This thesis aims at estimating vital vehicle states and developing control algorithms for automotive suspensions and vehicle stability. A parametric model of an automotive monotube damper is developed and several control algorithms for semi-active suspensions have been developed. An extensive comparison of different control algorithms has been done. Skyhook, Groundhook, Hybrid, Acceleration-driven, Power-driven, Groundhook-linear, Linear Quadratic Regulator (LQR) optimal, Genetic algorithm optimized Linear Quadratic Regulator optimal, Model-reference adaptive, H∞ robust, µ-synthesis, fuzzy-logic based, and Deep Reinforcement learning based control algorithms have been developed and simulated. A shock dyno is instrumented and skyhook and groundhook control algorithms have been implemented as well. In addition to this, a semi-active suspension switching based control algorithm is developed for reducing the effort of a direct moment yaw rate controller, and improve stability of a vehicle when turning. Accelerometer based intelligent tires have been used to estimate vehicle states like vertical load on tire, velocity of the vehicle, unsprung mass acceleration, and forces on a tire. All these estimations would be helpful in observing various parameters of a vehicle using data from only a tri-axis accelerometer inside the tire. Data was collected in an instrumented Volkswagen Jetta and a Trailer setup as well. The test vehicle was instrumented with a tri-axis accelerometer inside the tire, encoder, Inertial Measurement Unit (IMU), and VBOX Racelogic Global Positioning System (GPS) based velocity measurement unit. For payload estimation, the data collected by the in-tire accelerometer was converted into frequency domain using Welch's method of averaging, followed by feature extraction. The extracted features were fed to a trained bagged trees model. Root mean squared error of 11% was observed on the test dataset. For velocity estimation, the data collected by the accelerometer was fed to a variational mode decomposition process. The extracted mode was converted to time-frequency domain using Hilbert transform and features for machine learning were extracted. A root mean squared error of 1.02kmph was observed on the trained dataset. A Gaussian process model was trained for this application. For unsprung mass acceleration estimation, the test vehicle was instrumented with an accelerometer near the wheel spindle as well. For this estimation problem, Convolutional neural networks (CNN) were used. The time-frequency spectrogram of x, y, and z axis data of the in-tire accelerometer were considered as the three color channels of an image. With this, an image of 224 x 224 x 3 dimensions was generated, which represented the time and frequency variation of data. These images were used for training the CNN and a 96.8% coefficient of correlation was obtained for this regression task. For the last wheel force estimation problem, the concept of training the images generated by overlapping time-frequency matrices was used and an accuracy of 90.1% was achieved. With these estimation of vehicle states, better control algorithms can be developed and deployed for better handling, safety and comfort of vehicles using data from only tri-axis accelerometer in the tire. / Master of Science / The main objective of this thesis is to aid in the development of better control systems for vehicles, using data from accelerometer-based intelligent tire. Payload on the vehicle's tire, vehicle velocity, wheel acceleration, and wheel forces are vital parameters, which if estimated correctly can be instrumental in having better understanding of the vehicle's condition. A tri-axis accelerometer is mounted inside the tire, and is used for estimating these vehicle parameters. Statistical models are developed based on features extracted from the accelerometer data. The main challenge was to use the data collected by only intelligent tire to estimate vehicle states. This makes the developed algorithms independent of other sensors and hence economic. Tires are the only component which serve as a link between the vehicle and road. Hence, these parameter estimations can be accurately observed simultaneously using the in-tire accelerometer data. Testing is done on an instrumented trailer-test setup and a Volkswagen Jetta. The vehicle is instrumented with the intelligent tire, a Global positioning system (GPS) based velocity measuring unit, Inertial measurement unit (IMU), and encoder. Testing is done for different loading conditions, road surfaces, inflation pressures, and vehicle velocities. In this way, it has been attempted to make the developed statistical models robust and expose them to a multitude of test conditions. In addition to this, several suspension semi-active control algorithms have been developed for improving vehicle ride comfort and road holding. A parametric damper model has been developed, and several control algorithms have been simulated. A shock dyno experimental setup has been instrumented and some of the control algorithms have been implemented. With this, several suspension semi-active control algorithms have been developed, and statistical models have been developed for estimation of various vehicle parameters. This research can be helpful for developing accurate control algorithms for active safety systems in a vehicle.

