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NVH Workshop
Presenters:
A. E. Duncan Material Sciences Corp.
G. Goetchius Material Sciences Corp.
S. Gogate DaimlerChrysler Corp.
Sponsored By:SAE Noise and Vibration Committee
Structure Borne NVH BasicsSAE 2007 NVH Conference; St. Charles,
Illinois
Wednesday Evening, May 16, 2007
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NVH Workshop
NVH Workshop Topic Outline Introduction Fundamentals in NVH
Automotive NVH Load Conditions Low Frequency Basics Live Noise
Attenuation Demo Mid Frequency Basics Utilization of Simulation
Models Closing Remarks
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NVH Workshop
The Fundamental Secret ofStructure Borne
NVH Performance
The Fundamental Secret ofStructure Borne
NVH Performance
Revealed here today !
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NVH Workshop
Primary References (Workshop Basis: 4 Papers)
1. A. E. Duncan, et. al., Understanding NVH Basics, IBEC,
1996
2. A. E. Duncan, et. al., MSC/NVH_Manager Helps Chrysler Make
Quieter Vibration-free Vehicles, Chrysler PR Article, March
1998.
3. B. Dong, et. al., Process to Achieve NVH Goals: Subsystem
Targets via Digital Prototype Simulations, SAE 1999-01-1692, NVH
Conference Proceedings, May 1999.
4. S. D. Gogate, et. al., Digital Prototype Simulations to
Achieve Vehicle Level NVH Targets in the Presence of
Uncertainties,
SAE 2001-01-1529, NVH Conference Proceedings, May 2001
Structure Borne NVH References
Available online at www.AutoAnalytics.com
Structure Borne NVH Workshop - on Internet
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NVH Workshop
Supplemental References5. T.D. Gillespie, Fundamentals of
Vehicle Dynamics, SAE 1992
(Also see SAE Video Lectures Series, same topic and author)6. D.
E. Cole, Elementary Vehicle Dynamics, Dept. of Mechanical
Engineering, University of Michigan, Ann Arbor, Michigan, Sept.
1972
7. J. Y. Wong, Theory of Ground Vehicles, John Wiley & Sons,
New York, 1978
8. Kompella, M. S., and Bernhard, J., Measurement of the
Statistical Variation of Structural-Acoustic Characteristics of
Automotive Vehicles, SAE No. 931272, 1993
9. Freymann, R., and Stryczek, R., A New Optimization Approach
in the Field of Structural-Acoustics, SAE No. 2000-01-0729,
2000
Structure Borne NVH References
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NVH Workshop
NVH Workshop Topic Outline Introduction
Fundamentals in NVH
Automotive NVH Load Conditions
Low Frequency Basics
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NVH Workshop
Rideand
Handling
NVH Durability
ImpactCrashWorthiness
Competing Vehicle Design Disciplines
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NVH Workshop
NVH Workshop Topic Outline Introduction
Fundamentals in NVH
NVH Load Conditions
Low Frequency Basics
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NVH Workshop
Fundamentals in NVH
What is N, V and H?
Time and Frequency Relation
Subjective to Objective Conversions
Single Degree of Vibration and Vibration Isolation Principle
Automotive NVH Frequency Range
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NVH Workshop
What is N, V and H?(in Automotive Context)
Noise : Vibration perceived audibly and characterized as
sensations of pressure by the ear
Together, they define the measure of vehicle NVH Quality
Based on SAEJ670e Standard (Vehicle Dynamics Committee July
1952)
Vibration : Perceived tactually (at vehicle occupant interface
points of steering column, seats, etc.
Harshness : Related to transient nature of vibration and noise
associated with abrupt transition in vehicle motion. It could be
perceived both tactually and audibly
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NVH Workshop
Time and Frequency Relation
TactileTactile
AcousticAcoustic
Operating loads Operating loadsOperating loads
TactileTactile
Time (Sec)
Tact
ile o
r Aco
ustic
Res
pons
e
Responses perceived in vehicle vary with time as vehicle
operates under loads
Responses are usually steady state and periodic in nature
It is convenient and intuitive to consider responses in
frequency domain while preserving the signal content
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NVH Workshop
Time and Frequency Relation Conversion to frequency domain lends
to formulation of principles for addressing structure borne NVH
Am
plitu
de
Time
Frequency (Hz)
5 Hz(Vehicle RigidBody Mode)
15 Hz(SuspensionMode)
25 Hz(Vehicle FlexibleBody Mode)
40 Hz(ColumnMode)
Overall Response, X(t)
Time (Sec)
Phas
ed S
umm
atio
n
X(f)
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NVH Workshop
Time and Frequency Relation
X ( f ) = Fourier Transform of X ( t )
Mathematically Speaking .
