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ÖgeModel predictive control and differential braking based steering redundancy for an autonomous vehicle(ITU Graduate School, 2025)With the widespread adoption of autonomous driving technologies, traditional mechanical systems in vehicles are increasingly being replaced by electronic and software-based systems. One of the most prominent examples of this transformation is observed in steering systems. Steer-by-wire systems, which replace conventional mechanical steering linkages, transmit steering commands via electronic signals without any physical connection, thereby enabling the steering task. This innovative structure provides significant advantages such as design flexibility, weight reduction, more precise control capabilities, and high integration with advanced driver assistance systems. However, in the event of an electrical or software failure in the steering system, the risk of a complete loss of steering capability arises. Such a condition may not only compromise the safety of autonomous vehicles but also pose serious threats to passenger safety. Therefore, steering redundancy strategies involving alternative steering methods for steer-by-wire systems are of great importance. This thesis proposes a novel differential braking-based steering redundancy method supported by Model Predictive Control (MPC), which aims to maintain vehicle controllability under potential failure scenarios in steer-by-wire systems. In this method, steering moments are generated by applying different magnitudes of braking forces to the left and right wheels, thereby creating an alternative steering input. Through this approach, the vehicle can maintain its ability to follow the desired path even when the steer-by-wire system is nonfunctional. The proposed control architecture is designed as a two-layer hierarchical structure. In the upper layer, two PID controllers operate based on the lateral position error of the vehicle's center of gravity and the yaw angle error. These controllers generate reference values for the steering angle and curvature required for safe driving. These reference values are transmitted to the lower control layer, where an MPC based controller computes the optimal braking forces for the left and right wheels. The MPC controller predicts the future behavior of the vehicle model over a defined time horizon and generates control decisions that ensure both vehicle stability and path tracking. The calculated braking forces are then sent to the ABS controller, which applies them in a way that prevents wheel lock while generating the desired yaw moment. In the literature, differential braking is commonly used to enhance vehicle stability or correct deviations in sideslip angle or yaw rate. However, in this study, differential braking has been redefined as a primary steering redundancy mechanism, and physical effects such as self-aligning moment and scrub radius arising from tire-road interactions are also incorporated into the optimization. In this way, the vehicle can be actively steered solely through braking forces, even in the absence of a functioning steering system. This integrated approach enhances system reliability and increases the fault tolerance of steer-by-wire architectures. To evaluate the effectiveness of the proposed method, simulations were conducted using the MSC ADAMS/Simulink co-simulation environment. The FED-Alpha, a high-performance military prototype vehicle model, was used for this purpose. Simulation scenarios included NATO Double Lane Change (DLC) maneuvers performed at both low speed (35 km/h) and high speed (60 km/h). In these scenarios, it was assumed that the steer-by-wire system was deactivated, and the vehicle was required to follow the reference trajectory using only differential braking control. Two different steering models were compared within the simulation environment. The first is a simplified model that represents the steering system as a basic dynamic structure using only general stiffness, damping, and mass parameters. The second is a detailed model that includes physical effects such as the mass and inertia of subcomponents, the position of the center of gravity, scrub radius, and self-aligning moment to more accurately represent the steering dynamics. The results showed that under low-speed conditions, both models provided similar path-following performance. However, under high-speed maneuvers, the detailed model exhibited a clear advantage in terms of both trajectory tracking and maintaining vehicle stability. This model enabled more accurate and timely braking force estimations, prevented loss of balance, and ensured more effective coordination with the ABS system. These findings confirm that differential braking-based steering redundancy can be successfully applied even at high speeds. In conclusion, this thesis demonstrates that differential braking can be used as a primary steering mechanism to enhance the safety of steer-by-wire systems. Through the MPC algorithm, steering can be achieved using only braking forces, allowing the vehicle to maintain operational capability even in failure scenarios. Furthermore, the integration of detailed physical parameters such as self-aligning moment and scrub radius into the control system significantly improves control performance. This study is particularly important for the development of fail-safe vehicle systems, as it highlights how advanced control strategies can be integrated into automotive applications. Future studies may focus on real-time embedded implementation, adaptive control techniques, and hardware-in-the-loop testing to further validate the approach. At the same time, the integration of a more realistic steering mechanism into the model is also planned. In this context, not only the general stiffness and damping coefficients but also the detailed dynamic characteristics of all steering system components will be considered. In particular, the rotational inertia of the steering assembly, wheel–tire system inertia, and the inertial properties of connecting elements such as tie rods and bushings will be separately calculated and included in the model. Through this more comprehensive modeling, the system's response under real-world failure conditions will be more accurately simulated, and controller behavior will be improved accordingly. Additionally, nonlinear effects such as tire relaxation length will be incorporated, as they play a significant role in tire force generation, especially during high-speed maneuvers. With the inclusion of such factors, the controller's performance particularly under demanding dynamic scenarios will be significantly enhanced. In addition, nonlinear effects arising from tire–road interaction, such as tire relaxation length, are also planned to be incorporated into the modeling. These effects play a critical role in the generation of tire forces, especially during high-speed maneuvers, and therefore have a direct impact on the performance of the controller. In this context, by achieving a more accurate representation of tire dynamics and enhancing the physical realism of the steering system, the accuracy and stability of the control system under high-speed scenarios are expected to improve significantly.
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ÖgeKonvansiyonel bir ağır ticari vasıtanın elektrifikasyonu ve performans değerlendirmesi(İTÜ Lisansüstü Eğitim Enstitüsü, 2025)İçten yanmalı motorlara sahip araçların fosil yakıt tüketimi sonucunda atmosfere saldığı yanmamış hidrokarbon bileşenleri ve zararlı partiküller, çevresel kirliliğin artmasına, iklim değişikliğinin hızlanmasına ve küresel sera gazı salınımına etkisinin güçlenmesine yol açmaktadır. Bu sebepten dolayı, sıfır emisyon ve temiz enerji kaynaklarıyla çalışabilen elektrikli araçlara olan yönelim gün geçtikçe artmaya başlamıştır. Buradaki tez çalışmasının temel amacı da, içten yanmalı dizel motor ile çalışan bir ağır ticari taşıtın güç aktarım sistemini, bataryalı ve elektrikli güç aktarım sistemine dönüştürerek, aracın tamamen elektrikli bir kamyona evrimini modellemektir. Elektrifikasyon sürecinde, geleneksel kamyonun teknik özellikleri dikkate alınarak uygun elektrik motoru ve batarya hücresi seçimi yapılmıştır. Elektrikli kamyonun güç aktarım sistemini oluştururken iki temel model geliştirilmiştir: mekanik model ve elektrik modeli. Mekanik model içerisinde yer alan elektrikli aracın hız profilinin belirlenmesi, taşıta etki eden direnç kuvvetleri ve kullanılacak olan elektrik motorlar ilgili teknik hesaplamalar yapılmıştır. Bu hesaplamalar, elektrik modelinin ihtiyaç duyduğu güç ve performans gereksinimlerini belirlemiştir. Elektrik modeli, hesaplanan güç talepleri doğrultusunda batarya paketi ve elektrik motorunun uyum içinde çalışmasını sağlamak amacıyla geliştirilmiştir. Elektrifikasyon sürecinin doğru yönetilmesi, aracın modellenmesi ve analiz sonuçlarının doğruluğunu artırmakta, uygun bir güç aktarım sisteminin geliştirilmesini öncülük edecektir. Elektrikli kamyonun modellenmesi ve analizleri MATLAB/Simulink yazılımı kullanılarak gerçekleştirilmiştir. Simülasyon sürecinde, ileri yönlü yaklaşım metodu benimsenmiş ve model, aracın teknik parametreleri ile elektrik motoru ve batarya hesaplama sonuçları kullanılarak çalıştırılmıştır. Simülasyon sonuçları analiz edilerek, seçilen elektrik motoru ve batarya paketinin aracın performans gereksinimlerini karşıladığıyla ilgili validasyon yapılmıştır. Bu akademik çalışmada, teorik yöntemler kullanılarak geleneksel dizel motora sahip bir ağır ticari kamyonun belirlenen hız profilinde tükettiği yakıt miktarıyla elektrikli kamyonun aynı sürüş çevriminde harcadığı elektrik enerjisi hesaplanmıştır. Çalışmanın temel amacı, farklı güç aktarım sistemlerine sahip ağır ticari araçların harcanan enerji ile yakıt tüketimlerini karşılaştırarak, tahrik sistemlerinin verimliliklerini değerlendirmektir. Elde edilen veriler doğrultusunda, elektrikli güç aktarım sistemlerinin konvansiyonel dizel motorlara kıyasla daha yüksek enerji verimliliğine ve çevresel sürdürülebilirliğe sahip olduğu gösterilmiştir. Ayrıca, elektrifikasyon dönüşümü gerçekleşen bataryalı ağır ticari elektrikli taşıt ile referans çalışmadaki geleneksel dizel motora sahip ağır vasıta ekonomik açıdan karşılaştırıldığında, elektrik motora sahip güç aktarım sistemlerinin geleneksel dizel motora daha ekonomik olduğu kanıtlanmıştır.
