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Switching roller tappets allow switching between full lift and zero lift (valve or cylinder deactivation) in engines with a bottom-mounted 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 outer housing is guided in the cylinder head between the camshaft and pushrod. The inner housing is pressed against the end stop on the outer 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 pushrod to the valve. In the unlocked condition, the valve remains closed and the cam lift is converted to a differential lift between the inner and outer housing.
Modifications compared to standard valve train: