|January 31, 2006
The Audi Q7: Drivetrain
Powerful and cultivated
The Audi Q7 is available on its debut with a petrol engine and a diesel engine. A second petrol engine will follow in the second half of 2006. Typically for Audi, all three power plants work with performance-enhancing, efficient direct-injection technologies.
The engines of the new Audi Q7 deliver a level of performance promised by the vehicle’s powerful outward appearance. Torques of up to 500 Newton-metres deliver superior tractive power in all speed ranges. Two power plants are available for the launch of the new SUV with the four-ring badge: a new 4.2 litre V8 with FSI petrol direct injection and the powerful yet quiet 3.0 TDI with common rail system using piezo inline injectors. In the second half of the year a 3.6 litre V6 petrol engine, also with FSI technology, will be added.
With a displacement of 4,163 cc, the V8 is a close relative of the engine used in the new Audi RS 4. In the Audi Q7, in line with the character of the performance SUV, it develops 257 kW/350 bhp at 6,800 rpm. But its torque curve is even beefier than in the RS 4: it achieves 440 Nm. This power output is the best in its class and is available at 3,500 rpm – 85 per cent is unleashed from as low as 2000 rpm. The engine has a sonorous tone and is highly cultivated throughout the entire speed range.
Three chains for the four camshafts
The powerful V8 belongs to the present V engine family of the brand, notable for a 90° cylinder angle and a distance of 90 millimetres between cylinders. A maintenance-friendly two-stage chain drive system, comprising three single roller chains, activates the four camshafts; it is located at the rear of the engine to save space. A fourth chain drives the ancillaries.
The cylinder housing of the V8 engine is cast from an aluminium-silicon alloy; the pistons and rings glide in the liners on the hard silicon crystals.
Separate liner inserts are not necessary: this permits a narrow bridge width of only 5.5 millimetres and saves weight accordingly. Modifications to the sump and the oil pump ensure adequate lubrication even on challenging terrain – in a similar form, these measures will also benefit other engines in the Audi Q7.
The V8 draws its fuel through a newly designed two-stage variable intake manifold made of magnesium. Electric motors control the manifold length and tumble, and therefore the charge movement, by means of flaps. Two high-pressure pumps, driven by the intake camshafts, deliver the fuel to two interconnected chambers made of stainless steel. One of the most modern engine management systems on the world market controls the whole process – the Motronic MED 9.1.1.
Direct injection with a lambda value of 1
Like the engine in the RS 4, the V8 in the Audi Q7 uses FSI petrol direct injection technology. Here the petrol is not delivered to the intake manifold but injected directly into the combustion chamber, where an even air/fuel mixture to the value of lambda 1 is produced. Thanks to the cooling effect of the directly injected fuel, Audi’s development engineers have at the same time been able to increase the engine’s compression ratio.
The result is a more efficient combustion process and consequently greater power output – this is demonstrated most effectively by the spontaneous response. FSI engines deliver more power than the conventional power plant with manifold injection – and they do so with outstanding fuel economy. A significant strong point of the V8 FSI is demonstrated in the frequently used part-load range, where it uses five to seven per cent less fuel than an engine with manifold injection.
A sprint in 7.4 seconds
The figures confirm the impressive power potential of the eight-cylinder engine. The performance SUV with the V8 sprints from zero to 100 km/h in just 7.4 seconds. Top speed is 244 km/h. Versions with adaptive air suspension, by virtue of the lowered body and less aerodynamic drag, can achieve a further 4 km/h.
Thanks to FSI technology, consumption amounts to only 13.6 litres of premium plus fuel per 100 km; the V8 will also run on premium fuel, but with a slight drop in performance. It goes without saying that the V8, with its FSI technology, complies with the Euro 4 standard. Two upstream pre-catalytic converters and two downstream catalytic converters are integrated into the exhaust system. Air-gap insulated sheet-metal manifolds ensure that the emission control system quickly reaches the optimal operating temperature.
The V6 musters up 206 kW/280 bhp
The second petrol engine available in the second half of 2006 will be a V6 with a displacement of 3.6 litres. It is derived from the six-cylinder engine that powers the top versions of the Audi A3 and the TT. By enlarging the bore, displacement has increased from 3,189 cc to 3,597 cc. Its torque is available across a wide range: 360 Nm from 2,500 to 5,000 rpm. With a power output of 206 kW/280 bhp at 6,200 rpm, the V6 represents yet another impressive power pack for the performance SUV.
With an included angle between cylinder banks of 10.6 degrees the V6 is unusually compact. Its engine block is fashioned from grey cast iron; the valves are actuated by low-friction roller cam follows with hydraulic clearance adjustment. Intake and exhaust camshafts, which are chain-driven, are continuously adjustable to reduce emissions and further improve fuel economy. The variable intake manifold also contributes towards an improvement in cylinder charging. Like the V8, the V6 uses FSI, the direct injection technology developed by Audi engineers, which enhances performance and efficiency.
The performance figures are correspondingly impressive: the Audi Q7 3.6 FSI accelerates from zero to 100 km/h in 8.3 seconds; its top speed is 220 km/h (provisional value).
500 Nm: the 3.0 TDI
A further power pack will be introduced in the Audi Q7 from launch in the form of the V6 3.0 TDI. With a displacement of 2,967 cc, this engine achieves outstanding power and torque potential of 171 kW/233 bhp and 500 Nm. The peak torque is available from as low as 1,750 rpm – giving the driver powerful acceleration in all speed ranges.
Like the V8, the V6 four-valve engine with turbocharger technology belongs to Audi’s new family of compact V engines. It measures only 440 millimetres in length. Its cylinder housing is made of high-strength vermicular graphite cast iron, which is 15 per cent lighter in weight compared with grey cast iron. Despite maximum rigidity the engine weighs a mere 226 kilograms.
