Design For NVH

*

Design For NVH

MPD575 DFX

Jonathan Weaver

*

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 : D. Gaines, E. Donabedian, R. Hall, E. Sheppard, J. Randazzo, J. Torres, B. Dhruna, J. Stevens, D. Kammerzell

*

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

*

● Vibration is movement, and vibration that reaches the

passenger compartment at the right frequency is noise.

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

● It is relatively easy to reduce noise and vibration by adding weight thereby changing the natural frequency, 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.

Introduction to NVH What is

NVH?

*

Introduction to NVH What is

NVH?

Noise:

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

•Variations are detected by ear

•Characterized by frequency, level & quality

•May be Undesirable (Airborne)

•May be Desirable (Powerful Sounding Engine)

*

Introduction to NVH What is NVH?

Vibration– An oscillating motion about a reference point

which occurs at some frequency or set of frequencies

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

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

track, toe board, and mirrors (visible vibrations)

*


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

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

frequencies but human perception of it is different.• Perceived tactilely and/or audibly• Rough, grating or discordant sensation• Unpleasant

*

Introduction to NVH What is NVH

Airborne Noise:● Sound most people interpret as noise, and travels

through gaseous mediums like air.● Some people classify human voice as airborne noise, a

better example is the hum of your computer, or an air conditioner.

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

● Treatment/Countermeasures: Elimination of the source if possible; Barriers or Absorbers if not.

*


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

*


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 installed. A partially open door is a less effective barrier than a totally closed door.

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

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

*


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

Note: Active Noise Cancellation (ANC) is a recent method discussed in this DFX. For airborne noise it can work between 30 and 1000 Hz to change the noise heard. ANC units offset unwanted sound by emitting opposing frequencies that “cancel” the unwanted sound. ANC technology is available in cars like the Lincoln MKS, Honda Odyssey, and Infiniti Q50

*


Absorbers:•Reduces sound by absorbing the energy of the sound waves, and dissipating it as heat. Examples: headliner and hood insulator•Absorbers are ranked by the ability to absorb sound that otherwise would be reflected off its surface•Good absorber design contains complex geometries that trap sound waves and prevent reflection back into the air•Absorber performance varies with frequency

Absorbers: Design Parameters

•Area of absorbing material (large as possible)

•Type of material (cost/weight)

•Thickness (package/installation)

*


*


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 and location specific added mass

*


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

*


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.

*


Isolation by Bushings and Mounts:•Excitations are generally applied to or by 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.

Introduction to NVH How is NVH Measured?

One of the challenges of measuring and analyzing powertrain NVH is the large range in the absolute levels of sounds and vibrations that occur. Measurement and analysis require observation of small (low-level) signals in the presence of large (high-level) signals. This is required due to the capability of the human ear to process signals at a wide range of levels.


Amplitude Scales: The ratio between the largest and smallest signals that we can analyze is the dynamic range. Using a linear amplitude measurement scale limits our ability to display a wide dynamic range simultaneously as shown on Graph A. However, as shown on Graph B of the same sound, a logarithmic amplitude scale compresses large amplitude signals and expands small ones so that we can display a wide dynamic range simultaneously for analysis. This is why we use the logarithmic

decibel (dB) scale to measure sounds and vibrations


Amplitude Scales: The decibel (dB) is a logarithmic representation of an amplitude ratio. It is 20 times the base 10 logarithm of the ratio of the measured amplitude to a reference. In the case of sound, the units of measure are pressure and the reference is typically the threshold of hearing. On the dB scale, 0 dB approximately corresponds to the normal threshold of human hearing and 140 dB approximately corresponds to the threshold of pain. Each 1 dB step approximately represents the smallest change in sound level that normal human hearing can detect 50% of the time. The table compares dB levels for various sounds at 1 meter and 10 meters. To become more familiar with dB levels.


