System and method for controlling valve timing of continuous variable valve duration engine

A method for controlling intake and exhaust valves of an engine, the method comprising:

• determining, by a controller, a target opening duration of the intake valve, a target opening duration of the exhaust valve based on an engine load and an engine speed;
• modifying, by an intake continuous variable valve duration (CVVD) device, current opening and closing timings of the intake valve based on the target opening duration of the intake valve;
• modifying, by an exhaust CVVD device, current opening and closing timings of the exhaust valve based on the target opening duration of the exhaust valve;
• advancing, by the intake CVVD device, the current opening timing of the intake valve while simultaneously retarding the current closing timing of the intake valve by a predetermined value, or retarding the current opening timing of the intake valve while simultaneously advancing the current closing timing of the intake valve by a predetermined value, based on the target opening duration of the intake valve;
• and
• advancing, by the exhaust CVVD device, the current opening timing of the exhaust valve while simultaneously retarding the current closing timing of the exhaust valve by a predetermined value, or retarding the current opening timing of the exhaust valve while simultaneously advancing the current closing timing of the exhaust valve by a predetermined value, based on the target opening duration of the exhaust valve.