2007 SAE Structure Borne NVH Workshop

Structure Borne NVH Basics
SAE 2007 NVH Conference; St. Charles, Illinois
Wednesday Evening, May 16, 2007

Presenters:

A. E. Duncan Material Sciences Corp.

G. Goetchius Material Sciences Corp.

S. Gogate DaimlerChrysler Corp.

Sponsored By:
SAE Noise and Vibration Committee
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

NVH Workshop

The Fundamental Secret of
The Fundamental Secret of
Structure Borne
Structure Borne
NVH Performance
NVH Performance

Revealed here today ! NVH Workshop

Structure Borne NVH References
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 Workshop - on Internet
Available online at www.AutoAnalytics.com NVH Workshop

Structure Borne NVH References
Supplemental References
5. 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

NVH Workshop

• Introduction

NVH Workshop

Competing Vehicle Design Disciplines

Ride Impact
and CrashWorthiness
Handling

Durability
NVH

NVH Workshop

• Introduction
• NVH Load Conditions

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

NVH Workshop

What is N, V and H?
(in Automotive Context)
Based on SAEJ670e Standard (Vehicle Dynamics Committee July 1952)

Noise : Vibration perceived audibly and characterized as
sensations of pressure by the ear

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

Together, they define the measure of vehicle
NVH Quality
NVH Workshop

Time and Frequency Relation
Acoustic
Acoustic

Tactile or Acoustic Response
Tactile
Tactile
Tactile
Tactile

Time (Sec)

Operating
Operating loads
Operating loads
loads

• 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
NVH Workshop

• Conversion to frequency domain lends to formulation of
principles for addressing structure borne NVH
Frequency (Hz)

40 Hz
(Colum
n
Amplitude

Mode)

25 H
(Vehicle z
Flexible
Body M
o d e)

n
15 Hz

io
(Suspe

at
nsion

m
Mode)
X(f)

m
Overall Response, X(t)

Su
ed
5 Hz

as
(Vehicle
Rigid Ph
Body M
o d e)

Time (Sec)
Time
NVH Workshop

• Mathematically Speaking …….

X ( f ) = Fourier Transform of X ( t )

NVH Workshop

• Responses can be obtained in frequency
domain either through Fourier Transform of time
domain signal or directly in frequency domain
Test World

X ( t ) Fourier X ( f )
F(t)
Vehicle System
Transform

Fourier
Transform

F(f) X(f)
Vehicle System

Common in Simulation World
NVH Workshop

NVH Model of Unibody Passenger Car
Symbolic Outline

8

4
3 5
1 2
7
6

Tires 350.3 N/mm
Total 2178.2 Kg (4800LBS)
KF 43.8 N/mm
Mass Sprung 1996.7 Kg
KR 63.1 N /mm
Unsprung 181.5 Kg (8.33% of Total)
Beam mass lumped on
Powertrain 181.5 Kg
grids like a beam
M2,3,4 =2 * M1,5
From Reference 6 NVH Workshop

Excitation Bum p Profile
20.0

Profile
Profile Height (m m )

15.0

10.0

5.0

0.0
400 On to 100,380
0 100 200 300 500

Distance (mm)

NVH Workshop

Pitch at Mid-Car DOF3
1.0E-04
8.0E-05
R o ta tio n - R a d ia n s

Base Model
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 3
Time (sec.)
NVH Workshop

Pitch Response - Baseline Model
1.E-04

Base Model
R o tat io n R a d ian s

1.E-05

1.E-06

1.E-07

1.E-08

0.0 5.0 10.0 15.0 20.0
Frequency Hz
NVH Workshop

Transform Input Force to F(f)
FFT of the Input Bump
1.E-01
Bump FFT

1.E-02
Amplitude mm

1.E-03

20 Hz Amplitude is Approximately
@ 45 MPH
1.E-04
Constant over the
Frequency Range
1.E-05

1.E-06
Constant Displacement
0.E+00 4.E-03 8.E-03 1.E-02 2.E-02 2.E-02
Cycles / mm
20.0 Hz
0.0
NVH Workshop

