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Camshaft adjustment, function - GF07.10-P-1016MMY

ENGINE 157.9, 278.9 in MODEL 166 as of model year 2016 

ENGINE 157.9, 278.9 in MODEL 292 

Function requirements for camshaft adjustment, general points 

Camshaft adjustment, general points 

With camshaft adjustment all four camshafts can be adjusted continuous for up to 40° CKA (CrankAngle). 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 sensors for 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 [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 (with engine 278).

With engine 157, the engine oil temperature is recorded by the oil sensor (oil level, temperature and quality) (B40).

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.

Release of adjustment of the exhaust camshafts takes place by means of a comparison to the intake camshafts, at first at a high rotational speed. 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 four camshafts are adjusted, adjustment of the exhaust camshafts takes place after a delay (later). 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 (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 left and right intake camshaft solenoids (Y49/4, Y49/5) and the left and right exhaust camshaft solenoids (Y49/6, Y49/7) are 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 quantities (hydraulic fluid) for the camshaft positioners are controlled according to their position. The vane plungers which are firmly connected to the camshafts are thus turned by the hydraulic fluid 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 camshaft and exhaust camshaft solenoids.

The upper half of the illustration shows: 

Filling of oil reservoir galleries (A), oil reservoir galleries (B) open.

The lower half the illustration shows: 

Filling of oil reservoir galleries (B), oil reservoir galleries (A) open.

Shown is oil flows in the intake camshaft positioner 

Fig 1: Camshaft Adjustment Function Diagram
G10076401Courtesy of MERCEDES-BENZ USA

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.

The smallest valve overlap for gas exchange occurs if the exhaust camshaft are adjusted to the maximum BTDC (advanced) and the intake camshaft to the maximum ATDC (retarded).

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

Function sequence for camshaft positions monitoring 

The camshafts positions are detected by the intake camshaft Hall sensors and the exhaust camshaft Hall sensors, 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 [ME] 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 on intake camshaft adjustment 

Fig 2: Identifying Intake Camshaft Adjustment Components
G10076402Courtesy of MERCEDES-BENZ USA

Shown: intake camshaft positioner 

Fig 3: Identifying Intake Camshaft Positioner Adjustment Components
G10076403Courtesy of MERCEDES-BENZ USA
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