THE INPACT OF NEW AND INNOVATIVE PARTS MADE OF

the inpact of new and innovative parts made of vibroacustic materials on acustic vehicle comfort zorica pantelić milinković, predrag m

THE INPACT OF NEW AND INNOVATIVE PARTS MADE OF VIBROACUSTIC MATERIALS
ON ACUSTIC VEHICLE COMFORT
Zorica Pantelić Milinković, Predrag Milenkovic, Milan Milovanovic,
Zoran Marjanovic
"Zastava automobili" DRA, Kragujevac, Srbija,
[email protected]
"Fiat Automobili Srbija", Kragujevac, Srbija, [email protected]
"Zastava automobili" DRA, Kragujevac, Srbija, [email protected]
"Zastava automobili" DRA, Kragujevac, Srbija, [email protected]
In this paper will be taken under the consideration the possibility of
acoustic comfort improvement by using vibro acoustic materials. The
noise reduction on its transmission routes i.e. the possibility of
reducing already raised sound energy by reducing its conductivity to
passenger compartment, in particular will be analyzed. The insulation
and absorption materials tooks the cpecific place in solving of this
problem. The impact of the material shape, mode of production and
instalation methodes, at acustic comfort, was analized. Researching
was made in laboratory conditions and at road tests as well. In this
paper is given a part of resultes obtained by testing of insulation
and apsorption materiales. Also, the parametars of vehicle acustic
comfort were determinated.
Key words: vehicle, noise, absorption material, insulation material,
acoustic comfort, firewall insulation
Introduction. The car market is much more demanding in terms of
comfort and environmental pollution. The fact is that the enjoyment of
driving a car depends on the acoustic, as well. That is why there are
many investments in car acoustic development. However, there is no
valid general development strategy on this subject because a lot of
influence of subjective feelings, which vary depending not only on
manufacturer but also on world markets specificities. Struggle with
noise requires different procedures on the sources and routes of its
transmission. Obtaining adequate compromise between acceptable noise
levels and noise requirements that do not fall into the domain of
acoustics requires a deep knowledge of the occurrence. Noise in the
cabin is caused by series of incentives and pathways. A large number
of processes and mechanisms produce vibration and acoustic energy, but
it is evident that power train is the main source of noise in the car.
If the vehicle noise is taken under the consideration, it is necessary
to differentiate the motor space with noise source and the cabin. The
noise produced by motor which can be heard inside of cabin can be
structural, air-noise or both. Generated noise is partially
transferred to the passenger compartment directly through the
partition wall, floor, roof, body channels and other body parts. Only
way to eliminate the noise once passed into the cabin is to use some
absorbing materials. To prevent the sound penetration into the
passenger compartment the combination of insulating and dumping
materials is used.
The analyse of noise sorces and noise transmission on vehicle acoustic
The sound is transmited from source to recipients in passenger
compartment or eviroment, by different ways. The great influence on
those paths has vehicle conseption i.e. enviroment encountered by the
sound. It is very important to find out the paths of sound
transmission and to block them in aim to isolate an arise sound. It is
possible to do by using proper vibro-acoustic materials, i.e. “passive
insulation”. In order to adequate determine the use of vibro-acoustic
materials, it is necessary to research the vibro-acoustic
characteristics of vehicle body by which the noise transmission is
going on and which is also a secondary noise source.
Based on complete analyses of body, source of noise in the vehicle,
its path passes, vibro-acoustic properties of materials, selects the
material type and its plasment are chosen in the order to have
efficiant noise insulation. Until recently, noise transmission through
body channels has been neglected. It will be shown here that the
blocking of noise pathes through the box-body parts has a large impact
on the acoustic comfort.
The paths of noise transmission to passenger compartment
The noise heared in passenger compartment is consist of noise
trasmited by air and the one transmited by solids. Noise emited from
motor block surface is transmited through the air and inuce the big
car body surfaces to vibrate. Those vibrations are emited in form of
sound. Otherwise, the drive unit vibrations transmit trough motor
rubbor bushings, metal motor supports, cross body supports and trough
the axes. Those vibrations affect the metal surface and produce noise
in the cabin. Such noise is called the noise carried by a solid body.
All listed primary sources create sound field centered around the
walls surrounding the passenger compartmant as a resonator. All the
walls that surround the cabin and all acoustic openings in them
contribute to the transfer of noise through the air environment.
Soundproofing car noise transferred by air is an important effect of
acoustic treatment by the vibro-acoustic materials. By decreasing of
generated sound and by blocking the noise transmission paths in
vehicle designing process, the good acoustic characteristics of
vehicle will be obtained for both, vehicle users and the environment.
Figure 1 provides a model for noise transfer showing the necessity of
large loss of acoustic energy in walls of the cabin during the
transfer. Special attention is paid to the partition wall, but the
transverse trough partition wall is not the only path of sound, so the
effects of using isolation are limited by the sound transmission
trough the other walls of the cabin.

