Numerical analysis of the lubricant gap in external gear pumps considering micro level surface features

Abstract: The design procedure has made the manufactures through experience aware thatthe tolerances in gear machines plays a significant influence on the system. In liter-ature there is only a few studies that investigates the phenomena of the geometricalmicro details. This due to the complexity of the problem since it involves multipledomains and scales. This work will prove how it is possible to investigate the probleminvolving micro level details and the goal has been to study the effects with the aimof quantifying and proving the impact of a chamfer on the gears lateral side.The work has been performed by coupling the tooth space pressures solved byHYGESim (Hydralic Gear machines Simulator) with a numerical solver developed inan OpenFOAM environment. The simulations are carried out by solving Reynoldsequations which has been proven to give accurate solutions to problems involvingfluid films. Simulations involving both with and without the balancing squeeze termhas been performed.Two different chamfers has been compared to a case without a chamfer at a fixedand constant gap height. The different cases are compared to each other by firstseparation the terms in Reynolds equation and then comparing the leakages to thedrain and the power losses. It was found out that chamfer generates translationalsqueeze effects, which makes this study first of its kind. It was also found out that thegenerated hydrodynamic effects tends to increase with an increased chamfer. When itcomes to the leakages, the chamfer has a positive effect, i.e decreased leakages. Whencomparing the power losses for one of the chamfers, the smaller one gives decreasedlosses while the bigger one generates increased losses.Simulations are also performed with the normal squeeze term taken into account,this to balance the generated forces by tilting the bushing. The results indicate thatthe hydrodynamic pressures generated to balance the bushing mainly originate fromthe tilt and not from the chamfer, even though the chamfer tends to decrease themaximum generated pressure and decreasing the tilt constant, t.