In order to reveal the development laws of cavitation during high-speed operation of gear pumps, the oil suction characteristics of high-power dual gear pump for wheel loaders were studied. The effects of speed and suction pressure on the cavitation and output flow characteristics of the dual gear pump were analyzed through full flow field simulation and test. The results show that the critical speed for significant cavitation in the dual gear pump is 2400 r/min. When the speed exceeds 2400 r/min, the gas content inside the pump increases sharply, which has serious impact on the continuity and stability of the output flow. The critical suction pressure of the dual pump is 0.19 MPa and the output flow pulsation will increase if the suction port pressure continues to increase. The critical suction pressure of the dual gear pump is 0.19 MPa. If the suction pressure is continued to increase, the flow pulsation of the pump would be also increased. Compared with the suction pressure of 0.1 MPa and 0.19 MPa, when the suction pressure at 0.19 MPa, the gas volume fraction of gear pair 1 and gear pair 2 decreases by 0.059 and 0.067 respectively, and the effective flow rate increases by 7.96% and 9.24%, respectively. By appropriately increasing the inlet pressure of the pump, there is a significant improvement effect on the suppression of cavitation and the improvement of effective flow rate in gear pump, which has positive engineering practical significance.

Pilot-operated electro-hydraulic proportional relief valve is a pressure control valve that is used to control the oil pressure in the system. It can control the electromagnetic force with electric signal according to the requirements of working conditions, so as to achieve the pressure control of the hydraulic system, and is composed of pilot valve, main valve and hand-adjustable safety valve. Due to the control valve port flow state is complex, the use of flow experience formula and the traditional hydrodynamic formula is difficult to accurately calculate the orifice flow and spool hydrodynamic force, resulting in large differences between the mathematical model calculations and the experiments. In order to accurately obtain the static characteristics of the relief valve, the Fluent software is used to simulate the flow field of the main valve and pilot valve to obtain the spool force and orifice flow under different orifice openings and differential pressures. The interpolation model is obtained by interpolating the spool force and orifice flow, according to which the static mathematical model is solved to obtain the static characteristic curve of the relief valve. The results show that the static characteristic curve obtained from the interpolation model is more consistent with the experiment curve.

Taking a post compensated flow sharing multi-way valve as the research object. Under the condition of unsaturated flow, it analyzes the pressure compensation function of the compensator during compound action, and the characteristic of the compensating pressure varying with load was investigated. By analyzing the influence of the flow area for main spool and the minimum opening of the compensator on the flow of each action, the theoretical calculation formula of variable load compound action flow distribution is proposed, considering the influence of those factors. The multi-way valve compound action experiment is carried out to verify it. The error analysis establishes its certain accuracy, which provides a theoretical basis for the flow distribution design of the multi-way valve in actual application.

In view of the complex structure of the hydraulic bracket directional valve components to form irregular flow paths, the traditional primary momentum theorem can not accurately find out the spool flow force, as well as due to the flow force is too large or unstable, the dynamic and static characteristics of the valve is reduced, with the bracket directional valve as the object, based on the analysis of its structural composition and principle of operation, a division of the whole basin control volume method is put forward. The momentum theorem is used to analyze the amount of momentum change in each control volume, and the influence of structural parameters of upstream and downstream components of the spool on the flow force is considered, so that the steady-state flow force formula of the spool is derived more accurately, and theoretical calculations are carried out. By analyzing the formula, the method of optimizing the structural parameters of the valve components to compensate the steady-state flow force is derived, and the change rule of steady-state flow force with the spool opening is simulated by CFD method. The results show that after the optimization of structural parameters, the peak and change amplitude of the flow force suffered by the spool are lower than the original structure of the flow force. After optimizing the inner diameter structure of the valve sleeve, the peak flow force and the amplitude of change were reduced by 56.25% and 48.12% respectively compared to the original structure. After optimizing the diameter of the top rod of the return spool, the peak value and variation amplitude of the flow force were reduced by 28.79% and 32.71% respectively compared to the original structure. After optimizing the inclination angle of the return spool end face, the peak value and variation amplitude of flow force were reduced by 31.87% and 37.16% respectively compared to the original structure, which effectively alleviates the problem of reduced dynamic and static performance of the valve due to the steady state flow force applied to the spool of the stent-operated directional valve.

