Otomatik transmisyon vites değişim tepkilerini objektif olarak değerlendirmeye yönelik model bazlı yaklaşım geliştirilmesi
A model based approach for objective evaluation of automatic transmission shift quality
Yazar: HİLMİ ERSİN OKTAR
Danışman: PROF. DR. ÖZGEN AKALIN
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Makine Mühendisliği Ana Bilim Dalı / Otomotiv Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2020
Konu: Makine Mühendisliği = Mechanical Engineering

Özet:
Bir güç grubunda motor ve tekerlek arasındaki koordinasyonu sağlayan, otomotivdeki en kritik optimizasyon aracı transmisyondur. İçten yanmalı motor ile tahrik edilen bir güç grubunun tork ve hız arasındaki koordinasyonunu sağlayarak, sistemin daha verimli çalışmasına imkan sağlayan transmisyonlar, konfor ve verimlilik yönünden araç üzerinde büyük bir etkiye sahiptirler. 
Otomotivde her geçen gün, teknolojinin gelişmesine paralel olarak, kullanım iyileştirmeleri yapmak ve en iyiyi yakalamak mümkün hale gelmektedir. Teknolojideki bu gelişmeler, transmisyon geliştirmeleri üzerinde de büyük faydalar sağlamaktadır.
Geleneksel otomatik transmisyona sahip araçların seri üretime başlandığı 1939 yılından beri (Hydramatic), yaşanan gelişmeler ile birlikte otomatik transmisyonlar, sürüş konforunu ve verimini önemli seviyede arttırmış ve buna mukabil satış oranları da hızla artış göstermiştir. Bu durumun ana sebepleri olarak, üretim kalitesinin artması, elektro-hidrolik kontrol araçlarının gelişmesi, çeşitlenmesi ve kalibrasyon testlerinin önemli seviyede artması olarak gösterilebilir.
Bir otomatik transmisyonun geliştirilmesi sürecinde test mühendisleri, farklı kontrol parametrelerini manuel olarak değiştirerek, elektro-hidrolik kontrolü sağlanan vites değişimlerinin kalibrasyonunu sağlar. Test mühendisinin subjektif değerlendirmeleriyle yapılan kalibrasyon çalışmaları sonucunda, tekrarlanabilirliği olmayan ve test yapan mühendisin tecrübesine bağlı sonuçlar elde edilir. Bu nedenle, geliştirme sürecinde manuel olarak yapılan kalibrasyon çalışmalarının  model öngörüsünün desteği ile objektif olarak değerlendirilmesine yönelik yapılan çalışmalar, bugün hala otomatik transmisyon üzerine yapılan çalışmaların başında gelmektedir.
Bu tez çalışmasında, geleneksel otomatik transmisyona sahip, 8x8 konfigürasyonda bir ağır vasıta araç güç grubuna yönelik model öngörüsüyle ve bu güç grubunun çoklu hedeflerine yönelik oluşturulan objektif değerlendirme metodundan yararlanarak, güç grubunun kalibrasyonuna yönelik bir yöntem sunulmuştur.
Çalışmaya öncelikle, araç güç grubunun dinamiklerini içeren modelin oluşturulması ile başlanmış ve özellikle alt sistem testleri ile doğrulanmış  olan otomatik transmisyon ve kontrol komponentleri, detaylı olarak modellenmiştir. Sonrasında, literatürde yer alan, subjektif değerlendirmelerin anket bazlı korelasyonundan oluşan objektif değerlendirme parametrelerinden de yararlanılarak, araç güç grubunun vites değişimi konforu ve enerji verimliliği yönünden hedeflerine uygun bir objektif değerlendirme metodu oluşturulmuştur. 
Çalışmada, vites değişim konforuna yönelik araç ivmelenmesinin türevi olan jerk değeri ve verimlilik yönünden ise enerji kaybı değerleri metrik olarak kullanılmıştır. Ayrıca, hız ve tork değerlerinin de meydana gelen dalgalanmalar gözle kontrol edilerek değerlendirilmiştir.
