In VANOS, the relative timing between inlet and exhaust valves is changed. At lower engine speeds, the position of the camshaft is shifted so that the valves are opened later, because this betters the idling quality and smooth power development. As the engine’s speed starts to increase, the valves are opened earlier: this increases the torque, reduces fuel consumption and lowers emissions and at high engine speeds, the valves are later opened again as this provides full power delivery. In 1992 VANOS was first introduced by BMW on its M50 engine and was used in 3 and 5 Series. The first – generation single VANOS system adjusted the timing of the intake camshaft in distinct steps (for example, the camshaft is advanced / retarded at certain engine speeds).
The purpose of BMW’s bi – VANOS technology was to adjust the beginning and end of the input and outlet camshaft opening period from advanced to retard and vice – versa. Unlike the technically less complicated systems with only two shift positions, this system adjusted the camshafts infinitely and fully automatically throughout the entire speed range. This fully variable adjustment ensured that valve timings are always set properly to both engine speed and engine load. The first double VANOS system was introduced on the S50B32 engine in 1996. The second – generation double VANOS system adjusted the timing of the input and exhaust camshafts with continuous variable adjustment which is based on engine speed and throttle opening.