method of operating an electric heating device is provided, wherein the electric heating device comprises - a resistive heating unit that includes at least one resistive heating member and that has a total nominal resistance value, - a controllable electric power supply that is configured for supplying electric power to the resistive heating unit, and - a heater control unit for controlling a level of electric current supplied to the resistive heating unit by the electric power supply.

[0036] The proposed method comprises at least the following steps: - determining an actual electric resistance of the resistive heating unit, - determining, at least in a portion of the potential range for the actual electric resistance, an adapted level of an electric current to be supplied to the resistive heating unit in dependence of the determined actual electric resistance, and - controlling the electric power supply for supplying the determined adapted level of the electric current to the resistive heating unit.

[0037] The proposed method of adapting the level of electric current to be supplied to the electric heating unit can adjust the electric power level provided for heating and, at the same time, keep the electric current level below a specified maximum amperage. By that, a larger average electric power can be provided to the electric heating unit, resulting in an improved heat-up performance with a shortened time for achieving a desired temperature level. Moreover, wider tolerance margins for the electric resistance of the resistive heating members can be allowed. Further, a larger design flexibility for the electric heating device with respect to the electric resistance of the resistive heating members can be accomplished.

[0038] For an electric heating device, whose resistive heating unit has an actual electric resistance lying in a resistance range around the nominal resistance value between a minimum electric resistance and a maximum electric resistance, the step of determining, at least in a portion of the potential range for the actual electric resistance, an adapted level of an electric current to be supplied to the resistive heating unit is preferably carried out in dependence of a relation between the actual electric resistance and at least one out of the minimum electric resistance and the maximum electric resistance. By that, the proposed adapting of the level of electric current to be supplied to the electric heating unit can be individually arranged in dependence of production-specific tolerance margins with respect to the actual electric resistance.

[0039] In preferred embodiments of the method, the step of determining an actual electric resistance of the resistive heating unit is carried out in the course of the production of the electric heating device, and the step of determining further comprises providing the determined actual electric resistance to the heater control unit. This embodiment of the method is most economical and part-saving and can provide all the benefits described before with the exception of considering the effects of aging, strain, compression and environment.

[0040] In preferred embodiments of the method of operating an electric heating device, which is equipped with electric current measurement means that are configured to provide data on an electric current flowing through the resistive heating unit to the heater control unit in support of determining the actual electric resistance, the step of determining an actual electric resistance of the resistive heating unit is carried out in an installed state of the electric heating device. Further, the step includes providing the data on an electric current flowing through the resistive heating unit determined by the electric current measurement means to the heater control unit in support of determining the actual electric resistance. This embodiment of the method is most suitable in cases, in which large aging effects or environmental effects such as temperature changes with strong impact on the actual electric resistance of the resistive heating unit are expected.

[0041] In preferred embodiments of the method, the adapted level of the electric current to be supplied to the resistive heating unit is determined according to . | R

Kr " Lyre, with Kr = Rn wherein /„-2 denotes a predetermined electric current level, Ryax denotes the maximum electric resistance and R denotes the actual electric resistance.

[0042] Such embodiments of the method are most suitable for realizing the ‘Matched Power’ strategy, by which, as described earlier, the use of resistive heating members with lowered tolerance requirements can be enabled.

[0043] In preferred embodiments of the method, the adapted level of the electric current to be supplied to the resistive heating unit is determined according to kg Lyre wherein I... denotes a predetermined electric current level, and k, is given by __R kr = Reyp wherein R,,, denotes a predefined typical electric resistance and R denotes the actual electric resistance, if the actual electric resistance is smaller than a predefined typical electric resistance value R,,,, and according to

Kr = 1 if the actual electric resistance is equal to or larger than the predefined typical electric resistance value Reyp.

[0044] Such embodiments of the method are most suitable for realizing the ‘Maximized Power’ strategy, by which, as described earlier, an improved heat-up performance can be enabled.

