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

GF07.61-P-4021MIG 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 40° 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:
- Hot film MAF sensor (B2/5), 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), engine 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
^ Diagnosis function sequence

Camshaft adjustment enable function sequence
Camshaft adjustment is enabled by the ME-SFI [ME] control unit depending 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.

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.
A return spring is located in each exhaust-side vane-type adjuster for support.

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 dependent on load:
- 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

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 [ME] control unit with a PWM (pulse width modulated) signal.
The control plungers are adjusted via the performance map- dependent duty cycle. The oil quantities (pressure oil) for the vane- cell adjusters are controlled according to their position. The vane plungers in the vane-cell adjusters which are firmly connected to the camshafts are turned by the pressure oil.

Adjustment range function sequence
Intake camshafts: 4° CKA before TDC ( Top Dead Center) to 36° CKA after TDC
Exhaust camshafts: 20° CKA before TDC to 20° CKA after TDC

Start position function sequence
Intake camshafts: A 36° CKA after TDC
Exhaust camshafts: 20° 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.

Shown is oil flows in the intake camshaft vane-cell adjuster

Component Identification:

The upper half of the illustration shows: Filling oil galleries (A), oil galleries (B) open. The lower half the illustration shows: Filling oil galleries (B), oil galleries (A) open.

Valve overlap function sequence
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. In this case less fresh air is suctioned in while exhaust gases which are still low in oxygen remain in the cylinders. This lowers the combustion temperature and reduces the formation of nitrogen oxides (NOx).
The inducted air mass is reduced by the quantity of exhaust gases remaining. The ME-SFI [ME] 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 the exhaust camshaft Hall sensors, and sent to the ME-SFI [ME] 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.

Diagnosis function sequence
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 required adjustment has been reached after the engine has been running for a short time. Output stage errors (in the ME-SFI [ME] control unit) of the camshaft solenoids and camshaft Hall sensor faults are also detected.