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Noise Vibration and Harshness (NVH)

Noise Vibration and Harshness (NVH)

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Noise Vibration and Harshness (NVH)

CONTENTS

Introduction of NVH Overview Environmental Noise Interior NVH Type of Vehicle Noise Type of Vehicle Vibration Road Testing for NVH Diagnosis Case Study

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Noise Vibration and Harshness (NVH)

Introduction of NVHThe Noise, vibration and harshness which occur on vehicles consist of
Noise of combustion within the engine cylinders, the engine noise including air-intake and fan noise and the exhaust noises related to the combustion, all of these are transmitted to the interior of the vehicle. Vibration includes that is caused by engine vibration itself or unbalanced propeller shaft, etc. Such vibrations are transmitted to the vehicle body itself through the driveline, suspension or steering system. There is moreover, an almost unlimited number of other possible causes which could be mentioned - such as friction of the parts, the gearing components and the bearing surfaces - that could contribute to the generation of noise and vibration. Generally speaking, assuming that each mechanism and component of the vehicle is in normal condition, noise and vibration are suppressed to a level low enough so that there are few if any complaints from drivers and passengers. Complaints are soon heard from both driver and passenger. However, if the noise and/or vibration from these mechanism or components exceed the established standards, or if the devices or systems designed to isolate or reduce such noise and vibration no not perform as expected. As described previously, the great number of components related to noise and vibration make it exceedingly difficult to determine the cause and make the necessary remedy. On the other hand, there are certain conditions and characteristics concerning the occurrence of noise and vibration, and once these conditions and characteristics are fully realized, it is possible to determine the cause and perform the repair work with relative efficiency. The reason that it is ordinarily difficult to determine the cause of noise and vibration and to make the sub-sequence repair is because it is difficult, if not Impossible, to actually pinpoint the direct cause with ease, and because other related components are also affected. Thus, in order to resolve problems of this problem, it becomes necessary to know a great number of facts concerning troubleshooting. Noise and vibration characteristics, and repair; to know the components related to noise and vibration; and to know the general characteristics of noise and vibrations on vehicles in order to make repairs most effectively.

Overview
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Noise Vibration and Harshness (NVH) Noise, Vibration and Harshness (NVH) is an automotive industry term associated with the treatment of unwanted vehicle vibrations, audible sounds, shocks and other ride quality issues.The human ear can detect vibration frequencies in the range of about 20 to 2000 Hertz.Vibrations above and below this range may not be audible to the ear, but may be felt through the steering wheel, seat, floor or control pedals. Excessive or unwanted vibrations and shocks need to be addressed for customer satisfaction and vehicle performance and longevity concerns. There are 2 types of vibrations we need to understand; Structure Borne and Airborne. [Definitions] Hertz (Abbreviation: Hz) - The standard unit of frequency equal to one cycle per second.

? Structure Borne vibrations
are predominately the ones that you “feel” like the deep booming base frequencies generated by the stereo in the car next to you at a stop light. These low frequency vibrations may be audible to the driver’s ear, but are primarily “felt” through your sense of touch. Structure Borne vibration is strictly categorized as vibration that is transferred through a solid or semi-solid medium from the source. These frequencies are classified as less than 1000Hz. Structural vibrations are treated in 2 ways: Damping or Isolation. Damping is defined as a treatment of an unwanted vibration to reduce the magnitude of the vibration. For example: The power impulses of an engine result in torsional vibration in the crankshaft. A vibration damper (“harmonic balancer”) mounted on the front of the crankshaft controls this vibration. If this torsional vibration were not controlled, the crankshaft might actually break at certain speed.

[Definitions] Torsional Vibration - The motion of a bar in which it twists back and forth about its longitudinal axis. Example: The small but sometimes significant angular oscillations a crankshaft undergoes, as the alternately ignited cylinders deliver torque spikes to the shaft via the pistons and connecting rods.

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Noise Vibration and Harshness (NVH)

Isolation is defined as a method of detaching or separating the vibration from another system or body. By definition, Isolation does nothing to reduce the vibration magnitude, it simply separates the vibration from the vehicle’s area you wish to protect. Suspension bushings and engine / transaxle mounts are examples of isolators.

