Two-stroke engine having a membrane valve integrated into the transfer channel

A two-stroke engine including a two-stroke engine in a portable handheld work apparatus, the two-stroke engine comprising:

• a crankcase;
• a cylinder connected to said crankcase;
• said cylinder having a cylinder wall defining a cylinder bore open to said crankcase;
• 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;
• said piston being operatively connected to said crankshaft for driving said crankshaft;
• a mixture inlet in said crankcase;
• a transfer channel for flow connecting said crankcase to said combustion chamber and said transfer channel having a first end open to said crankcase and a second end communicating with said combustion chamber;
• a bypass channel for conducting an essentially fuel-free gas;
• said bypass channel having an opening into said transfer channel at a location between said first and second ends thereof;
• said transfer channel being configured as a closed channel over the length thereof in said cylinder wall;
• a membrane valve assembly including a membrane axially inserted into said transfer channel through said first end thereof;
• said membrane being fixed on said cylinder in the region of said first end and projecting in said transfer channel up to in front of said opening;
• said membrane being movable between a closed position wherein said opening is closed and an open position wherein said fuel-free gas can flow through said opening and into said transfer channel;
• said membrane valve assembly further including an essentially stiff membrane carrier for supporting said membrane in said open position thereof;
• and,
• said membrane carrier projecting beyond said opening of said bypass channel and said membrane carrier having a break-through opening formed therein at the elevation of said opening of said bypass chamber.

A two-stroke engine including a two-stroke engine in a portable handheld work apparatus, the two-stroke engine comprising:

• a crankcase;
• a cylinder connected to said crankcase;
• said cylinder having a cylinder wall defining a cylinder bore open to said crankcase;
• 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;
• said piston being operatively connected to said crankshaft for driving said crankshaft;
• a mixture inlet in said crankcase;
• a transfer channel for flow connecting said crankcase to said combustion chamber and said transfer channel having a first end open to said crankcase and a second end communicating with said combustion chamber;
• a bypass channel for conducting an essentially fuel-free gas;
• said bypass channel having an opening into said transfer channel at a location between said first and second ends thereof;
• said transfer channel being configured as a closed channel over the length thereof in said cylinder wall;
• a membrane valve assembly including a membrane axially inserted into said transfer channel through said first end thereof;
• said membrane being fixed on said cylinder in the region of said first end and projecting in said transfer channel up to in front of said opening;
• said membrane being movable between a closed position wherein said opening is closed and an open position wherein said fuel-free gas can flow through said opening and into said transfer channel;
• said membrane valve assembly further including an essentially stiff membrane carrier for supporting said membrane in said open position thereof;
• and,
• said membrane valve assembly further including:
• a finished insert part separate from said cylinder;
• a seal seat formed on said insert part for said membrane when in said closed position;
• said insert part being inserted into said transfer channel through said first end thereof;
• and,
• means for fixing said insert part to said cylinder in said transfer channel.

A two-stroke engine including a two-stroke engine in a portable handheld work apparatus, the two-stroke engine comprising:

• a crankcase;
• a cylinder connected to said crankcase;
• said cylinder having a cylinder wall defining a cylinder bore open to said crankcase;
• 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;
• said piston being operatively connected to said crankshaft for driving said crankshaft;
• a mixture inlet in said crankcase;
• a transfer channel for flow connecting said crankcase to said combustion chamber and said transfer channel having a first end open to said crankcase and a second end communicating with said combustion chamber;
• a bypass channel for conducting an essentially fuel-free gas;
• said bypass channel having an opening into said transfer channel at a location between said first and second ends thereof;
• said transfer channel being configured as a closed channel over the length thereof in said cylinder wall;
• a membrane valve assembly including a membrane axially inserted into said transfer channel through said first end thereof;
• said membrane being fixed on said cylinder in the region of said first end and projecting in said transfer channel up to in front of said opening;
• said cylinder including a connecting stub formed thereon as one piece with said cylinder and said connecting stub communicates with said transfer channel;
• and,
• said bypass channel being connected to said transfer channel via said connecting stub.

A two-stroke engine including a two-stroke engine in a portable handheld work apparatus, the two-stroke engine comprising:

• a crankcase;
• a cylinder connected to said crankcase;
• said cylinder having a cylinder wall defining a cylinder bore open to said crankcase;
• 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;
• said piston being operatively connected to said crankshaft for driving said crankshaft;
• a mixture inlet in said crankcase;
• a transfer channel for flow connecting said crankcase to said combustion chamber and said transfer channel having a first end open to said crankcase and a second end communicating with said combustion chamber;
• a bypass channel for conducting an essentially fuel-free gas;
• said bypass channel having an opening into said transfer channel at a location between said first and second ends thereof;
• said transfer channel being configured as a closed channel over the length thereof in said cylinder wall;
• a membrane valve assembly including a membrane axially inserted into said transfer channel through said first end thereof;
• said membrane being fixed on said cylinder in the region of said first end and projecting in said transfer channel up to in front of said opening;
• said cylinder including an exhaust-gas discharge and said cylinder including two of said transfer channels on respective sides of a symmetry plane partitioning said mixture inlet and said exhaust-gas discharge;
• a first connecting stub formed on said cylinder as one piece therewith and communicating with the two transfer channels on a first side of said symmetry plane;
• said first connecting stub including an inner wall running in the channel longitudinal direction and partitioning said first connecting stub into two flow paths communicating with corresponding ones of the transfer channels on said first side;
• a second connecting stub formed on said cylinder as one piece therewith and communicating with the two transfer channels on a second side of said symmetry plane;
• and,
• said second connecting stub including an inner wall running in the channel longitudinal direction and partitioning said second connecting stub into two flow paths communicating with corresponding ones of the transfer channels on said second side.

A two-stroke engine including a two-stroke engine in a portable handheld work apparatus, the two-stroke engine comprising:

• a crankcase;
• a cylinder connected to said crankcase;
• said cylinder having a cylinder wall defining a cylinder bore open to said crankcase;
• 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;
• said piston being operatively connected to said crankshaft for driving said crankshaft;
• a mixture inlet in said crankcase;
• a transfer channel for flow connecting said crankcase to said combustion chamber and said transfer channel having a first end open to said crankcase and a second end communicating with said combustion chamber;
• a bypass channel for conducting an essentially fuel-free gas;
• said bypass channel having an opening into said transfer channel at a location between said first and second ends thereof;
• said transfer channel being configured as a closed channel over the length thereof in said cylinder wall and said transfer channel having an inside wall surface extending along said channel;
• a membrane valve assembly including a membrane axially inserted into said transfer channel through said first end thereof;
• said membrane being fixed on said cylinder against said inside wall surface in the region of said first end and projecting in said transfer channel up to in front of said opening;
• and,
• said membrane being movable between a closed position wherein said membrane lies seal tight against said inner wall surface so as to close said opening and an open position wherein said fuel-free gas can flow through said opening and into said transfer channel.