Transcript DFNVH - University of Detroit Mercy

Design For NVH
MPD575 DFX
Jonathan Weaver
1
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
2
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
3
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.
4
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)
5
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)
6
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
7
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
8
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
9
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
10
becomes the dominant factor in comparing barriers.
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
11
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.
12
Introduction to NVH
What is NVH?
Absorbers: Design Parameters
•Area of absorbing material (large as possible)
•Type of material (cost/weight)
•Thickness (package/installation)
13
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
14
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
15
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.
16
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.
17
Introduction to NVH
Why 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
18
Introduction to NVH
Why Design for NVH?
• NVH impacts Customer Satisfaction
• NVH impacts Warranty
• NVH has financial impact
19
Introduction to NVH
Why Design for NVH?
Corporate Leverage vs. Customer Satisfaction
NVH Customer Satisfaction Needs Improvement at 3 MIS
9
IMPROVE
SUSTAIN / BUILD
NVH
*
Relative
Leverage 6.9
Overall Handling
Cup holders
Exterior Styling
5
*
65%
REVIEW
*
MAINTAIN
77%
85%
20
Introduction to NVH
Why Design for NVH?
NVH Can Both Dissatisfy and Delight
+ Customer
Satisfaction
KANO Model
Sound Quality
TGR
Harley
Mustang
Lexus
Exciting Quality
(Surprise & Delight)
Performance Quality
(Attributes)
+ Degree of Achievement
+ Performance
- Performance
Dissatisfiers
Basic Quality
(Inhibitors)
Axle Whine Unusual Noises
Wind Noise
TGW
- Customer
Satisfaction
21
Introduction to NVH
Why 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
22
Introduction to NVH
Why Design for NVH?
Summary of Customer Importance (continued)
• About 1/5 of all Warranty costs are NVHrelated
– 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
23
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
24
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)
25
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
26
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
27
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
28
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)
29
DFNVH
Process Flow and Target Cascade
30
DFNVH
Process Flow and Target Cascade
Noise Reduction Strategy: Targets are even set for the
noise reduction capability of the sound package.
31
DFNVH
Process Flow and Target Cascade
Systems Engineering “V” and PD Process Timing
KO
SC
SI
PA
PR
Customer
Wants/Needs
Define Req’s
J1
CP
Customer
Satisfaction
Vehicle (VDS - P/T NVH etc)
Confirm
System (SDS - Force, Sensitivity,......)
Cascade Targets
& Iterate
Subsystem (stiffness, ....)
Components CDS
Verify & Optimize
Optimize
32
DFNVH
Process Flow and Target Cascade
Trade-Offs Flow Chart
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)
Vehicle Assumptions Fixed
SLA or McPherson Strut Suspension
Vehicle Level Target Ranges
Subjective (1-10) and Objective
Trade-Off Loop
Perform Iterations Until Assumptions
Comparable
SI
System & Sub-System
Targets
Force or P/F Targets
Determined with
Parametric Models
Component End Item
Targets
Component Resonant
Frequencies, etc.
PA
System/Sub-System Assumptions
McPherson vs. SLA, etc.
Requires Hardware Parametric
Model
Is Gross Architecture Feasible?
Design Optimization
CAE Optimization
Hardware Development
Development
33
DFNVH
Process Flow and Target Cascade
NVH Functional Attribute
Sub -Attributes
Road
Wind
P/T
Brake
Comp. S.Q.
S&R
Pass-by Noise (Reg.)
34
DFNVH
Process Flow and Target Cascade
Convert attribute target strategy to objective targets
POWERTRAIN
NVH
IDLE NVH
CRUISE NVH
ACCELERATION
NVH
ACCELERATION
WOT
DECELERATION
NVH
TRANSIENTS
NVH
TAKE-OFF
DRIVEAWAY
NVH
TIP-IN / TIP OUT
NVH
STEERING NVH
ENGINE START
UP / SHUT OFF
NVH
AUTOMATIC
TRANS. SHIFT
NVH
35
DFNVH
Process Flow and Target Cascade
Acceleration NVH Target Cascade
CUSTOMER
PERCEIVED P/T NVH
AIRBORNE NOISE
P/T RADIATED
NOISE
AIRBORNE
NOISE REDUCTION
STRUCTURE-BORNE
NOISE
BODY ACOUSTIC
SENSITIVTY
P/T VIBRATION
MOUNT
FORCES
MOUNT
DYNAMIC
STIFFNESS
36
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
37
components such as cross members and joints.
