FORBRENNINGSMOTORDRIVEN MOTORKEDJESAG ELLER LIKNANDE HANDHALLEN ARBETSMASKIN

摘要

The invention is directed to an ignition arrangement for an internal combustion engine of a handheld portable tool such as a chain saw or the like. The engine has a crankshaft and a fan wheel is seated on the crankshaft for rotation therewith. The ignition arrangement includes a permanent magnet. The magnet has two pole shoes and an exciter coil is mounted on the permanent magnet. The permanent magnet equipped in this way is fixedly mounted on the tool to save weight. A relatively light self-supporting annular member with projections is mounted in the fan wheel. The projections of the annular member and the permanent magnet with its pole shoes conjointly define a magnetic circuit. As the projections pass the pole shoes at a minimal spacing therefrom during operation of the engine, the projections alternately open and close the magnetic circuit thereby causing changes in the flux of this circuit. The flux changes cause a voltage to be inducted in the exciter coil which serves to generate the igniting spark via an appropriate electronic circuit.