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A combustion control apparatus operates an internal combustion engine in a split retard combustion mode during regenerating an exhaust purifier such as a particulate filter. In the split retard combustion mode, the combustion control apparatus controls a first fuel injection to cause preliminary com

A combustion control apparatus operates an internal combustion engine in a split retard combustion mode during regenerating an exhaust purifier such as a particulate filter. In the split retard combustion mode, the combustion control apparatus controls a first fuel injection to cause preliminary combustion at or near top dead center, and controls a second fuel injection to cause main combustion after an end of the preliminary combustion. In this manner, the combustion control apparatus controls an exhaust gas temperature, or an exhaust air-fuel ratio, without increasing exhaust smoke. During the split retard combustion mode, the combustion control apparatus controls an EGR rate of the engine. The EGR rate in the split retard combustion mode is set lower than in the normal combustion mode, in each operating point of the engine.

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What is claimed is: 1. A combustion control apparatus for an internal combustion engine, comprising: an exhaust purifier in an exhaust passage of the engine; a combustion controlling actuator for causing combustion in a combustion chamber of the engine; a controller for controlling the combustion

What is claimed is: 1. A combustion control apparatus for an internal combustion engine, comprising: an exhaust purifier in an exhaust passage of the engine; a combustion controlling actuator for causing combustion in a combustion chamber of the engine; a controller for controlling the combustion controlling actuator; and the controller configured to perform the following: switching a combustion mode between a normal combustion mode and a split retard combustion mode, in accordance with an condition of the exhaust purifier; determining a first EGR rate for the normal combustion mode and a second EGR rate lower than the first EGR rate for the split retard combustion mode, in accordance with an operating point of the engine; performing the following in the normal combustion mode: producing normal combustion to generate an output torque of the engine; and recirculating exhaust gas to the combustion chamber at the first EGR rate; and performing the following in the split retard combustion mode: producing preliminary combustion at or near top dead center, to release a predetermined quantity of heat in the combustion chamber; starting main combustion at a timing later than a start timing of the normal combustion in the normal combustion mode, after an end of the preliminary combustion, to generate the output torque of the engine; and recirculating exhaust gas to the combustion chamber at the second EGR rate. 2. A combustion control apparatus for an internal combustion engine, comprising: a fuel injector for injecting fuel directly into a combustion chamber of the engine; an EGR device for recirculating exhaust gas to the combustion chamber; a controller for controlling the fuel injector, and for controlling the EGR device; and the controller configured to perform the following: switching a combustion mode between a normal combustion mode and a split retard combustion mode, in accordance with an operating condition of the engine; determining two different EGR rates of a first EGR rate for the normal combustion mode and a second EGR rate for the split retard combustion mode, in accordance with an operating point of the engine; performing the following in the normal combustion mode: controlling a normal fuel injection to produce normal combustion to generate an output torque of the engine; and recirculating exhaust gas to the combustion chamber at the first EGR rate; and performing the following in the split retard combustion mode: controlling a first fuel injection to produce preliminary combustion at or near top dead center, to release a predetermined quantity of heat; starting a second fuel injection at a timing later than a start timing of the normal fuel injection in the normal combustion mode, to start main combustion after an end of the preliminary combustion, to generate the output torque of the engine; and recirculating exhaust gas to the combustion chamber at the second EGR rate. 3. The combustion control apparatus as claimed in claim 2, further comprising a condition sensor for collecting information needed to determine the operating condition of the engine. 4. The combustion control apparatus as claimed in claim 3, wherein the second EGR rate is lower than the first EGR rate, at each operating point of the engine. 5. The combustion control apparatus as claimed in claim 4, wherein: the condition sensor senses an engine speed of the engine; and the controller is configured to perform the following: determining a fuel injection quantity of fuel injection to generate the output torque of the engine, in accordance with the operating condition of the engine; and determining the operating point of the engine, based on the engine speed and the fuel injection quantity. 