PROPORTIONAL VALVE WITH SHAPE MEMORY ALLOY (SMA) ACTUATOR

摘要

A proportional valve for the control of the outlet pressure of a fluid flowing therethrough comprising a valve body (1) with an inlet port (15) and an outlet port (17) for the fluid and an inner chamber (8), within which there is formed a valve seat (9) whose opening is varied by means of a shutter (10) axially movable from and towards the valve seat, the movement of the shutter being controlled by a SMA actuating member (11) acting antagonistically to elastic means (12), the temperature of the fluid being lower than the transition temperature of the shape memory alloy. The actuating member and the elastic means are connected to the valve body (1) at opposite sides with respect to the valve seat and power means (105) are provided to be activated for circulating an electric current through said actuating member to heat it by Joule effect from a temperature lower than the transition temperature to an higher one. At least a vent hole (18) for the fluid is formed on the valve body (1) for putting the part of the chamber (8) upstream of said valve seat (9) into communication with the outside or a collection network, the actuating member (11) being housed in said part of chamber in correspondence to the inlet port of the fluid, whereby a continuous flow of fluid around the actuating member is ensured for accelerating the cooling process. A closed-loop control circuit for the power means (105) is provided for controlling the circulating current as a function of a pressure signal generated by fluid pressure sensing means (19) and in such a way to offset the retarding effect produced by the fluid during the heating step of the actuating member.