Nozzle-flapper Servo Valve Research Articles

Mathematical Modeling of an Armature Assembly in a Flapper–Nozzle Servo Valve Based on the Finite Element Method

Mathematical Modeling of an Armature Assembly in a Flapper–Nozzle Servo Valve Based on the Finite Element Method

Vibration suppression of an armature assembly in hydraulic servo valve based on distributed parameters mathematical models

As a commonly used hydraulic control component, the nozzle-flapper servo valve has the advantages of small structure and sensitive dynamic response. Due to the small size and complex structure of the servo valve, the classical control methods based on various feedback information cannot effectively improve its performance. In order to effectively improve the performance of the servo valve, this paper implemented the feedforward control method to suppress the dynamic performance of the armature assembly of the servo valve. The distributed parameters mathematical models of the armature assembly are established and verified which can accurately predict the vibration of the armature assembly. With the mathematical model, the feedforward control signal is calculated based on the real-time velocity, acceleration, and deflection of the armature assembly, respectively. The applicability of different signals is analyzed and the signals calculated by velocity and deflection are verified which can effectively suppress the vibration amplitude of armature assembly. The numerical simulation and experimental methods are implemented to verify the performance of different control signals and the optimal feedforward control signal under different external loads is obtained.

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

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.

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

Cavitation suppression in the nozzle-flapper valves of the aircraft hydraulic system using triangular nozzle exits

Hydraulic control system is one of the fundamental subsystems of the various aircraft systems, e.g., flight control system, brake system and fuel regulation system. As a pivotal actuator of the hydraulic control system, the nozzle-flapper servo valve converts the control signals to the hydraulic output. The flow cavitation in the valves could lead to some intractable problems, e.g., vibration, noise and erosion, which could produce detrimental effects on the performance and reliability of the hydraulic system, even damage the aircraft. This work provides a numerical investigation on the cavitation attenuation in the nozzle-flapper valve using triangular nozzle exit. The flow imaging and mass flow rate measurement are conducted to qualitatively and quantitatively verify the numerical model, respectively. It is observed that the presence of the vapour phase is remarkably suppressed under the effect of the triangular nozzle exit. For both circular and triangular nozzle exits, the occurrence of the vapour phase is highly affected by the nozzle-to-flapper distance, inlet pressure and chamber diameter while the flapper diameter exerts an insignificant impact on the formation of the vapour phase. Compared with the circular nozzle exit, the triangular nozzle exit could effectively reduce the flow cavitation at the same geometry and inlet pressure. The physical mechanism behind the cavitation suppression may be ascribed to the generation of the inclined impinging jet upon the chamber wall and the wall jet without impingement.

Dynamic Characteristics of the Jet Force on the Flapper of the Pilot Stage in a Flapper Nozzle Servo Valve Under the Flow-Solid Interaction

Nowadays, more and more attention has been paid to improve the performance of the nozzle flapper servo valve. As a core part of nozzle flapper servo valve, the armature assembly is affected by electromagnetic force, jet force and feedback force at the same time. Due to the complex structure of the pilot stage flow field and the high jet pressure, the prediction of the jet force has always been difficult in modeling the transient motion of the servo valve. Whereupon, a numerical simulation method based on the flow-solid interaction(FSI) is applied to observe the variation of the jet force when the flapper is moving. Different parameters are employed to seek a suitable numerical simulation model which can balance the accuracy and computational cost. By comparing with the experiment results, the effectiveness of numerical simulation method in predicting the variation of the jet force and cavitation is verified. By this numerical simulation model, the distribution of flow field and the force on the flapper predicted by the moving and fixed flapper are compared. The results show that more dynamic details are achieved by the transient simulation. By analyzing the numerical simulation results of different inlet pressures and flapper vibration frequencies, the relationship between the movement of the flapper, the flow field distribution, the jet force and the inlet pressure is established, which provides a theoretical basis for the subsequent modeling of the armature assembly.

