Bir ticari motorun zamanlama dişlilerinin iyileştirilmesi
Optimization of timing gears of a commercial engine
Yazar: İLKER ÖZER
Danışman: DR. HACI MUSTAFA ÖZKIRIM
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Makine Mühendisliği Ana Bilim Dalı / Konstrüksiyon Bilim Dalı
Derece: Yüksek Lisans, 2017
Konu: Makine Mühendisliği = Mechanical Engineering

Özet:
Gün geçtikçe gelişmeye devam eden otomotiv teknolojisi, firmaları hayatta kalmak için zorlamaktadır. Motor üreticilerinin müşterilerinin dar kısıtlamaları,üreticileri farklı tasarım önerileri ortaya çıkartmaya zorlamaktadır. Bu bağlamda, en önemli kriterlerden bir tanesi de, ağırlık olarak göze çarpmaktadır. Doğrudan yakıt sarfiyatına, ve toplam güce etkiyen ağırlık değerlerinin azaltılması yönünde otmotiv sanayisi büyük bir çalışma yapmaktadır .
Zamanlama dişlisi sistemi, üretilen gücün diğer bölümlere dağıtılması açısından önemli bir sistemdir. Hızla gelişen teknoloji, dayanıklılık, ağırlık, NVH, fiyat istekleri, dişlilerin her geçen gün bu şartları sağlamaya zorlamaktadır. Bu bağlamda daha hafif, daha sessiz, daha ekonomik ve daha hızlı tasarlanan sistemlerin oluşturulmasına ihtiyaç duyulmuştur. Yüksek güçlere dayanacak şekilde çalışması istenen dişlilerin, dikkatle tasarlanması gerekmektedir. 
Bu çalışma içerisinde, dişli sistemi üzerinde dişlilerin birbirleri ile etkileşimleri incelenerek, ilk başta mevcut sistemin dayanım özellikleri ortaya konacak, ardından  belirlenmiş emniyet katsayısı değerlerinden düşmeden gereken miktarda yük taşıyabilecek olan dişli profilleri tasarlanacak ve ardından daha fazla yük azaltılma imkanı olan dişlilerde sonlu elemanlar yöntemi ile ağırlık azaltılması yapılacaktır. 
Kisssoft üzerinde ilgili dişli sisteminin modelleri kurularak dişli çiftlerinin birbirleri ile ilgili etkileşimleri belirlenmiştir. Hızlı bir biçimde, dişli üzerinde birbirlerine aktarılan kuvvetler tayin edilmiştir. Aynı zamanda, mevcut emniyet katsayılarının derecesi tayin edilmiştir. Bu bağlamda ne kadar diş kalınlığı azaltılması yapılacağı görülmüştür. 
Mevcut dişlinin analizi ile beraber, Kisssoft optimizasyon araçları kullanılarak, başta diş genişlikleri olmak üzere dişli çiftleri ile ilgili tüm parametreler gözden geçirilip, hedefler doğrultusunda en optimum çözüme gidilmiştir. Birbirlerine yakın biri helisel, biri düz dişli olmak üzere iki adet alternatif diş profili önerisi geliştirilmiştir. Catia üzerinde dişlilerin tasarımı tamamlanmıştır. 
Tasarımı yapılan dişli geometrilerinden, farklı boşluklar açılmasının imkanı olan dişlilerde Sonlu elemanlar yöntemi kullanılarak gerilme analizleri gerçekleştirilip, program içerisine boşluk optimizasyonuna gidilmiştir. Bu sayede, maksimum seviyede boşluk kazanımı sağlanması hedeflenmiştir. Dişliye etki eden kuvvetler Kisssoft sonuç rapolarından alınmıştır. Bu kuvvetler, dişlilere uygulanmış ve iyileştirme süreci tamamlanmıştır.
Hesaplamalardan ve analizlerden çıkan sonuçlara göre, en uygun sistem önerileri belirlenmiştir. Yapılan öneriler ilgili paydaşlara sunulmuş olup, kullanılmasına karar verilmiştir

Abstract:
Humans having excessive amount of need to transport from one point to another for any kind of purposes in their regular life. This need pushes some sectors such as automotive, locomotive etc. to improve their capabilities in order to survive in their markets.
One of  these transportation focused sectors is automotive sectors. Since the invention of the first car, automotive technology continues to grow day by day, and companies are pushing for survival.They need to archive their targets such as lowering their increased costs due to technology and the mass, homologation problems, changing regulations,changing trends,their markets share etc. The narrow constraints of engine manufacturers to their customers force manufacturers to create different design proposals. 
While new R&D studies are starting each day, on-going product development processes are never stopped. Each released model are facing with unpredicted problems. Some of them are solved by without attracting customers attention but some of the serious later occured problems are creating havocs within industry.
This rapid development is the result of the increasing technology. New testing methods are developed. This testing techniques shortened the engine development process. For example, some of the single cylinder engines carries transparent cylinder heads. A slow motion camera records whole ignition process. Therefore, engineers can see the effects of their design changes easily and change their designs if necessary. Also, computer technology is developed too. Engineers still need real time testing methods but correlated analysis results with tests eliminates the need of this real time tests. Engineers used to relay on their hand made calculation results and they forced to make a lot of tests before any kinds of serial production. 
