Steering wheel touch sensor system with additional circuitry for functional testing, associated procedure and use

Abstract

The invention relates to a steering wheel touch sensor system (1) comprising: a touch sensor electronics system (7) with a sensor electrode (4) which is fixed to a conductive steering wheel core (5) of a steering wheel, electrically insulated from the steering wheel core (5) and connected to the steering wheel core (5) via a parasitic capacitance (C par) is coupled; an additional circuit (2) arranged outside the steering wheel, which is configured to establish an electrically conductive connection via a grounding conductor (9) leading to the steering wheel core (5) for applying a predetermined measuring potential (GND*) to the steering wheel core (5) during a touch detection phase in which the touch sensor electronics (7) performs touch detection; and the additional circuit (2) is further configured to perform a test phase outside the touch detection phase in which the additional circuit (2) applies a predetermined test potential (GND) exclusively to the sensor electrode (4) and a defined pre-charged reference capacitor (C ref ) via a coupling capacitor (C k ) and couples electrically to the steering wheel core (5) via the grounding conductor (9) while simultaneously isolating it from the measuring potential (GND*) in order to create a charge displacement between the reference capacitor (C ref ) and coupling capacitor (Ck ) to cause the charge displacement to be determined in order to trigger the output of an error message and / or the initiation of a fault condition if a predetermined value is undershot; associated procedure and use.

Description

[0001] The invention relates to a steering wheel touch sensor with an additional circuit for functional testing, an associated method, and an associated use. The steering wheel of a motor vehicle is increasingly equipped with a hands-off detection (HOD) system. This technology is used in vehicles with advanced driver assistance systems to monitor whether the driver has their hands on the steering wheel. This function plays a crucial role in safety by warning the driver when they remove their hands from the steering wheel and activate the HOD function, for example, when using lane keeping assist. If the system detects that the driver's hands have been removed from the steering wheel while a driver assistance system is active, a warning signal is triggered to prompt the driver to react.The associated touch sensor electronics comprise a capacitive or inductive detecting measuring device and a sensor electrode integrated in the grip area of ​​the steering wheel, which is conductively connected to the measuring device. The sensor electrode can be designed as a heating wire and be part of a heating electronics unit.

[0002] In all variants, the sensor electrode extends along and is insulated from a steering wheel core forming the grip area of ​​the steering wheel. This core is made of a metallic and therefore conductive material, resulting in an undesirable capacitance, also known as parasitic capacitance, between the steering wheel core and the sensor electrode. This capacitance influences the measurement by the touch sensor electronics. Therefore, it is desirable to apply a predefined measurement potential to the steering wheel core, which should be kept constant at least during the touch detection phase. A ground connection of the steering wheel core via the steering wheel's pivot bearing has proven unreliable. Therefore, an additional connection is provided by a grounding conductor separate from the bearing elements. This grounding conductor can, for example, form a sliding contact with the steering wheel core or a material- or force-fit connection with the steering wheel core.For safety reasons, regular testing of this conductive connection is therefore necessary. In one type of known steering wheel touch sensor, the integrity of this connection is verified by an additional circuit, similar to a continuity test. A disadvantage of this method is that, in addition to the ground wire, a further connecting wire is required between the steering wheel core and the additional circuit located outside the steering wheel, which further increases susceptibility to interference. If either of these wires is not properly connected, a fault is detected. This can also occur if, with an intact ground wire, the other connection via the additional connecting wire is interrupted.

[0003] In previously known steering wheel touch sensors of a second type, the existence of a ground connection during a test phase is determined by means of a signal capacitively or inductively coupled into the steering wheel core via the sensor electrode. Here, the additional circuit measures a magnitude of the signal coupled into the steering wheel core, whereby, at least during the test phase, the steering wheel core must be isolated from the vehicle ground. This increases the technical complexity regarding the steering wheel core and its mounting via the steering wheel bearing; for example, its conductive connection via the steering bearing is only possible with an additional decoupling switch.

[0004] Furthermore, the known solutions use a resistive connection between the auxiliary circuit and the steering wheel core. In certain situations, this can lead to leakage currents and thus to errors in the control unit.

[0005] Against this background, the object of the present invention is to provide a steering wheel touch sensor system by means of which the reliability of applying a measuring potential to the steering wheel core during a touch detection phase via an earthing conductor can be ensured in a comparatively simple technical manner with an additional circuit by checking this connection established via the earthing conductor in a test phase.

