Catch Motor Torque Generation in Steer-by-Wire Systems
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Solution Overview
Problem
Steer by wire (SbW) systems lack mechanical linkage between the steering wheel and road wheels, leading to a disconnect between driver input and vehicle response, resulting in lag and a 'catch' condition where the driver must exert excessive effort due to the system's inability to maintain the desired steering ratio, especially under rapid inputs or load conditions.
Innovation Solution
A method for generating catch motor torque in a SbW system, where a controller computes a tracking error between the commanded and actual rack positions, and modifies the handwheel torque command by adding catch motor torque to simulate the 'catch' condition, providing increased resistance to the driver only when the system cannot honor the commanded position, thereby synchronizing driver input with vehicle response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If mechanical linkage is used between steering wheel and road wheels, then driver feels connected to road, but system complexity and weight increase
Solution Approach 1:
The patent replaces the traditional mechanical linkage between steering wheel and road wheels with an electronic control system. The handwheel actuator and roadwheel actuator are mechanically disconnected but communicate through a controlled area network (CAN) interface, substituting physical connection with digital communication to maintain simplicity while enabling precise control and feedback.
Solution Approach 2:
The patent introduces a controller as an intermediary that computes tracking error and generates catch motor torque commands. This mediator processes information between the handwheel actuator and roadwheel actuator, enabling the system to simulate mechanical linkage effects through software-based torque generation without physical connection.
2Ease of operation
If catch motor torque is added to simulate mechanical linkage, then driver feels connected to road, but handwheel torque command complexity increases
Solution Approach 1:
The patent implements a feedback mechanism where the controller continuously computes tracking error based on the difference between commanded position and actual rack position. This feedback loop enables the system to generate appropriate catch motor torque in real-time, maintaining driver feedback while using simple proportional control logic rather than complex predictive algorithms.
3Speed
If catch motor torque is generated based on tracking error, then lag is reduced, but computational requirements increase
Solution Approach 1:
The patent applies catch motor torque only when tracking error exceeds zero, rather than continuously adjusting torque based on predicted driver intent. This partial action approach reduces computational burden by calculating torque only when position deviation occurs, while still achieving rapid response by immediately correcting the error when it arises.
Data Source
AI summary
According to one or more embodiments described herein, a steer by wire steering system includes a pair of actuators, a handwheel actuator that provides a commanded position to a roadwheel actuator, which moves a rack of the vehicle to a rack position based on the commanded position from the handwheel actuator. The steer by wire steering system further includes a controller that generates a handwheel torque command, the handwheel actuator generates a feedback torque based on the handwheel torque command. The controller further computes a tracking error based on a difference between the commanded position and the rack position. The controller further determines a catch motor torque value using the tracking error. The controller further modifies the handwheel torque command using the catch motor torque, the handwheel actuator generates an amount of torque that is substantially a sum of the feedback torque and the catch motor torque.