A pride of lions

With emphasis on “going green” growing across the globe, the bus industry has a few tricks up its sleeve. MAN Nutzfahrzeuge (the commercial vehicle division of MAN SE – see this month’s Global FOCUS) used the International Association of Public Transport congress in Vienna early in June to show off the latest additions to its city bus line-up.

First off was the series production version of the MAN Lion’s City Hybrid, prototypes, which have already chalked up a total of around 70 000 km of operation in cities such as Nuremberg and Paris, and are due to enter service in Munich and Vienna in 2010. The vehicle on show employed a series hybrid system in which the low-floor portal drive rear axle is permanently coupled to twin 75-kW Siemens asynchronous electric drive motors through a summation gearbox, with the Enhanced Environmentally Friendly Vehicle standard D0836, 254-hp (184-kW) rear-mounted vertical diesel engine only called up, through its 150 kW Siemens generator, to recharge the high-power, long-life capacitor storage system (used in place of more conventional batteries), or provide supplementary motive power, when required.

The 12-module Maxwell Ultracap high-performance energy storage system and power electronic control system are located in an aerodynamically-shaped aluminium structure integrated into the vehicle’s roof, above the front axle, to optimise cooling and mass distribution. MAN estimates that city buses spend between 25 and 40% of their operating time stationary at stops and terminals, during which time the hybrid unit will keep its diesel engine firmly shut down. Auxiliary units, such as the air-conditioning system and power steering, and the onboard network, can also draw their power needs from the energy storage system. Moving off, the vehicle is first driven by its electric motors only while stored power is available, and, when it decelerates, current is returned to the Ultracap system through the 150-kW regenerative braking capability. The electronically-activated foundation brake system would only be required for emergency stops. MAN claims fuel savings of up to 30%, and the elimination of 10 t of greenhouse gas emissions over 60 000 km of annual operation, if the hybrid bus is burning second generation biofuels in its diesel engine. The Lion’s City Hybrid is based on the current low-floor conventional drive Lion’s City rigid model, while an equivalent version of the articulated bus train variant is being prepared for introduction in 2012.

The second new model on display was the three-axle MAN Lion’s City C in 13.7 m overall length format. Primarily intended for the Swedish market, this model can accommodate up to 120 passengers, with 34 to 44 seats, and provision for one or two wheelchairs. This new model is similar in basic layout to the double-decker vehicles recently supplied by the MAN Group for service in Berlin and Dubai. When compared to the previously available
14.7-m Lion’s City L, the wheelbase has been shortened by removing a 1-m section from immediately in front of the second doorway, which results in reduced turning circle and rear swing-out clearance dimensions. A total of three doorways are provided as standard, and these can also be of the latest outward-swinging and sliding type.

Power is provided by EEV-compliant common-rail diesel engines of 320 or
360 hp output (240 or 270 kW), while, from 2010, MAN’s E2876 LUH03 compressed natural-gas-fueled engine, developing 320 hp (240 kW), will also become available in this variant, as well as in all MAN low-floor city bus and bus chassis models. The use of CNG fuel removes the need for closed particulate filters, while retaining full EEV compliance. The Lion’s City C, which is available only in left-hand-drive form, tares out at between
13 and 14 t, and has a gross vehicle mass (GVM) rating of 24 t.

MAN also announced the introduction of new gearbox choices for its low-floor city buses at the UITP congress. These include the installation, as standard equipment, of ZF’s new EcoLife six-speed automatic transmission with TopoDyn gear-change software from mid-2009 (see below). An alternative option will be the fifth generation Voith DIWA.5 gearbox, which features SensoTop topography-dependent gear-change technology, including a maintenance-free altimeter, electronic drivetrain integration, mechanical-hydraulic power distribution, and a secondary retarder.

NEW ZF TECHNOLOGY FOR BUSES

Driveline component manufacturer, ZF Friedrichshafen, is introducing a number of new technology aggregates, which have already drawn wide support from the bus-building community. As mentioned above, MAN will be standardising fitment of the ZF EcoLife transmission, with TopoDyn control software, in its low-floor buses, and will be joined, from mid-2009, in this selection, by Mercedes-Benz, for its Citaro and CapaCity models, and UK manufacturer Alexander Dennis for its Enviro 400 bus. Swedish manufacturer, Volvo, commenced installation of EcoLife with TopoDyn in its B9TL model since 2007.

The six-speed EcoLife has a torque capacity of 2 000 Nm, and employs a new ZF Sachs torque converter with torsional damper. It is also fitted with a more powerful and better-cooled 650-Nm Citybus retarder, to cope with the 15% higher operating temperature regimen of Euro 5- and EEV-compliant engines. The TopoDyn software continuously registers and processes data relating to the topography and all other driving resistances, including road surface and corner angles, and adjusts the shifting characteristics to the appropriate route profile making use of five specific gear-change programmes.

ZF claims that EcoLife will bring better acceleration at lower engine speeds, and effect fuel savings during initial acceleration through faster closing of the lock-up clutch. Total fuel savings of around 19% are reportedly anticipated. ZF is also currently developing a hybrid version of EcoLife, which will substitute a
120-kW hybrid electric motor module for the normal torque converter, and provide the full range of stop/start, power boosting and recuperating, electric starting and driving functionality within the same dimensional “package” as the conventional EcoLife transmission unit. ZF is planning for initial production volumes of
35 000 car and commercial hybrid modules per annum, eventually ramping up to a total of 200 000 units.