ELECTROMECHANICAL THERMOSTATIC MIXING VALVE

摘要

An electromechanically controlled thermostatic mixing valve (10) comprises a movable mixing valve member (114) resiliently held between a temperature responsive coiled spring (132) and a bias spring (134). The temperature responsive spring is made of a material such as a shape memory alloy (SMA) having a modulus of elasticity that varies with temperature. The bias spring is supported by an electric drive (46) controlled by an electric control circuit (32) to adjust the preload on the bias spring. In contrast to the bias spring which is subjected to deformation from its free state to its fully compressed state, the SMA spring is held in such a manner that it is subjected to a limited strain throughout the stroke of the valve member. As a result, premature fatigue of the SMA spring is avoided. Transient fluctuation in water temperature is primarily compensated for by a mechanical feedback control performed by the SMA spring. Any persistent offset of temperature is compensated for by electrical feedback control carried out by the electrical control circuit that adjusts the preload on the bias spring preload such that the actual water temperature is brought to the desired temperature.