Monitoring electrical ground offset in a vehicle

Abstract

The invention relates to determining a ground offset in the vehicle between a controller for controlling a touch-sensitive sensor device and a second ground potential (M2) of a vehicle component (31) having an at least partially electrically conductive base body (31) and / or at least one electrically conductive component. A detection apparatus (10) comprising a voltage divider circuit (11) and a computing unit (13) is provided for this purpose. The voltage divider circuit (11) is connected to the computing unit (13) by means of a first input connection (11a) and an output connection (11b), the first ground potential (M1) being able to be tapped at the output connection (11b). The voltage divider circuit (11) is connected to the base body (31) or the respective component by means of a second input connection (11c), the base body (31) and / or the respective component being connected to the second ground potential (M2). The computing unit (13) is designed to measure a first input voltage (Ua), which can be tapped between the first input connection (11a) and the output connection (11b). The first input voltage (Ua) is set as a function of a second input voltage (Ug), which is present between the second input connection (11c) and the output connection as a function of the potential offset between the first and second ground potentials (M1, M2). The computing unit (13) is furthermore designed to check whether the first input voltage (Ua) deviates from a predefined target value range (Usoll). The deviation occurs precisely when the first and second ground potentials (M1, M2) exhibit the potential offset.

Description

[0001] Monitoring of electrical ground offset in a vehicle

[0002] Capacitive sensors are increasingly being used in modern vehicles, for example, to detect a driver's input or to determine whether the driver is touching the steering wheel. However, it has been shown that this type of sensor can be relatively easily disrupted or otherwise adversely affected by electric fields.

[0003] If a capacitive sensor is used, for example, near relatively large conductive, particularly metallic, structures, the conductive structure can influence the sensor in an undesirable way. Such a conductive structure can be provided, for example, by a base body or a skeleton of a steering wheel, which is usually made of metal. The electrical reference potential or ground potential of the base body usually has a significant influence on the sensor compared to the electrical reference potential or ground potential of the capacitive sensor, especially when a difference between the two ground potentials changes. This change is also referred to as a potential offset or variable ground offset.

[0004] The presence of a ground offset, for example, can lead to an undesired coupling of the capacitive sensor device with the vehicle component, which can distort the measurement results of the capacitive sensor. This can lead to, for example, a loss of reliable touch detection. However, touch detection is used in many vehicles in safety-relevant systems, such as driver assistance systems, and therefore must function as precisely and smoothly as possible.

[0005] There can be various causes for this influence. One cause, for example, is capacitive coupling, which leads to an electrical charge shift in the sensor system and is caused by a ground offset that can occur between the base body and the sensor system. One way to reduce this type of influence is to establish a highly conductive, direct, and, in particular, low-inductance electrical connection or line between the steering wheel base body and the ground potential of the sensor system. Furthermore, no other currents should flow through this connection, as otherwise the remaining electrical resistance of the connection could create a voltage drop. However, an undesirable variable ground offset can still occur, particularly if the voltage drop changes or varies over time.

[0006] The use of such a connection has the disadvantage that so-called ground loops can occur or that control units in the vehicle are no longer adequately protected against electrostatic discharge (ESD). Therefore, instead of a direct connection between the sensors and the base body, relatively long and therefore inductive connections are usually provided. These connections connect, on the one hand, the control unit ground to a negative terminal of a vehicle battery and, on the other hand, the negative terminal to the base body via a central connection point (base body ground) of the vehicle chassis. This is intended to balance the ground potentials of the sensors and the base body.

[0007] However, these connections are also partially traversed by other currents of different origins and with variable temporal progression. This creates a virtually unpredictable, variable ground offset between the electrical potential of the steering wheel base, which is usually connected to the vehicle chassis, and the ground potential of the sensors, which is usually obtained via a vehicle wiring harness or a separate electrical cable.

[0008] Another cause of the variable ground offset is, for example, the ground connection of the capacitive sensor and / or the base body changing its electrical impedance, particularly becoming high-resistance or even completely interrupted. This can happen, for example, if the connection to the vehicle chassis or the wiring harness is defective, such as corroded. This can cause the ground connection of the base body to be floating relative to the ground connection of the sensor, or vice versa.

[0009] It is the object of the present invention to detect a mass offset in the vehicle in a simple manner.

[0010] The object is achieved by the subject matter of the independent claims. Advantageous developments of the invention are disclosed by the dependent patent claims, the description, and the figures. The invention is based on the finding that the simplest possible detection of a ground offset in a vehicle can be achieved using an electrical voltage divider. By means of the voltage divider, both a voltage drop due to a ground line through which other currents flow, at least in sections, and an impedance change as the cause of the ground offset can be detected. In order to be able to determine and, if necessary, correct any undesired influence caused by a variable ground offset, the voltage divider can be used in a measuring device or detection device for detecting the ground offset.The measurement information obtained in this way can, for example, be taken into account when evaluating the sensor data from capacitive sensors.

[0011] According to one aspect, the invention proposes a detection device for a vehicle for determining a potential offset or ground offset between a first ground potential of a control unit for controlling a touch-sensitive sensor device of the vehicle and a second ground potential of a vehicle component with an at least partially electrically conductive base body and / or at least one electrically conductive component to which the sensor device is assigned. The aim is therefore to detect or recognize a difference between the first and second ground potentials, in particular a change in this difference, using the detection device.

[0012] The detection device comprises a voltage divider circuit with a voltage divider and a computing unit. The voltage divider circuit is connected to the computing unit by a first input terminal and an output terminal. The first ground potential can be tapped at the output terminal, wherein the first ground potential preferably corresponds substantially to the reference potential of the vehicle battery, wherein the reference potential is preferably the negative pole of the vehicle battery. This means that the first ground potential is present at the output terminal. The voltage divider circuit is connected to the base body of the vehicle component by a second input terminal, which is designed as a center tap of the voltage divider. The base body is connected to the second ground potential. This means that the second ground potential can be tapped at the second input terminal or is present there.

[0013] The computing unit is designed to detect a first input voltage that can be tapped or is present between the first input terminal and the output terminal. This input voltage is adjusted as a function of a second input voltage that can be tapped or is present between the second input terminal and the output terminal as a function of the potential offset between the first and second ground potentials. This means that the first and second input voltages change depending on whether or not there is a potential difference between the ground potentials. The cause of the potential difference is the ground offset described above or an impedance change between the control unit ground and the ground of the base body.

[0014] To determine the potential offset, the computing unit is designed to check whether the first input voltage deviates from a predefined setpoint range. "Deviation" refers specifically to exceeding or falling below the setpoint range. The setpoint range is a predefined range of values ​​that occurs when the first and second ground potentials have essentially the same potential value. The setpoint range can be determined, for example, through tests or simulations.

[0015] The deviation of the first input voltage from the setpoint range occurs precisely when the first and second ground potentials have a potential offset. This means that the first input voltage only differs from the setpoint range when a ground offset is present. If, on the other hand, the first input voltage is in or within the setpoint range (no deviation), there is no ground offset. In this case, the second input voltage has a value of zero or at least a negligibly small value and therefore does not influence the first input voltage or only influences it insignificantly. The change in the first input voltage based on the deviation can therefore be used as a measure of the potential offset or ground offset. For example, a deviation value that indicates the size of the deviation can be used to calculate or determine the potential offset.

[0016] The described detection device has the advantage that a simple voltage divider can be used to detect the potential offset. This eliminates the need to install additional cables in the vehicle that could contribute to ground loops or electrostatic discharge. Using the voltage divider also avoids or reduces additional interference with the ground connections between the control unit and the vehicle component. In this case, the computing unit can be understood, for example, as a data processing device with one or more connecting circuits. The computing unit can therefore perform computing operations to process data. The computing operations can, for example, involve identified access to a data structure, such as a look-up table (LUT).