The sealing performance and service life of metal hard sealed tri-eccentric butterfly valve are determined by the sealing specific pressure in a closed state, and optimizing the structure parameter of the metal hard sealing components is very important. The DN600 tri-eccentric butterfly valve is taken as the research object. Using the finite element analysis method, the distribution law of the sealing specific pressure on the sealing surface is analyzed. The circumferential clearance index of the sealing mating surface is proposed to estimate the sealing performance of the butterfly valve. The Box-Behnken response surface optimization method is used to optimize the structure of the sealing component. The influence of the cutting thickness of the major, minor diameter ends of the composite valve plate seat, the diameter of the composite valve plate seat and their interaction on the maximum sealing specific pressure of the sealing surface is discussed, and a optimal design solution is obtained. The research results show that the maximum sealing specific pressure of the sealing surface is dropped from 202.96 MPa to 128.44 MPa after optimizing the composite valve plate seat parameters, and the sealing performance of the valve is still good. The reliability of the sealing performance of the optimized butterfly valve is verified through a closed pressure sealing test.

The slide valve integrated into existing valve-controlled digital hydraulic cylinder usually adopts a full-circular opening, resulting in high flow gain and significant hydraulic forces on the valve spool, which seriously affect the dynamic response characteristics during startup and switching. This article focuses on six typical non-circular opening value structures, calculates the flow area of each valve spool throttle groove, and determines the structural parameters of one-section stage (U, V, K shape) and two-section stage (UU, UV, UK shape) throttle groove under the same flow area. The response of the digital hydraulic cylinder with different non-circular opening slide valve under step input signals and step load disturbance were studied and compared. The simulation and experimental results show that, compared to other valve port forms, the digital hydraulic cylinder has a better response to the step input signals when the throttle groove adopts K-shaped and UK-shaped structures. Compared to UK-shaped throttle groove, when the valve core adopts the K-shaped throttle groove, the load stiffness of the digital hydraulic cylinder controlled by the slide valve is better, and the speed impact is smaller, but the working pressure of the piston rodless cavity is slower. Additionally, with UK-shaped throttle groove, the digital hydraulic cylinder controlled by the slide valve exhibits faster response speeds under the same load interference.

Pilot valve is the key structure of continuous damping control shock absorber solenoid valve, which mainly regulates the opening pressure of the main relief valve, and its performance directly affects the damping characteristics of continuous damping control shock absorber. Taking a double-reset continuous damping control shock absorber pilot valve as the research object, firstly, Maxwell, Femm simulation and experimental data of the pilot valve are compared to verify the correctness of the simulation model. Then, the effects of enamelled wire diameter, enamelled wire temperature resistance class, soft magnetic material and structure size on the performance of the pilot valve are analyzed through parametric simulation and temperature rise test. The results show that the electromagnetic force is positively correlated with the wire diameter, and the steady force characteristic of the pilot valve deteriorates gradually when the wire diameter increases to the critical point of 0.45 mm. The temperature resistance grade of the enameled wire 240 ℃ limits the maximum operating current 2 A of the pilot valve, the knee position of the soft magnetic material affects the steady force characteristic of the pilot valve, and the performance of the pilot valve is improved by reducing the lateral clearance as much as possible. The height of the magnetic permeator has the most significant effect on the performance of the pilot valve. The research aims to provide a useful theoretical reference for the design of continuous damping control shock absorber pilot valve.

Online wear state recognition of key friction pairs in the axial piston pump is crucial for ensuring the stability and reliability of the whole hydraulic transmission and control system. However, wear state recognition performance is always hindered by strong noise interference in real working conditions. Although wear state recognition models can enhance noise robustness through adversarial training, their large number of parameters limits the application on edge computing devices. To balance noise robustness and model scale, a lightweight method based on adversarial distillation for online wear state recognition is proposed. A student model and a teacher model based on one dimension convolutional neural network are designed. The student model generates adversarial examples as a knowledge transfer dataset and learns robust feature knowledge from the teacher model through knowledge distillation. Through fault injection, comparison experiments, and ablation experiments, the proposed method demonstrates strong noise robustness and lightweight model structure advantages. Edge deployment and online verification experiments show that the proposed method can accurately recognize the wear state of the axial piston pump in real time.

In order to investigate the influence of the centrifugal turbine self-pressurizing device on the flow characteristics of the high-speed axial piston pump, a simulation model of the axial piston pump was established, and the pressure characteristics, velocity characteristics and cavitation characteristics of the whole basin flow field inside the pump when the centrifugal turbine was coupled with the piston pump were investigated by CFD simulation. The study shows that the oil suction capacity of the axial piston pump assembled with centrifugal turbine is significantly improved, and it has inhibiting effect on jet cavitation and suction cavitation, among which the inhibiting effect on suction cavitation is the most significant. After the application of the turbocharging system, the time-averaged gas phase volume of a single piston cavity during one week of rotation was reduced from 59.54 mm³ to 1.66 mm³, the maximum gas phase volume fraction was reduced from 0.155 to 0.029, and the jet velocity in the damping groove area was reduced from 100 m/s to 75 m/s, while the power consumed by the turbine accounted for 9.7% of the axial power of the piston pump.

