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Global

Technology

More Efficiency for the E-Bus
#digitalization #emobility

More Efficiency for the E-Bus

Min Reading Time
Electric buses only reach the maximum range if all power consumers are optimally coordinated. For this purpose, ZF is currently developing its own energy management system (EMS).
Andreas Neemann, May 26, 2021
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Andreas Neemann wrote his first ZF text in 2001 about 6HP transmissions. Since then, the automotive writer has filled many publications for internal and external readers, showcasing his passion for the Group's more complex subjects.
Since the dawn of the electromobility age, the battery has been considered the limiting factor. For this reason, engineers worldwide are working on converting the stored kilowatt hours for passenger cars and commercial vehicles into as many kilometers as possible. Since the battery packs are one of the biggest cost drivers, they cannot be increased arbitrarily. In addition, particularly in commercial vehicles, oversized batteries increase weight, reduce payload and impair vehicle handling. Another challenge for battery-electric city buses is that the electric motors for the drive are not the only power consumers. Many auxiliary systems also access the battery, for example the compressor, DC/DC converter or heating and cooling.

Consume less energy: holistic approach

Consume less energy: holistic approach
If the energy requirements of all power users can be optimally coordinated, fuel consumption will decrease. This is precisely the task of an energy management system (EMS). Right from the start, the EMS software coordinates the ramp-up, availability and interaction of all components in the vehicle that are relevant for the energy flow. Both the vehicle's range and the system costs benefit from this, because a smaller battery may also suffice for a constant range. Precisely because the EMS is so important for the overall system, it will be part of the ZF portfolio in the future. Since ZF also uses the electric drive control unit for the energy management system, no additional control units are required. Winfried Gr√ľndler, who is responsible for electromobility in ZF's Commercial Vehicle Technology Division, explains: "Only such an integrative approach will make it possible to further increase efficiency in electric vehicles. This shows the strategic importance that software competence has for us." The ZF system is particularly interesting for bus and truck manufacturers who lack the development capacities required for their own EMS.
In a test vehicle with the CeTrax electric central drive, ZF is testing its energy management system (EMS). Objective: Increase the vehicle's range by improving the coordination of all power consumers.

ZF energy management in practical applications

ZF energy management in practical applications
A test vehicle that is already making laps in Plant 2 in Friedrichshafen is equipped with the ZF-EMS. In order to make energy management even more efficient, ZF relies on GPS-based information for its EMS. It is the same information used by the "ePreVision" technical solution, which has already been produced in volume production. Specifically, this means that the EMS software also takes the topographical route into account. One example explains the function: The compressor in the bus reports energy requirements in order to fill the compressed air supply for the brakes. However, instead of immediately fulfilling the requirement and using battery power to do so, the EMS delays execution. After all, ePreVision has accounted for a longer downhill gradient within a few hundred meters. The compressor jumps in only during the downhill driving and supplements the compressed air supply. The energy for this does not come from the batteries, rather directly from the recuperation of the electric drive. "This improved coordination between the different consumers provides an efficiency advantage and reduces the vehicle's energy consumption," says Maximilian Wagner. He is an engineer in the eMobility Project House of the ZF Commercial Vehicle Technology and Industrial Technology divisions.
"As a supplier of the electric drive including power electronics and driving software for city buses, it is consistent for us to offer an energy management system (EMS) that controls all electrified auxiliary systems in an energy-efficient manner."
Maximilian Wagner, ZF eMobility Project House

Intelligent EMS preserves the batteries

Intelligent EMS preserves the batteries
ZF's energy management system offers even more advantages. By using recuperation energy directly instead of needing to temporarily store this energy, the battery's EMS saves countless charging and discharging processes over the course of a vehicle's life. This increases the battery life. The advantages of an optimal energy management system can also be seen in the bus depot. After all, the ZF-EMS also coordinates the current consumption on the charger. This becomes possible because the EMS already knows the route on which the electric bus will be traveling the next day. For example, if the journey starts with a long downhill gradient, the EMS causes the battery to be charged incompletely with power. This also saves costs and preserves battery cells. ZF's EMS, which is currently being developed, even optimizes maintenance. By reading out messages from the auxiliary systems before each trip, the EMS reports irregularities early on and thus shortens downtimes. ZF will initially offer its energy management system as an option for those customers who have already ordered the electric drive from the Group. For these customers, the software can be easily installed on the existing control units.

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