Along with the six-cylinder OM 5 engine, after 1926 Mercedes-Benz developed a new one-cylinder engine which it fitted into the OE diesel tractor in 1928. The engine displaced 4.2 litres and had an output of 19 kW (26 hp) at 800 rpm.

The Lo 2000 was the world’s first light truck to be fitted with a diesel engine as standard. Daimler-Benz AG introduced it in 1932 at the Geneva Motor Show. It was powered by the new 3.8-litre prechamber diesel OM 59. This innovative vehicle design was a response of Daimler-Benz to the difficult economic situation following inflation and a world economic crisis. Customers had a high opinion of this economical and light truck.

The letters “Diesel” on the radiator next to the Mercedes star became a symbol mainly of heavy goods transport in the 1930s. Whereas the diesel engine’s share of the power plants of big trucks already reached 90 percent in Germany in 1931, and trucks of five tons payload and more were fitted exclusively with diesel engines after 1934, the compression-ignition engine was much slower establishing itself in the light truck segment. The new OM 59 of 1932 was an important argument for diesel technology: the engine was less than half the size of the OM 5, but was nearly as powerful. And it gave the Lo 2000 a top speed of 65 km/h; in 1932 this definitely sufficed to have it called an express delivery van.

The semitrailer tractors built in Gaggenau from February 1933 on also profited from the success of the Lo 2000. With the LZ 4000, LZ 6000 and LZ 8000 series (four, six and eight tons) the diesel truck model range of Daimler-Benz continued to grow. In the mid 1930s Daimler-Benz built trucks with petrol engines almost only for export.

High-speed, light diesel engines proved a key to the success of the semitrailer tractors: relatively small-volume engines with rated speeds of 2000 rpm and displacements between 3.8 litres (40 kW/55 hp) and 7.4 litres (70 kW/95 hp) powered the semitrailer tractor. In 1938 a tractor for ten tons payload was added; its six-cylinder diesel developed 74 kW (100 hp). The advantage of uncoupling tractor and semitrailer was used by the buyers of tractors not only in the haulage sector: semitrailers were even supplied equipped as buses – this configuration went into the vernacular as “Tatzelwurm” (a mythical Alpine dragon).

Nine years after the merger of Benz & Cie. and Daimler-Motoren-Gesellschaft in 1926, the diesel engine was playing an increasingly important role in the commercial vehicle sector for Daimler-Benz AG: in Gaggenau the 10,000th commercial vehicle of the brand featuring a compression-ignition engine was delivered to a customer on 6 April 1935.

The engine range was correspondingly diversified, including engines for light and heavy-duty trucks with four and six cylinders as well as engines for urban buses.

A new era in diesel technology for commercial vehicles began at
Mercedes-Benz during the Second World War: in 1940 the engineers of the Stuttgart brand took up work on an entirely new generation of diesel engines, the 300 series. The first prototype was the in-line six-cylinder OM 302, parallel to which the designers worked on the four-cylinder OM 301 unit.

Characteristics of the new engine were its compact dimensions and innovative components, for example a seven-bearing crankshaft and leaded bronze bearings with steel backings for the main and connecting rod bearings. Production commenced in 1942, but work on the 300 engine series could not be resumed until after the war.

On the basis of the OM 302, at war’s end Mercedes-Benz Development resumed work on a modern commercial vehicle diesel engine. The condition was that the new unit had to be produced on machines on which Daimler-Benz manufactured a licensed version of the Opel Blitz during the latter war years and until 1949. This Mercedes-Benz L 701, as the vehicle with its wooden cab was called, the first truck of the Stuttgart brand after the war, was still powered by a petrol engine. On the other hand, under the bonnet of the first post-1945 heavy-duty truck, the L 4500, was the tried and tested OM 67/4 in-line six-cylinder diesel, which developed 82 kW (112 hp) at 2250 rpm.