[0045] In preferred embodiments of the method, wherein the resistive heating unit has a predefined typical electric resistance R,,, that lies within the resistance range, the adapted level of the electric current to be supplied to the resistive heating unit is determined according to . | R

Kr " Lyre, with Kr = Roman wherein L,.. denotes a predetermined electric current level, Ryax denotes the maximum electric resistance and R denotes the actual electric resistance, for an actual electric resistance that lies within a predefined range around the typical electric resistance R,,,, and the adapted level of the electric current to be supplied to the resistive heating unit can be expressed by kg Lyre, wherein I... denotes a predetermined electric current level and ky, is given by

R kp=—

RB Reyp wherein R.,,, denotes the typical electric resistance and R denotes the actual electric resistance, if the actual electric resistance is smaller than a lower limit of the predefined range around the typical electric resistance, and according to

Kr = 1 if the actual electric resistance is equal to or larger than an upper limit of the predefined range around the predefined typical electric resistance value R,,,.

[0046] Such embodiments of the method are most suitable for realizing the ‘Balanced Power with Current Alignment’ strategy, by which, as described earlier, besides a lowered range of electric power and thus low part-to-part variation, also an improved heat-up performance can be enabled.

[0047] In yet another aspect of the present invention, a computer program for automatically carrying out the method is provided.

[0048] The method steps to be conducted are converted into a program code of the computer program, wherein the program code is implementable in a digital memory unit of the electric heating device and is executable by a processor unit of the electric heating device. Preferably, the digital memory unit and/or processor unit may be a digital memory unit and/or a processing unit of the heater control unit of the electric heating device. The processor unit may, alternatively or supplementary, also be another processor unit that is especially assigned to execute at least some of the method steps.

[0049] The computer program can enable a robust and reliable execution of the method and can allow for a fast modification of method steps.

[0050] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0051] It shall be pointed out that the features and measures detailed individually in the preceding description can be combined with one another in any technically meaningful manner and show further embodiments of the invention. The description characterizes and specifies the invention in particular in connection with the figures.

Brief Description of the Drawings

[0052] Further details and advantages of the present invention will be apparent from the following detailed description of not limiting embodiments with reference to the attached drawing, wherein:

Fig. 1 illustrates various strategies for supplying electric power to a resistive heating unit in dependence of an actual electric resistance of the resistive heating unit and a resistance range of £10 %,

Fig. 2 is a plot of calculated factors for adapting a level of the electric current to be supplied to the resistive heating unit in accordance with the strategies illustrated in

Fig. 1,

Fig. 3 is an embodiment of an electric heating device in accordance with the invention, and

Fig. 4 is aflowchart of an embodiment of a method of operating the electric heating device pursuant to Fig. 3.

[0053] In the different figures, the same parts are always provided with the same reference symbols or numerals, respectively. Thus, they are usually only described once.

Description of Preferred Embodiments

[0054] Fig. 2 is a plot of calculated adaptation factors ky for adapting a level of the electric current to be supplied to a resistive heating unit in accordance with the strategies illustrated in Fig. 1.

[0055] As described before, the factors kj for adapting a level of the electric current to be supplied to the resistive heating unit are determined - for the ‘Matched Power’ strategy according to kp = |= wherein R,,,, denotes the maximum electric resistance and R denotes the actual electric resistance; - for the ‘Maximized Power’ strategy according to kp = =, wherein R.,,, denotes a predefined typical electric resistance value typ and R denotes the actual electric resistance, if the actual electric resistance R is smaller than the predefined typical electric resistance value R,,p, and kr = 1 if the actual electric resistance is equal to or larger than the predefined typical electric resistance value R,,p; and - for the ‘Balanced Power with Current Alignment’ strategy according to kp = |= wherein R,,,, denotes the maximum electric resistance and R denotes the actual electric resistance, for an actual electric resistance R that lies within a predefined range, in this specific embodiment a range of + 3%,

around the typical electric resistance R,,,, and kp = oe wherein R denotes the actual electric resistance, if the actual electric resistance R is smaller than or equal to a lower limit of the predefined range around the typical electric resistance R,,,, i.e. in this specific embodiment R;,,, - 3%, and kr = 1, if the actual electric resistance R is equal to or larger than an upper limit of the predefined range around the predefined typical electric resistance

Reyp, Le. in this specific embodiment Rp + 3%.

[0056] An improvement in heat-up performance in comparison to the conventional electric heating device (line marked with circle symbols) can be derived from a measure given by the size of the area below the characteristic in Fig. 1. A lowered part-to-part variation can be taken from the reduced range or span of electric power in the field of operation.

[0057] Fig. 3 is an embodiment of an electric heating device 10 in accordance with the invention. The electric heating device 10 may for instance be employed as a steering wheel heater in a passenger car. The electric heating device 10 includes a resistive heating unit 12, a controllable electric power supply 14 and a heater control unit 16.