DFNVH
Process Flow and Target Cascade
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.
38
DFNVH
Process Flow and Target Cascade
•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.
39
DFNVH
Process Flow and Target Cascade
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
40
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.
41
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
42
DFNVH Process Fundamentals
Source-Path-Responder
Excitation
Sensitivity
Response
Excitation Source Examples: • Engine Firing Pulses
•
•
•
•
•
•
Driveshaft Imbalance
Rough Road
Tire Imbalance
Speed Bump
Gear Meshing
Body-Shape Induced
Vortices
43
DFNVH Process Fundamentals
Source-Path-Responder
Excitation
Sensitivity Response
Sensitivity:
Tendency of the path to transmit energy from
the source to the responder, commonly referred
to as the transfer function of the system
44
DFNVH Process Fundamentals
Source-Path-Responder
Example: Body Sensitivity
Interior Sound
Pressure
Tactile
 Point mobility (v/F)
(Structural velocity induced by force)
STRUCTURE
p (dB)
Force Input
at Driving Point
V (mm/s) Vibration Velocity
F (N)
Acoustic
 Airborne (p/p)
at Driving Point
Interior Sound
Pressure
STRUCTURE
p (dB)
(Airborne sound pressure induced by pressure waves)
 Structureborne (p/F)
(Airborne sound pressure induced by force)
p (dB)
Airborne Noise
45
DFNVH Process Fundamentals
Source-Path-Responder
Body Sensitivity Demonstration
Typical Point Mobility Spectrum for Compliant & Stiff Structures
Point Mobility (V/F)
Point Mobility
More
Compliant
Less
Compliant
50
Frequency ( f )
140
46
DFNVH Process Fundamentals
Source-Path-Responder
Excitation
Response:
S/W = Steering Wheel
Sensitivity Response
Objective
Subjective
(measurable)
(customer perception)
• S/W Shake
• S/W Nibble
• Seat Track (Triax)
• Spindle Fore/Aft
• Tie Rod Lateral
• S/W Shake (vertical)
• S/W Nibble (rotational)
• Seat Track (non-specific)
47
DFNVH Process Fundamentals
Tailpipe
Body Acoustic
Attenuation (dB)
Intake Orifice
Engine Radiated
Sound
Airborne NVH
Airborne P/T NVH
Source-Path-Responder
Powertrain
Noise Model
Body Acoustic
Attenuation (dB)
Active Engine
Vibration
(X, Y, Z)
Mount
Stiffness (N/mm)
Body Acoustic
Sensitivity
Active Exhaust
Vibration
(X, Y, Z)
Mount
Stiffness (N/mm)
Body Acoustic
Sensitivity
Structure-borne NVH
Structure-borne P/T NVH
Driver Right Ear
(dBA)
48
DFNVH Process Fundamentals
Source-Path-Responder
Road Noise (P)
Road Noise
Model
NPA
+
Chassis Forces
to Body (F)
Body/Frame
Sensitivity (P/F)
Sub-structuring
Tire/Wheel Forces
Road Profile
+
Suspension
Force Isolation
MA
Tire/Road Force
Transfer Function
Suspension/Frame
Modes
Tire/Wheel Modes &
Design Parameters
Suspension/Frame
Design Parameters
Modal
Analysis (MA)
Body Modes
Body Design
Parameters
49
DFNVH Process Fundamentals
Source-Path-Responder
Driveline
Model
50
DFNVH Process Fundamentals
Sound 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
51
DFNVH Process Fundamentals
Sound 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)
52
DFNVH Process Fundamentals
Sound 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
53
DFNVH Process Fundamentals
Sound Quality
Binaural Acoustic “Heads”
Stereo Sound
Recording
representing
sound wave
interaction w/
human torso
54
DFNVH Process Fundamentals
Sound Quality
Sound Quality Listening Room
Used for
Customer
Listening
Clinics.
