Seri hibrit taşıt tasarımı
Series hybrid electric vehicle design
Yazar: ANILCAN ÖZKAN
Danışman: DR. ÖĞR. ÜYESİ HİKMET ARSLAN
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Makine Mühendisliği Ana Bilim Dalı / Otomotiv Bilim Dalı
Derece: Yüksek Lisans, 2019
Konu: Makine Mühendisliği = Mechanical Engineering

Özet:
Bu tezde İstanbul'da en çok kullanılan konvansiyonel araçlardan biri seçilerek güç aktarma organları seri hibrit konfigürasyonuna dönüştürülmüştür. Seri hibrit konfigürasyonunun seçilmesinin en önemli sebepleri içten yanmalı motoru en verimli olduğu noktada çalıştırabilme imkanı sunması,paralel hibrite göre daha basit bir kontrol stratejisine ihtiyaç duyması,taşıt tahriki tamamen elektrik motoru tarafından sağlandığından tek bir vites oranı ile transmisyonu basitleştirebilme imkanı sunması olarak sıralanabilir. Buna bağlı olarak taşıt boyutları aynı tutularak ve konvansiyonel taşıtın ivmelenme performansı referans alınarak seri hibrit taşıt için gerekli elektrik motorun tork ve güç ihtiyacı hesaplanarak tasarıma başlanmıştır. Elektrik ve hibrit elektrikli araç uygulamalarında kullanılan elektrik motorları ile ilgili literatür çalışması yapılarak hangi tür elektrik motorunun bu taşıt için en uygun olduğu belirlenmiştir. Menzil arttırıcılar üzerine literatür çalışması yapılarak menzil arttırıcıların gereken özellikleri belirlenmiştir. Seri hibrit konfigürasyonunun bir diğer avantajı da konvansiyonel taşıtlar için yetersiz kalan bazı içten yanmalı motor teknolojilerinin menzil arttırıcı olarak kullanılabilmesine olarak sağlamasıdır. Bu nedenle İTÜ Otomotiv Laboratuvarı'nda bulunan Wankel motoru ve tek silindirli benzin motoru iki silindirli olarak düşünülerek menzil arttırıcı olarak AVL Cruise programında denenmiştir. Menzil arttırıcıların pilleri şarj etmedeki performansı incelenmiştir. AVL Cruise'da yapılan simülasyonlar, gerçek sürüş koşullarını en iyi şekilde yansıttığından,transient bir çevrim olduğundan WLTP çevriminde yapılmıştır. Taşıtta kullanılacak pil kapasitesinin belirlenmesinde de WLTP çevriminden yararlanılmıştır. Literatürdeki çalışmalara göre seri hibrit araçlar için en uygun tasarımın günlük sürüş menzilinin(50-70 km) pillerden karşılanması ve daha yüksek güç ihtiyacı için menzil arttırıcının devreye girmesi yönündedir. Buna bağlı olarak hibrit taşıtın WLTP çevrimindeki güç tüketimine göre pil kapasitesi belirlenmiştir. Ayrıca seri hibrit taşıt ile konvansiyonel taşıtın WLTP çevrimindeki güç tüketimleri karşılaştırılmıştır.
Hibrit araçlardaki enerji depolama aracı olan piller ile ilgili literatür çalışması yapılarak taşıtta kullanılacak pil seçilmiştir. Taşıtın tahrik bileşenleri belirlendikten sonra AVL Cruise iki farklı seri hibrit taşıt modeli oluşturulmuştur. Bu modellerden birinde menzil arttırıcı iki silindirli benzin motoru,diğerinde ise Wankel motorudur. Oluşturulan modeller WLTP çevriminde koşularak tahrik bileşenlerinin performansı incelenmiştir. Tezde ayrıca termostat kontrol strateji de incelenmiştir. Pillerin şarj seviyesi belirlenen minimum değere ulaştığında menzil arttırıcı çalıştırılmıştır.