Mathematical modeling of an armature assembly in pilot stage of a hydraulic servo valve based on distributed parameters

The dynamic performance of a nozzle-flapper servo valve can be affected by several factors such as the disturbance of the input signal, the motion of the armature assembly and the oscillation of the jet force. As the part of vibrating at high frequency, the armature assembly plays a vital role during the operation of the servo valve. In order to accurately predict the transient response of the armature assembly during the vibration, a mathematical model of armature assembly is established based on the distributed parameters method (DPM) and Hamilton principle. The new mathematical model is composed of three main parts, the modal eigenfunction, modal mechanical response expressions of the spring tube and the motion equation of the other armature assembly. After programing, the purpose of using the DPM to predict the dynamic response of different positions located on the armature assembly is achieved. For verifying the validity of the mathematical model, the finite element method (FEM) and classic model (CM) of armature assembly are applicated by commercial software under the same condition. The comparison results prove that the DPM can effectively predict the axial and tangential deflection of the armature assembly different positions which the CM can’t duing to its over-simplification. A certain error is generated when predicting the axial deformation at different heights by DPM, which is caused by an approximate method to simulate the torsion of the spring tube. The comparison results of the spring tube deflection at different vibration frequencies shows that the adaptability of DPM is significantly higher than the classic model, which verify the model is more adaptable for predicting the dynamic response of the armature assembly.

Numerical Simulation and Experimental Research on Flow Force and Pressure Stability in a Nozzle-Flapper Servo Valve

In the nozzle flapper servo valve, the transient flow force on the flapper is the fundamental reason that affects the pressure stability. The pressure pulsation in the pilot stage causes forced vibration of the flapper, and its deviation will directly influence the control pressure difference, which will make the pressure appear unstable. In order to grasp the principle and characteristics of transient flow force and its influence on pressure stability, a mathematical model of flapper displacement and control pressure is derived. For collecting the dynamic changes of the transient flow force and recording the motion behavior of the flapper, a three-dimensional model of the pilot-stage is established. Numerical simulations of turbulence phenomenon analysis are conducted with a variation of flapper displacement ranging from 5 μm to 20 μm. It can be concluded that the change trend of the flapper displacement is similar to the steady-state flow force and the transient flow force pulsation amplitude. Under the same structural parameters, the pulsating frequency of the flow force remains basically constant. The fluctuation of the flow force of the pilot stage will cause the pressure of the servo valve control cavity to vibrate to a certain extent, which is a factor that cannot be ignored that affects the output stability of the servo valve.

Distributed parameters modeling for the dynamic stiffness of aspring tube in servo valves

The stability and dynamic performance of a flapper-nozzle servo valve depend on several factors, such as the motion of the armature component and the deformation of the spring tube. As the only connection between the armature component and the fixed end, the spring tube plays a decisive role in the dynamic response of the entire system. Aiming at predicting the vibration characteristics of the servo valves to combine them with the control algorithm, an innovative dynamic stiffness based on a distributed parameter model (DPM) is proposed that can reflect the dynamic deformation of the spring tube and a suitable discrete method is applied according to the working condition of the spring tube. With the motion equation derived by DPM, which includes the impact of inertia, damping, and stiffness force, the mathematical model of the spring tube dynamic stiffness is established. Subsequently, a suitable program for this model is confirmed that guarantees the simulation accuracy while controlling the time consumption. Ultimately, the transient response of the spring tube is also evaluated by a finite element method (FEM). The agreement between the simulation results of the two methods shows that dynamic stiffness based on DPM is suitable for predicting the transient response of the spring tube.

