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Five buses in five-day major efficiency test
Start and finish line for the three Mercedes-Benz Citaros and the two Setras of the ComfortClass 500 is Wiesbaden, the capital of the German state of Hesse. With the exception of two refuelling stops each day, the five buses will operate around the clock for five days straight.
Three Citaros to run in urban regular service in Wiesbaden
For the urban bus comparison the new Euro VI-certified Mercedes-Benz Citaro will compete as a standard bus with OM 936 h engine and 220 kW (299 hp) against its predecessor. The Euro V Citaro starts in two versions: powered by the OM 906 hLA engine and 210 kW (286 hp) of power and the OM 457 hLA engine (220 kW/299 hp). In each case power is transferred by the fully automatic ZF Ecolife torque converter transmission. Also identical is the final drive ratio of i=5.771.
All Citaros will operate in line service on the demanding route 17 in Wiesbaden. It traverses the city centre of Hesse’s capital including the pedestrian zone and outlying areas. However, the test vehicles are loaded with ballast in place of passengers.
To ensure realistic operating conditions, each of the buses will follow behind an urban bus of the Wiesbaden transport authorities in regular service. To prevent the three test buses from influencing one another they will stop several minutes apart. Route 17 is 18.6 km long with a 400-m change in elevation. The buses will complete about 20 round trips each day. The buses will stop at each bus stop where the buses will be lowered using the kneeling function and the passenger doors will be opened.
Two Setras will complete 1800 km on motorways each day
In the touring coach comparison the Euro VI-certified Setra ComfortClass S 515 HD will compete against its Setra ComfortClass S 415 GT-HD predecessor. The two-axle high-deck touring coaches each measure a little over 12 metres in length. The ComfortClass S 515 HD is powered by the OM 470 engine with 315 kW (428 hp). Its OM 457 LA predecessor in the ComfortClass S 415 GT-HD has the identical power output. The touring coaches are equipped with the Mercedes GO 250-8 PowerShift (ComfortClass 500) respectively the Mercedes GO 240-8 PowerShift transmission. Their gear ratios are identical as is the final drive ratio of i=3.583 of both high-deck coaches.
The touring coaches also use Wiesbaden as the starting point, in this case for a trip to Leipzig. From there they will make a 897-km daytime loop on the A 38, A 71, A 70, A 9, A 72, A 4 and A 14 motorways from Leipzig via Erfurt, Schweinfurt, Bayreuth, Dresden to Bautzen and back. At night the two Setras will drive a 929-km route that leads from Leipzig via Potsdam to Hamburg and back on the A 9, A 10 and A 24 motorways.
In this way the touring coaches will cover a distance of almost 1800 km a day. Some 90 per cent of the distance will be driven on motorways, the remaining ten per cent on main and country roads. The legal speed limit of 100 km/h or 80 km/h will be observed whenever possible.
Identical conditions, technology and refuelling stops monitored
In addition to the transmissions and the final drive ratios, the loads as well as the tyre brand and tread depth are also identical within each respective model series. The three Mercedes-Benz Citaros are loaded at 50 per cent of capacity with exactly 3.5 tonnes of ballast. The touring coaches of the Setra ComfortClass are designed for a gross vehicle weight of 18 tonnes.
All buses will have been broken in at the start of the Record Run Buses 2012 with around 10,000 km on the odometer. The buses will be driven by skilled test drivers as well by trainers from Omniplus Ecotraining. A crew of two drivers mans each of the buses. The buses will be operated in three shifts around the clock. In addition, the drivers for the Record Run Buses 2012 on route 17 in Wiesbaden have received briefings from driving instructors of the transport authority.
The test vehicles and their operations will be monitored by Dekra, an independent specialist automotive organisation. All components relevant to fuel consumption as well as the fuel tanks will be sealed; all refuelling stops will be monitored. All refuelling stops will be at the same filling stations in Wiesbaden or Leipzig and even at the same pumps. Even the position of the vehicles at each pump is defined. Furthermore, the tyre pressure is checked at each refuelling stop.
The buses are also equipped with instruments for measuring fuel consumption. Any movement of the five buses in the Record Run Buses 2012 can be monitored with the help of the FleetBoard telematics system.
Arrival at the finish line in Wiesbaden after 20,000 km on 26 October 2012
All five buses will cross the finish line of the Record Run Buses 2012 in Wiesbaden around midday on 26 October 2012. By that time the touring coaches will each have covered a distance of some 9000 km, the urban regular-service buses each just shy of 1500 km. All recorded data will be analysed over the weekend that follows and the eagerly awaited results will be announced at a press conference on 29 October 2012.
Citaro and ComfortClass 500: maximum efficiency
The engineers from Daimler Buses employed all available means to achieve maximum efficiency of the Mercedes-Benz Citaro and the Setra ComfortClass 500. A multitude of measures counteract the inevitable added weight of the additional or larger components that the move from Euro V to Euro VI entails. For this reason the new ComfortClass 500 actually weighs less than the predecessor model.
The centrepieces of the drive system are the new BlueEfficiency Power engines. Both the in-line six-cylinder Mercedes-Benz OM 936 h engine in the Citaro as a standard bus and the OM 470 engine in the Setra ComfortClass 500 are characterised by robustness, longevity and maximum cost-efficiency with regard to fuel, motor oil and AdBlue consumption, as well as by long maintenance intervals. A typical trait of the engines is a high torque at very low engine speeds and an excellent throttle response. Both qualities are part of the prerequisites for successfully taking the place of the predecessor engines that to some extent had significantly more displacement – the keyword in this context is downsizing.
In addition to the drive system the development engineers carefully examined the ancillary components with an eye on fuel economy and longevity, for the Mercedes-Benz Citaro as well as for the Setra ComfortClass 500. Alternators, battery management, radiator fan and air compressor – these and other components play a major role in fuel consumption and in both model series were optimised down to the last detail.
Citaro Euro VI: ancillary components optimised in particular
Two distinctive features on the Euro VI-certified Citaro deserve special mention, both of which are major factors in an urban regular-service bus. A lowered entrance height reduces the amount of air needed for kneeling and consequently the amount of energy required. The second point concerns the energy management: free electricity generated in overrun mode is stored in dual-layer capacitors (supercaps) and is available the next time for acceleration. This relieves the burden on the alternators and consequently reduces fuel consumption.
Setra ComfortClass 500: outstanding aerodynamics
Outstanding aerodynamic properties are essential for the Setra ComfortClass 500 touring coach. From the rounded front with Aquablade clipless wipers and optimised exterior mirrors to smooth flanks and the tapered rear with its separation edge, the aerodynamic efficiency of the ComfortClass 500 sets new touring coach benchmarks. The result is an outstanding drag coefficient of just 0.33. The drag is also reduced by a trick that is unmatched in the industry: at speeds of 95 km/h and above the bus is lowered by 20 mm.
Prediction: reduction in fuel consumption between four and six per cent
The development engineers of Daimler Buses expect these measures to add up to a reduction in fuel consumption of the Mercedes-Benz Citaro by four to five per cent as the result of the move from Euro V to Euro VI emission standards. For the switch from the Setra ComfortClass 400 to the new ComfortClass 500 the engineers expect a fuel economy advantage for the new model of five to six per cent. In both cases the improved fuel economy goes hand in hand with a significant reduction in AdBlue consumption. These predictions must now be substantiated under real-life conditions during the Record Run Buses 2012.
Credits: Daimler AG
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