Servo Valve Research Articles

Study of Novel Oil-Immersed Torque Motor for Two-Dimensional Valve

The electro-mechanical converters of valves are mostly dry type, which cannot work for a long time under high currents due to heat dissipation. This paper presents a novel oil-immersed torque motor (OTM) that can carry out the 2D motion. The OTM has a separate wet working chamber and heat dissipation structure, and the coil is external to prevent oil contamination from causing short circuits. The equations of motion were established based on the equivalent magnetic circuit (EMC) method and its own characteristics, and the effect of oil damping in the working chamber on the dynamic characteristics of the novel OTM was studied. After analyzing its working principle and dynamic and static characteristics by finite element and numerical analysis software, a prototype was designed and machined, which could be operated in dry and immersed mode by adding parts. In addition, a dynamic and static test bench and a temperature rise test bench were established, and comparison experiments with a conventional dry-type torque motor (CDTM) were conducted. Experimental results showed that the prototype had a good thermal resolution in immersed mode, and when the coil was fully loaded (2.4 A), it still worked in the safe temperature range. The prototype had good current-torque characteristics and hysteresis linearity at a coil magnetomotive force (MMF) of 0–450 A. The output torque could reach 0.7 Nm when MMF exceeds 1000 A. The prototype had an approximately 4% faster step response in immersed mode and about 17.8% wider bandwidth than in dry mode, while the torque motor system was more stable due to the increased damping ratio. The measured open-loop dynamic and static characteristics met the requirements of the electro-mechanical converter of 2D servo valves.

Analysis of Pressure Impact Characteristics of a Hydraulic Position Servo System Based on Series Servo Valves

As one of the causes of system vibration and noise, pressure impact is always undesired. Analysis of pressure impact characteristics of a hydraulic position servo system based on a two-stage series servo valve is carried out to reduce the system impact. The influence of factors such as system flow rate, additional servo valve opening gain, external load, and system overflow pressure on the system pressure impact is analyzed. The results show that the series servo valve scheme can bring down the peak impact pressure at the inlet of the hydraulic cylinder by 8%~11% when the system flow rate or overflow pressure is low to a certain extent. In most other cases, the suppression effect of the impact peak pressure is unapparent. The impact pressure overshoot is always decreased accompanied by an easier trend to overflow for the system. At last, another new idea of application promotion with higher reliability and adaptability is proposed.

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.

Mathematical modeling of pressure characteristics of the deflector-jet pilot stage considering boundary layer flow

The performance of a deflector-jet servo valve significantly depends on the pressure characteristics of its pilot stage. The complex flow field within the deflector-jet pilot stage presents enormous difficulty and challenge in establishing its mathematical model. In this work, according to the energy conversion characteristics of the flow field, the flow process within the pilot stage is divided into five phases for modeling: inside-pipe flow, first jet, first pressure recovery, secondary jet, and secondary pressure recovery. To better reveal the intrinsic operating mechanism of a deflector-jet pilot stage, the boundary layer is introduced into the model. Computational fluid dynamic (CFD) simulation and experiment are conducted to validate the developed mathematical model at different supply pressures. The result demonstrates that the velocity distribution of the jets and the pressure characteristics of the pilot stage are significantly influenced by the boundary layer. The boundary layer flow within the V-groove has a greater impact on the pressure characteristics than that within the nozzle. Verified by the CFD simulation and experiment, the developed model can accurately predict the velocity distribution of the jets and pressure characteristics. At different supply pressures, the maximum relative error between the theoretical and experimental results of the dimensionless pressure characteristic is 5.36%.