[0017] For this purpose, the computing unit can in particular comprise one or more computers, one or more microcontrollers and / or one or more integrated circuits, for example one or more application-specific integrated circuits (ASICs), one or more FPGAs (field programmable gate arrays) and / or one or more systems on a chip (SoC). The computing unit can also contain one or more processors, for example one or more microprocessors, one or more central processing units (CPUs), one or more graphics processing units (GPUs) and / or one or more signal processors, in particular one or more digital signal processors (DSPs). The computing unit can also comprise a physical or virtual cluster of computers or other of the aforementioned units.

[0018] In particular, the computing unit may comprise one or more hardware and / or software interfaces and / or one or more memory units. A memory unit may be a volatile data memory, for example, a dynamic random access memory (DRAM) or static random access memory (SV-RAM), or a non-volatile data memory, for example, a read-only memory (ROM), a programmed read-only memory (P-ROM), an erasable programmable read-only memory (E-PROM), an electrically erasable programmable read-only memory (EE-PROM), a flash memory or flash EE-PROM, a ferroelectric random access memory (F-RAM), a magnetoresistive random access memory (M-RAM), or a phase-change random access memory (PC-RAM).

[0019] In this case, the computing unit can, in particular, comprise an analog-to-digital converter (ADC) to which the first input terminal is connected. Using the ADC, the first input voltage, which is present as an analog voltage signal, can be converted into a suitable digital signal for further processing, for example, comparison with the target value range.

[0020] The vehicle component is, for example, a steering wheel of the vehicle. Further examples of this will be described in detail later. The base body is, for example, a load-bearing component or framework on which the vehicle component is built. The component can, for example, be an additional component that is installed in addition to the vehicle component. It can, for example, be a control element or a switch or a fastening element such as a screw or rivet. Alternatively or additionally, the component can be a design element of the vehicle component, such as a chrome frame for a switch. The base body and / or the component can be constructed or composed entirely or partially of electrically conductive material.In the context of a steering wheel, for example, the steering wheel spokes can be made of a metallic, conductive material, while the steering wheel rim is made of a non-conductive material, such as carbon or carbon fiber. Conductive in this context means that an electrical current can flow through or via the component, with the current flow having a value that can cause a significant ground offset and thus potentially a malfunction of the sensor device. Small currents, on the other hand, whose influence on the sensor device is negligible, are considered non-conductive.

[0021] The touch-sensitive sensor device can form a sensor system with which an actuation or a touch of the vehicle component by a user can be detected or measured. In the context of the steering wheel, this can be so-called hands-on detection or finger recognition. For this purpose, the sensor device can be designed, for example, as a capacitive sensor system, for example with one or more capacitive sensors or a sensor surface. Each sensor can, for example, comprise one or more electrical capacitors. The sensor device can measure or record the change in an electrical capacitance or the electrical impedance of the respective sensor in response to the actuation of the vehicle component. Alternatively or additionally, it is conceivable to use an inductive or resistive sensor device for touch detection.Another variant involves using a sensor based on the principle of differential current measurement. A combination of the aforementioned sensor variants can also be installed.

[0022] The control unit is designed to operate or control the sensors. The control unit can be designed as a data processing device, similar to the processing unit. Operation includes, for example, evaluating the measured sensor signals, such as a change in capacitance or impedance, or a differential current, in order to distinguish user activation from other influences. The use and operation of a touch-sensitive sensor device of the aforementioned type in a vehicle are known per se and follow well-known operating procedures.

[0023] The respective ground potential is used as the ground or reference potential for all signal or operating voltages of the respectively assigned functional unit, in this case the control unit and the vehicle component. Preferably, the ground potentials are linked or connected to a vehicle ground of the vehicle. The vehicle ground is provided, for example, by the negative potential of the vehicle battery. In connection with the control unit, the connection to the vehicle ground can be made using a wiring harness and / or a separate electrical line. The wiring harness or the line can, for example, be connected to a negative terminal of the vehicle battery. In connection with the vehicle component, the ground connection to the vehicle ground can, for example, be made via the vehicle chassis; in particular, the vehicle chassis can also represent the vehicle ground. The vehicle component, in particular the base body, is electrically connected to the chassis.The vehicle chassis can be connected to the negative pole by means of an electrical cable.

[0024] The invention includes embodiments which provide additional advantages.

[0025] According to one embodiment, the voltage divider is designed as a resistive voltage divider with at least two electrical resistors. The resistors are connected in series between the first input terminal and the output terminal. The center tap is located in the series connection between the at least two resistors. The center tap refers in particular to a line in the series connection that is routed out between the two resistors. The center tap is connected to the second input terminal and, via this, to the base body of the vehicle component.

[0026] As an alternative to the resistive voltage divider design, the voltage divider can be designed as a capacitive voltage divider. In a capacitive voltage divider, electrical capacitors are used instead of electrical resistors. Of course, the detection device can also be operated with another known voltage divider design. The voltage divider preferably has more than two electrical resistors, in particular three electrical resistors. An embodiment with more than two resistors will be described in more detail later.

[0027] According to one embodiment, the detection device comprises a supply unit. The supply unit supplies the detection device, in particular the voltage divider circuit, with electrical energy. For this purpose, the voltage divider circuit is connected to the supply unit via a supply terminal. The supply terminal is coupled or connected to the output terminal via the voltage divider. Furthermore, the supply terminal is preferably coupled or connected to the first input terminal. The supply unit is designed to provide an electrical supply signal between the supply terminal and the output terminal. This means that the electrical energy is transmitted or provided to the detection device in the form of the supply signal. The supply signal can be an electrical voltage or an electrical current.To provide the supply signal, a supply potential is available at the supply connection or is present there. The supply potential can be understood as the operating potential. In particular, the supply unit also provides electrical power to the computing unit.

[0028] According to one embodiment, the supply unit is connected to the voltage divider by means of a first switching unit. The first switching unit is designed to disconnect or connect the supply unit to the voltage divider depending on an expectation signal indicating that the potential offset is potentially or shortly to be expected. Preferably, the computing unit controls the switching unit to disconnect and / or connect. In particular, the computing unit controls the switching unit to disconnect the supply unit from the voltage divider as long as the expectation signal is not present or has not been detected. In contrast, the computing unit controls the switching unit to connect the supply unit to the voltage divider when the expectation signal is present or is detected.

[0029] This means that the supply unit and thus the supply signal are designed to be switchable. This means that the voltage divider is only supplied with energy or current when monitoring the ground offset appears necessary. The need for monitoring can be determined based on the expected signal or can be monitored regularly, particularly cyclically, on suspicion. The computing unit can receive the expected signal, for example, from a central control unit (ECU) of the vehicle. Using the ECU, the potential consumption of connected loads or consumers that are connected to the control unit via the wiring harness can be calculated. If consumption changes, parasitic voltages can be injected as interference signals into the supply line from the vehicle ground to the ground connection of the control unit. This results in an impedance change and a ground offset occurs.Alternatively, the expectation signal can be provided, for example, by a vehicle monitoring device. The monitoring device can, for example, comprise one or more cameras for detecting a movement of the vehicle driver. This can, for example, detect or recognize a movement to touch the vehicle component.

[0030] A switching unit can be understood here and below as an electronic switch. The switching unit can comprise at least one switching element, such as a semiconductor switch. The respective switching element can be operated in switching mode by means of the processing unit. In switching mode, the switching element can be switched between at least two different switching states. In one switching state, the electrical connection or line between the supply unit and the voltage divider is electrically or galvanically isolated, while in another switching state it is electrically or galvanically connected.

