Engine Speed Slip Target Control for Split-Friction Differentials

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Solution Overview

Problem

Existing vehicle engine speed controllers struggle to manage wheel slip effectively in conditions of split friction or μ-split, leading to reduced tractive force and safety concerns due to differential wheel speeds caused by open differentials and varying road conditions, loads, and tire wear.

Innovation Solution

A method and system that adapt the slip target by comparing maximum and minimum wheel speeds to a preconfigured offset, adjusting the slip target to ensure all wheels operate below peak slip, using a reduction factor to balance wheel speeds and enhance tractive force.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If open differential is used to allow wheel speed variation, then wheel slip control becomes problematic and tractive force decreases, but wheel speed adaptation to road conditions is improved

Engineering Contradiction:

Improvewheel speed adaptationVSAvoidtractive force

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The system continuously monitors wheel speeds from all driven wheels and uses this feedback to dynamically adjust the slip target. When speed differences exceed a threshold, the system reduces the slip target to prevent excessive slip on high-friction wheels, thereby maintaining tractive force while adapting to differential road conditions.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The slip target is made dynamic rather than fixed. The controller adjusts the slip target in real-time based on the measured wheel speed difference, transitioning between different control modes (normal vs. reduced slip target) to optimize performance under varying road conditions.

Inventive Principle:

Principle #15Dynamics

2Reliability

If slip target is reduced to maintain sub-peak slip, then tractive force increases, but wheel speed difference between left and right wheels worsens

Engineering Contradiction:

Improvetractive forceVSAvoidwheel speed uniformity

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

The system changes the slip target parameter dynamically based on wheel speed differences. When differential wheel speeds are detected, the slip target is reduced to maintain sub-peak slip conditions, which increases tractive force. This parameter adjustment resolves the contradiction by adapting the control target to current operating conditions.

Inventive Principle:

Principle #35Parameter changes

3Speed

If wheel slip controller uses output shaft speed for fast response, then control speed improves, but control accuracy decreases under split friction conditions

Engineering Contradiction:

Improvecontrol response speedVSAvoidslip measurement accuracy

Core Design Contradiction:

SpeedVSMeasurement precision

Solution Approach 1:

Instead of using a single output shaft speed signal, the system segments the measurement by individually monitoring wheel speeds from all driven wheels. This segmentation allows the system to detect differential wheel speeds and adjust the slip target accordingly, maintaining measurement accuracy under split friction conditions while preserving fast response through direct wheel speed feedback.

Inventive Principle:

Principle #1Segmentation

Data Source

PatentUS20250214589A1Determination of slip target for a vehicle engine speed controller

Publication Date: 2025.07.03 VOLVO TRUCK CORP

AI summary

Techniques for determining a modified slip target for a vehicle engine speed controller are disclosed. A method comprises comparing a difference between a maximum wheel speed and a minimum wheel speed for wheels of open differential and driven axles controlled by the vehicle engine speed controller to a preconfigured wheel speed offset. The method comprises setting, at least when the difference exceeds the preconfigured wheel speed offset, the modified slip target to be lower than a requested slip target for the vehicle engine speed controller.