Heat-engines using shape memory alloy (SMA) were expected to be employed as heat-engines driven by low-temperature thermal energy. Therefore, some trial products of heat-engines using SMA were produced and studied. However, since the inhomogeneous temperatures of the SMA element result during heating / cooling of the SMA element, the product-life cycle of conventional heat-engines using SMA becomes short. Moreover, if large power outputs are to be achieved, these engines would become large in size. Therefore, conventional SMA heat-engines have not been put into practical use. We propose a new actuator using a SMA spiral spring. By using this system, the uniform heating / cooling of the SMA element (improvement of the product life) and downsizing of the equipment are expected. Therefore, we manufactured a prototype of a heat-engine using a SMA spiral spring actuator, and the output characteristics of this heat-engine were investigated.

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