Audi valvelift system (AVS)The Audi valvelift system (AVS) is a technology for variable valve control. Audi uses it for different purposes in different engines, but the working principle is the same for all engines: Sleeves are mounted onto the camshafts which have cam profiles with varying contours. Electromagnetically actuated pins push the sleeves axially several millimeters by engaging into spiral-shaped slots on their outer contours. Either the low cam or the high cam opens the valve, depending on the position of the sleeve.
In the new 3.0 TFSI, the 2.9 TFSI and the 2.0 TFSI with 140 kW (190 hp), the AVS acts on the intake valves. It adjusts their lift and timing (opening duration) over two levels according to engine load and speed, and thereby controls the amount of air that is inducted. In part-load operation, the lift and opening duration are relatively small. The throttle valve can remain wide open, and this largely eliminates throttle losses. At higher loads, the AVS switches to a higher lift and later valve closing. The combustion chamber charge increases in size, and the engine can aspirate air freely for more power and torque.
In some four-cylinder gasoline engines and in the 2.5 TFSI with its five cylinders, the AVS varies the lift of the exhaust valves. This reduces flushing losses in the combustion chamber and ensures optimal flow of exhaust gas to the turbocharger, particularly in the low rpm range. The results are dynamic engine response and increased torque.
In the 1.4 TFSI the system serves to deactivate half of the cylinders at a moderate driving pace, which reduces fuel consumption. The deactivated cylinders largely run without losses, like compressed gas springs, while the active cylinders operate at the better efficiency levels found in higher load regions.
The 4.0 TDI presents another variant of this technology. Here, the Audi valvelift system manages the two turbochargers, which are switched according to a strategy based on stages. The exhaust gases, which each cylinder discharges from its two exhaust valves, flow through separate channels within a dual-flow manifold system. Each channel supplies one of the two turbochargers. At low loads and engine speeds, the AVS keeps one of the two exhaust valves closed so that the full exhaust flow reaches what is referred to as the ‘active’ turbocharger. With increasing engine speed, the second exhaust valve opens, and this activates the second turbocharger as well. Other AVS units are mounted on the intake camshafts; they serve to regulate the amount of intake air charge in the combustion chambers as needed.