Zero emissions, but plenty of torque The AVE 130 electric portal axle

More and more city buses are powered by electricity. To make this possible, they need a driveline solution that is highly versatile – such as ZF’s AVE 130 electrically driven portal axle.

Versatility is one of the key criteria for drive technology in electric city buses – simply because there’s no such thing as one single type of electric bus. There are hybrid buses, which use diesel engines as generators. There are fuel-cell buses, in which fuel cells generate electricity by the chemical reaction of hydrogen and oxygen. Some electric buses use overhead contact lines or inductive charging to draw their drive energy from the urban power grid. Others store electricity in onboard batteries.

The AVE 130 is a drive axle that can be used in all these different buses. Mounted inside the electric portal axle are two water-cooled induction motors, one next to each wheel. They have some unusual features. First, they are manufactured without rare earths. And second, they use relatively high engine speeds to deliver a total output of 125 kilowatts per wheel – a combined output of 250 kilowatts, equivalent to 335 bhp (340 PS). For this reason, the AVE 130 also includes two-stage reduction gearing next to the wheel-hub motors. From standstill, each motor is capable of delivering a maximum torque of 485 newton meters. The gearing ratios then turn this into a drive torque of up to 11,000 newton meters per wheel – a level of performance currently unmatched by any other electric drive for city buses.

More space in the rear of the bus, with all the advantages of a low-floor layout

Video: The AVE 130 electric portal axle

Flexible solutions: how the AVE 130 low-floor portal axle for city buses works

This enormous traction means that a single electric axle is capable of driving even fully laden articulated buses. What’s more, it gives the axle other highly desirable properties that cause the AVE 130 to shine in real-world situations. These include impressive climbing abilities – especially important in cities such as Stuttgart or Bonn in Germany, where buses must be capable of making long, steady uphill climbs and where the AVE 130 has completed intensive trials.

ACE 130: ZF system scope

In recent years, more than 300 of these axles have covered a total of well over 8.5 million miles, proving that city buses can be operated very economically and with zero local emissions. This is also due to the energy management system – something ZF offers customers as an option – that regulates the interplay of power draw, energy regeneration (recharging batteries from energy recovered during braking) and energy storage. By installing this control system, with its built-in inverter, customers can maximize overall efficiency – an all-electric solution driven by the AVE 130 uses up to 75 percent less energy than a diesel driveline, as shown by sample calculations during a pilot project in Stuttgart.

The system is also versatile in one other important respect: it fits into the same space and has the same interface dimensions as portal axles for conventional buses driven by combustion engines. Meaning that bus manufacturers can “electrify” their existing model ranges using existing, well-established vehicle technology.

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