Vanos Mechanical Operation

VANOS MECHANICAL OPERATION




With the engine switched off the 100 bar pressure is drained from the VANOS hydraulic unit The default position for the camshafts with no pressure applied is - Intake cam in retard position/exhaust cam in advance position. The hydraulic operation of the VANOS system is as follows:
- When the engine starts, oil from the main engine oil pump is fed under pressure (5 Bar) to the pressure reducing valves.
- The oil pressure is dropped to approximately .5 Bar and fed to the high pressure radial pump.
- The pump is driven by the intake camshaft and the 100 bar pressure is built up in the accumulator and fed to the front side of both adjustment pistons. Both pistons are held in the default position by the high pressure oil.
- At the same time the high pressure oil is available at the intake solenoids of both adjustment pistons.
- VANOS adjustment is carried out by pulsing the intake and exhaust solenoids to allow pressurized oil to the back side of the adjustment pistons. The surface area on this side of the piston is larger so that the oil pressure is greater and the adjustment piston will move causing the valve timing to change.
- The piston is connected to the adjustment shaft. As the piston moves, the shaft turns on the helical splines causing the camshaft gears to turn.




When hydraulic pressure is applied to the front side of the vanos piston, the piston moves outward causing the splined shaft to move. The helical cut splines rotate inside the camshaft gear causing the timing to be advanced/retarded.

VANOS ELECTRICAL OPERATION

The MS S52 (ECM) control module regulates the operation of the VANOS solenoids based on the programmed maps for valve timing adjustment. The crankshaft position sensor serves as a reference signal for all camshafts. The camshaft position sensor inputs serve as feedback signals for the current position of the camshafts.

The ideal camshaft positions for any given engine operating condition are stored in several characteristic maps in the engine control module (idle, warm up, etc.). The main parameters for camshaft positioning are engine speed and load. Additional factors, such as engine operating temperature are taken into account when selecting an adjustment map.

Complete electrical operation of the VANOS control will be covered in the MS S52 section of this program.