Electric Power Steering Torque Sensor Fault Handling
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Solution Overview
Problem
Unreliable torque measurements in electric power assisted steering systems can lead to unsafe conditions, as existing solutions either completely remove steering assistance or provide inadequate assistance, especially when torque sensors fail, potentially causing dangerous steering difficulties.
Innovation Solution
The system generates an assistance torque signal based on a changeable datum that resets when the steering direction changes, combining terms that vary with steering angle, vehicle speed, and column angular velocity to provide tailored assistance, ensuring safe and responsive steering even without reliable torque measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the assistance torque is completely removed when torque measurement becomes unreliable, then safety is improved, but steering becomes very heavy and may make the vehicle undriveable
Solution Approach 1:
The patent applies partial action by providing a reduced assistance torque signal during fault conditions rather than completely removing assistance. The controller calculates a reduced assistance torque signal that maintains some steering assistance while ensuring safety, preventing the steering from becoming completely heavy and undriveable.
Solution Approach 2:
The patent implements beforehand cushioning by gradually reducing the assistance torque from the last known safe value rather than suddenly removing it. This gradual transition cushions the system against the harmful effect of sudden loss of assistance, especially at high speeds, making the vehicle continue to be driveable while maintaining safety.
2Reliability
If the assistance torque is gradually reduced from the last known safe value, then safety is improved, but steering response may be degraded
Solution Approach 1:
The patent applies dynamics by making the assistance torque signal adaptive based on the detected fault condition and steering state. The controller dynamically adjusts the assistance torque level, switching between normal operation mode and fault mode with reduced assistance, thereby optimizing both safety and steering response according to real-time conditions.
Solution Approach 2:
The patent implements parameter changes by modifying the assistance torque parameter based on the fault detection state. When a fault is detected, the controller changes the assistance torque parameter from the normal high level to a reduced level, allowing the system to adapt to fault conditions while maintaining adequate steering response through the changed parameter.
3Ease of operation
If a crude estimate of torque is provided based on angular position, then some steering assistance is maintained, but the assistance is inadequate and steering response is poor
Solution Approach 1:
The patent applies the intermediary principle by using a torque estimation model that acts as an intermediary between the unavailable torque sensor data and the assistance torque calculation. The model uses angular position, vehicle speed, and steering angular velocity as intermediate parameters to generate a reasonably accurate torque estimate, bridging the gap caused by sensor failure.
Solution Approach 2:
The patent implements mechanics substitution by replacing the mechanical torque sensor measurement system with an electronic estimation model. Instead of relying on direct mechanical torque measurement, the system uses computational models that process angular position and velocity data to substitute the lost torque information, enabling continued steering assistance without the physical sensor.
4Speed
If the datum is reset when steering direction changes, then steering response from rest is improved, but the system complexity increases
Solution Approach 1:
The patent applies feedback by monitoring the direction of rotation of the steering and using this information to determine when to reset the datum. The system continuously feedbacks the steering angular velocity or direction information to the controller, which then adjusts the datum position accordingly, creating a closed-loop control mechanism that improves steering response while managing system complexity through intelligent feedback processing.
Data Source
AI summary
A method of operating an electric power assisted steering system of the kind in which an electric motor applies an assistance torque to a part of the steering system as a function of an assistance torque signal, the assistance torque reducing the force required by the driver to turn a steering wheel, comprises during normal operation generating an assistance torque signal that is dependent on the torque applied by the driver, and during a fault operation in which the torque applied by the driver is not reliably known to the system generating an assistance torque signal that is derived from a first term that has a value that varies as a function of the angular position of the steering relative to a changeable datum, the angular position of the changeable datum being updated in the event that the direction of rotation of the steering changes.