Dynamic Modeling and Design of a Radial Hydrostatic Piston Pump for Integrated Electric Motor-Pump

Abstract There is a current trend towards the electrification of mobile machines that have traditionally been dominated by diesel engine-driven hydraulics, necessitating hydraulic pumps that are driven by electric motors. The benefits to power density are possibly by integrating an electric motor and hydraulic pump inside a single casing. In comparison to coupling a separate electric motor and pump, the integrated machine eliminates a set of bearings and a shaft seal. Additionally, the leakage from the hydraulic pump can be used as a coolant for the electrical machine, improving power density. In this paper, a hydrostatic radial piston pump is proposed to integrate with an axial flux PM machine. This pump uses spherical head pistons that can tilt while reciprocating inside the cylinders, eliminating the need for joints at the slippers. To reduce the frictional loss between the slipper pad and the cam at high speeds, the cam freely rotates. In the earlier work, a detailed model of the pump was developed, including the losses, and the pump performance was predicted for an integrated machine. This work focuses on the standalone pump prototype test, which required a separate driver and shaft sealing unlike the integrated machine. The pump mathematical model was therefore modified to account for the shaft seal losses and experimental churning losses. With these modifications, the standalone pump performance was predicted from the mathematical model and then compared with experimental results for an actual pump prototype.