Abstract: Electro-hydraulic pump(EHP) is a new type of hydraulic power unit. It highly fuses the electric motor and hydraulic pump which share the same rotor and housing, and has such advantages as more compact structure, higher power-to-weight ratio, etc. The energy conversion efficiency of EHP is an important indicator of the great concern to the industry. An axial piston EHP is introduced; the losses of electromagnetic, mechanical and volumetric are analyzed; the corresponding partial efficiencies and overall efficiency calculation models of EHP are established; the oil gap loss, the partial efficiencies as well as overall efficiency of EHP varying with speed, pressure and temperature are respectively presented, and further influences by the oil gap loss and the efficiency characteristics of EHP are analyzed. With the contrast between theoretical calculation model and experimental results, an accurate calculation model is available. The calculation depicts that, at 50 ℃ with the speed of 4000 r/min and the pressure of 28 MPa, the oil gap loss of EHP is 1.85%, which is much lower than the van and mechanical losses of motors in traditional motor-pump sets, and the overall energy conversion efficiency of the axial piston EHP is 81.2%, which is higher than motor-pump sets.

Key words: electro-hydraulic pump;axial piston electro-hydraulic pump(EHP);axial piston pump;electric motor;efficiency;oil gap loss