Structure borne nvh basics

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

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 ofStructure Borne

NVH Performance

The Fundamental Secret ofStructure Borne

NVH Performance

Revealed here today !

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

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

NVH Workshop

NVH Workshop Topic Outline Introduction

Fundamentals in NVH

Automotive NVH Load Conditions

Low Frequency Basics

NVH Workshop

Rideand

Handling

NVH Durability

ImpactCrashWorthiness

Competing Vehicle Design Disciplines

NVH Workshop


Fundamentals in NVH

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)

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

NVH Workshop


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

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)

NVH Workshop


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

Mathematically Speaking .

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

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

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

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

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

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

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

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

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

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

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.

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

NVH Workshop

NVH Workshop Outline Introduction

Fundamentals in NVH

NVH Load Conditions


NVH Workshop

Two Main Sources

Noise and Vibration Sources

Suspension Powertrain

NVH Workshop

Typical NVH Pathways to the Passenger

PATHS FOR

STRUCTURE BORNE

NVH

NVH Workshop

Powertrain Induced

NVH Workshop


Fundamentals in NVH

NVH Load Conditions


NVH Workshop

RECEIVER

PATH

SOURCE

Low Frequency NVH Fundamentals

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

1 2 4 5

6 7

8

3

TiresWheels

SuspensionSprings

Engine Mass

EngineIsolator

Flexible Beam for Body

NVH Workshop



Provide Isolation

Mode Management


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



Provide Improved Isolation

Mode Management


Dynamic Absorbers

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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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

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

NVH Workshop

8 Degree of Freedom Vehicle NVH ModelRemoved Double Isolation Effect

1 2 4 5

6 7

8

3

WheelMass

Removed

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

NVH Workshop



Provide Isolation

Mode Management


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

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

Documents

Structure borne nvh basics