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

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







With camshaft adjustment, all four camshafts can be continuously adjusted up to a 42° 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 14° crank angle before TDC up to 28° after TDC Exhaust camshaft a 17° crank angle before TDC up to 25° 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 28° crank angle after TDC
Exhaust camshaft, a 17° crank angle before TDC.

At a lower engine speed and load, a large valve overlap is set to obtain an inner exhaust gas recirculation. In doing so, less fresh gases are drawn in, since exhaust gas low in oxygen still remains in the cylinder. The combustion temperature drops and formation of NOx is reduced. The inducted air mass is reduced by the quantity of exhaust gases remaining. In line with this, the ME-SFI [ME] control unit meters less fuel.

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

The camshaft solenoids are actuated by the ME-SFI [ME] control unit by means of a PWM signal (pulse width modulated signal). The integrated control plungers are adjusted via the performance map dependent duty cycle. The oil quantities (switching oil) for the swivel motor adjuster are controlled according to their position. The rotors in the swivel motor adjusters which are firmly connected to the camshafts are turned by the switching oil.

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.

Every position of the camshafts is detected by the respective camshaft Hall sensor and reported to the ME-SFI [ME] control unit. Detection of the positions of the camshaft takes place through detection of the positions of pulse wheels which are located at the front on the camshafts.

Release of the camshaft adjustment by the ME-SFI [ME] control unit takes place dependent on the vehicle speed, 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.

Release of the camshaft adjustment occurs for:
- Vehicle speed > 10 km/hour
- Engine speed >1000 rpm (except for TWC heating)
- Engine oil temperature > -10 °C

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. Output stage faults of the camshaft solenoids (in the ME-SFI [ME] control unit) and a defective camshaft Hall sensor are also detected.