Abstract
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.
Highlights
Two stage servovalves are fundamental components for closed loop control systems requiring high precision, fast response speed, and high reliability, being widely used both in aircraft and industry [1,2,3].The main stage is typically a spool valve, whereas the pilot stage may employ a double nozzle flapper, a deflector jet, or a jet pipe, each actuated by a torque motor to generate a differential pressure at the extremities of the main spool to force it to move, modulating flow
We studied a novel architecture of servovalve based on the use of two ring benders in place of the torque motor
A scheme of the proposed architecture employing ring benders is shown in Figure 3; it is composed of two small two-way two-position (2/2) piezo-valves, which are tasked with changing the pressure at the extremities of a main spool of a typical four-way valve
Summary
Two stage servovalves are fundamental components for closed loop control systems requiring high precision, fast response speed, and high reliability, being widely used both in aircraft and industry [1,2,3]. Recenttransformer studies showed thatfor thethe problem related to theofweight canposition Another associated that withcan these valveshigher is the high complexity number benders of parts bender, whichdrawback is a piezo-actuator provide actuation forces and thanhigh rectangular of the torque motorcompact assembly, which significantly affect manufacturing cost torquea while being more and lighter than piezo-stacks. Some piezo-actuators available on the market are lighter than both stack actuators and amplified stack actuators, namely rectangular benders These actuators have recently been employed to drive the pilot stage of servovalves [17,18,19,20]; in this case, the main drawback is the very low actuation forces provided by these actuators. The transient behavior of the obtained valve configuration is assessed using the full numerical model solved by SimScape Fluids [24]
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