Electric Power Steering Torque Sensor Plausibility Estimation
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Solution Overview
Problem
Dual channel torque sensors in electric power assisted steering systems face challenges in determining which channel is faulty when both signals differ but are within a normal range, leading to safety concerns and inability to apply assistance torque.
Innovation Solution
An electric power assisted steering apparatus with an error determining circuit, torque plausibility estimator, and torque channel selector that generate control signals based on the consistency and plausibility of torque signals from two channels, allowing for selection of reliable signals even if one channel is faulty, using additional sensors for verification and crosscheck diagnostics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dual channel torque sensor is used to provide safety margin, then the reliability of torque measurement is improved, but the ability to continue operation when one channel is faulty is lost
Solution Approach 1:
The system performs preliminary validation of torque signals by comparing readings from two independent channels before control actions are taken. Error determining circuits continuously monitor both channels and pre-identify discrepancies, allowing the system to switch to a single valid channel before a complete failure occurs, thus maintaining steering assistance availability while ensuring reliability
Solution Approach 2:
An intermediary processing layer is introduced between the dual channel torque sensor and the motor control system. This intermediary includes error determining circuits and plausibility estimators that mediate the conflicting requirements by filtering and validating signals, selecting the reliable channel when discrepancies are detected, thereby enabling continued operation with maintained reliability
2Measurement precision
If both torque channels are monitored for fault detection, then the measurement precision is improved, but the device complexity increases
Solution Approach 1:
The error detection function is segmented into modular components: error determining circuits for each channel, plausibility estimators, and a torque channel selector. This segmentation allows independent validation of each torque channel while maintaining manageable complexity through functional decomposition, enabling precise torque measurement with systematic fault detection
Solution Approach 2:
Feedback mechanisms are implemented where error determining circuits continuously compare torque channel readings and provide feedback signals indicating signal validity. The plausibility estimator uses this feedback to determine which channel is reliable, creating a self-regulating system that maintains measurement precision through automatic validation without requiring overly complex external monitoring
Data Source
AI summary
An electric power assisted steering apparatus comprises an upper column shaft that is connected to a steering wheel of the vehicle; and a lower column shaft. A torsion bar interconnects the upper column shaft and the lower column shaft; and an electric motor is connected to the lower column shaft of the torque sensor assembly. A first sensor circuit generates a first torque signal based on angular deflection of the torsion bar, and a second sensor circuit generating a second torque signal based on angular deflection of the torsion bar, the apparatus further including: an error determining circuit which produces two error signals, each indicative of the validity of a respective torque signal, and a torque plausibility estimator which generates two plausibility signals each indicative of the plausibility of a respective one of the two torque signals.