Fig. 1 Transfer of sound power from engine compartment to cabine
If there is an active noise source in engine compartmant, the sound
power in cabine will be:

(1)
P- sound power in the cabine if the active noise source is in the
engine compartment
P1- the transmission through the partition wall
P2- the transmission through the lateral chanels
P3- the transmission through the floor
P4- the transmission through the other walls of cabine
Despite to all the interventions that are performed on the car to make
the internal noise lower, a part of the acoustic energy still gets
into the passenger compartment. Reduction of sound energy due to
passenger compartment can be done by absorption. For this purpose, the
absorption materials are commonly used, although the acoustic
resonators can be used, as well as the active noise control, which
still is not being applied in series production. On Fig.2, is given
the pattern of sound energy transformation that is transmitted from
the environment into the passenger compartment.

Fig. 2 The transformation of energy due to the cabin
Calculation of sound energy transformation in the passenger
compartment
According to law of conservation of energy:

(2)
Where: Ei – energy due to the cabin, Ea – the absorbed energy, Er –
the reflected energy, Et – transmitted energy
The absorption coefficient is:

(3)
Unit that is equivalent to absorbtion of the cabin, can be written as:


(4)
Fig. 3 Tercoktave analyse of noise level, engine in idle running
In order to have an overview what part of noise spectrum generate in
the motor compartment came into the cabin at Figure 3 we compared the
noise spectrum in engine and passenger compartments. Considering the
diagram in Figure 3, it is obvious that increased loss of transmitted
acoustic energy is in the range of frequencies where the cotribution
of seconnd-order is low. Tipical contribution of engine noise
transmitted by radiation has to be expected in frequental range of
500Hz to 8000Hz Fig.3.
The experimental researching in laboratory and at the vehicle
Examination of the absorption characteristics of porous materials is
done in the laboratory, in Kundt-tube, by using B & K equipment.
Ispitivanja apsorpcionih karakteristika poroznih matrijala rađena su u
laboratoriji, u Kundt-ovoj cevi, oprema B&K. The vehicle noise
measuring are made outdoor, by using B&K equipment (sound meter,
microphone), A/D converter, computer, rev-counter and HP frequency
analyzer.
The laboratory tests resultes

Fig.4 The resultes of measurment made in Kundt-tube
In Kundt-tube were made the measurements of absorbtion coefficient of
carpet and rugs with poros 700. Poros 700 is absorbing material based
on cotton fibers with some kind of binders.
The obtained resultes are shown at Fig. 4. The absorbtion coefficient
of carpet is lower than 30% at high frequencies. By adding of material
porosso 700 on carpet, the absorption coefficient is increased in rate
of 60%. This kind of testing has shown that it can increase the sound
absorbtion in vehicle by adding an absorbent material and on that way
improve the acoustic comfort in a part.
The previous model of the vehicle was observed in which weak points
were defined by analyzing of noise transmission paths:
- Boxy body parts along the sides (channels) transmit the noise in the
cabin by air. By setting the expansive materials (PUR, expansive
rubber or PVC plastics) in the duct body intersects the path of noise.
The PUR foam was used in these examinations.
- Isolation of the partition wall has a numerous of acoustic windows.
Cutting holes in the minimum order is the way to prevent the passage
of noise into the cabin 1.
- At the rear fenders and trunk space is just a carpet with a low
coefficient of absorbtion. By adding the absorbent material to improve
its absorption coefficient. The complite analyse of noise transmission
into the cabin showes that there is a possibility of acoustic comfort
emprovement by inovate of exising package of vibroacoustic materiales:
Package I – Existing isolation model (S) + Paths of noise transmission
trough chanales blocked by inserting polyurethan (marked by green
cycles) Figure 5.
Package II – Existing isolation +PUR foam + innovation of existing
insulation (at the rear fender carpetadded poroso 700, zb)
Package III – Existing isolation + PUR + Inovation of existing
insulation (insulation of the partition wall is made in one piece with
acoustic holes reduced to a minimum, pz.)
Package IV – Existing isolation + PUR + zb + pz + Inovation of
existing insulation (on carpet in trunk added poroso 1000, g)
At Figures 5, 6 and 7 the new and innovative materiales are showen and
its poins of use.

Fig. 5 Package I (PUR – foaming points-green cucitesi)

Fig. 6 Left- partition wall insulation before reconstruction.
Right-innovated insulation of partition wall (pz)

Fig. 7 Innovated fender lining (zb), left and innovated trunk lining (g)
The results of vehicle tests
All tests were done at driver's ear during light acceleration. All
analyses were performed for each set of activities and for each new or
renwed vibroacoustic material. At Figure 8 are showen the influences
of packages from II to V at interior vehicle noise. Package I has low
effect so it was not considered futhermore. That analyzing is not
worth even speaking with financial party. The results of internal
noise levels measurements are shown in Fig.8 and Fig.9.

