Closed loop air fuel ratio control system using exhaust composition sensor

Claim 1

A closed loop mixture control system for an internal combustion engine having an air intake passage, a throttle therein, means for supplying air and fuel thereto and exhaust means, comprising: means for generating a first signal indicative of the deviation of the air-fuel ratio within said exhaust means from a fixed reference; an integrating controller including integrator means for providing integration of said first signal to suppress a control oscillation caused by a time lag inherent in the closed loop, said integrator means including an operational amplifier having a first input receptive of said first signal and a second input connected to a predetermined potential, and a capacitor connected between said first input and output of said amplifier to generate a control signal effective to cause said air fuel supply means to vary the ratio of air and fuel supplied to said engine in accordance with the direction of the deviation of said air-fuel ratio from said fixed reference; means for sensing when said throttle is in a fully open position; and switching means selectively providing a short-circuit path across said capacitor in response to the sensing means so that, with the throttle fully open, the output from said integrating controller is operated in a proportional mode and maintained at such a value that said air fuel supply means is caused to supply an enriched mixture to said engine, and when said throttle is varied from said fully open position to a part throttle position, said integrating controller commences operation in an integration mode for integration of said first signal and generates an output effective to cause said air fuel supply means to supply a leaner mixture to said engine.