R901134478 Bosch Rexroth Directional servo-valve

Valves of type 4WSE3E... are electrically operated, 3-stage directional servo valves. They are mainly used to control position, force or pressure and velocity. These valves consist of a 2-stage pilot control valve of type 4WS2EM 6 (1), a main stage with a main control spool in a sleeve (2), an inductive position transducer (3), and the integrated control electronics (4). The pilot control valve (1) consists of an electro-mechanical converter (torque motor), a hydraulic amplifier (nozzle flapper plate principle) and a pilot spool in a sleeve, which is connected to the torque motor via a mechanical feedback. Electric currents in the coils of the torque motor generate a force by means of a permanent magnet which acts on the armature, and in connection with a torque tube results in a torque. This causes the flapper plate which is connected to the torque tube via a bolt to move from the central position between the two control nozzles, and a pressure differential is created across the front sides of the pilot control spool. The pressure differential results in the control 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 pilot control spool is connected to the flapper plate or the torque motor by means of a bending spring (mechanical feedback). The position of the control spool is changed until the flapper plate position and hence the pressure differential across the nozzle flapper plate system becomes zero due to the feedback torque, which acts via the bending spring against the electro-magnetic torque of the torque motor. In doing so, the stroke of the pilot control spool and hence the flow of the pilot control valve is controlled proportionally to the electrical input signal. In the main stage, the main control spool (2) is operated by the pilot control valve and its position is sensed by an inductive position transducer (3). The position transducer signal is compared to the command value by integrated control electronics (4). Any possible control deviation is amplified electrically and fed to the pilot control valve as control signal. The pilot control valve starts to move and the main control spool is re-positioned. The stroke of the main control spool and consequently the flow of the servo valve are controlled proportionally to the command value. It must be noted that the flow depends on the valve pressure differential. The valve zero point can be adjusted by means of an externally accessible potentiometer. The valves are set at the factory with a dither default setting with the constant frequency of 400 Hz. Notice! Changes in the zero point and/or the dither amplitude may result in damage to the system and may only be implemented by instructed specialists. The pilot control valve may only be maintained by Bosch Rexroth employees. An exception to this is the replacement of the filter element.