Steering Wheel Torque Detection Using Notch Filtering
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Solution Overview
Problem
Existing methods for detecting if a driver has their hands on a steering wheel are costly and complex, particularly when additional sensors are required, and they may not accurately differentiate between hands-on and hands-off conditions.
Innovation Solution
A control system and method that utilize a torque sensor and a control module with notch or bandpass filters to determine the hands-on wheel condition by attenuating normal column mode frequencies and comparing the filtered torque signal with threshold values, thereby reducing the need for additional sensors and improving accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If additional sensors are placed on the hand wheel to detect hands-on condition, then detection accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The torque sensor, originally designed for steering assistance functions, is repurposed to also detect hands-on conditions. The control module analyzes torque signal characteristics (frequency content, magnitude patterns) to differentiate between hands-on and hands-off states, making a single sensor perform multiple functions without adding complexity
Solution Approach 2:
The patent replaces mechanical contact-based detection (capacitive touch sensors, physical switches) with signal-based detection using existing torque sensor data. By analyzing the mechanical torque signal's frequency and magnitude characteristics, the system infers hands-on status without direct mechanical contact sensors
2Device complexity
If torque-based detection is used to determine hands-on condition, then device complexity is reduced, but measurement precision deteriorates due to inability to differentiate hands-on from hands-off conditions
Solution Approach 1:
The patent exploits vibrational characteristics of the steering wheel under different conditions. When hands are on the wheel, they dampen certain vibrational modes and introduce different frequency signatures. By analyzing the frequency spectrum of torque signals, the system distinguishes hands-on from hands-off states based on these vibrational patterns
Solution Approach 2:
The control module monitors changes in torque signal parameters (frequency, magnitude, spectral density) to detect hands-on conditions. By tracking how these parameters change under different operating conditions, the system achieves accurate detection using only the existing torque sensor without additional hardware
3Loss of information
If normal column mode frequency is not attenuated, then signal information is preserved, but detection accuracy decreases due to interference from hands-off vibrational modes
Solution Approach 1:
The control module extracts and removes the normal column mode frequency components from the torque signal through filtering. By eliminating these known hands-off vibrational modes, the system isolates the remaining signal components that are characteristic of hands-on conditions, improving detection accuracy without losing relevant information
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 approach effectively determines the hands-on wheel condition with reduced complexity and cost, enhancing the reliability of steering system operations and enabling features like torque assist commands for lane monitoring systems.
Implementation Method 1
The control module includes a notch filter to attenuate a normal column mode frequency from the amount of applied torque to produce a filtered torque signal
Implementation Method 2
a sensor that monitors an amount of applied torque exerted upon a hand wheel
Data Source
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AI summary
A control system to determine a hands on wheel (HOW) condition is provided. The control system includes a sensor (50) that monitors an amount of applied torque exerted upon a hand wheel (34), and a control module (60) for monitoring the sensor. The control module includes a notch filter to attenuate a normal column mode frequency from the amount of applied torque to produce a filtered torque signal. The normal column mode frequency represents a range of vibrational modes of the hand wheel based on a hands off wheel condition. The control module includes a state detector to receive the filtered torque signal from the notch filter. The state detector determines if the HOW condition exists based on if the filtered torque signal exceeds an ON threshold torque value.