Amplitude Scales: The formula for calculating sound pressure level (SPL) in decibel (dB) is:

Adding decibel (dB): Because the dB scale is a logarithmic ratio, we cannot add dB levels directly. To add two dB values, we must apply the rules of logarithms as follows:

*

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

*


• NVH impacts Customer Satisfaction

• NVH impacts Warranty

• NVH has financial impact

*


65%

85%

5

9

RelativeLeverage

IMPROVE

REVIEW MAINTAIN

Overall Handling

Cup holders Exterior

Styling

* *

6.9

77%

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

*NVH SUSTAIN / BUILD

*


NVH Can Both Dissatisfy and Delight

+ Performance

+ CustomerSatisfactio

n

- Performance Dissatisfiers

Harley Mustang

Lexus Loudness

Unusual NoisesTGW

Sound QualityTGR

KANO Model

+ Degree of Achievement

Basic Quality(Inhibitors)

Performance Quality(Attributes)

- CustomerSatisfactio

n

Exciting Quality(Surprise & Delight)

Axle Whine Wind Noise

*


• Customers place a high value on NVH performance in vehicles

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

• Often times, cost and weight targets prevent avoidance of NVH issues An example is a 2-pc driveshaft, which is less expensive, lighter, and has fewer joints than a 3-pc driveshaft, but has boom at a certain RPM. The 3-pc driveshaft does not demonstrate the boom.

What do you do???• NVH countermeasures CAN work harmoniously within the system as long as they are

DESIGNED INTO the system from the beginning.How do I go about doing it?

– Get management buy-in. Costs for NVH countermeasures are never put into programs early enough. This needs to change to ensure success.

– Run CAE early, using the best simulations available. Determine the frequency range and driving mode. Trust your CAE.

– Develop NVH countermeasures and make sure they are on the first phase of prototype vehicles (NOT the last)

– In this case, a torsional damper on the rear of the driveshaft solves the issue, but interferes with the fuel tank

– Since packaging studies were run early, the fuel tank was modified prior to hard tooling to provide clearance for the damper.

• Result– A well-packaged driveshaft which is lighter, less expensive, and more durable than

the alternate design, which fully satisfies all customer and corporate requirements.

Heuristic: NVH is always a late guest to the party. Plan countermeasures ahead to ensure you have enough energy, time and tools to entertain your guest!

NVH: Cost & Weight Considerations

*


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

source of NVH problem– Dealers 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

*




*

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)

*

• 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


*

• Don't confuse the functioning of the parts with 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 vehicle designs require the ability to develop requirements for the parts by cascading functional requirements from the system.


*




*

• 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

*


*

DFNVH Process Flow and Target Cascade Noise Reduction Strategy: Targets are set for the noise

reduction capability of the sound package.

*


Systems Engineering “V” and PD Process Timing

Define Req’s

Cascade Targets & Iterate

Optimize

Verify & Optimize

ConfirmVehicle (VDS - P/T NVH etc)

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

Subsystem (Stiffness,...)

Components SDS

CustomerSatisfaction

PS PA CPPRSCKOO

CustomerWants/Needs

J1

*

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 MacPherson 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 Chart

Is Gross Architecture Feasible? Development


*


NVH Functional Attribute

Sub -Attributes

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

*


Convert attribute target strategy to objective targets

POWERTRAIN NVH

IDLE NVHACCELERATION

NVH

CRUISE NVHDECELERATION

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

*


CUSTOMER PERCEIVED P/T NVH

AIRBORNE NOISE STRUCTURE-BORNE NOISE

P/T RADIATED NOISE

AIRBORNE NOISE REDUCTION

BODY ACOUSTIC SENSITIVITY

MOUNT FORCES

P/T VIBRATIONMOUNT

DYNAMIC STIFFNESS

Acceleration NVH Target Cascade

*


NVH Classification Parameters •Operating Condition (idle, acceleration, cruise on a rough road, braking, wind…)•Phenomenon (boom, shake, noise…) this is strongly affected by the frequency of the noise and vibration or input. •Source (powertrain, road, wind ..etc) •Classifying NVH problems provides a guidance for design, for example: low frequency problems such as shake historically involve major structural components such as cross members and joints.


Operating Condition NVH Concerns

Idle Shake and boom due to engine torque.

Lugging Shake and boom due to engine torque.

