Valvetronic

Valvetronic is BMW's variable valve lift system. It continuously varies how far the intake valves open, letting the engine control airflow at the valves themselves instead of through a conventional throttle butterfly. This reduces pumping losses and improves fuel efficiency, throttle response, and emissions.

First introduced in 2001 on the N42 four-cylinder engine, Valvetronic uses an eccentric shaft, an intermediate lever, and a DME-controlled electric motor to adjust intake valve lift across a wide range. It works alongside VANOS, BMW's variable valve timing system: Valvetronic controls how far the intake valves open (lift), while VANOS controls when they open and close (timing). Together they give the DME continuous control over intake valve behavior across the engine's operating range.

Valvetronic has gone through three generations since its introduction. The first generation debuted on the N42 (inline-4), N62 (V8), and N73 (V12) engines. It used a contact pad on the intermediate lever where it met the eccentric shaft, with a minimum valve lift of 0.3 mm. This contact pad was prone to uneven wear over time, which could cause rough idle and misfires. The second generation arrived in 2004 with the N52 inline-6. Its key improvement was replacing the contact pad with a roller on the intermediate lever, which significantly reduced wear. It also lowered the minimum valve lift to 0.18 mm, improving idle quality and reducing emissions further. The third generation launched around 2010 with the N55 inline-6 and N20 inline-4. It introduced a brushless actuator motor compact enough to fit inside the valve cover, with an integrated eccentric shaft position sensor rather than a separate external sensor. This generation carries through to current BMW gasoline engines including the B48 (inline-4) and B58 (inline-6).

The system works on the "lost motion" principle. Rather than acting directly on the valve, the intake camshaft pushes against an intermediate lever that rides on the eccentric shaft. The DME rotates that eccentric shaft through roughly 225 degrees using an electric motor and worm gear, which pivots the intermediate lever toward or away from the camshaft. Pivoting it closer transfers more of the cam lobe's profile to the follower and increases valve lift; pivoting it away transfers less and reduces lift. Because the DME adjusts the eccentric shaft position continuously, valve lift can be set anywhere between minimum and maximum in under 300 milliseconds.

Although BMW describes Valvetronic as enabling "throttle-free load control," all Valvetronic-equipped engines retain a conventional throttle body. During normal operation the throttle is held wide open or close to it, with the DME controlling engine load through valve lift rather than the throttle plate. The DME still modulates the throttle slightly, most noticeably at idle, to maintain a small amount of intake manifold vacuum for the crankcase ventilation and EVAP systems. If the Valvetronic system faults, the DME disables it and reverts to conventional throttle control as a fail-safe, so the engine continues to run, though with reduced efficiency. Because intake pressure stays close to atmospheric under Valvetronic operation, these engines also rely on a separate vacuum pump for brake assist.