The New Audi TT: emotive Technology
The third-generation Audi TT is more dynamic than ever before, and with an output of 228 kW (310 bhp), the compact TTS sports car is advancing into the high-performance range. The TT also offers impressive efficiency – the 2.0 TDI clean diesel emits only 110 grams of CO2 per kilometer (177.03 g/mile). These strengths reflect the combined engineering expertise of the brand with the four rings – in engine and transmission development, running gear, construction and weight-saving design.
Lightweight construction – the Body
As early as with the second-generation TT, Audi had already succeeded in reducing the weight by introducing the Audi Space Frame (ASF). As a result of the high proportion of aluminum in the ASF, the new model was up to 90 kg (198.42 lb) lighter than its predecessor. For the third generation, Audi has reduced the weight even further: The unladen (driverless) weight of the TT 2.0 TFSI with front-wheel drive and manual transmission comes in at a mere 1230 kg (2711.69 lb), which is 50 kg (110.23 lb) lighter than its predecessor. Thanks to this low overall weight, Audi has achieved a new record in weight-saving design within the segment.
The lightweight construction philosophy is not confined to one specific material: It is more about using the right amount of the right material in the right place for optimal functions. In line with this philosophy, Audi engineers developed a new hybrid ASF body for the new TT made from aluminum and steel: The front end of the vehicle and the undercarriage comprise high-strength and ultra-high-strength steel components; the structure is made from standard cast aluminum, extruded profiles, and sheet metal. — a structure typified by Audi.
The TT body uses components from the MQB platform, with the TT boasting the shortest wheelbase of all MQB-based models at 2505 mm (8.22 feet). The underbody comprises the longitudinal members, A-pillar components, cowl, floor, rear wheel housings and tail end.
Hot-formed steel panels in the underbody constitute approximately a quarter of the total structural weight (39.5 kg or 87 lb). The blanks are heated in a furnace to almost 1000 °C (1832 °F) and shaped immediately thereafter at around 200 °C (392 °F) in a water-cooled pressing die. The abrupt change in temperature imbues an iron/carbon joint with an extremely high tensile strength. On account of their strength, hot-formed steels require only relatively low wall thicknesses and are therefore relatively lightweight.
The hot-formed components form the backbone of the passenger compartment – they are used in the transition sections between the front longitudinal members and the cowl, at the center tunnel, in the reinforcement profile between the B-pillars and the rear longitudinal members. High-strength, cold-formed steel components together with extruded aluminum profiles for the side sills and sheet aluminum for the rear wheel housings complete the underbody.
The passenger compartment, which at only 68 kg (149.91 lb) sets new standards in lightweight construction, has an aluminum frame with four cast aluminum nodes. Large nodes on the A-pillars are used to connect the side roof frame profile with the sills, the windscreen cross member and the upper longitudinal profile in the passenger cell. Two smaller cast nodes above the rear window connect the roof arch with the flat C-pillars and rear roof cross member. The roof arch is made of a hydroformed aluminum profile: After extruding the straight aluminum profile, it is first stretch formed, placed inside a forming die, subjected to fluid injection at a pressure of 2000 bar to give it its final shape, and then calibrated.
The entire body shell of the new TT – the front fenders, the sidewalls and the roof – is made from aluminum, as are the add-on parts, including the hood, doors and the tailgate. These latter two components alone save approximately 15.5 kg (34.17 lb) in weight compared to their steel counterparts. Overall, the entire body including add-on parts weighs in at a total 276 kg (608.48 lb).
Lightweight construction – joining techniques
The body is constructed at the Audi Győr plant in Hungary, where a number of different joining techniques are employed. The TT body is held together by a total of 3020 spot welds, 1113 rivets, 44 solid punch rivets, 128 self-tapping screws, 199 clinched joints, 1.9 meters of MIG/MAG (metal-inert/metal active gas) welded connections and 4.9 meters of laser-welded seams on the side sills and A-pillars.
