Fuel injection control system for internal combustion engines

Claim 1

A fuel injection control system for an internal combustion engine having a throttle valve and being provided with electromagnetically operable injection valves operated by electronic control means in relation to the operating parameters of said engine, characterized by the provision of a pulse generator for generating output pulses corresponding in number to the number of revolutions of the engine, and a blocking circuit comprising: a waveform shaping circuit including a monostable multivibrator circuit connected to said pulse generator for developing constant length digital output signals of frequency corresponding to the frequency of said generator output pulses, digital-analog converter circuit means connected to said multivibrator circuit for converting the said constant length digital output signals of said waveform shaping circuit into an analog output voltage varying in magnitude only in correspondence to the frequency of said digital signals, means for developing a reference voltage corresponding in magnitude only to a predetermined number of revolutions of the engine, comparator circuit means including said voltage developing means and connected to said converter means for comparing the magnitudes of said reference voltage and analog output voltage for producing an output only when the latter exceeds the former, a switch adapted to be closed when the throttle valve of the engine is fully or substantially fully closed, and logical product circuit means connected to said comparator means and said switch and adapted for connection to said injection valves for producing an output signal only when said switch is closed while said comparator means produces its said output to thereby stop the operation of said injection valves.