[0058] The resistive heating unit 12 comprises a plurality of resistive heating members (not shown), which for instance may be designed as a foil heater with screen-printed resistive tracks. In alternative embodiments, the resistive heating members may be formed by wire-based heaters, or other heating members that appear suitable to those skilled in the art. The resistive heating unit 12 has a total nominal resistance value, which is subject to production tolerances. Therefore, each resistive heating unit 12 from a production line has an actual electric resistance R lying in a resistance range around the nominal resistance value between a minimum electric resistance R,,,;;, and a maximum electric resistance Rmax (Fig. 1 and 2).

[0059] The controllable electric power supply 14 (Fig. 3) is operationally coupled to the resistive heating unit 12 and to a vehicle battery 18, and is configured for supplying electric power to the resistive heating unit 12 out of the vehicle battery 18 with an available supply voltage V.

[0060] In this specific embodiment, the controllable electric power supply 14 is integrated in the housing of the heater control unit 16. However, in other embodiments the controllable electric power supply may be a separate unit.

[0061] The heater control unit 16 includes a digital data memory unit, a processor unit with data access to the digital data memory unit, and a control interface that is operatively connected to the controllable electric power supply 14 for controlling a level of the electric current that is to be supplied to the resistive heating unit 12 by the electric power supply 14. The digital data memory unit, the processor unit and the control interface are not shown in Fig. 3 for clarity reasons. Though, the skilled person is familiar with such arrangements.

[0062] As will be described in detail in the following, the heater control unit 16 is configured for adapting, at least in a portion of the potential range for the actual electric resistance R, the level of the electric current to be supplied to the resistive heating unit 12 in dependence of a relation between the actual electric resistance R and at least one out of the minimum electric resistance R,,;,, and the maximum electric resistance Rax-

[0063] The electric heating device 10 further comprises a temperature sensor 20, whose signal output is provided to the heater control unit 16 for controlling purposes, as is known in the art.

[0064] In the following, an embodiment of the method of operating the electric heating device 10 pursuant to Fig. 3 will be described also with reference to Fig. 4, which provides a flow chart of the method. In preparation of operating the electric heating device 10, it shall be understood that all involved units and devices are in an operational state and configured as illustrated in Fig. 3.

[0065] In order to be able to automatically execute the method, the heater control unit 16 comprises a computer program. The method steps to be conducted are converted into a program code of the computer program. The program code is implemented in the digital data memory unit of the heater control unit 16 and is executable by the processor unit of the heater control unit 16. Alternatively, the computer program may as well reside in and may be executable by another control unit of the vehicle, and established data communication means between the heater control unit 16 and the vehicle control unit would be used for enabling mutual data transfer.

[0066] In a step 24 of the method, an actual electric resistance R of the resistive heating unit 12 is determined. This step 24 may be carried out in the course of the production of the electric heating device 10. The step 24 of determining then actual electric resistance R of the resistive heating unit 12 then further comprises providing the determined actual electric resistance R to the heater control unit 16.

[0067] Alternatively, the embodiment of the electric heating device 10 may be equipped with electric current Measurement means 22, as is indicated in Fig. 3 by dashed lines. The electric current Measurement means 22 are configured to provide data on an electric current flowing through the resistive heating unit 12 to the heater control unit 16 in support of determining the actual electric resistance R, which in this case is already available in the heater control unit 16. Hence, the step 24 of determining an actual electric resistance R of the resistive heating unit 12 is carried out in an installed state of the electric heating device 10, and the step 24 includes providing the data on an electric current flowing through the resistive heating unit 12 determined by the electric current measurement means 22 to the heater control unit 16 in support of determining the actual electric resistance R.

[0068] In a next step 26 and, depending on the selected strategy of adapting the level of the electric current to be supplied to the resistive heating unit 12, at least in a portion of the potential range for the actual electric resistance R, an adapted level of an electric current to be supplied to the resistive heating unit 12 in dependence of a relation between the determined actual electric resistance R and at least one out of the minimum electric resistance R,,;, and the maximum electric resistance

Rmax IS determined. Results of this step 26 are illustrated in Fig. 2 for the various strategies disclosed herein.

[0069] In another step 28 then, the electric power supply 14 is controlled for supplying the determined adapted level of the electric current to the resistive heating unit 12.