To join steel and aluminum components, Audi uses cold joining techniques such as rivets, screws and clinches; adhesives help to strengthen the joint and prevent contact corrosion. The bond seams amount to a total length of 76 meters (249.34 feet) on the new TT. Once again demonstrating Audi’s unswerving focus on quality, robot-assisted hybrid laser welding is used to create the zero joint seam between the roof and the side panels.
The new hybrid steel and aluminum ASF construction of the Audi TT impresses on a number of levels: The body weighs less than its predecessor; the center of mass has been cut by 10 mm (0.39 inches), thereby significantly benefiting driving dynamics; and thanks to the MQB underbody, it is possible to include a number of lightweight MQB technology components – from the auxiliary frame through the air conditioning unit.
Torsional strength enhanced
In all other respects too, the hybrid ASF has proved a perfect fit for the Audi TT. In comparison to its predecessor, which already boasted extreme rigidity, the static torsional strength of the new TT has been retained by 23% while retaining the high level of dynamic rigidity. Rigidity forms the basis for characteristics that really impress customers, such as dynamic handling and drive comfort.
The Audi TT is at the top of its game when it comes to crash safety. The hot-formed components offer optimum strength and protection for the passenger cell, even in the event of a rear-end collision. In the event of a side-impact collision, the solid cross member profile beneath the rear seating compensates for the absence of a continuous B-pillar. The roof frame offers optimum rollover protection.
Thanks to a drag coefficient of 0.30 (on the 2.0 TFSI with manual transmission), the new aerodynamic Audi TT simply cuts through the wind. All exterior details have been carefully tuned to aerodynamic performance – from the struts in the air intakes, the base of the side mirror through the tail lights. The underbody has a virtually smooth surface on account of its large area cladding. In development of the new TT, considerable attention was paid to engine compartment flow.
An additional highlight is the fuel flap that is traditionally situated in the right side panel. The circular, aluminum look flap, which is surrounded by six outlined screws, opens by gently tapping the raised TT lettering. There is no longer a fuel tank cap beneath the flap. The filler nozzle slots straight into the tank filler, just like in motor racing. Two flaps are pressed out of the way in the process, only returning to seal the tank neck once again when the nozzle is removed.
Lightweight construction – the complete car
Audi’s focus on lightweight design not only applies to the body – its philosophy includes all technological areas. In the vehicle’s electrical system, for instance, the main wire to the battery is made from aluminum. The cross-sections in many of the other wires have been reduced – saving 2.6 kg (5.73 lb) in total. The underbody cladding also offers acoustic insulation – the absence of additional insulation material resulting in a saving of one kg (2.20 lb). The foam used to prevent unwanted echoes in cavities such as pillars and sills, as well as the luggage compartment liner, are also very lightweight.
Aluminum windows reduce the weight by an additional kilogram (2.20 lb), and using a lightweight trim on the door panels saves a further 0.5 of a kilogram (1.10 lb). The new sports seats are 5 kg (11.02 lb) lighter than their counterparts in the previous model. The lightweight 17-inch wheels on the running gear have the positive effect of significantly reducing the unsprung and rotatory masses. In the TTS, aluminum fixed caliper brakes on the front axle save 5 kg (11.02 lb) in weight.
The newly developed standard sports seats with integrated headrests are more deeply mounted than in the previous model, reducing the weight by around 2.5 kg (5.51 lb). As an optional extra, Audi provides the seats with an electrically adjustable lumbar support.
As an alternative (or as standard on the TTS), the streamlined S sports seats are supplied with their highly contoured sides. The seat depth, seat angle and adjustable lumbar support settings mean they also provide optimum support for the body. A loop makes folding the backrest easier. The S sports seats can be further refined with electrical controls and pneumatic adjustment of the sides of the backrest.
