Hybrid technology on its way to series production – the MAN Lion's City Hybrid city bus
Given the worldwide increase in the cost of fossil fuels, more attention is focusing on hybrid drive technology, especially in the development of commercial vehicles. MAN sees opportunities for the future precisely in local and distribution transport - it is here that vehicles with hybrid drives burn considerably less fossil fuel, thus contributing to increased transport efficiency and to a mitigation of the CO2 problem. MAN is a pioneering force in the development of these alternative drive concepts – its engineers have been working since the 1970s on different technologies for utilising braking energy. To date the solutions have come to nothing because of their complexity, a barrier against cost-attractive implementation. The new MAN low-floor Lion's City Hybrid bus will soon go into series production. At the UITP Congress 2009 a pre-series vehicle in the final design and packaging of components was presented; in 2010, several vehicles like this will be going into service in various European cities. The MAN TGL Hybrid has also shown promise for deployment in distribution transport but will not be going into series production in the immediate future.
EfficiencyDesign: the future of the city bus has a face
The series version of the new MAN Lion's City Hybrid city bus, presented for the first time to interested trade visitors at the UITP, has a compellingly attractive "EfficiencyDesign" which underscores the particular importance of this vehicle in the MAN transport efficiency offensive. Characteristic of this design are the ultracap high-power energy storage system, which is installed on the forebody with a view to achieving favourable aerodynamics and weight distribution, the top-quality "AeroLine" in matt aluminium, which is drawn dynamically from the B-column to the roof curves, and the aerodynamically enclosed rear wheel housings. The Hybrid logo located near the B-column points out unobtrusively but nonetheless clearly that the vehicle on the go here represents the state of the art.
EfficiencyDesign: the future of the city bus has a face
The series version of the new MAN Lion's City Hybrid city bus, presented for the first time to interested trade visitors at the UITP, has a compellingly attractive "EfficiencyDesign" which underscores the particular importance of this vehicle in the MAN transport efficiency offensive. Characteristic of this design are the ultracap high-power energy storage system, which is installed on the forebody with a view to achieving favourable aerodynamics and weight distribution, the top-quality "AeroLine" in matt aluminium, which is drawn dynamically from the B-column to the roof curves, and the aerodynamically enclosed rear wheel housings. The Hybrid logo located near the B-column points out unobtrusively but nonetheless clearly that the vehicle on the go here represents the state of the art.
Stylistic elements of the current MAN Lion's City generation have been interpreted for the supplementary design of the hybrid components in such a way that these merge seamlessly into the clear design fundamentals of the existing range of vehicles. They mediate between tradition and continuity in the MAN bus family on the one hand and the continual development of technical standards and possibilities on the other. The holistic formal language runs right through the entire design, which is why the hybrid bus - a modern, high-tech product - makes such an appealing impression. To the viewer, the vehicle appears just as streamlined and dynamic as its modern technology really is. The additional attachments and technical components are so well integrated from a design point of view that they don't appear to be added on like foreign bodies. On the whole, the MAN Lion's City Hybrid keeps its typical design, one that has been admired world-wide since 2004 and has won various awards. The hybrid-specific features add value to the vehicle, clearly accentuating the high level of development competence of the MAN Nutzfahrzeuge Group.
The strongly rounded and considerably higher domed front extends the A column in a dynamic curve across the entire roof structure. At the front, it is equipped with characteristically formed louvres, while the side panels that round it off also serve to render various energy storage systems and additional components wholly invisible. From a formal aspect, this visual linkage in the same colour as the body integrates the attachments into the overall vehicle design. The body-coloured curvature ends at the silver-coloured roof-surrounding panel, the characteristic AeroLine, which runs over the entire roof. At the same time, this high-quality panel screens the electric cabling and connections behind it from view. Moreover, it provides the optimum routing for air and the air-cooling of the electrical components. Its anodised, aluminium-like colour gives the vehicle elegance and haptics. Savings are a side-effect, because the part no longer needs to be painted. And so this design element combines functional aerodynamic with visual enhancing characteristics, making this vehicle simply unmistakeable.
The AeroLine runs formally over the B-column swan-neck typical for MAN with a downward bend that strives towards the front of the vehicle. The dynamic swan-neck is an important identification feature of the MAN range of buses and can under no circumstances be omitted from the Lion's City Hybrid, where it clearly distinguishes the former from the conventional Lion's City. The panel ends elegantly at the rear of the vehicle where it is bordered by the rear spoiler. This renders the roof-mounted components invisible from behind. The front dome and the rear spoiler with its modelled, flow-separation edges have been tested, optimised and adjusted by means of air-flow simulations. The value was improved by more than ten percent relative to conventional roof structures such as those used on gas-fuelled buses, while at the same time, the cooling of the roof-mounted units was optimised.