P itc h a t M id -C a r D O F 3
1 .0 E-0 4
RotationRadians

Tim e D o m a in F F T
1 .0 E-0 5
F F T o f In p u t

1 .0 E-0 6

1 .0 E-0 7

1 .0 E-0 8
0 5 10 15 20
F re q u e n c y Hz

NVH Workshop

Subjective to Objective Conversions

Subjective NVH Ratings are typically based on a
10 Point Scale resulting from Ride Testing
Receiver Sensitivity is a Key Consideration

A 2 ≈ 1/2 A 1
Represents 1.0 Rating Change

TACTILE: 50% reduction in motion

SOUND : 6.dB reduction in sound pressure level
( long standing rule of thumb )
NVH Workshop

Single Degree of Freedom Vibration
APPLIED FORCE

F = FO sin 2 π f t

√
f
1 + ( 2 d fn ) 2
TR = FT / F = f
( 1- f 2 ) 2 + ( 2 d f ) 2
2

m fn n

Transmitted
Force
c
k d = fraction of critical damping
FT
fn = natural frequency √(k/m)
f = operating frequency

NVH Workshop

Vibration Isolation Principle
4
0.1
APPLIED FORCE
Transmissibility Ratio

0.15

F = FO sin 2 π f t
3

TR = FT / F
m
0.25

c
k FT
2 Transmitted
0.375 Force
0.5
1.0
1
Isolation Region
Isolation Region

0
1.414
0 1 2 3 4 5
Frequency Ratio (f / fn)
NVH Workshop

Isolation from an Applied Force
Excitation Force Coming
from Engine F0

Transmissibility
Force Ratio is FT/F0
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
FT must be below 16.6 Hz.

Support Forces
Transmitted to Body

NVH Workshop

Automotive NVH Frequency Range

Structure Borne Noise
Airborne Noise
Response

Absorption
+
Local Stiffness Mass
+ +
Damping Sealing
Global Stiffness
“High”
“Low” “Mid”

~ 150 Hz ~ 1000 Hz ~ 10,000 Hz

Log Frequency
NVH Workshop

NVH Workshop Outline
• Introduction
• NVH Load Conditions

NVH Workshop

Noise and Vibration Sources

Suspension
Powertrain

Two Main Sources
NVH Workshop

Typical NVH Pathways to the Passenger

PATHS
FOR
STRUCTURE
BORNE
NVH

NVH Workshop

Powertrain
Induced

NVH Workshop

Low Frequency NVH Fundamentals

RECEIVER

PATH

SOURCE

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

NVH Workshop

8 Degree of Freedom Vehicle NVH Model
Engine Mass
8
Engine Flexible Beam for Body
Isolator
3 4 5
2
1
Suspension
Springs
6 7
Wheels
Tires

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.

NVH Workshop


• Provide Improved Isolation
• Mode Management

NVH Workshop

Force Applied to Powertrain Assembly
Feng
8

3 4 5
2
1

6 7

Forces at Powertrain could represent a First Order
Rotating Imbalance

NVH Workshop

Engine Isolation Example
Response at M id Car
1.0000
15.9 Hz
F~A
Constant Force Load;
8.5 Hz
Velocity (mm/sec)

0.1000
7.0 Hz

0.0100

0.0010

700 Min. RPM First Order Unbalance
Operation Range of Interest
0.0001
5.0 10.0 15.0 20.0
Frequency Hz

NVH Workshop

Concepts for Increased Isolation
“Double” isolation is the typical strategy for
further improving isolation of a given vehicle
design.

Second Level of
Isolation is at Subframe
to Body Mount

Subframe is
Intermediate Structure

Suspension Bushing is first level

NVH Workshop

Removed Double Isolation Effect

8

3 4 5
2
1

Wheel
Mass
6 7

Removed

NVH Workshop

Double Isolation Example
Vertical Response at DOF3
6.0E+00

Base Model
5.0E+00
(mm/sec)

Without Double_ISO

4.0E+00

3.0E+00
Velocity

1.414*fn
2.0E+00

1.0E+00

0.0E+00
5.0 10.0 15.0 20.0
Frequency Hz
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

NVH Workshop

Need for Mode Management
Beam Stiffness which represents the body stiffness was
adjusted to align Bending Frequency with Suspension Modes
and then progressively separated back to Baseline.