The diesel engine in the new L 3250 truck presented in May 1949 at the Hanover Trade Fair was now the OM 312, the first member of an extremely successful engine family. Passing through numerous stages of development, the 300 series would be the backbone of the medium-duty commercial vehicle diesel engine range from Mercedes-Benz for more than 50 years. In its first version the OM 312 in the L 3250 already developed 66 kW (90 hp) at 2800 rpm.

A 1949 brochure underscored the advantages of the new design and left no doubt as to the importance of the new truck for the commercial vehicle range of the brand: “The water-cooled, flexible six-cylinder diesel engine with an output of 90 hp and featuring controlled cylinder wall temperature and oil temperature is a particularly interesting new technical creation with its average fuel consumption of 14.4 litres per 100 km. Outstanding performance characteristics, highest operating reliability, tremendous economic efficiency, simple operation and thriftiest consumption, combined with excellent handling qualities and safe roadholding are the essential features of the new L 3250.”

In the heavy-duty segment too, in 1950 a 300-series engine superseded the diesel technology which still dated from the 1930s: the Mercedes-Benz L 6600 was powered by an OM 315 8.3-litre in-line six-cylinder, which was good for 107 kW (145 hp) at 2100 rpm.

The new generation also furnished a basis for technical innovations during the following years. Mercedes-Benz took an important step to boost performance by introducing the exhaust-gas turbocharger for commercial vehicle diesel engines. In a TLF 15/36 TA pump water tender, the Stuttgart company presented the first diesel engine which utilised the energy of flowing exhaust gases for charging the cylinders. The type OM 312 A engine (the A stands for Abgasturbolader = exhaust-gas turbocharger) developed 85 kW (115 hp), 18 kW (25 hp) more than the naturally aspirated basic engine.

But there had already been a few turbocharged commercial vehicle diesel engines from Mercedes-Benz before that: from 1948 the Esslingen-based Eberspächer company had been offering a suitable turbocharger as a retrofit kit for the OM 312. However, turbocharged commercial vehicle diesel engines did not gain broad acceptance until around 30 years later.

The new diesel engines from Mercedes-Benz not only were a success in trucks and cars. Special-purpose vehicles like the Unimog (“Universal-Motorgerät” for universal working machine) also were equipped with the diesel power unit. From the start of Unimog production to November 1957, 20,000 diesel engines were built for this powerful all-wheel-drive vehicle alone.

Originally, the diesel engines of the Unimog were identical with those of the Mercedes-Benz diesel passenger cars. In May 1963 the Unimog U 406 came out on the market with a 48 kW (65 hp) OM 312 under its bonnet. This was Mercedes-Benz’s answer to the increasing demand for a high-powered variant of the special-purpose vehicle with the wide range of applications. The Unimog no longer saw use only in agriculture, but long since had proved its mettle in municipal service, as a fire-fighting vehicle, with the military and in other areas.

The designations existing for the different truck models in the Mercedes-Benz range in the 1950s said nothing about the output of the engine used in each truck. The letters only indicated the basic configuration (conventional or cab-over-engine vehicle) and body. In 1963, therefore, Daimler-Benz decided to abolish the old nomenclature. During the following months, the letter and number combinations which we know today were introduced. The last two digits stand for one tenth of the engine output in horsepower (rounded off). Before that the gross vehicle weight in tons (rounded off) is stated. Thus, the heavy-duty all-wheel-drive truck LA 2620 of 1964 has a permissible GVW of 26 tons and an output of roughly 200 hp (147 kW). Actually, the OM 346 engine developed 154 kW (210 hp) at 2200 rpm from its six cylinders with a total displacement of 10.8 litres.

The OM 352 engine introduced at the 1964 Geneva Motor Show by Mercedes-Benz was the first direct-injection diesel for commercial vehicles. Direct injection results in lower consumption and higher output. Initially, however, the engines did not run as smoothly as their prechamber cousins. Particularly if single-hole injection nozzles were used with central combustion in a spherical combustion chamber, extremely loud noises and a high peak pressure were generated. Multi-hole injection nozzles and flat combustion chambers in the pistons were better still for fuel consumption, but likewise led to loud combustion noises and high peak pressures. The Mercedes-Benz design engineers ultimately decided to use a four-hole injection nozzle positioned almost dead-centre in the cylinder. However, it sprayed the fuel into the cylindrical combustion chamber at an angle of about 30 degrees. The fuel spray was directed at the wall of the combustion chamber; a swirl duct in the cylinder head provided for the necessary turbulence of the diesel mist in the cylinder. The ignition pressure in the direct-injection diesel rose to around 80 bar compared with 60 bar in the prechamber engine.

