Lumped Parameter Modelling of Hydraulic Systems: Advanced Techniques for Design and Analysis

The present thesis focuses on lumped parameter modelling of oil hydraulic systems in AMESim environment, particularly engine lubrication systems and lubricant pumps. Three modelling approaches are proposed, sharing the fundamental characteristic of being developed by making use of only elementary submodels already available to any user, properly assembled to build complex and comprehensive systems capable to provide accurate results still avoiding heavy computational requirements. They are intended to bridge the gap between elementary modelling and complex advanced techniques requiring the adoption of very onerous models, to answer to the demand for reduced time to results. The proposed models address real and current engineering problems with quick, robust, and reliable numerical tools, facilitating the development of oil systems since the very beginning of the design process. The first model addresses the design of the lubrication system of heavy-duty V8 engines by originally considering a large variety of components and related phenomena. The model accounts for fluid properties including air release phenomena, real piping geometry of the complex duct network, the hydraulic characteristic of the users, and dynamic behaviour of journal bearings. It is a powerful tool since it provides many numerical results for different operating conditions, guiding the design improvement to comply with overall performances and functional requirements. It provides useful information regarding the pressure distribution, flow uniformity, both lengthwise and transversally, oil velocity within the pipes, and feeding conditions at every oil user. Moreover, heat dissipation capacity can be addressed by monitoring oil flow rate at engine bearings and piston cooling jets. In addition, the capability to withstand variable loads can be assessed by evaluating the eccentricity ratio of the bearings. The development of engine lubrication systems through lumped parameter models has been addressed also by means of a tool devoted to the simulation of the filling process, to verify whether oil consumers receive adequate oil feed during the engine start-up phase. It is intended as a suitable alternative to the commonly adopted 3-D CFD simulation, which requires very demanding computational resources. By introducing a detailed modelling technique, several modelling criteria are presented for the discretization of complex geometries not directly attributable to embedded submodels of the software. The validity of the procedure is assessed by running the filling simulation for a test case engine lubrication system considering different temperatures and comparing the results with the ones obtained through the state-of-the art CFD method. The result comparison concern both the flow pattern and filling time up to the users, revealing a good capability of predicting the filling time of the proposed method. Differences in simulation effort are considered as well, confirming great advantages of the proposed lumped parameter approach. Last model is dedicated to the simulation of external gear pumps, focusing on the internal phenomena. It extends the capabilities of the numerical tools already available in literature works by implementing peculiar features aimed at evaluating the internal forces, gear micro-motions and the instantaneous tip clearances through an open formulation. It is a powerful tool since it permits to predict the performance of the machine based on few geometrical parameters as well as evaluating the effects of possible design improvements. The modelling approach is applied to a test case external gear pump, and numerical results are compared to experimental data, demonstrating good predictive capabilities. The validated model is then utilized to simulate a potential design upgrade aimed at reducing the fluid borne noise by decreasing the pressure ripple, revealing the possibility to increase the pump performance by acting on relief grooves.