Audi’s e-tron quattro EV: evolutionary powertrain with a dash of revolution for production in 2018; MLB evo
24 September 2015
Audi’s e-tron quattro battery-electric SUV concept, which made its formal debut at IAA in Frankfurt (earlier post), is a strong indicator of Audi’s series-production electric SUV due in 2018—especially in terms of the powertrain.
The e-tron quattro is based on Audi’s MLB evo—the second-generation of the modular longitudinal matrix toolkit (MLB, earlier post), and is, at the same time, potentially contributing to the development of the elements of that toolkit, especially with respect to a modular electric drive component. This could eventually have a role comparable to that of the Volkswagen Group’s modular diesel and modular gasoline engine kits (MDB and MOB). (“Baukasten” = German for construction kit)
The e-tron quattro features a three-motor (one front, two rear) all-wheel drive system that delivers total output (while boosting) of up to 370 kW (496 hp) and total torque of more than 800 N·m (590 lb-ft). Power is provided by a liquid-cooled 95 kWh Li-ion pack. The SUV—which would sit between the current production Q5 and Q7, accelerates from 0 to 100 km/h (62.1 mph) in 4.6 seconds, with an electronically governed top speed of 210 km/h (130.5 mph).
The controller continuously computes the optimal interplay of the electric motors for every driving situation.
Leveraging the interplay of the two motors on the rear axle, the e-tron quattro can “turn like a hunting dog after a rabbit” without any heaviness or wallowing through sharp corners, said Siegfried Pint, Audi’s new Head of Electric Powertrain. (Pint has been at Audi for about six months, coming from BMW where he worked on the electric powertrains for the i3 and i8.) Audi has several development models already on the road.
Drive system: evolutionary with a dash of revolution. Audi already has developed a wealth of IP on quattro four-wheel drive, torque vectoring and electric drive systems. The new e-tron quattro marks the company’s combination of all of those elements into a fully-electric quattro drive.
|The e-tron quattro SUV can “turn like a hunting dog after a rabbit.”|
The e-tron quattro drive system uses an axial motor for the front and two co-axial, Audi-designed motors in the rear. At low load, the motor on the front axle is solely responsible for propulsion.
Due to their short axial length and high relative output, axial flux motors offer size, weight, performance, and efficiency advantages when compared to traditional radial flux electric motors.
The new two-motor rear axle system leverages the work Audi has already done with the two-motor rear-wheel drive on the R8 e-tron sports car. (Earlier post.) The two powerful motors (individual output is not yet specified) enable superb lateral dynamics with huge potential for torque vectoring, Pint noted. The rear motors offer a good balance between maximum and continuous output.
The key is clearly the software control of the interplay of the torque of the two motors—not just for performance, but also for safety. Regulators want to ensure that the car will drive straight, Pint said. “Mis-torque vectoring” must be precluded. (A differential torque of 5,000 N·m is possible, Pint added.)
|Developed by Prof. Dr. Hackenberg, the first-generation modular longitudinal matrix was used in 2007 for the A5, followed by the A4, A6, A7 Sportback, A8, Q5 and Q7 as well as the Porsche Macan. A highlight was the new arrangement of the clutch and torque converter behind the differential, resulting in a longer wheelbase.|
|Dr. Hackenberg then conceived the transverse matrix, the MQB, applied in the new Audi A3 in 2012, with the TT debuting in 2014. The Audi A3 Sportback e-tron plug-in hybrid drive is also an MQB vehicle, as are the Volkswagen brand's Golf GTE, Passat GTE and Tiguan GTE plug-in hybrids.|
|The first vehicle to the the second generation MLB eve was the Audi Q7, now followed by the new A4. Strengths of the MLB evo include the extremely wide bandwidth of drive concepts, the multi-material bodyshell designs and the flexible architecture for operation and display, infotainment and driver assistance systems.|
The Audi team is very far along with the high level Torque Control Manager, which works together with the Electronic Stabilization Control (ESC) to distribute the power between the rear wheels, and on the regen controls, Pint said. There is still work to be done on the field control for the electric machines themselves, Pint added. This specific work marks the more radical component of the powertrain development (“partway between evolution and revolution”).
The resulting two-motor system could become part of the MLB evo kit, said Prof. Dr. Ulrich Hackenberg, Audi Board Member for Technical Development, and the originator of the MLB and the Baukasten system which is now evolving throughout the Volkswagen Group. Elements could also be taken over to and used in the transverse MQB, he noted.
Dr. Heinz-Jakob Neußer, Member of the Board of Management for the Volkswagen brand with responsibility for Development, and responsible for Powertrain Development of the Volkswagen Group, observed that although the electric drive in the e-tron quattro is being developed within the second-generation MLB toolkit:
It is not an MLB platform anymore. The MLB is characterized by the longitudinal installation of the powertrain. Everyone knows that it makes no sense to install the electric motor longitudinally when you need the rotation the other way. This is quite a new platform. However, we can use many of the existing platform systems for the future. These [electric] cars are able to be produced in the existing factories. For that, it is quite clear that the MLB and MSB [managed by Porsche] are the deliverers of the platform for these e-mobility cars.
However, Audi is proceeding with caution, and will essentially wait to see how the market receives the production version of the all-electric SUV.
The car can be built in an MLB factory, once the equipment is installed for testing and safety for the mounting of the parts. We can use all the other components which are based on MLB; the bodywork of the car is based on that. Only the floor is different [due to the battery]. Also, because of the higher weight, we had to do something with the crash structure of the car. We made some improvements, but in general it is the same.