The operating noise of the direct-injection diesel had been sharply reduced by the time the engine was ready for production in 1964. In the car sector though, for the time being the classic prechamber diesel with its refined characteristics remained the power plant of choice for Mercedes-Benz. In the commercial vehicle sector, by contrast, the first direct-injection diesel was received very well. For buyers of trucks and buses, not only the boost in power counted. The better efficiency compared with the prechamber power plants reduced the thermal load on the engines; they proved to be particularly reliable. A pleasant side effect of the reduced load on the engine oil: the servicing intervals for oil changes were extended to 18,000 kilometres.

A four-cylinder injection engine, the OM 314, also was brought out in 1964. The first units of the new model had a displacement of 3.8 litres and developed 59 kW (80 hp) at 2800 rpm. The four-cylinder engines were used in light cab-over-engine trucks, vans, and special-purpose vehicles like the Unimog.

A number of customers increasingly asked for a Mercedes-Benz diesel engine with fuel injection and exhaust-gas turbocharger. The turbocharger was supposed to provide the power necessary mainly for journeys through mountain regions. For where the atmosphere gets thin, boosting the volume of air in the combustion chamber gives rise to an especially sharp increase in output.

Initially the OM 352 A was intended for use in snow cutters. Following successful road testing the turbocharged unit was also installed in trucks. The new engine premiered in the L 1413, where the turbocharged injection engine developed 115 kW (156 hp). The use of improved turbochargers from Eberspächer, Garrett® (Honeywell) and KKK (Kühnle, Kopp & Kausch) made this high-powered compression-ignition engine even more reliable.

In the Mercedes-Benz Mannheim works, an anniversary was celebrated in January 1969: the 100,000th diesel engine for commercial vehicles built in the plant on the River Neckar came off the assembly line.

Mercedes-Benz displayed the first prototype of the OE 302 hybrid electric bus at the 1969 International Motor Show in Frankfurt/Main. The aim of optimizing the propulsion system of line-service buses in this project was mainly to reduce their emissions in downtown areas: battery current served to power the buses in the sensitive zones of city centres; on highways and in less densely populated city districts the serial hybrid drive changed to the diesel engine. In the serial hybrid system, however, the compression-ignition engine did not act directly upon the wheels, but supplied the electric traction motor with energy via a generator.

The successor to the OE 302 was presented in 1978 at the “transport 78” trade show in Munich: the OE 305 hybrid electric bus again had an electric traction motor which a diesel engine powered via the generator. The heavy batteries notwithstanding, the capacity of the drive system was designed so that the bus attained the performance of a comparable diesel-powered O 305 urban bus. Despite the high load on them, the storage batteries survived an average of 800 recharging operations. In the course of 1979 a total of twenty OE 305 hybrid electric buses took up local public transport service in the cities of Stuttgart and Wesel. By 1983 the vehicles had covered more than 1.3 million kilometres.

In 1979 Daimler-Benz also introduced a second hybrid bus: besides the standard diesel engine, the Duo Bus or dual-powered bus was equipped with an electric motor which was supplied with current by an overhead cable. Whereas the electric motor was used in the city, in the country the bus operated on its diesel drive. Before the end of 1979, three of the vehicles commenced trial operation in regular service in Esslingen. During the next few years more than 50 of these vehicles would be used internationally in regular service.

These test vehicles of the 1970s presaged the part that the diesel drive would play in advanced hybrid concepts for passenger cars after the year 2000. Other bus concepts with innovative drive systems were the diesel-electric O 405 GTD dual-powered bus (1986) and the diesel-electric O 405 GNTD bus (1994). This low-floor articulated bus had a diesel engine that powered a generator that supplied electric energy for the wheel hub motors.