The new TT will be revving up on the start line with three redeveloped, powerful four-cylinder engines, one TDI and one TFSI for the TT and a TFSI in the TTS. Their engine displacements are two liters (0.07 cubic feet) and the performance ranges from 135 kW (184 bhp) to 228 kW (310 bhp) – up to 28 kW (38 bhp) more than its predecessor. All three engines represent the downsizing philosophy followed by Audi – displacement is replaced by charging and, together with the direct injection, this ensures a high level of efficiency. The standard start/stop system also enhances the overall efficiency. All engines satisfy the Euro 6 emissions standard.
All three power units have the same mounting position: the intake side is at the front and the vertical axis can be inclined rearwards by 12 degrees. This solution from the modular transverse matrix, combined with the compact dimensions of the new engines offers huge advantages: The developers were able to put the front suspension far forward, thus improving the crash behavior, the design and the distribution of axle loads. Another common feature is the sound actuator, which is installed with the optional Audi drive select dynamic driving system (standard on the TTS). When set to dynamic, it produces a more sporty and sonorous intake noise.
The 2.0 TDI
The 2.0 TDI clean diesel with manual transmission and front-wheel drive is ready to go as soon as the TT starts up. The engine offers performance of 135 kW (184 bhp) and a torque on the crankshaft that ranges from 1750 to 3250 rpm 380 Nm (280.27 lb-ft). The diesel engine in the compact Coupé accelerates from 0 to 100 km/h (62.14 mph) in 7.2 seconds and reaches a top speed of more than 235 km/h (146.02 mph).
In the NEDC cycle, it consumes only 4.2 liters (1.11 gallons) per 100 km, equating to CO2 emissions of just 110 grams per km (177.03 g/mile). The high level of efficiency means the TT 2.0 TDI clean diesel gets the Audi “ultra” label.
The 2.0 TDI clean diesel produces its 1968 cubic centimeter displacement from a bore of 81.0 millimeters (3.19 inches) and a stroke of 95.5 millimeters (0.31 feet). Many areas have been totally re-designed. The balance shafts now rotate inside the crankcase and have roller bearings. The reduced tension of the piston ring also reduces internal friction. The valve train is a separate module with a stiff and lightweight frame for the camshafts. The star valve has been rotated by
90 degrees and the two camshafts running on needle bearings each operate one intake and exhaust valve per cylinder. The intake camshaft can be adjusted by a crank angle of up to 50 degrees – the control timings can also be adjusted.
There is also high level thermal management. The crankcase and cylinder head have separate cooling water circuits each with independent controllers. During the warm-up phase, micro-circulation is active, which quickly heats up the cylinder block. The oil pump has two pressure level options, thereby saving drive energy.
The common rail system injects fuel at up to a 2000 bar pressure via eight-hole nozzles – the high pressure ensures fine atomization inside the combustion chambers and therefore efficient, low-emission combustion. The turbocharger uses adjustable vanes and their pneumatic actuator has additional refinements. The charge air cooler is integrated into the intake manifold; which results in short gas paths and high levels of responsiveness, control quality and efficiency.
There are also additional newly developed exhaust gas treatment components – the DeNOx storage catalytic converter and the diesel particulate filter. They are located directly on the engine and the shortened gas paths significantly improve the emission control response. The new assembly contains the connection point for low-pressure exhaust gas recirculation – a solution that keeps the pressure losses to a minimum.
The 2.0 TFSI
The 2.0 TFSI is available in two variants. In the TT, the gasoline engine is rated at 169 kW (230 bhp) and at 228 kW (310 bhp) in the TTS. Compared to the previous engine model, voted “International Engine of the Year” in its category by an international jury of journalists five times in a row since 2005, the two-liter has improvements in many areas. But the engine capacity remains unchanged at 1984 cm3 (bore x stroke 82.5 x 92.8 millimeters (3.25 x 3.65 inches).
