Vehicle Yaw Mitigation on Low Mu Grades

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Solution Overview

Problem

Vehicles experience stability issues during hill start and crawl mode operations on low friction surfaces, leading to potential sliding and yawing, as existing brake pressure trapping systems fail to maintain stability effectively when all brakes are locked, causing unintended acceleration and engine stall risks.

Innovation Solution

A stability control system that detects yaw conditions while the vehicle is at standstill and de-actuates less than all wheel brakes to increase side friction, identifying the uphill wheel leading the yaw and de-actuating it along with a diagonal wheel to maintain longitudinal braking force and reduce yawing, while maintaining approximately half of the braking force to prevent sudden acceleration.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If all wheel brakes are actuated to maintain vehicle stability during hill start, then longitudinal braking force is maintained, but side friction is insufficient causing vehicle yaw and slide on low mu surfaces

Engineering Contradiction:

Improvevehicle stabilityVSAvoidvehicle yaw and slide

Core Design Contradiction:

Stability of the object's compositionVSObject-affected harmful factors

Solution Approach 1:

The system segments the brake actuation by wheel groups, selectively de-actuating only the uphill wheel and diagonal wheel while maintaining actuation on other wheels. This segmentation allows the vehicle to generate side friction through selective wheel rotation while maintaining longitudinal stability through continued braking on opposing wheels.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The system dynamically adjusts brake actuation based on detected yaw conditions. When yaw is detected, the control system transitions from a static all-brakes-actuated state to a dynamic state where specific brakes are de-actuated to generate corrective side friction, then re-evaluates the condition continuously.

Inventive Principle:

Principle #15Dynamics

2Object-affected harmful factors

If all wheel brakes are de-actuated to increase side friction and reduce yaw, then vehicle yaw is reduced, but longitudinal braking force is lost causing sudden acceleration and engine stall risks

Engineering Contradiction:

Improvevehicle yawVSAvoidvehicle stability

Core Design Contradiction:

Object-affected harmful factorsVSStability of the object's composition

Solution Approach 1:

Instead of de-actuating all brakes (excessive action), the system applies partial action by de-actuating only the specific uphill wheel and diagonal wheel that are contributing to the yaw condition. This partial de-actuation generates sufficient side friction to correct yaw while maintaining longitudinal braking force through the other two wheels.

Inventive Principle:

Principle #16Partial or excessive action

Solution Approach 2:

The system applies different brake actuation states to different wheels based on their specific roles in the yaw condition. The uphill wheel and diagonal wheel are de-actuated to generate side friction, while the opposing wheels maintain actuation to provide longitudinal braking, creating local quality differences in brake application across the four wheels.

Inventive Principle:

Principle #3Local quality

3Stability of the object's composition

If brake pressure trapping is used to hold the vehicle stationary, then hill start assist is achieved, but the vehicle cannot generate side friction to prevent yaw on low friction surfaces

Engineering Contradiction:

Improvevehicle hold capabilityVSAvoidvehicle yaw on low mu surface

Core Design Contradiction:

Stability of the object's compositionVSObject-affected harmful factors

Solution Approach 1:

The system takes preliminary anti-action by detecting yaw conditions and de-actuating specific brakes before the vehicle can significantly yaw or slide. This proactive intervention generates side friction to counteract the impending yaw motion caused by brake pressure trapping on low friction surfaces.

Inventive Principle:

Principle #9Preliminary anti-action

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

The system effectively reduces yawing and prevents engine stalls by increasing side friction, providing a more secure driving experience by minimizing sudden acceleration and maintaining vehicle stability during hill start and crawl mode operations on low friction surfaces.

Implementation Method 1

The de-actuated wheels increase a side friction force between the tire and the surface of the road for reducing the yaw condition

Methodology Applied

Scientific EffectFriction: Friction

Data Source

PatentUS11173885B2Standstill management yaw mitigation on low mu grades

Publication Date: 2021.11.16 ZF ACTIVE SAFETY US INC

AI summary

A stability control system of a vehicle utilizing an electronic control unit that detects a yaw condition while each of the wheel brakes are actuated by EBCM and the wheel speeds are zero. An electronic control unit includes an electronic braking control module that controls actuation and de-actuation of vehicle brakes on an inclined surface. A yaw condition is identified while all vehicle brakes are actuated on the inclined surface and each wheel speed is zero. The electronic control unit identifies which uphill wheel is leading a direction of the yaw and identifies a wheel of an opposing axle diagonal to the identified uphill wheel. The electronic control unit in cooperation with the electronic braking control module de-actuates the vehicle brakes of the identified uphill wheel and diagonal wheel to increase a side friction to the identified diagonal wheels to reduce further yawing of the vehicle.