Two-stroke engine having charge stratification

#The present invention relates to a two-stroke engine, especially as a drive engine in a portable, manually guided implement such as a power chain saw, a brushcutter, a trimmer, a blower, a cut-off machine, or the like.

#An engine of this type is disclosed in U.S. Pat. No. 4,253,433. The mixture path of the carburetor opens into a feed channel that opens into the combustion chamber approximately across from the exhaust port, with the other end of the feed channel being open to the crankcase. The crankcase has a diaphragm-controlled air inlet, whereby the feed channel is configured in such a way that only a small portion of the drawn-in rich mixture enters the crankcase. The feed channel is embodied as a curved channel that extends from the base region of the crankcase up to the combustion chamber. Such a channel is not capable of being die cast; it can be produced only in a complicated and expensive manner, and is therefore not very suitable for mass production.

#It is therefore an object of the present invention to provide a two-stroke engine of the aforementioned general type that has a feed channel that is embodied in a more straightforward manner to allow an economical mass production of the engine.

#This object, and other objects and advantages of the present invention, will appear more clearly from the following specification in conjunction with the accompanying schematic drawings, in which:

#FIGS. 1a to 1f schematically illustrate the manner of operation of an inventive two-stroke engine over one operating cycle;

#FIG. 2 is a partial cross-sectional view of a first exemplary embodiment of a cylinder having an external feed channel;

#The two-stroke engine of the present invention comprises a cylinder in which is formed a combustion chamber that is delimited by a reciprocating piston, wherein by means of a connecting rod the piston drives a crankshaft that is rotatably mounted in a crankcase that is provided with an air inlet for combustion air, which passes from the crankcase into the combustion chamber via at least one transfer channel that at one end opens into the combustion chamber via a transfer window and at the other end communicates with the crankcase, wherein the cylinder is provided with an exhaust port for the discharge of exhaust gases from the combustion chamber and, approximately across from the exhaust port, with an intake port that forms one end of a feed channel that is provided for supplying a fresh mixture, wherein the other end of the feed channel opens into the crankcase, wherein the intake port opens into the combustion chamber and when viewed in a stroke direction of the piston toward an upper dead center position thereof, the intake port of the feed channel is disposed, in terms of height, above the air inlet to the crankcase; a mixture-forming device for a fuel/air mixture is provided, wherein between the ends thereof, the feed channel communicates with the mixture-forming device; also provided is a component that is external to the cylinder, wherein at least a portion of a feed channel is disposed in this component.

#The intake port of the feed channel into the combustion chamber is, in the stroke direction of the piston, disposed above the air inlet, for which reason the supply of the mixture and of air is possible in a straightforward manner via a double-flow carburetor or the like. In this connection, a portion of the feed channel is formed as an external component of the engine, as a result of which the remaining channel portions are capable of being die cast, in other words, extend essentially radially, tangentially or axially relative to the cylinder axis.

#Thus, the intake port of the feed channel into the combustion chamber is formed with an essentially linear, but also angled, intake portion in the cylinder connector that adjoins an intermediate portion of the feed channel that is provided in a carburetor flange. The carburetor flange is disposed between the cylinder and the mixture-forming device, and is fixedly connected to these components. The intermediate portion of the feed channel can establish the connection to an external tube that, as an external feed channel, is connected to the crankcase.