CVVT (Continuously Variable Valve Timing) System Description and Operation

Description

The Continuously Variable Valve Timing (CVVT) system advances or retards the intake and exhaust valve timing according to the control signal from the ECM, which is calculated based on engine speed and load. CVVT control provides valve overlap or underlap, which improves fuel economy, reduces exhaust emissions (NOx, HC) and improves engine performance by reducing pumping losses, providing internal EGR effect, improving combustion stability, improving volumetric efficiency and increasing expansion work. This system consists of the CVVT Oil Control Valve (OCV), which supplies engine oil to the cam phaser or drains engine oil from the cam phaser according to the PWM (Pulse Width Modulation) control signal from the ECM, and the Cam Phaser, which changes the camshaft phase using the hydraulic force of the engine oil. Engine oil flowing from the CVVT oil control valve changes the camshaft phase in the advance direction (intake advance/exhaust retard) or in the direction opposite to engine rotation (intake retard/exhaust advance) by rotating the rotor connected to the camshaft inside the cam phaser.

Operating Principle

The CVVT has a mechanism that rotates the rotor vane with hydraulic force generated by engine oil supplied to the advance or retard chamber, controlled by the CVVT oil control valve.

A separate solenoid valve is installed on the intake-side chain cover to lock and release the separate stop pin.

[CVVT System Mode]

(1) Low Speed/Low Load	(2) Partial Load
(3) Low Speed/High Load	(4) High Speed/High Load

Driving Condition	Exhaust Valve		Intake Valve
	Valve Timing	Effect	Valve Timing	Effect
(1) Low Speed /Low Load	Fully Advance	* Lower valve overlap * Improved combustion stability	Fully Retard	* Lower valve overlap * Improved combustion stability
(2) Partial Load	Retard	* Reduced HC	Retard	* Retards intake valve closing timing to reduce pumping losses * Increases expansion work
(3) Low Speed /High Load	Retard	* Increased expansion work	Advance	* Prevents intake backflow (improves volumetric efficiency)
(4) High Speed /High Load	Advance	* Reduced pumping losses	Retard	* Improved volumetric efficiency