A generic design procedure to determine the optimal profile of porting grooves in external gear machines
In many positive displacement machines for high pressure hydraulic applications, the transitions of the displacement chamber from the inlet and outlet ports is realized through appropriate grooves. These grooves limit undesirable effects due to fluid compressibility such as: the instantaneous pressure peaks or localized cavitation inside the displacement chamber and the increment of port flow fluctuations. These effects result in instabilities and noise emission in these machines. Since the reduction of abovementioned effects is often achieved by a groove design that introduces a certain crossflow between the outlet and the inlet ports, volumetric efficiency is another important parameter to be considered in the design of such grooves. Typical examples of these grooves are those machined on the valve plate of axial piston machines (often referred as “silencing grooves” or “relief grooves”) or those present on the lateral bushings of external gear machines. The design of these grooves is often performed by the pump or motor manufacturers through empirical or simplified numerical procedures; and a well-established design procedure is not existing. This research presents an effort in formulating and establishing a design procedure to automatically determine the optimal designs of the grooves present on the lateral bushings of the external gear machine units. The optimization of the porting grooves is carried out in two steps, in the first step, optimal area of the connections in meshing region that connects the TSV to the porting grooves is determined; in the second step, a groove morphology is realized which can trace similar area of the connections obtained from step one. The proposed procedure has the important feature of not assuming a certain geometric morphology of the grooves. The proposed procedure does not assume a certain geometric morphology of the grooves, and it solves the multi-objective optimization problem of finding the best designs to simultaneously: 1) minimize flow fluctuations,; 2) minimize internal pressure peaks,; 3) minimize localized cavitation onset and; 4) maximize volumetric efficiency. This design procedure is implemented to optimize the relief grooves of one of the commercial external gear pump and comparisons of important pump performance features have been made. It is observed that the optimized grooves show a reduction of 58% in the pressure ripple energy compared to the reference grooves.^
Andrea Vacca, Purdue University.