CVVT (Continuous Variable Valve Timing) Description and Operation

Description

The Continuous Variable Valve Timing (CVVT) system advances or retards the valve timing of the intake and exhaust valves according to the control signal of the ECM, calculated from engine speed and load. Valve overlap or underlap is controlled by CVVT, which improves fuel economy and reduces exhaust emissions (NOx, HC). CVVT improves engine performance by reducing pumping losses and internal EGR effect, improving combustion stability and volumetric efficiency, and increasing expansion work. This system consists of:

• CVVT Oil Control Valve (OCV), which supplies engine oil to the cam phaser or drains engine oil from the cam phaser according to the ECM PWM (Pulse Width Modulation) control signal,
• CVVT Oil Temperature Sensor (OTS), which measures engine oil temperature,
• and Cam Phaser, which changes the cam phase by hydraulic force of engine oil.

Engine oil flowing from the CVVT oil control valve changes the cam phase in the advance direction (intake advance / exhaust retard) or in the opposite direction (intake retard / exhaust advance) relative to engine rotation, by rotating the rotor connected to the camshaft inside the cam phaser.

Operating Principle

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

[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	* Increased expansion work * Reduced pumping losses * Reduced HC	Retard	* Reduced pumping losses
(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