A Numerical Research on Vortex Street Flow Oscillation in the Double Flapper Nozzle Servo Valve

The oscillating flow field of the double nozzle flapper servo valve pre-stage is numerically analyzed through Large Eddy Simulation (LES) turbulent modeling with the previous grid independence verification. The vortex street flow phenomenon can be observed when the flow passes through the nozzle flapper channel, the vortex alternating in each side produces the periodical flow oscillation. The structural and flow parameter effects on the oscillating flow are emphasized, and it could be determined that the pressure on the flapper is nearly proportional to the flow velocity and inversely proportional to the actual distance between the flapper and the nozzle. On the other hand, the main frequency of oscillation decreases with the velocity and increases with the distance between the nozzle flapper. The main stage movement is further considered with a User Defined Function (UDF), and it could be determined that the influences of the structural and flow parameters on the flow oscillation are rarely changed, but the main frequencies drop, generally.

A dual lane piezoelectric ring bender actuated nozzle-flapper servo valve for aero engine fuel metering

Amongst many other high performance flow control applications, servo valves are used to control aero engines by metering the fuel delivered from the fuel pump. Conventionally, a fuel metering servo valve has a pilot stage with an electromagnetic torque motor moving a flapper which differentially restricts a pair of nozzles to create a hydraulic signal (i.e. a pressure difference). These valve pilot stages use mature, optimised technology such that to achieve improvements requires a novel approach. Torque motors in particular present reliability and manufacturing difficulties, and news solutions should ultimately allow a reduction in manual assembly and set-up, improve repeatability, and eliminate failures associated with fine wire devices. In this paper, a pilot stage actuated by piezoelectric ring benders is proposed, designed, built and tested, and test results are compared with a model used to predict pressure-flow characteristics. A particular challenge is the need to include redundancy, and thus a pair of ring benders is used, allowing isolation between duplicated electrical control channels. Another challenge is the mounting of the ring bender, which has to flex to allow the outer edge of the ring bender to deform, yet be stiff enough to adequately react against generated forces. O-ring mounts made from three different elastomer materials are compared in this study. In aerospace, an added complication is the large range of fuel temperature; F70 fluorosilicone O-rings have been chosen with this in mind, and successfully demonstrated in the range −50 °C to +180 °C. With one active and one inactive ring bender to simulate a failure condition, the new dual lane pilot stage achieves +/−50 μm displacement under test, giving control port flows up to +/−0.6 l min−1, and a control port pressure variation of 40 bar using a 100 bar supply pressure difference (supply minus return pressure). This research establishes that a piezoelectric aero engine fuel valve is feasible, and in particular, that piezoelectric ring bender actuators with elastomeric mountings are highly suited to this application.

Cavitation and flow forces in the flapper-nozzle stage of a hydraulic servo-valve manipulated by continuous minijets

Electro-hydraulic servo-valves play key roles in modern electro-hydraulic power systems in many industrial applications. As one of the widely used hydraulic servo-valves, cavitation in the flapper-nozzle servo-valve could produce deleterious effects of noise, flapper vibration and cavitation erosion. In this work, a numerical investigation has been conducted on the manipulation of the flapper-nozzle pilot valve using continuous minijets. Two minijets are symmetrically deployed around the main jet of each nozzle. Vapor fraction and flow forces under the effect of the continuous minijets are compared in detail between the traditional nozzle and the nozzle with the minijets. It is found that cavitation in the flapper-nozzle stage is greatly weakened under the effect of the continuous minijets. The remarkable drop in the radial jet velocity results in the suppression of the swirling structures in the annulus, which may be responsible for the cavitation reduction. The variation trend of the flow forces with the inlet pressure remains unchanged while the magnitude of the flow forces is varied slightly, depending on the various surfaces of the flapper.

