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The temperature-induced variation in operating force of flow control valves may result in performance degradation or even jam faults of fuel metering unit (FMU), which significantly affects the safety of aircrafts. In this work, an analytical modeling approach of temperature-sensitive operating-force of servo valve is proposed to investigate the temperature characteristics in varying temperature conditions. Considering the temperature effects, a new extended model of flow force is built and an analytical model of valve friction is also derived theoretically based on the dynamic clearance induced by thermal effects. The extremum condition of friction is obtained to analyze the characteristic-temperature points where jam faults occur easily. The numerical results show that flow force increases firstly and then decreases as temperature increases under a constant valve opening. The maximum friction of flow servo valve can be uniquely determined when the structural parameters and ambient temperature are given. The worst situation just happens at the characteristic-temperature points, which are linearly related to the axial temperature gradients of valve spool. Such evaluations may give an explanation for the temperature-induced jam faults of vulnerable valves and provide a reference for designers to determine a suitable working-temperature range of valves in practice.

The vibroacoustical reciprocity is proved for systems with a limited number of degrees of freedom. In an experiment, this property is used to check the dynamic validity of the orifice equation for the flow rate of a servovalve. The frequency response function between an impact hammer force and oil pressure next to the servovalve is compared with the frequency response function between the flow rate from the orifice equation and velocity at the impact point. In the frequency range between 100 and 450 Hz, good agreement is obtained. Version of record

Purpose The purpose of this paper is to propose a new simplified numerical model, based on a very compact semi-empirical formulation, able to simulate the fluid dynamics behaviors of an electrohydraulic servovalve taking into account several effects due to valve geometry (e.g. flow leakage between spool and sleeve) and operating conditions (e.g. variable supply pressure or water hammer). Design/methodology/approach The proposed model simulates the valve performance through a simplified representation, deriving from the linearized approach based on pressure and flow gains, but able to evaluate the mutual interaction between boundary conditions, pressure saturation and leak assessment. Its performance was evaluated comparing with other fluid dynamics numerical models (a detailed physics-based high-fidelity one and other simplified models available in the literature). Findings Although still showing some limitations attributable to its simplified formulation, the proposed model overcomes several deficiencies typical of the most common fluid dynamic models available in the literature, describing the water hammer and the nonlinear dependence of the delivery differential pressure with the spool displacement. Originality/value Although still based on a simplified formulation with reduced computational costs, the proposed model introduces a new nonlinear approach that, approximating with suitable precision the pressure-flow fluid dynamic characteristic of a servovalve, overcomes the shortcomings typical of such models.

In the design and development phases of electro-hydraulic actuators (EHAs) used for aircraft flight controls, it is often necessary to carry out accurate and high-fidelity fluid dynamics simulations to evaluate the system behaviour within its entire operating range and, if necessary, investigate its most critical issues. These high-fidelity simulations (nowadays achievable with different techniques and commercial software) generally become pretty expensive from a computational perspective. Therefore, especially in the preliminary design phases or implementing system health monitoring algorithms (in real-time), the need to adopt simplified models emerges definitely (albeit capable of guaranteeing the appropriate level of detail and accuracy). These simplified models are also essential for developing effective and reliable model-based prognostic strategies capable of performing early health assessments of EHA valves. This work proposes a new lumped-parameters simplified numerical model, which, despite having a very compact formulation and reduced computational costs, simulates the internal fluid dynamics of the valve, overcoming some critical issues typical of other models available in the literature. It evaluates valve performance as a function of spool position and environmental conditions (e.g. supply pressure), better-assessing flow rate feedback, internal leakages, and other operating conditions (e.g. spool fine adjustment, pressure supply variable, overpressure, or water hammer). The performance of this numerical model is evaluated comparing with other simplified models published in the literature. Moreover, it is validated with a high-fidelity digital twin that simulates the behaviour of the valve, taking into account the geometry of the spool, the properties of the hydraulic fluid, and the local internal fluid-dynamics (laminar or turbulent regime, cavitation, etc.).

