Araçlarda bir kalite metriği olarak kabin hava kaçağı ve kabin içi gürültü seviyesine etkisi
Vehicle body air leakage as a quality metric and its effect on cabin interior noise performance
Yazar: CİHAN ÖZTÜRK
Danışman: PROF. DR. İSMAİL AHMET GÜNEY
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Makine Mühendisliği Ana Bilim Dalı / Otomotiv Bilim Dalı
Derece: Yüksek Lisans, 2018
Konu: Makine Mühendisliği = Mechanical Engineering

Özet:
Günümüz teknoloji ilerleme hızında,otomotiv şirketlerinin sektör içerisindeki
rekabetçi konumlarını koruyup, ön sıralarda yer almaları için yüksek müşteri
beklentilerini karşılamaları gerekmektedir. Otomotiv şirketlerinin amacı müşteri
beklentilerini karşılayarak, memnuniyetini ve bağlılığını sağlamaktır.
Müşteri memnunuyeti ve bağlılığı, otomotiv şirketleri tarafından çeşitli anketleme
yöntemleri ve servis verilerinden takip edilmekte, edinilen bu verilere göre hem ileri
model ürün geliştirme çalışmaları şekillenmekte hem de mevcut üretim araçlarındaki
sorunların giderilmesi için ürün geliştirme çalışmaları yapılmaktadır.
Ürün geliştirme çalışmalarının önemli bir kısmını araç özellikleri geliştirme
çalışmaları oluşturmaktadır. Araç özellikleri konularını genel olarak saymak gerekirse;
konfor, kalite algısı, araç ergonomisi, araç dinamiği, performans hissi, yakıt tüketimi,
ağırlık, sürücü destek sistemleri ve gürültü/titreşim kontrolü olarak sıralanabilir. Bu
konular içerisinde bulunan gürültü ve titreşim kontrolü, hassas müşterilerin en çok
dikkat ettiği konulardan biridir ve genellikle uzun bir geliştirme süreci sonununda
hedeflenen seviye sağlanabilir.
Araç içerisinde oluşan gürültünün kaynağı ile müşterinin kulağı arasındaki iletim yolu
ikiye ayrılır, bunlar; hava yoluyla iletim ve gövde yoluya iletimdir. Gövde yoluyla
iletim araç gövdesinin motor ve yoldan aldığı gürültüyü titreşim ile müşteri kulağına
taşımasıdır. Bu konuya örnek olarak; tren raylarına kulağımızı dayadığımız zaman
uzaktan gelen tren sesini hissedebilmemiz verilebilir. Hava yoluyla iletim ise motor ve
rüzgar gürültüsünün , yol ile lastikler arasında oluşan gürültünün, kabin içerisine
girerek müşteri kulağına ulaşmasıdır. Hava yoluyla iletime örnek olarak; evimizin
camı kapalıyken bizi rahatsız etmeyen ve duymadığımız dışarıdaki gürültünün,
camımızı çok az açmamızla içeri dolmasını ve bizi rahatsız etmesini verebiliriz.
Burada bahsedilen gürültü hava yoluyla taşınarak kulağımıza ulaşır. Kabin içerisine
açılan aralıkların ve kaçak noktalarının bulunması ve kapatılması kabin içerisine hava
yoluyla alınan gürültünün engellenmesi için çok önemlidir.
Kabin hava kaçağı önemli bir kalite metriğidir çünkü kabin içi gürültü seviyesi dışında;
araç iklimlendirme sistemleri performansı, toz ve CO girişi, su girişi gibi çok önemli
kalite metrikleri kabin hava kaçağı performansına bağlıdır.
Bu tezde; kabin hava kaçağının kabin içi gürültüsüne olan etkisi irdelenecektir. Çeşitli
hava kaçak noktası belirleme ve hava kaçak ölçme yöntemlerinden bahsedilecektir.
Daha sonra kabin hava kaçağının, kabin iç gürültü seviyesine olan etkisi, motor
gürültüsü azaltım performansı metrikleri kullanılarak anlatılacaktır. Bu kısımda ayrıca
motor gürültüsü azaltım performansı ölçüm yöntemi açıklanacaktır.

Abstract:
Due to today's rapidly developing technologies, automotive companies have to meet
customer expectations in order to be competitive. Understanding customer
expectations will also bring customer satisfaction and commitment to a certain
automobile brand. In order to measure and track customer satisfaction, automotive
companies conduct surveys and rely on technical service feedbacks. Survey results and
service feedbacks influence both product development strategies of new model vehicle
programs and priorities for solving problems that create customer complaints.
Important portion of the product development efforts focus on improving vehicle
attributes. These attributes consist of driver/passenger comfort, quality perception,
vehicle ergonomics, vehicle dynamics, performance feel, fuel economy, weight, driver
assistance systems and noise/vibration control. Noise and vibration control is
especially important for sensitive customers and require longer times of development
with many trade-off decisions that need to be made in order to meet vehicle level
targets.