[0031] According to one embodiment, the supply unit is designed as a current source. It is preferably a constant current source. The supply signal can thus be provided as a current signal, preferably with a constant value. When using a current source, the ohmic voltage divider preferably comprises exactly two electrical resistors. This allows a direct connection between the first input terminal and the supply terminal to be realized.

[0032] According to one embodiment, the supply unit is designed as a voltage source. Additionally, the voltage divider comprises at least three electrical resistors. One of the resistors is connected between the first input terminal and the supply terminal. The remaining two or more electrical resistors preferably form, as previously mentioned, the series circuit between the first input terminal and the output terminal. In other words, a further electrical resistor is preferably provided in series with the two resistors of the voltage divider, which couples the first input terminal to the supply terminal.

[0033] By using the voltage source, an electrical voltage, preferably a direct current (DC), i.e., a voltage signal with a constant value, can be provided as the supply signal. The additional electrical resistance ensures that the current flow at the first input terminal connected to the computing unit is limited. The resistor is dimensioned such that a current limit of the computing unit, for example, specified by a manufacturer, can be maintained.

[0034] According to one embodiment, the voltage source is designed to provide a non-constant electrical voltage, in particular an alternating electrical voltage, as a supply signal. The computing unit is designed to take into account a fluctuation in the temporal profile of the provided voltage to specify the target value range. This means that the supply signal is an electrical voltage signal that has a variable temporal profile. The supply signal can, for example, have a periodically or cyclically changing polarity. Alternatively or additionally, the supply signal can have a signal profile with a combination of a direct and alternating voltage. In order to calculate out the influence of the resulting signal fluctuations in the supply signal, the computing unit can take the fluctuations into account.For this purpose, the computing unit can, for example, also measure the supply signal—i.e., the AC voltage—in addition to the first input voltage and, for example, relate it to the first input voltage. To ensure that signal fluctuations are also taken into account in the calculation result, the computing unit can adapt the setpoint range—i.e., the size or dimension of the setpoint range—to the measured signal fluctuations. The computing unit can derive the limits for the setpoint range, for example, from a characteristic map or a predefined characteristic function, such as a lookup table.

[0035] According to one embodiment, the computing unit and / or the supply unit are provided by the control unit of the touch-sensitive sensor device. This means that the computing unit and / or the supply unit can, for example, be integrated into the control unit and thus used to control or operate the touch-sensitive sensor device. Preferably, the detection device is integrated entirely into the control unit. Alternatively, it is of course possible to design the detection device entirely as a separate component from the control unit. This means that the computing unit and / or the supply unit can, for example, be provided as a separate control unit for operating the voltage divider circuit. The detection device can forward or transmit its respective measurement information to the control unit of the touch-sensitive sensor device, for example, via a suitable interface.

[0036] According to one embodiment, the output terminal is connected to the voltage divider by means of a second switching unit. To determine the potential offset, the second switching unit is configured to first connect and then disconnect the output terminal. This means that the switching unit can be switched such that the output terminal is alternately connected to and disconnected from the voltage divider. The control or switching of the second switching unit is preferably performed by the computing unit. Furthermore, the computing unit is configured to compare the first input voltage in the connected state with the first input voltage in the disconnected state according to a predetermined comparison criterion.

[0037] In other words, the output terminal is designed to be switchable, so that the voltage divider can either be disconnected from the first ground potential or connected to it. To do this, the processing unit can control the second switching unit and switch it in switching mode so that the output terminal is first connected to the voltage divider and then disconnected, or vice versa.

[0038] The measurement principle for determining the ground offset is based on the fact that the first input voltage must not change, or only slightly, when the switching unit is switched on and off, provided there is no undesirable ground offset in the vehicle, and the ground connection via the base body is low-impedance. If, however, the first input voltage changes during switching, a ground offset or a high-impedance ground connection of the base body is present.

[0039] To determine the ground offset, the input voltage values ​​are compared in the connected and disconnected states. For the comparison, a difference between the input voltage values ​​can be calculated, for example. This difference provides a comparison value that should lie within a specified comparison value range if there is no ground offset. If the difference exceeds or falls below the comparison value range, the ground offset is present. The comparison value range can be specified, for example, by the comparison criterion. The comparison value range can be determined in tests or simulations.

[0040] This design, based on signal difference generation, is particularly well-suited for detecting ground offsets resulting from component tolerances. These ground offsets are generally difficult to detect without switching, as the influence of small static ground offsets is usually too small to distinguish from the influence of component tolerances.

[0041] According to one embodiment, the computing unit is configured to determine the comparison value, which indicates the difference between the first input voltage in the connected state and the first input voltage in the disconnected state, and to compare it with a sensor signal of the touch-sensitive sensor device according to a predetermined coupling criterion to check for undesired electrical coupling between the touch-sensitive sensor device and the detection device. The result of the comparison thus provides information about whether the sensor device and the detection device are coupled in an undesired manner, for example, capacitively or electromagnetically, and whether the measured values ​​of the sensor device are thereby falsified.

[0042] In other words, measurable changes in the input voltages, especially changes in the input voltages synchronous with the switching, can be used to compare them in the processing unit with the output signal of the capacitive sensor. This allows any undesired coupling or interference between the capacitive sensor and the detection device to be detected. It can therefore be verified whether the detection device is negatively or undesirably influencing or distorting the measurement results of the sensor device. The control unit can, for example, transmit the sensor signal or the output signal of the sensor device to the processing unit.

[0043] According to one embodiment, the computing unit is designed to check whether the first input voltage is greater or smaller than the target value range and, depending on this, to determine a polarity, a temporal profile, and a magnitude of the potential offset, thereby providing clues to its cause. This means that conclusions can be drawn about the trigger of the ground offset. The computing unit can output or communicate the cause, for example, to a central control unit of the vehicle. This allows the ECU to record errors in the system based on ground etching. During repair or maintenance of the vehicle, a fault pattern can be retrieved, and the cause of the ground offset can be traced and remedied particularly easily if necessary.

[0044] When determining the cause, a distinction can be made between a positive and negative ground offset. If the first input voltage is lower than the target value range, a negative ground offset exists. Due to the use of the voltage divider, the negative ground offset occurs when at least one interference voltage, in particular a voltage drop, is impressed in the supply lines or there is a poor, i.e. high-impedance, ground connection between the control unit and the vehicle battery. If, on the other hand, the first input voltage is higher than the target value range, a positive ground offset exists. The cause for this can be, on the one hand, a high-impedance connection between the control unit and the steering wheel base or between the steering wheel base and the vehicle battery. On the other hand, different interference voltages in the supply lines to the output connection or the ground connections can be the cause.

[0045] According to one embodiment, the second input terminal, in particular the center tap, is connected to the voltage divider by means of a third switching unit. In a test mode, the third switching unit is designed to separate the second input terminal from the voltage divider. The third switching unit can, for example, control or switch the third switching unit. Furthermore, the computing unit is designed to check in the test mode whether the first input voltage lies within a predetermined test setpoint range. In order to determine the potential offset, the computing unit is thus designed to check whether the first input voltage deviates from a predetermined test setpoint range. "Deviation" means, in particular, exceeding or falling below the test setpoint range.The test setpoint range is a predefined value range that occurs when the first and second ground potentials have essentially the same potential value. The test setpoint range can be determined, for example, through tests or simulations. The test setpoint range differs from the setpoint range used in the normal operation described above. The value ranges for the setpoint voltages differ because, in test mode, the voltage across the resistor in the voltage divider, which is directly connected to the output terminal, must no longer be equal to zero, but must be significantly greater than zero.

