Locally emission-free and almost silent. Citaro with all-electric drive system

The all-electric Mercedes-Benz Citaro runs locally emission-free and almost silently, taking electric mobility using city buses to a new level. The concept of the Citaro with all-electric drive system was exclusively presented in the context of the annual appraisal of Daimler Buses in march 2018 (all pictures shown here display prototypes of the new citaro with all-electric drive system). The 12-metre variant will celebrate its world premiere in September at the IAA Commercial Vehicles show, with the start of series production also taking place this year.The new Citaro offers thanks to his innovative thermal management an impressive and hitherto unknown standard of energy efficiency. The intelligent modular concept for its battery and charging technology is similarly compelling.

Citaro: from low-emission bus to zero-emission bus

With a wide range of low-emission and, going forward, emission-free city buses, Mercedes-Benz has the appropriate answers to questions about environmentally friendly local public transport. All variants are based on the global best-seller, the Citaro. Back in 2012, this became the first city bus in the world to meet what is currently the most stringent emissions standard, Euro VI.

The all-electric Citaro is now taking the next step from low-emission bus to locally emission-free bus. In doing so, it adds to the range a variant that sets new standards in terms of electric mobility.

Electric portal axle, modular battery concept, flexible charging technology

The basis of its drive system is provided by an electric portal axle 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, so ensuring appropriate dynamic performance even with a full complement of passengers.

Lithium-ion batteries with a total capacity of up to about 243 kWh are responsible for providing the power. These are split between up to a maximum of ten modules. As well as two battery modules on the roof, the standard equipment includes four modules in the rear of the bus. Depending upon customer requirements, a further two or four battery modules may be mounted on the roof.

With the maximum complement of ten battery modules, the all-electric Citaro with standard equipment weighs around 13.7 tonnes. In conjunction with a permissible gross vehicle weight of 19.5 tonnes, this corresponds to a payload of 5.8 tonnes or around 80 passengers – even in the rush hour, as is commonly necessary.

The Citaro's engineering has been future-proofed. Since the development of battery technology is progressing at a rapid pace, provision has already been made for the transition to the next generation.

The charging technology used is similarly flexible. For the start of series production, charging via a Combo 2 connector is envisaged. If, in order to extend the range of the vehicle, there is a requirement for opportunity charging, there will in future also be an option to charge the Citaro via a pantograph. The Citaro thus allows for all variants currently in use.

This intelligent modular concept for the battery and charging technology means that Mercedes-Benz is able to offer transport operators the opportunity to configure the Citaro precisely to the individual requirements of the company, or even of each separate route.

Thermal management: new approaches for heating and climate control

Compared with the current Citaro with combustion engine, the energy requirement for heating, ventilation and climate control has fallen by about 40 percent.The passenger compartment of the Citaro is heated in an energy-efficient manner by a heat pump. The heating and climate control systems are configured in accordance with the requirements of the Association of German Transport Companies (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.

Viable range under difficult conditions

When it comes to giving figures for the vehicle's range, Mercedes-Benz prefers to consider a "worst-case scenario", taking its direction from the challenging 'Standardised On-Road Test cycle', SORT2. According to this, the Citaro with a full complement of batteries can achieve 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 coverage of a city bus without opportunity charging.

Rethinking urban mobility: the integrated eMobility system

The all-electric Citaro forms part of Daimler Buses' integrated eMobility system. This encompasses the expert advice service eConsulting, even before any purchase is made. Experts analyse the various routes, evaluating the runs and establishing links between them. A simulation programme then calculates the energy needs. This work produces detailed recommendations and calculations relating to charging infrastructure, energy consumption, load capability of the power supply at the depot and charging management.

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