Characteristics of NVH

8/3/2019 Characteristics of NVH

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Characteristics of NVHCharacteristics of NVH


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Audible Range ofAutomotiveAudible Range ofAutomotive

SoundsSo

unds

Automobiles have a full range of soundsAutomobiles have a full range of sounds

Low speed Drones, very low pitch and can beLow speed Drones, very low pitch and can be

felt but hardly heard.felt but hardly heard.

Brake Squeal, High pitch sound that can beBrake Squeal, High pitch sound that can be

heard but hardly felt.heard but hardly felt.


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NoisesNoises

There are many noises that occur in anThere are many noises that occur in an

Automobile.Automobile.

The 4 main noises that a technician needsThe 4 main noises that a technician needsto be able to identify are;to be able to identify are;

DroningDroning

BeatBeat

Road NoiseRoad Noise

Brake SquealBrake Squeal


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DroningDroning

Adiscomfort in theAdiscomfort in the

ear caused by suddenear caused by sudden

changes inchanges in

atmosphericatmosphericpressure.pressure.

The three types ofThe three types of

droning are:droning are:

Low speed DroningLow speed Droning

Middle speed DroningMiddle speed Droning

High speed DroningHigh speed Droning


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All spee

ds of

droning consist of a non

All spee

ds of

droning consist of a non--directional, low pitched, and long duration noise.directional, low pitched, and long duration noise.

Low speed Droning; is hard to hear and feelsLow speed Droning; is hard to hear and feels

like pressure in the ears.like pressure in the ears.

High speed Droning; a humming noise that isHigh speed Droning; a humming noise that isuncomfortable to the ears.uncomfortable to the ears.


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Droning can occurDroning can occur

while accelerating orwhile accelerating or

decelerating, ordecelerating, or

through variousthrough variousengine or vehicleengine or vehicle

speeds.speeds.


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It is important for aIt is important for a

technician to pinpointtechnician to pinpoint

the vehicle speedthe vehicle speed

and/or engine speedand/or engine speedin which the NVHin which the NVH

concern occurs.concern occurs.


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Likely Causes of DroningLikely Causes of Droning

Bending resonance of exhaust pipes.Bending resonance of exhaust pipes.

Resonance of auxiliary equipment.Resonance of auxiliary equipment.

Bending resonance ofdrive shaft.Bending resonance ofdrive shaft. Resonance of suspension links.Resonance of suspension links.

Transmission of engine vibration.Transmission of engine vibration.

Transmission of exhaust noise.Transmission of exhaust noise. Transmission of intake air noise.Transmission of intake air noise.


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BeatBeat

Must have 2 sources.Must have 2 sources.

The sensation of aThe sensation of abeat sound is mostbeat sound is most

noticed when thenoticed when theFrequency differenceFrequency differenceis 1 to 6 Hz.is 1 to 6 Hz.

If two frequencies areIf two frequencies are

more than 6 Hz apart,more than 6 Hz apart,there sounds arethere sounds aredistinguishable fromdistinguishable fromeach other.each other.


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Likely Causes of a BeatLikely Causes of a Beat

Engine andAir Conditioning Compressor.Engine andAir Conditioning Compressor.

Engine and Power Steering HydraulicEngine and Power Steering Hydraulic

PumpPump Engine and vibration of the drive shaftEngine and vibration of the drive shaft

Tire nonTire non--uniformityuniformity


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Road NoiseRoad Noise The impact betweenThe impact between

the road surface andthe road surface andtires cause the tries totires cause the tries tovibrate.vibrate.

This vibration isThis vibration istransmitted to thetransmitted to thesuspension and body.suspension and body.

The resonanceThe resonance

characteristic of thecharacteristic of thepassengerpassengercompartmentcompartmentamplifies the roadamplifies the road

noise.

noise.


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Brake SquealBrake Squeal

The most common NVH Noise Concern.The most common NVH Noise Concern.

Drum Brakes; emit a lower pitched noiseDrum Brakes; emit a lower pitched noise

that gets louder with increased brakethat gets louder with increased brakepedal pressure.pedal pressure.

Disc Brakes; generally a high pitchedDisc Brakes; generally a high pitched

squeal that occurs with light pedalsqueal that occurs with light pedal

pressure.pressure.


