Circuit arrangement for multi-zone heating operation with optional capacitive measurement operation for proximity detection, associated steering wheel and method

Abstract

The invention relates to a circuit arrangement (1) for multi-zone heating operation, comprising: a plurality of heating wires (2, 2 '), which can be supplied in parallel by a heating voltage, for heating a touch surface (19) comprising a plurality of zones (20, 20'); wherein a respective heating wire (2, 2 ') is associated with a zone (20, 20'); at least one first switching element (3a, 3a ') for each heating wire (2, 2'), which is coupled between the heating wire (2, 2 ') and one of the two different heating potentials (VH +, VH-) of the heating voltage in such a way that, in a heating mode, a heating current is applied to the respective heating wire (2, 2') in the conducting state of the first switching element (3a, 3a '), and interrupting the heating current in the OFF state of the first switching element (3a, 3a '); a control circuit (12, 6a, 6a ', 6b, 6b') configured to generate, for each heating wire (2, 2 '), individual pulse width modulated first control signals (ST1, ST1') to switch the first switching elements (3a, 3a ') between an on state and an off state, respectively, the individual pulse width modulated first control signals being applied to first control terminals (Ga, G'a) of the first switching elements (3a, 3a'), respectively; wherein the control circuits (12, 6a, 6a ', 6b, 6b') are further designed to apply a respective associated heating current to a plurality of heating wires (2, 2 ') in a common heating stage in parallel, in an overlapping manner and / or in an alternating manner, and wherein at least two of the first control signals (ST1, ST1') differ in terms of their duty cycles.

Description

Technical Field

[0001] The present invention relates to a circuit structure for multi-zone heating with optional capacitive measurement, particularly for a steering wheel in a motor vehicle. Motor vehicle steering wheels are often equipped with an electric heater as a comfort function. To this end, heating wires are passed through the steering wheel rim, allowing heating of a gripping area defined by the rim's surface. Typically, the gripping area is divided into zones with varying thermal conductivity and / or heat capacity. This differentiation can arise from different materials. For example, the steering wheel rim may only be partially made of wood, and the associated wooden gripping area may have different thermal conductivity than the remaining gripping area made of leather or artificial leather. Furthermore, a metal core is often embedded in the steering wheel rim, surrounded by a layer structure containing the heating wires. Variations in the circumferential structure of the steering wheel rim can occur if the cross-section of the metal core varies in size and shape in the circumferential direction, while the surrounding layer structure is non-uniform in terms of material selection and thickness. This results in uneven heat distribution in the grip area. Background Art

[0002] For safety reasons, but also to implement additional comfort functions, it is also necessary to be able to perform touch detection or at least proximity detection, such as so-called grip detection, in which the grip of the steering wheel rim is monitored. Therefore, it is appropriate for the heating wire to be used as an electrode for capacitive proximity detection in the non-heating phase in the so-called measuring operation. Since the heating operation is usually carried out with a pulse-width modulated control signal, which controls one or more switching elements that interrupt the heating current, there are phases in which no heating current is applied, which phases are used for the measuring operation. In order to avoid scattering "across the board", that is, from all poles of the heating voltage that provide the heating current to the heating wire as a capacitive electrode and the reference electrode or ground potential in the measuring operation, it is known, for example from DE 11 2014 002 044 T5, in the measuring operation, the heating wire is separated at all poles (allpolig), that is, from all poles that provide different heating potentials, by a correspondingly arranged switching element, which is called a high-side switch or a low-side switch. Capacitive touch or proximity detection is also subject to the inhomogeneities described at the beginning of the circumferential structure of the steering wheel rim, because, for example, varying circumferential distances of the heating wires to the steering wheel core or to the closest section of the gripping area or local variations in the material of the steering wheel rim that acts as a dielectric cause the sensitivity of the capacitive touch detection to vary in position. Summary of the Invention

[0003] Against this background, the object of the present invention is to provide a circuit arrangement for a multi-zone heating operation with an optional capacitive measuring operation, wherein at least the common heating operation is better adapted to the thermal environment conditions of the individual zones (also called heating zones).

[0004] This object is achieved by the circuit arrangement of claim 1. Further features, embodiments, characteristics, and advantages are apparent from the dependent claims, the description, and the drawings. A steering wheel having the described circuit arrangement and a method for implementing multi-zone heating operation are each the subject matter of the independent claims.