[0046] The third switching unit can be designed analogously to the first and / or second switching unit. By using the third switching unit, the second input connection is designed to be switchable. By controlling it, the computing unit can specifically switch the line to the base body, in particular to the ground potential of the base body, on and off. When switched off, the voltage divider is unloaded. This has the advantage that the voltage divider can be tested for damage independent of external influences by the base body. In particular, it is important to check whether, for example, the resistors of the voltage divider have changed their values ​​due to aging or damage. If, when switched off or disconnected, the first input voltage lies within the test target value range, then the voltage divider is undamaged.It can therefore be assumed that the voltage divider will not cause any measurement errors if the line, i.e., the second input connection for determining the ground offset, is subsequently closed or connected again. However, if the input voltage is outside the test setpoint range, a defect in the voltage divider, particularly its components, can be assumed. If a defect exists, this can negatively impact the measurement of the ground offset, and the measurement results may be distorted, for example.

[0047] According to one embodiment, the detection device is configured to trigger the control unit with a compensation signal to implement a predetermined compensation measure for controlling the touch-sensitive sensor device only when the first input voltage deviates from the target value range. The goal is therefore to react to an existing ground offset. In particular, the ground offset is to be compensated or corrected. For example, when triggered with the compensation signal, the sensor system can be operated in a compensation mode that differs from normal operation. In the compensation mode, the existing ground offset is taken into account, in particular compensated or corrected, when evaluating the measurement results.

[0048] Preferably, the compensation measure is only implemented temporarily or intermittently, especially as long as the ground offset is present or being measured. This means that the computing unit preferably only provides the compensation signal as long as the first input voltage deviates from the target value range. If the check shows that the first input voltage is within the target value range, the compensation measure is terminated, and the compensation signal is no longer provided. Upon termination of the compensation measure, the sensor device returns to normal operation.

[0049] According to one embodiment, the compensation measure comprises changing, in particular reducing, the sensitivity of the touch-sensitive sensor device. This means that the compensation measure can raise or increase a threshold value for detecting actuation by a driver. As a result, for example, in the case of a capacitive sensor system, a larger change in the capacitance or impedance of the respective sensor of the sensor device is necessary for it to be detected as an actuation.

[0050] According to one embodiment, the compensation measure comprises deactivating the touch-sensitive sensor device. This means that the actuation detection can be at least temporarily deactivated or terminated.

[0051] According to one embodiment, the computing unit is configured to determine a potential offset value from the determined deviation, which indicates a value of the potential offset between the first and second ground potentials. The compensation measure comprises specifying the potential offset value as a reference value for evaluating the measurement results of the touch-sensitive sensor device. This means that the determined ground offset can be used to calculate out disturbances in the measurement results of the capacitive measurements that are attributable to the ground offset. For example, for the capacitive measurement, a reference potential can be raised or lowered by means of the sensor device depending on the ground offset. Thus, a correction or adjustment of the reference value can be implemented during the capacitive evaluation.

[0052] According to one aspect, the invention relates to a vehicle with a detection device as described above. The vehicle comprises a touch-sensitive sensor device with a control unit and at least one vehicle component with an electrically conductive base body. The sensor device is assigned to the vehicle component. The sensor device is designed to detect actuation of the at least one vehicle component by a user, for example, a passenger or a driver of the vehicle. The actuation can comprise, for example, touching or approaching. As a result, for example, an operating request can be detected by means of the sensor device, or hands-on detection or finger detection, i.e., touch or approach detection, can be carried out.As previously mentioned, the actuation detection is carried out according to known capacitive measuring methods, for example by means of impedance measurement or capacitance measurement or differential current measurement using suitable sensors of the sensor device.

[0053] The vehicle is preferably designed as a motor vehicle, in particular a motor vehicle or motor vehicle, in particular as a passenger car or lorry or passenger bus or motorcycle.

[0054] According to one embodiment, the vehicle component is designed as a steering control of the vehicle or a door handle of a vehicle door or as an operating element of an electronic entertainment unit of the vehicle or an operating element of at least one driving function or driver assistance function of the vehicle. A steering control can be, for example, a steering wheel or joystick with which a driver of the vehicle can intervene in the steering of the vehicle. The electronic entertainment unit can be, for example, the infotainment system or the on-board computer of the vehicle. For example, the entertainment unit can be mounted in a center console of the vehicle. A driver assistance function can be, for example, an adaptive cruise control system.

[0055] In the case of the steering mechanism, the base body can be, for example, a metallic skeleton or framework on which the steering mechanism is built. In the case of the door handle, the base body can be, for example, the metallic structure from which the door handle is formed. In the case of the control element, the base body can be, for example, the metallic housing of the entertainment unit.

[0056] According to one aspect, the invention also relates to a method for determining a potential offset between a first ground potential of a control unit for controlling a touch-sensitive sensor device of the vehicle and a second ground potential of a vehicle component with an at least partially electrically conductive base body and / or at least one electrically conductive component to which the sensor device is assigned. For this purpose, a detection device is provided, as described above by way of example. The detection device comprises the voltage divider circuit with the voltage divider and the computing unit. The voltage divider circuit is connected to the computing unit with its first input terminal and its output terminal, wherein the first ground potential can be tapped off from the output terminal.The voltage divider circuit is connected to the base body and / or the at least one component of the vehicle component with its second input terminal, the base body and / or the at least one component being connected to the second ground potential. The computing unit then detects the first input voltage, which can be tapped between the first input terminal and the output terminal. The first input voltage is adjusted as a function of the second input voltage, which can be tapped between the second input terminal and the output terminal as a function of the potential offset between the first and second ground potentials. The computing unit then checks whether the first input voltage deviates from a predetermined target value range, the deviation occurring precisely when the first and second ground potentials exhibit the potential offset.

[0057] The method can be an operating method for operating a detection device, as described above by way of example. The described method, in particular the measuring of the first input voltage and the checking of the first input voltage, can be carried out or executed in particular by means of the computing unit of the detection device.

[0058] Embodiments of the method according to the invention and of the vehicle according to the invention follow directly from the various embodiments of the detection device according to the invention, and vice versa. In particular, individual features and a corresponding explanation as well as advantages of the various embodiments of the detection device according to the invention can also be transferred analogously to corresponding embodiments of the vehicle according to the invention and of the method according to the invention. In particular, the detection device according to the invention is designed or programmed to carry out a method according to the invention. In particular, the detection device according to the invention carries out a method according to the invention.

[0059] Further features of the invention emerge from the claims, the figures and the description of the figures. The features and combinations of features mentioned above in the description as well as the features and combinations of features mentioned below in the description of the figures and / or shown in the figures can be encompassed by the invention not only in the respectively specified combination, but also in other combinations. In particular, the invention can also encompass embodiments and combinations of features that do not have all the features of an originally formulated claim. Furthermore, the invention can encompass embodiments and combinations of features that go beyond the combinations of features set out in the backreferences to the claims or deviate from them.

[0060] The invention is explained in more detail below using specific embodiments and associated schematic drawings. In the figures, identical or functionally equivalent elements may be provided with the same reference numerals. The description of identical or functionally equivalent elements may not necessarily be repeated for different figures.

[0061] The figures show:

[0062] Fig. 1 is a schematic representation of a detection device for a vehicle for determining a mass offset;

[0063] Fig. 2 is a schematic process flow diagram for a method for operating the detection device,

[0064] Fig. 3 is a schematic representation of a steering wheel of the vehicle that can be coupled to the detection device,

[0065] Fig. 4a is a schematic representation of a section of the detection device according to a first embodiment,

[0066] Fig. 4b is a schematic representation of a section of the detection device according to a second embodiment,

[0067] Fig. 5 is a schematic representation of a section of the detection device according to a third embodiment,

[0068] Fig. 6a is a schematic representation of a section of the detection device according to a fourth embodiment, and Fig. 6b is a schematic representation of a section of the detection device according to a fifth embodiment.

