Variator (variable valve timing)
A variator is a common type of variable valve timing (VVT) system used on automotive engines.
Many VVT systems use a variator to advance/delay the camshaft relative to the crankshaft. This simple system cannot change the duration or lift of the valves.
Alfa Romeo system
Alfa Romeo first applied VVT in 1980 to the long-established Twin Cam engine used in the Alfa Romeo Spider.[1] It is best known for its use throughout the Twin Spark engine introduced with the Alfa 75. The technique derives from work carried in the 1970s by Ing. Giampaolo Garcea.[1] On their twin cam engine, VVT is only used for the intake valves.
Volkswagen system
Volkswagen use a variator system with two variators, one for each camshaft. Like the Alfa Romeo system, these are electrically-controlled hydraulic units, mounted in the camshaft's timing belt pulley.[2] These systems are fitted to the Volkswagen VR5 and VR6 engines, and also to the W8 and W12 engines. The multiple-bank W engines have four variators in total, one for each camshaft.
The Volkswagen variator is referred to as a fluted variator, owing to the shape of the hydraulic components. The internal components of the variator resemble a paddle wheel inside a loose casing, which allows side-to-side movement. By applying hydraulic pressure one one side of these paddles, a phase shift is achieved.[2]
Other variator-based VVT systems
- Variable Cam Timing, Ford
- VANOS, BMW
References
- ^ a b "Alfa Romeo Spider FAQ" (PDF).
- ^ a b "Variable Valve Timing with fluted variator" (pdf). Volkswagen Self-study programme.