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INTRODUCTION
WHAT IS “NVH”?

NVH stands for noise, vibration, and harshness
...
Harshness is generally used to describe the severity and discomfort associated
with unwanted sound and/or vibration, especially from short duration events
...
The new design methods are
starting to consider NVH issues throughout the whole design process
...
New materials and
techniques are also being developed so that the damping treatments are lighter, cheaper,
and more effective
...
The
carpeting treatments include varying types of foam padding combined with different
weights of rubber-backed carpet
...
The rubber or asphalt materials are attached to various car panels to

add damping and mass loading to reduce vibration levels and the rattling sounds from the
panels
...
Expandable foam
injected between panels, such as the dashboard and firewall, helps to add stiffness and
vibration absorption
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However, some of the treatments become
almost ineffective at lower frequencies below 200 Hz
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FUNDAMENTALS OF NVH
Frequency and Cycle
Most vibrations consist of movements back and forth or up and down that
repeat as long as the causal conditions exist
...

The rate at which these cycles occur within a given time is called the frequency
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The term Hertz (Hz) is also
used as a measurement of frequency
...


The NVH concern of steering wheel nibble can demonstrate frequency
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The number of times the steering wheel goes through this range of motion in one second
is its frequency
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Resonance

Point of Resonance
Resonant frequency refers to the frequency of the applied force on an object
that results in the greatest vibration
...
The natural frequency refers to the
frequency range during which an object tends to vibrate
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Two identical
looking objects with different material composition will have different natural
frequencies and a different resonant frequency when acted upon by an identical applied
force
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Suppose that this same
vehicle has an unbalanced tire
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At some point, the frequency of the force created by the
tire imbalance will be the same as the natural frequency of the
suspension system, causing the suspension system to vibrate
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Amplitude

Amplitude of Vibration
The term amplitude, when applied to vibration, indicates the actual amount
of component movement
...
Referring back to the NVH concern of steering wheel
nibble, amplitude can be demonstrated by the amount of steering wheel movement
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Sound
Sound is the result of the disturbance of air caused by a vibration
...
(The normal range of human hearing
is 20-20,000 Hz
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The vibrations
create air pressure variations, or waves, that we hear as sound
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Increasing the frequency of a sound increases the pitch of the sound
...
Simply speaking, pitch refers to the highness
or lowness of a sound
...
The illustration shows two sound waves with the same
frequency, but with different intensity levels (amplitudes)
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VIBRATION
DEFINITION OF VIBRATION
Vibration is a shaking or trembling that can be felt by the customer when an
object/component moves back and forth or up and down consistently
...

There are three types of vibrations:
• Free vibration – a vibration that continues after the cause has been removed
...

• Forced vibration – a vibration that only occurs as long as the force that initiated the
vibration remains
...
Another example would be an unbalanced tire, which would stop
vibrating when it stops rotating
...

• Torsional vibration – vibration caused by a constant twisting force that is felt in the
floor and seats of the vehicle
...

Under normal circumstances, a rotating component will not produce a
noticeable vibration
...
If the frequency and amplitude of the vibration can be measured, then
those characteristics along with the vehicle speed and engine RPM at which the vibration
occurs, can be matched with components that would likely cause the vibration at that
particular speed
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Vibration Transfer Path

Item

Description

1

Origin (Imbalance)

2

Conductor (Transfer Path)

3

Reactor

Vibrations are often noticed in a component far removed from where they
are generated
...
For example, an out-of-balance
front tire and wheel assembly may result in a noticeable steering wheel shake
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Damaged or worn engine and body mounts or a grounded exhaust hanger
are components that could transmit (conduct) a normal engine vibration (originator) into
the passenger compartment (reactor) as an NVH concern
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There are three types of vibration dampers:
• Torsional – rotational inertia ring
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• Mass changer – changes the weight to change the natural
frequency
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Order of Vibration

First and Second Order
Item

Description

1

First Order Vibration (Once Per Revolution)

2

First Order Vibration (Once Per Revolution)

Rotating components with more than one abnormal condition may generate
more than one vibration per revolution
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This would be called a first order vibration
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This would be called a
second order vibration
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For
example, it would be necessary to divide the frequency of a second order vibration by
two to identify the originating component

