Road Friction Estimation via Rack Force Mapping
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Solution Overview
Problem
Existing methods for determining road surface friction, such as those based on slip angle, require high accuracy and are not efficient for the full range of lateral wheel forces during normal driving, necessitating an improved approach for friction estimation.
Innovation Solution
A method that acquires rack force and lateral wheel force values, maps these to a model with predetermined relations, and determines friction estimates without relying on slip angle measurements, utilizing the relationship between rack force and lateral wheel force to estimate friction, which is particularly advantageous during steering operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If slip angle is used for road friction estimation, then friction can be determined, but high accuracy determination of slip angle is required for the full range of lateral wheel forces
Solution Approach 1:
The patent extracts the friction estimation from the slip angle determination process by using rack force measurements directly. Instead of calculating slip angle as an intermediate step, the method directly relates rack force to friction coefficient through a simplified model, eliminating the complex slip angle calculations while maintaining estimation accuracy
Solution Approach 2:
The patent introduces rack force as an intermediary measurement that directly connects the steering system to friction estimation. By measuring the force on the rack and relating it to lateral wheel forces through a model, the system obtains friction information without needing to determine slip angle, thus simplifying the measurement chain
2Productivity
If slip angle-based methods are used, then friction estimation is possible, but the method is not efficient for the full range of lateral wheel forces during normal driving
Solution Approach 1:
The patent creates a universal friction estimation method that works across the full range of lateral wheel forces encountered during normal driving. The rack force-based approach is designed to be valid for both low and high friction conditions, as well as for various steering scenarios, making it universally applicable without requiring different methods for different operating conditions
Solution Approach 2:
The patent changes the measurement parameter from slip angle to rack force. This parameter change enables continuous and reliable friction estimation across all driving conditions, as rack force is directly measurable and its relationship to friction remains valid regardless of the specific lateral force magnitude or steering scenario
Data Source
Figure 1a
Figure 1b~1c
Figure 2a~2b
AI summary
The present invention relates to a method for determining a friction estimate between a road surface and a tire (101a-b) of a vehicle, the tire being arranged on a steerable wheel of the vehicle, and the vehicle an axle rack (104) pivotably attached to a linkage arm (106) connected to the steerable wheel such that a translational motion of the axle rack causes the linkage arm to rotate about a kingpin element (108) such that the linkage arm causes a turning motion of the steerable wheel, the method comprising the steps of: acquiring (S402) a plurality of rack force values; acquiring (S404) a plurality of lateral wheel force values; mapping (S406) a relation between the plurality of rack force values and the lateral wheel force values to a model, and determining (S408) the lateral friction estimate based on the mapping.