Steer-by-Wire Rack Offset Learning for Straight-Line Calibration
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Solution Overview
Problem
Steer-by-wire (SbW) steering systems lack effective methods to determine the absolute 0 rack position offset due to the absence of mechanical connections between the road wheels and steering wheel, making traditional EPS steering system inputs ineffective for estimating rack position offset.
Innovation Solution
A system and method for rack position offset learning in SbW systems using vehicle characteristics such as rack position, velocity, force, and yaw rate to calculate a straight-line distance, start a counter when the distance exceeds a threshold, and determine a rack position offset value using a low pass filter to synchronize the rack to a zero position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional EPS steering system inputs are used to estimate rack position offset, then the method is simple and effective in mechanically connected systems, but it becomes ineffective in SbW systems due to the absence of mechanical connections
Solution Approach 1:
The patent replaces mechanical connection-based offset determination with a sensor-based approach. Instead of relying on mechanical linkages between steering wheel and rack, the system uses sensors to detect vehicle characteristics (acceleration, velocity, position) and calculates rack position offset through computational algorithms, thereby adapting the system to SbW architecture without mechanical connections
Solution Approach 2:
The patent introduces vehicle characteristics (acceleration, velocity, position) as intermediary parameters to indirectly determine rack position offset. These characteristics serve as mediators between the steering system and the rack, allowing offset calculation without direct mechanical coupling, thus solving the adaptability issue in SbW systems
2Manufacturing precision
If rack position offset is not accurately determined, then the steering system can operate without complex calibration, but the vehicle cannot travel straight and steering precision is compromised
Solution Approach 1:
The patent implements preliminary offset learning during vehicle operation by continuously monitoring vehicle characteristics and calculating rack position offset in advance. This preliminary action allows the system to determine accurate offset values before they are needed for precise steering control, enabling high steering precision without adding complexity to the real-time control algorithm
Solution Approach 2:
The patent employs feedback mechanisms where the calculated rack position offset is continuously fed back to the steering control system. This feedback loop allows the system to adjust and refine offset values based on actual vehicle behavior, achieving accurate offset determination through iterative learning rather than complex one-time calibration procedures
Data Source
AI summary
A method for rack position offset learning includes receiving at least one vehicle characteristic value, and determining, based on the at least one vehicle characteristic value, whether a vehicle associated with the at least one vehicle characteristic value is traveling in a straight line. The method also includes, calculating, for a predetermine period, a straight line distance traveled by the vehicle based on a vehicle speed and a length of the predetermined period. The method also includes determining whether the calculated straight line distance is greater than or equal to a straight line distance threshold, starting a counter, and, in response to a counter value of the counter being greater than or equal to a counter threshold, determining a rack position offset value based on a rack position of a rack of a steering system of the vehicle.