In the case of the Audi TT, the 2.0 TFSI delivers torque ranging from 1500 to 4500 rpm constant 370 Nm (272.90 lb-ft). The six-speed manual transmission and front-wheel drive enable the Coupé to accelerate from 0 to 100 km/h (62.14 mph) in six seconds and to a top speed of 250 km/h (155.34 mph). Together with the six-speed S tronic and quattro all-wheel drive, the key data are: 5.3 seconds to go from 0 to 100 km/h, a top speed of 250 km/h and 6.8 liters per 100 km (34.59 US mpg) (158 grams of CO2 per km [254.28 g/mile]).
The 2.0 TFSI also has highly complex thermal management. Two rotary disks, combined in one module and electrically driven by a worm gear, ensure that the engine oil heats up quickly. The refrigerant temperature ranges from 85 to 107 degrees Celsius depending on the driving situation. The exhaust manifold is integrated into the cylinder head and is washed there by the water. This solution also contributes to rapid warm-up, at full load it lowers the temperature of the exhaust gas, thereby reducing consumption because it is no longer necessary to enrich the refrigerant mixture.
In terms of filling the combustion chambers, Audi’s engineers have provided greater freedom of choice. The input and exhaust camshafts can be adjusted; on the outlet the Audi valve lift system also varies the valve lift as necessary, in order to minimize pumping losses further. The turbocharger uses extremely dynamic means to build its relative charge pressure of up to 0.8, while its electric wastegate actuator provides quick and accurate control. The turbine can handle an exhaust gas temperature of up to 980 degrees.
Another great innovation in the 2.0 TFSI is additional indirect injection. It supplements FSI gasoline direct injection and is active in the partial load range. It injects the fuel on the end of the intake manifold in the area of the tumble flaps, where it is swirled around intensively along with the air. The improved mixture preparation reduces fuel consumption and lowers particulate emissions.
The direct injection FSI with its maximum 200 bar pressure comes into its own at startup and with higher loads.
Even including all of these technologies, the two-liter gasoline engine weighs only slightly more than 140 kilograms (308.65 lb) – the narrow wall thickness of cast-iron crankcase also helps to keep the weight down. These only measure around three millimeters (0.12 inches) and reduce the weight by around 2.4 kilograms (5.29 lb). The pistons are made of a new, enhanced strength alloy. Lightweight plastic is used for the oil sump and many of the screws are made of aluminum.
A new type of coating on the piston skirts, a roller bearing system from the balancer shafts and reduced crankshaft main bearing diameters lower internal friction. The lightweight crankshaft is available with four counterweights. The regulated oil pump uses minimal energy, and a high-precision electric system cools the piston crowns with oil spray.
The 2.0 TFSI in the Audi TTS
In the Audi TTS, the 2.0 TFSI applies a torque of 380 Nm (280.27 lb-ft), which is available at 1800-5700 rpm. In combination with the six-speed S tronic, the top model effortlessly achieves standard sprint in 4.7 seconds, at 250 km/h (155.34 mph) it runs in the electronic limiter. At 100 km (62.14 miles), the Audi TTS with S tronic consumes 7.1 liters of fuel (7.50 US quarts) (146 grams CO2 per km [234.96 g/mile]) on the NEDC cycle.
A true sports engine, the 2.0 TFSI spontaneously reacts when the gas pedal is pressed – up to the speed limit at 6800 rpm. When the Audi drive select dynamic driving system is operating in dynamic mode, it responds more directly; short intermediate taps on the accelerator accentuate the S tronic gear change. With a higher load and rotational speed, two sound flaps in the exhaust system open up, creating a fuller sound.
A host of details underline the high performance of the top-quality engine. Modified aluminum pistons and high-strength connecting rods with new bearings guide the power to the crankshaft. The crankcase has been reinforced at the main bearing blocks and the main bearing cap.
The cylinder head is made of an extremely strong light aluminum-silicon alloy with a high temperature resistance and there are new springs and seat rings on the valves. The large turbocharger compresses 1000 kg per hour (2204.62 lb) with a maximum 1.2 bar of charge pressure, i.e. 850,000 liters (8981849.74 US quarts) of air. A powerful air-intercooler significantly lowers the temperature.
