Electric Power Steering Sensor Error Compensation
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Solution Overview
Problem
Electric power steering systems face challenges in accurately determining the absolute position of the steering wheel due to periodic errors in sensor output signals, which are costly to correct through improved sensor precision and mechanical tolerances.
Innovation Solution
A method is introduced where the steering wheel position sensor output is sampled at multiple angular positions to establish a curvilinear relationship with the motor position sensor output, approximating this with a straight line to reduce periodic errors and determine a position offset for the system zero position, allowing for accurate steering wheel centering without requiring high-precision sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sensor precision and mechanical tolerances are improved to correct periodic errors, then measurement precision is improved, but manufacturing cost increases
Solution Approach 1:
The patent changes the parameter of sensor output by introducing a compensation value that transforms the periodic error signal into a corrected signal. Instead of improving physical sensor precision, the system modifies the electrical parameter (sensor output signal) through mathematical compensation based on pre-stored error data, thereby achieving high measurement precision without increased manufacturing cost
Solution Approach 2:
The patent performs preliminary action by pre-measuring and storing periodic error values in a lookup table before normal operation. During operation, the system retrieves pre-calculated compensation values based on motor position, eliminating the need for real-time complex calculations and enabling rapid error correction without requiring higher precision hardware
2Measurement precision
If a second sensor is added to determine absolute reference for center position, then measurement capability is improved, but device complexity increases
Solution Approach 1:
The patent introduces an intermediary approach by using the motor position sensor (already present in the system) as a reference and creating a mathematical relationship between motor position and steering wheel position. Instead of directly adding another physical sensor to measure steering wheel position, the system uses software-based correlation and error compensation to derive absolute position information from existing sensors, thereby reducing device complexity while maintaining measurement capability
Data Source
AI summary
An electric power steering system includes a steering wheel, an electric assist motor operatively coupled to the steering wheel, and an electronic controller operatively coupled to the assist motor. A steering wheel position sensor provides an output indicative of an angular position of the steering wheel. A motor position sensor provides an output indicative of a relative angular position for the motor. Steering wheel position sensor output is acquired at each of a plurality of angular positions of the motor, thereby establishing a set of points defining a curvilinear relationship between steering wheel sensor output and motor position sensor output. The set of points is sampled to calculate a straight line which approximates the curvilinear relationship, thereby reducing periodic errors in the steering wheel sensor output. The straight line is employed to determine a position offset for the motor position sensor output corresponding to a system zero position. The system zero position is a position for which the vehicle will travel along a linear, substantially straight-ahead path.