? Airborne vibrations
are those most people would categorize as sound and travel through gaseous mediums (the air). These vibration are detected by your ear and may be impossible to detect with your sense of touch. There are 2 ways to treat unwanted airborne vibrations: Barriers and Absorbers. Barriers perform a blocking function to the path of the airborne sound. A closed door is a simple example of a Barrier. The performance of the Barrier is strongly related to the openings or air gaps surrounding the Barrier. If the door is only partially closed or has a large air gap under or above it, then it will be less effective at blocking the unwanted sound vibrations. Barrier performance is dependent on the frequency of the sound vibration and is most effective with high frequencies. Absorbers reduce sound vibrations by absorbing the energy of the sound waves and dissipating them as heat (the heat generated is so small it can only be detected by very sensitive instruments). The carpeting in your house is an example of an Absorber. Good Absorbers generally contain complex surface shapes to trap sound vibration waves, rather than reflecting them back into the air. As with all other NVH treatments, Absorber performance varies with frequency.

Environmental Noise

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Noise Vibration and Harshness (NVH) Environmental Noises are external noise vibrations radiated by the vehicle to the environment and their relation to noise regulations. These noise vibrations can be generated by a number of components including (but not limited to):? The Engine ? The Radiator Cooling Fan ? The Engine Exhaust ? The Engine Intake System ? Transaxle System ? The Tires ? Aerodynamic Noise created by the vehicle’s disruption of the surrounding air

NOTES:

Interior NVH

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Noise Vibration and Harshness (NVH) Interior NVH is the result of many issues and sometimes requires skillful detective work to recognize and diagnose. It would be impossible to present you with every situation you may encounter in the field. However, the following are some of the most prevalent. ?Road Noise structure Borne vibrations transmitted from the tire / pavement interface to the occur at freeway speeds on “grainy” freeway surfaces or on rain grooves. ?Steering Wheel Shake Structure Borne vibrations of the steering wheel that may be caused by a number of conditions. ?Wind Noise A sometimes buffeting medium to high pitch noise created by leaks in door and window seals and by compression of the air stream as it passes over obstacles (mirrors, roof rack, moldings, etc.). ? Vehicle Cavity Boom A strong low frequency interior Airborne noise vibration that can be very annoying. This noise is the result of interior panel vibrations that have resonated into the interior cabin. The resulting ‘Standing Waves’ are at frequencies below 100 Hz and are often both felt and geared by the vehicle occupants. ?Standing Wave A wave characterized by lack of vibration at certain points, between which areas of maximum vibration occur periodically. Standing waves are produced whenever a wave is confined within boundaries, as in the vibrating string of a musical instrument. ?Brake Squeal High frequency Airborne noise vibration that is heard in the vehicle during Brake operation and is often heard at the end of a stop (sometimes referred to as Pinch-Out Squeal). ?Judder A pulsating Structure Borne vibration felt through the brake pedal during braking. ?Moan, Groan A low frequency Structure Borne noise vibration in the vehicle structure related to brake vibration. ?Tread Noise A Structure Borne recurring pattern noise vibration related to the tire tread pattern interaction with the pavement. This noise is speed-dependent and sometimes referred to as Snow Tire Noise.

Type of Vehicle Noise

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Noise Vibration and Harshness (NVH) Noise are presented vehicles in the following ways. Vibration of various sections of the vehicle body is transmitted from the vibration of various components of the vehicles, and the noise and the noise transmitted from various components to inside the vehicle resonates and becomes high. Noise also occurs when wind noise enters the vehicle during driving. In this case direction of wind, strength of wind, and attached accessories out of the vehicle should be concerned. The basic components of the vehicle which are the main causes of noise are described as follows; - Booming: - Rattle: - Beat:

? Booming Noise
- Booming from intake / exhaust system

Booming noise caused when vibration is transmitted from the engine mounts and the exhaust brackets, and booming noise caused when the noise which occurs during intake of air into the air cleaner is transmitted.

- Booming caused by vibration of the drive shaft Vibration of unbalanced drive shaft, vibrations from the center bearing resulting from torque fluctuations caused by the joint angle, and suspension vibrations are transmitted to the vehicle body, and the booming noise is accompanied by slight vibration of the vehicle body.