This Bachelors Thesis, conducted together with Öhlins racing AB, aims to develop a deeper understanding of the vehicle dynamics of snowmobiles, focusing particularly on the behavior of the rear suspension under various motions and applied forces. The rear suspension called the bogie, consists of several linkages, springs, and dampers whose geometry and parameters influence the movement of the bogie. The study aims to attain industry-standard knowledge of snowmobile dynamics by developing a simulation model in Matlab to further understand and examine the behavior of the bogie during heave and pitch, as well as consulting with professionals in snowmobile simulation to understand industry practices.The simulation model is built on two main components, the kinematic- and the dynamic calculations. The kinematics is determined by measuring existing snowmobiles to get data on how the points in the bogie are distanced. Subsequently, the motion of the bogie during heave is calculated by iteratively lifting the rail a small distance upwards from the initial points determined by the measurements. The motion will be dictated by the center arm since the rail is not allowed to rotate and the center arm can't be compressed. The dynamics of the bogie are then modeled by integrating springs to examine how the application of force varies throughout the motion. This, together with the forces exerted on the rail by the arms will result in a net heave force which is the force that is needed to initiate the heave motion.The heave simulation reveals that the application point of the heave force shifts forward during the compression of the bogie, a behavior that positively impacts the vehicle's turning ability by effectively shortening the wheelbase. Additionally, the motion ratios for the center and rear springs were analyzed, showing distinct variations. The motion ratio analysis for the center spring revealed only slight variations in the front, whereas the rear motion ratio exhibited substantial changes due to the rear arm and spring moving in opposite directions.Limitations of the study include the absence of empirical validation as well as simplifications of the suspension linkage, specifically the exclusion of coupled mechanisms. Future work should involve simultaneous pitch and heave movements and incorporate feedback from professional snowmobile drivers to refine the suspension settings. The insights gained from these simulations can guide the design of more efficient and responsive snowmobile bogies, ultimately enhancing the vehicle's performance and safety.

A comprehensive evaluation of roll and yaw stability of tractor/semitrailers with single and dual trailers in city and highway conditions is conducted. Commercial vehicles fundamentally behave differently in city driving conditions than at high speeds during highway driving conditions. In order to closely examine each, this study offers two distinct evaluations of commercial vehicles: 1) low-speed driving in tight turns, representative of city driving; and 2) high-speed lane change and evasive maneuvers, typical of highway driving. Specifically, for city driving, the geometric parameters of the roadway in places where tight turns occur—such as in roundabouts—are closely examined in a simulation study in order to evaluate the elements that could cause large vehicle body lean (or high rollover index), besides the truck elements that have most often been studied. Two roundabout geometries, 140-ft single-lane and a 180-ft double-lane, are examined for various truck load conditions and configurations. The vehicle configurations that are considered are a straight 4x2 truck, a tractor with a 53-ft semi-trailer (commonly known as WB-67), and two trucks in double-trailer configurations. Five potential factors are identified and thoroughly studied: circulatory roadway cross-section, roundabout tilt, truck configurations, truck apron geometry, and truck load condition. The results of the study indicate that when the rear axles of the trailer encounter the truck apron in the roundabout, the climbing and disembarking action can cause wheel unloading on the opposite side, therefore significantly increasing the risk of rollover. Interestingly, in contrast to most high-speed rollovers that happen with fully-loaded