Introduction To Automotive NVH [PDF]

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VIT M. TECH. (AUTO) COURSE (Noise, Vibration and Harshness )

INTRODUCTION TO AUTOMOTIVE NVH

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Necessity of NVH Awareness SOUND IS A PROPAGATING TYPE OF ENERGY. NOISE IS A UNWANTED SOUND. ƒ NOISE

- AUDIBLE

ƒ VIBRATION

- TACTILE

ƒ HARSHNESS - TACTILE AND AUDIBLE (15Hz - 300Hz)

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Necessity of NVH ¾ Noise Pollution – CMVR, CPCB & NCNPC ¾ Customer Awareness Of Vehicle Ride Comfort ¾ Marketability ¾Trend Towards Higher Power And Smaller Size Power trains. ¾ Sound Quality ¾ Design Optimization ¾ Consistency In Production

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PASS BY NOISE

RIDE COMFORT

SPL OEL

EXTERIOR

INTERIOR

NOISE

NOISE

SOUND QUALITY

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Noise Contributions from Various Systems Other Structural Components 10%

Miscellaneous 3% Engine 21%

Fan & Radiator Assembly 6%

Drive Line 14% Exhaust System 32%

Intake System 14%

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Automotive Noise Sources-Levels and Frequency Bands

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NVH Classification „

By Noise Type „ Road NVH „ Wind noise „ Powertrain/Driveline NVH „ Squeak and Rattle

„

By Vehicle Systems „ Body NVH „ Chassis NVH „ Powertrain/Driveline NVH „ Vehicle components „ Climate control system „ Wipers „ Seat motors „ Switches

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NVH Sources and their inter-relation Power-train

Sound Quality

Ride Comfort

Engine Transmission

Intake system Cooling system

Harshness

Others

Exhaust system

Mount

Vibration

Brake System Road and Tyre Wind

Noise

Suspension Air

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Sound Quality

Sound quality (SQ) is the perceptual reaction to the sound of a product that reflects the listener’s reaction to the acceptability of that sound for that product; the more acceptable, the greater the SQ Both objective & subjective assessments need to be made

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Pass-by Noise of Automotive Vehicles

¾ ¾

Community Noise Pollution.(IS-3028/ISO-362) Maximum Sound Pressure level in “dB(A) measured at a distance of 7.5m from the vehicle during vehicle accelerated to full throttle

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Pass-by Noise of Automotive Vehicles A’

B’ Microphone location point 1.2 ± 0.1 m above ground

7.5 ± 0.2 m

C

C’ 7.5 ± 0.2 m Microphone location point 1.2 ± 0.1 m above ground 10 ± 0.2m

A

10 ± 0.2m

B

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Pass-by Noise of Automotive Vehicles

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Legislative Noise Requirements 2 Wheelers < 80 cc

75

80 cc & 175 cc

77

> 175 cc

80 3 Wheelers

< 175 cc

77

> 175 cc

77 4 w heelers

M1

74 M2/N1

GVW < 2 ton

76

2 – 3.5 ton

77 M2/M3

< 150 Kw

78

>= 150 kW

80 N2/N3

< 75 kW

77

75 – 150 kW

78

> 150 kW

80

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Interior Noise of Vehicle ¾ ¾ ¾ ¾ ¾ ¾

One of the most decisive selling points for passenger car is the level and quality of interior noise. Like exterior noise engine is the main source of vehicle interior noise.It gets transmitted inside the vehicle by, Direct infiltration: Improper sealing , Holes in the lower dash panel Structural vibrations Engine mounts, loops in the exhaust system Drive shafts, support bearing ,rear axle drive shaft.

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Interior Noise Sources Intake System

Exhaust System

Surface Noise Radiation Orifice Noise System Vibrations

Wind Noise

Surface Noise Radiation Tailpipe Noise System Vibrations

Transfer Behaviour

Wheel Suspension

Vehicle Interior Noise Drive Train

of Noise and Vibration

Tyre

Power Train

Engine and Gearbox Surface Global Power Train Mode Local Mode (P/T Mode, P/T Mount Brackets Accessories)

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Interior Noise of Vehicle

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Power Train –Engine Noise Types of Engine Noise ¾

Airborne Noise : Exhaust and Intake

¾

Structure borne Noise : Vibrating surfaces of engine structure and connected covers

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Power Train –Engine Noise

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Power Train –Engine Noise Main Excitation Forces and Structure borne Engine Noise : Combustion Noise: Unidirectional gas & Inertia forces cause combustion noise. Mechanical Noise : Reversible forces created due to crank mechanism induce mechanical noise.

