Camshaft Adjustment

Camshaft Adjustment

The intake and exhaust camshafts are adjusted by way of a vane adjuster. The DME control unit determines the current position of the camshaft in relation to the crankshaft (actual angle) on the basis of the speed sensor signal and the Hall sender signal. The position controller in the control unit receives the desired nominal angle via the programmed map values (speed, load, engine temperature). A regulator in the DME control unit activates a solenoid hydraulic valve according to the desired adjustment when there is a difference between the nominal angle and actual angle. The adjustment angle is 52° in relation to the crankshaft on the intake side and 22° in relation to the crankshaft on the exhaust side.

When idling, the camshafts are set that the intake camshaft opens and closes late. The exhaust camshaft is adjusted that it closes well before TDC. This results in stable idling on account of the low residual gas content in the combustion process.

In order to attain a good power output at high rpms, opening of the exhaust valves is retarded. This allows the expansion effect of the combustion process to act on the piston for a prolonged period. The intake valve opens after TDC and closes late after BDC. This way, the dynamic ram effects of the inflowing air are utilized to increase power output.

In order to attain maximum torque, high volumetric efficiency is required for the cylinders. To this end, the intake valves must be opened early. As a result of early opening they also close early, thereby avoiding the expulsion of fresh gases. The exhaust camshaft closes shortly before TDC.

Internal exhaust gas recirculation is carried out while the intake and exhaust camshafts are being adjusted. This results in an overflow of the exhaust gas from the exhaust port into the intake port during valve overlap (intake and outlet valves open). The size of valve overlap determines the quantity of exhaust gas returned in the course of internal exhaust gas recirculation. To this end, the intake camshaft is set such that it opens well before TDC while the exhaust camshaft closes only shortly before TDC. Both valves are thus open and exhaust gas is recirculated. The advantages of internal exhaust gas recirculation as opposed to the external alternative are the fast response of the system and uniform distribution of the recirculated exhaust gases.

The camshaft adjustment system comprises the following components:
- Two vane adjusters
- Two electromagnetic valves
- Timing chain housing







The DME control unit actuates electromagnetic valves 4 and 5 to adjust the camshafts. The valves subsequently open oil passages in the timing chain housing. The engine oil then flows via the timing chain housing and the camshaft into the vane adjuster. The vane adjusters turn, adjusting the camshafts in accordance with the instructions from the DME control unit.