Wang X. Vehicle Noise and Vibration Refinement

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Body structure noise and vibration reﬁ nement 385

In previous sections, generic targets for various body NVH metrics have

been proposed. These targets are summarized in Table 15.2.

15.10 References

Achram L, Chidamparam P, Goetchius G, Thompson J (1996), ‘Applying NVH

basics to body design’, Proceedings of the 1996 International Body Engineering

Conference.

Cremer L, Heckl M (1988), Structure Borne Sound, Springer-Verlag, New York.

Dong B, Goetchius G, Duncan A, Balasubramanian M, Gogate S (1999), ‘Process

to achieve NVH goals: Subsystem targets via “digital prototype” simulations’,

Proceedings of the 1999 SAE Noise and Vibration Conference.

Duncan A, Su F, Wolf W (1996), ‘Understanding NVH basics’, Proceedings of the

1996 International Body Engineering Conference.

Duncan A, Goetchius G, Guan J (2009), Structure Borne Noise Workshop, 2009

SAE Noise and Vibration Conference.

Dunn J (1978), ‘Standardization techniques for the dynamic performance of mono-

coque vehicle structures’, Proceedings of the Inst. Measurement and Control

Symposium, Vehicle Ride and Maneuvering Characteristics Volume.

Gogate S, Duncan A (2001), ‘ “Digital prototype” simulations to achieve vehicle

level NVH targets in the presence of uncertainties’, Proceedings of the 2001 SAE

Noise and Vibration Conference.

Huang J, Sin H (2001), ‘Aluminum rail rivet and steel rail weld DOE and CAE

studies for NVH’, Proceedings of the 2001 SAE Noise and Vibration Conference.

Nashif A, Jones D, Henderson J (1985), Vibration Damping, John Wiley & Sons,

New York.

Norton M (1989), Fundamentals of Noise and Vibration Analysis for Engineers,

Cambridge University Press, Cambridge.

Onsay T, Akanda A, Goetchius G (1999), ‘Vibro-acoustic behavior of bead-

stiffened ﬂ at panels: FEA, SEA, and experimental analysis’, Proceedings of the

1999 SAE Noise and Vibration Conference.

Table 15.2 Generic target and best practice summary

Generic target/best practice Value Comments

Point mobility (V/F) −10 dB mm/sec/N (reference:

1 mm/sec/N)

Body-to-isolator attachment stiffness

ratio (K

ratio

)

5 : 1 Unitless ratio

Body acoustic transfer function (P/F)60 dB(Pa)/N (reference: 2e − 5 Pa)

Body panel loss factor 0.1 Unitless ratio

Body panel ﬁ rst mode 200 Hz

Body panel damping area coverage 70%

Modal separation (mode

management)

10% Global body modes

and panel modes

Spot weld pitch 30 mm

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386 Vehicle noise and vibration reﬁ nement

Patil A, Goetchius G (2009), ‘Effect of damping on sound transmission loss through

automotive body panels’, Proceedings of the 2009 SAE Noise and Vibration

Conference.

Plunt J (2005), ‘Examples of using Transfer Path Analysis (TPA) together with

CAE-models to diagnose and ﬁ nd solutions for NVH problems late in the vehicle

development process’, Proceedings of the 2005 SAE Noise and Vibration

Conference.

Raichel D (2006), The Science and Applications of Acoustics, Springer, New York.

Williams R, Balaam M (1989), ‘Understanding and solving noise quality problems’,

Proceedings of the 1989 Auto Tech Conference.

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387

Vehicle noise and vibration strategy-based

diagnostics

X. WANG, RMIT University, Australia

Abstract: This chapter introduces noise and vibration induced by

run-outs, material property variations, imbalance of tyre/wheel and

propshaft, and incorrect driveline angles. Root-cause diagnosis methods

and problem-solving methodology are illustrated in detail in order to

help eliminate conventional customer complaints in terms of vehicle

noise and vibration problems.

Key words: run-out, static imbalance, dynamic imbalance, ﬁ rst-order

vibration, second-order vibration, tyre/wheel balance, propshaft

balancing, driveline angle, propshaft phasing, tyre/wheel force variation.

16.1 Introduction

When a person does not feel well, with symptoms such as high temperature,

vomiting, diarrhoea, dizziness, headache, etc., he goes to see a medical

doctor. The doctor would listen to his description of the symptoms, collect

the information, and carry out a series of medical tests in order to identify

the root causes for his sickness and make decisions for the solutions such

as prescriptions, surgery, etc. A machine or a vehicle will have noise and

vibration symptoms if it is poorly designed or is liable to mechanical or

structure failure. The mechanic follows the same diagnosis and solution

process, which is to collect information by talking with customers and to

reproduce the symptoms by doing test drives in relevant driving conditions.

