Arrangement consisting of a steering wheel with an electrode and evaluation electronics better protected against overvoltage coupled on the electrode side for capacitive touch detection, as well as associated motor vehicle

Abstract

Arrangement (1) for a motor vehicle comprising a steering wheel (2) having an electrode (6) and an evaluation electronics (3) which is electrically connected to the electrode (6) for capacitive detection of a touch of the steering wheel (2), wherein the steering wheel (2) has a steering wheel rim (5) and an electrically conductive steering wheel core (4) for fixing to a steering wheel shaft (9), wherein the evaluation electronics (3) is configured to apply an electrical measuring potential to the electrode (6) for touch detection in order to detect the touch of the steering wheel rim (5) on the basis of an associated change in measuring capacitance; wherein the evaluation electronics (3) is furthermore electrically connected to a second ground connection (12), wherein the first ground connection (11) and the second ground connection (12) are electrically connected via a ground connection (14);characterized in that the steering wheel core (4) is electrically connected to a first ground connection (11) via a first ohmic loss resistance (R), that a connection (15) is provided between the electrode (6) and the steering wheel core (4) which has an overvoltage dissipation element (13), such that the connection (15) is high-resistance when a measuring potential is applied on the electrode side and low-resistance when there is an overvoltage on the electrode side, in order to dissipate the overvoltage via the steering wheel core (4) to the first ground connection (11) in the latter case, that the overvoltage dissipated at the first ground connection (11) is reduced by a loss voltage drop across the first loss resistance (R) to protect the evaluation electronics (3) before it reaches the second ground connection (12) of the evaluation electronics (3) via the ground connection (14).

Description

[0001] The invention relates to an arrangement comprising a steering wheel with an electrode for capacitive touch detection and evaluation electronics electrically connected to the electrode for detecting touch to the steering wheel, in particular the steering wheel rim. Steering wheels have evolved from simple input devices for manual steering inputs to multifunctional input devices, optionally with steering control monitoring. Thus, in addition to steering a motor vehicle, it also serves for touch-based inputs, including gesture inputs, to control other components of the motor vehicle. Furthermore, it is increasingly designed to monitor the driver's steering control, for example, while driving the motor vehicle, but especially when transitioning to and from an autonomous driving mode.A disadvantage of capacitive touch detection is its susceptibility to overvoltages, i.e., voltages, particularly transient voltages, whose maximum voltage exceeds the magnitude of the measuring potential used for touch detection by one or more orders of magnitude. This can potentially disrupt the touch input or even damage the evaluation electronics. It is therefore known to protect the evaluation electronics on its input side connected to the electrode from overvoltages by means of a protective circuit, wherein the protective circuit includes at least one overvoltage dissipation element provided in an electrical connection between the input side or electrode and the vehicle ground. This protective circuit ensures that any unintentionally present overvoltage on the input side connected to the electrode is dissipated to the vehicle ground.A disadvantage of this is that, with typical protection circuits, the overvoltage is transmitted almost without loss to the ground connection, through which the evaluation electronics are usually grounded. This temporary potential shift can lead to unpredictable malfunctions in touch evaluation or touch detection by the evaluation electronics, such as false detections. This is particularly unacceptable when monitoring the driver's steering control or during the transition from autonomous driving mode to driver control, or vice versa.

[0002] An arrangement comprising a steering wheel having an electrode for capacitive touch detection and an evaluation electronics electrically connected to the electrode according to the preamble of claim 1 is known from DE 10 2019 120 136 A1.

[0003] Against this background, there was a need for a solution in which an arrangement comprising a steering wheel with an electrode for capacitive touch detection and evaluation electronics electrically connected to the electrode for detecting a touch of the steering wheel is better protected against overvoltage coupled to the electrode. This problem is solved by an arrangement according to claim 1. An equally advantageous motor vehicle is the subject of the dependent claim. Advantageous embodiments are the subject of the dependent claims. The description, particularly in conjunction with the figures, further characterizes and specifies the invention.

[0004] The invention relates to an arrangement for a motor vehicle comprising a steering wheel with an electrode and evaluation electronics that must be protected against electrical overvoltage. The term "motor vehicle" is intended to also include a software-based simulation of a motor vehicle, in which the steering wheel serves as an input device for effecting a virtual steering movement of a simulated motor vehicle. Generally, the steering wheel is a component of a motor vehicle's steering system, with which the driver effects a change in the direction of the real or virtual motor vehicle by turning it, for example, by changing the steering position of one or more of the motor vehicle's wheels.

