每日一词｜飞行控制伺服阀Flightcontrolservovalves

飞行控制伺服阀
Flight control servo valves

Nature and Purpose
A servo valve is an electrically- operated valve that uses feedback to precisely control the position of an internal device (either flapper nozzle or jet pipe) to control the fluid flow. The term electrohydraulic servo valve is often used because servo valves are controlled through an electrical signal and are usually used in hydraulic systems. Servo valves operate with very high accuracy, very high repeatability, very low hysteresis, and very high frequency response. Servo valve systems feature high response characteristics, high reliability, accurate position control, velocity control and force control.
Servo valves are used when accurate position control is required, such as control of a primary flight control surface. Position control is achieved through a closed loop control system, consisting of command sensor, feedback sensor, digital or analog controller, and the servo valve. Servo valves can be used to control hydraulic actuators or hydraulic motors. A servo valve and actuator combination are referred to as a servo- actuator. The main advantage of a servo valve is that a low power electrical signal can be used to accurately position an actuator or motor.
The primary components in a servo valve are a torque motor, flapper nozzle or jet pipe, and one or more spools (servo). Servos in aerospace servo valves are typically zero lapped, which means the width of the lap and the width of the flow port are equal. Thus, there is only one position for zero flow. This configuration generally results in the tightest control and is commonly selected for high precision servo valves.
The servo valve has a hydraulic pressure inlet and an electrical input for the torque motor. The input current controls the flapper position. The flapper position controls the pressure in the chambers of the actuator. So, a current ( or -) will position the flapper, leading to a pressure differential on the servo, which causes the servo to move in one direction or the other. Movement of the servo ports hydraulic pressure to one side of the actuator or the other, while porting the opposite side of the actuator to return.
Most servo valves incorporate a feedback spring between the pilot spool and the flapper. If the flapper moves to the left, the pressure differential on the pilot spool moves the spool to the right. The feedback wire will then pull the flapper back towards the neutral position. Hence the feedback wire provides a stabilizing force to the flapper and helps improve stability and response of the flapper system. Servo position is determined by a force balance on the spool, which includes the pressure differential created from the flapper nozzle, friction forces, spring forces and flow forces acting on the spool.
Thrust vector control (TVC) is used when the aerodynamic surfaces are inadequate to control the missile or when a greater agility may be required of the missile. The TVC subsystem is used to gimbal the entire rocket engine (typical for liquid engines) or gimbal the rocket nozzle (typical for solid rocket motors) or move jet vanes in the nozzle section of the thrust chamber to provide precise steering for the missile. The gimbal or jet vane movement is accomplished by actuators. The motions of the hydraulic actuators are controlled by servo valves, which in turn are controlled by commands from the vehicle"s guidance system.
Servo valves are encountered in a wide range of modern industrial applications because of their ability to handle large inertia and torque loads and, at the same time, achieve fast responses and a high degree of both accuracy and performance. Typical applications include active suspension systems, control of industrial robots, and processing of plastic. They are also ubiquitous in commercial aircraft, satellites, launch vehicles, flight simulators, turbine control.
性质和用途
伺服阀是一种电动操作阀门，利用反馈精确控制内部设备的位置(喷嘴挡板或喷管)，从而控制液流。由于伺服阀通过电信号控制并通常用在液压系统中，因此常常会使用电液伺服阀一词。伺服阀在工作时具有极高的精度、极高的开始重复使用性、极低的磁滞性和极高的频率响应性。伺服阀系统具有高响应特性、高可靠性以及精确位置控制、速度控制和力控制等特点。
伺服阀用于精确位置控制，如主飞行控制面的控制。位置控制通过闭合回路控制系统实现，后者包括指令传感器、反馈传感器、数字或模拟控制器以及伺服阀。伺服阀可用于控制液压作动器或液压马达。伺服阀和作动器组合成为伺服-作动器。伺服阀的主要优点是低功率电信号可用于精确定位作动器或马达。
伺服阀的主要部件是一台力矩马达、一个喷嘴挡板或喷管以及一个或多个滑阀(伺服)。航空航天伺服阀的伺服机构一般是零遮盖，这就意味着遮盖宽度和流口宽度相等。因此，只有一个零流量位置。这种配置一般可以实现最严格的控制，常常用于高精度伺服阀。伺服阀有一个液压进口和一个力矩马达电输入。输入电流控制挡板位置。挡板位置控制作动器室压。因此，电流(正或负)将定位挡板，在伺服机构上产生一个压差，使伺服机构在某个方向或其他方向运动。伺服机构运动将液压施加到作动器的一侧或另一侧，同时令作动器的相对一侧返回。
大多数伺服阀在先导滑阀和挡板之间有一个反馈弹簧。如果挡板向左运动，先导滑阀上的压差使滑阀向右运动。反馈线然后将挡板拉回中间位置。因此，反馈线为给挡板提供了一个稳定力，有助于提高挡板系统的稳定性和响应性。伺服位置由滑阀上的力平衡确定，包括挡板喷嘴产生的压差、摩擦力、弹簧力和作用在滑阀上的流动力。
当气动面不足以控制导弹或需要导弹具有更大的敏捷性时就会使用推力矢量控制(TVC)。推力矢量控制分系统同于保持整个火箭发动机(一般为液体发动机)的平衡，或者保持火箭喷管(一般为固体火箭发动机)的平衡，或者使推力室喷管段的喷气舵运动来提供导弹的精确操纵。常平架或喷气舵运动由作动器来完成。液压作动器的运动由伺服阀控制，伺服阀由飞行器制导系统发出的指令控制。
伺服阀有着广泛的工业应用，这是因为伺服阀能够应对较大的惯性和力矩载荷，同时能够实现快速响应和较高的精度和性能。典型应用包括主动悬挂系统、工业机器人控制、塑料加工等。伺服阀也常见于商业飞机、卫星、运载火箭、飞行模拟器、涡轮控制。

伺服阀种类
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Appearance
Servo valves used in flight control systems may be constructed from stainless steel and have mounting swivels at either end. Hydraulic and electrical connections will be found on the side of the device. Position indicators provide feedback signals to the flight computer and may be available through a separate electrical connector.
Flight control servo valves are fairly robust pieces of equipment but they have sensitive position indicator mechanisms attached or built into the case. Typical packaging includes cardboard or wooden boxes. They are securely attached to the shipping container to avoid movement and probably packed in foam shaped like the part. They are often wrapped in a moisture-proof bag.
外观
飞行控制系统使用的伺服阀可以用不锈钢制造，可在任意一端安装转环。伺服阀旁边通常是液压和电气连接装置。位置指示器向飞行计算机提供反馈信号，可通过独立的电连接器获得。
飞行控制伺服阀属于坚固器件，但其内置的位置指示器机构十分敏感。常用硬纸板箱或木箱进行包装。这些器件通常会被牢牢固定在运输集装箱内，以免来回移动，并且可能用与其形状比较相似的泡沫进行包装。一般情况下，还用防潮袋包裹。
来源：2017年MTCR附件手册