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Power Train –Engine Noise

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Intake Noise Noise Generated due to ¾ Opening and closing of the valves. ¾

Inlet air column oscillation by sharp pressure pulse from cylinder.

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Exhaust Noise ¾ ¾

Exhaust valve opens and releases gas at high pressure into the exhaust system. The principal component of noise - Fundamental and harmonics of firing frequency.

Exhaust system design is a compromise between noise reduction and engine power loss due to increase in back pressure.

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Clutch Noise Clutch Judder is basically torsional vibration in the drive line during starting of engagement. This results in rough starts and affects the ride comfort. The major causes are : ¾ Friction characteristics of the clutch i. e. relationship between slip speed and the friction coefficient ¾ Torsional vibirations due to variation in axial load resulting from misalignment of the driveline ¾ The clutch pedal vibrations can cause interior noise problems

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Transmission Noise Driveline noise and vibration sources results from transmission of power from the engine to wheels. Transmission gear noise: ¾ Bending dynamics of the individual gear tooth. ¾ Both bending and torsional dynamics of gear shafts. ¾ Type and precision of gears used. ¾ Fundamental and second harmonics of the gear mesh frequency - most significant components of gear noise.

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Transmission Noise Driveshaft and Propeller shaft : ¾ Excitation at rotational(fundamental) speed. ¾ Universal joint can provide excitation at second order due to high angles of coupling. ¾ Rear wheel drive vehicles employ a constant velocity joint in the center joint of two piece propeller shaft - provides axial compliance in the driveline which decouples vibration from rear axle.

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Driveline-Axle Noise

–Gear whine generated by gear mesh of the differential. See WHINE.

¾ Vibration excited by tooth meshing action of the axle gear set. ¾ Noise is narrow band and annoying even at low levels in the passenger compartment of the vehicle. ¾ Noise due to resonance mode of the axle may be reduced by altering axle mass and stiffness so that resonance lie outside the normal operating range.

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Belt Noise • Impact generated by collision of tooth of belts against bottomland of sprocket at the beginning of meshing • Transverse and torsional vibration of the belt • Airflow between belt and pulley at meshing • Friction between belt and pulley and slip of the belt • Vibration of the pulley

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Chain Noise •impact of chain with sprocket and polygonal effect • Roller impacts of chain at higher speed • Torsional vibration of camshaft causes significant tension fluctuation in chains and magnifies chain transverse vibrations • Chain natural frequencies • Cover frequencies

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Tyre Noise Tyre noise is generated by, ¾ Rolling contact of the tyre ( a resonant system)with surface of random roughness( the road). ¾ Tread vibration - Radial vibration of tread - primary contributor noise. ¾ Tread squirm - Localized lateral vibration of tread - high frequency part of noise spectrum.

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Tyre Noise ¾Air pumping - Air is expelled from tread or road cavities at front end and sucked back at trailing edge into tread or road cavities. Tread pattern is significant in generating air pumping. ¾Aerodynamic noise -Generated by turbulent flow air around the tyre. It contributes least to tyre noise

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Wind Noise It is generated by , ¾

Flow of air around the vehicle exterior - broad band in characteristic - it may have pure tone due to vortex shedding proturbulences such as rear view mirror.

¾

Air flow into or out of the cabin due to imperfect sealing around the door frames and glass areas.

¾

Adequate window and door seals are fundamental to successful wind noise control.

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Noise Sources and Corresponding Transfer Paths

Structure- Borne Noise

Air Borne Noise

Excitation • Noise Radiation of P/T and Accessories

Transfer Behaviour • Vehicles Body Noise

• Intake and Exhaust System Shell Noise

- Firewall

• Intake Orifice Noise

- Under floor

• Tailpipe Noise • Global Engine Vibration - Local Mode - P/T Structure - P/T Mount Brackets • Accessory Vibration

Measurement Engine Test Bench

• Engine Mounts • Contact Points

Measurement Prototype Series Vehicle

Interior Noise Share Airborne Interior Noise (Amplitude + Noise) Share 1 Share n Structure-Borne Interior Noise (Amplitude + Noise)

Summation with correct phase

Interior Noise Simulation

Share 1 Share n

Calculation

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NVH Glossary – Automotive Phenomena „

Axle Noise: „

„ „

„

Gear whine generated by gear mesh of the differential.

