###### Abstract  
The integrated electric-hydraulic pump has the advantages of no leakage, compact structure, and low noise. Here, we propose a novel integrated electric-hydraulic vane pump (IEHVP) to solve the problem of low reliability of the existing ordinary axially arranged hydraulic oil source in the harsh deep-sea environments. IEVP combines an external-rotor brushless motor and a balanced vane pump. In order to obtain the external characteristic curve of the designed IEHVP, the theoretical analysis of coupling analysis between the operating characteristics of the electric motor and the vane pump is designed. The results reveal that the output flow of the proposed IEHVP increases linearly with the increase of the input voltage and decreases non-linearly as the outlet pressure increase. Finally, the proposed IEHVP is tested. The relationship between the output flow and volumetric efficiency and its outlet pressure and input voltage is obtained. The experimental results verify the characteristics of the proposed IEHVP design. integrated electro-hydraulic vane pump; external characteristic analysis; experimental verification +
Footnote †: journal: _Applied_  
other is to combine the rotor of the driving motor and the hydraulic pump. Although the former has made significant improvements in space occupation and leakage prevention, it is still essentially a mechanical connection between an electric motor and a hydraulic pump, which causes the loud noise and volume to be unavoidable. In contrast, the latter is a coupling design of the electric motor rotor and the hydraulic pump, which can eliminate the axial mechanical coupling to reduce the volume [8; 9; 10; 11]. Integrated electric hydraulic pumps present a diversified development trend according to different operation requirements. Figure 1 shows that EPAI of VOITH integrates the internal gear pump in the rotor of the three-phase asynchronous motor [12]. When working, the motor stator winding is forced to cool by the circulating hydraulic oil, and the external fan is no longer necessary for heat dissipation. The structure is 50% smaller than the conventional hydraulic power unit, and the noise is significantly reduced [13; 14]. Figure 2 demonstrates the hydraulic motor vane pump designed by [PERSON] et al. The pump core is inserted inside the motor rotor [15; 16; 17]. The test results indicate that compared to the traditional motor-pump unit, the volume, the axial size, and the noise of the motor vane pump are reduced by 50%, 61%, and about 7 dB, respectively. Nevertheless, the above two designs belong to the combination of a constant delivery pump and a constant speed motor, which is difficult to require a higher matching between the relevant parameters of the hydraulic pump and the motor. Although an external frequency converter can be used to adjust the motor speed, it increases the complexity and economic cost of the entire device. Figure 1: EPAI of VOITH. Figure 2: The hydraulic motor vane pump designed by [PERSON]. Figure 3 indicates that the RP series rotary pump of Daikin Company integrates the plunger pump in the rotor of the asynchronous motor, and the displacement of the device can be changed by changing the inclination angle of the plunger pump swash plate [18]. The RP series rotor pump comprises a variable pump and a constant speed motor. The motor still maintains a higher rated speed even when running under no-load or light load conditions, resulting in a lot of energy waste, low efficiency, and loud noise. Meanwhile, the structure of the variable displacement device is more complex, and the mass is larger. Figure 4 displays that the integrated electric hydraulic pump designed by Beihang University [19] integrates the internal gear pump and the axial piston pump in the rotor of a brushless DC motor or a permanent magnet synchronous motor.