Kia Forte BD Quiz
Emission Control System

CVVT (Continuously Variable Valve Timing) System

In this manual: Emission Control System
General Information — 8Maintenance — 32Engine Mechanical System — 47Engine Electrical System — 17Emission Control System — 10Engine Control System/Fuel System — 32Clutch System — 11Manual Transmission — 11DCT (Dual Clutch Transmission) System — 16Drive Shaft and Axle — 8Suspension System — 26Steering — 9Restraints — 11Brake System — 27Body (Interior and Exterior) — 119Body Electrical System — 98Heating, Ventilation, and Air Conditioning — 27
~2min read

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 and reduces exhaust emissions (NOx, HC) and improves engine performance by reducing pumping losses, internal exhaust gas recirculation effect, improving combustion stability, improving volumetric efficiency, and increasing expansion work.

This system consists of the following:

  • CVVT Oil Control Valve (OCV), which regulates the flow of engine oil to and from the cam phaser according to the ECM Pulse Width Modulation (PWM) signal.

  • 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 camshaft 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

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

[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

Test yourself

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