Patent ID: 8650943
Filing Date: 2014-02-18
Classification: F02B,F02D,Y02T

Abstract:
1. An air-fuel ratio imbalance among cylinders determining apparatus of an internal combustion engine, applied to a multi-cylinder internal combustion engine having a plurality of cylinders, comprising: compression ratio varying means for varying a compression ratio of said engine in accordance with an operating state of said engine; a catalyst disposed, in an exhaust passage of said engine, and at an exhaust gas aggregated portion into which exhaust gases discharged from combustion chambers of at least two or more of cylinders of a plurality of said cylinders merge or at a portion downstream of said exhaust gas aggregated portion; fuel injectors, each being disposed so as to correspond to each of said at least two or more of cylinders and so as to inject a fuel to be contained in a mixture supplied to each of said combustion chambers of said at least two or more of cylinders; an upstream air-fuel ratio sensor, which is disposed at said exhaust gas aggregated portion or at a position between said exhaust gas aggregated portion and said catalyst in said exhaust passage, which includes a diffusion resistance layer with which an exhaust gas which has not passed through said catalyst contacts, and an air-fuel ratio detecting element, which is covered by said diffusion resistance layer, and which outputs, as an output value of said upstream air-fuel ratio sensor, a signal in accordance with an air-fuel ratio of an exhaust gas reaching said air-fuel ratio detecting element after passing through said diffusion resistance layer; imbalance determining means for obtaining an imbalance determining parameter with using at least said output value of said upstream air-fuel ratio sensor, said imbalance determining parameter being larger as a degree of an imbalance among individual cylinder air-fuel ratios being larger, each of said individual cylinder air-fuel ratios being an air-fuel ratio of a mixture supplied to each of said at least two or more of cylinders, and for performing a determination as to whether or not an air-fuel ratio imbalance state among cylinders is occurring, based on a comparison result as to whether or not said obtained imbalance determining parameter is larger than or equal to a predetermined threshold; and wherein, said imbalance determining means is configured so as to vary, in accordance with said compression ratio of said engine varied by said compression ratio varying means, at least one of said predetermined threshold and said imbalance determining parameter.