Sintered internal rotor gears are widely used in oil pumps for engines and transmissions, and Sumitomo Electric of Itami, Japan, is one of the leaders in developing and commercialising sintered rotors featuring proprietary tooth profiles, which improve the efficiency of oil pumps and hence reduce energy losses attributed to the pumps.
Energy losses are said to account for approx. 10% of total engine energy loss in the case of an engine lubrication oil pump which increases to 20-30% for automatic transmissions, and between 5 and 10% for oil pumps used in hybrid vehicles. The typical structure and mechanism of an oil pump with internal sintered inner and outer rotors is shown in Fig. 1 with the outer rotor having one more tooth than the inner one.
Sumitomo Electric has now added a new ‘Geocloid’ design of oil pump rotors which the company states allows oil pumps to be downsized to reduce drive torque, but without sacrificing the pump’s volumetric efficiency. As can be seen in Fig.2 the new Geocloid motor is 11% smaller in diameter compared with the ‘Parachoid’ design but has the same discharge volume.
In a report by K. Yoshida, etal, in SEI Technical Review, No.74, 2012, the company reports that it started supplying the new Geocloid oil pump rotors for use in hybrid vehicle transmissions in 2011. Sumitomo Electric is also developing the next generation tooth profile to improve the latest design even further.
Posted by: Paul Whittaker, Editor ipmd.net, [email protected]