Principle of variable intake system

Principle of variable intake system

◆ When the engine speed is low, the intake flow rate is relatively low, which is not conducive to ensuring the best gas distribution at low speed. If the length of the intake pipe can be shortened, the intake velocity can be increased, thereby controlling the intake flow rate within a reasonable range.

The specific method is to close or open some valves in the intake duct, so that the airflow can take a shortcut or go around far to achieve the purpose of changing the length of the intake pipe.

◆ For example, when the engine is running at a low speed of 2000r/min, the black control valve is closed, and the airflow is forced to flow into the cylinder from the long manifold. At this time, the natural frequency of the intake manifold is reduced to adapt to the low speed airflow. When the engine speed rises to a certain level, such as 5000r/min, the control valve is opened at this time, and the airflow bypasses the lower conduit and directly injects into the cylinder, which is more conducive to high-speed air intake.

◆ The V12 engine assembled by BMW uses another design with continuously variable intake pipe length. It designs a rotor in the middle of the intake mechanism to control the length of the intake manifold. Through the change of the rotor angle, the length of the intake air flow entering the cylinder is continuously variable. This can better meet the intake efficiency requirements at various speeds, and improve power output and fuel economy.