The movement of the cam should be transmitted directly, or with a certain ratio, to the valve. The hydraulic lifter ensures automatic
adjustment. More and more often roles are being used with rocking- or relay levers, or even with bucket tappets, to generate lower
friction and thus fuel savings.
The fuel consumption can be reduced with petrol engines even further by approx. 10% if the throttle plate is omitted and the valves open according to the engine load. In this case, the ratio is changed either mechanically, by oil hydraulics, or by electromechanical systems.
How it works
For longer transfer ways, (e.g. with under head camshafts) push rods (picture 1) are used. Shorter ways between camshaft and valve are bridged with
rocking levers (picture 2), towing
levers, or rocker arms (picture 3), bell cranks (picture 4) or directly (picture 5). With the towing lever or rocker arm, the camshaft is positioned on the same side of the fulcrum as the valve, with the rocker arm both are
arranged on different sides of the fulcrum. For the direct connection between camshaft and valve, bucket tappets are used. They increase the friction surface of the valve towards the cam, and keep by their guidance in
the cylinder, the valve free from side forces. From the middle of the cam staggered bucket tappets or slightly bevelled cam tracks move the tappets into a slight rotation and provide for steady wear.
constructions feature roler relay levers with hydraulic tappets which are not part of the moved masses and, therefore, do not burden the valve springs.
Besides the relay lever, the rocking lever (picture) can be also equipped with friction-decreasing roles and hydraulic valve clearance. Not to load, however, the moved masses, he would have to be mounted in the
fulcrum, which is difficult due to a lack of space.