The world’s largest truck and bus fleet with hybrid drive
World debut of the Mercedes-Benz Atego BlueTec Hybrid and
Citaro G BlueTec Hybrid
Trucks with parallel hybrid, buses with serial hybrid
New Mercedes-Benz Citaro G BlueTec Hybrid: a technological trailblazer
Orion VII HybriDrive: world market leader among hybrid buses
Mitsubishi Fuso Aero Star Eco Hybrid: Asia’s first hybrid bus
in series production
Citaro with fuel cell drive system: two million kilometres
Mercedes-Benz Atego with hybrid drive: weight-optimised
Mitsubishi Fuso Canter Eco Hybrid: series successful, now to
be launched in Great Britain
Freightliner M2 Hybrid: electrically powered peripheral units
Freightliner Van: reliable and economical, series production starting
Around 3000 trucks and buses with alternative drive systems from Daimler Trucks and Daimler Buses are in day-to-day operation around the world. Hybrid-drive vehicles such as regular-service city buses by Orion and trucks by Freightliner in North America, the Mitsubishi Fuso Canter Eco Hybrid light truck and the Aero Star Eco Hybrid city bus in Japan, or fuel-cell-powered buses in Europe, Australia and Asia – they have all successfully won their spurs in terms of technology. No other manufacturer in the world has produced more commercial vehicles with alternative drive systems.
World debut for new hybrid vehicles
And yet this is only a start, for the Mercedes-Benz Atego BlueTec Hybrid and the Citaro G BlueTec Hybrid are now celebrating their world debut. The Canter Eco Hybrid is due to start its customer trials in Great Britain, and Freightliner is producing a series of 1500 hybrid trucks. They are all witness to the outstanding expertise of Daimler Trucks and Daimler Buses in the field of alternative drive systems, and are major steps on the way to the ambitious goal of the Zero Emission Vehicle.
With 1500 city buses in regular service, Orion is the world’s leading manufacturer of hybrid buses. More than two dozen step-in vans by Freightliner are already in operation in North America, and this number is set to increase to 100. With the Mitsubishi Fuso Canter Eco Hybrid, Fuso has already produced more than 200 units of the world’s cleanest light truck, while Mercedes-Benz has successfully completed trials of 36 fuel-cell-powered buses on three continents and can look back on almost 40 years of experience with hybrid-drive commercial vehicles. And this is only a part of the impressive balance sheet of Daimler Trucks and Daimler Buses when it comes to developing alternative drive systems.
All vehicles have proved their worth in everyday customer operations
One of the major factors is that these are not just one-off experimental vehicles in clinical trials, but that these and other vehicles are in operation with customers and are demonstrating their everyday viability. The unrivalled worldwide expertise of the individual brands is networked: for example, Mitsubishi Fuso is the world centre of competence for light trucks with hybrid drive within Daimler Trucks.
Trucks with parallel hybrid, buses with serial hybrid
Joint developments have been created from this, together with the practical experience gained across the continents. Whatever the drive unit required for different vehicle sizes or brands, the engineers at Daimler Trucks have opted for a common architecture in their hybrid-drive system. With a view to costs, reliability and the technical parameters, Daimler Trucks is focused on parallel hybrid drive for all its vehicles. In this configuration the additional electric motor is located behind the engine and clutch, but in front of the transmission. This arrangement allows purely electric drive, and has proved to be the best compromise between design complexity, dimensions, weight and performance. At the same time, the truck remains mobile even if the hybrid drive fails, which enhances overall reliability.
The completely different operating parameters of city buses in particular have led Daimler Buses to decide in favour of serial hybrid drive in the USA, Europe and Japan. One characteristic of serial drive is the lack of a mechanical link to the drive axles. This technology makes the "bus stop function" possible, allowing the bus to pull up to bus stops, and pull away from them, ultra-quietly and without any emissions. The drive units can be accommodated almost completely independently within the vehicle, which is a particular advantage given the limited installation space available in a low-floor city bus.
Owing to the more critical environmental impact and an operating profile which typically involves frequent stops and starts, both Daimler Trucks and Daimler Buses are concentrating on alternative drive systems for short-radius traffic. Both Daimler Trucks and Daimler Buses have initially opted for lithium-ion batteries in their hybrid vehicles. This battery technology excels with a particularly high energy density and a high development potential. Both Daimler Trucks and Daimler Buses are very mindful of the Zero Emission goal, and depending on the interpretation this goal has already been achieved with hybrid vehicles over short distances.
World debut: Mercedes-Benz Citaro G BlueTec Hybrid
Daimler Buses has produced a technologically pioneering hybrid-drive system in the Citaro G BlueTec Hybrid low-floor articulated bus, which celebrates its world debut in Stuttgart. Equipped with serial diesel-electric hybrid drive, this allows emissions-free driving under battery power alone over short distances.
In the Citaro with serial hybrid drive, the four-cylinder diesel engine no longer acts as a continuous propulsion unit but drives the generator to produce electric power as required. This is then stored by maintenance-free lithium-ion batteries on the roof of the Citaro. The batteries are not only charged by the diesel generator, but also by energy regained when braking in a process known as recuperation. The actual drive to the wheels of the Citaro G BlueTec Hybrid is provided by four electric wheel hub motors at the centre and rear axles of the articulated bus. Even under difficult operating conditions, their total output of 320 kW is very generous for an articulated bus, and two driven axles also ensure superior traction. An intelligent operating strategy ensures that the power is distributed among the different components in an efficient manner.
Citaro G BlueTec Hybrid is intended to cover half its route under electric power only
The recuperated braking energy obtained when approaching bus stops or traffic lights is used both to supply the vehicle at standstill and for moving off after a stop. This allows the hybrid bus to operate under electric power alone, and therefore practically without emissions, at bus stops, at standstill and when accelerating, accompanied by a significant reduction in noise. The aim is for the Citaro G BlueTec Hybrid to cover around half of a demanding inner-city route under electric power alone, without the diesel engine running.
Downsizing: a compact diesel engine is enough
Downsizing is one of the great advantages of the serial hybrid technology in the Citaro: instead of the large, 12-litre in-line six-cylinder engine usually installed in articulated buses, a compact 4-cylinder engine with a displacement of 4.8 litres and an output of 160 kW (218 hp) is sufficient. As a result the engine weight is reduced from around 1000 kg to just 450 kg or so.
As the diesel engine in the hybrid Citaro is not used as a drive unit, it is not required to deliver peak performance levels and can therefore operate very economically and ecologically, near its optimum operating point and within a narrow engine speed range. The bus is able to dispense with a conventional automatic transmission, which improves efficiency and reduces weight at the same time. Owing to these downsized major units, the additional weight of the Citaro G BlueTec Hybrid prototype is only around one tonne compared to a conventional articulated bus with diesel drive, and further improvements appear possible.
Ancillary units such as the air conditioning compressor, steering servo pump and
air compressor are no longer driven by the internal combustion engine, but individually by electric motor. This means a further improvement in efficiency, as all these units are only powered when they are required. Moreover, thanks to this electric power the ancillary units can be positioned almost anywhere, for example on the roof of the bus. This concerted optimisation of all the individual units makes the Citaro G BlueTec hybrid bus unique worldwide.
Up to 30% lower consumption
Depending on the type of operation, the developers expect the Citaro G BlueTec Hybrid to consume around 20 to 30% less fuel (expressed in litres per 100 km) than with conventional diesel drive. Despite the extra cost for the hybrid drive, which is around one third, the investment in the Citaro G BlueTec Hybrid should be amortised within about six years. In addition to environmental aspects, economic considerations therefore also play an important part in the development process. The bus will be able to demonstrate its potential in the coming year, when it enters customer trials in regular service. Series production is planned for 2009.
Next step: Citaro with fuel cell hybrid drive
The Citaro with hybrid drive is a logical step on the way to the fuel-cell-powered city bus. It already features a capable electric drive system and batteries as an energy reservoir, therefore only the diesel engine would need to be replaced by a fuel cell system. With these comparatively minor design modifications, the goal of practically emissions-free operation in inner city areas would be achieved – the Zero Emission Vehicle without particulates, nitrogen oxides or CO2, and with a very quiet drive system. The next step on this road is therefore obvious: the Citaro with fuel cell hybrid drive – a vision becoming reality.
