What is the principle of BMW variable valve lift?

BMW's variable valve lift system mainly changes the valve lift by adding an eccentric shaft, a servo motor and an intermediate push rod to its valve mechanism. When the motor works, the worm gear and worm mechanism will drive the eccentric shaft to rotate, and then push the valve through the middle push rod and rocker arm. When the eccentric wheel rotates at different angles, the camshaft pushes the valve to generate different lifts through the middle push rod and rocker arm, thus controlling the valve lift. The following information is relevant:

Requirements of variable valve lift system at low speed;

At different engine speeds, the demand for valve stroke varies greatly. Because the intake air volume is small, if the valve stroke is large, it will not produce enough intake negative pressure. After fuel injection, the fuel injector cannot fully mix with the inhaled air, resulting in low combustion efficiency, greatly reduced low-speed torque and increased emissions.

Rolling friction:

The contact surface between the pressure rod and the middle push rod of the roller valve is an inclined platform, and the rolling friction at the inclined platform can reduce the mechanical loss. The pressure rod and the push rod are divided into different grades, and the components of the same grade are always installed on the same cylinder.

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