It combines the thousandfold proven platform of the world's best-selling city bus with new technological solutions. The all-electric Mercedes-Benz eCitaro takes electric mobility using city buses to a new level altogether.
The new eCitaro offers an impressive and unprecedented standard in energy efficiency, courtesy of its innovative thermal management system that uses innovative components available for the first time with the launch of the eCitaro. Its performance enables the eCitaro to cover a large part of the requirements of the transport operators right from the start. In addition, it is ready for the battery technology of the near future – the performance capabilities will increase quickly. At the same time, due to the high development effort and extensive testing, it comes to the starting line already fully matured. In addition, the intelligent modular concept of battery and charging technology is compelling. Its design fuses the basic shape of the Citaro with elements of the Mercedes-Benz Future Bus into a distinct appearance. It is also more than just a city bus: Mercedes-Benz takes a holistic view of electric mobility, embedding the eCitaro firmly in its overall eMobility system. In addition, the eCitaro is the starting signal on the road to an electric future.
The eCitaro gets a tailor-made exclusive exterior
The new eCitaro is also a true Citaro – but a very special one. That is because the exceptional characteristics of the new Mercedes-Benz eCitaro correspond to its equally exceptional design. It is based on the familiar looks of the Citaro, but takes up elements from the design idiom of the revolutionary Mercedes-Benz Future Bus concept vehicle and transports the unmistakable design of the Citaro into the future.
The bumper with integrated number plate bracket and the three-dimensionally carved hallmark A0-pillars of the model frame the face of the eCitaro. They are painted in vehicle colour. Another feature of the city bus is its curved windscreen. Visually stretched by the glossy black front panel, it elegantly sweeps up to the roof and integrates the destination display. Visually, the windscreen smoothly transitions into the roof with dark bars on the left and right. At its middle, the roof sports an "island" in vehicle colour that almost seems to float, likewise one of the design elements of the Future Bus. It is not only a visual element, but also forms the end of the roof membrane.
The interior: new coffered ceiling with high-tech lighting
In the passenger compartment, the eCitaro rings in a general update of the interior of the entire Citaro family of models. A stand-out feature in the interior is the coffered design ceiling above the centre aisle and the sweeping roof-edge flaps. They hide a new air circulation system with textile ducts in place of the current plastic air ducts. They are even easier and simpler to install.
Particularly noteworthy are the technology modules as connectors between the individual elements of the coffered ceiling. They combine the interior lights and the loudspeakers in one element. With this step, the interior lights are switched to LED as standard. The lighting is ingenious: The light of the LED lamps is refracted in a way to make the technology modules appear to the observer as one homogeneous light panel.
In addition to the closed look and the new interior lights, the advantage of the new ceiling is a significantly reduced number of individual parts. Together with the new air circulation system, this lowers the already low interior noise in the passenger compartment even further, which means more comfort. Also new is the black trim on the sills and window posts.
Proven electric axle, new modular battery concept
The powertrain of the new eCitaro is based on the proven and optimised electric portal axle ZF AVE 130 with electric motors at the wheel hubs. The peak output of the motors is 2 x 125 kW, while torque is 2 x 485 Nm. It is an inherent feature of such motors that this is fully available right from the start, ensuring appropriate dynamic performance even with a full complement of passengers.
Lithium-ion batteries supply the power. New: their total capacity is up to 292 kWh. Background information: the batteries are now split between up to twelve modules, instead of the initial ten, each supplying around 25 kWh. The basic equipment sees two battery modules on the vehicle roof plus four fitted at the rear. Depending on customer requirements, up to six further battery modules are mounted on the roof of the eCitaro.
Each battery module is made up of 15 cell modules as well as a control unit for monitoring purposes and as a means of balancing the charge of the battery cells. Each separate cell module houses twelve battery cells. Mercedes-Benz uses easily manageable prismatic cells with a capacity of 37 Ah each. With a minimum of six and up to a maximum of ten possible battery modules, transport operators can adapt their usage and charging strategy very precisely to individual needs. Opting for the largest number maximises the range of the buses, while a smaller number reduces the weight as well as the cost of purchase and allows more space for passengers - but potentially makes time-consuming opportunity charging necessary.
With the full complement of twelve batteries, the eCitaro as a two-door model with standard equipment weighs around 14.1 tonnes. With a permissible gross vehicle weight of 19.5 tonnes this corresponds to seats for around 75 passengers – very practicable during rush hour.
Flexible charging technology: charging at the depot as standard, optional pantograph
The eCitaro's charging technology also allows it to adjust to the individual wishes and requirements of the transport operators. For the start of series production, plug-in charging is intended. To this end, the city bus features a socket for a Combo-2-plug above the front wheel arch on the right-hand side of the vehicle in the direction of travel as per the provisions of the German Association of Public Transport Operators (VDV). This ensures the simplest, fastest and at the same time cheaper power supply variant.
If opportunity charging is required to extend the range, there will also be an option to charge the eCitaro via a pantograph in future. This option will be gradually phased-in once series production has started. There will be two possible variants: in phase 1, an integral pantograph on the roof; in phase 2, charging rails on the roof that will allow charging via a stationary pantograph of a charging station. In both cases, the installation space will be level with the front axle.