In part I of this study, we experimentally and numerically investigated the pilot stage of a novel two-stage servovalve architecture. The novelty of the proposed configuration is the torque motor being removed and replaced with two small two-way two-position (2/2) valves actuated by piezoelectric ring benders, which can effectively control the opening degree of a main spool valve. With this novel architecture, the typical drawbacks of two-stage servovalves can be overcome, such as the high complexity of the torque motor and the high internal leakage in the pilot stage when the main valve is at rest in the neutral position (null). The low complexity and the negligible internal leakage of the piezo-valves are accompanied by the high response speed typical of piezoelectric actuators. The valve assessment is completed in the present study, since the entire valve architecture (main stage + pilot stage) is investigated. In particular, a simplified numerical model is developed to provide a design tool that allows, for a given main stage spool, the values of the geometrical parameters of the pilot stage to be chosen along with the characteristics of the ring bender. This design procedure is applied to a 7 mm diameter main spool; afterward, a detailed numerical model of the entire valve, solved by SimScape Fluids software, is employed to demonstrate that the response of the main stage valve is very rapid while ensuring negligible internal leakage through the piezo-valves when the main stage is closed (resulting in lower power consumption). For this reason, the proposed valve can be regarded as a “clean” component for energy conversion, having lower energy consumption than commercially available servovalves.

In this paper, we investigate the idea of using, in place of recent linear force motors, amplified piezo-stack actuators for the actuation of direct drive servovalves, in order to exploit the fast response of piezoelements accompanied by the increased displacement ensured by mechanical amplification systems. Some possible architectures are proposed in this paper for the direct actuation of four-way three-position (4/3) servovalves using one or two commercially available amplified piezo-stack actuators having a diamond amplification mechanism. The simplest architecture, which employs only one actuator, is assessed using wellestablished equations implemented in Simulink, allowing the hydraulic, mechanical and electrical parts of the valve to be accurately simulated. Three spools of different size are considered in the simulations in order to obtain performance predictions for different valve flow ratings. From the analysis of the inherent characteristics of the amplified piezo-stack and from the results of the simulations, advantages and disadvantages of this possible architecture are drawn and discussed in detail. Among the advantages, there are the simplicity of construction and the high potential in terms of step response speed and frequency response; the large dimensions, low chip shear force capability and high costs are the main disadvantages.

This paper provides a review of the state of the art of electro-hydraulic servovalves, which are widely used valves in industrial applications and aerospace, being key components for closed loop electrohydraulic motion control systems. The paper discusses their operating principles and the analytical models used to study these valves. Commercially available units are also analysed in detail, reporting the performance levels achieved by current servovalves in addition to discussing their advantages and drawbacks. Adetailed analysis of research that investigates these valves via computational fluid dynamic analysis is also provided. Research studies on novel control systems and novel configurations based on the use of smart materials, which aim to improve performance or reduce cost, are also analysed in detail.

Electrohydraulic servomechanisms (EHAs) are particularly interesting for aviation application, in fact tanks to the high power to weight ration are widely diffused in medium to large cargo and passengers planes or fighters. This work is focused on the proposal of a new dry friction numerical algorithm, based upon Coulomb’s approach, which can be integrated into simulation algorithms obtained by degrading the systems dynamic models (e.g. an over-damped second-order system reducible to a simpler first-order one). This approach, if correctly applied, significantly reduces the computational burden, without significant losses in simulation accuracy. The authors evaluated the approach proposed by a numerical test bench simulating the behaviour of an electrohydraulic linear actuator commonly used in primary flight controls.

This paper presents research aimed at understanding the effects of geometrical imperfections and tolerances upon the internal leakage occurring around null in the main stages of servovalves. Specifically, a two-dimensional (2D) computational fluid dynamic analysis was used to predict the direct leakage flow as a function of the overlap and clearance between the spool and bushing sleeve, as well as the roundness on the edges of the spool and bushing sleeve. Predictions of direct leakage flow against edge overlap, which have general validity, are provided in the paper for three selected values of the pressure drop. For different values of the pressure drop, analytical correlations can be applied using the data retrieved from these graphs. The analysis shows that the leakage flow is highly affected by the above-mentioned geometrical parameters. As expected, for given values of overlap and radial clearance, the greater the roundness of the edges caused by manufacturing processes or wear, the higher the leakage flow. For low leakage and hence low power loss requirement, the radii on the spool and bushing sleeve as well as the clearance must be maintained as low as possible. In addition, it is well-known that overlap between the spool and its bushing sleeve can help to reduce the leakage flow at null, and the effect of edge roundness on this reduction is now revealed.

