The Audi RS 5 TDI Concept
1 electric turbo + 2 exhaust turbos = 385 hp and 553 lb-ft
Imagine a diesel sports coupe with three turbos that gets more than 44 mpg and you have the all-new Audi RS 5 TDI concept car. While it’s not yet confirmed for production, the RS 5 TDI is a study in the future of diesel power. In addition to two conventional exhaust-driven turbos, the RS 5 TDI uses an electric turbo to motivate 385 hp and 553 lb-ft of torque out of a 3.0L V-6 engine. That’s enough power to rocket the luxury coupe from 0 to 60 mph in less than 4 seconds flat, with the e-turbo giving it the responsiveness to pull out of corners like a gas-powered sports car.
What’s an Electric Turbo?
Conventional naming suggests a forced-induction device with a mechanically driven turbine should be called a supercharger, but Audi calls its invention an electric turbo. We won’t argue with Audi because it’s the first to bring this technology into the diesel realm -- plus, we like the terminology because it looks like a conventional turbo. In the RS 5 TDI, the electric turbo (or e-turbo, as we’ve taken to calling it sometimes) is driven by a dedicated 48-volt power supply. This is separate from the 12-volt supply used for the rest of the vehicle, and power is stored in a compact lithium-ion battery instead of a conventional lead-acid battery.
When the e-turbo receives power, it takes only a few hundredths of a second for it to spin up to 70,000 rpm. This is about half the maximum speed of an exhaust-driven turbo, but the fast-acting design makes it ideal for takeoffs and engine speeds less than 3,000 rpm. There’s an electric bypass valve inside the intake path that stays closed until the exhaust-driven turbos kick in, which helps the e-turbo maximize it’s participation in building power consistently throughout the powerband.
Performance and MPG
In combination with the two exhaust turbos, the e-turbo helps the RS 5 TDI engine reach a peak of 553 lb-ft of torque at just 1,250 to 2,000 rpm. Unlike a traditional diesel that makes about twice as much torque as horsepower, this tri-turbo engine is able to produce 385 hp at 4,200 rpm. That means the RS 5 TDI is much more responsive to throttle inputs and able to build engine speed much faster than a conventional turbodiesel. The engine attached to all three of the turbos is the current Audi 3.0L V-6, but if the coupe makes it into production, it will probably have the new version of that engine that was recently announced. That engine will be up to 13 percent more efficient than the current model, which means the RS 5 TDI could end up getting even better fuel economy than its already impressive rating of 44.4 mpg.
The RS 5 Sport Coupe
The TDI version of the RS 5 uses the 8HP eight-speed Tiptronic shiftable automatic by ZF with its locking torque converter instead of the seven-speed dual clutch found in the gas version. Other than that, the diesel is very similar to the standard RS 5 with its quattro permanent all-wheel drive that has a mechanical locking center differential with a rear-biased 40:60 ratio and the ability to send up to 70 percent of power to the front, or up to 85 percent to the rear. In between the rear wheels is a sport differential with individual electrically actuated clutch packs that lock each wheel independently. The RS 5 also uses a “torque vectoring system” that employs yaw sensors and the large in-wheel brakes to prevent traction losses while the car is cornering.
Soft-compound 275/35R20 summer tires surround 20x9-inch wheels around large 14.4-inch front and 12.6-inch rear brakes, or optional 15.0-inch ceramic front brakes. The suspension is made mostly of aluminum parts, with a five-link setup in front, a trapezoidal trailing arm design in the rear, and coilovers at each corner. Riding on the suspension is a taut steel unibody chassis with aluminum front fenders. Inside the cabin, you’ll find the same luxury appointments as the $69,600 gas-powered RS 5, including a thick sport steering wheel that’s flat on the bottom, Napa leather, and sport pedals.
The Future of the Electric Turbo
Dr. Ulrich Hackenberg, board member for technical development for Audi, says, “48-volt systems and electric turbocharging are important technologies for the future,” and that’s good news for fans of diesel power. The RS 5 TDI luxury sport coupe was used to showcase e-turbo technology, but there are plenty of vehicles wearing four rings on the grille that could end up with a version of this powerplant. Although we would love to see the RS 5 TDI sold here in the U.S., our guess is that the tri-turbo 3.0L engine will debut in the SQ5 TDI SUV, which is only sold overseas.