Wide Open Throttle (WOT)

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

Cruise (smooth road) Shake, roughness, and boom due to tire and powertrain imbalance and tire force variation, wind noise, and tire noise. Transmission and Axle whine.

Cruise (rough road) Road noise and shake

Tip-in "Moan" due to powertrain bending.

Braking Squeal, grind, moan and shudder.

*


•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.

*


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

*


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 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.•NVH from audio system interaction is also important with pulse width modulated signals for loads that couple with audio speakers.

*

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



*

DFNVH Process FundamentalsSource-Path-

Responder

SensitivityExcitation Response

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

Vortices• Brake Roughness

Excitation Source Examples:

*


Responder


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

Sensitivity:

*


ResponderExample: Body Sensitivity

Tactile

∙ Point mobility (v/F) (Structural velocity / induced by force)

Acoustic

∙ Airborne (p/p)(Airborne sound pressure induced / by pressure waves)

∙ Structure-borne (p/F)(Airborne sound pressure / induced by force)

F (N)

V (mm/s)

p (dB)

Force Inputat Driving Point

Vibration Velocityat Driving Point

Interior SoundPressureSTRUCTURE

p (dB)

p (dB)

Interior SoundPressureSTRUCTURE

Airborne Noise

*


ResponderBody Sensitivity Demonstration

Point Mobility Typical Point Mobility Spectrum for Compliant and Stiff Structures

Poi

nt M

obil

ity

(V/F

)

MoreCompliant

LessCompliant

Frequency ( f )50

140

*


Responder

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

*


Responder

Air

born

e P

/T

NV

HS

truc

ture

-bor

ne 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

e N

VH

Str

uctu

re-b

orne

NV

H

Powertrain Noise Model

*


ResponderRoad 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

*


Responder

Driveline Model

*

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

*


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)

*


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

*


Binaural Acoustic “Achen Heads”

Stereo Sound Recording representing sound wave interaction with a partial human torso

*


Sound Quality Listening Room

Used for Customer Listening Clinics.

*


Poor Sound Quality Good Sound Quality

*


Quantifying Door Closing Sound Quality

1. Sound Level (Loudness)

2. Frequency Content (Sharpness)

3. Temporal Behavior

*


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.


Example: Qualifying Door Closing Sound Quality

Good Bad

Level (dBa) (color)

Fre

quen

cy (

Hz)

(y-

axis

)

Time (sec.) (x-axis)

*


Design for Sound QualityDoor Closing Example

Perceived Sound

Structure-borne Airborne

Seal Trans Loss

Latch Forces Str. Compliance

Inertia Spring Rates Material

Radiated Snd.

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


*

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



*

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

*

NVH Design Principles

Tube Inlet/Outlet Noise

ExcitationSource, Energy

Input

StructureSensitivity

Customer

Air

born

e N

VH

Stru

ctur

e-bo

rne

NV

H

Air Impingement Noise

Source Path Responder

Impactive Noise

Radiated/Shell Noise Acoustic Attenuation

Acoustic Attenuation



EnvironmentSensitivity

IsolationStiffness

IsolationDamping

*

Mechanism:

• Structural surface vibration imparts mechanical energy into an adjacent acoustic fluid in the form of pressure waves at same frequency 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

*

Design Action(s):

• Stiffen: Add ribbing, increase gage thickness, change material to one with higher elastic modulus, and add internal structural supports

• Minimize surface area: Try to avoid 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

*

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

*

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

volume (muffler)• Locate inlet/outlet as far away from customer as

possible• Design for symmetrical (equal length) branches


*


V6 Intake Manifolds

*

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

*


Air Pumping

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

*

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)


*

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

*

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

circumferential ring• Optimize fan diameter and flow to achieve lowest

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

airflow

Design Principles – Airborne NVHAir Impingement Noise

*




Input


Customer

Air

born

e N

VH

Str

uctu

re-b

orn

eN

VH



Impactive Noise






IsolationStiffness

IsolationDamping

*

Design Principles – Airborne NVHAirborne Noise Path Treatment

Noise Reduction

EngineCompartment

Absorption

Body & Insulator Blocking(Panels)