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Likely Causes ofBrake SquealLikely Causes ofBrake Squeal

Worn Brake LiningsWorn Brake Linings

NonNon--uniform thickness of brake disc ofuniform thickness of brake disc of

drumdrum Excessive run outExcessive run out

Contamination of friction surfacesContamination of friction surfaces

Damaged brake liningsDamaged brake linings


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VibrationsVibrations

The main characteristics of vibrations are:The main characteristics of vibrations are:

Ride ComfortRide Comfort

ShakeShake ShimmyShimmy

Brake ShudderBrake Shudder


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Ride ComfortRide Comfort

When un sprung components start toWhen un sprung components start to

resonate with sprung components.resonate with sprung components.

PitchingPitching

RollingRolling

BouncingBouncing


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ShakeShake

Vibrations felt in theVibrations felt in thesteering wheel, seat,steering wheel, seat,or floor.or floor.

Two types of shakeTwo types of shakeare:are: VerticalVertical

LateralLateral

Generally has aGenerally has afrequency between 10frequency between 10to 30 Hz.to 30 Hz.


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Vertical Shake;Vertical Shake; a severe vertical vibrationa severe vertical vibration

of the seat, body, or steering wheel. Aof the seat, body, or steering wheel. A

trembling engine hood or rear view mirrortrembling engine hood or rear view mirror

may also be a symptom.may also be a symptom.

Lateral ShakeLateral Shake; a severe side to side; a severe side to side

vibration of the seats, body, or steeringvibration of the seats, body, or steering

wheel. The shake of the drivers waist maywheel. The shake of the drivers waist may

also be a symptom.also be a symptom.


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Possible Causes of a ShakePossible Causes of a Shake

Roughness of the roadRoughness of the road

Tire imbalanceTire imbalance

NonNon--uniform tiresuniform tires Bent or out or roundness of wheelsBent or out or roundness of wheels

DrivelineDriveline

EngineEngine


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ShimmyShimmy

Vibration that causes the steering wheel toVibration that causes the steering wheel to

oscillate.oscillate.

Typically has a frequ

ency between 5 andTypically has a freq

uency between 5 an

d15 Hz.15 Hz.

The two main types of shimmy are:The two main types of shimmy are:

Low speed shimmyLow speed shimmy

High speed shimmyHigh speed shimmy


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Low speed shimmyLow speed shimmy; when the steering; when the steering

wheel begins to vibrate when driving overwheel begins to vibrate when driving over

a bump at low speeds. (Bump Steer)a bump at low speeds. (Bump Steer)

High speed shimmyHigh speed shimmy; when the steering; when the steering

wheel vibrates on smooth roads atwheel vibrates on smooth roads at

highway speeds.highway speeds.

Typically occurs within a limited speed range.Typically occurs within a limited speed range.


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Main Causes of a ShimmyMain Causes of a Shimmy

Roughness of roadRoughness of road

Tire ImbalanceTire Imbalance

NonNon--uniform tiresuniform tires

Bent or out ofBent or out of

roundness of theroundness of the

wheelwheel


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Brake ShudderBrake Shudder

Causes the instrument panel, steeringCauses the instrument panel, steering

wheel, and sometimes the entire body towheel, and sometimes the entire body to

vibrate vertically and back and forth.vibrate vertically and back and forth.

Peaks at 40 to 50 mph and has aPeaks at 40 to 50 mph and has a

frequency of 5 to 30 Hz.frequency of 5 to 30 Hz.

The major sources of shudder are:The major sources of shudder are:

Brake rotor run outBrake rotor run out

NonNon--uniform thicknessuniform thickness


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Certain operating conditions can greatlyCertain operating conditions can greatly

affect these vibrations:affect these vibrations:

Extended periods where the vehicle is not inExtended periods where the vehicle is not in

operation.operation.

Brake disc surface irregularities caused byBrake disc surface irregularities caused by

foreign substances (saltwater, antifreeze, etc)foreign substances (saltwater, antifreeze, etc)

Deformation of brake drum cause by poorDeformation of brake drum cause by poorinstallation.installation.


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HarshnessHarshness

Many customers use the word harshnessMany customers use the word harshness

to describe ride comfort concerns.to describe ride comfort concerns.

Occ

urs when a vehicle vibrates when

Occ

urs when a vehicle vibrates whenmoving across road joints, projections,moving across road joints, projections,

depressions or stepped paved roaddepressions or stepped paved road

surfaces.surfaces.

Typically has a vibration of 30 to 60 Hz.Typically has a vibration of 30 to 60 Hz.


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The level of theThe level of the

vibration or harshnessvibration or harshness

changes withchanges with

suspension andsuspension andbushing design andbushing design and

type.type.

Documents

Characteristics of NVH