A series of noise and vibration tests are carried out to identify the root

causes for the noise and vibration problems, and solutions such as modiﬁ ca-

tion of the source, structure or transmission path are determined.

Customer complaints or callbacks are common issues in vehicle warranty

periods. A lot of complaint issues concern noise and vibration symptoms.

In order to resolve them in a reasonably short period of time (such as one

or two weeks) and satisfy the customers, noise and vibration-based diagno-

sis strategy or methodology is necessary for both engineers and their

employers.

The objective of this chapter is to formulate systematic noise and vibra-

tion diagnosis strategy or methodology and solutions by investigating the

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388 Vehicle noise and vibration reﬁ nement

root causes such as run-outs, force variations, imbalances of tyres/wheels

and propshaft, and driveline angles, which can be used to resolve most noise

and vibration issues.

A conventional vehicle noise and vibration strategy-based diagnostics

process ﬂ ow is shown in Fig. 16.1 in which seven steps are followed. Before

getting started, a few basic concepts must be understood. As in any diag-

nostics process, one must gather information, decipher it, and perform a

Diagnostic flow

Verify complaint

Preliminary checks

(visual, operational,

DTC)

Check bulletins and

trouble-shooting

highlights

Perform service

manual system

check(s)

Hard code No code

No matching

symptom in service

manual

Intermittent

Perform service

manual

diagnostic

procedures

Select symptom

from service

manual symptom

chart and

perform

procedure

Analyse and develop

diagnostics from

wiring chart and

theory

Refer to

intermittent

diagnostic details

Operating as

designed

Call or explain to

customer

Find/isolate the

problem

Re-examine the

complaint

Repair/resolve and

verify fix

Yes

555cdba

16.1 Noise and vibration strategy-based diagnostics.

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Vehicle noise and vibration strategy-based diagnostics 389

correction based on the results. Basically, we follow a process of elimina-

tion. For example, the following is such an elimination process:

1. A customer brings his/her vehicle to the dealer complaining of a pulsa-

tion when the brakes are applied.

2. The service advisor questions the customer and writes the pertinent

details on the repair order.

3. Next, the technician reads the information, and road tests the vehicle

using the normal and the parking brake to stop the vehicle. He is gather-

ing information.

If the pulsation was present only while using the parking brake, the logical

approach would be to inspect the rear brakes ﬁ rst for an out-of-round or

similar condition. This would, in turn, dictate the type of repair necessary

to eliminate the complaint. If the technician measured the rear brake drums

and found excessive run-out present, he would then most likely resurface

the drums and evaluate the vehicle to make sure that the method of repair

he chose was the correct one, based on the information that was

gathered.

This process of elimination can be very useful when applied to correcting

vibrations in two steps:

1. The service advisor gathers information about the complaint from the

customer.

2. The technician then road tests the vehicle in a manner intended to sys-

tematically eliminate different parts of the vehicle. This information

supplements the customer information.

By concentrating repair efforts on the areas that have not been eliminated,

repairs can be made more quickly and effectively.

To take another example, a customer brings his or her car to the dealer-

ship, complaining of a vibration at 60 km/h. During the road test, the techni-

cian discovers the same vibration can be felt while the car is stopped at the

same time revving the engine to about 1200 rpm. The logical approach,

based on this information, would be to concentrate on components related

to the engine, since tyres, wheels and the driveline have already been elimi-

nated as a possible cause. This is because they are not rotating when the

vehicle is standing still. Take the time to gather additional information relat-

ing to the complaint. It saves a tremendous amount of time in the long run.

16.2 Wheel and tyre vibrations

Vibrations related to wheel and tyre are low-frequency vibrations and

sensitive to vehicle speed. In this section, the following speciﬁ c vehicle

components will be addressed according to vibration frequency and systems:

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390 Vehicle noise and vibration reﬁ nement

• Tyres

• Wheels

• Wheel hubs

• Brake rotors.

We will go through the steps necessary to systematically approach and

repair problems found in these areas.

16.2.1 First-order vibrations

The following are symptoms of ﬁ rst-order vibrations caused by tyre/wheel

assemblies:

• They are always vehicle-speed related. If the vibration is affected by the

speed of the engine, or is eliminated by placing the transmission in

neutral and coast down test vehicle, then it is not related to the compo-

nents in this group.

