Otomotiv Endüstrisinde Kullanılan Akustik Malzemeler Ve Malzeme Özelliklerinin Akustik Parametrelere Etkisinin İncelenmesi

Abstract

Günümüzde gelişen teknoloji ile birlikte otomotiv endüstrisinde araç sürüş konforu önemli hale gelmiş ve müşterilerin beklentileri de buna bağlı olarak artmıştır. Bu da tüm bu beklentileri karşılayabilmek için otomotiv üreticileri müşteri beklentilerinden taviz vermeden pazardaki zorlu rekabet şartlarında ayakta kalabilmek ve maliyetleri minimize edebilmek için araçlarda kullanılan tüm malzemelerin özelliklerinin çok iyi bilinmesine ve problemlere karşı optimum çözüm sağlayabilecek malzemelerinin araştırılmasını ve geliştirilmesini beraberinde getirmektedir. Üretilmesi planlanan otomobilin bilgisayar ortamındaki dizayn, prototip ve proje fazlarında aracın akustik performansı önemli derecede takip edilmekte ve optimum dizayn için farklı malzeme örnekleri kullanılarak geliştirmelere yapılmaktadır. Bu testler aracın dizayn aşamasında bilgisayar destekli analiz programlarıyla yapıldığı gibi proje fazlarında ise ilk yatırım maliyeti çok yüksek olan rüzgar tüneli testlerinde araç üzerinden objektif veri elde edilmesi yoluyla ve yetişmiş test operatörleri yardımıyla subjektif olarak aracın belirli yol ve test şartlarında değerlendirilsi ile yapılmaktadır. Bu çalışmanın amacı otomobillerde sürücü ve yolcuların şikayet etmelerine sebep olan akustik kaynakların tanıtılması, araç üzerinde Akustik malzeme uygulanan parçaların tanıtılarak uygulama yöntemlerinin incelenmesi, akustik malzemelerin özelliklerinin ve malzeme özelliklerinin akustik parametrelere etkisinin incelenmesi, akustik parametre ölçüm metodlarının incelenmesi ve son olarak farklı numuneler üzerinden akustik parametre ölçüm metodlarından biri olan alfa kabin testinde farklı malzeme özelliklerinde akustik sönüm kabiliyetinin incelenmesidir.