Fig. 8 Noise levels in the vehicle at the idle running
The greatest impact on lowering of the internal noise level has
foaming of expanding polyurethane in body channels and improvement of
partition wall. The internal noise reduction goes up to 4 dB(A) at the
idle running of engine. By using those two packages the level of
internal noise can be decrease in average up to 2dB(A) at the idle.

Fig. 9 The noise level; driver's right ear: at second gear (on left)
and fourth gear (on right)
The whole package of activities reduces the level of internal noise in
the second gear for about 1-2 dB (A) depending on the number of the
engine rpm. In the third gear this contribution is reduced. In the
fourth gear, the wholw package of activities does not change the level
of internal noice (Fig. 8 right). In 4th and 5th gear the vehicle
speed is larger and aerodynamic noise masks the noise of powertrain.
According to the objective rating, the noise, frequency spectrum,
loudness and articulations index are the parameters marked as most
imporant for acoustic comfort. It is very important wich frequencies
are dominant. Sometimes, the quiet vehicle may have some frequences of
high level so could annoy the user. Besides the sygnal level a
significiant role in the assessment of comfort takes the frequency
analyse. The frequent analyses are done at driver's ear at speeds
ranging from 1000 rpm, in steps of 500 rpm. At Fig.10, 11, 12 and Fig.13
are shown just some of the results.

Fig .10 Frequency spectrum at the idle, at the driver's ear: 2500 rpm
(on left), 5000 rpm (on right)

Fig. 11 Frequency spectrum above 200Hz, at the driver's ear: 2500rpm
–left and at 3500 rpm-right

Fig. 12 Frequency spectrum II gear: 2000rpm-left and 5000 rpm-right

Fig. 13 Frequency spectrum above 200Hz at the driver's ear: 2500rpm1-left
and 3500 rpm-right
From the diagram of noise frequency analysis is seen that the largest
contribution of applied packages is in the field of frequencies above
200Hz. At some frequencies the decrease is up to 10 dB. At diagrams on
Fig. 14 the influence of packages on articulation index in test
vehicle, is shown. Articulation index is a measure of intelligibility
of speech, music and other useful sounds in the presence of noise.
L isten
Read phonetically
Fig. 14 The articulation indexes for II and III gear
Using of noise inssulation materiales has a significant impact on
noise level inside the vehicle, especialy in speaking range.
The greatest contribution in acoustic comfort emprovement was
obtainedd by using package I (S+PUR) and package III (S+PUR+ zb+pz).
By installing package III, the articulation index increased for about
10 %.
Conclusion
Passenger and engin comparmants have to be isolated of eacother so the
as les as possible amonth of sound energy, generated in drive unit,
can pass to the cabin. By theoretical analyses and laboratory tests of
vibroacoustic maaterials, only the qualitative guidance in the means
of the function they designed for. Good acoustic processing of vehicle
by appropriate vibroacoustic materials leads to desired results in
terms of acoustic comfort.
Proper use of vibroacoustic materials gives great conribution to
decreasing of vehicle interial noise and improves the acoustic comfort
of vehicle.
Partes for acoustic insulation should be made as one piece, without
cuttings and holes, if it is possible to do according to installation
tehnology. If the cutting is nesseary, it is recomanded to seal the
holes after installation. So, disintegratedness of insulating
coverings reduces overall power insulation bulkheads so this needs to
consider in insulating parts designing proces. Disintegratedness of
insulating coverings or the holes in it significantly reduce the
insulation effect.
It is not enough for car comfort avalution to here an subjectiv
opinion of some experts group. For serious analyse and acoustic
comfort avalution it is nessesary to know about the shape of acoustic
tercocave spectrum. It is the base to definine the total noise
character, what is very important for rating of vehicle acoustic
comfort.
REFERENCES
1. Z. Pantelić Milinković, S.Jovanović, Z.Marjanović, "Razvoj
vibroakustičkih materijala u automobilskoj industriji"donji Milanovac,
7 - 11. juna 2010. godine
2. Z.Pantelić Milinković, A.Dišić, "THE INFLUENCE OF THE FIREWALL
INSULATION ON THE VEHICLE ACOUSTIC COMFOR", CAR20051009, Pitesti,
Romania, 2-4. 2005.
3. R. Basshuysen, G. Kuipe, H. Hollerweg, "Akustik der Audi 100 mit
direkt einspritzendem Turbo-Diselmotor" ATZ 92/1990
4. Von Quang-hue Vo, I.Wulf Sebbesse, "Entwicklung eines subjektiv
angenehmen Innengeräusches" ATZ, Automobiltechnische Zeitsrift 95,
1993.
5. Z. Pantelić Milinković, N.Vitošević, “Uticaj akustičkih отvora na
izolaciju pregrade kod vozila” Međunarodni naučno stručni skup XXI
NAUKA I МОТОRNА VOZILA 2007. od 23.-25. арrila 2007.Beograd, Srbija,
NMV0760S
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