dfnvh - Technical Entrepreneurship Case Studies Curricular

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 becomes the dominant factor in comparing barriers .

10

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

*

Overall Handling

Relative

Leverage 6.9

Cup holders

5

*

65%

REVIEW

77%

Exterior Styling *

MAINTAIN

85%

20

Introduction to NVH

Why Design for NVH?

NVH Can Both Dissatisfy and Delight

KANO Model + Customer

Satisfaction

Exciting Quality

(Surprise & Delight)

Performance Quality

(Attributes)

Sound Quality

TGR

Harley

Mustang

Lexus

+ Degree of Achievement

+ Performance

- Performance

Dissatisfiers Basic Quality

(Inhibitors)

Axle Whine

Wind Noise

Unusual Noises

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







– Airborne NVH



• Impactive Noise





• 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







– Airborne NVH



• Impactive Noise





• 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


30

DFNVH


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

31

DFNVH


Systems Engineering “V” and PD Process Timing

KO SI

Customer

Wants/Needs

Define Req’s

SC PA PR

Vehicle (VDS - P/T NVH etc)

CP J1

Customer

Satisfaction

Confirm

Cascade Targets

& Iterate

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

Subsystem (stiffness, ....)

Verify & Optimize

Components CDS

Optimize

32

DFNVH


Trade-Offs Flow Chart

Program Specific Wants

PALS (QFD, VOC, etc.)

Functional Images for

Segment - R202

Vehicle Assumptions Fixed

SLA or McPherson Strut Suspension

SI

Vehicle Level Target Ranges

Subjective (1-10) and Objective

System & Sub-System

Targets

Force or P/F Targets

Determined with

Parametric Models

Preliminary Target Ranges

Future Functional Attribute

Targets

Objective Target Ranges -

VDS

Trade-Off Loop

Perform Iterations Until Assumptions

Comparable

System/Sub-System Assumptions

McPherson vs. SLA, etc.

Requires Hardware Parametric

Model

Affordable Business

Structure (ABS)

Is Gross Architecture Feasible?

Component End Item

Targets

Component Resonant

Frequencies, etc.

PA

Design Optimization

CAE Optimization

Hardware Development

Development

33

DFNVH


NVH Functional Attribute

Sub -Attributes

Road Wind P/T Brake Comp. S.Q.

S&R Pass-by Noise (Reg.)

34

DFNVH


Convert attribute target strategy to objective targets

POWERTRAIN

NVH

IDLE NVH CRUISE NVH

ACCELERATION

NVH

DECELERATION

NVH

TRANSIENTS

NVH

STEERING NVH

ACCELERATION

WOT

TAKE-OFF

DRIVEAWAY

NVH

TIP-IN / TIP OUT

NVH

ENGINE START

UP / SHUT OFF

NVH

AUTOMATIC

TRANS. SHIFT

NVH

35

DFNVH


Acceleration NVH Target Cascade

CUSTOMER

PERCEIVED P/T NVH

AIRBORNE NOISE

P/T RADIATED

NOISE

AIRBORNE

NOISE REDUCTION

STRUCTURE-BORNE

NOISE

BODY ACOUSTIC

SENSITIVTY

MOUNT

FORCES

P/T VIBRATION

MOUNT

DYNAMIC

STIFFNESS

36

DFNVH


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. 37

DFNVH


Operating Condition NVH Concerns

Idle

Lugging

Shake and boom due to engine torque.

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

Braking

"Moan" due to powertrain bending.

Squeal due to brake stick-slip.

38

DFNVH


•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


NVH Aspect Subjective Response

Boom Low frequency sound 20 - 100 hz.

Drone

Growl

Groan

Moan

Squeak

Whine

Large amplitude pure tone in the region 100-200 hz

Modulated low/medium frequency broad band noise

100-1000 hz

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

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

High pitched broadband transient noise.

