Scania, Siemens Plan Electric “Trolley Assist” for Heavy Trucks

European partners hope to commercialize a diesel-electric powertrain for highway trucks than can sometimes tap power directly from overhead wires or inductively from the road itself.

Siemens AG has already demonstrated the concept with its eHighway system, which borrows technology from the German company's electric railroad unit. Swedish truckmaker Scania AB will contribute its expertise in electrically powered vehicles.

A truck with so-called "trolley-assist" operates as a hybrid on normal roads, using a generator powered by a diesel engine that feeds the propulsion motor. The diesel never powers the wheels directly.

When sensors detect a section of road equipped with special overhead power lines, the system raises a roof-mounted pantograph that skims along the wire and draws electricity from it. Power from the wire feeds the truck's motor directly, allowing the diesel engine to idle or stop entirely.

Siemens says the pantograph mechanism can be raised and lowered at speeds as great as 90 kph (56 mph). It automatically adjusts to variations in the wire's height and the truck's position within its lane.

Unlike electric railways, the system uses a two-pole, two-way transmission architecture that completes the electric circuit entirely through the overhead wires.

The partners say a similar approach could be used to enable the truck to receive power remotely from a section of roadway embedded with an inductive transfer system. Siemens has been testing the eHighway system at a track outside Berlin. The Swedish government is considering a plan to electrify several miles of public roadway to test prototypes.