55
DFNVH Process Fundamentals
Sound Quality
Poor Sound Quality
Good Sound Quality
56
DFNVH Process Fundamentals
Sound Quality
Quantifying Door Closing Sound Quality
1. Sound Level (Loudness)
2. Frequency Content (Sharpness)
3. Temporal Behavior
57
DFNVH Process Fundamentals
Sound Quality
What Makes A Good Door Closing Sound?
Good Sound
Quiet
Low Frequency
(Solid)
One Impact
No Extraneous Noise
Poor Sound
Loud
High Frequency
(Tinny, Cheap)
Rings On (Bell)
Rattles, Chirps, etc.
58
DFNVH Process Fundamentals
Sound Quality
Example: Qualifying Door Closing Sound Quality
Bad
Frequency (Hz)
(y-axis)
Good
Level (dBa)
(color)
Time (sec.)
(x-axis)
59
DFNVH Process Fundamentals
Sound Quality
Design for Sound Quality
Door Closing Example
Perceived Sound
Structure-borne
Radiated Snd.
Latch Forces
Inertia
Spring Rates
Airborne
Seal Trans Loss
Str. Compliance
Material
60
DFNVH Process Fundamentals
Sound 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
61
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
62
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
63
Airborne NVH
NVH Design Principles
Source
Path
Radiated/Shell Noise
Acoustic Attenuation
Tube Inlet/Outlet Noise
Acoustic Attenuation
Impactive Noise
Acoustic Attenuation
Air Impingement Noise
Acoustic Attenuation
Responder
Environment
Sensitivity
Structure-borne
NVH
Customer
Excitation
Source, Energy
Input
Isolation
Stiffness
Structure
Sensitivity
Isolation
Damping
64
Airborne NVH
NVH Design Principles
Source
Path
Radiated/Shell Noise
Acoustic Attenuation
Tube Inlet/Outlet Noise
Acoustic Attenuation
Impactive Noise
Acoustic Attenuation
Air Impingement Noise
Acoustic Attenuation
Responder
Environment
Sensitivity
Structure-borne
NVH
Customer
Excitation
Source, Energy
Input
Isolation
Stiffness
Structure
Sensitivity
Isolation
Damping
65
Design Principles – Airborne NVH
Radiated/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
66
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)
67
Design Principles – Airborne NVH
Tube 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
68
Design Principles – Airborne NVH
Tube 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
69
Design Principles – Airborne NVH
Tube Inlet/Outlet Airflow Noise
V6 Intake Manifolds
70
Design Principles – Airborne NVH
Impactive 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
71
Design Principles – Airborne NVH
Impactive Noise
Air Pumping
Air forced in and out of voids is called “air pumping”
72
Design Principles – Airborne NVH
Impactive 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)
73
Design Principles – Airborne NVH
Air 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
74
Design Principles – Airborne NVH
Air 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
75
Airborne NVH
NVH Design Principles
Source
Path
Radiated/Shell Noise
Acoustic Attenuation
Tube Inlet/Outlet Noise
Acoustic Attenuation
Impactive Noise
Acoustic Attenuation
Air Impingement Noise
Acoustic Attenuation
Responder
Environment
Sensitivity
Structure-borne
NVH
Customer
Excitation
Source, Energy
Input
Isolation
Stiffness
Structure
Sensitivity
Isolation
Damping
76
Design Principles – Airborne NVH
Airborne Noise Path Treatment
Noise Reduction
Engine
Compartment
Absorption
Interior
Absorption
Body &
Insulator Blocking
(Panels)
Pass-Thru Sealing
(Components)
77
Design Principles – Airborne NVH
Airborne 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
78
Design Principles – Airborne NVH
Airborne Noise Path Treatment
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 (1030 mm) absorb sound
• Pass-thru penetration
seals weaker than steel
79
Airborne NVH
NVH Design Principles
Source
Path
Radiated/Shell Noise
Acoustic Attenuation
Tube Inlet/Outlet Noise
Acoustic Attenuation
Impactive Noise
Acoustic Attenuation
Air Impingement Noise
Acoustic Attenuation
Responder
Environment
Sensitivity
Structure-borne
NVH
Customer
Excitation
Source, Energy
Input
Isolation
Stiffness
Structure
Sensitivity
Isolation
Damping
80
Design Principles – Airborne NVH
Airborne 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
81
Airborne NVH
NVH Design Principles
Source
Path
Radiated/Shell Noise
Acoustic Attenuation
Tube Inlet/Outlet Noise
Acoustic Attenuation
Impactive Noise
Acoustic Attenuation
Air Impingement Noise
Acoustic Attenuation
Responder
Environment
Sensitivity
Structure-borne
NVH
Customer
Excitation
Source, Energy
Input
Isolation
Stiffness
Structure
Sensitivity
Isolation
Damping
82
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.
