The nozzle baffle servo valve is a two-stage electro-hydraulic servo valve, and its pilot stage uses a nozzle baffle mechanism as a hydraulic amplifier. It is the most classic and widely used structural form among high-performance electro-hydraulic servo valves.
The core working principle is to use a torque motor to convert weak electrical signals into mechanical motion (small displacement of the baffle), and generate a control pressure difference by changing the gap between the baffle and two nozzles. This pressure difference then drives the second stage power spool valve core to move, thereby controlling the flow of high flow pressure oil to the hydraulic actuator (cylinder or motor).
Detailed explanation of the core working principle
A complete nozzle baffle servo valve usually consists of the following three parts:
1. Electrical mechanical converter (torque motor)
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Composition: permanent magnet, magnetic conductor, armature, coil (usually two, connected to differential current signal), and elastic support (such as spring tube).
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Function: Receive weak electrical signals (usually ± 10mA or ± 40mA) from the servo amplifier, and generate a torque that causes the armature to deflect clockwise or counterclockwise based on the polarity (positive or negative) and magnitude of the signal. The armature is connected to a baffle.
2. Pilot stage of hydraulic amplifier (nozzle baffle mechanism)
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Composition: baffle, two symmetrical nozzles, two fixed throttling holes (usually located at both ends of the valve core).
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Working process:
one
Pressure oil (Ps) passes through two fixed throttle holes and enters the chambers at both ends of the spool valve (usually referred to as control chambers), and then sprays out through nozzles and flows back to the oil tank (T).
two
When there is no signal input to the torque motor, the baffle is in the neutral position and the gap between the two nozzles is equal. The same oil leakage resistance at the two nozzles results in equal control pressure (P ₁ and P ₂) at both ends of the valve core. Under the action of the reset spring, the valve core remains in the neutral position (zero position) and there is no flow output.
three
When there is an electrical signal input, the torque motor drives the baffle to deflect. For example, the baffle is close to nozzle A and away from nozzle B.
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The gap between nozzle A decreases, causing an increase in discharge resistance and resulting in an increase in its back pressure, that is, the control pressure P ₁ at the end of valve core A.
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The gap between nozzle B increases, reducing the discharge resistance and causing a decrease in its back pressure, that is, the control pressure P ₂ at the end of valve core B.
four
So, a pressure difference (Δ P=P ₁ – P ₂) is generated at both ends of the valve core. This pressure difference drives the power stage spool to move towards the low-pressure end (i.e. P ₂ end).
3. Hydraulic amplifier power stage (slide valve) and feedback mechanism
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Composition: Four way slide valve core, valve sleeve, feedback rod (also known as spring tube).
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Work process and feedback:
1
The valve core moves under the pressure difference generated by the pilot stage, thereby opening the corresponding oil port and directing the main pressure oil (Ps) to one working chamber of the actuator, while the other working chamber is connected to the return oil (T).
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The movement of the valve core simultaneously drives the ball head at the end of the feedback rod to bend and deform.
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The deformation of the feedback rod will generate a reverse mechanical torque acting on the armature component, which is opposite in direction to the electromagnetic torque generated by the torque motor.
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When the two torques reach equilibrium, the armature and baffle will return to the near center position, and the pressure on both sides of the pilot stage will be balanced again. The valve core stops moving and stays at an open position that is precisely proportional to the size of the input electrical signal.
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This mechanical feedback process constitutes a closed-loop control system, ensuring that the displacement of the power stage valve core can accurately reproduce the input electrical signal, which is the key to achieving high precision and high-frequency response of the valve.