The all-new 4.0 TDI generates its power from a displacement of 3,956 cc, combining superior performance with low consumption. With 320 kW (435 hp) and 900 Nm (663.8 lb-ft) of torque between 1,000 and 3,250 rpm, the SUV sets new benchmarks in the segment. The V8 diesel engine accelerates the Audi SQ7 TDI from 0 to 100 km/h (62.1 mph) in 4.8 seconds, and on up to an electronically governed top speed of 250 km/h (155.3 mph). In the NEDC, however, it consumes just 7.2 liters pro 100 Kilometer (32.7 US mpg), corresponding to 189 grams CO2 per kilometer (304.2 g/mi).
The new 4.0 TDI is a biturbo that is supported in the lower range by an electric powered compressor (EPC). Its two exhaust-gas turbochargers feature a variable turbine geometry and produce up to 2.4 bars of boost pressure (relative). The EPC supports the turbochargers whenever the exhaust gas provides too little energy for the rapid development of power.
The electric powered compressor is placed in a bypass downstream of the intercooler, i.e. close to the engine. Instead of a turbine wheel, it houses a compact electric motor. It accelerates the engine’s compressor wheel up to 70,000 rpm in less than 250 milliseconds. With the support of the electric powered compressor, the power of the 4.0 TDI is always available spontaneously and without delay when the accelerator is depressed,
even at low engine speeds. When driving off, the SUV immediately jumps out to a lead of several meters over its competitors When driving with a focus on comfort, the electric powered compressor technology prevents an unnecessarily large number of downshifts, thus keeping the rev level low. Sporty drivers will appreciate the passing power and immediate delivery of power when exiting a curve.
Output up to 13 kW: the new 48 volt electrical subsystem
The power for the electric powered compressor can be as high as 7 kW. It is drawn from a 48 volt electrical subsystem, another groundbreaking innovation in the Audi SQ7 TDI. A compact lithium-ion battery in the lower level of the luggage compartment stores around 0.5 kWh of energy and delivers a peak output of up to 13 kW. A DC/DC converter provides the connection to the 12 volt electrical system, which is supplied with 3 kW of power from a novel, efficiency-optimized alternator.
Sequential charging: switching via the Audi valvelift system
The two exhaust-gas turbochargers, each of which is supplied with fresh air from both cylinder banks, are managed according to the sequential charging principle. Control is via the Audi valvelift system (AVS), which here is making its debut in a TDI engine. Electromagnetic actuators displace contour sleeves on the camshafts so that the exhaust valves are either activated or deactivated.
The exhaust, which each cylinder discharges from both exhaust valves, flows through separate channels within a dual-flow manifold system. Each exhaust valve supplies one of the two turbochargers. At low and intermediate load and rpm, the Audi valvelift system (AVS) keeps one valve closed so that the entire exhaust flow reaches the so-called “active” turbocharger. If engine speed increases to the range between 2,200 and 2,700 rpm, the respective second exhaust valve is opened. Now the second turbocharger will also be activated.
A recirculation valve ensures that it spins up quickly and reliably. The V8 TDI achieves its maximum output when both exhaust-gas turbochargers are spun up. Additional AVS units are located at the intake camshafts. Here two cam contours with different timings ensure optimal filling of the combustion chamber, both during EPC supported starts and at high engine speeds. At low engine speeds, combustion is stabilized. At high rpm, cylinder filling is optimized for the high specific engine output. The intake side of the 4.0 TDI is on the outside; the exhaust side with the turbochargers is located in the 90-degree inside V. The short gas paths support the spontaneous response. The common rail system develops fuel injection pressures up to 2,500 bar – a new top figure for a V diesel. The elevated pressure contributes to increasing the specific engine output while simultaneously achieving low emissions under part load. For a given injection duration, more fuel – and thus more chemical energy – can be injected into the combustion chamber and converted there with high specific efficiency to mechanical energy. Ignition pressure reaches the 200-bar mark in broad sections of the characteristic. Continuously variable thermal management and sophisticated measures in the crankshaft and camshaft drive reduce friction. The combination of a NOx storage-type converter combined with an SCR converter integrated into the diesel particulate filter ensures effective and efficient exhaust treatment. A sound actuator in the exhaust system amplifies the sonorous eight-cylinder sound. The driver can configure the sound via the Audi drive select system.
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.