Pass-Thru Sealing

(Components)

InteriorAbsorption

*

Design principle(s):• Eliminate noise source• 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


*

air absorption materials


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

41% increase in weight

• Mastic or laminated steel improves low frequency sound quality

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

• Pass-thru penetration seals are weaker than steel

*




Input


Customer

Air

born

e N

VH

Stru

ctur

e-bo

rne

NV

H



Impactive Noise






IsolationStiffness

IsolationDamping

*

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

*




Input


Customer

Air

born

e N

VH

Stru

ctur

e-bo

rne

NV

H



Impactive Noise






IsolationStiffness

IsolationDamping

*

• 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 achieved to avoid NVH issues.

Design Principles – Structureborne NVH

*

• 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.)


*


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

*


● Powertrain modes need to be separated from the 1st and 2nd body bending and torsion modes by at least 2Hz.

● Cowl and cross car beam modes must be separated from steering column modes by as much as possible (minimum of 1Hz)

Natural frequencies of major structures need to be separated to avoid magnification.

*

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

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


*




Input


Customer

Air

born

e N

VH

Stru

ctur

e-bo

rne

NV

H



Impactive Noise






IsolationStiffness

IsolationDamping

*

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

*

Design action(s):

• Achieve high overall structural rigidity

• Minimize unbalance

• Achieve high stiffness at attachment points of the excitation objects (shock towers, frame mounting points, or subframe mounting points)


*


A/C Compressor – Bad Example

Cantilever Effect → Less Rigid

*


A/C Compressor - Good Example


Example: Axle Whine

Characteristics:- Tonal noise 300 - 800 Hz- Occurs between 40 - 70 mph in drive or coast modes under moderate to wide open throttle.- Frequency = # Pinion teeth x Driveshaft Speed in RPM / 60.- Caused by gear transmission error (TE), which is the difference between the actual position of the output gear and the position of a theoretical or “perfect gear”, measured in “arc-second”.


Requirement Cascade- Vehicle level: Driver audible target in dB(A) and 0.5 micron pinion nose vibration.- System level: 12 arc-sec.

- Component level: 7 arc-sec at nominal mesh position (single flank).Noise factors:

- Manufacturing: gear cutting, heat treat and lapping variation.

- Assembly: Pinion and differential shiming - Gear mesh deflection, gear wear

- Driveline modal response (torsional and bending modes)

Development Flow- <Program Target Confirmed> Define “health chart” Axle whine cascade

(CAE).- <M1 Design Judgment> Verify targets are compatible (CAE)- <Final Design Judgment> Single Flank TE, Axle TE and Vehicle NVH

measurements

Options to reduce whine at the source- Increase contact ratio.

- Fine tooth combination

- Long tooth face width

- More spiral angle

- Reduce gear mesh deflection- Increase component stiffness (bearings, differential case, carrier).

- Reduce gear wear- Reduce input torque, sliding velocity

- Improve lubrication

- Reduce gear manufacturing tolerance.- 3D hypoid gear hobbing is industry standard for high volume automotive

applications.

- Reduce tolerance on hard finishing (lapping).

- Reduce assembly tolerances for pinion and ring gear mounting distances.- Measure gap and shim to compensate (build to pattern).

- Use threaded adjuster to position ring gear in proper mesh

- Measure all components critical dimensions prior to assembly and shim to

achieve proper stack (build to position).

-


*




Input


Customer

Air

born

e N

VH

Stru

ctur

e-bo

rne

NV

H



Impactive Noise






IsolationStiffness

IsolationDamping

*

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

*

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.


*


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

*




Input


Customer

Air

born

e N

VH

Stru

ctur

e-bo

rne

NV

H



Impactive Noise






IsolationStiffness

IsolationDamping

*

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

*

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

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.


*

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

*


Body Modes and Body Architecture

*


Body Modes and Mass DistributionEffect 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.

*

l 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


*

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

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.

Guiding Heuristic - Know what to get right first and what can be tuned later


*




*

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.

