Abstract: An inter-cylinder air-fuel ratio imbalance determination apparatus (determination apparatus) according to the present invention obtains, as an “EGR supplying state imbalance determination parameter”, a value corresponding to a differential value d(abyfs)dt of a detected air-fuel ratio abyfs represented by an output value of an air-fuel ratio sensor when an EGR gas is being supplied, and obtains, as an “EGR stop state imbalance determination parameter”, a value corresponding to a differential value d(abyfs)dt when an EGR gas supply is being stopped. The determination apparatus obtains an “EGR-causing imbalance determination parameter Pegr” by subtracting the EGR stop state imbalance determination parameter Poff from the EGR supplying state imbalance determination parameter Pon, and determines that an inter-cylinder air-fuel ratio imbalance state has occurred due to the supply of the EGR gas when the parameter Pegr is larger than a threshold Pegrth.

Abstract: An apparatus for determining an air-fuel ratio imbalance among cylinders based on an output value of an air-fuel ratio sensor, an imbalance determination parameter which becomes larger or smaller as a difference among air-fuel ratios becomes larger, and performs determining an air-fuel ratio imbalance among cylinders based on a result of a comparison between the imbalance determination parameter and a imbalance determination threshold. The determining apparatus calculates a purge correction coefficient which compensates for a change in the air-fuel ratio due to an evaporated fuel gas which is generated in a fuel tank, while the evaporated fuel gas is being introduced into an intake passage, and corrects a fuel injection amount with the purge correction coefficient FPG.

Abstract: An air-fuel ratio imbalance detection apparatus includes an air-fuel ratio sensor that is arranged in an exhaust passage of an internal combustion engine and that includes an electrode and a diffusion layer provided on the electrode; an estimating unit configured to estimate or detect an output variation amount that is an amount of variation in an output of the air-fuel ratio sensor due to an influence of a pressure pulsation of exhaust gas from the internal combustion engine; and a determination unit configured to determine whether there is an air-fuel ratio imbalance among cylinders of the internal combustion engine, on the basis of the output variation amount and a determination value based on the output of the air-fuel ratio sensor.

Abstract: A catalyst deterioration diagnosing apparatus is provided with means for performing stoichiometric feedback control on the air-fuel ratio based on at least output from an upstream air-fuel ratio sensor provided upstream of a catalyst, means for measuring the oxygen storage capacity of the catalyst, and means for correcting the measured value of the oxygen storage capacity based on at least the output behavior of a downstream air-fuel ratio sensor provided downstream of the catalyst during the stoichiometric feedback control. The measured value of the oxygen storage capacity is corrected using the output behavior of the downstream air-fuel ratio sensor during stoichiometric feedback control. The diagnostic is performed after eliminating the effects from sulfur by correcting the measured value to a value corresponding to when low sulfur fuel is used, which makes it possible to prevent an erroneous diagnosis from being made.

Abstract: A monitoring apparatus including a catalytic converter, an upstream air-fuel ratio sensor, and a downstream air-fuel ratio sensor; calculates a sub feedback amount to have an air-fuel ratio represented based on an output value of the downstream air-fuel ratio sensor coincide with a stoichiometric air-fuel ratio; and controls an fuel injection amount based on an output value of the upstream air-fuel ratio sensor and the sub feedback amount, in such a manner that an air-fuel ratio of a mixture supplied to an engine coincides with the stoichiometric air-fuel ratio.

Abstract: A cylinder-to-cylinder air/fuel ratio imbalance determination system obtains an imbalance determination parameter that increases or decreases as a difference between the air/fuel ratios of different cylinders increases, based on output values of an air/fuel ratio sensor, and makes a cylinder-to-cylinder A/F imbalance determination, based on the result of comparison between the imbalance determination parameter and a threshold value for imbalance determination. The determination system changes the amount of fuel injected into one or more of the cylinders so as to create a forced imbalance condition in which the air/fuel ratio of a particular cylinder deviates from the air/fuel ratio of the remaining cylinders, and obtains an air/fuel ratio sensor evaluation parameter (e.g., rate of change ?AF of the detected air/fuel ratio) in this condition.

Abstract: An electronic control device calculates the maximum actual oxygen storage capacity of a catalyst. The gradient of a linear expression formed between the catalyst temperature and the maximum oxygen storage capacity of the catalyst is stored for each degradation level of the catalyst. The gradient can be learned in accordance with the same temperature of the catalyst and the maximum actual oxygen storage capacity. When the maximum actual oxygen storage capacity is calculated, it is revised in accordance with the temperature of the catalyst, a reference temperature, the linear expression, and the learned gradient. The revised maximum oxygen storage capacity which is the maximum oxygen storage capacity when the temperature of the catalyst during the same calculation period is equal to the reference temperature is then calculated. If a response delay is detected in the output of an oxygen sensor, the gradient of the learned linear expression is discarded.

