Camshaft adjustment, function - GF07.61-P-4021MAS

ENGINE 156.984 in MODEL 216.377, 221.077 /177 as of Model Year 09 /AEJ 08

Function requirements of camshaft adjustment, general points

Circuit 87M ON (engine control ON)
Engine running

Camshaft adjustment, general points

The camshaft adjustment allows all four camshafts to be adjusted continuously by up to 42° CKA (Crank Angle). This means the valve overlap in the event of a load change 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 (N3/10) control unit reads the following sensors:

Oil temperature sensor (B1)
LH and RH hot film MAF sensor (B2/6, B2/7), engine load
LH and RH intake camshaft Hall sensors (B6/4, B6/5), intake camshaft positions
LH and RH exhaust camshaft Hall sensors (B6/6, B6/7), exhaust camshaft positions
Coolant temperature sensor (B11/4)
Crankshaft Hall sensor (B70), motor speed

Camshaft adjustment function sequence

The function sequence is described in the following steps:

Camshaft adjustment enable function sequence
Adjustment function sequence
Adjustment range function sequence
Start position function sequence
Valve overlap function sequence
Camshaft positions monitoring function sequence
Function sequence: diagnosis

Camshaft adjustment enable function sequence

The ME-SFI control unit enables camshaft adjustment according to vehicle speed, engine speed and engine oil temperature.

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.

If the oil pressure is inadequate, first of all adjustment of the exhaust camshafts is not guaranteed, as these must be adjusted when the engine speed is dropping (low oil pressure) opposite to the direction of rotation of the engine.

Release of the camshaft adjustment occurs for:

Vehicle speed >10 km/hour
Engine speed >1000 rpm (except during catalytic converter heating)
Engine oil temperature >-10 °C

Adjustment function sequence

The LH and RH intake camshaft solenoids (Y49/4, Y49/5) and the LH and RH exhaust camshaft solenoids (Y49/6, Y49/7) are actuated by the ME-SFI control unit with a PWM (pulse width modulated) signal.

The control plungers are adjusted via the performance map-dependent duty cycle. Depending on their positions, the oil quantities (pressure oil) are controlled for the swivel motor adjuster. In the swivel motor adjusters, the rotors, fixed to the camshafts, are therefore displaced by the pressure oil.

Adjustment range function sequence

Intake camshafts: 14° CKA before TDC (T op D ead Center) to 28° CKA after TDC

Exhaust camshafts:17° CKA before TDC tO ₂ 5° CKA after TDC

Start position function sequence

Intake camshafts:28° CKA after TDC

Exhaust camshafts:17° CKA before TDC

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.

Exploded view of camshaft adjustment (LH exhaust camshaft)

Fig 1: Identifying Left Exhaust Camshaft Housing, Switching Oil Pilot Bushing And Swivel Motor Adjuster

Courtesy of MERCEDES-BENZ USA

Exploded view of swivel motor adjuster

Fig 2: Identifying View Of Swivel Motor Adjuster

Courtesy of MERCEDES-BENZ USA

Valve overlap function sequence

At low engine speed and load, the ME-SFI 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 (NO _X ).

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

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

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

Camshaft positions monitoring function sequence

The camshafts positions are detected by the intake camshaft Hall sensors and exhaust camshaft Hall sensors, and communicated to the ME-SFI control unit. Detection 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 required adjustment has been reached after the engine has been running for a short time. Output stage errors (in the ME-SFI control unit) of the camshaft solenoids and camshaft Hall sensor faults are also detected.

Electrical function schematic, camshaft adjustment ME	Model 216	PE07.61-P-2773-97CAC
Electrical function schematic, camshaft adjustment ME	Model 221	PE07.61-P-2773-97SAC
ME-SFI [ME] control unit, component description	N3/10	GF07.61-P-6000MAS