Rack Force Compensation Using Frequency Extraction in SBW Steering
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Solution Overview
Problem
Steer-by-wire (SBW) systems experience disturbances in estimating rack force, which degrade the driver's steering feel due to amplified specific frequency signals and disturbances in the estimated rack force values.
Innovation Solution
A device and method using a processor to minimize the error between actual and estimated rack force values by applying an optimization algorithm, extracting a specific frequency component, and compensating for it to remove disturbances from the actual rack force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a filter (such as low pass filter, notch filter, or Kalman filter) is used to remove disturbance from the estimated rack force, then the disturbance is reduced, but a delay occurs in acquiring the estimated value of rack force
Solution Approach 1:
The patent extracts the specific frequency component containing disturbance from the estimated rack force signal using frequency domain analysis (FFT). By identifying and separating the disturbance frequency component, the system removes it without applying traditional time-domain filters that cause delay, thus achieving disturbance removal while maintaining real-time response.
2Measurement precision
If the rack force is estimated using vehicle dynamics model or steering system model, then the transverse force can be recognized, but specific frequency signals are amplified and disturbance occurs due to SBW system mechanism and road surface state
Solution Approach 1:
The patent applies feedback by comparing the estimated rack force with the actual rack force sensor output. The difference (error signal) is processed through frequency domain analysis to identify disturbance components. This feedback mechanism allows continuous correction of the estimated rack force by removing identified disturbance frequency components, thereby improving measurement precision while eliminating harmful disturbances.
Solution Approach 2:
The patent introduces frequency domain analysis (FFT) as an intermediary between the model-based estimation and the final rack force value. This intermediary process transforms the signal to frequency domain, identifies disturbance components, and selectively removes them before transforming back, thus mediating between the estimation model and the final output to eliminate harmful frequency amplification.
3Measurement precision
If an optimization algorithm is used to minimize error between actual and estimated rack force, then the estimation accuracy is improved, but computational complexity increases
Solution Approach 1:
The patent replaces complex iterative optimization algorithms with a frequency-domain based disturbance removal approach. Instead of using computationally intensive optimization methods to minimize error, the system transforms the error signal to frequency domain, identifies disturbance components, and removes them directly. This substitution reduces computational complexity while maintaining or improving estimation accuracy.
Data Source
AI summary
Disclosed is a device for compensating for a disturbance in a rack force. The device includes a memory that stores instructions, and processors that determine an optimally estimated value of a rack force for minimizing an error representing a difference between an actual value of the rack force and an estimated value of the rack force, extract a specific frequency component from the optimally estimated value of the rack force, and compensate for the extracted specific frequency component to the actual value of the rack force to remove a disturbance reflected in the actual value of the rack force.