Design, Manufacture and Performance of Internal Gear Pumps : 1st Report, Non-Involute Type Pumps for Easy Manufacture

Abstract

For easy manufacture of internal gear pumps, an internal gear with a convex tooth profile and an external gear, of which tooth-top edge contacts with the convex profile, are used for the gear pumps. Gearing theory of these gears and the theoretical delivery of the internal gear pumps with these gears are clarified. The prominent characteristic found in the gear pumps is that the theoretical torque caused by delivery pressure is zero for the external gear (idler). In practice, a small value of the resistance torque appears on the idler due to viscous friction, etc. It is shown that the resistance torque has no detrimental effects on the tooth surface up to a delivery pressure of about 2 MPa in the present experiments because the Hertzian contact pressure is less than the allowable contact stress of a low hardness steel when the tooth-top edge is rounded to a radius of about 0.5 mm. Six kinds of gear pumps were designed and made by the authors, and almost all characteristics of these gear pumps were clarified by experiments with the support of the theoretical results obtained in the present investigation.