[0005] According to the invention, the evaluation electronics are conductively connected to one or more electrodes for the capacitive detection of contact with the steering wheel. The steering wheel, according to the invention, has a steering wheel rim and an electrically conductive steering wheel core for attachment to a steering shaft on the vehicle side. The steering wheel core is, for example, made of a metal or a metallic alloy and forms a steering wheel hub for detachable attachment to a steering shaft of the vehicle. For example, a screw connection is provided between the steering shaft and the steering wheel hub. For example, the screw connection is covered by a bumper cover. For example, the steering wheel rim is annular or alternatively designed as one or more ring segments. The steering wheel core extends, for example, from the steering wheel hub via the steering wheel spoke to the steering wheel rim, so that the latter is fixed to the steering wheel hub, for example, by one or more steering wheel spokes.For example, the electrode is integrated into the steering wheel rim.

[0006] According to the invention, the steering wheel core is electrically connected to a first ground connection via a first ohmic loss resistance.

[0007] According to the invention, an evaluation electronics component belonging to the arrangement is designed to apply an electrical measuring potential to the electrode for touch detection in order to detect contact with the steering wheel rim based on an associated change in measuring capacitance. Furthermore, according to the invention, the evaluation electronics are electrically connected to a second ground connection.

[0008] In one embodiment, the first and second connections can coincide. Preferably, however, "second connection" means that it is not the same as the first connection. According to the invention, the first and second ground connections are electrically connected via a ground connection, so that they preferably define a common ground potential.

[0009] According to the invention, a connection is provided between the electrode and the steering wheel core, which includes an overvoltage discharge element. This connection is high-impedance when a measuring potential is applied to the electrode, thus hindering or preferably blocking the current flow between the electrode and the steering wheel core. Conversely, when an overvoltage is present on the electrode side, the connection is low-impedance, thus allowing the current flow between the two as unimpeded as possible. In the latter case, the overvoltage is dissipated from the electrode via the steering wheel core to the first connection. For example, the low-impedance and high-impedance states differ by more than one, preferably more than three, orders of magnitude in ohms. The overvoltage differs from the measuring potential by more than one, preferably more than three, orders of magnitude in volts.

[0010] The solution according to the invention directs the overvoltage via the first ohmic loss resistor first to the first ground terminal, in order to reach the evaluation electronics via the ground connection. This reduces the overvoltage by at least the voltage drop across the first ohmic loss resistor, resulting in a potential shift caused by the overvoltage not occurring at all or at most being reduced at the second terminal. Consequently, the evaluation electronics are not subjected to the potential resulting from the overvoltage discharge at their ground output, or at least to a reduced potential. Therefore, the touch detection by the evaluation electronics does not need to be interrupted and is not disrupted in the event of an overvoltage. The function of capacitive touch detection is based, for example, on the change in the electric field in the area in front of the electrode (active zone).The evaluation electronics, for example, feature an RC oscillator circuit. During application of the measuring potential, the capacitance between the electrode and the electrical ground potential is measured. Instead of a ground potential, a counter electrode with a corresponding ground or counter potential can also be used. When a metallic or non-metallic material approaches the electrode, particularly when touching the steering wheel rim, the capacitance increases and thus affects the oscillation amplitude of the RC oscillator. This change causes a downstream trigger stage to "flip" and change its output state, thereby positively detecting a touch. Consequently, a ground potential shift at the evaluation electronics due to overvoltage has a devastating effect on touch detection.

[0011] The surge protection element can be part of a multi-component electronic circuit that establishes the electrical connection between the electrode and the steering wheel core. Preferably, the surge protection element provided in the electrical connection between the electrode and the steering wheel core is a diode, such as a transient absorption Zener diode or a transient voltage suppressor diode. Preferably, the surge protection element is located closer to the evaluation electronics than to the steering wheel core.

