The hydraulic servo valve includes slide valve servo valve, nozzle baffle servo valve and jet pipe servo valve. Slide valve servo valve: adopt moving coil force motor, with simple structure, large power amplification factor, small hysteresis and large working stroke; The fixed orifice has large size and is not easy to be blocked by dirt; The control oil pressure at both ends of the main slide valve has a large action area, which increases the driving force, so that the slide valve is not easy to get stuck and works reliably. Nozzle flapper servo valve: due to the existence of force feedback, the torque motor works near its zero point, i.e. armature deflection angle θ Very small, so the linearity is good. In addition, by changing the stiffness of the feedback spring rod 11, the displacement of the spool valve can be changed at the same input current. The servo valve has the advantages of compact structure, small overall size and fast response. However, the working clearance of nozzle baffle is small, which requires high cleanliness of oil. Jet pipe servo valve: low requirements for oil cleanliness. The disadvantage is that the zero leakage is large; It is significantly affected by the change of oil viscosity and has poor low temperature characteristics; The moment motor drives the jet pipe, the load inertia is large, and the response speed is lower than that of the nozzle baffle valve. 1、 Slide valve servo valve The utility model is composed of a permanent magnet moving coil force motor, a pair of fixed orifices, a pre opening bilateral slide valve preamplifier and a three-way slide valve power stage. The two pre opening throttle control sides of the front control slide valve and two fixed orifices form a hydraulic bridge. The valve core (control valve core) of the slide valve pair is directly connected with the moving coil framework of the force motor, and the (control valve core) slides in the valve sleeve. The valve sleeve of the pre stage is also the valve core of the power stage slide valve amplifier. Input the control current to balance the electromagnetic force generated by the moving coil of the force motor with the spring force of the centering spring, so as to move the moving coil and the valve core (control valve core) of the front stage (control stage), and its displacement is directly proportional to the moving coil current. If the pre stage valve core (control valve core) moves to the right, the control port · area of the right chamber of the slide valve increases and the control pressure of the right chamber decreases; The area of the left control port decreases and the control pressure of the left chamber increases. The pressure difference acts on both ends of the power stage slide valve core (i.e. the valve sleeve of the front stage), which moves the power stage slide valve core (main slide valve) to the right, that is, the valve sleeve (main slide valve) of the front stage slide valve to the right, gradually reducing the area of the right control hole until it stays at a certain position. At this position, the area of the two variable throttle control holes of the front stage slide valve pair is equal, and the pressure at both ends of the power stage slide valve core (main slide valve) is equal. This direct feedback makes the power stage spool valve core follow the pre stage spool valve core, and the displacement of the power stage spool valve core is directly proportional to the input current of the moving coil. 2、 Nozzle baffle servo valve In the figure, the upper half is an armature force motor, and the lower half is a nozzle baffle type and slide valve type hydraulic amplifier. The armature is connected with the baffle plate and the spring rod and is supported by a spring tube fixed on the valve body. The lower end of the spring rod is a ball head, which is embedded in the groove of the slide valve, and the permanent magnet and the guide magnet form a fixed magnetic field. When there is no current in the coil, the magnetic flux in the four air gaps between the armature and the conducting magnet is equal and the direction is the same, and the armature and the baffle are in the middle position, so the slide valve has no oil output. When a control current flows into the coil, the magnetic flux in one group of diagonal air gaps increases and the magnetic flux in the other group of diagonal air gaps decreases. Therefore, under the action of magnetic force, the armature overcomes the elastic reaction force of the spring tube and deflects with a point in the spring tube as the fulcrum θ And deflect until the torque generated by the magnetic force is balanced with the reverse torque generated by the elastic reaction force of the spring tube. At this time, the slide valve has not moved, and the baffle deflects due to the deflection of the armature, which changes the gap between it and the two nozzles. One gap decreases and the other gap increases. The pressure oil flowing into the servo valve flows out through the oil filter, two symmetrical fixed orifices and left and right nozzles to the return oil. When the baffle deflects and the two gaps of the nozzle baffle are not equal, the pressures PA and Pb behind the two nozzles are not equal. They act on the left and right end faces of the slide valve to move the slide valve in the corresponding direction for a certain distance, and the pressure oil is transmitted to the actuator through one valve port on the slide valve, and the oil returned by the actuator is led to the return oil through another valve port on the slide valve. When the slide valve moves, the ball head at the lower end of the spring rod moves with it, which generates torque on the armature baffle assembly, deflects the armature in the corresponding direction, and reduces the offset of the baffle between the two nozzles, which is called force feedback. As a result of the feedback action, the differential pressure at both ends of the spool valve is reduced. When the sum of the torque of the slide valve acting on the baffle through the spring rod, the torque of the nozzle acting on the baffle and the counter torque of the spring tube is equal to the electromagnetic torque generated by the torque motor, the slide valve will no longer move and keep its valve port at this opening. The greater the control current connected to the coil, the greater the torque to deflect the armature, the deflection deformation of the spring rod, the greater the differential pressure at both ends of the slide valve and the offset of the slide valve, and the greater the output flow of the servo valve. Due to the displacement of the slide valve, the gap between the nozzle and the baffle and the armature angle are in direct proportion to the input current, so the output flow of this valve is also in direct proportion to the input current. When the input current is reversed, the output flow is also reversed. 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