Otobüs açılır tavan mekanizması konstrüksiyonu
Bus opening roof mechanism construction
Yazar: ÖMER YILDIRIM
Danışman: PROF. DR. CEMAL BAYKARA
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Makine Mühendisliği Ana Bilim Dalı / Konstrüksiyon Bilim Dalı
Derece: Yüksek Lisans, 2019
Konu: Makine Mühendisliği = Mechanical Engineering

Özet:
Otobüs, içerisinde sürücüsüyle beraber yolcu taşımak için tasarlanmış yol aracıdır. Günümüzde taşımacılıkta otobüslerin yerini alması beklenen raylı sistemler her ne kadar gelişmiş olsa da otobüslere olan talebin bitmeyeceği öngörülmektedir. Yapılan ar-ge çalışmaları, geliştirilen yeni nesil elektrikli otobüsler ve pazar ihtiyaçları bu talepleri destekler niteliktedir. Ancak rekabetin çok yüksek olduğu günümüzde otobüs firmaları da birbirlerinden üstün duruma geçme çabası içerine girmektedirler. Bu üstünlük genellikle performans, yakıt sarfiyatı, güvenlik ve konfor ile sağlanmaktadır. 
Projemize konu olan açılır tavan mekanizması da konfor faktörünü etkilemektedir. Otobüslerde özellikle şoför mahallinde kullanılır ve açıldığında aydınlık bir ortam oluşturmaktadır. Ancak her ar-ge çalışmasında olduğu gibi mamul tasarım, analiz, test ve geliştirme safhalarına girmektedir. Tasarımdan sonra çıkan bir takım problemler analiz ve testlerle doğrulandıktan sonra geliştirme safhasında tekrar ele alınır ve gerekli revizyonlarla son ve sorunsuz mamul ortaya çıkarılır. Projemize konu olan açılır tavan konstrüksiyonu ticari taşıt olan otobüste kullanılacağı için binek taşıtlara göre daha büyük tasarlanmıştır ve bu durum da ağırlıktan dolayı bir takım ses ve sıkışma problemlerini ortaya çıkarmıştır. Özellikle sürüş esnasında çıkan bu problemler için, belirli bir yol güzergâhından mekanizmanın olduğu bölgeye yerleştirilen algılayıcılar sayesinde toplanan ivme değerleri ile sistem analiz edilip ortaya yeni bir tasarım çözümü çıkarılması hedeflenmiştir. 
Toplanan ivme değerleri x, y ve z yönündedir, ancak yapılacak olan analizde aracın gidiş yönü olan x yönü kullanılmayıp y ve z yönündeki ivme değerleri dikkate alınmıştır. Böylece açılır tavan mekanizmasının y ve z yönündeki davranışı incelenip probleme sebep olup olmadığı irdelenmiştir. Sistem öncelikle kendisinden daha küçük bir alt sisteme indirgenmiş ve problemin gerçekten konstrüksiyonun istenmeyen hareketlerden kaynaklanıp kaynaklanmadığı gözlemlenmiştir. Bunun neticesinde bir sonraki analizde boyutsal olarak gerçek sistem ile aynı olan yapı analiz edilmiş ve sonuçlarına göre yeni tasarım çözümü önerilmiştir. Son olarak önerilen tasarım çözümünün de analizi yapılmış ve mekanizmanın istenen davranışları sergileyip sergilemediği kontrol edilmiştir. Kontrol sonrasında çıkan olumlu sonuca binaen tasarım sonuçlandırılmıştır.

Abstract:
The bus is a road vehicle designed to carry passengers with the driver. In general, vehicles are divided into 3 categories M1, M2 and M3. Buses belonging to the M3 category which is motor vehicles with a maximum mass of over five tons, used for passenger transport, with more than eight seats except the driver's seat, can also be found in 3 groups Class 1, Class 2 and Class 3. Class 1 type buses are passenger vehicles with standing passenger transport areas and are used especially in urban transportation where passenger boarding is frequent. Class 2 buses are designed and equipped for inter-urban transport, and has no spaces designed specifically for standing passengers; however, over short distances, the passageway only. Lastly, Class 3 buses are designed to carry all passengers in a sitting position without standing passengers.
Nowadays in transportation, demand for buses will not end although developing rail systems, which are expected to replace the buses in transportation. R & D studies developed new generation electric buses and market needs support these demands. R&D studies, new generation electric buses and market needs support these demands. However, nowadays, when the competition is very high, bus companies enter into an effort to be superior to each other. This superiority is usually achieved by high performance, low fuel consumption, safety and comfort. 
