Taşıt titreşim kaynağı tespit yöntemleri ve uygulaması
Determinaton methods of vehicle vibration sources, and the application
Yazar: ECE ŞENVELİ
Danışman: PROF. DR. İSMAİL AHMET GÜNEY
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Makine Mühendisliği Ana Bilim Dalı / Makine Dinamiği, Titreşimi ve Akustiği Bilim Dalı
Derece: Yüksek Lisans, 2018
Konu: Makine Mühendisliği = Mechanical Engineering
Dizin: Burulma titreşimi = Torsional vibration ; Diferensiyel özdeğer problemi = Differential eigenvalue problem ; Mekanik titreşim = Mechanical vibration ; Motorlu taşıtlar = Motor vehicles ; Serbest titreşim analizi = Free vibration analysis ; Serbest titreşimler = Free vibrations ; Tekerlekli taşıtlar = Wheeled vehicles

Özet:
Bu çalışmada bir taşıt titreşim probleminin kaynağını tespit etmek için yapılması
gereken temel kontroller ve teorisi anlatılmış; daha sonra da 8x8 bir askeri araçta
görülen titreşim probleminin tespitinde bu yöntemlerin uygulaması gösterilmiştir.
Literatür araştırmalarından elde edilen veriler doğrultusunda, taşıtların titreşim
kontrolünde öncelikle, temel titreşim kaynağı motor olduğu için; motora doğrudan
bağlı parçaların doğal frekansları kontrol edilir. Motor tahrik frekansı aralığında bir
doğal frekans olmamalıdır, aksi takdirde motor tahriğinden kaynaklı olarak rezonans
meydana gelebilir.
İkinci temel kontrol, güç aktarma elemanlarının burulma titreşimleri ile ilgilidir.
Tahriğin başladığı yer olan motordan, taşıt hareketinin oluştuğu tekerleğe kadar olan
tüm dönen elemanların, burulma yönündeki doğal frekansları kontrol edilir. Problemin
hissedildiği frekans aralığında rezonansa sebep olacak bir burulma modunun olup
olmadığı tespit edilir.
Çalışmada bahsedilen diğer bir kontrol ise motor ve şanzıman ikilisinin gövde bağlantı
takozlarının titreşim geçirgenlik analizleridir. Burada, takozların titreşim sönümleme
işlevlerini ne kadar yerine getirebildiği tespit edilir. Takozların taşıdığı kütle, kütle
merkezinin konumu, takozların bağlantılarının rijitliği ve bağlantı bölgesinin rijitliği
takoz geçirgenliğini etkileyen parametrelerdir. Takozun iyi bir sönüm yaptığını
söyleyebilmek için takoz bağlantısının aktif ve pasif tarafından alınan ivme
ölçümlerinin arasında en az 10 – 15 dB kadar fark olmalıdır.
Tüm bu yöntemler, bir 8x8 askeri aracın titreşim probleminin kaynağını tespit etmek
üzere uygulanmıştır. Bu uygulamalar sırasında, motor bağlantıları ve motora direkt
bağlı parçaların doğal frekansları motor tahrik frekansı aralığının dışında
hesaplanmıştır. Güç aktarma organlarının burulma modları da benzer şekilde, titreşim
probleminin hissedildiği frekans aralığı olan 70 – 100 Hz arasında saptanmamıştır.
Son olarak, güç paketi bağlantı takozları geçirgenlik analizi için, motor
kompartımanının sonlu elemanlar analiz modeli genişletilerek bölgenin rijitliği
gerçeğe en yakın olacak şekilde modellenmiştir. Gerçekleştirilen frekans cevap
analizleri sonucunda takozların aktif ve pasif bölgelerinin frekans cevap fonksiyonları
elde edilmiştir. Bu fonksiyonlar karşılaştırıldığında sağ ön takoz bağlantısında 70 –
100 Hz arasında negatif geçirgenlik oluştuğu gözlemlenmiştir.
Analizlerden elde edilen bu geçirgenlik problemini fiilen de tespit etmek ve analiz
modelinin test ile korelasyonunu sağlamak için operasyonel ve statik bazı testler
gerçekleştirilmiştir. Operasyonel testler sırasında güç paketi takozlarının aktif ve pasif
bölgelerinden toplanan ivme değerleri karşılaştırıldığında; analizdekine benzer
şekilde, sağ ön takozda 70 – 100 Hz aralığıda negatif geçirgenlik görülmüş, ve bu
frekans aralığında gövdede hissedilen ivme değerlerinde de artış görülmüştür. Statik
olarak gerçekleştirilen modal testlerde de görülen sağ ön takoz bölgesinde 70 – 100xx
Hz'de görülen doğal frekans bu bölgede bir rezonans olduğunu doğrulamıştır. Ve ivme
değerlerinin artış gösterdiği bölge şanzıman çıkış devrine göre 2.mertebe üzerinde
görüldüğünden; rezonansı tahrik edenin şazıman çıkış şaftının bağlantı açısı tasarımı
olduğunu işaret etmektedir.

Abstract:
In this study, basic controls and theory to detect the source of a vehicle vibration
problem are explained; then the application of these methods in the detection of the
vibration problem in an 8x8 military vehicle has been shown. To do this, a large
literature search was first carried out, in which tests and analyzes were used to find the
vibration in the vehicle and the source of the noise that caused this vibration.
