The exhaust purification system comprises an exhaust purification catalyst, downstream side air-fuel ratio sensor, and control device. The control device performs average air-fuel ratio control which alternately sets a target average air-fuel ratio between a rich air-fuel ratio and a lean air-fuel ratio and inter-cylinder air-fuel ratio control which controls the target air-fuel ratios of the cylinders so that the target air-fuel ratio becomes the rich air-fuel ratio at least at one cylinder among the plurality of cylinders even if the target average air-fuel ratio is set to the lean air-fuel ratio. The control device uses a cumulative value of a first oxygen amount from when switching the target average air-fuel ratio to the lean air-fuel ratio to when again switching it to the rich air-fuel ratio and a cumulative value of a second oxygen amount from when switching the target average air-fuel ratio to the rich air-fuel ratio to when again switching it to the lean air-fuel ratio as the basis for correcting a parameter relating to the air-fuel ratio so that the difference of these becomes smaller as learning control.

A method is provided for monitoring an emission device coupled to an engine. In one example approach, the method comprises: following a deceleration fuel shut-off duration, indicating degradation of the emission device based on an amount of rich products required to cause a sensor to become richer than a threshold. The amount of rich products required may be correlated to an amount of oxygen stored in the emission device.

An exhaust purification system comprises an exhaust purification catalyst, a downstream side air-fuel ratio sensor and a control device. The control device makes the air-fuel ratio of the exhaust gas change to an air-fuel ratio at a rich side from the prior air-fuel ratio as air-fuel ratio rich increasing control when the air-fuel ratio of the exhaust gas is made a rich air-fuel ratio and the output air-fuel ratio of the downstream side air-fuel ratio sensor is maintained at a lean judged air-fuel ratio or more, and judges that the downstream side air-fuel ratio sensor suffers from an abnormality, when, due to the air-fuel ratio rich increasing control, the air-fuel ratio of the exhaust gas is made to change to the rich side air-fuel ratio and the output air-fuel ratio of the downstream side air-fuel ratio sensor changes to the lean side.

Methods are disclosed for determining an oxidation state of a catalyst using RF signals. The method may include introducing radio-frequency signals into a resonant chamber including a catalyst, modulating an air-fuel ratio of an engine upstream of the catalyst to generate a sequence of uniform pulses and at least one altered pulse that differs from the uniform pulses, and comparing a frequency response of two or more resonant modes of the radio-frequency signals during the sequence to determine an oxidation state of the catalyst. The method may further include adjusting the air-fuel ratio based on the comparing step. Two or more altered pulses may be inserted into the air-fuel ratio sequence. The altered pulse may have a pulse width and/or amplitude that differs from the uniform pulses. The methods may be used to adjust an air-fuel ratio to correct or impart a bias.

An internal combustion engine comprises an exhaust purification catalyst, a downstream side air-fuel ratio sensor which is arranged at a downstream side of the exhaust purification catalyst, and an air flow meter which detects an amount of intake air. The control system of the internal combustion engine controls the exhaust air-fuel ratio to a target air-fuel ratio by feedback control, sets the target air-fuel ratio at a lean air-fuel ratio when the output air-fuel ratio of the downstream side air-fuel ratio sensor becomes a rich air-fuel ratio, and sets the target air-fuel ratio at a rich air-fuel ratio when the output air-fuel ratio of the downstream side air-fuel ratio sensor becomes a lean air-fuel ratio. When a change in the amount of intake air occurs so that it increases, the lean degree is set lower than before, in at least part of the time period during which the target air-fuel ratio is set to the lean air-fuel ratio, and the rich degree is set lower than before, in at least part of the timer period during which the target air-fuel ratio is set to the rich air-fuel ratio.

The invention relates to a method for operating an internal combustion engine comprising at least one turbocharger, at least one catalytic converter and a variable valve train, a valve overlap parameter being determined in at least one operating mode of the internal combustion engine and being used to set the valve train. According to the invention, the valve overlap parameter is adapted on the basis of at least one parameter for the condition of the catalytic converter and/or at least one parameter for the condition of the turbocharger, prior to being used to set the valve train. The invention also relates to an internal combustion engine.

The internal combustion engine comprises an exhaust purification catalyst and a downstream side air-fuel ratio sensor which is arranged at a downstream side of the exhaust purification catalyst. The control system performs feedback control so that the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst becomes a target air-fuel ratio and performs learning control which corrects the control center air-fuel ratio based on the output air-fuel ratio of the downstream side air-fuel ratio sensor. The target air-fuel ratio is switched between the lean air-fuel ratio and the rich air-fuel ratio. In the learning control, when the target air-fuel ratio is set to the rich air-fuel ratio and the output air-fuel ratio of the downstream side air-fuel ratio sensor is maintained in an air-fuel ratio region in proximity to the stoichiometric air-fuel ratio for the stoichiometric air-fuel ratio judgment time or more, stoichiometric air-fuel ratio stuck learning is performed which corrects a control center air-fuel ratio so that the air-fuel ratio of the exhaust gas changes to the rich side.

A catalyst deterioration determination system determines deterioration of an exhaust gas purification catalyst on the basis of its oxygen storage capacity. The system includes a downstream oxygen concentration sensor having characteristics by which as rich gas components in exhaust gas increase, the oxygen concentration sensor outputs a measurement value of the oxygen concentration corresponding to a richer air-fuel ratio. The system performs a rich shift mode and a lean shift mode based on the measurement value of the oxygen concentration sensor. The rate of change of the exhaust gas air-fuel ratio in at least the lean shift mode is limited to a predetermined rate of change or lower, and the rate of change of the exhaust gas air-fuel ratio in the rich shift mode is set higher than the rate of change of the exhaust gas air fuel ratio in the lean shift mode.

The present invention provides a deterioration diagnosis apparatus for an exhaust gas purification apparatus, including a first sensor that measures the oxygen concentration of the exhaust gas flowing into the exhaust gas purification apparatus, a second sensor that measures the oxygen concentration of the exhaust gas flowing out of the exhaust gas purification apparatus, and diagnosing means for diagnosing deterioration of the exhaust gas purification apparatus on the basis of a difference that appears between a measurement value of the first sensor and a measurement value of the second sensor when the air-fuel ratio of the exhaust gas flowing into the exhaust pas purification apparatus is switched from a lean air-fuel ratio to a rich air-fuel ratio, wherein, when the air-fuel ratio of the exhaust gas is switched from a lean air-fuel ratio to a rich air-fuel ratio, a water-gas shift reaction is generated upstream of the first sensor.

A vehicle system includes an upstream oxygen monitoring module that monitors an upstream exhaust oxygen sensor and determines an upstream transition period based on a time at which the upstream exhaust oxygen sensor detects a rich-to-lean fueling transition. A delay determining module determines a delay period associated with the upstream exhaust oxygen sensor's detection of the fueling transition. An upstream correcting module determines a corrected upstream transition period based on the upstream transition period and the delay period. A downstream oxygen monitoring module monitors a downstream exhaust oxygen sensor and determines a downstream transition period based on the response of the downstream exhaust oxygen sensor to the fueling transition. An oxygen storage capacity (OSC) determining module determines an OSC period based on the corrected upstream transition period and the downstream transition period. A catalyst fault detection module selectively adjusts operating parameters of the engine based on the OSC period.