trailers, at low speeds, the highest risks are associated with lightly loaded or unloaded trucks. For high-speed driving conditions, typical of highway driving, a semi-truck with a double 28-ft trailer configuration is considered, mainly due to its increasing use on U.S. roads. The effect of active safety systems for commercial vehicles, namely Roll Stability Control (RSC) for trailers and Electronic Stability Control (ESC) for the tractor, is closely examined in a test study. Various trailer loading possibilities are evaluated for different combinations of ESC/RSC on the tractor and trailer, respectively. The results of the study indicate that 1) RSC systems reduce the risk of high-speed rollovers in both front and rear trailers, 2) the combination of ESC (on tractor) and RSC (on trailer) reduce the risk of rollover and jackknifing, and 3) RSC systems perform less effectively when the rear trailer is empty. / PHD / Traffic accidents involved with heavy trucks are more likely to result in fatality, excessive property damage, and traffic congestion. Unfortunately, heavy trucks commonly have lower stability than passenger cars due to heavy axle load and high center of gravity, which means they are easier to roll over or lose control. Therefore, it is necessary for us to understand the dynamics of heavy trucks in order to improve their stability and reduce the likelihood of severe accidents. Because heavy trucks are commonly operated for freight transport, they are subjected to two different driving conditions. When a truck is used within an urban area, it will be driven at low speeds and will need to negotiate tight turns, such as those normally seen at city traffic intersections and roundabouts. In this condition, the tight turns and roadway geometry (i.e. curb, truck apron, etc.) can considerably increase the likelihood of truck rollovers. On the contrary, non-collision accidents like rollovers that happen to heavy trucks during highway driving, where there are no tight turns or significant roadway input, are commonly due to the unstable dynamics of trucks rather than external excitation. This is because heavy trucks are more prone to exhibiting unstable dynamics at high speeds, especially when performing quick and aggressive maneuvers, such as those applied when changing lanes or avoiding an obstacle on the road. In this dissertation, the dynamic stability of heavy trucks in both driving conditions are evaluated. For low-speed conditions, a simulation study is conducted to learn how roadway geometry and truck elements affect the likelihood of rollovers during city driving. For high-speed conditions, a test study is performed to investigate how active safety systems reduce the likelihood of heavy truck rollovers and other non-collision accidents during highway driving. This dissertation provides valuable information for researchers or engineers who are interested in urban traffic design, heavy truck dynamics, and active safety systems for commercial vehicles.

This analytical study evaluates the response characteristics of a two-degree-of freedom quarter-car model, using passive and semi-active dampers, along with a seven-degree-of-freedom full vehicle model. The behaviors of the semi-actively suspended vehicles have been evaluated using skyhook, groundhook, and hybrid control policies, and compared to the behaviors of the passively-suspended vehicles. The relationship between vibration isolation, suspension deflection, and road-holding is studied for the quarter-car model. Three main performance indices are used as a measure of vibration isolation (which can be seen as a comfort index), suspension travel requirements, and road-holding quality. After performing numerical simulations on a seven-degree-of-freedom full vehicle model in order to confirm the general trends found for the quarter-car model, these three indices are minimized using optimization techniques. The results of this study indicate that the hybrid control policy yields better comfort than a passive suspension, without reducing the road-holding quality or increasing the suspension displacement for typical passenger cars. The results also indicate that for typical passenger cars, the hybrid control policy results in a better compromise between comfort, road-holding and suspension travel requirements than the skyhook and groundhook control policies. Finally, the numerical simulations performed on a seven-degree-of-freedom full vehicle model indicate that the motion of the quarter-car model is not only a good approximation of the heave motion of a full-vehicle model, but also of the pitch and roll motions since both are very similar to the heave motion. / Master of Science