Normal Engine Order Vibration
Engines have vibrations created by firing frequency
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The force of the combustion
creates one pulse, and the cylinders firing in order create a normal vibration
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For example, six-cylinder engines fire half of its cylinders with each
crankshaft revolution
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A fourth order vibration
would be common with eight-cylinder engines since four cylinders fire with each
crankshaft revolution
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A vibrating object oscillates
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A pendulum
set in motion vibrates
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Vehicles driven on rough terrain
vibrate, and geological activity can cause massive vibrations in the form of earthquakes
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We can touch a vibrating
object and feel the vibration
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Sometimes vibration creates sounds that we can hear or heat that we can
sense
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In industrial plants there is the kind of vibration we are concerned about:
machine vibration
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Any component that moves back and
forth or oscillates is vibrating
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A machine component may
vibrate over large or small distances, quickly or slowly, and with or without perceptible
sound or heat
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(Not all kinds of machine vibration are undesirable
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)
At other times machine vibration can be unintended and lead to machine
damage
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This article is
about the monitoring of undesirable machine vibration
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NOISE
NOISE & SOUND
When we consider term “NOICE”, then we thing what is term “SOUND”?
Music is an art from whose medium is sound organized in time
...
e
...

This is from music, speech and other thing like film dialogs etc
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Noise is a sound from one and more at a time which can not heard clearly and
only mixed sound will be heard
...
If a meeting
there will be a noise among the people talking each other besides the speaker going on
talking
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In a office one is talking on mobile, phone ringing another side, ring tone in some
person’s hand, loud conversations with one and another, student talking in class room in
absence of lecturer etc,
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In general, sound is vibration from particular machine, place or material
which can be heard clearly whereas noise is a mixed vibration that will come to us from
all directions
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Noise is random
unwanted background

DEFINITION OF NOISE
Generally, specific primary noises can be associated with a certain portion of
the vehicle, such as the engine, driveline, axle, brakes, or body components
...
Roof
racks are a classic example of this situation
...
Unless
you are aware of these conditions, an incorrect diagnosis could be made
...
In this case,
for example, you may hear a chirping noise in the area of the instrument panel, only to
find that the noise is being produced in the rear brakes
...
This is a situation where following a strict

road test procedure will help to locate the cause since the noise will only occur when the
brakes are applied or released
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The transfer path for a noise that is generated by a vibration is identical to a
vibration’s transfer path
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Noises that are produced by wind, turbulence, and air leaks are
independent from noises produced by moving components
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Turbulence created by loose or protruding moldings, or
by gaps between rubber seals, moldings, and drip rails, can produce wind noise
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Normal Noise
A gear-driven unit, especially an automotive drive axle, will produce a
certain amount of noise
...
The noise is not
harmful but is disturbing to the owner
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A slight
chatter may be heard during low-speed turns, which is nothing more than the clutches
doing their job
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This can often be
accomplished with a comparison drive in a known normal vehicle
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After you have determined that a problem exists, the symptom must be
diagnosed and the cause repaired
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Harshness is usually due to:
• Deterioration of vehicle components – such as worn or damaged
suspension components that cannot move within their normal range
of motion, or that have lost their isolating grommets or bearings
...

• Improper tire inflation – over- or under-inflated tires can cause a
harsh ride
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A customer may
perceive that the ride of a vehicle is harsh, when in reality it is a normal operating
characteristic of the vehicle
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This would be an example of normal
harshness and comparison to a known good vehicle could resolve this concern for the
customer
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”
Every automobile parches by anyone wants’ it perfect, comfortable, active and
healthy
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They need to develop an automobile having
 Excellent Model Design
 Good Comfort


Technology

 Should be Noise Proof
 Healthy interior environment
 Efficient
 In reasonable Cost
To overcome all this factors NVH analysis is used
...
)

Recent NVH Test Equipment’s:
 PC based analyzers,
Multichannel NVH data acquisition systems,
 Acoustic holography devices,
 Laser vibrometer’s, and
 Anechoic test cells
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Analytical Diagnosis
2
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ANALYTICAL
TOOLS
VIBRATION DIAGNOSTIC TOOLS
There are several diagnostic tools that can be used to identify vibrations
...

In this section, we will describe these tools and equipment
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The sirometer contains a wire that is coiled inside of a casing
...
Find the length of wire that vibrates with the highest amplitude
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The sirometer operates on the principle of resonant

frequency
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Once
the scrolled wire's natural frequency matches the vibrating component’s natural
frequency, this is the point of resonance (or its resonant frequency)
...