Baseline Bending 18.2 Hz

Baseline Suspension 10.6 Hz
8

Flexible Beam for Body
3 4 5
2
1
Suspension
Springs
6 7
Wheels
Tires

NVH Workshop

8 DOF Mode Separation Example
Response at Mid Car 18.2 Hz Bending
13.Hz Bending
100.00
10.6 Bending
Prog
re
“veh ssive re
d
icle”
bend uction in
10.6 Hz ing m the
Velocity (mm/sec)

ode

13.0 Hz
10.00
18.2 Hz

1.00

Suspension Mode

0.10

5 10 15 20
Frequency Hz

NVH Workshop

Mode Management Chart
EXCITATION SOURCES
Inherent Excitations (General Road Spectrum, Reciprocating Unbalance, Gas Torque, etc.)
Process Variation Excitations (Engine, Driveline, Accessory, Wheel/Tire Unbalances)
0 5 10 15 20 25 30 35 40 45 50
Hz
First Order Wheel/Tire Unbalance V8 Idle
Hot - Cold

CHASSIS/POWERTRAIN MODES
Suspension Hop and Tramp Modes
Ride Modes Suspension Longitudinal Modes
Powertrain Modes Exhaust Modes
0 5 10 15 20 25 30 35 40 45 50
Hz

BODY/ACOUSTIC MODES
Body First Torsion Steering Column First Vertical Bending
Body First Bending First Acoustic Mode

0 5 10 15 20 25 30 35 40 45 50
Hz
(See Ref. 1)
NVH Workshop

Campbell Diagram
• Campbell Diagram simultaneously represents excitations and
vehicle system modes on a RPM vs. Frequency axis system
• A more convenient way (compared to mode management
charts) of understanding the interaction among modes and
excitation and mapping onto ERPM and vehicle speed

Steering Column
Global Body Torsion
3rd Harmonic

Vertical
Engine RPM

2nd Harmonic
600 RPM

1st Harmonic

Frequency (Hz)
30Hz 32Hz
NVH Workshop

Mount at Nodal Point
First Bending: Nodal Point Mounting Example

Front input forces Rear input forces

Locate wheel centers at node points of the first bending modeshape
to prevent excitation coming from suspension input motion.

NVH Workshop

Mount at Nodal Point
Nodal Point Mounting Examples

Passenger sits at
node point for First
Torsion.

Rear View
Mount system is placed to support Engine
Powertrain at the Nodal Locations of
the First order Bending Mode.
3 4 5
2
1

6 7
Transmission Mount of a
3 Mount N-S P/T is near
the Torsion Node.
NVH Workshop

Bending Node Alignment with Wheel Centers
Redistribute Beam Masses
to move Node Points to
8
Align with points 2 and 4

3 4 5
2
1

6 7

NVH Workshop

First Bending Nodal Point Alignment
Response at Mid-Car
4.0E+00

Node Shifted
Base Model
(m m /sec)

3.0E+00

2.0E+00
Velocity

1.0E+00

0.0E+00

5.0 10.0 15.0 20.0
Frequency Hz
NVH Workshop

Dynamic Absorber Concept
Auxiliary Spring-Mass-Damper
m = M / 10
4.0
x x
Displacement mm

3.5
SDOF 2DOF
3.0
M M
2.5
YO YO
2.0
1.5

1.0
0.5

0.0
0.0 0.5 1.0 1.5 2.0
Frequency Hz
NVH Workshop

Powertrain Example of Dynamic Absorber

Anti-Node Identified
at end of Powerplant

c
k
m
Absorber attached at anti-node acting in
the Vertical and Lateral plane.