In the new Audi TT, installed as standard is a six-speed manual transmission with a lightweight magnesium housing. This guides the power and can be easily and accurately shifted over short distances. The six-speed S tronic can optionally be installed, and also stands out on account of its high performance. As with the manual transmission, the low gears are set at lower ratios for a sporty response, while the sixth gear is designed with a high ratio to reduce consumption.
The six-speed S tronic
The six-speed S tronic changes gears within hundredths of a second with no perceptible interruption in traction. It shifts smoothly and very comfortably and the driver has the option of automatic mode or manual mode, selecting the gears with paddles on the steering wheel or directly with the shift lever. On the automatic level, D mode is designed for low consumption. In the S vehicle map the shift strategy is sportier and the engine speed is higher.
Another feature of the six-speed S tronic is fuel-saving free-wheeling. This is activated when the Audi drive select driving dynamics system is set to efficiency mode and the driver takes their foot off the accelerator. In the Audi TTS, the Launch Control startup program manages maximum acceleration from a standing start with optimal tire slip.
Like all dual-clutch gearboxes, the six-speed S tronic consists of two separate transmissions. Two radially arranged multi-plate clutches operate the gears. The large K1 clutch guides the engine power via a solid shaft to the pinions for gears 1, 3, 5 and 7. A hollow shaft rotates around the solid shaft. It is connected to the compact K2 clutch, which is integrated within its larger counterpart and controls the pinions for gears 2, 4, 6 and reverse gear.
Both transmission structures are continuously active, but only one is powered at a time by the engine. The shifting process takes place as the clutch changes. For example, when the driver accelerates the TT in third gear, the fourth gear is already engaged and clutch C2 is open. As soon as the switching command is received, C1 opens and C2 closes. Each transition is associated with a conventional switching unit, so the driver can, change directly from sixth to fourth gear, for example.
The quattro all-wheel drive
The quattro permanent all-wheel drive system (optional feature on the TT 2.0 TFSI, and standard on the TTS) is a unique feature of the compact Audi sports car. The key innovation is an advanced electro-hydraulic multi-plate clutch, as well as new all-wheel drive software developed specifically for the TT.
The weight-optimized design and eliminating the accumulator enabled a weight reduction of 1.5 kilograms (3.31 lb) compared to the previous component. The clutch sits at the end of the propeller shaft in front of the rear axle – an installation position that benefits axle load distribution. For a required torque from the wheel software, the electric axial piston pump builds hydraulic pressure up to 38 bar. The friction plates are pressed together and this action sends driving torque continuously to the rear axle.
Audi has completely redesigned electronic control of the torque distribution and tailored specifically it to the TT. This is the first time the all-wheel drive system has been integrated into the Audi drive select dynamic driving system. As the new control philosophy includes more driving dynamics relevant sensor sizes than beforehand, the driver has the ideal torque distribution to all four wheels in every situation. This means that the traction control system can already send driving torque to the rear axle when the driver turns the steering wheel during sporty driving. As soon as the driver steps on the gas, the driving torque pushes the Coupé seamlessly into the bend, without any initial understeering. For load changes, torque distribution allows targeted turning of the TT into the bend, ensuring a sporty driving feel. For drifts, it offers maximum control and reliability – when exiting a bend the front axle straightens out the Coupé.
When developing the new all-wheel drive software, one particular area of focus was enhancing the performance level. The precise determination of driving conditions, road characteristics and driver type means that torque distribution can be calculated for optimal performance and set via the all-wheel drive system. Because the software always knows the exact all–wheel requirements, in efficiency mode, even temporary cutoff is possible . However due to sensitive monitoring of driving conditions, the all-wheel drive is activated on a predictive basis; this process occurs even before the torque is required again at all four wheels. This measure allows emissions to be reduced even further by up to 1.5 g CO2 per km (2.41 g/mile).