In order to meet the demand of bus customers for dynamic vehicle design, the rear wheel houses are covered in tramway style. This not only gives the bus a tram-like, gliding, all-of-a-piece appearance; it also has a lot of other advantages. The coverings also function as water-repellent splashguards, and the sides of vehicle are not soiled with water spraying from the rear wheels. This also means that fewer particles of dust and dirt enter the engine air intakes, which are mounted on the sides. And on top of that, the attractively-formed coverings offer the operator additional surface for advertising, with a potential increase in advertising revenue for the transport company.
The overall appearance of the vehicle with its EfficiencyDesign points to power and a self-contained character. The design of the interior and exterior with smooth, easy-to-clean surfaces, worked out to the last detail and supported by dynamic lines and modern stylistic elements, creates a friendly and inviting effect while at the same time being dynamic and self-assured.
But the form isn't just for its own sake: it is the answer to various technical requirements that required solution approaches. Despite the high standard of quality, the design concept actually helps reduce manufacturing costs. Various sections of the interior and exterior cladding can be opened without difficulty for improved ease of maintenance. They also consists of several parts, making them simple to replace. The many details and the high-quality aura of the surfaces and materials set new standards in the city-bus segment and prove that the days of the rectangular standard bus that was purely a mechanical engineering product are over forever.
The impression made by the plastic design of the exterior appearance continues inside the bus. The attractive touch is accentuated by the uncluttered and comfortable interior in typically bright MAN colours and easy-care surfaces, where the customer has the option of selecting materials in certain colours. The colours of the parts are harmoniously coordinated and result in a pleasing colour scheme. In the rear of the vehicle, all the components are pleasantly concealed by the familiar panelling of the vertical D08 engine tower. In the series-production version, the hybrid components that in the prototypes had up to now been installed next to the engine tower are integrated on the roof. This ensures the smooth-surfaced, design-oriented installation of all assemblies in the vehicle's interior, with no seating being lost any more relative to the diesel variant. Apart from the slightly lower overall capacity of the hybrid variant, the solo bus is a fully-fledged and highly-efficient mode of transport for the future.
MAN Lion's City hybrid technology:
efficient and low in emissions
Local public transport is an ideal scenario for the use of braking energy. Here, solo vehicles of up to 18 tonnes are driven at low average speeds, accelerating no end of times to between 40 and 50 km/h, only to slow down again shortly afterwards for a stop. Conventional buses convert a large amount of kinetic energy into heat when they brake and it is consequently lost; the Lion's City Hybrid regenerates it and can accelerate away from a stop using only the stored braking energy in the form of electricity. On average, city buses spend about 25 to 40 percent of their time at stops, where an optimised automatic system for stopping and starting can save expensive fuel. In the Lion's City Hybrid, MAN has created a whole package of measures to produce very respectable savings.
MAN's engineers reckon with a fuel saving of up to 30 percent and at the same time, substantially reduced emissions. This is also verified by the results of around 70,000 kilometres operation covered in regular service by three different prototypes in Nuremberg, Paris and other cities without any major problems. To produce exact data, conventional vehicles of similar performance and the same payload operated a reference service. The MAN Lion's City Hybrid is also suitable for operation with second-generation biofuels (biomass to liquid, or "BtL", gas to liquid, or "GtL"), which improves the already very good CO2 balance still further. With an assumed average of 60,000 kilometres per year the MAN hybrid bus saves the environment approximately ten tonnes of greenhouse gas. Thanks to the already highly efficient series D08 common-rail engine, which complies with the voluntary EEV standard and is always very quiet in its optimum speed range, the other harmful emissions are also considerably reduced. In particular, the noise emission when moving off under electrical power is usually below the audible threshold for passengers and is hardly experienced as irritating.
The EEV diesel engine as a source of energy for powerful electric motors
The new hybrid low-floor bus from MAN is based on tried and trusted series-production hybrid technology, whose particularly high degree of efficiency in recovering braking energy makes it predestined for urban traffic. A largely series-standard D0836 six-cylinder MAN PURE DIESEL® engine with 6.9-l capacity, EEV-compliant, with 184 kW / 254 hp rated output and electronically controlled CRTec® particulate filter supplies the energy for the high-performance generator, which in turn powers two industrial-grade electric motors. The six-cylinder engine is operated mainly in its optimum speed range with reduced dynamic performance. The engineers speak of a "phlegmatised diesel engine", which also contributes its share to reduced fuel consumption with an exemplary low level of emissions. In addition, phlegmatising also avoids peak loads being put on engines and particulate filters, which in turn lengthens overall service life, saving the operator money.
