Electro-hydraulic Servo Valve Research Articles

Characteristic Progress and New Solutions for Nozzle Baffle Type Electro-Hydraulic Servo Valve

Background: This article outlines the working principle of the nozzle baffle type electro- hydraulic servo valve and analyzes the progress of research on its characteristics more fully. Objective: Firstly, it summarizes the research progress on the characteristics of the cavitation phenomenon, which is a common failure of nozzle baffle type electro-hydraulic servo valves; secondly, it comprehensively discusses the structural characteristics of nozzle baffle type electrohydraulic servo valves: moving-iron torque motors and moving-coil torque motors, as well as the progress of the research on the characteristics of the power-stage valve spools and direct-injection valve spools. Method: It suggests to the readers other optimization methods that can be made for the cavitation phenomenon in the future, and brings innovative ideas for the readers in terms of moving-iron vs. moving-coil torque motors and other aspects that can be improved for the power-stage spools vs. direct-injection spools. Again, for the typical technical problems of nozzle baffle type electrohydraulic servo valves, we have searched and organized the related technical patents at home and abroad and clearly outlined the current improvements for nozzle baffle type electro-hydraulic servo valves. Results: Through the discussion of related articles and patents, it is found that although many methods have been proposed at home and abroad to address the shortcomings of the nozzle baffle type electro-hydraulic servo valve, it still has a high failure rate and has not been comprehensively solved, there is still a lot of room for optimization. Conclusion: Finally, the new solutions proposed for the performance deficiencies of nozzle baffle type electro-hydraulic servo valves are summarized, and the future development trend of nozzle baffle type electro-hydraulic servo valves is predicted and outlooked.

Research of closed loop characteristics of single and double chamber structure for fuel metering mechanism

There are two forms of engine fuel metering devices which are single and double chamber structures using electro-hydraulic servo valves as electro-hydraulic conversion devices to realize accurate fuel flow measurements and constant pressure differential valve is used to maintain the constant pressure difference of the metering valve. The main purpose of this article is to analyze the time domain and frequency domain characteristics of constant pressure differential valve assembly and compare the closed-loop characteristics of two metering mechanisms. Firstly, the mathematical model of constant pressure differential valve assembly (including the fuel pump and constant pressure differential valve) is established and its time and frequency domain characteristics are analyzed. The conclusion that the constant pressure differential of the metering valve can meet the practical requirements is obtained. Secondly, the mathematical models of single and double-chamber fuel metering mechanisms are established considering the specific working conditions. Finally, the characteristics of two kinds of metering mechanisms are compared and analyzed under the same control method in the time and frequency domain. The extension overshoot with a maximum value of 3.564% of the single chamber control metering valve mechanism is smaller than that of the double chamber control metering valve mechanism with a maximum extension overshoot of 6.04%. The negative overshoot with a maximum value of 1.391% of the single chamber control metering valve mechanism is bigger than the double chamber control metering valve mechanism with a maximum negative overshoot value of 1.17%. In terms of steady-state error, the steady-state error of a single chamber control metering valve mechanism with a maximum value of 0.194 mm and minimum value of 1.25e-6 mm is smaller than that maximum value of 0.302 mm and minimum value of 1.95e-6 mm of double chamber control metering valve mechanism under the same controller parameters. The bandwidth of the extension motion of the single and double chamber control metering valve is greater than that of the retraction motion. Under the same proportional control parameter, the bandwidth of the double chamber control metering valve extension motion system is greater than that of the single chamber extension motion system.

Mathematical modeling and time-frequency characterization of aero-engine actuators

The actuator is an essential part of the aero-engine control system, and its performance directly determines the efficiency of the whole system. The mathematical model of the aero-engine actuators, including electro-hydraulic servo valves, hydraulic cylinders, and actuators, is modeled and the time-frequency characteristics are analyzed using the Simulink module. Then, the system response is simulated and its time-frequency characteristics are analyzed. The simulation results show that the simulation error of the established actuator model is within the allowable range. The displacement response and the servo valve flow response fluctuate slightly near the steady state value, and the error value is only 0.857% at the maximum fluctuation value, and the system still works normally when a dynamic load is added to the system.

Research on Electro-hydraulic Servo Valve Structure and Control Algorithm of System with Servo Valve

Background: With the continuous progress of electronic information technology, people have begun to study the combination of electronic information technology and hydraulic technology to achieve more accurate and flexible control. Electro-hydraulic servo technology was thus developed. Much attanetion has been paid to electro-hydraulic servo valve,a key component of electrohydraulic servo technology. Objective: The number of stages of the electro-hydraulic servo valve, the structure form of the electro- hydraulic servo valve hydraulic front stage, the feedback form of the electro-hydraulic servo valve, the output form of electro-hydraulic servo valve, and the control algorithm based on the application of electro-hydraulic servo valve are analyzed and commented respectively. Combined with associated patents, the research direction and hot topics of electro-hydraulic servo valves are analyzed. Method: The electro-hydraulic servo valves were briefly classified; and then the problems of different types of valves were discussed in depth. Results: By analyzing the problems of electro-hydraulic servo valves, the problems of how to improve the control accuracy, response speed, anti-interference ability, service life and cost reduction of electro-hydraulic servo valves are analyzed comprehensively, and the future development prospect of electro-hydraulic servo valves is predicted and outlooked. Conclusion: Analyzing and discussing the existing hot issues of electro-hydraulic servo valves helps to update and change the electro-hydraulic servo valves, and makes corresponding references for the subsequent research of electro-hydraulic servo valves.

An innovative experimental device for characterizing the responses of monopiles subjected to complex lateral loading

Offshore wind turbines are usually founded on monopiles. During the operation period, the structure is subjected to complex lateral loading from wind, wave and current. The soils surrounding those monopiles may deform with increasing the number of loading cycles, leading to tilting of the whole structure; hence, it is vital to carry out physical model tests to examine the long-term performance of monopiles. This study proposes an innovative experimental setup for centrifuge modelling of the response of monopiles under complex lateral loading. Hydraulic actuators are adopted to apply lateral loads on model pile, and electrohydraulic servo-valves and associated controllers are used to achieve a closed loop position or load control. A carefully designed spherical hinge and load bars are used to connect the model pile and actuator shafts. This enables that the pile can rotate freely and can move vertically freely. A centrifuge test on a winged monopole subjected to perpendicular lateral loading was carried out at 100g. The experimental results shed light on pile responses in the cyclic loading and constant loading directions.

Modeling and Fault Simulation of a New Double-Redundancy Electro-Hydraulic Servo Valve Based on AMESim

The feedback spring rod of the armature assembly was eliminated in the double-redundancy electro-hydraulic servo valve (DREHSV), which employed a redundant design in contrast to the typical double-nozzle flapper electro-hydraulic servo valve (DNFEHSV). The pilot stage was mainly composed of four torque motors, and the double-system spool was adopted in the power stage. Consequently, the difficulty of spool displacement control was increased. By artificially changing the structural parameters of the simulation model in accordance with the theoretical analysis through AMESim, this paper aimed to study the dynamics and static characteristics of the DREHSV. The advantage of redundant design was further demonstrated by disconnecting working coils and setting the different worn parts of the spool. On the test bench, the necessary experiments were performed. Through simulation, it was discovered that when the clogged degree of the nozzle is increased, the zero bias value increases, the pressure and flow gain remain unchanged, and the internal leakage decreases. The pressure gain changes very little, the flow gain close to the zero position grows, the zero leakage increases significantly, and the pilot stage leakage changes very little as a result of the wear of the spool throttling edge. The basic consistency between the simulation curves and the experimental findings serve to validate the accuracy of the AMESim model. The findings can serve as a theoretical guide for the design, debugging, and maintenance of the DREHSV. The simulation model is also capable of producing a large amount of sample data for DREHSV fault diagnosis using a neural network.

LabVIEW-based servo valve dynamic and static test system

As a key component of the electro-hydraulic servo control system, the electro-hydraulic servo valve’s performance directly affects the stability of the system’s operation. Therefore, according to the company’s requirements, a servo valve testing system was designed based on LabVIEW. Firstly, the hydraulic system was designed according to the dynamic and static testing requirements of the servo valve. Then, the electrical control system and software system were designed based on PLC and LabVIEW. Finally, dynamic and static characteristic tests of the servo valve were conducted on the designed test bench. A flow-pressure dual closed-loop steady-state control method for testing the no-load flow characteristics was proposed, effectively improving the testing accuracy and meeting the company’s requirements.

