Steering Rack Force Model for Road Friction Estimation
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Solution Overview
Problem
Existing methods for determining the road friction coefficient are limited, particularly when the vehicle is turning, as they often require steady-state conditions and cannot provide continuous updates, affecting the generation of tire forces and vehicle control.
Innovation Solution
A steering system that computes a model rack force value based on vehicle speed, steering angle, and road-friction coefficient, determining the difference between this value and a load rack force, and iteratively updates the road-friction coefficient using signal processing techniques, enabling continuous detection and adaptation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing methods for determining road friction coefficient are used, then the measurement can be obtained under steady-state conditions, but the detection speed and continuity are insufficient for dynamic vehicle control
Solution Approach 1:
The patent transitions from steady-state measurement to dynamic measurement by using steering system signals during transient turning maneuvers. The method computes model rack force values based on vehicle speed, steering angle, and road-friction coefficient, then compares these with actual load rack force values to continuously update the friction coefficient estimate during dynamic operation, eliminating the need for steady-state conditions.
Solution Approach 2:
The patent implements a feedback mechanism where the difference between model rack force values (computed from vehicle dynamics model) and actual load rack force values (measured from steering system) is used to iteratively update the road-friction coefficient estimate. This closed-loop feedback enables continuous refinement of the friction coefficient during vehicle operation, improving both detection speed and accuracy.
2Reliability
If steady-state conditions are required for measurement, then measurement reliability is improved, but the adaptability to various driving conditions and continuous updates are reduced
Solution Approach 1:
The system is designed to operate during dynamic turning maneuvers rather than requiring steady-state conditions. By utilizing the steering system's rack force measurements during transient conditions and comparing them with model predictions, the method achieves reliable friction coefficient estimation across varying driving conditions including different speeds, steering angles, and road surfaces.
Solution Approach 2:
The patent changes the measurement parameters from steady-state wheel slip (traditional method) to dynamic rack force during steering maneuvers. This parameter transformation allows the system to adapt to various driving conditions by utilizing steering system signals that are naturally available during turning operations, providing continuous friction coefficient updates without requiring specific steady-state conditions.
Data Source
AI summary
According to one or more embodiments, a method includes computing, by a steering system, a model rack force value based on a vehicle speed, steering angle, and a road-friction coefficient value. The method further includes determining, by the steering system, a difference between the model rack force value and a load rack force value. The method further includes updating, by the steering system, the road-friction coefficient value using the difference that is determined.