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One possibility to achieve a higher power density is to increase the rotational speed of the power unit. Schröter et al. illustrate the potential of high-speed drives and compare a standard motor (nmax = 3 000 rpm and P = 15 kW) with a high-speed drive with two shiftable gear stages (nmax = 22 500 rpm, P = 22 kW) and a directly coupled high-speed motor (nmax = 35 000 rpm, P = 15 kW, without housing) /4/. They also showed that the power to weight ratio is increased by factor 5 for the high-speed drive and by factor 34 for the high-speed motor, compared to the standard motor /4/. Furthermore, the power density of the hydraulic pump can be increased by raising the rotational speed. The aim of the study is to increase the rotational speed limit of the pump up to 10 000 rpm. For this purpose, an internal gear pump is chosen. As part of the project, an electro-mechanical high-speed drive will be developed. The high peripheral speed poses challenges for the design of a gear stage, such as an increased risk of scuffing damages, a more complex lubrication, as well as high requirements for the machine elements, such as bearing and sealing. Furthermore, increasing the rotational speed of the internal gear pump entails addressing topics, such as cavitation, overheating and filling problems of the tooth spaces. In this paper, the authors compare different pump geometries. The aim of this work is to evaluate the influence of the gear dimensions for the rotational speed limit of internal gear pumps. A Computational Fluid Dynamics (CFD) simulation model is built up. Thereby, four different pump variants are analysed qualitatively concerning their tendency for cavitation. The simulation results affect the future concept for the high-speed pump.

Design study of a high speed power unit for electro hydraulic actuators (EHA) in mobile applications