Analysis of the static and dynamic characteristics of the electro-hydraulic pressure servo valve of robot

In this study, we comprehensively investigate the structure and operational principles of the Rotary Direct Drive Electro-Hydraulic Pressure Servo Valve (RDDPV). Our objective is to establish the dynamics equations governing the motor, slide valve, and bias mechanism of the valve. Additionally, we construct a mathematical model for the servo valve controller, while ensuring the linearization of the controller model. Furthermore, we conduct an in-depth analysis of the static characteristics of the valve, including linearity, dead zone, hysteresis loop, and zero drift. Regarding the dynamic characteristics, we establish a dynamic mathematical model for the RDDPV valve. Subsequently, we subject the servo valve to analysis with a focus on frequency response and dynamic response, using the control current as the input and the pressure as the output. To perform these analyses, we employ the software package SIMULINK of MATLAB, facilitating dynamic simulations. Remarkably, the simulation results exhibit the valve's conformity to design requirements, underscoring its suitability for subsequent research and development endeavors. Through our rigorous investigation, we offer essential technical support for the forthcoming stages of the valve's research and development, thereby laying a robust foundation for its further advancement.

Direct-Drive Electro-Hydraulic Servo Valve Performance Characteristics Prediction Based on Big Data and Neural Networks.

Direct-drive electro-hydraulic servo valves play a key role in aerospace control systems, and their operational stability and safety reliability are crucial to the safety, stability, and efficiency of the entire control system. Based on the prediction of the performance change of the servo valve and the resulting judgement and prediction of its life, this can effectively avoid serious accidents and economic losses caused by failure due to performance degradation in the work. On the basis of existing research, factors such as opening, oil contamination, and pressure difference are used as prerequisites for the operation of direct-drive electro-hydraulic servo valves. In addition to the current research on pressure gain and leakage, the performance parameters of servo valves, such as overlap, threshold, and symmetry, are also expanded and selected as research objects, combined with pressure design servo valve performance degradation experiments for testing instruments such as flow and position sensors, and data are obtained on changes in various performance parameters. The experimental data are analyzed and a prediction model is built to predict the performance parameters of the servo valve by combining the existing popular neural networks, and the prediction error is calculated to verify the accuracy and validity of the model. The experimental results indicate that as the working time progresses, the degree of erosion and wear on the valve core and valve sleeve of the servo valve increases. Overall, it has been observed that the performance parameters of the servo valve show a slow trend of change under different working conditions, and the rate of change is generally higher under high pollution (level 9) conditions than under other conditions. The prediction results indicate that the predicted values of various performance parameters of the servo valve by the prediction model are lower than 0.2% compared to the experimental test set data. By comparing the two dimensions of the accuracy and prediction trend, this model meets industrial needs and outperforms deep learning algorithm models such as the exponential smoothing algorithm and ARIMA model. The experiments and results of this study provide theoretical support for the life prediction model of servo valves based on neural networks and machine learning in artificial intelligence, and provide a reference for the development of direct-drive electro-hydraulic servo valves in aerospace and other industrial fields for use and failure standards.

Dynamic Prediction of Performance Degradation Characteristics of Direct-Drive Electro-Hydraulic Servo Valves

Direct-drive electro-hydraulic servo valves are widely used in the aerospace industry, in the military, and in remote sensing control, but there is little research and discussion on their performance degradation and service life prediction. Based on previous research, erosion wear is the primary physical failure form of direct-drive electro-hydraulic servo valves, and parameters such as opening, oil contamination, and pressure difference are used as influencing factors of direct-drive electro-hydraulic servo valves. Pressure gain and leakage are used as performance degradation indicators of servo valves, and multiple types of sensors are used for data monitoring. Experimental benches are arranged and verified through experiments. Based on the data and laws obtained from the experiments, the exponential smoothing algorithm and the ARIMA model algorithm were used to establish a prediction model for the servo valve, and the dynamic prediction of the performance indexes was carried out. The error calculation and analysis of the prediction results and the experimental results were then carried out using the Copula function and other mathematical knowledge to verify the accuracy and applicability of this prediction model. This study provides theoretical support and practical guidance for applying and designing direct-drive electro-hydraulic servo valves in industrial applications such as aerospace, sensor experiments, and remote sensing control.

Multisource electrohydraulic servo valve fault status diagnostic algorithm based on a message propagation mechanism

Fault identification of electrohydraulic servo valves is crucial to maintain the reliability and safety of high-precision electrohydraulic servo systems. Because the nonlinear characteristics and fault characteristics of electrohydraulic servo systems under noise conditions are implicit, it is difficult to obtain a large number of fault data of electrohydraulic servo valves. Therefore, an electrohydraulic servo valve fault diagnosis model based on characteristic distillation is proposed in this paper. First, the original fault data model is obtained based on an electrohydraulic servo valve fault test platform, the data are standardized, and the data of more than one cycle are extracted using a combination of down sampling and a sliding window for data enhancement. Second, a neural network fault diagnosis algorithm based on stack graph convolution is proposed, which is suitable for detecting different types of states (normal state, wear state, stuck state and coil short-circuit state) of electrohydraulic servo valves. The accuracy of the test set fluctuates between 0.7 and 1.0. Then, because there is a certain relationship between the characteristic smoothing phenomenon of a stack graph convolution model and the number of layers, a multilayer stack graph convolution model is bound to have problems such as model degradation. Therefore, a residual model is introduced into the stack model to improve the convergence speed of the model during the optimization process. The results show that the average accuracy of this method is 100%.

