US Patent 7185491 Steam engine

A steam engine has a looped fluid container, in which working fluid is filled. A heating device, a cooling device and an output device are arranged at the fluid container. A lower side valve is provided at a fluid passage of the fluid container between the heating device and the output device. An upper side valve is provided at another fluid passage of the fluid container between the cooling device and the output device. The upper and lower valves are respectively controlled to open and close the respective fluid passages at proper timings, to increase heat efficiency.