DETECTING METHOD OF NUMBER OF REVOLUTION OF ENGINE

PURPOSE:To eliminate rotating variation component for exerting a bad influence on a control by averaging a prescribed crank angle rotation necessary time based on a crank angle signal of every equal crank angle, updating it successively, and detecting a number of revolution of engine. CONSTITUTION:Basing on a crank angle signal of every equal crank angle of every 30 deg., etc., a necessary time required for a rotation of 30 deg. of a crank shaft is measured, and a necessary time of the first storage means is updated. An average operation of said necessary time and a mean value of a necessary time before that time stored in the second storage means is executed and a mean necessary time of the second storage means is updated. Also, a number of revolution of engine is detected from the latest mean necessary time. Accordingly, in a high speed rotation area, a number of revolution of engine which has averaged a variation of the number of revolution of engine is detected, and in a low speed rotation area, a number of revolution of engine which has not averaged more than required a variation of the number of revolution engine is detected, a rotating variation component for exerting a bad influence on a control of the number of revolution is eliminated, and a number of revolution which can be controlled properly extending from a high speed to a low speed is detected.