[0070] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments.

[0071] Other variations to be disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality, which is meant to express a quantity of at least two. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting scope.

List of Reference Symbols electric heating device 12 resistive heating unit 14 controllable electric power supply 16 heater control unit 18 vehicle battery temperature sensor 22 electric current measurement means 24 determine actual electric resistance 26 determine adapted level of electric current to be supplied 28 control electric power supply for supplying determined adapted level of electric current to resistive heating unit kg adaptation factor

R actual electric resistance

Rmin minimum electric resistance

Rmax maximum electric resistance

Reyp typical electric resistance

T desired temperature

V available supply voltage

Claims

1. An electric heating device (10), comprising - a resistive heating unit (12) that includes at least one resistive heating member and that has a total nominal resistance value, wherein the resistive heating unit (12) has an actual electric resistance (R), - a controllable electric power supply (14) that is configured for supplying electric power to the resistive heating unit (12), and - aheater control unit (16) is configured for controlling a level of electric current supplied to the resistive heating unit (12) by the electric power supply (14), characterized in that the heater control unit (16) is configured for adapting, at least in a portion of the potential range for the actual electric resistance (R), the level of the electric current to be supplied to the resistive heating unit (12) in dependence of the actual electric resistance (R).

2. The electric heating device (10) as claimed in claim 1, wherein the resistive heating unit (12) has an actual electric resistance (R) lying in a resistance range around the nominal resistance value between a minimum electric resistance (R,in) and a Maximum electric resistance (Rax), characterized in that the heater control unit (16) is configured for adapting, at least in a portion of the potential range for the actual electric resistance (R), the level of the electric current to be supplied to the resistive heating unit (12) in dependence of a relation between the actual electric resistance (R) and at least one out of the maximum electric resistance (Ra) and a predefined typical electric resistance (R,,p) of the resistive heating unit (12).

3. The electric heating device (10) as claimed in claim 2, characterized in that the relation is given by the rule that the level of the electric current to be supplied to the resistive heating unit (12) can be expressed by kg Lye, With kp = I= wherein /,, denotes a predetermined electric current level, R,,,, denotes the maximum electric resistance and R denotes the actual electric resistance.

4. The electric heating device (10) as claimed in claim 2, characterized in that the relation is given by the rule that the level of the electric current to be supplied to the resistive heating unit (12) can be expressed by kg Lyre, wherein I... denotes a predetermined electric current level, and k, is given by __R kr = Reyp wherein R,,, denotes the predefined typical electric resistance value and R denotes the actual electric resistance, if the actual electric resistance (R) is smaller than the predefined typical electric resistance value (R,,p), and Kr = 1 if the actual electric resistance (R) is equal to or larger than the predefined typical electric resistance value (Reyp).

5. The electric heating device (10) as claimed in claim 2, wherein the resistive heating unit (12) has a predefined typical electric resistance (R,,,) that lies within the resistance range, characterized in that the relation is given by the rule that the level of the electric current to be supplied to the resistive heating unit (12) can be expressed by . | R Kr ' Lyre, with Kr — Ro wherein I,,., denotes a predetermined electric current level, R,,,, denotes the maximum electric resistance and R denotes the actual electric resistance, for an actual electric resistance (R) that lies within a predefined range around the typical electric resistance (R,,p), and the level of the electric current to be supplied to the resistive heating unit (12) can be expressed by kg Lyre, wherein I... denotes a predetermined electric current level and ky, is given by kg = = wherein R,,, denotes the typical electric resistance and R denotes the actual electric resistance, if the actual electric resistance (R) is smaller than or equal to a lower limit of the predefined range around the typical electric resistance (R,yp), and kr=1 if the actual electric resistance (R) is equal to or larger than an upper limit of the predefined range around the predefined typical electric resistance value (Ry).

6. The electric heating device (10) as claimed in any one of the preceding claims, characterized in that the heater control unit (16) includes a digital data memory unit, a processor unit with data access to the digital data memory unit, and a control interface that is operatively connected to the controllable electric power supply (14) for controlling the electric current that is to be supplied to the resistive heating unit (12).

7. The electric heating device (10) as claimed in any one of the preceding claims, characterized by electric current measurement means (22) that are configured to provide data on an electric current flowing through the resistive heating unit (12) to the heater control unit (16) in support of determining the actual electric resistance (R).

