Audi is a diesel-engined S model to its Q7 model line. The newly developed 4.0-liter V8 diesel delivers 320 kW (435 hp) and 900 N·m (663.8 lb-ft), with estimated NEDC fuel consumption of 7.4 liters of fuel per 100 kilometers (31.8 mpg US), corresponding to CO2 emissions of 194 grams per kilometer (312.2 g/mi). The SQ7 accelerates from 0 to 100 km/h (62.1 mph) in 4.8 seconds; top speed is 250 km/h (155.3 mph) (governed).
Among its features are an electric compressor with a supporting 48V subsytem that augments the work of the two turbochargers. Audi engineers will present a paper on the new V8 TDI at the upcoming Vienna Motor Symposium in April.
Audi developed the 4.0 TDI from the ground up. The V8 engine has a displacement of 3,956 cc. Two exhaust-gas turbochargers are activated selectively according to the concept of sequential charging, since exhaust gas only flows through one turbocharger at low and intermediate load. The second turbine is only activated at higher loads. The electric-powered compressor (EPC) augments the work of the two turbochargers, particularly in the lower engine speed range, providing for dynamic off-the-line performance.
The EPC—a first in a production vehicle—is placed in the air path downstream of the intercooler, close to the engine. Because the EPC does not require any exhaust-gas energy to develop boost, it can be used at any time, thus making it the solution for the traditional weaknesses of the classic exhaust-gas turbocharger.
The EPC provides the engine the boost energy needed for the dynamic delivery of power in less than 250 milliseconds. Driven by a compact electric motor, its compressor wheel spins up to 70,000 revolutions per minute. The 4.0 TDI thus develops its immense power with no perceptible lag: It is available immediately upon depressing the accelerator.
The Audi valvelift system (AVS) is also making its debut in a diesel model from Audi. The inlet and exhaust cam shafts each have two cam contours per valve. On the inlet side, one cam contour supports starting off in conjunction with the EPC, while the other optimizes cylinder filling and thus power at high engine speeds. The AVS system on the exhaust side enables activation of the second exhaust-gas turbocharger.
The sequential charging system controls the two exhaust-gas turbochargers so that only one turbocharger is used at low engine speeds. The second is activated additionally at higher loads and engine speeds. The customer benefits from very good torque delivery and dynamic response across the entire engine speed range.
The exhaust streams from the two exhaust valves are hermetically separated, with each driving one of the two turbochargers. In the lower engine speed range, one valve per cylinder remains closed, so that the full exhaust stream flows to the active turbocharger. When load and engine speed increase, the AVS opens the second exhaust valves. This directs flow to and activates the second exhaust-gas turbocharger. The engine achieves its maximum output in this biturbo mode. The switching by the AVS enables fast and precise activation of the second exhaust-gas turbine.
The biturbo V8 combined with the EPC is a core element of the global Audi diesel strategy. With high torque even at low engine speeds and low consumption figures, it is also ideally suited for markets such as the United States. Its engine characteristic combines supreme pulling power with sporty agility – ample off-the-line performance and spontaneous response.
The power for the EPC, which reaches a maximum of 7 kW, is provided by the 48‑volt electrical subsystem. The SQ7 TDI uses this higher-power electrical system, which also facilitates the high-power systems electromechanical active roll stabilization (EAWS) in addition to the EPC.
To meet their high power and energy requirements, the electrical subsystem includes its own 48‑volt lithium-ion battery mounted beneath the luggage compartment with a nominal energy content of 470 watt-hours and peak output of up to 13 kilowatts. A DC/DC converter connects the 48‑volt and 12‑volt electrical systems.
The required energy is provided by a more powerful and highly efficient generator with an efficiency of more than 80% at an output of up to 3 kW. This is a MOSFET generator (Metal Oxide Semiconductor Field Effect Transistor), which reduces electric losses and increases efficiency. MOFSETs replace the diodes used previously. In addition, the 48‑volt storage unit supports the 12‑volt electrical system when required. This also reduces the load on the 12‑volt lead battery.
Further highlights. The intake side of the 4.0 TDI is on the outside, the exhaust side with the two turbochargers is on the inside of the 90-degree internal V. This layout provides for short gas paths, i.e. spontaneous response and short paths for the emissions control system. The common-rail system generates up to 2,500 bars of injection pressure. Ignition pressure reaches the 200‑bar mark in broad sections of the characteristic.
The innovative thermal management and sophisticated measures in the crankshaft and camshaft drive reduce friction. With the combination of a NOx oxidizing catalytic converter and a downstream SCR catalytic converter, which is integrated into the diesel particulate filter and uses AdBlue injection to reduce oxides of nitrogen, the V8 TDI has an efficient emissions control system.
A sound actuator in the exhaust system amplifies the sonorous eight-cylinder sound. SQ7 TDI drivers can choose how much attention they want to draw to themselves by using the Audi drive select system to vary the amount of sound.
The new V8 is paired with a redesigned eight-speed tiptronic.
Networked suspension control. Audi offers the SQ7 TDI with an optional driving dynamics package comprising three technology modules: sport differential, electromechanical active roll stabilization and all-wheel steering. The highly integrated suspension control unit is used in the SQ7 TDI. It assumes the central control of the adjustable shock absorbers, the air springs, the sport differential and roll force distribution. By bundling all relevant suspension functions into a central control unit, the developers achieved an optimal networking and coordination of the functions among themselves.
The electromechanical active body roll stabilization uses a compact electric motor with a three-stage planetary gearbox separating the two halves of the stabilizer. On an uneven road surface, they are actively decoupled from one another, resulting in improved ride comfort. During sporty driving, the tubes are interconnected and twisted against each other. That significantly reduces body roll, i.e. the lean of the car. Together with the transmission, the electric motors produce anything up to 1,200 N·m (885.1 lb‑ft) of torque. The effect is taut, sporty handling—the car leans less in bends and the tendency to understeer is further reduced.
The front and rear stabilizer can be adjusted independently of each other. This active distribution of stabilizer forces between the front and rear axle has a positive effect on road behavior. Steering precision and the agility of the car improve significantly.
Compared with conventional hydraulically switched stabilizers, the 48‑volt-based system from Audi offers major advantages. It can develop more power, it works faster and it is activated even at low speeds. Because it requires no oil, the electromechanical active roll stabilization is also maintenance-free and environmentally friendly.
All-wheel steering. With all-wheel steering, the rear wheels turn in by as much as five degrees, making parking easier. The more direct front-axle steering ratio of the SQ7 TDI improves the handling characteristics. Depending on the situation, the rear wheels steer opposite or in the same direction as the front wheels, improving dynamics and stability.
In Europe, the Audi SQ7 TDI can be ordered beginning spring 2016. It will be offered in Germany for a base price of €89,900 (US$98,000).