Orientador: Pablo Siqueira Meirelles / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-20T08:25:52Z (GMT). No. of bitstreams: 1 Piveta_Alessandro_M.pdf: 20999298 bytes, checksum: 60bf64ff246a3515b0455a01ccb8e817 (MD5) Previous issue date: 2012 / Resumo: No desenvolvimento de projetos mecânicos é comum o uso de valores determinísticos para definir parâmetros que descrevem o sistema, atribuindo elevados coeficientes de segurança a fim de contornar o problema de incertezas relacionadas aos valores das cargas externas aplicadas, da variabilidade das propriedades dos materiais, das condições ambientais, entre outros fatores que possam afetar o desempenho do sistema. Atualmente, com o desenvolvimento de alguns métodos, pode-se introduzir modelos estocásticos que consideram estas incertezas e variações, deixando assim o modelo mais próximo da realidade. Este trabalho analisa o efeito da variabilidade simultânea de determinados parâmetros no desempenho de dois tipos de suspensão: convencional e hidropneumática. Utilizou-se um modelo matemático que representa um veículo completo com sete graus de liberdade implementado no software Matlab®. É desenvolvida a formulação para modelar a suspensão hidropneumática considerando que o gás contido no acumulador sofre uma mudança de estado politrópico. Inicialmente são apresentadas as respostas dos modelos determinísticos devido a excitações transientes representadas por funções que descrevem uma lombada e um degrau com diferentes dimensões. Em seguida, é realizada a análise de sensibilidade da rigidez hidropneumática com o intuito de descobrir quais parâmetros possuem maior influência sobre este sistema. O Método de Monte Carlo é utilizado como solver estocástico nas simulações, tendo como objetivo avaliar a influência das variações dos parâmetros sobre a dinâmica vertical do veículo. A distribuição de probabilidade escolhida para cada parâmetro é a função gama. Por último, são analisadas as respostas resultantes dos modelos probabilísticos. As saídas avaliadas são: aceleração vertical do centro de gravidade, razão de amortecimento, valor da força de contato entre pneu e via e ângulo de rolagem da massa suspensa / Abstract: Deterministic values are largely used in mechanical design to define the parameters which describe the system. Large coefficients of safety are used because of the uncertainties related to these parameters. There are uncertainties related to the external loadings, to the variability of the material properties and to the environmental conditions, among other important parameters which affect the performance of the system. In the last decade, stochastic models have been used to consider these uncertainties and variations. The present work analyzes the effect of the simultaneous variability of certain parameters on the performance of the conventional and the hydropneumatic suspension of automotive vehicles. A mathematical model of a full vehicle with seven degrees of freedom has been used. This model was implemented in the software Matlab®. In the present formulation of the hydropneumatic suspension, it is considered that the gas contained in the accumulator undergoes a polytrophic process. First, the deterministic model of the vehicle is subjected to two transient excitations, namely a function describing a bump and a function describing a step with different dimensions. Then, an analysis of sensibility of the stiffness of the hydropneumatic suspension is performed, which aims to identify which parameters are the most influential on that system. Monte Carlo method is used as the stochastic solver throughout the simulations which study the influence of the parameter variability on the vertical dynamics of the vehicle. The Gamma function is used as the probability density function for each parameter. Finally, the response of the probabilistic models is studied. This work investigates the acceleration of the center of gravity, damping factor, pitch angle of the suspended mass and contact force between the tires and the road / Mestrado / Mecanica dos Sólidos e Projeto Mecanico / Mestre em Engenharia Mecânica

This thesis presents a new nonlinear automobile dynamical model and investigates the possibility of automobile dynamic control with wheel torque utilizing this model. The model has been developed from first principles by applying classical mechanics. Inputs to the model are the four independent wheel torques, while the steer angles at each wheel are specified as independent time-varying signals. In this way, consideration of a variety of steering system architectures, including rear-wheel steer, is possible, and steering introduces time-varying structure into the vehicle model. The frictional contact at the wheel-road interface is modeled by use of the LuGre dynamic friction model. Extensions to the existing two-dimensional LuGre friction model are derived and the steady-state of the friction model is compared to existing static friction models. Simulation results are presented to validate the model mathematics and to explore automobile behavior in a variety of scenarios. Vehicle control with wheel torque is explored using the theory of input-output linearization for multi-input multi-output systems. System relative degree is analyzed and use of steady-state LuGre friction in a control design model is shown to give rise to relative degree singularities when no wheel slip occurs. Dynamic LuGre friction does not cause such singularities, but instead has an ill-defined nature under the same no-slip condition. A method for treating this ill-defined condition is developed, leading to the potential for the system to have relative degree. Longitudinal velocity control and combined longitudinal and angular vehicle velocity control are demonstrated in simulation using input-output linearization, and are shown to produce improved vehicle response as compared to the open-loop behavior of the automobile. Robustness of the longitudinal velocity control to friction model parameter variation is explored and little impact to the controller's ability to track the desired trajectory is observed.