This study experimentally evaluates the dynamic response of a single vehicle suspension incorporating a magneto-rheological (MR) damper. A full-scale two-degree-of-freedom (2DOF) quarter-car test apparatus has been constructed at the Advanced Vehicle Dynamics Lab at Virginia Tech to evaluate the response of a vehicle suspension under the different control schemes of skyhook, groundhook, and hybrid semiactive control. The quarter-car apparatus was constructed using materials from 80/20 Incorporated and a hydraulic actuation system from MTS. A dSPACE AutoBox was used both for controlling the MR dampers and acquiring data. The first task was to understand the baseline dynamic response of the quarter-car system with only a passive damper. Next, the passive damper was replaced with a controllable MR damper. The control schemes of skyhook, groundhook, and hybrid semiactive control were applied to the MR damper. The physical response of the quarter-car with the different control schemes was then compared to the analytical prediction for the response, with favorable results. The response of the quarter-car with the semiactive damper was also compared to the response of the quarter-car with a passive damper, and the resulting limitations of passive damping are discussed. Finally, the practical implications of this study are shown in a discussion of the physical implementation of the MR dampers in the Virginia Tech FutureCar, a full-size Chevrolet Lumina. Although the actual skyhook, groundhook, and hybrid semiactive control schemes were not implemented on the vehicle, the results were promising and generated several recommendations for future research. / Master of Science

O objetivo deste trabalho é estudar a influência da rigidez do quadro na dirigibilidade de um veículo de competição fórmula SAE (protótipo E2-M, da equipe EESC-USP) em ambiente multicorpos com o software Adams/Car. Um modelo contendo os subsistemas de suspensão, direção, pneumático, powertrain, barra estabilizadora e quadro foi construído em ambiente multicorpos com componentes modelados como corpos rígidos. Posteriormente foram elaborados três modelos de quadros flexíveis com diferentes valores de rigidez torcional para substituir o quadro rígido. Estes foram obtidos através da análise modal com o auxílio do método dos elementos finitos. Para comparação da dinâmica lateral dos modelos, típicas manobras do estudo de dirigibilidade foram consideradas tais como rampsteer, step-steer e single lane change. Os resultados obtidos foram de aceleração lateral e velocidade de guinada. Pelas condições avaliadas, pode-se concluir que a rigidez torcional de um quadro para o protótipo E2-M pode estar entre 700 e 1500 N.m/o. Essa variação de rigidez representou 5 kg de massa no quadro. Porém deve-se fazer uma avaliação modal com a massa suspensa calibrada para verificar se não existe acoplamento de modos e freqüências com outros subsistemas. / This dissertation is intended to study the influence of frame stiffness in handling of a Formula SAE vehicle (E2-M prototype from EESC-USP Formula SAE team) in multibody with Adams/Car software. A model containing the subsystems of suspension, steering, tires, powertrain, frame and stabilizing bar was built considering rigid bodies. Subsequently, three models of flexible frames were developed with different values of torsional stiffness to replace the rigid frame. They were obtained through modal analysis with the aid of finite element method. For the handling investigation, maneuvers such as ramp-steer, step-steer and single lane change were considered. The results evaluated were lateral acceleration and yaw velocity. According to results, the torsional stiffness for the E2-M prototype can be between 700 and 1500 Nm/o. But an eigenvalue analyses is also necessary to verify if there is no coupling of modes of the calibrated sprung mass with other subsystems.