The new Citaro G BlueTec Hybrid continues a great tradition and draws on nearly 40 years of experience in using alternative drive systems in buses: as early as 1969 Mercedes-Benz presented the world’s first hybrid bus in the form of the OE 302. It was followed by the OE 305, and then duo-buses like the OE 305 GTD and its successor, the OE 405 GTD. Mercedes-Benz supplied more than 200 of these models to the Ecuadorian capital of Quito, and around 50 units of the O 405 GTD were operational in Europe – indeed some of them are still in operation in Esslingen near Stuttgart. Other steps on the way to the new Citaro BlueTec Hybrid included the 0 405 NÜH, a low-floor inter-urban bus with wheel hub drive, a diesel engine and traction batteries, as well as the electrically powered Cito which was in series production from 1999 to 2003.
Orion VII HybriDrive: world market leader among hybrid buses
The hybrid buses produced by the American brand Orion are well beyond the testing stage. With its Orion VII HybriDrive solo, low-entry regular-service city bus, Orion has won tenders in numerous American and Canadian cities from New York to San Francisco since 2003. More than 1000 vehicles are now in daily operation, and together with orders yet to be completed the grand total is almost 1500 hybrid buses. This makes Orion the world market leader in this segment. The total fleet of Orion hybrid buses currently in operation covers a mileage of around 50 million kilometres per year.
The Orion VII HybriDrive has a serial hybrid-drive system. In the case of Orion the diesel engine runs constantly and transfers its power to a generator, which in turn supplies the electric motor and is located immediately behind the rear axle. Power is transferred to a conventional drive axle with a differential. The compact diesel engine transversely mounted in the rear has a displacement of 5.9 litres, generates an output of 191 kW (260 hp) and is equipped with a particulate filter. The electric motor has an output of 184 kW (250 hp), with even 235 kW (320 hp) possible for short periods.
Compared to diesel-powered city buses, and depending on the type of operation, the Orion VII HybriDrive achieves a reduction in fuel consumption of around 20% to 25%. Particulates are reduced by 90% versus a diesel engine with no filter, nitrogen oxide emissions by 40% and carbon monoxide by around 30%. Over its entire service life, each bus saves 75,000 litres of diesel fuel and avoids emissions of four tonnes of nitrogen oxides and 195,000 kilograms of CO2.
Remarkably, these hybrid buses have proved to be more reliable than conventional diesel buses in New York. Thanks to their electric drive they accelerate more rapidly and smoothly, with no jerking due to gearchanges. The operating life of the brakes is twice as long, and both the diesel engine and electric motor look set to have an extremely long operating life as well.
Mitsubishi Fuso Aero Star Eco Hybrid: new hybrid bus
The Japanese brand Mitsubishi Fuso, a member of the group, has also opted for hybrid drive in its city bus. Since as early as 2004, five Aero HEV vehicles have been operating successfully in three Japanese cities and have each driven around 150,000 km without problems.
The technical architecture of the serial drive is similar to that of the North American Orion: a diesel engine transversely mounted at the rear operates with an optimised characteristic map and drives a generator. This supplies two electric traction motors. These are located immediately behind the rear axle, and transfer their torque to a portal axle with super-single tyres via a power collecting gear. In this case the batteries carried on the roof are lithium-ion accumulators.
The development of hybrid buses is advancing in leaps and bounds: at the end of 2007 Mitsubishi Fuso presented the second generation under the name Aero Star Eco Hybrid. The completely redesigned drive system now uses a compact four-cylinder diesel engine with a displacement of only 4.9 litres. It has an output of 132 kW (180 hp) and serves only to generate electricity. This downsizing saves considerably on both space and weight, and moreover also reduces fuel consumption even further. The generator driven by the engine in turn supplies the power to two electric motors each with an output of 79 kW.
When stopping at traffic lights and bus stops, the diesel engine of the low-entry bus switches off automatically. For this reason the doors and ancillary units such as the power steering pump, air compressor and air conditioning are now powered by electricity only. The bus also moves off under electric power, the diesel engine not cutting in to generate power until a medium speed is reached. Kinetic braking energy is transformed into electrical energy and fed to the batteries (recuperation).
The Aero Star Eco Hybrid is available as a city bus with a 4800 mm wheelbase or as a suburban version with a wheelbase of 5300 mm. Passenger capacity amounts to 65 persons in both cases.
Mitsubishi Fuso presented a first battery-powered city bus back in 1973. In 1994 the company introduced a system to recuperate braking energy, and a further environmentally friendly vehicle was a natural-gas-powered city bus launched in the year 2000.