[0005] The present invention relates to a circuit structure for multi-zone heating operation. The circuit structure comprises multiple heating wires that can be supplied in parallel with a heating voltage for heating a touch surface comprising multiple zones. Each heating wire is assigned to a zone of the touch surface. These zones preferably do not intersect. According to a preferred embodiment, at least two zones are distinguished by the surface structure and / or material properties of the associated touch surface. The heating wires are, for example, resistance wires, such as nickel-chromium wires. When electrically connected to two poles of a heating voltage at two different heating potentials, a heating current flows through the heating wires, generating a heating voltage.

[0006] According to the invention, at least one first switching element is provided for each heating wire, which is connected between the heating wire and one of two different heating potentials of the heating voltage in such a way that, in the conductive state of the first switching element, a heating current is applied to the heating wire, which constitutes a heating operation of the respective heating wire. In the blocked state of the first switching element, the heating current and thus the associated heating operation are interrupted.

[0007] Furthermore, the control circuit provided according to the present invention is configured to generate a separate pulse-width-modulated first control signal for each heating line, which is applied to the first control terminal of the first switching element, so that the first switching element can be switched between the on state and the off state independently of the first switching elements of the remaining heating lines.

[0008] According to the invention, the control circuit is further configured to apply the respective heating currents to the plurality of heating wires in a common heating stage in parallel, overlappingly, and / or alternatingly, preferably over a periodic series of a plurality of heating operations, wherein at least two of the first control signals differ in their duty cycle, so that the respective heating currents differ in their temporal profile, and the heating power for at least two heating wires differs in their temporal profile over the common heating stage because the duration of consecutive heating operations of the plurality of periodic series of heating operations varies compared to the duration of non-heating operations that lie temporally between them. For example, during heating in the common heating stage, the heating power of the respective heating wire is thus adapted to the thermal conditions prevailing locally on the respective heating wire, such as the specific heat capacity of the surrounding environment.

[0009] A common heating stage means that a permanent disconnection of the heating lines or a change of the heating stages of one or more heating circuits should be excluded when heating in a common heating stage.

[0010] Preferably, the common heating stage is characterized by a consistent and therefore common desired surface temperature for the plurality of heating zones. More preferably, the common heating stage is characterized by the fact that, after a 10-minute heating phase, the actual surface temperatures determined on the corresponding zones of the touch surface for all zones deviate in absolute value by no more than 5° C., most preferably no more than 3° C., from the consistent common desired surface temperature.

[0011] However, the term "heating stage" should not necessarily imply that multiple heating stages are required. Thus, according to the present invention, only one heating stage may be provided, but multiple heating stages may also be provided. However, in a heating stage configured to cover all heating lines, all heating lines are supplied with heating current in parallel, overlapping, and / or alternating fashion. According to the present invention, at least two control signals applied temporally during the common heating operation differ in their duty cycle, i.e., in the ratio of the duration of the heating operation to the duration of the non-heating operation. It is conceivable that the duty cycle of these two control signals changes with the transition to another heating stage of the common heating operation.

[0012] It is preferably provided that all first control signals differ in their pulse duty factors during heating in a common heating stage.

[0013] Preferably, the control circuit has, for each heating line, a circuit component consisting of two transistors connected as a current mirror for generating a pulse-width-modulated first control signal applied to each first switching element. For example, the circuit component is configured to adapt the logic level of the pulse-width-modulated output signal output by a microcontroller associated with the control circuit to the control level of the first control signal required for the first switching element, while maintaining the pulse-width modulation and, therefore, the frequency of the output signal. Compared to conventional so-called level shifters or voltage multipliers, such as charge pumps, the use of current mirrors enables higher edge steepness, in particular due to the relatively large possible variation in the duty cycle, and thus, in particular for different desired surface temperatures. This allows for more precise setting of the heating power for the individual zones.

[0014] Preferably, the first switching elements are each a p-channel metal oxide semiconductor field effect transistor. More preferably, the p-channel metal oxide semiconductor field effect transistor is connected as a high-side switch, ie, arranged between the heating voltage potential with a higher absolute value of the two heating voltage potentials and the heating line.

[0015] According to a preferred embodiment, the circuit assembly includes a second switching element for at least one heating wire, preferably a plurality of heating wires, which can be switched between a blocked state and a conductive state by the control circuit by applying a first control signal or a second control signal to a second control terminal of the second switching element. The control circuit is configured to switch the first switching element and the second switching element to the blocked state for each heating wire during a measuring operation, which occurs outside of the heating operation of the corresponding heating wire, in order to switch the corresponding heating wire off at all poles. In this embodiment, the circuit assembly also includes at least one detection circuit configured to determine the capacitance of at least one heating wire that is switched off at all poles relative to a reference potential by applying an AC voltage from an AC voltage source to the corresponding heating wire during the measuring operation. The reference potential is, for example, the potential applied to a reference electrode or vehicle ground. This change in capacitance can be used to detect, for example, the approach of a vehicle occupant, or at least the approach of a vehicle occupant's hand. Various methods are known for determining this capacitance. According to the present invention, a method is used in which the capacitance can be reliably detected by applying an AC voltage to the heating wire serving as a transmitting electrode. The amplitude-modulated detection circuit supplies a high-frequency alternating current (eg, 20 kHz) to the capacitor to be tested formed by the heating wire and detects the resulting reactive current.

