| abstract |
An exhaust filter 38 includes a filter for trappingnparticulate matter contained in exhaust gas and a NOxnstorage reduction catalyst coated on the filter. As an Snrelease control of the exhaust filter 38, a fuel addingnvalve 68 intermittently adds fuel to exhaust gas. While fuelnis added to exhaust gas, the degree of a temperaturenincrease due to the fuel addition is monitored after thenfirst addition of fuel. Based on the results of monitoring,nwhether the second and subsequent additions of fuel need tonbe performed is determined. Accordingly, sulfur oxidesnoccluded by the NOx storage reduction catalyst arenadequately reduced. |