Wheel Slip Friction Estimation for Sensor-Free Road Grip Assessment

Solution Overview

Problem

Existing methods for assessing road surface friction between vehicle wheels and the road surface are inaccurate and unreliable, particularly for inexperienced drivers and autonomous vehicles, leading to potential safety risks.

Innovation Solution

A method that involves carrying out a test acceleration of the vehicle by acting on a test wheel, ascertaining the wheel slip and a test load characteristic, and using these parameters to calculate a reference friction value without the need for environment sensors.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Extent of automation

If sensor-based approaches (optical sensors, cameras) are used to detect road surface conditions, then the assessment of friction values can be automated, but the reliability and accuracy are reduced due to sensor limitations and inability to account for vehicle-specific aspects

Engineering Contradiction:

Improveautomation of friction value assessmentVSAvoidreliability of friction value assessment

Core Design Contradiction:

Extent of automationVSReliability

Solution Approach 1:

The system uses the vehicle's own wheel slip data and load characteristics to determine friction values, eliminating the need for external optical sensors. The vehicle essentially assesses road conditions through its own driving behavior and physical responses, making the system both automated and highly reliable by using intrinsic vehicle data rather than extrinsic sensor data

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The patent replaces optical/mechanical sensor-based detection systems with a calculation-based approach using wheel slip and load characteristic data. Instead of physically detecting road surface properties through sensors, the system substitutes this with computational determination based on vehicle dynamics parameters that are already available from the vehicle's operation

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Extent of automation

If optical sensors are used to detect road surface conditions, then automation is achieved, but the measurement precision is reduced because sensors only capture road surface aspects and neglect vehicle-specific aspects like tire properties

Engineering Contradiction:

Improveautomation of friction value assessmentVSAvoidprecision of friction value assessment

Core Design Contradiction:

Extent of automationVSMeasurement precision

Solution Approach 1:

The system uses the vehicle's own wheel slip data and load characteristics to determine friction values, eliminating the need for external optical sensors. The vehicle essentially assesses road conditions through its own driving behavior and physical responses, making the system both automated and highly reliable by using intrinsic vehicle data rather than extrinsic sensor data

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The patent changes the parameters used for friction assessment from external optical measurements to internal vehicle dynamics parameters (wheel slip, load characteristics). By measuring how the vehicle itself responds to driving conditions rather than how the road looks, the system achieves higher precision that accounts for both road surface and vehicle-specific factors

Inventive Principle:

Principle #35Parameter changes

3Ease of manufacture

If conventional cameras are used for road surface detection, then the system can operate during the day, but the reliability deteriorates under poor lighting conditions and cannot be used at night

Engineering Contradiction:

Improvesimplicity of sensor-based systemVSAvoidreliability under various lighting conditions

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent replaces optical/mechanical sensor-based detection systems with a calculation-based approach using wheel slip and load characteristic data. Instead of physically detecting road surface properties through sensors, the system substitutes this with computational determination based on vehicle dynamics parameters that are already available from the vehicle's operation

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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

This method provides a more accurate and reliable estimation of friction values, enhancing safety for both human drivers and autonomous vehicles by improving the assessment of road surface conditions.

Implementation Method 1

The wheel slip of wheels of the vehicle can be used to ascertain a friction value between the wheels of the vehicle and the road surface

Methodology Applied

Scientific EffectFriction: Friction

Data Source

PatentUS20250289435A1Method for approximating a friction value

Publication Date: 2025.09.18 ZF CV SYST GLOBAL GMBH

AI summary

A method approximates a friction value between wheels of a vehicle and a road surface. The method includes the following steps: carrying out at least one test acceleration of the vehicle by acting on at least one test wheel; ascertaining a wheel slip of the test wheel for at least one period of the test acceleration; ascertaining a test manipulated variable provided during the period in order to act on the test wheel; ascertaining a test load characteristic present on the test wheel during the period; and ascertaining a reference friction value for the test acceleration on the basis of the ascertained test load characteristic, the ascertained test manipulated variable and the ascertained wheel slip of the test wheel. A driver assistance system is configured to perform the method. A vehicle includes the driver assistance system.