[0012] According to a preferred embodiment, the steering wheel core is further connected to the second vehicle-side ground connection via a capacitor. This has the advantage that a potential applied to the steering wheel core is stabilized during the application of the measuring capacitance to the electrode or during changes in the measuring capacitance, and electromagnetic interactions between the steering wheel core and the electrode are minimized when the electrode functions as a measuring electrode, i.e., outside the case of overvoltage dissipation by the overvoltage dissipation element. Preferably, a second ohmic loss resistor, which is larger than the first ohmic loss resistor, is connected in parallel with the capacitor to form an RC circuit. The second ohmic loss resistor is chosen to be larger to ensure a higher discharge current through the steering wheel core and the first connection in the case of overvoltage and discharge.

[0013] Preferably, the first ohmic loss resistance is in the range of 500 Ω to 10 kΩ, preferably in the range of 800 Ω to 1.2 k Ω.

[0014] Preferably, the overvoltage is routed via the steering wheel shaft to the first ground connection. Preferably, the first ohmic loss resistance is formed essentially by a contact resistance in the area of ​​the steering wheel shaft bearing. The first ohmic loss resistance can be determined, for example, as a resistance averaged over the entire adjustment range of the steering wheel from one steering stop to the opposite steering stop.

[0015] Preferably, the first ground connection and the second ground connection are spatially separated, maintaining a minimum spatial distance of 0.5 m from each other.

[0016] Preferably, the first ground connection and the second ground connection are connected via the ground connection in a potential-equalizing manner, i.e., with approximately zero resistance and defining a common ground potential, or preferably with low resistance, i.e., having a maximum electrical resistance of one or two digits.

[0017] According to one embodiment, at least one ground connection is formed by a detachable electromechanical connection device, such as a detachable friction-fit connection device, consisting of the first and second ground connections. Preferably, both ground connections, the first and the second, are each formed by a detachable electromechanical connection device, such as a detachable friction-fit connection device.

[0018] Preferably, the electrode is formed by a heating wire of a steering wheel heating device. For example, the heating operation is carried out by applying a pulse-width modulated heating current to the heating wire, while the touch detection takes place during a dead time of this application.

[0019] Preferably, the evaluation electronics and the surge protection element are arranged outside the steering wheel. For example, the evaluation electronics and the reading unit are arranged behind a steering column cover or a panel of the dashboard or center console of the vehicle.

[0020] The invention further relates to a motor vehicle with the arrangement in one of the embodiments described above. In this embodiment, the electrically conductive ground connection between the first ground terminal and the second ground terminal is formed, at least partially, by a body and / or a chassis of the motor vehicle.

[0021] The invention is explained in more detail with reference to the following figures. The figures are to be understood as examples only and each represents merely one preferred embodiment. They show: Fig. 1 a schematic representation of a first embodiment of the arrangement according to the invention; Fig. 2 a schematic representation of a second embodiment of the arrangement according to the invention.

[0022] Fig. Figure 1 shows an embodiment of the arrangement 1 according to the invention. The arrangement 1 according to the invention comprises a steering wheel 2 and evaluation electronics 3 arranged outside the steering wheel 2. The evaluation electronics 3 are protected against input overvoltage by an overvoltage dissipation element 13, which is also arranged outside the steering wheel 2. The evaluation electronics 3 are designed for capacitive detection of a touch on the steering wheel 2, and thus the measuring input of the evaluation electronics 3 is connected via an input resistor R. E electrically connected to an electrode 6 located on or in the steering wheel 2.

[0023] The steering wheel 2 is shown only partially and not in detail in the figures. It has a conductive steering wheel core 4, preferably made of a metal or metallic alloy, which is fixed to a steering wheel shaft 9 of the motor vehicle (not shown). The steering wheel core 4 forms a steering wheel hub 8, which serves to fix it to the steering wheel shaft 9, and extends over at least one steering wheel spoke 7 to a steering wheel rim 5 belonging to the steering wheel 2. Within the steering wheel core 4, an inner skeleton forms a stabilizing framework for the steering wheel rim 5, which is surrounded by a plastic, leather, or wooden casing. The steering wheel rim 5 is, for example, ring-shaped or at least in the form of a ring segment and forms the gripping surface for a driver, the contact of which is to be detected.An electrode 6 extending along the circumference of the steering wheel rim 5 is provided in this outer casing of the steering wheel rim 5. Apart from the connection 15 for overvoltage dissipation described below, this electrode 6 is electrically insulated from the steering wheel core 4. It should be clear to those skilled in the art that, depending on the desired detection result, several electrodes, such as an electrode array, may also be provided, for example, to enable spatially resolved touch detection on the contact surface of the steering wheel rim 5.