In the light of the information obtained from the literature, firstly vehicle-related
analyzes were carried out; the analysis model was verified with the help of tests and
the source of the problem was investigated.
In the direction of the data obtained from the literature studies, first of all, in the
vibration control of the vehicles, the basic vibration source is the engine; the natural
frequencies of parts directly connected to the engine are checked. There should not be
a natural frequency in the drive frequency range, otherwise it may resonate due to the
engine drive.
The second basic control concerns the torsional vibrations of the power transmission
elements. The natural frequencies in the direction of torsion of all rotating elements,
(beginning from the engine which starts excitation, up to the wheel of the vehicle
motion) are controlled.
The powertrain is completely reduced to the mass - spring system. The stiffnesses used
are the stiffness in the direction of torsion, and the inertias are in the direction of
rotation. The directions, except the direction of the powertrain's rotation, are
considered constant. By using these informations, modal analysis is run. And, it should
been determined whether there is a torsional mode which will cause resonance in the
frequency range where the rotation speed.
Another control referred to in the study is the vibration attenuation analysis of the body
linkage mounts of the engine and transmission pair. Here, it is determined how much
the mounts can fulfill the vibration damping functions. The masses carried by the
mounts are the parameters affecting the position of the center of mass, the rigidity of
the connections of the mount and the rigidity of the connection zone. One
accelerometer is connected to active and passive zones. The active side is driven by
applying a force. The values read on each accelerometer are then normalized to the
applied force. It is to calculate the transfer function, or in other words, the frequency
response function. These frequency response functions are compared for the active and
passive sides. If the passive side has more acceleration value than the active side due
to the unit strength, it is concluded that the region between the active and the passive
is the effect of vibrating in the power pack mounts in our work. Conversely, if less
acceleration is achieved on the passive side, the vibration is damped in the active -
passive connection. Additionally, in order to be able to say that the mount has a goodxxii
attenuation, there must be a difference of at least 10 - 15 dB between the acceleration
measurements taken by active and passive mount connection.
The damping performances of the mounts can also be obtained operationally.
Accelerometers are positioned as if they were in the last method. The results are also
evaluated by comparing the accelerations on the active and passive sides. The
difference, however, is that the acceleration values are not normalized depending on
the force. The point to note is that an operational cycle check must be done to drive all
frequencies.
All these methods have been applied to detect the source of the vibration problem of
an 8x8 military vehicle by analaysis and tests.
During these applications, firstly finite element model was prepared for the engine, the
transmission and their connections. There is a cradle to carry the powerpack and the
auxiliary systems. And, the cradle was also added on FE model.
The analysis model was prepared by considering boundary conditions as fixed at the
body connection points. After modal analysis of the power pack's cradle, it is
calculated no natural frequency that belongs to connections of the power pack between
70 – 100 Hz.
Secondly, one dimensional analysis model was prepared for the powertrain. From the
engine up to the wheel, every parts were used as inertia or rotational spring. Modal
analysis was run with boundary conditions free in only the direction of rotation. The
torsional modes of the powertrain were similarly not detected between 70 - 100 Hz,
which is the frequency range at which the vibration problem is felt.
As the third, attenuation analyzes were conducted to check how well the power pack
mounts could fulfill their damping functions. For this, the body and other equipment
in the engine compartment are added in detail to the finite element model. So, finite
element model of the engine compartment is modeled so that the stiffness of the zone
is closest to reality.
With this model, natural frequencies were calculated by performing modal analysis
first. Then, the mount attenuation was examined by calculating the frequency response
functions of the active and passive regions of the mounts. It was seen that frequency
response functions were compared for active and passive regions for each mount; the
right front mount acts as a negative attenuation around 70 - 100 Hz. Turning to the
results of modal analysis; it has been found that the cause of this negative attenuation
problem is a mode of body sheet, which affects the right front - body connection region
of the power pack carrier structure.
Finally, the mount damping performances were checked with operational tests on
different conditions, and the characterization of the problem was determined by the
acceleration measurements taken on the vehicle. And then, it is detected attenuation
problem obtained from the analyzes and to correlate the analysis model with the test.
When the acceleration values collected from the active and passive regions of the
powerpack mounts are compared during the operational tests, similar to the analysis,
there was a negative attenuation in the range of 70 - 100 Hz on the right front mount,
and the acceleration values felt in the body in this frequency range also increased. The
natural frequency seen at 70 - 100 Hz in the right front mount region, which is also
seen in the statically performed modal tests, confirms a resonance in this region. Andxxiii
since the region where the acceleration values are increasing is seen on the 2nd order
compared to the transmission output speed.
All these analysis and testing studies show that the vibration in the vehicle is caused
by the resonance of the right frontal sheet in the engine compartment. The driver of
this resonance is the unbalance created by the connection angle of the cardan shaft
between the transmission and the transfer box.
Becaouse the connection angle design of the output shaft excites the resonance, it is
the revisions that need to be made to reduce the shaft angle and to fix the problem of
stiffening the sheet so that the resonance of the body sheet can be removed.