[0006] This problem is solved by the steering wheel touch sensor of claim 1. Further features, embodiments, properties, and advantages will become apparent from the dependent claims, the description, and the figures. An equally advantageous method according to the invention for testing a steering wheel touch sensor, as well as the use of the steering wheel touch sensor according to the invention, are each the subject of the dependent claims.

[0007] The invention relates to a steering wheel touch sensor system. This system comprises touch sensor electronics with a sensor electrode that is fixed to a conductive steering wheel core, electrically insulated from the steering wheel core, and coupled to the steering wheel core via a parasitic capacitance. The parasitic capacitance depends on the geometry of the steering wheel and is typically between 60 pF and 600 pF. Preferably, the parasitic capacitance is greater than 50 pF, and more preferably greater than 100 pF.

[0008] The touch sensing electronics are, for example, arranged on the steering wheel; preferably, they are arranged outside the steering wheel. The touch sensing electronics are, for example, configured to detect a touch or a lack of touch capacitively and / or inductively by means of the sensor electrode during a touch detection phase, in particular by projected capacitive detection, especially based on the amplitude and / or phase shift of an associated detection signal.

[0009] According to the invention, an additional circuit is provided outside the steering wheel, configured to apply a predetermined measuring potential to the steering wheel core, while the touch sensor electronics perform touch detection during a touch detection phase by establishing an electrically conductive connection to the steering wheel core via the grounding conductor. Preferably, the additional circuit couples the predetermined measuring potential to the steering wheel core via a coupling capacitor. The term "grounding conductor" used below does not necessarily imply contact with earth or vehicle chassis.The term "grounding conductor" implies a material- or force-fit contact and / or fixing to the steering wheel core to establish an electrical connection with the steering wheel core and a node located outside the steering wheel, also referred to as a node, preferably bypassing the steering wheel bearing provided for the rotatable mounting of the steering wheel.

[0010] For example, a sliding contact between the grounding conductor and the steering wheel core, or a material- and / or force-fit conductive connection between the steering wheel core and the grounding conductor, is provided. The measuring potential can correspond to the vehicle ground potential.

[0011] According to the invention, the additional circuit is designed to perform a test phase outside the touch detection phase, in which the additional circuit applies a predetermined test potential, preferably the electrical vehicle ground potential, hereinafter referred to as vehicle ground, to the sensor electrode exclusively and electrically couples a defined pre-charged reference capacitor to the steering wheel core via the coupling capacitor and the grounding conductor while simultaneously disconnecting it from the measurement potential, in order to effect a charge displacement between the reference capacitor and the coupling capacitor, for example by discharging the reference capacitor and displacing charge into the coupling capacitor according to the predetermined test potential applied to the sensor electrode and its capacitive coupling via the parasitic capacitance to the steering wheel core and via the grounding conductor, provided that the electrical connection via the grounding conductor exists.

[0012] According to the invention, the charge displacement is determined in order to trigger an error message and / or the initiation of a fault condition if it falls below a predetermined value, since an interruption of the electrical connection via the grounding conductor is likely, meaning that reliable application of the measuring potential to the steering wheel core during the touch detection phase can no longer be ensured. Preferably, the fault condition, namely the detection of an interruption of the electrical connection to the steering wheel core established via the grounding conductor, which is intended to reliably apply a predetermined measuring potential to the steering wheel core during a touch detection phase, includes the deactivation and / or blocking of an autonomous driving state.

[0013] Thus, a steering wheel touch sensor system is provided, by means of which the reliability of applying a measuring potential to the steering wheel core during a touch detection phase via an earthing conductor can be ensured relatively easily with an additional circuit by checking this connection established via the earthing conductor in a test phase.

[0014] According to a preferred embodiment, the sensor electrode forms a heating wire of a heating electronics circuit. This circuit is supplied with a heating current by connecting the heating wire to two different heating potentials and is completely disconnected from these potentials during the touch detection phase. During the test phase, the test potential corresponds to one of the heating potentials required for generating the heating current, for example, the vehicle ground. The touch detection phase is performed outside of the heating phase, during which the sensor electrode, acting as the heating wire, is supplied with a heating current. For example, the heating current is pulse-width modulated, and the touch detection phase occurs within a switching interval of the pulse-width modulated heating current. The complete disconnection refers to the temporary isolation of the sensor electrode, acting as the heating wire, from both heating potentials.The latter is achieved, for example, by the high-resistance state of two switching elements, such as field-effect transistors. For instance, only one switching element—namely, the one of the two that connects the sensor electrode to the vehicle ground with low resistance during the heating phase, known as the low-side switching element—maintains the low-resistance connection between the sensor electrode and the vehicle ground during the test phase.

