Cable drive mechanism for self tuning refrigeration gas expander

A refrigeration device includes a gas displacing piston ( 362 ) movable within a gas expander cylinder ( 364 ). The volume of a gas expansion space ( 362 ) is varied as the gas displacing piston ( 362 ) is moved over an expansion stroke range. The device includes a compression spring ( 622 ) disposed to bias the gas displacing piston ( 362 ) toward a compression stroke top end position ( 85 ). A cable element ( 606 ) extends into the gas expansion cylinder ( 364 ) and attaches to the gas displacing piston ( 362 ). A motive drive device ( 302 ) applies a tensioning force to the cable ( 606 ) and the tension force opposes the spring biasing force and moves the gas displacing piston ( 362 ) to a compression stroke bottom end position ( 83 ). In a further embodiment the expansion stroke is self-tuning when a pneumatic force generated by refrigeration gas contained within the expansion space ( 362 ) exceeds a threshold gas pressure and the pneumatic force overcomes the spring biasing force and pneumatically forces the gas displacing piston ( 362 ) to the bottom end position ( 83 ).