Because of its excellent tribological performance, polyether–ether–ketone (PEEK)-based coatings have been used extensively under mixed and boundary water-lubrication conditions. To verify that the PEEK-based coating is applicable to aviation kerosene, one advanced coating was proposed and two typical metals, namely, alloy steel 38CrMoAlA and tin bronze ZQPb17-4-4, were selected as counterparts. Four sets of experiments that involved a scuffing (step load) and Stribeck curve (step speed), constant load, and strengthened load were carried out, which showed that the counterpart material’s properties, such as its hardness, thermal conductivity, and composition, had an important effect on the tribological performance of the PEEK-based coating. Scuffing experiments showed that the PEEK-based coating against ZQPb17-4-4 exhibited better scuffing performance. Stribeck curve experiments showed that the PEEK-based coating against 38CrMoAlA was under the mixed lubrication condition over a wider range of speeds, and wear experiments (constant load and strengthened load) showed that the PEEK-based coating against 38CrMoAlA exhibited a relatively low coefficient of friction and low wear rate. The formation and appearance of the tribofilm on the surface of the counterparts influenced the wear mechanism of the PEEK-based coating. The PEEK-based coating showed excellent properties, especially when rubbed against 38CrMoAlA.

To investigate the effect of the number of teeth on the cavitation characteristics of the cavity at high speed, a simulation model of the flow field with six to nine teeth of the gear pump is created. To study the influence of the number of teeth on the internal cavitation characteristics of the circular arc spiral gear pump and its outlet flow characteristics under high-speed conditions. The results show that the gear pump cavitation characteristics are significantly affected by the number of teeth and the speed; as the number of teeth increases, the extent of the effect of cavitation on the outlet flow decreases significantly. The critical speeds at which the gas volume fraction of the six- to nine-teeth gear pump changes significantly are 9000 RPM, 9000 RPM, 10,000 RPM, and 10,000 RPM, respectively, and after exceeding these critical speeds, the volumetric efficiency begins to decrease while the gas content in the cavity increases abruptly, which seriously affects the continuity and stability of the outlet flow. In addition, when designing gear pumps, increasing the number of teeth helps to inhibit cavitation, improve volumetric efficiency, and reduce pulsating flow.

Hydro-pneumatic springs often work under high pressure and alternating load conditions, which can easily cause seal damage, leakage, and serious failure. Relevant studies have shown that the dynamic seal failure of hydro-pneumatic springs is the main cause of hydro-pneumatic spring failure, and the sealing performance of GS sealing rings directly determines the service life of hydro-pneumatic springs. The influence of different sealing structure parameters on the sealing performance of GS sealing of hydro-pneumatic springs has been studied, which can provide effective theoretical guidance for the design of sealing structures related to hydro-pneumatic springs. However, the existing research on hydro-pneumatic springs mainly focuses on the characteristics of damping and stiffness; there is a relative lack of research on sealing performance and sealing structure, and the performance change law of GS seals under different working conditions is unclear. In this paper, a GS seal ring is selected as the main seal of the hydro-pneumatic spring, the material parameters of the GS seal ring are obtained via the single-axis compression test, and the finite element simulation method is used to establish the sealing model under different compression ratios of 10–30% and different pressure impacts of 5–30 MPa. By doing so, the stress nephogram, sealing ring shape, and sealing contact pressure of the GS sealing ring under different simulation parameters are obtained. From the test results, the decrease in compression ratio after the wear of the sealing ring is the main reason for the seal leakage of the hydro-pneumatic spring. The maximum contact stress of the sealing ring occurs at the lip of the step ring, and the maximum sealing pressure of the sealing ring is determined by the contact pressure of sealing surfaces II and III. The sealing performance of the GS-type combination sealing ring is affected by the compression ratio of the sealing ring and the impact pressure; when the compression ratio of the sealing ring is 15%, the sealing ring can meet the sealing work needs below 25 MPa. The research results provide a theoretical basis for the design of GS sealing of hydro-pneumatic springs and the effective improvement of the life and reliability of related equipment.

A nonlinear friction(moment) compensation controller of force (moment) control system is developed. Friction is one of the important factors which affect system performance. Due to the influence of friction nonlinearity to the electro-hydraulic passive force servo system, we develop a nonlinear friction(moment) controller which is applied in force(moment) control system. This controller, which is based on the Lyapunov theorem, doesn't need precision friction model. It only needs parameters upper bounds. It is a nonlinear friction (moment) compensation controller which is based on non-precision friction model. The simulation results show that compared with PID controller, the controller designed in this paper is better at eliminating the friction(moment) influence. This controller has the use for reference in friction(moment) eliminating of low moment or low velocity force(moment) control system.

In order to study the strong force/position coupling problem of passive electro-hydraulic force servo system, taking the valve control swing motor of passive electro-hydraulic force servo system as an object, a new principle of structure coupling is proposed, which based on the analysis of the force/position coupling mechanism and influence factors. The concrete way is to design the load actuator into a compound bilayer structure, which the outer synchronous motor is used to track the bearing motor for position synchronization control, and the inner motor is used to load. Through the load actuator of the compound structure, the passive load is modified into active load, and the problem of force/position coupling is solved fundamentally. The principle of parameter matching, the design of the seal, and the structure of the compound swing motor are given, and the rationality of the oil duct in the inner and outer motors is simulated and tested. Finally, through simulation analysis of passive electro-hydraulic force servo system under small gradient loading, the correctness and effectiveness of structure decoupling are verified. Furthermore, it provides a new approach for the development of passive electro-hydraulic force servo system for ultimate parameter and performance index.

To address the weak adaptability of the passive X-type interconnection hydropneumatic suspension to different road surfaces and the poor performance of traditional single-control methods, an active controller based on the extended state observer (ESO) and model predictive control (MPC) was designed for the X-type interconnection hydropneumatic suspension of heavy-duty special vehicles. First, the structure of the X-type interconnection hydropneumatic suspension was analyzed. A three-degree-of-freedom (DOF) linearized hydropneumatic suspension model with disturbances was established based of the seven-DOF full-vehicle model of the active X-type interconnection hydropneumatic suspension. The disturbances were analyzed, and a disturbance ESO was developed. A controller for MPC was subsequently designed based on the linearized state space model, forming a controller for ESO-MPC. Simulations were conducted on both C-class random roads and convex pavement, with fuzzy PID control included for comparison. The simulation results demonstrated that, compared with the passive X-type interconnection hydropneumatic suspension, the active suspension with the controller for ESO-MPC achieved reductions in body vertical acceleration, pitch angular acceleration, and roll angular acceleration of 18.7%, 24.7%, and 26.1%, respectively, on Class C random roads. With fuzzy PID control, the reductions were 5.59%, 7.99%, and 15.54%, respectively. For convex pavement, the controller for ESO-MPC reduced body vertical acceleration, pitch angular acceleration, and roll angular acceleration by 36.5%, 21.2%, and 18.1%, respectively, whereas fuzzy PID control resulted in reductions of 14.04%, 10.6%, and 7.92%, respectively. Compared with fuzzy PID control, the controller for ESO-MPC significantly improved the performance of the hydropneumatic suspension system, achieving precise control of the X-type interconnection hydropneumatic suspension system for heavy-duty special vehicles, thereby enhancing ride comfort and stability.