Continuous Variable
Valve Timing (CVVT) system advances or retards the valve timing of the
intake and exhaust valve in accordance with the ECM control signal which
is 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) and improves engine performance
through reduction of pumping loss, internal EGR effect, improvement of
combustion stability, improvement of volumetric efficiency, and increase
of expansion work.
This system consist
of
-
|
the CVVT Oil Control Valve (OCV) which
rgulates engine oil to and from the cam phaser in accordance with
the ECM PWM (Pulse With Modulation) control
signal, |
-
|
and the Cam Phaser which varies the cam
phase by using the hydraulic force of the engine
oil. |
The engine oil getting
out of the CVVT oil control valve varies the cam phase in the direction
(Intake Advance/Exhaust Retard) or opposite direction (Intake
Retard/Exhaust Advance) of the engine rotation by rotating the rotor
connected with the camshaft inside the cam phaser.

The CVVT has the
mechanism rotating the rotor vane with hydraulic force generated by the
engine oil supplied to the advance or retard chamber in accordance with
the CVVT oil control valve control.


(1) Low Speed / Low
Load
|
(2) Part
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
|
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
|