[0016] In a frequency-modulated detection circuit, the capacitor to be measured is connected together with an inductor to form an oscillating circuit as part of an LC oscillator. The frequency of the LC oscillator is measured by comparing this oscillating circuit with a reference frequency. In another variant of the frequency-modulated detection circuit, the measuring capacitor is part of an astable multivibrator. Preferably, the detection circuit is designed to measure the current curve generated between the heating conductor and the AC voltage source due to the application of the AC voltage during measurement operation, thereby determining the capacitance based on the phase shift between the AC voltage and the current curve. For example, the current curve is measured by means of a voltage drop across a shunt resistor ("shunt") with signal amplification via a measuring amplifier.

[0017] According to a preferred embodiment of the circuit arrangement according to the invention, a shielding circuit is further provided, which is designed to apply an AC voltage from an AC voltage source to the first control terminal of a first switching element and / or the second control terminal of a second switching element of at least one heating line that is switched off at all poles during measurement operation. The use of the term "AC voltage" here is intended to ensure that the AC voltage applied to the heating line and the AC voltage applied to the control terminals are substantially identical in amplitude, frequency, and phase during measurement operation in order to achieve optimal shielding. This implicitly ensures that the AC voltage and / or the corresponding switching element are designed to prevent switching operations of the corresponding switching element during measurement operation.

[0018] The present invention further relates to a steering wheel for a motor vehicle, which at least partially comprises the circuit structure described in one of the above embodiments, wherein the plurality of heating wires are integrated into a steering wheel rim of the steering wheel forming a touch surface.

[0019] According to a preferred embodiment of the steering wheel, control signals that differ in terms of duty cycle are respectively assigned to heating lines that differ in terms of thermal coupling between the respective heating line and the associated area of ​​the touch surface, for example in terms of thermal conductivity between the respective heating line and the associated area of ​​the touch surface.

[0020] The present invention also relates to a method for performing multi-zone heating operation, comprising the following steps. In the providing step, a circuit structure is provided, comprising a plurality of heating wires that can be supplied in parallel with a heating voltage for heating a touch surface comprising a plurality of zones, wherein each heating wire is assigned to a zone. The provided circuit structure comprises at least one first switching element for each heating wire, which is connected between the heating wire and one of two different heating potentials such that, in the conductive state of the first switching element during heating operation, a heating current is applied to each heating wire, and in the blocked state of the first switching element, the heating current is interrupted, thereby interrupting the heating operation. Furthermore, a control circuit is provided, which is configured to generate a separate pulse-width modulated first control signal for each heating wire to switch each first switching element between the conductive state and the blocked state, wherein the separate pulse-width modulated first control signal is applied to a first control terminal of each first switching element. In the heating step of the method according to the invention, heating is performed in a common heating stage, wherein the plurality of heating wires are acted upon by a control circuit in parallel, overlapping, and / or alternating manner, preferably in a periodic sequence of a plurality of heating operations, with at least two of the first control signals differing in their duty cycle, so that the associated heating currents differ in their temporal profile, and the heating power results differently for at least two heating wires in the temporal profile of the common heating stage, since the duration of consecutive heating operations of the plurality of periodic sequences of heating operations varies compared to the duration of non-heating operations located temporally in between. For example, during the heating in the common heating stage, the heating power at the respective heating wire is thus adapted to the thermal conditions prevailing locally on the respective heating wire, such as the specific heat capacity of the surrounding environment.

[0021] A common heating stage means that, when heating in a common heating stage, a permanent disconnection of the heating line or a change of the heating stage of one or more heating circuits is to be excluded.

[0022] Preferably, the common heating stage is characterized by a consistent desired surface temperature across the plurality of heating zones. More preferably, the common heating stage is characterized by the fact that, after a 10-minute heating phase, the actual surface temperatures determined on the corresponding zones of the touch surface for all zones deviate from the consistent desired surface temperature by no more than 5° C. in absolute value.

