Camshaft Adjustment, Function - GF07.10-S-1016TRC

Engine 274 in model 447, 448 

except code XM0 (Facelift) 

Function requirements for camshaft adjustment, general points 

• Circuit 87M ON (Engine management ON)
• Engine runs

Camshaft adjustment, general points 

With camshaft adjustment all four camshafts can be adjusted continuously by up to a 40°CKA (Crank Angle). 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.

Valve overlap

The intake valves open before the exhaust valves close.

For camshaft adjustment, the ME-SFI [ME] control unit (N3/34) reads in the following signals over direct line:

• Intake camshaft Hall sensor (B6/29)
• Exhaust camshaft Hall sensor (B6/30)
• Coolant temperature sensor (B11/21)
• Intake manifold pressure sensor (B28/24)
• Crankshaft Hall sensor (B70/2)

Function sequence for camshaft adjustment 

The function sequence is described in the following steps:

• Function sequence for release of the camshaft adjustment 
• Function sequence for oil pressure 
• Function sequence for camshaft adjustment 
• Function sequence for adjustment range 
• Function sequence for start position 
• Function sequence for valve overlap 
• Function sequence for camshaft positions monitoring 
• Function sequence: diagnosis 

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.

The temperature and therefore the viscosity of the engine oil is important in order to provide sufficient oil pressure (>1.5 bar) for adjusting the camshaft, also for hot engine oil.

Enable of adjustment of the exhaust camshaft relative to the intake camshaft only a higher rotational speed compared to. In this way it is ensured that the locking position is reached against the "retarded" reaction torques of the exhaust camshaft, even at a low oil pressure level. A return spring (1/3) is located in each camshaft positioner (2) for support.

If both camshafts are adjusted, adjustment of the exhaust camshaft 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:

• For an 80°C engine oil temperature from about 600 rpm
• For a 120°C engine oil temperature (inlet side) from about 800 rpm
• For a 120°C engine oil temperature (exhaust side) from about 1050 rpm

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 camshaft 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 position of the control plunger (1/2) and therefore the oil filling capacities for the camshaft positioner (2) are controlled over the characteristics dependent duty cycle.

In the camshaft positioners (2) the vane-cell piston (2/4) which is firmly connected to the camshaft is turned by the oil pressure.

Function sequence for adjustment range 

• Intake camshaft: (3): 4°CKA BTDC (top dead center) up to a 36°CKA after TDC (intake open)
• Exhaust camshaft: 25°CKA BTDC up to 15°CKA after TDC (exhaust closes)

Function sequence for start position 

• Intake camshaft: (3): a 36°CKA ATDC (intake opens)
• Exhaust camshaft: 25°CKA BTDC (exhaust closes)
• The camshafts are locked by the catch bolt (2/1) in a fixed position for the start. This start position is unlocked for the first adjustment request hydraulically.

Oil flows in the camshaft positioner (2) of intake camshaft (3) 

Courtesy 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 oxide (NO_X ).

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 is adjusted to the maximum before TDC (advanced) and the intake camshaft (3) to the maximum after TDC (retarded). 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 through the position of the pulse wheel and monitored by the ME-SFI [ME] control unit.

Adjusting the intake camshaft (3) 

Courtesy of MERCEDES-BENZ USA

Remove camshaft positioner (2) for intake camshaft (3) 

Courtesy of MERCEDES-BENZ USA

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.

	Electrical function schematic for camshaft adjustment	Engine 274 in model 448 except code XM0 (Facelift)	PE07.10-S-2716-97VDC
		Engine 274 in model 447 except code XM0 (Facelift)	PE07.10-S-2716-97TRC
	Overview of system components for gasoline injection and ignition system with direct injection		GF07.70-S-9998TRC