- Booming caused by vibration of the drive line Torsional and bending vibration of the driveline is transmitted into the vehicle body by the vibration of the suspension, and it becomes a booming noise inside the vehicle. When it is caused by torsional vibration, the differential gear noise (“crank-noise”) may occur along with it.

- Booming caused by non-uniformity of tires

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Noise Vibration and Harshness (NVH) The vibration which occurs at the tires (fluctuations of radial-direction reaction force which occurs at tires and wheels) is transmitted through the suspension and causes a booming noise together with slight vibration of the vehicle body.

- Booming Noise at low speed (at 30 ~ 40km/h) This booming noise is accompanied by a comparatively slight vibration of the body panels, the instrument panel, and the seats and is a low sound which seems to strongly press on the ears. The main cause of this noise is the resonance of the wind-up vibrations of the suspension due to fluctuation of the engine torque and this vibration is transmitted to the vehicle body through the supporting parts of the suspension, becoming the booming noise.

Sound: ‘Booo~’, ‘Booong’Frequency: 30~100 Hz ◎ Probable cause - Resonance from exhaust pipe. - When engine is running, the vibration is transmitted from engine to exhaust pipe, because it is directly connected with engine. - If engine vibration and pipe vibration are resonated together, then the vibration from exhaust pipe is more increased. - Exhaust pipe vibration is transmitted into the booth through muffler hanger and muffler support, it generates the booming noise. - Noise is emitted from the exhaust pipe and exhaust noise are transmitted through the body, becoming noise. ◆ Remedy : Remove the muffler hangers or muffler supports in order. Then you can find where the vibration is transmitted. - Booming Noise at medium speed (at 40 ~ 80km/h) and high speed (at 80km/h ~) This noise tends to occur comparatively strongly at certain speeds, and also occurs frequently during engine running. ◎ Probable cause

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Noise Vibration and Harshness (NVH) - Resonance of Drive shaft Drive torque of engine is transmitted to Transaxle → Drive shaft → Axle hub and the bending vibration is emitted from drive shaft due to engine vibration. If engine vibration and drive shaft vibration are resonated together, then the drive shaft vibration is amplified. This amplified vibration is transmitted to the vehicle body through knuckle and suspension bush and it makes noise. ◆ Remedy : Generally, long drive shaft can make the resonance easily at 100 km/h. In this case, this problem may be solved with attachment of the dynamic damper.

? Beat Noise
Beat occurs when two sinusoidal oscillations, whose frequencies do not differ greatly, are superposed. They are periodic. Their basic frequency is the difference between the frequencies of the superposed sinusoidal oscillations. A Beating noise having a frequency 2 ~ 6 Hz is mostly noticeable. In this example, the beating noise can be explained as a sound synthesized from two sounds. The beating noise is also caused by two different vibrations when the vibration is the actual source of noise.There are two main causes for the so-called “beat-noise” (which occurs during driving) with loudness which changes periodically. 1) Noises caused by the combination of vibrations resulting from the slippage of the torque converter in automatic transaxle are combined. 2) Noises caused by the combination of vibrations from the engine and vibrations from auxiliary equipment (cooling fan, generator, power steering pump or air compressor for air conditioning system).

- Vibration by slippage of the torque converterBeat noise occurs frequently in vehicles with a torque converter in automatic transaxle. Slippage occurs when
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Noise Vibration and Harshness (NVH) torque is transmitted from the pump impeller to the turbine runner. Therefore, the position (phase) at which the turbine runner engages with the pump impeller of the torque converter, which is equivalent to the clutch, changes constantly because of slippage. At the time, because the direction of the engine imbalance and the direction of the transaxle and drive shaft imbalance periodically are same or are opposite, imbalance becomes great and small. As a result, the vibration is caused by this imbalance produces noise through body panel.

