Statens väg- och trafikinstitut (VTI) - Fack - 581 01 Linköping Nr 34 - 1978National Road & Traffic Research Institute - Fack - 581 01 Linköping - Sweden ISSN 0347-6030

34

The Attenuation of Tire Noise Emission

by Tire Enclosingby Ulf Sandberg, National Road & Traffic Research Instituteand Ove Bennerhult, IFM Akustikbyrån AB .

Reprint from the 1978 International Conference on Noise Control Engineering

(INTER-NOISE 78)ProceedingsSan Francisco, USA, 8 10 May 1978

Statens väg- och trafikinstitut (VTI) - Fack - 581 01 Linköping Nr 34 - 1978National Road & Traffic Research Institute - Fack - 581 01 Linköping - Sweden ISSN 0347-6030

34

The Attenuation of Tire Noise Emission

by Tire Enclosingby Ulf Sandberg, National Road & Traffic Research Instituteand Ove Bennerhult, IFM Akustikbyrån AB

Reprint from the 1978 International Conference on Noise Control Engineering

(INTER-NOISE 78)

Proceedings

San Francisco, USA, 8 10 May 1978

THE 1978 INTERNATIONAL 0 o 1CONFERENCE ON NOISE Inkef nove SandbergCONTROL ENGINEERINGJack Tar HotelSan Francisco, USA8-10 May 1978

THE ATTENUATION OF TIRE NOISE EMISSION BY TIRE ENCLOSING

Ulf Sandberg and Ove Bennerhult

National Swedish Road and Traffic Research Institute,

Fack, S 581 01 Linköping, Swedenresp.IFM Akustikbyrån AB, Warfvinges Väg 26, S 112 51 Stockholm, Sweden

INTRODUCTION

A previous Swedish research project has shown that it ispossible to reduce the tire noise emission from a truck by 5dB(A), by covering the tires entirely except for a 5 100 mmclearance nearest to the road surface (ref 1,2). The enclosures

were made of steel sheets and used a flexible rubber curtain for

the lowest 100 mm.

Using the same vehicle the study has now been extended to

investigate the effect of still larger clearances between road andenclosure, as well as the removal of the front wheel enclosure.

The purpose was to get information whether more practical enclosures than the initially tested samples still could be effective.

TEST PROGRAM

A Scania L 7538 two axle truck (six wheels) was used for the

tests. The total load was 122 kN with 20 kN per tire. The testedalternatives were:

1. Truck with standard mudguards (fig 1).2a. Enclosures on the rear wheels only. Clearance 200 mm (fig 2).

2b. Enclosures on the rear wheels only. Clearance 100 mm.

3a. Enclosures on all wheels. Clearance 200 mm (fig 3).

3b. Enclosures on all wheels. Clearance 150 mm.

3c. Enclosures on all wheels. Clearance 100 mm.

The lower clearances were attained by vertically adjustable rubber

curtains. No sound absorber was used but the steel sheet housing

was covered by vibration absorbing material.The tires were chosen to be "typical for the vehicle. The

front tires were rib type and the rear tires were block/rib type(all steel radials). See fig 4.

Tests were made on the following road surfaces:

2

Sandberg

l. Rolled asphalt, medium smooth with chippings < 12 mm (fig 5).The same surface, artificially wetted (water depth 0,3 mm).

3. Surface treatment, relatively rough with chippings 12 16 mm.Dry. (Fig 6).

The speeds were 50 and 70 km/h. All results are medium values

derived from at least 5 vehicle passes. The measurement method

utilized was a Swedish method described earlier (ref 3,4), essen

tially similar to SAE J57a. However it is prescribed in the methodthat the energy equivalent sound level (L ) during a 75 m vehicle

.pass should be measured as well as the max1mum level.

All measurements are normalized to the respective nominalspeed. Thus dB(A) values for vehicle speeds differing (up to i 3km/h) from the nominal speed are corrected.

N

RESULTS

The results are given in fig 7 10. Using the vehicle equippedwith standard mudguards as a reference, the results can be summa

rized as follows (for 70 km/h and Leq values):

0 Enclosures on all wheels and with clearances of 100, 150 or

200 mm all gave 3,5 4 dB(A) noise reduction on the "medium?textured surface (dry condition).

o When the surface was wet the noise reduction was l dB(A) for

200 mm rising to 3 dB(A) for 100 mm clearance.

0 For enclosures on the back wheels only, noise reduction was

2 dB(A) with 200 mm and 3 dB(A) for 100 mm clearance. When the

surface was wet the noise reduction was only l dB(A).o On the rough surface the noise reduction was less than 1,5

dB(A).o For 50 km/h the enclosures were generally 0 l dB(A) less effec

tive than at 70 km/h.o Water on the asphalt pavement generally caused a 10 dB(A)

increase in sound levels.0 The surface treatment caused between 0 and 4 dB(A) increase in

sound level relative to the asphalt surface.0 The tire temperature rise caused be the enclosure was in the

order of 500 (typically from 46 to 5100) for 2 h continous

driving at 40 80 km/h with 24OC ambient temperature.0 The attenuation for tonal components in the spectrum is better

than the overall figures (Le ) show. Consequently the subjectivenoise reduction should be better than indicated by Leq values.

0 The statistical uncertainty is for Le medium values typicallyi 0,4 dB(A) for 9522 confidence and for Lmax typically t 0,7dB(A). Thus Leq measurement gives somewhat better precision.

The difference in attenuation characteristics on the threeroad surfaces is believed to be caused by different generatingmechanisms and associated emitting surfaces; the medium textured"surface giving a tonal dominated spectrum and the rough surfacegiving a random type spectrum. E.g. it is plausible that the increased noise on the wet road is generated near the tire/road

interface and thus will be very little reduced. The contrary might

be true for the tone dominated noise on the asphalt road where the

position of the source can be higher.

