Combustion control system of internal combustion engine

A combustion control system of an internal combustion engine employing an exhaust purifying device in an exhaust passage, comprising:

• sensor means for detecting operating conditions of the engine;
• a control unit being configured to be electronically connected to the sensor means, for combustion control and fail-safe purposes;
• the control unit comprising:
• (a) means for estimating an operating condition of the exhaust purifying device;
• (b) means for determining, based on the operating condition of the exhaust purifying device, whether a request for a rise in an exhaust temperature is present;
• (c) means for executing, by way of fuel injection control in presence of the request for the exhaust temperature rise, a split retard combustion mode in which a main combustion needed to produce a main engine torque and at least one preliminary combustion occurring prior to the main combustion are both achieved and additionally the preliminary combustion takes place near top dead center on a compression stroke and additionally the main combustion initiates after the preliminary combustion has been completed;
• (d) means for predicting a temperature of the exhaust purifying device to determine a predicted temperature value;
• and
• (e) means for executing a fail-safe process according to which an injection timing of main fuel injection for the main combustion is compensated for in a timing-advance direction, when the predicted temperature value exceeds a predetermined temperature threshold value.

A method of executing a fail-safe function for an exhaust purifying device disposed in an exhaust passage of an internal combustion engine capable of recovering an operating condition of the exhaust purifying device, the method comprising:

• estimating the operating condition of the exhaust purifying device;
• determining, based on the operating condition of the exhaust purifying device, whether a request for a rise in an exhaust temperature is present;
• executing, by way of fuel injection control in presence of the request for the exhaust temperature rise, a split retard combustion mode in which a main combustion needed to produce a main engine torque and at least one preliminary combustion occurring prior to the main combustion are both achieved and additionally the preliminary combustion takes place near top dead center on a compression stroke and additionally the main combustion initiates after the preliminary combustion has been completed;
• predicting a temperature of the exhaust purifying device to determine a predicted temperature value;
• and
• executing a fail-safe process according to which an injection timing of main fuel injection for the main combustion is compensated for in a timing-advance direction, when the predicted temperature value exceeds a predetermined temperature threshold value.

A method of executing a fail-safe function for an exhaust purifying device including (i) a NOx trap catalyst that traps nitrogen oxides contained in exhaust gases when an exhaust air-fuel mixture ratio is lean, and (ii) a particulate filter that accumulates particulate matter contained in the exhaust gases and is disposed downstream of the NOx trap catalyst, both disposed in an exhaust passage of an internal combustion engine capable of recovering an operating condition of the exhaust purifying device, the method comprising:

• disposing a first exhaust temperature sensor downstream of the NOx trap catalyst and upstream of the particulate filter;
• disposing a second exhaust temperature sensor downstream of the particulate filter,
• predicting a temperature of the NOx trap catalyst based on an exhaust temperature detected by the first exhaust temperature sensor;
• predicting a temperature of the particulate filter based on both of the exhaust temperature detected by the first exhaust temperature sensor and an exhaust temperature detected by the second exhaust temperature sensor;
• estimating the operating condition of the exhaust purifying device;
• determining, based on the operating condition of the exhaust purifying device, whether a request for a rise in an exhaust temperature is present;
• executing, by way of fuel injection control in presence of the request for the exhaust temperature rise, a split retard combustion mode in which a main combustion needed to produce a main engine torque and at least one preliminary combustion occurring prior to the main combustion are both achieved and additionally the preliminary combustion takes place near top dead center on a compression stroke and additionally the main combustion initiates after the preliminary combustion has been completed;
• and
• executing a fail-safe process according to which an injection timing of main fuel injection for the main combustion is phase-advanced, when the at least one of the NOx-trap-catalyst temperature predicted and the particulate-filter temperature predicted exceeds a predetermined temperature threshold value.