[0069] Fig. 1 shows a schematic representation of a detection device 10 for a vehicle (not shown in Fig. 1). The detection device 10 can be used to determine a potential offset or ground offset between a first ground potential M1 of a control unit 20 for controlling a touch-sensitive sensor device of the vehicle and a second ground potential M2 of a vehicle component with an electrically conductive base body 31. This involves monitoring electrical ground offsets in a vehicle.

[0070] In the present case, the vehicle component is, for example, a steering wheel 30 of the vehicle. The base body 31 is a metallic skeleton or framework on which the steering wheel 30 is constructed or based for its intended use in the vehicle. The steering wheel 30, in particular the base body 31, is fastened or attached to a vehicle chassis 32 by means of a steering rod. The second ground potential M2 can be tapped off or applied to the base body 31 as a reference potential for the steering wheel 30. The chassis 32 forms a ground connection for the steering wheel 30 to a vehicle ground M3. The steering wheel 30 is thus connected to an on-board electrical system of the vehicle via the chassis 32.

[0071] The sensor device is assigned to the steering wheel 30. This means that the sensor device can perform its respective sensor function for the steering wheel 30 or on the steering wheel 30. For example, the sensor device is used to detect a driver's operating instructions and / or to determine whether the driver is touching the steering wheel. This is also referred to as so-called hands-on detection (hand-on-steering-wheel detection). In the following exemplary embodiment, the use of a capacitive sensor device in connection with hands-on detection (HoD) is described in more detail by way of example. Of course, the use of other sensor variants and / or other measuring principles is analogously applicable.

[0072] For this purpose, the sensor device, as shown in Fig. 1, comprises a capacitive sensor system 21 which is attached to the steering wheel 30. The capacitive sensor system 21 can, for example, comprise one or more sensors or sensor surfaces with which the change in electrical capacitance can be measured or detected, for example in response to the driver's touch or actuation. The sensors can, for example, be provided in the form of electrical capacitors or in the form of a capacitor system comprising several capacitors, or can be designed as capacitive sensor surfaces. The change in capacitance is determined according to known measuring principles, for example based on a capacitance measurement or an impedance measurement by means of the sensor system 21.

[0073] The control unit 20 is provided for operating the sensor system 21. In this case, operation can include, in particular, controlling the sensor system 21 and / or evaluating sensor signals detected by the capacitive sensor system 21. The operation of such a capacitive sensor system 21, for example, for hands-on detection (HoD) or for recognizing operating requests, is well known.

[0074] As shown in Fig. 1, the control unit 20 for operating the sensor system 21 comprises a computing unit 13 and a supply unit 14. The computing unit 13 can be designed, for example, as a microcontroller or microprocessor. The computing unit 13 can be used, for example, to evaluate the signals or to control the sensor system 21. The supply unit 14 can be designed, for example, as a voltage source. The other components of the control unit 20 and / or the sensor system 21 can be supplied with electrical energy by means of the supply unit 14. For this purpose, the supply unit 14 can provide an electrical supply signal, in this case, for example, a supply voltage Us. The supply voltage Us can be a direct voltage or an alternating voltage.As an alternative to the described embodiment as a voltage source, the supply unit can be designed as a current source, in particular as a constant current source.

[0075] For connection to the vehicle's electrical system, the control unit 20 has two control unit connections, namely a first control unit connection 10a and a second control unit connection 10b. The first control unit connection 10a serves as the ground connection for the control unit 20. The first ground potential M1 can be tapped at the first control unit connection 10a or is present there.

[0076] The vehicle's electrical system includes a vehicle battery 40, which is designed, for example, as an accumulator. The vehicle battery 40 serves to supply electrical energy to the vehicle electrical system. In addition to the control unit 20, it also supplies or operates the other components or control units in the vehicle. The vehicle battery also provides the vehicle ground, i.e., a common reference potential for all vehicle electrical system components. The vehicle battery 40 comprises a negative terminal 40a and a positive terminal 40b, each of which forms connection contacts. A negative potential can be tapped at the negative terminal 40a as the reference potential. A positive potential can be tapped at the positive terminal 40b as the operating potential. An electrical voltage can be tapped between the negative terminal 40a and the positive terminal 40b, which results from the potential difference between the negative and positive potentials. This electrical voltage is used to supply energy to the vehicle electrical system.

[0077] For power supply, the components of the vehicle electrical system, including the control unit 20 and the steering wheel 30, are connected or linked to the vehicle battery 40. The connection is made via corresponding connecting lines 15a, 15b, 33. As shown in Fig. 1, the first control unit connection 10a is connected to the negative pole 40a of the battery 40 via a connecting line 15a. The second control unit connection 10b is connected to the positive pole 40b of the battery 40 via a connecting line 15b. The connecting lines 15a and 15b can be designed, for example, as electrical lines in a cable harness. The steering wheel 30 is connected, as previously described, via the chassis 32, which is also connected to the negative pole 40a of the battery 40 via a connecting line 33. The connecting line 33 can be implemented, for example, using suitable electrical cabling.By means of the described connection, the first and second ground potential M1, M2 are thus provided or generated on the basis of the negative potential provided at the negative pole 40a.

[0078] Under certain conditions, however, a so-called ground offset or potential offset can occur between the first ground potential M1 and the base body 31 and consequently the second ground potential M2. The reason for this is that the base body 31, which is made of metal, for example, can exert a non-negligible influence on the sensor system 21. The influence occurs, for example, through capacitive coupling, i.e., for example, charge shifts in the base body 31, or, for example, because the ground connections of the control unit 20 and / or the base body 31 change their electrical impedance, in particular becoming high-resistance or even being completely interrupted. A high-resistance connection occurs, for example, if the connecting lines 15a and 33 or the electrical contacts along the path from the chassis to the steering column to the steering wheel base body are defective, i.e., for example, if they are corroded.This can result in the second ground potential being floating relative to the first ground potential M1, or vice versa. Capacitive coupling occurs, for example, when interference voltages occur in the connecting lines 15a, 33 or along the electrical connection from the chassis to the steering column and further to the steering wheel base. This can happen, for example, if several control units are connected via the wiring harness to which the connecting line 15a belongs or the chassis, and their power requirements, i.e., the load on the wiring harness, suddenly change.

[0079] For hands-on detection to function flawlessly, it is important that the two ground potentials M1, M2, or the ground connection of the base body 31 to the chassis, have values ​​that are as identical as possible, or that their values ​​do not change unexpectedly, i.e., that there is no variable ground offset. A ground offset can lead to false detections in the sensor system 21, and the sensor system 21 can, for example, output a sensor signal S that corresponds to the presence of a hand on the steering wheel even though the driver has not placed a hand on the steering wheel. Therefore, it is important to detect ground offsets when they occur and to contain their effects, particularly to compensate for them.

[0080] For this purpose, the detection device 10 mentioned at the beginning is provided. In the present exemplary embodiment according to Fig. 1, the detection device 10 is integrated into the control unit 20. In particular, the detection device 10 also uses the computing unit 13 and the supply unit 14 of the control unit 20. In addition, the detection device 10 comprises a voltage divider circuit 11 with a voltage divider 12. In the present case, the voltage divider 12 is designed, for example, as an ohmic voltage divider with several electrical resistors. In the exemplary embodiment, the voltage divider 12 comprises, for example, three electrical resistors Rp, Rd, Rg, which are connected to one another in electrical series. As an alternative to the circuit shown in Fig.1, other types or designs of voltage dividers can of course also be used, such as a capacitive voltage divider or an ohmic voltage divider with a higher or lower number of electrical resistors.