The new hybrid low-floor bus from MAN is based on tried and trusted series-production hybrid technology, whose particularly high degree of efficiency in recovering braking energy makes it predestined for urban traffic. A largely series-standard D0836 six-cylinder MAN PURE DIESEL® engine with 6.9-l capacity, EEV-compliant, with 184 kW / 254 hp rated output and electronically controlled CRTec® particulate filter supplies the energy for the high-performance generator, which in turn powers two industrial-grade electric motors. The six-cylinder engine is operated mainly in its optimum speed range with reduced dynamic performance. The engineers speak of a "phlegmatised diesel engine", which also contributes its share to reduced fuel consumption with an exemplary low level of emissions. In addition, phlegmatising also avoids peak loads being put on engines and particulate filters, which in turn lengthens overall service life, saving the operator money.
The two strapped-down and fast-running asynchronous driving motors each deliver 75 kW rated power through a summation gearbox to the standard low-floor portal axle – and they do that with an enormous torque totalling around 3,000 Nm, even at the lowest speeds. And they do this completely without the interruptions in tractive power or jolting during gear changes that are the rule with conventional diesel engines because there are no gears and no gearbox. The driver experiences a whole new dimension of bus driving - easy on the passengers and easy on his nerves.
The way the electric motors are installed in the vehicle keeps the unsprung masses low by comparison with other concepts while protecting the motors against jolts to the axle or even to the wheel. This clever combination means that despite its own "small" diesel engine the city bus delivers performance similar to a conventional ten-litre diesel engine from the MAN D20 Common Rail series.
Highly-sophisticated energy management
One of the most important features of the hybrid bus is its ability to pull away from stops without any emissions at all, using only electrical power. At the technological heart of this ability is highly-sophisticated energy management system which MAN itself developed and is continually improving. This activates the diesel engine only when the demand for power increases, which on average occurs after the vehicle has travelled several hundred metres, using the generator and not the 24-V starter, i.e. usually outside the area of the bus stop. Low levels of power, needed, for example, to supply auxiliary units or the onboard network when the engine is not running, can as a rule be drawn from the energy storage system. Switching the diesel engine off and starting it is carried out by MAN's own energy management system i-MEM (intelligent MAN Energy Management), which in future will also be auto-adaptive and which, amongst other functions, controls the automatic stop/start technology. Thanks to its intelligence, the system does not need to be adjusted to new routes or drivers but still loses nothing of its savings potential.
While the bus is travelling, the diesel engine, in addition to delivering the required driving power, produces power on demand for the electrical auxiliary units depending on the available charge in the energy storage system. By contrast with the diesel bus, the air-conditioning compressor and system as well as the power-steering pump are electrically powered, which means that continuous operation of the diesel engine can be dispensed with. The i-MEM also controls the interplay between the two on-board networks: the 24-V network for the "conventional" technology and the high-voltage network for the hybrid technology. Influence is exerted on the various energy flows via the water-cooled charger-converter and the power electronics of the auxiliaries. It goes without saying that all the important components are efficiently and comprehensively insulated. The entire electrical system is kept at its own temperature level by means of a secondary cooling circuit. In practice, neither the driver nor the passengers notice very much of this sophisticated technology. Simultaneously with the market introduction, MAN is training its staff at the Service outlets to deal professionally with this state-of-the art technology.
Energy storage for a long-lived bus: high-power ultracaps
The innovative energy-storage system is contained in a compact pre-grouped unit on the forebody. It consists of six high-power capacitor modules known as "ultracaps" (UC), which are powerful enough to efficiently store the resultant braking energy (recuperation energy). The ultracap storage system is monitored by an ultracap management system.
The advanced technology of the ultracap storage system obtains its energy from the braking of the vehicle and/or when the bus is operated in overrun. Controlled via the brake pedal or in overrun operation, the system delivers up to 150 kW of power to the UC energy storage. The driving motors function here as generators - in a sense their electrical function is reversed. In this way, the braking energy is transformed into electrical energy for use when the vehicle pulls away again. In about 80 percent of cases, pulling away is purely electrical to start with: depending on the available charge and the number of passengers on board this could be up to several hundred metres. Then the energy management decides automatically whether to cut in the diesel engine as well. If the energy storage is already full when the vehicle brakes and there is no demand for any more recovered energy, an electrical braking resistor is activated to ensure the sustained-action brake function. In critical driving situations the standard EBS service brake of the Lion's City is electronically activated in addition, but otherwise it is largely spared.
