PROPORTIONAL VALVE WITH SHAPE MEMORY ALLOY (SMA) ACTUATOR

摘要

A proportional valve is disclosed for controlling the outlet pressure of a fluid flowing therethrough. The valve comprises a valve body having an inlet port and an outlet port for the fluid. The valve also has an inner chamber, within which there is formed a valve seat that may be opened and closed variably by a shutter axially movable from and towards the valve seat. Movement of the shutter is controlled by a shape memory alloy (SMA) actuating member operating antagonistically to an elastic member, the temperature of the fluid being lower than the transition temperature of the shape memory alloy. The actuating member and the elastic member are connected to the body valve at opposite sides relative to the valve seat. A power control circuit is also provided for circulating an electric current through the actuating member so as to heat the same by Joule effect from a temperature lower than the transition temperature to one that is higher. At least one vent hole is formed in the valve body for putting a portion of the chamber upstream of the valve seat into fluid communication with the outside or a collection network. The actuating member is housed in that portion of chamber corresponding 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 control circuit controls the circulating current as a function of a pressure signal generated by fluid pressure sensing means and in such a way as to offset the retarding effect produced by the fluid during heating of the actuating member.