| abstract |
The present invention provides a urea water injection amount control device capable of accelerating the reduction in excess and deficiency of the NH3 supply amount by improving the estimation accuracy of the NO / NO2 ratio. In a DOC oxidation catalyst, NO is converted into NO2 by being oxidized by oxygen with NO, and NO conversion rate in which NO2 is converted to NO as carbon is oxidized by NO2 in DPF. Based on this, the ratio (NO / NO2 ratio) between NO and NO2 flowing into the SCR NOx reduction catalyst is estimated. Based on the NO / NO2 ratio thus estimated, the injection amount of urea water injected from the injection valve is controlled. [Selection] Figure 2 |