Refined modeling and experimental verification of a torque motor for an electro-hydraulic servo valve

The Permanent Magnet Torque Motor (PMTM) is the key electro-mechanical conversion device in an Electro-Hydraulic Servo Valve (EHSV). In this work, a refined model of a PMTM is developed, considering the non-working air-gaps between the upper or lower yoke and the armature, the fringing effect at the limiting holes, and the nonlinear permeability of soft magnetic material. Based on the refined model, the influences of various factors on the calculation accuracy of the magnetic flux at the pole surfaces of the armature and the output torque are investigated. For verifying the validity of the refined model, a Finite Element Analysis (FEA) of the PMTM is conducted, and a test platform is constructed. Compared with existing models, the refined model can better reveal the intrinsic mechanism of the PMTM, and its calculations are more consistent with the FEA results. The experimental results of the armature deflection displacement show that the refined model can accurately describe the output characteristics of the PMTM.

Experimental study on the correlation between erosion microstructure and performance degradation of hydraulic servo spool valve

Surface topography plays an important role in determining the performance of hydraulic components, which often leads to component failure. The dual nozzle electro-hydraulic servo valve is composed of torque motor, pilot nozzle flapper valve and servo spool valve, whereas the failure is at the level of servo spool valve. In more details, the degradation of the static characteristic parameters of the hydraulic servo valve, which is experimentally studied by artificially controlling the fillet radius of the spool working edges, is one of these failures. In addition, the microstructure characteristics of the MOOG J761 valve working edges and the circumferential distribution law of the fillet radius are obtained. The research shows that valve orifice erosion caused fillet on the working edges and increases the dispersion of the circumferential distribution. The erosion micromorphology of the working edge is mainly characterized by surface peeling, notches, grooves, and chamfers. The average and variance of the fillet of the spool working edge at the high-pressure oil exceed those of the working edge of the return oil. When the average fillet radius of the working edge increases by 2.71 times and the average fillet variance increases by 2.55 times, the maximum leakage increases by 5.08 times, the flow gain decreases, and the positive and negative flow gains are asymmetric, decreasing by 7.78% and 1.75%, respectively. The pressure gain decreases significantly by 40.30%. The relation between the microstructure of the orifice working edge and the performance degradation provides a new idea for the performance evaluation and manufacture of hydraulic spool servo valve.

Failure diagnosis of electro-hydraulic servo valve based on SA-PSO-SVM

Failure diagnosis of electro-hydraulic servo valve based on SA-PSO-SVM

An indirect flow measurement based high-precision slide valve grinding mechanism for hydraulic servo valve

As a crucial power amplifying component for electro-hydraulic servo valves, the servo-valve spool valve largely determines the overall performance of an electro-hydraulic servo system. Due to the machining errors during the servo-valve manufacturing process, however, it is extremely difficult to characterize such response characteristics in engineering practice, and thus, there may exist certain nonlinearity between the flow rate and valve spool displacement caused by the spool and valve sleeve overlap. To accurately characterize the relationship between the flow rate and spool displacement to facilitate servo-valve production, an indirect flow measurement-based servo-valve spool valve grinding (FM-SVG) scheme is proposed in this study. Specifically, a valve spool overlap measurement mechanism is presented first based on the valve spool grinding principle, and then a data processing method is devised to eliminate the errors introduced by the fluctuations of differential pressure at the valve ports. Meanwhile, a closed-loop control system is also devised to maintain a constant differential pressure at the servo-valve ports. Finally, the FM-SVG scheme is embedded onto a lab-customized electro-hydraulic servo valve platform, and experiments are conducted to verify the feasibility and effectiveness of the FM-SVG scheme. Results show that, by utilizing the devised control scheme to maintain a differential pressure around 2.00 MP, the proposed grinding scheme helps achieve a grinding accuracy of 2.0 μm. With only grinding process needed, such a grinding scheme helps improve both grinding accuracy and production efficiency in practice.

CFD-Based Physical Failure Modeling of Direct-Drive Electro-Hydraulic Servo Valve Spool and Sleeve.

