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İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Makine Mühendisliği Anabilim Dalı / Malzeme ve İmalat Bilim Dalı

2018

2018 model ağır ticari araçların hava kutusu braketinin elektrik soketi kapaklarına çarpmasını önlemek amacıyla yapılan tolerans optimizasyonu

A tolerance optimization what is to prevent aircleaner bracket touches electrical socket brackets on 2018 model year high commercial vehicles

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Her geçen gün gelişen otomobil pazarının bir parçası olan kamyonlarda ergonomik kalite otomobillerde olduğu gibi önemli bir parametre haline gelmiştir. Bu durumu yıllardır süregelen kamyon pazarına bakarak anlayabiliriz. Özellikle çekici tip araçlarda, fiyatın yanında dış görünüm, iç dizayn, araç iç ve dış ergonomisi daha da ön planda olmaya başlamıştır. Arkasına trailer diye tabir ettiğimiz römorku bağlanıp yük taşımacılığında kullanılan bu araçlarda, trailer yapılan ile göre araçtan çıkarılır ve başka bir trailer tipi takılabilir. Bu işlem sırasında trailer bağlı olan mekanik ve elektrik aksamları da araçtan ayrılır. Bu işlemlerin bir kısmı elle veya otomatik olarak gerçekleştirilir. Bu durum haricinde aynı şekilde araç üzerinde bulunan elektrik kaynağı, gerek trailerde, gerekse başka bir amaç için kullanılabilir. Kullanım sırasında şoförun zorlandığı bir durum ortaya çıkarsa bu durum müşteri memnuniyeti açısından olumsuz bir durum oluşturur. Çalışma özelinde bu kalite parametrelerin biri sayılacak olan elektrik soketlerinin tam açılmasını sağlamak için yapılan revizyonlar incelenmiştir. İlk durumda elektrik soketinin kapağı ile hemen üzerinde bulunan hava kutusu braketinin etekleri girişim halinde bulunmaktaydı. Zira bu durum ilk başta problem olarak bahsedilmemişti. Ancak prototip fazında bu durumun müşteri memnuniyeti açısından problem olacağı üst yönetim tarafından dile getirildi ve düzeltilmesi talep edildi. İlk olarak braketin, soket ile girişim halinde olan bölgesi ve filtre ayağına kadar olan kısım traşlandı. Filtre ayağı geçilmedi, çünkü filtre ayağının oynatılması kalıp değişikliği ve ek maliyet demektir. Bu sayede her iki taraftan soket kapaklarına 2.4mm mesafe elde edildi. Bu aksiyonun performansı VisVSA tolerans analiz programında kontrol edildi. Elde edilen sonuçlarda alınan bu aksiyonun yeterli olmadığı, yapılacak olan 4 montajdan birinin tekrar filtre braketi ayağına takılacağı görüldü. Bu sonucun da şirketin beklentisi olan 6σ çıktılarına uymadığı görüldü. Bu sonucun üzerine soket kapağı ile filtre braketi arasında mesafeyi artırmak için filtre ayağına müdahale edildi be aradaki mesafe 6.5mm'ye çıkarıldı ve sonuçlar tekrar incelendi. Bu sefer sonuçların 6σ çıktılarına uyduğu görüldü. Çalışma bu şekilde tamamlandıktan sonra araç üzerinde yapılan fiziki denemelerde de bir problem olmadığı görüldü ve çalışma bu şekilde tamamlandı.

Summary:

As passenger cars have, the trucks have and air induction system too and system design really important for truck performance and NVH quality. First of all, there is a maximum pressure drop target for the turbo efficiency and this effects the vehicle performance and fuel consumption. Air induction system directly effects this target due to its design because air goes inside air induction system path, in order to prevent deviating from this target it must avoided from sharp bends and nonstraight and long routing. Aircleaner is the most important member of the system and it has important roles for vehicle and driver. If the aircleaner is big enough, accordingly the service life of it will be longer and driver does not need to get clean it often, that means it will not cause more waste of time and not seen any wearing due to cleaning process. Moreover volume of the aircleaners directly effect the system pressure restriction like other components of the system, smaller aircleaner volume is worse because it means bigger restriction for air flow. Also NVH (noise vibration harshness) performance of the vehicle is related with aircleaner volume, bigger aircleaner volume is better for NVH performance, aircleaner volume works like an expansion chamber for the noise which is coming from turbo inlet or air which goes to the intake manifold. Materials of the system parts are important as well due to effecting appearance of the parts. Some materials can be cause degredation under some hard conditions. Those conditions may be temperature, ozone effect, high pressure and chemical abrasion. Outer parts which is exposed to the sunshine, may be face weathering issue, especially it might be a threaten for rubber parts. So natural rubber usage is not allowed in this condition. It may cause a unacceptable appearance for the customers, also it may progress to cracking by embrillement. In order to avoid this failure mode, natural rubber must reinforced by peroxide and other additives. There are much rubber materials like that. Another failure mode is high temperature. Plastic or rubber parts may be close a heat source like exhaust manifold and exhaust gas recirculation pipes, accordingly part materials must be chosen this requirements. For example, for the plastic parts, if the temperature is between 0-110⁰C, PE and PP can used, but the temperature is between110-140⁰C, PP can be used by reinforced by talc and glass fiber. If temperature is higher than 140⁰C, PA and its reinforced derivatives which is supported by talc and glass fiber, can be used. If any plastic materials are not suitable regarding temperature, aluminium or stell material can chosen, those will be heavier but more durable for high temperature. Another risk for the plastic and rubber materials is high pressure, it is valid for the parts which are connected after turbo charger part. Because of this risk, especially rubber parts are reinforced by textile pattern, there are different types of textile materials (poliester, kevlar, etc.). Generally textile material and number of pleats are defined by experimentally. If design fails under required pressure value, pleat number may be increased or stronger textile materials may be selected. Final potential threat is chemical contaminants which are come from environment and engine rooms. For example, there is a port which called cranck case ventilation that is connected to the air induction systems routing. It carries oil and fuel steam from oil pan, engine room and cyclinder. These contaminants may harm to rubber parts like swelling and abrasion and leakage issue may be occured. In order to prevent this problem, especially inner side of the pipe must be chemical resistant material. On the other hand ergonomic quality is the one of the biggest parameter of the high commercial vehicles market what is raised day by day as passenger car market.We can recognize it by seeing to high commercial vehicle market, customer expectations are similar to passenger cars in truck market as well. Truck manufacturer can provide different options on the vehicle attract the customers. For example, there is a sleeper cab option on the trucks, that means there is a inside the cabin just behind the driver and passenger side. Bed width may be important for the customers, because they are mostly using the vehicle on long way so that effects the comfort. Outer appearance, interior design, interior and exterior ergonomi are being important beside cost for especially on tractor vehicles. There is a part which is called as trailer is connected to just behind the vehicle and it is attached or removed from the vehicle regarding content of the work. Duration of this action, electrical and mechanical feautures on the trailer split up the vehicle. These actions are taken by manuel or automatically and it is expected that this operation should be easy enough for the driver to decrease problem may be taken after selling. Electrical hub may be used on trailer or for another reason and if there is a problem or diffuculty to use this source for driver, it would be negative sensation for customer satisfaction. Specific to this study, the action what is implemented to provide to full opening the electrical socket cover, is investigated. There was interference between the aircleaner bracket extension and socket covers and this status was not assessed as a problem by vehicle attribute team beginning of the study. However a collision and touch condition are observed by attribute team on second prototype phase of 2018MY vehicles and it was determined that it may be a problem regarding customer saticfaction. Thus upper management evaluate that it is not acceptable for customer expectation and they request to improve this condition. First of all, the alternative electrrical hubs are investigated by powertrain team and proposed some of them. But electrical team rejected those options by mentioning they were not suitable option for current connection strategy. Moreover orientation options of the socket is tried to be changed but it did not help to provide full opening postion as well. Then extension of the aircleaner bracket is trimmed to create more space to socket cover opening zone. Filter leg assumed as limit due to avoid additional tooling change. By this action socket cover opening zone expansed to 2.4mm both side. This action analysed on VisVSA program and it is seen that trimmed area is not enough to provide 6σ output requirements. Analysis results showed that aircleaner bracket has interferences with socket covers on each one of 4 samples and it does not fit to the output requirement of the 6σ. After that, filter leg shifted to right side to increase the clearance to 6.5mm between bracket and cover and package is run on VisVSA again and results are checked. It is seen that the results are fitted to the output requirement of the 6σ and the bracket is revised accordingly. Consequently, best design option used on first serial production phase and checked opening performance of the sockets. It is seen that there is no interference or touch condition between the aircleaner bracket and sockets. Also measured clearance values between the parts were close to the analysis results. By this way new proposal has been verified by trials. You can see the pictures end of the report.