√ k/m
Tuning Frequency =
[Figure Courtesy of DaimlerChrysler Corporation]
NVH Workshop

Baseline Sound Level
Baseline Sound Level
63 Hz Dynamic Absorber
63 Hz Dynamic Absorber
63 + 110 Hz Absorbers
63 + 110 Hz Absorbers

NVH Workshop

• Mode Management
The above attenuation concepts have been demonstrated using
simulation model results. A similar demonstration using
physical hardware would have required more cost and time.
Hardware testing in low frequency range could be used as a final
verification tool
NVH Workshop

• Introduction
• Mid Frequency Basics Greg Goetchius
• Closing Remarks
NVH Workshop

• Introduction
• Mid Frequency Basics
Alan Duncan
• Closing Remarks

NVH Workshop

Mid Frequency NVH Fundamentals

RECEIVER

PATH

SOURCE
This looks familiar!
Frequency Range of Interest has changed to
150 Hz to 500 Hz
NVH Workshop

Typical NVH Pathways to the Passenger
Noise Paths are the
Noise Paths are the
same as Low
same as Low
Frequency Region
Frequency Region

PATHS
FOR
STRUCTURE
BORNE
NVH

NVH Workshop

Mid-Frequency Analysis Character
Structure Borne Noise
Airborne Noise

• Mode separation is less practical in
• Mode separation is less practical in
High modal density mid-frequency
mid-frequency
and coupling in
source, path and
• New Strategy is Effective Isolation:
• New Strategy is Effective Isolation:
receiver
Achieved by reducing energy transfer
Achieved by reducing energy transfer
locally between source and receiver at
locally between source and receiver at
key paths.
key paths.
Response

Absorption
+
Local Stiffness Mass
+ +
Damping Sealing
Global Stiffness
“High”
“Low” “Mid”
Log Frequency
~ 150 Hz ~ 1000 Hz ~ 10,000 Hz

NVH Workshop

• Important characteristics of mid frequency analysis

Effective Isolation

&

Identifying Key Noise Paths

NVH Workshop



Effective Isolation

&


NVH Workshop

Isolation Effectiveness
Classical SDOF: Rigid
Source and Receiver
“Real Structure”
Flexible (Mobile)
1.0 Source and
Receiver

Isolation Region f/fn
Isolation Region

1.0 1.414 10.0
Effectiveness deviates from the classical development as resonances
occur in the receiver structure and in the foundation of the source.

NVH Workshop

Mobility
• Mobility is the ratio of velocity response at the excitation point on structure
where point force is applied

Velocity
Mobility =
Force

• Mobility, related to Admittance, characterizes Dynamic Stiffness of
the structure at load application point

Frequency * Displacement
Mobility =
Force

Frequency
=
Dynamic Stiffness

NVH Workshop

Isolation
• The isolation effectiveness can be quantified by a theoretical model based on
2003, 2005 ERRATA
analysis of mobilities of receiver, isolator and source

• Transmissibility ratio is used to objectively define measure of isolation
Force from source without isolator
TR =
Force from source with isolator

V Receiver Vr
V Receiver Vr
Fr
V
Fr =
Fs
Yi + Y r + Y s F ir
V ir
Fs
Isolator
Vs V is
Source
F is
V
Fs
F s=
Vs
Yr +Ys
Source

NVH Workshop

Isolation
• The isolation effectiveness can be quantified by a theoretical model based on
analysis of mobilities of receiver, isolator and source

• Transmissibility ratio is used to objectively define measure of isolation
Force from source with isolator
TR =
Force from source without isolator

V Receiver Vr
V Receiver Vr
Fr
V
Fr =
Fs
Yi + Y r + Y s F ir
V ir
Fs
Isolator
Vs V is
Source
F is
V
Fs
F s=
Vs
Yr +Ys
Source

NVH Workshop

Isolation
Receiver
Force from source with an isolator Vm
TR =
Force from source without an isolator
Fm
F im
TR = ⏐ ( Y r + Y s ) / ( Y i + Y r + Y s ) ⏐ V im
Isolator V if
Y r : Receiver mobility
F if
Y i : Isolator mobility
Y s : Source mobility Ff
Vf
Source

