Kia Optima DL3 Quiz
Emission Control System

Continuously Variable Valve Timing (CVVT) System

In this manual: Emission Control System
General Information — 8Advanced Driver Assistance System (ADAS) — 21Maintenance — 27Engine Mechanical System — 45Engine Electrical System — 11Emission Control System — 11Engine Control System/Fuel System — 25Automatic Transmission — 20Drive Shaft and Axle — 7Suspension System — 22Steering — 7Restraints — 11Brake System — 22Body (Interior and Exterior) — 116Body Electrical System — 90Heating, Ventilation, and Air Conditioning — 32
~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). CVVT improves engine performance by reducing pumping losses, providing internal exhaust gas recirculation effect, improving combustion stability, improving 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,

  • and Cam Phaser, which changes the cam phase by hydraulic force of engine oil.

Engine oil flowing through 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 phaser.

Operating Principle

CVVT has a rotor vane mechanism that is rotated by hydraulic force from engine oil supplied to the advance or retard chamber according to the control of 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

Test yourself

A quick Kia Optima DL3 quiz: every answer comes with an explanation and a link to the manual page.