A new engine series for heavy-duty trucks came out on the market in 1970. The 400 family of Mercedes-Benz diesel engines made its debut in the new LP 1632 as a V10 engine with a displacement of 16 litres and an output of 235 kW (320 hp) at 2500 rpm. The new units were the designers’ response to a proposed law intended to speed up over-the-road freight transport: in 1968 the German Federal Minister of Transport, Georg Leber, introduced a bill stipulating that from 1972 on new vehicles must have an engine output of 6 kW (8 hp) per ton of gross combination weight.

Medium-duty and light trucks, which are more likely to be used in short-radius distribution work and pull trailers less frequently than their heavyweight brothers, were not so much affected by this regulation. But for long-distance trucks and tractors and other heavy-duty commercial vehicles, the output of the 300-series engines was no longer adequate under the conditions set by the new laws. From 1969 Mercedes-Benz thus set about developing the new engine generation.

The veil was lifted on the OM 403 with diesel direction injection in 1970. Together with the engine, the LP 1632 truck presented another innovation – a tilt cab. This appreciably simplified the servicing of the engine in a COE truck and invalidated a major argument in favour of conventional trucks. In 1972 the bigger engine was complemented by the OM 402 V8 diesel, with 12.8 litres displacement and 188 kW (256 hp) output at 2500 rpm. For medium-duty trucks, the OM 401, a V6 diesel with 9.6 litres displacement and 141 kW (192 hp) at 2500 rpm, followed in 1975.

Iranian Diesel Engine Manufacturing Company (IDEM) in Tabriz, Iran, began assembling diesel power units for commercial vehicles in 1970. Daimler-Benz had owned a stake in the company since 1969. Engines of the 300 family were built there: around 180,000 units of the OM 314, OM 352 and OM 352 A engines were produced in the first 30 years of this cooperation.

The commercial vehicle diesels from Mercedes-Benz conquered the world during this decade: in 1979 Mercedes-Benz awarded licenses for the 300 and 400 series to Industrial Development Company of South Africa (IDC). Diesel engines of Stuttgart origin were built and adapted to various vehicles and pieces of equipment in the engine plant of Atlantis Diesel Engine (ADE) north of Cape Town.

In Germany, too, the manufacture of commercial vehicle diesels was running at full swing. In 1975 a V6 diesel from the OM 401 series became the one-millionth commercial vehicle diesel engine to be built at the Mercedes-Benz plant in Mannheim. The 141 kW (192 hp) engine was donated to the city of Mannheim, which installed it in a Mercedes-Benz fire truck.

As early as the mid-1970s Mercedes-Benz began developing commercial vehicle engines which featured an intercooler in addition to the exhaust-gas turbocharger. Cooling reduces the temperature of the air compressed by the turbocharger, thus increasing the oxygen content. This permits obtaining higher power in engines with the same technical data: the OM 422 A V8 diesel developed 243 kW (330 hp) with 14.6 litres displacement, whereas its intercooler-equipped brother introduced in 1980 developed an output of 276 kW (375 hp).

This OM 422 LA engine was the first commercial vehicle engine from Mercedes-Benz to have an intercooler. It was followed in 1982 by a 300 series engine, the OM 362 LA, with the same technology and an output of 141 kW (192 hp) at 2600 rpm. 300 series engines like this were built in large numbers mainly for export.

Within 17 years, 500,000 engines of the OM 400 series were built. The anniversary engine originated in Mannheim in January 1987. From the original OM 403 V10 engine, meanwhile, various V6 and V8 drive units had emerged whose power output in production trucks ranged from 140 to 320 kW (190 to 435 hp). A special heavy-duty hauling variant of the V10 engine even boasted 368 kW (500 hp).