• For Effective Isolation (Low TR) the Isolator
Mobility must exceed the sum of the Source and
Receiver Mobilities.
NVH Workshop

Identifying Key NVH Paths
Key NVH paths are identified by Transfer Path Analysis (TPA)

Tactile Acoustic
Tactile Acoustic
Transfer Transfer
Transfer Transfer

Fi Break the system at the
points where the forces
enter the body (Receiver)

Operating loads Operating loads

• TPA is a technique to perform phased summation of partial responses
through all NVH paths to give total tactile or acoustic response under
operating loads at a given frequency

• TPA is applicable in both testing and simulation scenarios to identify key
paths

NVH Workshop

Noise Path Analysis
Acoustic Transfer (P/F)i

Fi Operating loads create
Forces (Fi) into body at
All noise paths

• Total Acoustic Response is summation of partial responses
over all noise paths
Pt = Σ paths [Pi ] = Σ paths [ (P/F) i * Fi ]

Pi : Partial contribution of path i due to operating force
(P/F) i : Acoustic Transfer Function of the ith Path

NVH Workshop

Transfer Path Analysis
• TPA allows path rankings based on contribution to
total response of noise paths at a given frequency

• TPA thus helps identify key noise paths
• TPA is mainly used for acoustic response in mid
frequency range
Total
( contributors + )
Front
Noise
Front
Upper Shock
Control Absorber Rear

( )
Rear
Arm Shock All
Upper
… Absorber Arm
Paths

( reducers - )
Front Front
Stabilizer Spring
NVH Workshop

Designing for Mid Frequency

Effective Isolation

&


NVH Workshop


When designing a new vehicle, the first phase is to
satisfy generic targets for key parameters along all
noise paths in order to achieve effective isolation.

What are these generic targets and
What are these generic targets and
key parameters ?
key parameters ?

NVH Workshop

Generic Noise Path Targets
P/V
P/F
V/F
(Kbody)

F
ΔX
KBsng

Ksource


Transmissibility along a given noise path (TRi)
TR = ⏐ ( Y r + Y s ) / ( Y i + Y r + Y s ) ⏐
1 1
1 1 1
TR = ⏐ ( ) /( )⏐
+ + +
K source K body K iso. K source
K body

NVH Workshop

1 1
1 1 1
TR = ⏐ ( ) /( )⏐
+ + +
K body K source K body K iso. K source
K source
K body K iso
1.0 5.0 Infinite
K iso

1.0 0.67 0.54 0.50

5.0 0.54 0.28 0.17

Infinite 0.50 0.17 0.00

As a generic target, body to bushing stiffness ratio
of at least 5.0 and very high source to bushing
stiffness ratio (~ infinite) is desired to achieve
“good” TR of 0.17
NVH Workshop

Relationship of Body-to-Bushing Stiffness
Ratio to Transmissibility
Series2
For an infinite source
TR = ⏐ ( K bsg ) / ( K bsg + K body ) ⏐
0.50.5

0.40.4
0.30.3 Target Min. = 5
gives TR = .17
0.20.2
0.10.1
00.01 2 3 4 5 6 7 8 9 10
1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10
Stiffness Ratio; K body / K bsg
K body.
K bsg
NVH Workshop


Fi Operating loads create
Forces (Fi) into body at
All noise paths


Pt = Σ paths [Pi ] = Σ paths [ Fi * (P/F) i ]
= Σ paths [ Fi * (P/V) i * (V/F)i]

(P/F) Acoustic Sensitivity
(V/F) Structural Point Mobility (Receiver)
NVH Workshop

For example, for Acoustic Response Pt

= Σ paths [ Fi * (P/V) i * (V/F)i]

• For a given force generated at a source attachment to
body, lowering sensitivities (P/F) or (V/F) along a path
would reduce total response

• Typical generic targets,

- Acoustic Sensitivity (P/F) in 50 - 60 dBL/N range

- Structural Mobility (V/F) less than 0.2 - 0.3 mm/sec/N
NVH Workshop

K body K source
>= 5.0 ~ infinite
K iso K iso

Acoustic 50 - 60
<
Sensitivity dBL/N

Structural
< .2 to .3 mm/sec/N
Mobility

How does one achieve these generic targets ?
NVH Workshop

How does one achieve

K body Structural
< .2 - .3
>= 5.0
Mobility
K iso

• Increase local body attachment stiffness (Kbody)
through structural modifications

