Abnormality diagnosing device for internal combustion engine and abnormality diagnosing method therefor

Abstract

A temperature of a catalyst disposed in an exhaust system is raised to a target bed temperature by supplying an unburned fuel component to the catalyst. A learned value is updated based upon a catalyst bed temperature under a temperature increase control and the target bed temperature so that the learned value corresponds to a difference between the respective temperatures. Whether the learned value is out of a proper range or not is determined whenever the learned value is updated. Abnormality is determined when determination that the learned value is out of the proper range is made over several successive updates of the learned value.

1 . An abnormality diagnosing device for an internal combustion engine comprising:
 a temperature increase control section for executing a temperature increase control for increasing a temperature of a catalyst disposed in an exhaust system to a target bed temperature by supplying an unburned fuel component to the catalyst;   an updating section for executing updating of a learned value based upon a catalyst bed temperature under the temperature increase control by the temperature increase control section and the target bed temperature so that the learned value corresponds to a difference between the respective temperatures;   a learned value determining section for determining whether the learned value is outside of a proper range or not when the learned value is updated; and   an abnormality determining section for determining that an abnormality is present only when the learned value determining section determines that the learned value falls outside of the proper range over several successive updates of the learned value.   
   
   
       2 . The abnormality diagnosing device for an internal combustion engine according to  claim 1 , wherein
 the internal combustion engine has a supplemental fuel valve for supplying supplemental fuel upstream of the catalyst in the exhaust system.   
   
   
       3 . The abnormality diagnosing device for an internal combustion engine according to  claim 1 , wherein
 the exhaust system of the internal combustion engine has a filter for trapping particulate matter, the temperature increase control for increasing the temperature of the catalyst to the target bed temperature is executed by supplying the unburned fuel component to the catalyst when to burn the particulate matter to regenerate the filter so that an accumulation amount of the particulate matter trapped in the filter is to less than a prescribed amount.   
   
   
       4 . The abnormality diagnosing device for an internal combustion engine according to  claim 1 , further comprising:
 a counting section for increasing a count value when the learned value determining section determines that the learned value has fallen outside of the proper range and for resetting the count value to an initial value when the learned value determining section determines that the learned value is in the proper range, wherein   the abnormality determining section determines that the abnormality is present when the count value is equal to or greater than a determination value that is equal to or greater than a value that is incremented at least twice from the initial value, and   the counting section resets the count value to the initial value when the filter regeneration is completed.   
   
   
       5 . The abnormality diagnosing device for an internal combustion engine according to  claim 1 , further comprising:
 a counting section for increasing a count value when the learned value determining section determines that the learned value has fallen outside of the proper range and for resetting the count value to an initial value when the learned value determining section determines that the learned value is in the proper range, wherein   the learned value is updated when the catalyst bed stably maintains a catalyst bed temperature that is equal to or higher than the temperature at which the particulate matter is capable of being burned, and   the abnormality determining section determines that the abnormality is present when the count value given by the counting section is equal to or greater than a determination value that is equal to or greater than a value that is incremented at least twice from the initial value, and determines the abnormality regardless of the count value if the filter regeneration is not completed after the elapsed time from when the filter regeneration starts reaches or exceeds a permissible time period.   
   
   
       6 . The abnormality diagnosing device for an internal combustion engine according to  claim 4 , wherein
 the counting section increases “1” per once,   the initial value is “0,” and   the determination value is an integer which is equal to or greater than “2”.   
   
   
       7 . The abnormality diagnosing device for an internal combustion engine according to  claim 1 , wherein
 the abnormality determining section determines that the abnormality is present when the learned value determining section determines that the learned value varies to be larger than the proper range over several successive updates of the learned value.   
   
   
       8 . The abnormality diagnosing device for an internal combustion engine according to  claim 1 , wherein
 the unburned fuel component is supplied to the catalyst by an auxiliary injection made in an exhaust stroke or an expansion stroke after fuel injected for combustion in a combustion chamber from a fuel injector.   
   
   
       9 . An abnormality diagnosing method for an internal combustion engine comprising:
 executing a temperature increase control for increasing a temperature of a catalyst disposed in an exhaust system to a target bed temperature by supplying an unburned fuel component to the catalyst;   executing updating a learned value based upon a catalyst bed temperature under the temperature increase control and the target bed temperature so that the learned value corresponds to a difference between the respective temperatures;   determining whether the learned value falls outside of a proper range or not every time the learned value is updated; and   determining abnormality when it is determined that the learned value falls outside of the proper range over several successive updates of the learned value.   
   
   
       10 . The abnormality diagnosing method for an internal combustion engine according to  claim 9 , wherein
 the exhaust system of the internal combustion engine has a filter for trapping particulate matter, the temperature increase control for increasing the temperature of the catalyst to the target bed temperature is executed by supplying the unburned fuel component to the catalyst when a filter regeneration is made to burn the particulate matter so that an accumulation amount of the particulate matter trapped by the filter is to be less than a preset amount.   
   
   
       11 . The abnormality diagnosing method for an internal combustion engine according to  claim 9 , further comprising:
 increasing a count value when the learned value is determined to fall outside of the proper range, and resetting the count value to an initial value when the learned value is determined to be in the proper range, wherein an abnormality is determined to be present when the count value is equal to or greater than a determination value which that is equal to or greater than a value that is incremented at least twice from the initial value, and   the count value is reset to the initial value when the filter regeneration is completed.   
   
   
       12 . The abnormality diagnosing method for an internal combustion engine according to  claim 9 , further comprising:
 increasing a count value when the learned value is determined to be outside the proper range and resetting the count value to an initial value when the learned value is determined to be in the proper range, wherein   the learned value is updated when the catalyst bed temperature is stably maintained at a temperature that is equal to or above the temperature at which the particulate matter is capable of being burned, and   the abnormality is determined to be present when the count value is equal to or greater than a determination value that is equal to or greater than a value that is incremented at least twice from the initial value, and the abnormality is determined to be present regardless of the count value if the filter regeneration is not completed a time period has elapsed from a start moment of the filter regeneration reaches or exceeds a permissible time period.