NVN Intake and Exhaust System Acoustics
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Transcript of 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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Contents
Legislation Airborne Acoustic Sources
Establishing a Brand ID Target Setting
Engineering the Brand ID
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Contents
Legislation Airborne Acoustic Sources
Establishing a Brand ID Target Setting
Engineering the Brand ID
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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
Legislation Airborne Acoustic Sources
Establishing a Brand ID Target Setting
Engineering the Brand ID
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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
structure-borne contributor
source path
structure-borne contributor
source path
air-borne contributor
source path
air-borne contributor
source path
air-borne contributor
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
Legislation Airborne Acoustic Sources
Establishing a Brand ID Target Setting
Engineering the Brand ID
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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
transfer path analysis
system modificationsbecome system level
targets
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
transfer path analysis
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
Legislation Airborne Acoustic Sources
Establishing a Brand ID Target Setting
Engineering the Brand ID
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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
1D Gas Dynamic Simulation (WAVE)
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
1D Gas Dynamic Simulation (WAVE)
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