8 A method of operating an electric heating device (10) comprising - a resistive heating unit (12) that includes at least one resistive heating member and that has a total nominal resistance value, - a controllable electric power supply (14) that is configured for supplying electric power to the resistive heating unit (12), and - a heater control unit (16) for controlling a level of electric current supplied to the resistive heating unit (12) by the electric power supply (14), the method being characterized by at least the following steps: - determining (24) an actual electric resistance (R) of the resistive heating unit (12), - determining (26), at least in a portion of the potential range for the actual electric resistance (R), an adapted level of an electric current to be supplied to the resistive heating unit (12) in dependence of the determined actual electric resistance (R), and - controlling the electric power supply (14) for supplying the determined adapted level of the electric current to the resistive heating unit (12).

9. The method as claimed in claim 8, wherein the resistive heating unit (12) has an actual electric resistance (R) lying in a resistance range around the nominal resistance value between a minimum electric resistance (Ryin) and a maximum electric resistance (Rmax), and the step of determining (26), at least in a portion of the potential range for the actual electric resistance (R), an adapted level of an electric current to be supplied to the resistive heating unit (12) is carried out in dependence of a relation between the actual electric resistance (R) and at least one out of the maximum electric resistance (Rmax) and a predefined typical electric resistance (R,,p) of the resistive heating unit (12).

10. The method as claimed in claim 8 or 9, wherein the step of determining (24) an actual electric resistance (R) of the resistive heating unit (12) is carried out in the course of the production of the electric heating device (10), and the step of determining (24) further comprises providing the determined actual electric resistance (R) to the heater control unit (16).

11. The method as claimed in claim 8 or 9 of operating an electric heating device (10) as claimed in claim 7, wherein the step of determining (24) an actual electric resistance (R) of the resistive heating unit (12) is carried out in an installed state of the electric heating device (10), and the step of determining (24) includes providing the data on an electric current flowing through the resistive heating unit (12) determined by the electric current measurement means (22) to the heater control unit (16) in support of determining the actual electric resistance (R).

12. The method as claimed in any one of claims 8 to11, wherein the adapted level of the electric current to be supplied to the resistive heating unit (12) is determined according to kg Lye, With kp = I= wherein /,, denotes a predetermined electric current level, R,,,, denotes the maximum electric resistance and R denotes the actual electric resistance.

13. The method as claimed in any one of claims 8 to 11, wherein the adapted level of the electric current to be supplied to the resistive heating unit (12) is determined according to kg Lyre, wherein I... denotes a predetermined electric current level, and k, is given by __R kr = Reyp wherein R,,, denotes the typical electric resistance and R denotes the actual electric resistance, if the actual electric resistance (R) is smaller than the predefined typical electric resistance value (R,,,,), and according to Kr = 1, if the actual electric resistance (R) is equal to or larger than the predefined typical electric resistance value (Reyp).

14. The method as claimed in any one of claims 8 to 11, wherein the resistive heating unit (12) has a predefined typical electric resistance (R,,,) that lies within the resistance range, and wherein the adapted level of the electric current to be supplied to the resistive heating unit (12) is determined according to Kr Lye, With kg = |= R ‘pre: WI R — Rmax" wherein /,, denotes a predetermined electric current level, R,,,, denotes the maximum electric resistance and R denotes the actual electric resistance, for an actual electric resistance (R) that lies within a predefined range around the typical electric resistance (R,,p), and the adapted level of the electric current to be supplied to the resistive heating unit (12) can be expressed by kg Lyre, wherein I... denotes a predetermined electric current level and ky, is given by kr = = wherein R,,, denotes the typical electric resistance and R denotes the actual electric resistance, if the actual electric resistance (R) is smaller than a lower limit of the predefined range around the typical electric resistance (R,,), and according to kr=1 if the actual electric resistance (R) is equal to or larger than an upper limit of the predefined range around the predefined typical electric resistance value (Ry).

15. A computer program for automatically carrying out the method as claimed in any one of claims 8 and 11 to 14, wherein the method steps to be conducted are converted into a program code of the computer program, wherein the program code is implementable in a digital memory unit of the heater control unit (16) of the electric heating device (10) as claimed in any one of claims 1 to 7 or a separate electronic control unit and is executable by a processor unit of the heater control unit (16) of the electric heating device (10) as claimed in any one of claims 1 to 6 or a separate processor unit.