Air/fuel ratio estimation system for internal combustion engine

A system for controlling air/fuel ratios of individual cylinders of a multicylinder internal combustion engine connected to an exhaust pipe via an exhaust manifold that constitutes an exhaust system of the engine, said system having;

• an air/fuel ratio sensor installed at the exhaust system of the engine;
• a detection circuit for receiving an output of said air/fuel ratio sensor to determine an air/fuel ratio at a confluence point of the exhaust system;
• modeling means for modeling a behavior of the exhaust system by an equation established based on an assumption that the air/fuel ratio at the confluence point is expressed as a sum of products of past firing histories of the individual cylinders and weighting coefficients thereof;
• observer establishing for establishing an observer to obtain a state variable that indicates the air/fuel ratios of the individual cylinders
• estimating means for estimating the air/fuel ratios in the individual cylinders from the equation;
• fuel injection quantity determining means for determining a fuel injection quantity to be supplied to the engine at least based on a base value and the estimated air/fuel ratios of the individual cylinders;
• and
• a fuel injector for injecting fuel based on the determined fuel injection quantity;
• wherein the improvement comprises:
• engine operating condition detecting means for detecting the operating condition of the engine;
• and
• said observing establishing a plurality of observer matrices with respect to the operating condition of the engine and selecting one from among the observer matrices in response to the detected operating condition of the engine.

A system for controlling air/fuel ratios of individual cylinders of a multicylinder internal combustion engine connected to an exhaust pipe via an exhaust manifold that constitutes an exhaust system of the engine, said system having:

• an air/fuel ratio sensor installed at the exhaust system of the engine;
• a detection circuit for receiving an output of said air/fuel ratio sensor to determine an air/fuel ratio at a confluence point of the exhaust system;
• modeling means for modeling a behavior of the exhaust system by an equation established based on an assumption that the air/fuel ratio at the confluence point is expressed as a sum of products of past firing histories of the individual cylinders an weighting coefficients thereof;
• observer establishing for establishing an observer to obtain a state variable that indicates the air/fuel ratios in the individual cylinders
• estimating means for estimating the air/fuel ratios in the individual cylinders from the equation;
• fuel injection quantity determining means for determining a fuel injection quantity to be supplied to the engine at least based on a base value and the estimated air/fuel ratios of the individual cylinders;
• and
• a fuel injector for injecting fuel based on the determined fuel injection quantity;
• wherein the improvement comprises:
• a variable valve timing mechanism which switches at least one of a valve timing and a valve lifting between a plurality of valve timing characteristics;
• valve timing detecting means for detecting the valve timing characteristic switched by said variable valve timing mechanism;
• and
• said observer establishing changing observer matrix in response to the detected valve timing characteristic.

A system for controlling air-fuel ratios of individual cylinder of a multi-cylinder internal combustion engine connected to an exhaust pipe via an exhaust manifold constituting an exhaust system of the engine, said system comprising:

• an air/fuel ratio sensor installed at the exhaust system of the engine;
• a fuel injector for injecting fuel into the internal combustion engine;
• a controller for controlling the fuel injector, said controller being configured to
• receive an output of said air/fuel ratio sensor, and determine an air/fuel ratio at a confluence point of the exhaust system;
• model a behavior of the exhaust system by an equation established based on a principle that the air/fuel ratio at the confluence point is expressed as a sum of products of past firing histories of the individual cylinders and a weighting coefficient C, each indicative of a contribution thereto of the individual cylinders;
• setting the weighting coefficient C to 0 for a cylinder other than the most recent m (2.gtoreq.m>n) cylinders when a number of cylinders to have their air/fuel ratios estimated is 3.gtoreq.n;
• estimate the air/fuel ratios in the individual cylinders from the equation;
• determine a fuel injection quantity to be supplied to the engine by the fuel injection quantity to be supplied to the engine by the fuel injector at least based on a base value and the estimated air/fuel ratios of the individual cylinders;
• and
• controlling said fuel injector to inject fuel based upon the determined fuel injection quantity.

A system for controlling air/fuel ratios of individual cylinders of a multicylinder internal combustion engine connected to an exhaust pipe via an exhaust manifold, said exhaust pipe and exhaust manifold constituting an exhaust system of the engine, said system comprising:

• an air/fuel ratio sensor installed at the exhaust system of the engine;
• a fuel injector for injecting fuel into said engine;
• a microprocessor connected to said air/fuel ratio sensor and said fuel injector, said microprocessor controlling the air/fuel ratios of the individual cylinders, and configured to
• receive an output of the air/fuel ratio sensor and to determine an air/fuel ratio at a confluence point of the exhaust system;
• model a behavior of the exhaust system by an equation established based on a theory that the air/fuel ratio at the confluence point is expressed as a sum of products of past firing histories of the individual cylinders and weighting coefficients thereof;
• detect an operating condition of the engine based on operating information input thereto;
• establish an observer to obtain a state variable which indicates the air/fuel ratios of the individual cylinders, and establish a plurality of observer matrices with respect to the operating condition of the engine, and to select one from among the observer matrices in response to the detected operating condition of the engine;
• estimate the air/fuel ratios in the individual cylinders from the equation;
• determine a fuel injection quantity to be supplied to the engine at least based on a base value and the estimated air/fuel ratios in the individual cylinders;
• and
• control the fuel injector to inject fuel based upon the determined fuel injection quantity.

A system for controlling air/fuel ratios of individual cylinders of a multicylinder internal combustion engine connected to an exhaust pipe via an exhaust manifold, thereby constituting an exhaust system of the engine, said system comprising:

• an air/fuel ratio sensor installed at the an exhaust system of the engine;
• a variable valve timing mechanism which switches at least one of a valve timing and a valve lifting between a plurality of valve timing characteristics;
• a fuel injector for injecting fuel into said internal combustion engine;
• a microprocessor connected to said air/fuel ratio sensor and said fuel injector, said microprocessor configured to
• receive an output of said air/fuel ratio sensor and to determine an air/fuel ratio at a confluence point of the exhaust system;
• model a behavior of the exhaust system by an equation established upon a theory that the air/fuel ratio at the confluence point is expressed as a sum of products of past firing histories of the individual cylinders and weighting coefficients thereof;
• detect the valve timing characteristic switched by said variable valve timing mechanism;
• establish an observer to obtain a state variable that indicates the air/fuel ratios in the individual cylinders, said observer changing an observer matrix in response to the detected valve timing characteristic;
• estimating the air/fuel ratios in the individual cylinders from the equation;
• determining a fuel injection quantity to be supplied to the engine at least upon a base value and the estimated air/fuel ratios of the individual cylinders;
• and
• controlling the fuel injector to inject fuel based upon the determined fuel injection quantity.