• Reduce attachment isolator stiffness (Kiso) while
balancing the conflicting requirement of other
functionalities such as Ride & Handling

NVH Workshop

K source
~ infinite
K iso

• Increase source side attachment stiffness (Ksource)

• Reduce attachment isolator stiffness (Kiso)

In Automotive Structures, it is realistic to expect
that the Source to isolator stiffness ratio is high
since Source usually corresponds to a stiff
structure (such as powertrain or axle).
NVH Workshop

Acoustic 50 - 60
<
Sensitivity dBL/N

• At a given frequency, Acoustic Sensitivity (P/F) is

Frequency
P/F = (P/V) X
Body stiffness

• Based on the above equation, increasing body
stiffness usually reduces Acoustic Sensitivity.

NVH Workshop

How does one achieve: Acoustic 50 - 60
<
Sensitivity dBL/N

• There are situations when increasing body
stiffness does not reduce Acoustic Sensitivity

• In such cases, the Acoustic Sensitivity can be
reduced by reducing the overall body panel velocity
through application of damping treatments

NVH Workshop

Application of Damping Treatment
Effect on sound response of damping treatment
applied on key identified contributing panels

5.0 dBA

12.5dBA
Reduction
SPL (dBA)

Floor with
damping
treatment

Floor without
damping treatment

Frequency (Hz)

NVH Workshop


While designing a new vehicle, generic targets are
set for key parameters along all noise paths in
order to achieve effective isolation.

Is it really necessary to achieve generic targets for
Is it really necessary to achieve generic targets for
all noise paths ?
all noise paths ?

Probably Not !!
Probably Not !!

NVH Workshop

Driver’s Ear Noise Improved Noise
Original Noise Path
Path Contributions
Contributions

Transfer
Path
Analysis

Vehicle Level Response Some noise paths are Impose more strict
more dominant than requirements for these
others dominant paths and
relax requirements for
Driver’s Ear Noise
other paths to achieve
Reduced Noise
more “rebalanced”
Original Noise
noise

Vehicle Response to Meet NVH Targets

NVH Workshop

Mid Frequency NVH Goal Achievement Process
Initial Sub-System Targets

Rebalance
Trade-Off
Evaluate Sub-System
Performance

Re-Design Yes
or
Sub-System
Time Out
Meet
Sub-System Evaluate Vehicle Goals
Goals?
No

Yes
Meet
or
Vehicle
Time Out
Goals?
No
NVH Workshop

Principles to follow

• At the beginning of program, work towards generic
targets for all noise paths in order to achieve effective
isolation.

• As the design is firmed out, shift focus to key
contributing noise paths using Transfer Path Analysis in
order to meet target for all NVH operating load conditions.

• Perform path “rebalancing” to arrive at revised path
targets if Sub-System goal achievement is not possible
due to architectural constraints.

NVH Workshop

Mid Frequency NVH Improvement
(Sports Utility Vehicle Example)

Full Vehicle Model
Full Vehicle Model

NVH Workshop


Powertrain/Axle/Suspension Model
Powertrain/Axle/Suspension Model
NVH Workshop


Acoustic Cavity Model
Acoustic Cavity Model
NVH Workshop

Mid-Frequency NVH improvement
Axle Whine Example : 300-500 Hz
Front and Rear Axle
Gear-Pinion Mesh Trimmed Body
Transmission Error

θ
Chassis

θ

Interior Acoustic Cavity

SOURCE ------------- PATH ---------------- RECEIVER
NVH Workshop

Axle Whine Example
• Design work was focused in the beginning towards achieving
generic targets for all noise paths
• As the design was firmed out, full vehicle analysis revealed
under target performance for Driver’s ear SPL response
which was dominated by rear excitation
FR + RR Excitation

Target Level
SPL(dBA)

