Abstract: A cyclone separator having a circular cross section is arranged upstream of an air filter. An introduction passage extends from a branch air inlet, which is provided at a position displaced from a main passage, to the cyclone separator. A margin space where at least part of air introduced in the introduction passage flows is formed in the introduction passage before the cyclone separator. A swirl flow occurring in the cyclone separator starts at this margin space.

Abstract: Provided is a portable power working machine that is designed to suppress mixing of dust into air sucked into an air intake system of an air-cooled internal combustion engine mounted as a driving power source for working units, for example, and reliably prevent an air cleaner provided to the air intake system of the internal combustion engine from being clogged with dust, and thus eliminate the necessity of frequently cleaning the air cleaner. An air intake port of an air intake passage is arranged on the opposite side of the internal combustion engine with respect to a straightening passage formed around a cooling fan, so that, of the air released from a discharge port of the straightening passage, at least part of air released toward the opposite side of the internal combustion engine with respect to the straightening passage is taken into the air intake passage via the air intake port.

Abstract: A cyclone separator having a circular cross section is arranged upstream of an air filter. An introduction passage extends from a branch air inlet, which is provided at a position displaced from a main passage, to the cyclone separator. A margin space where at least part of air introduced in the introduction passage flows is formed in the introduction passage before the cyclone separator. A swirl flow occurring in the cyclone separator starts at this margin space.

Abstract: It is intended to effectively prevent blow-by with no need for large changes in typical structures of two-cycle internal combustion engines. A main scavenging passage (24) for supplying air-fuel mixture from a crankcase to a combustion chamber for scavenging purposes has a branch scavenging passage (26) that extends upward aslant toward an intake port (14). The main scavenging passage (24) communicates with a first scavenging port (20) located nearer to an exhaust port (16). The branch scavenging passage (26) communicates with a second scavenging port (22). A mean cross-sectional area of the branch scavenging passage (26) is smaller than that of the main scavenging passage (24). Cross-sectional area of a portion (24b) next to an inlet port (24a) of the main scavenging passage (24) opening to the crankcase is smaller than the sum of cross-sectional areas of the first and second scavenging ports (20, 22).

Abstract: It is intended to effectively prevent blow-by with no need for large changes in typical structures of two-cycle internal combustion engines. A main scavenging passage (24) for supplying air-fuel mixture from a crankcase to a combustion chamber for scavenging purposes has a branch scavenging passage (26) that extends upward aslant toward an intake port (14). The main scavenging passage (24) communicates with a first scavenging port (20) located nearer to an exhaust port (16). The branch scavenging passage (26) communicates with a second scavenging port (22). A mean cross-sectional area of the branch scavenging passage (26) is smaller than that of the main scavenging passage (24). Cross-sectional area of a portion (24b) next to an inlet port (24a) of the main scavenging passage (24) opening to the crankcase is smaller than the sum of cross-sectional areas of the first and second scavenging ports (20, 22).

Abstract: A muffler for a small two-cycle engine includes: a muffler body having an expansion chamber; an exhaust-gas guide member covering an outlet for exhaust gas, the outlet being provided on the muffler body and a cover hood that covers a discharge port for exhaust gas, the discharge port being provided on the exhaust-gas guide member. A guide that guides the exhaust gas in the exhaust-gas guide member is gradually widened toward a top surface of the cover hood as proceeding to the discharge port.

Abstract: A muffler includes a muffler body disposed on a lower portion of an engine and a passage that extends upward from the muffler body and is opened in an upper front portion of a chain saw body. Thus, exhaust gas can be discharged forward from the chain saw body, so that exhaust sounds can be dispersed forward. Consequently, the exhaust sounds propagated to an operator can be reduced and therefore a work environment can be improved. Also, since exhaust gas is discharged after the exhaust gas passes through a long passage extending upward from the muffler body, the exhaust gas can be cooled down. Accordingly, in the chain saw body typically covered with a synthetic-resin case in which exhaust outlets are formed on positions corresponding to outlets of the passage, peripheries of the exhaust outlets can be prevented from being discolored by heat of exhaust gas.

Abstract: A stratified scavenging two-cycle engine includes: an air passage for delivering pure air to a scavenging passage; an air valve for opening and closing the air passage; and an auxiliary air passage for delivering the pure air to the scavenging passage when the air valve is completely closed. An amount of air for air-fuel mixture sucked in a crank chamber is reduced to increase the concentration of the air-fuel mixture, and air that supplements the reduced amount of the air for air-fuel mixture is fed into the scavenging passage through the auxiliary air passage, which enables the engine to be smoothly accelerated even when being suddenly accelerated from an idling state with an appropriate concentration of the air-fuel mixture sucked in a cylinder chamber during idling.

Abstract: A stratified scavenging two-cycle engine includes: an air passage for delivering pure air to a scavenging passage; an air valve for opening and closing the air passage; and an auxiliary air passage for delivering the pare air to the scavenging passage when the air valve is completely closed. An amount of air for air-fuel mixture sucked in a crank chamber is reduced to increase the concentration of the air-fuel mixture, and air that supplements the reduced amount of the air for air-fuel mixture is fed into the scavenging passage through the auxiliary air passage, which enables the engine to be smoothly accelerated even when being suddenly accelerated from an idling state with an appropriate concentration of the air-fuel mixture sucked in a cylinder chamber during idling.

Abstract: A stratified scavenging two-cycle engine, whose simple configuration can satisfy the regulation of emission rate of THC in exhaust gas, includes: a cylinder block (4), housing a piston (1) so as to be vertically slidable and having an exhaust port (14) and a scavenging port (16) in a sidewall; a scavenging flow passage (22), for connection between a crank chamber (8) and the scavenging port (16); an air supply flow passage (24), connected to the scavenging flow passage (22) and supplying air through a check valve (26); and a mixture supply flow passage (20), for supplying mixture to the crank chamber (8). The supply quantity ratio R=qa/Qf, which is the ratio of a supply quantity qa of air flowing through the air supply flow passage (24) to a supply quantity Qf of mixture flowing through the mixture supply flow passage (20) during a suction stroke in which pressure in the crank chamber (8) is negative, is in the range of 0.7≦R≦1.4.