VANOS stands for variable camshaft control (German: Variable Nockenwellen Steuerung), and is a trademark of BMW AG. It represents a device for influencing the valve timing of the engine by controlling the camshaft. This regulation of the valve opening times allows an increase in the efficiency of the engine, depending on the respective load behavior, which can be used to increase performance and torque and to save fuel. In camshaft drives without such an adjustment, the rotational movement of the crankshaft is transmitted in a certain ratio to the camshaft via a geometrically fixed connection.
The VANOS unit was introduced by BMW in the early 1990s, and is located between the camshaft and the drive gear. While in a conventional valve train, the relative angular position of the camshaft to the crankshaft is always constant, regardless of the engine load, the VANOS makes it possible to set the position of the camshaft in relation to the drive gear, depending on engine speed, load and engine oil temperature. Thereby the relative timing between inlet and exhaust valves is changed.
The first generation: Single VANOS
In a single VANOS, only the intake camshaft is adjusted, which serves primarily to set the inlet closing of the valves, which can optimize torque and performance. Depending on the cam contour, the maximum torque or maximum power can be positively influenced. A back flow of the gases from the combustion chamber into the intake passage can be avoided by the speed adjustment of the closing timing of the intake valve.
The adjustment of the intake camshaft is used in the lower speed range for internal exhaust gas recirculation and increasing the torque. At higher speeds, the aim of the adjustment is an improved power output.
The second generation: Double VANOS
With a Double VANOS, both the intake and exhaust camshafts are adjusted. The variable displacement mainly controls the amount of residual gas. This allows an improved fuel consumption, because with increasing residual gas content, the engine throttling and the charge exchange losses decrease. In addition, the process temperature drops, which leads to lower nitrogen oxide formation.
Another advantage of the VANOS on the exhaust side is the possibility to improve the exhaust dynamics in the lower speed range and thus to increase the torque. The adjustment of the exhaust camshaft thus serves the optimum idling quality or to achieve maximum exhaust gas recirculation rates.
Similar systems are also used by other car manufacturers, such as:
- Ti-VCT – Ford
- VarioCam – Porsche
- Neo VVL – Nissan
Some early VANOS systems are prone to problems with the inner seal rings on high mileage engines. In this case, the factory-installed O-rings made of nitrile rubber are affected because they tend to wear, which leads to problems in the adjustment of the camshaft. A repair is not complicated, but time consuming.