Brake Squeal: Very high-frequency sound generated by braking

Brake Judder: „

Low-frequency shaking of the vehicle generated by braking. Usually due to brake disk thickness variation

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NVH Glossary – Automotive Phenomena „

„

„

Boom: „ Low frequency sound „ 20-100Hz,Power train,Road/suspension,Impact „ Buzz, Squeak and Rattle Chuckle: „ (shock absorber) Interior vehicle noise induced by force variation of the shock absorber. Multiple transient sounds. Clunk: „ Transient, low-frequency, broadband sound

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NVH Glossary – Automotive Phenomena „

„

Drone: „ A large-amplitude, single tone sound 100200Hz. A deep, sustained murmuring, humming or buzzing sound Gear rattle: „ (usually manual transmissions only) A noise resulting from torsional vibrations causing loss of contact and impact of transmission gear teeth. Often sounds very similar to engine pre-ignition/knock

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NVH Glossary – Automotive Phenomena „

„

„

Growl: „ Broadband, 100-1000Hz, noticeable time variation Moan: „ Low-amplitude, low frequency tone, 20-200Hz Rattle: „ Random Impact Noise. See “Gear Rattle”

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NVH Glossary – Automotive Phenomena „

„

Road and Tire Noise: „ Any noise perceived to be generated by the road and tires Roughness: „ Sound with noticeable time variation – modulation. Usually 100-500Hz tone with rapid modulation. nd „ Also, vibration from 2 -order wheel imbalance.

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NVH Glossary – Automotive Phenomena

„

„

Rumble: „ Low- to mid-frequency broadband noise, 150-500 Hz, with noticeable time variation Shake: „ A low-frequency vibration, 5-30Hz. Usually steady-state (e.g. wheel imbalance at highspeed)

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NVH Glossary – Automotive Phenomena „

„

Shuffle/Bobble: „ A fore/aft vehicle motion. Usually produced by 1st torsion mode of the powertrain. Shudder: „ A low frequency vibration; usually felt and not heard. Sometimes defined as fore/aft lateral movement. Usually somewhat transient event, as in vehicle start-up.

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NVH Glossary – Automotive Phenomena „

„

„

Tick & Hash: „ Miscellaneous time varying noises Whine: „ Mid to high frequency, 200-5000Hz, tone, sometimes with harmonics Wow: „ Low-frequency modulation of a tonal noise. Usually caused by speed variation, as with an electric motor

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Time and Frequency Domains „

NVH must take into account both time domain and frequency domain information

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Harmonics „

Harmonic: Any of a series of musical tones whose frequencies are integral multiples of the frequency of a fundamental tone. Source: The American Heritage® Dictionary of the English

Language, Fourth Edition

Frequency

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Waterfall Plots and Order Analysis

RPM

Order

Overall Level Frequency Order Level

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Engineering Measures of Sound „

„

„

Sound pressure – actual pressure change caused by sound, usually measured in Pascals (Pa). 1 Pa = 1 N/m2 Sound intensity – average amount of acoustic power passing through a unit area that is perpendicular to the direction of sound propagation. A vector quantity of sound. Can be used to indicate the source of noise, or to calculate sound power. Measured in Watts/square meter (W/m2) Sound power – acoustic power of sound, measured in Watts (W)

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Sound Weighting Schemes „

„

dB(A), dB(B), dB(C) „ Basic method of representing or approximating how humans perceive sound level Sound Quality Metrics: „ More advanced methods of approximating human perception of sound „ Sones, speech intelligibility, roughness „ Filters applied to sound signals to provide metrics which correlate with human perceptions

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Source/Path/Receiver

Source „ „ „ „

X

Path Sensitivity

= Response

Source - causes disturbance Path - may isolate or amplify disturbance Receiver - responds to disturbance NVH strategy

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NVH Tools and Methods „

„

„

„ „ „

„

Source identification „ Sound Intensity „ Sound Acoustic Holography Modal analysis „ Experimental Modal Testing „ Operating Deflection Shapes „ Operational Modal Analysis Operating Measurements „ Order tracking Noise Path Analysis CAE Sound Quality „ Sound synthesis Jury Evaluation

