Driving the 747-Mile EV Range Mercedes Vision EQXX

Today’s benchmark for EV driving range is commonly regarded as 300 miles, or about 500 kilometers. Drivers concerned that they’ll be unable to complete intercity trips want the reassurance that they won’t be stopping to recharge too frequently.

This caused Mercedes-Benz executives to wonder just how far a road-legal car could actually drive without recharging, and without carrying an absurdly huge battery pack. They set a target of 1,000 km and gave the company’s vaunted engineers a seemingly impossible deadline: design and build a car to make a 1,000 km road trip in just a year and a half.

The engineering team charged with meeting this challenge wasn’t even sure whether it was possible, but they exceeded the target when the Mercedes-Benz Vision EQXX concept car drove 1,202 km from Stuttgart to Silverstone, England, in June. This followed the car’s accomplishment of its assignment with an earlier 1,008 km cold-weather drive from Sindelfingen, Germany, over the Swiss Alps, through Germany to Cassis, France.

The average speed for the 1,008 km (626 miles) drive was 54 mph, while the EQXX averaged 52 mph during its 1,202 km (747 mile) drive. During both drives, the car hit its electronically limited top speed of 87 mph while cruising the German autobahn. This was accomplished using a 100 kWh battery pack, which is about the same capacity as that in a Tesla Model S.

Related:Engineering Solutions By Design News Talks EQXX Concept Car

To gauge Mercedes’ success in building the Vision EQXX, I had the chance to drive the car at the company’s Immendingen proving ground in southern Germany. In my 20-minute spin around the rolling terrain of the proving grounds, I averaged 29 mph on its narrow roads and the car consumed electric power at a rate of 7.78 kilowatt-hours per 100 km. This topped the results drivers achieved during faster highway driving of the company’s demonstration runs when they reached 8.7 kWh/100km.

My driving style was gentle, but it did include a power-sucking 0-60 mph acceleration blast up a steep hill. I didn’t time the run under the circumstances, but it served the purpose of demonstrating solid seat-of-the-pants acceleration despite a maximum power of 180 kW (241 horsepower) from its single electric motor driving the rear wheels.

But because Mercedes optimized the EQXX for efficiency, with minimal mass, rolling resistance, and aerodynamic drag, the car delivers better-than-expected performance considering a power rating that is modest by today’s absurdly high standards.

But if the acceleration is pretty typical, nothing else about the EQXX’s performance or specifications is. Like the production Lucid Air, the EQXX employs 920-volt power electronics built using silicon carbide technology. Unlike other EVs, it weighs a relatively paltry 3,858 lbs.

Related:Mercedes Concept Car Gets Silky, Sustainable Treatment

"Electric range sounds easy but is a complex technical challenge,” noted Joerg Bartels, Vice President for Vehicle Engineering and Overall Vehicle Functions. “The easiest way is to put a bigger battery in the car. However, this leads to diminishing returns due to size and weight.”

Instead of a bigger battery, Mercedes went with a better battery. Tapping the Formula 1 experts at Mercedes-AMG High-Performance Powertrains (HPP) in Brixworth (United Kingdom), they developed a battery that is half the physical size of the one in the EQS production car with 30 percent less weight, but the same power storage capacity.

The energy density of nearly 400 watt-hours of power per liter of physical volume is possible thanks to advances in the chemistry of the cells’ anodes. Their higher silicon content and advanced composition mean they can hold considerably more energy than commonly used anodes, according to Mercedes. The battery actively balances the cells, so the car draws energy evenly from the cells while driving, which contributes to its ability to maximize the range.

The lid on the 1,091-lb. battery pack is made from a unique, sustainable composite material derived from sugar cane waste, reinforced with carbon fiber. Another feature that contributed to the impressive energy density is the high level of integration in the battery pack, which incorporates the power electronics in a module Mercedes calls the OneBox.

Engineers pursued every possible detail in boosting the EQXX’s range, anticipating that it would take contributions from every area to achieve this astonishing accomplishment. “I never witnessed this amount of teamwork before,” remembered electric drive special projects engineer Julien Pillas.

