Patent ID: 7634980

Claim:
A crankcase scavenged two-stroke internal combustion engine ( 1 ) having an additional air supply ( 2 ) arranged to its transfer ducts ( 3 ), each transfer duct having a transfer duct having a transfer port ( 5 ), which transfer ducts connect a crankcase volume ( 4 ) and a transfer port ( 5 ), and the additional air supply ( 2 ) to the transfer ducts ( 3 ) is arranged via an air duct ( 21 ) connected to the cylinder ( 9 ) and via the cylinder wall ( 29 ) leading to an air supply port ( 22 ) that is connected to the transfer port ( 5 ) via a first recess ( 24 ) in the piston ( 7 ) for certain first piston positions, characterized in that there is at least one second function recess ( 6 , 24 ) in piston ( 7 ) arranged below a piston ring ( 10 , 11 ) and further there is a flow channel ( 12 ; 13 ; 14 ) arranged in the piston or in a cylinder wall ( 29 ) of the engine cylinder ( 9 ), and the second recess is arranged to register with the transfer port ( 5 ) and the flow channel ( 12 , 13 , 14 ), the flow channel connecting the crankcase volume ( 4 ) with the second recess for certain piston positions, i.e. to create a communication between the transfer port/s and the crankcase volume.