[0015] Preferably, the charge displacement is determined based on the voltage that develops at a node of the auxiliary circuit between the reference capacitor and the coupling capacitor. The three capacitances—parasitic capacitance, coupling capacitor, and reference capacitor—are selected, for example, such that the voltage measured at the node allows for an unambiguous determination of whether the grounding conductor is interrupted. Preferably, the coupling capacitor is larger, and usually several orders of magnitude larger, than the reference capacitor (and the parasitic capacitance). For example, the reference capacitor has a capacitance of 10 to 1000 pF, and the coupling capacitor has a capacitance of 0.4 to 40 µF.

[0016] Preferably, the test potential corresponds to the vehicle ground, with the steering wheel core additionally being electrically connected to the vehicle ground via a steering wheel bearing, so that in addition to the capacitive coupling via the parasitic capacitance to the sensor electrode lying on vehicle ground during the test phase, there is a parallel connection to the vehicle ground, which increases the reliability of the functional test of the grounding conductor.

[0017] The invention further relates to the use of the steering wheel touch sensor technology in one of the previously described embodiments in a motor vehicle.

[0018] The invention further relates to a method for testing a steering wheel touch sensor system comprising the following steps. In a provisioning step, a steering wheel is provided with a conductive steering wheel core and touch sensor electronics belonging to the steering wheel touch sensor system, comprising a sensor electrode fixed to the steering wheel core that is electrically isolated from the steering wheel core, coupled to the steering wheel core via a parasitic capacitance, and an additional circuit belonging to the steering wheel touch sensor system that is arranged outside the steering wheel.

[0019] In a touch detection step, according to the invention, touch detection is performed in a touch detection phase by the touch sensing electronics, wherein the additional circuit establishes an electrically conductive connection to the steering wheel core via the grounding conductor for applying a predetermined measuring potential to the steering wheel core during the touch detection phase. Preferably, the additional circuit couples the predetermined measuring potential to the steering wheel core via a coupling capacitor.

[0020] In a further test step, referred to as the test phase, which occurs outside the touch detection phase, the auxiliary circuit applies a predefined test potential exclusively to the sensor electrode and electrically couples a defined pre-charged reference capacitor to the steering wheel core via the coupling capacitor and the grounding conductor, while simultaneously disconnecting it from the measurement potential. This is done to induce a charge displacement between the reference capacitor and the coupling capacitor. The circuit then determines this charge displacement. If a predefined value is undershot, the auxiliary circuit triggers the output of an error message and / or the initiation of a fault condition. This is because an interruption of the electrical connection via the grounding conductor is likely, meaning that reliable application of the measurement potential to the steering wheel core during the touch detection phase can no longer be guaranteed.Preferably, the disturbance condition, namely the detection of an interruption of the electrical connection to the steering wheel core established by the grounding conductor, which is intended to reliably apply a predetermined measuring potential to it in a touch detection phase, includes the inactivation and / or blocking of an autonomous driving state.

[0021] Thus, a method is provided by which the reliability of applying a measuring potential to the steering wheel core during a touch detection phase via an earthing conductor can be ensured relatively easily with an additional circuit by checking this connection established via the earthing conductor in a test phase.

[0022] According to a preferred embodiment of the method, the sensor electrode forms a heating wire of a heating electronics unit. During a heating phase, this heating wire is supplied with a heating current derived from two different heating potentials. During the touch detection phase, the heating wire is completely disconnected from the heating electronics. In the test phase, the test potential corresponds to one of the heating potentials required for generating the heating current, for example, the vehicle ground. The touch detection phase is performed outside of a heating phase, during which the sensor electrode, acting as a heating wire, is supplied with a heating current. For example, the heating current is pulse-width modulated, and the touch detection phase occurs within a switching interval of the pulse-width modulated heating current. The complete disconnection refers to the temporary isolation of the sensor electrode, acting as a heating wire, from both heating potentials.The latter is achieved, for example, by the high-resistance state of two switching elements, such as field-effect transistors. For instance, only one switching element—namely, the one of the two that connects the sensor electrode to the vehicle ground with low resistance during the heating phase, known as the low-side switching element—establishes the low-resistance connection between the sensor electrode and the vehicle ground as the test potential during the test phase.

