Electric power to revolutionize heavy-duty distribution trucks

  • 09-Aug-2016 04:30 EDT
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Daimler's Urban eTruck will be on display at the IAA Hanover CV Show in September.

Daimler Trucks will display its Mercedes-Benz Urban eTruck concept vehicle at the IAA Commercial Vehicles show in Hanover, Germany, this September. The company claims the Urban eTruck is the first battery-electric 26-tonne gross weight commercial vehicle ever produced.

Based on the Europe-market Mercedes-Benz Antos heavy truck, the eTruck is expected to be available with two or three axles, allowing gross vehicle weights up to 26 tonnes (57,320 lb). A production version is not expected until 2020; however, the vehicle previewed to Off-Highway Engineering prior to the IAA Show was based on an Antos 6x2 LNA chassis with rear steering and lifting axle.

“Interest in electric trucks is on the rise. Customers deliver day and night and noise is an issue,” said Dr. Wolfgang Bernhard, responsible for Daimler Trucks and Buses at the Board of Management. “London will only permit Euro-VI compliant vehicles from 2020, Paris plans to ban conventional drivetrains from 2020 and Beijing operates tight standards.”

The 26-tonne Antos variants have been designed with a target fully laden range of 200 km (124 mi), reckoned to be enough for a single day’s use with a vehicle operating on an urban distribution route. The projected range includes a test with air-conditioning and ancillary equipment operating, said Mercedes-Benz.

The batteries are arranged in three separate packs housed between the chassis rails, mostly between the first and second axles. One battery pack is positioned beneath the cab floor, where the diesel engine would normally be located. In total there are 1080 high-energy-density 4-V cells, with 12 cells grouped in modules; each main pack contains 10 or 15 modules. In total, battery capacity is 212 kW·h at approximately 720 V. Mercedes-Benz calculates that 212 kW·h offers the energy equivalent of 20 L (5.3 gal) of diesel fuel.

The battery packs were designed with a 150-kW rapid recharging capability, although as Daimler acknowledges, a maximum of 50 kW currently is available through European vehicle-charging networks. The company expects 100-kW charging to be available soon and a rapid charge with 100 kW could fully recharge the vehicle in a claimed two hours.

Daimler has opted to use an external DC charging unit to save vehicle weight and cost for customers. A Combo Standard Type 2 (CCS Combo) charging connector is fitted to the vehicle to permit DC rapid charging. Using a 20-kW charging point, it would take approximately 10 hours to recharge the batteries.

“Inductive charging is possible, but there are performance issues. Plug-in charging is preferable at the moment,” said Dr. Maik Ziegler, Advanced Engineering, Daimler Trucks.

The truck's three battery packs weigh approximately 2.5 tonnes (5500 lb), but Daimler expects battery energy density to increase in the next two years—this could eliminate the current payload disadvantage of the electric truck compared with an equivalent diesel-powered model. Under current EU regulations that allow a higher gross vehicle weight for alternative-fueled vehicles, Mercedes-Benz said the vehicle can run with an increased gross weight of 1 tonne. This means that the Urban eTruck would be limited to 700 kg (1540 lb) less than its diesel equivalent, but the expected improvement in battery energy density could potentially negate this disadvantage.

The drive axle is based on a modified ZF AVE 130-400 V AC electric portal axle, similar to that used with Mercedes-Benz hybrid buses, with a weight rating of 11.5 tonnes (25,350 lb). This axle does not employ hub motors; instead, it uses liquid-cooled asynchronous traction motors mounted inboard of the brake assembly. Each motor can deliver a total output of 125 kW at a maximum of 11,000 rpm, with a continuous rating of 60 kW. Daimler quotes maximum torque from standstill of 500 N·m (369 lb·ft). Two-stage reduction gears can deliver up to 11,000 N·m (8110 lb·ft) per wheel. At a gross weight of 25 tonnes, Daimler indicated each motor can deliver a traction force of 22 kN on a 17% uphill gradient.

The motors also provide regenerative braking, with up to 180 kW of braking resistance. Daimler said that the portal axle with drive motors located at the wheels offers significant advantages over a centrally mounted single drive motor because it provides additional space for batteries, while additional drive axles could be added if required.

In addition to powering the drive motors, the high-voltage circuit is used to feed the air compressor used to pressurize the vehicle’s foundation-brake circuits. Two cooling circuits are provided for the electrical equipment; a high-temperature circuit cools the drive motors when used for braking, while a low-temperature circuit cools the electric inverters, electrical auxiliaries and drive motors. A separate chiller is used to cool the high-voltage batteries. A conventional 24-V low-voltage circuit is used for regular equipment such as vehicle lighting and windshield wipers.

“Electric trucks are now part of Daimler’s strategy,” said Bernhard. “Hybrid, hydrogen and natural gas are still under consideration.”

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