83
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.)
84
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.
85
Design Principles – Structureborne NVH
Natural frequencies of major structures need to be separated to
avoid magnification.
86
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.
87
Airborne NVH
NVH Design Principles
Source
Path
Radiated/Shell Noise
Acoustic Attenuation
Tube Inlet/Outlet Noise
Acoustic Attenuation
Impactive Noise
Acoustic Attenuation
Air Impingement Noise
Acoustic Attenuation
Responder
Environment
Sensitivity
Structure-borne
NVH
Customer
Excitation
Source, Energy
Input
Isolation
Stiffness
Structure
Sensitivity
Isolation
Damping
88
Design Principles – Structureborne NVH
Excitation 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.
89
Design Principles – Structureborne NVH
Excitation Source
Design action(s):
• Achieve high overall structural rigidity
• Minimize unbalance
• Achieve high stiffness at attachment points of
the excitation objects
90
Design Principles – Structureborne NVH
Excitation Source
A/C Compressor – Bad Example
Cantilever
Effect 
Less Rigid
91
Design Principles – Structureborne NVH
Excitation Source
A/C Compressor - Good Example
92
Airborne NVH
NVH Design Principles
Source
Path
Radiated/Shell Noise
Acoustic Attenuation
Tube Inlet/Outlet Noise
Acoustic Attenuation
Impactive Noise
Acoustic Attenuation
Air Impingement Noise
Acoustic Attenuation
Responder
Environment
Sensitivity
Structure-borne
NVH
Customer
Excitation
Source, Energy
Input
Isolation
Stiffness
Structure
Sensitivity
Isolation
Damping
93
Design Principles – Structureborne NVH
Path - 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.
94
Design Principles – Structureborne NVH
Path - 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.
95
Design Principles – Structureborne NVH
Path - Isolation Strategy
Tuning and Degree of Isolation
By moving
natural
frequency down
for this system
it increased
damping at 100
Hz
96
Airborne NVH
NVH Design Principles
Source
Path
Radiated/Shell Noise
Acoustic Attenuation
Tube Inlet/Outlet Noise
Acoustic Attenuation
Impactive Noise
Acoustic Attenuation
Air Impingement Noise
Acoustic Attenuation
Responder
Environment
Sensitivity
Structure-borne
NVH
Customer
Excitation
Source, Energy
Input
Isolation
Stiffness
Structure
Sensitivity
Isolation
Damping
97
Design Principles – Structureborne NVH
Structure 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
98
Design Principles – Structureborne NVH
Structure 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.
99
Design Principles – Structureborne NVH
Structure 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
100
Design Principles – Structureborne NVH
Structure Sensitivity Strategy
Body Modes and Body Architecture
101
Design Principles – Structureborne NVH
Structure Sensitivity Strategy
Body Modes and Body Architecture
102
Design Principles – Structureborne NVH
Structure 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.
103
Design Principles – Structureborne NVH
Structure 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
104
Design Principles – Structureborne NVH
Structure 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 antinodes.
105
Design Principles – Structureborne NVH
Structure 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.
106
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
107
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.
108
Wind Noise Example
Wind Noise Target Cascade Diagram
Vehicle level
Wind Noise
Transmission
Loss
Excitation
Sources
Seals
Antenna /
Accessories
Green House
Shape
Mirror
Shape
Open
Windows /
Sunroof
Aspiration
Leaks
Glass / Panels
Static
Sealing
Dynamic
Sealing
Door
System
Stiffness
109
Wind Noise Example
110
Wind Noise Example
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
111
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
112
• 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
113
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.
114
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.
115
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.
116
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.
117
Design For NVH
2002 Mercury Mountaineer
Body sculpted for less wind resistance with glass and door edges
shifted out of airflow.
118
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
119
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
120
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
121
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
122