[0023] However, the term "heating stage" should not necessarily imply that multiple heating stages are required. Thus, according to the present invention, only one heating stage may be provided, but multiple heating stages may also be provided. However, in a heating stage configured to cover all heating lines, all heating lines are supplied with heating current in parallel, overlapping, and / or alternating fashion. According to the present invention, at least two of the control signals applied temporally during the common heating operation differ in their duty cycle, i.e., in the ratio of the duration of the heating operation to the duration of the non-heating operation. It is conceivable that the duty cycle of these two control signals changes as the system switches to another heating stage of the common heating operation.

[0024] It is preferably provided that all first control signals differ in their pulse duty factors during heating in a common heating stage.

[0025] It is preferably provided that control signals differing in terms of the pulse duty cycle are respectively assigned to heating lines which differ in terms of thermal coupling, for example thermal conductivity, between the respective heating line and the associated region of the touch surface.

[0026] The control circuit provided preferably has, for each heating line, a circuit component consisting of two transistors connected as a current mirror for generating a pulse-width-modulated first control signal applied to the first switching element. For example, the circuit component is configured to adapt the logic level of the pulse-width-modulated output signal output by a microcontroller associated with the control circuit to the control level of the first control signal required for the first switching element, while maintaining the pulse-width modulation and, therefore, the frequency of the output signal. Compared to conventional so-called level shifters or voltage multipliers, such as charge pumps, the use of current mirrors achieves higher edge steepness, particularly due to the relatively large possible variation in the duty cycle, and thus, in particular for different desired surface temperatures. This allows for more precise setting of the heating power for the individual zones.

[0027] Preferably, the first switching element of the provided circuit assembly is a p-channel metal oxide semiconductor field effect transistor. More preferably, the p-channel metal oxide semiconductor field effect transistor is connected as a high-side switch, that is, arranged between the heating voltage potential of the two heating voltage potentials with a higher absolute value and the heating line.

[0028] According to a preferred embodiment, the provided circuit assembly includes a second switching element for at least one heating wire, preferably a plurality of heating wires, which can be switched between a blocked state and a conductive state via a control circuit by applying a first control signal or a second control signal to a second control terminal of the second switching element. The control circuit is configured to switch the first switching element and the second switching element of each heating wire to the blocked state during a measurement operation, which occurs outside of the heating operation of the corresponding heating wire, in order to switch the corresponding heating wire off at all poles. In this embodiment, the provided circuit assembly also includes at least one detection circuit. The method includes performing a measurement operation in which an AC voltage from an AC voltage source is applied to the corresponding heating wire to measure the capacitance of at least one heating wire that is switched off at all poles relative to a reference potential. The reference potential is, for example, the potential applied to a reference electrode or vehicle ground. This change in capacitance can be used to detect, for example, the approach of a vehicle occupant, or at least the approach of a vehicle occupant's hand. Various methods are known for determining this capacitance. According to the present invention, a method is used in which the capacitance can be reliably detected by applying an AC voltage to the heating wire serving as a transmitting electrode. The amplitude-modulated detection circuit supplies a high-frequency alternating current (eg 20 kHz) to the capacitor to be tested formed by the heating wire and detects the resulting reactive current.

[0029] In a frequency-modulated detection circuit, the capacitor to be measured is connected together with an inductor to form an oscillating circuit as part of an LC oscillator. The frequency of the LC oscillator is measured by comparing this frequency with a reference. In another variant of the frequency-modulated detection circuit, the measuring capacitor is part of an astable multivibrator. Preferably, the detection circuit is designed to measure the current curve generated between the heating conductor and the AC voltage source due to the application of the AC voltage during the measurement operation, in order to thereby determine the capacitance based on the phase shift between the AC voltage and the current curve. For example, the current curve is measured by means of a voltage drop across a shunt resistor ("shunt") with signal amplification using a measuring amplifier.

[0030] According to a preferred embodiment of the method according to the invention, the provided circuit assembly further comprises a shielding circuit, which is designed to apply an AC voltage from an AC voltage source to the first control terminal of a first switching element and / or the second control terminal of a second switching element of at least one heating line that is switched off at all poles during a measuring operation. The use of the term "AC voltage" here is intended to ensure that, during the measuring operation, the AC voltage applied to the heating line and the AC voltage applied to the control terminals are substantially identical in amplitude, frequency, and phase, in order to achieve optimal shielding. This implicitly ensures that the AC voltage and / or the corresponding switching element are designed to prevent switching operations of the corresponding switching element during the measuring operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The invention will be explained in more detail with the aid of the following drawings. The drawings are to be understood as exemplary only and only illustrate preferred embodiments.