Investigation of the Dynamic Characteristics of a Two-Stage High-Speed On/Off Valve with Adjustable Maximum Opening

The effective way to improve the reliability of the fuel metering system in an aero-engine is to use a high-speed on/off valve (HSV) instead of a servo valve as the pilot stage of the fuel metering valve. However, the dynamic performance of the fuel metering valve is easily affected by the HSV, so a novel two-stage high-speed on/off valve with adjustable maximum opening (AMOHSV) is proposed in which the maximum stroke of the main valve is regulated with an adjustable rod. Firstly, the structure and working principle of the proposed valve are presented. Then, an entire mathematical model is established and verified based on a multi-physical field coupling mechanism. Finally, simulations and experiments prove that when the maximum opening is 0.2 mm, the total opening time and total closing time of the AMOHSV are within 5 ms. In addition, an upward inflection point and a downward inflection point on the pressure curve of the control chamber can be used to identify the total opening time and total closing time, respectively. The research results also prove that the proposed structure solves the conflict between the maximum flow rate and the dynamic performance of the traditional HSV.

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.

Analysis of Frequency Adjustable Control of Permanent Magnet Synchronous Motor for Pump-controlled Actuators

Recently the pump-controlled system has actively been proposed as a replacement for conventional valve-controlled systems, to improve the energy efficiency in non-road mobile machinery. Earlier research demonstrated that a pump-controlled hydraulic system combines the best properties of traditional hydraulics and electric intelligence. This pump-controlled system can be realized via direct control of hydraulic pimp/motor by varying speed of electric motor without complex servo valves. Nowadays, a wide range of different electric motors is known and available with efficiency higher than 95% One of the most attractive option of electric motor is Permanent Magnet Synchronous Motor (PMSM) due to its size, power, and high efficiency.
 However, control of electric motors in pump-controlled systems has are not yet considered and not well researched.
 In this paper, the main objective of this investigation is determination of control values for the pump-controlled actuator and analysis of system’s behavior in different applications.
 Therefore, model of PMSM drive with pump-emulated load is proposed. Field Oriented Control (FOC) gives wide range of the speed regulation and smooth characteristics, but tuning of controllers is challenging.
 Case of the steering-modeled load represented that such operations need more power than other modes. More complex frequency converters allow to reach higher level of accuracy and decrease torque ripples, but complexity of such systems increases rapidly.

Oil Particle-Induced Erosion Wear on the Deflector Jet Servo Valve Prestage

Severe oil particle-induced erosion to the prestage component progressively degrades the overall performance of the deflector jet servo valve (DJSV), even leading to valve failure. Herein, we present an approach for evaluating degradation in performance and predicting the erosion lifespan of the DJSV on different levels of oil pollution. Specifically, a mathematical model of the whole valve was built based on a previously established working principle and physical mechanism. In addition, considering the horizontal and rotational particle motions, combined with impact of particle size distributions under different oil contamination degrees, an erosion model was constructed. Then, after simulating and analyzing the pressure characteristics before and after the erosion of prestage, the performance degradation of the whole valve was examined, thereby predicting the erosion life of the valve. Investigations revealed that the maximum erosion rate occurred at the shunt wedge of the receiving holes, which increased with the contamination degree and accelerated after level 7. After erosion, however, the control pressure difference decreased significantly, and erosion life followed exponential distribution corresponding to the distribution of particles under different pollution levels. The aforementioned investigation can thus help diagnose faults and optimize the design of the servo valves in service.

Open-source lower controller for twelve degrees of freedom hydraulic quadruped robot with distributed control scheme

Nowadays, hydraulic quadruped robot shows high power density, good impact resistance and robustness in the research. The controller is the key to realize these features. This paper shows the design of an open-source single-leg controller for the hydraulic quadruped robot Spurlos using a distributed control scheme. The single-leg system of the hydraulic quadruped robot Spurlos contains three angle encoders, three servo valves and six pressure sensors, which has the same components as most single-leg systems. Through the chips designed in the controller, the signal can be received from the encoders and the sensors, meanwhile the signal can be delivered to the servo valves. The software part of the controller adopts the MBD (Model-Based Design) method, which can greatly improve the development efficiency. According to the experiments, the controller design is reasonable, stable operation, and can satisfy the requirements of the hydraulic quadruped robot for leg motion control. The controller designed in this paper provides a solution to the problem that there is no ready-made control board for hydraulic quadruped robot which have three degrees of freedom for each leg. It enables the control researches for hydraulic quadruped robots to be more easily implemented.