Takes the parallel liquid-filled pipelines of a certain type of automobile turbocharger as the research object, and adopts a research method combining simulation and experimental verification to study the fatigue failure problem of the liquid-filled pipelines under random vibration.Firstly, the fluid-structure coupling dynamic model of the liquid-filled pipelines is established, and the accuracy of the model is verified by modal test.Secondly, based on the established dynamic model and the S-N curve measured by the pipelines the fatigue life of the liquid-filled pipelines under the random vibration load spectrum is further predicted, and compared with the experimental results. Finally, the fatigue life of the liquid-filled pipelines is improved by optimizing the wave height and the wall thickness of the bellows. The research conclusion shows that the fatigue life of the liquid-filled pipelines increases and then decreases with the increase of the wave height dimension and wall thickness dimension of the bellows. When the bellows wave height and wall thickness are adjusted to 3.5 mm and 0.33 mm, respectively, the optimization effect is obvious, and the expected fatigue life of liquid-filled pipelines is increased from 1.056×10⁶ times to 1.80×10⁷ times.

For the high performance electro-hydraulic proportional valve required large thrust drive, five structural forms of voice coil motor are proposed. Using the electromagnetic simulation tool ANSYS Maxwell, the thrust and magnetic field distribution characteristics of voice coil motors with different structures are calculated, and the effects of core radius and coil displacement on the thrust and magnetic field distribution of voice coil motors with different structures are analyzed. The results show that among the five structures, the internal magnetic type without iron core, the coil tightly attached to the shell, and the segmented design of the permanent magnet had the maximum thrust, reaching 75.29 N, which was verified through experiments; Adding magnetic rings on both sides of the permanent magnet and appropriately segmenting the permanent magnet can effectively enhance the thrust of the voice coil motor.

The reason for the abnormal ejection of the actuator cylinder of an aircraft hatch cover is that the oil contains gas, which leads to the decrease of the volumetric modulus of elasticity of the oil, the increase of compressibility, and the easy occurrence of the ejection phenomenon, and the relationship between the gas content and the volumetric modulus of elasticity of the oil is obtained based on the IFAS model. The sealing area of the hydraulic maneuvering system of the hatch cover is sealed by O-ring, but the existence of rough surface features of the key components constitutes a gas leakage channel, which leads to the mixing of gas in the hydraulic maneuvering system of the hatch cover. Therefore, this paper proposes a leakage rate calculation method based on the Roth model, in which the contact relationship between the O-ring and the metal rough surface is regarded as the contact relationship between the elastic metal smooth surface and the rigid metal rough surface, and the triangular peaks of the metal roughness surface contour are arranged in a homogeneous manner, so that the leakage path is defined as a trapezoidal channel. Based on the finite element software ABAQUS, the sealing performance coefficient of the seal is calculated, and the effects of surface roughness as well as bias loading condition on the gas leakage rate are analyzed, and finally, the results are compared with the theoretical results by ANSYS simulation analysis. This work has important guiding significance for the design of high-precision seal structure processing.

The cylinder speed is controlled by the speed control valve in the circuit. The cushion valve affects the energy absorption of the cushioning device. For optimal cushioning and improved cylinder efficiency, two valves must be adjusted based on a specific openness relationship. A cylinder cushioning test bench is built to conduct experiments and find the corresponding relationship between the number of valve turns. An AMESim model simulates the cushioning effect at various valve openings. The sonic velocity discharge method measures the effective throttle area of pneumatic components, revealing the area matching relationship between the cushion valve and speed control valve when effective cushioning occurs. The results indicate that only certain openings of the speed control valve achieve effective cushioning, with the cushion valve adjustable within a narrow range, making precise adjustments difficult. The area matching relationship diagram helps enable quicker cushion adjustments.

Torque pulsation stands as one of the principal causes of vibration and noise in cam lobe motors. A U-groove distributor plate has been designed to attenuate torque pulsation. Based on the flow-pressure pulsation of the motor's piston chambers, a theoretical model is established for the variation of damping slot distribution area and motor torque pulsation. Utilizing the AMESim platform, a dynamic simulation model of the cam lobe motor is established, and the response surface methodology is employed for parameter optimization of the U-groove. The results demonstrate that torque pulsation is influenced by multiple mechanisms associated with the structural parameters of the U-groove. Compared to the undamped slot, the optimized U-groove distributor plate has achieved a 44.55% reduction in torque pulsation level.

