07-04-2009, 09:37 PM
The Valvetronic system is the first variable valve timing system to offer continuously variable timing (on both intake and exhaust camshafts) along with continuously variable intake valve lift, from ~0 to 10 mm, on the intake camshaft only. Valvetronic-equipped engines are unique in that they rely on the amount of valve lift to throttle the engine rather than a butterfly valve in the intake tract. In other words, in normal driving, the 'gas pedal' controls the Valvetronic hardware rather than the throttle plate
First introduced by BMW on the 316ti compact in 2001, Valvetronic has since been added to many of BMW's engines. The Valvetronic system is coupled with BMW's proven double-VANOS, to further enhance both power and efficiency across the engine speed range. Valvetronic will not be coupled to BMW's N53 and N54, 'High Precision Injection' (gasoline direct injection) technology due to lack of room in the cylinder head.
Cylinder heads with Valvetronic use an extra set of rocker arms, called intermediate arms (lift scaler), positioned between the valve stem and the camshaft. These intermediate arms are able to pivot on a central point, by means of an extra, electronicly actuated camshaft. This movement alone, without any movement of the intake camshaft, can open or close the intake valves.
Because the intake valves now have the ability to move from fully closed to fully open positions, and everywhere in between, the primary means of engine load control is transferred from the throttle plate to the intake valvetrain. By eliminating the throttle plate's 'bottleneck' in the intake track, pumping losses are reduced, fuel economy and responsiveness are improved.
