Abstract: A free piston engine has a pair of opposed cylinders on opposite sides of a fluid pumping assembly. An inner piston assembly includes a pair of inner pistons, one each in a respective one of the cylinders, with a push rod connected therebetween. The push rod forms a fluid plunger. An outer piston assembly includes a pair of outer pistons, one each in a respective one of the cylinders, with a pull rod connected therebetween. The pull rod forms a fluid plunger. The movement of the inner and outer piston assemblies during engine operation will cause the fluid plungers to pump fluid from a low pressure container into a high pressure chamber as a means of storing the energy output. A hydraulic coupler synchronizes the inner and outer piston assemblies.

Abstract: A free piston engine is configured with a pair of opposed engine cylinders located on opposite sides of a fluid pumping assembly. An inner piston assembly includes a pair of inner pistons, one each operatively located in a respective one of the engine cylinders, with a push rod connected between the inner pistons. The push rod extends through an inner pumping chamber in the fluid pumping assembly and forms a fluid plunger within this chamber. Also connected between the pistons are a position sensor and a calibration position sensor that are employed to determine the position and velocity of the inner piston assembly. An outer piston assembly includes a pair of outer pistons, one each operatively located in a respective one of the engine cylinders, with at least one pull rod connected between the outer pistons. The pull rod extends through an outer pumping chamber in the fluid pumping assembly and forms a fluid plunger within this chamber.