Two-stroke internal combustion engine

A two-stroke internal combustion engine (1) comprising:

• a base (50) with a seat for receiving a crank shaft (10), such a crank shaft (10) is rotatably associated with the base with respect to a rotation axis (R) and comprises a first cylindrical section (15) coaxial to the rotation axis (R), a second cylindrical section (20) opposed to the first cylindrical section (15) and coaxial to the rotation axis (R), and a crank (25) which connects the first cylindrical section (15) and the second cylindrical section (20) and is rigidly integral in rotation thereto, and wherein the crank shaft (10) is rotatably associated to the base by interposing a pair of bearings (55), of which one is coupled to the first cylindrical section (15) and the other is coupled to the second cylindrical section (20),
• a head (90) fixed to the base (50) and in which a cylindrical cavity (95) is formed,
• a piston (40) slidably received in the cylindrical cavity (95), so as to define a combustion chamber (110) and a pumping chamber (105), and movable in the cylindrical cavity (95) between a bottom dead center, in which the volume of the combustion chamber (110) is maximum and the volume of the pumping chamber (105) is minimum, and a top dead center, in which the volume of the combustion chamber (110) is minimum and the volume of the pumping chamber (105) is maximum,
• a transfer duct (145) provided with an inlet mouth (150) adapted to be placed in fluid communication with the pumping chamber (105), and with an outlet mouth (155) adapted to be placed in fluid communication with the combustion chamber (110),
• an exhaust duct (160) provided with an inlet mouth (165) adapted to be placed in fluid communication with the combustion chamber (110),
• a connecting rod (45) adapted to connect the piston (40) to said crank shaft (10), wherein the two-stroke internal combustion engine (1) implements, by means of the movement of the piston (40) between the top dead center and the bottom dead center, an operating step during which the inlet mouth (165) of the exhaust duct (160) and the outlet mouth (155) of the transfer duct (145) are simultaneously in fluid communication with the pumping combustion chamber (105,110),
• a movable partition housed inside the pumping chamber (105) and operatively connected to the crank shaft (10) to occlude the inlet mouth (150) of the transfer duct (145) during a first portion of said operating step, and to put in fluid communication the inlet mouth (150) of the transfer duct (145) with the pumping chamber (105) during a second portion of the operating step, wherein the end of the first portion of the operating step is between 30° of rotation of the crank shaft (10) before the bottom dead center and 30° of rotation of the crank shaft (10) after the bottom dead center, wherein the movable partition comprises:
• a disc-shaped body (170), which is rigidly integral in rotation to the crank shaft (10) and is positioned so as to occlude the inlet mouth (150) of the transfer duct (145) at least during the first portion of the operating step;
• a through slot (180) formed in the disc-shaped body (170) and positioned in such a way as to place in fluid communication the inlet mouth (150) of the transfer duct (145) with the pumping chamber (105) during the second portion of the operating step;
• and
• a further through slot (195) made in the disc-shaped body (170), in a portion of the disc-shaped body (170) proximal to the crank shaft (10) and at a distance from the rotation axis (R) substantially equal to the distance of the bearings (55) from the rotation axis (R).