Combustion control system of internal combustion engine

Abstract

In an internal combustion engine equipped with a fuel injection system and an exhaust purifying device, such as NOx trap catalyst and/or diesel particulate filter (DPF), a control unit is provided. The control unit controls the fuel injection system to permit the engine to have a predetermined combustion mode in which, under a predetermined condition of the exhaust purifying device, the fuel injection system causes the engine to carry out a main combustion to produce a torque and at least one preliminary combustion prior to the main combustion. The at least one preliminary combustion is effected at a timing in the vicinity of top dead center of compression stroke, and the main combustion is effected at a first timing after completion of the preliminary combustion. The control unit further controls the fuel injection system in such a manner that upon switching of the engine operation from a previous combustion mode to the predetermined combustion mode, the main combustion that takes place after completion of the preliminary combustion is effected at a second timing that is retarded as compared with the first timing.

1 . A combustion control system of an internal combustion engine, comprising: 
 a fuel injection system provided at an intake system of the engine;    an exhaust purifying device provided at an exhaust system of the engine; and    a control unit that controls the fuel injection system to permit the engine to have a predetermined combustion mode, the predetermined combustion mode being a mode in which, under a predetermined condition of the exhaust purifying catalyst, the fuel injection system causes the engine to carry out a main combustion to produce a torque and at least one preliminary combustion prior to the main combustion, the at least one preliminary combustion being effected at a timing in the vicinity of top dead center of compression stroke, the main combustion being effected at a first timing after completion of the preliminary combustion,    wherein the control unit further controls the fuel injection system in such a manner that upon switching of the engine operation from a previous combustion mode to the predetermined combustion mode, the main combustion that takes place after completion of the preliminary combustion is effected at a second timing that is retarded as compared with the first timing.    
   
   
       2 . A combustion control system as claimed in  claim 1 , in which the second timing for the main combustion is controlled to have a value that gradually reaches a target value.  
   
   
       3 . A combustion control system as claimed in  claim 2 , in which a fuel injection timing for the main combustion is gradually retarded to have a target fuel injection timing.  
   
   
       4 . A combustion control system as claimed in  claim 1 , in which the main combustion after completion of the preliminary combustion is carried out after a fluctuation of the intake system, that is induced by the switching to the predetermined combustion mode from the previous combustion mode, subsides.  
   
   
       5 . A combustion control system as claimed in  claim 1 , in which a fuel injection quantity for the preliminary combustion is determined to a quantity that permits an incylinder temperature at the second timing of fuel injection for the main combustion to be higher than a temperature that enables a self ignition of the main combustion.  
   
   
       6 . A combustion control system as claimed in  claim 1 , in which a combustion start timing of the main combustion is retarded from a combustion start timing of the preliminary combustion by over 20 degrees in crank angle.  
   
   
       7 . A combustion control system as claimed in  claim 1 , in which the main combustion is completed at a timing of over 50 degrees in crank angle after top dead center of compression stroke.  
   
   
       8 . A combustion control system as claimed in  claim 1 , in which the exhaust temperature of the engine is controlled by controlling a fuel injection timing for the main combustion.  
   
   
       9 . A combustion control system as claimed in  claim 1 , in which the exhaust purifying device is a PM filter that collects particulate matter in the exhaust gas, and in which under a predetermined condition of the filter, the control unit controls the fuel injection system in a manner to increase the exhaust temperature for burning the particulate matter accumulated on the filter.  
   
   
       10 . A combustion control system as claimed in  claim 1 , in which the exhaust purifying device is a NOx trap catalyst that traps NOx in the exhaust gas when the exhaust air/fuel ratio is lean, and in which under a predetermined condition of the NOx trap catalyst, the control unit controls the fuel injection system in a manner to make the exhaust air/fuel ratio richer thereby to release the trapped NOx from the catalyst.  
   
   
       11 . A combustion control system as claimed in  claim 1 , in which the exhaust purifying device is a NOx trap catalyst that traps NOx in the exhaust gas when the exhaust air/fuel ratio is lean, and in which under a predetermined condition of the NOx trap catalyst, the control unit controls the fuel injection system in a manner to increase the exhaust temperature to release a sulfur poisoning from the catalyst.  
   
   
       12 . A combustion control system as claimed in  claim 1 , in which the predetermined condition of the exhaust purifying device is a condition wherein the exhaust purifying device is under inactivation condition.  
   
   
       13 . A combustion control system as claimed in  claim 1 , in which the combustion of the previous combustion mode contains mainly a diffusive combustion that is produced when a main fuel injection is effected during a combustion induced by a pilot fuel injection.  
   
   
       14 . In an internal combustion engine that is equipped at an intake system with a fuel injection system and at an exhaust system with an exhaust purifying device, 
 a method for controlling the engine, comprising:    controlling the fuel injection system to permit the engine to have a predetermined combustion mode in which, under a predetermined condition of the exhaust purifying device, the fuel injection system causes the engine to carry out a main combustion to produce a torque and at least one preliminary combustion prior to the main combustion;    controlling the fuel injection system in such a manner that the at least one preliminary combustion is effected at a timing in the vicinity of top dead center of compression stroke, and the main combustion is effected at a first timing after completion of the preliminary combustion; and    controlling the fuel injection system in such a manner that upon switching of the engine operation from a previous combustion mode to the predetermined combustion mode, the main combustion that takes place after completion of the preliminary combustion is effected at a second timing that is retarded as compared with the first timing.