? Noise on steering wheel
- Troubleshooting Chart

- Squealing noise This noise may be heard just after very cold engine start (-20°C or less), caused by fluid characteristics at extreme low temperatures. Actually, this is not a malfunction. - Squeaking noise A slight “beat noise” is produced by the oil pump operation, but this is not a malfunction. This noise occurs particularly when a stationary steering effort is made.
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Noise Vibration and Harshness (NVH)

? Brake Noise
When the brakes are applied under the abnormal condition, the noises can be produced. The abnormal conditions are as follows; 1) Disc brake If noise such as scraping, grinding, rattling and groaning by the frictional force of the pad and the disc is occurred, because of improper adjustment, foreign material or rust. 2) Drum brake If friction between the brake drum and brake shoe is occurred, it may make the noise. The possible noises are frictional noise, swish, squealing, grinding and rattling. Brake squeal is one of the most annoying and frequently reported airborne noise vibrations. However, it is also one of the easiest to alleviate. Make sure you have identified the source (front or rear brakes) and apply the proper countermeasure(s) to dampen the noise vibrations. The following is a list of product applications that will dampen selected areas of the brake system for squeak/squeal control: 1) Disk brake pads 2) Disk brake caliper pins [Repairs] Replace pads, turn/replace rotors as necessary and apply countermeasure product. Thoroughly clean all caliper guide pins, replace damaged guide pin/piston seals and apply proper countermeasure products. 3) Drum brake adjuster screws and backing plate ledge [Repairs] Replace shoes, turn/replace drums as necessary and apply countermeasure products to all contact surfaces. - Troubleshooting Chart

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Noise Vibration and Harshness (NVH)

? Wind Noise
Wind Noise is one of the most difficult airborne vibrations to diagnose. However, once it is diagnosed, it is usually very easy to repair. There are a few tools available to diagnose wind noises from applying tape to suspect areas to expensive (and sometimes difficult to interpret) Ultrasonic* Detectors. The ultrasonic detectors can only detect air and water leaks occurring inside the vehicle cabin. However, even though the wind noise may be generated from a molding or outside mirror, and ultrasonic detector may narrow your search by eliminating any cabin leak sources. Also, by their very nature, ultrasonic waves bounce off of objects and can escape the vehicle cabin a distance

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Noise Vibration and Harshness (NVH) away from the actual leak source. If you do use an Ultrasonic detector in your shop, be sure to get thorough training on its use as a degree of interpretation is required for a positive outcome.

? A soap and water solution sprayed in the suspect area can reveal air and water leaks around windows and doors

[Definitions] Ultrasonic: The acoustic frequencies above those audible to the human ear. Or, above approximately 20,000 Hz.

If a wind noise condition cannot be pinpointed with the NVH tools or the Soap Bubble Test, you may have to tape the door and/or body panel exterior seams to locate the source. The idea is to seal the seam in the suspect areas with tape and, then remove the pieces of tape one at a time while test driving the vehicle. The wind noise condition will reappear when the tape covering the source has been removed. If the wind noise is still there with all of the seams taped, then the source is coming from an outside mirror, roof rack, side molding, etc.

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Noise Vibration and Harshness (NVH)

[Notice] Do not leave the tape on a vehicle out in the sunlight or on the painted surface for more time than absolutely necessary. The glue may react with the sunlight and adhere to the paint.

In almost case, the wind noise is heard, when the vehicle is running with faster than 80 km/hr. Normal wind noise can be occurred, in most cases, when the vehicle is running with 70 to 80 km/h with all windows are closed. The frequency range of noise is between 500 and 5000 Hz approximately. Depending on the vehicle speed and direction of running, frequency and type of noise can be changed. - Noise caused by protrusions of the vehicle body. Hissing or whistle noise is generated when wind hits protrusions or brackets. This makes a swirl of air behind the body surface. This generated noise enters the passenger booth through the gaps of the door, window glass or body panel. - Noise caused by the gaps of windows or vehicle body. While the vehicle is running with a high speed (more than 60 Km/h), the pressure of outside is lower than the pressure of inside. Therefore, the air inside is forced to go to outside through gaps of weather strips or window glass or panel joints, etc. This generates the noise like it hits the outside air flow. It would be allowed to call as “wind throb”.- Inspection Procedure

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Noise Vibration and Harshness (NVH)

? Road / Tread Noises, Moans & Groans
These types of structure borne noise vibrations are, for the most part, straightforward and easily diagnosed with the NVH tools (ex. Chassis Ears in USA). Simply attach the necessary number of leads to the suspect areas and take the vehicle on a road test. Moans and groans are usually the product of brake components, make sure the drums and rotors are not discolored and polished and that all brake hardware pivot and contact points are dampened. As with all NVH conditions, be sure to isolate the vibrations and verify any and all conditions have been remedied before returning the vehicle to the customer. Sometimes it is a good idea to go on a test drive with the customer to ensure the condition has been alleviated.

