Here’s all the details about Audi’s new 4.0 TFSI engine with “cylinder on demand” technology.
Audi has once again lowered the fuel consumption of its engines. The 4.0 TFSI, which will make its appearance at the beginning of 2012 in the Audi S6, S6 Avant, S7 Sportback and S8, features the new “cylinder on demand” technology. Bentley was also involved in the development process of this new engine and will install the engine in the Continental GT in the near future.
When this twin-turbo V8 is operating at part-load, four of its cylinders are deactivated. This lowers fuel consumption according to the NEDC test cycle by about five percent and reduces emissions by approximately 10 to 12 g/km (16 to 19 g/mile) of CO2. Add to this the effect of the engine start-stop system – fitted in the Audi S models – that shuts down the engine when the car is standing still, and the reduction in emissions on Audi models can be as high as 24 g/km (38.62 g/mile) of CO2.
The occupants of cars equipped with this new technology enjoy the same high standard of journey comfort as ever. When the 4.0 TFSI is running on four cylinders, no unpleasant noise or vibration is evident inside the car. This is achieved with two accompanying high-end Audi technologies: Active noise control (ANC) and active engine mounts.
Cylinder deactivation on the new 4.0 TFSI is activated at low loads, low to moderate engine speeds and in third gear or higher. If these operating characteristics are present, the system closes the inlet and exhaust valves of cylinders 2, 3, 5 and 8. Efficiency is then higher in the active cylinders because the operating points are displaced toward higher loads.
An enhanced version of the Audi valvelift system closes the valves by means of sliding sleeves on the camshafts. Just before this happens, the combustion chambers are filled with fresh air. Fuel injection and ignition are shut down. The reduced internal cylinder pressure in relation to the injection of exhaust gas is an important efficiency factor.
The instrument-cluster display indicates when the four-cylinder operating mode is active. If the driver depresses the accelerator pedal firmly, the deactivated cylinders cut in again. All these changeovers take place quickly and smoothly.
The “cylinder on demand” system is permanently ready for use, even with the automatic transmission in the “S” mode and the dynamic setting of Audi drive select. In the NEDC test it reduces fuel consumption by around five percent. Add to this the effect of the start-stop system that stops the engine when the car is at a standstill, and the system can reduce fuel consumption by as much as 12 percent. The engine’s efficiency potential becomes especially evident at the speeds at which the car is most frequently driven. At 80 km/h (49.71 mph), for instance, the gain in efficiency is 12 percent for all S models, and can still be as high as seven percent even at a road speed of 130 km/h (80.78 mph).