Wheel-Road Friction Estimation Using Torque Vectoring Slip
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Solution Overview
Problem
Existing methods for determining the coefficient of friction between a vehicle wheel and road surface in steer-by-wire systems are inaccurate, complex, and unreliable, necessitating improved accuracy and simplicity in friction coefficient determination.
Innovation Solution
A method involving an individual wheel drive system with electric motors applies a wheel drive torque to induce slip, calculating friction coefficient using the difference between wheel drive torque and moment of inertia, derived from frictional torque and normal force, without changing vehicle direction, and utilizing a tire model for enhanced accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing estimation methods considering lateral or longitudinal dynamics are used, then the coefficient of friction can be determined, but the determination is inaccurate and complex
Solution Approach 1:
The patent segments the friction coefficient determination into distinct operational phases: initial straight-line driving phase for baseline measurement, and subsequent steering phase for friction calculation. This segmentation allows separate measurement of longitudinal and lateral forces, improving accuracy while maintaining computational simplicity through phased data collection and processing.
2Reliability
If torque vectoring with individual wheel drive is implemented, then vehicle dynamics control is improved, but the friction determination becomes more complex
Solution Approach 1:
The patent makes the individual wheel drive system serve dual functions: primary vehicle dynamics control through torque vectoring and secondary friction coefficient determination. By utilizing the same actuators and sensors for both vehicle stabilization and friction measurement, the system achieves reliable dynamics control without adding separate determination hardware, thus resolving the complexity issue.
3Measurement precision
If wheel slip is induced to measure friction, then the coefficient of friction can be directly determined, but vehicle direction may change
Solution Approach 1:
The patent applies preliminary counteracting steering torque through the individual wheel drive system before and during the friction measurement maneuver. This preliminary anti-action compensates for the directional changes caused by wheel slip, maintaining vehicle stability on the road course while still inducing sufficient slip for accurate friction coefficient determination.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables simple, accurate, and reliable determination of the coefficient of friction, providing precise data for vehicle dynamics control and driver assistance systems.
Implementation Method 1
determining a friction coefficient between a wheel of a motor vehicle and a road surface
Implementation Method 2
wheel drive motors (15, 150) are each connected to the steerable wheels (7, 70) via drive shafts (27) and the wheel drive motors (15, 150) are electric motors
Data Source
Figure 1~2
Figure 3
AI summary
The invention relates to a method for determining a friction coefficient (μ) between a wheel (7, 70) of a motor vehicle and a road surface (16), wherein the motor vehicle has an individual wheel drive, which is designed to drive the wheel (7, 70) independently from the at least one other wheel (7, 70) of the motor vehicle, wherein the following method steps are provided: applying a wheel drive torque (MImpuls) to the wheel (7, 70) of the motor vehicle via the individual wheel drive, in such a way that the wheel (7, 70) is caused to slip; and determining the friction coefficient (μ) by means of the friction torque ( MReibung), which results from the difference between the wheel drive torque (MImpuls) and an inertia moment (MTrägheit) of the wheel (7, 70).