The present invention provides a stirling engine, which is capable of
reducing a frictional loss and eliminating possibility of deterioration
of a heat exchanger due to lubricant oil applied to piston rings and the
like. The stirling engine includes cylinders (22,32), pistons (21,31)
reciprocating inside the cylinder while keeping an air-tight condition
between the piston and the cylinder by means of a gas bearing (48), and
an linear approximation mechanism (50) coupled directly or indirectly to
the piston and disposed so that the piston may make approximately linear
motion when the piston reciprocates inside the cylinder. The stirling
engine has a piston engine which is in a ringless (i.e., without piston
rings) and oilless (i.e., without lubricant oil) state so as to reduce
the frictional loss and to prevent the deterioration of the heat
exchanger by the lubricant oil. Since the linear approximation mechanism
enables the piston to make approximately linear motion, side force on the
piston is virtually eliminated. The stirling engine is effectively used
with a gas bearing which has low pressure resistance to side force.