Steer-by-Wire Reaction Force Estimation for Quiet Tactile Feedback
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Solution Overview
Problem
Current steer by wire systems fail to effectively simulate the reaction forces from the road surface, leading to uncomfortable steering sensations and potential safety risks due to the absence of mechanical feedback.
Innovation Solution
A control device and method for steer by wire that utilizes a first motor for steering via a feedback actuator and a second motor for wheel steering, incorporating a base SAT torque calculation and rack force estimation to switch between simulated feedback and bilateral control modes based on vehicle speed and road conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a feedback actuator is used to simulate reaction force in steer by wire system, then steering comfort is improved, but road surface noise is transmitted to driver causing discomfort
Solution Approach 1:
The patent introduces a reaction force simulation ECU as an intermediary that processes the raw reaction force from the road wheel actuator. This ECU calculates the simulated reaction force based on steering angle and vehicle speed, then adds a filtered portion of the actual reaction force to create a balanced feedback signal that maintains steering comfort while reducing noise transmission to the driver.
Solution Approach 2:
The patent changes the parameters of the reaction force feedback by calculating a simulated reaction force using specific formulas that incorporate steering angle and vehicle speed. The system adjusts the magnitude and characteristics of the feedback force based on these parameters, and selectively adds only the necessary portion of actual reaction force, thereby transforming the raw noisy signal into a controlled, comfortable steering feedback.
2Reliability
If mechanical connection between steering wheel and steering rack is removed in steer by wire system, then safety is improved through better control, but reaction force feedback from road surface is lost
Solution Approach 1:
The patent implements a feedback mechanism where the road wheel actuator detects the actual reaction force from the road surface, and this information is fed back through the reaction force simulation ECU to the feedback actuator. The ECU processes this feedback by calculating the simulated reaction force and adding the filtered portion of actual reaction force, ensuring that essential road surface information is transmitted to the driver while maintaining safe electronic control.
Solution Approach 2:
The patent replaces the direct mechanical connection between steering wheel and steering rack with an electronic control system. The reaction force simulation ECU uses sensors and calculation algorithms to substitute the mechanical force transmission, converting physical reaction force into electronic signals that are then converted back into simulated tactile feedback through the feedback actuator, thereby maintaining safety through electronic control while preserving essential road surface information.
Data Source
AI summary
A control device method for steer by wire, the control device including a first motor controlling steering via an FBA and a second motor controlling a steering angle of a wheel via an RWA and being capable of bidirectionally controlling the first motor and the second motor includes a base SAT that obtains a reference torque based on an angle of the first motor and a vehicle speed, and a rack force estimation portion that estimates rack force as a reaction force based on a steering angle of a wheel and an RWA. A first control mode controls a reference torque of the first motor and a second control mode controls the first motor based on a reaction force estimation by the rack force estimation portion, the first and second control modes are switched based on output of the base SAT and output of the rack force estimation portion.