Switching tappets allow switching between two valve lift lengths (valve lift switching) or between full lift and zero lift (valve or cylinder deactivation) in engines with an overhead camshaft. As a result, the thermodynamic efficiency of the engine can be optimised as a function of the engine load.
The switching tappet consists of two nested housings, the inner and outer housing. The inner housing is located between the engine valve and camshaft and transmits the zero or partial lift to the valve. The outer housing is pressed against the end stop on the inner housing by a lost motion spring. Both housing parts can be linked by means of a coupling mechanism. In the locked condition, the high lift is transmitted via the outer housing to the valve. As in the standard tappet, valve lash adjustment can be by hydraulic or mechanical means.
Modifications compared to standard valve train: