1 Design For NVH MPD575 DFX Jonathan Weaver 2 Development History Originally developed by Cohort 1...

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Design For NVH

MPD575 DFX

Jonathan Weaver

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Development History

• Originally developed by Cohort 1 students: Jeff Dumler, Dave McCreadie, David Tao

• Revised by Cohort 1 students: T. Bertcher, L. Brod, P. Lee, M. Wehr

• Revised by Cohort 2 students: D. Gaines, E. Donabedian, R. Hall, E. Sheppard, J. Randazzo

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Design For NVH (DFNVH) • Introduction to NVH• DFNVH Heuristics• DFNVH Process Flow and Target Cascade• DFNVH Design Process Fundamentals• Key DFNVH Principles

– Airborne NVH• Radiated/Shell Noise• Tube Inlet/Outlet Noise• Impactive Noise• Air Impingement Noise

– Structure-Borne NVH• Wind Noise Example• 2002 Mercury Mountaineer Case Study• Summary

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Introduction to NVH What is NVH?

•Movement is vibration, and vibration that reaches the

passenger compartment in the right frequencies is noise.

•The science of managing vibration frequencies in automobile design is called NVH - Noise, Vibration, and Harshness.

•It is relatively easy to reduce noise and vibration by adding weight, but in an era when fuel economy demands are forcing designers to lighten the car, NVH engineers must try to make the same parts stiffer, quieter, and lighter.

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Noise:

•Typically denotes unwanted sound, hence treatments are normally to eliminate or reduce

•Variations are detected by ear

•Characterized by frequency, level & quality

•May be Undesirable (Airborne)

•May be Desirable (Powerful Sounding Engine)

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Vibration– An oscillating motion about a reference point

which occurs at some frequency or set of frequencies

• Motion sensed by the body (structureborne)– mainly in 0.5 Hz - 50 Hz range

• Characterized by frequency, level and direction• Customer Sensitivity Locations are steering column, seat

track, toe board, and mirrors (visible vibrations)

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• Harshness– Low-frequency (25 -100 Hz) vibration of the

vehicle structure and/or components– Frequency range overlaps with vibration but

human perception is different.• Perceived tactilely and/or audibly• Rough, grating or discordant sensation

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Introduction to NVH What is NVH

Airborne Noise:

•Kind of sound most people think of as noise, and travels through gaseous mediums like air.

•Some people classify human voice as airborne noise, but a better example is the hum of your computer, or air conditioner.

•Detected by the human ear, and most likely impossible to detect with the sense of touch.

•Treatment / Countermeasures: Barriers or Absorbers

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Structureborne: • Vibration that you predominately “feel”, like the deep

booming bass sound from the car radio next to you at a stoplight.

• These are typically low frequency vibrations that your ear may be able to hear, but you primarily “feel”

• Treatment / Countermeasure: Damping or Isolation

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Barriers:

•Performs a blocking function to the path of the airborne noise. Examples: A closed door, backing on automotive carpet.

•Barrier performance is strongly correlated to the openings or air gaps that exist after the barrier is employed. A partially open door is less effective barrier than a totally closed door.

•Barrier performance is dependent on frequency, and is best used to treat high frequencies.

•If no gaps exist when the barrier is employed, then weight becomes the dominant factor in comparing barriers.

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Barriers: Design Parameters • Location (close to source)• Material (cost/weight)• Mass per Unit Area• Number and Thickness of Layers• Number and Size of Holes

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Absorbers:

•Reduces sound by absorbing the energy of the sound waves, and dissipating it as heat. Examples: headliner, and hood insulator.

•Typically, absorbers are ranked by the ability to absorb sound that otherwise would be reflected off its surface.

•Good absorber designs contain complex geometries that trap sound waves, and prevent reflection back into the air.

•Absorber performance varies with frequency.

