by Adrian-Liviu Dorofte

The new Mercedes-Benz Citaro in detail: Safe, weight-optimised construction


Stuttgart/Mannheim, Germany, May 20, 2011

A number of decisive advances have also taken place out of sight beneath the attractive exterior of the new Citaro. Although the bodyshell continues to be based on the proven technique of annular frame members – one of the innovations from the first-generation Citaro – it has been made even more rigid to afford passengers yet greater protection in a side-on collision.

Intelligent engineering lowers weight while increasing strength

A series of individual measures have been implemented to give the bodyshell superior strength despite its lower weight. One example is the newly designed pressed sheet-metal parts on the new Citaro, which combine the horizontal and vertical bodyshell elements around the window posts into a single multi-dimensional section resembling the hilt of a sword. Because they are built from a single pressed part, they are both lighter and stronger. Shifting the laser welding further out from the joints has produced a very sturdy connection. The developers have achieved similar results with the new castings for the door portals: although they have been reinforced, their walls are thinner, making them lighter than the previous design.

The expansive glazing on the new Citaro is lighter in many parts too: partially reducing the glass thickness from 4.0 to 3.15 mm compensates for the larger windows’ greater initial weight.
The roof frame is also new: it is based on two longitudinal hoops running almost the entire length, and now weighs just 110 kg on the 12 m rigid bus compared to the previous 137 kg – without sacrificing stability in any way. This new construction furthermore allows flexible positioning of any superstructures on the roof, while also reducing the number of different variants from over 50 to just 15.

New crash element to protect the driver in a collision

An outstanding safety feature that has been integrated into the extended front end of the new Citaro is a crash element to provide additional collision protection. This, together with the strengthened A-zero pillars and a frame design that has been engineered to channel impact forces directly into the substructure, means that the new Citaro already fulfils the requirements of the future pendulum impact test for coaches as laid down in the European ECE R29 standard.

The Citaro already complies with future ECE standards today

The bodyshell of the new Citaro was developed with the future ECE R 66/01 standard in mind too. This specifies a much larger survival space for the interior in the event of the vehicle tipping over than was previously the case. Although the new regulations only come into force in 2017, the new Citaro already complies with them today.

Considerable reduction of load on rear axle

The 55 mm increase in wheelbase length to 5900 mm together with the repositioning of the batteries underneath the driver’s area on rigid vehicles has produced a significant shift in weight, so reducing the load on the rear axle. The leverage effect of the batteries’ new location alone relieves the rear axle of 171 kg of weight. The resulting gain in axle load capacity at the rear is required in anticipation of future exhaust legislation and the heavier assemblies that will need to be fitted in the rear overhang as a consequence. The batteries are furthermore perfectly accessible in their side-by-side arrangement. In the articulated Citaro G, the batteries remain in their previous position on a level with the centre axle, where weight is not a critical consideration.

No heavier despite larger body

Despite the extra body length, the considerable increase in window surface area at the sides and the further major improvements to impact protection on the Euro V version, the new Mercedes-Benz Citaro is lighter overall than its predecessor. At the same time, passenger capacities are at least the same as before – a key criterion for transport operators’ profitability calculations.

Flexible and reliable electrics with PCB architecture

The central electrical compartment in the form of a cabinet behind the driver has also been redesigned. The new electrical system with PCB (printed circuit board) architecture is highly flexible and extremely reliable. It can be easily equipped for additional equipment and is very clearly arranged, resulting in good accessibility for maintenance work too. This dispenses with a great deal of complicated wiring and means there are fewer variants too.

Further improving reliability and durability was also the reason for rerouting cables from the underbody area so that they pass underneath the roof in the interior of the new Citaro, where they are safely protected from environmental influences. It was also possible to reduce the number of attachment points by half in the process, with standardised clips now being used mostly instead of bolts. Cable routing plays a particularly important role in the articulated bus. The switch from the previous S-shaped to the new C-shaped arrangement for routing electrical cables across the articulated section increases operational reliability.

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