Direct-drive electro-hydraulic servo valves are used extensively in aerospace, military and control applications, but little research has been conducted on their service life and physical failure wear. Based on computational fluid dynamics, the main failure forms of direct-drive electro-hydraulic servo valves are explored using their continuous phase flow and discrete phase motion characteristics, and then combined with the theory of erosion for calculation. A mathematical model of the direct-drive electro-hydraulic servo valve is established by using Solidworks software, and then imported into Fluent simulation software to establish its physical failure model and carry out simulation. Finally, the physical failure form of the direct drive electro-hydraulic servo valve is verified by the simulation results, and the performance degradation law is summarized. The results show that temperature, differential pressure, solid particle diameter and concentration, and opening degree all have an impact on the erosion and wear of direct-drive electro-hydraulic servo valves, in which differential pressure and solid particle diameter have a relatively large impact, and the servo valve must avoid working in the range of high differential pressure and solid particle diameter of 20–40 um as far as possible. This also provides further theoretical support and experimental guidance for the industrial application and life prediction of electro-hydraulic servo valves.

Analysis and simulation of typical faults of electro-hydraulic proportional servo valve

In this paper, the simulation of three typical faults of electro-hydraulic proportional servo valve is presented, and the physical model of servo valve and its faults is constructed by AMESIM software. Electro-hydraulic proportional servo valve has high steady-state accuracy, excellent dynamic performance, stability and reliability, and has been gradually applied in the control field. Therefore, higher requirements are put forward for real-time state monitoring and typical fault research of electro-hydraulic proportional servo valve. In this paper, aiming at the requirement of real-time monitoring of the servo valve, the mathematical model of three typical faults, such as stuck, spool wear and zero deviation, is sought, and the feasibility of the model is verified through simulation.

Simulation and analysis of electro-hydraulic proportional servo valve port under erosion wear

Electro-Hydraulic Proportional Servo Valve (EHPSV) is one of the essential components of airborne hydraulic system. When the EHPSV is used for a period of time, there will be a certain degree of erosion wear at the valve port. This wear will change the precise structure of the valve port, cause the flow leakage, and then affect the accuracy of control. This paper establishes the motion model of oil and particles in the spool valve, simulates the erosion at the valve port with Fluent, and explore the main influence factors such as pressure, the port opening size, the particle, and the structure of port on the erosion of the valve port, and the adverse effect of erosion at the valve port on the performance of the valve, which is helpful to provide guidance for exploring the failure process and control of the EHPSV.

A Cooperative Control Method for Excavation Support Robot with Desired Position/Posture

Desired deviation of the position/posture of Excavation Support Robot (ESR) have a critical impact on the efficiency of underground mining. In this paper, a control method of desired position/posture coordinated adjustment by real-time posture data and sliding position mode control algorithm is proposed. The action stroke of the non-longitudinal Adjustment Hydraulic Cylinder (AHC) is controlled by adaptively adjusting the opening and time of the Electro-Hydraulic Servo (EHS) valve, thereby adjusting the position offset and posture coordination of the ESR. The mathematical model of hydraulic system is deduced. Considering the kinematic characteristics of the ESR and the coupling relationship between the stroke and posture of the lateral AHC, a coupled kinematics model of the robot and the support body is derived. The overall structure of the posture adjustment control system and the calculation method of the stroke adjustment amount of the AHC are presented, and the controller is further optimized. The simulation analysis model and test verification system of the desired posture adjustment control system are determined. These results show that the control method is effective and significant compared with the manual control system, which can meet the functional and precision requirements of position deviation and posture adjustment.

Design methods of planar six-bar mechanism in servo applications

ABSTRACT Aiming at improving the reliability of the hydraulic servo actuator constructed using a nozzle-flapper servo valve, the design of a servo actuator with a combination of electro-hydraulic and mechanical manipulations is proposed. This solution enables the system to be switched to a mechanical operation pattern in the event of failure of the electro-hydraulic servo valve, which results in a loss of control. A 2-degrees of freedom planar six-bar lower-pair mechanism is proposed to achieve mechanically operated hydraulic servo-driven actions in a switched pattern. The dimensional synthesis of the mechanism is completed by applying the adaptive particle swarm optimization (APSO), and optimized numerical solutions are obtained. The virtual prototype of the mechanism is designed, and the kinematic properties of the output link along with the sinusoidal motion of the given input links are assessed using the mathematical software ADAMS. The simulation results show that the optimally designed planar six-bar mechanism has small geometric errors, thus verifying that APSO can be satisfactorily applied in dimensional synthesis.