Crank angle detector for an engine

Claim 1

A crank angle detector for an engine having a plurality of cylinders, a crank shaft, a cam shaft, a crank angle sensor for sensing a rotational position of said crank shaft and for producing a crank pulse and a cam pulse, a starter switch for starting said engine and producing a start signal, and a controller responsive to said cam pulse and crank pulse sensed by said crank angle sensor to control ignition timing of said respective cylinders of said engine, comprising: a pair of rotor plates having a plurality of projections on a periphery thereof for indicating said crank pulse, in which one of said plates calculates a crank angle and an engine speed, and the other of said plates indicates a fixed ignition timing at starting said engine; a cam rotor plate connected to an end of said cam shaft, and having a projection on a periphery thereof for discriminating a cylinder number and for producing said cam pulse; said controller operatively to control an ignition timing by said crank pulse indicating said fixed ignition timing when said engine is judged to be in a starting state in dependency on said start signal from said starter switch; and said controller having an interrupt terminal connected to an input interface therein for masking said interrupt terminal of said input interface to control an ignition timing when said fixed crank pulse is input and when said engine is judged to be in the complete firing state in dependency on an OFF state of said start signal from said starter switch.