Deterioration Rate Determination Method of Lambda Sensor and System Thereof

Abstract

A degradation rate decision method of a lambda sensor, may include an injection step injecting a reducing agent so as to regenerate a nitrogen oxide purification catalyst, a lambda value detection step detecting a lambda value of the lambda sensor from a fuel/air ratio of exhaust gas after injecting the reducing agent, a reaching time decision step determining a time period that the lambda value takes to reach a predetermined criterion value after injecting the reducing agent, and a degradation rate decision step determining that the lambda sensor is degraded when the time period is equal to or longer than a predetermined time period.

1 . A degradation rate decision method of a lambda sensor, comprising:
 an injection step injecting a reducing agent so as to regenerate a nitrogen oxide purification catalyst;   a lambda value detection step detecting a lambda value of the lambda sensor from a fuel/air ratio of exhaust gas after injecting the reducing agent;   a reaching time decision step determining a time period that the lambda value takes to reach a predetermined criterion value after injecting the reducing agent; and   a degradation rate decision step determining that the lambda sensor is degraded when the time period is equal to or longer than a predetermined time period.   
     
     
         2 . The degradation rate decision method of  claim 1 , wherein the predetermined criterion value is selected from stored map data. 
     
     
         3 . A degradation rate decision system of a lambda sensor, comprising:
 a nitrogen oxide purification catalyst trapping nitrogen oxide included in exhaust gas flowing in an exhaust line;   the lambda sensor mounted on the exhaust line to detect a lambda value as a concentration of a reducing agent included in the exhaust gas;   an injector that is mounted at an upstream side of the nitrogen oxide purification catalyst to inject the reducing agent; and   a control portion detecting regeneration timing of the nitrogen oxide purification catalyst and controlling the injector to inject the reducing agent,   wherein the control portion includes a set of instructions to perform the method of  claim 1 .   
     
     
         4 . The degradation rate decision system of  claim 3 , wherein the lambda sensor includes a front lambda sensor disposed at an upstream side of the nitrogen oxide purification catalyst, and a rear lambda sensor disposed at a downstream side of the nitrogen oxide purification catalyst. 
     
     
         5 . The degradation rate decision system of  claim 4 , wherein the injector injects fuel at an upstream side of the front lambda sensor. 
     
     
         6 . The degradation rate decision system of  claim 4 , wherein the control portion firstly detects degradation rate of the front lambda sensor, and secondly detects degradation rate of the rear lambda sensor. 
     
     
         7 . The degradation rate decision system of  claim 6 , wherein the control portion determines that the regeneration of the nitrogen oxide purification catalyst is finished at a dropping time of the lambda value, after the lambda value of the rear lambda sensor reaches a predetermined criterion value in a predetermined time period measured from a time that the reducing agent is injected. 
     
     
         8 . A degradation rate decision system of a lambda sensor, comprising:
 a nitrogen oxide purification catalyst trapping nitrogen oxide included in exhaust gas flowing in an exhaust line;   a lambda sensor mounted on the exhaust line to detect a lambda value as a air fuel ratio included in the exhaust gas;   a control portion detecting regeneration timing of the nitrogen oxide purification catalyst and making a reducing atmosphere of the exhaust gas by a post injection of a fuel,   wherein the control portion includes a set of instructions to perform the method of  claim 1 .