Type of Vehicle Vibration

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Noise Vibration and Harshness (NVH) There are two types of shake. One is the vertical shake, the other is the lateral shake. These vibrations are produced when driving at a high speed (about 80 km/h or higher). The whole vehicle body slightly shakes up and down or from side to side, and columnar resonance of air is produced inside the vehicle, resulting in a booming noise that is oppressive to the ears.

? Steering Wheel Vibration
[Vertical shake] [Lateral shake] Shimmy is the vibration of the steering system including tire (axial direction of linkage and the rotational vibration of the steering wheel). This is caused by kinetic unbalance of tires when the vehicle is being driven. The exciting force of this imbalance resonates with the steering system, becoming shimmy. This vibration is governed by the balance of the tires and by the damping force of the frictional parts of the steering system.

Steering Wheel Shimmy Definition Symptom Cause Path Source Remedy Path Reduced Suspension/Steering wheel sensitivity Suspension geometry & Steering wheel sensitivity Proper wheel/Tire balance and uniformity Enhanced suspension geometry Rotational vibration of the steering wheel while driving Usually happens at 100~150km/h Source Wheel/Tire Unbalance and non-uniformity

1) Shimmy and Judder

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Noise Vibration and Harshness (NVH)

? SHIMMY - Unbalance of Hub - Poor Wheel Alignment - Non-uniformity of Wheel/Tire

? JUDDER - Brake torque variation - Uneven wear of Disc - Disc thickness variation, Run-out - Brake pressure variation

* Path: Wheel & Tire Tie Rod Gear Box Universal Joint Steering Column Steering Wheel

2) Shake, Shimmy and Judder
SHAKE Direction of Steering wheel vibration Vehicle speed Frequency Source Up/Down, Left/Right 25~50 Hz Road SHIMMY Rotational direction 80~160 km/h 10~20 Hz Wheel/Tire unbalance or non-uniformity Unbalance, Suspension, Link JUDDER Rotational direction ~160 km/h 10~20 Hz Uneven frictional (braking) force Disc, Frictional material

Related factors

Steering wheel, Body

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Noise Vibration and Harshness (NVH)

- Troubleshooting Chart

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Noise Vibration and Harshness (NVH)

? Brake JudderBrake judder is usually caused by brake components that have deviated from
design specifications. Either the rotors may have warped or the drums may no longer be round and require machining or replacing. Measure all suspected parts for run out with a dial indicator and brake micrometer. Inspect the calipers for sticking (dragging brake pads can cause the rotors to overheat and warp). Make sure the emergency brake adjustment is within spec and it releases fully. There are other causes that may contribute to brake judder including: a. b. c. d. Worn suspension components (control arm ball joints or bushings) Tire Lateral Force Variations Worn steering components (tie rods, tie rod ends or rack-and-pinion play) Worn wheel bearings

Worn suspension and steering components usually do not pose a problem until the vehicle has 50,000 or more miles accumulated. However, if all the brake components have been eliminated and tire balance (including checking for RFV) is okay, check the ball joints, tie rods (and ends) for looseness and all control arm and radius arm bushings for wear. Make sure the steering rack-and-pinion play is within specs and the wheel bearings for wear. Consult the service manual for the vehicle you are working on for proper specifications and inspection procedures. [Definition] Lateral Force Variation (LFV): Lateral force variation is similar to RFV except that it causes a side-to-side vibration instead of the up-and-down vibration RFV causes.

When the brakes are applied under the abnormal condition, this vibration can be produced. The abnormal conditions are as follows; 1) Disc brake
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