NVN Intake and Exhaust System Acoustics

8/13/2019 NVN Intake and Exhaust System Acoustics

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www.ricardo.com

Ricardo plc 2009

Intake and Exhaust System Acoustics:

A Tool for Niche Brand Identification?

A Presentation to Niche Vehicle Network

Corin Wren

Chief Engineer, Advanced Technology

Ricardo UK Ltd

30th July 2009


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Intake and Exhaust System Acoustics

Unrestricted April 2009RD.09/151501.1

Contents

Legislation Airborne Acoustic Sources

Establishing a Brand ID Target Setting

Engineering the Brand ID


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Contents





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Intake and Exhaust Noise Measurement

Vehicle Exterior Noise

Intake and exhaust noise are amongst the most

significant contributors to vehicle exterior noise (pass-

by noise), which is limited by legislation

Pass-by noise test methods

Old EU test method ISO362:1998

Full load acceleration starting from 50km/h,

in both second and third gear

New EU test method ISO362:2007

Combination of full load and constant speedtests, according to reference acceleration,

to correlate with actual urban conditions

In whichever gear(s) gives closest to thereference acceleration

50km/h (13.89m/s) in centre of zone

Pass-by noise source ranking

Sources are suppressed using infinite mufflersand covers

Individual contributions are evaluated by revealing

each source in turnEngine firing order harmonicsEngine firing order harmonics

Gas flow noiseGas flow noise

Engine firing order harmonicsEngine firing order harmonics

Gas flow noiseGas flow noise

Exhaust Tailpipe Contribution


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Contents





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Introduction

Acoustic sources Cyclic pressure pulsations from intake and exhaust valve opening events

Manifold geometry (particularly path length) is crucial in determining how pulses from multi-

cylinder engines mix

Gas flow noise from turbulence

Shock waves from non-linear

acoustic behaviour

Acoustic propagation inside intake and

exhaust systems

Independent of bulk flow

Acoustic radiation

From orifices

Shell noise (radiation from external surfaces)


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Intake and Exhaust Noise Measurement

Vehicle Interior Noise

Transfer Path Analysis

Intake and exhaust noise are amongst the

most significant contributors to vehicle

interior noise

These systems can be used to generate

positive sound quality

Noise level is proportional to

accelerator pedal input, giving gooddriver feedback

Transfer Path Analysis Allows calculation of individual structure-

or air-borne contributions to vehicle

interior noise

Key sources include: exhaust, intake,

engine sound and vibration

The transfer paths describe the vehicle

body structure and trim

TPA is used in two ways: upwards to evaluate system level

behaviour at the vehicle level

downwards to cascade vehicle level

targets to the system level

structure-borne contributor

source path


source path


source path

air-borne contributor

source path


source path


source path

background sound

from other sources

vehicle interior sound

I&EIntakeSource.wav

I&EIntake.wav

EngineTopSource.wav

EngineTop.wav

Speed[rev/min]

System level: source

0 200 400 600 800

2000

3000

4000

5000

6000

7000

37

43

49

55

61

67

73

79

85

NTF[dB(Pa/ms^-^2)re2e^-^5] System level: left path

X:\TPA\NTFs\RH -X (left ear).txt

Speed[rev/min]

Vehicle level: left interior sound

2000

3000

4000

5000

6000

7000

I&EIntakePath.wav

EngineTopPath.wav


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Exhaust Systems

Non-Linear Acoustics

Shock waves can be generated in the exhaust system when there is a long, uninterrupted front pipe with a strong

resonance and a strong thermal gradient (thus especially bad when exhaust is cold)

Strong shocks have an impulsive and metallic character, sometimes called rasping or Schmttern

Mild non-linearity produces over-tones (higher harmonics) which give a particularly rich sporty sound quality

Exhaust systems which use this phenomenon have been successfully developed using WAVE

Target Target Rasping

Full Load Acceleration Blipped Throttle Cold Hot

Prediction

Full Load Acceleration

Non Lin Target WOT.wav Non Lin Targ et Blip.wav

Non Lin Predicted WOT.wav

Rasping Cold.wav Rasping Hot.wav


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Contents





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Target Setting

Noise targets are commonly set in the following categories

Vehicle interior and exterior noise (vehicle level)

Intake and exhaust orifice noise (system level)

Targets can be based on benchmark data for these systems,

or cascaded from vehicle level using TPA

Sound quality targets can also be set at the vehicle level

What is sound quality?

The degree of excellence of sound, as perceived by people,relative to their expectations for the product and/or brand

Why engineer sound quality?

Sound can powerfully convey the product image to the driver/passengers and onlookers

Sound can communicate the cars operating conditions (speed and acceleration) to the

driver

How to set sound quality targets?

