Heated Steering Wheel Capacitive Sensing for Accurate Hands-Off Detection
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Solution Overview
Problem
Current steering wheel torque control systems, such as those using capacitive or optical sensing, face issues with false readings due to steering wheel movement, even when the driver's hands are not on the wheel, complicating the Hands Off Detection function in Advanced Driver Assistance Systems.
Innovation Solution
A single device integrating heating and capacitive sensing capabilities for the steering wheel, utilizing a flexible conductive element with dedicated heating and sensor tracks, and a microcontroller-compatible capacitance reading module, which includes a capacitor to reduce saturation levels and prevent false touches by environmental factors, and uses a MOSFET to manage current and temperature sensors for efficient heating and sensing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a torque sensor is used to sense whether the driver has hands on the steering wheel, then the Hands Off Detection function is provided, but false readings occur due to steering wheel movement even when the driver's hands are not on the wheel
Solution Approach 1:
The patent divides the steering wheel into multiple capacitive sensing zones (first capacitive element and second capacitive element) with different functionalities. The first capacitive element detects hand presence while the second capacitive element detects steering wheel rotation, allowing the system to distinguish between genuine hands-off conditions and false readings caused by wheel movement.
Solution Approach 2:
The patent introduces a processing unit that acts as an intermediary between the capacitive sensing elements and the hands-off detection function. This processing unit analyzes signals from multiple capacitive elements and uses algorithms to differentiate between capacitance changes caused by hand presence versus those caused by steering wheel rotation, thereby eliminating false readings.
2Device complexity
If a single device integrates both heating and capacitive sensing functions, then device complexity is reduced and space is saved, but the heating tracks may interfere with capacitive sensing accuracy
Solution Approach 1:
The patent implements periodic action by cyclically connecting and disconnecting the heating track to and from the power source and ground. During capacitance reading periods, the heating track is disconnected and placed at the same potential as the capacitive sensor track, eliminating thermal and electrical interference. Heating occurs during dedicated heating periods when capacitive sensing is not performed, thus preventing false touches from environmental factors like humidity.
Solution Approach 2:
The patent applies equipotentiality by ensuring that during capacitance reading, the heating track is held at the same electrical potential as the capacitive sensor track. This potential equalization prevents voltage differences that could cause false capacitive readings, allowing accurate sensing even in the presence of the heating track structure.
3Adaptability or versatility
If capacitive elements of different sizes are used, then the device can adapt to different steering wheel geometries, but the microcontroller must be replaced to accommodate different capacitance values
Solution Approach 1:
The patent implements parameter changes by introducing a series capacitor that transforms the capacitance measurement range. The series capacitor modifies the total capacitance value seen by the microcontroller, allowing the same microcontroller to handle a wide range of capacitive element sizes. This parameter transformation enables the system to accommodate different steering wheel geometries without requiring microcontroller replacement.
Solution Approach 2:
The patent achieves universality by designing a capacitive sensing system that can detect hands-off conditions across steering wheels of various sizes and geometries using a single microcontroller. The system uses multiple capacitive elements with different configurations but processes all signals through the same microcontroller with unified handling logic, making the device universally applicable to different steering wheel designs.
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 provides reliable and accurate capacitive sensing and heating for the steering wheel, reducing false readings and improving the Hands Off Detection function, allowing for better driver monitoring and vehicle safety features without the need for microcontroller replacement, regardless of the steering wheel size or geometry.
Implementation Method 1
a heating track (12) configured to be used as heating means
Implementation Method 2
a capacitive sensor track (14) configured to be used as sensor means
Implementation Method 3
by providing at least one capacitor, in particular a capacitor in series with the capacitive track (or sensor track), the capacitance value input to the microcontroller
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
Heating and capacitive sensing device (100) for a steering wheel (V) of a motor vehicle, the device (100) comprising: a support (11) made of electrically insulating flexible material to which at least an electrically conductive first track (12) and at least an electrically conductive second track (14) are fixed; an electronic control unit (20) comprising a capacitance reading module (40) electrically connected to the at least one second track (14); wherein the electronic control unit (20) is configured to control the at least one first track (12) and at least one second track (14), so that the at least one first track (12) is suited to generate heat for heating the steering wheel (V), and at least one second track (14) is adapted to operate as capacitive sensor means, by sending capacitance values to the electronic control unit (20).