Electric Power Steering Torque Estimation Without Motor Sensors
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Solution Overview
Problem
Existing electric power steering systems face challenges in accurately estimating road reaction torque, especially at high steering frequencies due to motor voltage noise and phase lag from low-pass filtering, which reduces estimation accuracy and fails to estimate rack thrust during steering wheel return to normal position.
Innovation Solution
An electric power steering system that calculates road reaction torque based on steering torque and assist torque, eliminating the need for motor voltage and accounting for motor inertia torque, allowing accurate estimation even at high steering frequencies by using a control unit with a road reaction torque estimator and assist command current calculator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If motor voltage is mathematically differentiated to estimate motor inertia torque, then motor inertia torque can be estimated, but noise in motor voltage increases and estimation accuracy deteriorates
Solution Approach 1:
The patent extracts and eliminates the problematic element (motor voltage differentiation) from the estimation process. Instead of differentiating motor voltage to obtain angular velocity, the system uses a different approach that avoids noise amplification while still enabling accurate road reaction torque estimation through alternative signal processing of motor current and voltage.
Solution Approach 2:
The patent introduces an intermediary approach by using motor current and voltage signals processed through specific algorithms (avoiding direct differentiation) as mediators to estimate motor inertia torque and road reaction torque. This intermediary method provides accurate estimation without directly amplifying noise through mathematical differentiation.
2Object-affected harmful factors
If motor voltage is low-pass filtered to eliminate noise, then noise is reduced, but phase lag occurs and estimation accuracy for high steering frequency patterns deteriorates
Solution Approach 1:
The patent changes the processing parameters by avoiding low-pass filtering that causes phase lag. Instead, it uses alternative signal processing methods that maintain the high-frequency characteristics of the motor voltage signal while still eliminating noise, thereby preserving estimation accuracy for high steering frequency patterns like sharp steering.
3Measurement precision
If rack thrust estimation is limited to increased steering angle time, then estimation accuracy is improved, but rack thrust cannot be estimated during steering wheel return to normal position
Solution Approach 1:
The patent makes the estimation system universal by enabling rack thrust and road reaction torque estimation during all steering operations, including both increased steering angle phases and steering wheel return phases. The system achieves this through continuous monitoring and estimation algorithms that work across different steering states, eliminating the need to limit estimation to specific time windows.
Data Source
AI summary
An electric power steering system includes steering a torque detector that detects steering torque, and a motor that provides assist torque based on the detected steering torque, wherein for the purpose of estimating, without detecting motor rotation angular information and rotation angular velocity information, the road reaction torque in which the influence of the motor inertia torque is eliminated, a value corresponding to rotation velocity of a steering shaft is calculated based on the steering torque and the assist torque, to calculate road reaction torque based on the value corresponding to the rotation velocity of the steering shaft.