Highly detailed computer models are required for design and development of modern flight control systems, capable of emulating with high accuracy the behaviour of on-board equipment. At the same time, different simplified models are needed, specifically intended for operations such as the optimization of preliminary design and the development of diagnostic or prognostic strategies. These simplified models are required to combine sufficient levels of accuracy and reliability with reduced computational costs, to minimize the computational burden associated with prognostic and optimization algorithms. In this work, we focus on electro-hydraulic actuators, since they are critical subsystems in terms of safety and availability of the aircraft. Advanced monitoring and prognostic algorithms require new numerical models, combining an acceptable computational effort with a satisfying ability to simulate their performance and dynamics. To this purpose, this paper proposes a new simplified numerical model of the servovalve fluid-dynamic behaviour. This numerical algorithm, based on a very compact semi-empirical formulation, is intended to take into account in a simplified but sufficiently accurate way several typical effects related to the SV spool geometry and the operating conditions. To evaluate the approximations introduced by this model into a system-level simulation, it has been integrated into a dedicated numerical model simulating a simple electrohydraulic on-board actuator, and compared with a higher fidelity servovalve model.

The development of modern flight control system requires more and more highly detailed computer models in order to analyze their specific behavior as a whole or related to their components and subsystems; on the other hand, especially in the phases of preliminary design or development of diagnostic or prognostic algorithms, it is necessary to implement simplified models that are able to combine sufficient levels of accuracy and reliability with reduced calculation times and computational costs. In this paper, the authors analyze the possibility of building more simple, synthetic models, with the aim to maintain an acceptable level of accuracy but being able to analyze the dynamic behavior of entire systems. This work focuses on the numerical models related to fluid-dynamics of servovalves, where the related algorithms are characterized by a semi-empirical formulation and will take into account the effects of variable supply pressure and leakage (which is related to the control ports connecting the valve to the motor elements). Two new models are proposed and compared with a detailed reference. This comparison is performed by evaluating the performance of the different models and their ability to describe the fluid dynamic behavior of the considered valve.

This paper proposes a novel architecture for the pilot stage of electro-hydraulic two-stage servovalves that does not need a quiescent flow and a torque motor as well as a flexure tube to operate. The architecture consists of two small piezoelectric valves, coupled with two fixed orifices, which allow variation of the differential pressure at the main stage spool extremities in order to move it with high response speed and accuracy. Each piezoelectric valve is actuated by a piezoelectric ring bender, which exhibits much greater displacement than a stack actuator of the same mass, and greater force than a rectangular bender. The concept is intended to reduce the influence of piezoelectric hysteresis. In order to assess the validity of the proposed configuration and its controller in terms of spool positioning accuracy and dynamic response, detailed simulations are performed by using the software Simscape Fluids. At 50% amplitude the −90° bandwidth is about 150Hz.

Servohydraulic systems are widely used for actuation where high force and fast response are needed, and the servovalve is the type of control valve which provides the highest performance for such systems. In aerospace, servovalves are used for many safety critical systems, such as flight control, steering and braking. However, during the last fifty years the conventional two stage servovalve design for aerospace applications has hardly changed. Due to the desire for increased energy efficiency, there is a need to make valves more efficient and lighter. A new type of servovalve for aerospace applications is therefore investigated. Increased efficiency implies that leakage should be small, and other key requirements are reliability, robustness and low manufacturing cost. The aim of this research is to provide background knowledge so that in the future an improved two stage servovalve can be manufactured. The prototype valve in this research will not be lightweight, but will provide knowledge for a future researcher or manufacturer to create a light weight servovalve.A two stage servovalve was designed with a multi-layer piezoelectric ring bender actuating a low leakage small spool as a first stage to control a second stage spool with electrical position feedback. The valve body was manufactured through Additive Manufacturing. A dynamic model of the complete valve was developed and correlated with experimental data. The model included the drive amplifier for the piezoelectric ring bender, the ring bender with hysteresis, first stage spool with overlap and the second stage spool. This showed that hysteresis and overlap had a significant effect on valve behaviour.A second stage spool position controller was developed to counteract the non-linear behaviour due to the piezoelectric hysteresis and the dead-band due to the first stage overlap. The controller also includes a feed forward path to increase the bandwidth of the valve. This controller outperforms a conventional Proportional-Integral controller and is also less sensitive to amplitude change.Mounting a ring bender sufficiently stiffly so that it can generate a high blocking force, but also in such a way that the deformation and hence the free displacement of the ring bender is not constrained, is a significant challenge. An analytical model to optimize the ring bender mount has been developed. This model can be used to find the optimum mount overlap at the outer edge of the ring bender, and the optimum thickness of the mount.An extensive investigation of the durability of the ring bender in Hyjet has been completed. Hyjet is a tradename for a fire-resistant phosphate-ester hydraulic fluid commonly used in civil aerospace. The ring bender will quickly start to break down if the Hyjet reaches the electrical connections. The Hyjet will penetrate the ceramic and create an electrical circuit between the electrical connection, the Hyjet and the outermost internal electrode. The breakdown of the ring bender can probably be eliminated by protecting the ceramic with an impermeable layer of material. In this research a metallic foil applied to the surface of the ring bender was investigated.