Citaro with fuel cell drive: two million kilometres
Hybrid drive in buses is a logical interim stage on the way from the internal combustion engine to the fuel cell and hydrogen power, i.e. on the way to the Zero Emission Vehicle. Exactly ten years ago Mercedes-Benz presented the "Nebus" (New Electric Bus), the world’s first fuel-cell-powered bus.
At the 2003 UITP Congress in Madrid, Mercedes-Benz presented the first fuel-cell-powered Citaro, and findings obtained since then clearly demonstrate its practical viability. In the world’s most extensive practical trials with fuel cell vehicles, 30 buses based on the Citaro entered operation with transport companies throughout Europe for a two-year period. Three further vehicles were also in operation in Australia for two years, and another three fuel cell buses are operational in the Chinese capital Beijing. In some cities the European trials were even extended for a further two years. No less than nine of these buses are currently in operation in Hamburg, with a further three in Amsterdam.
All in all, these vehicles have covered more than two million kilometres and accumulated a total of 125,000 operating hours. With an availability of 90 to 95 %, the buses have impressively demonstrated their suitability. As a next step in the right direction, the newly presented Citaro BlueTec Hybrid will be developed further into a Citaro G fuel cell hybrid. The infrastructure of the electric drive system can be retained, while the diesel engine and generator will be replaced by fuel cell stacks. Instead of tanks for diesel fuel and AdBlue, hydrogen tanks will be mounted on the vehicle roof.
The facts speak for the fuel cell as the drive system of the future. It will make the Zero Emission Vehicle a reality, with buses emitting no harmful exhaust gases, travelling extremely quietly and operating with a high efficiency. Hydrogen can be generated in a variety of ways. This drive system has demonstrated its efficiency and reliability in day-to-day operations.
World debut: Mercedes-Benz Atego BlueTec (7.5 t) with hybrid drive
Just as Daimler Buses leads the field in the hybrid bus segment, Daimler Trucks is the leader in the truck sector. No manufacturer offers a wider range, and no other manufacturer can boast as many vehicles in day-to-day customer operations. And the number is growing constantly: the Mercedes-Benz Atego BlueTec Hybrid is now celebrating its debut in Stuttgart, and will shortly be demonstrating its practical suitability during customer trials.
The Atego BlueTec Hybrid benefits from the worldwide Daimler Trucks network and a superb level of cooperation between the engineers in Stuttgart and Kawasaki, Japan, where around 200 light trucks have already been series-produced.
Daimler Trucks has generally opted for an architecture with a parallel hybrid. This has proved most suitable for the technical powertrain configuration of a truck, and also offers advantages during procurement. These costs are of lesser importance for a city bus, owing to their generally higher price and the long period of first ownership. The goal is for the hybrid drive to recoup the first owner’s investment in all cases.
Downsizing saves weight for the benefit of payload
With a view to weight optimisation, downsizing is the order of the day for the Mercedes-Benz Atego, which is in a payload-sensitive category with its permissible gross vehicle weight of 7.5 t. When it comes to hybrid drive, therefore, the engineers try to limit the extra weight of the second propulsion system while retaining the vehicle's performance by such measures as using smaller diesel engines. The compact, lightweight four-cylinder diesel engine with a displacement of 3.0 l develops an output of 92 kW (125 hp) and a maximum torque of 294 Nm. This is supplemented with a water-cooled electric motor generating a peak output of 35 kW and 200 Nm of torque. It is located between the clutch and the automated transmission. The electric motor mainly assists the diesel engine at lower and medium engine speeds. Once the truck is cruising along after acceleration, it runs economically on diesel power alone, but electric power only is used when moving off.
The electric motor obtains its energy from lithium-ion batteries mounted in a housing on the left side of the frame. The battery pack weighs 87.5 kg and has a capacity of 1.9 kWh. The water cooler for the hybrid drive is mounted on the opposite side. The batteries are charged by recuperated braking energy. The developers expect a fuel saving of up to 20% to be achieved during customer trials in the distribution sector.