Like the V8 FSI, the V6 FSI has chain-driven ancilliaries and camshafts. Low-friction roller cam followers with hydraulic valve-clearance compensation work in the cylinder head. The quick-start heater plugs are armed for extremely cold temperatures – they heat up to 1,000 degrees Celsius within the space of two seconds.
Common rail system with pressure of 1,600 bar
Mixture preparation is performed by a latest-generation common rail system. It has a high-pressure pump and an injection rail for each cylinder bank. The high injection pressure of up to 1,600 bar permits even finer atomisation of the fuel and therefore better mixture preparation and more efficient combustion.
The piezo inline injectors supplied by Bosch are the most important innovation of the current common rail system. They utilise the piezo effect, by which an electric voltage is applied to ceramic, altering its crystal structures. This results in a certain degree of expansion, which is transferred directly (inline) by the TDI injectors to the injector needle without any intermediate mechanism.
With piezo injectors, the number of injection processes per cycle can be varied and optimised almost at will.
The Audi TDI development engineers have opted for up to five injection processes for the 3.0 V6. In addition to the main injection process, double pilot injection takes place in the lower speed range and single pilot injection takes place in the medium range. Simple post-injection takes place up to around 2,500 rpm and under partial load.
This strategy reduces emissions and ensures a smoother combustion process, which primarily benefits the engine’s acoustic behaviour. In this area the 3.0 TDI engine undeniably sets the current benchmark in its class.
Powerful performance from the diesel engine
The Audi Q7 3.0 TDI delivers a driving performance that is hard to find elsewhere among SUVs with V6 engines. The speedo needle passes the 100 km/h mark a mere 9.1 seconds after driving off. The Audi Q7 3.0 TDI quattro reaches a top speed of 210 kilometres per hour and 216 km/h with adaptive air suspension.
The V6 diesel engine requires no more than 10.5 litres of fuel per 100 kilometres. This equates to a range of almost 1,000 kilometres; the fuel tank has a capacity of 100 litres. The TDI is equipped with an exhaust gas recirculation system, complies with the strict Euro 4 emissions standard and comes from the factory with a maintenance-free diesel particulate filter.
Six-speed automatic transmission
To optimally convert the high performance of the engines into forward propulsion, the Audi Q7 4.2 FSI and 3.0 TDI have the tiptronic automatic transmission on board as standard. Depending on the engine version, two technically different versions are employed, both of which have the same dynamic character.
The six gears of the tiptronic are wide-spaced and ideally exploit the torque potential of the engines – on the road and on difficult terrain, where the torque converter with its damping action and torque multiplication is particularly well suited for driving off; it also replaces a reduction gear.
Thanks to its enormous efficiency and ability to transmit up to 750 Nm of torque, the tiptronic is perfectly equipped for any situation. Typically for Audi, it is compact and light – the version for the V6 3.6 FSI weighs only 80 kilograms.
Transmission management is taken care of by the dynamic shift program DSP. It adapts to suit the individual style of the driver and the prevailing road conditions and responds to any changes. DSP controls a wide range; the shifts are precise, spontaneous, fast and smooth.
Faster shifts with the sports program
A special sports program – the S position – promotes a particularly dynamic driving style: in this mode, gear changes are delayed and performed faster. The Motronic double-declutches during downshifts in overrun. The driver can intervene in the process at any time, either via the special shift gate on the selector lever or via optional paddles on the steering wheel. Manual shifts too are particularly fast and sporty.
A number of changes were made to the tiptronic for use off-road on the Audi Q7. The transmission shafts, their mountings and the parking mechanism were reinforced; modifications to the oil sump and intake filter guarantee oil supply even under extreme conditions.
Four-wheel drive equals quattro, quattro equals over 25 years of experience
The classic technology for all high-performance Audi vehicles is quattro permanent four-wheel drive – a concept that has been celebrating victories in motorsport and in standard production vehicles for 25 years now. More than two million Audi quattro vehicles have come off the assembly line to date. quattro technology ensures excellent traction and lateral stability and minimises the effect of propulsive power on the vehicle’s self-steering properties. This provides the basis for dynamic handling and driving stability – on and off-road.
A self-locking centre differential in the drivetrain of the new Audi Q7 – with its longitudinally installed engines – automatically ensures optimum power distribution to all four wheels. The centre differential is a self-locking worm gear that is purely mechanical and so reacts instantly. Its locking action only takes effect under power, while allowing speed differences when the brakes are applied or when cornering.
Like the RS 4 and the S8, the Audi Q7 features the latest-generation self-locking centre differential. It has an asymmetric/dynamic torque split of 40 : 60 between front and rear wheels. In particular off-road situations or if the prevailing road conditions change, the differential can direct up to 65 per cent of the power to the front or up to 85 per cent to the rear. If a wheel at one axle starts to spin, the electronic different lock EDL takes control by means of appropriate brake intervention.
Superior agility and steering precision
The slightly tail-heavy basic characteristics of the quattro drive in the Audi Q7 signify even more agility. This is mainly noticeable when driving into bends – when the steering is virtually free of any noticeable torque steer. Thanks to direct servotronic control, which is standard on all Audi Q7 models, the driver enjoys a level of steering precision and clearly defined handling that up to now has been unimaginable in an SUV and which has only rarely been experienced in a sports car.
The transfer box on the Audi Q7 is installed directly next to the automatic transmission. A hollow shaft in the case delivers torque to the self-locking centre differential. It is then distributed – the somewhat larger proportion flows via the ring gear and the coaxial output shaft to the cardan shaft and from there to the rear. The smaller share is supplied to the sun gear, from where it travels by chain to a second cardan shaft, which leads past the transmission to the front axle.