[0032] Figure 1 shows a schematic top view of a steering wheel 10 having a plurality of heating zones and associated heating wires 2 , 2 ′ integrated into the heating zones and belonging to the circuit arrangement 1 according to the invention;

[0033] Figure 2 A schematic diagram of a circuit structure 1 according to the present invention is shown. DETAILED DESCRIPTION

[0034] Figure 1 The present invention shows the use of a circuit arrangement 1 in accordance with the present invention in a steering wheel 10 of a motor vehicle (not shown). A plurality of heating wires 2, 2' (e.g., resistance wires, such as nichrome wires) are integrated into a touch area 19 of the steering wheel 10, formed by the steering wheel rim. This touch area 19 can also be referred to as a grip area. The circuit arrangement 1, which is operated in a heating phase in a plurality of periodic sequences of heating operations, heats the touch area 19 of a vehicle occupant B gripping the steering wheel 10. Optionally, in a measuring mode, in which the circuit arrangement 1 is operated outside the heating mode, capacitive touch detection or proximity detection is performed, which relates to a touch of the touch area 20, 20' or an approach to the touch area 20, 20' by the hand of the vehicle occupant B. However, for safety reasons and also to implement additional comfort functions, this capacitive touch detection or at least proximity detection is performed by the circuit arrangement 1 in order, for example, to perform so-called grip detection, in which the grip of the touch surface 20, 20' is monitored, or to perform driver-passenger identification, which involves, for example, activating or deactivating certain comfort functions in a seating position-specific manner. Figure 1 As can be seen, the touch surface 19 has two zones 20, 20', which directly adjoin each other at the boundary 18. The zones 20, 20' differ primarily in the material properties and, therefore, in the thermal conductivity of at least the respective outer surface of the steering wheel rim forming the touch surface 19 and, thus, the outer layer of the respective zones 20, 20' of the touch surface 19, for example, a wood material on the one hand and a leather or synthetic leather material on the other. Each of the two zones 20, 20' is assigned to one of the two heating wires 2, 2'. Figure 1 As shown, in the corresponding heating operation, the heating wires 2, 2' are loaded with different heating potentials V of the heating voltage. H+ 、V H- The heating current is composed of H-In the measuring operation, the heating wire 2 is loaded with an AC voltage V by the circuit structure 1 according to the invention. AC .

[0035] In order to take into account the different material properties of the zones 20, 20' and given a consistent common desired surface temperature of the zones 20, 20', when heating the heating wires 2, 2', the heating power is set by means of a separate and therefore specific first pulse-width modulated control signal ST1, ST1' for each heating wire 2, 2', wherein these control signals differ in terms of the duty cycle, whereby the ratio of the duration of the heating operation to the duration of the non-heating operation can be set for each heating wire 2, 2', and thus the actual surface temperature of the zones 20, 20' differs from the common desired surface temperature of the heating stage by at most 5°, preferably at most 3°.

[0036] Figure 2 The schematic diagram shows a circuit structure 1 for a plurality of zones 20, 20' having associated heating lines 2, 2', wherein each of the heating lines 2, 2' is operated alternately and cyclically in heating and capacitive measurement mode. To this end, during the heating mode of the heating lines 2 and 2', a heating current flows which is supplied by two poles which are at two different heating potentials V. H+ 、V H- Between, a heating voltage drop is generated on the heating wires 2 and 2' respectively.

[0037] To this end, the circuit assembly 1 has a first switching element 3a or 3a' and a second switching element 3b or 3b' for each heating line 2 or 2'. The first switching elements 3a, 3a' are so-called high-side switches, since they are arranged between the positive or higher heating potential and the heating line 2 or 2', respectively, while the second switching elements 3b or 3b' are referred to as low-side switches. The first switching elements 3a, 3a' and the second switching elements are each designed as field-effect transistors, in particular self-blocking field-effect transistors, preferably metal-oxide-semiconductor field-effect transistors (MOS-FETs), with the first switching elements 3a, 3a' each being implemented as a P-channel MOS-field-effect transistor. The heating wire 2 or 2' is connected to the first switching element 3a, 3a' and the second switching element 3b, 3b', so that in the heating operation in which the first switching element 3a, 3a' and the second switching element 3b, 3b' are simultaneously in the conductive state, the corresponding first switching element 3a or 3a' and the corresponding second switching element 3b, 3b' and the corresponding heating wire 2, 2' are connected in series, so that the parallel-connected heating wires 2, 2' are respectively connected to two different heating potentials V providing a heating voltage. H+ 、V H-Conductive connection. Since the first switching element 3a, 3a' and the second switching element 3b, 3b' are turned on (conducting) during the heating operation of the corresponding heating wire 2, 2', a heating current flows through the heating wire 2 or 2'. If at least one switching element consisting of the first switching element 3a or 3a' and the second switching element 3b or 3b' is in a non-conducting or blocked state, no heating current is applied. By periodically switching with the help of a pulse-width modulated control signal, here the first control signal ST1 or ST1' or the second control signal ST2 or ST2', that is, by manipulating at least one switching element consisting of the first switching element 3a, 3a' and the second switching element 3b or 3b', switching between the heating operation and the non-heating operation of the heating wire 2 or 2' is performed, respectively, wherein the independent first control terminal G applied to the first switching element 3a, 3a' is respectively switched. a , G' a The first control signal ST1 or ST1' on each heating line 2 or 2' enables individual control and, therefore, independent regulation of the heating power by selecting the duty cycle of the first control signal ST1 or ST1', since the duration of the heating operation determines the heating power. Therefore, the first control signal ST1 or ST1' generates different duty cycles when operating in a common heating stage and is selected, taking into account the different thermal conductivity of the materials forming the zones 20 or 20', such that, at least after a suitable heating phase of 10 to 30 minutes, the respective actual surface temperature is as close as possible to the desired surface temperature predefined for the heating stage.

