Road Friction Estimation via Cornering Force Ratio Lookup
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Solution Overview
Problem
Existing road friction coefficient estimation methods face difficulties in measuring the friction coefficient, especially in the saturated range, where the relationship between cornering force and tire sideslip angle is non-linear, making it challenging to apply vehicle models effectively.
Innovation Solution
A road friction coefficient estimating unit and method that calculate the friction coefficient by utilizing the ratio of cornering force to tire sideslip angle, employing sensors and a microcomputer-based EPS control unit to estimate the friction coefficient in real-time, even on unknown road surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a vehicle model is applied in the saturated range where cornering force and tire sideslip angle have a non-linear relationship, then the road friction coefficient can be estimated, but it becomes difficult to apply the vehicle model because the relationship is non-linear and a road friction coefficient term appears in the estimating equation
Solution Approach 1:
The patent divides the estimation process into two distinct phases: a learning phase where the system collects data and builds a lookup table mapping cornering force ratios to road friction coefficients, and an estimation phase where the pre-built table is used for quick reference. This segmentation avoids the complexity of real-time non-linear calculations while maintaining accuracy across different road conditions.
Solution Approach 2:
The system performs preliminary data collection and processing during a learning phase before actual estimation is needed. By pre-calculating and storing the relationship between cornering force ratios and road friction coefficients in a lookup table, the system eliminates the need for complex real-time computations during the estimation phase, thereby reducing device complexity while preserving measurement precision.
2Adaptability or versatility
If the cornering force is calculated using a vehicle model that includes road friction coefficient, then the estimation can be performed in saturated range, but the measurement becomes difficult because the road friction coefficient term appears in the equation making it circular
Solution Approach 1:
The patent extracts the road friction coefficient estimation problem from the complex vehicle model equations by focusing specifically on the cornering force ratio (ΔCF/Δβ) as the key parameter. By isolating this ratio and creating a dedicated lookup table for it, the system removes the circular dependency issue while maintaining the ability to estimate friction coefficients under various road conditions.
Solution Approach 2:
The patent introduces a lookup table as an intermediary data structure that mediates between the cornering force measurements and the road friction coefficient estimation. This lookup table stores pre-computed relationships, acting as a bridge that eliminates the need for direct real-time solution of complex equations with circular dependencies, thereby simplifying the measurement process while preserving adaptability.
3Productivity
If real-time estimation of road friction coefficient is implemented, then the steering assistance can be improved, but the computational load increases
Solution Approach 1:
The system performs all complex computational work during an offline learning phase, pre-calculating and storing the relationship between cornering force ratios and road friction coefficients. During real-time operation, the system simply queries the pre-built lookup table, which requires minimal computational energy while maintaining fast response speed for improved steering assistance.
Solution Approach 2:
The patent replaces the traditional mechanical approach of real-time equation solving with a data-driven lookup table approach. This substitution eliminates the need for continuous complex computations during steering operations, significantly reducing computational energy consumption while maintaining real-time estimation capability for responsive steering control.
Data Source
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AI summary
A road friction coefficient estimating unit (28) calculates a tire sideslip angle (β) and a cornering force (CF), and estimates a road friction coefficient on the basis of the ratio (ΔCF/Aβ) of the calculated cornering force (CF) to the calculated tire sideslip angle (β). A vehicle travels on multiple road surfaces that differ in road friction coefficient (µ), and tire sideslip angles (β) and cornering forces (CF) on the road surfaces are detected in advance. The road friction coefficient estimating unit (28) stores, in a memory (29), a correlation among the detected tire sideslip angles, the detected cornering forces, and the road friction coefficients in the form of numerical values or a mathematical expression, and estimates a road friction coefficient using the correlation stored in the memory (29).