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Absorbers: Design Parameters

•Area of absorbing material (large as possible)

•Type of material (cost/weight)

•Thickness (package/installation)

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Damping:

•Defined as a treatment of vibration to reduce the magnitude of targeted vibrations

•Damping is important because it decreases the sensitivity of the body at resonant frequencies

•Vehicle Sources of Damping are: Mastics, sound deadening materials, weather-strips/seals, tuned dampers, and body/engine mounts

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Damping: Design Parameters•Density (low as possible)

•Stiffness (high as possible)

•Thickness (damping increases with the square of thickness)

•Free surface versus constrained layer

Constrained layer damping is more efficient than free surface damping on a weight and package basis, but is expensive, and raises assembly

issues.

Note: Temperature range of interest is very important because stiffness and damping properties are very temperature sensitive

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Isolation:

•Method of detaching or separating the vibration from another system or body.

•By definition: does nothing to reduce the magnitude of vibration, simply uncouples the vibration from the system you are protecting.

•All isolation materials perform differently at different frequencies, and if engineered incorrectly, may make NVH problems worse instead of better.

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Isolation by Bushings and Mounts:

• Excitations are generally applied to components such as engine or road wheels.

• The force to the body is the product of the mount stiffness and the mount deflection, therefore strongly dependent on the mount spring rates

•Compliant (softer) mounts are usually desirable for NVH and ride, but are undesirable for handling, durability and packaging (more travel/displacement space required).

• Typically, the isolation rates (body mount/engine mount stiffness) that are finally selected, is a result of the reconciliation (trade-off) of many factors.

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Introduction to NVHWhy Design for NVH?

“NVH is overwhelmingly important to customers. You never, ever get lucky with NVH. The difference between good cars and great cars is fanatical attention to detail.”

Richard Parry-Jones, 11/99

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• NVH impacts Customer Satisfaction

• NVH impacts Warranty

• NVH has financial impact

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SUSTAIN / BUILD

65% 85%5

9

RelativeLeverage

IMPROVE

REVIEW MAINTAIN

Overall Handling

Cup holdersExterior Styling

* *

NVH

6.9

77%

Corporate Leverage vs. Customer SatisfactionNVH Customer Satisfaction Needs Improvement at 3 MIS

*

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NVH Can Both Dissatisfy and Delight

+ Performance

+ CustomerSatisfaction

- Performance

Dissatisfiers

Harley Mustang

Lexus Loudness

Unusual NoisesTGW

Sound QualityTGR

KANO Model

+ Degree of Achievement

Basic QualityBasic Quality((InhibitorsInhibitors))

Performance QualityPerformance Quality((AttributesAttributes))

- CustomerSatisfaction

Exciting QualityExciting Quality((Surprise & DelightSurprise & Delight))

Axle Whine Wind Noise

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• Customers place a high value on NVH performance in vehicles

• About 1/3 of all Product / Quality Complaints are NVH-related

Summary of Customer Importance

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• About 1/5 of all Warranty costs are NVH-related– Dealer may spend many hours to determine

source of NVH problem– Dealer may have to repair or rebuild parts that

have not lost function but have become source of NVH issue.

• NVH can provide both dissatisfaction and delight

Summary of Customer Importance (continued)

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Design For NVH Heuristics

• Design the structure with good "bones"– If the NVH problem is inherent to the architecture,

it will be very difficult to tune it out.

• To remain competitive, determine and control the keys to the architecture from the very beginning.– Set aggressive NVH targets, select the best

possible architecture from the beginning, and stick with it (additional upfront NVH resources are valuable investments that will return a high yield)

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• Cost rules– Once the architecture is selected, it will be

very costly to re-select another architecture. Therefore, any bad design will stay for a long time


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• Don't confuse the functioning of the parts for the functioning of the system (Jerry Olivieri, 1992).– We need to follow Systems Engineering principles

to design for NVH. Customers will see functions from the system, but sound designs requires our ability to develop requirements of the parts by cascading functional requirements from the system


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• During the early stages of a vehicle program, many design trade-offs must be made quickly without detailed information.

