Crankcase Ventilation System

Crankcase Ventilation System

General

During combustion, every engine blows some of the combustion gases past the pistons towards the crankcase - these gases are called blow-by gases. If these gases are not removed, the pressure in the crankcase would increase considerably. A vent connection is fitted in the crankcase for this reason. For environmental protection reasons, these gases are not released into the atmosphere but are returned to the engine for combustion via the intake system.

These crankcase ventilation gases naturally contain a high proportion of engine oil and other combustion residues as well as a high level of fuel residues in some cases. If these gases enter the intake duct, they will contaminate the intake air and can then impair running smoothness and exhaust emissions and also reduce knock resistance. These reasons show why effective oil separation is important for the engine.

Crankcase ventilation system for the naturally aspirated engine

The two pre-separators C, which are integrated in the cylinder head cover, allow most of the transported oil to be drawn off into the crankcase. The remaining blow-by gases are routed to the fine separator via hoses.







Fine oil separator

A valve (5) is installed below the oil reservoir (4) which either allows or prevents the reservoir from being emptied depending on the vacuum.

Since the valve is open only when a vacuum is present, the reservoir size is chosen so that it has sufficient capacity to store a corresponding volume until the vehicle has to be refuelled even if the vehicle is operated only at full throttle so that the reservoir is never emptied.







Internal design of the oil separator







Separation of small quantities of blow-by gases

If there is only a small amount of blow-by gases, these enter the cyclone, where air is separated from oil. The oil then passes into the reservoir, while the air is routed out of the tank and fed back to the engine by the intake system.







Separation of larger quantities of blow-by gases

If the blow-by gases increase as a result of higher engine speeds, for example, the two pressure control valves open and an additional bypass is opened in order to separate the oil. The air is again fed to the engine and the oil goes into the reservoir. The oil reservoir is always drained whenever there is a vacuum in the system, i.e. permanently, except for at full throttle.