NOx SENSOR ABNORMALITY DETECTOR

Abstract

A NOx sensor abnormality detector for a NOx sensor includes a measurement chamber, a pump cell, and a sensor cell. The NOx sensor abnormality detector includes a signal receiving section configured to receive the detection value of the sensor cell, a reduction process executing section configured to execute a reduction process that reduces the discharge function of the pump cell, and an abnormality determining section configured to perform abnormality determination of the NOx sensor. The NOx sensor abnormality detector is configured to execute abnormality detection control in which the abnormality determining section performs abnormality determination of the NOx sensor based on the detection value of the sensor cell, which is input to the signal receiving section, after the reduction process executing section starts the reduction process.

1 . A NOx sensor abnormality detector for a NOx sensor, wherein
 the NOx sensor includes
 a measurement chamber, which is located in an exhaust passage of an internal combustion engine and into which exhaust gas is introduced, 
 a pump cell having a discharge function of discharging oxygen from the measurement chamber, and 
 a sensor cell having a decomposition function of decomposing NOx in the measurement chamber into nitrogen and oxygen and a detection function of detecting an oxygen concentration in the measurement chamber, 
   the NOx sensor is configured to output, as a signal corresponding to a NOx concentration in the exhaust gas, a detection value of oxygen concentration detected by the sensor cell while causing the discharge function of the pump cell to take effect,   the NOx sensor abnormality detector comprises:
 a signal receiving section configured to receive the detection value of the sensor cell; 
 a reduction process executing section configured to execute a reduction process that reduces the discharge function of the pump cell; and 
 an abnormality determining section configured to perform abnormality determination of the NOx sensor, and 
   the NOx sensor abnormality detector is configured to execute abnormality detection control in which the abnormality determining section performs abnormality determination of the NOx sensor based on the detection value of the sensor cell, which is input to the signal receiving section, after the reduction process executing section starts the reduction process.   
     
     
         2 . The NOx sensor abnormality detector according to  claim 1 , further comprising an accumulated value calculating section configured to accumulate detection values of the sensor cell, which are input to the signal receiving section, during a predetermined accumulation period, which starts after the reduction process starts,
 wherein the abnormality determining section is configured to determine that the NOx sensor operates abnormally when an accumulated value calculated by the accumulated value calculating section is less than or equal to a determination value.   
     
     
         3 . The NOx sensor abnormality detector according to  claim 1 , further comprising an idle determining section configured to determine whether the internal combustion engine is at idle,
 wherein the abnormality determining section is configured to execute the abnormality detection control when the idle determining section determines that the internal combustion engine is at idle.