Together with the new Actros heavy-duty truck, in 1996 Mercedes-Benz introduced a new, innovative engine family. The diesel power plants of the 500 series made their debut with a V6 engine, the OM 501 LA (230 kW/313 hp - 315 kW/428 hp) and a V8 engine, the OM 502 LA (350 kW/476 hp - 420 kW/571 hp). Equipped with exhaust-gas turbocharger and intercooler, the engines featured individual unit pumps and attained their maximum torque at 1080 rpm. While the V6 had one turbocharger for the entire engine, the V8 was distinguished by one turbocharger for each of the two cylinder banks.

Together with the 500 series Mercedes-Benz introduced the new 900 series of in-line diesel engines for the new Atego truck family, comprising mainly light and medium-duty vehicles. The four-cylinder OM 904 LA developed between 90 kW and 125 kW (122 hp and 170 hp), the six-cylinder OM 906 LA delivered 170 kW or 205 kW (231 hp or 279 hp).

With the two new engine families, plus the 457 series borrowed from South American production in 2001 for the new Axor family, Mercedes-Benz soon covered the entire commercial vehicle spectrum with different ultramodern diesel power units. The engines are perfectly matched to the other components of the drive system. An individual drivetrain can thus be put together from different modules. This results in an extraordinary variety of models and specification options.

In 1998 Mercedes-Benz introduced the Cito urban midibus. The innovative low-floor vehicle had a diesel-electric drive system. An OM 904 LA diesel engine with an output of 130 kW (177 hp) served to drive a generator. The generated electric power was fed into the electric traction motor. Thanks to this drive technology, the Cito excelled with smooth and continuous acceleration. This driving characteristic cannot be obtained with a purely mechanical drivetrain.

The unit consisting of diesel engine, generator and electric motor was installed in the rear of the vehicle and called a power pack. Mercedes-Benz developed the system together with Siemens. The Cito was built from 1999 to 2003. In 2000 it won the distinction of “Bus of the Year 2001.”

All variants of the OM 500 were revised in 2003. The V6 and V8 engines of the Actros got slightly higher power ratings. But most of all the torque of most of these diesel engines was markedly increased. The engines’ ease of servicing also was improved with wear-free materials and extended servicing intervals of as much as 150,000 kilometres in long-haul operation.

This special edition of the Actros, limited to 250 units, is equipped with the OM 502 LA engine, which develops 450 kW (612 hp) at 1800 rpm from a displacement of 16 litres, making this the first Mercedes production truck to clear the 600-hp hurdle.

A V8 diesel of the 500 family became the 500,000th reconditioned diesel engine for Mercedes-Benz commercial vehicles in 2006, coming off the assembly line at the Mannheim plant. Genuine reconditioned engines or factory-reconditioned components from Mercedes-Benz are the ideal solution for providing commercial vehicles with a virtually new drive system. Reconditioned engines are typically used for trucks and buses which run up high mileages in a short time – the so-called mileage millionaires. But also for vehicles with expensive special bodies and correspondingly high residual value, the replacing of the engine suggests itself when the original unit shows weaknesses.

In a reconditioned engine, not only all defective and worn-out parts are replaced, but all design changes, innovations and improvements made since original manufacture are incorporated into the unit. With that, the reconditioned component gets an entirely new identity, recognisable by the reconditioned-unit model plate. And Mercedes-Benz gives the same warranty on it as for a brand-new component.

Reconditioned engines are available for the 500, 900, 457, 300 and 400 series. The
V-engines of the heavy-duty 500 series are the heart of the Actros and are also premium engines operating in high-quality touring coaches like the Travego. The 900 series powers the Atego, Vario, Cito, Citaro and Unimog vehicles; the 457 family operates in the Axor and Citaro. But even for the older series, the 300 and 400, production of which was discontinued, there are still replacements available. For the most part, these engines are reconditioned using original production equipment. They are available then, for example, to the fans of vintage Unimog vehicles.

Engine reconditioning has a long tradition in Mannheim: since 1949 the factory has been dismantling commercial vehicle engines, completely overhauling them and returning them as good as new to customers. The 200 employees in engine reconditioning overhaul some 5000 units annually. This requires detailed knowledge: there are more than 2700 different engine variants on the list.

