Multicylinder internal combustion engine, inter-cylinder air/fuel ratio imbalance determination apparatus, and method therefor

Abstract

A multicylinder engine includes: combustion chambers; fuel injection valves corresponding to the individual combustion chambers; an exhaust control catalyst; an upstream-side air/fuel ratio sensor disposed upstream of the exhaust control catalyst; and a downstream-side A/F sensor disposed downstream of the catalyst. A first abnormality determination-purpose rich A/F control of controlling the A/F of the mixture formed in each combustion chamber to an A/F richer than stoichiometric is executed when it needs to be determined whether the downstream-side A/F sensor is abnormal. An inter-cylinder A/F imbalance determination of estimating the A/F of the mixture in each combustion chamber based on the output of the upstream-side A/F sensor is executed when the first abnormality determination-purpose rich A/F control is being executed, and it is determined whether there is a difference between the estimated A/Fs of the mixtures.

Description

[0001]The disclosure of Japanese Patent Application No. 2010-27674 filed on Feb. 10, 2010, including the specification, drawings and abstract is incorporated herein by reference in its entirety.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The invention relates to a multicylinder internal combustion engine, and to a determination apparatus and a determination method that determine the presence or absence of inter-cylinder air / fuel ratio imbalance.[0004]2. Description of the Related Art[0005]In a multicylinder internal combustion engine in which fuel injection valves are disposed corresponding to each one of a plurality of combustion chambers so that fuel is injected from the fuel injection valves into the corresponding combustion chambers, it is preferable that the amounts of fuel injected from the fuel injection valves be all controlled to equal and optimum amounts, in order to minimize the exhaust emissions discharged from the combustion chambers. That is, in the...

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Benefits of technology

[0010]The invention provides an apparatus and a method that accurately determines the inter-cylinder air / fuel ratio imbalance in an multicylinder internal combustion engine.

Problems solved by technology

That is, in the multicylinder internal combustion engine, for example, in the case where the amount of fuel to be injected from the fuel injection valves is set at an amount that will minimize the exhaust emissions discharged from the combustion chambers (i.e., an optimum amount), there is a possibility of the exhaust emissions from the combustion chambers increasing unexpectedly if the amount of fuel injected from any one of the fuel injection valves is not controlled to the foregoing optimum amount.

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