Steering-Column Torque Sensing for Hysteresis and Offset Calibration
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Solution Overview
Problem
Existing electromechanical power steering systems suffer from inaccuracies in torque determination due to friction and asymmetries in the steering column, universal joints, and the torque sensor unit, leading to errors in torque measurement.
Innovation Solution
A method for determining hysteresis and offset in the steering column torque sensor unit involves measuring torque under specific conditions, compiling data into a histogram, statistically analyzing it to quantify hysteresis and offset, and adjusting measured torque values using filtered hysteresis and offset values to improve accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If torque values are measured using a steering column torque sensor unit, then torque measurement is obtained, but friction and asymmetries in the steering column cause errors in torque determination
Solution Approach 1:
The patent converts the harmful effects of friction and asymmetries into beneficial information by using histogram analysis to identify and quantify hysteresis and offset values. These previously harmful factors become correctable parameters that can be compensated for in the torque determination process, transforming measurement errors into useful calibration data.
Solution Approach 2:
The patent implements a feedback mechanism where torque measurements are continuously analyzed through histogram evaluation, and the derived hysteresis and offset values are used to correct subsequent torque determinations. This closed-loop approach continuously refines measurement accuracy by feeding back correction parameters based on observed systematic errors.
2Measurement precision
If statistical evaluation of torque measurements is performed to correct offsets and nonlinearities, then measurement accuracy improves, but system complexity increases
Solution Approach 1:
The system performs self-calibration by automatically analyzing its own measurement data through histogram evaluation. The torque sensor unit and control unit work together to identify hysteresis and offset values from the measured torque values themselves, without requiring external calibration equipment or manual intervention, thus improving accuracy while maintaining relatively simple system architecture.
3Measurement precision
If hysteresis and offset values are determined through histogram analysis, then torque determination accuracy improves, but processing time increases
Solution Approach 1:
The patent performs histogram analysis and determines hysteresis and offset values in advance during periods when the vehicle is operating under normal conditions. These correction parameters are pre-calculated and stored, allowing for rapid torque compensation during actual steering operations without requiring real-time complex computations, thus balancing accuracy improvement with acceptable processing time.
Data Source
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AI summary
The invention relates to a method for determining hysteresis and offset of a steering-column torque determination process of an electromechanical power steering system (1) of a motor vehicle, said method comprising the following steps: - using a steering-column torque sensor unit to measure or estimate a torque introduced into a steering wheel (2), - entering torque values measured or estimated under certain conditions into a histogram, - analysing and statistically evaluating the histogram, and determining the hysteresis and the offset in the form of a hysteresis value (s, d) and an offset value (E, M3).