Technology demonstrator VISION EQXX

A single battery charge, 11 hours and 32 minutes pure driving time, two stops of 15 minutes each to switch drivers, a total of 1,008 kilometres driven and a reach of around 140 kilometres... On its maiden road trip from Sindelfingen, Germany across the Swiss Alps to Cassis on the French Riviera, the Mercedes-Benz VISION EQXX set an impressive record for reach. Over 1,000 kilometres with one battery charge. No wonder, as Tim Wölfel, Electric Drive Special Projects Lead and specialist for the electric drive of the VISION EQXX, said in his summary: “Reach is no longer an issue.”

On its second road trip two months later, the VISION EQXX substantiated the fact that this at least applies to prototypes. The car travelled 1,202 kilometres from Germany to England on one battery charge. To be more precise: from the Mercedes-Benz Museum in Stuttgart, Germany to Calais, France, with the train through the Channel Tunnel, and on the road again to end up in Silverstone, England. Along the way, the VISION EQXX stopped off at the Mercedes-Benz Grand Prix in Brackley. It was greeted there by the Formula One and Formula E experts who collaborated with the colleagues in Sindelfingen on the development of the progressive drive train. During the entire road trip, on average the VISION EQXX consumed only 8.3 kWh/100 km, despite heavy traffic and summer temperatures. The next milestone.

Brief flashback: VISION EQXX world premiere

On 3 January 2022, the software-based research prototype VISION EQXX celebrated its digital world premiere. CEO Ola Källenius, Chief Technology Officer Markus Schäfer and Chief Designer Gorden Wagener introduced it as “the most efficient electric vehicle that the ‘brand with the star’ has ever built”. A moment that made her “very proud” after a development period of only 18 months, recalled Jasmin Eichler, Head of Future Technologies at Mercedes-Benz and the project lead. But for the team, the standard formulated at the premiere also meant: “Now the pressure is on to deliver!” Ultimately, the VISION EQXX is not a show car. Instead, it is a technology demonstrator that puts what is technologically feasible for the developers, engineers, aerodynamics experts, drive experts and designers at Mercedes-Benz on the street.

In the three months between the world premiere and the maiden road trip, the group of experts showed what it can do in only a few weeks. “We put the VISION EQXX through its paces and extensively optimized once again,” said Eichler. The engineers saved a further 40 kilograms of weight and four more points were “gained in the aerodynamics”. At the end of the record trip, the VISION EQXX had consumed 8.7 kilowatt hours per 100 kilometres – “which was definitely below our target value,” as Eichler reported. On the second road trip, at 8.3 kWh/100 km, the car’s consumption was even lower.

The premiere: world’s top aerodynamics ready to go

On the morning of Tuesday, April 12, at 7 a.m. everyone was ready to go. The prototype started off on its first record trip in relatively bad weather – 3 °C – in Sindelfingen, in front of the new Mercedes-Benz Electric Software Hub building. An auditor from TÜV Süd, who had officially sealed the charge port earlier, monitored the entire road trip as the passenger in one of the two EQS accompanying vehicles. At up to 140 km/h, they took motorway 81 to the northeastern border to Switzerland. With its low cW value of 0.17, the prototype presented almost no target for the wind. The world’s top aerodynamics among vehicles with approval for road use were the result of the interplay among many individual activities. Beginning with the basic form of the body, which integrates the smooth dome of the passenger compartment and flows to the rear with the elegance of a drop of water.

Other features supporting low drag are a low front surface of 2.12 m² and reduced rear track width. It is narrower than the front by 50 mm, which means that the rear wheels roll in the slipstream of the front wheels. The active rear diffuser automatically extends at 60 km/h. It improves the airflow and makes a key contribution to reducing drag. “We have the interplay among all the disciplines involved to thank for this record. At this speed, aerodynamics are responsible for more than 60 per cent of the resistance that impacts this type of car. They were the decisive factor,” said Laura Vranos, who is the expert for the efficiency of the VISION EQXX and monitored the trip in the mission control centre. “Each edge, each air gap on the VISION EQXX was optimised such that the car provided as little cross sectional area as possible and the air could flow ideally.”

The road trip continued on past Zurich towards Lake Lucerne in stop-and-go traffic, and then went up to the Gotthard, through the tunnel and into Italy. Past Como, the car weathered Milan’s traffic jams and went towards Genoa and then Nice. That evening, upon arriving at the destination, the small town of Cassis on the French Riviera, the sun was still shining. “Our main aim was to test the reach under real conditions,” said Tim Wölfel, the specialist for the car’s electric drive. “We didn’t want to drive around in circles at 30 km/h somewhere on a test track.” If you enter the route “Sindelfingen – Cassis” in Google Maps, you will be shown alternative routes that take you to the destination faster. “But we wanted the extra challenge of driving through the Alps in the VISION EQXX.” 12 April was actually the day on which the VISION EQXX was driven on a public road for the first time. “We didn’t test the trip in advance,” explained Wölfel.