3

Sandberg

PRACTICAL CONSIDERATIONS

It is admitted that there are many drawbacks and practicaldifficulties associated with the enclosures. The greatest problemsare believed to be: Clearance to road and obstacles, tire and

brake temperature, snow obstruction. It is obvious that not everyvehicle type can be equipped with the enclosures e.g. vehiclesfor temporary use in rough terrain or construction areas will needsome kind of clearance adjustment. The tire temperature rise was5 C in these tests and 5 lOOC in earlier tests with a ground clearance of only 50 mm (ref 1,2), and this is not felt to be unaccep

table. Probably it means that the performance of the vehicle islimited somewhat or that tire wear increases. The brake temperature was not measured because of accessibility problems but pre

vious fading tests indicated that braking performance was not noticably impaired. Also, the Splash and spray generation was significantly reduced (ref 1). Further operational tests are planned,

including long term in traffic tests.

CONCLUSIONS

The 5 dB(A) insertion loss with a 100 mm clearance that was

measured in a previous project could not be reproduced this time,probably depending on the fact that different road surfaces and

tires were utilized. However the results, indicating that 3 4dB(A) can be attained on a dry normal textured surface, either

with enclosures on all wheels down to 200 mm from the road, or

enclosures only on back wheels down to 100 mm from the road, are

very promising as this means a relatively simple enclosing arrangement. If the practical and economical problems can be satisfactorily solved, tire enclosures can be an effective complement toother vehicle noise abatement procedures.

ACKNOWLEDGEMENT

It is gratefully acknowledged that the work was financed by

the Swedish National Board for Technical Development. It is reported in Swedish in ref 5 and 6.

REFERENCES

1. P. 'Voigt, Däckskärmning ("Tire enclosing"), STU Report No74 4601, Swedish National Board for Technical Development,Stockholm (1976). (In Swedish).

2. G. Gadefelt and P. Voigt, Tire Noise Screening, SAE HighwayTire Noise Symposium, Soc. Aut. Eng., Warrendale (1976), pp211 213.

3. G. Gadefelt, O. Bennerhult and U, Sandberg, Förslag till metodför mätning av externt däckbuller från motorfordon ("A proposedmethod for measurement of external tire noise from motor ve

hicles"), STU Report No 74 4746 a+b, Swedish National Board forTechnical Development (1976). (In Swedish).

4. O. Bennerhult, A Standard Method for Measurement of Tire Noise,

IFM Akustikbyran AB, Stockholm (1977).5. U. Sandberg, O. Bennerhult, Skarmning av dackbuller ("Tire

noise screening ), STU Report No 76 6619, Swedish National

Board for Technical Development, (1977). (In Swedish).6. U. Sandberg, O. Bennerhult, Skarmning av dackbuller ( Tire

noise screening ), Report No 151, National Swedish Road andTraffic Research Institute, Linköping (1978). (In Swedish).

4

Sandberg

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42

Fig 1. Test truck equipped Fig 2. Rear wheels enclosed by

with standard mudguards. steel sheet housing. Clearance

to road surface: 200 mm.

»CCCCCCCICCC!

Illllllttlli Fig 3. All wheels enclosed. Fig 4. Tread print of tires.Clearance 200 mm. For lower Firestone steel radial 9.00 20.

clearances a flexible rubber Front tire (top): TranSport 1000.curtain was used at bottom. Rear tire (bottom): SAT 1000.

Fig 5. Road surface: Rolled Fig 6. Road surface: Surfaceasphalt, chippings < 12 mm. treatment, chippings 12 16 mm.

Sandberg

Attenuation Road surface: Rolled asphalt (dry)[dB(A)] Texture: "Medium"

L44lm rm

m- bm

2.

l

200 mm 100 mm 200 mm 150 mm 100 mm clearance

heightL - A l _ ]

enclosure on enclosure on all wheels enclosure

rear wheels type

A4 Road surface: Rolled asphalt (wet)

Texture: Medium

34 rn

21 "'

lé ftizi

Al _44 Road surface: Surface treatment (dry)

Texture: Rough"

3-1

2-1

li ?"?

Fig 7. Noise attenuation for the tested enclosures with reference

to truck equipped with standard mudguards.

Left bar: Attenuation in equivalent level (L ),

Right bar: Attenuation in maximum level (L

Solid lines: Vehicle Speed 70 km/h.Dotted lines: Vehicle speed 50 km/h.

max/'

6

Sandberg

dB REL 20 uPa

90

80

70

60

50

20

10

Fig. 8.

Frequency spectra (1/3 octave band)for truck on dry medium texturedasphalt road. 70 km/h.

overall level

(max.) dB(A)

with standard mudguards 80,0

encl. rear wheels,100 mm 77,3

- encl. all wheels, 200 mm 76,5

encl. all wheels, 100 mm 76,5

50 30 100 160 200 315 400 630 000 1250 1600 2500 3150 5000 6300 1000063 125 250 500 1000 2000 4000 8000

Fig 9.

As fig 8, but on

wet pavement.

- - st. mudg.

--»--- rear, 100

-~-~- all, 200

--- all, 100

Fig 10.

Frequency spectra for truck on dry

rough textured surface treatment.

70 km/h.

overall level

(max.) dB(A)

- with standard mudguards 79,4

.."." encl. rear wheels,100 mm 79,0

------- encl. all wheels, 200 mm 78,7

---- encl. all wheels, 100 mm 78,2

50 80 100 160 200 315 400 630 800 1250 1000 2500 3150 5000 6300 10000

63 125 2 50 500 1000 2000 4000 8000

frequency [Hi]