Numerical Simulations on Flow Characteristics of a Nozzle-Flapper Servo Valve With Diamond Nozzles

Nozzle-flapper servo valves are widely used in modern electro-hydraulic control systems of many engineering applications. Flow cavitation in the nozzle-flapper pilot stage could produce noise and cavitation erosion, reducing the performance stability and reliability of the servo valves. In this paper, diamond nozzles are proposed to replace the traditional circular nozzles to reduce the flow cavitation in the nozzle-flapper stage. Numerical simulations using CFD software ANSYS/FLUENT were conducted to explore the flow characteristics of the nozzle-flapper pilot stage. Mass flow rate and image measurements were performed to verify the simulation results. Vapor fraction, lateral velocity, pressure distribution, and flow force are compared in detail between the pilot stage with the traditional nozzles and with the diamond nozzles. It is found that the vapor fraction is greatly reduced under the effect of the diamond nozzles. Finally, to explore the effect of the diamond nozzles on the performance of the nozzle-flapper servo valve, the pressure-flow characteristics and time step response of the load flow rate are examined using the software AMESim. The simulation results show that the pressure-flow characteristics and time step response of the load flow rate almost remain the same. This suggests that the diamond nozzles could suppress the cavitation in the nozzle-flapper servo valve without varying its performance.

Numerical simulation and experimental research of the flow force and forced vibration in the nozzle-flapper valve

Abstract In the pilot stage of nozzle-flapper servo valve, the flow force on the flapper is the key reason that leads to forced vibration of the armature assembly, which may result in the fatigue of the flexure tube in torque motor. To master the principles and features of the flow force and the source of the forced vibration of the armature assembly, mathematical models of flow force and the forced vibration are deduced in this paper. For validating the model, a three-dimensional model is built and a finite element analysis of the flow force with different inlet pressure and deflections is presented and an innovative and experimental rig for measuring the steady and dynamic frequency of flow force is also designed. The characteristic of the main flow force, minor flow force and total flow force are analyzed contrastively, and the experimental results agree well with the CFD results and mathematical model analysis. To find the source of forced vibration of the armature assembly, a knocking method is proposed to measure the natural frequency of armature assembly. By comparing the spectrum of the pressure and vibration movement through experiments, a conclusion can be drawn that the inlet pressure fluctuation near the natural frequency of armature assembly and the asymmetric structure of pilot stage are the necessary and sufficient conditions to make the armature assembly yield forced vibration. In the end, some suggestions have been made to decrease the intensity of forced vibration of the pilot stage according to the findings.

Comparison of jet pipe servo valve with flapper nozzle servo valve


 
 
 Electro-hydraulic servo valves (EHSVs) serve as an interface between electrical devices and hydraulic systems. They are capable of converting low power electrical input into movement of a spool to control precisely high power, low speed hydraulic actuators. Nowadays, jet pipe electro-hydraulic servo valve and flapper nozzle electro-hydraulic servo valve are typical two-stage control flow servo valve and are the most popular in use. This paper recommends and compares characteristics, working principle and structure for two kinds of servo valve. Besides, the simulation was carried out in a commercially software of Ansys, hence some features of jet pipe servo valve such as outstanding advantages of working feature or reliability are analysed. 
 
 

Dynamic modeling and experimental investigations of a magnetostrictive nozzle–flapper servovalve pilot stage

A magnetostrictive nozzle–flapper servovalve pilot stage is presented in this article, which is directly driven by a giant magnetostrictive actuator and features three nozzles for the development of large flow rate servovalve. According to the energy conversion sequence in this servovalve, a giant magnetostrictive actuator magnetization model, a giant magnetostrictive material rod eddy loss model and a servovalve dynamic pressure model are all established to enable quantitative depiction and modelling of the dynamic pressure response process of magnetostrictive nozzle–flapper servovalve pilot stage. Consequently, the matched simulation model of the magnetostrictive nozzle–flapper servovalve pilot stage with the mathematic model is followed to be established, and two unknown parameters of complex permeability are determined using the test data from the giant magnetostrictive actuator. By running this simulation model, flapper displacement and output pressure under different structural parameters and variational excited frequencies are determined, certain parameters that are sensitive to the dynamic characteristics of magnetostrictive nozzle–flapper servovalve pilot stage driven by giant magnetostrictive actuator are found and the accompanying rules are revealed. Finally, the experimental system of a magnetostrictive nozzle–flapper servovalve pilot stage driven by giant magnetostrictive actuator was built; both the step-input voltage response curve and the sine-input voltage response curve were captured; and these curves show that the amplitude bandwidth (−3 dB) and the phase bandwidth (−90°) of a magnetostrictive nozzle–flapper servovalve pilot stage can approach 150 and 110 Hz, respectively, which exhibit good agreement with the simulation results. Therefore, the magnetostrictive nozzle–flapper servovalve pilot stage offers a very promising prospect of the novel servovalves with the high-frequency response and the large flow rate.

