Catalyst degradation diagnosis device and diagnosis method for internal combustion engine

Abstract

The oxygen storage capacity preceding a previous oxygen storage capacity and the previous oxygen storage capacity of each of an upstream catalyst and a downstream catalyst are measured, and a present oxygen storage capacity of the downstream catalyst is measured. Then, sulfur poisoning of the upstream catalyst and the downstream catalyst is detected on the basis of an oxygen storage capacity change amount of each of the upstream catalyst and the downstream catalyst from the oxygen storage capacity preceding the previous one to the previous oxygen storage capacity, and the oxygen storage capacity change amount of the downstream catalyst from the previous oxygen storage capacity to the present oxygen storage capacity. The presence/absence of the sulfur poisoning can be accurately detected by utilizing the difference between the manners of sulfur poisoning of the two catalysts.

1 . A catalyst degradation diagnosis device for an internal combustion engine equipped with an upstream catalyst and a downstream catalyst in an exhaust passageway of the internal combustion engine which diagnoses presence/absence of degradation of the upstream catalyst and the downstream catalyst, comprising:
 a measurement device that measures an oxygen storage capacity of each of the upstream catalyst and the downstream catalyst; and   a sulfur poisoning detection device that detects sulfur poisoning of the upstream catalyst and the downstream catalyst based on an oxygen storage capacity change amount of the upstream catalyst from an oxygen storage capacity of the upstream catalyst preceding a previous oxygen storage capacity of the upstream catalyst to the previous oxygen storage capacity, an oxygen storage capacity change amount of the downstream catalyst from an oxygen storage capacity of the downstream catalyst preceding a previous oxygen storage capacity of the downstream catalyst to the previous oxygen storage capacity, and an oxygen storage capacity change amount of the downstream catalyst from the previous oxygen storage capacity to a present oxygen storage capacity of the downstream catalyst, when the oxygen storage capacity of each of the upstream catalyst and the downstream catalyst preceding the previous oxygen storage capacity and the previous oxygen storage capacity of each of the upstream catalyst and the downstream catalyst have been measured by the measurement device, and the present oxygen storage capacity of the downstream catalyst has been measured by the measurement device.   
   
   
       2 . The catalyst degradation diagnosis device according to  claim 1 , further comprising:
 a determination device that determines the presence/absence of degradation of the upstream catalyst and the downstream catalyst based on the oxygen storage capacity measured by the measurement device; and   a determination prohibition device that prohibits determination performed by the determination device when the sulfur poisoning of the upstream catalyst and the downstream catalyst is detected by the sulfur poisoning detection device.   
   
   
       3 . The catalyst degradation diagnosis device according to  claim 2 , wherein
 the oxygen storage capacity preceding the previous oxygen storage capacity and the previous oxygen storage capacity of each of the upstream catalyst and the downstream catalyst are a value measured during a trip preceding a previous trip and a value measured during the previous trip, respectively, which are before and after refueling.   
   
   
       4 . The catalyst degradation diagnosis device according to  claim 1 , wherein
 the oxygen storage capacity preceding the previous oxygen storage capacity and the previous oxygen storage capacity of each of the upstream catalyst and the downstream catalyst are a value measured during a trip preceding a previous trip and a value measured during the previous trip, respectively, which are before and after refueling.   
   
   
       5 . A catalyst degradation diagnosis device for an internal combustion engine equipped with an upstream catalyst and a downstream catalyst in an exhaust passageway of the internal combustion engine which diagnoses presence/absence of degradation of the upstream catalyst and the downstream catalyst, comprising:
 a measurement device that measures an oxygen storage capacity of each of the upstream catalyst and the downstream catalyst; and   a sulfur poisoning detection device that detects sulfur poisoning of the upstream catalyst and the downstream catalyst based on an oxygen storage capacity change amount of the upstream catalyst from a previous oxygen storage capacity of the upstream catalyst to a present oxygen storage capacity of the upstream catalyst, and an oxygen storage capacity change amount of the downstream catalyst from a previous oxygen storage capacity of the downstream catalyst to a present oxygen storage capacity of the downstream catalyst, when the previous oxygen storage capacity and the present oxygen storage capacity of each of the upstream catalyst and the downstream catalyst have been measured by the measurement device.   
   
   
       6 . The catalyst degradation diagnosis device according to  claim 5 , further comprising:
 a determination device that determines the presence/absence of degradation of the upstream catalyst and the downstream catalyst based on the oxygen storage capacity measured by the measurement device; and   a determination prohibition device that prohibits determination performed by the determination device when the sulfur poisoning of the upstream catalyst and the downstream catalyst is detected by the sulfur poisoning detection device.   
   
   
       7 . A catalyst degradation diagnosis device for an internal combustion engine equipped with an upstream catalyst and a downstream catalyst in an exhaust passageway of the internal combustion engine which diagnoses presence/absence of degradation of the upstream catalyst, comprising:
 a measurement device that measures an oxygen storage capacity of the upstream catalyst; and   a sulfur poisoning detection device that detects sulfur poisoning of the upstream catalyst based on an oxygen storage capacity change amount of the upstream catalyst from a previous oxygen storage capacity to a present oxygen storage capacity, when the previous oxygen storage capacity and the present oxygen storage capacity have been measured by the measurement device.   
   
