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

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







With camshaft adjustment, all the four camshafts can be adjusted progressively up to a crank angle of 40°. This means the valve overlap in the event of a load change can be varied within wide limits. In the event of valve overlap, the intake valves open even before the exhaust valve has fully closed.

Adjustment range of camshafts in ° crank angle:
Intake camshaft 4° BTDC up to 36° ATDC
Exhaust camshaft 20° BTDC up to 20° ATDC.

Interlocked start position in ° crank angle:
Intake camshaft 36° ATDC
Exhaust camshaft 20° BTDC.

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, as some exhaust gas low in oxygen still remains in the cylinder. The combustion temperature drops and the formation of NOx is reduced. The inducted air mass is reduced by the quantity of exhaust gases which remain. In line with this, the ME control unit meters less fuel.

The smallest valve overlap in the event of a load change takes place when the exhaust camshafts are turned to the maximum "Early" and the intake camshafts are turned to the maximum "Late". The increased fresh gas proportion leads to a greater torque and performance.

Enabling of the camshaft adjustment is dependent on the engine speed and engine oil temperature, to ensure sufficient oil pressure, even when the engine oil is hot (oil pressure for adjustment at least around 1.5 bar). If 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 and thus at a lower oil pressure to the direction of rotation of the engine. A return spring is located in each exhaust-side vane-type adjuster for support.

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

Enabling of the load-dependent and speed-dependent camshaft adjustment takes place:
- from around 600 rpm at 80 °C engine oil temperature
- from around 800 rpm at 120 °C engine oil temperature (intake side)
- from around 1050 rpm at 120 °C engine oil temperature (exhaust side)

The solenoids upstream of the camshafts are actuated by the ME control unit on the ground side. The control plungers of the vane type actuators are operated via the map-dependent duty cycle. Depending on their position, the oil volume in the vane-type adjusters is controlled.

Camshaft adjustment takes place gradually when all camshafts must be further adjusted simultaneously to prevent oil supply problems. In doing so, the intake camshaft adjustment is projected.

Each camshaft position is detected via a camshaft Hall sensor. These are located upstream of the camshaft adjusters and detect the window positions in the pulse wheels. During diagnosis, a check is performed to establish whether the camshafts are in the interlocked start position and whether following a short waiting time, the required adjustment has also been performed. In addition, output stage errors for the solenoids and defective camshaft Hall sensors are detected.











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.