Kia Rio YB Quiz
Emission Control System

CVVT (Continuously Variable Valve Timing) System

In this manual: Emission Control System
General Information — 8Maintenance — 31Engine Mechanical System — 44Engine Electrical System — 14Emission Control System — 9Engine Control System/Fuel System — 30Clutch System — 10Manual Transmission — 10Automatic Transmission — 23Drive Shaft and Axle — 8Suspension System — 15Steering — 9Restraints — 14Brake System — 22Body (Interior and Exterior) — 115Body Electrical System — 84Heating, Ventilation, and Air Conditioning — 28
2steps
~12min
1/5difficulty
Done 0 of 2

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.

By controlling CVVT, valve overlap or underlap is produced, which improves fuel economy, reduces exhaust emissions (NOx, HC), and improves engine performance by reducing pumping losses, creating an internal exhaust gas recirculation effect, improving combustion stability and volumetric efficiency, and increasing expansion work.

This system consists of the following:

  • CVVT Oil Control Valve (OCV) 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 the engine oil temperature.

  • Cam Phaser: changes camshaft phase using hydraulic pressure from engine oil.

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

[CVVT Intermediate Lock]

This increases the retard amount compared with the default state in order to expand the operating range of the variable valve timing system.

The camshaft phase is locked mechanically, so that it is held at the intermediate position.

 ▷Effect
Improves fuel efficiency by approx. 1.7%.

Widens the operating range of intake CVVT.
(Increases the retard amount up to 30° compared with the default state.)
∇
LIVC (Late Intake Valve Closing)
∇
1. Improves fuel efficiency by reducing pumping losses.
2. Improves knock characteristics by reducing the compression ratio.
Default position: Middle
CVVT operates in the advance/retard directions.

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.

  1. CVVT Intake

  2. CVVT Exhaust

[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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