Continuously Variable Valve Timing (CVVT) System

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. Valve overlap or underlap is controlled by CVVT, 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 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; the CVVT Oil Temperature Sensor (OTS), which measures engine oil temperature; and the Cam Phaser, which changes the camshaft phase using hydraulic pressure from the engine oil. Engine oil supplied 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 cam phaser.

[CVVT Intermediate Lock]

This increases the retard amount compared with the default state to widen the operating range of the valve timing system. The camshaft phase is locked mechanically so that it is held at the middle 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

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 CVVT oil control valve control.

The Variable Force Solenoid (VFS) changes its force depending on the PWM duty to control the stroke of the OCV. It also controls the lock, unlock, advance, retard and hold functions.

1. 1
   CVVT Intake

   

2. 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 Advanced	* Lower valve overlap * Improved combustion stability	Fully Retarded	* 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

Circuit Diagrams

Wiring Diagram

Variable Force Solenoid (VFS)

Harness Connector

CVVT Oil Control Valve (OCV)

Harness Connector

Repair Procedures

Inspection

Variable Force Solenoid (VFS)

Refer to Engine Control/Fuel System - "E-CVVT Motor".

CVVT Oil Control Valve (OCV)

Refer to Engine Control/Fuel System - "CVVT Oil Control Valve (OCV)".

Removal

Variable Force Solenoid (VFS)

Refer to Engine Control/Fuel System - "E-CVVT Motor".

CVVT Oil Control Valve (OCV)

Refer to Engine Control/Fuel System - "CVVT Oil Control Valve (OCV)".

Installation

Variable Force Solenoid (VFS)

Refer to Engine Control/Fuel System - "E-CVVT Motor".

CVVT Oil Control Valve (OCV)

Refer to Engine Control/Fuel System - "CVVT Oil Control Valve (OCV)".