In design philosophy, voice of customer is an important factor for shaping designs. Some of the customers want to have a car which shows themselves as a person who has elegance pleasure. Therefore, this demand pushes car designers to design more stylish shapes, interior and exterior trims. At the same time, some of the customers want to have a car which has high performance and which  doesn't let them upset under harsh conditions. To reach that goal, an engine designer has high responsibility and must design an engine which meets this demands. This engine needs to archive high performance as good as possible while this new designed engine ensures to stand against harsh conditions such as cold, heat, durability issues, thermal issues etc. Lots of criteria must be reviewed before the starting the engine design process and archieved at the end of this process. In order to archive these criterias, it needs to be simple and  well defined.
In this context, one of the most important criteria is low fuel consumption. This demand is a critic factor for most of the customer. Each company forces themselves to find a solution to be competetive in automotive market. Some of the solutions includes optimizing combustion process by improving the quality of combustion process or optimizing the combustion chamber geometry. Also, one of the important factor of to lower the fuel consumption is weight. The automotive industry is working hard to reduce the weight values that directly affect fuel consumption and total gross. To archive that goal, all of the engine parts must be designed as light as possible. New materials are introduced while following that goal. Also, new optimization techniques by using computers enabled designers to simulate the parts working conditions before its production. With the help of that, designing a part which is durable, robust and lightweight is way more easier than before. 
The challenge of these problems requires deep knowledge of the most disciplines such as fluid mechanics, thermodynamics, knowledge of design methodologies and design of internal combustion engines concerned with the production and service of the vehicle and tractor engines.
While designing parts, engine manufacturers needs to ensure the engines durability. Motor vehicles are working under different conditions during their useful lives. These conditions can be caused by wheather, the type of roads, purpose of using vehicle as well as driver types. All kinds of conditions pushes engineers to design parts which stays inside its useful life while reaching fuel economy goals.Lots of tests needs to be completed before serial production. These tests are seriously linked with economy. Therefore, well defined analysis procedures needs to be invented and with these new methods, need to testing parts should be eliminated.
In terms of gears, these needs are reduced to almost none. From past to nowadays, lots of scientists tested gears in possible ways and created standarts for their needs. DIN and ISO are pioneers of this issue. Their results from their tests covers most of the working conditions. But still, we need to test gears if we want to reduce their weight by modifying their bodies.
In this project, timing gear system is investigated. The Timing Gear system is an important system in terms of distributing the generated power to the other parts. The rapidly developing technology, durability, weight, NVH, economic conditions, gears are pushed by these conditions every day. In this context, it has been necessary to create systems that are lighter, quieter, more economical and faster. Designed to work with high strengths, the gears need to be carefully designed.
This study includes theory about both spur and helical gear. The tooth geometry is the most important geometry on a gear. Researches about how to optimize their geometry are included and the results are followed in each step. Kisssoft used to determine the tooth profile geometry and see its effects on whole system. Ansys used to see the stresses which can't be seen on Kisssoft. Catia used to shape the gears in CAD environment.
Several constraints are determined at the beginning of the step.In this context, any modification of engine package in terms of enlarging it is an unwanted result of this process. In order to keep our study within this boundary, any modification on engine block is forbidden. Therefore, center distances are kept as before and any tooling / molding need is eliminated. Each element at the end of each gear path needs to work at specific speed, therefore all speed ratios are kept same. Minimum safety factor is defined and all calculation process are completed by following that rule. 
In this optimization process, there are several goals needs to be archieved. First and most important goal is defined as weight. First prototypes of this engine model have heavy geartrain along with other heavy systems which turns engine into an unwanted engine in the engine bazaar. Therefore, all the subsystems of the engine as well as its geartrain needs a weight reduction process. Throughout of this process, commonizing is another goal. Also, reducing element number is another goal if possible. 
The interactions of the gears with each other on the gear system will be investigated first and the strength characteristics of the existing system will be revealed after investigation. Safety factor limit will be defined for all kinds of conditions. Then the gear profiles will be designed which will carry the required amount of load without lowering the specified safety coefficient values and then the weight will be reduced by using the finite element method techniques. 
On Kisssoft, modeling of the related gear system was established, and the interactions of gear pairs related to each other were determined. The forces transmitted to each other on the gear are determined quickly. At the same time, the grade of the existing safety factors has been determined. In this context, it has been seen how much reduction of the tooth thickness can be done. Also, there were chance to improve contact ratio of this systems which enables the system to have lesser sound while working. 
Along with the analysis of the existing gears, all parameters related to the gear pairs, especially the tooth widths, were examined by using Kisssoft optimization tools. To reach that goal, from modulus to gear thickness, all of the elements of gear are investigated. Fine sizing module of Kisssoft offered lots of different solutions for each gear and most reliable solution was chosen. Two alternative tooth profile proposals have been developed, one helical gear and the other one is spur gear. 
Kisssoft gives solid gears, without any modification on 3D model. This data needs to be modified to use it in both FEM and production. CATIA is used for shaping gears in 3D environment. In appropriate gears, gaps are created to archive possible lightest design. 
In the gears which are possible to open different gaps from the designed gear geometries, stress analysis was performed by using the finite element method and the gap was optimized in the program. It is aimed to achieve a maximum gain on the level. The forces acting on the teeth were taken from the Kisssoft results reports. These forces were applied to the teeth and the optimization process was completed. Whole system weight decreased %23. 
While improving the capabilities of gears, system commonized as good as possible. There was difference on PTO gears. One of the gears were using roller bearing due to insufficient oiling conditions. A design correction made on geartrain case to improve this condition. This was only one opportunity to eliminate different type of element in whole system. Therefore, system element total number decreased too. 
According to the results from the calculations and the analysis, the most suitable system recommendation was determined. Suggestions have been presented to relevant stakeholders and it has been decided to be used.