Patent ID: 6012428
Filing Date: 2000-01-11
Classification: F02D,Y02T

Abstract:
An air-fuel ratio controlling method in an internal combustion engine comprising an exhaust emission control catalyst provided in an exhaust passage common to plural cylinders, and a fuel injection valve provided at each of the cylinders, the method comprising the steps of switching an air-fuel ratio for each of the cylinders from a rich ratio to a lean ratio and from a lean ratio to a rich ratio in a sequential manner among all the cylinders when switching a target air-fuel ratio from rich to lean and lean to rich, respectively, by decreasing and increasing respectively an amount of fuel injected from each of said fuel injection valves at predetermined time intervals greater than a time interval between successive fuel injections to a cylinder, and, in the course of switching of said air-fuel ratios, controlling the fuel injection valves to produce a condition in which at least one cylinder is being provided with a lean air-fuel ratio fuel injection and a plurality of cylinders are being provided with a rich air-fuel ratio fuel injection, and said plurality of cylinders are in an order of discharge of an exhaust gas from the cylinders for causing the rich air-fuel ratio to be continuous.