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Benchmarking Sources „

„

Measurements on „ Road tests „ Lab tests „ Equipment/components CAE „ Multi-body dynamics „ Finite element analysis „ Computational fluid dynamics

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Sound Source Identification „

„

Sound Intensity „ Obtain vector quantity of sound at various points/grid locations around the test article using a 2-microphone probe

Acoustical Holography/Beam Forming „ Obtain a visual representation of the sound radiated from a test article using a microphone array y microphone

source

y x

focal point (level max)

o

antenna

x

z

focal point (level min)

Focusing plane = source plane

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Noise Contribution of Various Components of Engine

Exhaust system-35%

Intake system15%

Engine Block35%

Others-35%

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What is Modal Analysis? F(t)

X(t) [ H(ω ) ]

Measurement

H ij

Mode 1

Mode 3

Mode 2

Modal Parameter Estimation

Frequency ω r Damping Ratio ζ r Mode Shape φ r etc.

Modal Parameters

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ODS – Operating Deflection Shapes „

„

Operating Deflection Shapes – „ Measure motion transmissibility functions relative to one fixed location, ( acci / accj ) at a lot of points, like with Modal Analysis „ It looks like a duck, but IT’S NOT A DUCK (mathematically, these are forced response shapes, not mode shapes it’s NOT modal analysis) Can be time-domain or frequency domain

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Vibro-acoustic Prediction Technique

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Vibro-acoustic Prediction Technique

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Multi-body dynamics Software „ „ „

„ „ „

Components modeled as rigid, lumped mass part Connections through springs and dampers Understand trajectory and time-response of system „ As in suspension systems, steering systems, rigid-body vibration modes of powertrain (bounce, pitch, roll) Low frequency (below 100 HZ) ADAMS is popular CAE software for this type of modeling Used as support for Boundary Condition for FEM

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Noise Prediction by FEM Technique

FE Modal Analysis Dynamic Response Analysis Coupled Analysis

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BEM Technique It is one of Numerical techniques used to solve the acoustic problems like Finite Element Method(FEM). • In BEM only the boundary of the domain is dicsretized. For complex Geometries the BEM modeling leads to significant savings of manpower and computational time.

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Other CAE Techniques

„

„

Statistical Energy Analysis „ Higher Frequency computational NVH technique, usually used at frequencies higher than 300 Hz in automotive applications Computational Fluid Dynamics „ Applied to fluid-flow and air-flow (e.g. wind noise)

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Correlation Between FE Technique and Experimental Testing Test

Initial FRFs

Model

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Correlation Between FE Technique and Experimental Testing VIBRATION VELOCITIES WITH COMBUSTION FORCES

MEASURED VIBRATION VELOCITIES V-Loc 1 V-Loc 3

LOC 01

LOC 2

LOC 03

LOC 07

1.97E+02

Vibration Velocity_

Vibration Veloc ity

2.17E+02

V-Loc 2 V-Loc 7

1.77E+02 1.57E+02 1.37E+02 1.17E+02 9.70E+01

630

800

1000

1250

1600

2000

Centre Band Frequency in " Hz "

2500

3150

200 250 315 400

500 630 800 1000 1250 1600 2000 2500 3150 4000

Centre Band Frequency (Hz)

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STRUCTURE BORNE ENGINE NOISE CONTROL. Noise Reduction methods • MECHANICAL NOISE : METHODS SUGGESTED TO REDUCE PISTON SLAP -- Offsetting gudgeon pin -- Reducing piston - liner clearance -- Minimum r/l ratio

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STRUCTURE BORNE ENGINE NOISE CONTROL. METHODS SUGGESTED TO REDUCE PISTON SLAP -- Lengthening piston skirt -- Lubrication of skirt with oil film in the liner to dampen piston slap

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STRUCTURE BORNE ENGINE NOISE CONTROL. Noise Reduction methods METHODS SUGGESTED TO REDUCE PISTON SLAP -- Low clearance in gudgeon pin and Connecting rod bearings -- Rigid liner with minimum deformation and ovality.

