Steer-by-Wire Drift Compensation via Handwheel Offset Control
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Solution Overview
Problem
Steer by wire systems face challenges in maintaining vehicle direction stability under conditions such as strong winds and tire pressure mismatches, where operators must adjust the handwheel to offset angles, leading to unnatural handling and potential loss of control.
Innovation Solution
A steer by wire system with a controller that adjusts the roadwheel actuator and handwheel actuator to compensate for drift by reducing the difference between the handwheel orientation offset value and a predetermined zero value, using a rack force observer to provide torque feedback and maintain vehicle direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If operators manually adjust the handwheel to offset angles to counteract drift, then vehicle direction stability is improved, but handling naturalness deteriorates and operator workload increases
Solution Approach 1:
The system automatically detects handwheel orientation offset and calculates compensation commands without operator intervention. The controller monitors the handwheel position sensor, identifies drift conditions, and autonomously adjusts the roadwheel actuator to compensate, eliminating the need for operators to manually counteract drift while maintaining vehicle stability
Solution Approach 2:
The system implements a closed-loop feedback mechanism where the handwheel position sensor continuously provides orientation data to the controller. The controller compares the current handwheel orientation against the stored offset value, detects when manual adjustment occurs, and automatically generates compensation commands to counteract the drift, creating a self-correcting system that maintains natural handling
2Ease of operation
If the system automatically compensates for handwheel orientation offset, then handling naturalness is improved, but system complexity increases
Solution Approach 1:
The system stores a copy of the handwheel orientation offset value in memory during drift conditions. This stored offset value is then used by the controller to calculate compensation commands, allowing the system to replicate the compensation action without requiring complex real-time analysis of drift causes, thereby managing system complexity while maintaining handling naturalness
Solution Approach 2:
The controller acts as an intermediary between the handwheel position sensor and the roadwheel actuator. It receives handwheel orientation data, compares it against the stored offset, and generates intermediate compensation commands that are sent to the roadwheel actuator. This intermediary processing layer simplifies the overall system architecture by centralizing the compensation logic in a single control unit
3Measurement precision
If the handwheel actuator applies torque to center the handwheel, then handwheel positioning accuracy is improved, but torque feedback to the operator increases
Solution Approach 1:
The handwheel actuator applies torque only partially, sufficient to center the handwheel within a predetermined threshold rather than forcing it to exact zero position. This partial action achieves adequate positioning accuracy while limiting the torque feedback to the operator to acceptable levels, avoiding excessive force that would degrade handling naturalness
Solution Approach 2:
The system changes the torque parameter dynamically based on the handwheel orientation offset magnitude. When drift is detected, the controller calculates the required compensation torque and applies it through the handwheel actuator. The torque magnitude is adjusted according to the offset value, providing just enough force to center the handwheel without creating excessive feedback that would alert the operator to the intervention
Data Source
AI summary
Disclosed is a steer by wire system that includes a controller operable to operate a roadwheel actuator such that a position command to the roadwheel actuator based on a handwheel orientation is a magnitude corresponding to a handwheel orientation offset value in an opposite direction to reduce a difference between the handwheel orientation offset value and a predetermined handwheel zero value.