Electromobility How the Electric Bus Gets Going
The future is electric – also for city buses. But how is electricity best transmitted and stored for the drive? Seven solutions from electromobile cities.
Electric buses that are already running in many cities contribute to better air and less traffic noise in city centers – thanks to electric axles from ZF. ZF's combined systems expertise in electric motors, chassis, transmissions, electronics and low-floor technology paves the way for locally emission-free city buses with a larger passenger space and more comfort for urban public transport. For this purpose, engineers developed the AVE 130 portal axle system with two asynchronous motors that allow for relatively high speeds of up to 11,000 rpm at a maximum output of 2×125 kW. This ZF axle by the way also reliably drives the "2017 Bus of the Year," the Urbino 12 electric of Polish bus manufacturer Solaris.
The future of e-mobility for buses depends on the charging and storage concepts that will prevail in the cities. We present seven current versions:
A new technology from China has been undergoing testing in four electric buses in Graz since November 2016. Instead of one large battery, many fast charging capacitors made of carbon store the electricity while the passengers get on or off the bus. Just 30 seconds at the charging station should be enough for a five kilometer urban trip. The Chinese bus manufacturer Higer provides two of the four electric buses for the one-year test run in Graz. The electric portal axle AVE 130 from ZF provides the responsive drive.
The two battery buses of Stadtwerke Osnabrück do not need any interim charging. The capacity of the bus battery lasts a whole day in regular service. The energy accumulator is replenished at night via a power cable at the depot.
The Sileo articulated bus in Bonn has a range of 200 kilometers and does thus not require any charging stops in regular service. As in Osnabrück, the buses are connected to the power grid at night.
Battery bus of Hamburger Hochbahn (Hamburg Elevated Railway). The two high voltage batteries are recharged several times during the day via charging towers at the depot and at the line's first and last stops.
Pantographs constantly supply the electric motors in trolley buses with energy. The concept using power lines above the track was already applied at the beginning of the 20th century, but in the meantime is hardly still popular. The photo shows a trolley bus of Stadtwerke Esslingen.
In Mannheim, raised induction plates charge the batteries of the electric buses before and during regular service. Cameras on the underside of the bus facilitate the engagement. The inductive charging works wirelessly, comparable to electric toothbrushes. Rhein-Neckar-Verkehr GmbH relies on ZF technology: The Hess buses run with electric ZF driven axles. At the same time, the charging processes of the batteries with a range of 19 kilometers are monitored via the ZF Openmatics telematics platform to facilitate project evaluation.
In Stuttgart, a fuel cell bus was tested between the district of Plieningen and the airport. Its fuel cells obtain electrical energy from the chemical reaction of hydrogen with oxygen. The energy is either used for driving or can be stored temporarily in the batteries. Hydrogen tanks and high-voltage batteries are located on the roof of the bus. This is another example of an electric bus being powered by the electric portal axle AVE 130, which is manufactured by ZF in Passau.