[0038] The first control signal ST1 or ST1 'is generated by a pulse width modulated output signal PWM or PWM' of a central microcontroller 12 belonging to the control circuit 12, 6a, 6a', 6b, 6b'. In order to level-match the output signal PWM or PWM' with the required switching level of the first switching element 3a, 3a' of each heating wire 2 or 2', a respective control signal ST1 or ST1' is provided which is also part of the control circuit 12. a , 6a', 6b, 6b', a circuit component 6a or 6a', consisting of two transistors connected as a current mirror, ultimately generates a pulse-width-modulated first control signal ST1 or ST1', respectively, applied to the first switching element 3a, 3a', i.e., while maintaining the frequency of the pulse-width modulation and, therefore, the corresponding output signal PWM or PWM'. Compared to conventional so-called level shifters or voltage multipliers, such as charge pumps, the use of a current mirror achieves higher edge steepness, in particular due to the relatively large possible variation in the duty cycle, and thus, in particular for different desired surface temperatures. This allows for a more precise setting of the heating power for the individual zones 20, 20'.

[0039] and Figure 2The difference is that the first control signal ST1 or ST1' can also be applied to the second control terminal G when the second switching element 3b or 3b' is switched at the same time. b , G' b In this embodiment, this is not the case. Accordingly, circuit components 6b and 6b' can also be designed corresponding to circuit component 6a or 6a' and each include two transistors connected as a current mirror.

[0040] applied to the second control terminals G of the second switching elements 3b, 3b', respectively. b , G' b The second control signal ST2, ST2' is obtained from the output signal of the microcontroller 12 by level matching with the help of the circuit component 6b or 6b' and is selected so that the second switching element 3b or 3b' is switched to the off state as much as possible between the edges of the first control signal ST1, ST1' within the non-heating phase (= cut-off state of the first switching element 3a or 3a') respectively preset by the first control signal ST1 or ST1' for a preset duration, so as to be able to achieve separation of the corresponding heating wire 2 or 2' at all poles for undisturbed measurement operation.

[0041] According to the invention, for carrying out the measuring operation, the detection circuit 9 is provided so that in the measuring operation, which is respectively situated outside the heating operation, an AC voltage V of an AC voltage source 11 (here a sine generator controlled by a microcontroller 12) is applied to each heating wire 2, 2'. AC The capacitance of the respective heating wire 2 or 2' relative to a reference potential (e.g. vehicle ground) is determined. By means of this change in capacitance, for example, the approach of a vehicle occupant B or at least the approach of the hand of the vehicle occupant B can be detected. In this case, the detection circuit 9 is designed to measure the capacitance of the respective heating wire 2 or 2' relative to a reference potential (e.g. vehicle ground). The change in capacitance can be used to detect the approach of a vehicle occupant B or at least the approach of the hand of the vehicle occupant B. In this case, the detection circuit 9 is designed to measure the capacitance of the respective heating wire 2 or 2' relative to a reference potential (e.g. vehicle ground). AC The resulting current flow between the heating conductor 2 and the AC voltage source 11 is used to generate the AC voltage V AC Specifically, the current change is measured by a measuring amplifier of a detection circuit 9 using the voltage drop across a shunt resistor 8 with signal amplification, and the measurement result is transmitted to a microcontroller 12.