[0023] Preferably, the charge displacement is determined based on a voltage that develops at a node of the auxiliary circuit between the reference capacitor and the coupling capacitor.

[0024] Preferably, the test potential corresponds to the vehicle ground, with the steering wheel core additionally being electrically connected to the vehicle ground via a steering wheel bearing, so that in addition to the capacitive coupling via the parasitic capacitance to the sensor electrode lying on vehicle ground during the test phase, there is a parallel connection to the vehicle ground, which increases the reliability of the functional test of the grounding conductor.

[0025] The invention is explained in more detail with reference to the following figure. The figure is to be understood as merely exemplary and represents only one preferred embodiment. It shows: Fig. 1 a schematic circuit diagram of the steering wheel touch sensor system according to the invention 1.

[0026] Fig.Figure 1 shows a steering wheel touch sensor 1 according to the invention. This sensor comprises touch sensing electronics 7 with a sensor electrode 4, which is fixed to a conductive steering wheel core 5 (shown only symbolically) of a steering wheel (not shown in detail). The sensor electrode 4 is electrically insulated from the steering wheel core 5 and connected to the steering wheel core 5 via a parasitic capacitance C. par coupled. The touch sensing electronics 7 can be arranged on the steering wheel, preferably it is also arranged outside the steering wheel. The touch sensing electronics 7 are designed to detect a touch or a non-touch capacitively, in particular projected capacitively, by means of the sensor electrode 4 in a touch detection phase.

[0027] Furthermore, an additional circuit 2 is provided located outside the steering wheel. This circuit includes a microcontroller 6, which is designed, on the one hand, to control heating electronics 3, so that a heating phase is carried out in sync with a touch detection phase performed by the touch sensor 7, and, on the other hand, to establish a conductive connection during the touch detection phase from node K2 via the grounding conductor 9 to the steering wheel core 5 in order to apply a predefined measuring potential GND* to the steering wheel core 5 while the touch sensor 7 performs touch detection during the touch detection phase, and, on the other hand, to perform a test phase outside the touch detection phase, which can take place within a heating phase but preferably also outside the heating phase. In the test phase, the electrical connection via the grounding conductor 9 is checked by capacitive coupling based on a charge displacement.The microcontroller 6 has an integrated A / D converter with a corresponding AD input. After charging a reference capacitor C belonging to the auxiliary circuit 2. ref Before the test phase, the additional circuit 2 applies a predetermined test potential GND, here the electrical vehicle ground potential, referred to as vehicle ground, to the sensor electrode 4 exclusively and couples the defined pre-charged reference capacitor C. ref via the serially connected coupling capacitor C k and electrically connected to the steering wheel core 5 via the grounding conductor 9 while simultaneously isolating it from the measuring potential GND* by moving the further switch FET into the high-impedance state by means of the output signal D5 of the microcontroller 6.

[0028] Node K2 is connected exclusively via the coupling capacitor C. kNode K3 is connected to node K2, so that nodes K2 and K3 are capacitively isolated. In other words, nodes K2 and K3 are connected in such a way that alternating quantities can pass through via charge displacement, but direct quantities cannot. Node K3 is connected to the additional switch FET. This additional switch FET connects node K3 to the measurement potential during the touch detection phase. During the touch detection phase, the steering wheel core 5 is thus referenced to the measurement potential GND* via nodes K2 and K3. Node K3 is also connected to nodes K4 and K5. Node K4 is connected to the voltage-measuring analog-to-digital converter input AD of the microcontroller 6. Node K5 is connected to a first digital input D1 of the microcontroller 6 and also to the reference capacitor C. ref connected. The reference capacitor C refis connected between node K5 and a second digital input D2 of the microcontroller 6.

