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NVH Category. NVH CharacteristicFrequency (Hz) Steady State Frequency Response Ride< 5 Shake5 - 40 Boom20 - 100 Moan100 - 150 Structural Borne Noise150 – 500 Air Borne Noise> 500 Transient Response Harshness20 - 100. Control by Damping. Control by Dynamic - PowerPoint PPT Presentation

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NVH Category

NVH Characteristic Frequency (Hz)Steady State Frequency Response• Ride < 5• Shake 5 - 40• Boom 20 - 100• Moan 100 - 150• Structural Borne Noise 150 – 500• Air Borne Noise > 500

Transient Response• Harshness 20 - 100

Single Degree of Freedom

Frequency (Hz)

Am

plit

ud

e (2

0% D

amp

ed)

Control byDynamicStiffness

Control byMass

Control byDamping

Isolation Region

2fn * fn

Dynamic Stiffness

Dynamic Stiffness:

(K - m ω2) – j C ω

K* = ----------------------------------

(K - m ω2)2 + (C ω)2

Mass M

Damping CStiffness K

ω = 2* π*f

f is the frequency

Pure Tone

• Sound at a single frequency

• Sound Pressure– Objective measurement

• dB– Logarithmic of sound pressure

• dBA– A-Weighted to adjust for ear sensitivity

Human Sensitivity

• More constant across frequency range with velocity

• Hearing range 20 – 2000 Hz

• Depends on overall level

• Sound at one frequency may mask by other frequencies

• Depends on age, sex and other factors

Tactile ResponseSubjective-Objective

Acceleratio

nA

cceleration

FrequencyFrequency

SR = 6SR = 6

SR = 5SR = 5

Tactile ResponseSubjective-Objective (2)

Velo

cityV

elocity

FrequencyFrequency

SR = 6SR = 6

SR = 5SR = 5

Sound Pressure Level and A Weighting

NVH Classification

• Operating Condition– Idle, Low Speed, Cruising, POT, WOT

• Subjective Evaluation– Shake, Boom, Noise, Harshness

• Objective Measurement– Sound Pressure, Acceleration

• Frequency Range• Source

– Powertrain, Road, Exhaust

NVH Subjective Rating

MostTargetsNo Sale

NVH Objectives

• Assess vehicle responses relative to design targets:–Tactile responses

• Seat track• Steering column• Toe pan

–Acoustic responses• Driver’s ear• Front Passenger’s ear• Rear passenger’s ear

Shake

• 5 – 40 Hz

• Idle Shake

• Isolated Road Shake

• Rough Road Shake

• Smooth Road Shake– Wheel/Tire Imbalance– Tire Force Variation

Design For Shake

• Body vertical, lateral bending and torsion modes

• Front end bending and torsion modes• Front floor modes• Steering column modes• Seat modes• Avoid stickiness of the shock and CV

joints that causes high force input and resonance in smooth road shake

Design For Shake (2)

• Mode separation and mode shape management of engine bounce, roll, pitch and yaw rigid body modes

Boom

• 20 - 100 Hz

• Idle Boom

• Isolated Road Boom

• Rough Road Boom

Body Design for Boom

• 1st and 2nd fore-aft acoustic modes• Body 1st and 2nd order vertical bending• Front floor vertical bending• Dash panel fore-aft bending• Quarter panel bending• Fuel tank bounce• Spare tire tub bounce• Decklid, liftgate or lower back panel pumping

Structural Borne Noise

• 100 - 500 Hz

• Powertrain Noise

• Rough Road Noise

• Gear Whine

Design For Noise

• Most of the vibration energy imparted to the vehicle is below 150 Hz.

• Below 150 Hz:– Body structure is important for controlling noise and

vibration – Lack of structure usually results in costly design and

tooling changes• Above 150 Hz:

– Can be resolved with relatively simple structure modifications, such as bead patterns, or damping treatments.

Design For Noise (2)

• Powertrain Bending Isolation• Powertrain Bracket Isolation

0 5 10 15 20 25 30 35 40 45 50

CHASSIS/POWERTRAIN MODES

Ride ModesPowertrain Modes

Suspension Hop and Tramp Modes

Suspension Longitudinal ModesExhaust Modes

0 5 10 15 20 25 30 35 40 45 50

BODY/ACOUSTIC MODES

Body First Bending (22Hz)

Body First Torsion (25Hz) Steering Column First Vertical Bending (29Hz)

0 5 10 15 20 25 30 35 40 45 50

EXCITATION SOURCES

Inherent Excitations (General Road Spectrum, Reciprocating Unbalance, Gas Torque, etc.)Process Variation Excitations (Engine, Driveline, Accessory, Wheel/Tire Unbalances)

