Friction Estimation in Electric Power Steering
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Solution Overview
Problem
In power steering systems, accurately estimating friction is crucial for maintaining directional control and enhancing steering feel, but existing methods fail to effectively detect excessive friction, which can impact driver control and steering performance.
Innovation Solution
A control module estimates steering load gain and hysteresis using sensor data and a reference model, determining friction levels by analyzing lateral acceleration and steering load, and generating notifications or control signals based on these estimates to manage the steering system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If friction estimation is performed using conventional methods, then the system can detect some friction conditions, but the measurement precision is insufficient to accurately detect excessive friction that impacts driver control
Solution Approach 1:
The friction detection process is segmented into multiple independent estimation steps: first estimating steering load gain from steering angle and torque data, then estimating steering load hysteresis separately, and finally determining friction by comparing with a reference model. This segmentation allows each parameter to be measured and analyzed independently, improving overall measurement precision for friction detection.
Solution Approach 2:
The system uses feedback by comparing the estimated steering load gain and hysteresis against a reference model to determine actual friction levels. This feedback mechanism enables continuous monitoring and accurate detection of friction conditions, allowing the system to reliably identify when friction exceeds acceptable thresholds and impacts directional control.
2Measurement precision
If friction estimation is performed using conventional methods, then the system structure remains simple, but the measurement precision of friction is insufficient
Solution Approach 1:
The control module performs multiple functions using the same sensor inputs (steering angle and torque sensors). It simultaneously estimates steering load gain, steering load hysteresis, and friction levels, all while maintaining system stability. This multi-functionality approach improves measurement precision without requiring separate dedicated hardware for each measurement, thus avoiding increased device complexity.
3Ease of operation
If the system monitors friction continuously, then steering feel can be optimized, but the loss of computational resources increases
Solution Approach 1:
The control module performs friction estimation periodically rather than continuously, calculating steering load gain and hysteresis at regular intervals and comparing them against the reference model. This periodic action maintains accurate friction monitoring for steering feel optimization while significantly reducing computational energy consumption compared to continuous real-time calculation.
Data Source
AI summary
A method of estimating friction in a steering system controlled by a control module is provided. The method includes performing by the control module, estimating a steering load gain; estimating a steering load hysteresis; and determining friction based on the steering load gain, the steering load hysteresis, and a reference model.