[0029] During the test phase, a charge displacement is carried out between the reference capacitor C. ref and coupling capacitor C k This is caused by discharging the charged reference capacitor C. ref and shifting charge into the coupling capacitor C k according to the predetermined test potential application GND of the sensor electrode 4 and its capacitive coupling via the parasitic capacitance C par to the steering wheel core 5 and via the grounding conductor 9, provided the electrical connection via the grounding conductor 9 exists. The charge displacement is quantitatively determined by measuring the voltage at junction K4 between the reference capacitor C. ref and the coupling capacitor C kThe system is designed to trigger an error message and / or initiate a fault condition when a predefined value is undershot, i.e., when the charge displacement falls below a predefined value. This occurs because an interruption of the electrical connection via the grounding conductor 9 is likely, meaning that reliable application of the GND* measuring potential to the steering wheel core 5 during the touch detection phase can no longer be guaranteed. The fault condition, namely the detection of an interruption in the electrical connection to the steering wheel core 5 via the grounding conductor 9—a connection intended to reliably apply a predefined GND* measuring potential to the core during the touch detection phase—involves the deactivation and / or blocking of an autonomous driving mode. The GND* measuring potential corresponds to the vehicle ground potential.

[0030] As shown, a sliding contact 10 is provided between the grounding conductor 9 and the steering wheel core 5, or alternatively, a material- and / or force-fit conductive connection is provided between the steering wheel core 5 and the grounding conductor 9. This provides a steering wheel touch sensor 1, by means of which the reliability of applying a measuring potential GND* to the steering wheel core 5 during a touch detection phase via a grounding conductor 9 can be ensured relatively easily by checking this connection established via the grounding conductor 9 in a test phase using the additional circuit 9.

[0031] As previously explained, the sensor electrode 4 also forms a heating wire 4 of a heating electronics 3 arranged on a heating mat 8, which is connected to two different heating potentials V. +and GND is supplied with a heating current and is completely disconnected from the heating potentials during the touch detection phase. Several conductor tracks can also be arranged on the heating mat 8, one of which, for example, is used exclusively for the steering wheel heating and a second as a sensor electrode 4. Multiple sensor electrodes 4 are also conceivable.

[0032] During the testing phase, the test potential GND corresponds to one of the heating potentials V required for generating heating current. +and GND, namely the vehicle ground. The touch detection phase is performed outside of a heating phase, during which the sensor electrode 4, functioning as a heating wire, is supplied with a heating current via nodes K1 and K6. Here, the heating current is pulse-width modulated by the microcontroller 6 via its outputs D3 and D4, which are used to control the switching elements HS and LS, and the touch detection phase occurs within a keying interval of the pulse-width modulated heating current. All-pole isolation refers to the temporary isolation of the sensor electrode 4, functioning as a heating wire, from both heating potentials V. +and GND. This is achieved by the high-impedance state of the two switching elements HS and LS, which are each field-effect transistors. Only one switching element, LS—namely, the one of the two switching elements LS and HS that connects the sensor electrode 4 to the vehicle ground GND with low resistance during the heating phase (referred to as the low-side switching element)—establishes the exclusive, low-impedance connection of the sensor electrode 4 to the vehicle ground as the test potential GND during the test phase.

[0033] As mentioned previously, the charge displacement during the test phase is measured by a voltage at node K4 of the auxiliary circuit 2 between reference capacitor C. ref and coupling capacitor C k certainly.

[0034] The steering wheel core 5 is additionally electrically connected to the vehicle ground GND** via the steering wheel bearing LL, so that in addition to the capacitive coupling via the parasitic capacitance Cpar The sensor electrode 4, which lies on the vehicle ground during the test phase, has a parallel connection to the vehicle ground, which increases the reliability of the functional test of the earthing conductor 9.