[0081] The voltage divider circuit 11 comprises a first input terminal 11a and an output terminal 11b. The first input terminal 11a is connected to the computing unit 13. Preferably, the voltage divider circuit 11 can comprise a further electrical resistor (not shown in Fig. 1) as a component, which is connected between the first input terminal 11a and the computing unit 13. The further resistor can be provided as overvoltage protection for the computing unit. The output terminal 11b is connected to the first control unit terminal 10a. Thus, the first ground potential M1 can be tapped at the output terminal 11b or is present there. The voltage divider circuit is also connected to the computing unit 13 via the output terminal 11b. The resistors Rd and Rg are connected in series between the first input terminal 11a and the output terminal 11b.A second input terminal 11c of the voltage divider circuit is designed as a center tap between the resistors Rd and Rg. The voltage divider circuit 11 is connected to the base body 31 via the second input terminal 11c. The voltage divider circuit is thus connected to the second ground potential M2 via the second input terminal 11c.

[0082] Since the supply unit 14 is embodied here as a voltage source, the resistor Rp is connected to the first input terminal 11a. Furthermore, the resistor Rp is connected to a supply terminal 11d of the voltage divider circuit 11. The voltage divider circuit 11 is connected to the supply unit 14 via the supply terminal 11d and the output terminal 11b. The supply voltage Us can be provided or applied between the supply terminal 11d and the output terminal 11b by means of the supply unit 14.

[0083] Suitable values ​​or the dimensioning of the resistors Rg, Rd, and Rp can be determined, for example, in test experiments through simulations. In particular, the values ​​of the resistors Rp, Rd, and Rg can be adapted to the desired measurement resolution for detecting the ground offset. The supply voltage Us can also be determined, for example, in test experiments or determined through simulations. In particular, the supply voltage Us can be adapted, for example, to the manufacturer's specifications of the computing unit 13, in particular of the analog-to-digital converter. For example, the supply voltage Us can be 3.3 volts or 5 volts.

[0084] Additionally or alternatively, it is conceivable for the supply unit 14 to be designed as a constant current source instead of a voltage source, which can deliver a constant current for supplying the voltage divider circuit 11. This means that the resistor Rp in particular can be omitted, since no additional overcurrent protection is necessary for the input of the computing unit 13. During operation of the voltage divider circuit 11, a first input voltage Ua is present between the first input terminal 11a and the output terminal 11b. The computing unit can detect or measure the first input voltage Ua. To detect the first input voltage Ua, the computing unit can comprise, for example, an analog-to-digital converter. The input voltage Ua depends, among other things, according to the known calculation rules of a voltage divider, on a second input voltage Ug, which can be tapped between the second input terminal 11c and the output terminal 11b or is present there.The second input voltage Ug drops across the resistor Rg when there is a ground offset.

[0085] For the voltage divider 12 used in the embodiment according to Fig. 1, the first input voltage Ua results from the following calculation rule:

[0086] Rd + Rg

[0087] Ua = Us ■ — - - —

[0088] Rd + Rp + Rg

[0089] In the undisturbed normal case, i.e., when there is no ground offset, the resistor Rg is short-circuited by the connection via the steering wheel, the steering column, the vehicle chassis 32, and the supply line (connecting line 33) to the vehicle battery 40. Also, in the undisturbed normal case, no significant additional voltage drops occur in the connecting line 33, etc., so the resulting voltage drop across Rg, i.e., the second input voltage Ug, can be assumed to be 0. Because there is no voltage drop across Rg, the first input voltage Ua at the analog input of the computing unit 13 is set as follows:

[0090] Rd Ua = Us ■ — -

[0091] Rd + Rp

[0092] If, for example, currents from other consumers or other control units cause additional voltage drops in one of the connecting lines 15a, 33, the ground offset between the ground potentials M1 and M2 occurs, as previously described. This also results in a voltage drop across Rg. The resistor Rg can therefore no longer be considered short-circuited. An additional, sufficiently low-resistance voltage drop is present in the steering column, the chassis 32, and / or one of the connecting lines 33, 15a to the battery 40. The resulting voltage drop, i.e., the first input voltage Ug, will therefore differ significantly from the value 0 and will be either positive or negative. This also leads to a change in the voltage, i.e., the first input voltage Ua, at the analog output. In this case, the first input voltage Ua is calculated as follows:

[0093] Since the second input voltage Ug has either a positive or negative value, both a negative and a positive ground offset can be measured or calculated or determined in the computing unit 13. To measure or determine the ground offset and, if necessary, compensate for hand detection, the computing unit uses a specific evaluation method, which will be described in more detail later with reference to Fig. 2. The ground offset will lie within certain limits that depend on the choice of resistance values ​​for Rp, Rd and Rg as well as the size of the supply voltage Us. In addition, the measurement limits depend on the size of the supply voltage of the computing unit or the analog-to-digital converter used, which usually limits and defines the usable input voltage range of the analog input.

[0094] Even if an increased contact resistance Rü occurs, for example, if one of the connecting lines 15a, 33 becomes high-resistance (impedance change), the resistance Rg can no longer be considered short-circuited. The contact resistance Rü can be a parasitic line resistance. It can occur, for example, in the connecting lines 15a, 33, but also in the chassis, steering column, or transition to the steering wheel body. Figure 1 shows some examples of locations where a contact resistance Rü can occur.

[0095] In the voltage divider circuit 11 according to Fig. 1, such a contact resistance Rü acts as a parallel resistance to the resistance Rg, which is greater than zero (not shown in Fig. 1). In Fig. 1, the contact resistance Rü can thus be drawn in electrical parallel with the resistance Rg. The second input voltage Ug thus drops across the total resistance from the parallel connection of Rg and Rü, which is referred to below as Rg'. The first input voltage Ua is thus calculated according to the following formula:

[0096] Rd + Rg'

[0097] Ua = Us ■ — — - — - Rd + Rp + Rg with

[0098] Thus, an increased contact resistance Rü, i.e., a high-impedance connection, can also be detected using the voltage divider 12. The additional contact resistance Rü can be detected by the computing unit 13 as a positive ground offset.

[0099] With the design of the voltage divider 12 shown in Fig. 1, it is possible to detect both positive and negative ground offsets and a high-impedance ground connection. For example, if the resistor Rd is omitted or set to zero in the voltage divider 12, measuring or detecting negative ground offsets of the steering wheel base body 31 relative to the control unit ground is no longer readily possible because, in normal, undisturbed conditions, the analog input receives or measures a voltage of zero, and even smaller voltages cannot be detected due to the design of an analog-to-digital converter.

[0100] If, however, the resistance Rg is omitted or made infinitely large, both a negative and a positive ground offset, as well as an increased contact resistance, could be detected. However, the magnitude of the measurable or detectable ground offset would be small. This means that the resolution with which the computing unit 13 could detect ground offsets might not be sufficient, especially for safety-relevant systems such as hands-on detection. Rg can thus be used to set the measuring range for the ground offset, although the size or dimensions of Rd and Rp also influence the measuring range.Furthermore, in the event of a complete interruption of the connection via the steering wheel, the steering column, the vehicle chassis 32 and its supply lines (connecting line 13) to the vehicle battery 40, there would no longer be any galvanic connection of the steering wheel 30 and any electrostatic discharges that might occur there would no longer be sufficiently dissipated to ground.

[0101] An exemplary evaluation method with which the computing unit 13 can determine or calculate the ground offset will now be described with reference to Fig. 2. For this purpose, Fig. 2 shows a schematic process flow diagram for a method for operating the detection device 10. The method is carried out or executed in particular by means of the computing unit 13. In a step S1, the computing unit 13 first detects the first input voltage Ua. For example, the analog-to-digital converter of the computing unit 13 can measure the first input voltage Ua. The method then continues in a step S2.

