Control Diagnostic Apparatus for Internal Combustion Engine

Abstract

To prevent the deterioration of exhaust emissions of an internal combustion engine due to air-fuel ratio variation among multiple cylinders, and to identify an abnormal cylinder during an abnormality of cylinder air-fuel ratio variation. An control apparatus of an internal combustion engine comprising upstream air-fuel ratio detection means for detecting upstream air-fuel ratio of the catalyst that purifies exhaust emissions discharged from multiple cylinders, and configured to control air-fuel ratio of the multiple cylinders based on the upstream air-fuel ratio, wherein the air-fuel ratio variation among the multiple cylinders is increased and the upstream air-fuel ratio is controlled to become rich. Further, an abnormality of the air-fuel ratio variation among the multiple cylinders and an abnormal cylinder are identified based on an output of an air-fuel ratio sensor in downstream of the catalyst when the air-fuel ratio variation is increased, or an estimated value of an air-fuel ratio (central air-fuel ratio) at which the purification efficiency of the catalyst becomes optimal.

1 . A control apparatus of an internal combustion engine, comprising:
 a catalyst for purifying exhaust emission discharged from multiple cylinders;   upstream air-fuel ratio detection means for detecting an air-fuel ratio of exhaust gas that flows into the catalyst; and   air-fuel ratio control means for controlling a fuel injection amount of the multiple cylinders based on the upstream air-fuel ratio, wherein   the control apparatus is adapted to control the fuel injection amount of the multiple cylinders when the air-fuel ratio among the multiple cylinders varies, such that the upstream air-fuel ratio is richer than the upstream air-fuel ratio detected before the air-fuel ratio among the multiple cylinders varies.   
     
     
         2 . The control apparatus of an internal combustion engine according to  claim 1 , wherein
 a degree of control to make the upstream air-fuel ratio richer is increased in accordance with a degree of the air-fuel ratio variation among the multiple cylinders.   
     
     
         3 . The control apparatus of an internal combustion engine according to  claim 1 , wherein
 the internal combustion engine comprises downstream air-fuel ratio detection means for detecting an air-fuel ratio of an exhaust gas that flows out from the catalyst, and   the control apparatus determines an abnormality of the air-fuel ratio variation among the multiple cylinders based on the downstream air-fuel ratio detected after the air-fuel ratio among the multiple cylinders has varied.   
     
     
         4 . The control apparatus of an internal combustion engine according to  claim 1 , wherein
 the control apparatus comprises means for increasing the air-fuel ratio variation among the multiple cylinders by increasing or decreasing a fuel injection amount of at least one cylinder by a predetermined proportion relative to fuel injection amounts of other cylinders.   
     
     
         5 . The control apparatus of an internal combustion engine according to  claim 4 , wherein
 a determination of air-fuel variation abnormality among the multiple cylinders is made if the downstream air-fuel ratio detected after the air-fuel ratio among the multiple cylinders is varied departs from a predetermined range.   
     
     
         6 . The control apparatus of an internal combustion engine according to  claim 1 , the control apparatus being configured to estimate an oxygen storage amount to be stored in the catalyst from an accumulated value of differences between at least the upstream air-fuel ratio and a central air-fuel ratio at which three exhaust components consisting of HC, CO, and NOx react with oxygen in exhaust gas without excess and deficiency, and control the upstream air-fuel ratio such that the oxygen storage amount comes into a predetermined range, wherein
 the central air-fuel ratio is corrected toward the rich side in accordance with the air-fuel ratio variation among the multiple cylinders.   
     
     
         7 . The control apparatus of an internal combustion engine according to  claim 6 , wherein the control apparatus is configured to increase the air-fuel ratio variation among the multiple cylinders by increasing or decreasing a fuel pulse width only for one particular cylinder; to correct the central air-fuel ratio toward the rich side when the downstream air-fuel ratio becomes richer than a predetermined range; to correct the central air-fuel ratio toward the lean side when the downstream air-fuel ratio becomes leaner than a predetermined range; and to determine an abnormality of the air-fuel ratio variation among the multiple cylinders based on a correction amount of the central air-fuel ratio, the central air-fuel ratio being calculated while the air-fuel ratio variation among the cylinders is increasing.