Claims

[1] Steering wheel touch sensor system (1) comprising: a touch sensing electronics (7) with a sensor electrode (4) which is fixed to a conductive steering wheel core (5) of a steering wheel, electrically insulated from the steering wheel core (5) and connected to the steering wheel core (5) via a parasitic capacitance (C par ) is coupled; an additional circuit (2) arranged outside the steering wheel, which is designed to establish an electrically conductive connection via an earthing conductor (9) leading to the steering wheel core (5) for the purpose of applying a predetermined measuring potential (GND*) to the steering wheel core (5) during a touch detection phase in which the touch sensing electronics (7) performs a touch detection; and the additional circuit (2) is further configured to perform a test phase outside the touch detection phase, in which the additional circuit (2) applies a predetermined test potential (GND) exclusively to the sensor electrode (4) and a defined pre-charged reference capacitor (C) ref ) via a coupling capacitor (C k ) and couples electrically to the steering wheel core (5) via the grounding conductor (9) while simultaneously isolating it from the measuring potential (GND*) in order to create a charge displacement between the reference capacitor (C ref ) and coupling capacitor (C k ) to determine the charge displacement in order to trigger the output of an error message and / or the initiation of a fault condition if a predetermined value is undershot. [2] Steering wheel touch sensor (1) according to the preceding claim, wherein the additional circuit (2) applies the predetermined measuring potential (GND*) in the touch detection phase via the coupling capacitor (C k) couples with the steering wheel core (5). [3] Steering wheel touch sensor (1) according to one of the preceding claims, wherein the sensor electrode (4) forms a heating wire of a heating electronics (3) which, in a heating phase outside the touch detection phase, is heated with a heating current from two heating potentials (V + , GND) is acted upon and during the touch detection phase is affected by the heating potentials (V + , GND) is disconnected on all poles and in the test phase the test potential (GND) is connected to one of the heating potentials (V + , GND). [4] Steering wheel touch sensor (1) according to one of the preceding claims, wherein the charge displacement is determined by means of a voltage being set at a node (K3) of the auxiliary circuit (2) between reference capacitor (C ref ) and coupling capacitor (C k ) is determined. [5] Steering wheel touch sensor (1) according to one of the preceding claims, wherein the test potential (GND) corresponds to the vehicle ground and the steering wheel core (5) is additionally permanently electrically connected to the vehicle ground (GND**) via a steering wheel bearing (LL). [6] Steering wheel touch sensor (1) according to one of the preceding claims, wherein the disturbance state includes the inactivation and / or blocking of an autonomous driving state. [7] Use of the steering wheel touch sensor technology (1) according to any of the preceding claims in a motor vehicle. [8] Method for verifying a steering wheel touch sensor system (1) comprising the following steps: Providing a steering wheel with a conductive steering wheel core (5) and touch sensor electronics (7) belonging to the steering wheel touch sensor system (1) with a parasitic capacitance (C) that is electrically insulated from the steering wheel core (5) and connected to the steering wheel core (5) via a parasitic capacitance (C). par) coupled sensor electrode (4) fixed to the steering wheel core (5) and an additional circuit (2) belonging to the steering wheel touch sensor system (1) arranged outside the steering wheel; Touch detection in a touch detection phase by the touch sensing electronics (7), wherein, for the purpose of applying a potential to the steering wheel core (5) with a predetermined measuring potential (GND*) during the touch detection phase in which the touch sensing electronics (7) performs a touch detection, the additional circuit (2) establishes an electrically conductive connection via an earthing conductor (9) leading to the steering wheel core (5); Performing a test phase outside of the touch detection phase, in which the additional circuit (2) applies a predetermined test potential exclusively to the sensor electrode (4) and a defined pre-charged reference capacitor (C) ref ) via a coupling capacitor (C k) and couples electrically to the steering wheel core (5) via the grounding conductor (9) while simultaneously isolating it from the measuring potential (GND*) in order to create a charge displacement between the reference capacitor (C ref ) and coupling capacitor (C k ) to cause the charge displacement to be determined in order to trigger the output of an error message and / or the initiation of a fault condition by means of the additional circuit (2) if a predetermined value is undershot. [9] Method according to the preceding claim, wherein the additional circuit (2) applies the predetermined measuring potential (GND*) during the touch detection phase via the coupling capacitor (C k ) couples with the steering wheel core (5). [10] Method according to one of the preceding claims 8 or 9, wherein the sensor electrode (4) forms a heating wire of heating electronics (3) which, in a heating phase outside the touch detection phase, is heated with a heating current from two heating potentials (V +, GND) is acted upon and during the touch detection phase is affected by the heating potentials (V + , GND) is disconnected on all poles and in the test phase the test potential (GND) is connected to one of the heating potentials (V + , GND). [11] Method according to any one of the preceding claims 8 to 10, wherein the charge displacement is determined by means of a voltage being applied at a node (K3) of the auxiliary circuit (2) between reference capacitor (C ref ) and coupling capacitor (C k ) is determined. [12] Method according to any one of the preceding claims 8 to 11, wherein the test potential (GND) corresponds to the vehicle ground and the steering wheel core (5) is additionally permanently electrically connected to the vehicle ground (GND**) via a steering wheel bearing (LL). [13] Method according to any one of the preceding claims 8 to 13, wherein the disturbance state includes inactivating and / or blocking an autonomous driving state.

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