Noise immune crankshaft pulse position developing apparatus

Claim 1

A digital system for providing a series of voltage pulses that occur at predetermined angular positions of the crankshaft of an internal combustion engine comprising, an engine having a crankshaft, sensor means including means driven by said crankshaft for developing a square wave signal that has a plurality of high level voltage pulses that occur at predetermined angular positions of the crankshaft separated by low level periods, the spacing between corresponing edges of said pulses corresponding to a predetermined amount of angular rotation of said crankshaft, said high level voltage pulses and said low level periods lasting for predetermined time periods that vary with variation in engine speed, digital filter means having an input and an output, said input of said digital filter means coupled to said sensor means, said digital filter means comprising means for determining whether or not the time periods of said high level pulses or said low level periods exceed predetermined time periods, means coupled to said determining means for preventing a high level voltage pulse of said square wave signal from being passed to said output when said high level voltage pulse has a time period that was determined to be less than said predetermined time period, and means coupled to said determining means for passing a high to low level transition of said square wave to said output when just prior to said transition said square wave had a high level period that was longer than said predetermined time period.