每日一词｜飞行控制伺服阀Flightcontrolservovalves(2)

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.