A NUMERICAL MODEL FOR THE SIMULATION OF EXTERNAL GEAR PUMPS

External gear pumps are the most widely employed source of power in hydraulic applications, allowing good performance and low manufacturing costs. The present paper reports the description of a numerical model for the simulation of these kind of machines, developed by the authors. The model has been implemented using the software AMESim®, introducing new in-house C++ models, with the main aim of an accurate prediction of the pressure ripple at the delivery port and the calculation the flow rate time course through the pump. In fact the reduction of flow pulsations is one of the crucial targets in the development of these machines. The fluid dynamic model of the pump is based on a finite volumes framework: each chamber presents uniform fluid proprieties and is connected with the adjoining ones by variable orifices. The pump is described by the interaction between a fluid dynamic model, that predicts the instantaneous pressures and the flow rates between the chambers, with a geometrical sub-model for the evaluation of the actual values of the variable volumes (defined by teeth, housing, and side wear plates) and the throat areas, as functions of the shaft angular position. This paper reports a deep description of the fluid dynamic model and a comparison between its numerical results and data available from experiments, showing how a correct evaluation of the flow when the chambers expand (and oil is pushed from the supply tank) or decrease (and oil is ejected into the outlet port) allows a good prediction of the pump characteristics. The results reported in the paper show how the model can be a powerful tool for design and development of external gear pumps, e.g. it easily allows the prediction of the maximum and minimum pressure reached inside the teeth space volumes, giving important information to prevent cavitation and damages as well as to reduce the pump noise. Moreover the simulation environment easily allows the evaluation of the pump behaviour when it works in a given hydraulic system