   
       8 . The catalyst degradation diagnosis device according to  claim 7 , further comprising:
 a determination device that determines the presence/absence of degradation of the upstream catalyst based on the oxygen storage capacity measured by the measurement device; and   a determination prohibition device that prohibits determination performed by the determination device when the sulfur poisoning of the upstream catalyst is detected by the sulfur poisoning detection device.   
   
   
       9 . A catalyst degradation diagnosis method for an internal combustion engine equipped with an upstream catalyst and a downstream catalyst in an exhaust passageway of the internal combustion engine which diagnoses presence/absence of degradation of the upstream catalyst and the downstream catalyst, comprising:
 measuring an oxygen storage capacity of each of the upstream catalyst and the downstream catalyst; and   detecting sulfur poisoning of the upstream catalyst and the downstream catalyst based on an oxygen storage capacity change amount of the upstream catalyst from an oxygen storage capacity of the upstream catalyst preceding a previous oxygen storage capacity of the upstream catalyst to the previous oxygen storage capacity, an oxygen storage capacity change amount of the downstream catalyst from an oxygen storage capacity of the downstream catalyst preceding a previous oxygen storage capacity of the downstream catalyst to the previous oxygen storage capacity, and an oxygen storage capacity change amount of the downstream catalyst from the previous oxygen storage capacity to a present oxygen storage capacity of the downstream catalyst, when the oxygen storage capacity of each of the upstream catalyst and the downstream catalyst preceding the previous oxygen storage capacity and the previous oxygen storage capacity of each of the upstream catalyst and the downstream catalyst have been measured, and the present oxygen storage capacity of the downstream catalyst has been measured.   
   
   
       10 . The catalyst degradation diagnosis method according to  claim 9 , further comprising:
 determining the presence/absence of degradation of the upstream catalyst and the downstream catalyst based on the oxygen storage capacity measured; and   prohibiting determination regarding the degradation when the sulfur poisoning of the upstream catalyst and the downstream catalyst is detected.   
   
   
       11 . The catalyst degradation diagnosis method according to  claim 10 , wherein
 the oxygen storage capacity preceding the previous oxygen storage capacity and the previous oxygen storage capacity of each of the upstream catalyst and the downstream catalyst are a value measured during a trip preceding a previous trip and a value measured during the previous trip, respectively, which are before and after refueling.   
   
   
       12 . The catalyst degradation diagnosis method according to  claim 9 , wherein
 the oxygen storage capacity preceding the previous oxygen storage capacity and the previous oxygen storage capacity of each of the upstream catalyst and the downstream catalyst are a value measured during a trip preceding a previous trip and a value measured during the previous trip, respectively, which are before and after refueling.   
   
   
       13 . A catalyst degradation diagnosis method for an internal combustion engine equipped with an upstream catalyst and a downstream catalyst in an exhaust passageway of the internal combustion engine which diagnoses presence/absence of degradation of the upstream catalyst and the downstream catalyst, comprising:
 measuring an oxygen storage capacity of each of the upstream catalyst and the downstream catalyst; and   detecting sulfur poisoning of the upstream catalyst and the downstream catalyst based on an oxygen storage capacity change amount of the upstream catalyst from a previous oxygen storage capacity of the upstream catalyst to a present oxygen storage capacity of the upstream catalyst, and an oxygen storage capacity change amount of the downstream catalyst from a previous oxygen storage capacity of the downstream catalyst to a present oxygen storage capacity of the downstream catalyst, when the previous oxygen storage capacity and the present oxygen storage capacity of each of the upstream catalyst and the downstream catalyst have been measured.   
   
   
       14 . The catalyst degradation diagnosis method according to  claim 13 , further comprising,
 determining the presence/absence of degradation of tile upstream catalyst and the downstream catalyst based on the oxygen storage capacity measured; and   prohibiting determination regarding the degradation when the sulfur poisoning of the upstream catalyst and the downstream catalyst is detected.   
   
   
       15 . A catalyst degradation diagnosis method for an internal combustion engine equipped with an upstream catalyst and a downstream catalyst in an exhaust passageway of the internal combustion engine which diagnoses presence/absence of degradation of the upstream catalyst, comprising:
 measuring an oxygen storage capacity of the upstream catalyst; and   detecting sulfur poisoning of the upstream catalyst based on an oxygen storage capacity change amount of the upstream catalyst from a previous oxygen storage capacity to a present oxygen storage capacity, when the previous oxygen storage capacity and the present oxygen storage capacity have been measured.   
   
   
       16 . The catalyst degradation diagnosis method according to  claim 15 , further comprising:
 determining the presence/absence of degradation of the upstream catalyst based on the oxygen storage capacity; and   prohibiting determination regarding the degradation when the sulfur poisoning of the upstream catalyst is detected.