Air-fuel ratio control for an internal combustion engine

Apparatus for controlling the air-fuel ratio in an internal combustion engine having an air flow sensor in an intake pipe, said apparatus comprising:

• a bypass path providing an air path, bypassing said air flow sensor;
• air control valve means for dithering the air-fuel ratio about a basic air-fuel ratio to a predetermined extent by allowing air to flow through said bypass path in an ON mode and prohibitting air to flow through said bypass path in an OFF mode;
• means for running the engine on the basis of said dithered air-fuel ratio;
• means for monitoring and detecting changes in operating conditions of said engine;
• processing means for:
• (1) correcting the basic air-fuel ratio in a desirable direction corresponding to the direction of change of the air-fuel ratio during said dithering which improved the specific fuel consumption, as determined by the monitored operating conditions, (2) determining a fundamental fuel injection pulse .tau. based on said corrected basic air-fuel ratio, and (3) correcting said fundamental fuel injection pulse .tau. by the application of a fuel correction coefficient (K.sub.1) which is derived by using maps which indicate the relationship between said fuel correction coefficient (K.sub.1) and one of (a) a number of fuel injections since said air control valve transitioned between said ON and OFF modes, (b) a number of engine rotations since said air control valve transitioned between said ON and OFF modes, and (c) a period of fuel injection since said air control valve transitioned between said ON and OFF modes;
• and
• said running means including means for injecting fuel in accordance with said corrected fundamental fuel injection pulse.

A method for controlling the air-fuel ratio in an internal combustion engine having an air flow sensor in an intake pipe to improve specific fuel consumption comprising the steps:

• dithering a basic air-fuel ratio to a predetermined extent to produce a dithered air-fuel ratio by changing the mode of a bypass air control valve disposed in a bypass path providing an air path bypassing said air flow sensor between an ON mode allowing air to pass through said bypass path and an OFF mode prohibitting air to pass through said bypass path;
• running said engine with said dithered air-fuel ratio;
• monitoring the operating conditions of said engine including an air flow rate measured by said air flow sensor;
• detecting the changes in said operating conditions caused by said dithered air-fuel ratio;
• calculating a fundamental fuel injection quantity .tau. based on said basic air-fuel ratio;
• supplying said fundamental fuel injection quantity to said engine;
• determining whether said bypass air control valve is in said OFF or said ON mode;
• determining a number of fuel injections occurring since said bypass air control valve changed mode;
• determining a fuel correction coefficient K.sub.1 from a data map based upon said number of fuel injections since said bypass air valve changed mode;
• reading an air flow rate Q.sub.a (ON) measured by said air flow sensor occurring during a previous fuel injection period when said bypass air control valve was in said ON mode;
• reading an air flow rate Q.sub.a (OFF) measured by said air flow sensor occurring during a previous fuel injection period when said bypass air control valve was in said OFF mode;
• calculating K.sub.2, a rate of change in air flow by the equation ##EQU3## calculating a corrected fuel injection quantity .tau..sub.1 by the equation
• .tau..sub. =.tau. (1+K.sub.1 (K.sub.2 /3%));
• and
• supplying said corrected fuel quantity to said engine.

Apparatus for controlling the air-fuel ratio in an internal combustion engine to improve specific fuel consumption comprising:

• means for monitoring the operating conditions of said engine including an air flow sensor disposed in an intake passage of said engine;
• a bypass path providing an air path bypassing said air flow sensor;
• air control valve means for allowing air to flow through said bypass path in an ON mode and for prohibitting air from flowing through said bypass path in an OFF mode;
• means for dithering a basic air-fuel ratio to a predetermined extent to produce a dithered air-fuel ratio by causing said valve means to alternate between said ON and OFF modes;
• means for running said engine with said dithered air-fuel ratio;
• processing means for:
• (a) detecting the changes in said operating conditions caused by said dithered air-fuel ratio, (b) calculating a fundamental fuel injection quantity .tau. based on said basic air-fuel ratio, said running means supplying said fundamental fuel injection quantity to said engine, (c) determining whether said bypass air control valve is in said OFF or said ON mode, (d) reading a number of fuel injections occurring since said bypass air control valve changed mode, (e) reading a fuel correction coefficient K.sub.1 from a data map based upon said number of fuel injections since said bypass air valve changed mode, (f) reading an air flow rate Q.sub.a (ON) measured by said air flow sensor occurring during a previous fuel injection period when said bypass air control valve was in said ON mode, (g) reading an air flow rate Q.sub.a (OFF) measured by said air flow sensor occurring during a previous fuel injection period when said bypass air control valve was in said OFF mode, (h) calculating K.sub.2, a rate of change in air flow by the equation ##EQU4## (i) calculating a corrected fuel injection quantity .tau..sub.1 by the equation
• .tau..sub. =.tau. (1+K.sub.1 (K.sub.2 /3%));
• and
• said running means including means for supplying said corrected fuel quantity to said engine.