Active suppression of pressure pulsation is the key technology to improve the control accuracy and reliability of digital hydraulic valve control system. However, the current active suppression method lacks an in-depth understanding of its characteristics when suppressing pressure pulsations, resulting in unsatisfactory suppression effects. Therefore, a pressure pulsation test bench was designed, and the changes of pressure pulsation at different positions in the system were analyzed. The influence of hydraulic pumps and high-speed on-off valves on pressure pulsation at different positions was further explored. The results show that the main pressure pulsation in the digital hydraulic valve control system comes from the water hammer phenomenon caused by the continuous on/off of the high-speed on-off valve, and the frequency of the pressure pulsation is always consistent with the on/off frequency of the valve. This study provides a new idea for the design of feedforward active suppression system, and also provides a reference for the development of more efficient pressure pulsation attenuator.

The film temperature distribution of the port plate pair in piston pump affects the lubrication, leakage, and friction. The test platform was constructed to measure the three-point film thickness and multi-point temperature of the port plate pair. The wedge-shaped oil film model was established according to the three-point film thickness test data. The axial force balance equation of the piston cylinder was derived regarding the static pressures in the piston chambers and in the film on the cylinder, and the force between the micro-convex surfaces of the port plate pair. The film heat balance model was developed considering the energy loss, the heat conduction, and the oil viscosity-temperature characteristics. The results indicate that the film maximum temperature increases with the rise of the loading pressure and the swash plate inclination angle. The maximum temperature point falls in the range of -20°~20° on both sides of the symmetric line of the high-pressure waist groove. The maximum temperature relative error between theoretical and experimental results is less than 8%.

A novel control technique is proposed to improve the response speed, robustness, and control accuracy of actuators by combining an extended state observer with a backstepping integral terminal sliding mode preset performance controller. Firstly, the nonlinear disturbance observer is integrated with the extended state observer to achieve observation of state variables, external disturbances, and matching disturbances. Then, integral terminal sliding mode and specified performance constraints are introduced into the controller to accelerate the convergence speed of the tracking error of the actuator when the displacement error is far from the equilibrium point, and ensure that the transient and steady-state position responses are within the required bounded range. Finally, stability analysis of the controller is conducted based on the Lyapunov method. The results indicate that under the condition of tracking composite trajectories with external load disturbances, the designed controller can guarantee transient performance and the specified tracking accuracy. Compared to the backstepping sliding mode controller and PID controller, the proposed controller exhibits better control performance.

With the goal of reducing the flow force acting on the valve spool during operation, and using the external structural parameters of the valve spool as optimization variables,the method of optimizing the structure of the hydraulic servo valve spool is studied. The SPEA2 algorithm is utilized to optimize the external shape of the spool. The Pareto-optimal designs of the spool shape are obtained. The flow field and pressure distribution of the spool before and after optimization are simulated using CFD software, and the optimization effect is verified. An experimental platform is built to test the hydrodynamic force of the spool before and after optimization. This platform is capable of calculating the steady-state flow force acting on the spool during operation. Experimental results show that the flow force of the optimized spool decreases under different opening displacements, with an average decrease of 14.86% in the steady-state hydrodynamic force. The change trend is consistent with the simulation calculation, and the optimization effect is maximized when the opening displacement of the spool is 0.6 mm, further verifying the feasibility of the optimization scheme.

In order to reduce the pressure loss of hydraulic control logic valve, improve the flow efficiency of the oil, a simulation model of the flow field in the logic valve is established based on CFD, and considering the influence of fluid cavitation. The flow characteristics of the hydraulic oil and the flow-pressure characteristics of the valve are analyzed, and the test is carried out. Finally, the influence of different structural parameters of valve port on the pressure loss is explored. The results show that when the inlet flow rate is greater than 60 L/min, the simulation results and test errors of whether to consider cavitation are 4.16% and 22.41%, respectively. The pressure loss can be reduced by using a smooth transition at the sharp edge, increasing the valve sleeve aperture and reducing the diameter of the valving element, which can provide reference for the optimal design of the logic valve.

