Abstract: An apparatus and a method for detecting abnormal air-fuel ratio variation among cylinders of a multi-cylinder internal combustion engine are provided. The apparatus includes: a catalyst that is provided in an exhaust passage of the multi-cylinder internal combustion engine; a catalyst temperature detection unit that detects a temperature of the catalyst; a catalyst temperature estimation unit that estimates a temperature of the catalyst based on an engine operating state; and an abnormality detection unit that determines whether abnormal air-fuel ratio variation among the cylinders has occurred based on the detected temperature of the catalyst and the estimated temperature of the catalyst.

Abstract: An apparatus for detecting an abnormal air-fuel ratio variation among cylinders of a multi-cylinder internal combustion engine includes: a catalyst that is arranged in an exhaust passage of the multi-cylinder internal combustion engine; a catalyst temperature detecting unit that detects a temperature of the catalyst; and an abnormality detecting unit that detects an abnormal air-fuel ratio variation among the cylinders on the basis of the detected catalyst temperature, wherein the abnormality detecting unit calculates a temperature parameter on the basis of the detected catalyst temperature, and the abnormality detecting unit detects the abnormal air-fuel ratio variation among the cylinders on the basis of the temperature parameter at the time when a predetermined period of time has elapsed after a cold start of the internal combustion engine.

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: 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 fuel injection amount from fuel injection valves is actively controlled and an input air-fuel ratio is caused forcibly to oscillate. A system from the fuel injection valves to the air-fuel ratio sensor is simulated by a first order delay system, and a gain and time constant are identified on the basis of the input air-fuel ratio relating to the model and an output air-fuel ratio obtained from the air-fuel ratio sensor. The presence of an air-fuel ratio abnormal variation is diagnosed on the basis of whether or not the identified values of the gain and the time constant are less than a first and second predetermined values respectively.

Abstract: In an abnormality diagnostic device and an abnormality diagnostic device for an air-fuel ratio sensor that detects the air-fuel ratio of exhaust gas of an internal combustion engine, a system extending from a fuel injection valve to the air-fuel ratio sensor is model by a first order response delay, and a parameter in the first order response delay is identified based on an input air-fuel ratio that is given to the air-fuel ratio sensor and an output air-fuel ratio that is output from the air-fuel ratio sensor. Then, the presence/absence of abnormality regarding a predetermined characteristic of the air-fuel ratio sensor is determined based on the parameter identified. Thus, abnormality is diagnosed regarding individual characteristics of the air-fuel ratio sensor.

Abstract: An apparatus for detecting abnormal air-fuel ratio variation among cylinders of a multi-cylinder internal combustion engine includes: a catalyst element that oxidizes hydrogen contained in exhaust gas to remove the hydrogen; a first air-fuel ratio sensor that detects an air-fuel ratio of exhaust gas that has not passed through the catalyst element; a second air-fuel ratio sensor that detects an air-fuel ratio of exhaust gas that has passed through the catalyst element; and a unit that determines whether abnormal air-fuel ratio variation among the cylinders has occurred based on an amount by which a value detected by the second air-fuel ratio sensor is leaner than a value detected by the first air-fuel ratio sensor

Abstract: A system extending from a fuel injection valve to an air-fuel ratio sensor is modeled by using a first order response delay element. Parameters of the first order response delay element T, k are identified based on an input u(t) based on an input air-fuel ratio that occurs when the input air-fuel ratio is relatively sharply changed in accordance with an engine operation requirement, and an output y(t) of the air-fuel ratio sensor that changes in response to a change in the input air-fuel ratio. Then, an abnormality of characteristics (response rate and output) of the air-fuel ratio sensor is determined based on the identified parameter.

Abstract: An abnormality diagnostic device for an air-fuel ratio sensor that detects the air-fuel ratio of exhaust gas of an internal combustion engine is provided. The abnormality diagnostic device includes: a device that an device that models a system extending from a fuel injection valve to the air-fuel ratio sensor by using a first order response delay element and a waste time element, and that identifies at least a waste time of the waste time element based on an input given to the air-fuel ratio sensor and an output obtained from the air-fuel ratio sensor; and another device that performs determination about an abnormality of the waste time based on the identified waste time.

Abstract: A NOx amount capable of being absorbed by a criteria catalyst as a boundary between degradation and normality is supplied to a NOx storage reduction catalyst and thereafter, a reducer amount corresponding to the NOx amount is supplied by a rich spike operation. Degradation of the NOx catalyst is determined based upon the output of the NOx sensor at this time. Since the degradation of the NOx catalyst is determined only by a magnitude of the NOx sensor output, the degradation diagnosis can be performed with high precision. While the catalyst is normal, the excessive reducers are not supplied and therefore, deterioration of the fuel consumption can be prevented.

