The Race for EVs
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|Christoph Hammerschmidt||July 28th 2016|
So far, electric driving used to be matter of passenger vehicles and sports cars; trucks and buses stuck to their traditional diesel powertrains, despite all their drawbacks of noise and harmful emissions. This is no longer true: Daimler, not only a manufacturer of coveted luxury cars but also one of the world’s largest players in the market for commercial vehicles, has introduced a relatively large truck with an all-electric powertrain, and the company signalizes that the time is right to bring electric trucks to the global markets. “After 120 years of diesel-driven trucks, electric mobility has arrived at this market”, said Wolfgang Bernhard, general Manager of Daimler’s trucks and buses business unit.
Hitherto, electric trucks could not compete against conventional ones in terms of cost, performance and driving range. “Ten years ago, the battery alone made up one third of the weight of the entire vehicle”, Bernhard said. Now, the technology is advanced enough to match and surpass diesel-driven trucks, albeit only in certain model roles.
The benefits of electric powertrains come to fruition in application fields where the absence of noise and exhaust gases is an advantage and the still relatively short range is not a disadvantage. This holds true in urban and metropolitan goods distribution.
And this is exactly what Daimler’s urban eTruck is designed for. With a total weight of 26 metric tons and a motor performance of 2 x 125 kW, the eTruck is a rather grown-up vehicle. The driving range is 200 km (about 125 miles) – enough for tasks like urban goods distribution, but still not enough for long-distance transport, Berhnard admits. Unlike the smaller and older Canter eCell truck that represents a conventional design where the diesel engine has been replaced by en electric motor, the urban eTruck is design from scratch for an electric powertrain. The batteries are arranged between the longitudinal stringers of the chassis which provides protection against side impacts. Instead of a central electric motor, the vehicles is driven by two independent electric motors on the rear axle. Though they are not implemented as wheel hub drive, they are located near the wheels for optimum weight and torque distribution. There is no transmission, but the motors drive the wheels across an 1:23 gear reduction.
The power is stored in three battery packs with a total capacity of 212 kWh. On a fast high-performance DC/DC charging station, the batteries can be charged to 80% of their capacity within less than two hours – provided however that the charging station delivers a performance of 150 kW, which currently is not yet the case. Here seems to be the Achilles heel of the technology: At a standard charging station with 20 kW, it still takes 10 hours to charge the battery to 100%.
Nevertheless, the batteries seem to have a much better performance than eight years ago, when Daimler offered a 3.5 tons van that was a flop. To illustrate the progress in battery technology, Martin Zeilinger from Daimler Advanced Engineering presented a little calculation: The energy content of the battery (212 kWh) equals the energy content of 20 liters of diesel fuel. On 20 liters of diesel, an average truck has a range of about 100 km, whereas its electric competitor drives up to 200 km. This equals an energy efficiency twice as high as a diesel engine, explained. While the purchase price of such an electric vehicle is still higher than the price of a diesel truck, the cost of ownership are significantly lower, Zeilinger said.
Most of the electronic components and subsystems are new designs, custom made for the new eTruck, including the 720V high-voltage system, the battery management, the high-temperature and low-temperature cooling units for the motors and the so-called chiller for the battery. This unit has dual functions. First, it cools the battery if the temperature runs too high, and seconds, it warms up the battery in cold environments. Though the motors turn into generators to convert the kinetic energy into electric one when the driver hits the brake, the truck is also equipped with braking resistors, much like an old electric locomotive. What at first sight looks a bit ridiculous however makes sense. “In the rare case that the truck has to brake when the battery is full, recuperation is not possible”, Zeilinger explained. In such cases, the electric energy generated is diverted to the resistors.
An important feature is connectivity for electric cars in general and for the eTruck in particular. The reason is that the vehicle’s range management depends significantly from informations from outside the car, such as traffic situation. However, Daimler refused to go more into details with respect to connectivity services. “We want to leave this topic to the forthcoming IAA (the International Automotive Exhibition for Commercial Vehicles in September), Zeilinger said.
The urban eTruck is a near-series prototype and will be exhibited at the IAA. Series production will start as early as 2020 – certainly a while before competitors have comparable designs ready.