Steering Wheel Touch Electrode Circuit for Surge Voltage Protection
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Solution Overview
Problem
Capacitive touch detection in steering wheels is susceptible to overvoltages, leading to disruptions and potential damage to evaluation electronics, especially during transitions between autonomous and driver-controlled driving states.
Innovation Solution
The implementation of a protective circuit with an overvoltage dissipation element in the electrical connection between the electrode and the steering wheel core, utilizing a high-resistance path for measuring potential and a low-resistance path for overvoltage diversion, ensuring that overvoltages are directed to the first ground connection, reducing potential shifts and protecting the evaluation electronics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protective circuit with surge arrester element is added to protect evaluation electronics from overvoltage, then the reliability of the system is improved, but the device complexity increases
Solution Approach 1:
A first loss resistance is introduced as an intermediary element between the surge arrester element and the first ground terminal. This resistance acts as a mediator that limits the current flow and reduces potential shifts on the ground connection, thereby protecting the evaluation electronics while maintaining circuit simplicity
Solution Approach 2:
The ground connection for the evaluation electronics is spatially separated from the main ground terminal and connected through a dedicated path containing the loss resistance. This extraction of the ground connection creates an independent protective path that isolates the evaluation electronics from overvoltage effects
2Reliability
If the first ground terminal and second ground terminal are spatially separated and connected through a metallic body, then the grounding is improved, but potential shifts occur between the terminals leading to detection errors
Solution Approach 1:
A first loss resistance is introduced as an intermediary element between the surge arrester element and the first ground terminal. This resistance acts as a mediator that limits the current flow and reduces potential shifts on the ground connection, thereby protecting the evaluation electronics while maintaining circuit simplicity
Solution Approach 2:
The patent aims to maintain equipotential conditions between the first and second ground terminals by using the loss resistance to limit potential differences. The resistance ensures that even when current flows through the ground connection, the potential shift remains minimal, preserving accurate touch detection
3Reliability
If overvoltage is diverted to the first ground terminal through a low-resistance path, then the protection effectiveness is improved, but potential shifts occur on the ground connection affecting the second ground terminal
Solution Approach 1:
A first loss resistance is introduced as an intermediary element between the surge arrester element and the first ground terminal. This resistance acts as a mediator that limits the current flow and reduces potential shifts on the ground connection, thereby protecting the evaluation electronics while maintaining circuit simplicity
Solution Approach 2:
The patent changes the resistance parameter in the ground connection path by introducing a controlled loss resistance. This parameter change transforms the ground connection from a low-resistance path that causes large potential shifts to a controlled resistance path that limits both current flow and potential shifts, protecting the evaluation electronics
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively prevents overvoltage-induced disruptions in touch detection, ensuring continuous and accurate capacitive touch evaluation by reducing overvoltage impact on the evaluation electronics and maintaining reliable steering control monitoring.
Implementation Method 1
a first loss resistance (R) which limits a current flow and/or voltage drops during an overvoltage
Implementation Method 2
a connection (15) between the electrode (6) and the steering wheel core (4), which connection has an overvoltage discharge element (13)
Implementation Method 3
capacitive detection of a contact with the steering wheel (2)
Data Source
Figure 1
Figure 2
AI summary
The invention relates to an assembly (1) for a motor vehicle, the assembly being composed of: - a steering wheel (2) having an electrode (6); and - evaluation electronics (3) to be protected against surge voltage, the evaluation electronics being electrically connected to the electrode (6) in order to capacitively detect touching 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 fastening to a steering wheel shaft (9); the steering wheel core (4) is electrically connected to a first ground terminal (11) via a first ohmic loss resistance (R); the evaluation electronics (3) are designed to apply a measurement electric potential for touch detection to the electrode (6), in order to detect the touching of the steering wheel rim (2) on the basis of a change in a measurement capacitance formed between the electrode (6) and the steering wheel core (4); the evaluation electronics (3) are also electrically connected to a second ground terminal (12); the first ground terminal (11) and the second ground terminal (12) are spatially separated from each other and are electrically connected by means of a ground connection (14); an electrically conductive connection (15) between the electrode (6) and the steering wheel core (4), the electrically conductive connection having a surge-arresting element (13) such that the the connection (15) is of high resistance when there is measurement potential at the electrode and is of low resistance when there is surge voltage at the electrode, so that in the latter case the surge voltage is led away via the steering wheel core (4) to the first ground connection (11). The invention also relates to a motor vehicle having the assembly.