To address issues such as uncontrollable pressure difference, limited flow regulation range, and low flow control precision in pre-compensated multi-way valves, a principle of active pressure-difference control is proposed. By using a proportional pressure-reducing valve to regulate the force on the compensator spool to achieve proportional control of pressure-difference, actively adjusting according to working conditions, and improving the flow-control range. Additionally, a variable gain control strategy is developed, integrating closed-loop main spool position control, flow gain adjustment, and flow force compensation to mitigate adverse factors, match target flow curves, and enhance flow-control precision. Results show that adjusting the pressure-reducing valve allows the main valve pressure-difference to be continuously regulated within 0~1.28 MPa, increasing the flow-control range to 0%~131% of the original valve's capacity. Closed-loop control of the spool position improved accuracy, reducing flow hysteresis from 4.6% to 2%, a decrease of over 50% compared to the original valve. This method enables multiple flow gain configurations with the same main valve without altering the spool structure. By using the pressure-difference control unit to balance hydraulic forces on the compensator, disturbances from flow forces on the pressure-difference are eliminated, further enhancing flow-control precision.

Aiming at the typical faults of airborne electro-hydrostatic actuator (EHA), the fault principle was analyzed and the simulation model was established in MATLAB/Simulink. To identify fault types efficiently, a fault diagnosis algorithm based on genetic algorithm (GA) and particle swarm optimization (PSO) hybrid optimization support vector machine (SVM) was proposed. GA has good robustness and global search ability, but its convergence speed is slow. PSO is insensitive to sample size and has memory function, but it's easy to fall into local optimization. Thus, the two algorithms were combined to find the optimal parameters of SVM. In addition, the traditional multi-classification methods of SVM ‘one to many’ and ‘one to one’ are easy to be inseparable, to solve the problem, a method with partial binary tree structure was proposed. For solving the collected original data were highly coincident, time domain feature statistics were introduced to improve the classification performance. The experimental results show the proposed GA-PSO has faster optimization speed and better parameters. At the same time, the classification effect of SVM optimized by this algorithm is better than other five commonly used machine learning models, and the accuracy of fault identification is 97.7%.

At present, it is difficult to further improve the matching characteristics of output force switching electromagnetic for mining by relying on the traditional electromagnet optimization design under the dual limitations of intrinsic safety and power. The electromagnet on the mine electromagnetic pilot valve is taken as the research object, aiming at the problem of poor matching between the output electromagnetic force and the load reaction, the influence of the structure parameters of the electromagnet on the output force characteristics is analyzed by finite element method, and the optimization idea combining finite element analysis and multi-objective genetic algorithm is adopted to correct the output force characteristic curve of the electromagnet. The experimentals show that the matching relationship between the inside diameter of the pole shoe and the outside diameter of the armature has a significant influence on the electromagnetic force characteristics. The horizontal section of the electromagnetic force displacement characteristic is doubled after optimization, and the matching with the load reaction force is obviously improved. The results have laid a foundation for improving the efficiency of mechanized mining face.

As the core component of pneumatic proportional control system, pilot-operated pneumatic proportional valve has hysteresis characteristics in time response, which affects the control response speed of the system. Aiming at the problem, based on its internal structure and working principle, the dynamic characteristics of pilot-operated control stage, main valve spool and the gas flow process in the valve are modeled and analyzed, and the equivalent spring stiffness and Stribeck friction coefficient in the valve are identified by genetic algorithm. AMESim is used to simulate and analyze the pilot-operated pneumatic proportional valve, and the influence of the main parameters such as the upper chamber volume, equivalent spring stiffness and the entrapment area of the pilot-operated inlet channel on the response hysteresis and control accuracy is obtained. Aiming at minimum hysteresis, the optimal parameters are determined by quadratic programming algorithm. The results show that the dead-time is reduced from 0.041 s to 0.031 s, and the time to steady-state is shortened by 20.79% after the sequential quadratic planning design. By optimizing the proportional valves of different calibers, the response hysteresis is reduced by about 20% under the premise of ensuring the control accuracy. The research results can provide a theoretical basis for the parameter design of pilot-operated pneumatic proportional valve.

