|October 2, 2007
The Audi A4: Transmissions
Those who buy the new A4 have the choice between various high-tech transmission systems. Either a manual gearbox or an automatic transmission transmits engine torque to the front wheels, or to all four wheels by way of the quattro driveline, the settings of which are incidentally more dynamic than ever before in this new Audi saloon.
Dynamic, sporty driving and a luxury-car standard of comfort – this ambitious combination of objectives was pursued when developing the driveline for the new Audi A4 as well. The manual gearbox is a totally new design; the six-speed tiptronic and multitronic continuously variable transmissions have undergone an extensive improvement process. All the transmissions are notable for exceptional ease of control, high efficiency and precise function. They conform to the A4’s new basic layout with the differential immediately behind the engine and therefore ahead of the clutch or torque converter.
The quattro permanent four-wheel-drive system has been a sporty classic in the Audi product portfolio for many years. The new A4 3.2 FSI and the A4 3.0 TDI have this driveline as standard equipment. For the new saloon, the technology of the quattro driveline, with its asymmetric/dynamic torque split, is sportier and more fascinating than any previous A4.
Two versions: the manual gearbox
The six-speed manual gearboxes that transmit power to the road wheels on the A4 have been newly developed. Audi uses them in two different versions. The basic version, suitable for either front-wheel drive or quattro drive, can transmit up to 350 Nm of torque – sufficient for the petrol engines and the four-cylinder TDI. For the V6 TDI, which has 500 Nm of torque and drives all four wheels, an even higher-capacity version is available.
Both manual gearboxes are installed with the differential ahead of the clutch. Drive from the gearbox to the differential is by way of a hollow shaft inclined at an angle of 7.2 degrees, with special splines at both ends. The dual-mass flywheel and the hydraulically actuated single dry-plate clutch are not bolted to the crankshaft in the usual way, but supported on the gearbox input shaft.
Various measures have been taken to reduce internal friction and thus improve the already high efficiency of the gearbox still further. Special selector fork mountings decouple the gear lever from the driveline so that the driver does not sense any vibration. What he or she does enjoy is a precise shift action with short, clearly defined lever movements.
For all versions of the new A4, including those with a manual gearbox, the optional driver information system (standard on the 3.2 FSI, 2.7 TDI and 3.0 TDI Ambition) features a factory-fitted gearshift indicator; this makes it easier to select the correct gear for maximum economy. It indicates which gear is actually in use, and if a different gear would be more suitable while the car is being driven at a steady speed, makes the appropriate recommendation.
Further intensive development: tiptronic
The new A4 3.2 FSI will be available with the quattro driveline as standard equipment, six-speed tiptronic automatic transmission as an alternative to the manual gearbox from 2008 onwards. This classic automatic transmission, with the Sport program and the additional manual-shift mode, has been thoroughly revised in design in the transfer-case and torque-converter areas.
The torque converter is now equipped with a novel form of two-stage torsional vibration damper that permits the lock-up clutch to remain engaged for long distances. This boosts overall efficiency and reduces the car’s fuel consumption. When the car is at a standstill, a controlled drive-off clutch disconnects the transmission from the engine even if the selector lever remains in position D. This clutch is engaged as soon as the driver releases the brakes.
For the new Audi A4, the tiptronic transmission is distinctly more dynamic than the version used on the previous model; it reacts more rapidly and performs much faster shifts without any lack of refinement in the way that these are carried out. These improvements are due to an improved layout of the oil passages used to fill the converter, and more powerful software for the Dynamic Shift Program (DSP), which uses an adaptive operating principle. During an upshift the control unit now lowers engine torque by as much as 80 percent, and during a downshift it opens the throttle for a predetermined time.
Audi offers the multitronic continuously variable transmission for the A4 2.7 TDI; it combines the advantages of a manual gearbox with those of a conventional automatic transmission with torque converter. From 2008 onwards it will also be available for the 1.8 TFSI and 2.0 TDI. The highly convenient but also extremely dynamic acceleration it offers make it ideal for the sporty driver who values relaxed, stress-free travel. With its high efficiency and widely spread ratios, multitronic ensures that the engine runs in its optimal operating range whenever possible and thus keeps fuel consumption low. Internal losses have been reduced still further by improvements to component geometry, the shaft bearings and the design of the oil pump.
The multitronic’s new variator permits a wider spread of transmission ratios: 6.73 instead of the previous 6.25 between the highest and lowest ratios. In the lowest ratio the A4 accelerates powerfully, whereas the highest enables the engine’s fuel-saving potential to be fully utilised even at low engine speeds. The drive-off ratio has been specially lowered so that the A4 sets off vigorously from a standing start. The multitronic transmission has an adaptive control system that varies its settings according to driving style and road topography.
In the D mode of this successful unit, the effective transmission ratio changes steplessly, but a button can also be pressed to activate the dynamic Sport program, which selects lower ratios in all circumstances. When accelerating, the fixed characteristics of the Dynamic Shift Program select eight specific ratios in succession – an impressively sporty way to make rapid progress. The third operating mode has provision for manual selection of these eight fixed ratios by the driver, either at the selector lever or as an optional extra at shift paddles behind the steering wheel.
Unsurpassed: the quattro driveline
The new Audi A4 3.2 FSI and 3.0 TDI always transmit their power to the road by way of quattro permanent four-wheel drive. This gives the cars the supreme capabilities that have become an Audi trademark in the years since this driveline was first introduced in 1980: enhanced traction, road dynamics, safety and directional stability – together making up Audi’s proverbial ‘Vorsprung durch Technik’.
The quattro models in the new A4 line are dynamic saloon cars with unshakable stability in all weather conditions. And thanks also to their powerful engines, they are also ideal for towing a trailer.
In the new Audi A4, as before, the key element in the quattro driveline is a centre differential: this is a self-locking worm and wheel device. It is a purely mechanical unit and therefore takes effect without the slightest delay. Its locking action only develops in response to an applied load; when braking or cornering, it permits the wheels to rotate at different speeds.
In normal driving conditions, 40 percent of engine power reaches the front wheels and 60 percent the rear wheels, permitting sporty handling with slight rear-end emphasis. Should the wheels on any axle start to spin, however, the differential redirects most of the torque to the axle revolving more slowly and therefore with better traction.
The centre differential can direct up to 65 percent of the power to the front axle and up to 85 to the rear axle; as a result, the new A4 can often master situations close to the handling limit without ESP having to make a brake application. If one wheel on an axle begins to spin, this is eliminated by the electronic differential lock (EDL) without any brake application being needed – though this situation seldom arises. EDL also acts as an aid when driving off.
The equipment, data and prices stated here refer to the model range offered for sale in Germany. Subject to amendment; errors and omissions excepted.