Steering Control Apparatus Hands-Off Detection
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Solution Overview
Problem
Existing methods for determining a hands-off state in a motor vehicle's steering system often result in erroneous detection, leading to incorrect identification of whether the driver's hands are on or off the steering wheel, especially when the vehicle is moving straight and minimal driver input is required.
Innovation Solution
A control method that calculates the steering wheel torque and its derivative, using a counter to differentiate between hands-on and hands-off states by adjusting based on threshold limits, and employs low-pass filtering to reduce noise and vibrations, allowing for more reliable detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If simple threshold checking of steering shaft torque is used to determine hands-off state, then the detection method is simple, but the detection accuracy is poor and erroneous detection occurs
Solution Approach 1:
The detection method is segmented into multiple independent evaluation dimensions: torque magnitude threshold checking, torque derivative threshold checking, and counter-based state determination. Each dimension independently evaluates a specific aspect of driver input, and their combined results provide comprehensive and accurate hands-off state detection, resolving the contradiction between simplicity and accuracy.
Solution Approach 2:
The detection approach transitions from a single-dimension torque magnitude check to a multi-dimensional evaluation system that includes both torque magnitude (M) and its time derivative (∂M/∂t). This dimensional expansion allows the system to distinguish between transient torque fluctuations and genuine driver input, significantly improving detection accuracy while maintaining computational efficiency.
2Speed
If steering shaft torque vibrations are not dampened to detect hands-off state, then the detection response is fast, but false detection occurs due to undampened vibrations
Solution Approach 1:
The system performs preliminary evaluation of torque magnitude and derivative against predefined thresholds before final state determination. This preliminary filtering action prevents transient vibrations from triggering false hands-off detection, while the counter mechanism ensures fast response when genuine hands-off conditions are detected, resolving the contradiction between response speed and reliability.
3Measurement precision
If counter-based state determination with multiple thresholds is used, then the detection accuracy is improved, but the computational complexity increases
Solution Approach 1:
The counter mechanism automatically accumulates evidence for hands-off state determination through incremental counting when both torque and derivative thresholds are satisfied. This self-service approach eliminates the need for complex decision logic or multiple processing stages, achieving high detection accuracy through a simple, efficient counting algorithm that minimizes computational overhead.
Data Source
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AI summary
The invention proposes a method for controlling a steering device with steering power support means (7, 8, 9) for a motor vehicle with at least one steerable road wheel (4), whereby the steering device comprising: • a steering shaft (1) with a first end to adopt a steering wheel (2), • a control device (10) controlling said power support means (7, 8, 9), • sensing means (11) detecting steering shaft torque introduced in said steering shaft (4), • means to determine a hands-off situation in which the driver does not introduce a torque into said steering shaft (1), wherein the steering power support means (7, 8, 9) support the driver on the basis of a driver demand introduced into the steering shaft (1), whereby the method is characterized by the following steps: • determining a steering wheel torque (M) on basis of the steering shaft torque; • determining a time derivative (∂M/∂t) of the detected steering wheel torque (M); • if the absolute value of the steering wheel torque (M) is lower than a threshold torque limit (ε1) and if the absolute value of the derivative of steering wheel torque (∂m/∂t) is lower than a threshold derivative torque limit (ε2), a counter (C) is increased by one count, • if the absolute value of the steering wheel torque (M) is higher or equal than a threshold torque limit (ε1), or/and if the absolute value of the derivative of steering wheel torque (∂M/∂t) is higher or equal than a threshold derivative torque limit (ε2), said counter (C) is decreased by one count, if said counter (C) has a value equal to or higher than a threshold count limit (N1) the hands-off state is determined.