Two-cycle internal combustion engine

The present invention relates to a two-cycle internal combustion engine which is suited for use in a portable power working machine, and in particular to a two-cycle internal combustion engine which is designed to introduce air into a combustion actuating chamber (though it may be also called combustion chamber, actuating chamber, cylinder chamber, etc., these chambers are generically referred to as combustion actuating chamber in the present specification) prior to the introduction of air-fuel mixture, thereby making it possible to minimize the quantity of so-called blow-by or the quantity of air-fuel mixture to be discharged without being utilized for the combustion. A two-cycle internal combustion engine which is capable of inhibiting air-fuel mixture from being mixed with the air introduced in advance into the combustion actuating chamber during the scavenging period, thereby realizing a complete lamellar scavenging. This engine is constructed such that one or more pairs of Schnürle type scavenging passageways (), each allowing the combustion actuating chamber () disposed above a piston () placed in a cylinder () to be communicated with the crank chamber (), are symmetrically provided on both sides of a longitudinal section (F-F) which imaginatively divides an exhaust port () into two equal parts, thereby enabling air (A) to be introduced into the scavenging passageways () and also enabling an air-fuel mixture (M) to be introduced into the crank chamber (); and that in the descending stroke of the piston (), the exhaust port () is opened at first, and then, the scavenging port which is disposed at a downstream end of the scavenging passageway is opened, thereby enabling air (A) to be introduced via the scavenging passageway into the combustion actuating chamber () prior to the introduction of air-fuel mixture (M) into the combustion actuating chamber (); said internal combustion engine being characterized in that said one or more pairs of Schnürle type scavenging passageways () are respectively provided, near the end portion thereof located close to the crank chamber (), with a throttled portion ().