Patent ID: 7077080

Claim:
A free piston engine comprising: a coupling assembly including a body having a first side, a second side in opposed relation to the first side, a push rod bore extending generally parallel to an axis of motion, a pull rod bore extending generally parallel to the axis of motion, and a cross connecting passage extending between the push rod bore and the pull rod bore; a first combustion cylinder assembly located adjacent to the first side and including a first cylinder liner having a generally cylindrical wall that defines a first engine cylinder, which extends generally parallel to the axis of motion; a second combustion cylinder assembly located adjacent to the second side and including a second cylinder liner having a generally cylindrical wall that defines a second engine cylinder, which extends generally parallel to the axis of motion; an inner piston assembly having a first inner piston that is located and telescopically slidable within the first engine cylinder and has a head portion that faces away from the first side, a second inner piston that is located and telescopically slidable within the second engine cylinder and has a head portion that faces away from the second side, and a push rod including a first end affixed to the first inner piston and a second end affixed to the second inner piston and a middle portion that includes an inner plunger telescopically slidable in sealing engagement within the push rod bore, defining an inner coupler pumping chamber in fluid communication with the cross connecting passage; an outer piston assembly having a first outer piston that is located and telescopically slidable within the first engine cylinder along the axis of motion and has a head portion that faces the first inner piston, a second outer piston that is located and telescopically slidable within the second engine cylinder along the axis of motion and has a head portion that faces the second inner piston, and a pull rod including a first end affixed to the first outer piston and a second end affixed to the second outer piston and a middle portion that includes an outer plunger telescopically slidable in sealing engagement within the pull rod bore, defining an outer coupler pumping chamber in fluid communication with the cross connecting passage; and a liquid located in and filling the cross connecting passage, the inner coupler pumping chamber and the outer coupler pumping chamber.