6. The combustion control apparatus as claimed in claim 5, wherein the controller is configured to increase the second EGR rate in accordance with decreasing engine speed. 7. The combustion control apparatus as claimed in claim 5, wherein the controller is configured to increase the second EGR rate in accordance with decreasing fuel injection quantity. 8. The combustion control apparatus as claimed in claim 3, wherein the controller is configured to perform the following in the split retard combustion mode: determining an excess air ratio in accordance with the operating condition of the engine; and recirculating exhaust gas to the combustion chamber at the second EGR rate, during the excess air ratio being higher than 1. 9. The combustion control apparatus as claimed in claim 8, wherein the controller is configured to decrease the second EGR rate in accordance with decreasing excess air ratio. 10. The combustion control apparatus as claimed in claim 3, further comprising an exhaust purifier in an exhaust gas passage of the engine, wherein the condition sensor senses information needed to determine the condition of the exhaust purifier; and the controller is configured to switch the combustion mode, in accordance with the condition of the exhaust purifier. 11. The combustion control apparatus as claimed in claim 10, wherein the condition of the exhaust purifier includes a quantity of a trapped substance in the exhaust purifier. 12. The combustion control apparatus as claimed in claim 10, wherein the exhaust purifier comprises at least one of a particulate filter and a NOx trap. 13. The combustion control apparatus as claimed in claim 12, wherein the exhaust purifier comprises one of the particulate filter and the NOx trap; and the controller is configured to perform the following: producing a regeneration request for regenerating an associated one of the particulate filter and the NOx trap, in accordance with the condition of the exhaust purifier; and selecting the split retard combustion mode in response to the regeneration request. 14. The combustion control apparatus as claimed in claim 12, wherein the exhaust purifier comprises both of the particulate filter and the NOx trap; and the controller is configured to perform the following: producing a PM regeneration request for regenerating the particulate filter, in accordance with the condition of the exhaust purifier; producing a NOx regeneration request for regenerating the NOx trap, in accordance with the condition of the exhaust purifier; and selecting the split retard combustion mode in response to the PM regeneration request and the NOx regeneration request. 15. A combustion control apparatus for an internal combustion engine, comprising: exhaust purifying means for purifying exhaust gas; combustion controlling means for causing combustion in a combustion chamber of the engine; control means for controlling the combustion controlling means; and the control means configured to perform the following: switching a combustion mode between a normal combustion mode and a split retard combustion mode, in accordance with an condition of the exhaust purifying means; determining a first EGR rate for the normal combustion mode and a second EGR rate lower than the first EGR rate for the split retard combustion mode, in accordance with an operating point of the engine; performing the following in the normal combustion mode: producing normal combustion to generate an output torque of the engine; and recirculating exhaust gas to the combustion chamber at the first EGR rate; and performing the following in the split retard combustion mode: producing preliminary combustion at or near top dead center, to release a predetermined quantity of heat in the combustion chamber; starting main combustion at a timing later than a start timing of the normal combustion in the normal combustion mode, after an end of the preliminary combustion, to generate the output torque of the engine; and recirculating exhaust gas to the combustion chamber at the second EGR rate. 16. A method of controlling combustion for an internal combustion engine including an exhaust purifier, the method comprising: switching a combustion mode between a normal combustion mode and a split retard combustion mode, in accordance with an condition of the exhaust purifier; determining a first EGR rate for the normal combustion mode and a second EGR rate lower than the first EGR rate for the split retard combustion mode, in accordance with an operating point of the engine; performing the following in the normal combustion mode: producing normal combustion to generate an output torque of the engine; and recirculating exhaust gas to the combustion chamber at the first EGR rate; and performing the following in the split retard combustion mode: producing preliminary combustion at or near top dead center, to release a predetermined quantity of heat in the combustion chamber; starting main combustion at a timing later than a start timing of the normal combustion in the normal combustion mode, after an end of the preliminary combustion, to generate the output torque of the engine; and recirculating exhaust gas to the combustion chamber at the second EGR rate.