RR Excitation Only
(Dominates Total Content)

FR Excitation Only

10dBA

Sound Response with Varying Excitation

Frequency (Hz)
300 Hz 500 Hz
400 Hz
NVH Workshop

Axle Whine Example
• Before embarking on identifying the root cause for
under-target performance at dominant noise paths, it is a
good practice to perform a reasonableness check on the
response.
• Steps for Reasonableness Determination:
Judging the response based on System Knowledge
• Total response content is dominated by rear excitation. This is
reasonable since vehicle has IFS and solid axle rear suspension
which is harder to isolate for noise

Forced Mode Animation
• Operating deformed shape motion is rear axle pitching about ring
gear axis. This was expected since input excitation is MTE imposed
as enforced angular rotation between ring and pinion gear

Disconnect Studies
• Disconnecting rear suspension noise paths (shock in particular) had
the most significant effect on Driver’s SPL response
NVH Workshop

Axle Whine Example
• Transfer Path Analysis

• Dominant Paths
• Rear left shock vertical
• Rear LCA vertical : Left is positive whereas right is negative contributor
• Rear Right shock vertical

• The conclusion matches with reasonableness checks
NVH Workshop

Axle Whine Example
• Is it high forces or high acoustic sensitivity at shock to
body attachment ?
Acoustic Sensitivity (dBL/N)

5dBL/N

Acoustic sensitivity was
Acoustic sensitivity was
better than generic target
better than generic target

• The issue is with high forces into the body through shock
attachment due to stiff shock bushings
• Stiff shock bushings gave low body-to-bushing stiffness
ratio
NVH Workshop

Axle Whine Example
Solution
• Soften shock vertical bushings by 65%

• To balance this against Ride and
Handling requirement of stiff bushing,
local attachment stiffness between
shock and body was improved
through a new bracket design

• This addition of bracket improved
right shock mobility 3 times
whereas
left shock mobility by 1.5 times
thereby improving isolation
effectivenessDaimlerChrysler Corporation]
of shock bushing
[Figure Courtesy of
NVH Workshop

Axle Whine Example
Response Improvement due to proposed solution

NVH Workshop

Axle Whine Example
How Robust is the proposed solution ?
• Parameter variations such as weld deletion in “new
bracket” and gage changes were considered to study
robustness of solution
Deterministic Response
Baseline Model
of Baseline Model
10 dBA
Scatter
- Response scatter of model
with proposal does not
overlap baseline model Driver’s Ear SPL (dBA)

response scatter indicating
a robust solution

Deterministic Response
- The problem peak has now of Model with proposal
Scatter of model
shifted to a new vehicle
With proposals
speed of 50.7 mph which
requires a new contribution
analysis 54.4
53.2
48.2 49.5 50.7 51.9
Vehicle Speed (mph)
NVH Workshop

Final Remarks on Mid Frequency Analysis
• Effective isolation at dominant noise paths is critical

• Reduced mobilities at body & source and softened
bushing are key for effective isolation

• Other means of dealing high levels of source input
(Tuned dampers, damping treatments, isolator
placement at nodal locations) are also effective

• It is important to balance NVH requirements against
other functionalities (Ride and Handling, Impact)

• It is important to understand the robustness of
design recommendations
NVH Workshop

Utilizing NVH Simulation Models
Considerations
• Some Agreement: Math Models can be used as Trend Predictors.
(but not for absolute levels, yet.)

• Q. How do I know my model is good?
• ANS. We require correlation work to know the simulation compares
to test values to some degree.

• Q. How do I make design decisions before hardware is available?
• ANS. Correlation must be performed on existing hardware to
establish modeling methods and correlation criteria to be applied to
the future design.
(The Reference Baseline Ref. 3)
A model of the new design is built with the same Methodology as the
Reference Baseline to predict the change in performance as the
design process progresses but before prototypes are available.

NVH Workshop

Utilizing NVH Simulation Models

Considerations
• Q. How do I compare my model to test measurement and how close
does it have to be to assure it can be used as a trend predictor?
• ANS. If model predictions were within the band of variability of the
test measurement, for a statistically significant number of samples,
this would increase confidence in the predictive capability.

