Patent ID: 8327624

Claim:
A system for purifying an exhaust gas comprising: a diesel catalyzed particulate filer (DPF) trapping particulate matters (PM) contained in the exhaust gas; a diesel oxidation catalyst (DOC) oxidizing carbon monoxide and hydrocarbon contained in the exhaust gas, a selective catalyst reduction (SCR) apparatus reducing nitrogen oxide contained in the exhaust gas; a dosing module located upstream of the selective catalyst reduction apparatus and dosing a reducing agent into the exhaust gas; and an electronic control unit; wherein the catalyzed particulate filter, the diesel oxidation catalyst, the selective catalyst reduction apparatus, and the dosing module are mounted on an exhaust pipe, and the selective catalyst reduction apparatus is mounted downstream of the catalyzed particulate filter and the diesel oxidation catalyst; and wherein a back pressure control valve is mounted between the catalyzed particulate filter and the diesel oxidation catalyst on the exhaust pipe; and wherein the electronic control unit is configured to control the flow of the exhaust gas by controlling an operation of the back pressure control valve when a heating mode enter condition is satisfied.