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ÖgeRide quality evaluation methods for off-road vehicles(Graduate School, 2022)Analyses were made on the FED-Alpha vehicle model using the ADAMS Car program to observe the effect of road characteristics on ride quality. The vehicle was developed by Ricardo Inc. as a fuel-efficient all-terrain military vehicle. The FED-Alpha is a 4x4 wheeled vehicle and the front and rear axles have an independent double-wishbone suspension system. The suspension system has air bellows and titanium helical springs and dampers. The dampers give different damping characteristics at low and high frequencies. In the ride quality evaluation standards, the constraints of analysis or test have been determined. The constraints mentioned were discussed and analysis studies were performed with these constraints. For example, speed deviation, which is one of the absorbed power method constraints, is examined and the effect of this value on ride quality is examined by exceeding the restricted value. Analyses were made by collecting data on three axes at three different vehicle locations. Waviness, phase angle, wavenumber, wavelength and roughness were chosen as the road parameters to examine ride quality effects. Synthetic roads were created by changing the road parameter to be examined. Synthetic roadways were modeled in a format that could be analyzed with ADAMS Car. Absorbed power, vibration dose value, and frequency weighted rms acceleration methods were used for ride quality evaluation in the scope of this thesis. Absorbed power was calculated with the transfer function and the FFT method, and the different results between the two methods were examined. Since the difference in results was negligible, the calculations continued with the transfer function. MATLAB and SIMULINK software were used simultaneously in the ride quality evaluation method calculations. The acceleration data was collected from the driver seat base, passenger seat base, and middle point of the rear passenger seat base. Acceleration data were exported from the ADAMS Car. With the help of MATLAB code, the tab files were imported to SIMULINK and the acceleration data was passed through transfer functions. Obtained results are converted into graphics with the help of MATLAB. Analyses were made between the speed of 8,05 km/h and 24 km/h to determine vehicle 6-Watt speed in the z-axis on synthetic roads. First, the found absorbed power values are plotted in the speed domain. Then, 6-Watt speed was determined by fitting a second-degree polynomial to the plotted graph in the speed domain. Finally, using the fitted second-degree polynomial, 6-Watt speed was calculated. Using the same second-degree polynomial calculation model, the vibration dose value and frequency weighted rms acceleration values corresponding to the 6-watt speed were calculated. The purpose of comparing these values is to determine how other methods evaluate the 6-watt ride quality limit defined in the absorbed power method. A higher correlation rate was detected with frequency weighted rms acceleration and a slightly lower correlation with vibration dose value. Ride quality result graphs were plotted in three axes by analyzing four rms roughness values. As the road rms roughness value increases, all vibration evaluation values in the z-axis increase. This result means that ride quality deteriorated in the z-axis due to roughness. It has been determined that the ride quality decreases depending on the increasing speed. It has been observed that the absorbed power values are most affected by the change of vehicle speed in the z-axis. It has been determined that with the increase of the road rms roughness, the ride quality decreases in the x and y axes. But the change is not continuously increasing depending on the speed. Analyses were made at three different waviness values and ride quality graphs were plotted for each axis. As the waviness increase, the ride quality increase in the z-axis. The ride quality decrease depending on the speed increase. No change was detected in the ride quality in the y-axis depending on the waviness change. The decrease in the waviness led to a decrease in the ride quality in the x-axis. Still, no correlation could be observed in the change depending on the speed in the x-axis. Analyses were made on roads with four different wavenumber bandwidths. It is observed that the ride quality change as the wavenumber bandwidth change in the z-axis. The ride quality increase on wider bandwidth at low wavenumber range. The ride quality increase on narrow bandwidth at high wavenumber range at low speed. The ride quality increase on narrow bandwidth at high wavenumber range at high speed. As the speed increases, the ride quality in the z-axis decrease, but it has been observed that the slope of the speed-related increases differs on the roads with different wavenumber bandwidths. It was determined that one of the parameters affecting the ride quality in the x and y axes is the wavenumber bandwidth, but no correlation could be detected. Analyzes were made on the road with four different phase angles. It has been determined that as the phase angle increases, the ride quality in the z-axis increase. As the speed increases, the ride quality values in the z-axis decrease. As the phase angle increases, the ride quality on the y-axis decrease. It is evaluated that the ride quality decrease is the roll motion