Air-fuel ratio control system in internal combustion engine

Claim 1

An air-fuel ratio control system in an internal combustion engine comprising: a carburetor in which a basic air-fuel ratio is set on the lean side rather than at a controlled air-fuel ratio; a fuel injection valve for injecting feed of fuel so that the air-fuel ratio can attain a controlled air-fuel ratio; and a control circuit for basically controlling the fuel flowrate injected from said fuel injection valve according to RPM of the engine and an air intake pressure, and for correcting and controlling said fuel flowrate according to operating conditions of the engine during transient operating conditions, wherein said control circuit comprises: a multiplexer fed with an output from the throttle valve open-close speed sensor, an output from the intake air pressure sensor, and an output from the engine cooling water temperature sensor; an analog-digital converter for converting an output from said multiplexer into a digital value; a first counter, a pulse oscillator and a crankshaft angle sensor, said first counter counting the number of pulses generated by said pulse oscillator per output generated by said crankshaft angle sensor; a microcomputer for performing calculations based on outputs from said analog-digital converter and said first counter; a random access memory for provisionally storing constants and the like required for operation in said microcomputer; a read only memory for storing programs and the like required for fuel injection; a second counter for counting the number of pulses generated by said pulse oscillator per output generated by said microcomputer; a power transistor for on-off controlling the current flowing to an exciting coil of said fuel injection valve based on an output from said second counter; and a bus line for connecting between said components.