World debut: Atego BlueTec Hybrid with 12 t gross vehicle weight
For high performance requirements, there is also an Atego twelve-tonner. This enters the scene with an identical architecture, i.e. parallel hybrid drive, but has different components adapted to suit the greater vehicle weight. In this case Daimler Trucks benefits from the cooperation with Eaton: the powertrain consists of the Mercedes-Benz OM 924 four-cylinder engine developing an output of 160 kW (218 hp) and 810 Nm of torque, plus the electric unit from the component manufacturer Eaton.
The electric motor generates a peak output of 44 kW and a maximum torque of 420 Nm. Power is transferred by an automated Mercedes-Benz G 85 transmission. In the Atego BlueTec Hybrid, both units working together produce a performance which can only be equalled by a truck with a powerful six-cylinder diesel engine. Thanks to the use of a lightweight four-cylinder engine, the Atego BlueTec Hybrid weighs only around 60 kg more despite the additional hybrid-drive components and the lithium-ion batteries.
The Atego BlueTec Hybrid with a gross vehicle weight of 12 t is likewise due to undergo rigorous day-to-day testing soon: in the coming year six units will be entering customer trials for a period of one year.
Canter Eco Hybrid: successful start-up in Japan
The greatest success so far for a hybrid-drive truck has been achieved by the Mitsubishi Canter Eco Hybrid. Introduced in the summer of last year, around 200 units of this light truck have left the production lines to date. The Canter Eco Hybrid is the first light truck to have met the stringent exhaust emission standards in force in Japan since the summer, and also excels with a very favourable fuel consumption approx. 20% lower than that of a comparable diesel truck.
The drive system is based on a 3.0-litre four-cylinder diesel engine developing an output of 92 kW (125 hp) and a torque of 294 Nm – a very compact and lightweight power unit in relation to the overall weight. This engine also features exhaust gas recirculation and a particulate filter. It is combined with an electric motor which acts as a generator when braking (output 35 kW), as well as a lithium-ion battery pack with a capacity of 1.9 kWh. The batteries are charged by recuperated braking energy. To augment this effect the drive unit is disengaged during braking. Power is transferred by an automated manual transmission. A start-stop function switches the engine off when the vehicle is idling at standstill.
The Canter Eco Hybrid changes its operating mode depending on the driving situation. Electric drive is used when moving off. The diesel engine is switched on in addition when strong acceleration is required, and this powers the truck alone when cruising speed is reached. With a net weight of 2.9 t and a permissible gross vehicle weight of 4.5, 6.5 or 7.5 t, the Canter has a high payload despite its hybrid-drive system.
Canter Eco-D study: medium-heavy tipper with hybrid drive
The 2007 Tokyo Motor Show saw the presentation of the first concept study of a hybrid-drive tipper truck based on the Mitsubishi Fuso Canter. The outstanding feature of the Mitsubishi Fuso Canter Eco-D is the electrically powered tipper body. This considerably reduces noise and exhaust emissions, as the necessary power comes from the batteries and the diesel engine remains off while tipping is in progress. It would also be conceivable to drive other implements and attachments electrically, e.g. crane bodies or platform hoists. In the case of the actual propulsion system, the benefits of the Canter Eco Hybrid remain unchanged.
New: Canter Eco Hybrid entering its first customer trials in Europe
The Canter Eco Hybrid from the Daimler Trucks worldwide centre of competence for hybrid systems is such a convincing proposition that it is also making its way to Europe now. Before the end of this year, the first of 10 vehicles will be entering customer trials for a period of 3 years in Great Britain. This is a genuine first, for these are the first customer trials with hybrid trucks in Europe. In technical terms the powertrain is the same as on the Japanese Canter Eco Hybrid, however the vehicles are configured for European requirements and the engines for the European emissions standards..
Freightliner M2 Hybrid: electrically powered ancillary units
Freightliner, the largest truck manufacturer in North America and part of Daimler Trucks, is also developing hybrid vehicles using parallel systems like the other brands in the group. The latest, a medium cab-behind-engine truck in the M2 series with a permissible gross vehicle weight of 15 tonnes, is however configured expressly for North American conditions.
Here vehicles with platform hoists play an important role as service vehicles because overhead power lines are in widespread use. Accordingly Freightliner not only uses the electric drive unit as an alternative, and to assist the vehicle’s diesel engine, but also for emissions-free and quiet operation of the power take-off for a platform hoist, whose hydraulics are powered by a high-voltage battery. This advantage can be applied to numerous other applications, e.g. to drive tail-lift pumps for tankers or firefighting vehicles and many other equipment items. This approach also avoids unnecessary idling by the diesel engine.