• For example, on the basis of economics and timing,

power plants (engines) which are known to be noisy are chosen. The program should realize that extra weight and cost will be required in the sound package. (Historical Data)

• If a convertible is to be offered, it should be realized that a number of measures must be taken to stiffen the body in torsion, and most likely will include stiffening the rockers. (Program Assumptions)

DFNVH Process Flow and Target Cascade

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Noise Reduction Strategy: Targets are even set for the noise reduction capability of the sound package.

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Systems Engineering “V” and PD Process Timing

& Iterate

Define Req’s

Cascade Targets

Optimize

Verify & Optimize

ConfirmVehicle (VDS - P/T NVH etc)

System (SDS - Force, Sensitivity,......)

Subsystem (stiffness, ....)

Components CDS

Wants/Needs CustomerSatisfaction

SI PA CPPRSCKO

Customer

J1

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Trade-Off Loop

Perform Iterations Until Assumptions Comparable

System/Sub-System Assumptions

McPherson vs. SLA, etc.

Requires Hardware Parametric Model

Vehicle Assumptions Fixed

SLA or McPherson Strut Suspension

Vehicle Level Target Ranges

Subjective (1-10) and Objective

Program Specific Wants

PALS (QFD, VOC, etc.)

Functional Images for Segment - R202

Preliminary Target Ranges

Future Functional Attribute Targets

Objective Target Ranges - VDS

Affordable Business Structure (ABS)

SISystem & Sub-System

Targets

Force or P/F Targets Determined with Parametric Models

Component End Item Targets

Component Resonant Frequencies, etc.

Design Optimization

CAE Optimization

Hardware Development

PA

Trade-Offs Flow ChartTrade-Offs Flow Chart

Is Gross Architecture Feasible? Development


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NVH Functional Attribute

Sub -Attributes

Road P/TWind Brake Comp. S.Q. S&R Pass-by Noise (Reg.)

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Convert attribute target strategy to objective targetsPOWERTRAIN

NVH

IDLE NVHACCELERATION

NVHCRUISE NVH

DECELERATION NVH

STEERING NVH

AUTOMATIC TRANS. SHIFT

NVH

TIP-IN / TIP OUT NVH

TAKE-OFF DRIVEAWAY

NVH

ENGINE START UP / SHUT OFF

NVH

TRANSIENTS NVH

ACCELERATION WOT

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CUSTOMER PERCEIVED P/T NVH

AIRBORNE NOISE STRUCTURE-BORNE NOISE

P/T RADIATED NOISE

AIRBORNE NOISE REDUCTION

BODY ACOUSTIC SENSITIVTY

MOUNT FORCES

P/T VIBRATIONMOUNT

DYNAMIC STIFFNESS

Acceleration NVH Target Cascade

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NVH Classification Parameters •Operating Condition (idle, acceleration, cruise on a rough road, braking…)

•Phenomenon (boom, shake, noise…) this is strongly affected by the frequency of the noise and vibration.

•Source (powertrain, road, wind ..etc)

•Classifying NVH problems provides a guidance for design, for example, low frequency problems such as shake, historically, involves major structural components such as cross members and joints.

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Operating Condition NVH Concerns

Idle Shake and boom due to engine torque.

Lugging Shake and boom due to engine torque.

WOT Noise and vibration due to engine, exhaust vibration, and radiated noise.

Cruise (smooth road) Shake, roughness, and boom due to tire and powertrain imbalance and tire force variation, Wind noise, Tire Noise

Cruise (rough road) Road noise and shake

Tip-in "Moan" due to powertrain bending.

Braking Squeal due to brake stick-slip.

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•The customer’s experience of NVH problems involves two factors, 1) the vehicle operating conditions, such as braking or WOT, and 2) the very subjective responses such as boom, growl, and groan.

•It is critical that objective and subjective ratings be correlated so the customer concerns can be directly related to objective measures. This requires subjective-objective correlation studies comparing customer ratings and objective vibration measurements.

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NVH Aspect Subjective Response

Boom Low frequency sound 20 - 100 hz.

