Crank case ventilation system

An internal combustion engine having a crank case ventilation system, said ventilation system comprising an air inlet system for supplying the engine with air, an engine air charge pressure boosting system for boosting the pressure of said air supply, and a crank case evacuation system for drawing crank case gasses from a crank case and introducing said gasses into the air inlet system, wherein:

• a) the air charge boosting system has in series a first boost stage and a second boost stage, the first boost stage being upstream of the second boost stage;
• b) the crank case evacuation system includes a first conduit and a second conduit for introducing the crank case gasses into the air inlet system, the first conduit introducing said gasses upstream of the first boost stage, and the second conduit introducing said gasses downstream of the first boost stage and upstream of the second boost stage;
• and
• c) the crank case evacuation system includes flow control means for controlling the flow of crank case gasses in the first conduit and in the second conduit.

A method of ventilating a crank case of an internal combustion engine, the engine comprising a crank case, an air inlet system, an engine air charge pressure boosting system including a first boost stage and a second boost stage, and a crank case evacuation system linked to both the crank case and air inlet system, the crank case evacuation system including a flow control means, the method comprising the steps of:

• i) using the air inlet system to supply air to the engine;
• ii) boosting the pressure of said air supply using the first boost stage and the second boost stage;
• iii) using the crank case evacuation system to draw crank case gasses from the crank case and introduce said gasses into the air inlet system;
• and
• iv) using the flow control means to control the introduction of said gasses into the air inlet system at a plurality of locations in the air inlet system, including a first location upstream of the first boost stage, and a second location downstream of the first boost stage and upstream of the second boost stage.