So, the drive system can be fitted into the MLB. However, we want to start with this one car, and to gauge how the market responds. We then have to bring this knowledge to the dealerships and so on. It makes no sense at this point to make a switch, to come to the market with three or four different [MLB-based electric] cars. We'll start with this one. It will be built in one factory to keep the volume quite reasonable.—Dr. Hackenberg
The battery pack: evolutionary development provides the boost in density. Audi has already announced (earlier post) that LG Chem and Samsung SDI will be providing the cells as the e-tron quattro moves toward production. LG Chem will provide its prismatic cells, Samsung SDI its pouch cells. The two Audi partners plan to invest in the cell technology in Europe and will supply the Ingolstadt-based car producer from their European plants.
It is very important that the batteries are produced locally. Shipping from Korea is too costly, and complicated. The suppliers will invest in Europe. We need cell production in Europe , and we need it close to the markets where we produce the cars.—Dr. Hackenberg
The batteries have already improved enormously, Dr. Hackenberg said. Audi and Volkswagen started with a 25 Ah prismatic cell in their first production electric vehicles; the technology has now advanced to yielding 50 Ah cells for plug-in hybrid applications, and between 60–61 Ah for battery-electric vehicle cells such as will be applied in the production version of the e-tron quattro.
It's a big battery, 95 kWh, but for the customer it is necessary to have a range sufficient to fulfill personal mobility demands. If I buy a car, as a customer, I want to be free to from from A to B whenever I like, and, if I change my mind, to be able to take another route. If it is necessary to make a plan two days before, that's not so good. But with 500 km or a bit more, I think it is possible [to provide that freedom]. I think for the customer, such a car will be attractive.—Dr. Hackenberg
Ultimately, Audi is targeting costs of around $100/kWh. Considering that the company started with costs around $700-$800/kWh, they have come a long way, Dr. Hackenberg said, but the $100 target is still a long way off.
The technology study’s lithium-ion battery is positioned between the axles below the passenger compartment. This installation position results in a low center of gravity and a balanced axle load distribution of 52:48 (front/rear), endowing the sporty SUV with outstanding driving dynamics and driving safety compared with other vehicles in the segment.
The large battery block is bolted to the floor structure of the Audi e-tron quattro concept. The modular approach means that Audi will always be able to use the best cell technology available on the market, regardless of whether prismatic, pouch or round cells. Further due to its modular design, the battery is in principle also suitable for other automobile concepts.
Dr. Neußer said that the Volkswagen Group now has a common battery strategy based on platform battery stacks used in each car in the group—a common group specific stack.
We have two suppliers. We need two, I would like to have an additional one. With these common stacks we have many synergies, and we have the highest development speed, especially in terms of the energy density of the cells.—Dr. Neußer
Audi Wireless Charging (AWC). The Audi e-tron is equipped with Audi Wireless Charging technology for contactless induction charging. A charging plate with an integrated spool is placed on the parking space and connected to the grid supply. Using its piloted parking system, the Audi e-tron quattro concept accurately positions iteself over the charging plate; the charging process then begins automatically.
The magnetic alternating field induces an AC current in the secondary spool mounted across the gap in the underside of the car. The AC current is converted to DC by the vehicle’s power electronics and the battery is charged with up to 11 kilowatts of power.
As soon as the battery is fully charged the process stops again. The Audi Wireless Charging technology is more than 90% efficient.
Aerodynamics. The e-tron quattro technology study offers much more in the way of innovation than just in the powertrain. The aerodynamics engineers and exterior designers worked closely together in the wind tunnel to develop the exterior of the Audi e-tron quattro concept.
Active aerodynamics and static aerodynamic measures combine to deliver an outstanding drag coefficient of 0.25. Audi has combined a front spoiler, steeply pitched separating edges at the rear and aerodynamically optimized wheels for the first time, as well as an aerodynamically optimized, microstructured floor pan.
The aerodynamics concept also includes the new, in part movable elements at the front, on the sides and at the rear of the Audi e-tron quattro concept. At speeds above 80 km/h (49.7 mph), they direct the flow of air to improve flow around and through the car.
In the engine hood, two seals, each with four louvers, regulate the flow of air through the thermal management components installed in the front end. The suction effect on the surface of the hood makes it possible to reduce the electrical power of the fan.
At higher speeds the spoiler on the rear hatch extends by as much as 100 millimeters (3.9 in), thus elongating the separating edge. At the same time the diffuser extends to the rear. The targeted merging of the air flows from the roof and the underfloor regions provides for positive aerodynamic effects.
Compact electric motors in the side sills are activated at higher speeds. These force the rear segments of the strips 50 millimeters (2.0 in) outward like a funnel so that the air flows past the rear wheels.
Solar roof and heat pump. The solar roof of the Audi e-tron quattro concept is 1.98 meters (6.5 ft) long—the largest module yet installed in an automobile. It feeds electricity at up to 320 watts into the battery as soon as the Audi e-tron quattro concept is parked or driven in the sun. In the central European climate, it can contribute up to 1,000 kilometers (435.0 mi) of additional range per year.
In the summer, the solar roof produces enough power to run the auxiliary cooling for the interior, to provide a pleasant temperature inside the vehicle before the journey even starts.
The heat pump also contributes to the efficiency of the concept study. It uses the waste heat of the electrical components to climatize the interior and is thus a central component of the thermal management system.
Audi hosted Green Car Congress at the IAA in Frankfurt.