First of all, it is necessary to accept that everyone's perception of comfort is different from others. It is difficult to reach a common idea that will satisfy everyone in the perception of comfort that changes according to the needs and expectations. The vehicle may be too comfortable for one and not enough comfort for another. Thus, vehicle manufacturers also work on designs and technical details that will provide major common comfort and satisfy the majority.
The opening roof mechanism, which is the subject of our project, also affects the comfort factor. In buses, they are used especially at the driver's location and when they are opened they provide a bright environment. There are three types of sunroof types in the automotive sector. These are "Pop-up" , "Spoiler" and "Panoramic" sunroof mechanisms. For buses that are larger than the automobile segment, the sunroof model is preferred panoramic model with no air contact. The glass on the sliding structure in the front roof area of the bus provides plenty of light to enter. Furthermore, since the glass is mounted on the bus structure fixedly, there is no air intake when the sliding structure is opened.
The sunroof consists of a cover, a sliding mechanism and an electric motor that acts as a movement. The cover is made of composite materials and supported with aluminum structure. The sliding mechanism includes rails and wheels. Rails are aluminum extrusion and wheels are polyamide. The system operates with the help of a button on the driver's control unit. When the sunroof is operated in the opening direction, the electric motor is activated and the cover is pulled. The wheels attached to the cover also move on the sliding unit to open the cover. When the sunroof is operated in the closing direction, the electric motor starts in reverse and pushes the cover. The wheels attached to the cover also move on the sliding unit to close the cover. 
However, as in every R&D work, a system includes product design, analysis, testing and development stages. A number of problems that appear after design phase are verified by analysis and testing. These problems are improved in development phase and the latest and faultless product is produced with the necessary revisions. The construction of the sunroof, which is the subject of our project, will be used in the commercial vehicle bus, so it is designed larger than the passenger cars, and this situation can cause some noise and stuck problems due to the weight. For these problems, especially when driving, it is aimed to create a new design solution by analyzing the system with the acceleration values collected by the sensors placed in the region where the mechanism is located. 
Before starting analysis and design solutions, patent researches were carried out for similar systems. During the patent research, the sunroof mechanisms used in the automotive sector were examined. However, the sunroof mechanisms found in passenger cars are smaller in size and lighter in mass compared to our mechanism used for our bus. For this reason, sliding door mechanisms and sliding units, which are larger in size and larger in vehicles, were examined.
The acceleration values are in the x, y and z directions, but the direction of x values is not used and the acceleration values in the direction of y and z are taken into consideration. Thus, the behavior of the opening roof mechanism in the y and z directions is examined and whether or not it causes problem. The system was first reduced to a smaller sub-system and it was observed whether the problem was actually caused by unexpected movements of the construction. After that, in the next analysis, the structure that is the same as the real system is analyzed. The result of the analysis was similar to the previous result, undesirable movements were encountered. So, the first design solution is proposed according to the results. A protruding path was designed on the lower edge of aluminum rail. The groove was also designed on the wheels. We expected that the wheel would move on the aluminum rail without slipping on the y-axis. But in the first design solution, the same results were found with the current design. So that solution did not work. After that, the second design solution was created and analyzed and it was checked whether the mechanism showed the desired behaviors. In this design solution, the protruding path is designed not only on the lower edge of the aluminum rail but also on the upper edge. This time, it was found that unwanted movements disappeared in the second design solution. The upper edge protruding path was limited the movement of the system on the y-axis and eliminated the sound problem. After the positive result of the second design, we found that some parts on the system could be removed from the design and we decided to cancel these elements. Thus, the final design was created considering all the outputs. The final design was also analyzed under the same boundary conditions. The result was positive. After the control of system design, solution was finalized. 
However, with these studies and design changes, system should be verified with road tests and serial production should be started in this way. Moreover, we wanted to give some suggestion and warning for final design solution. 
For recommendations; In addition to the canceled parts in the final design, it was found that there is a section on the aluminum rail that can be shortened. Thus, the system will gain weight. 
For warnings; Modifications made on Aluminum Rail are thought to cause more friction and slow down the movement of the system in the x direction. For this reason, sound problems should be examined on road tests, but the speed of the system should be examined by opening and closing the sunroof during the journey.
The change in the final design revision of Aluminum rails creates the need for a new extrusion die. Since the wheels are manufactured on the lathe, there is no need to make new dies. After the sub-industry mold manufacturing and final products are revealed, the system assembly will be completed and will be used in the vehicles.