The drive system of the M2 combines a compact 6.4-litre Mercedes-Benz OM 906 (US designation: MBE 906) six-cylinder in-line engine developing 186 kW/252 hp with an electric motor. This generates a peak output of 44 kW and a maximum torque of 420 Nm. Power is transferred by an automated six-speed transmission. Electric power is supplied by lithium-ion batteries with a total capacity of 5.5 Ah, which are charged by recuperation of braking energy. Fuel savings amount to around 25 to 30%.
The Freightliner M2 has successfully passed its practical trials, and celebrated its public debut in the summer of last year. The concept of this truck is so convincing that Freightliner now plans to produce a series of 1500 M2s with hybrid drive.
Freightliner Van: reliable and economical, entering series production
Courier services frequently make deliveries to businesses and households in particularly emissions-sensitive locations, such as residential areas and pedestrian precincts. Frequently they are also on the roads at night. Among parcel services large numbers of these vehicles are in operation in North America. The Freightliner subsidiary Freightliner Custom Chassis Corporation (FCCC) produces many thousands of chassis for distribution vehicles each year. As what are called walk-in vans they are tailor-made for the typical requirements of American distribution operations, with a practical box body, a gross vehicle weight of 7.3 tonnes and a load capacity of 17.9 cubic metres.
For more than three years, 25 of these vans with hybrid drive have been successfully undergoing practical trials with a large fleet customer. During this period they have achieved outstanding results: large fuel savings and a high level of reliability amounting to an availability of 99%. A further 75 vehicles are being delivered as a result of this success.
The architecture of the van’s drive system follows the familiar parallel hybrid principle, and is based on a 900-series (US designation: MBE 900) four-cylinder diesel engine with a displacement of 4.25 litres and an output of 125 kW (170 hp). The electric motor delivers 44 kW and is supplied with power by lithium-ion batteries.
Hybrid drive undergoing long-distance trials
Frequently changing acceleration and braking cycles, as well as a particularly emissions-sensitive operating environment, mean that hybrid drive is eminently suitable for short-radius transport. Depending on the topography, however, it can also produce noticeable fuel savings in long-distance operations. According to calculations by Daimler Trucks these amount to around 4% on average.
Owing to the high mileages covered, with a correspondingly high annual fuel consumption, the absolute advantages are potentially even greater than in the case of distribution vehicles in short-radius operations. This must be offset against a reduced payload and limited installation space in semitrailer tractors or touring coaches. Daimler Trucks and Daimler Buses are also planning practical trials with hybrid-drive long-distance trucks and touring coaches in the future.
Excellent future prospects for hybrid drive
Specialists agree that hybrid drive has excellent future prospects. Clear advantages include highly reliable components, no additional maintenance requirements despite the additional powertrain components, environmental compatibility thanks to a considerably lower fuel consumption, quiet operation in electric mode and emissions-free driving over short distances. The favourable fuel consumption automatically leads to low CO2 emissions, and the emission of fine particulates is also significantly reduced.
The problem of electric energy storage, previously a great handicap of hybrid vehicles, appears to have been solved. Modern lithium-ion batteries combine a high power density with a large storage capacity, and they are also able to cope with rapid charging/discharging cycles. They can also be expected to last for the entire operating life of the vehicle, though only extensive long-term tests can finally confirm this.
Emission measuring cycles are still lacking for hybrid vehicles
There are still problems that remain to be solved, however. Classification according to emission standards and the measuring cycle used to measure emissions are outstanding issues, for example. Rapid progress in these areas is essential to ensure that operators know where they stand. A standardised measuring cycle appears to be emerging in Japan, for example.
The considerable additional technology in a hybrid vehicle is naturally reflected in significantly higher procurement costs. In order to make hybrid vehicles a paying proposition for the first owner, and in order to increase the vehicle population rapidly with a view to environmental protection, the question of public subsidies cannot be ignored.
There are examples of this in Japan and in the USA. In the latter case there are federal and state subsidies towards the extra cost of procuring buses with hybrid drive. In Japan the procurement of a Canter Eco Hybrid is already amortised after five to seven years, thanks to a subsidy towards part of the additional costs for the hybrid-drive system and the fuel savings during operation.