Acoustic Signature for Automotive Seat Rattle

Tuan Quach, Joseph Hasna,

Khai Win Er, Wenhao Li

School of Aerospace, Mechanical and Manufacturing Engineering

Supervisors: Dr. M. Fard (RMIT) Tony Baxter (FUTURIS)

Introduction

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Why is it important to investigate NVH?

• Characteristics of noise and vibration are important factors in terms of design quality and build for mechanical systems.

• Vital to a vehicle’s success that noise and vibration be reduced as much as possible.

• Automotive seat rattle is particularly important as there is direct interaction between passenger and the seat.

• In order to mitigate noise and vibration, the sources must be identified.

Project Objective

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Main Objectives• Analyse seat structural behaviour and sound characteristics.

• Characterise rattle behaviour to locate noise sources.

• Provide recommendations to diagnose rattle prior to design phase.

RESEARCH EXPERIMENT VALIDATE RECOMMENDATIONS

Characterising rattle

Experimental Process

Correlate & Validate Managing rattle

NVH – Seat Rattle Optimization of experiment

Rattle Noise Database

Importance of Research

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Why focus on Seat Rattle noises?• Seat serves as a final link for vibrational sources.

• Overall vehicle satisfaction directly correlates to interior quietness

Rat

ing

of O

vera

ll Ve

hicl

e Q

ualit

y

Rating of Overall Interior Quietness

Overall vehicle satisfaction

Importance of Research

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Why focus on Seat Rattle noises?• Resonance can lead to violent vibration

• Constant resonant noises can be hazardous to concentration

Methodology

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Modal Analysis TestingTo determine the resonance frequencies of the seat along with its respective mode shapes.

Acoustic Camera Testing Recommendation

Results

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g.N

Am

plitu

de250e-3

Lateral Mode 8.65 Hz

Twisting Mode 237.16 Hz

Twisting Mode 122.88 Hz

Bounce Mode16.97 Hz

Methodology

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Acoustic Camera TestingTo pin-point the source of the rattle noise at its respective resonance frequencies.

Modal AnalysisTesting

Recommendation

Results

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Lateral Mode- 8.65 Hz

Twisting Mode 2- 37.16 HzTwisting Mode 1- 22.88 Hz

Bounce Mode- 16.97 Hz

Results Refinement

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• Some spectrogram shows unclear results due to noise from the overall seat. • Refinement of the excitation range would pin-point the main source of noise (rattle).

Conclusion

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• Controlling of rattle in early design phase is challenging and industry is still

using find & fix for rattle.

• Strong correlation has been found between seat structure dynamics and

rattle noise (structural vibration modes).

• Management of the three main seat vibration modes in early design phase

can significantly reduce time and cost.

• Experiments revealed resonant frequencies at 8.65Hz, 16.97Hz, 22.88Hz

and 37.16Hz.

Recommendation

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Altering the natural frequency of the seat• Resonance occurs when the input frequency is the same as the natural

frequency of the seat.

• Vibration sources such as engine’s combustion usually vibrate below 30Hz.

• By shifting the natural frequency to a higher frequency, resonance could possibly be avoided.

• This could be done by changing the material properties of the seat (stiffness and mass).

Natural Frequency

Recommendation

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Minimize the impacting surface area• From the results, it was found that most of the noises come from

connection points.• By minimizing the impacting surface area, it could restrict the movement at

the connection points, therefore further reduce the sound emitted.

• This could be by changing the direction of the pin at the point of interest.

Mode Recommendation

Lateral Mode 8.65 HzRestriction in the

horizontal directionRestriction in the vertical

directionBounce Mode 16.97 Hz

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Thank you.

Questions