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AxTrax AVE: A Small Axle with Big Results

Tags: Third party articles, Zero emissions, E-Mobility, Efficiency, Technology
Big cities are calling for a reduction in emissions. In answer to that call, ZF has developed the AxTrax AVE portal axle, an electric drive that will make city buses cleaner. A third-party article by Thomas Flehmer.
Thomas Flehmer, October 30, 2018
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Thomas Flehmer is the general manager and editor at FM Autoportal GmbH. This article was first published on the company website, www.autogazette.de.
Driving bans and speed limits are the primary methods for dealing with everyday traffic in city centers. For example, Berlin is trying to prevent an increase in emissions by introducing speed limits of 30 km/h in certain areas of the city. In contrast, ZF is focusing on the vehicles themselves, for example, by electrifying city buses. “The AxTrax AVE portal axle is one way of contributing to electromobility in urban areas,” explains Gerhard Obermaier in an interview with the Autogazette. Obermaier is head of strategic development of axle systems for buses in the Commercial Vehicle Technology Division at ZF. The propulsion system is designed for city buses with a maximum load of 13 tons. An electric motor is installed close to each wheel in the portal axle and each has an output of 125 kW/170 HP and a torque of 485 Newton meters with speeds of up to 11,000 revolutions per minute.

The electric motor is just 165 millimeters long

The electric motor is just 165 millimeters long

“The electric motor in the AxTrax AVE is designed as a high rev engine,” explains Obermaier. Due to its “speed-induced high output,” this electric motor was designed with smaller dimensions and therefore offers benefits when it comes to integration. It measures just 165 millimeters in length with a diameter of 300 millimeters. “Since the electric motor is highly integrated into the wheel head of the axle, interfaces identical to those of a conventional drive axle can be realized. This enables the axle suspension parts to be shared, including the control arms and spring carriers as well as air springs and shock absorbers. The axle’s mechanical connections in the vehicle design are identical,” adds the expert from the ZF plant in Passau. This produces synergy effects.
Moreover, the engines mounted on the rear axle are designed for low-floor installation, which creates space inside the bus. This enables the rear rows of seats to be installed individually, regardless of where the drive units are located in the bus. For Obermaier, there is another benefit. “This innovative concept also means that the bus is completely accessible from the rear.” A must for city buses.
“The AxTrax AVE portal axle is one way of contributing to electromobility in urban areas.”
— Gerhard Obermaier, Head of Strategic Development of Axle Aystems for Buses.

AxTrax AVE reduces bus weight by up to 500 kilograms

AxTrax AVE reduces bus weight by up to 500 kilograms

In addition to more space, this solution also reduces the weight of the bus. The entire axle unit with electric motors, control arms, springs and shock absorbers weighs a mere 1220 kilograms. Compared to other solutions with a central electric motor, the ZF solution means a weight reduction of 500 kilograms. In other words, 500 kilograms less that have to be moved. This also saves energy that can be converted into a greater drive range.
Just as valuable is the portal axle’s versatility. According to Obermaier, the axle is, in principle, compatible with all drive concepts, so it can function as a hybrid together with a fuel cell or a battery or an overhead line. However, this will probably not occur because “in practice, manufacturers are increasingly focusing on all-electric drives rather than battery-electric drive configurations.”
Buses are electrically driven with the ZF AxTrax AVE portal axle.

Portal axle on the road in the Bus of the Year

Portal axle on the road in the Bus of the Year

“In cities with a challenging topography or in mountain regions, both rear axles can be powered in articulated buses. This is possible using identical interfaces from conventional low-floor axles,” explains Obermaier.
The electric portal axle portal axle in volume production has been in volume production for more than a year and is already deployed in city buses in several cities, including Stuttgart, Mannheim or Bonn. At the same time, the axle is not limited to a specific bus manufacturer, but is already being used in the Bozankaya Sileo solobus and articulated bus as well as in the Urbino 12 electric – the current Bus of the Year. In fact, it was recently announced that the Daimler Citaro – named the 2013 Bus of the Year – will soon be equipped with the AxTrax AVE, which means yet another award-winning bus will carry this innovative axle. And those who want to take a bus tour of Paris and enjoy the Eiffel Tower without having to listen to the sounds of a diesel engine will soon be sitting in the electric sight-seeing double-decker bus from Ankai.
With AxTrax AVE soon to travel locally emission-free in several major cities: The NewFlyer Xcelsior CHARGE.
The engines mounted on the rear axle are designed for low-floor installation.