The design of flow resistance characteristics of labyrinth channel is the key to achieving throttling and pressure reduction in labyrinth adjusting valve. However, the structure of the labyrinth channel is complex, and particle in the fluid can easily lead to clogging of the channel, affecting the throttling and pressure reducing performance. The flow resistance and anti-clogging performance of channels are studied, and the flow field and particle transport laws of different channels are analyzed. The Tesla-shaped is selected as the basic maze channel structure. Through orthogonal experimental design, the relationship between the structure parameters of Tesla-shaped channel and flow resistance coefficient and particle passing time is elucidated, and a multiple nonlinear regression model is established.Multi-objective optimization algorithm based on NSGA-II is used and the optimization design of labyrinth channel with high flow resistance and low clogging rate is carried out with the maximum flow resistance coefficient and the minimum particle passing time as the optimization objectives. The results show that reducing the width and depth of the Tesla-shaped channel can increase the flow resistance coefficient, reducing the length of the outlet section can decrease the particle passing time. After optimization, the flow resistance coefficient of the Tesla-shaped channel is increased by 55.3%, and the particle passing time is decreased by 1.58%, effectively improving the flow resistance characteristics and anti-clogging performance.

When using a variable speed motor to drive a fixed pump as an electro-hydraulic power source, pressure control is achieved by controlling the speed, which is difficult to adapt to the rapidly changing load flow conditions. Using a servo motor to drive a fixed pump through direct torque control to achieve pressure control has the advantage of faster dynamic response compared to variable speed pressure control. However, due to the influence of nonlinear factors such as rotational speed, there is a non-linear correspondence between torque and pressure, which leads to significant pressure control deviation in open-loop control. Therefore, this research proposes to use a 2D chart of speed and pressure control deviation that can be iteratively generated offline for speed compensation in open-loop pressure control. Through theoretical analysis and digital simulation, the results show that under the same conditions, compared with the pressure control scheme using fitted curves for speed compensation, the pressure control error is reduced to 2%. This scheme can better achieve pressure control.

Fluid-structure interaction vibration widely exists in hydraulic pipeline system. In order to study the influence of fluid flow and clamp constraint on the fluid-structure interaction vibration of pipeline, the pipeline is simulated by ANSYS Workbench software, and the experimental platform is established. The law between different flow rates and the vibration response of horizontal pipeline is analyzed by hammering method, and the influence of different clamp materials and constraint positions on the vibration characteristics of spatial pipeline system is studied. Simulation and experimental results indicate that as the fluid flow rate in the pipeline system increases, the inherent frequency of the system decreases. Changing the clamp materials and its constraint positions can effectively adjust the inherent frequency of the pipeline to avoid system resonance.

Aimed at the serious energy losses caused by frequent lifting and start-stop braking of hybrid forklift, a combined recovery system of hybrid forklift potential energy and braking energy was designed, focusing on the key technologies of potential energy recovery of hybrid forklift and energy efficiency improvement of dual-power energy distribution control strategy. On the basis of improving and optimizing the original parallel hybrid system of traditional hybrid forklift, the simulation model is built by using forward modeling idea. In order to control the displacement of hydraulic cylinder accurately, a fuzzy PID adaptive control system is proposed. In order to optimize the working efficiency of engine and drive motor of hybrid forklift during driving and to recover braking energy, a control strategy of braking energy recovery based on the optimal working curve of engine is proposed. Finally, based on the JB/T 11988—2014, a variety of working conditions are formulated, and AMESim and Simulink are used to carry out simulation and comparative tests under various working conditions, which verifies the effectiveness of the proposed method and improves the energy recovery efficiency, and the combined recovery efficiency of potential energy and braking energy can reach up to 56.86%.

To meet the demand for high-precision coupled control of displacement and force in the electro-hydraulic servo systems of bidirectional hydraulic press, a kind of separate meter in and meter out electro-hydraulic servo system for bidirectional hydraulic presses is designed. A corresponding mathematical model is established, revealing the physical laws of the displacement-force coupled control system based on linear loads. A decoupling method for displacement-force coupled control of the bidirectional hydraulic press is proposed, simulation analysis and experimental validation are conducted based on linear loads. The results show that once the system stabilizes, the maximum overshoot of force is 1.42%, the maximum overshoot of displacement is 0.8%, the standard deviation of the force closed-loop tracking error is 447.5 N, and the standard deviation of the displacement closed-loop tracking error is 0.037 mm. This method not only achieves the high-precision coupled control requirements of displacement and force for the bidirectional hydraulic press but also enhances the system's degrees of freedom, offering a new approach to the study of decoupling methods in the displacement-force coupled control.

