A catalyst degradation detection apparatus includes an air-fuel ratio detector disposed downstream of a catalyst and configured to detect an air-fuel ratio of exhaust gas flowing out from the catalyst, and an electronic control unit configured to control an air-fuel ratio of inflow exhaust gas flowing into the catalyst and determine whether the catalyst is degraded. The electronic control unit is configured to execute degradation determination control that brings the air-fuel ratio of the inflow exhaust gas to an air-fuel ratio leaner or richer than a stoichiometric air-fuel ratio. The electronic control unit is configured to determine whether precious metal of the catalyst is degraded based on the air-fuel ratio detected by the air-fuel ratio detector when an oxygen storage amount of the catalyst is varying in the degradation determination control.

Methods and systems are provided for continually monitoring a functionality of an exhaust catalyst based on roll-down of a monotonically decreasing catalyst activity parameter representing catalyst storage capacity. Catalyst degradation may be indicated responsive to the estimate of catalyst storage capacity lowering below a threshold. Engine operating parameters may be adjusted based on a current level of catalyst storage capacity.

An apparatus includes a processing circuit structured to receive a first signal indicative of an upstream air-fuel equivalence ratio from a first sensor positioned upstream of an intake of a catalyst, receive a second signal indicative of a downstream air-fuel equivalence ratio from a second sensor positioned downstream of the intake of the catalyst, determine an actual oxygen storage capacity of the catalyst based at least in part on the received first signal and the received second signal, compare the actual oxygen storage capacity to a maximum storage capacity, and provide a fault signal in response to the actual oxygen storage capacity exceeding the maximum storage capacity. The apparatus also includes a notification circuit structured to provide a notification indicating that the second sensor is faulty in response to receiving the fault signal.

A method comprising adjusting a fuel injection amount based on a fractional oxidation state of a catalyst, the fractional oxidation state based on reaction rates of grouped oxidant and reductant exhaust gas species throughout a catalyst and a low-dimensional physics-based model derived from a detailed two-dimensional model to obtain a one-dimensional model averaged over time and space that accounts for diffusion limitations in the washcoat and accurately predicts emissions during cold start.

The control system of an internal combustion engine performs normal operation control including lean control for making the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst a lean air-fuel ratio, and rich control for making the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst a rich air-fuel ratio. The normal operation control includes judgment reference decreasing control decreasing the judgment reference storage amount in the lean control when during the time period of performing the lean control, the air-fuel ratio of the exhaust gas flowing out from the exhaust purification catalyst becomes the lean judged air-fuel ratio or more. The control system judges that the exhaust purification catalyst is abnormal when the judgment reference storage amount becomes less than a deterioration judgment value.

An abnormality diagnosis system of an internal combustion engine which is provided with an exhaust purification catalyst 20 which can store oxygen is provided with a downstream side air-fuel ratio sensor 41 downstream of the catalyst and a catalyst abnormality diagnosis system which uses an output air-fuel ratio of the downstream side air-fuel ratio sensor when performing active air-fuel ratio control as the basis for diagnosing an exhaust purification catalyst for abnormality. The catalyst abnormality diagnosis system uses the amount of oxygen which is stored in or released from the exhaust purification catalyst in an air-fuel ratio reversal time period in active air-fuel ratio control as the basis to calculate the maximum storable oxygen amount of the exhaust purification catalyst and uses this as the basis to diagnose the exhaust purification catalyst for abnormality.

A control device for an internal combustion engine, said control device implementing a lean control, whereby the air-fuel ratio of the exhaust gas flowing into an exhaust purification catalyst is set to a lean air-fuel ratio setting, and a rich control, whereby the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst is set to a rich air-fuel ratio setting. When the amount of oxygen absorbed by the exhaust purification catalyst during lean control reaches or exceeds a criterion storage amount, a control is executed to switch to rich control. In addition, a control is executed to set the lean air-fuel ratio setting for a first intake air amount so as to be richer than the lean air-fuel ratio setting for a second intake air amount that is less than the first intake air amount.

An internal combustion engine comprises an exhaust purification catalyst arranged in an exhaust passage of the internal combustion engine and being able to store oxygen in inflowing exhaust gas and an air-fuel ratio sensor arranged at a downstream side of the exhaust purification catalyst in a direction of exhaust flow and detecting an air-fuel ratio of exhaust gas flowing out from the exhaust purification catalyst and stops or decreases a feed of fuel to a combustion chamber as fuel cut control. The abnormality diagnosis system calculates a characteristic of change of an air-fuel ratio based on an output air-fuel ratio output from the air-fuel ratio sensor at the time when the output air-fuel ratio first passes a part of an air-fuel ratio region of a stoichiometric air-fuel ratio or more after an end of the fuel cut control, and diagnoses abnormality of the air-fuel ratio sensor based on the characteristic of change of the air-fuel ratio. As a result, the diagnosis system can diagnose the abnormality of deterioration of response of the downstream side air-fuel ratio sensor when necessary without fail when performing fuel cut control.

A system according to the principles of the present disclosure includes a storage capability module and at least one of an engine speed control module and a spark control module. The storage capability module determines a capability of a catalytic converter to store oxygen. The engine speed control module controls a speed of an engine based on the oxygen storage capability of the catalytic converter. The spark control module controls a spark timing of the engine based on the oxygen storage capability of the catalytic converter.

A method for operating an exhaust gas purification system of an internal combustion engine, which can be operated in a lean operating mode and in a rich operating mode, is disclosed. The exhaust gas purification system has, arranged one after the other in the direction of flow of the exhaust gas, an ammonia-forming catalyst, a first exhaust gas sensor, an ammonia-SCR catalyst, a nitrogen oxide storage catalyst and a second exhaust gas sensor. Exhaust gas sensors emit a first signal correlating with the nitrogen oxide content of the exhaust gas and a second signal correlating with the lambda value of the exhaust gas. In diagnostic operation, the ammonia storage capacity of the ammonia-SCR catalyst and the oxygen and optionally the nitrogen oxide storage capacity of the nitrogen oxide storage catalyst can be determined by analyzing the signals of the first and second exhaust gas sensors.