Increasing the rotating speed is considered as an efficient approach to upgrade the power-to-weight ratio in an axial piston pump, but penalized by more leakage and more severe wear resulting from the adverse cylinder block tilt. Previous studies mainly focused on the bearing characteristic of the valve plate/cylinder block pair, but the spline coupling also plays a key role in the undesired cylinder block tilt, which has been little studied. A theoretical model for the rotating assembly is presented to investigate the effect of the spline coupling length on the cylinder block tilt and the performance of the valve plate/cylinder block pair. A typical high-speed axial piston pump with the displacement of 5.2 mL/r at 10,000 r/min was studied by simulation and experiment. It shows that the optimal spline coupling length is one value increased by 2 mm from the original, bringing a remarkable leakage reduction under the high-speed condition by decreasing the cylinder block tilting angle. The experiment result matches well with the simulation. The influences of the spline coupling on the cylinder block tilt and the leakage were demonstrated.

Increasing the rotating speed of the axial piston pump is effective in improving the power-to-weight ratio. However, the cylinder block tilts severely at high speed, which causes significant leakage. In this paper, a dynamic model of the rotating assembly in a high-speed axial piston pump is established to investigate the tilt behavior of the cylinder block when fully considering the relevant factors within the whole rotating assembly, such as the tilt moments due to the inertia of piston-slipper assemblies and the periodic pressure in piston chambers, the elastic deformation of the shaft, and the nonlinear bearing characteristics of the oil film. Furthermore, the cylinder block tilt behavior is measured to validate the established dynamic model. The theoretical and experimental results show that the tilt angle of the cylinder block increases with the increasing rotating speed. And at high rotating speed, the cylinder block tilts much more severely under low outlet pressure. Finally, the bearing capacities of the oil film and the spline coupling are analyzed to find out the dominant factors affecting the tilt behavior of the cylinder block.