First Order Wheel/Tire Unbalance (5-75MPH)V8 Idle (500-550RPM)

Hot Cold

Hz

Hz

Hz

First F/A Acoustic Modes (48Hz)

Modal Chart

Body-in-White Targets

• Static Stiffness– Bending– Torsion

• Normal Modes– Vertical bending– Torsion– Lateral bending

Trimmed Body Targets

• Normal Modes– Vertical bending– Torsion– Lateral bending– Front end bending– Front end torsion

Instrument Panel/Column Targets

• Normal Modes– Vertical bending– Lateral bending

Seat Targets

• Normal Modes– On Bedplate

• Fore aft• Lateral

– In Vehicle• Fore aft• Lateral

• Different row may have different target

Idle Load

recipreciprecip amF *

borecrankboregas APPF *)(

tan**)( hFFT recipgastotal

r

h

Pbore

Pcrank

mrecip

arecip

L

Idle Torque

coscos rLh

2sin1cos LL

cossin1 2 rLh

2sin1cos

L

r sinsin

r

h

Pbore

Pcrank

mrecip

arecip

L

Piston Displacement

dt

duvw

dt

dvuw

dt

dwuv

dt

duvwdt

dv

dt

du

dt

vuddt

dunu

dt

du

dt

d

dt

ddt

d

dt

d

nn

)(

sincos

cossin

1

r

h

Pbore

Pcrank

mrecip

recip

L

Trigonometric Derivatives

222

222

2

sin

sincossin

sin

sincossin

)coscos(

rL

rr

rL

rr

dt

d

rLdt

d

dt

dhv

r

h

Pbore

Pcrank

mrecip

arecip

L

Piston Velocity

23222

224

222

22

222

)sin(

sincos

sin

2coscos

)sin

sincos(sin)(

rL

r

rL

rr

rL

r

dt

dr

dt

dva

r

h

Pbore

Pcrank

mrecip

arecip

L

Piston Acceleration

Smooth Road Shake

Wheel/Tire Imbalance Definition

• Simulation– Shake caused by the unbalanced inertia forces from the

high speed rotation of the unbalanced wheel in vehicle cruising

• Load– 1.0 oz-inch (Sensitivity) unbalanced force at the spindles– Both vertical and fore-aft loads with vertical load trailing

fore-aft load by 90 degrees

• Applications– Front wheel in-phase, Front wheel out-of-phase, Rear

wheel in-phase and Rear wheel out-of-phase

Wheel/Tire Imbalance Calculation

• F = mr2

– F is imbalance Force (N)– m is imbalance mass (Mg)– r is imbalance radius (mm) is rotation speed (rad/sec)

• F = 1.0 oz-in = 1.0 * 28.3 * 10-6 (Mg/oz) * 25.4 (mm/inch) * 4 * 2 * f2 = 0.0284 * f2 (N)– f is frequency (cycles/sec)

Wheel/Tire ImbalanceSpeed Map

• The wheel/tire speed map (frequency v.s. vehicle speed) is dependent on the wheel/tire size, the wheel/tire stiffness and the payload

• V = 2 * π * Tire Effective Radius * Frequency• However, the Frequency/Vehicle Speed(MPH) is

typically around 0.2• Based on the above assumption, the frequency

range of interest from 25 MPH to 125 MPH is– 5 Hz to 25 Hz

Tire Force Variation Definition

• Simulation– Shake caused by the variation of the radial stiffness of

the tires

• Load– 1.0 lbf (Sensitivity) variation force at the spindles

– Vertical load only

• Applications– Front wheel in-phase, Front wheel out-of-phase, Rear

wheel in-phase and Rear wheel out-of-phase

Tire Force VariationSpeed Map

• The wheel/tire speed map (frequency v.s. vehicle speed) is dependent on the wheel/tire size, the wheel/tire stiffness and the payload

• V = 2 * π * Tire Effective Radius * Frequency• However, the Frequency/Vehicle Speed(MPH) is

typically around 0.2• Based on the above assumption, the frequency

ranges of interest from 25 MPH to 125 MPH are– First Order : 5 Hz to 25 Hz– Second Order : 10 Hz to 50 Hz

Rough Road Noise

Spatial PSD Road Profile

• Spatial Frequency ( Cycles / mm)– Wave number– 1 / wavelength

• PSD Amplitude (mm^2 / (cycles / mm))• Power Regression Analysis (Y = 1.7872 * X-0.6729)

Spacial PSD Road Profile

y = 1.7872x-0.6729

R2 = 0.6538

1

10

100

1000

0.0001 0.0010 0.0100 0.1000

Wave Number (cycles/mm)

PS

D (

mm

^2

/(c

yc

les

/mm

))

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