Jerk ve enerji kaybı değerinin minimize edilmesine yönelik oluşturulan amaç fonksiyonu ile vites değişimi esnasında ilgili kavrama gruplarında oluşturulan basınçlandırma sürelerinin belirlenmesi ve tahrik unsuru olan içten yanmalı motorun sunduğu tork miktarında, uygun oranda kısıtlamaların yapılması üzerine pareto optimizasyonu yapılmış ve optimal kontrol çözümleri sunulmuştur.
Optimizasyon çalışması öncelikle, motorun 25 saniye boyunca tam yükte çalışması ile tüm vites aralıklarının test edildiği senaryo üzerinde gerçekleştirilmiştir. Böylece hızlı bir simülasyon çalışması ile tüm vites aralıkları için optimizasyon çalışması gerçekleştirilmiştir. İlk senaryodaki elde edilen optimal sonuçların, taşıtın daha olağan bir sürüş koşulunda değerlendirebilmesi amacıyla, bir seyir çevrimi hızı hedefiyle, ilk senaryoya göre daha  uzun süreçli başka bir senaryo daha oluşturulmuştur. İlk senaryoda oluşturulan optimal çözümler kullanılarak, oluşturulan ikinci senaryoda minimum enerji kaybı ve jerk değerine sahip parametre seti çalışmanın çıktısı olarak sunulmuştur.
Böylece, kalibrasyon çalışmalarının objektif değerlendirilmesi ve optimizasyonun model öngörüsü ile yapılmasıyla, uzun süreli ve maliyetli kalibrasyon testleri kısalacak ve optimum seviyede çıktıların alınması mümkün olacaktır.

Abstract:
Nowadays, the customer expectations on the subject of mobility and comfort are very high. Hence, these topics are becoming evermore significant in the automotive industry, like in the other sectors.
The vehicle transmission, which mediates powerflow between the engine and the driving wheels, is the most critical optimization tool in a powertrain. The transmission that enable the vehicle to operate more efficiently by adjusting between torque and speed, is a prime mover on the subject of drive comfort and energy efficiency.
Since the mass production of vehicles equipped with traditional automatic transmission started in 1939 (Hydramatic), there have been a lot of refinements that significantly increase drive comfort and efficiency on automatic transmissions. The main reasons for these refinements are the increase in the manufacturing quality, the development and diversification of electro-hydraulic control tools, and also the significant increase of calibration tests. Hence, parallel to these improvements, vehicles equipped with automatic transmission have increased their market share steadily.
According to the traditional calibration method that still exists today, transmission test engineers manually change different control parameters on the powertrain, and make calibration of shift sequences with electro-hydraulic control during the development of an automatic transmission.
In this method, test engineers gain experiences within the large amount of calibration works for application. Then, they present the best recipe among the attempted versions during their works.
Since the method includes subjective evaluations of test engineers, the same results on each vehicle occupants may not get. Also, since the recipe selected among only worked conditions, it may not be the best method. Therefore, this method needs to be developed, or reorganised in order to perform a robust calibration work. 
In accordance with these purposes, many studies have been performed, however, it still remains to be one of the key issues, which should work on more, for automatic transmission in the literature. 
In the context of this work, a model based approach has been presented for the calibration of the powertrain. Also, the objective evaluation method of automatic transmission shift quality has been created for the multiple targets of a 8x8 heavy duty vehicle powertrain equipped on the model.
The study started with the detailed creation of a mathematical model that includes the longitudinal dynamics of a 8x8 heavy duty vehicle powertrain. In order to develop a robust model, all powertrain components such as, internal combustion engine and its control unit (ECU), automatic transmission, and its control units (TCU), cardan shafts, transfer case, differential, axles, tire, and driver modelled in detail.
The engine model contains a 3D engine torque map based on the pedal ratio and engine speed, while the ECU model provides controls of other basic parameters and modulation of the supplied torque.
On the other hand, the transmission model includes torque converter, planetary gear sets, wet clutch packs, and their hydraulic and control units in detailed. All submodels have been created by using individual tests results, according to test procedures standardised by SAE subcommutees.
The torque converter model, which is one of the most important transmission components, has K-factor and torque ratio chart based on speed ratio, which get from performance tests.
Besides, the planetary gear mechanism, which mediates the powerflow with 3 planetary gear sets, their connection's shafts, and 5 wet clutch packs has been modelled. Thus, analytical methods have been performed to analyze the performance of the powerflow according to reliable gear formulas.