[0102] In step S2, a check is made to see whether the first input voltage Ua deviates from a predetermined setpoint range Usoll. This deviation occurs precisely when the first and second ground potentials M1, M2 have a ground offset that exceeds the setpoint range. For the check, the computing unit 13 can compare the first input voltage Ua with the setpoint range. The setpoint range corresponds to the value or value range of the first input voltage Ua when the resistor Rg is considered to be completely or almost short-circuited. This means that Usoll is calculated as:

[0103] Rd

[0104] Usoll = Ua = Us

[0105] Rd + Rp

[0106] If the input voltage Ua is within the setpoint range Usoll, no deviation exists (N) and the method continues at step S3. In step S3, the computing unit 13 determines that, in response to the check according to step S2, there is no ground offset (M1 = M2). Therefore, no further measures are necessary, for example, to compensate for the ground offset. Starting from step S3, the method can be restarted with step S1. Preferably, the method can be carried out by the computing unit, for example, continuously or repeatedly at specific time intervals.

[0107] If, however, step S2 reveals that the first input voltage deviates from the target value range Usoll (Y), the process continues in step S4. The deviation here means that the first input voltage Ua either exceeds or falls below the target value range Usoll, depending on the cause of the ground offset. If the value is exceeded, a positive ground offset occurs, while if the value is undershot, a negative ground offset occurs. This allows the computing unit, for example, to distinguish between the causes of the ground offset, as described above.

[0108] In step S4, the computing unit 13 determines that a ground offset exists. The first ground potential M1 thus differs from the second ground potential M2 (M1 M2). To determine a value for the ground offset, the computing unit 13 can, for example, determine or calculate a potential offset value depending on the size of the deviation between Ua and Usoll. The deviation of the first input voltage Ua from the target value range Usoll thus provides a measure of the size of the ground offset. Starting from step S4, the computing unit can now determine that a measure to compensate for the ground offset is necessary. For this purpose, the method can be continued in a step S5.

[0109] In step S5, the computing unit 13 can generate a compensation signal K for controlling the sensor system 21. By applying or using the compensation signal for controlling the sensor system 21, a compensation measure associated with the compensation signal K can be carried out by means of the control unit 20, i.e., in the controller. A compensation measure can, for example, comprise reducing the sensitivity of the capacitive sensor device at least temporarily. The reduction in sensitivity can, for example, be adjusted depending on the size of the determined potential offset value. By reducing the sensitivity, it is possible to adjust the point at which the sensor system 21 determines a capacitance change as relevant. A further compensation measure comprises, for example, deactivating the capacitive sensor device at least temporarily.This means that by controlling it with the compensation signal K, the sensor system 21 can, for example, be deactivated or switched off, or its output signal can be discarded. Alternatively, the capacitive evaluation of the computing unit 13 can, for example, be temporarily suspended. A further compensation measure includes, for example, correcting the tracking of a reference value during the capacitive evaluation. For this purpose, the calculated potential offset value can, for example, be specified as the reference value for the capacitive evaluation. This allows the interference due to the ground offset to be actively calculated out during the capacitive evaluation. The described compensation measures can be carried out individually or together one after the other, for example depending on the determined potential offset value. The aim of the compensation measure is to eliminate or correct the disruptive influence of the ground offset as best as possible.

[0110] As described at the beginning, the supply voltage Us can be a non-constant voltage, for example, an alternating voltage or a partial alternating voltage, in particular a combination of direct and alternating voltage. In this case, it is important for compensation that the supply voltage Us is also measured and its influence is taken into account when evaluating the analog input, i.e., the first input voltage Ua. This means that the fluctuations in the temporal characteristic of the supply voltage Us should be calculated out. To do this, the recorded value of the supply voltage Us can, for example, be set in relation to the recorded first input voltage Ua.

[0111] In the following, exemplary further design options for the detection device 10 are described in more detail, which can be provided in combination or as an alternative to the designs according to Fig.1 and Fig.2.

[0112] Fig. 3 shows an example of an alternative or additional embodiment of the steering wheel 30. The steering wheel comprises, for example, two control elements 34 equipped with a touch-sensitive sensor system as described above. The control elements 34 can be capacitive buttons or steering wheel switches that are triggered or actuated by contact with a user's finger. In the present case, the control elements 34 are attached, for example, to the spokes of the steering wheel rim 30. Of course, more or fewer than two such control elements 34 can also be provided. The electrically conductive part of the control elements 34 can be provided, for example, by design elements such as chrome plating and / or a metallic frame.

[0113] 4a to 6b show exemplary embodiments for designing the voltage divider circuit 11 so as to be switchable. According to Fig. 4a and Fig. 4b, for example, the supply unit 14 can be designed so as to be switchable in order to supply current to the voltage divider 12 only when monitoring for ground connection is necessary. For switching off, for example, a switching unit 16a can be provided, via which the voltage divider 12 is connected to the supply connection 11d. The switching unit 16a can be connected, as shown in the figures, for example between the resistor Rp and the supply connection 11d (Fig. 4a) or between the first input connection 11a and the resistor Rp. The switching unit 16a can be controlled, i.e. switched, for example, by means of the computing unit.

[0114] Additionally or alternatively, the line connecting the steering wheel 30 to the voltage divider 12, i.e., the second input terminal 11c, can be designed to be switchable or interruptible. For this purpose, as shown in Fig. 5, a switching unit 16b can be provided, which can be controlled or switched, for example, by the computing unit 13. This allows the computing unit 13 to specifically switch the line to the base body 31 on and off. This has the advantage that the voltage divider consisting of the three resistors Rp, Rd, and Rg can be checked for damage by the steering wheel 31, independent of external influences. In this case, damage means whether the resistors of the voltage divider 12 have changed their values, for example, due to aging or damage (e.g., due to ESD).If, in the switched-off or disconnected state, in which the voltage divider is therefore unloaded, the first input voltage Ua lies within the aforementioned setpoint range valid for this switching state, then it can be assumed that the voltage divider is OK and will not cause any measurement errors when the line to the base body 31 is later closed again and the ground offset is to be measured.

[0115] Additionally or alternatively, it would be conceivable for the line connecting Rg to the control unit ground to be switchable or interruptable. For this purpose, for example, a corresponding switching unit 16c can be installed between the center tap 11c and the output terminal 11b. According to the exemplary embodiment in Fig. 6a, the switching unit 16c can be connected, for example, between the center tap 11c and the resistor Rg. Alternatively, the switching unit 16c can be connected, for example, between the resistor Rg and the output terminal 11b. The switching unit 16c can be controlled or switched, for example, by means of the computing unit 13. If the switching unit 16c is only switched on and off, there must be no change in the first input voltage Ua if there is no undesirable ground offset in the vehicle and the ground connection via the steering wheel 31 is low-resistance.If, however, the first input voltage Ua changes during switching, a ground offset or a high-impedance connection of the steering wheel 30 is present, and a corresponding response can be made, for example, with one of the respective compensation measures. This implementation option, based on signal difference calculation of the values ​​of the input voltages Ua between the two switching states, is particularly suitable for detecting whether a ground offset exists due to tolerances in the components used. Without switching, such ground connections would be difficult to detect due to component tolerances. The influence of small static ground offsets is too small to distinguish it from the influence of component tolerances.

[0116] Based on this, any changes in the first input voltage 11a that can be measured in this way, in particular changes in the first input voltage 11a that are synchronous with the switching, can be used to compare them in the computing unit 13 with the output signal or sensor signal of the capacitive sensor system 21. This allows any existing and / or undesired coupling or influence between the capacitive sensor system 21 and the detection device 20 to be detected.

[0117] The switching units 16a, 16b and 16c can be designed, for example, as electronic switches or semiconductor switches, preferably as MOSFETs or transistors or circuits thereof.

[0118] Overall, the embodiments show the monitoring of electrical ground offset in motor vehicles.

