Patent ID: 7398759

Claim:
A four-stroke engine ( 1 ) comprising: a cylinder ( 2 ); a piston ( 3 ) movably mounted in the cylinder in order to rotatingly drive a crankshaft ( 4 ) via a connecting rod ( 5 ); the cylinder and the piston conjointly delimiting a combustion chamber ( 6 ); the cylinder having an intake opening ( 7 ) and an intake valve ( 8 ) for opening and closing the intake opening; the cylinder having an exhaust opening ( 9 ) and an exhaust valve ( 10 ) for opening and closing the exhaust opening, followed by an exhaust duct ( 28 ); a mixture-preparation device ( 15 ) for supplying an air/fuel-lubricant mixture or for supplying in two steps an air/lubricant mixture and an air/fuel mixture; a crankcase ( 11 ) connected to the cylinder and delimiting together with the underside of the piston ( 3 ) a crankcase volume ( 12 ), to which at least air ( 13 ) and lubricant ( 14 ) is supplied by the mixture preparation device; an intake channel ( 16 ) connecting to the intake opening ( 7 ) with intake valve ( 8 ) to supply to the intake at least air; a valve drive assembly ( 18 ) driven by said crankshaft ( 4 ) for actuating the intake valve ( 8 ) and the exhaust valve ( 10 ), characterized in that it further comprises: a valve drive assembly housing ( 19 , 20 , 21 , 21 ′, 22 ) comprising one or more sections ( 19 , 20 , 21 , 21 ′, 22 ), and the intake channel ( 16 ) is supplied with a connecting duct ( 17 ) communicating with the crankcase volume ( 12 ) either by being connected to the crankcase or cylinder, or by being connected to the valve drive assembly housing ( 19 , 20 , 21 , 21 ′, 22 ), which communicates with the crankcase volume ( 12 ), and the communication from the intake channel ( 16 ) to the crankcase volume is arranged through at least one valve ( 49 ) that opens and shuts only once per engine cycle.