Steering Wheel Touch Detection With Reference Load Self-Check
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Solution Overview
Problem
Current steering wheel hands-off detection systems, such as those using pressure sensing and capacitance sensing, face accuracy issues due to variations in driver grip strength and sensitivity reduction when wearing gloves, and are prone to false positives from accidental or intentional contact, failing to meet the required Automotive Safety Integrity Level (ASIL) C/D standards.
Innovation Solution
A method and apparatus for steering wheel touch detection that incorporates an additional reference load with preset capacitance and resistance values, allowing for normal operation verification of touch detection channels through measurement and IQ modulation-demodulation, ensuring accurate detection by adjusting carrier signals and reference values as needed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pressure sensing means is used for HOD, then the system can detect pressure changes on the steering wheel, but the detection accuracy deteriorates due to variations in driver grip strength
Solution Approach 1:
The patent introduces a capacitance sensor as an intermediary measurement mechanism. Instead of directly measuring pressure (which varies with grip strength), the system measures capacitance changes caused by the driver's hand approaching or touching the steering wheel. This intermediary measurement method eliminates the influence of grip strength variations while still reliably detecting hands-off conditions.
Solution Approach 2:
The patent replaces the mechanical pressure sensing system with an electrical capacitance sensing system. By substituting the mechanical measurement approach (pressure sensors) with an electrical field-based approach (capacitance sensors), the system achieves more consistent and reliable detection that is not affected by mechanical grip strength variations.
2Reliability
If capacitance sensing means is used for HOD, then the system can detect hand presence on the steering wheel, but detection sensitivity deteriorates when the driver wears gloves
Solution Approach 1:
The patent employs multiple capacitance sensors arranged at different positions on the steering wheel rather than relying on a single sensor. This redundant measurement approach ensures that even if gloves reduce the sensitivity of individual sensors, the combined signal from multiple sensors maintains reliable detection capability. The system uses excessive sensing elements to compensate for the reduced sensitivity caused by gloves.
3Reliability
If capacitance sensing means is used for HOD, then the system can measure capacitance changes, but false positives occur when other body parts or substitutes accidentally touch the steering wheel
Solution Approach 1:
The patent divides the steering wheel into multiple touch detection regions, each monitored by dedicated capacitance sensors. By segmenting the detection area and analyzing the spatial distribution of capacitance changes, the system can distinguish between intentional hands-off conditions and accidental touches from other body parts. The segmented approach allows for more nuanced interpretation of sensor signals to reduce false positives.
Solution Approach 2:
The patent implements a comprehensive evaluation mechanism that considers multiple sensor inputs and temporal patterns to verify hands-off conditions. The system uses feedback from multiple capacitance sensors to cross-validate detection results, ensuring that a single accidental touch does not trigger a false positive. The feedback mechanism analyzes the consistency and pattern of capacitance changes to confirm genuine hands-off events.
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
Enhances the accuracy and reliability of steering wheel touch detection, effectively addressing the limitations of existing systems by providing a robust and self-testing solution that meets higher safety standards, reducing false positives and improving sensitivity.
Implementation Method 1
the touch detection channel is used to measure a capacitance value and resistance value of the reference load; on the basis of the preset reference capacitance value and reference resistance value, and the measured capacitance value and resistance value, it is determined whether the operation of the touch detection channel is normal
Implementation Method 2
The sensor AS8579 generates a sine wave, by means of a transmitting module, to drive a load, a receiving module measures the current of the load, and then converts the current into a voltage, and demodulates same to in-phase (I) and orthogonal phase (Q), and an external processor can read an I value and a Q value, and calculate the corresponding resistance value and reactance value
Data Source
AI summary
A method for steering wheel touch detection is disclosed. The steering wheel is partitioned into at least one touch detection region and each touch detection region includes at least one touch detection sensor that is provided with a touch detection channel. For each touch detection channel, the method includes configuring a reference load with a preset capacitance value and reference resistance value, measuring a capacitance value and resistance value of the reference load, and determining from the reference and measured capacitance and resistance values whether the operation of the touch detection channel is normal. If the operation of the touch detection channel is normal, the touch detection channel is used to perform touch detection of the steering wheel based on measured resistance and capacitance.