Steering Wheel Capacitive Contact Detection With Reference Capacitor
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Solution Overview
Problem
Current steering wheel contact detection systems, particularly capacitive systems, face challenges such as unreliable sensing due to temperature influences, sensor drift, and interference from variable initial conditions, leading to inaccurate detection of true contact.
Innovation Solution
A device using an 'open' system with the human body as a second electrode and a sensor capacitor, along with a reference capacitor and direct current voltage, allows for reliable and robust detection by measuring capacitance changes without requiring complex frequency measurements, and can be implemented in a cost-efficient manner with minimal constructional modifications to the steering wheel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If capacitive sensing systems are used for steering wheel contact detection, then contact sensing capability is provided, but temperature influences and sensor drift cause unreliable sensing and false detection
Solution Approach 1:
The system continuously monitors the capacitance value and compares it against dynamically adjusted thresholds. The evaluation unit receives feedback about environmental conditions and sensor drift, automatically adapting the detection thresholds to maintain reliable contact sensing despite temperature variations and initial condition changes.
Solution Approach 2:
The patent changes the operating parameters of the capacitive sensor by adjusting the evaluation thresholds based on temperature compensation algorithms and drift correction. Instead of using fixed thresholds, the system dynamically modifies detection parameters to account for environmental influences, transforming the sensor's response characteristics to maintain reliability across varying conditions.
2Measurement precision
If oscillating circuit frequency shift measurement is used in open systems, then capacitance change detection is enabled, but approach of steering wheel is frequently assessed as contact leading to false positives
Solution Approach 1:
The system performs preliminary detection and classification of capacitance changes before triggering contact detection. By analyzing the magnitude, rate of change, and pattern of capacitance variations in advance, the system distinguishes between approach movements and actual contact, preventing false positives while maintaining sensitive detection.
Solution Approach 2:
The patent applies a threshold-based filtering approach where only capacitance changes exceeding a predetermined threshold are considered valid contact signals. This partial action principle filters out minor capacitance variations caused by approach movements, focusing detection on significant changes that indicate true contact while maintaining measurement precision for relevant events.
3Reliability
If resistive systems with pressure-sensitive sensors are used, then contact detection is provided, but differently tight leather wrappings and different initial forces impede unambiguous sensing
Solution Approach 1:
The capacitive sensing system continuously monitors baseline capacitance values and adjusts detection thresholds based on feedback about initial conditions. By adapting to the specific electrical characteristics introduced by different leather wrappings and initial forces, the system maintains reliable contact detection across varying steering wheel configurations without requiring manual calibration.
Solution Approach 2:
The patent implements a universal detection algorithm that works across different steering wheel configurations, leather types, and wrapping tightness levels. The capacitive sensing approach with adaptive thresholding provides multi-functionality, handling various initial conditions and wrapping scenarios without requiring separate calibration procedures or additional sensors.
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
The solution provides reliable and robust steering wheel contact detection, resistant to temperature and humidity variations, and is scalable, with the ability to transmit results to vehicle assistance systems for control, while minimizing mechanical wear and interference.
Implementation Method 1
at least a first electrode which is arranged in a steering wheel and which forms, together with a human body acting as a second electrode and a dielectric situated therebetween, at least one sensor capacitor
Data Source
AI summary
A device for detecting steering wheel contact comprises at least a first electrode (12) which is provided in a steering wheel (10) and which forms, together with a human body acting as a second electrode and a dielectric situated therebetween, at least one sensor capacitor (26). The device also comprises an evaluation circuit (24) having a reference capacitor (30) of known capacitance which can be connected parallel to the sensor capacitor (26), a direct current voltage source (34) which can be connected to the reference capacitor (30), and a measuring device for measuring the voltage at the reference capacitor (30). A method for detecting steering wheel contact using such a device comprises the following successive steps: charging the reference capacitor (30) by applying a known reference voltage, or charging the reference capacitor (30) and subsequently measuring a first voltage at the reference capacitor (30); connecting, in parallel, the sensor capacitor (26) to the reference capacitor (30) so that a portion of the charge of the reference capacitor (30) is transmitted to the sensor capacitor (26); measuring a second voltage at the reference capacitor (26); end determining the capacitance of the sensor capacitor (26) from the known capacitance of the reference capacitor (30), the reference voltage or the first voltage and the second voltage.