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NVH Workshop
Time and Frequency Relation Responses can be obtained in
frequency domain either through Fourier Transform of time domain
signal or directly in frequency domain
Vehicle System Fourier TransformX ( t ) X ( f )F ( t )
Test World
X ( f )
Common in Simulation World
Vehicle SystemF ( f )
Fourier Transform
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NVH Workshop
Total 2178.2 Kg (4800LBS)Mass Sprung 1996.7 Kg
Unsprung 181.5 Kg (8.33% of Total)Powertrain 181.5 Kg
Tires 350.3 N/mmKF 43.8 N/mmKR 63.1 N /mmBeam mass lumped on
grids like a beam M2,3,4 =2 * M1,5
31
8
2
6
4
7
5
NVH Model of Unibody Passenger CarSymbolic Outline
From Reference 6
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NVH Workshop
Excitation Bump Profile
0.0
5.0
10.0
15.0
20.0
0 100 200 300 400 500
Distance (mm)
Pro
file
Hei
ght
(mm
) Profile
On to 100,380
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NVH Workshop
Pitch at Mid-Car DOF3
-1.0E-04
-8.0E-05
-6.0E-05
-4.0E-05
-2.0E-05
0.0E+00
2.0E-05
4.0E-05
6.0E-05
8.0E-05
1.0E-04
0 1 2 3Time (sec.)
Ro
tati
on
- R
adia
ns Base Model
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NVH Workshop
Pitch Response - Baseline Model
1.E-08
1.E-07
1.E-06
1.E-05
1.E-04
0.0 5.0 10.0 15.0 20.0Frequency Hz
Ro
tati
on
Rad
ian
s
Base Model
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NVH Workshop
FFT of the Input Bump
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
0.E+00 4.E-03 8.E-03 1.E-02 2.E-02 2.E-02
Cycles / mm
Ampl
itude
mm
Bump FFT
Transform Input Force to F(f)
20 Hz @ 45 MPH
0.0 20.0 Hz
Amplitude is Approximately Constant over the Frequency Range
Constant Displacement
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NVH Workshop
P itch at M id -C ar D O F 3
1 .0 E-0 8
1 .0 E-0 7
1 .0 E-0 6
1 .0 E-0 5
1 .0 E-0 4
0 5 1 0 1 5 2 0F req u en cy H z
Ro
tati
on
Rad
ian
s Tim e Dom ain F F TF F T of Input
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NVH Workshop
Subjective to Objective Conversions
Subjective NVH Ratings are typically based on a 10 Point Scale
resulting from Ride Testing
A 2 1/2 A 1Represents 1.0 Rating Change
TACTILE: 50% reduction in motion
SOUND : 6.dB reduction in sound pressure level ( long standing
rule of thumb )
Receiver Sensitivity is a Key Consideration
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NVH Workshop
m
APPLIED FORCE
F = FO sin 2 f t
k c FT
TR = FT / F
TransmittedForce
Single Degree of Freedom Vibration
= f 2fn 2 ) 2ffn
( 2 d ) 21 +1 + ffn( 2 d ) 21 +
( 1- ffn( 2 d ) 2+
d = fraction of critical dampingfn = natural frequency (k/m)f =
operating frequency
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NVH Workshop
0 1 2 3 4 50
1
2
3
4Tr
ansm
issi
bilit
y R
atio
1.414
0.5
0.1
0.15
0.375
1.0
0.25
Frequency Ratio (f / fn)
