FIELD: mechanical engineering; four-stroke internal combustion engines. SUBSTANCE: invention can be used in four-stroke internal combustion engines with special devices for changing working volume of combustion chamber. Proposed device contains cylinder, piston, cylinder head accommodating intake and exhaust valves, movable cylindrical undervalve cup installed in hole of cylinder, camshaft with cam mechanism for operating intake and exhaust valves and drive mechanism of undervalve cup. Undervalve cup is provided with air or fuel-air mixture intake hole at side of engine intake manifold, and with valve seat, from side of piston. Sealing member is fitted at outer side on undervalve cup and least one guide rod is made on wall under valve cup at side opposite to piston. At working stroke undervalve cup with intake valve separates combustion chamber from intake manifold in extreme position relative to piston. At exhaust stroke undervalve cup moves towards piston, thus eliminating clearance (dead) volume of combustion chamber, forcing exhaust gases out of combustion chamber, and at extreme lower position relative to top dead center of piston, it separates combustion chamber from cylinder space. At suction stroke, with piston moving from top dead center to bottom dead center, undervalve cup shifts into extreme upper position relative to piston, and intake valve opens. After completion of suction stroke, intake valve closes at unchanged position of undervalve cup. EFFECT: increased efficiency of engine, reduced fuel consumption and improved performance of engine. 7 cl, 6 dwg