*

Wind Noise Target Cascade Diagram

Vehicle level Wind Noise

Excitation Sources

Antenna / Accessori

esMirror Shape

Green House Shap

e

Open Windows

/ Sunroof

Seals

Aspiration Leak

s

Transmission Los

s

Glass / Panels

Static Sealin

gDynamic Sealing

Door System Stiffness

Wind Noise Example

*

Wind Noise Example

*

Aerodynamic excitation

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

turbulence

• Exterior ornamentation turbulence

• Cavity resonances• Air flow induced panel

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

and offsets

Wind Noise Example

*

Aspiration leakage

• Dynamic sealing– Closures

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

– Moon roof• Glass runs

– Back-lite 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

*

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



Design For NVH (DFNVH)

*

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.

*

Design For NVH 2002 Mercury Mountaineer

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

*

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.

*


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.

*


Mountaineer Body sculpted for less wind resistance with glass and door edges

shifted out of airflow.

NVH in EVs• NVH perceived quality and characteristics inherent to vehicle

branding have been well defined and tuned over the years, based on combustion engine sound sources.

• With the evolution of electric vehicles, however, this applied NVH knowledge has unfortunately not translated well to electric vehicles. ➢ Customer expectations for electric vehicle sound quality

have not been well defined. ➢ The lack of refined requirements, coupled with more

stringent environmental and federal regulations, has made it difficult for NVH engineers to tune to their system attribute.

➢ Is NO pass-by noise acceptable? What about pedestrians, who may inadvertently step in front of an oncoming EV?

*

NVH in Evs (Cont.)

• Based on new sound sources, it is necessary to➢ Review the foundation diagrams to understand system

interactions, and external factors➢ Conduct customer research to determine customer

expectations for sound quality and powertrain NVH➢ Develop targets based on customer feedback.

*

Electrical Noise Prevention for Internal Combustion and emerging

Electric VehiclesAEV 5070 Class Presentation

M. Lunn

Customer Expectation of Vehicles – SE Requirements – Quiet, Green with features• Requirement of customer for any vehicle is quiet

and no “unassociated” noises or undesirable noises

• Fuel Economy for IC engines and Effective Range for EV’s wants efficient use of power, rule of thumb is 0.04 mpg/A.

• Features to heat interior, operate lighting, cool engine area(EV’s have cooling fans and liquid cooled electronics also), blow air in interior, pump fuel and control suspension use electrical power.

Electrical power control – Pulse Width Modulation challenges no noise!

• Inefficient power control is a A/C blower motor with variable motor control. DC current to a motor sinks voltage in a MOSFET load(waste). Excess energy is sunk to limit speed, heat is excess from engine for IC.

• Efficient power control is Pulse Width modulated heater(PTC heating elements like toaster) with no wasted energy and PWM motor control.

• Pulse Wi is a square wave signal for power with variable duty cycle(positive time/ period), allows variable control. Try an example on next slide!

Example of Electrical control – DC and AC simulation – Sine waves shown.

Packaging diagram of PWM signals with audio noise issue on heated seatsNote corouting of PWM heated seats with audio

Single ended PWM Load on the heated seatsIs issue.Prior to schematics or Package any single circuitWith PWM current over ___ Amps is suspectFor noise to audio.Analysis is easy, if PWMEnters the body withAudio then its possible toHave noise

How noise is induced on a device or wires by a PWM or time varying signal

As built route to right side, separate power and and ground, noise heard

Top Yellow signal is current probe on the heated seats at 10 mV/A and range of 9.3 A, Delta time is 200 HZ, 5 ms.

Bottom is LH front speaker wires with noise pulse on rise and falls of the current. This is on line level output, through the ANC, then on speaker amplified by AMP.

As built route to right side, separate power and ground, noise heard

• Heated seat current is on the audio speaker as shown.

PWM square waves are sum of Sine waves – these make noise!

Systems Engineering V – how to prevent noise issues?

• These noise issues are usually detected late in vehicle testing, how to do early in development?

• The single V does not use the analysis early tofind noises fromexperience, fixedin late changes Is pattern.Better to preventIn design left sidevs. V&V on right side!