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

40

DFNVH


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




• Process Flow and Target Cascade



– Airborne NVH



• Impactive Noise





• 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




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



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)

STRUCTURE

Interior Sound

Pressure p (dB)

Force Input at Driving Point

F (N)

V (mm/s)

Vibration Velocity at Driving Point

STRUCTURE p (dB)

Airborne Noise

Interior Sound

Pressure p (dB)

45



Body Sensitivity Demonstration

Typical Point Mobility Spectrum for Compliant & Stiff Structures

More

Compliant

Point Mobility

50 Frequency ( f )

Less

Compliant

140

46




Response:

S/W = Steering Wheel

Objective

(measurable)

• S/W Shake

• S/W Nibble

• Seat Track (Triax)

• Spindle Fore/Aft

• Tie Rod Lateral

Subjective

(customer perception)

• S/W Shake (vertical)

• S/W Nibble (rotational)

• Seat Track (non-specific)

47



Tailpipe

Body Acoustic

Attenuation (dB)

Intake Orifice Powertrain

Noise Model

Engine Radiated

Sound

Body Acoustic

Attenuation (dB)

Driver Right Ear

(dBA)

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

48



Road Noise (P) Road Noise

Model

+

Chassis Forces to Body (F)

Sub-structuring

NPA

Body/Frame

Sensitivity (P/F)

Tire/Wheel Forces

+

Modal

Analysis (MA)

Road Profile

Tire/Road Force

Transfer Function

Suspension

Force Isolation

MA

Suspension/Frame

Modes

Body Modes

Tire/Wheel Modes &

Design Parameters

Suspension/Frame

Design Parameters

Body Design

Parameters

49



Driveline

Model

50


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


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


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


Sound Quality

Binaural Acoustic “Heads”

Stereo Sound

Recording representing sound wave interaction w/ human torso

54


Sound Quality

Sound Quality Listening Room

Used for

Customer

Listening

Clinics.

55


Sound Quality

Poor Sound Quality Good Sound Quality

56


Sound Quality

Quantifying Door Closing Sound Quality

1. Sound Level (Loudness)

2. Frequency Content (Sharpness)

3. Temporal Behavior

57


Sound Quality

What Makes A Good Door Closing Sound?

Good Sound Poor Sound

Quiet

Low Frequency

(Solid)

One Impact

No Extraneous Noise

Loud

High Frequency

(Tinny, Cheap)

Rings On (Bell)

Rattles, Chirps, etc.

58


Sound Quality

Example: Qualifying Door Closing Sound Quality

Good Bad

Level (dBa)

(color)

Time (sec.)

(x-axis)

59


Sound Quality

Design for Sound Quality

Door Closing Example

Perceived Sound

Structure-borne Airborne

Radiated Snd.

Seal Trans Loss

Latch Forces Str. Compliance

Inertia Spring Rates Material

60


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




• Process Flow and Target Cascade



– Airborne NVH



• Impactive Noise





• 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


Source Path Responder

Radiated/Shell Noise

Tube Inlet/Outlet Noise

Impactive Noise

Air Impingement Noise

Acoustic Attenuation




Environment

Sensitivity

Customer

Excitation

Source, Energy

Input

Isolation

Stiffness

Isolation

Damping

Structure

Sensitivity

64


Responder Source



Impactive Noise


Path





Environment

Sensitivity

Customer

Excitation

Source, Energy

Input

Isolation

Stiffness

Isolation

Damping

Structure

Sensitivity

65

Design Principles – Airborne NVH


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 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


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


• Reduce the resistance in the fluid flow

68



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



V6 Intake Manifolds

70


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


Impactive Noise

Air Pumping

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

72


Impactive Noise


• Reduce the stiffness of the impacting surfaces

• Increase damping of impacting surfaces


• 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



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


• Reduce the turbulence in the fluid flow

74




• 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





Impactive Noise


Path





Environment

Sensitivity

Customer

Excitation

Source, Energy

Input

Isolation

Stiffness

Isolation

Damping

Structure

Sensitivity

76


Airborne Noise Path Treatment

Noise Reduction

Engine

Compartment

Absorption

Body &

Insulator Blocking

(Panels)

Pass-Thru Sealing

(Components)

