Positive Crankcase Ventilation
Blow-by gas in the crank case is returned to the intake manifold to improve ventilation efficiency. This allows the intervals of engine oil change to be extended. When the engine is in the low-middle load condition as shown in the figure
, the blow-by gas goes to the intake manifold via the PCV valve.
In the general driving conditions, the capacity of the PCV valve is sufficient for treating the blow-by gas and a little amount of the fresh air. The fresh air enters to the rocker cover from the air duct via a hose, and is guided to the crankcase. When the engine is in the high load condition as shown in the figure
, blow-by gas flows backward in the blow-by hose and gets sucked into air duct.