• Q. How wide is the band of variability?
• ANS. Let’s EXPLORE it !!!!

NVH Workshop

Discussion of Product Variability

Topics

• Kompella and Bernhard Observations

• Freyman NVH Scatter Results

• Model Confidence Criteria

• Conclusions

NVH Workshop

Magnitude of 99 Structure – borne FRF’s for the
Rodeo’s for the driver microphone
( Ref. 8 ) ©1993 Society of Automotive Engineers, Inc.
Mag. of FRF

Frequency ( Hz )

NVH Workshop

Acoustic scatter numerically determined in the vibro – acoustic behavior of a vehicle
due to possible tolerances in the component area and in the production process

Sound Pressure [ dB( lin )]

Frequency ( Hz )
Phase [o]

Frequency ( Hz )
( Ref. 9 ) ©2000 Society of Automotive Engineers, Inc.
NVH Workshop

Reference Baseline Confidence Criterion
For Operating Response Simulations

Test Variation Band
10. dB; 50-150 Hz
20. dB; 150-500 Hz
FUDGE
REF. 8
FACTORS

Simulation Prediction

Confidence Criterion:
Simulation result must
Test Upper Bound fall within the band of
Test Band Average test variation.
Test Lower Bound

NVH Workshop

Axle Whine Example
• Design work was focused in the beginning towards
achieving generic targets for all noise paths
• As the design was firmed out, full vehicle analysis revealed
under target performance for Driver’s ear SPL response
which was dominated by rear excitation
FR + RR Excitation

Target Level
SPL(dBA)

RR Excitation Only
(Dominates Total Content)

FR Excitation Only

10dBA

Sound Response with Varying Excitation

Frequency (Hz)
300 Hz 500 Hz
400 Hz
NVH Workshop

Conclusions:
Significant Product Variation exists even in best-in-class vehicles.

Correlation should be considered as being within the band of variability
whether test or simulation.

The Confidence Criteria, for operating responses, is a relatively challenging
condition to meet when considering the following:

It uses the same bandwidth as Kompella (Ref. 8), determined from simple
FRF’s, while the criteria is for operating responses which are subject to
additional variation in the operating loads.
It assumes that one test will generate the mean response level in the
band subject to the condition that a “qualified” median performer will be
tested. This requires a test engineer extremely experienced with the
vehicle line in order to “qualify” the vehicle.

Best hope for reduced product development times is a coordinated effort of
Virtual Vehicle Simulation and Reference Baseline and Physical
Prototype Testing to grasp the complexities of NVH responses and the
robustness of their sensitivity to variation.

NVH Workshop

The Fundamental Secret of Structure
Borne NVH Performance
To Minimize Structure Borne NVH, connect
between Source and Receiver Sub-Systems at
Locations where the Motion is at a Minimum.

Meets Conditions of the Attenuations Strategies
• Minimize the Source Load
• Manage Mode Placement
• Mount at Nodal Points
• Provide Dynamic Absorber
•Reduce Source - Receiver Mobility
NVH Workshop


Ist Corollary
First Best Principle for NVH
Improvement is Minimization /
Understanding of the Source Excitation.

2nd Corollary
Effectively Isolate the remaining source
from the receivers at Key paths

NVH Workshop

That’s All Folks !
Meets Conditions of the Attending the
Thank You for Attenuations Strategies
2007 Structure Borne NVH Workshop
• Minimize the Source Load
Your Presenters today were:
• Manage Mode Placement
Alan Duncan, Material Sciences Corp.
Greg Goetchius, Material
• Mount at Nodal PointsSciences Corp.
• Provide Dynamic Absorber
Sachin Gogate, DaimlerChrysler Corp.
Visit: www.AutoAnalytics.com/papers.html (or www.sae.org)
•Reduce the 2007 Structure Borne NVH Mobility
Source - Receiver Workshop
to download
NVH Workshop

2007 SAE Structure Borne NVH Workshop

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2007 SAE Structure Borne NVH Workshop