• The vibration will ‘feel’ like a shake, usually in the steering wheel or

seat.

• At low speed (10 to 60 km/h) the customer may complain of a ‘waddle’

(see Section 16.3.6 Lateral force variation).

The frequency of the vibration will correspond to the ﬁ rst-order of tyre

rotation. This will usually be in the 10–20 Hz range, depending on the speed

of the vehicle and the size of the tyre. The smaller the tyre, the faster it will

rotate at any given speed.

The available range of human hearing begins at 20 Hz. For this reason,

ﬁ rst-order tyre vibrations rarely produce a noise. The exception to this

would be if the tyres display an irregular tread pattern or ﬂ at spots, causing

a ‘growling’ or ‘slapping’ noise. Tyre/wheel vibrations felt in the steering

wheel are most likely related to the front tyre/wheel assemblies. Tyre/wheel

vibrations felt in the seat or ﬂ oor are most likely related to the rear tyre/

wheel assemblies. This may not always hold true but is a general rule that

may serve to initially isolate a problem to the front or rear.

First-order tyre/wheel vibrations are usually the result of one of ﬁ ve

conditions:

• Excessive radial run-out

• Excessive lateral run-out

• Excessive imbalance

• Excessive radial force variation

• Excessive lateral force variation.

All ﬁ ve of these conditions must be eliminated step by step, in order to

attain a set of tyres free from vibration-causing elements. Substituting a set

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Vehicle noise and vibration strategy-based diagnostics 391

of tyres from another vehicle should only be performed as a last resort, and

then only if the tyres used have been evaluated on a similar vehicle under

the same conditions.

Due to vehicle-to-vehicle sensitivities and differences between the

mounting hubs of any two vehicles, correcting the existing tyre/wheel

assemblies is the most accurate and least time-consuming approach in the

long term.

16.2.2 Run-out

Because the run-out of a tyre/wheel assembly will directly affect the amount

of imbalance and radial force variation, radial and lateral run-out can be

corrected at the same time. There are two methods to measure run-out of

tyre/wheel assemblies:

• On the vehicle (mounted to the hub – the wheel bearing must be in

good condition)

• Off the vehicle (mounted on a spin-type wheel balancer)

• Initial on-car inspection should be made prior to off-car runout check.

Measuring the tyre/wheel run-out off the vehicle is easiest. It is usually

easier to mount a dial indicator in the correction location as shown in Fig.

16.2, and the chances of water, dirt or slush getting on the indicator are

decreased. Once the run-out has been measured and corrected off the

vehicle, a quick visual recheck of run-out on the vehicle will indicate if any

further problems exist. If there is a large difference in the run-out measure-

ments from on-vehicle to off-vehicle, then the run-out problem is due to

either stud pattern run-out, hub ﬂ ange run-out, or a mounting problem

between the wheel and the vehicle.

(a) (b)

16.2 (a) Radial and (b) lateral run-out.

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392 Vehicle noise and vibration reﬁ nement

Before measuring or attempting to correct excessive run-out, carefully

check the tyre for uneven bead seat. The distance from the edge of the ring

to the concentric rim locating ring should be equal around the entire cir-

cumference. If the beads are not seated properly, the tyre should be

remounted, otherwise excessive run-out and imbalance may result.

16.2.3 Measuring tyre/wheel assembly run-out

If the vehicle has been sitting in one place for a long time, ﬂ at spots may

exist at the point where the tyres were resting on the ground. These ﬂ at

spots will affect the run-out readings and should be eliminated by driving

the vehicle long enough to warm up the tyres. Do this before any run-out

measurements are taken, and do the following:

1. Lift the vehicle on a hoist or support with jack-stands.

2. In order to get an initial indication of how much run-out exists, spin

each tyre and wheel on the vehicle by hand (or at a slow speed using

the engine to run the drive wheels), visually checking the amount of

run-out from the front or rear.

3. Mark the location of each tyre/wheel assembly in relation to the wheel

studs and to their position on the vehicle (right front, left rear, etc.) for

future reference.

4. Remove the tyre/wheel assemblies one at a time and mount on a spin-

tyre wheel balancer.

