Free-piston engine

A free-piston engine, comprising a combustion part (1), a hydraulic control system (2), an energy consumption system (3) and an engine control system, said combustion part (1) comprising, among other parts, a combustion cylinder (5) with at least one combustion piston (4), which defines one side of a combustion space (6) and which is reciprocatable in the combustion cylinder (5) between a first position (A) in which the volume of the combustion space (6) is at a maximum, and a second position in which this volume is at a minimum, said hydraulic control system (2) serving, among other functions, to supply the energy required for compression of the combustion air to the combustion piston (4) during a compression stroke, which coincides with the movement from the first position (A) to the second position, to drain off part of the energy released in combustion during an expansion stroke, which coincides with the movement of the second to the first position, and that to store this energy in a pressure accumulator (14), and which also allows the combustion piston (4) to stand still in the first position (A), said hydraulic control system (2) comprising, among other parts, a hydraulic piston (9) which, together with a combustion piston (4), forms a piston assembly (24), and which has a first surface (10) that, when under hydraulic pressure, exerts a force on the piston assembly (24) that is directed towards the combustion space (6), and a second surface (11), smaller than the first surface (10), that, when under hydraulic pressure, exerts a force on the piston assembly (24) that is directed away from the combustion space (6), a hydraulic cylinder (23) into which the hydraulic piston (9) at least near the first position (A) sealingly fits, a starting valve (20;

• 37, 45, 46) provided in a first channel between a first chamber (12), which is defined by the first surface (10) and the hydraulic cylinder (23) in the first position (A) of the piston assembly (24), and a second chamber (13), which is defined by the second surface (11) of the hydraulic piston (9) and the hydraulic cylinder (23), and a second channel through which oil can flow from the pressure accumulator (14) to the second chamber (13), in which the first chamber (12) can be provided with oil in the first position (A) via the first channel by merely opening the starting valve (20;
• 37, 45, 46), characterized in that a non-return valve (30) is provided in the second channel between the second chamber (13) and the pressure accumulator (14).