Abstract: A fuel injection amount control apparatus includes an air-fuel ratio sensor which is disposed between an exhaust gas merging portion HK and an upstream catalyst. The control apparatus performs a feedback correction on an amount of fuel to be injected by the fuel injection valve in such a manner that an air-fuel ratio represented by an output value of an upstream air-fuel ratio sensor becomes equal to a target air-fuel ratio which is set at stoichiometric air-fuel ratio. The control apparatus obtains an air-fuel ratio imbalance indicating value, which becomes larger as a difference in air-fuel ratio of each of the mixtures supplied to each of the combustion chambers among the cylinders becomes larger, and performs an increasing correction to the amount of fuel to be injected by the injection valve in such a manner that an air-fuel ratio becomes a richer air-fuel ratio than the stoichiometric air-fuel ratio as the obtained air-fuel ratio imbalance indicating value becomes larger.

Abstract: An inter-cylinder air-fuel imbalance determination apparatus according to the present invention obtains, based on the output value of the air-fuel ratio sensor, an air-fuel ratio fluctuation indicating amount whose absolute value becomes larger as a fluctuation of the air-fuel ratio of the exhaust gas passing through the air-fuel ratio sensor becomes larger, and further obtains an imbalance determination parameter which becomes larger as an absolute value of the air-fuel ratio fluctuation indicating amount becomes larger. In addition, the determination apparatus obtains an average value of the air-fuel ratio of the exhaust gas when the imbalance determination parameter is being obtained, and obtains an imbalance determination threshold which becomes smaller as the average value of the air-fuel ratio is closer to the stoichiometric air-fuel ratio.

Abstract: An air-fuel ratio imbalance among cylinders determining apparatus according to the present invention comprises an air-fuel ratio sensor having a protective cover and an air-fuel ratio detection element accommodated in the protective cover, and imbalance determining means. The imbalance determining means obtains a detected air-fuel ratio abyfs based on an output Vabyfs of the air-fuel ratio sensor every elapse of a constant sampling time ts, and obtains, as an indicating amount of air-fuel ratio change rate, a difference (detected air-fuel ratio change rate ?AF) between a present detected air-fuel ratio abyfs which is newly detected and a previous air-fuel ratio abyfsold which was detected the sampling time ts ago, an average of the detected air-fuel ratio change rate ?AF, and the like.

Abstract: An apparatus for determining an air-fuel ratio imbalance among cylinders based on an output value of an air-fuel ratio sensor, an imbalance determination parameter which becomes larger or smaller as a difference among air-fuel ratios becomes larger, and performs determining an air-fuel ratio imbalance among cylinders based on a result of a comparison between the imbalance determination parameter and a imbalance determination threshold. The determining apparatus calculates a purge correction coefficient which compensates for a change in the air-fuel ratio due to an evaporated fuel gas which is generated in a fuel tank, while the evaporated fuel gas is being introduced into an intake passage, and corrects a fuel injection amount with the purge correction coefficient FPG.

Abstract: An inter-cylinder air-fuel ratio imbalance determining apparatus for an internal combustion engine includes an air-fuel ratio sensor; fuel injection valves; an instructed fuel injection amount control unit; and an imbalance determination unit configured: to acquire a time-differential-value corresponding value that is an amount of change per predetermined time in an output value of the sensor or a detected air-fuel ratio represented by the output value; to acquire a positive gradient corresponding value based on a positive value of the time-differential-value corresponding value; to acquire a negative gradient corresponding value based on a negative value of the time-differential-value corresponding value; to determine an imbalance determination threshold based on a magnitude of a ratio of the negative gradient corresponding value to the positive gradient corresponding value; and to determine whether inter-cylinder air-fuel ratio imbalance has occurred by comparing a magnitude of the negative gradient corresp

Abstract: An inter-cylinder air-fuel ratio imbalance determination apparatus that obtains, based on an output value Vabyfs of an air-fuel ratio sensor, an air-fuel ratio fluctuation indicating amount (AFD) which becomes larger as an air-fuel ratio fluctuation of an exhaust gas passing through a position at which the air-fuel ratio sensor is disposed becomes larger, during a parameter obtaining period. The determination apparatus estimates an air-fuel ratio sensor element temperature (Temps) having a strong relation with responsiveness of the air-fuel ratio sensor during the parameter obtaining period, and obtains a corrected air-fuel ratio fluctuation indicating amount by correcting the AFD based on the estimated Temps.

