Variable Valve Timing Actuator: Description and Operation

VANOS Diagram:

PURPOSE
The Variable Camshaft Control (VANOS) actuator advances or retards camshaft timing.

VANOS "Retarded Cam Timing":

OPERATION
In the normal or "Off" position, the spool valve is held by spring pressure directing the engine oil to the back side of the two position piston. This pulls the attached helical gear cup forward and maintains a late valve timing position.

VANOS "Advanced Cam Timing":

When the Digital Motor Electronic (DME) control unit applies a ground to the solenoid, the spool valve pushes against the spring pressure diverting the oil pressure to the front side of the piston. This pushes the helical gear cup further into the matched helical camshaft/secondary gear drive.

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 camshaft and causes the camshaft to "advance" 12.5°.



Control unit is activated by relevant engine control unit. The control unit operates a regulating element via a solenoid. In this manner, engine-oil pressure is supplied to both sides of a hydraulic plunger.

Hydraulic plunger is held in one of both possible positions by way of mechanical stops and applied engine-oil pressure. A rotating splined shaft gear is integrated in hydraulic plunger. This splined-shaft gear uses its helical-bevel splines to convert plunger stroke into rotation of camshaft - relative to driven chain sprocket.

Hydraulic plungers with splined-shaft gear are located in a pressure cast aluminum housing on face end of cylinder head, coaxial to intake shaft.

Nominal positions of intake camshaft (advanced or retarded) are different for M50 B20 and M50 B25 engines. Adjustment of camshaft is activated by relevant engine control unit depending on engine load, engine speed and coolant temperature.

The 4/2-way operating valve is designed in such a manner that when one pressure chamber is pressurized, the other is without pressure (feedback) As soon as operating valve solenoid receives current, it moves control piston against spring force into advanced position via an armature. A coil spring returns the unit to retard position. This means that, if the armature is defective or the control unit fails, the camshaft will be retarded automatically.

In this manner it is still possible to start engine even when control unit fails. It would not be possible to start engine with camshaft adjusted in advanced timing direction.

Control edges of valve are designed in such a manner that emergency operation properties of engine are guaranteed even when control piston would seize in an undefined intermediate position.