Analysis and tests of the taper angle of flow distribution pair in a piston type energy recovery motor

Abstract: A piston-type energy recovery motor is integrated the hydraulic motor and generator into a new generation of hydraulic energy recovery device. Among them, the flow distribution (friction) pair is composed of the cylinder block and flow distribution shaft. The taper angle of the friction surface on the flow distribution pair can pose an important impact on the oil flow distribution, load-bearing, friction and wear characteristics of the motor. In this study, an optimal combination of the taper angle was explored using the theoretical analysis, numerical simulation, and experimental test. Firstly, the available range of a taper angle was determined, according to the structure and size of the flow distribution pair in the motor. Four taper angles of 36°, 39°, 42°, and 45°were then selected as the research objects. Secondly, the fluid domain models were established to grid the four taper distribution pairs. The pressure contours and velocity vector diagrams were obtained for the four taper angles, in order to analyze the oil pressure fluctuation in the piston chamber and the leakage in the oil film. The solid domain grid models of distribution pairs were achieved at the taper angles of 42°and 45°and then to evaluate the stress and deformation of the cylinder block and the flow distribution shaft. Finally, the friction test pieces were made according to the motion and friction surface between the cylinder and the flow distribution shaft for the friction test. Specifically, the materials of the upper and lower test pieces were matched with those of the cylinder block and flow distribution shaft. The friction coefficient and wear amount of pairs were obtained at the taper angles of 42°and 45°during friction and wear experiments. The result showed that the oil pressures were 4.66 and 4.62 MPa in the piston chamber located in the high-pressure dead point at the taper angles of 42°and 45°, respectively, whereas, the amplitudes of pressure fluctuation were 3.307 and 3.246 MPa, respectively. Furthermore, the amplitudes of oil pressure fluctuation in the piston chamber were 0.324 and 0.322 MPa, respectively, in the process of connection between the piston chamber and the high pressure oil hole. There were the smaller amplitudes in the three-group data among the four taper angles. As such, the higher volume efficiency of the motor was achieved in the smaller leakage of the flow distribution pair, where the oil was transited smoothly at the taper angles of 42°and 45°in the piston chamber. The maximum equivalent stress of the flow distribution shaft was much less than the yield strength at the taper angle of 42°and 45°. There was 0.74 percentage points larger proportion of the maximum equivalent stress to the yield strength of cylinder block at the taper angle of 42°, compared with the taper angle of 45°. The maximum deformation of cylinder block was 0.251 μm. There was no failure risk of strength invalidation for the components of flow distribution pair at the two taper angles. Only a slightly impact was observed on the normal operation of the flow distribution pair, although the slight elastic deformation existed in this case. The average friction coefficient was less than 0.012 at the taper angle of 42°, indicating the small fluctuation and excellent stability. More importantly, the wear rates of the upper and lower pieces were 1.966×10-6 and 7.601×10-6 mm3/(N·mm) less at the taper angle of 42°than those of 45°, respectively. Therefore, the taper angle of 42° was conducive to the stable and efficient operation of the energy recovery motor. The finding can provide a strong reference to design the flow distribution pair of piston-type energy recovery motor.