Drone Large amplitude pure tone in the region 100-200 hz

Growl Modulated low/medium frequency broad band noise 100-1000 hz

Groan Transient broadband noise with noticeable time variation and tone content, 50-250 hz

Moan A sound in the 80 to 200 Hz range, frequently consisting of one or two tones

Squeak High pitched broadband transient noise.

Whine Mid-frequency to high frequency pure tone (possibly with harmonics), 200-2000 hz

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DFNVH Process Flow and Target Cascade Summary

•Noise reduction targets should be set for important operating conditions such as WOT (wide open throttle).

•Noise reduction targets must be set for the radiated sound from the various sources.

•The sound package must be optimized for barrier transmissibility and interior absorption.

•Classifying NVH problems provides guidance for design and a means to communication among engineers.

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Design For NVH (DFNVH) • Introduction to NVH• DFNVH Heuristics• Process Flow and Target Cascade• DFNVH Design Process Fundamentals• Key DFNVH Principles



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DFNVH Process FundamentalsSource-Path-Responder

SensitivityExcitation Response

• Engine Firing Pulses• Driveshaft Imbalance• Rough Road• Tire Imbalance• Speed Bump• Gear Meshing• Body-Shape Induced

Vortices

Excitation Source Examples:

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Tendency of the path to transmit energy from the source to the responder, commonly referred to as the transfer function of the system

Sensitivity:

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DFNVH Process FundamentalsSource-Path-ResponderExample: Body Sensitivity

Tactile Point mobility (v/F)

(Structural velocity induced by force)

Acoustic Airborne (p/p)

(Airborne sound pressure induced by pressure waves)

Structureborne (p/F)(Airborne sound pressure induced by force)

F (N)

V (mm/s)

p (dB)

Force Inputat Driving Point

Vibration Velocityat Driving Point

Interior SoundPressure

STRUCTURE

p (dB)

p (dB)

Interior SoundPressure

STRUCTURE

Airborne Noise

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Body Sensitivity Demonstration

Point Mobility

Typical Point Mobility Spectrum for Compliant & Stiff Structures

Poi

nt

Mob

ilit

y (V

/F)

MoreCompliant

LessCompliant

Frequency ( f )50 140

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Subjective(customer perception)• S/W Shake (vertical)• S/W Nibble (rotational)• Seat Track (non-specific)

Objective (measurable)• S/W Shake• S/W Nibble• Seat Track (Triax) • Spindle Fore/Aft• Tie Rod Lateral

Response:


S/W = Steering Wheel

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Air

born

e P

/T N

VH

Str

uctu

re-b

orne

P/T

NV

H

Tailpipe

Intake Orifice

Engine RadiatedSound

Active EngineVibration(X, Y, Z)

Active ExhaustVibration(X, Y, Z)

Body AcousticAttenuation (dB)

Body AcousticAttenuation (dB)

MountStiffness (N/mm)

Body AcousticSensitivity

MountStiffness (N/mm)

Body AcousticSensitivity

Driver Right Ear(dBA)

Air

born

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VH

Str

uctu

re-b

orne

NV

H

Powertrain Noise Model

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Road Noise (P)

Chassis Forces to Body (F)

NPA

Body/Frame Sensitivity (P/F)

+ SuspensionForce Isolation

Tire/Wheel Forces

Suspension/Frame Modes

Suspension/Frame Design Parameters

Tire/Wheel Modes &Design Parameters

Body Modes

Body Design Parameters

Sub-structuring Modal Analysis (MA)

MATire/Road Force

Transfer Function

+

Road Profile

Road Noise Model

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Driveline Model

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DFNVH Process FundamentalsSound Quality

What is Sound Quality?

• Historically, Noise Control meant reducing sound level

• Focus was on major contributors (P/T, Road, Wind Noise)

• Sound has multiple attributes that affect customer perception• All vehicle sounds can influence customer satisfaction

(e.g., component Sound Quality)

• Noise Control no longer means simply reducing dB levels

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Why Sound Quality?