The platform of hydraulic leveling system exists over-running load during back down process, and with the load center of gravity shift and platform tilt changes, the load force acting on the outrigger hydraulic cylinder will also change. The traditional hydraulic system load control valve or counterbalance valve in the balance variable over-running load speed control effect is poor, easy to speed jitter. In order to solve this problem, the independent metering control technology is adopted, and for the variable over-running load condition of the hydraulic cylinder when the platform is falling back, the pressure-flow composite control method is proposed to control the hydraulic cylinder rod chamber in the hydraulic leveling system, and the flow control in the rodless chamber, and the mathematical model is established and verified by the joint simulation of AMESim and Simulink. The results show that, in the event of a sudden change in the load force, the hydraulic cylinder rod chamber pressure and rodless chamber flow can be restored to the control value within 0.2 s, balancing out the system variable beyond the load at the same time, to meet the system speed control requirements.

Flow pulsation is an inherent property of the delivery oil of axial piston pumps. The pressure pulsation induced by flow pulsation affects the working quality and service life of axial piston pumps and even the entire hydraulic system. To clarify the causes and components of flow pulsation, a three-dimensional transient CFD model of an axial piston pump is established, a test platform for pressure pulsation at the outlet of an axial piston pump is built to verify the numerical model experimentally. In addition, the pressure pulsation components due to geometric pulsation, backflow pulsation, leakage pulsation and dead zone pulsation are obtained by adjusting the geometrical structure parameters of the simulation model. The verified simulation model is employed to analyze the amplitude contributions of each flow pulsation component under different operating conditions. The simulation results indicate that geometric pulsation and backflow pulsation have positive contributions to the flow pulsation, while leakage pulsation and dead zone pulsation have negative contributions to the flow pulsation. The geometric pulsation, backflow pulsation, dead zone pulsation,and leakage pulsation account for 9%, 214%, -35% and -88%, respectively, of the total delivery flow pulsation at a discharge pressure of 10 MPa and a rotational speed of 1000 r/min. The research results provide an important theoretical basis for the formation mechanism and suppression methods of the delivery flow pulsation in axial piston pumps.

Aircraft fuel pipeline internal fluid flow characteristics are complex, the interaction between the oil and the pipe wall produces the fluid-solid coupling effect seriously affects the safety of the pipeline, in-depth study of the fluid-solid coupling characteristics of the pipeline to reduce vibration and wear of the pipeline is of great significance. The specific dimensions and mechanical parameters of the welded joint area are obtained through metallographic testing and microtensile testing, and the fluid-solid coupling model of the butt-welded fuel line with a 90° bend is established. Realizable k-ε turbulent flow model is adopted to carry out the study, and the effects of different inlet flow rates on the flow characteristics and the stress response law in the fluid domain and the response of the equivalent force in different regions are comprehensively analyzed under the constant velocity flow field and the results of the response of the equivalent force in different regions are also analyzed under the pulsating flow field. It is found that: under constant velocity flow field, the maximum equivalent force at the outlet bend section is significantly affected by the flow velocity; under pulsating flow field, the maximum equivalent force at the welded joint appears in the weld area and the stress level is more concentrated. This will provide an important reference for improving configuration design and system performance of aircraft fuel lines.

In order to reduce the energy consumption of conventional hydraulic excavator, a distributed direct-drive hydraulic system with a single variable pump-controlled cylinder is proposed. Taking a medium hydraulic excavator as a test case, pump-controlled technology is adopted to replace the dual-pump dual-circuit valve-controlled technology. Firstly, the principles of the valve-controlled system and the proposed pump-controlled system are analyzed. Subsequently, mechanical models, hydraulic system models, and a speed feedback PID position feedback controller are established and combined in MATLAB/Simulink. Experimental tests for the valve-controlled system and simulations for the pump-controlled system are conducted under the same excavation cycle conditions. The results indicate that under aidentical operating condition, the energy consumption of the working apparatus in the two systems is fundamentally similar (pump-controlled system is 8.6% higher than valve-controlled system); However, the efficiency of the pump-controlled system at 62.1% is 2.6 times that of the valve-controlled system at 23.5%. As a result, the total energy consumption of the pump-controlled system is lowered by 62.4%.

Underwater hydraulic manipulators are pivotal apparatuses for underwater special operations. Currently, the control of hydraulic manipulators for underwater operations mainly relies on visual feedback to determine the position. However, various operating errors can occur, such as camera distortion and water flow interference, which often result in sticking or jamming issues, severely impacting the efficiency and safety of operations. To address these, an active/passive compliant control system specifically designed for underwater hydraulic manipulators is proposed. By designing an end clamp, position and deflection errors are compensated to achieve passive compliance. Active compliance is achieved by the virtual decomposition control method, combined with a force observer and impedance control. Furthermore, the effectiveness of the active/passive compliant control method is verified through experiments, providing a reference for the design of safe and compliant control for underwater hydraulic manipulators.

