Electric Power Steering Torque Estimation for Abnormal Sensor Handling
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Solution Overview
Problem
Existing electric power steering systems face issues in maintaining excellent steering feeling and reliability when the vehicle is turning, particularly due to abnormal yaw rate and steering angle sensor readings, which can lead to excessive steering assist force and self-steering states, especially on positive cant roads.
Innovation Solution
The system employs a torque estimating apparatus that calculates a self-aligning torque based on the vehicle speed and the smaller absolute value between the measured yaw rate and the steering-angle standard yaw rate, correcting the steering assist force to prevent excessive torque and ensure reliable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional friction torque is increased to reduce driver tiredness during long turning, then driver tiredness is reduced, but steering wheel becomes heavy for further steering operations
Solution Approach 1:
The additional friction torque is made variable rather than fixed. The torque magnitude dynamically changes based on the vehicle's turning time duration, providing higher torque for prolonged steady turning to reduce tiredness, while automatically reducing torque for brief steering operations to maintain light steering feel
Solution Approach 2:
The control parameter (additional friction torque magnitude) is changed based on the turning time parameter. The system monitors how long the vehicle has been turning and adjusts the friction torque level accordingly, transitioning from a static torque value to a time-dependent variable torque
2Ease of operation
If steering assist force is increased based on measured yaw rate, then steering effort is reduced, but abnormal sensor readings cause excessive torque and self-steering states
Solution Approach 1:
A yaw rate calculation unit is introduced as an intermediary between the steering angle sensor and the steering assist control. This unit calculates a standardized yaw rate from steering angle and vehicle speed, providing a filtered and more reliable input for torque control, especially when direct yaw rate sensor readings are abnormal
Solution Approach 2:
The system implements feedback control by continuously monitoring both the measured yaw rate and the calculated steering-angle standard yaw rate, comparing them, and adjusting the steering assist force based on the more reliable value to prevent excessive torque and self-steering conditions
Data Source
AI summary
An electric power steering apparatus provides a steering assist force to the steering system of a vehicle by controlling driving of an assist motor in accordance with a steering force acting on the steering wheel. The electric power steering apparatus includes a yaw rate sensor that obtains a measured yaw rate of the vehicle, a vehicle speed sensor that detects the speed of the vehicle, a steering angle sensor that detects the steering angle of the steering wheel, and a torque estimating apparatus that estimates a self-aligning torque on the basis of the vehicle speed and data having a smaller absolute value among the measured yaw rate and the steering-angle standard yaw rate and that corrects the steering assist force on the basis of the estimated self-aligning torque.