Steering Rack Force Compensation Using Short- and Long-Term Offsets
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Solution Overview
Problem
Existing steering systems face inaccuracies in estimating rack force due to short-term and long-term offset factors, leading to vehicle pull and driver feedback issues, which are not effectively addressed by current compensation methods.
Innovation Solution
A method and system for determining separate short-term and long-term offset factors in rack force estimation, applying compensation values to achieve accurate estimated rack force, and controlling steering functions accordingly, using a controller to filter and learn offset factors under specific conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional rack force estimation methods are used, then the steering system can operate with simple control logic, but the estimation accuracy deteriorates due to offset factors causing vehicle pull and driver feedback issues
Solution Approach 1:
The offset compensation is divided into two distinct segments: short-term offset factor and long-term offset factor. Each offset factor is determined separately through independent filtering processes with different time constants, allowing the system to address different types of estimation errors independently and improve overall accuracy without overwhelming complexity
Solution Approach 2:
The system implements feedback mechanisms where the estimated rack force is continuously monitored and compared against actual rack force measurements. The offset factors are adjusted based on the difference between estimated and actual values, creating a closed-loop control system that automatically corrects estimation errors over time
2Reliability
If offset compensation is applied to improve steering accuracy, then vehicle stability and steering response improve, but the computational load and processing requirements increase
Solution Approach 1:
The system performs preliminary filtering and offset determination during periods when the vehicle is traveling straight ahead, before actual steering maneuvers occur. By pre-calculating and storing offset factors during these idle periods, the system reduces computational load during critical steering operations while maintaining high reliability
Solution Approach 2:
The offset factor determination is implemented as a periodic process that alternates between filtering operations and compensation applications. The system periodically updates offset factors based on vehicle operating conditions, rather than continuously recalculating, thereby reducing processor energy consumption while maintaining accurate compensation
Data Source
AI summary
A method for controlling a steering system of a vehicle includes, using a processing device, obtaining a plurality of values corresponding to operation of the steering system, determining, based on the plurality of values, an estimated rack force, determining a long-term (LT) offset factor over a first learning period, determining a short-term (ST) offset factor over a second learning period different from the first learning period, compensating the estimated rack force using both the LT offset factor and the ST offset factor to obtain a compensated estimated rack force, and controlling at least one function of the steering system using the compensated estimated rack force.