ОПРЕДЕЛЕНИЕ ГИДРОДИНАМИЧЕСКОЙ СИЛЫ, ДЕЙСТВУЮЩЕЙ НА ЗОЛОТНИК ЭЛЕКТРОГИДРАВЛИЧЕСКОГО УСИЛИТЕЛЯ МОЩНОСТИ С ПРИМЕНЕНИЕМ СРЕДСТВ ВЫЧИСЛИТЕЛЬНОЙ ГИДРОДИНАМИКИ

The development and design of servo valve spools with high performance requirements require accurately calculating the impacts on the spool. During the operation of the servo valve, the most significant impact on the spool is exerted by the flow force, which is determined by the flow rate of the liquid and the angle of deflection of the jet. Existing methods for calculating the magnitude of the flow force do not take into account the actual shape of the sleeve and spool collars, which negatively affects the accuracy of the calculations. This article develops a method for calculating the impact of the flow force on a servo valve spool using computational fluid dynamics, taking into account the shape of the sleeve and spool collars. The article presents a simulation of the fluid flow through the spool sleeve of a servo valve in various positions of the spool at a pressure drop across the valve of 7 MPa under no load conditions. Based on the simulation results, for each of the spool position under consideration, the actual flow rate through the servo valve and the jet deflection angles are determined, taking into account the actual structure of the spool sleeve. Based on the actual flow rates, the flow rate coefficients of the servo valve are defined and the flow characteristics are built. Using the data on the jet deflection angles and the obtained flow characteristic, the dependence of the resulting impact of the flow force on the spool of the servo valve on the spool position is calculated. As the result of the study, a step-by-step method for calculating the resulting impact of the flow force on the spool is developed, which is applicable for various operating modes of the servo valve, determined by the supply pressure and the load values.

Comparison of proportional and servo valves in a hydraulic quadruped robot

Comparison of proportional and servo valves in a hydraulic quadruped robot

Finite Element Modeling and Optimal Design of an Electromagnetic Pneumatic Flow Servo Valve

The electromagnet pneumatic proportional servo valve is widely used in industrial automation, medical equipment, scientific composition detectors, and other fields that require precise adjustment of high‐pressure air flow due to its simple working structure, large output power, large working frequency response, and good control performance. However, the output pressure of the valve is small, making it vulnerable to the impact of the external environment. Based on the practical electromagnet‐type pneumatic proportional servo valve, this paper establishes a finite element dynamic mathematical model, conducts finite element analysis on the electromagnet magnetic field in the valve, then improves the structural parameters of the original proportional valve through the analysis of the valve performance parameters and structural optimization, and finally, the physical experiment proves that the optimized electric proportional valve can effectively reduce the hysteresis within the working pressure range and has good response characteristics to step signals. This paper can provide support for performance analysis and structural parameter improvement of the electric proportional valve.

Improved Design of a Hydraulically Expanded Overhead Cylinder for an Automotive Torsion Beam

The design of hydro-bulge molds, able to provide hollow parts with special-shaped cross-sections, is still a pretty complicated task (especially for what concerns the design of the related hydraulic system and its “synchronization”). In the present work, this task is addressed through the introduction of a new type of overhead cylinder hydraulic synchronization system, able to correct automatically any deviation from the optimal process. Using the AMESim software, the displacement synchronization curve of the piston rods of the two cylinders is obtained and it is verified that the system is able to implement an automatic deviation correction function by adjusting the bidirectional servo valve. A mathematical model for the synchronization system is presented, and the transfer function of the closed-loop control system is determined accordingly. The results show that the system response is generated at about 0.1∼0.2 s with the system reaching an equilibrium state at about 0.2 s.