Digital twin leads the way

Of course that doesn’t mean that the real VISION EQXX was unprepared when it set off on its maiden road trip with the two pilots. In the mission control centre in Sindelfingen, the car’s digital twin had started off somewhat earlier. A digital twin is a “software in the loop” simulation tool that is fed with data on the weather and traffic along the route in real time. It was always on the route one hour earlier than the real car. This way, the crew in the mission control centre always knew what was awaiting the VISION EQXX along the route. Alongside the digital twin, there was also a real twin, fondly called “eMMA” in reference to the MMA e-mobility platform from Mercedes. A black EQB 250 served as the testing & development vehicle. Connected to a test bench in Sindelfingen, it “drove” the route simultaneously with the VISION EQXX. “Like in Formula One, we were able to track the drive train and data of all systems in parallel and at the same time, take many developers along on the trip,” Wölfel recounted. The approximately 25 experts from a range of disciplines who participated in the development sat in the mission control centre on premiere day and evaluated the real-time data, ready to intervene if necessary.

“There actually was a delicate moment: on the way up to the Gotthard Tunnel, the DC/DC converter of the VISION EQXX went down for a short time,” said Project Lead Jasmin Eichler. Explanation: The DC/DC converter connects the high-voltage battery to the 12-volt onboard network and feeds it. When the converter goes down, the 12-volt battery empties. The car has to stop. “We noticed early on that something was wrong, analysed the data and got a small group together – including colleagues from Formula One and Formula E, who can solve problems incredibly quickly. During the previous tests, we often considered what we could do in a situation like that.” In the case of the DC/DC converter, the experts decided to restart. The driver and co-pilot in the VISION EQXX were informed of the plan. “I have to confess that there was a bit of tension at that point,” said Wölfel. “Luckily, a red light came on just at the right moment,” added Eichler. The system could be restarted and the trip continued smoothly.

Efficiency is a mosaic of many measures

The enormous level of efficiency that the technology demonstrator featured on its trip to the French Riviera is the sum of many small, innovative details. Take its tyres for example, which at 4.7 per thousand have extremely low rolling resistance. Mercedes-Benz developed them for the VISION EQXX with its partner, Bridgestone. To compare: The current EU Tyre Label requires a rolling resistance of 6.5 per thousand for the best rating in class A. Another striking special feature is the new tyre dimension, 185/65 R 20 97 T, which stands for a large diameter with narrow tread. Further, the flow transition from tyre to rim was optimised in collaboration with the aerodynamics team from Mercedes-Benz.

Although all disciplines “went the extra mile” in the weeks before the maiden road trip, as efficiency expert Laura Vranos emphasised, it was a nerve-wracking experience – not only because of the initially bad weather before the Gotthard: “There was a point of no return on the trip. We had to decide whether or not to stop and call it a day, and try again the next morning. Or continue. We always had our eye on efficiency, overlaid the current weather and compared it to the forecasts. In the interim, there was also a minor issue with the dashboard. The current consumption was not displayed constantly and had to be calculated by a colleague. Five kilometres before the point of no return, you could have heard a pin drop in mission control – the air was literally thick enough to cut with a knife. When we were able to announce: ‘If nothing out of the ordinary happens now, we’ll make it’ you could see how everyone immediately relaxed. That moment was my personal highlight,” said Vranos.

Solar roof: power boost from the sun

After the Gotthard, everything became easier. After all, as on the maiden road trip in the Po Valley near Milan and all the more so during the summer trip to Silverstone, the VISION EQXX gets a power boost from its permanently installed solar roof and not a charging station. The 117 solar cells feed the 12-volt battery, which in turn supplies the auxiliary loads and the navigation system with power. The added value is measurable: the high-voltage battery is relieved accordingly, and this can be seen on the display of the on-board computer. Overall, the solar booster extends the reach by more than 2 per cent – which adds up to a good 25 kilometres on a route of over 1,000 kilometres.

Over the hills and far away: advantage for lightweights

Another special feature of the VISION EQXX is its consistent lightweight construction, which has a positive impact on gradients above all. The VISION EQXX impressively demonstrated this advantage on the approach to the Gotthard Tunnel. On one section of the route between Amsteg and Göschenen, there is a 14-kilometre climb with a gradient of up to 5 per cent. Here, where every gram of extra weight gobbles up power, the VISION EQXX used its tare weight of 1,755 kilograms to its advantage. The lightweight construction concept of the VISION EQXX is comprehensive: from the materials used to the innovative, bionic structures that yield a favourable ratio of strength to weight. Take for example the sustainable carbon fibre-sugar composite material also used in Formula One that comprises the top section of the battery, and the BIONEQXXTM rear floor produced with a cast aluminium process. The lightweight metal structural component yields a weight savings of up to 20 per cent as compared to a conventionally produced component.

