Abstract: An air filter unit (1) for a carburetor (2) of a portable handheld work apparatus includes a filter element (3) and at least one clean air channel (10, 11) arranged between the filter element (3) and the carburetor (2). At least one condensation rib (29, 30, 31, 32) is arranged in the clean air channel (10, 11) running in flow direction.

Abstract: An air filter unit (1) for a carburetor (2) of a portable handheld work apparatus includes a filter element (3) and at least one clean air channel (10, 11) arranged between the filter element (3) and the carburetor (2). At least one condensation rib (29, 30, 31, 32) is arranged in the clean air channel (10, 11) running in flow direction.

Abstract: A two-stroke engine is for a portable handheld work apparatus such as a motor-driven chain saw, cutoff machine, brushcutter or the like. A combustion chamber (3) is configured in the cylinder (2) of the engine (1) and is delimited by a reciprocating piston (5). The piston (5) drives a crankshaft (7) via a connecting rod (6). The crankshaft (7) is rotatably journalled in the crankcase (4). The two-stroke engine includes a discharge opening (10) for conducting exhaust gases out of the combustion chamber (3) and an inlet (11) via which an air/fuel mixture is conducted to the crankcase (4). The air/fuel mixture passes via at least one transfer channel (12, 15) from the crankcase (4) into the combustion chamber (3). The transfer channels (12, 15) open at one end with a transfer window (13, 16) into the combustion chamber (3) and are connected at the other end to the crankcase (4). A bypass channel (20) conducts essentially fuel-free gas and opens via a membrane valve (19) into the transfer channel (15).

Abstract: An internal combustion engine (20) has a cylinder (1) wherein a piston (2) is mounted. The piston (2) drives a crankshaft (10) which is rotatably journalled in a crankcase (11). The piston (2) delimits a combustion chamber wherein an air/fuel mixture is compressed and is ignited by an ignition device (19). The ignition time point (Z) is determined in a first operating state of the engine (20) in accordance with a first characteristic line (22) and in a second operating state of the engine (20) in accordance with a second characteristic line (23). A switching element switches over between the first characteristic line (22) and the second characteristic line (23) in dependence upon an engine characteristic variable. A method for operating the engine (20) provides that an engine characteristic variable is determined during operation of the engine (20) and that a switchover between the ignition characteristic lines (22) and (23) takes place for a pregiven change of the characteristic variable.

Abstract: A two-stroke engine is for a portable handheld work apparatus such as a motor-driven chain saw, cutoff machine, brushcutter or the like. A combustion chamber (3) is configured in the cylinder (2) of the engine (1) and is delimited by a reciprocating piston (5). The piston (5) drives a crankshaft (7) via a connecting rod (6). The crankshaft (7) is rotatably journalled in the crankcase (4). The two-stroke engine includes a discharge opening (10) for conducting exhaust gases out of the combustion chamber (3) and an inlet (11) via which an air/fuel mixture is conducted to the crankcase (4). The air/fuel mixture passes via at least one transfer channel (12, 15) from the crankcase (4) into the combustion chamber (3). The transfer channels (12, 15) open at one end with a transfer window (13, 16) into the combustion chamber (3) and are connected at the other end to the crankcase (4). A bypass channel (20) conducts essentially fuel-free gas and opens via a membrane valve (19) into the transfer channel (15).

Abstract: An internal combustion engine (20) has a cylinder (1) wherein a piston (2) is mounted. The piston (2) drives a crankshaft (10) which is rotatably journalled in a crankcase (11). The piston (2) delimits a combustion chamber wherein an air/fuel mixture is compressed and is ignited by an ignition device (19). The ignition time point (Z) is determined in a first operating state of the engine (20) in accordance with a first characteristic line (22) and in a second operating state of the engine (20) in accordance with a second characteristic line (23). A switching element switches over between the first characteristic line (22) and the second characteristic line (23) in dependence upon an engine characteristic variable. A method for operating the engine (20) provides that an engine characteristic variable is determined during operation of the engine (20) and that a switchover between the ignition characteristic lines (22) and (23) takes place for a pregiven change of the characteristic variable.

Abstract: The invention relates to a carburetor arrangement of a portable handheld work apparatus and includes a carburetor (1), an accelerator pump (2) and a venting pump (3). The venting pump (3) acts on the accelerator pump (2) via a venting line (4). A check valve (5) is mounted in the venting line (4) in such a manner that its outlet end (6) is directed in the direction of the venting pump (3). A pretensioning device (7) is provided which holds a valve body (8) of the check valve (5) closed below a selected difference pressure between the outflow end (6) and an opposite-lying inflow end (9). A support device (10) which acts on the valve body (8) and is actuable, at one end, by pressure at the outflow end (6) without considering pressure at the other end (9) or by pressure on the inflow end (9) without considering the pressure on the other end (6).

