Potential of a numerical tool for the simulation of the flow in external gear machines

This paper deals with the numerical prediction of the flow in external gear machine. As well known, a crucial aspect of gear machines is the variable offset of the axes of rotation of both gears in operation, as produced by pressure distribution in the chamber: which means that gears work in different positions from the nominal ones, i.e. those deduced from the machine drawings. In this work, on the basis of simulated results, several considerations about the effects of the actual position of gears centres on the main characteristics of the flow in external gear machine are developed. The model used for the calculations has been developed by the authors and is named HYGESim (HYdraulic Gear machines Simulator). HYGESim permits a detailed evaluation of the flow inside gear pumps and motors, accounting for the main geometrical design parameters (e.g. shape and dimensions of the grooves on the bearing blocks, tooth profile, etc.). HYGESim consists of three different models strictly connected: a geometrical model (developed in the Pro/Engineer® environment), a fluid dynamic model and a module for the evaluation of forces and toques acting on the gears. These two latter are lumped parameters models (implemented in the AMESim® environment), utilizing a high number of parametric sub-models, written directly in C++ language. Through the latest improvements implemented in HYGESim, the results discussed in the paper – referring to comparisons with data coming from experiments carried out on a stock pump – highlight how this simulation tool can be useful for an estimation of the actual position of both gears as a function of load pressure and shaft speed.