Todays NVH properties in automotive industry become incrementally the most important factor on customer satisfaction. That makes automobile manufacturers investigate all types of acoustic materials and their properties to be able to take place in automotive market. NVH term is abbreviation of key elements of vehicle driving comfort wording Noise, Vibration and Harshness. Noise is shortly what the costomer hears. It is characterized by frequency (20- 20 kHz) and its level is defined by dB. It can be desirable like powerful sounding engine or fine tuned exhaust or undesirable like road NVH. Vibration is what the customer feels and sees. Motion which is sensed by the human body mainly in 0.5 Hz – 50 Hz range and it is characterized by frequency, level and direction. Harshness is conbined effects of noise and vibration. It means rough, grating and discordant sensation. This project aims are providing information about noise and vibration sources at automobiles which make the customer dissatisfaction, introduction to accoustic materials used on automobiles and their assembly strategies, providing information about the acoustic materials properties and effects on acoustic parameters, at the end of the project, investigation of the material properties effects on accoustic parameters by using alpha cabin. Sound absorption materials are also used for thermal resistancy, fuel consumption improvements. In this study different types and sizes of materials like polyurethane foam, polyproplyn foam and shoddy will be compared in terms of noise absorption capacity and also material cost. At the end of the study a car floor mat will be measured in alpha cabin and shoddy versus ABS material sound absorption skills will be compared. Vehicle noise and vibration performance has a big affect on drive comfort and travel comfort. Vehicle vibration and noise which emerge depending on the different parameters can be optimize regarding to provide a comfortable drive. During design, prototype and launch periods vehicle NVH is always has a big effect on launch period milestones and vehicle enginering teams of big car manufacturer work on alternative materials to get the optimum design of the vehicle NVH properties. Objective and subjective evaluations show the vehicle NVH properties. During design phase teams are working on CAE tools, at prototype phase vehicles are tested in ‘Wind Tunnel’ and subjective evaluations by trained auditors on test tracks. Automotive and absorption material manufacturers are taking big efforts on improving materials which have better absorption capacity. There are various of testing systems to verify the absorption capacity, these are reverberation room, impedance tube and alpha cabin measurements. Reverberation room consists of 200 m3 with reflective walls to maintain a diffuse sound field. It is defined in ASTM C-423, EN 20354 standards. In impedance tube method the components are analyzed by the two microphones. Normal incidence noise which enters the material at 90º is used. Useful for comparing acoustic absorbers. It is defined in ASTM E 1050 standard. Alpha cabins are small reverberation rooms which were designed for automotive industry and they have 6.44 m3 standard volume to support 400 Hz center frequency. It has no standard yet. In this study noise sources during vehicle driving will be analyzed and defined. There are different types of error states which makes the customer dissatisfaction. These are aerodynamic noises, road noises, HVAC noises, powertrain noises and road noise. The biggest sound source of the vehicle is engine. The engine plays a very important role for internal noise of vehicles. Internal combustion engines are generally strong sources of noise and vibration, whereas electric engines are often much quieter. The vibrations from the engine are mainly generated by the reciprocating and rotational masses such as pistons, connecting rods and shafts; for this reason balancing of these masses is very importantThere are many sources of noise in a vehicle: in the past the engine was the most important, and the first NVH studies were applied to reduce noise and vibrations generated by the engine and powertrain. As a result current engines and powertrain systems show a strongly reduced level of noise, and consequently other sources of noise such as road noise become very significant. Moreover, the increase of the speed of vehicles has strongly increased the importance of aerodynamic. Description of the main noise sources in vehicles. Diesel engine has much more noise than the petrol engine. The engine noise is being transfered by vehicle body path into the vehicle interior cabin. Engine mounts are designed with dampers to eliminatw high impact of the noise and vibration. This noise and vibration transfer path is called structure-borne noise path. Also noise is transfered into the vehicle cabin by the gaps which is created by the poor absorption strategy. This noise path is called airborne noise path. Controlling airborne noise is done by using sound barriers and sound absorbers. Sound barriers working strategy is reducing transmission of sound energy by reflecting it back to its source. examples of sound barriers are lead, eva and polymeric films. There are lots of sound absorption materials to eliminate different types of noises. Absorbers dissipates sound energy through internal friction within a porous medium into heat energy. Absorption materials examples are non-wovens, foam, shoddy and fiberglass. Controlling structure borne is done by isolaters and dampers. Isolators works for reducing tramission of vibration energy between structural elements. Examples of isolators are rubber or liquid-filled pads for engine mounts. Dampers is used for to attach to panels to reduce vibration. Dissipating vibration energy to utilizing viscous-elastic properties of the damper. Examples of dampers are asphalt and damping foils During low speed drives tyre noise is the most herable noise, when the engine load increases then the engine- powertrain noises becames more herable. During the high speed drives flow-acoustic aerodynamic noises becames more herable. Acoustic PVB coated winshield is used For eliminating aerodynamic road and wind noise issues during high speed drives. There is a PVB (Polyvinilbutral) layer implemented by pressure and temperature effect between inner and outer windshield. Also for the structure-borne noise refinement addtional PVC and deadener pad application is being implemented on vehicle body to eliminate the noise and vibration transfer from vehicle body. Other sound absorption materials used on the vehicle body are shoddy for dash panel and floor mat isolator, PET material usage under the trim parts and under the wheelArches to eliminate tyre road noise. Material properties has big affect on sound absorption capacity. These properties are density, aitr flow resistance, thickness, porosity and porosity open/closed cell types are the most important material spesifications. In this study these main material properties sound absorption capacity will be compared in alpha cabin.