VANOS Control

With the introduction of double VANOS, the valve timing is changed on both the intake and the exhaust camshafts.

Double VANOS provides the following benefits:

Torque increase in the low to mid (1500 - 2000 RPM) range without power loss in the upper RPM range.
Less incomplete combustion when idling due to less camshaft overlap (also improves idle speed characteristics).
Internal exhaust gas recirculation (EGR) in the part load range (reduces NOx and post-combustion of residual gasses in the exhaust)
Rapid catalyst warm up and lower "raw" emissions after cold start.
Reduction in fuel consumption

Double VANOS consists of the following parts:

Intake and exhaust camshafts with helical gear insert
Sprockets with adjustable gears
VANOS actuators for each camshaft
2 three-way solenoid switching valves
2 impulse wheels for detecting camshaft position
2 camshaft position sensors (Hall effect)

The "initial" timing is set by gear positioning (refer to the appropriate REPAIR INSTRUCTIONS article for details) and the chain tensioner. As with the previous VANOS, the hydraulically controlled actuators move the helical geared cups to regulate camshaft timing. The angled teeth of the helical gears cause the pushing movement of the helical cup to be converted into a rotational movement. This rotational movement is added to the turning of the camshafts and cause the camshafts to "advance" or "retard". The adjustment rate is dependent oil temperature, oil pressure, and engine RPM.

NOTE: With extremely hot oil temperatures VANOS is deactivated (Powerloss). If the oil is too thick (wrong viscosity) a fault could be set.

When the engine is started, the camshafts are in the "fail-safe" position (deactivated). The intake camshaft is in the RETARDED position - held by oil pressure from the sprung open solenoid. The exhaust camshaft is in the ADVANCED position - held by a preload spring in the actuator and oil pressure from the sprung open solenoid.

After 50 RPM (2-5 seconds) from engine start, the ECM is monitoring the exact camshaft position.

The ECM positions the camshafts based on engine RPM and the throttle position signal. From that point the camshaft timing will be varied based on intake air and coolant temperatures.

The double VANOS system is "fully variable". When the ECM detects the camshafts are in the optimum positions, the solenoids are modulated (approximately 100-220 Hz) maintaining oil pressure on both sides of the actuators to hold the camshaft timing.

CAUTION: The VANOS MUST be removed and installed exactly as described in the Repair Instructions!

NOTE: If the VANOS camshaft system goes to the fail-safe mode (deactivated) there will be a noticeable loss of power. This will be like driving with retarded ignition or starting from a stop in third gear.

Fig 1: Identifying VANOS System Components

Courtesy of BMW OF NORTH AMERICA, INC.

Fig 2: Identifying VANOS In Deactivated & Activated Modes

Courtesy of BMW OF NORTH AMERICA, INC.

The dual VANOS in conjunction with the variable intake manifold provides an additional emission control feature.

Because of the improved combustion, the camshaft timing is adjusted for more overlap.

The increased overlap supports internal exhaust gas recirculation (EGR) which reduces tailpipe emissions and lowers fuel consumption.

During the part load engine range, the intake camshaft overlap opens the intake valve. This allows limited exhaust gas reflow the intake manifold.

The "internal" EGR reduces the cylinder temperature thus lowering NOx. This feature provides EGR without the external hardware as seen on previous systems.

Fig 3: Identifying Airflow Through Cylinder Head With VANOS

Courtesy of BMW OF NORTH AMERICA, INC.