GF07.61-P-4021MAS Camshaft Adjustment, Function

GF07.61-P-4021MAS Camshaft Adjustment, Function
- as of model year 09

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 ( Top Dead Center) to 28° CKA after TDC
Exhaust camshafts: 17° CKA before TDC to 25° 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.

Component Identification:

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 (NOx).
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.