[0024] In this embodiment, electrode 6 is formed by a heating wire from a steering wheel heater (not shown), which is supplied with a pulse-width modulated heating current. During the dead time of this heating current, electrode 6 is available for touch detection. Electrode 6 is supplied with a measuring potential via an electrically conductive connection 16 by the evaluation electronics 3. In addition to the electrical connection 16 to electrode 6, the evaluation electronics 3 is also connected to a supply voltage V via a second ground connection 12. This ground connection is formed by a detachable, friction-fit, electromechanical connection device to establish an electrical connection with the vehicle body or chassis. A corresponding change in measuring capacitance is used by the evaluation electronics 3 to detect contact with the steering wheel rim 5.The function of capacitive touch detection is based, for example, on the change in the electric field in the area in front of electrode 6, more precisely in the region of the surface of the steering wheel rim 5. The evaluation electronics 3, for example, have an RC oscillator circuit. During the application of the measuring potential, the capacitance between electrode 6 and the electrical ground potential is measured. Alternatively, instead of a ground potential, a counter electrode with a corresponding counter potential can also be provided. As the driver's hand approaches electrode 6, especially when touching the steering wheel rim 5, the capacitance increases and thus influences the oscillation amplitude of the RC oscillator.This change causes a downstream trigger stage belonging to the evaluation electronics 3 to "flip" and change its output state, thereby positively detecting a touch. The detection result is then output via a digital output 10, for example, as part of a bus system such as a CAN bus. The sensitivity of the evaluation electronics 3 can generally be adjusted by selecting the switching distance. Consequently, a ground potential shift at the evaluation electronics due to overvoltage at the second ground terminal has a devastating effect on touch detection.

[0025] A connection 15 is provided between the electrode 6 and the steering wheel core 4, which includes an overvoltage discharge element 13. This connection is high-impedance when a measuring potential is applied to the electrode, thus preventing or preferably blocking current flow. Conversely, when an overvoltage is present on the electrode side, the connection is low-impedance, thus allowing current flow as freely as possible, in order to conduct the overvoltage to the steering wheel core 4. For example, the low-impedance and high-impedance states differ by more than one, preferably more than three, orders of magnitude in ohms. The overvoltage differs from the measuring potential by more than one, preferably more than three, orders of magnitude in volts.Since the steering wheel core 4 is electrically connected to a first ground connection 11 via a first ohmic loss resistor R, the overvoltage at the first ground connection 11 is dissipated and reduced by the loss voltage across the first loss resistor R before it reaches the second ground connection 12 of the evaluation electronics 3 via the common ground connection 14, which is formed, for example, by the vehicle body or chassis (not shown). A further loss resistor R. MThe resistance resulting from a distance of more than 0.5 m between the first ground connection 11 and the second ground connection 12, which can be in the range of 0.01 to 99.99 ohms, provides support. The first ground connection 11 is also formed by a detachable, friction-fit, electromechanical connection device to establish an electrical connection with the vehicle body or chassis. The first ohmic loss resistance R is, for example, in the range of 500 Ω to 10 kΩ, preferably in the range of 800 Ω to 1.2 kΩ. Here, the overvoltage is conducted to the first ground connection 11 via the steering wheel shaft 9. The first ohmic loss resistance R is essentially formed by a contact resistance in the area of ​​the steering wheel shaft 9 bearing (not shown).The first ohmic loss resistance R is to be determined, for example, as a resistance averaged over the entire adjustment range of the steering wheel 2 from one steering stop to the opposite steering stop.

[0026] The solution according to the invention directs the overvoltage via the first ohmic loss resistor R first to the first ground terminal 11 in order to reach the evaluation electronics 3 via the ground connection 14, thereby reducing it by at least the loss voltage drop across the first ohmic loss resistor R, which means that a potential shift caused by the overvoltage at the second ground terminal 12 does not occur at all or is reduced, and the evaluation electronics 3 is not or at least less affected at its ground output by the potential resulting from the discharge of the overvoltage.