Abstract:
Due to the exhaust emissions of internal combustion engines,limited reserves of fossil fuels,environmental and air pollutions automotive industry is searching for alternative propulsion systems. Electric vehicles are one of the options for transportation in the future. Electric vehicles have zero emissions and electrification of the drivetrain has several advantages over conventional internal combustion engine powered vehicles. Torque-speed characteristic of electric motor is very close to ideal for transportation. It enables excellent acceleration performance. Electric motors operate quieter than internal combustion engines. Also,electrification of the drivetrain can simplify the transmission since electric motors do not need a multigear transmission. But a full electric vehicle has some disadvantages as well. Today,batteries still have problems with range,charging and cost. Low energy density,long charging time and high costs prevent the industy to develop the pure electric vehicles. Thus,the most realistic solution is to combine the electric propulsion and internal combustion engines. There are different hybrid electric vehicle configurations such as series,parallel,series-parallel and complex hybrids. They all have different advantages and disadvantages. But the series hybrid configuration has easier control than the others and it combines the electic propulsion and internal combustion engines in a precise manner. In series hybrid electric vehicles,electic motor is the only component that propels the vehicle. When the internal combustion engine is shut off,vehicle operates as a pure electric vehicle using the energy in the batteries. When the state of charge of the batteries is depleted,internal combustion engines starts to operate to charge the batteries. Other hybrid configurations need more complex control strategy. In paralel hybrid vehicles,internal combustion engine is also connected to wheels,thus requiring a multigear transmission. In series hybrid vehicles,internal combustion engine is not mechanically connected to the wheels and so the internal combustion engine can be operated anywhere in its speed-torque diagram including the most efficient operating points. Thus,series hybrid electric vehicles are considered as the bridge between conventional internal combustion engine powered vehicles and pure electric vehicles. Researches suggest that the most realistic,optimum solution for electrification of vehicles is to design a vehicle that is powered by the battery for daily distance driving and adding an internal combustion engine range extender to recharge the battery. Another advantage of this configuration is that it allows to use different internal combustion engines that were insufficient for conventional vehicles such as Wankel engine,2 stroke engines etc. Thus this thesis is focused on the design principles of series hybrid electric vehicles and range extenders. A conventional internal combustion powered vehicle is selected and its powertrain is modified to series hybrid configuration without changing the vehicles dimensions. 
At the beginning of this design study,power rating of the electic motor is determined. Same acceleration performance of the conventional and series hybrid vehicle is considered to compare two vehicles better. Maximum power of the conventional vehicle was 88 kW. Power rating of the electic motor for series hybrid vehicle is calculated as 120 kW for same acceleration performance i.e. 11 seconds from 0 to 100 km/h. Series hybrid vehicle is 200 kg heavier than the conventional vehicle because of the weight of the batteries and generator. Thus,it required higher power demand than the conventional vehicle. Another parameter that affected the power rating of the electic motor was the speed ratio. Different electic motor types such as induction motors,permanent magnet motors,switched reluctance motors have different speed ratios. This changes the base speed of the electic motor and thus its acceleration performance and power rating. Electic motor selection was made according to literature review on electic motors. After determining the power rating of the electic motor,a literature review was made on range extenders and their requirements. As range extenders,two internal combustion engines in ITU Automotive Laboratory were selected. One is Wankel engine,the other is normally a single cylinder gasoline engine but its power output was insufficient for range extender application so it was considered as a two cylinder gasoline engine. Performance of these range extenders on recharging the batteries was investigated in AVL Cruise. Two models were constructed in AVL Cruise. One has the Wankel engine as its range extender and the other has two cylinder gasoline engine. Engine on-off or thermostat control strategy was used as control strategy of the vehicle. In this control strategy,range extender is shut off until the state of charge of the batteries reaches a predefined minimum level. When the state of charge is minimum range extender starts to operate at a predefined speed. WLTP was selected for simulations since it is more transient and closer to the real driving conditions than other cycles such as NEDC. At the beginning of the simulation,initial state of charge was defined as maximum,intermediate and minimum levels. Maximum state of charge was set as 80 %,intermediate state of charge was set as 55% and minimum state of charge was set as 30%. Effect of regenerative braking on batteries was also investigated. It was observed that when the regenerative braking is off battery depletion had higher rate. Regenerative braking slowed down the battery depletion. For 80 % and 55 % state of charge levels,approximately same graphics were obtained. There was only a small difference due to the charge and discharge characteristic of batteries. In all cases,electric motor curves for electric motor's speed,tork,mechanical power,electrical power,power loss are the same since the vehicle follows the same velocity profile and electic motor can receive required electric power to propel the vehicle from the batteries. Mechanical power that the electic motor produced was obtained as 40 kW. This is the power that propels the vehicle. Electrical power consumption of electric motor as obtained as 45 kW. Approximately 5 kW power loss occured for electric motor. For batteries,power loss was calculated as 1 kW. When the state of charge of the batteries was set as the minimum value(30%) at the beginning of the simulation,range extender started to operate to charge the batteries. When two cylinder gasoline engine was use as the range extender final state of charge reached 45%. When Wankel engine was used as the range extender, final state of charge at the end of the cycle was 50%. Wankel engine operated at 4000 rpm,5 bar delivering 22,3 kW output power. Two cylinder gasoline engine operated at 2500 rpm and delivered 18,66 kW output power. There was 10% power loss in the generator.
In order to expand this study and investigate the performance of these range extenders further,a highway cycle can be used. WLTP cycle is very transient and has high power demand at the end of the cycle. WLTP was combined with engine on-off control strategy is this study. Maximum SOC control strategy is another common control strategy for hybrid vehicles. As another driving condition,a steady driving in a highway and maximum state of charge control strategy can be used to analyze these range extenders further.