In order to investigate the internal basin cavitation characteristics of a novel low-speed high-torque internal curve piston pump, the internal drainage model of the fluid distribution of the internal curve piston pump is established. The cavitation distribution and generation in the fluid distribution basin are studied by CFD fluid simulation. The cavitation characteristics of the fluid distribution basin under different conditions are analyzed. The research findings demonstrate that cavitation mainly takes place at the oil discharge non-return valve port and the high-speed on-off valve port, and the gas phase volume fraction directly reflects the intensity of cavitation. Pump shaft speed and load pressure have an obvious effect on cavitation, however, too low oil suction pressure will cause the piston to suck air. The structure of fluid distribution internal basin is optimized by increasing the local inner diameter of the flow path and reducing the length of the flow path, thereby reducing the oil flow rate and weakening cavitation. The latter optimization method is superior to the former.

As a core component of the flow control system, the Venturi regulator has a decisive impact on the system's control accuracy and stability. The flow characteristics of the Venturi regulator were investigated. The envelope method was used to optimize the design of the spool contour. The design was validated through CFD simulation and experiment. The results indicate that the paraboloid-shaped spool can achieve a linear variation between the flow area of the regulator and the spool displacement. Under the operating condition with an inlet-to-outlet pressure ratio of 0.5, both the CFD simulation and the water-medium flow characteristic experiment of the regulator have validated the high linearity of the displacement-flow curve. These results further demonstrate the accuracy and effectiveness of the paraboloid-shaped spool design. Simultaneously, in conjunction with the visualization experiment figures, the significant fluctuations in the flow coefficient curve when the spool displacement is relatively small are due to the change in cavitation flow status.

Gas sealing technology is the main mechanism for maintaining the stability of the immersion flow field. The gas jet impinges on the wafer surface to prevent the leakage of the immersion liquid, which can lead to overlay errors and exposure defects. The interaction between the immersion flow field and the sealing gas flow and the behavior characteristics of the gas-liquid interface are necessary to investigate. The background oriented schlieren technique is used for observing the gas jet. The measurement principle and hardware construction of this visualization technology are introduced. Through the optimized optical path design, synchronous observation of both the gas-liquid and internal-external flow fields, enabling a comprehensive study of interface behavior characteristics. This study can offer valuable guidance for the application of non-contact measurement techniques such as background oriented schlieren technology in ultra-clean fluidics.

The stable gripping of flexible container bags is an important part of the feeding process, and the gripping quality of container bags has a great impact on the subsequent packaging process. Therefore, the effect of vacuum sucker on the grab quality of container bags is studied. Using the principle of vacuum adsorption, by designing a pneumatic vacuum system and observing the numerical changes in the digital pressure gauge, establish an adsorption suspension theoretical model and conduct experimental measurements. Study the variation law of the number of vacuum generators, suckers, and vacuum degree, as well as determine the layout method of the critical parameters for axial and radial deformation failure of the suckers themselves. The final determination is that the vacuum degree during grasping must not be lower than 45 kPa, and the critical values for axial and radial deformation failure of the suckers are 4 mm and 5 mm, respectively, provides a reference for the same type of flexible grasping.

As a fundamental element of the pneumatic conveying system, the fan's performance will impact the operational efficiency of the cotton harvester. Optimized design of centrifugal fan blades for improved maximum airflow of pneumatic conveying system. A CFD numerical model has been established and 20 sample sets have been generated in the design space through the use of Latin hypercube experiments. Using the available sample data, we established an estimation model for the outlet air volume and design variables. An intelligent optimisation algorithm was then used to achieve the desired design plan. Compared to the prototype, the optimized design has notably enhanced the air outlet velocity. Additionally, according to the CFD analysis, the air volume has significantly increased by 17.27% under the rated speed condition.

A control method based on motor speed control mode and torque control mode is proposed to address the issue of efficient recovery and utilization of braking energy in the hydraulic electric hybrid drive rotary device. Firstly, conduct theoretical and theoretical analysis on the hydraulic electric hybrid drive rotary system. Afterwards, the system was simulated and analyzed in AMESim, providing reference for subsequent experiments. Finally, the differences between torque mode and speed mode were compared and analyzed through experiments. The experimental results show that the torque mode operates more smoothly compared to the speed mode, with no power fluctuations. The speed mode is more effective in utilizing the energy of the accumulator, saving 48.4% compared to traditional excavators and 42% more than the torque mode. The overshoot of torque mode is 8% greater than that of speed mode. Overall, the speed mode is superior to the torque mode.