Interior

Absorption

77


Airborne Noise Path Treatment


• Absorb noise from the source

• Block the source noise from coming in

• Absorb the noise after it is in


• 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


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 (10-

30 mm) absorb sound

• Pass-thru penetration seals weaker than steel

79





Impactive Noise


Path





Environment

Sensitivity

Customer

Excitation

Source, Energy

Input

Isolation

Stiffness

Isolation

Damping

Structure

Sensitivity

80


Airborne Noise Responder Treatment


• Absorb noise at listener

• Block noise at listener

• Breakup of acoustic wave pattern


• Surround listener with absorbing materials

• Ear plugs

• Design the surrounding geometry to avoid standing waves

• Add active noise cancellation/control devices

81





Impactive Noise


Path





Environment

Sensitivity

Customer

Excitation

Source, Energy

Input

Isolation

Stiffness

Isolation

Damping

Structure

Sensitivity

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


• 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


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

85


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

86


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





Impactive Noise


Path





Environment

Sensitivity

Customer

Excitation

Source, Energy

Input

Isolation

Stiffness

Isolation

Damping

Structure

Sensitivity

88


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.


• Reduce the level of interactions as much as possible.

• Take additional actions when it is impossible to reduce interactions.

89


Excitation Source


• Achieve high overall structural rigidity

• Minimize unbalance

• Achieve high stiffness at attachment points of the excitation objects

90


Excitation Source

A/C Compressor – Bad Example

Cantilever

Effect 

Less Rigid

91


Excitation Source

A/C Compressor - Good Example

92





Impactive Noise


Path





Environment

Sensitivity

Customer

Excitation

Source, Energy

Input

Isolation

Stiffness

Isolation

Damping

Structure

Sensitivity

93


Path - Isolation Strategy

Mechanism:

• Path transfers mechanical energy in the form of forces or vibration. Normally path is mathematically simulated by spring or damper.


• 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




• 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



Tuning and Degree of Isolation

By moving natural frequency down for this system it increased damping at 100

Hz

96





Impactive Noise


Path





Environment

Sensitivity

Customer

Excitation

Source, Energy

Input

Isolation

Stiffness

Isolation

Damping

Structure

Sensitivity

97


Structure Sensitivity Strategy

Mechanism:

• Structural motion that results when input force causes the structure to respond at its natural modes of vibration.


• Reduce the amplitude of structural motions by

– controlling stiffness and mass (quantity and distribution),

– managing excitation input locations

98




• 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



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




101




102



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



 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



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



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







– Airborne NVH



• Impactive Noise





• 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 Target Cascade Diagram

Vehicle level

Wind Noise

Transmission

Loss

Excitation

Sources

Antenna /

Accessories

Open

Windows /

Sunroof

Mirror

Shape

Green House

Shape

Dynamic

Sealing

Aspiration

Leaks

Door

System

Stiffness

Seals

Glass / Panels

Static

Sealing

109


110


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


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



• Key DFNVH Principles

– Airborne NVH



• Impactive Noise




• 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

dfnvh - Technical Entrepreneurship Case Studies Curricular

Noise:

Introduction to NVH

Cost rules

Sensitivity:

What is Sound Quality?

Why Sound Quality?

The Sound Quality Process

Conclusions

Design action(s):

Design principle(s):

f

f

Design action(s):

A/C Compressor – Bad Example

A/C Compressor - Good Example

Design action(s):

Tuning and Degree of Isolation

Mechanism:

Design principle(s):

Design action(s):

Wind Noise Target Cascade Diagram

Aerodynamic excitation

Aspiration leakage

Design For NVH

Design For NVH

Design For NVH

Related documents

Products

Support

dfnvh - Technical Entrepreneurship Case Studies Curricular

Noise:

Introduction to NVH

Cost rules

Sensitivity:

What is Sound Quality?

Why Sound Quality?

The Sound Quality Process

Conclusions

Design action(s):

Design principle(s):

f

f

Design action(s):

A/C Compressor – Bad Example

A/C Compressor - Good Example

Design action(s):

Tuning and Degree of Isolation

Mechanism:

Design principle(s):

Design action(s):

Wind Noise Target Cascade Diagram

Aerodynamic excitation

Aspiration leakage

Design For NVH

Design For NVH

Design For NVH

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