Hyundai i20 Quiz
Emission Control System

CVVT (Continuously Variable Valve Timing) Description and Operation

In this manual: Emission Control System
General Information — 17Engine Mechanical System — 79Engine Electrical System — 50Emission Control System — 22Engine/Fuel Control System — 107Clutch System — 27MANUAL TRANSMISSION SYSTEM — 21Drive Shaft and Axle — 18Suspension System — 29Steering System — 21Restraint — 41Braking System — 53Body Work (Interior and Exterior) — 190Body Electrical System — 181Heating, Ventilation and Air Conditioning — 58
~2min read

Description

The Continuously Variable Valve Timing (CVVT) system advances or retards the intake and exhaust valve timing based on the ECM signal, calculated from engine load and speed. CVVT control creates valve overlap, resulting in better fuel economy and reduced exhaust emissions (NOx, HC). CVVT improves engine performance by reducing pumping losses and the internal exhaust gas recirculation effect, which improves combustion stability and efficiency. This system consists of:
  • CVVT oil control valve (OCV) that supplies engine oil to the cam phaser or drains engine oil from the cam phaser according to the PWM (Pulse Width Modulation) signal from the ECM,
  • CVVT oil temperature sensor (OTS) that measures the engine oil temperature,
  • and a cam phaser that changes the cam phase by hydraulic force of engine oil.
Engine oil supplied through the CVVT oil control valve changes the cam phase in the advance direction (intake advance/exhaust retard) or the opposite direction (intake retard/exhaust advance) of engine rotation by rotating the rotor connected to the camshaft inside the cam phaser.

Principle of Operation

The CVVT has a mechanism that rotates the rotor vane with hydraulic force generated by 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

Operating
Condition		 Exhaust Valve Intake Valve
Valve
Timing		 Effect Valve
Timing		 Effect
(1) Low Speed
/ Low Load		 Fully
ADVANCE		 * Valve overlap
* Improved combustion stability		 Fully
RETARD		 * Valve overlap
* Improved combustion stability
(2) Partial Load RETARD * Improved relaxation work
* Reduced pumping loss at load changes
* Reduced HC		 RETARD * Reduced pumping loss at load changes
(3) Low Speed
/ High Load		 RETARD * Improved relaxation work ADVANCE * Prevention of reverse intake flow (improved volumetric efficiency)
(4) High speed
/ high load		 ADVANCE * Reduced pumping loss at load changes RETARD * Improved volumetric efficiency

Test yourself

A quick Hyundai i20 quiz: every answer comes with an explanation and a link to the manual page.