Two piston, concentric cylinder, alpha free piston Stirling machine

A free piston, alpha, two piston, concentric cylinder, Stirling cycle machine having a casing confining a working gas and comprising within the casing:

• (a) a first cylinder having an expansion space opening into one end of the first cylinder and a compression space opening at the opposite end of the first cylinder, the first cylinder surrounded by an expansion space heat exchanger, a regenerator and a compression space heat exchanger in series fluid connection between the expansion space and the compression space;
• (b) a second cylinder coaxially aligned with the first cylinder and adjacent the compression space;
• (c) a compression piston sealingly reciprocatable in the second cylinder and having a cylindrical bore opening toward the first cylinder and coaxial with the cylinders;
• (d) an expansion piston sealingly extending into both the first cylinder and the cylindrical bore, the expansion piston having the same diameter within both the first cylinder and the cylindrical bore;
• and
• (e) a spring connecting the compression piston to the expansion piston.