Traveling from Sindelfingen across the Swiss Alps and Northern Italy, to its destination of Cassis on the Côte d’Azur, the VISION EQXX electric concept (earlier post) from Mercedes-Benz covered more than 1,000 km (621 miles) in everyday traffic on a single battery charge.
The journey started in cold and rainy conditions, and was undertaken at regular road speeds, including prolonged fast-lane cruising at up to 87 mph on the German autobahn and near the speed limit elsewhere. The battery’s state of charge on arrival was around 15%, amounting to a remaining range of around 140 kilometers (87 miles), and the average consumption was a record-breaking low of 8.7 kWh per 100 kilometers (7.1 kWh per 62 miles).
The VISION EQXX has thus taken electric vehicle efficiency to a whole new level in real-life conditions and with independent proof. The long-distance drive was completed with the charging socket sealed and accompanied by an independent expert from certification body TÜV Süd.
This officially confirms the effectiveness of the new Mercedes-Benz development approach—thinking holistically about efficiency from the drivetrain to aerodynamics and beyond, down to the smallest detail, as well as working with even greater interfunctional collaboration and with external partners. This new blueprint for automotive engineering has delivered a new benchmark for electric vehicle efficiency and range, and the technology in the VISION EQXX will be deployed in upcoming series-production Mercedes vehicles.
The route profile—from motorway to mountain passes, including roadworks—and the weather conditions presented the VISION EQXX with a wide variety of challenges. Departing from the Sindelfingen R&D center near Stuttgart in cold conditions, temperatures from start to finish ranged from 3 to 18 degrees Celsius. North of the Alps there was light rain and further south a gentle headwind blew in the sunshine. The various sections of the route helped document the effect of the many efficiency measures.
The first leg from Sindelfingen to the north-eastern border of Switzerland runs along Autobahn 81. At times, the VISION EQXX sliced through the wind at speeds of up to 140 km/h (87 mph). With its low cd value of 0.17, it gives the wind virtually nothing to grab hold of. This world-beating figure for a road-legal vehicle results from the intelligent interaction of many individual measures. It starts with the basic shape of the body, cradling the smooth-surfaced dome of the greenhouse as it flows like a water droplet towards the rear. Equally beneficial to the aerodynamics are the small frontal area of 2.12 m² and the reduced rear track. Because this is 2 inches narrower than at the front, the rear wheels roll in the slipstream of the front wheels. The active rear diffuser, which automatically deploys at 37 mph, provides better airflow and thus contributes significantly to the reduced drag.
The technology vehicle gains further efficiency benefits from its tires, with their extremely low rolling-resistance rating of 4.7. Bridgestone developed these specifically for the VISION EQXX in partnership with Mercedes-Benz. By way of comparison, the current EU tire label requires a figure of 6.5 for the top rating in Class A.
The EQS uses tires with a rolling resistance of 5.9, which is significantly lower. With the VISION EQXX, Mercedes-Benz is now going one step further. A striking feature is the size of the new tires. The dimensions 185/65 R 20 97 T mean they have a large diameter and a narrow tread.
The specialist Turanza Eco tires combine two innovative Bridgestone technologies that enable a higher range: ENLITEN technology reduces both rolling resistance and weight by up to 20%. Bridgestone’s ologic technology reduces tire deformation while driving, in part through a more tensioned belt section. In addition, the transition from the tire to the wheel rim was optimized in cooperation with the Mercedes-Benz aerodynamics team.
The VISION EQXX’s special features also include its carefully thought-through lightweight construction, which has a particularly positive effect on uphill climbs. Any keen cyclist knows why it’s always the same type of rider out in front on mountain stages. The heavier, more muscular sprinters are always staring at the taillights of the wiry featherweights on the uphill treks. The decisive factor is the power-to-weight ratio. It’s not about sheer performance in the sense of “faster; higher; further” but about endurance and lower energy consumption.
