Patent ID: 7210432

Claim:
An internal combustion engine including a two-stroke engine for a portable handheld work apparatus, the internal combustion engine having a predetermined piston displacement measured in cm 3 and comprising: a crankcase; a cylinder connected to said crankcase; said cylinder having a cylinder wall defining a cylinder bore; a piston displaceably mounted in said cylinder bore and said piston and said cylinder conjointly defining a combustion chamber; a crankshaft rotatably mounted in said crankcase; a connecting rod connecting said piston to said crankshaft so as to permit said piston to drive said crankshaft as said piston reciprocates in said cylinder between bottom dead center and top dead center; said cylinder having a discharge outlet formed therein for conducting exhaust gases away from said combustion chamber; an inlet for conducting an air/fuel mixture to said crankcase; a transfer window; a transfer channel having a first end communicating with said combustion chamber via said transfer window and having a second end communicating with said crankcase for conducting said air/fuel mixture from said crankcase into said combustion chamber; a controlled opening; a bypass channel for conducting essentially fuel-free air; said controlled opening being interposed between said transfer channel and said bypass channel and said bypass channel communicating with said transfer channel via said controlled opening; said transfer window having an area measured in mm 2 ; and, said area and said piston displacement defining a ratio lying in a range of approximately 1.4 mm 2 /cm 3 to 5.90 mm 2 /cm 3 .