This article focuses on the development and experimental verification of a friction model to be implemented in a fully functional friction clutch. The resulting clutch model is intended to be employed in commercial software code AVL Excite, which imposes special requirements also for the underlying friction model. These requirements are related to model implementation, available input data, required output data, model complexity, numerical stability, and model parameters. Since for a fully functional clutch the ability to render true stick is crucial, the elasto-plastic friction model is chosen as a basis. This model is investigated in detail and modified adequately in order to meet all of the requirements and to deliver stable and satisfactory results. For validation purposes, a special test bed was built to measure the transmitted torques through the friction contact under various realistic load cases, including all operation phases of the friction clutch. Parallel to experimental measurements, multi-body simulations were done with the modified friction model within the target software. A very satisfactory agreement of simulation and measurement results was achieved.
This paper deals with a theoretical and numerical study of various viscosity terms in the modified elasto-plastic friction model and their influence on the resulting friction force-torque, transmitted through the contact of the friction clutch. Various simple viscous definitions for fluids considering shear rate dependent viscosity were investigated. The Carreau fluid model was chosen as a basis for the research, since it can describe Newtonian, dilatant, and pseudo plastic fluids. In addition to theoretical investigations, numerical simulations under realistic friction clutch operation conditions were carried out. The results were compared to the results of a validation case for a dry friction clutch simulation using the modified elasto-plastic friction model. This research showed significant differences between various viscosity definitions and revealed the drawbacks of such approach, were simple viscous models were used.In addition to viscosity, calculating the heat generated due to friction and its influence on the contact temperatures are discussed briefly. The basic theory and equations are given along with the directions for future work. The requirements for an accurate temperature calculation in the friction contact are outlined.
This paper deals with the development and validation of a mathematical friction model for numerical friction clutch simulation within a dynamic multi-body system of complete vehicle powertrains to be used by the commercial numerical code AVL EXCITE. The corresponding requirements and demands of the automotive industry and the given software environment are presented along with the advantages of the new friction model. The focus is to find a model capable rendering important friction dynamics and true stick. Detailed tribological analysis of the developed friction model is done and results for the so called STICK/SLIP test are given, to show the capabilities and properties of the friction model. Validation of the developed friction model on a special test bed is presented. A comparison of experimental validation measurement results and numerical simulation results shows a remarkably good agreement.
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