ZF's successful AVE 130 electric portal axle already boasts new gear geometry and low noise levels. But the technology company refuses to rest on these laurels: In 2015, it will bring its low-floor axle to market with significantly increased performance and torque values for the two motors mounted near the wheels, thus providing additional practical advantages to public transport authorities. In a further step, ZF offers the AVE 130 with an electronic control unit developed in-house. This ECU specifically was developed to make the electric drive system even more efficient.
Particularly in busy urban areas plagued by noise and emissions, public transport operators demand environmentally friendly, alternative, yet economical drive concepts. The AVE 130 low-floor electric portal axle from ZF has long since fulfilled these requirements: In recent years, on more than 14 million total kilometers, more than 300 of these axles have proven that lane-independent city buses can be operated economically with zero emissions. In articulated buses manufactured by EvoBus, for instance, the AVE 130 is being used in serial hybrid operation together with a downsizing diesel generator. In this configuration, the low-loss electric drive of the AVE 130 provides significant fuel savings of up to 30 percent in driving operation compared to conventional diesel drives.
Achieve maximum efficiency
Nevertheless, ZF is bringing the next evolutionary stage of the AVE 130 to market toward the end of 2015. The maximum electric output of the two water-cooled, asynchronous motors integrated into the axle will increase from the existing 2 x 120 kW to 2 x 125 kW. At the same time, the effective nominal voltage of the electric motors will increase from 350 to 400 V, while the maximum torque climbs from 2 x 465 Nm to 2 x 485 Nm. Even 2 x 11 000 Nm output torque are provided directly at the wheels since a fixed, power-split two-stage transmission is installed directly behind each motor on the AVE 130. Thanks to this improvement, in most cases one single electric drive axle is sufficient even for articulated buses. Lastly, the AVE 130 also boasts higher climbing capacity and higher tractive force than other concepts that is also maintained when the vehicle is fully loaded.
The technology company achieves additional efficiency for the AVE 130 offering additional decisive system components from a single source. This particularly concerns an electronic control unit developed in-house – i.e. hardware and software directly from ZF – which will manage the complex interplay of the electric components in a tailor-made fashion. Furthermore, vehicle manufacturers can further optimize the overall system with an inverter recommended and released by ZF. First field tests with prototypes were quite promising: The AVE 130's advantage with regard to the energy consumption of the motor in a purely electric driveline configuration might amount to 75 percent compared to a 220 kW auto-ignition in the same bus type. This value was calculated, for instance, on a very challenging public transport route in Stuttgart.
Convenient low-floor technology with compatible installation
Many of the features that have long set the AVE 130 apart in mass transit have been maintained in the further developments. For instance, passengers of city buses equipped with the AVE 130 notice no interruption of the tractive force since the electric motors require no gear changes. With optimal vehicle design, other advantages arise because the AVE 130 is installation-compatible with ZF's well-known AV 132 portal axle, and its lightweight drive motors are directly located in the hub units of the axle. Since the conventional drive shaft and propeller shaft in the rear are no longer needed, the space can be used to install additional standing areas and seats. In addition, the AVE 130 allows for a passenger area with a completely level aisle and, thanks to the low-floor technology, convenient, stepless entry and exit. Not least, the AVE 130 yields significant weight advantages: Thanks to its two integrated electric motors, it weighs up to 500 kg less than all other solutions with electric central motor.
ZF placed a great deal of importance on ensuring that the AVE 130 can be used in conjunction with normal tire/wheel combinations. Furthermore, easily accessible disk brakes were applied, which are also used in ZF's conventional bus axles.
The future might also see applications where the axle in articulated trolleybuses supports diesel drivelines or applications which can react flexibly to alternative track widths thanks to the simple construction of the axle bridge. On the same note, the focus will remain on the combination with alternative energy concepts, e.g. overhead contact lines, energy accumulators, or fuel cells.