O objetivo deste trabalho é estudar a influência da rigidez do quadro na dirigibilidade de um veículo de competição fórmula SAE (protótipo E2-M, da equipe EESC-USP) em ambiente multicorpos com o software Adams/Car. Um modelo contendo os subsistemas de suspensão, direção, pneumático, powertrain, barra estabilizadora e quadro foi construído em ambiente multicorpos com componentes modelados como corpos rígidos. Posteriormente foram elaborados três modelos de quadros flexíveis com diferentes valores de rigidez torcional para substituir o quadro rígido. Estes foram obtidos através da análise modal com o auxílio do método dos elementos finitos. Para comparação da dinâmica lateral dos modelos, típicas manobras do estudo de dirigibilidade foram consideradas tais como rampsteer, step-steer e single lane change. Os resultados obtidos foram de aceleração lateral e velocidade de guinada. Pelas condições avaliadas, pode-se concluir que a rigidez torcional de um quadro para o protótipo E2-M pode estar entre 700 e 1500 N.m/o. Essa variação de rigidez representou 5 kg de massa no quadro. Porém deve-se fazer uma avaliação modal com a massa suspensa calibrada para verificar se não existe acoplamento de modos e freqüências com outros subsistemas. / This dissertation is intended to study the influence of frame stiffness in handling of a Formula SAE vehicle (E2-M prototype from EESC-USP Formula SAE team) in multibody with Adams/Car software. A model containing the subsystems of suspension, steering, tires, powertrain, frame and stabilizing bar was built considering rigid bodies. Subsequently, three models of flexible frames were developed with different values of torsional stiffness to replace the rigid frame. They were obtained through modal analysis with the aid of finite element method. For the handling investigation, maneuvers such as ramp-steer, step-steer and single lane change were considered. The results evaluated were lateral acceleration and yaw velocity. According to results, the torsional stiffness for the E2-M prototype can be between 700 and 1500 Nm/o. But an eigenvalue analyses is also necessary to verify if there is no coupling of modes of the calibrated sprung mass with other subsystems.

The wheel-rail contact is at the core of all research related to vehicletrackinteraction. This tiny interface governs the dynamic performanceof rail vehicles through the forces it transmits and, like any high stressconcentration zone, it is subjected to serious damage phenomena. Thus,a clear understanding of the rolling contact between wheel and rail is keyto realistic vehicle dynamics simulation and damage analysis. In a multi-body dynamics simulation, the demanding contact problemshould be evaluated at about every millisecond for several wheel-rail pairs.Hence, a rigorous treatment of the contact is highly time-consuming.Simplifying assumptions are therefore made to accelerate the simulationprocess. This gives rise to a trade-o between the accuracy and computationaleciency of the contact model in use. Conventionally, Hertz+FASTSIM is used for calculation of the contactforces thanks to its low computational cost. However, the elliptic patchand pressure distribution obtained by Hertz' theory is often not realisticin wheel-rail contact. Moreover, the use of parabolic traction bound inFASTSIM causes considerable error in the tangential stress estimation.This combination leads to inaccurate damage predictions. Fast non-elliptic contact models are proposed by others to tacklethis issue while avoiding the tedious numerical procedures. The studiesconducted in the present work show that the accuracy of these models iscase-dependent. To improve the accuracy of non-elliptic patch and pressure estimation,a new method is proposed. The method is implemented in an algorithmnamed ANALYN. Comparisons show improvements in patch and, particularly,pressure estimations using ANALYN. In addition, an alternative to the widely-used FASTSIM is developed, named FaStrip. Unlike FASTSIM, it employs an elliptic traction boundand is able to estimate the non-linear characteristic of tangential stressdistribution. Comparisons show more accurate estimation of tangentialstress and slip velocity distribution as well as creep forces with FaStrip. Ultimately, an ecient non-elliptic wheel-rail contact model consistingof ANALYN and FaStrip is proposed. The reasonable computationalcost of the model enables it to be used on-line in dynamics simulationand its accuracy can improve the damage predictions. / <p>QC 20160202</p>

This thesis describes an investigation into vehicle handling control using active differentials in the rear axle of a motor vehicle. Such devices are able to transfer torque between the rear wheels and have traditionally been used to improve traction whilst minimising the impact on vehicle handling. However, the capacity to generate a lateral torque difference across an axle also gives them the potential to be used for yaw moment control. In order to generate a rigorous assessment of this potential, the investigation is carried out in three distinct phases. Firstly, an analysis of the scope for modifying vehicle handling given unrestricted control over torque transfer between the rear wheels is carded out in the simulation environment. For this purpose an idealised yaw sideslip controller is developed. This is used to show that an ideal active differential can have significant yaw moment authority in terms of generating both understeer and oversteer and that this can be used to actively modify a vehicle's handling balance and apply stability control at the limits of adhesion. In the second phase, the capabilities of two types of contemporary active differential, the torque vectoring differential (TVD) and active limited slip differential (ALSID), are then assessed against the ideal differential and against a brake based yaw moment controller. TVDs are found to be able to offer very similar performance to both their ideal counterpart and to the brake based system. They Gan also deliver this performance with a fraction of the energy loss that is observed in the brakes, thus making TVDs a viable proposition for applying continuous yaw control below the limits of adhesion. ALSDs, on the other hand do not offer equivalent functionality to an ideal active differential but are still shown to be very effective stability control devices. In the third phase, the ALSID results are validated on a prototype vehicle where it is shown that they do indeed offer substantial stability improvements both on high and low-P surfaces. However in order to deliver such benefits and be practical for implementation, it is also shown that significant redevelopment of the idealised controller is required. Finally, with the ALSID operating alongside a commercial brake based stability control system, it is proven that substantial reductions in brake intervention can be achieved without significant controller integration.

