Variator (variable valve timing)
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A variator is a common type of variable valve timing (VVT) system used on automotive engines.
Variable valve timing overview
In internal combustion engines, Variable valve timing (VVT) is the process of altering the timing of a valve lift event, and is often used to improve performance, fuel economy or emissions.[1]: 4–5 There are many ways in which this can be achieved, ranging from mechanical devices to electro-hydraulic and camless systems.
A variator is a common VVT device, whice advances/delays the camshaft timing (relative to the crankshaft). This simple system cannot change the duration or lift of the valve events. Other VVT systems, such as the helical camshaft and cam switching are able to vary valve lift and duration.
Alfa Romeo system
Alfa Romeo first applied VVT in 1980 to the long-established Twin Cam engine used in the Alfa Romeo Spider.[2] It is best known for its use throughout the Twin Spark engine introduced with the Alfa 75, which uses the 8-valve Twinspark engine.
The technology derives from work carried in the 1970s by Ing. Giampaolo Garcea and was termed "variatore de fase" by the Italian engineers.[2] 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.[1] 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, the valve timing shift is achieved.[1] The hydraulic fluid is engine oil, controlled by a solenoid valve mounted on the cylinder head and controlled by the ECU. A Hall effect sensor also monitors the camshaft position.[1]: 8
Other variator-based VVT systems
- Variable Cam Timing, Ford
- VANOS, BMW
References
- ^ a b c d "Variable Valve Timing with fluted variator" (pdf). Volkswagen Self-study programme.
- ^ a b "Alfa Romeo Spider FAQ".