• Generally not tied to any warranty issue

• Important to Customer Satisfaction- Purchase experience (door closing)- Ownership experience (powertrain/exhaust)

• A strong indicator of vehicle craftsmanship- Brand image (powertrain)

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The Sound Quality Process

1. Measurement (recording)2. Subjective evaluation (listening studies)

• Actual or surrogate customers3. Objective analysis

• Sound quality Metrics4. Subjective/Objective correlation5. Component design for sound quality

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Binaural Acoustic “Heads” Stereo Sound Recording representing sound wave interaction w/ human torso

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Sound Quality Listening Room

Used for Customer Listening Clinics.

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Poor Sound Quality Good Sound Quality

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Quantifying Door Closing Sound Quality

1. Sound Level (Loudness)

2. Frequency Content (Sharpness)

3. Temporal Behavior

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What Makes A Good Door Closing Sound?

Good Sound Poor Sound

Quiet Loud

Low Frequency High Frequency (Solid) (Tinny, Cheap)

One Impact Rings On (Bell)

No Extraneous Noise Rattles, Chirps, etc.

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Example: Qualifying Door Closing Sound Quality

Good Bad

Level (dBa)(color)

Fre

qu

ency

(H

z)(y

-axi

s)

Time (sec.) (x-axis)

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Design for Sound Quality

Door Closing Example

Perceived Sound

Structure-borne Airborne

Seal Trans Loss

Latch Forces Str. Compliance

Inertia Spring Rates Material

Radiated Snd.

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Conclusions• Sound Quality is critical to Customer Satisfaction• Understand sound characteristics that govern

perception• Upfront implementation is the biggest challenge • Use commodity approach to component sound

quality• Generic targets, supplier awareness, bench tests


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Design For NVH (DFNVH) • Introduction to NVH• DFNVH Heuristics• Process Flow and Target Cascade• DFNVH Design Process Fundamentals• Key DFNVH Principles



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NVH Design Principles• Dynamic System NVH Model:

Source X Path = Response• Always work on sources first

– Reduce the level of ALL sources by using quiet commodities

• Path is affected by system architecture. Need to select the best architecture in the early design phase.– Engineer the paths in each application to tailor the

sound level• Only resort to tuning in the late stage of design

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NVH Design Principles

Tube Inlet/Outlet Noise

ExcitationSource, Energy

Input

StructureSensitivity

Customer

Air

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VH

Stru

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VH

Air Impingement Noise

Source Path Responder

Impactive Noise

Radiated/Shell Noise Acoustic Attenuation

Acoustic Attenuation



EnvironmentSensitivity

IsolationStiffness

IsolationDamping

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Input


Customer

Air

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VH

Stru

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VH



Impactive Noise






IsolationStiffness

IsolationDamping

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Mechanism:

• Structural surface vibration imparts mechanical energy into adjacent acoustic fluid in the form of pressure waves at same frequency content as the surface vibration. These waves propagate through the fluid medium to the listener. Examples: powertrain radiated noise, exhaust pipe/muffler radiated noise

Design principle(s):• Minimize the vibration level on the surface of the

structure

Design Principles – Airborne NVHRadiated/Shell Noise

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Design Action(s):

• Stiffen: Add ribbing, increase gauge thickness, change material to one with higher elastic modulus, add internal structural support

• Minimize surface area: Round surfaces

• Damping: Apply mastic adhesives to surface, make surfaces out of heavy rubber

• Mass loading: Add non-structural mass to reduce vibration amplitude --- (Only as a last resort)

Design Principles – Airborne NVH Radiated/Shell Noise

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Mechanism:• Pressure waves are produced in a tube filled with

moving fluid by oscillating (open/closed) orifices. These waves propagate down tube and emanate from the inlet or outlet to the listener. Examples: induction inlet noise, exhaust tailpipe noise

