Electric Power Steering Torque Sensor Fault Isolation
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Solution Overview
Problem
Existing electric power assisted steering systems face challenges in safely applying assistance torque when a fault is detected in dual channel torque sensors, as it is unclear which channel is faulty, and there is no protection against subsequent faults in the remaining good channel.
Innovation Solution
The system employs a torque sensor assembly with a processing means that generates an absolute output shaft position signal by combining motor position and torsion bar deflection data, allowing identification of faults and continued operation by producing a virtual torque signal for cross-checking, ensuring reliable torque measurement even if one channel fails.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dual channel torque sensor is used to provide safety margin, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent creates a virtual copy of the torque sensor functionality by using the motor position sensor to generate a virtual torque signal. This virtual sensor replicates the measurement function without requiring additional physical hardware, thereby maintaining reliability through redundancy while avoiding the complexity of a dual-channel physical torque sensor.
Solution Approach 2:
The motor position sensor serves multiple functions: it provides motor position feedback for control and simultaneously generates a virtual torque signal for fault detection. This multi-functionality eliminates the need for dedicated dual-channel torque sensors, reducing device complexity while maintaining safety margins.
2Reliability
If assistance torque is stopped when fault is detected, then reliability is improved, but productivity deteriorates
Solution Approach 1:
The virtual torque signal created from motor position data serves as a backup measurement channel. When the physical torque sensor detects a fault, the system can switch to using the virtual torque signal to maintain assistance functionality, ensuring continuous productivity while maintaining reliability through the virtual copy.
Solution Approach 2:
The system pre-establishes the virtual torque signal generation capability before faults occur. This preliminary preparation allows immediate switching to the virtual sensor upon fault detection, avoiding interruption of steering assistance and maintaining productivity while ensuring reliability.
3Measurement precision
If motor position sensor is used to generate absolute output shaft position signal, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The motor position sensor's data is repurposed to generate both the absolute output shaft position signal and the virtual torque signal. This multi-functional use of the same sensor data improves measurement precision for multiple parameters without adding hardware complexity, though it does increase signal processing requirements.
Data Source
AI summary
An electric power assisted steering system includes an upper column shaft connected to a steering wheel, a lower column shaft connected to road wheels, a torsion bar interconnecting the upper column shaft and the lower column shaft, and a processor that produces a torque signal indicative of torsion bar torque. An electric motor is connected to the lower column shaft, and a motor position sensor provides a motor position signal dependent on the angular position of the motor rotor that repeats after the motor rotates through an angular range. The processor determines a base motor position at start up by comparing the motor position signal with a signal from a sensor associated with the upper column shaft to determine three candidates and, during subsequent unpowered motion of the steering system rules out two candidates until only one plausible candidate for the base motor position remains.