Steer-by-Wire Rack Force Estimation Using Dual Models
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Solution Overview
Problem
Existing steer-by-wire steering systems struggle to accurately determine rack force, particularly under varying road conditions and when the gear is stationary, leading to suboptimal steering feel and behavior.
Innovation Solution
A method that combines vehicle model-based and steering gear model-based estimation of rack force, using weighted components to improve accuracy, with non-linear models and Kalman filters for enhanced feedback and adaptive friction modeling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a simple model based on lateral acceleration and steering angle is used to estimate rack force, then the device complexity is reduced, but the measurement precision deteriorates because it does not account for road surface conditions and other disruptive influences
Solution Approach 1:
The patent combines multiple estimation approaches (vehicle model-based estimation and steering gear model-based estimation) into a unified rack force determination system. The control unit integrates results from both models, allowing the system to leverage the strengths of each approach while compensating for their individual weaknesses, thereby improving overall measurement precision without excessive complexity increase
Solution Approach 2:
The system dynamically adjusts the weighting of different estimation components based on operating conditions. The control unit varies the influence of vehicle model-based versus steering gear model-based estimation depending on factors like vehicle speed, steering angle, and detected road conditions, allowing optimal precision across diverse driving scenarios
2Productivity
If the rack force is estimated using a model that does not account for static friction, then the calculation can be performed when the gearbox is stationary, but the measurement precision deteriorates because static friction effects are not considered
Solution Approach 1:
The patent segments the rack force estimation into two distinct components: a vehicle model-based component that handles dynamic conditions and a steering gear model-based component that specifically addresses static friction effects. This segmentation allows each component to be optimized for its specific operating regime, improving overall precision across all conditions including when the gearbox is stationary
3Device complexity
If a single estimation model is used for all driving conditions, then the device complexity is reduced, but the adaptability deteriorates because the model cannot account for varying road surface conditions and driving scenarios
Solution Approach 1:
The patent creates a universal rack force determination system that functions across all driving conditions by integrating multiple estimation models. The control unit is designed to select and weight appropriate estimation components based on the current operating state, making the system adaptable to various road conditions, vehicle speeds, and steering scenarios while maintaining a unified architecture
Data Source
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AI summary
The invention relates to a method for determining a rack force (Fr,estcomplrack) for a steer-by-wire steering system (1) for a motor vehicle, wherein the rack force (Fr,estcomplrack) is determined from two components, wherein a first component of the rack force (Fr,estvehicle) is generated in a module for the vehicle model-based estimation of the rack force (15) by means of a vehicle model, and a second component of the rack force (Fr,estrack) is generated in a module for the steering-mechanism-model-based estimation of the rack force (16) by means of a steering-mechanism model.