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İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Makine Mühendisliği Anabilim Dalı / Konstrüksiyon Bilim Dalı

2015

Adblue tankı kafesi şasi bağlantı braketi tasarımı ve yapısal dayanım analizi

Design of adblue tank cage chassis attachment brackets and dynamic structral analysis

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Tezi Bul
Özet:

Tez kapsamında ticari bir araçta adblue olarak bilinen üre çözeltisini ihtiva eden tankın kafesinin şasi bağlantı braketlerinin tasarımı yapılmıştır. Gelişen emisyon standartlarıyla birlikte bu çözeltiye olan ihtiyaç oldukça artmıştır. Bu sebeple sisteme ait pompa, tank hacmi gibi unsurların ağırlığı ve hacmi artmıştır. Ek olarak, adblue tankı ve ilgili sistemlerin şasi bağlantısı için en uygun konum aynı zamanda ticari aracın tasarımı gereği bir takım hareketli parçalara oldukça yakındır. Bunların yanında, ticari araç ailelerinde aynı motor ve emisyon sistemlerine sahip farklı amaçlar ile tasarlanmış pek çok araç varyantı vardır. Yapılan tasarım tüm bu varyantları kapsamalıdır. Bu üç madde düşünüldüğünde sistemi şasiye bağlayacak braketlerin tasarım zorlukları anlaşılabilinir. Tasarım çalışmaları yapılacak ilgili sistemlerin detayları açıklanarak, tasarımdan sağlanması beklenilen gereklilikler ortaya koyulmuştur. Bu gereklilikler tasarıma yön veren temel limitlerdir. Gerekliliklerin analitik olarak ortaya koyulmasının ve tasarımcı tarafından özümsenmesinin ardından tasarım çalışmalarına başlanmıştır. Her bir gereklililiğin sağlandığının kontrolü yapılmalıdır. Gerekliliğin sağlandığı kontrolü gerekliliğin niteliğine bağlı olarak projenin farklı aşamalarında yapılmıştır. Geometrik olarak konsept tasarımın ortaya koyulmasından, prototip parça ile saha testlerinin tamamlanmasına kadar nihai tasarıma uzanan süreçteki her bir aşamada sağlanan gereklilikler belirtilmiştir. Geometrik olarak konsept tasarımın oluşturulmasıyla birlikte paket ile ilgili gerekliliklerin kontrolü yapılmıştır. Akabinde parçanın dinamik olarak yapısal dayanım analizinin yapılmasıyla birlikte ilgili gerekliliğin karşılandığı gösterilmiş olup, prototip parça imalatına ve saha testlerine hazırlık ile ilgili çalışmalara başlanmıştır. Prototip parça imalatı öncesinde tasarımcının konsept tasarıma ait detaylı teknik resimleri oluşturması gereklidir. Bu amaçla imalatçı ile üretilebilinir toleranslar üzerine anlaşıldıktan sonra, sisteme tolerans analizi yapılarak teknik resimlerde bu değerler belirtilmiştir. İmalatı tamamlanan prototip parçalarda bu teknik resimler uygunluk şartı aranmıştır. Bağlantı elemanı olarak civata kullanılan sistemlerde, prototip parçaların saha testlerinde kullanılacak araçlara montajı için tork bilgisi gereklidir. Tork bilgisinin elde edilmesi amacıyla her bir bağlantı için gerekli testler tamamlanıp, test sonuçlarından elde edilen değerler üretim sırasındaki sıkma toleransları göz önünde bulundurularak güncellenmiştir. Güncel tork değerlerinin en alt limitinden saha testleri için prototip parçaların araç montajı tamamlanmıştır. Montaj sırasında bağlantı yüzeyi ve bağlantı elemanı görsel olarak tork kaybı kontrolleri yapılabilmesi için işaretlenmiştir. Saha testleri sırasında belirli aralıklarla görsel kontrolleri yapılarak hem parçanın bütünlüğü hem de tork kayıplarına karşı incelemeler yapılarak, başarılı bir şekilde saha testleri tamamlanmıştır. Tez sonucu olarak Eu6 emisyon seviyesine sahip ticari bir araçta adblue tankı kafesini şasiye bağlayan braketlerin nihai tasarımı, bu tasarıma giden süreçte yapılan çalışmalar açıklanarak, ortaya koyulmuştur.

