Steering Rack Force Estimation With LT and ST Offset Compensation
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Solution Overview
Problem
Existing vehicle steering systems face inaccuracies in estimating rack force due to short-term and long-term offset factors, leading to issues such as vehicle pull and imbalanced steering effort, 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 correct for these offsets, and controlling steering functions using a compensated estimated rack force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If rack force estimation is performed using conventional methods, then steering system operation is maintained, but estimation accuracy deteriorates due to offset factors causing vehicle pull and imbalanced steering effort
Solution Approach 1:
The patent segments the offset compensation into two distinct components: short-term offset factor (STOFF) and long-term offset factor (LTOFF). The STOFF addresses immediate steering imbalances while the LTOFF corrects gradual drifts. This segmentation allows each offset type to be compensated independently, improving overall estimation accuracy without causing vehicle pull or steering effort imbalance.
Solution Approach 2:
The patent implements feedback mechanisms where the estimated rack force and offset factors are continuously monitored and adjusted. The controller uses feedback from steering wheel torque, rack position, and vehicle dynamics to update both STOFF and LTOFF values in real-time, ensuring accurate rack force estimation that adapts to changing operating conditions and maintains balanced steering effort.
2Measurement precision
If offset compensation is applied to rack force estimation, then steering accuracy is improved, but system complexity increases due to separate LT and ST offset factor determination
Solution Approach 1:
By dividing the offset compensation into separate STOFF and LTOFF determination processes, the patent manages complexity through modular design. Each offset factor is calculated using dedicated algorithms that process specific types of errors, making the overall system more manageable and easier to implement than a single complex compensation mechanism.
Solution Approach 2:
The patent changes the parameters being compensated by introducing two distinct offset factors with different characteristics and time constants. The STOFF handles high-frequency variations while LTOFF handles low-frequency drifts. This parameter differentiation allows the system to address multiple sources of error simultaneously without requiring an overly complex unified approach.
Data Source
AI summary
A method for controlling a steering system of a vehicle includes obtaining a plurality of values corresponding to operation of the steering system, determining, based on the plurality of values, an estimated rack force, separately determining a long-term (LT) offset factor of the estimated rack force and a short-term (ST) offset factor of the estimated rack force, determining a total compensation value based on a combination of the LT offset factor and the ST offset factor, applying the total compensation value to the estimated rack force to obtain an compensated estimated rack force, and controlling at least one function of the steering system using the compensated estimated rack force.