Adaptive Torque Limiting for Autonomous Steering Safety
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Solution Overview
Problem
Current power assisted steering systems with autonomous steering functions face limitations in torque capability, as the safety torque limit is set too low to prevent unwanted lane departures, constraining the performance of advanced autonomous steering functions like Emergency Lane Keeping Aid, which requires higher torque to handle steeper curves and collision avoidance.
Innovation Solution
A method and arrangement for safe limiting of torque overlay intervention in power assisted steering systems, where the steering wheel overlay torque is modeled and limited to a safe set interval dependent on vehicle velocity and pinion angle, allowing both positive and negative torques, and rate limiting is applied to prevent rapid pinion angle acceleration, ensuring the driver has time to intervene in case of a fault.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the safety torque limit is increased to provide sufficient torque capability for advanced autonomous steering functions, then the performance of functions like Emergency Lane Keeping Aid is improved, but the risk of unwanted lane departures due to erroneous high torque increases
Solution Approach 1:
The patent applies dynamics by making the torque limit adaptive rather than fixed. The torque limit is dynamically adjusted based on driver interaction state (hands-on vs hands-off detection) and steering conditions (pinion angle, vehicle velocity). This allows the system to provide high torque capability when needed (hands-off with proper conditions) while maintaining safety through dynamic adaptation to current operating conditions.
Solution Approach 2:
The patent changes the parameter of torque limit from a constant value to a variable parameter that depends on multiple factors including driver hands-on/hands-off state, pinion angle, and vehicle velocity. This parameter change enables the system to optimize torque capability for different driving scenarios while maintaining safety through context-aware limitation.
2Reliability
If a fixed torque limit is applied to ensure safety, then the risk of unwanted lane departures is reduced, but the scope and performance of autonomous steering functions are constrained
Solution Approach 1:
The system transitions from a static fixed torque limit to a dynamic adaptive torque limit that responds to real-time driving conditions. The torque limit is continuously adjusted based on driver interaction detection and steering parameters, enabling the system to maintain safety while adapting to different autonomous steering function requirements.
Solution Approach 2:
The torque limit parameter is transformed from a fixed constant to a dynamic variable that changes based on multiple input parameters including driver hands-on/hands-off state, pinion angle, and vehicle velocity. This parameter transformation enables both safety maintenance and functional versatility.
3Reliability
If the torque limit is set low to allow driver reaction time, then driver safety is maintained, but the torque available for lane keeping and collision avoidance functions is insufficient
Solution Approach 1:
The system uses dynamic adjustment of torque limits based on driver interaction state. When the driver is detected to be hands-off, the system can apply higher torque for autonomous steering functions. When the driver is hands-on, the torque limit is adjusted to preserve driver control and reaction capability. This dynamic approach resolves the contradiction by adapting the torque limit to the current control situation.
Solution Approach 2:
The system implements feedback through driver interaction detection (hands-on/hands-off sensing) to continuously adjust the torque limit. This feedback mechanism ensures that torque availability is optimized based on actual driver engagement, maintaining safety when the driver is actively steering while enabling sufficient torque for autonomous functions when the driver is not interfering.
Data Source
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AI summary
Disclosed herein is a method and arrangement for safe limiting of torque overlay intervention in a power assisted steering system of a road vehicle having an autonomous steering function arranged to selectively apply a steering wheel overlay torque to a normal steering assistance torque. A wheel self-aligning torque (fR) of the road vehicle (1) is modelled for a current vehicle velocity (v) and pinion angle (δw). A steering wheel overlay torque request (τR) is received. Based on the received steering wheel overlay torque request (τR) is provided a steering wheel overlay torque (τA) in hands-off applications limited to a safe set interval that is symmetrical around the modeled wheel self-aligning torque (fR).