A CRANKCASE-SCAVENGED TWO-STROKE INTERNAL COMBUSTION ENGINE HAVING AN AUTOMATIC DECOMPRESSION VALVE

摘要

A crankcase-scavenged two-stroke engine (1) having a cylinder (9), a reciprocating piston (7) movable back and forth in the cylinder (9), and a conduit (21) ported by the piston (7) for supply of additional air into the interior of the cylinder (9) for the scavenging. The engine has an automatic decompression valve (30) for reducing compression in order to facilitate starting of the engine (1), said decompression valve (30) being connected to a combustion chamber (13) of the engine (1) and being closed by underpressure periodically created in a section of the engine (1) when the engine piston (7) is moving back and forth, said section including the additional air conduit (21), said decompression valve (30) being connected to the additional air conduit (21) by an underpressure conduit (37) having a check valve (38) for preservation of the underpressure so as to keep the decompression valve (30) closed when the engine (1) is running, and a bleed conduit (45) for eliminating the underpressure within a few seconds after the engine (1) has stopped so as to open the decompression valve (30).