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STRUCTURE BORNE ENGINE NOISE CONTROL. Noise Reduction methods • MECHANICAL NOISE : METHODS SUGGESTED TO REDUCE PISTON SLAP -- Offsetting gudgeon pin -- Reducing piston - liner clearance -- Minimum r/l ratio

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STRUCTURE BORNE ENGINE NOISE CONTROL. Noise Reduction methods •TIMING GEAR NOISE : -- Use of low inertia gears. -- Replacement of standard timing gears with double helix gears. -- Gears with low pressure angle

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STRUCTURE BORNE ENGINE NOISE CONTROL. Noise Reduction methods •TIMING GEAR NOISE : -- Isolating timing cover by using noise shield.

-- Reduce torsional vibrations of crankshaft

-- Design of camshaft for low impacts.

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STRUCTURE BORNE ENGINE NOISE CONTROL. Noise Reduction methods Engine Structure Modification : Major Influencing Factors :: • Design of lower crankcase • Movement of Crankshaft journals during firing • Design of engine covers

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STRUCTURE BORNE ENGINE NOISE CONTROL. Noise Reduction methods Engine structure modifications : Cylinder Block : • Stiffening of structural elements, connection surfaces, and panels • Close shielding of major noise radiating surfaces

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STRUCTURE BORNE ENGINE NOISE CONTROL. Noise Reduction methods Engine structure modifications : Engine Covers: • Isolation from vibrating connection to the engine structure surface • Damping of cover material • Addition of ribs to change the stiffness for less response at critical frequencies • Improvement in acoustical properties by use of alternate materials

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STRUCTURE BORNE ENGINE NOISE CONTROL. Noise Reduction methods Engine structure modifications : Fuel Injection Equipment: • Reduced noise pump structure • Low vibration transmission pump mountings • Improved injector characteristics for smoother combustion initiation

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STRUCTURE BORNE ENGINE NOISE CONTROL. Noise Reduction methods Engine structure modifications :

Cylinder head :

• Improved combustion features e.g. ports and combustion bowl optimization for smoother combustion initiation

Manifolds :

• Vibration isolation and damping added to the manifolds

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STRUCTURE BORNE ENGINE NOISE CONTROL. Transmission gear noise Control: Possible means for reduction of transmission error : Shifting of resonances of each gear from gear meshing freq. Shifting of critical speed of shafts away from gear meshing freq. Shifting of freq. of housing away from gear mesh frequency Vibration Isolation Tuned vibration absorbers Constraint Layer Damping Reduction of shaft deflection due to dynamic loading NVH & CAE LABORATORY

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STRUCTURE BORNE ENGINE NOISE CONTROL. Belt Noise Control • Vibration of the pulley • By reducing the clearance,rattle can be reduced • Covers of highly damped materials • Profile with decreased tooth flank area which leads to higher tooth tip width • Modified sprocket profile with soft contact at bottom land of belt and tooth tip of sprocket.

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STRUCTURE BORNE ENGINE NOISE CONTROL. Chain Noise Control •Fine pitch and accurately matched pitches • Damping of large sprockets • Use of guide wheel and rubber ring to driving sprockets • Changing torsional behaviour of cam shaft

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Acoustical Treatment

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Ride Comfort Ride

- Tactile And Visual Vibrations, 0 - 25 Hz Ride Perception

Vibrations - Noise Aural (25 Hz - 20 kHz) EXCITATION SOURCES Road roughness Tire/Wheel Driveline Engine

VEHICLE DYNAMIC RESPONSE

VIBRATIONS

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Vehicle Ride Comfort > Ride comfort in a vehicle is a subjective perception normally associated with level of comfort experienced during travelling in a vehicle. > Perceived ride is cumulative effect of many factors. > In the vibration spectrum, Ride - 0 -25 Hz Noise - 25Hz - 20KHz. > Ride is a tactile and visual vibrations.

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VIT M. TECH. (AUTO) COURSE (Noise, Vibration and Harshness )

Vehicle Ride Comfort > Vertical frequencies which feels most uncomfortable falls in the range of 20Hz - 200Hz. > Fatigue occurs most rapidly when subjected to vibrations in the range of 4Hz to 8Hz or in the low band below 0.75 Hz where dizziness and motion sickness can results > Lateral or fore/aft frequencies in the same range are also uncomfortable because it disturb balance of inner ear. > ISO:2631 for exposure limits of whole body vibrations and ISO:5349 for exposure to hand arm vibrations.

NVH & CAE LABORATORY

VIT M. TECH. (AUTO) COURSE (Noise, Vibration and Harshness )

NVH & CAE LABORATORY