Glavni predmet v okviru magistrskega dela je zasnovati in zgraditi dve identični servohidravlično osi, ki bi bili primerni za uporabo v testnih sistemih, bodisi za testiranje materialov in strojnih sklopov ali pa za testiranje in razvoj raznovrstnih regulacijskih algoritmov. Tako bo omogočeno testiranje različnih konceptov regulacije na primerih regulacija sile, regulacija položaja, regulacija ob spremembi bremena, povišani dinamiki s podvojenim pretokom, itd. Prvi del naloge je posvečen spoznavanju različnih izvedb servohidravlični linearnih osi, študiju področij uporabe tovrstnih osi in njihovih posameznih gradnikov. V nadaljevanju bo problematika usmerjena v načrtovanje mehanskih sestavnih delov servohidravlične osi, kjer bo v ospredju ustrezna togost izvedbe osi, kot integraciji ostalih komponent kot je merilni sistem položaja, priključna plošča za en oziroma dva servoventila in hidravličnih akumulatorjev. Dimenzioniranje mehanskih delov servo osi z ustreznimi spremenljivkami bo izvedeno s pomočjo programskega orodja “SOLIDWORKS”. Naslednje poglavje bo namenjeno izbiri in vgradnji senzorskih in krmilnih naprav in merilnik položaja ter servoventil, pri čemer bodo v ospredju karakteristike omenjenih komponent. Za krmiljenje teh komponent bo izbrana ustrezna oprema za zajemanje signalov in vodenje servo osi. Vse omenjene komponente bodo sestavljene v funkcionalno celoto, ter preverjeno njihovo delovanje. V zaključnem poglavju bo prikazan še pristop k snovanju ustreznega fizikalnega modela linearne osi, ki bo služil kot simulacijski model za kasnejše aplikacije regulacij The main goal of the present thesis is to design and build two identical hydraulic servo linear actuators for testing applications. In this term, modelling and analysing the rigidity and performance of servocylinder by taking account of the pressured fluid flow into the cylinder and on cylinder extend are illustrated. An electrically operated valve that controls how hydraulic fluid is ported to the cylinder is mounted. Electronic devices such as linear displacement transducer for position measurement and servo amplifier are integrated. In order to drive the electro-hydraulic servo actuator, closed-loop servo system is realized. The first part of the thesis is an introduction to hydraulic servo systems, in which figures the importance and uses of electro-hydraulics servo linear actuator in industrial applications. The following part describes all hydraulic components used, at which specify more about their characteristics and specificities. Final results evaluate the cylinder capabilities and the differences analysis by using a single direct-operated servovalve. Model aspect using two servovalves will be introduced. The chapter will also associate the design of a corresponding mounting plate and assembly table, which are respectively designed for the use of a single servovalve. A hydraulic base plate is also needed for the install. Design dimensioning of the mechanical parts of the servocylinder with their relevant variables will be realized by using 3D CAD Design software program. Final realization contributes to test different problem concepts of electro-hydraulics servo systems in term of control mechanism such as position control, force control, speed control under (or without) load changes.