caused by the opposite movement of the right and left wheel. It was observed that the phase angle change in the x-axis did not have much effect on the ride quality. Analyzes were made at different speed profiles on the 5,08 cm rms roughness road. As a result, it has been determined that even if the speed deviation factor specified in the standard is exceeded and the average speed is maintained and driven for approximately 300 meters, the absorbed power values in the z-axis will not change. However, this result needs to be supported by the results of the analysis to be made in different vehicles. When the ride quality evaluation methods are compared, it has been determined that the absorbed power will give the most sensitive results changing by vehicle speed. It is considered that the absorbed power, vibration dose value and frequency weighted rms acceleration methods will be sufficient for the evaluation of the ride quality in the z-axis. However, it is thought that it is necessary to include the suspension and wheel parameters in the x and y-axis evaluations.
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ÖgeViability of differential braking based steering redundancy for an autonomous vehicle(Graduate School, 2024-01-17)The exploration of differential braking as an alternative steering method for autonomous vehicles is a pivotal theme of this research, particularly in the context of steering system failure. Differential braking, which applies varying braking forces to the wheels, has been integral to enhancing vehicle stability and maneuverability in systems like Electronic Stability Control and Differential Braking Assisted Steering. This thesis underscores the importance of redundant systems in autonomous vehicles, given the rapid advancements in autonomous driving technologies and the inherent risks of steering system failures, especially at high speeds. Differential braking emerges as a promising safety net in such critical situations. The historical progression of differential braking is examined, from its initial role in cornering stability to its integration with advanced control strategies that enable sophisticated vehicle control tasks. The technology has evolved significantly, now being combined with active steering systems to improve vehicle handling. The research methodology involves assessing differential braking as an emergency steering system through double lane change maneuvers based on NATO standard. A reference trajectory is generated for the vehicle, and two PID controllers are optimized to minimize trajectory and yaw angle deviations. The optimization process uses a heuristic algorithm inspired by natural swarms, Particle Swarm Optimization, which iteratively updates to find the optimal solution. The algorithm's parameters are carefully chosen to ensure stability and convergence, with the optimization process tailored to reduce computation time. A pseudo-ABS system is introduced to manage wheel slip during intense braking, ensuring optimal braking performance and preventing loss of traction. The system adjusts braking force based on longitudinal slip, with control margins customized to the tire and ground characteristics. A co-simulation approach is employed, integrating a high-fidelity vehicle model with the controller, to evaluate the system. The simulations are conducted at different vehicle speeds, with the optimized controller gains derived from the higher speed. The vehicle model used is well-documented and validated, ensuring the reliability of the simulation results. The findings reveal that at higher speeds, the vehicle can successfully navigate the maneuver within the course boundaries, though with some response lag. The pseudo-ABS system effectively controls longitudinal slip, maintaining tire traction. At lower speeds, the vehicle performs the maneuver with minimal delay, but the gains tuned for higher speeds may be too aggressive, indicating the need for speed-dependent tuning. The impact of front wheel geometry on differential braking performance is also explored, with the scrub radius identified as a critical suspension parameter. Simulations with varying scrub radii show that there is a threshold below which the necessary steering torque for successful maneuvers is not produced. While larger scrub radii improve differential braking effectiveness, they are not typically preferred for road vehicles due to the negative implications for steering effort, tire wear, and road feel. The study concludes that the default scrub radius offers an optimal balance, allowing the vehicle to follow the reference path with minimal steering wheel oscillations. In conclusion, the research confirms the viability of differential braking as a redundant steering system for autonomous vehicles, as demonstrated by successful simulations of obstacle avoidance maneuvers. The simple yet effective PID controllers could be further enhanced by optimizing control parameters for specific vehicle speeds. The significant influence of front wheel geometry, particularly the scrub radius, on the success of differential steering is highlighted, with an optimal radius being necessary to generate sufficient steering torque while minimizing unwanted steering vibrations. The potential of differential steering as a reliable redundant steering system is underscored, with future work aimed at leveraging predictive model-based control systems to refine such systems in autonomous vehicles.