Abstract: The invention relates to a carburetor arrangement of a portable handheld work apparatus and includes a carburetor (1), an accelerator pump (2) and a venting pump (3). The venting pump (3) acts on the accelerator pump (2) via a venting line (4). A check valve (5) is mounted in the venting line (4) in such a manner that its outlet end (6) is directed in the direction of the venting pump (3). A pretensioning device (7) is provided which holds a valve body (8) of the check valve (5) closed below a selected difference pressure between the outflow end (6) and an opposite-lying inflow end (9). A support device (10) which acts on the valve body (8) and is actuable, at one end, by pressure at the outflow end (6) without considering pressure at the other end (9) or by pressure on the inflow end (9) without considering the pressure on the other end (6).

Abstract: A method is provided for producing a cylinder in a two-cycle engine. The cylinder bore is first machined as a preparation for the provision of a coating. The thereby resulting window edges that surround an inlet window are then at least partially chamfered. The cylinder bore is consequently provided with the coating, which at least partially overlaps the chamfered window edge. There thereby results in the region of the window edge a location of least spacing relative to the axis of the transfer channel. The piston liner or gliding surface is finally machined to a finished dimension such that in the region of the chamfered and coated window edge or corner there is formed a coating edge having a wall spacing relative to the location of least spacing, which such wall spacing having a maximum value of 0.7 mm.

Abstract: A diaphragm carburetor for an internal combustion engine is provided, and has a housing with an impulse pressure driven fuel pump. Provided in the housing is a chamber that is divided by a diaphragm into a pump chamber and a drive chamber that is acted upon by impulse pressure fluctuations during operation of the internal combustion engine. In order with the least available impulse pressure differences of the engine to effectively deflect the diaphragm in the chamber, the freely movable diaphragm surface of the diaphragm is maximized and the conveying stroke of the diaphragm is enhanced by a spring. The movable diaphragm surface assumes a major portion of the surface of the plane of separation in which the diaphragm is disposed. For this purpose, a fuel intake valve and a fuel outlet valve are spaced from the diaphragm, and in particular are removed from the plane of separation in which the diaphragm comes to rest.

Abstract: A method is provided for producing a cylinder in a two-cycle engine. The cylinder bore is first machined as a preparation for the provision of a coating. The thereby resulting window edges that surround an inlet window are then at least partially chamfered. The cylinder bore is consequently provided with the coating, which at least partially overlaps the chamfered window edge. There thereby results in the region of the window edge a location of least spacing relative to the axis of the transfer channel. The piston liner or gliding surface is finally machined to a finished dimension such that in the region of the chamfered and coated window edge or corner there is formed a coating edge having a wall spacing relative to the location of least spacing, which such wall spacing having a maximum value of 0.7 mm.

Abstract: A diaphragm carburetor for an internal combustion engine is provided, and has a housing with an impulse pressure driven fuel pump. Provided in the housing is a chamber that is divided by a diaphragm into a pump chamber and a drive chamber that is acted upon by impulse pressure fluctuations during operation of the internal combustion engine. In order with the least available impulse pressure differences of the engine to effectively deflect the diaphragm in the chamber, the freely movable diaphragm surface of the diaphragm is maximized and the conveying stroke of the diaphragm is enhanced by a spring. The movable diaphragm surface assumes a major portion of the surface of the plane of separation in which the diaphragm is disposed. For this purpose, a fuel intake valve and a fuel outlet valve are spaced from the diaphragm, and in particular are removed from the plane of separation in which the diaphragm comes to rest.

Abstract: A two-stroke engine for driving a crankshaft includes a cylinder defining a longitudinal elevation axis and having a top wall and a cylindrical side wall terminating in the top wall. A piston is mounted in the cylinder so as to be movable along the side wall for driving a crankshaft. The cylinder and the piston conjointly define a combustion chamber wherein combustion gases are generated during operation of the engine and the side wall of the cylinder has an exhaust window which opens into the combustion chamber for conducting away the combustion gases. The exhaust window defines a longitudinal center axis passing approximately through the elevation axis and the side wall of the cylinder has a surface portion lying opposite the exhaust window. A plurality of main channels and a plurality of support channels open into the combustion chamber for conducting fuel mixture into the combustion chamber.