R901166826 Bosch Rexroth Directional servo-valve

Valves of the type 4WS2EM are electrically operated, 2-stage directional servo valves with porting pattern according to ISO 4401-05-05-0-05. They are mainly used to control position, force, pressure or velocity. These valves are made of an electro-mechanical converter (torque motor) (1), a hydraulic amplifier (principle: nozzle flapper plate) (2) and a control spool (3) in a sleeve (2nd Stage) which is connected with the torque motor via a mechanical feedback. An electrical input signal at the coils (4) of the torque motor generates a force by means of a permanent magnet which acts on the armature (5), and in connection with a torque tube (6) results in a torque. This causes the flapper plate (7) which is connected to the torque tube (6) via a bolt to move from the central position between the two control nozzles (8), and a pressure differential is created across the front sides of the control spool (3). The pressure differential results in the spool changing its position, which results in the pressure port being connected to one actuator port and, at the same time, the other actuator port being connected to the return flow port. The control spool is connected to the flapper plate or the torque motor by means of a bending spring (mechanical feedback) (9). The position of the spool is changed until the feedback torque across the bending spring and the electromagnetic torque of the torque motor are balanced and the pressure differential at the nozzle flapper plate system becomes zero. The stroke of the control spool and consequently the flow of the servo valve are regulated proportionally to the electrical input signal. It must be noted that the flow depends on the valve pressure drop. External control electronics (separate order) External control electronics (servo amplifier) serve the actuation of the valve, amplifying an analog input signal (command value) so that with the output signal, the servo valve is actuated in a flow-controlled form. Typ 4WS2EM 10…XH