Kia Picanto JA: Exhaust Emission Control System / CVVT (Continuous Variable Valve Timing) System

Kia Picanto (JA) 2017-{YEAR} Service & Repair Manual / Emission Control System / Exhaust Emission Control System / CVVT (Continuous Variable Valve Timing) System

Description and operation

Description

Continuous Variable Valve Timing (CVVT) system advances or retards the valve timing of the intake and exhaust valves in accordance with the ECM control signal calculated by the engine speed and load.

By controlling CVVT, the valve over-lap or under-lap occurs, which makes better fuel economy and reduces exhaust gases (NOx, HC). CVVT improves engine performance by reducing pump loss and internal EGR effect, improving combustion stability and volumetric efficiency, and increasing expansion work.

This system consists of:

–	the CVVT Oil Control Valve (OCV) which supplies the engine oil to the cam phaser or runs out the engine oil from the cam phaser in accordance with the ECM PWM (Pulse With Modulation) control signal,

–	the CVVT Oil Temperature Sensor (OTS) which measures the engine oil temperature,

–	and the Cam Phaser which varies the cam phase by using the hydraulic force of the engine oil.

The engine oil released from the CVVT oil control valve varies the cam phase in the direction (Intake Advance/Exhaust Retard) or in the opposite direction (Intake Retard/Exhaust Advance) of the engine rotation by rotating the rotor connected to the camshaft inside the cam phaser.

Operation Principle

The CVVT has the mechanism of rotating the rotor vane by hydraulic force generated by the engine oil supplied to the advance or retard chamber in accordance with 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
Driving Condition	Valve Timing	Effect	Valve Timing	Effect
(1) Low Speed /Low Load	Completely Advance	* Valve Under-lap * Improvement of combustion stability	Completely Retard	* Valve Under-lap * Improvement of combustion stability
(2) Part Load	Retard	* Increase of expansion work * Reduction of pumping loss * Reduction of HC	Retard	* Reduction of pumping loss
(3) Low Speed /High Load	Retard	* Increase of expansion work	Advance	* Prevention of intake back flow (Improvement of volumetric efficiency)
(4) High Speed /High Load	Advance	* Reduction of pumping loss	Retard	* Improvement of volumetric efficiency

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