Crank angle detecting system for engines

Claim 1

An ignition system for a multi-cylinder internal combustion engine, comprising: (a) a plurality of engine cylinders in which spark plugs are installed respectively, said cylinders being classified into a plurality of groups and each group being constituted by a pair of cylinders such that while the one cylinder is in an explosive stroke, the other is in an exhaust stroke; (b) indicating means disposed so as to synchronize with an engine crankshaft and formed with a large number of slits and a small number of slits, the large number of slits being provided for indicating crankshaft angular positions and the small number of slits being provided for indicating predetermined piston strokes and wherein said small number of slits have mutually different widths from each other to distinguish between piston strokes of at least the groups of cylinders; (c) sensing means for sensing crankshaft angular positions in cooperation with the large number of slits of the indicating means and outputting a crank angle signal representing the crankshaft angular position and for sensing the predetermined piston strokes in cooperation with the small number of slits and outputting different width piston stroke signals corresponding to said different width slits; (d) discriminating means for identifying each cylinder group and outputting cylinder group identification signals on the basis of the different width stroke signals derived from the sensing means; (e) ignition timing determining means for generating an ignition timing signal on the basis of the crank angle signal; (f) ignition coil controlling means for generating ignition coil current signals corresponding to said cylinder group identification signals; and (g) ignition timing controlling means for generating cylinder group ignition signals in response to the ignition coil current signals and ignition timing signal so that the spark plugs of each cylinder group are ignited at a proper time.