Purification system for variable post injection in LP EGR and control method for the same

A purification system for variable post injection in LP EGR, the system comprising:

• a turbo charger disposed downstream of a diesel engine;
• a DPF (diesel particulate filter) disposed downstream of the turbo charger;
• a NOx reduction apparatus disposed upstream or downstream of the DPF;
• a bypass line diverged from the DPF for mixing exhaust gas and air inflowing the turbo charger;
• an exhaust gas control portion disposed downstream of the DPF for controlling flowing of the exhaust gas;
• and
• a lean/rich controlling portion for controlling a lean/rich state of the exhaust gas wherein the lean/rich controlling portion comprising:
• a post injector disposed upstream of the NOx reduction apparatus;
• and
• an injector control portion that determines injecting timing of the post injector according to NOx concentration and amount of the NOx and modulates fuel injection patterns according to engine driving conditions,
• wherein the exhaust as control ortion comprises:
• a first throttle flap that controls flowing of the exhaust gas flowing to the NOx reduction apparatus;
• and
• a second throttle flap that controls flowing of the exhaust gas flowing to the bypass line,
• wherein the first throttle flap is fixed to the second throttle flap and the first throttle flap and the second throttle flap are vertically disposed to each other,
• wherein the exhaust gas control portion further comprises a DC motor and the DC motor controls openings of the first throttle flap and the second throttle flap simultaneously.