Influence of nozzle structure on the flow field of the prestage of nozzle flapper servo valve

Influence of nozzle structure on the flow field of the prestage of nozzle flapper servo valve

Elektro-Hidrolik Servo Valf Sisteminin Arı Algoritması (AA) Kullanılarak Modellenmesi

In this study, a method is proposed to find the unknown simulation parameters of an industrial electro-hydraulic proportional valve. Electro-hydraulic servo systems are one of the most widely used actuator systems, and proportional valves are commonly found in hydraulic systems. Hydraulic systems are complicated to linearize, because nearly whole elements are nonlinear, with the inclusion of the valve actuators. The system model must be linearized to make it feasible for analysis of the system linearly or the characteristics must be identified by comparison the output responses suitable for the inputs. However, it is not easy to obtain a perfect system model for use in simulation studies without prior knowledge of the system. Obtaining a perfect model of a system that is not easy to model can be done in two different ways; applying one of the system identification methods after collecting experimental data or using manufacturers' datasheets. In this paper, simulation parameters of MOOG brand D675 series proportional servo valve system were obtained using The Bees Algorithm, an optimization algorithm, to match the dynamic specifications in the datasheet provided by the manufacturer. The obtained system model and the answers are shown graphically and the effectiveness of the proposed method is discussed.

Analysis of pressure oscillation and structural parameters on the performance of deflector jet servo valve

The performance of deflector jet servo-valve is highly affected by the flow field characteristics in the pilot stage of the deflector jet servo-valve. This research used the large eddy simulation method to study the pressure pulsation characteristics of the front stage flow field of DJSV, which has a high significance for the reasonable design of DJSV and the suppression of self-excited oscillation. The geometric model of the three-dimensional flow field of the jet pilot stage of the servo valve deflection plate was established. LES method was used to analyze the influence of the geometric parameters of the jet outlet, amplifier and receiving port on the flow field distribution characteristics of the pre-stage. The results show that pressure oscillation is highly affected by the inlet pressure. Structure optimization is a good solution for decreasing pressure oscillation in deflector jet 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

Research on Hydraulic Servo Valve Control Based on Fuzzy RBF

Aiming at the problems of low control precision and slow response speed of traditional control of actuators in hydraulic systems, the mathematical model of the valve-controlled cylinder is established as the research object, and the control strategy of fuzzy RBF neural network is proposed to control hydraulic servo valves On the basis of traditional fuzzy control, fuzzy control and RBF neural network control are integrated. According to the mathematical model of the system, a tracking controller is designed to realize precise control and real-time feedback of the valve-controlled cylinder system. The simulation results show that compared with traditional PID and fuzzy PID systems, the fuzzy RBF neural network strategy has high control precision, fast response speed, better robustness, and stability.

Analysis on parametric vibration of hydraulic opposing cylinders controlled by a servo valve considering pressure pulsation

During the working process of the system of hydraulic opposing cylinders controlled by a servo valve, the fluid equivalent stiffness changes dynamically due to the pressure pulsation of the pump source. Therefore, the transmission system has obvious nonlinear effects, and its dynamic performance is difficult to improve further. Thus, a nonlinear dynamic model of the system of hydraulic opposing cylinders controlled by a servo valve was established. By using the multiscale method, the steady-state approximate solutions of the primary resonance and the combination resonance of the system were derived to reveal their characteristic laws. The results showed that the dominant frequency of the system's primary resonance is the frequency of the external excitation source, and the dominant frequency of the system's combination resonance is the sum of the natural frequency of each order and the fluctuation frequency of the fluid equivalent stiffness. The amplitude of the combination resonance was smaller than that of the primary resonance. The maximum error between the theoretical natural frequency and the experimental modal frequency was 3.77%, which verified the correctness of the system's nonlinear dynamic model. The research can provide a theoretical reference for the dynamics optimization design of the hydraulic transmission system.