Vehicle Road Friction Estimation via Torque Compensation
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Solution Overview
Problem
Existing methods for estimating road surface friction, such as using the slip angle, require wheel excitation like acceleration or cornering, limiting their availability and accuracy.
Innovation Solution
A method and system that apply specific drive torques to vehicle wheels to measure rack force, steering angle, and vehicle velocity without affecting the vehicle's course or speed, allowing friction estimation without excessive excitation, and enabling separate friction calculations for each track.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If slip angle is used for road friction estimation, then friction estimate can be obtained, but wheel excitation such as acceleration or cornering is required which reduces availability
Solution Approach 1:
The patent segments the vehicle's wheel torques into individual wheel components and applies compensation specifically to the wheels involved in friction estimation. By isolating and compensating for the effects of drive and brake torques on individual wheels, the method enables friction estimation without requiring overall vehicle excitation maneuvers, thereby improving availability while maintaining accuracy.
Solution Approach 2:
The patent changes the approach from using slip angle (which requires excitation) to using rack force measurements combined with torque compensation. This parameter change allows friction estimation to be performed during normal driving conditions without requiring acceleration or cornering events, thus improving availability while maintaining estimation accuracy.
2Measurement precision
If drive torque is applied to a single wheel for friction measurement, then rack force can be measured, but vehicle yaw torque affects the vehicle course
Solution Approach 1:
The patent applies counteracting torques to other wheels to compensate for the yaw torque generated by the measurement wheel. By applying opposing torques to diagonally opposite or adjacent wheels, the system neutralizes the net yaw effect on the vehicle while maintaining the necessary rack force measurement, thus preserving both measurement accuracy and course stability.
Solution Approach 2:
The patent employs asymmetric torque distribution across the wheels, where one wheel receives the measurement torque while other wheels receive compensating torques. This asymmetric approach allows the system to isolate the measurement on a single wheel while using the other wheels to balance the vehicle's rotational dynamics, maintaining course stability during measurement.
3Measurement precision
If propulsion torque and braking torque are applied to different wheels, then longitudinal net force is compensated, but vehicle yaw torque must be compensated to maintain course
Solution Approach 1:
The patent makes the steering system serve multiple functions: it not only steers the vehicle but also applies compensating torques to counteract yaw effects during friction measurement. By utilizing the existing steering mechanism for dual purposes (steering and torque compensation), the system avoids adding separate complexity while achieving both course maintenance and accurate measurement.
Solution Approach 2:
The patent merges the torque compensation function with the existing wheel torque application system. Instead of creating separate compensation mechanisms, the method integrates torque management into the existing drive and brake systems, combining multiple functions into unified control actions that reduce overall system complexity.
Data Source
Figure 1a
Figure 1b~2a
Figure 2b
AI summary
The present invention relates to a method for computing a friction estimate (µ) between a road surface and a tire (101a-d) of a vehicle when said vehicle (100) is in motion along a course, said tire being arranged on a steerable wheel (1 02a-b) of the vehicle, and said vehicle comprising two front wheels (1 02a-b) and two rear wheels (1 02c-d) and an axle rack (104) pivotably attached to a linkage arm (106) connected to said steerable wheel such that a translational motion of said axle rack causes said linkage arm to rotate about a kingpin element (108) such that said linkage arm causes a turning motion of said steerable wheel. The present invention further relates to a corresponding system and vehicle.