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

GF07.61-P-4021CY Camshaft Adjustment, Function
- up to model year 08

With camshaft adjustment, all four camshafts can be continuously adjusted up to a 40° crankshaft angle. In this way the valve overlap for gas cycle can be altered within wide limits (valve overlap: intake valves open before the exhaust valve are closed).

Adjustment range
Intake camshaft, a 4° crank angle before TDC up to a 36° after TDC Exhaust camshaft, a 20° crank angle before TDC up to a 20° after TDC

The camshafts are locked in a fixed position for starting by catch bolts (locked). This start position is locked hydraulically for first actuation of the camshaft solenoids.

Start position
Intake camshaft, a 36° crank angle after TDC
Exhaust camshaft, a 20° crank angle before TDC

At a lower engine speed and load, a large valve overlap is set to obtain an inner exhaust gas recirculation. Here less fresh air is suctioned in since exhaust gases low in oxygen still remain in the cylinders. The combustion temperature drops and formation of NOx is reduced. The inducted air mass is reduced by the quantity of exhaust gases remaining. The ME-SFI [ME] control unit (N3/10) meters less fuel in line with this.

The smallest valve overlap for gas exchange occurs if the exhaust camshafts are adjusted to the maximum BTDC (advanced) and the intake camshafts to the maximum after TDC (retarded). This brings more engine torque and engine output due to the increased proportion of fresh gases.

Left or right intake camshaft solenoids (Y49/4, Y49/5) and left or right exhaust camshaft solenoids (Y49/6, Y49/7) are actuated by the ME- SFI [ME] control unit by means of a PWM signal (pulse width modulated signal).
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 pistons in the vane-cell adjusters, firmly connected to the camshafts, are turned by the pressure oil.

The positions of camshafts are detected by left or right intake camshaft Hall sensors (B6/4, B6/5) and the left or right exhaust camshaft Hall sensors (B6/6, B6/7) and sent to the ME-SFI [ME] control unit. Detection of positions takes place through detection of the positions of pulse wheels which are located at the front on the camshafts.

Release of camshaft adjustment by the ME-SFI [ME] control unit takes place dependent on the engine speed and engine oil temperature. The temperature 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.

If oil pressure is inadequate, initially adjustment of exhaust camshafts is not guaranteed, since these must be adjusted when the engine speed is dropping (a lower oil pressure) against the direction of rotation of the engine.
A return spring is located in each exhaust-side vane-type adjuster for support.

If all four camshaft should adjusted adjustment of the exhaust camshaft takes place delayed (later). Oil supply problems are prevented and secure functioning of the locking mechanism achieved.

The engine oil temperature is determined by the ME-SFI [ME] control unit using various operating data (e.g. engine load, time, coolant temperature, time) and a stored temperature model determined.

Release of 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
^ From a 120 °C engine oil temperature (exhaust side) from about 1050 rpm

Diagnosis
During diagnosis of the camshaft adjustment, a check is performed to establish whether the camshafts are in the start position and whether following a short waiting time, the required adjustment has also been performed. The output stage faults (in the ME-SFI [ME] control unit) of the solenoids and defective Hall sensors are also recognized.

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.