This intelligent modular concept of battery and charging technology means that Mercedes-Benz is able to offer transport operators the opportunity to configure the eCitaro precisely to the individual requirements of the company or even of individual routes.
In addition, the eCitaro is also able to generate electrical energy through an energy recovery process. In this case, the two electric motors at the wheel hubs of the drive axle act as alternators during braking, transforming the kinetic energy of the vehicle into electricity.
Thermal management: new approaches for heating and climate control
However, the battery capacity alone provides little indication of the actual performance capability and, above all, the range of an all-electric city bus - the true measure is that of energy consumption. In the case of a city bus, this is impacted significantly by climatic conditions and consequently by the need to cool and, above all, to heat the interior.
At an outside temperature of minus ten degrees Celsius, the energy consumption of a city bus doubles compared to journeys where no heating is required - thereby cutting the range by half. The cause: The extreme efficiency of an electric motor means that, compared to a combustion engine, the amount of usable waste heat is negligible. The heating system must therefore be fed from the vehicle's own energy supply. In addition, there is the large interior and the frequent opening of up to three double-wide doors at bus stops that let in outside air.
The engineers have therefore put a considerable amount of thought into the issue of thermal management. It is one of the outstanding features of the eCitaro and has been honed and refined in every detail: Compared with the current Citaro with combustion engine, the energy requirement for heating, ventilation and climate control has fallen by about 40 percent. This exceptional energy efficiency provides the basis for the eCitaro's practical operating range even under unfavourable conditions. This is accomplished with the use of innovative components that only reached market readiness in concert with the eCitaro.
Climate comfort tailored to the needs of passengers
Another boon: the interior can be conditioned up to and even beyond the desired temperature while the batteries are still being charged at the depot. The bus will therefore have been heated or cooled to reflect the season before it sets off.
The heating and climate control systems are configured in accordance with the requirements of the Association of German Transport Operators (Verband Deutscher Verkehrsbetriebe (VDV)). If the temperature outside is extreme, comfort levels at either end of the scale are reduced somewhat in favour of energy consumption and thus range. Instead of the interior temperature being set to a consistent level all year round, it is adjusted according to the situation to ensure the comfort of passengers. As passengers generally spend only a short time in the vehicle and are normally dressed in accordance with the time of year, the inside temperature is set higher on hot summer days and lower on cold winter days, without at any point compromising passengers' feeling of comfort.
When it comes to the driver's workplace, Mercedes-Benz pursues a somewhat different strategy: since the driver spends all his or her working hours on the city bus, the requirements here are greater. Driver-fitness safety must also be ensured at all times. That is why the climate control system for the driver's workplace is controlled separately, with a target temperature of 24 degrees, even in extreme outside temperatures.
High efficiency: practical range also under difficult conditions
Operating range figures for all-electric-powered city buses are often difficult to compare and caution is advised, since reference values can be missing and the figures have often been calculated under ideal conditions. Things are different with the eCitaro: In the interests of reliable data, Mercedes-Benz prefers to consider a "worst-case scenario" and therefore takes its direction from the challenging standardised city driving cycle known as SORT2. To make things even trickier, Mercedes-Benz also adds the energy requirements of the ancillary consumers into the equation. According to SORT2, the Citaro with a full complement of batteries achieves an operating range of around 150 kilometres in the summer. In other words, it is already possible to serve some sub-networks within the daily workload of a city bus without opportunity charging. Without opportunity charging, the eCitaro already covers about one third of all requirements of the transport operators. In other words, it can seamlessly replace one in three city buses powered by a combustion engine. Under ideal conditions, the eCitaro even drives around 250 kilometres without opportunity charging.
The future is electric: Innovation offensive kicks off
Ahead of its time: eCitaro’s battery technology is geared to ensure a relevant range in the best possible way over a long period of use. As the development of battery technology progresses in rapid steps, in concept the switch to future battery technology can already be foreseen.
This applies, for example, to the lithium-ion batteries currently in use. Their next generation, with larger capacity and therefore increased range, will be available to eCitaro customers in 2021. With a total capacity of up to 330 kWh eCitaro can cover around 50 percent of all routes. This battery capacity also makes the introduction of an eCitaro G articulated bus realistic.
Concurrently, a further step can be mapped out with reference to the optional use of lithium-polymer batteries, also known as solid or solid-state batteries, in the future. These batteries are characterized by a particularly long life and high energy density.
With a nominal battery capacity of around 400 kW in a standard bus and an even higher capacity in an articulated bus, eCitaro then covers about 70% of all operational requirements without requiring an intermediate charge. Solid-state batteries differ markedly from NMC batteries (lithium-nickel-manganese-cobalt-oxide cells): They have a different form, are larger and not suitable for fast charging. Thus, city buses equipped with them cover other use profiles. That is why eCitaro will be available with optional NMC and solid-state batteries (lithium-polymer batteries) beginning in late 2020. From 2020 forward eCitaro will also be available in an additional model variant as an articulated bus.
In 2022 eCitaro’s range will be increased again by a range extender in the form of a fuel cell to generate power (hydrogen-based fuel cell charges high-voltage battery with power). It is designed to cover nearly 100 percent of all urban bus requirements. This technology makes intermediate charging and the necessary complex charging infrastructure superfluous in almost all cases: eCitaro can then replace city buses with combustion engines on a nearly equal basis.