[0027] Fig.Figure 2 shows a second embodiment of the arrangement 1 according to the invention. Here, the steering wheel core 4 is further connected to the second vehicle-side ground connection 12 via a capacitor C. This has the advantage that a potential applied to the steering wheel core 4 is stabilized during the application of the measuring capacitance to the electrode 6 or during changes in the measuring capacitance, and electromagnetic interactions between the steering wheel core 4 and the electrode 6 are minimized when the latter functions as a measuring electrode, i.e., outside the case of overvoltage dissipation by the overvoltage dissipation element. Optionally, a second ohmic loss resistor R is connected to the capacitor C. S , which is greater than the first ohmic loss resistance R, is connected in parallel to form an RC circuit. The second ohmic loss resistance R Sis chosen to be larger in order to ensure a higher leakage current via the steering wheel core 4 and the first ground connection 11 in the event of overvoltage and leakage.

Claims

[1] Arrangement (1) for a motor vehicle comprising a steering wheel (2) having an electrode (6) and an evaluation electronics (3) which is electrically connected to the electrode (6) for capacitive detection of a touch of the steering wheel (2), wherein the steering wheel (2) has a steering wheel rim (5) and an electrically conductive steering wheel core (4) for fixing to a steering wheel shaft (9), wherein the evaluation electronics (3) is configured to apply an electrical measuring potential to the electrode (6) for touch detection in order to detect the touch of the steering wheel rim (5) on the basis of an associated change in measuring capacitance; wherein the evaluation electronics (3) is furthermore electrically connected to a second ground connection (12), wherein the first ground connection (11) and the second ground connection (12) are electrically connected via a ground connection (14); characterized by, that the steering wheel core (4) is electrically connected to a first ground connection (11) via a first ohmic loss resistance (R), that a connection (15) is provided between the electrode (6) and the steering wheel core (4) which has an overvoltage dissipation element (13), so that the connection (15) is high-resistance when the measuring potential is applied on the electrode side and low-resistance when there is an overvoltage on the electrode side, in order to dissipate the overvoltage via the steering wheel core (4) to the first ground connection (11) in the latter case, that the overvoltage dissipated at the first ground connection (11) is reduced by a loss voltage drop across the first loss resistance (R) to protect the evaluation electronics (3) before it reaches the second ground connection (12) of the evaluation electronics (3) via the ground connection (14). [2] Arrangement (1) according to claim 1, wherein the overvoltage dissipation element (13) is a diode, such as a transient absorption Zener diode or a transient voltage suppressor diode. [3] Arrangement (1) according to one of the preceding claims, wherein the steering wheel core (4) is further connected to the second ground connection (12) via a capacitor (C). [4] Arrangement (1) according to the preceding claim, wherein a second ohmic loss resistor (R) is connected to the capacitor (C). S ), which is greater than the first ohmic loss resistance (R), is connected in parallel. [5] Arrangement (1) according to one of the preceding claims, wherein the first ohmic loss resistance (R) is in the range of 500 Ω to 10 kΩ. [6] Arrangement (1) according to one of the preceding claims, wherein the overvoltage is directed via the steering wheel shaft (9) to the first ground connection (11). [7] Arrangement (1) according to one of the preceding claims, wherein the first ohmic loss resistance (R) is formed by a contact resistance in the area of ​​the bearing of the steering wheel shaft (9). [8] Arrangement (1) according to one of the preceding claims, wherein the first ground connection (11) and the second ground connection (12) are arranged spatially separated, maintaining a minimum spatial distance of 0.5 m from each other. [9] Arrangement (1) according to the preceding claim, wherein the first ground connection (11) and the second ground connection (12) are electrically connected via the ground connection (14) in a potential-equalizing manner and thereby defining a common ground potential. [10] Arrangement (1) according to one of the two preceding claims, wherein the first ground connection (11) and the second ground connection (12) are each formed by a detachable electromechanical connection device. [11] Arrangement (1) according to one of the preceding claims, wherein the electrode (6) is formed by a heating wire of a steering wheel heating device. [12] Arrangement (1) according to one of the preceding claims, wherein the evaluation electronics (3) and the surge discharge element (139) are arranged outside the steering wheel (2). [13] Motor vehicle with an arrangement (1) according to one of the preceding claims, wherein the conductive ground connection between the first ground terminal and the second ground terminal is formed at least sectionally by a body and / or chassis of the motor vehicle.

Images