Internal combustion engine exhaust gas control apparatus and control method thereof

Abstract

An exhaust gas control apparatus includes a PM trapping filter provided in an exhaust gas passage of an internal combustion engine, an oxygen concentration sensor provided upstream of the filter, a device that estimates the air-fuel ratio of exhaust gas supplied to the oxygen concentration sensor, and a device that estimates the amount of PM trapped in the filter based on the estimated exhaust gas air-fuel ratio and the oxygen concentration sensor output. The amount of PM trapped in the filter is estimated using the fact that the oxygen concentration sensor output value changes according to the exhaust gas air-fuel ratio and the amount of PM accumulated on the oxygen concentration sensor. As a result, the structure of the exhaust passage is able to be kept simple because only an oxygen concentration sensor is added upstream of the filter.

1 .- 13 . (canceled) 
   
   
       14 . An exhaust gas control apparatus for an internal combustion engine, comprising:
 a filter which is provided in an exhaust passage of the internal combustion engine and traps a particulate matter in an exhaust gas;   an upstream oxygen concentration sensor provided in the exhaust passage upstream of the filter;   a downstream oxygen concentration sensor provided in the exhaust passage downstream of the filter;   an air-fuel ratio estimating device that estimates an air-fuel ratio of the exhaust gas supplied to the upstream oxygen concentration sensor; and   an estimating device that estimates an amount of the particulate matter trapped in the filter based on the air-fuel ratio of the exhaust gas estimated by the air-fuel ratio estimating device, an output of the upstream oxygen concentration sensor, and an output of the downstream oxygen concentration sensor.   
   
   
       15 . The exhaust gas control apparatus according to  claim 14 , wherein the upstream oxygen concentration sensor includes an exhaust gas side electrode and a porous body which covers the exhaust gas side electrode and on which the particulate matter in the exhaust gas can accumulate, the output of the upstream oxygen concentration sensor changing according to the amount of the particulate matter in the exhaust gas accumulated on the porous body. 
   
   
       16 . The exhaust gas control apparatus according to  claim 15 , wherein the upstream oxygen concentration sensor includes a heater for burning off the particulate matter accumulated on the porous body. 
   
   
       17 . The exhaust gas control apparatus according to  claim 14 , wherein the upstream oxygen concentration sensor and the downstream oxygen concentration sensor each include the an exhaust gas side electrode and at least one of a pinhole and a porous body for determining the amount of oxygen to be transported to the exhaust gas side electrode, and the outputs change according to an exhaust gas pressure. 
   
   
       18 . The exhaust gas control apparatus according to  claim 14 , wherein the estimating device estimates the amount of the particulate matter trapped in the filter by monitoring a differential pressure between the exhaust passage upstream of the filter and the exhaust passage downstream of the filter, based on the output of the upstream oxygen concentration sensor and the output of the downstream oxygen concentration sensor. 
   
   
       19 . The exhaust gas control apparatus according to  claim 14 , further comprising:
 a filter recovery controlling apparatus that executes a predetermined filter recovery control when the amount of the particulate matter trapped in the filter estimated by the estimating device exceeds a predetermined amount.   
   
   
       20 . The exhaust gas control apparatus according to  claim 19 , wherein the estimating device a) stores a plurality of different estimated air-fuel ratios estimated by the air-fuel ratio estimating device together with corresponding initial outputs of the upstream oxygen concentration sensor, a respective one of the estimated air-fuel ratios being stored together with a respective one of the initial outputs, before a predetermined period of time passes after the filter recovery control has ended, and b) estimates the amount of the particulate matter trapped in the filter based on the difference between the output of the upstream oxygen concentration sensor and the initial output of the upstream oxygen concentration sensor. 
   
   
       21 . A control method of an exhaust gas control apparatus for an internal combustion engine that includes a filter which is provided in an exhaust passage of the internal combustion engine and traps a particulate matter in an exhaust gas, the control method comprising:
 estimating an air-fuel ratio of the exhaust gas supplied to an upstream oxygen concentration sensor provided in the exhaust passage upstream of the filter; and   estimating an amount of the particulate matter trapped in the filter based on an estimated air-fuel ratio of the exhaust gas, an output of the upstream oxygen concentration sensor, and an output of a downstream oxygen concentration sensor provided in the exhaust passage downstream of the filter.