City buses equipped with the new Siemens series hybrid drive system Elfa consume one-third less fuel than conventional buses, according to the company. Rather than powering the rear axle via an automatic transmission, as usually, the diesel engine in the Elfa system drives a generator that uses power electronics to supply electricity to one or more drive motors.
In the Elfa system from Siemens, the electric motors act as generators during braking and thus feed electricity back into the batteries. This power can then be subsequently used to drive the vehicle, which means at times the bus can run fully electrically and without producing any emissions. The vehicle range depends on battery capacity and can vary between a few hundred meters and several kilometers.
In combination with a clever power management system, Elfa not only reduces fuel consumption but also noise, since the diesel engine doesn’t provide acceleration and therefore operates only at quiet and economical engine speeds. As a result, fuel consumption falls by around one-third.
Buses with Elfa drives are now being used in a number of cities worldwide, including a test fleet of double-deckers in London. Hamburg, meanwhile, is planning to introduce buses with an Elfa hybrid drive equipped with a fuel cell system rather than a diesel engine. This new drive technology is also targeted for other commercial vehicles that make frequent stops, such as garbage trucks or light delivery trucks. The Elfa system forms part of the Siemens environmental portfolio, which generated around €28 billion in sales for the company in fiscal year 2010.