FIELD: mechanical engineering; internal combustion engines. SUBSTANCE: valves 4-7 arranged in piston 2 pass air charge, and valves 8-11 of piston 3 pass exhaust gases. Pistons 2 and 3 are located in cylinder 1. Intensity of charge swirling in period of scavenging is provided by opening first exhaust valve 9 in piston 3 and then intake valve 4 in piston 2 displaced in longitudinal plane relative to valve 9, after which valves 10,5,11,6,7 and 8 open in turn. To increase intensity, greater displacement is set and opening of valves is provided in the following sequence: 10, 4,11,5,8,6,9,7. This provides adequate swirling of charge and intensity of cleaning and filling of cylinder 1 are improved. EFFECT: enhanced efficiency of free piston engine with valves in pistons by successive opening of exhaust and intake valves. 1 dwg
