Patent ID: 7258085

Claim:
In a free piston engine comprising: a housing including a cylinder in its interior; a first piston installed in the cylinder being allowed to move back and forth in an axial direction of the cylinder; a second piston installed in the cylinder opposing to the first piston, being allowed to move back and forth in the axial direction and forming a combustion chamber between the first piston and the second piston; a first and a second biasing units for respectively biasing the first and the second pistons in respective directions so that the first and second pistons move closer to each other; an intake means for supplying the combustion chamber with mixed gas of air and fuel; and an exhaust means for exhausting combustion gas of the mixed gas from the combustion chamber, wherein the mixed gas in the combustion chamber is auto-ignited by being compressed when the first and the second pistons move closer to each other, the first and the second pistons are moved in directions away from each other due to an explosion of the mixed gas, and the first and the second pistons are subsequently moved closer to each other again by biasing forces of the first and the second biasing units, so that a fresh mixed gas is compressed and auto-ignited, a control device for the free piston engine comprising; a first drive means for adjusting by a magnetic force a first displacement of the first piston from a first reference position; a second drive means for adjusting by a magnetic force a second displacement of the second piston from a second reference position; a detection means for detecting a physical quantity by which a condition of the combustion of the free piston engine can be estimated; and a displacement control means for controlling, by means of the first and the second drive means, the first and the second displacements with respect to the first and second reference positions according to the detected physical quantity, so that the mixed gas in the combustion chamber is auto-ignited at a timing which is equal to or close to an end of a compression stroke during which the first and second pistons are moved closer to each other.