Power Steering Torque Estimation via Derivative Blending
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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 driving on bumpy roads or releasing the steering wheel, due to deviations in torque sensor measurements.
Innovation Solution
A power steering system comprising a gain module for generating an estimated driver torque and a blending module that determines a blend value based on the derivative of the estimated driver torque, applied to the return torque of a handwheel, allowing for accurate estimation without additional sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a torque sensor is added on the steering wheel to accurately measure driver torque, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent introduces an intermediary estimation system that uses readily available sensor data (motor torque, steering angle, rack position) combined with a mechanical model to derive driver torque. This intermediary approach avoids the need for direct measurement with additional sensors while achieving accurate torque estimation through computational mediation.
Solution Approach 2:
The patent replaces the mechanical sensor-based measurement system with a computational estimation system. By using a mechanical model of the steering system and substituting direct torque measurement with calculated torque estimation based on system dynamics and available sensor data, the solution eliminates the need for additional physical sensors.
2Speed
If controlled velocity return is always applied to return the steering wheel to center position, then steering responsiveness is improved, but it causes instability during driver input or disturbances
Solution Approach 1:
The patent implements a dynamic control system that continuously adjusts the controlled velocity return based on real-time conditions. The system monitors driver torque input, rack force disturbances, and steering state to dynamically enable or disable the return function, allowing the steering system to adapt its behavior to current operational conditions rather than applying a fixed control strategy.
Solution Approach 2:
The patent employs feedback mechanisms that monitor the steering system state, driver input, and disturbance conditions to determine when to apply controlled velocity return. The system uses feedback from torque sensors, position sensors, and model-based estimation to continuously assess whether the return function should be active, ensuring stable operation during driver input while enabling responsive return when appropriate.
Data Source
AI summary
A power steering system includes a gain module that generates an estimated driver torque, and a blending module for determining a blend value. The blend value is based at least in part on a derivative of the estimated driver torque, and the blend value is applied to a return torque of a handwheel.