Vibration Isolation Principle
m
APPLIED FORCEF = FO sin 2 f t
k c FT
TR = FT / F
TransmittedForce
Isolation RegionIsolation Region
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NVH Workshop
Excitation Force Comingfrom Engine F0
FT
Transmissibility Force Ratio is FT/F0
Isolation from an Applied Force
Support Forces Transmitted to Body
Example:A 4 Cyl. Excitation for Firing
Pulse at 700 RPM has a second order gas pressure torque at 23.3
Hz. Thus, to obtain isolation, the engine roll mode must be below
16.6 Hz.
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NVH Workshop
Structure Borne NoiseAirborne Noise
Res
pons
e
Log Frequency
LowGlobal Stiffness
Mid
Local Stiffness+
Damping
High
Absorption+
Mass+
Sealing
~ 150 Hz ~ 1000 Hz ~ 10,000 Hz
Automotive NVH Frequency Range
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NVH Workshop
NVH Workshop Outline Introduction
Fundamentals in NVH
NVH Load Conditions
Low Frequency Basics
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NVH Workshop
Two Main Sources
Noise and Vibration Sources
Suspension Powertrain
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NVH Workshop
Typical NVH Pathways to the Passenger
PATHS FOR
STRUCTURE BORNE
NVH
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NVH Workshop
Powertrain Induced
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NVH Workshop
NVH Workshop Topic Outline Introduction
Fundamentals in NVH
NVH Load Conditions
Low Frequency Basics
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NVH Workshop
RECEIVER
PATH
SOURCE
Low Frequency NVH Fundamentals
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NVH Workshop
Vibration and Noise Attenuation Methods
Main Attenuation Strategies Reduce the Input Forces from the
Source
Provide Isolation
Mode Management
Nodal Point Mounting
Dynamic Absorbers
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NVH Workshop
8 Degree of Freedom Vehicle NVH Model
1 2 4 5
6 7
8
3
TiresWheels
SuspensionSprings
Engine Mass
EngineIsolator
Flexible Beam for Body
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NVH Workshop
Vibration and Noise Attenuation Methods
Main Attenuation Strategies Reduce the Input Forces from the
Source
Provide Isolation
Mode Management
Nodal Point Mounting
Dynamic Absorbers
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NVH Workshop
Reduction of Input Forces from the Source
Road Load Excitation Use Bigger / Softer Tires Reduce Tire Force
Variation Drive on Smoother Roads
Powertrain Excitation Reduce Driveshaft Unbalance Tolerance Use
a Smaller Output Engine Move Idle Speed to Avoid Excitation
Alignment Modify Reciprocating Imbalance to alter Amplitude or
Plane of Action of the Force.
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NVH Workshop
Vibration and Noise Attenuation Methods
Main Attenuation Strategies Reduce the Input Forces from the
Source
Provide Improved Isolation
Mode Management
Nodal Point Mounting
Dynamic Absorbers
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NVH Workshop
8 Degree of Freedom Vehicle NVH ModelForce Applied to Powertrain
Assembly
Forces at Powertrain could represent a First OrderRotating
Imbalance
1 2 4 5
6 7
8
3
Feng
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NVH Workshop
Engine Isolation Example
Response at Mid Car
0.0001
0.0010
0.0100
0.1000
1.0000
5.0 10.0 15.0 20.0Frequency Hz
Velo
city
(mm
/sec
)
Constant Force Load; F ~ A 15.9 Hz8.5 Hz7.0 Hz
700 Min. RPM First Order UnbalanceOperation Range of
Interest
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NVH Workshop
Concepts for Increased IsolationDouble isolation is the typical
strategy for further improving isolation of a given vehicle
design.
Subframe is Intermediate Structure
Suspension Bushing is first level
Second Level of Isolation is at Subframe
to Body Mount
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NVH Workshop
8 Degree of Freedom Vehicle NVH ModelRemoved Double Isolation
Effect
1 2 4 5
6 7
8
3
WheelMass
Removed
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NVH Workshop
Double Isolation ExampleVertical Response at DOF3
0.0E+00
1.0E+00
2.0E+00
3.0E+00
4.0E+00
5.0E+00
6.0E+00
5.0 10.0 15.0 20.0Frequency Hz
Velo
city
(m
m/s
ec)
Base Model
Without Double_ISO
1.414*fn
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NVH Workshop
Vibration and Noise Attenuation Methods
Main Attenuation Strategies Reduce the Input Forces from the
Source
Provide Isolation
Mode Management
Nodal Point Mounting
Dynamic Absorbers
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NVH Workshop
Mode Management
Provide Separation between:
Critical modes of Sub-systems in Vehicle (e.g. Body, Suspension,
Powertrain, etc.)
Critical modes of Sub-systems and Excitation
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NVH Workshop
1 2 4 5
6 7
8
3
Beam Stiffness which represents the body stiffness was adjusted
to align Bending Frequency with Suspension Modes and then
progressively separated back to Baseline.
Need for Mode Management
Baseline Bending 18.2 Hz
Baseline Suspension 10.6 Hz
TiresWheels
SuspensionSprings
Flexible Beam for Body