With its lightweight Formula One auxiliary frame, plus brake discs and traction battery made of aluminium, the chassis is responsible for a major share of the weight efficiency. At 100 kWh, the newly developed storage battery of the VISION EQXX almost has the same amount of power as the EQS battery, which achieved top ratings in the worldwide comparison of electric cars in series production. However, it has 50 per cent less volume and is 30 per cent lighter. “In general, the collaboration with the colleagues from Formula One was extremely productive for the project,” commented Tim Wölfel. And Project Lead Jasmin Eichler added: “It was a brilliant team overall – Mercedes as a whole really delivered. I’ll never forget feeling how everyone was pulling in the same direction.”

Back down into the valley with aluminium disc brakes

After the Gotthard Tunnel, the VISION EQXX went downhill for kilometres. The prototype used the topography there in line with its means: VISION EQXX regenerated its power reserves. In the case of electric cars, the term is “regeneration”: recovering brake energy. In this discipline as well, the VISION EQXX raises the bar thanks to its high-efficiency electric drive train. The VISION EQXX can use the regeneration effect on any type of downward slope and any braking action. A positive side effect: thanks to the electric brakes, the mechanical brakes are almost never used. In turn, this made it possible to use innovative aluminium brake discs for the first time. They weigh considerably less than their steel counterparts.

Innovative eATS: powerful, responsive, and enduring

The electric drive train (eATS) of the VISION EQXX was developed in collaboration with the Formula One racing sport specialists from Mercedes-AMG High Performance Powertrains (HPP) and Mercedes-Benz-Grand Prix (MGP). It consists of an electric motor, gear box and power electronics – and has a peak output of 180 kW. Torque is present from the very first motor revolution and the VISION EQXX has a very low drag. As a result, its full potential was basically never tapped during the entire road trip to Cassis. But other factors are more important than maximum power: The eATS is as compact, lightweight and highly efficient as the battery. The average efficiency coefficient for this application is 95 per cent. In other words, 95 per cent of the power from the battery reaches the wheels.

“One of the best ways to increase efficiency is to reduce losses,” explained Eva Greiner, Chief Engineer Electrical Drive Systems. “We worked on every part of the system to reduce power consumption and losses through system design, material selection, lubrication and heat management. And our simulation tools helped us to quickly find out what worked and what didn’t.”

The engineers from Mercedes-Benz successfully reduced the total losses in the drive train (motor, inverter and gear box) by 44 per cent. That also added up under the bottom line: 1 per cent more efficiency equals 2 per cent more reach. The battery of the VISION EQXX also supports this effect, thanks to its remarkable energy density of just under 400 Wh/l and an extremely high operating voltage of over 900 volts. Speaking of high voltage: the technology was used for the first time ever and proved itself during the entire road trip. There were no problems like cable overheating: everything was OK. Active cell balancing also contributed to efficiency gains. It ensured that the power was evenly drawn from the cells during the trip. As electric drive trains develop little waste heat, passive cooling was sufficient during the entire first record road trip. The cooling plate in the underbody used the air flowing past and ensured even cooling.

Efficiency assistant: active support for saving power

In the efficiency assistant, both the driver and co-pilot had useful support with tips on the best possible way to drive at their side. It provided them with information on the energy flow, battery status, topography and even on the direction and intensity of the wind and sun. Zane Amiralis, User Experience Designer, said: “The software that we developed in only 18 months did indeed ensure that the driver in the VISION EQXX had his very own mini mission control centre aboard. He could use it for an overview of all the key data on the screen and knew: ‘Yes, VISION EQXX can!’”

The UI/UX had a completely new, one-piece display that goes across the entire width of the interior. Elements of the UI support the seamless interaction between the driver and the vehicle. Among other aspects, through artificial intelligence that imitates the function of the human brain. In the VISION EQXX, Mercedes-Benz is following a radically new UI/UX approach. A game engine lifts the UI graphics to an entirely new level. The user interface shows how real-time graphics open up new digital opportunities. They react immediately to the driver’s needs and bring the real world into the vehicle.

Lessons learned for future series vehicles

“The aim for the VISION EQXX was not to build yet another show car,” explained Eichler. “The mission was to develop a technology program that would support the complete transformation of Mercedes-Benz.” Courage and creativity are a must for a project like this – at the beginning of the development, the team was not yet at the 1,000 kilometre-reach mark. But Jasmin Eichler is certain: “In all vehicles of the future, Mercedes-Benz will benefit from the creative engineering achievements that made the VISION EQXX a success.”