Positive Crankcase Ventilation: Description and Operation

Positive Crankcase Ventilation







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 were not removed, the pressure in the crankcase would increase considerably. A vent connection is installed 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 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. It is obvious for these reasons why effective oil separation is important for the engine.

The crankcase ventilation has been completely redesigned. Apart from the prevention of excess pressures, positive ventilation of the crankcase has been implemented. The aim of ventilation is to flush the crankcase with fresh air. This is done by taking air from the pressure pipe upstream of the throttle valve and feeding it through a separate restrictor and line straight into the crankcase.

As boost pressure builds in the pressure pipe and connecting line, the crankcase is positively ventilated and flushed with fresh air.

The advantage of positive crankcase ventilation is a reduction in the penetration of fuel and water into the oil. Under certain operating conditions (in particular during a cold start and when at full throttle), molecules of fuel and water are deposited on the cylinder wall. These can make their way past the piston rings into the crankcase. Any mixing of these elements with the oil impairs the lubricating properties of the oil.