This is exactly what the VISION EQXX demonstrated on the approach to the Gotthard Tunnel heading for Italy. On the section between Amsteg and Göschenen, there’s a 9-mile uphill stretch with an incline of up to five percent. It is here, where every gram of extra weight eats up energy, that the VISION EQXX scores sustainable points with its unladen weight of only 3,869 lbs.
The lightweight design concept of the VISION EQXX is comprehensive—from the materials used to innovative bionic structures that deliver a favorable power-to-weight ratio. Examples of this are the sustainable carbon-fiber-sugar composite material used for the upper part of the battery, which is also used in Formula 1, and the BIONEQXX rear floor, manufactured using an aluminum casting process.
The light metal structural component replaces a much heavier assembly of several interconnected parts. It has gaps in places where structural strength is not required, thus saving material. This innovative design approach results in a weight saving of up to 20% compared to a conventionally manufactured component.
A large part of the weight efficiency is also due to the dedicated electric chassis with lightweight F1 subframe and aluminum brake discs. Another is the battery. At 100 kWh, the power storage unit developed specifically for the VISION EQXX has almost the same amount of energy as the battery of the EQS, which is already a global benchmark among electric cars currently on the market.
However, it has 50% less volume and is 30% lighter. The outcome is that the compact battery, measuring just 200 x 126 x 11 cm (79 x 50 x 4 in), is also comparatively light at 1,091 lbs and fits in a compact car. The electric drive was developed in cooperation with the experts from Mercedes-AMG Petronas F1 Team.
After the Gotthard Tunnel, the road goes downhill for a very long way. The VISION EQXX can use the recuperation effect on any type of gradient and during every braking maneuver, thus extending its range. A positive side effect of this electric braking is that the mechanical brakes are barely used. This makes it possible for the first time to use new types of aluminum brake discs that weigh significantly less than their steel counterparts.
The VISION EQXX solar roof’s 117 solar cells feed the 12-volt battery, which supplies power to auxiliary consumers such as the navigation system. The added value is measurable through the load this removes from the high-voltage battery, displayed by the onboard computer. Overall, the solar booster increases the range by more than 2%—which adds up to 25 kilometers (16 miles) on a journey of more than 1,000 kilometers (621 miles).
The electric drive unit in the VISION EQXX—consisting of the electric motor, transmission and power electronics—was developed together with the F1 specialists at HPP, and has a peak output of 180 kW. Just like the battery, the electric drive unit is compact, lightweight and highly efficient. Its average efficiency in this application is 95%.
This goes hand-in-hand with further efficiency benefits such as the reduction of losses in the drivetrain. The engineers at Mercedes-Benz have succeeded in reducing the total losses in the drivetrain (motor, inverter and transmission) by 44% compared to an e-drive that is not based on this project.
This makes a big difference for the bottom line, with one percent more efficiency bringing two percent more range. This effect is further amplified by the battery of the VISION EQXX, due to its energy density of almost 400 Wh/l and particularly high operating voltage of more than 900 volts.
There are further efficiencies from the active cell balancing that ensures that energy is drawn evenly from the cells during the journey, which increases the usable energy and thus the range even more.
Because the electric drivetrain generates minimal heat waste thanks to its high efficiency, passive cooling is sufficient throughout the journey. The cooling plate in the underbody uses the airflow to ensure even cooling. This aerodynamically efficient solution increases the range by 20 kilometers (12 miles), while the cd value remains unchanged at a low 0.17.
Even on the ascent to the Gotthard Tunnel, the air shutters remain closed. The air control system would only open an additional airpath if there was an increased demand for cooling the electric drive or for climate control inside the cabin on hot days or if the heat pump was running on cold days. The airpath then connects the high-pressure zone at the front of the vehicle with the low-pressure zones along the top of the hood. This enables highly efficient thermal management with minimal air resistance. With the shutters open, the cd value would increase by only seven points (0.007).