Steering Reaction Force Control for Steer-by-Wire Systems
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Solution Overview
Problem
In steer-by-wire type steering systems, the mechanical separation of the steering wheel and steered wheels makes it difficult for drivers to grasp road conditions through tactile feedback, as the road reaction force is not effectively transmitted to the steering wheel, limiting the accuracy and speed of steering operations and reducing driver confidence.
Innovation Solution
A vehicle control apparatus is designed with multiple calculation circuits to calculate command values for motors, incorporating ideal and estimated axial forces based on steering conditions, blending ratios, and axial force deviations to generate a more accurate steering reaction force, enhancing tactile feedback and road condition awareness for the driver.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a steer-by-wire type steering system is used to mechanically separate the steering wheel and steered wheels, then the steering control precision is improved, but the driver's ability to grasp road conditions through tactile feedback deteriorates
Solution Approach 1:
The patent introduces a reaction force generation unit that acts as an intermediary to synthesize and transmit road condition information to the driver. This unit generates reaction forces based on detected vehicle state variables (lateral acceleration, yaw rate, steering operation amount) and applies them to the steering shaft, thereby mediating the information flow from steered wheels to steering wheel despite mechanical separation
Solution Approach 2:
The patent implements a feedback mechanism where vehicle state variables detected during steering operations are fed back to the reaction force generation unit. This unit then generates appropriate reaction forces based on this feedback information, allowing the driver to perceive road conditions through the steering wheel while maintaining mechanical separation in the steer-by-wire system
2Reliability
If the steering wheel and steered wheels are mechanically separated, then the steering system reliability is improved, but the transmission of road reaction force to the steering wheel deteriorates
Solution Approach 1:
The patent replaces the mechanical force transmission path with an electronic control system. Instead of relying on mechanical connection to transmit road reaction forces, the system uses sensors to detect vehicle states, processes this information electronically, and generates reaction forces through a reaction motor, thereby substituting mechanical transmission with an electronically controlled force generation system
Data Source
AI summary
A control apparatus calculates an axial force deviation, which is a difference between an ideal axial force and an estimated axial force. The ideal axial force is based on a target pinion angle of a pinion shaft configured to rotate in association with a turning operation of steered wheels. The estimated axial force is based on a state variable (such as a current value of a steering operation motor) that reflects vehicle behavior or a road condition. The control apparatus changes a command value for a reaction motor in response to the axial force deviation. For example, the control apparatus includes a basic control circuit configured to calculate a basic control amount, which is a fundamental component of the command value. The basic control circuit changes the basic control amount in response to the axial force deviation. The command value based on the basic control amount reflects the road condition.