Abstract: The concentration of a portion of components in the hydrocarbon in exhaust gas flowing into a catalyst is detected or estimated, and the concentration of the portion of components in the hydrocarbon in the exhaust gas flowing out of the catalyst is detected. On the basis of the concentrations of the portion of components in the hydrocarbon flowing into the catalyst and the concentration of the portion of components in the hydrocarbon flowing out of the catalyst, it is determined whether or not the catalyst has been deteriorated.

Abstract: An apparatus and a method for detecting abnormal air-fuel ratio variation among cylinders of a multi-cylinder internal combustion engine are provided. The apparatus includes: a catalyst that is provided in an exhaust passage of the multi-cylinder internal combustion engine; a catalyst temperature detection unit that detects a temperature of the catalyst; a catalyst temperature estimation unit that estimates a temperature of the catalyst based on an engine operating state; and an abnormality detection unit that determines whether abnormal air-fuel ratio variation among the cylinders has occurred based on the detected temperature of the catalyst and the estimated temperature of the catalyst.

Abstract: When an internal combustion engine including a plurality of cylinders is operating steadily, an index value relating to an actual hydrogen content in exhaust gas downstream of a portion where exhaust passages from the cylinders merge, and upstream of a catalyst is detected. When an index value relating to the actual hydrogen content in the exhaust gas is larger than a determination index value relating to a hydrogen content corresponding to a permissible limit of air-fuel ratio variation, it is determined that there is abnormal air-fuel ratio variation between the cylinders.

Abstract: An apparatus or a method for detecting an abnormality of inter-cylinder air-fuel ratio dispersion in a multi-cylinder internal combustion engine according to the invention is equipped with a catalytic element that purifies exhaust gas of hydrogen, a first air-fuel ratio sensor that detects an air-fuel ratio of exhaust gas that has not passed through the catalytic element, a second air-fuel ratio sensor that detects an air-fuel ratio of exhaust gas that has passed through the catalytic element, a device that detects an abnormality of inter-cylinder air-fuel ratio dispersion on the basis of a divergence state of a detected value of a second air-fuel ratio to a lean side from a detected value of a first air-fuel ratio, and a device that forcibly reduces fuel injection amounts in cylinders individually when an abnormality on dispersion is detected by the abnormality detector, detects a divergence state of the detected value of the second air-fuel ratio to the lean side from the detected value of the first air-fue

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: When an internal combustion engine including a plurality of cylinders is operating steadily, an index value relating to an actual hydrogen content in exhaust gas downstream of a portion where exhaust passages from the cylinders merge, and upstream of a catalyst is detected. When an index value relating to the actual hydrogen content in the exhaust gas is larger than a determination index value relating to a hydrogen content corresponding to a permissible limit of air-fuel ratio variation, it is determined that there is abnormal air-fuel ratio variation between the cylinders.

Abstract: An abnormality diagnostic device for an air-fuel ratio sensor that detects the air-fuel ratio of exhaust gas of an internal combustion engine is provided. The abnormality diagnostic device includes: a device that an device that models a system extending from a fuel injection valve to the air-fuel ratio sensor by using a first order response delay element and a waste time element, and that identifies at least a waste time of the waste time element based on an input given to the air-fuel ratio sensor and an output obtained from the air-fuel ratio sensor; and another device that performs determination about an abnormality of the waste time based on the identified waste time.

Abstract: An air-fuel ratio sensor that outputs a sensor signal used for the feedback control of an air-fuel ratio is provided. It is determined whether an element crack is present by applying a reverse voltage to the air-fuel ratio sensor. The value of the sensor signal output from the air-fuel ratio sensor is corrected during a time period “A”. The time period “A” consists of a reverse-voltage application time period in which the reverse voltage is applied, and a return time period “T” after application of the reverse voltage ends. The return time period “T” is set based on sensor impedance correlated with the internal resistance of the air-fuel ratio sensor. The return time period “T” decreases as the sensor impedance decreases.

Abstract: A system extending from a fuel injection valve to an air-fuel ratio sensor is modeled by using a first order response delay element. Parameters of the first order response delay element T, k are identified based on an input u(t) based on an input air-fuel ratio that occurs when the input air-fuel ratio is relatively sharply changed in accordance with an engine operation requirement, and an output y(t) of the air-fuel ratio sensor that changes in response to a change in the input air-fuel ratio. Then, an abnormality of characteristics (response rate and output) of the air-fuel ratio sensor is determined based on the identified parameter.

Abstract: In an abnormality diagnostic device and an abnormality diagnostic device for an air-fuel ratio sensor that detects the air-fuel ratio of exhaust gas of an internal combustion engine, a system extending from a fuel injection valve to the air-fuel ratio sensor is model by a first order response delay, and a parameter in the first order response delay is identified based on an input air-fuel ratio that is given to the air-fuel ratio sensor and an output air-fuel ratio that is output from the air-fuel ratio sensor. Then, the presence/absence of abnormality regarding a predetermined characteristic of the air-fuel ratio sensor is determined based on the parameter identified. Thus, abnormality is diagnosed regarding individual characteristics of the air-fuel ratio sensor.