Hyundai Elantra HD: CVVT (Continuously Variable Valve Timing) System. Description and Operation
Description
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.
Operation
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.
| 1. |
The above figure shows the relative operation structures of the
housing vane to the rotor vane.
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| 2. |
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
Note that a difference may exist in the position according to the engine
running state (rpm, oil temperature, and oil pressure).