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
The Fundamental
Fundamental Secret
Secret of
of
Structure
Structure Borne
Borne
NVH
NVH Performance
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
NVH Workshop Topic Outline
Introduction
Fundamentals in NVH
Automotive NVH Load Conditions
Low Frequency Basics
NVH Workshop
Competing Vehicle Design Disciplines
Ride
and
Handling
NVH
Impact
CrashWorthiness
Durability
NVH Workshop
NVH Workshop Topic Outline
Introduction
Fundamentals in NVH
NVH Load Conditions
Low Frequency Basics
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
Acoustic
Acoustic
Tactile
Tactile
Tactile
Tactile
Operating
loads
Operating loads
Tactile or Acoustic Response
Time and Frequency Relation
Time (Sec)
Operating 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
Time and Frequency Relation
Conversion to frequency domain lends to formulation of
principles for addressing structure borne NVH
Frequency (Hz)
Amplitude
40 Hz
(Colum
n
Mode)
15 Hz
(Suspe
nsion
Mode)
Overall Response, X(t)
Ph
as
ed
X(f)
Su
m
m
at
io
n
25 H
(Vehicle z
Flexible
Body M
o d e)
5 Hz
(Vehicle
Rigid
Body M
o d e)
Time (Sec)
Time
NVH Workshop
Time and Frequency Relation
Mathematically Speaking .
X ( f ) = Fourier Transform of X ( t )
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
Test World
F(t)
X ( t ) Fourier X ( f )
Vehicle System
Transform
Fourier
Transform
F(f)
Vehicle System
X(f)
Common in Simulation World
NVH Workshop
NVH Model of Unibody Passenger Car
Symbolic Outline
8
1
2178.2 Kg
1996.7 Kg
181.5 Kg
181.5 Kg
From Reference 6
Total
Mass Sprung
Unsprung
Powertrain
(4800LBS)
(8.33% of Total)
Tires
350.3 N/mm
KF
43.8
N/mm
KR
63.1
N /mm
Beam mass lumped on
grids like a beam
M2,3,4 =2 * M1,5
NVH Workshop
Excitation Bum p Profile
Profile Height (m m )
20.0
Profile
15.0
10.0
5.0
0.0
0
100
200
300
400 On to 100,380
500
Distance (mm)
NVH Workshop
Pitch at Mid-Car DOF3
1.0E-04
R o ta tio n - R a d ia n s
8.0E-05
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
Time (sec.)
NVH Workshop
Pitch Response - Baseline Model
1.E-04
R o tat io n R a d ian s
Base Model
1.E-05
1.E-06
1.E-07
1.E-08
0.0
5.0
10.0
Frequency Hz
15.0
20.0
NVH Workshop
Transform Input Force to F(f)
FFT of the Input Bump
1.E-01
Bump FFT
Amplitude mm
1.E-02
1.E-03
1.E-04
20 Hz Amplitude
@ 45 MPH
is Approximately
Constant over the
Frequency Range
1.E-05
1.E-06
0.E+00
4.E-03
1.E-02 Displacement
2.E-02
2.E-02
Constant
8.E-03
Cycles / mm
0.0
20.0 Hz
NVH Workshop
P itc h a t M id -C a r D O F 3
RotationRadians
1 .0 E-0 4
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
10
F re q u e n c y
Hz
15
20
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 f t
TR = FT / F
1 + ( 2 d fn ) 2
f
2
( 1- f 2 ) 2 + ( 2 d f ) 2
fn
Transmitted
Force
FT
d = fraction of critical damping
fn = natural frequency (k/m)
f = operating frequency
NVH Workshop
Vibration Isolation Principle
4
Transmissibility Ratio
0.1
APPLIED FORCE
0.15
F = FO sin 2 f t
TR = FT / F
0.25
2
0.375
FT
Transmitted
Force
0.5
1.0
1
Isolation
Isolation Region
Region
0
0
1.414
Frequency Ratio (f / fn)
5
NVH Workshop
Isolation from an Applied Force
Excitation Force Coming
from Engine
F0
Transmissibility
Force Ratio is FT/F0
FT
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.
Support Forces
Transmitted to Body
NVH Workshop
Automotive NVH Frequency Range
Structure Borne Noise
Response
Airborne Noise
Global Stiffness
Local Stiffness
+
Damping
Absorption
+
Mass
+
Sealing
Low
Mid
High
~ 150 Hz
~ 1000 Hz
~ 10,000 Hz
Log Frequency
NVH Workshop
NVH Workshop Outline
Introduction
Fundamentals in NVH
NVH Load Conditions
Low Frequency Basics
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
NVH Workshop Topic Outline
Introduction
Fundamentals in NVH
NVH Load Conditions
Low Frequency Basics
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
Engine
Isolator
1
Flexible Beam for Body
2
Suspension
Springs
6
Wheels
Tires
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
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
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
NVH Workshop
8 Degree of Freedom Vehicle NVH Model
Force Applied to Powertrain Assembly
Feng
8
Forces at Powertrain could represent a First Order
Rotating Imbalance
NVH Workshop
Engine Isolation Example
Response at M id Car
1.0000
Constant Force Load;
15.9 Hz
F~A
Velocity (mm/sec)
8.5 Hz
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
8 Degree of Freedom Vehicle NVH Model
Removed Double Isolation Effect
8
Wheel
Mass
Removed
NVH Workshop
Double Isolation Example
Vertical Response at DOF3
6.0E+00
Velocity
(mm/sec)
Base Model
5.0E+00
Without Double_ISO
4.0E+00
3.0E+00
1.414*fn
2.0E+00
1.0E+00
0.0E+00
5.0
10.0
15.0
20.0
Frequency Hz
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
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
8
18.2 Hz
Baseline Suspension 10.6 Hz
Flexible Beam for Body
1
Suspension
Springs
6
Wheels
Tires
NVH Workshop