Reed Tachometer

A reed tachometer is used to identify the frequency of a repetitive
vibration
...
The only difference between the two is face
plate labeling since RPM values can be calculated from Hz values by multiplying by 60
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The reeds range from 10 to 80 Hz or 600 to 4800 RPM, so the reed
tachometer will only identify vibrations within this range
...
When the knob is turned, the reeds are held in place
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Electronic Vibration Analyzer (EVA)

The EVA allows for a systematic collection of information that is necessary to
accurately diagnose and repair NVH problems
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Accurately obtaining these
characteristics of a vibration can significantly reduce vehicle service time
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The EVA includes the following components:
• EVA unit with a five-foot power cord and protective cover
• Software cartridge
• Vibration sensor with a 20-foot cord
• Magnet
• Velcro holding strap
• Putty
• Instructions
• Carrying case

Vibration Diagnostic Tool Comparison
The sirometer is portable and easy to use with a little practice
...
The
sirometer, like the other vibration tools, may not be able to locate the frequency of the
vibration concern if other vibrations of strong amplitude are present
...
Another
disadvantage of the reed tachometer is that it displays many frequencies at once and can
be difficult, if not impossible, to get a good reading on a road test
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The EVA is the most accurate tool in measuring frequency and amplitude
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Other advantages of the EVA include the fact that it displays amplitude readings, makes
recordings, and has remote sensors
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These tools
can be very helpful in isolating problems and making your diagnosis easier
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ChassisEAR

Advanced electronic listening devices, such as the ChassisEAR, can be
used to quickly identify a noise and its location under the chassis while the vehicle is
being road-tested
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For example, the
ChassisEAR has a 6-position input selection control switch with 6 microphone clamps
that are attached to 16-foot leads
...
The ChassisEAR provides instant comparisons between any of the six
channels during the road test
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EngineEAR

Another electronic listening device, the EngineEAR, is available to detect
bad bearings and bushings, noisy lifters, exhaust manifold leaks, and broken or chipped
gear teeth
...
It is
so sensitive that even the faintest bearing rattle in an alternator, water pump, A/C
condenser, and power steering pump can be heard
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The directional
sensing tip is used to listen to various components
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Ultraphonic Detector Receiver and Transmitter

An ultraphonic detector receiver and transmitter (formerly known as an ultrasonic
leak detector) is used to detect wind noises caused by leaks or gaps in areas of the vehicle
where there is weather-stripping or other sealing material
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The transmitter is placed inside the vehicle
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As the source of the leak is approached, the emitted sound gets louder
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The reason
why these frequencies are used is that sound waves in the audible range penetrate walls
and component parts, and are reflected off other surfaces
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Ultrasonic sound waves do not penetrate solids; these waves however, pass easily
through gaps and voids in gaskets or weld seams
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Old
techniques are replaced with sophisticated tools, equipment, and data collecting methods
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This data can be charted on graphs or charts to
determine sources of NVH concerns
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The diagnostic process starts with the repair order
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It is important for you, the technician, to know when the NVH
concern occurs
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The job aid is used to make sure that all important
symptom information is recorded
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The NVH Diagnostic Guide assists in understanding and duplicating an
NVH concern
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This guide serves as a place to record
diagnostic information as testing is performed
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It also eliminates some of the
confusion created by differences in descriptive language, and helps you identify the
customer’s concern more accurately
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In the long run, you will save time by adhering to the diagnostic procedures demonstrated
in this course
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For NVH concerns, it is necessary to classify the customer’s concern into
one of the three categories: noise, vibration, or harshness
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In cases where there are combination symptoms,
you, the technician, need to know which diagnostic path to follow: noise, vibration, or
harshness
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For example, if
a customer has a concern involving a noise and a vibration, and you determine that it is
vehicle speed related (Neutral coast down speed test), you would follow the vibration
diagnostic path
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COMPUTER SOFTWARE DIGNOSIS
RICARDO

Ricardo is a leading global provider of product innovation,
engineering solutions, clean technology and strategic consulting since 1915
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Key features
 Direct and indirect vibrations solution
 Rayleigh and BEM (boundary element method) solution method
 Automatic creation of BEM meshes

NVH tools and techniques
The Ricardo NVH team is able to deploy the very latest methods and software
These are just some of the tools and techniques available
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Ricardo uses a 24bit multi-channel noise analyzer for cylinder pressure based
combustion noise assessment with a user-programmable structural attenuation
*
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Power train Combustion Mechanical Breakdown (CMB) analysis techniques have been
developed to provide detailed understanding of combustion noise improvement
opportunities
Noise source identification:
*
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Acoustic camera for rapid concern identification

Sound quality engineering:
*
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Ricardo WAVE software used for development of intake and exhaust acoustics
*
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ADAMS multibody dynamic simulation for powertrain mounts development
Transfer Path Analysis (TPA):
*
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Ricardo NVH department routinely use time domain and matrix inversion TPA
techniques to separate interior noise into airborne and structure borne components
derived from vibration and noise sources

NVH Director
NVH Director is a software product of “Altair Hyper Works”
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NVH Director is most advanced NVH Analysis software
up till now
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•Most complete diagnostic outputs:
- Modal participation
- Structure and fluid grid participation
- Energy – all varieties
- Grid point forces
- Power flow/Mech
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