NVH TECHNOLOGY IN THE BMW 1

SERIES

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(Presented by) A. Fleszar – LMS Americas

J. Florentin, F. Durieux – LMS International

T. Yamamoto, Y. Kuriyama – Nippon Steel Corporation

• Introduction

• Hybrid Interior Noise Synthesis Approach

• Measurements on Vehicle

• Panel CAE Model Creation

CONTENTS

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• Panel CAE Model Creation

• Panel Optimization for NVH and Crash

• Conclusion

25% Lighter

ULSAB

CO2 <110g/km

ULSAB-AVC

500 1000 1500 2000 2500 Vehicle Mass (kg)

CO

2

(g/k

m)

500

400

300

200

100

0

Introduction

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– Lighter vehicles for reduced CO2 emission

– Preservation of safety and comfort

Objective: Lightweight steel solution for noise performance

Panel investigation

using Test and CAE Hybrid Approach

Introduction

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Candidate vehicle / panel� Compact and comfortable vehicle� Firewall on direct engine noise path

Firewall of BMW Series 1

Step 1: Vehicle measurement

Step 4: Panel modification

Step 2: Panel measurement

Step 3: Panel CAE model

PROJECT CONTENT

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Project Framework

Engine Noise

Structure Borne

0 – 400 Hz

Step 5: Modified panel in vehicle

Step 4: Panel modification

OriginalNoise Improvement Evaluation

In full Vehicle

INTERIOR NOISE SYNTHESIS

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Design

Modification

• On Vehicle

– Acoustic Source Quantification

• Measure firewall and cabin response to structural excitation

• Isolate firewall contribution

• Estimate other panel contributions

MEASUREMENTS

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• Estimate other panel contributions

– Acoustic characterization of passenger cabin

• On Panel

– Trim package evaluation

– Structure characterization

FE model

validation

Windshield

Floor

Windshield

Roof

ACOUSTIC SOURCE

QUANTIFICATION

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Firewall seen from engine compartment

Right windowWheel housing

Windshield

Firewall

• Firewall and floor are the

dominant steel structures

in the low frequency

range

65.3

55.2 57.8

51.4

73.8 74.7

0

20

40

60

80

90-140 Hz 150-400 Hz 60-400 Hz

dB

Firewall (CAE prediction)

Floor (ASQ estimation)

ACOUSTIC SOURCE

QUANTIFICATION

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• Floor dominates the

higher frequencies40.0

50.0

60.0

70.0

80.0

Fir

ew

all

Flo

or

Ro

of

Win

ds

hie

ld

Sid

e

Win

do

ws

dB

90-140 Hz

150-400Hz

• Acoustic-acoustic FRF measurements

• Measure cabin dimensionsSourceSource

MicrophonesMicrophones

ACOUSTIC CHARACTERIZATION

OF PASSENGER COMPARTMENT

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Build and validate acoustic FE model

Acoustic

source

Microphones

on panel

102 Hz141 Hz

Modes of firewall in range of interest

ACOUSTIC CHARACTERIZATION

OF PASSENGER COMPARTMENT

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Mode 1 – 58 Hz

144 Hz

141 Hz

Roving hammer measurements:

STRUCTURAL

CHARACTERIZATION

CowltopFirewall

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Components purchased from BMW dealer

Trim Package

Roving hammer measurements:

– Components

– AssemblyTransverse

beam

Steel Components

Passenger

cabin FEM

Scanned firewall components

PANEL CAE MODELING

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cabin FEM

Firewall structure

coupled with

acoustic model

Firewall is spot-welded structure

with full vehicle boundary

conditions + Trim

MeasurementsCAE model

• Structural response shows the model is successful for 40 Hz – 300 Hz

PANEL CAE

Acceleration on Firewall Central Location

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Firewall Noise Contribution At Driver’s Right Ear

TEST ASQ (limited set of points)

CAE (full set of points)

• Vibro-acoustic CAE model catches the mid-range firewall contribution (80 Hz – 200 Hz)

• Test is under predicting due to small number of measurement locations on firewall

Mode Contribution Analysis

144 Hz

Use CAE model to identify structural weak points:� Lower firewall

� Firewall region behind the beam

Element contribution analysis

102 Hz 141 Hz

IDENTIFICATION OF

DESIGN IMPROVEMENTSSensitivity of acoustic model

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Mode Contribution Analysis

130 Hz

Element contribution analysis

144 Hz

118 Hz

144 Hz

130 Hz

118 Hz

• 40+ modifications

investigated

• Optimized design

Tailored

Blank

1.9mm

1.5mmFront

Original:1.7mm

PANEL MODIFICATIONS

FOR NOISE REDUCTION

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• Optimized design

– Modified transverse beam

with new M-shape,

reduced thickness, holes

and Tailored Welded Blank

Blank

Beads

0.7mm (same as original)

Back

• Static analyses

• 2 load cases: front and side

Original design

CRASHWORTHINESS

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5000N

Final design

5000N

- 1.64 dB

MODIFIED PANEL INFLUENCE

ON OVERALL VEHICLE NOISE

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Firewall contribution to sound

- 0.90 dB

Full vehicle sound pressure

Original Advanced Steel Solution

BMW1 FirewallTWB + Beads

+ M-Shaped Beam + Holes

0.7mm0.7mm

PERFORMANCE IMPROVEMENT

SUMMARY

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Panel + Beam 8.43 kg

Damping sheets 0.40 kg

Panel + Beam 8.19 kg

Damping sheets 0 kg

Weight reduction 0.64 kg (5.1%)

Noise level –0.90 dB (10 – 400Hz)

1.9mm1.5mm1.7mm

• Hybrid Interior Noise Synthesis

– Efficient, simple and flexible

– Potential to be used at early design stages

– Short calculation time, allows a large number of iterations and in-depth sensitivity analysis

• Elaborate steel designs are successful at

CONCLUSIONS

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• Elaborate steel designs are successful at

– Achieving better noise performance

– While improving the mass

– Not compromising crashworthiness

– 1 dB improvement on firewall contribution of high end vehicle

• For even larger improvements…– Address NVH earlier in the design process