This book deals with the development and testing of high-response piezo-servovalves for improved performance of electrohydraulic cylinder drives. Performance improvement means in the context of this work an enhancement of reference and disturbance response of the drive in a closed-loop pressure and position control. Reference and disturbance responses determine the precision of the drive which influences product quality and motion accuracy in stationary and mobile applications. This thesis shows by means of linearised mathematical models that the drive performance can be significantly improved by high dynamics of the control valve. The increase in valve dynamics can be achieved by the use of piezoelectric actuators, which outmatch the response of common electromechanical valve actuators. Within the scope of this work two different novel high-response piezo-servovalves are prototyped. These are four-way directional flow control valves with linear spools. The book presents different steps of the design and development process of the valves such as conceptual design, calculation, dimensioning, manufacturing, design of internal valve control, testing according to the internationally standardized procedures and comparison to the performance of common servovalves. The achieved dynamics of the piezo-servovalves surpasses the response of the conventional valves. Exemplary investigations of an electrohydraulic cylinder drive show an improved reference response of pressure control by 50% and an enhanced disturbance response of position control by 40% due to the use of the piezo-servovalve at the drive. This work demonstrates that the commercially available piezo-actuators can be successfully implemented in industrial hydraulic valves, bringing advantages for the overall drive performance. The high reliability and endurance of the piezo-actuators have already been proven by the use in common rail fuel injectors in the automobile industry since 2002. Taking into account falling costs of the actuators due to the mass production for the automobile industry they can become a very attractive alternative or supplement for hydraulic valve technology.

Made available in DSpace on 2014-06-11T19:27:14Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-02-05Bitstream added on 2014-06-13T20:55:57Z : No. of bitstreams: 1 alegre_dm_me_ilha.pdf: 954109 bytes, checksum: 3e5701b2e8747b004da37b4ca12ca513 (MD5) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) O presente trabalho apresenta a metodologia dos observadores de estado para a detecção e localização de falhas em sistemas contendo elementos finitos de placas de Kirchoff. Tal metodologia consiste na montagem de um banco de observadores de estado, o qual é capaz de detectar falhas presentes no sistema, além de localizar o componente danificado e a porcentagem de falha. As matrizes de ganho dos observadores de estado foram determinadas por dois métodos distintos: o método Regulador Quadrático Linear e das Desigualdades Matriciais Lineares. Nesse trabalho, foi utilizada uma placa plana fina montada sobre um sistema de suspensão similar ao de uma plataforma veicular, representando um veiculo simplificadamente. A modelagem da plataforma utilizada foi realizada mediante a utilização do método dos elementos finitos, considerando-se diferentes números de elemento no modelo. O tipo do elemento finito utilizado foi o elemento de placa de Kirchoff. Adicionalmente foi analisada a influência de elementos de controle junto à suspensão da plataforma no movimento da mesma. O modelo considerado, juntamente com os programas computacionais desenvolvidos, foram utilizados para a simulação do movimento da plataforma. Na literatura, normalmente são apresentadas simulações para o movimento de apenas ¼ do veículo, neste trabalho, no entanto, os programas desenvolvidos podem simular o movimento do veiculo inteiro. Foram realizadas simulações computacionais para o movimento da plataforma com a finalidade de se detectar e localizar falhas introduzidas nos elementos da suspensão e também foram realizados testes experimentais, com os mesmos fins. Mediante tais testes (teóricos e experimentais) verificou-se a eficácia da metodologia desenvolvida e a sua principal limitação: o número de elementos finitos considerado no modelo relacionado com o número de medidas efetuadas e a observabilidade do sistema. This work presents the state observers methodology for the detection and location of faults in systems containing finite elements of plate of Kirchoff. This methodology consists in the assembly of a bank of state observers, which is capable of detecting faults in the system, and also to locate the damaged component and the percentage of failure. The gain matrices of the state observers were determined by two different methods, these are the method Linear Quadratic Regulator and the Linear Matrix Inequalities. In this work was considered a thin plate mounted on a suspension system that is similar to a vehicle platform, representing a vehicle in a simplified way. The modeling of the platform used was performed by using the finite element method, considering different numbers of element in the model. The finite element used was the Kirchoff’s plate element. It was also studied the influence of elements of control, together with the suspension of the platform, into its movement. The model considered, together with the developed computational programs, were used to simulate the movement of the platform. In the literature, usually are presented simulations for the movement of only ¼ of the vehicle, in this work, the developed programs can simulate the movement of the entire vehicle. It was realized computational simulations for the movement of the platform in order to detect and locate faults introduced in the elements of the suspension and experimental tests were also conducted with the same purpose. Through such tests (theoretical and experimental) it was verified the effectiveness of the developed methodology and its major limitation: the number of finite elements considered in the model related with the number of outputs and the observability of the system.