5. Measure the tyre/wheel assembly run-out as shown in Fig. 16.3.

On tyres with an aggressive tread pattern, it will be necessary to wrap the

outer circumference with tape when measuring radial run-out. This allows

for a smooth reading to be obtained from the dial indicator. Lateral run-out

should be measured on a smooth area of the sidewall, as close to the tread

as possible. Any jumps or dips due to the sidewall splices should be ignored

and an average amount of run-out obtained by the following procedure:

Radial run-out

Tape

Lateral

run-out

Lateral

run-out

Place dial indicator in a

smooth area as close

to the tread as possible

16.3 Measuring tyre/wheel assembly radial and lateral run-out.

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Vehicle noise and vibration strategy-based diagnostics 393

1. Slowly rotate the assembly one complete revolution and ‘zero’ the dial

indicator on the spot.

2. Rotate the assembly one more complete revolution and note the total

amount of run-out indicated.

The maximum allowable assembly radial and lateral run-out is 1.5 mm

when measured off the vehicle and 1.8 mm on the vehicle.

16.2.4 Match-mounting

If the run-out is excessive, mark the location of the high and low spot on the

tyre and the wheel. The next step is to determine if the run-out problem exists

in the tyre, wheel or a combination of both, then to correct it. The procedure

used to accomplish this is called match-mounting or system matching:

1. Place a mark on the tyre sidewall at the location of the valve stem. This

will be referred to as the 12:00 position. The location of the high spot

will always be referred to in relation to its ‘clock position’ on the wheel.

2. Mount the tyre/wheel assembly on a tyre machine and break down the

bead. Do not dismount the tyre from the wheel at this time.

3. Rotate the tyre 180° on the rim so the valve stem reference mark is now

at 6:00 in relation to the valve stem itself. Reinﬂ ate the tyre and make

sure the bead is seated properly. The bead may have to be lubricated

in order to easily rotate the tyre on the wheel.

4. Mount the assembly on the tyre balancer and remeasure the run-out.

Mark the new location of the run-out high point on the tyre. If the

run-out is now within tolerance, no further steps are necessary. The tyre

may be balanced and mounted on the vehicle.

5. If the clock location of the high spot remained at or near the clock loca-

tion of the original high spot, the wheel is the major contributor to the

run-out problem as shown in Fig. 16.4. It should be measured for exces-

sive run-out and replaced if that is the case.

Tyre reference mark at 12:00

Tyre reference mark at 6:00

Tyre

Rim

Valve stem

at 12:00

First measurement

(high spot)

Second measurement

(high spot)

16.4 Match-mounting (1): the wheel is the major run-out contributor.

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394 Vehicle noise and vibration reﬁ nement

Always measure the run-out of new wheels when replacing old ones. Do

not assume that a new wheel is automatically a ‘known good’ component.

If the high spot is now at or near a position 180° (6 hours) from the original

high spot, the tyre is the major contributor and should be replaced as shown

in Fig.16.5. Always measure the tyre/wheel assembly run-out after replacing

the tyre and make sure the run-out is within tolerance before continuing.

In the majority of cases, the ﬁ rst 180° turn of the tyre will either correct the

run-out problem or indicate which component to replace. If the high spot

is between these two extremes, then both the tyre and the wheel are con-

tributing to the run-out. Try rotating the tyre an additional 90° (3 hours)

in both clockwise and counterclockwise directions, measuring the run-out

after each rotation. Once run-out has been brought within the tolerance,

the assembly should be balanced.

16.2.5 Wheel run-out

If run-out cannot be brought within tolerance by match-mounting, dis-

mount the tyre from the wheel and measure wheel run-out. Wheel run-out

should be measured on the inside bead area of the wheel. Measure the

run-out in the same fashion as tyre run-out. Ignoring any jumps or dips due

to paint drips, chips or welds, measure both inboard and outboard as shown

in Fig. 16.6.

If the run-out of the wheel is within tolerance, and the tyre/wheel assem-

bly run-out cannot be reduced to an acceptable level by using the match-

mounting technique, the tyre must be replaced. Always remeasure assembly

run-out after replacing the tyre. If there is a large difference in the run-out

measurement from on-vehicle to off-vehicle, the run-out problem is due to

either stud pattern run-out, hub ﬂ ange run-out, or a mounting problem

between the wheel and the vehicle. If run-out measurements are within

tolerance but are marginal, some sensitive vehicles may still be affected. It

Tyre reference mark at 12:00

Tyre

First measurement

(high spot)

Rim

Valve stem

at 12:00

Tyre reference

mark at 6:00

Second measurement

(high spot)

16.5 Match-mounting (2): the tyre is the major run-out contributor.

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