Audi's target for the E-Tron is the same SUV buyer who might also have shopped for a Q7, Mertens said (the E-Tron’s wheelbase sits between the Q5 and Q7 in Audi’s SUV lineup). To that end, early in the development process, Audi surveyed its customer base to learn just what kind of EV they would use. The questions included how many business trips they take and whether they live in detached homes or in multi-family dwellings.
"The things that the customer looks for, they are basically the same no matter if it's a combustion-engine car or a battery-electric car,” Mertens said. “In the end, we needed to design the E-Tron so that it would appeal to normal car buyers, not to electromobility freaks." Selling mainly to EV zealots “would be too narrow a segment,” Mertens said. "If you look at our product plan right now, selling 30 percent electric cars in 2025, there are not enough electric-car freaks."
Range and fast-charging targetsThe E-Tron’s program parameters were defined over four years ago. The engineering team particularly focused on making the EV-specific systems (i.e., the battery and the brakes) transparent to Audi customers who are familiar with combustion-engine models.
Even before digital simulation work began on the E-Tron, Audi engineers established a target range of more than 500 km (310 miles) on the then-current NEDC (NEFZ) European cycle to minimize range anxiety issues. The result is a 95-kW·h, 400-V lithium-ion pack that weighs around 700 kg (1,543 lb) and will offer a range of over 248.5 miles (400 km) using the WLTP cycle (which would have been over 500 km on the old test). EPA numbers for U.S. models are not due until closer to the E-Tron's on-sale date, but they will be lower than the WLTP figures.
The battery pack is made up of 36 modules. The base layer houses 31 modules with five on a “second floor” that fits under the rear seats. Each module contains 12 pouch-type 60-A·h cells housed in an aluminum-coated polymer outer skin. Audi has said it can use “technically equivalent prismatic cells” in this pack, but battery-development engineer Andreas Deindl would not say how many prismatic cells would fit into each module.
Another battery target was to enable 150-kW DC fast charging – a first for a series-production vehicle. The E-Tron pack accepts both AC and DC charging, with AC limited to 22 kW and DC fast charging accepting up to 150 kW. This requires some enhanced infrastructure, like a CCS connector on a cooled cable. Mertens said all of the DC fast-charge stations currently being installed by Electrify America and Ionity have cooled cables. Without this feature the limit is unlikely to climb over 140 kW.
In the desert heat of the E-Tron’s December 2018 media launch in the UAE, a temporary EVTEC station set up did not have a cooled cable and was only able to offer a maximum 137 kW. Based on the in-car display, this energy flow would be enough to put over 350 miles (217 km) of range into the pack per hour.
No automotive pack currently in production offers such fast-charging capability, even those that are liquid cooled like the E-Tron’s. DC fast charging will fill a pack to around 80% state of charge, then slow the charge rate for the remaining capacity to avoid cell damage. The E-Tron does this automatically, but the dash screen still gives a charging rate in distance/hour, another sign of tailoring the experience for Audi owners accustomed to ICE nomenclature.
Boxes-in-a-boxThe E-Tron’s battery pack is a boxes-in-a-box design with a dedicated aluminum impact-protection structure. The battery package is bolted to the E-Tron’s body structure at 35 points, which increases torsional rigidity by a claimed 27%. Audi engineers said the E-Tron’s overall torsional rigidity is 45% higher than its conventional SUVs.
The battery’s thermal management system is designed to keep the pack at a peak temperature of 35°C while also lowering the risk of fire in a crash. The system uses 5.8 gallons (22 L) of coolant flowing through 131.2 feet (40 meters) of pipe just outside the battery modules. The coolant channels are fastened to the modules using a thermally conductive adhesive.
The thermal management system also cools the power electronics, the charger and the electric motors – including the rotors. According to Audi engineers, waste heat from the electric motors (up to 3 kW of actual power losses), can be used by the E-Tron's thermal management system to heat or cool the cabin. This energy recycling can increase the E-Tron’s range by up to 10%, they noted.
Regenerative braking with ICE feelStepping on the brake pedal in the E-Tron feels like braking on most any recent SUV. Deceleration is controlled by a new electro-hydraulically integrated brake control system that Audi claims is 30% lighter than a conventional brake system, weighing less than 13.2 lb (6 kg). Deceleration up to 0.3 g is handled by the electric motors in regenerative braking mode, and three levels of regenerative braking are adjusted by +/- paddles on the steering wheel.
Level Zero lets you “sail” on the highway in Volkswagen Group’s terminology, with no regenerative-braking activation. Level 1 applies minimal deceleration when you step off the accelerator pedal, and Level 2 applies more re-gen, but not enough for one-pedal driving. The software calibration results in smooth motor ramp-out and no harsh feedback in the pedal.
In developing the E-Tron, Audi has engineered out traditional EV quirks in order to broaden the vehicle’s appeal. You can’t drive an ICE-powered car with one pedal, and you can’t drive the E-Tron that way, either. Even the labeling for the paddles on the steering wheel is meant to make Audi drivers feel right at home. The left paddle, which downshifts the transmission in Audi ICE models, activates a higher regen level in the E-Tron, despite the “minus” symbol.
A new, temporary E-platformThe E-Tron rides on its own platform, which attracted a fair share of new hires to help develop it. About half the platform team were fresh faces according to chassis development engineer Victor Underberg. “In the early phase, it's really important that the new guys work closely with the veterans,” Underberg explained, “because they have the huge know-how.” The E-Tron’s air suspension, for example, is similar to that found on other Audi models. “In a car like this, you need a really high knowledge of how to apply the suspension system,” he said. “So guys who worked on the Audi Q7 or Q8 also worked on the E-Tron.”
Despite the work devoted to the E-Tron platform, it will basically be a one-off (not counting the E-Tron Sportback spin-off) as the VW Group has a new platform called PPE under development. The PPE platform will incorporate lessons from both the E-Tron and the J1 platform that underpins the upcoming E-Tron GT and the Porsche Taycan. VW uses the MEB platform for it smaller EVs, including the I.D. variants.
In deploying the E-Tron, Audi will need to educate owners on fast-charging, and the car launches in Europe with side-view cameras in lieu of mirrors, another technology that will require customer familiarization. But on most other fronts, Audi has managed to engineer an EV that offers the benefits of an electric powertrain without making the E-Tron look or drive like something foreign to its customer base. With its closest competitors likely the Tesla Model X and the new Jaguar I-Pace, the E-Tron is designed to help make EVs mainstream, and appears set to help accomplish that goal. Continue reading »