The interior of the RS 5 features a thick sport steering wheel with a flat bottom and paddle shifters to control the eight-speed automatic transmission. The gauges have a white-on-black theme and the red needles on the speedometer and tachometer jump up to the limits when the ignition is turned on. The seats are made of Napa leather and optional features include carbon trim pieces, automatic cruise control, adaptive lights that turn with the RS 5, and a sound system by Bang & Olufsen.
The powertrain of the Audi RS 5 TDI uses a tri-turbo 3.0L V-6 engine, an eight-speed shiftable transmission, a full-time all-wheel-drive system, and an electronically locking rear differential. The ZF 8HP transmission has a locking torque converter and shifts between gears in just 200 milliseconds. The quattro all-wheel-drive setup uses a crown gear mechanically locking center differential that can send up to 70 percent of power to the front wheels or up to 85 percent to the rear. The sport rear differential has individual electrically actuated locking clutch packs for each rear wheel.
The engine inside the RS 5 TDI is a 3.0L V-6 with a 48-voltpowered electric turbo, a low-pressure exhaust turbo, and a high-pressure exhaust turbo. Air compressed by the exhaust turbos is sent through an intercooler before being pushed through the e-turbo at engine speeds up to 3,000 rpm. Then, a bypass valve opens in the intake to allow the engine to breathe freely. A throttle valve in the intake tract also helps manage the flow of air to minimize the effects of turbo lag. The diagrams indicating the intake flow show the original engine design from 2012 when there was just a single exhaust turbo and the electric turbo was mounted on the engine. The new three-turbo setup is capable of producing a maximum of 34.8 psi of boost.
Audi recently introduced the newest generation of its 3.0L V-6 TDI engine that is more powerful, more fuel efficient, and cleaner than ever before. This engine would possibly be used if the RS 5 TDI makes it to production. Audi says this engine will be the first in automotive history to combine a NOX storage catalytic converter, diesel particulate filter, and DEF injection into a single assembly. Improvements to the previous version include a new crankcase design, new cylinder heads with separate coolant loops, piston rings and pins that have been optimized to minimize friction, and a new variable-load oil pump.
|Audi RS 5 TDI Specifications|
|Body:||Steel unibody with aluminum front fenders|
|Displacement:||3.0L (2,967 cc)|
|Horsepower:||385 hp at 4,200 rpm|
|Torque:||553 lb-ft at 1,250 to 2,000 rpm|
|Bore x Stroke:||83.0 mm x 91.4 mm (3.27 inches x 3.60 inches)|
|Valvetrain:||DOHC four valves per cylinder|
|Fuel Injection:||2,400 bar common-rail|
|Induction:||1 electric and 2 exhaust-driven turbos|
|Maximum Boost:||34.8 psi|
|Electrical Systems:||12-volt for vehicle and 48-volt for electric turbo|
|Drive Type:||All-wheel drive with locking center differential|
|Transmission:||ZF 8HP eight-speed shiftable automatic with locking torque converter|
|Front & Rear:||Independent multi-link|
|Type:||Electrical rack and pinion|
|Turning Circle:||37.4 feet|
|Wheels:||20x9-inch cast aluminum|
|Tires:||275/30R20 97Y XL summer|
|Type:||Antilock brakes with emergency brake assist|
|Front Brakes:||14.4-inch ventilated discs|
|Rear Brakes:||12.6-inch ventilated disc|
|Optional Front Brakes:||15.0-inch ceramic ventilated discs|
|Front Track:||62.4 inches|
|Rear Track:||62.3 inches|
|Drag Coefficient:||0.32 Cd|
|Front HeadRoom:||37.5 inches|
|Front Shoulder Room:||54.3 inches|
|Front Leg Room:||41.3 inches|
|Rear HeadRoom:||36.0 inches|
|Rear Shoulder Room:||52.8 inches|
|Rear Leg Room:||31.7 inches|
|Seating Capacity:||4 people|
|Fuel Capacity:||16.1 gallons|
|Coolant Capacity:||2.56 gallons|
|Trunk Capacity:||12.4 cubic feet|
|0-62 mph (100 kph):||4.0 seconds|
|0-124 mph (200 kph):||<16 seconds|
|Top Speed:||174 mph (electronically limited)|
|Fuel Economy:||44.4 mpg|