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Camshaft Adjustment, Function - GF07.10-P-1016KJ

ENGINE 281.910 in MODEL 453.0/3/4 

Function requirements for camshaft adjustment, general points 

Camshaft adjustment, general points 

The intake camshaft can be adjusted continuously with the camshaft adjustment to "advanced" and "retarded". This means the valve overlap in the event of a gas exchange can be varied within wide limits.

This optimizes engine torque characteristics and improves the exhaust characteristics.

IMPORTANT Valve overlap

The intake valves open before the exhaust valves close.

The ME-SFI [ME] control unit (N3/10) reads in the following signals regarding the camshaft setting:

Function sequence for camshaft adjustment 

The function sequence is described in the following steps:

Function sequence for release of the camshaft adjustment 

Camshaft adjustment is enabled by the ME-SFI [ME] control unit dependent on engine speed and engine oil temperature.

The engine oil temperature is determined by the ME-SFI [ME] control unit using various operating data (e.g. coolant temperature, time, engine load) and a stored temperature model determined.

IMPORTANT The engine oil temperature is important, even when the oil is hot, to ensure that there is sufficient oil pressure for adjusting the intake camshaft.

Function sequence for oil pressure 

The engine oil pressure is regulated via the engine oil pump valve (Y130) in order to ensure an adequate oil supply and to lower the oil pressure if necessary (a saving on fuel).

Function sequence for adjustment 

The variable camshaft adjustment valve (Y49/10) is actuated by the ME-SFI [ME] control unit by means of a pulse width modulated signal.

The control plungers are adjusted via the characteristics map-dependent duty cycle. The oil filling capacity (hydraulic fluid) for the camshaft positioner is controlled according to its position.

In this way the vane plungers in the camshaft positioner which is firmly connected to the intake camshaft are turned by the hydraulic fluid.

Function sequence for start position 

The intake camshafts are locked in a fixed position for starting by catch bolts (locked). This start position is unlocked hydraulically at first actuation of the variable camshaft adjustment valve.

Function sequence for valve overlap 

At low engine speed and load, the ME-SFI [ME] control unit sets a large valve overlap in order to produce internal exhaust gas recirculation. Less fresh air is admitted, as exhaust gases with low oxygen content are still present in the cylinders. This lowers the combustion temperature and reduces the formation of nitrogen oxides (NOx).

The intake air mass is reduced by the amount of exhaust gases present. The ME-SFI [ME] control unit shortens the injection period accordingly.

Function sequence for monitoring the camshaft position 

The position of the intake camshaft is detected by the intake camshaft Hall sensor and sent to the ME-SFI [ME] control unit. Acquisition of the positions takes place through detection of the positions of pulse wheels which are located at the rear on the intake camshaft.

Function sequence: diagnosis 

During diagnosis of the camshaft adjustment, the ME-SFI [ME] control unit checks whether the intake camshaft is in start position at engine start and whether the requested adjustment has been reached after the engine has been running for a short time. Furthermore an end stage fault of the variable camshaft adjustment valve and a defect in the intake camshaft Hall sensor is detected in the ME-SFI [ME] control unit.

  Electrical function schematic for camshaft adjustment   PE07.10-P-2716-97BBA 
  Overview of system components motor electronics (ME-SFI) fuel injection and ignition system   GF07.61-P-9997KJ 
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