Audi offers two transmission technologies for the new A7 Sportback: the tiptronic and the seven-speed S tronic. The latter comes in different versions for front-wheel drive and quattro drive. All transmissions are integrated in the engine’s thermal management system, achieve high efficiency ratios and interact ideally with the start-stop systems. Their lower gears feature short, sporty ratios, while the upper gears are long to reduce revs and fuel consumption.
These transmissions also make use of route data supplied by the optional MMI navigation plus to optimize gear shifting. Two automatic modes, D and S, are at the driver’s disposal. In manual mode, the driver can change gears using the shift knob or optional shift paddles on the steering wheel (standard with the 3.0 TDI biturbo and the 4.0 TFSI in the S7 Sportback).
The biturbo TDI is paired with an eight-speed tiptronic. This classic torque-converter transmission offers shifting that is smooth, spontaneous, speedy and supple. Its torque-converter lockup clutch connects the transmission directly to the engine under standard driving conditions. It works with limited slip in certain situations, which permits very low engine speeds in interplay with the integrated shock absorber, without the occurrence of vibrations. Whenever the new A7 Sportback comes to a stop, the clutch disengages the transmission from the engine.
A similar principle applies to the seven-speed S tronic. Its two multi-plate clutches operate two mutually independent sub-transmissions, which are essentially similar in nature to manual transmissions.
Both sub-transmissions are continuously active, but only one is connected to the engine at any one time. For example, when the driver accelerates in third gear, the fourth gear is already engaged in the second sub-transmission. The shifting process takes place as the clutch changes – K1 opens and K2 closes. Shifting gears takes only a few hundredths of a second and is completed with practically no interruption of traction. It is so fluid and smooth that it is hardly noticeable. When the standard Audi drive select system is in efficiency mode, the S tronic begins to freewheel as soon as the driver takes his or her foot off the gas pedal.
Plenty of innovations: the new S tronic for front-wheel drive
Audi has made a great many enhancements to the seven-speed S tronic – which has superseded the multitronic – for the A7 Sportback with front-wheel drive. In contrast to the quattro S tronic, the clutches are no longer radially stacked but rather axially positioned one behind the other. They can be separately supplied with oil as needed. Their compact size allows for low moments of inertia at whichever clutch is inactive. Power flows from the output shaft via a spur gear to the pinion shaft first and then to the front-axle differential.
The dual-clutch transmission houses a centrifugal governor in its dual-mass flywheel. Its masses, one attached to each side of the flywheel, move so as to offset the engine’s torsional vibrations. The centrifugal governor significantly reduces these unwanted vibrations – particularly between 1,200 and 1,400 rpm. The engine can consequently operate at very low engine speeds.
Audi’s new seven-speed S tronic has two separate oil supplies. A 4.5-liter circuit of ATF (Automatic Transmission Fluid) services the dual clutch and mechatronics, comprising the control/operation module as well as electronic, electrical and hydraulic components. The wheel set and the differential are lubricated by 3.5 liters of high-viscosity MTF (Manual Transmission Fluid). This division of oil supplies allowed developers to custom-design every component to fulfill its given purpose.
New solutions: oil supply
A clever approach to lubrication boosts the efficiency of the new seven-speed S tronic considerably. Dry-sump technology supplies oil to the wheel sets. A centrifugal pump generating just 0.1 bar and consuming very little electrical operating energy supplies oil to a shallow pan at the top of the wheel set. This pan in turn lubricates the gearing and bearings of the wheel set and the differential via multiple bores.
With respect to operating the dual clutch and the hydraulic gear actuator, the conventional mechanical oil pump has been superseded by an electric-powered tandem gear pump. The latter consists of a high-pressure pump with a flow rate of 0.8 cm3 and maximum pressure of 28 bar as well as a low-pressure pump with a flow rate of 5.5 cm3.
The electrical gear pump always supplies just the right amount of oil in any given situation. This pump is typically deactivated at steady highway speeds, as the corresponding oil pressure and a gas-pressure accumulator suffice to supply the oil needed to lubricate the transmission and clutch. Even when the start-stop system turns the engine off as soon as the vehicle comes to a stop, the accumulator ensures the transmission will continue to function.
A reduction in power loss played a key role during development of the new seven-speed S tronic. An angular-contact ball bearing is used for the highly loaded bearing assembly of the pinion top. Audi engineers avoid relying wherever possible on conventional pre-loaded taper roller bearings in order to reduce drag torque. Leakage is very low throughout the transmission. Hollow shafts – some of whose bores supply oil – and split gear wheels result in a lower weight.
Thanks to this attention to even the smallest details, the new seven-speed S tronic is noted for its outstanding efficiency ratio. At just 100 Nm (73.8 lb-ft) of torque, this ratio is at 94 percent. As load increases, so too does the efficiency – making it far more efficient than the competition’s automatic transmissions. The new dual-clutch transmission provides a very broad spread of gear ratios: from 7.4 to 8.4.
Purely mechanical and lightning-fast: quattro permanent all-wheel drive
The quattro permanent all-wheel drive system also ensures superior dynamics, traction and stability in the new Audi A7 Sportback. This is a purely mechanical system without any lag. Its principal component is a self-locking center differential. Under typical driving conditions, the planetary gear distributes 40 percent of the engine’s power to the front axle and 60 percent to the rear axle. Before problematic wheel slippage can occur, most of the power is transferred to the axle with better traction. Up to 70 percent can flow to the front wheels and up to 85 percent to the rear wheels.
The self-locking center differential operates in tight tandem with torque vectoring, an intelligent software feature of the Electronic Stabilization Control (ESC) system. Upon detecting that the front inside wheel (both inside wheels on quattro models) in a turn has been relieved too much, the ESC unit gently and precisely brakes the wheel concerned. The intervention causes excess torque to flow to the outside wheel. Thanks to the difference in propulsive forces, the five-door coupe turns very easily into the curve, which is helpful for the driver. Self-steering behavior remains neutral longer, and handling becomes more precise, agile and stable.
For engines with a power output of at least 200 kW (272 hp), the quattro drivetrain can be combined with the sport differential. The sport differential is an extension of the conventional rear differential. Torque is provided to one side or the other via additional gear steps and the hydraulic multi-plate clutch on a given side. Active torque distribution prevents unwanted understeering or oversteering. The sport differential function has been further improved significantly for the A7 Sportback. Torque distribution is even faster and even more responsive than ever before whenever the driver steers or accelerates in a curve. As usual, the driver can use Audi drive select to switch between various sport differential modes to suit his or her preference.
The equipment and data specified in this document refer to the model range offered in Germany. Subject to change without notice; errors and omissions excepted.