Rotational reference position detecting apparatus

Abstract

A crankshaft rotational reference position detecting apparatus is adapted for use with ignition timing control systems for internal combustion engines. The apparatus comprises a rotor disk fixedly mounted on the crankshaft of an engine and having rotational angle information indicating slits and a rotational reference position indicating mark which are formed along the periphery thereof, a first sensor for detecting each rotational angle information indicating slit and generating a first pulse signal corresponding thereto, the first sensor producing no first pulse signal when a rotational reference position is detected, a second sensor located at a position displaced from the first sensor in a desired rotational direction and adapted to generate a second pulse signal delayed in phase from the first pulse signal, a storage device responsive to the second pulse signals to store the output level of the first sensor, and a detection circuit responsive to a change in the output of the storage device which is indicative of the detection of the rotational reference position by the first sensor so as to generate a reference position detection pulse. In the event that the rotor disk is rotated in the reverse direction, the detection of the rotational reference position does not result in the generation of any reference position detection pulse.