That’s why there are 117 solar cells on the car’s roof. Solar cells can’t really make that much power, but the panel helps keep the EQXX’s 12-volt electric system powered for the car’s HVAC blower, lights, infotainment system, and other ancillaries, which in turn relieves some of the load on the car’s 920-volt powertrain.

The panel was developed in partnership with Europe’s largest solar energy research institute, the Fraunhofer Institute for Solar Energy Systems ISE, and under ideal conditions, it can 15 miles of driving range. The solar system includes a lightweight lithium-iron-phosphate battery for energy storage.

Finding energy anywhere and everywhere is the key to the EQXX team’s success. “Going from 90 percent efficiency to 95 percent efficiency means that you have to cut losses in half,” Pillas observed. “There are non-linear benefits from improving efficiency in recovering energy,” he said.

The car’s air-cooled battery is an example because eliminating the liquid cooling circuit saves weight and improves efficiency. The EQXX’s heat pump system gathers heat from both the drivetrain and ambient air temperature for cabin heating, and the car sheds heat through an innovative cooling plate on its underside rather than a conventional heat exchanger, which causes drag from forcing air through a radiator. The cooling plate is flat on the car’s underside and is cooled by the air passing beneath the car.

This is only one contributor to the car’s slippery 0.17 CoD. Another is the EQXX’s very shape; it tapers in the rear. But with a nod to concerns that the car looks normal to drivers, the taper is a fairly subtle 2 inches, which is not obvious to onlookers.

Length also reduces drag, but drivers aren’t interested in cars with absurdly extended tails. Mercedes’ solution is an active rear section that only extends at highway speeds to reduce drag while retracting to an easier-on-the-eyes and easier-to-park configuration at around-town speeds.

Such details let the EQXX’s design team make one large sacrifice to customers’ preferences: the rear wheels are exposed rather than enclosed behind wind-smoothing skirts. Cars like the original Honda Insight hybrid-electric enclose the rear wheels for the significant drag-reduction benefit, but Mercedes was determined that the EQXX retains the looks of a car its customers would aspire to own.

The project’s speed was another challenging factor and an area where Mercedes engineers were able to learn from the time-is-money Formula 1 operation in England. “We even improved our customs process at Mercedes-Benz,” Pillar said. “Four days [for components to clear customs] would be too many,” he said. The Formula 1 team’s processes were designed to speed parts through customs, and Mercedes brought that process over to aid with the EQXX’s development.

They also relied on software modeling. “Developing software before hardware exists speeds up development a lot,” Pillar explained. “We started developing digitally as soon as we sorted out the designs of the components. That’s when you go to software-in-the-loop testing.”

The team even modeled the eventual record-setting 1,000 km drive beforehand so they’d know what to expect, and then captured data during the actual drive to correlate with the model. “It really pays off to feed back this knowledge to the software-in-the-loop model,” he said.

The team built an EQB SUV engineering mule with the EQXX drivetrain so they could test hardware as it became ready. This rough test vehicle lacks climate control, so the engineers spent hours shivering as they put it through its test program. “We have a love/hate relationship with it,” Pillar joked. “We spent five weeks testing with it in Spain.”

This monumental effort paid off when the EQXX achieved its audacious goal of 1,000 km on a charge, and it only got better when the car later topped that. Perhaps the most astonishing aspect of the car is how polished the prototype is. I had the opportunity to drive the Automotive X-Prize-winning Edison2. That car was an exotic science project, while the Vision EQXX is an absolutely realistic daily driver that is put together solidly.

A suspension groan arose during our drive, and Pillar pointed out that this didn’t happen until Mercedes let journalists drive the EQXX. That detail aside, the car is fully ready for prime time. You can’t help thinking that Mercedes executives noticed the same thing. So maybe the Vision EQXX is a concept car whose technology and design will be incorporated into future models. Or maybe Mercedes will surprise us by offering a version of the car for sale. That would have to be easier than building the 1,000-km EV was.