Since the wet clutch packs are the most important components that effect the shifting related torque changes, more detailed wet clutch model has been developed by using the LuGre friction model in this work. Also, shifting elements, such as piston seal, return springs, automatic transmission fluid and etc. have been modelled by using experimental specifications.
In addition to detailed transmission model, the transmission control unit model has also been developed in detail. Oncoming and offgoing signals, which provides proper gear changes, have been generated by using TCU model. Also, torque converter units' control, and determining of the shift phase have been provided thanks to detailed TCU model.
The other powertrain components, such as cardan shafts, transfer case, differential, axles, and tire, have been modelled by representing them with mathematical equations. Especially, Pacejka's Magic Formula for dry tarmac road conditions, has been used in order to simulate tire slipping in the tire model.
Also, representative driver model has been developed in order to simulate acceleration and deceleration responses of a driver with respect to target speed on the model. If the vehicle should accelerate with respect to target speed, the representative model decides to increases the engine throttle position. Otherwise, if the vehicle needs to decelerate, it decides to decrease engine throttle position, and in the case needs more deceleration, it sets engine throttle position to zero, then increase braking on the axles. 
Afterwards, an objective evaluation method, which is suitable for the objectives of the heavy duty vehicle powertrain in terms of shift comfort and energy efficiency, has been created by using of the objective evaluation parameters, which consist of questionnaire-based correlation of subjective evaluations in the literature.
In this work, metrics have been used to objectively evaluate gear shifts. First metric on this method is the jerk value, which is the derivative of vehicle acceleration, for evaluation of shift comfort. Also, the other metric is that total energy loss value of transmission components (gear, clutch, torque converter, etc.) for energy efficiency of the transmission. In addition to these metrics, visual inspections on fluctuations in speed and torque values are the final evaluation steps in order to control consistency of the metrics.
With the purpose function that aims to minimize the jerk and energy loss value, optimization has been made and optimal control solutions have been provided. 
Optimization study has been made by using the pareto optimization tool available on the GT-Suite software. The optimization algorithm tries to determine the optimum control method by changing the variable inputs systematically according to the target function. The algorithm evaluates the output of the model by changing the input variables in the specified range and continues until it finds the optimum. Thanks to the smart choices on the determining of different control parameters by the algorithm, as few models as possible are created.
The most important control parameters of an automatic transmission is the changes on the oncoming and offgoing clutch pressure. In this work, this pressure changes have been defined on the model according to the characteristics of the valve and other shifting elements for torque phase of the shifting. In order to get critical pressure during inertia phase of the shifting, optimisation work, which presents proper time, has been made.
In addition to this, it is also possible to intervene on the engine torque during gear shifting with the electronic control of the powertrain in order to improve the shift quality. Thanks to optimisation tool, the appropriate reduction in the amount of torque, which is provided by the internal combustion engine, has been determined during shifting.
Thus, an integrated control strategy of the powertrain has been created with proper changes of the control parameters in order to get optimal shifting performances, which gives minimum jerk and energy loss value.
The optimisation works have been performed with two scenarios. In the initial scenario, the engine runs at full load during 25 seconds, and thus, all shift sequences has been tested with a rapid simulation study.
In order to increase the resolution of the solutions created by the first scenario and reflect a more realistic driving condition, another scenario has been created. In this method, representative driver model gives input the engine, and brake calipers in order to acquire speed target from a driving cycle. Thus, evaluation of shift quality has been performed in a healthier way. This scenario has a longer simulation process but reflects the driving conditions better. In order to compensate for the long simulation process, the control parameters obtained in the initial scenario have been used. Then, according to the results of the work, the parameter sets, which have minimum jerk value and energy loss, have been presented as the output of the study.
Consequently, the presented work enables the more consistent calibration tests on the contrary of traditional calibration methods. In this way, it reliefs heavy workload on transmission engineers and additional costs on the transmission manufacturer. Also, it offers more optimal outputs thanks to smart choices given by algorithm, compared to traditional method. In addition to these benefits of the purposed method, it offers a quick calibration of the automatic transmission for different vehicle platforms.