ELECTRO HYDRAULIC SERVO VALVE

Abstract

Fuel flow control is one of the most important aspects in aerospace applications and its accurate calibration is of the essence. Due to very high fuel inlet pressures, a normal proportional cannot be used and the servo valve is used to ensure safe and accurate functioning. To propose a working solution we are required to redesign an EHSV to make it light weight and more compact. All the flow and design parameter constraints are given by the industry (NESCOM). The working of the design can be explained by starting off with the torque motor. The torque motor in our project would receive an input signal from ranging from 0 to 150mA. Upon receiving a signal within this range the torque motor would rotate the armature to a certain angle which would be calibrated upon the input range and output flow range of 100 to 1100 L/Hr. Upon rotation of armature the armature comes closer to the nozzle. In the neutral position, the pressure difference ΔP is equal to zero. However, when the armature by a small angle and comes closer to the nozzle a pressure increase happens on one side of the spool. This increase in pressure creates a pressure difference across the ends of the spool and causes the spool to move. Movement of the spool creates the opening from the inlet towards the outlet port and the resulting flow can be calculated by a flow meter. We have simulated the working at 60 bar pressure and the pressure contours are monitored. The working prototype, however, has been designed for 15 bar inlet pressure as a safety precaution. The resulting flow at the input current signals has an error of only 5%.