Mathematical and computer modelling have been playing an increasingly important role in the Computer Aided Engineering (CAE) process. Simulation offers great advantages in the development and analysis phase of products and offers a faster, better and more cost effective way than using physical prototypes alone. The ever increasing demand for new and improved products in the vehicle industry has decreased the time available for the development of new vehicles, but at the same time the demands on quality, reliability and mass that are set for the vehicle are becoming ever more stringent. These requirements have lead to the investigation of procedures and methodologies such as virtual prototyping that will reduce the development time of new vehicles without inhibiting the quality of the vehicle. In order to perform effective and reliable simulations in the CAE process, accurate simulation models of the vehicle and its associated systems, subsystems and components are required. In the vehicle dynamics context simulation models of the tyres, suspension, springs, damper, etc, are needed. This study will look at creating a validated model of a leaf spring suspension system used on commercial vehicles. The primary goal set for the model is to be able to predict the forces at the points where the suspension system is attached to the vehicle chassis as the model is to be used in full vehicle durability simulations. The component which will receive a considerable amount of attention in this study is the leaf spring. Leaf springs have been used in vehicle suspensions for many years. Even though leaf springs are frequently used in practice they still hold great challenges in creating accurate mathematical models. It is needless to say that an accurate model of a leaf spring is required if accurate full vehicle models are to be created. As all simulation models in this study are required to be validated against experimental measurements a thorough experimental characterisation of the suspension system of interest, as well as two different leaf springs, are performed. In order to measure the forces between the suspension attachment points and the chassis, two six component load cells were developed, calibrated, verified and validated. This study will primarily focus on the modelling of a multi-leaf spring as well as a parabolic leaf spring. The study starts with a literature study into the various existing modelling techniques for leaf springs. A novel leaf spring model, which is based on a macro modelling view point similar to that used for modelling material behaviour, is developed. One of the modelling techniques found in the literature, i.e. neural networks, is also used to model the leaf spring. The use of neural networks is applied and some of the challenges associated with the method are indicated. The accuracy and efficiency of the physics-based elasto-plastic leaf spring model and the non physics-based neural network model are compared. The modified percentage relative error metric is compared to two other quantitative validation metrics that were identified from the literature study. It is concluded that the modified percentage relative error has certain limitations but that it is able to give an accurate and representative account of the agreement/disagreement between two periodic signals around zero. The modified percentage relative error is used to obtain the accuracies of the elasto-plastic leaf spring models and the neural network model. Both models give good results with the neural network being almost 3 times more computationally efficient. The elasto-plastic leaf spring model, for the multi-leaf spring, is further extended to model the behaviour of a parabolic leaf spring. Qualitative validation using experimental data shows that the elasto-plastic leaf spring model is able to accurately predict the vertical behaviour of both the multi-leaf spring as well as the parabolic leaf spring. The elasto-plastic leaf spring model was also combined with a method that is able to capture the effect of changes in the spring stiffness due to changes in the loaded length. Quantitative validation shows that the method proposed for accounting for the change in stiffness due to changes in the loaded length is able to capture this characteristic of the physical leaf spring. Following a systematic modelling approach the elasto-plastic multi-leaf spring model is incorporated into a model of a simplified version of the physical suspension system. The qualitative validation results from this model show that the model is able to accurately predict the forces that are transmitted from the suspension system to the chassis. The models created in this study can be used in future work and, with the addition of more detail the models, can be extended to create a model of the complete suspension system. / Thesis (PhD(Eng))--University of Pretoria, 2012. / Mechanical and Aeronautical Engineering / unrestricted

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Orientador: Auteliano Antunes dos Santos Jr / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-12T19:38:01Z (GMT). No. of bitstreams: 1 Antonio_SergioFranciscoDela_M.pdf: 2654431 bytes, checksum: a9d019fe7f3a17bc52fb361d8113f727 (MD5) Previous issue date: 2005 / Resumo: As cargas dinâmicas que ocorrem em veículos de carga quando estes estão em movimento, são fortemente responsáveis pela deterioração precoce do piso asfáltico das rodovias e logradouros no Brasil. Também são umas das principais responsáveis pelo desgaste excessivo e prematuro dos componentes do veículo. Estes dois fatores fazem com que os custos de transporte rodoviário no Brasil, de mercadorias e bens, fiquem mais elevados. O objetivo deste trabalho é avaliar uma metodologia para medir as cargas dinâmicas que ocorrem em veículos de carga. Na metodologia proposta, utilizou-se a própria suspensão do veículo como parte do sistema de medição, no caso, veículos com suspensão com feixes de molas. O sistema de medida das cargas dinâmicas é composto pelos feixes de molas e um transdutor de deslocamento. Gerou-se a curva de resposta do feixe de molas com relação aos deslocamentos ocorridos através da aplicação das cargas. Após os estudos preliminares, implantou-se este sistema na suspensão dianteira de um veículo de carga de porte médio. Estimaram-se as cargas dinâmicas em várias condições de piso com o veículo carregado, a partir dos deslocamentos medidos. Os resultados mostram que o sistema funcionou satisfatoriamente, e foi possível quantificar os níveis de cargas dinâmicas ocorridas em casos mais críticos. O maior nível encontrado foi de 33,9% acima da carga estática no lado esquerdo da suspensão dianteira, no trecho com lombadas. / Abstract: The dynamical loads and forces occurring in cargo vehicles under movement are among the major causes of the early deterioration on highway and road pavement in Brazil. These dynamical loads are also responsible for the premature and excessive wear on several vehicle components. These two factors combined are among the main reasons why road transportation costs are so expensive in Brazil. The objective of this work is to suggest and evaluate a methodology for measuring the dynamical loads and forces on moving cargo vehicles. This methodology utilizes the suspension system of the vehicle itself as part of the measurement system. In the experimental part of this study a force measuring system was conceived using the leaf spring assembly of the vehicle suspension combined with a simple displacement transducer strategically installed in the vehicle suspension. This force measuring system was installed in a mid-range cargo truck. The characteristic curve of the suspension leaf spring set was determined by the application of static loads onto the vehicle. After calibration and fine adjustments of the system, several experimental runs were performed in the loaded vehicle, measuring the dynamic loads in several pavement types and traffic conditions. The results showed that the system worked satisfactorily, and it was possible to determine the dynamic loads occurred on all experimental runs. The greatest dynamic load found in the field was 33,9 % above the static load on the left front suspension. / Mestrado / Mecanica dos Sólidos e Projeto Mecanico / Mestre em Engenharia Mecânica