In connection with the multi-valve technology it is at least a partial solution to the age-old problem, that the piston internal combustion engine only provides it's optimal torque in a certain RPM range. With the camshaft
adjustment, it can have good pulling power in the lower RPM area and also produce high performance in the upper RPM range. In addition, it reduces the emission and the fuel consumption in the otherwise
unfavourable RPM ranges. Further possibilities include: improvement of the idling-control as well as the internal exhaust gas
The camshaft adjustment is situated between the drive-wheel and the camshaft. The control device guides oil pressure through a magnetic valve to the adjustment. Thereby, the inside valve (picture 4 on the right ) is
twisted against the outside valve (picture 4 on the left), thus the camshaft is twisted against its drive-wheel.
The result can be seen in the above valve-lift diagram. In this case, only the intake camshaft is adjustable. In the lower speed range, up to approx. 2000 RPM, the (petrol) engine does not make use of the adjustment. A
low idling-speed and better pulling-off torque, is made possible by the small valve overlap. In the upper RPM-range, the opening and closing of the inlet valve timing is shifted forward by approx. 22°. In the upper RPM-
range, a larger valve overlap is an advantage. Nowadays, it is more common because of the internal exhaust gas re-circulation (with a lower NOX emission), to have a larger overlap in the lower RPM-
range and a smaller one in the upper range.
The camshaft adjustment alters only either the intake camshaft or both camshafts. It can also be altered twice over the RPM-range of the engine. In the case of timed magnetic valves, a continuous shifting is possible.
The time between the opening and the closing of the valves cannot be changed. This can only be done if you have a variable valve lift
control. A further possibility is, e.g., having a
bevelled cam-throw, which operates almost point-shaped on it's bucket tappet. This procedure is only possible if there are two camshafts: one for the inlet and one for the exhaust valves. This is then electronically
controlled and shifted lengthwise by hydraulics, it allows an infinitely variable timing setting and valve-lift alteration.
The adjustment between the two camshafts only affects one of the shafts. This is done by a somewhat too long chain and a chain-guide, which can be shifted up- and downwards (picture 5). We are assuming, that
both camshafts rotate in a clockwise direction. Should the connecting chain-guide be moved upwards by the oil pressure, the chain then gets longer at the top and shorter further down. The right camshaft sprocket is
twisted against the rotation direction of the left camshaft sprocket. Consequently, the valves on the right open and close later than before, compared with those on left. The procedure is reversed if the chain guide is
shifted downwards. 07/16