Numerical simulation and experimental study of heat-fluid-solid coupling of double flapper-nozzle servo valve

The double flapper-nozzle servo valve is widely used to launch and guide the equipment. Due to the large instantaneous flow rate of servo valve working under specific operating conditions, the temperature of servo valve would reach 120°C and the valve core and valve sleeve deform in a short amount of time. So the control precision of servo valve significantly decreases and the clamping stagnation phenomenon of valve core appears. In order to solve the problem of degraded control accuracy and clamping stagnation of servo valve under large temperature difference circumstance, the numerical simulation of heat-fluid-solid coupling by using finite element method is done. The simulation result shows that zero position leakage of servo valve is basically impacted by oil temperature and change of fit clearance. The clamping stagnation is caused by warpage-deformation and fit clearance reduction of the valve core and valve sleeve. The distribution rules of the temperature and thermal-deformation of shell, valve core and valve sleeve and the pressure, velocity and temperature field of flow channel are also analyzed. Zero position leakage and electromagnet’s current when valve core moves in full-stroke are tested using Electro-hydraulic Servo-valve Characteristic Test-bed of an aerospace sciences and technology corporation. The experimental results show that the change law of experimental current at different oil temperatures is roughly identical to simulation current. The current curve of the electromagnet is smooth when oil temperature is below 80°C, but the amplitude of current significantly increases and the hairy appears when oil temperature is above 80°C. The current becomes smooth again after the warped valve core and valve sleeve are reground. It indicates that clamping stagnation is caused by warpage-deformation and fit clearance reduction of valve core and valve sleeve. This paper simulates and tests the heat-fluid-solid coupling of double flapper-nozzle servo valve, and the obtained results provide the reference value for the design of double flapper-nozzle force feedback servo valve.

Design and experiment of novel piezoelectric double nozzle flapper electro-hydraulic servo valve

To improve the performance of the existing nozzle flapper type electro-hydraulic servo valve, a novel piezoelectric double nozzle flapper electro-hydraulic servo valve (PDNFESV) is proposed. An electricity-machine transducer is designed to replace the torque motor in the traditional nozzle flapper servo valve. The electricity-machine transducer is constructed by two identical piezoelectric bimorphs and a beryllium bronze board. The design and fabrication of the electricity-machine transducer is introduced. The structure and work principle of the novel PDNFESV is analysed. The static and dynamic characteristic of the electricity-machine transducer are tested, the experimental results show that the designed electricity-machine transducer can meet the demand of the novel PDNFESV. At last, the performance indexes of the novel PDNFESV are researched.

Nonlinear Simulation and Linearization of Twin Flapper-nozzle Servo Valve

To investigate the dynamic and static performance of electro-hydraulic servo control system in theory,the accurate mathematic model of twin flapper-nozzle servo valve needs to be established.Firstly,for the non-linear effect of flow in twin flapper-nozzle servo valve,the nonlinear characters of valve's electrical signal input to spool displacement output are analyzed,then a nonlinear model is set up to represent the actual system.Secondly,according to the character of actual system model,the localized linear model is achieved by nonlinear state feedback transforming,which is based on the input-output linearization method.then this model's validity is proved theoretically by stability analysis of the system's zero dynamic state.Finally,the linearization model of Taylor series expansion is chosen as the comparative object,the simulation and experiment results are provied to analysis the accuracy of the linear model.Results show that the local linear model achieved by nonlinear state feedback transforming more appropriate for the actual systems and has strong robustness.