Select image vehicles for benchmarking: previous models, competitors, well-loved,

historic or iconic cars Digitally manipulate benchmark recordings to enhance their acoustic features

Ask listeners for their opinions in relation to the desired product image the 1-10 scale is widely used

Senior management, marketing, NVH staff and customer focus groups

Ratings are analysed statistically, and the most favoured sound becomes the target sound

calculate baseline

transfer path analysis

no

yes

vehicle levelsound quality

target

vehicle level

target achieved?

identify significantcontributors

identify significant systems(sources/paths)

modify significant systems(by simulation)

calculate modified


system modificationsbecome system level

targets

calculate baseline


no

yes

vehicle levelsound quality

target

vehicle level

target achieved?

identify significantcontributors

identify significant systems(sources/paths)

modify significant systems(by simulation)

calculate modified


system modificationsbecome system level

targets

10 Exceptional

9 Excellent

8 Very Good

7 Good

6 Fair

5 Mediocre

4 Inadequate

3 Very Inadequate

2 Defective

1 Very Defective

Acceptable

Action

Needed

Unacceptable


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8.0 1.1Emotional, immediate, unique,

energetic, exhaust noise kick-

back

4.2 1.3Very muted, lifeless, uninspiring,

disappears to nothing

4.0 0.8Dull, normal, weak, no character,

uninspiring, not a supercar

5.9 0.7Nice mid-range growl, creamy,

rounded, deep punch

4.0 1.1Not distinctive, little character,

disappears to nothing,

uninspiring

6.6 0.7Full mid-high range, nice

character, smooth and balanced

SubjectiveColour MapSound

Exterior Sound Traffic Lights Start

6.4 0.8Nice, balanced, refined, powerful,modern

7.4 0.4Raspy but musical, relentless

power, addictive, assertive

3.8 0.6Too linear, balanced, notdistinctive or stimulating, lacking

emotion

4.6 1.2Bland start, better with nice

overtones at high speed, refined,

muted

5.2 1.0Slow, smooth, balanced, noemotion, not exciting, better at

high speed

5.6 1.0Nice tone, precise, smooth,

pleasant but not emotional

SubjectiveColour MapSound

Interior Sound 2nd Gear Full Acceleration

Target Setting

Case Study: Sports Car

Sound Quality

Desired Vehicle Image

Poised, communicating intent, potential energy and power available

Assertive, demonstrating immediacy of response, instantaneous stimulation

Relentless power delivery, a heavy-weight punch, a degree of harshness

Emotionally inviting, aurally stimulating, addictive, exhilarating, intoxicating

Inspirationally vivid, distinctive and immediately recognisable

Car A interior 2wot.wav

Car B interior 2wot.wav

Car C interior 2wot.wav

Car D interior 2wot.wav

Car E interior 2wot.wav

Car F interior 2wot.wav

Car A exterior t ls.wav

Car B exterior t ls.wav

Car C exterior tls .wav

Car D exterior tls .wav

Car E exterior t ls.wav

Car F exterior tls.wav

SELECTED

TARGET

SELECTED

TARGET


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Contents





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Top cover plate

Foam

Outlet pipe

Housing cover

Membrane

Housing

Decoupling elements

Top cover plate

Foam

Outlet pipe

Housing cover

Membrane

Housing

Decoupling elements

Intake Systems

Sound Generator Devices

A loudspeaker-like device to improve sporty sound quality

Diaphragm is driven by intake system pressure pulsations,rather than an electrical signal

Sound is ducted to passenger compartment

Increasing market penetration on sporty passenger cars

Application to:

Naturally-aspirated engines

Attached as a side-branch to the clean side intake system close to the manifold

Turbocharged engines

Attached as a side-branch to the high-pressure intake system close to the manifold

Diesel applications require an additional throttle in the side-branch to control load

dependency

Examples

Four cylinder gasoline: Without With

Four cylinder diesel: Without With

V8 twin-turbo gasoline: Without With

Gasoline Baseline.wav Gasoline SG.wav

Diesel Baseline.wav Diesel SG.wav

V8_Baseline.wav V8_SG.wav


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System Development

Many intake and exhaust systemlayouts can be calculated quickly

Typically 50~100 layouts in 2~4weeks

Evaluated subjectively andobjectively vs. targets

The most successful intake andexhaust system layouts are built asprototypes

Typically 2~3 layouts

Fitted to vehicle and tested

WAVE Analysis

Intake and exhaust orifice noise

Acoustic mode shape analysis

Back pressure analysis

WAVE Model Construction

1D gas dynamics simulation,simultaneously predicting engineperformance and intake and exhaustorifice sound (time domain)

WaveBuild3D automatic meshgenerator for detailed acoustic-qualitymodels

int_m.wav

int_p.wav

exh_m.wav

exh_p.wav

Intake Exhaust

Measured

Predicted

Special acoustic features:- Porous intake hose- Muffler absorption material

1D Gas Dynamic Simulation (WAVE)

Development Process


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V6 Gasoline Exhaust System LayoutV6 Gasoline Intake Manifold


Examples

intv6twin.aif.wavintv6clust.aif.wav

Each cylinder has

equal propagation

delay yielding a

pure, clean, tonal

sound character

Equal runners,

log plenums

Equal path lengths

to throttle

Each cylinder has

different

propagation delay

yielding a rich,

modulated soundcharacter

exh_base.wav exh_asym.wav exh_asym_strt.wav

Baseline Asymmetrical

banks

Asymmetrical

banks and

open muffler

Each bank mixes

equally, producing

3.0 order and

harmonics

Asymmetry

between banks

produces 1.5 order

and harmonics

Exhaust valve

opens to reduce

attenuation of

muffler


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V6 Gasoline Exhaust System LayoutV12 Gasoline Exhaust System Layout


Examples

Baseline Equalised Downpipes

Asymmetry between front and rear downpipes produces

1.5 order and harmonics

Equalisation of downpipe lengths produces

3.0 order and harmonics

V12_exhaust_unequal.wav V12_exhaust_equalised.wav

NVN Intake and Exhaust System Acoustics

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