Different from the existing fixed cam phase angle type, CVVT(Continuously Variable Valve Timing) is the device which varies cam phase angle continuously to be optimum. And with engine oil pressure, it operates. CVVT consists of OCV(Oil Control Valve) and cam phaser. OCV, mounted on cylinder head, controls the amount and direction of oil delivered to cam phaser by oil valve which is connected to a solenoid. Cam phaser, rotating cam phaser rotor with pressure and amount of oil produced by OCV, rotates cam shaft forcefully for(intake advance/exhaust retard) or against(intake retard/exhaust advance) the rotating direction and finally, cam shaft phase changes. With the appliance of CVVT, engine power, fuel efficiency and the quality of exhaust gas are improved.