Design principle(s):• Reduce the resistance in the fluid flow

Design Principles – Airborne NVHTube Inlet/Outlet Airflow Noise

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Design action(s):• Make tubes as straight as possible• Include an in-line silencer element with sufficient

volume• Locate inlet/outlet as far away from customer as

possible• Design for symmetrical (equal length) branches


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V6 Intake Manifolds

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Mechanism:• Two mechanical surfaces coming into contact with each other

causes vibration in each surface, which imparts mechanical energy into adjacent acoustic fluid in the form of pressure waves at the same frequency as the surface vibration. These waves propagate through the fluid medium to the listener.- Examples: Tire impact noise, door closing sound, power door lock sound

• Pressures waves caused by air pumping in and out of voids between contacting surfaces- Examples: Tire impact noise

Design Principles – Airborne NVHImpactive Noise

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Air Pumping

Air forced in and out of voids is called “air pumping”

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Design principle(s):• Reduce the stiffness of the impacting surfaces• Increase damping of impacting surfaces

Design action(s):• Change material to one with more compliance, higher

damping• Management of modal frequencies, mode shapes of

impacting surfaces (tire tread pattern, tire cavity resonance)


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Mechanism:• When an object moves through a fluid, turbulence is

created which causes the fluid particles to impact each other. These impacts produce pressure waves in the fluid which propagate to the listener. Examples: engine cooling fan, heater blower, hair dryer

Design principle(s):• Reduce the turbulence in the fluid flow

Design Principles – Airborne NVHAir Impingement Noise

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Design action(s):• Design fan blades asymmetrically, with

circumferential ring• Optimize fan diameter, flow to achieve lowest broad

band noise• Use fan shroud to guide the incoming and outgoing

airflow

Design Principles – Airborne NVHAir Impingement Noise

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Input


Customer

Air

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VH

Stru

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VH



Impactive Noise






IsolationStiffness

IsolationDamping

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Design Principles – Airborne NVHAirborne Noise Path Treatment

Noise Reduction

EngineCompartmentAbsorption

Body & Insulator Blocking

(Panels)

Pass-Thru Sealing(Components)

InteriorAbsorption

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Design principle(s):• Absorb noise from the source• Block the source noise from coming in• Absorb the noise after it is in

Design action(s):• Surround source with absorbing materials• Minimize number and size of pass-through holes• Use High-quality seals for pass-through holes • Add layers of absorption and barrier materials in noise path• Adopt target setting/cascading strategy


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air absorption materials


• Barrier performance is controlled mainly by mass– 3 dB improvement requires

41% higher weight

• Mastic or laminated steel improves low frequency

• Soft decoupled layers (10-30 mm) absorb sound

• Pass-thru penetration seals weaker than steel

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Input


Customer

Air

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VH

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VH



Impactive Noise






IsolationStiffness

IsolationDamping

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Design principle(s):• Absorb noise at listener• Block noise at listener• Breakup of acoustic wave pattern

Design action(s):• Surround listener with absorbing materials• Ear plugs• Design the surrounding geometry to avoid standing waves• Add active noise cancellation/control devices

Design Principles – Airborne NVHAirborne Noise Responder Treatment

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Input


Customer

Air

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VH

Stru

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VH



Impactive Noise






IsolationStiffness

IsolationDamping

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• Structureborne NVH is created due to interaction between source, path,and responder.

• Frequency separation strategy for excitation forces, path resonance and structural modes needs to be planned & achieved to avoid NVH issues.

Design Principles – Structureborne NVH

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• What happens if frequencies align?

• If a structural element having a natural frequency of f is excited by a coupled source at many frequencies, including f, it will resonate, and could cause a concern depending on the path. (This is exactly like a tuning fork.)


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The steering column vibration will have an extra large peak if the steering column mode coincides with the overall bending mode.

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Design Principles – Structureborne NVHNatural frequencies of major structures need to be separated to avoid magnification.

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In addition to adopting the modal separation strategy, other principles are listed below:

• Reduce excitation sources• Increase isolation as much as possible• Reduce sensitivity of structural response.


