Viscoelastic Damping in Rear Axle Track Bar

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Solution Overview

Problem

Existing rear suspension track bars are ineffective in damping mid-frequency gear whine vibrations (400-600 Hz) and lack sufficient mass and stiffness to optimally dampen vibrations in the rear differential or carrier gear set, leading to unwanted noise transmission into the passenger compartment.

Innovation Solution

A vibration-damping rear axle track bar featuring a viscoelastic, constrained layer damping material sandwiched between and bonded to tubular members, which absorbs and dissipates energy through shear deformation, increasing the track bar's mass and stiffness to effectively dampen mid-range frequency vibrations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional track bar materials are used, then the track bar maintains structural simplicity, but it fails to dampen mid-frequency vibrations effectively

Engineering Contradiction:

Improvevibration damping effectivenessVSAvoidtrack bar structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The track bar employs a composite structure consisting of an outer tubular member, an inner tubular member, and a viscoelastic damping material layer sandwiched between them. This composite construction combines the structural integrity of metal tubular members with the vibration-damping properties of viscoelastic material, effectively dampening mid-frequency vibrations (400-600 Hz) while maintaining structural functionality.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The damping structure utilizes a nested configuration where the inner tubular member is positioned within the outer tubular member, with the viscoelastic material layer sandwiched between them. This nested arrangement allows the damping system to be integrated within the existing track bar geometry without significantly increasing external dimensions or complexity.

Inventive Principle:

Principle #7Nested doll (Nesting)

2Reliability

If the track bar mass is increased to dampen vibrations, then vibration damping improves, but the track bar weight increases

Engineering Contradiction:

Improvevibration damping effectivenessVSAvoidtrack bar weight

Core Design Contradiction:

ReliabilityVSWeight of moving object

Solution Approach 1:

The composite structure combines lightweight tubular members with a viscoelastic damping layer, achieving effective vibration damping without requiring a substantial increase in overall mass. The viscoelastic material provides damping properties that are more mass-efficient than traditional solid metal constructions.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The viscoelastic damping material is applied as a thin film or layer between the tubular members, providing effective vibration damping with minimal added mass. This thin-film approach allows the track bar to achieve improved damping characteristics without significant weight penalty compared to using thicker or solid metal sections.

Inventive Principle:

Principle #30Flexible shells and thin films

3Reliability

If the track bar is stiffened to optimally dampen vibrations, then vibration damping improves, but the track bar becomes more rigid and heavier

Engineering Contradiction:

Improvevibration damping effectivenessVSAvoidtrack bar stiffness

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The composite construction of outer tubular member, viscoelastic layer, and inner tubular member creates a structure that optimizes the stiffness-damping balance. The tubular members provide the necessary structural stiffness and load-bearing capability, while the viscoelastic layer provides vibration damping without significantly increasing overall stiffness or weight.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The viscoelastic damping material is strategically positioned in specific regions of the track bar where vibration dampening is most needed, while the tubular members maintain structural stiffness in load-bearing areas. This localized application of different material properties optimizes both stiffness and damping performance without unnecessary weight or rigidity increases throughout the entire component.

Inventive Principle:

Principle #3Local quality

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 solution significantly reduces noise levels within the vehicle cabin by dissipating vibrational energy through shear deformation of the viscoelastic layer, achieving noise reduction of 3-10 dBA in mid-frequency ranges, while maintaining the track bar's structural integrity and appearance.

Implementation Method 1

a vibration absorbing, viscoelastic, constrained layer damping material sandwiched between and bonded to a first tubular member and a second tubular member

Methodology Applied

Scientific EffectViscoelasticity: Viscoelasticity

Implementation Method 2

When subjected to shear due to bending, the energy dissipating constrained layer damping material dampens audible frequencies that travel through the track bar

Methodology Applied

Scientific EffectShear deformation: Shear Stress

Data Source

PatentUS7648149B2Damped Rear Suspension Track Bar

Publication Date: 2010.01.19 FCA US LLC

AI summary

A track bar for a rear suspension of a vehicle has a first tubular member, an energy dissipating member wrapped around the first tubular member, and a second tubular member encompassing the energy dissipating member. Together, the tubular members and energy dissipating member dampen vibration transmitted through the track bar to lessen the audible vibrations that rear the interior of a vehicle cabin.