A hybrid Stirling engine is a Stirling engine with a free displacer and a crank coupled piston. The term ‘hybrid’ is a modern one, placing such engines somewhere between the full kinematic and the completely free-piston/free displacer engine. But the concept dates back at least to 1905 when Ossian Ringbom applied for a patent “on a hot air engine in which the movement of the displacing piston is obtained without the connection of rods or cranks or eccentrics or other mechanical parts...”