Design of Rotor for Internal Gear Pump Using Cycloid and Circular-Arc Curves

Abstract

In the case of internal gear pumps, the eccentricity of the outer rotor, which resembles a circular lobe, must be limited to a certain value in order to avoid the formation of cusps and loops; furthermore, the tip width of the inner rotor, which has a hypocycloid curve and an epicycloid curve, should not be allowed to exceed the limit value. In this study, we suggest that the tip width of the inner rotor be controlled by inserting a circular-arc curve between the hypocycloid and epicycloid curves. We also suggest that the outer rotor be designed using the closed-form equation for the inner rotor and the width correction coefficient. Thus, it is possible to design a gerotor for which there is no upper limit on the eccentricity, as in this case, undercut is prevented and there is no restriction on the tip width. We also develop an automated program for rotor design and calculation of the flow rate and flow rate irregularity. We demonstrate the superior performance of the gerotor developed in this study by analyzing the internal fluid flow using a commercial computational fluid dynamics (CFD)-code.