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Input


Customer

Air

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VH

Stru

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VH



Impactive Noise






IsolationStiffness

IsolationDamping

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Mechanism:• Excitation source can be shown in the form of forces

or vibrations. They are created by the movement of mass due to mechanical, chemical, or other forms of interactions.

Design principle(s):• Reduce the level of interactions as much as possible.• Take additional actions when it is impossible to

reduce interactions.

Design Principles – Structureborne NVHExcitation Source

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Design action(s):

• Achieve high overall structural rigidity

• Minimize unbalance

• Achieve high stiffness at attachment points of the excitation objects


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A/C Compressor – Bad Example

Cantilever Effect Less Rigid

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A/C Compressor - Good Example

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Input


Customer

Air

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VH



Impactive Noise






IsolationStiffness

IsolationDamping

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Mechanism: • Path transfers mechanical energy in the form of

forces or vibration. Normally path is mathematically simulated by spring or damper.

Design principle(s):• Force or Vibration is normally controlled through

maximizing transmission loss. – In the frequency range of system resonance, controlling

damping is more effective for maximizing transmission loss. – In the frequency range outside of the system resonance,

controlling stiffness or mass is more effective for maximizing transmission loss.

Design Principles – Structureborne NVHPath - Isolation Strategy

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Design action(s):• Maximize damping in the frequency range of

system resonance by using higher damped materials, (e.g. hydraulic engine mounts). Tuned damper can also be used.

• Adjust spring rate (e.g. flexible coupler or rubber mount) to avoid getting into resonant region and maximize transmission loss

• If nothing else works or is available, use dead mass as tuning mechanism.


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Tuning and Degree of IsolationBy moving natural frequency down for this system it increased damping at 100 Hz

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Input


Customer

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VH



Impactive Noise






IsolationStiffness

IsolationDamping

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Mechanism:• Structural motion that results when input force

causes the structure to respond at its natural modes of vibration.

Design principle(s):• Reduce the amplitude of structural motions by

– controlling stiffness and mass (quantity and distribution),

– managing excitation input locations

Design Principles – Structureborne NVHStructure Sensitivity Strategy

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Design action(s):• Select architecture that can provide the maximal

structural stiffness by properly placing and connecting structure members.

• Use damping materials to absorb mechanical energy at selected frequencies.

• Distribute structural mass to alter vibration frequency or mode shape.

• Locate excitation source at nodal points of structural modes.


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How Does Architecture Influence Body NVH? Governs the way external loads are reacted to and distributed throughout the

vehicle Affects Stiffness, Mass Distribution & Modes

What Controls Body Architecture? Mechanical Package Interior Package Styling Customer Requirements Manufacturing

Fixturing Assembly Sequence Stamping Welding Material Selection


Body Modes and Body Architecture

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Body Modes and Mass Distribution

Effect of Mass Placement on Body Modes• Adding mass to the body lowers the mode frequency

• Location of the mass determines how much the mode frequency changes.

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Metrics used to quantify body structure vibration modes :

Global dynamic and static response for vertical / lateral bending and torsion

Local dynamic response (point mobility – V/F) at body interfaces with major subsystems


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Where Possible Locate Suspension & Powertrain Attachment Points to Minimize Excitation:

– Forces applied to the body should be located near nodal points.– Moments applied to the body should be located near anti-

nodes.


Guideline: Body Modes & Force Input Locations

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Conclusions:

• The body structure is highly interactive with other subsystems from both design and functional perspective. Trade-offs between NVH and other functions should be conducted as soon as possible.

• Once the basic architecture has been developed, the design alternatives to improve functions become limited.


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Wind Noise Example• Any noise discernible by the human ear

which is caused by air movement around the vehicle.

• Sources: aerodynamic turbulence, cavity resonance, and aspiration leaks.

• Paths: unsealed holes or openings and transmission through components.

