Steer-By-Wire Rack Control Using LKAS Torque Overlay
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Solution Overview
Problem
The existing steer-by-wire systems face challenges in accurately controlling the position of a rack due to time delays when rotating the steering wheel, which affects the precision and responsiveness of vehicle steering direction changes.
Innovation Solution
A steer-by-wire system control apparatus and method that includes a torque overlay control module to determine a target steering angle based on a torque command from the Lane Keeping Assistance System, and an actuator control module to control the rack position, along with a steering wheel control module to manage the steering reaction force independently, improving the accuracy and responsiveness of vehicle steering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the steering wheel is rotated to change rack position, then the vehicle traveling direction can be changed, but time delay occurs and accurate control of rack position becomes difficult
Solution Approach 1:
The patent divides the steering control function into two independent modules: the steering wheel control module handles driver input and reaction force, while the torque overlay control module processes LKAS torque commands and generates steering angle commands. This segmentation allows the rack position to be controlled directly through torque commands without waiting for steering wheel rotation, eliminating time delay and improving control accuracy.
Solution Approach 2:
The patent introduces a torque overlay control module as an intermediary that receives torque commands from the LKAS, converts them to steering angle commands, and directly controls the rack steering actuator. This intermediary bypasses the mechanical steering wheel rotation process, enabling direct and accurate rack position control without time delay.
2Speed
If the steering wheel is rotated to change traveling direction, then vehicle steering is achieved, but the responsiveness of steering direction changes is reduced
Solution Approach 1:
The torque overlay control module pre-calculates the required steering angle command based on the torque command from the LKAS, before the actual steering action is needed. This preliminary calculation of the steering angle command enables the rack to be positioned immediately when the torque command is received, improving steering responsiveness and eliminating time delay.
Solution Approach 2:
The patent replaces the mechanical steering wheel rotation mechanism with an electronic control system that directly actuates the rack steering actuator through motor control. This substitution eliminates the mechanical inertia and friction of steering wheel rotation, significantly improving steering responsiveness and reducing time delay.
3Ease of operation
If the torque command is added to the steering system output, then the traveling direction is changed, but the control precision of rack position is affected
Solution Approach 1:
The patent implements a feedback mechanism where the steering angle sensor continuously monitors the actual steering angle and feeds it back to the torque overlay control module. The control module compares the actual steering angle with the target steering angle derived from the torque command, and adjusts the rack steering actuator accordingly. This closed-loop feedback ensures precise rack position control while maintaining the ease of torque overlay operation.
Data Source
AI summary
Proposed are a steer-by-wire system control apparatus and method, the apparatus including: a torque overlay control module configured to determine a target steering angle using a torque command input from a Lane Keeping Assistance System; and an actuator control module configured to control a position of a rack according to the target steering angle and thus to control a traveling direction of a vehicle.