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Camshaft Adjustment, Function - GF07.10-D-1016TSB

Engine 274 in model 907 

Block diagram 

G13786511

Function requirements for camshaft adjustment, general points 

Camshaft adjustment, general points 

With the camshaft adjustment, the intake and exhaust camshafts can be adjusted up to 40° CKA (crank angle) towards "advance" or 40° CKA towards "retard". This means the valve overlap in the event of a gas exchange can be varied within wide limits.

In this way the engine torque curve is optimized, the fuel consumption reduced and the exhaust characteristics improved.

IMPORTANT Valve overlap:

The intake valves open before the exhaust valves close.

The ME-SFI [ME] control unit (N3/36) reads in the signals of the following sensors for the camshaft adjustment:

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 control unit dependent on engine speed and engine oil temperature.

The ME-SFI [ME] control unit determines the engine oil temperature based on different operating data (e. g. coolant temperature, time, engine load) and a saved temperature model.

IMPORTANT The engine oil temperature is important, even when the oil is hot, to ensure that there is sufficient oil pressure (> 1.5 bar) for adjusting the camshafts.

Enable of adjustment of the exhaust camshaft does not occur until a higher rotational speed compared to the intake camshaft. In this way for exhaust, also at a low oil pressure level, reaching the locking position against the "retard" operating reaction torques of the camshaft are secured.

There is a return spring located for support in each camshaft positioner.

If all camshafts are adjusted, the adjustment of the exhaust camshaft is retarded. Oil supply problems are prevented and secure functioning of the locking mechanism achieved.

Release of the camshaft adjustment occurs load-dependent:

Function sequence for oil pressure 

The engine oil pressure is regulated via the engine oil pump valve (Y138) 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 intake camshaft solenoid (Y49/10) and the exhaust camshaft solenoid (Y49/11) are actuated by the ME-SFI [ME] control unit using a pulse width modulated signal (PWM signal). The control plungers are adjusted via the characteristics map-dependent duty cycle. The oil flows for the camshaft positioner are controlled according to its position. The vane pistons which are firmly connected to the camshafts are thus turned by the engine oil in the camshaft positioners.

Function sequence for adjustment range 

Function sequence for start position 

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

Shown is oil flows in the intake camshaft camshaft positioner 

G13786512

The upper half of the illustration shows: 

Filling of fluid reservoirs for retarding the ignition timing (A), fluid reservoirs for timing advance (B) open.

The lower half of the illustration shows: 

Filling of fluid reservoirs for timing advance (B), fluid reservoirs for retarding the ignition timing (A) open.

Function sequence for valve overlap 

At low engine speed and load, the ME-SFI 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 control unit shortens the injection period accordingly.

The smallest valve overlap during gas exchange arises if the exhaust camshaft is adjusted to the maximum BTDC ("advance") and the intake camshaft is adjusted to the maximum ATDC ("retard").

The resulting increased fresh air content produces more engine torque and engine power.

Function sequence for camshaft positions monitoring 

The camshaft positions are detected by the intake camshaft Hall sensor and the exhaust camshaft Hall sensor and communicated 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 front on the camshafts.

Function sequence: diagnosis 

During diagnosis of the camshaft adjustment, the ME-SFI control unit checks whether the camshafts are in start position at engine start and whether the requested adjustment has been reached after the engine has been running for a short time. Output stage errors in the camshaft solenoids (integrated with the ME-SFI [ME] control unit) and defective camshaft Hall sensors are also detected.

Shown is the intake camshaft adjustment 

G13786513

Shown: intake camshaft camshaft positioner 

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Electrical function schematic for camshaft adjustment PE07.10-D-2716-97TSA
Overview of system components for gasoline injection and ignition system with direct injection GF07.70-D-9998TSB 
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