In the automotive community, the term NVH has been widely used to explain
unwanted sound and vibration. In the current market scenario, vehicle sound and
vibration are major qualities that customers consider when they purchase a vehicle.
They are a measure of driving comfort and perceived quality and reliability. The
combination of vibration and noise is one of the most significant performance indexes
of a vehicle. Interior noise control and vibration reduction as well as sound quality
design of a vehicle are critical for attracting customers. The vehicle noise can be
broadly classified into Exterior and Interior Noise. The interior noise and vibration
problems in a vehicle can be typically caused by the vehicle powertrain, tire-road
interaction or the vehicle body interaction with the wind. The typical aim is to reduce
noise and/or vibration levels; to eliminate the characteristics that are annoying to the
customer; and enhane those that are delightful to the customer to give the customer the
needed impression about the vehicle such as sportiness, responsiveness, etc.
There are two different transport mechanisms for the sound originating from its source
traveling to driver's ear. These are structure-borne and air-borne transport
mechanisms. Structure-borne sound originites mostly from powertrain and road-tire
interaction and transported to driver's ear by vibrations through the chassis and the
body. One can better understand structure-borne sound transport mechansim with the
example of the sound of a train radiated through the rails. In-coming trains can be still
heard through the rails even if they are not in visual range. Air-borne sounds on the
other way are transported by sound waves through the air. For example, one can better
hear the sounds in the environment around the house if he/she opens the windows.
Like a house, vehicle should be close enough to the environment so that air-borne
sound transmission is minimized. Thus leakage points in the vehicle should be found
and eliminated to prevent air-borne transmission of annoying noises. During the 
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interior NVH development studies it is important to determine the transfer path of the
sound to the cabin which causes a noise problem. Because the development methods
and improvement areas on the vehicle are different for structure-borne and air-borne
related noise. For example, structure-borne interior noise level can be reduced with
optimizing engine mounts, cabin suspension systems or damping pad application on
cabin panels. However, to develop the windnoise performance of a vehicle, sealing
strategy, exterior shape of the vehicle or door gap setting process should be improved.
Air leakage amount of a vehicle cabin is an important quality metric since it is not only
related to noise comfort but also climate control performance; dust, CO and water
ingress. Any air leakage error state can cause these quality issues.These quality issues
may cause big warranty costs and customer dissatisfaction.
The process identifying an air leakage flow is called air leakage detection. Air leakage
requires the measurment of very small flow rates of gas. However , leak flow can be
described as volume leak flow or mass leak flow. Volume leak flow is the rate of
volume change over time, i.e., the air is measured in volume units over time. During
studies of this thesis, lt/s has been used the describe air leakage quantities. Air leakage
performance of a vehicle is measured several times during both development and
production phases of vehicle programs. This measurement is conducted by keeping a
stable pressure difference between inside and outside of the vehicle cabin and tracking
air flow rate going in or out of the vehicle.
In this thesis, the effect of air leakage performance to the interior noise is investigated.
First of all, information on air leakage performance is given in depth. The definition
of air leakage peformance, its use as a quality metric, air leakage measurement
techniques and leakage prevention methods are all described in the first chapter. In the
second chapter, basic acoustic terminology is described. Next chapter is dedicated to
different noises transmitted to the driver inside the vehicle cabin. Powertrain, road,
wind and exhaust noises are discussed in detail as well as structure-borne and air-borne
noise transmissions. Last chapter is about the effect of vehicle air leakage on the engine
noise reduction of the vehicle. In order to find a correlation, several air leakage and
engine noise reduction measurements are made with a vehicle. Leakage points inside
the vehicle are changed and both air leakage and engine noise reduction is measured
to investigate the correlation. Additionally a reverberant box is constructed with holes
drilled onto its walls. Holes are either taped or left open to create different
combinations of open holes. For each combination, air leakage and noise reduction
inside the box is measured to investigate the effect of air leakage on noise reduction
peformance of the hall.
All noise reduction measurements has been performed with reciprocal point source
method. The reciprocal point source method technique characterizes the ability of a
vehicle to attenuate powertrain radiated airborne noise. In this method several
microphones are placed in the engine bay on each face of the engine block and a high
frequency sound source placed inside the passenger cabin at defined location in the
front head spaces. The sound pressure level (SPL) inside the engine compartment is
the measured at each of the microphones then reference measurement taken from point
source. The engine noise reduction is calculated using equation from the difference
between the SPL of the reference source and that of each engine microphone. These
values are then averaged to give an overall engine noise reduction. 
Based on the obtained results, vehicle level iterations do not show any correlation
between air leakage and noise reduction performance due to effect of barriers like
interior trim, seat, etc. In order to understand effect of air leakage on noise reduction
performance same measurements has been performed on a reverberant box. With the
first opening on box wall, noise reduction value drops down dramaticly. When air
leakage amount is increased with the opening of another hole on the box wall, air
leakage value increased the same but noise reduction value did not change
significantly. Opening new holes after this point decreases noise reduction
performance further.