ZF presented its new line for electric powertrains, equipped with various innovations that are combined with great flexibility of adaptation. The new range is in fact conceived to be powered by both 400 and 800 Volts, an interoperability result of work on individual components such as motors and inverters, on which the company has begun to focus more closely after the experience gained at the system level. The innovations in particular concern the electric motor, the inverter, the transmission and a DC-DC converter for fuel-cell powertrains.
The motor generator is distinguished from others on the market by the texture of the windings in the stator. ZF switches from pigtail wraps to a braided weave, to which we owe many advantages. Roland Hintringer, head of the electric motor product line, explained some of them to reporters of the Society of Automotive Engineers: “The hairpin windings, which are today’s state of the art, were introduced five to seven years ago and require hundreds of laser welding spots. [La trama intrecciata] requires only 24 welds and also reduces raw material usage by 10%”. In fact, the SAE.org portal reports how the length of the single winding passes from 28 to 15 mm with the new braid.
In addition to the construction of the stator, another novelty of the ZF electric motor is its cooling. In fact, the oil circulates both through the external metal jacket and inside the stator, directly wetting the copper elements. So ZF also embraces the direct cooling strategy, thanks to which the heat exchange surface is maximized. Overall, the new ZF power unit is improved in performance, with maximum continuous power reaching 85% of peak power. The rare earth content is less than 1%, while the volume occupied by the stator windings is reduced by 10% compared to previous products.
The last one inverters produced by ZF instead boasts a modular architecture. The internal structure is in fact discretized down to the single silicon-carbon switch, so as to exploit its assembly to create 400 or 800 Volt modules. All this avoids differentiating the internal components between the two specifications, reducing production costs for the manufacturer. Moving on to the transmission instead, it is made up of two epicycloidal gears to achieve the desired transmission ratio to the wheel. Contrary to the past, however, the two reducers are not sequential but integrated into a single train, with two trains of coaxial satellites between them. ZF’s solution ensures equal distribution of drive power to the wheels of each axle, also integrating the function of mechanical differential. According to what was reported by Society of Automotive Engineers, the installation volume is reduced by 25%, with even 10% less mass and the attenuation of mechanical losses up to 20%. It also results in a higher power density than the previous offering.
However, ZF is not only looking at battery-electric mobility, but also at hydrogen fuel-cell mobility. The new range includes a high voltage DC-DC converter, with a declared efficiency of 99.6%. The result is also possible thanks to the work on the software front, equally central to the new line of e-drives presented by ZF as well as the innovative hardware solutions, a dualism that reflects the current scenario of electric propulsion
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