In order to improve the fluid dynamic lubrication performance of slipper pair of valve distribution (digital distribution) axial piston pump, this paper proposes a theory analytical model of fluid dynamic lubrication for slipper pairs with different surface structures of valve distribution pump and its tribological optimization mechanism of surface microstructure topography. In the model, based on the finite volume method, the least square method combined with the trust region dogleg was proposed to solve the nonlinear system of equations of slipper dynamic balance. The fluid lubrication mechanism of slipper pairs with different surface structures was analyzed, the probability of overturning and eccentric wear of slipper pairs with complex surface structure and the viscous friction torque were quantitatively analyzed, and experimental research was conducted. The results show that the surface microstructure topography has great influence on the fluid lubrication performance of slipper pairs. Compared with before optimization, the friction torque of slipper with single-support belt, double-support belt, and four-support belt is decreased by 8.58%, 13.65%, and 17.07% at most, respectively, but the probability of overturning and eccentric wear of slipper with double-support belt and four-support belt is increased and the oil film becomes thicker. Reducing the friction loss and enhancing the anti-overturning ability of the slipper pair are often difficult to be compatible. The research results lay a theoretical and technical foundation for the optimization of lubrication performance of slipper pair of valve distribution pump.

In order to study the frictional lubrication characteristics of a piston pump under varying loads and speeds in actual work, mathematical models, such as a cylinder dynamics model, cylinder micro-motion model, and external return spherical bearing pair lubrication model, were established under full working conditions. The influence of different parameters on the lubrication characteristics of the external return mechanism under full working conditions was analyzed. The results show that in a working cycle, when the pump was at low working pressure, the maximum value of the maximum oil film pressure increased with an increase in the cylinder block speed, which is basically consistent with the ideal conditions. With an increase in the working pressure, the maximum value first decreased and then increased with an increase in the cylinder block speed. When the cylinder block speed was constant, the total friction power increased with an increase in the working pressure and the internal as well as external swash plates’ inclination; considering the contact surface roughness of a friction pair under full working conditions, the total friction power increased by 46.8% compared with the ideal working conditions. The axial leakage flow increased with an increase in the external swash plate inclination and remained unchanged with an increase in the internal swash plate inclination. This research is beneficial for improving the lubrication theory of the external return mechanism and lays a foundation for improving its working performance.

To study the lubrication and wear reduction characteristics of the QAL9-4 and 17-4pH textured friction pair during water lubrication, the dynamic pressure bearing and cavitation characteristics were analyzed using a computational fluid dynamics method. Then, based on 13 groups of samples with different depths, diameters, and area ratios, relevant frictional and wear tests were carried out. The results showed that the texture affected the pressure distribution in the textured region and improved the liquid film bearing capacity, which increased gradually as the equivalent Reynolds number increased. Under test conditions, the texture parameters had a significant influence on lubrication and wear reduction performance. The optimum texture diameter, the depth, and the area ratio were 300 µm, 40 µm, and 10%, respectively. The wear tracks on the textured specimens were small in size and shallow in depth compared to those on the non-textured specimens. The wear tracks on the textured specimens were regional, and there were more wear tracks in the area without micro-dimples. In summary, it was feasible to apply surface texture to the QAL9-4 and 17-4PH friction pair to improve the lubrication and wear reduction characteristics with water lubrication.

Aiming at the problem of the lack of a cooperation mechanism of combined relief valves, this paper proposes a new pressure-regulating and pressure-limiting combined relief valve. Combined with the ordinary relief valve dynamic characteristic analysis method, the dynamic model of the combined relief valve under normal working conditions was established, and its dynamic characteristics were simulated using Simulink. The results showed that the multi-pressure stabilization design of the combined relief valve improves its usability and stability. Under the same structural parameters, the overshoot of the combined relief valve was 5.7, and the response time was 12ms, which is better than the ordinary relief valve. Besides, it effectively improves the instability problems, such as the vibration and the large pressure fluctuation of the ordinary relief valve under high pressure and large flow conditions. When the sum of the effective force area on the upper side of the flange of the pressure-regulating valve core and the area of the tail vertebra is equal to the effective force area of the lower side of the flange of the pressure-regulating valve core, the dynamic performance of the relief valve is optimal. For example, if the effective force area under the flange is 1.8cm², then the inlet pressure overshoot is 2.8, and the response time is 10ms. An appropriate volume of the sensitive cavity, the quality of the valve core, and the fluid resistance of the pressure relief valve are factors that can effectively improve the dynamic performance of the pressure-regulating and pressure-limiting combined relief valve.

To study the flow characteristics of a new swashplate rotary valve distribution double-row axial piston pump, an instantaneous flow model was developed for the pump, the influences of structural parameters on the flow pulsation and uneven coefficient of flow were determined, and the ideal plunger distribution parameters were derived. On this basis, a valve distribution model was developed for the pump, the flow superposition process in the plunger cavity was analyzed, and the high-speed switching valve's control strategy was optimized. Additionally, the effects of parameters such as the plunger motion frequency, the plunger cavity's dead zone volume, the spool valve's preloading force, and the spool's equivalent mass on the flow characteristics were studied. The results show that the new pump had a small flow pulsation when there were five plungers in both the inner and outer rows and the dislocation angle was 18^∘. The plunger's reverse-suction effect at the moment when the discharge valve opened and the suction valve closed and the plunger cavity's dead zone volume size were the primary factors affecting the size of the pump's flow spike. The discharge valve's opening was delayed by 3 ms to be consistent with the suction valve's closing time; for this case, the flow peak was small and the volumetric efficiency was the highest. The discharge valve began to close 2 ms early and closed completely at the critical point when the plunger transferred from the discharge stroke to the suction stroke, which helped the suction valve to open on time and improved the pump's oil absorption capacity. The active opening and closing control of the discharge valve improved the coordination of the flow distribution to a large extent, reduced the hysteresis of the suction valve, and ultimately improved the pump's volumetric efficiency and flow stability. The results of this study can provide theoretical guidance for the flow control of balanced double-row axial piston pumps with valve distribution.

To improve the performance of electrochemical deburring for microhole drilling (MD-ECD), the distribution and dynamic change of the current density in the machining area during the electrolysis process were analyzed, and the synchronous change relationship between the current density and the burr profile was studied. The effects of process parameters, such as machining voltage U, initial machining gap d, electrolyte concentration C, and electrode radius r₁ on the deburring process, were studied. The results show that the magnitude of the current density value in the burr area reflects the MD-ECD’s deburring performance. The current density near the burr tip is high, and the material is preferentially removed. The non-processed area has a low current density and slow material removal. As the machining progresses, the burr tip becomes blunt and the current in the burr area gradually transfers to the non-machining area, resulting in the transfer of the material removal area from the burr area to the adjacent non-machining area. Then, a chamfer is formed at the orifice; the chamfer width is larger than the chamfer height. When U = 4 V, d = 0.35 mm, C = 12%, and r₁ = 0.4 mm, the burr removal efficiency and accuracy can be guaranteed. The chamfer width and chamfer height obtained from the test are 29 μm and 17 μm, and the burr removal effect is good.