[0042] In the circuit arrangement 1 according to the invention shown, a shielding circuit 7 is also provided, which is designed to shield the first control terminal G of the first switching element 3a, 3a' during measurement operation. a , G' a and the second control terminal G of the second switching element 3b, 3b'. b , G' b Load AC voltage VAC The term AC voltage is used here on the basis that the AC voltage V is applied to the heating wire 2 or 2 ′ during measurement operation. AC and applied to the first control terminal G a , G' a and the second control terminal G b , G' b AC voltage V AC Be essentially identical in amplitude, frequency, and phase to achieve optimal shielding.

Claims

1. A circuit structure (1) for multi-zone heating operation, comprising: A plurality of heating wires (2, 2') which can be supplied with a heating voltage in parallel are used to heat a touch surface (19) comprising a plurality of zones (20, 20'); wherein, Each heating wire (2, 2') is assigned to a zone (20, 20'); At least one first switching element (3a, 3a') of each heating line (2, 2') is connected to the heating line (2, 2') and two different heating potentials (V H+ 、V H- ), so that in heating operation, a heating current is applied to the corresponding heating wire (2, 2') when the first switching element (3a, 3a') is in the on state, and the heating current is interrupted when the first switching element (3a, 3a') is in the off state; A control circuit (12, 6a, 6a', 6b, 6b') is configured to generate, for each heating wire (2, 2'), a separate first control terminal (G) applied to the corresponding first switching element (3a, 3a'). a , G' a ) on a first control signal (ST1, ST1') with a pulse width modulation to switch the first switching element (3a, 3a') between an on state and an off state, respectively; The control circuit (12, 6a, 6a', 6b, 6b') is further configured to apply corresponding heating currents to a plurality of heating wires (2, 2') in a common heating stage in parallel, overlappingly and / or alternately, wherein the duty cycles of at least two of the first control signals (ST1, ST1') are different from each other.

2. The circuit structure (1) according to claim 1, wherein: All associated first control signals ( ST1 , ST1 ′) have different pulse duty factors during the common heating stage.

3. The circuit arrangement (1) according to any one of the preceding claims, wherein: The control circuit (12, 6a, 6a', 6b, 6b') has, for each heating wire (2, 2'), a circuit component (6a, 6a') consisting of two transistors connected as a current mirror for generating a pulse-width-modulated first control signal (ST1, ST1') which is applied to each first switching element (3a, 3a').

4. The circuit arrangement (1) according to any one of the preceding claims, wherein: The common heating stage is distinguished by a uniform desired surface temperature of the plurality of zones (20, 20').

5. The circuit arrangement (1) according to any one of the preceding claims, wherein: The first switching elements are respectively P-channel metal oxide semiconductor field effect transistors.

6. The circuit arrangement (1) according to any one of the preceding claims, further comprising, for at least one heating wire (2, 2'), preferably a plurality of heating wires (2, 2'), a second switching element (3b, 3b'), which is switched on by the control circuit (12, 6a, 6a', 6b, 6b') by applying a first control signal (ST1, ST1') or a second control signal (ST2, ST2') to a second control terminal (G b , G' b ) and can be switched between a blocking state and a conducting state, wherein the control circuit (12, 6a, 6a', 6b, 6b') is configured to, in a measuring operation that is temporally outside a heating operation of the corresponding heating wire (2, 2'), switch the first switching element (3a, 3a') and the second switching element (3b, 3b') of each heating wire (2, 2') into the blocking state in order to shut down the corresponding heating wire (2, 2') at all poles; Furthermore, at least one detection circuit (9) is provided, which is designed to detect the presence of an alternating voltage (V AC ) to determine the capacitance of at least one heating wire (2, 2') switched off at all poles relative to a reference potential.

7. The circuit arrangement (1) according to claim 6, further comprising at least one shielding circuit (7) which is designed to provide a first control terminal (G) of the first switching element (3a, 3a') of the at least one heating line (2, 2') which is switched off at all poles during measurement operation. a , G' a ) and / or the second control terminal (G b , G' b ) Load the AC voltage (V AC ).

8. The circuit arrangement (1) according to claim 1, wherein: The detection circuit (9) is designed to measure, during measurement operation, the current between the heating conductors (2, 2') with all poles switched off and the AC voltage source (11) supplied with an AC voltage (V AC ) and the resulting current trend, so that the AC voltage (V AC ) and the phase shift between the current trend to determine the capacitance.

9. A steering wheel (10) for a motor vehicle, comprising at least partially a circuit arrangement (1) according to any one of the preceding claims, wherein: The plurality of heating wires (2, 2') are integrated into a steering wheel rim of the steering wheel (10), which is configured as the touch surface (19).

10. Steering wheel (10) according to the preceding claim, wherein Control signals (ST1, ST1') that differ in terms of duty cycle are respectively assigned to heating lines (2, 2') that differ in terms of thermal coupling between the respective heating line (2, 2') and the associated area (20, 20') of the touch surface (19), for example, in terms of thermal conductivity between the respective heating line (2, 2') and the associated area (20, 20') of the touch surface (19).