Audi drive select
The Audi drive select dynamic driving system is optional in the TT and installed as standard in the TTS. All the driver needs to do is press a button to select comfort, auto, dynamic and efficiency modes; he also has the option a freely programmable individual mode in conjunction with the MMI navigation system. Audi drive select influences the engine characteristics and power steering. In addition, the system includes several other modular options – the S tronic, the quattro drive, the sound actuator, cruise control and deluxe automatic air conditioning.
Another Audi drive select building block is the electronically controlled Audi magnetic ride shock absorber system (optional on the TT, standard on the TTS). The damper piston circulates a synthetic hydrocarbon oil containing microscopic magnetic particles. When voltage is applied to a coil it creates a magnetic field in which changes the orientation of the particles: Set transversely to the oil flow direction, they inhibit its flow through the piston channels. In the front dampers, the oil volume measures 140 milliliters (8.54 cubic inches) and in the rear dampers, 290 milliliters (17.69 cubic inches).
The control unit constantly analyzes the condition of the road and driving style. Depending on the mode, which is set in Audi drive select, the new TT drives relatively comfortably and either well-balanced or tautly. In dynamic mode, the TT displays its full dynamic potential: The closeness to the road provides an even more spontaneous steering response, rolling movements are largely suppressed and the targeted support of individual wheels during fast cornering makes the handling even more dynamic. When braking, Audi magnetic ride counteracts excessive nosedive.
The technological expertise behind the new Audi TT is also reflected in the running gear. The front suspension has McPherson struts and the control arms and sub-frames are made of aluminum. The rear suspension with its four steel rods handles longitudinal and lateral forces separately and separating their springs and shock absorbers guarantees a high precision response. The streamlined coordination of the Audi TT means it masters all handling tasks with flying colors. In the TTS, the S line sport package and the Audi magnetic ride, the suspension is set ten millimeters (0.39 inches) deeper.
Another TT highlight is the standard progressive steering. Due to their special toothed rack, the steering angle produces different transmission ratios – a little less direct in the center and very direct for heavy steering. When maneuvering, the progressive steering provides significant gains in comfort and makes handling even more sporty on winding roads. The servo assistance, which decreases with the speed, is in perfect harmony with this feature. The progressive steering, which is electro-mechanically driven and therefore highly efficient, works closely with three assistance systems – the break recommendation installed as standard and the optional Audi active lane assist and park assist.
The wheel program features 11 variants. The TT 2.0 TFSI and the 2.0 TDI roll off the assembly line on 17-inch lightweight alloy wheels, each weighing only around 8.7 kg (19.18 lb); the tires are 225/50. Audi and quattro GmbH will optionally supply wheels with an 18, 19 or 20-inch diameter, while the TTS format is 18 inches and the tires size is 245/40. The 19-inch forged wheels are also extraordinarily light, each one weighing 10.6 kg (23.37 lb).
Behind the imposing wheels are generously dimensioned brakes and the front discs are internally ventilated. The Audi TTS brakes on the front axle with newly developed aluminum fixed caliper brakes, which are particularly responsive and very resistant to brake fade. The lightweight design reduces the weight by almost 5 kg (11.02 lb) compared to its predecessor.
Electronic differential lock for even more precise handling
The Electronic Stability Control (ESC) adds the finishing touch to the sporty handling characteristics. In the front-wheel drive TT, the electronic differential lock (an ESC function) brakes the front turning wheel easily on bends. In the TT quattro, it takes over both inner turning wheels. The excess torque flows towards the opposite wheel and the difference in driving forces means that the car turns easily into the bend. The front-wheel drive TT, in particular, offers a major advantage in terms of dynamics and stability on account of the electronic differential lock.
The driver can turn the ESC off completely or partly via a switch on the center console. In “Sport” mode, the system remains active, but responds later and allows controlled drifting because engine intervention is largely suppressed. If the driver presses the button for longer than three seconds, the ESC is completely disabled, for example for a fast lap around a track.