Driver Torque Estimation Using Extended State Observer
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Solution Overview
Problem
Existing electric power steering systems face challenges in accurately estimating driver torque during dynamic transients and large rack force disturbances, such as when a driver releases the steering wheel or encounters bumpy roads, leading to deviations in torque sensor measurements.
Innovation Solution
A control system that includes an error module to generate an error signal based on the difference between estimated and actual output vectors, a scaling module to calculate a feedback correction signal using an observer gain value, an extended state vector estimation module to determine an extended state vector estimate, and a gain module to apply a gain to the estimate, generating an accurate driver torque signal for power steering system control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a torque sensor is used to approximate driver torque, then the system cost is reduced, but the measurement precision deteriorates during dynamic transients and large rack force disturbances
Solution Approach 1:
The patent introduces an extended state observer as an intermediary computational system that processes existing sensor measurements (torque sensor, motor current, steering angle) through mathematical modeling to generate an accurate estimate of driver torque. This observer acts as a mediator between the low-cost torque sensor and the control system, providing high-precision torque estimation during dynamic transients without requiring additional hardware sensors on the steering wheel.
2Measurement precision
If an additional driver torque sensor is added on the steering wheel, then the measurement precision is improved, but the device complexity and cost increase
Solution Approach 1:
The system uses its existing sensors and computational resources to self-generate accurate driver torque measurements. The extended state observer leverages data from the torque sensor, motor current sensor, steering angle sensor, and vehicle speed sensor, combined with a mathematical model of the steering system dynamics, to compute driver torque without requiring any additional measurement devices. This self-service approach eliminates the need for expensive additional hardware while maintaining high measurement precision.
3Device complexity
If a traditional torque sensor is used, then the device complexity is reduced, but the reliability deteriorates during dynamic transients and rack force disturbances
Solution Approach 1:
The extended state observer implements continuous feedback by constantly comparing the estimated system state with actual sensor measurements and adjusting the driver torque estimation accordingly. The observer uses feedback from torque sensor readings, motor current measurements, steering angle data, and vehicle speed information to maintain accurate and reliable torque estimation even during dynamic transients and rack force disturbances, significantly improving reliability over simple torque sensor approximation.
Data Source
AI summary
A control system for a power steering system includes an error module that generates an error signal based on a difference of an estimated output vector and an output vector, a scaling module that calculates a feedback correction signal based on the error signal and an observer gain value, an extended state vector estimation module that determines an extended state vector estimate based on the feedback correction signal and a motor torque command, and a gain module that applies a gain to the extended state vector estimate to generate an estimated driver torque signal, the estimated driver torque signal is applied in control of the power steering system.