11. A method for performing a multi-zone heating operation, comprising the following steps: A circuit structure (1) is provided, comprising a plurality of heating lines (2, 2') which can be supplied in parallel with a heating voltage, for heating a touch surface (19) comprising a plurality of zones (20, 20'); wherein: A respective heating line (2, 2') is assigned to a zone (20, 20'); each heating line (2, 2') has at least one first switching element (3a, 3a'), which is connected between the heating line (2, 2') and two different heating potentials (V H+ 、V H- ) between a heating potential in the first switching element (3a, 3a'), so that in heating operation, in the on-state of the first switching element (3a, 3a'), the heating wire is respectively loaded with a heating current, and in the off-state of the first switching element (3a, 3a'), the heating current is interrupted; a control circuit (12, 6a, 6a', 6b, 6b'), which is constructed to generate a separate pulse width modulated first control signal (ST1, ST1') for each heating wire (2, 2') to switch the first switching element (3a, 3a') between the on-state and the off-state, respectively, and the separate pulse width modulated first control signal is applied to the first control terminal (G) of the first switching element (3a, 3a') a , G' a )superior; Heating is performed in a common heating stage, wherein the plurality of heating wires (2, 2') are acted upon by the control circuit (12, 6a, 6a', 6b, 6b') with correspondingly associated heating currents in parallel, overlappingly and / or alternately, and at least two of the first control signals (ST1, ST1') differ in their duty cycle.

12. The method according to the preceding claim, wherein: All first control signals ( ST1 , ST1 ′) differ in their pulse duty factors during heating in a common heating stage.

13. The method according to any one of the two preceding claims, wherein: Control signals (ST1, ST1') that differ in terms of duty cycle are respectively assigned to heating lines (2, 2') that differ in terms of thermal coupling between the respective heating line (2, 2') and the associated area (20, 20') of the touch surface (19), for example, in terms of thermal conductivity between the respective heating line (2, 2') and the associated area (20, 20') of the touch surface (19).

14. The method according to any one of the preceding claims 11 to 13, wherein The common heating stage is distinguished by a uniform desired surface temperature of the plurality of zones (20, 20').

15. The method according to any one of the preceding claims 11 to 14, wherein The control circuit (12, 6a, 6a', 6b, 6b') has, for each heating wire (2, 2'), a circuit component (6a, 6a') consisting of two transistors connected as a current mirror for generating a pulse-width-modulated first control signal (ST1, ST1') which is applied to each first switching element (3a, 3a').

16. The method according to any one of the preceding claims 11 to 15, wherein The first switching elements (3a, 3a') are respectively p-channel metal oxide semiconductor field effect transistors.

17. The method according to any one of the preceding claims 11 to 16, wherein The provided circuit assembly (1) has a detection circuit (9) and has a second switching element (3b, 3b') for at least one heating wire (2, 2'), preferably a plurality of heating wires (2, 2'), which is activated via the control circuit (12, 6a, 6a', 6b, 6b') by applying a first control signal (ST1, ST1') or a second control signal (ST2, ST2') to a second control terminal (G) of the second switching element (3b, 3b'). b , G' b ) and can be switched between a blocking state and a conducting state, wherein the control circuit (12, 6a, 6a', 6b, 6b') is configured to, in a measuring operation that is temporally outside a heating operation of the corresponding heating wire (2, 2'), switch the first switching element (3a, 3a') and the second switching element (3b, 3b') of each heating wire (2, 2') into the blocking state in order to shut down the corresponding heating wire (2, 2') at all poles; A measuring operation is performed with the aid of the detection circuit (9), during which the corresponding heating wires (2, 2') are charged with an AC voltage (V AC ) to determine the capacitance of at least one heating wire (2, 2') switched off at all poles relative to a reference potential.

18. The method according to the preceding claim, wherein The provided circuit assembly (1) also has at least one shielding circuit (7) and during the measurement operation is operated with the AC voltage (V AC ) to load the first control terminal (G) of the first switching element (3a, 3a') of the at least one heating line (2, 2') that is switched off at all poles a , G' a ) and / or the second control terminal (G b , G' b ).

19. The method according to any one of the two preceding claims, wherein: In the measuring operation, the detection circuit (9) is used to measure the current between the heating conductor (2) which is switched off at all poles and the AC voltage source (11) which is supplied with an AC voltage (V AC ) and the resulting current trend, so that the AC voltage (V AC ) and the phase shift between the current trend to determine the capacitance.

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