Steer-by-wire state variable estimation for steering intention
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Solution Overview
Problem
The Steer-By-Wire system faces challenges in accurately determining a driver's steering intention without additional sensors, leading to increased manufacturing costs and potential errors due to the reliance on current and torque sensors, and lacks the ability to utilize existing tuning capabilities from Electric Power Steering systems.
Innovation Solution
A Steer-By-Wire system that estimates state variables using a state variable estimator, removing disturbances such as torque ripples, to calculate reaction and steering torque without current sensors, and generates steering reaction force based on virtual manual torque, reducing sensor and control unit requirements and enabling accurate steering intention recognition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a current sensor is used to measure phase current for calculating driver torque, then the accuracy of steering intention determination is improved, but the number of components and manufacturing costs increase
Solution Approach 1:
The patent replaces the current sensor-based electrical measurement system with a mechanical model-based estimation system. The state variable estimator uses the mechanical equations of motion for the steering wheel, reaction motor, and rack gear, combined with torque sensor data and motor command signals, to estimate phase current and calculate driver torque without requiring additional current sensors.
Solution Approach 2:
The system uses its existing components (torque sensor, motor position sensor, and motor control signals) to generate the information needed for steering intention determination. The state variable estimator leverages the system's own operational data to estimate phase current and driver torque, making the system self-sufficient without external additional sensors.
2Measurement precision
If a current sensor and additional electronic control unit are added to calculate driver torque, then the accuracy of steering intention determination is improved, but manufacturing costs increase
Solution Approach 1:
The existing electronic control unit is made multi-functional by integrating the state variable estimator functionality. The same control unit that manages motor control and processes sensor data now also performs state variable estimation and driver torque calculation, eliminating the need for a separate additional electronic control unit while maintaining driver torque calculation accuracy.
3Measurement precision
If the system relies on current sensor measurements to determine steering intention, then accuracy is improved, but reliability decreases due to potential sensor errors
Solution Approach 1:
The state variable estimator implements a feedback mechanism that continuously monitors the consistency between estimated state variables and actual sensor measurements. By comparing estimated phase current with actual current sensor readings (when available) and adjusting the estimation accordingly, the system can detect sensor errors and maintain reliable steering intention determination even when sensor measurements are erroneous.
4Ease of operation
If the system uses rack force calculation for reaction torque, then steering feeling is provided, but the ability to utilize existing EPS tuning capability is lost
Solution Approach 1:
The patent changes the fundamental parameter for reaction torque calculation from rack force to driver torque estimated through state variable estimation. This parameter change enables the system to use driver torque as the basis for calculating reaction torque, allowing existing EPS tuning data and methodologies to be applied to the Steer-by-Wire system while maintaining appropriate steering feeling.
Data Source
AI summary
The present disclosure relates to a Steer-By-Wire system including: a torque sensor configured to sense torsion bar torque generated when the driver operates the steering wheel; a steering angle sensor configured to sense a steering angle of the steering wheel; a reaction motor configured to provide reaction force in a direction opposite an operating direction of the steering wheel; a state variable estimator configured to receive information on the torsion bar torque and the steering angle and configured to estimate a plurality of state variables from which disturbances have been removed; and a reaction controller configured to determine a reaction torque to be output from the reaction motor using the plurality of state variables estimated by the state variable estimator, and further relates to a control method thereof. Accordingly, it is possible to accurately recognize the driver's steering intention.