An exhaust valve assembly for a two-stroke internal combustion engine has a valve actuator, and a two-part valve having a primary and secondary valves defining first and second decompression passages respectively. The primary valve is operatively connected to the valve actuator. The primary valve is in first, second and third primary valve positions when the valve actuator is in first, second and third actuator positions respectively. The secondary valve is in a first secondary valve position when the valve actuator is in the first or the second actuator position and in a second secondary valve position when the valve actuator is in the third actuator position. The first and second valve decompression passages fluidly communicate with each other when the valve actuator is in the second actuator position, and are fluidly separate from each other when the valve actuator is the first or the third actuator position.

An engine having a cylinder fastened to the engine ease with the biconcave internal partition, which divides the cylinder into the upper and bottom parts. Sparking plugs are mounted on both sides of the partition. The upper and the bottom parts of the cylinder have side scavenging channels which connect suction spaces to the working spaces of both parts of the cylinder. The upper and bottom parts of the cylinder have inlet and outlet orifices. Inside the upper and inside the bottom part of the cylinder and the upper and bottom piston are placed respectively, while both pistons are directed towards each other by the working surfaces. The pistons are connected by a rod that is led through the linear bearing that is embedded in the partition forming a seal. The connecting rod is fastened to the bottom piston and by its other end it is connected to the crankshaft.

To meet stringent emission standards and improve performance of two-stroke crankcase-scavenged engines, the muffler (13) of the engine is provided with mixing means (130, 31) for mixing the exhaust gases (42) resulting from the mixture participating in combustion and gases resulting from scavenging, so that a substantially homogenous gaseous mixture is formed within the muffler (13), and means (81) for sensing oxygen concentration is located in the homogeneous gaseous mixture and are configured to provide an output value to a control unit (80) for controlling supply of fuel to the engine and thereby the air-fuel ratio in the combustion chamber (41). The muffler (13) suitably is provided with a catalytic element (140), preferably a three-way catalyst. The engine (1) preferably is a stratified charge engine.

To meet stringent emission standards and improve performance of two-stroke crankcase-scavenged engines, the muffler (13) of the engine is provided with mixing means (130, 31) for mixing the exhaust gases (42) resulting from the mixture participating in combustion and gases resulting from scavenging, so that a substantially homogenous gaseous mixture is formed within the muffler (13), and means (81) for sensing oxygen concentration is located in the homogeneous gaseous mixture and are configured to provide an output value to a control unit (80) for controlling supply of fuel to the engine and thereby the air-fuel ratio in the combustion chamber (41). The muffler (13) suitably is provided with a catalytic element (140), preferably a three-way catalyst. The engine (1) preferably is a stratified charge engine.

A two-stroke engine according to the present invention includes: a separating wall which confines a tip end portion of an ignition device; an ignition promoting chamber which is formed by means of the separating wall, is independent of a combustion chamber, and encloses the tip end portion of the ignition device; and a plurality of communicating holes which are provided in the separating wall, each of which is provided with a first opening that opens in the combustion chamber and a second opening that opens in the ignition promoting chamber, and which provide communication between the combustion chamber and the ignition promoting chamber.

A two-stroke engine according to the present invention includes: a separating wall which confines a tip end portion of an ignition device; an ignition promoting chamber which is formed by means of the separating wall, is independent of a combustion chamber, and encloses the tip end portion of the ignition device; and a plurality of communicating holes which are provided in the separating wall, each of which is provided with a first opening that opens in the combustion chamber and a second opening that opens in the ignition promoting chamber, and which provide communication between the combustion chamber and the ignition promoting chamber.

A two-stroke engine piston (1) is disclosed comprising a piston top (3), a mantle surface (5), a stratified scavenging channel (7) in the mantle surface (5), and a weight reduction space (9) arranged between the piston top (3) and the stratified scavenging channel (7). The weight reduction space (9) has a largest first axial extent (a1) at the mantle surface (5) and a second axial extent (a2) radially inside the mantle surface (5), and wherein the second axial extent (a2) is greater than the largest first axial extent (a1). The present disclosure further relates to an engine (30), a hand-held tool (40), and a method of manufacturing an engine piston (1).

A two-stroke engine piston (1) is disclosed comprising a piston top (3), a mantle surface (5), a stratified scavenging channel (7) in the mantle surface (5), and a weight reduction space (9) arranged between the piston top (3) and the stratified scavenging channel (7). The weight reduction space (9) has a largest first axial extent (a1) at the mantle surface (5) and a second axial extent (a2) radially inside the mantle surface (5), and wherein the second axial extent (a2) is greater than the largest first axial extent (a1). The present disclosure further relates to an engine (30), a hand-held tool (40), and a method of manufacturing an engine piston (1).

A fuel supply device has a base body, in which an intake channel section is formed. At least one adjustable throttle element for controlling the free flow cross section of the intake channel section is provided. At least one fuel opening opens into the intake channel section. A partition wall section is arranged in the intake channel section upstream of the throttle element. The partition wall section and the throttle element divide, in a completely open position of the throttle element, the intake channel section upstream of the throttle element into a mixture channel, into which the fuel opening feeds fuel, and an air channel. In order to improve the cooling of the fuel supply device, the partition wall section has at least one element for increasing the surface area within the mixture channel.

A carburetor has a carburetor body wherein an intake channel is formed. A throttle flap is pivotably mounted by a throttle shaft in the carburetor body for controlling the free flow cross-section of the intake channel. The intake channel has a first longitudinal center axis in the region of the throttle shaft. The throttle flap has first and second end positions, wherein the throttle flap opens a larger flow cross-section of the intake channel in the second end position than in the first end position. A partition wall section, on which the throttle flap lies in the second end position, is arranged upstream of the throttle shaft. A choke flap is upstream of the partition wall section and is pivotable between first and second end positions. In their second end positions, the throttle flap and the choke flap overlap in the direction of the first longitudinal center axis.