The major differences between ultracaps and other means of energy storage such as batteries or flywheels are their particularly high power density, their extremely fast power input, their consistent reliability and their high degree of efficiency. Unlike batteries, no chemical conversion is involved in charging and discharging - electric charges are simply shifted. The absence of moving parts and the complete freedom from maintenance add to the high cost-effectiveness already being achieved. The capacitor solution also comes out on top in terms of weight – the low-floor bus can save the bother of a heavy battery pack and now weighs even less than a city bus powered by natural gas. A further reduction of the internal resistance produced a dramatic decrease in the storage losses of the ultracap system, and a marked increase in storage efficiency. Not forgetting that because of the improvement to the active air cooling by the EfficiencyDesign with its very efficient streaming of air through the new roof fairing, the service life of the high-power capacitors can equal that of the base vehicle itself. This is one of the outstanding advantages, contrasting with expensive battery systems whose service life is currently estimated at about six years and which have to be replaced at least once during the life of the vehicle.
Service and savings benefit the customer
The MAN Lion's City Hybrid is rewarding in use for its operator. Despite the system's undemanding nature, the driving performance satisfies even upscaled expectations. Not surprising, given the torque of up to 3,000 Nm that the two electric motors can deliver to the propshaft from a standstill. In the everyday world of passenger transport, hardly any compromises need to be made: the interior and its passenger-carrying capacity are very much the same as that of the base vehicle: the hybrid bus has the identical number of seats and a very slightly reduced total capacity in the three-door variant, which will be available shortly, as well as in the two-door variant, which will follow some time later.
The i-MEM energy management keeps the driver continually informed of the system's charge status and its readiness for operation. The driver workplace developed by MAN, as well as the VDV dashboard which will be available as series equipment at a later date, have a central display showing all the data needed for efficient, stress-free and economical operation. These include instruments showing the charge status, the current degree of energy recovery and general diagnostic information. The only difference in the hardware is an emergency cut-off switch, whose installation is required by Directive 2001/85/EU on buses.
A small series will be going on the road with selected operators as early as 2010. The series start of the Lion's City Hybrid as a solo bus is scheduled for 2011. With the new Lion's City hybrid bus, the MAN Nutzfahrzeuge Group once more provides evidence of its leadership in technology. Provided that still to be adopted subsidy guidelines and public support for the hybrid technology materialise, in the medium term MAN sees up to 50 percent of city buses in the complete-bus segment for operation in inner cities being ordered with hybrid drives.
Technical Data MAN Lion´s City Hybrid
Technical Data MAN Lion´s City Hybrid
| Diesel engine | MAN PURE DIESEL® MAN D0836 LOH six-cylinder in-line engine, vertical installation (tower design) at rear left, two-stage turbocharging and intercooling, common-rail direct injection, four-valve, low exhaust emissions as per EEV with CRTec® particulate filter. |
|---|---|
| Capacity | 6.871 cm³ |
| Rated output | 184 kW (254 hp) at 2,300 rpm |
| Maximum torque | 1,050 Nm at 1,200 to 1,750 rpm |
| Generator | PSM sync with 145 kW output |
| Drive motors | Two Siemens asynchronous electric motors, 75 kW each, driving through summation gearbox to rear axle. Total maximum torque on propshaft 3,000 Nm. |
| Storage system | Six air-cooled ultracap modules, maximum charging/discharging power 200 kW, system voltage range from 400 to 750 V. |
| Inverter | Water-cooled PWM inverter in IGBT technology |
| Special auxiliary units | Electrical power steering pump and backup unit DC/DC on-board network charger-converter (water-cooled) Electrical air-conditioning compressor and air-conditioning system |
| Energy management | i-MEM (intelligent MAN Energy Management), MAN's own system for overall optimisation of the energy flows of the vehicle and its auxiliary units. |
| Dimensions/ tyring | 11,950 x 2,500 x 3,280 mm / Show vehicle: super-wide tyres at rear. Series: standard twin tyres |
| Seats / standing room | 26+1 / 48 |
| Unladen/GVW | Approx. 12,600 kg depending on equipment / 18,000 kg |
Munich, June 8th 2009
More Information
MAN TGL 12.220 Hybrid
: The parallel hybrid for medium ranges
Thorsten Wagner
Dachauer Straße 66780995 München
| Phone: | +89-1580-67153 |
| Fax: | +89-1580-9167153 |
| E-Mail: | thorsten.wagner@man.eu |
