Electric Power Steering Assist Torque Estimation Without Hand Wheel Sensor
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Solution Overview
Problem
In electric power steering (EPS) systems, when the hand wheel torque sensor is un-enabled or not functioning properly, the system cannot provide adequate steering assist torque, leading to inadequate vehicle steering assistance.
Innovation Solution
A method and system that estimate the steering rack force using a modified static tire model, generating a steering assist torque command based on this estimation, and controlling the EPS system to provide assistance even without a functional hand wheel torque sensor, by utilizing a control module that includes a rack load estimator and an assist torque command generator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the hand wheel torque sensor is used to determine driver requested assist torque, then the steering assist torque can be accurately provided, but the system becomes vulnerable to sensor failures and cannot operate when the sensor is un-enabled
Solution Approach 1:
The patent introduces an intermediary estimation mechanism that uses readily available sensor data (hand wheel angle, vehicle velocity, brake status) to calculate steering rack force as a substitute for direct torque sensor input. This intermediary calculation layer allows the system to bypass the failed torque sensor while still providing appropriate steering assist torque based on inferred steering demand.
Solution Approach 2:
The system uses its own existing sensors and control state information to self-determine steering assist requirements when the torque sensor fails. By leveraging data already collected for other control functions (hand wheel angle from position sensors, velocity from vehicle speed sensors, brake status from brake control), the system performs self-diagnosis and self-adjustment without external assistance or additional hardware.
2Ease of operation
If the EPS system disables operation when torque sensor is un-enabled, then system safety is maintained, but steering assistance is lost completely
Solution Approach 1:
The patent implements beforehand cushioning by pre-establishing alternative calculation pathways and estimation models that are ready to activate immediately upon torque sensor failure. The system maintains backup algorithms that can compute steering rack force using other available sensors, ensuring that steering assistance is continuously available without interruption or complete disablement when the primary torque sensor becomes un-enabled.
3Reliability
If steering assist torque is provided without accurate torque sensor data, then system continuity is maintained, but steering precision may be compromised
Solution Approach 1:
The patent replaces the direct mechanical torque measurement system with a computational estimation approach. Instead of relying on the mechanical torque sensor to directly measure driver input torque, the system substitutes this with an algorithmic estimation of steering rack force based on kinematic relationships, vehicle dynamics models, and available sensor data, thereby maintaining operation while accepting estimated rather than directly measured values.
Data Source
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AI summary
A method of controlling an electric power steering system of a vehicle is provided. The method estimates steering rack force to be caused by a tire of the vehicle and a surface of a ground with which the tire is in contact in response to determining that one or more hand wheel torque sensors of the vehicle are not enabled. The method generates a steering assist torque command based on the estimated steering rack force. The method controls the electric power steering system using the steering assist torque command.