Audi have quite a nice setup for the high-revving RS4 motor (BNS).
Quote:
Function of fine oil separator
Blow-by gas volume is dependent on engine load and RPM. The fine oil ("oil spray") is separated by means of a cyclone separator. Cyclone separators only have a high separation efficiency over a small volumetric range. For this reason, one, two or three
cyclones of the fine oil separator operate in parallel depending on the gas flow rate.
The cyclones are released by the control piston. The displacement of the control piston against its spring force is dependent on the gas flow rate. Piston ring flutter at very high engine RPM and low engine load can result in a very high gas flow rate.
The crankcase internal pressure is set by the two stage pressure control valve.
The bypass valve together with the control piston ensures that the cyclones operate at the optimum operating point (if the volumetric flow rate is too high or too low, this will impair the functioning of the cyclones).
When the bypass valve opens, a fraction of the blow-by gas flows to the engine untreated, but the remainder is optimally treated by the cyclones.
The separated oil is collected in an oil reservoir beneath the cyclones. The oil cannot drain out of the reservoir until the oil drain valve is opened.
The oil drain valve is closed as long as the pressure in the crankcase, i.e. below the valves, is higher than in the oil separator. The valve opens automatically due to gravity only at very low engine RPM or when the engine is at a standstill, because the
pressure conditions above and below the valve are in equilibrium.
The crankcase ventilation system also includes the crankcase breather. Air is extracted downstream of the air filter and flows through a non-return valve into the crankcase from above.
The non-return valve is located at the end of the vent line and is bolted between the two cylinder banks in the engine block.
A damping chamber is located below the non-return valve in the engine block. This prevents non-return valve flutter and eliminates noise.
A restrictor bore connects this chamber to the inner chamber of the crankcase. It has the task of supplying only a defined volume of fresh air to the crankcase.
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