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Audi's AVS explained

2008-07-30 07:35
Audi, AVS

Egmont Sippel

Last year Audi introduced its own version of Honda’s successful V-Tec technology for variable valve lift, when AVS (Audi Valve-lift System) was launched on the 3.2-liter V6 used in the new A5.

AVS, quite simply, lifts valves higher and for a longer period of time to improve breathing and therefore engine performance at high revs.

Audi’s principle is the same as Honda’s: use a bigger cam lobe to do this.

But the technique differs.

Sideways motion

Instead of securing the bigger lobe via a side-pin, the lobe in question is pushed onto the valve by moving a whole cam lobe unit (consisting of a smaller and bigger lobe) sideways on the cam shaft.

When it's time for the smaller lobe to take over again, the selfsame unit simply glides back along the cam shaft to its original position.

This side-ways motion (facilitated by oil, of course) is controlled by an electrically-activated ejector pin positioned above the cam lobe unit.

When this pin retracts, the cam lobe unit operates in its normal position, via the smaller lobe.

When the pin is ejected, it catches a spiraling groove in the cam lobe unit. As the groove spirals out of a straight line, its one side-wall runs against the stainless-steel tipped pin which pushes the whole unit up along the camshaft, to position the bigger lobe over the valve.

When the ejector pin is retracted, there is nothing to hold the cam unit in this new position any more, so it will glide back to its original position to resume valve lift via the smaller cam lobe.

On both sides

Quite ingenious, actually, this system, which operates on the outlet-side only of Audi’s brilliant new 2.0-liter TFSI (with 155 kW and 350 Nm), but on both sides (inlet and outlet) of the 3.2-liter V6.

Audi admits that AVS is not as good and sophisticated as BMW’s complicated and expensive Valvetronic system, which achieves similar – if better – end results without throttle butterflies (cutting out the losses induced by the latter, for instance).

AVS, though, delivers 80% of Valvetronic results for 20% of the cost, says Audi.

Quite a bit of saving there, to be channelled – no doubt – into things like design and interiors (which explains why Audi’s are so much better in these areas than BMW’s – and also why BMW wins so many Engine of the Year awards).

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