Design For NVH

1
Design For NVH

• MPD575 DFX
• Jonathan Weaver

2
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

3
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

4
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.

5
Introduction to NVH What is NVH?

• 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)

6
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 (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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Introduction to NVH What is NVH?

• 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

8
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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Introduction to NVH What is NVH?

• 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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Introduction to NVH What is NVH?

• 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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Introduction to NVH What is NVH?

• 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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Introduction to NVH What is NVH?

• 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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Introduction to NVH What is NVH?

• Absorbers Design Parameters
• Area of absorbing material (large as possible)
• Type of material (cost/weight)
• Thickness (package/installation)

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Introduction to NVH What is NVH?

• 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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Introduction to NVH What is NVH?

• 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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Introduction to NVH What is NVH?

• 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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Introduction to NVH What is NVH?

• 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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Introduction to NVHWhy Design for NVH?

• NVH impacts Customer Satisfaction
• NVH impacts Warranty
• NVH has financial impact

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Introduction to NVHWhy Design for NVH?
Corporate Leverage vs. Customer Satisfaction NVH
Customer Satisfaction Needs Improvement at 3 MIS
9
IMPROVE
SUSTAIN / BUILD

Overall Handling
Relative Leverage
6.9
Cup holders

Exterior Styling

REVIEW
MAINTAIN
5
65
85
77
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Introduction to NVHWhy Design for NVH?
NVH Can Both Dissatisfy and Delight
Customer Satisfaction
KANO Model
Exciting Quality (Surprise Delight)
Performance Quality (Attributes)
Sound Quality TGR
Harley Mustang Lexus
Loudness
Degree of Achievement
Performance
- Performance
Dissatisfiers
Basic Quality (Inhibitors)
Unusual Noises TGW
Axle Whine Wind Noise
- Customer Satisfaction
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Introduction to NVHWhy Design for NVH?
Summary of Customer Importance

• Customers place a high value on NVH performance
  in vehicles
• About 1/3 of all Product / Quality Complaints are
  NVH-related

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Introduction to NVHWhy Design for NVH?
Summary of Customer Importance (continued)

• 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

24
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

25
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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Design For NVH Heuristics

• 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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Design For NVH Heuristics

• 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

28
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

29
DFNVH Process Flow and Target Cascade

• 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)

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DFNVH Process Flow and Target Cascade
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DFNVH Process Flow and Target Cascade
Noise Reduction Strategy Targets are even set
for the noise reduction capability of the sound
package.
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DFNVH Process Flow and Target Cascade
Systems Engineering V and PD Process Timing
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DFNVH Process Flow and Target Cascade
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DFNVH Process Flow and Target Cascade
NVH Functional Attribute
Sub -Attributes
Road
P/T
Wind
Brake
Comp. S.Q.
SR
Pass-by Noise (Reg.)
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DFNVH Process Flow and Target Cascade
Convert attribute target strategy to objective
targets
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DFNVH Process Flow and Target Cascade
Acceleration NVH Target Cascade
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DFNVH Process Flow and Target Cascade

• 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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DFNVH Process Flow and Target Cascade

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DFNVH Process Flow and Target Cascade

• The customers 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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DFNVH Process Flow and Target Cascade
41
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.

42
Design For NVH (DFNVH)

• Introduction to NVH
• DFNVH Heuristics
• 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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DFNVH Process FundamentalsSource-Path-Responder

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

Excitation Source Examples
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DFNVH Process FundamentalsSource-Path-Responder
Sensitivity
Tendency of the path to transmit energy from the
source to the responder, commonly referred to as
the transfer function of the system
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DFNVH Process FundamentalsSource-Path-Responder

• Example 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)

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DFNVH Process FundamentalsSource-Path-Responder
Body Sensitivity Demonstration Point Mobility
Typical Point Mobility Spectrum for Compliant
Stiff Structures
More Compliant
Point Mobility (V/F)
Less Compliant
Frequency ( f )
140
50
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DFNVH Process FundamentalsSource-Path-Responder
S/W Steering Wheel
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DFNVH Process FundamentalsSource-Path-Responder
Powertrain Noise Model
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DFNVH Process FundamentalsSource-Path-Responder
Road Noise Model
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DFNVH Process FundamentalsSource-Path-Responder
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

52
DFNVH Process FundamentalsSound Quality
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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DFNVH Process FundamentalsSound Quality
The Sound Quality Process

• 1. Measurement (recording)
• 2. Subjective evaluation (listening studies)
• Actual or surrogate customers
• 3. Objective analysis
• Sound quality Metrics
• 4. Subjective/Objective correlation
• 5. Component design for sound quality

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DFNVH Process FundamentalsSound Quality
Binaural Acoustic Heads
Stereo Sound Recording representing sound wave
interaction w/ human torso
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DFNVH Process FundamentalsSound Quality
Sound Quality Listening Room
Used for Customer Listening Clinics.
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DFNVH Process FundamentalsSound Quality
Poor Sound Quality
Good Sound Quality
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DFNVH Process FundamentalsSound Quality
Quantifying Door Closing Sound Quality
1. Sound Level (Loudness) 2. Frequency Content
(Sharpness) 3. Temporal Behavior
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DFNVH Process FundamentalsSound Quality
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.
59
DFNVH Process FundamentalsSound Quality
Example Qualifying Door Closing Sound Quality
Good
Bad
Frequency (Hz) (y-axis)
Time (sec.) (x-axis)
Level (dBa) (color)
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DFNVH Process FundamentalsSound Quality
Design for Sound Quality Door Closing Example
Perceived Sound
Structure-borne
Airborne
Seal Trans Loss
Radiated Snd.
Latch Forces
Str. Compliance
Inertia
Spring Rates
Material
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DFNVH Process FundamentalsSound Quality
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

62
Design For NVH (DFNVH)

• Introduction to NVH
• DFNVH Heuristics
• 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

63
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

64
NVH Design Principles
Source
Path
Responder
Radiated/Shell Noise
Acoustic Attenuation
Acoustic Attenuation
Tube Inlet/Outlet Noise
Environment Sensitivity
Airborne NVH
Impactive Noise
Acoustic Attenuation
Acoustic Attenuation
Air Impingement Noise
Customer
Excitation Source, Energy Input
Structure-borne NVH
Structure Sensitivity
65
NVH Design Principles
Source
Path
Responder
Radiated/Shell Noise
Acoustic Attenuation
Acoustic Attenuation
Tube Inlet/Outlet Noise
Environment Sensitivity
Airborne NVH
Impactive Noise
Acoustic Attenuation
Acoustic Attenuation
Air Impingement Noise
Customer
Excitation Source, Energy Input
Structure-borne NVH
Structure Sensitivity
66
Design Principles Airborne NVHRadiated/Shell
Noise

• 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

67
Design Principles Airborne NVH Radiated/Shell
Noise

• 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)

68
Design Principles Airborne NVHTube
Inlet/Outlet Airflow 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

69
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
• Locate inlet/outlet as far away from customer as
  possible
• Design for symmetrical (equal length) branches

70
Design Principles Airborne NVHTube
Inlet/Outlet Airflow Noise
V6 Intake Manifolds
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Design Principles Airborne NVHImpactive Noise

• 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

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Design Principles Airborne NVHImpactive Noise
Air Pumping Air forced in and out of voids is
called air pumping
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Design Principles Airborne NVHImpactive Noise

• 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)

74
Design Principles Airborne NVHAir Impingement
Noise

• 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

75
Design Principles Airborne NVHAir Impingement
Noise

• 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

76
NVH Design Principles
Source
Responder
Path
Radiated/Shell Noise
Acoustic Attenuation
Acoustic Attenuation
Tube Inlet/Outlet Noise
Environment Sensitivity
Airborne NVH
Impactive Noise
Acoustic Attenuation
Acoustic Attenuation
Air Impingement Noise
Customer
Excitation Source, Energy Input
Structure-borne NVH
Structure Sensitivity
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Design Principles Airborne NVHAirborne Noise
Path Treatment
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Design Principles Airborne NVHAirborne Noise
Path Treatment

• 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

79
Design Principles Airborne NVHAirborne Noise
Path Treatment

• 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

air absorption materials
80
NVH Design Principles
Source
Responder
Path
Radiated/Shell Noise
Acoustic Attenuation
Acoustic Attenuation
Tube Inlet/Outlet Noise
Environment Sensitivity
Airborne NVH
Impactive Noise
Acoustic Attenuation
Acoustic Attenuation
Air Impingement Noise
Customer
Excitation Source, Energy Input
Structure-borne NVH
Structure Sensitivity
81
Design Principles Airborne NVHAirborne Noise
Responder Treatment

• 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

82
NVH Design Principles
Source
Path
Responder
Radiated/Shell Noise
Acoustic Attenuation
Acoustic Attenuation
Tube Inlet/Outlet Noise
Environment Sensitivity
Airborne NVH
Impactive Noise
Acoustic Attenuation
Acoustic Attenuation
Air Impingement Noise
Customer
Excitation Source, Energy Input
Structure-borne NVH
Structure Sensitivity
83
Design Principles Structureborne NVH

• 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.