A utilização de motores elétricos diretamente nos cubos de roda é uma alternativa de propulsão para um veiculo elétrico ou híbrido muito interessante, pois não necessita do uso de sistemas complexos de transmissão, tornando o conjunto mecânico muito mais simples e, consequentemente, reduzindo a sua massa, atritos e custos. Entretanto, a adição dos motores nas rodas causa o incremento da massa não suspensa, e isto irá afetar o comportamento de dirigibilidade do veículo. Dessa forma, com ajuda da ferramenta de multicorpos, será identificado o que ocorrerá devido ao acréscimo de massa compatível com os motores elétricos de última geração. Para isto, uma série de análises comparativas será realizada, com modelos de veículos baseados na técnica de multicorpos, para o caso de um carro de passeio compacto. Primeiramente, uma análise modal comparando um carro convencional aos carros com a utilização dos motores, no eixo traseiro ou no dianteiro, e uma posterior avaliação das frequências obtidas. Em sequência, também foram realizadas manobras padrão com o modelo de veículo completo e foram observadas maiores influências nos resultados das análises em regime transiente, como a manobra de troca de faixa e a manobra do anzol (\"fishhook\"). Com a ajuda destes resultados, foi possível identificar que as instalações dos motores elétricos nos cubos traseiros causam uma menor influência negativa no desempenho de dirigibilidade, quando comparado com o caso instalado no eixo dianteiro. Através de uma otimização realizada com a ajuda de uma análise de sensibilidade das variáveis do sistema (D.O.E.), baseada na manobra do anzol, foi possível identificar que alterações nas molas, amortecedores e barra estabilizadora são capazes de mitigar os efeitos indesejáveis causados pelo incremento de massa não suspensa. / The electric motors directly in wheel hubs usage is an alternative of propulsion for a electric or hybrid vehicle, since it does not need the use of complex systems of transmission, making the mechanical assembly simpler and, consequently, reducing its mass , frictions and costs. However, the addition of the motors in the wheels causes an increase unsprung mass, and this will affect the vehicle handlings behavior. In that way, with the assistance of the multibody tool, it will be identified the consequences of mass addition, compatible with the moderns electric motors of. In this work, a series of comparative analyzes will be carried out, with vehicle models based on multibody techniques, in the situation of a compact car. First, a modal analysis comparing a conventional car to with the vehicle using hub driven motors, in rear or front axle, and an evaluation of the obtained frequencies. In the sequence, standard maneuvers were also performed with the complete vehicle model, and greater influences were observed in the transient analysis results, such as lane change and fishhook maneuver. With help of these results, it was possible to identify; that the installation of the electric motors in the rear hubs causes a smaller negative influence on the handling performance when compared to the case installed on the front axle. Through an optimization performed with the aid of a system variable sensitivity analysis (D.O.E.) based on the fish hook maneuver, it was possible to identify thtat changes on springs, shock absorbers and stabilizer bar are able to mitigate the undesirable effects caused by the increase of unsprung mass.