Patent ID: 8447497
Filing Date: 2013-05-21
Classification: F02D

Abstract:
1. An apparatus for determining an air-fuel ratio imbalance among cylinders applied to a multi-cylinder internal combustion engine having a plurality of cylinders, comprising: an air-fuel ratio sensor, disposed in an exhaust passage of said engine and at an exhaust gas aggregated portion into which exhaust gases discharged from at least two or more of cylinders among a plurality of said cylinders merge, or in said exhaust passage of said engine and at a position downstream of said exhaust gas aggregated portion, and outputting, as an output of said air-fuel ratio sensor, an output value in accordance with an air-fuel ratio of said exhaust gas reaching said air-fuel ratio sensor; a plurality of fuel injectors, each provided so as to correspond to each of said at least two or more of said cylinders, and each injecting a fuel to be contained in a mixture supplied to each of said combustion chambers of said two or more of said cylinders; a purge passage section for forming a passage which allows an evaporated fuel gas generated in a fuel tank for storing the fuel supplied to a plurality of said fuel injectors to be introduced into an intake passage of said engine; purge amount control portion configured so as to control an evaporated fuel gas purge amount which is an amount of said evaporated fuel gas flowed into said intake passage of said engine through said purge passage section; imbalance determination parameter obtaining portion configured so as to obtain, based on said output value of said air-fuel ratio sensor, an imbalance determination parameter which becomes larger or smaller as a difference among individual air-fuel ratios, each being an air-fuel ratio of said mixture supplied to each of said at least two or more of a plurality of said cylinders, becomes larger; imbalance determining portion configured so as to compare said obtained imbalance determination parameter with a predetermined imbalance determination threshold, and so as to determine whether or not said air-fuel ratio imbalance among cylinders has been occurring based on a result of said comparison; and allowing and prohibiting imbalance determining execution portion configured so as to determine whether or not an evaporated fuel gas effect occurring state is occurring in which said evaporated fuel gas flowing into said intake passage causes said imbalance determination parameter to change by an amount larger than or equal to a predetermined allowable amount, and so as to prohibit obtaining said imbalance determination parameter or to prohibit performing said imbalance determination, when it is determined that said evaporated fuel gas effect occurring state is occurring.