Husqvarna Ab

Mikael Bergman

Pär Martinsson

Bo P Carlsson

Par B Martinsson

Reine Gustafsson

Joel Berneklev

Mats Roberg

To meet stringent emission standards and improve performance of two-stroke crankcase-scavenged engines, the muffler () of the engine is provided with mixing means () for mixing the exhaust gases () resulting from the mixture participating in combustion and gases resulting from scavenging, so that a substantially homogenous gaseous mixture is formed within the muffler (), and means () for sensing oxygen concentration is located in the homogeneous gaseous mixture and are configured to provide an output value to a control unit () for controlling supply of fuel to the engine and thereby the air-fuel ratio in the combustion chamber (). The muffler () suitably is provided with a catalytic element (), preferably a three-way catalyst. The engine () preferably is a stratified charge engine.

Adjusting of air-fuel ratio of a two-stroke internal combustion engine

A two stroke crank case scavenged two-stroke internal combustion engine, the engine including: &#x2014;a cylinder () configured to reciprocatingly receive a piston () therein defining a combustion chamber (), the combustion chamber comprising an ignition means () for igniting an air/fuel mixture and an exhaust port () for evacuating the exhaust fumes, &#x2014;a crank case () including a crank shaft (), &#x2014;an indirect fuel supply system (), such as a carburettor () or a low pressure fuel-injection system, for supplying fuel to the crank case () to be scavenged to the combustion chamber (), &#x2014;at least one transfer duct (') each extending from the crank case () to at least one corresponding transfer port (&#x2032;) for connecting to the combustion chamber (), &#x2014;additional air filling means (&#x2032;) for at least partly filling the transfer duct/s (&#x2032;) with additional air from the transfer port (&#x2032;) towards the crank case (), &#x2014;and a direct injection means () for injecting fuel directly into the combustion chamber ().

Two-stroke internal combustion engine

A crankcase scavenged two-stroke engine () comprises a cylinder () including scavenging ports () and at least one exhaust port, a piston (), a connecting rod (), a crankshaft () and a generally sealed crankcase (). The crankcase inducts a fuel/air mixture and is connected to the scavenging ports () by means of transfer ducts () which, as the piston () is travelling from a lower position towards a higher position, are inducting pure air let in from connecting ports () near the scavenging ports () in the cylinder (). The transfer duct () volume is less than 20% of a volume swept by the piston () during an entire revolution of the crankshaft (). Recesses () are formed in an outer periphery of the piston (), said recesses () co-operating with the connecting ports () in the cylinder wall for controlling the filling of the transfer ducts () with air. An inlet tube () in the cylinder wall supplies the air/fuel mixture, said inlet tube () being connected to the crankcase () and covered by the piston () as the piston () is in the lower position, and open to the crankcase () as the piston () is in the higher position.

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Bankeryd, Sweden

Mikael Bergman