Claims

Patent claims 1. A detection device (10) for a vehicle for determining a potential offset between a first ground potential (M1) of a control unit (20) for controlling a touch-sensitive sensor device (21, 34) of the vehicle and a second ground potential (M2) of a vehicle component with an at least partially electrically conductive base body (31) and / or at least one electrically conductive component to which the sensor device is assigned, wherein the detection device (20) comprises a voltage divider circuit (11) with a voltage divider (12) and a computing unit (13), wherein the voltage divider circuit (11) is connected to the computing unit (13) by a first input terminal (11a) and an output terminal (11b), wherein the first ground potential (M1) can be tapped off at the output terminal (11b), wherein the first ground potential (M1), preferably substantially, corresponds to the reference potential (40a) of the vehicle battery (40),and the voltage divider circuit (11) is connected to the base body (31) and / or the at least one component of the vehicle component by means of a second input terminal (11c), which is designed as a center tap of the voltage divider (12), wherein the base body (31) and / or the at least one component is connected to the second ground potential (M2), wherein the computing unit (13) is designed to detect a first input voltage (Ua) which can be tapped between the first input terminal (11a) and the output terminal (11b), wherein the first input voltage (Ua) is set as a function of a second input voltage (Ug) which can be tapped between the second input terminal (11c) and the output terminal (11b) as a function of the potential offset between the first and second ground potentials (M1, M2), and the computing unit (13) is designed to checkwhether the first input voltage (Ua) deviates from a predetermined setpoint range (Usoll), whereby the deviation occurs exactly when the first and second ground potential (M1, M2) have the potential offset.

2. Detection device (10) according to claim 1, wherein the voltage divider (12) is designed as an ohmic voltage divider with at least two electrical resistors (Rp, Rd, Rg), wherein the resistors (Rp, Rd, Rg) are connected in series between the first input terminal (11 a) and the output terminal (11 b), and the center tap is implemented in the series circuit between the at least two resistors (Rp, Rd, Rg).

3. Detection device (10) according to one of the preceding claims, wherein the detection device (10) comprises a supply unit (14), and the voltage divider circuit (11) is connected to the supply unit (14) by a supply terminal (11d), wherein the supply unit (14) is designed to provide an electrical supply signal (Us) between the supply terminal (11d) and the output terminal (11b).

4. Detection device (10) according to claim 3, wherein the supply unit (14) is connected to the voltage divider (12) by means of a first switching unit (16a), wherein the first switching unit (16a) is designed to disconnect or connect the supply unit (14) to the voltage divider (12) depending on an expectation signal which indicates that the potential offset is potentially to be expected.

5. Detection device (10) according to claim 3 or claim 4, wherein the supply unit (14) is designed as a power source.

6. Detection device (10) according to claim 2 and claim 3 or claim 4, wherein the supply unit (14) is designed as a voltage source, and wherein the ohmic voltage divider has at least three electrical resistors, one of the resistors (Rp) being connected between the first input terminal (11 a) and the supply terminal (11 d).

7. Detection device (10) according to claim 6, wherein the voltage source is designed to provide a non-constant electrical voltage, in particular an alternating voltage as the supply signal (Us), and the The computing unit (13) is designed to take into account a fluctuation in the course of this voltage when specifying the setpoint range (Usoll).

8. Detection device (10) according to one of the preceding claims, wherein the computing unit (13) and / or the supply unit (14) are provided by the control unit (20).

9. Detection device (10) according to one of the preceding claims, wherein the output terminal (11b) is connected to the voltage divider (12) by means of a second switching unit, and the second switching unit is designed to determine the potential offset first to connect and then to disconnect the output terminal (11b), and to compare the first input voltage (Ua) in the connected state with the first input voltage (Ua) in the disconnected state according to a predetermined comparison criterion.

10. Detection device (10) according to claim 9, wherein the computing unit (13) is designed to determine a comparison value which indicates a difference between the first input voltage (Ua) in the connected state and the first input voltage (Ua) in the disconnected state, and to compare it with a sensor signal of the touch-sensitive sensor device according to a predetermined coupling criterion for checking for an undesired electrical coupling between the touch-sensitive sensor device and the detection device (10).

11. Detection device (10) according to one of the preceding claims, wherein the computing unit (13) is designed to check whether the first input voltage (Ua) is greater or smaller than the setpoint range (Usoll), and depending thereon to determine a polarity, a temporal profile and a size of the potential offset and thereby provide indications of its cause.

12. Detection device (10) according to one of the preceding claims, wherein the second input terminal (11c) is connected to the base body (31) of the vehicle component (30) by means of a third switching unit (16b), and the third switching unit is designed in a test mode to separate the second input terminal (11c) from the base body (31), and the computing unit (13) is designed is to check in the test mode whether the first input voltage (Ua) is within a specified test setpoint range (Usoll_prüf), whereby the test setpoint range differs from the setpoint range.

13. Detection device (10) according to one of the preceding claims, wherein the detection device (10) is designed to control the control unit (20) with a compensation signal (K) for carrying out a predetermined compensation measure for controlling the touch-sensitive sensor device only when the first input voltage (Ua) deviates from the setpoint value range (Usoll).

14. Detection device (10) according to claim 13, wherein the compensation measure comprises changing, in particular reducing, the sensitivity of the touch-sensitive sensor device.

15. Detection device (10) according to claim 13, wherein the compensation measure comprises deactivating the touch-sensitive sensor device.

16. Detection device (10) according to claim 13, wherein the computing unit (13) is designed to determine a potential offset value from the determined deviation, which indicates a value of the potential offset between the first and second ground potential (M1, M2), and the compensation measure comprises specifying the potential offset value as a reference value for an evaluation of the measurement results of the touch-sensitive sensor device.

17. Vehicle with a detection device (10) according to one of the preceding claims, wherein the vehicle comprises a touch-sensitive sensor device with a control unit (20) and at least one vehicle component with an at least partially electrically conductive base body (31) and / or at least one electrically conductive component to which the sensor device is assigned, wherein the sensor device is designed to detect actuation of the at least one vehicle component by a user.

18. The vehicle of claim 17, wherein the vehicle component is a steering control of the vehicle or a door handle of a vehicle door or a control element of an electronic entertainment unit.

19. A method for determining a potential offset between a first ground potential (M1) of a control unit (20) for controlling a touch-sensitive sensor device of the vehicle and a second ground potential (M2) of a vehicle component (30) with an at least partially electrically conductive base body (31) and / or at least one electrically conductive component to which the sensor device is assigned, wherein a detection device (10) is provided with a voltage divider circuit (11) with a voltage divider (12) and a computing unit (13), wherein the voltage divider circuit (11) is connected to the computing unit (13) with a first input terminal (11a) and an output terminal (11b), wherein the first ground potential (M1) can be tapped off at the output terminal (11b), wherein the first ground potential preferably substantially corresponds to the reference potential of the vehicle battery,and the voltage divider circuit (11) is connected to the base body (31) and / or the at least one component of the vehicle component by means of a second input terminal (11c), which is designed as a center tap of the voltage divider (12), wherein the base body (31) and / or the at least one component is connected to the second ground potential (M2), wherein a first input voltage (Ua), which can be tapped between the first input terminal (11a) and the output terminal (11b), is detected by means of the computing unit (13), wherein the first input voltage (Ua) is set as a function of a second input voltage (Ug), which can be tapped between the second input terminal (11c) and the output terminal (11b) as a function of the potential offset between the first and second ground potentials (M1, M2), and wherein the computing unit (13) checks whether the first input voltage (Ua) deviates from a predetermined setpoint range (Usoll),where the deviation occurs exactly when the first and second ground potential (M1 , M2) have the potential offset.,

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