Abstract: An inter-cylinder air-fuel ratio imbalance determination apparatus (determination apparatus) according to the present invention obtains, based on the output value of the air-fuel ratio sensor, an imbalance determination parameter which becomes larger as an air-fuel ratio fluctuation of an exhaust gas passing through a position at which the air-fuel ratio sensor is disposed becomes larger, during a parameter obtaining period. The determination apparatus energizes the heater of the air-fuel ratio sensor in such a manner that a temperature of the air-fuel ratio element during the parameter obtaining period is higher than a temperature of the air-fuel ratio element during a period other than the parameter obtaining period. Accordingly, the imbalance determination parameter is obtained while the responsiveness of the air-fuel ratio sensor is high, and thus, the inter-cylinder air-fuel-ratio imbalance determination having a high accuracy can be made.

Abstract: An apparatus for determining an air-fuel ratio imbalance among cylinders including an upstream air-fuel ratio sensor, a catalytic converter, and a downstream air-fuel ratio sensor disposed at positions downstream of an exhaust gas aggregated portion, calculates a sub feedback amount to have an output value of the downstream air-fuel ratio sensor coincides with a value corresponding to the stoichiometric air-fuel ratio, and performs an air-fuel ratio feedback control to have an air-fuel ratio of a mixture supplied to an engine based on the sub feedback amount and the output value of the upstream air-fuel ratio sensor.

Abstract: An inter-cylinder air-fuel ratio imbalance determination apparatus (determination apparatus) according to the present invention obtains, based on the output value of the air-fuel ratio sensor, an imbalance determination parameter which becomes larger as an air-fuel ratio fluctuation of an exhaust gas passing through a position at which the air-fuel ratio sensor is disposed becomes larger, during a parameter obtaining period. The determination apparatus energizes the heater of the air-fuel ratio sensor in such a manner that a temperature of the air-fuel ratio element during the parameter obtaining period is higher than a temperature of the air-fuel ratio element during a period other than the parameter obtaining period. Accordingly, the imbalance determination parameter is obtained while the responsiveness of the air-fuel ratio sensor is high, and thus, the inter-cylinder air-fuel-ratio imbalance determination having a high accuracy can be made.

Abstract: An inter-cylinder air-fuel ratio imbalance determination apparatus that obtains, based on an output value Vabyfs of an air-fuel ratio sensor, an air-fuel ratio fluctuation indicating amount (AFD) which becomes larger as an air-fuel ratio fluctuation of an exhaust gas passing through a position at which the air-fuel ratio sensor is disposed becomes larger, during a parameter obtaining period. The determination apparatus estimates an air-fuel ratio sensor element temperature (Temps) having a strong relation with responsiveness of the air-fuel ratio sensor during the parameter obtaining period, and obtains a corrected air-fuel ratio fluctuation indicating amount by correcting the AFD based on the estimated Temps.

Abstract: An inter-cylinder air-fuel ratio imbalance determination apparatus (determination apparatus) according to the present invention obtains, based on the output value of the air-fuel ratio sensor 67, an air-fuel ratio fluctuation indicating amount whose absolute value becomes larger as a fluctuation of the air-fuel ratio of the exhaust gas passing through a position at which the air-fuel ratio sensor is disposed becomes larger, and further obtains an imbalance determination parameter which becomes larger as an absolute value of the air-fuel ratio fluctuation indicating amount becomes larger. In addition, the determination apparatus obtains an average value of the air-fuel ratio of the exhaust gas during a period in which the imbalance determination parameter is being obtained, and obtains an imbalance determination threshold which becomes smaller as the average value of the air-fuel ratio is closer to the stoichiometric air-fuel ratio.

Abstract: An exhaust gas sensor abnormality diagnostic device includes an exhaust gas sensor, and a judgment means that judges whether execution conditions are established for making an abnormality diagnosis of element breakage in the exhaust gas sensor. The device also includes an abnormality diagnosis means that makes the abnormality diagnosis in accordance with an output signal generated by the exhaust gas sensor. Further, when the integrated value of intake air amounts of an internal combustion engine is not smaller than a predetermined value, the judgment means judges that the execution conditions are established. The abnormality diagnosis means cancels the establishment of the execution conditions when an intake air amount of the internal combustion engine remains less than a predetermined value for a predetermined period of time.

Abstract: An inter-cylinder air-fuel ratio imbalance determination apparatus (determination apparatus) according to the present invention obtains, as an “EGR supplying state imbalance determination parameter”, a value corresponding to a differential value d(abyfs)dt of a detected air-fuel ratio abyfs represented by an output value of an air-fuel ratio sensor when an EGR gas is being supplied, and obtains, as an “EGR stop state imbalance determination parameter”, a value corresponding to a differential value d(abyfs)dt when an EGR gas supply is being stopped. The determination apparatus obtains an “EGR-causing imbalance determination parameter Pegr” by subtracting the EGR stop state imbalance determination parameter Poff from the EGR supplying state imbalance determination parameter Pon, and determines that an inter-cylinder air-fuel ratio imbalance state has occurred due to the supply of the EGR gas when the parameter Pegr is larger than a threshold Pegrth.