84
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.)

85
Design Principles Structureborne NVH
The steering column vibration will have an extra
large peak if the steering column mode coincides
with the overall bending mode.
86
Design Principles Structureborne NVH
Natural frequencies of major structures need to
be separated to avoid magnification.
87
Design Principles Structureborne NVH

• 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.

88
NVH Design Principles
Source
Responder
Path
Radiated/Shell Noise
Acoustic Attenuation
Acoustic Attenuation
Tube Inlet/Outlet Noise
Environment Sensitivity
Airborne NVH
Impactive Noise
Acoustic Attenuation
Acoustic Attenuation
Air Impingement Noise
Customer
Excitation Source, Energy Input
Structure-borne NVH
Structure Sensitivity
89
Design Principles Structureborne NVHExcitation
Source

• 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.

90
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

91
Design Principles Structureborne NVHExcitation
Source
A/C Compressor Bad Example

Cantilever Effect ? Less Rigid
92
Design Principles Structureborne NVHExcitation
Source
A/C Compressor - Good Example

93
NVH Design Principles
Source
Responder
Path
Radiated/Shell Noise
Acoustic Attenuation
Acoustic Attenuation
Tube Inlet/Outlet Noise
Environment Sensitivity
Airborne NVH
Impactive Noise
Acoustic Attenuation
Acoustic Attenuation
Air Impingement Noise
Customer
Excitation Source, Energy Input
Structure-borne NVH
Structure Sensitivity
94
Design Principles Structureborne NVHPath -
Isolation Strategy

• 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.

95
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.

96
Design Principles Structureborne NVHPath -
Isolation Strategy
Tuning and Degree of Isolation

By moving natural frequency down for this system
it increased damping at 100 Hz
97
NVH Design Principles
Source
Responder
Path
Radiated/Shell Noise
Acoustic Attenuation
Acoustic Attenuation
Tube Inlet/Outlet Noise
Environment Sensitivity
Airborne NVH
Impactive Noise
Acoustic Attenuation
Acoustic Attenuation
Air Impingement Noise
Customer
Excitation Source, Energy Input
Structure-borne NVH
Structure Sensitivity
98
Design Principles Structureborne NVHStructure
Sensitivity Strategy

• 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

99
Design Principles Structureborne NVHStructure
Sensitivity Strategy

• 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.

100
Design Principles Structureborne NVHStructure
Sensitivity Strategy
Body Modes and Body Architecture

• 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

101
Design Principles Structureborne NVHStructure
Sensitivity Strategy
Body Modes and Body Architecture
102
Design Principles Structureborne NVHStructure
Sensitivity Strategy
Body Modes and Body Architecture
103
Design Principles Structureborne NVHStructure
Sensitivity Strategy
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.

104
Design Principles Structureborne NVHStructure
Sensitivity Strategy

• 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

105
Design Principles Structureborne NVHStructure
Sensitivity Strategy
Guideline Body Modes Force Input Locations

• 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.

106
Design Principles Structureborne NVHStructure
Sensitivity Strategy

• 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.

107
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

108
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.

109
Wind Noise Example
Wind Noise Target Cascade Diagram
110
Wind Noise Example
111
Wind Noise Example
Aerodynamic excitation

• Exterior ornamentation turbulence
• Cavity resonances
• Air flow induced panel resonances
• Air extractor noise ingress
• Door seal gaps, margins and offsets

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

112
Wind Noise Example
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

113

• Introduction to NVH
• 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

114
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.

115
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.
116
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.

117
Design For NVH 2002 Mercury Mountaineer

• Aachen Head was used to improve Mountaineers
  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.

118
Design For NVH 2002 Mercury Mountaineer
Body sculpted for less wind resistance with glass
and door edges shifted out of airflow.
119
DFNVH Summary

• 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

120
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

121
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

122
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