Internal combustion engine system controller

An internal combustion engine system controller for controlling an internal combustion engine system,

• the internal combustion engine system comprising:
• an internal combustion engine having a plurality of cylinders;
• a plurality of fuel injection valves provided so as to respectively correspond to the plurality of cylinders;
• an exhaust-gas purification catalyst disposed in an exhaust passage on a downstream side of an exhaust-gas accumulating portion, in which an exhaust gas from the plurality of cylinders accumulates, in an exhaust-gas flowing direction;
• a downstream-side air-fuel ratio sensor disposed in the exhaust passage at a position on the downstream side of the exhaust-gas purification catalyst in the exhaust-gas flowing direction, for generating an output corresponding to an air-fuel ratio of the exhaust gas at the position where the downstream-side air-fuel ratio sensor is disposed;
• and
• an upstream-side air-fuel ratio sensor disposed in the exhaust passage at a position on an upstream side of the exhaust-gas purification catalyst and the downstream-side air-fuel ratio sensor in the exhaust-gas flowing direction, for generating an output corresponding to the air-fuel ratio of the exhaust gas at the position where the upstream-side air-fuel ratio sensor is disposed,
• the internal combustion engine system controller comprising:
• a sub-feedback learning portion configured to acquire a sub-feedback learning value being an amount corresponding to a steady component of a sub-feedback amount, the sub-feedback amount corresponding to a control amount for performing feedback control on a fuel injection amount by each of the plurality of fuel injection valves so that the air-fuel ratio of the exhaust gas corresponding to the output of the downstream-side air-fuel ratio sensor becomes equal to a stoichiometric air-fuel ratio;
• a state determining portion configured to repeatedly determine, to which of at least three states including:
• (a) a stable state in which a fluctuating state of the sub-feedback learning value is stable;
• (b) an unstable state in which the fluctuating state greatly fluctuates;
• and
• (c) an intermediate state between the stable state and the unstable state, the fluctuating state of the sub-feedback learning value corresponds;
• and
• a learning update-speed setting portion configured to set an update speed of the sub-feedback learning value by the sub-feedback learning portion in accordance with a result of determination by the state determining portion so that the update speed becomes higher in the unstable state than in the intermediate state and higher in the intermediate state than in the stable state,
• wherein the state determining portion is configured:
• so as to determine the fluctuating state of the sub-feedback learning value in such a manner that the fluctuating state shifts between the stable state and the intermediate state or between the intermediate state and the unstable state;
• and
• so as to change the fluctuating state of the sub-feedback learning value when a shift pattern of the fluctuating state of the sub-feedback learning value determined by the state determining portion is identical with a predetermined pattern, the shift pattern being represented by a previous fluctuating state (status_old) which is the fluctuating state at a point in time at which the determination was previously made by the state determining portion, a current fluctuating state (status_now) which is the current fluctuating state at a point in time at which the determination is currently made by the state determining portion, and a next fluctuating state (status_next) which is the fluctuating state currently determined by the state determining portion.