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ÖgeKauçuk ömür testi için bir test düzeneğinin validasyonu(Lisansüstü Eğitim Enstitüsü, 2024-06-12)Kauçuk malzemeler, özellikle tekrarlı yükleme koşullarına maruz kalmakta ve çeşitli mühendislik uygulamalarında gerek birincil gerek ikincil fonksiyonlarda kritik bir rol oynamaktadır. Kauçuğun yorulma özelliklerini anlamak, ürün performansını ve dayanıklılığını öngörebilmek; kaliteyi ve emniyeti garanti ederken ticari olarak rekabetçi kalabilmek için hayati önem taşır. Kauçuk yorulma testi cihazları, kauçuğun tekrarlayan yüklemelere karşı performansını test etmek için kullanılan makinalardır. Kauçuğu sabitlemek ve ölçüm sonuçlarının gürültüden etkilenmemesi için sağlam bir çerçeveye, gerilmeyi uygulamak için aktüatörlere ve bunu ölçmek için sensörlere sahiptirler. Kontrol sistemi, gerilme seviyelerini ayarlar, verileri kaydeder. Bazı cihazlar farklı ortamları (sıcaklık, frekans, ...) taklit edebilirler. Bu cihazlar, kauçuk ürünlerin kalite standartlarını karşıladığından ve parçalar gerçek koşullarda kullanıldığında istenen ömür dayanımına sahip olmasını sağlar. Kauçuk ömrü; malzeme özellikleri, çevresel faktörler, yükleme koşulları, yükleme geçmişi, parça geometrisi, imalat süreçleri, işletme koşulları ve yaşlanma etkileri gibi birçok faktörün kombinasyonuna bağlıdır. Tüm bu faktörlerin takip edilerek kauçuk yorulma davranışının incelenmesini zorlaştırmaktadır. Bu nedenle test cihazları belli başlı karakteristiklere, birbirine göre avantajlı ve dezavantajlı olduğu senaryolara sahiptir. Bu farklılıklara; test edilebilen sıcaklık aralığı, frekans aralığı, yükleme tipleri, ölçüm hassasiyetleri, parça boyutları vb. birçok etken örnek verilebilir. R = -1, bileşenlerin simetrik tekrarlı yükleme koşullarına maruz kaldığı durumu temsil etmektedir. İncelenen test cihazının doğrulaması bu yükleme tipinde kauçuk ömrünün tespiti içindir. Kauçuk sektöründe genelgeçer kabul edilen standart R = 0 durumu sadece çekme durumu için ömür testine yöneliktir. İncelenen diğer çalışmalarda farklı yükleme tipleri haricinde, R = -1 koşulunun farklı bir mekanizmayla sağlandığı ya da cihaz validasyon çalışmalarının zayıf olduğu gözlemlenmiştir. Bu çalışmayla silindirik numuneleri eksenine göre farklı açılarda gerdirerek konumlandırdıktan sonra motordan alınan güç aracılığıyla numunelere dönme hareketi vermek suretiyle numunede sıkışan bölgede basma, genleşen bölgede çekme gerilmesi uygulamak suretiyle; sinüzoidal basma-çekme yükleme koşulunda kauçuk numunelerin ömür dayanımları tespit edilebilecektir. Yeni cihazla ve bu cihaza uygun test takozlarından elde edilen Wöhler eğrisiyle hesaplanan ömür tahminlerinin fiziki şaft askı lastiği ömür testlerinden çıkan sonuçlarla örtüşüp örtüşmediği irdelenmiştir.