Vehicle Steering Decoupling Front Axle Self-Alignment

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Solution Overview

Problem

Existing vehicle steering and control systems, particularly those with front and rear axle steering mechanisms, face challenges in maintaining correct tracking and direction stabilization, often resulting in unwanted interference felt by the driver, especially when one axle develops a fault or when active steering interventions occur.

Innovation Solution

The method involves interventions at the rear axle, including steering and selective braking/acceleration of rear wheels to create a yawing torque, which counteracts the restoring self-alignment of front wheels by temporarily maintaining or adjusting the front wheel steering angle, thereby ensuring smooth and comfortable driving without perceived torque on the steering wheel.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If active course maintenance systems intervene in the steering of the front axle, then the vehicle's direction is stabilized, but the driver perceives unwelcome interference

Engineering Contradiction:

Improvedirection stabilizationVSAvoiddriver perception of interference

Core Design Contradiction:

Stability of the object's compositionVSEase of operation

Solution Approach 1:

The patent introduces rear axle steering as an intermediary mechanism to achieve direction stabilization. Instead of directly interfering with front axle steering (which the driver feels), the system steers the rear wheels to counteract lane departure. This mediates the stabilization function while keeping the front steering wheel neutral, eliminating driver-perceived interference.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent segments the steering function into independent front and rear axle systems. The front axle handles driver input while the rear axle handles stabilization. This segmentation allows the stabilization function to be achieved without coupling the driver's steering actions with corrective torques, resolving the contradiction between stabilization and driver comfort.

Inventive Principle:

Principle #1Segmentation

2Stability of the object's composition

If rear axle steering is used to correct tracking, then the vehicle returns to the correct lane, but the front wheels' restoring self-alignment causes crabwise motion

Engineering Contradiction:

Improvetracking correctionVSAvoidvehicle motion pattern

Core Design Contradiction:

Stability of the object's compositionVSShape

Solution Approach 1:

The patent applies preliminary anti-action by using the front steering lock to prevent the natural restoring self-alignment of the front wheels that would otherwise occur when rear wheels are steered. This pre-emptive constraint on the front wheels counteracts the tendency toward crabwise motion, allowing rear axle steering to correct tracking without producing unwanted lateral vehicle body movement.

Inventive Principle:

Principle #9Preliminary anti-action

3Stability of the object's composition

If the front wheel steering angle is temporarily fixed to prevent self-alignment, then crabwise motion is avoided, but the driver cannot override the steering angle

Engineering Contradiction:

Improveprevention of crabwise motionVSAvoiddriver override capability

Core Design Contradiction:

Stability of the object's compositionVSAdaptability or versatility

Solution Approach 1:

The patent implements a dynamic front steering lock that can switch between locked and unlocked states. During automated tracking correction, the lock engages to prevent crabwise motion. When the driver applies additional steering input, the system detects this and releases the lock, transferring control to the driver. This dynamic behavior provides both crabwise motion prevention and driver override capability.

Inventive Principle:

Principle #15Dynamics

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 approach enables effective tracking and stabilization of the vehicle's trajectory with minimal driver effort, preventing unwanted crabwise motion and maintaining the set course, even for inexperienced drivers, by decoupling the front wheels from the rear axle's steering effects and providing assistive steering without perceived interference.

Implementation Method 1

interventions result in a yawing torque about the vertical axis of the vehicle

Methodology Applied

Scientific EffectYawing torque: Torque

Implementation Method 2

Since the front wheels are articulated to the front axle in a caster configuration, a deflection of the rear in one direction produces a lateral force in the opposite direction on the front axle

Methodology Applied

Scientific EffectCaster effect:

Implementation Method 3

Owing to the caster effect, when a steering angle is imposed a restoring torque is produced

Methodology Applied

Scientific EffectRestoring torque: Torque

Data Source

PatentUS10604183B2Method for steering a vehicle, controller for a motor vehicle, and motor vehicle

Publication Date: 2020.03.31 ZF FRIEDRICHSHAFEN AG

AI summary

A method of steering a vehicle having a front axle steering mechanism and, in particular, a rear axle steering mechanism. It is proposed that interventions are carried out at the rear axle to maintain the vehicle on course, at the same time, interventions are carried out at the front axle steering mechanism to avoid a restoring self-alignment of the front wheels.