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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