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Wind Noise Target Cascade Diagram

Vehicle level Wind Noise

Excitation Sources

Antenna / Accessories

Mirror Shape

Green House Shape

Open Windows /

Sunroof

Seals

Aspiration Leaks

Transmission Loss

Glass / Panels

Static Sealing

Dynamic Sealing

Door System Stiffness

Wind Noise Example

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Wind Noise Example

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Aerodynamic excitation

• A-pillar vortex• Mirror wake• Antenna vortex• Wiper turbulence• Windshield turbulence• Leaf screen turbulence

• Exterior ornamentation turbulence

• Cavity resonances• Air flow induced panel

resonances• Air extractor noise ingress• Door seal gaps, margins

and offsets

Wind Noise Example

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Aspiration leakage

• Dynamic sealing– Closures

• Dynamic weatherstrip• Glass runs• Beltline seals• Drain holes

– Moon roof• Glass runs

– Backlite slider• Glass runs• Latch

• Static sealing– Fixed backlite– Exterior mirror seal– Air extractor seal– Moon roof– Door handle & lock– Exterior door handles– Windshield– Trim panel & watershield– Floor panel– Rocker

Wind Noise Example

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• Introduction to NVH• DFNVH Design Process Fundamentals• Key DFNVH Principles



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Design For NVH 2002 Mercury Mountaineer SUV –Case Study

•Creating a quieter and more pleasant cabin environment, as well as reducing overall noise, vibration, and harshness levels, were major drivers when developing the 2002 Mercury Mountaineer.

“The vehicle had more than 1,000 NVH targets, that fell into three main categories: road noise, wind noise, and powertrain noise. No area of the vehicle was immune from scrutiny”– Ray Nicosia, Veh. Eng. Mgr.

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Design For NVH 2002 Mercury Mountaineer SUV

The body shell is 31% stiffer than previous model, and exhibits a 61% improvement in lateral bending. Laminated steel dash panel, and magnesium cross beam were added.

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Design For NVH 2002 Mercury Mountaineer SUV

• Improved chassis rigidity via a fully boxed frame with a 350% increase in torsional stiffness and a 26% increase in vertical and lateral bending.

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Design For NVH 2002 Mercury Mountaineer

“Aachen Head” was used to improve Mountaineer’s Speech Intelligibility Rating to a 85%. A rating of 85% means passengers would hear and understand 85% of interior conversation. Industry % average for Luxury SUV is upper 70s.

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Design For NVH 2002 Mercury Mountaineer

Body sculpted for less wind resistance with glass and door edges shifted out of airflow.

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• Preventing NVH issues up front through proper design is the best approach – downstream find-and-fix is usually very expensive and ineffective

• Follow systems engineering approach – use cascade diagram to guide development target setting. Cascade objective vehicle level targets to objective system and component targets

DFNVH Summary

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• Use NVH health chart to track design status

• Always address sources first

• Avoid alignment of major modes

• Use the Source-Path-Responder approach

DFNVH Summary

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References• Ford-Intranet web site:

– http://www.nvh.ford.com/vehicle/services/training• General NVH• NVH Awareness• NVH Jumpstart• NVH Literacy• Wind Noise

• Handbook of Noise Measurement by Arnold P.G. Peterson, Ninth Edition, 1980

• Sound and Structural Vibration by Frank Fahy, Academic Press, 1998

• http://www.needs.org - Free NVH courseware

http://www.needs.org/

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References• "Body Structures Noise and Vibration Design Guidance",

Paul Geck and David Tao, Second International Conference in Vehicle Comfort, October 14-16, 1992, Bologna, Italy.

• "Pre-program Vehicle Powertrain NVH Process", David Tao, Vehicle Powertrain NVH Department, Ford Advanced Vehicle Technology, September, 1995.

• Fundamentals of Noise and Vibration Analysis for Engineers, M.P. Norton, Cambridge University Press, 1989

• Modern Automotive Structural Analysis, M. Kamal,J. Wolf Jr., Van Nostrand Reinhold Co., 1982

• http://www.nvhmaterial.com• http://www.truckworld.com• http://www.canadiandriver.com

http://www.truckworld.com/

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