How to Prevent noise issues – how to implement?

• A double V approach is a solution – requires the CAE analytical modeling tools be used, time provided and staffing supported to allow application and prevent.– This is not a practice I see in the industry but electrical CAE

and EMC tools are capable! (Mentor, Dassault, etc.• Why not adopt these tools?

– Data for circuits, components and loads in the environment of in house, regional and supplier designs does with staffing, time provided does not allow these tools to be used.

• Most solutions are fast to implement if program supports cost/vehicle needed.– Cost less overall than the analytical approach???

Package Diagram of PWM signals with prevent action – no noise heard

• The PWM load is twisted with power to get out of the audio circuit path and cancel fields.

LH routing and twisted power and ground – no noise heard

Same top yellow trace for current probe at 10mV/A and 10.8 A, 200 Hz.

LH speaker shows almost no noise on the speaker circuits! No noise heard by customer.

LH routing and twisted power and ground – no noise heard

• CHB purple LH speaker is very low, not following current.

Overlay on engine compartment – no no noise heard and heated seats on

• CHA yellow is seat current, CHB purple is not used.

Overlay on engine compartment – no no noise heard and heated seats on

- First(200), third(600) and fifth(1000) harmonics shown.

Why is this significant to EV’s in future!• PWM Loads are increasing for EV’s from IC vehicles!

IC engine EV future FrequencyCooling fans – relay power 600W PWM 200 W20kHz above audioPower Steering- 1000 W peak 1000 W peak 20KHz above audio(audible harmonic in the AM and FM band on any car I know of!)Heated seats - 120 W 120 W 200 Hz audio and AMHeated interior – 900 W constant 900W constant 100 Hz in Audio and AM(within 12 inches of audio unit for inverse squared 1/r^2 relationship of fields !!)Active Suspension - 9A/108W) 9A/108W) 1000 Hz (TBD as of yet)Fuel Pump(ERHV) - 10A 10A 9600 Hz in audio, AM, FMStart/Stop on Engine – large changes large changes pulse but spikes heardA/C load - 10 A for comp clutch 50 A for compressor (TBD)

• Not using PWM will increase loads and decrease range of batteries or fuel economy! Approximately 0.04 MPG per A and range anxiety.

• Have you been in an EV or start/stop IC vehicle, noticed the only sound can be a tire noise on surface and brake caliper release! Switch travel is noise! Transition to rolling or start and you have pulse of current, potential noise.

Requirements of Vehicle designs on noise and EMC with Fuel Economy increases

• Vehicles for IC engines have been mostly sheet metal for cost and forming, assembly.– Also provides ground plane and E field shielding!!– Works until fuel economy goes to 54.5 MPG

• To support future MPG rules the weight and structure may change to alternatives– Aluminum is not as good a ground or shield in a body

construction.– Plastic or carbon fiber is not conductive or a shield.

All the alternatives make electrical interactions harder to prevent and more expensive!!

http://www.bloomberg.com/news/2011-06-14/bmw-carbon-lets-vehicles-follow-bicycle-road-to-lightness-cars.html

Questions & References and links• PHET AC and DC circuits:

http://phet.colorado.edu/en/simulation/circuit-construction-kit-ac-virtual-lab

• PHET Faradays Electromagnetic lab: http://phet.colorado.edu/en/simulation/faraday

• PHET Fourier: making waves: http://phet.colorado.edu/en/simulation/fourier

• All PHET Simulations, these are very useful and free - http://phet.colorado.edu/

• Also of interest for general knowledge and explainations - http://www.khanacademy.orgAlso of interest for general knowledge and explainations - http://www.khanacademy.org/

• I use these to explain ideas and issues vs. lots of words and “you don’t understand this”. Try with your kids!



http://phet.colorado.edu/en/simulation/faraday

http://phet.colorado.edu/en/simulation/fourier

http://phet.colorado.edu/

http://www.khanacademy.org/

http://www.khanacademy.org/

*

• 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

*

• 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

*

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/

*

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/

Design For NVH

Documents

Transcript of Design For NVH