A Small-Size Proportional Valve Using a Shape-Memory-Alloy Array Actuator.

To realize a small-size proportional valve, a small-size and sufficiently high-stiffness actuator is required to drive the spool. However, with conventional actuators, such as solenoid actuators, it was difficult to realize such performance. In this study, an actuator using shape-memory-alloy (SMA) fine wires in arrayed arrangement is proposed and experimentally examined; it is expected to realize both suffciently high stiffness and response. First, the basic characteristics are examined, and the high stiffiness of a differential actuator using a pair of nine SMA wires and effectiveness of forced oil-cooling are shown. Secondly, to further improve the response, both of a simple method to increase the cooling oil flow and PI control are attempted. The former method is proved to be effective, although it has limitations. The latter method is proved to improve the response sufficiently and also to eliminate the hysteresis. Finally, based on these results, a proportional valve is constructed. The experimental results show that the spool is able to respond practically up to 40 Hz, with amplitude of 25μm.