USE OF SHAPE MEMORY ALLOY FOR A PILOT STAGE ACTUATOR OF A WATER HYDRAULIC CONTROL VALVE

抄録

Shape memory alloys have many unique properties. These alloys can be plastically deformed with moderate forces at low temperature, and upon exposure to some higher temperature the alloys will return to its original shape prior to the deformation with more than decade higher force. The power density of shape memory alloys is high and the inactivity in harsh environments makes them enticing choice for valve actuators. Still the shape memory alloy has one disadvantage that makes valve actuator appliances hard to find. The transformation between different states of shape memory alloy is proportional to the energy supplied when the alloy is heated but the cooling is only proportional to the heat transfer ratio between the alloy and environment. Using pair of thin shape memory alloy fibers replacing a torque motor of a traditional nozzle flapper servovalve has been studied. The studied flapper actuator consists of two SMA-fibers arranged in antagonist fashion. When one fiber serves as an actuator the other one serves as a spring. Both fibers are immersed in water in order to increase heat transfer rate. The performance of developed shape memory fiber actuator has been simulated. Simulations have been verified by comparing simulation results to experimental tests. Based on experimental tests of actuator the performance of shape memory fiber actuated nozzle flapper pilot stage has been simulated with verified valve model. The attained overall performance of a 2-stage 4-way spool valve with the developed pilot stage has been discussed.