Summary:

In the thesis, hanger brackets which attach cage of adblue tank to chassis frame is designed. With recent emission requirements, demand to adblue which is a mixture of urea and water with certain concentration is highly increased. Adblue is used to decrease emissions in selective reduction catalysts in order to meet legal limits of Eu6 norms. As a result of that demand, volume of tank and complexity of related systems are increased. Effect of these changes are mainly on weight of all systems that designed bracket to be carried. Designed brackets should be durable enough to handle increased weight of overall related systems in all working conditions of commercial vehicle. In common approach, adblue tank and all related systems are located as possible as to engine in order to be closer to the location where adblue is dozed into exhaust system. Therefore, there are several dynamic parts in that location such as front and rear suspensions. It is expected from the design not to have interference with these dynamic parts in all manoeuvres and the design should also ensure that rest of the related systems are not interferencing with these dynamic parts. Beside these two items, it is known that there are lots of different vehicle variants with same engine and emission systems in commercial vehicle market. It is possible to have different designs for each variant but considering cost and complexity of the brackets in assembly line having one design for all vehicle variants is required. So the design should be able to cover all these vehicle complexity. Considering these three items, challenging sides of designing these hanger brackets can be understood well. As a first step of design process, all systems which would possibly have relation with the design should be investigated in details. In the case investigated in the thesis, these systems can be sorted as tank, cage, pump, chassis etc. Afterwards, requirements that are expected to be met by the design are defined in details. It can be said that these requirements are mainly leading all design stages. When the system is understood well and the requirements are clarified in details, design process can be continued. Every requirement should be validated. Depending on properties of the requirements, timing of validation can differ from the moment that first model is created till completion of field testing. In first modeling phase, the model should be checked againts interference with adjacent systems. In the thesis, CATIA is used as commercial software for modelling. For packaging check, the data showing all possible locations of dynamic parts should be populated so that checks can be done. In the requirements, limits of distance between components is given. Distances between the design and adjacent systems should be check with these limitations. Before passing to next stages of design process, the design should be checked regarding to durability perspective. CAE methods are used to decrease number of iterations till improving durability performance of the design to needed level. In the thesis, HYPERMESH program used to create Ağ structure, ABAQUS as solver and nCODE is used to calculate life of the design based on road load data which is collected in previous projects from chassis suitable locations. Natural frequency analysis is done and observed that minimum natural frequency of the desing is below 300Hz which is above all frequencies within road load data. Under the light of that information, life calculation is done without considering natural frequencies of the design. Calculated life of the design is compared with results from previous projects whose field feedbacks are known. Beside packing checks and durability assessments, design should be production feasible in manufacturing and assembly views. Manufacturing and assembling subjects are highly related to tolerances. In preparation to prototype part production phase, every detail regarding design is passed into technical drawings. Tolerances should be agreed among the manufacturer and the designer. That agreement process is an iterative process. Tolerance analysis is runned including all adjacent systems in order to calculate scrap rate. If scrap rate which is result of tolerance analysis is above a certain rate, assembly should be improved. Assembly can be improved by decreasing tolerances in cases which lower tolerance is possible or changing the design itself in order to compensate higher tolerance. After all technical drawings are prepared in details, including tolerances provide less scrap rate than a certain value, and agreed with manufacturer, prototype production is started. Considering that prototype parts will be used in expensive and time consuming field tests, there must be several approval steps before suppling parts. All supplied parts should be checked against every given details in technical drawings such as material, geometric accuracy of the part, welding quality, coating quality etc. Any missing point would possibly mislead designer in case of failure. For the designs which is connected with fasteners, there are several extra steps to determine tightening torque value. Before field testing, these extra steps are completed so the supplied parts could be assembled correctly on to field testing vehicles. The tightening torque value collected as result of related testing can be applied within a certain tolerances due to tightening tools variation. In field testing vehicles, the supplied parts are mounted with lower variation of the tightening tools. In order to be sure that torque is applied correctly, special equipments are used rather than using standart equipments which is in the assembly line. Bolt heads and mounted surfaces should be marked so visual inspection during the field testing can be done within certain periods of time. Beside checking markers to understand if torque lose is happened during testing, the design should be checked periodically to be known cycle which part might be damaged in case of failures. The cycle which damage is observed is really important to correlate CAE models for further workouts in case of failures. Purpose of the field testing is to represent all vehicles life in accelerated way in order to shorten validation time. As explained, there are several different vehicle variants in commercial vehicle market. Each of these variants have its own driving cycles. So the number of repeats and trucks are differing according to variant of vehicle. In order to cover all vehicles life, field testing requires expertise and experience in area of compling feedbacks from customers and field with testing cycles for each vehicle variants. All requirements exept the requirements related to field testing should be validated before starting to field testing. After completion of field testing successfully for all vehicle variants, all requirements are validated and the design which used in these tests will be final design. The final outcome of the thesis is final design of adblue tank cage chassis attachment brackets which is meeting all given requirements for all commercial vehicle variants.