This is copied from AllData, a popular web based technician reference for all cars:
CONTINUOUS VARIABLE VALVE TIMING
The CVVT (Continuously Variable Valve Timing) which is installed on the exhaust camshaft controls intake valve open and close timing in order to improve engine performance.
The intake valve timing is optimized by CVVT system depending on engine rpm.
This CVVT system improves fuel efficiency and reduces NOx emissions at all levels of engine speed, vehicle speed, and engine load by EGR effect because of valve over-lap optimization.
The CVVT changes the phase of the intake camshaft via oil pressure.
It changes the intake valve timing continuously.
- The CVVT system makes continuous intake valve timing changes based on operating conditions.
- Intake valve timing is optimized to allow the engine to produce maximum power.
- Cam angle is advanced to obtain the EGR effect and reduce pumping loss. The intake valve is closed quickly to reduce the entry of the air/fuel mixture into the intake port and improve the changing effect.
- Reduces the cam advance at idle, stabilizes combustion, and reduces engine speed.
- If a malfunction occurs, the CVVT system control is disabled and the valve timing is fixed at the fully retarded position.
The above figure shows the relative operation structures of the housing vane to the rotor vane.
If the CVVT is held a certain control angle, to hold this state, oil is replenished as much as oil leaks from the oil pump. The OCV (Oil-flow Control Valve) spool location at this time is as follows. Oil pump Advance oil chamber (Little by little open the inflow side to the advance oil chamber) -> Almost close the drain side Be sure there might be a difference in the position according to the engine running state (rpm, oil temperature, and oil pressure)
I know the pictures are big but there is nothing really i can do about that because of the small lettering, sorry.