In 2007, Mercedes-Benz presented the first prototype of a Citaro with diesel-electric hybrid drive to the public. The developers set themselves ambitious targets in that this diesel-electric serial hybrid drive is a technologically highly sophisticated system. It permits zero-emission operation on battery power alone. The drive configuration is equally advanced: it is installed in a Citaro G articulated bus and comprises four wheel hub motors which drive the central and rear axles. At this point in time, the Citaro Hybrid was the only vehicle to offer this combination.

In the serial Citaro Hybrid, the diesel engine no longer serves as a permanent drive unit but powers the generator which supplies the amount of electricity required at any point in time. There is therefore no mechanical connection between the diesel engine and the driven axles – a characteristic feature of serial hybrid drive. This creates new degrees of freedom in the design of the passenger compartment. The electricity produced by the generator is stored in maintenance-free lithium-ion batteries which are mounted on the roof of the Citaro. This battery technology stands out for a particularly high energy density and high storage capacity. The batteries generate 170 kW (231 hp), and their weight of 450 kilograms is comparatively low. They are fed with energy not only by the diesel-powered generator but also by the brakes – a process known as recuperation.

Downsizing is one of the major advantages for the technology of the particularly sophisticated serial hybrid in the Citaro: instead of the OM 457 hLA six-cylinder in-line engine with its very large displacement of twelve litres normally used in the articulated bus, the compact OM 924 LA is installed in the hybrid bus. It develops an output of 160 kW (218 hp) from a displacement of 4.8 litres. As a result, engine weight is reduced from around 1000 to just 450 kilograms. The use of the compact engine has been made possible by the fact that the diesel engine does not serve as prime mover of the Citaro Hybrid bus. It does not have to generate peak output, for instance, and can therefore be operated in the narrow engine speed band in which the highest fuel economy and lowest emissions are ensured. For this reason, the engine’s torque characteristics were adapted to its – partly stationary – operating conditions in the hybrid bus for optimised levels of emissions and fuel economy.

After the successful introduction of the long-distance Actros truck with BlueTec technology in early 2005, the company launched the models from the Atego and Axor truck series as well as Actros construction-site vehicles with BlueTec diesel technology onto the market in 2006. To ensure that the stringent limits of forthcoming emission norms are safely undercut and to achieve clear advantages in terms of fuel economy at the same time, since 2007 the company is consistently using SCR (Selective Catalytic Reduction) technology in all its commercial vehicles for the European market. SCR reduces pollutants in the exhaust gas by up to 80 percent and at the same time lowers the fuel consumption to a measurable extent.

SCR is based on the injection of an aqueous urea solution (AdBlue®) into the exhaust flow which together with the catalytic converter reduces nitrogen oxides (NOx) by around 80 percent. This is the most effective method in existence for reducing nitrogen oxides in diesel engines. In 2005 trucks and buses with BlueTec already met the particularly stringent Euro 4 and Euro 5 emission standards that would apply to the production of all engines beginning in the autumn of 2006 and 2009, respectively.

The basis of the first revolutionarily clean BlueTec diesels are the tried and tested 500- and 900-series engines. In the Actros the V6 power plant OM 501 LA in its weakest version develops 235 kW (320 hp) at 1800 rpm. The engine achieves its maximum torque of 1650 Newton metres at 1080 rpm. In addition to turbocharger and intercooler, the engine has a central, high-set camshaft, fully electronic engine management with single-cylinder injection pumps, and centrally arranged eight-hole nozzles providing an injection pressure of up to 1800 bar.

The most powerful unit of the 500 series is the OM 502 LA with 16 litres displacement, an output of 440 kW (598 hp) at 1800 rpm and torque of 2800 Newton metres at 1080 rpm. Injection is based on the same principle as in the V6 unit, except that seven-hole nozzles are used. Both V-engines have a four-valve-per-cylinder design. Whereas in the V6 version the rated outputs remain largely the same and a new top V6 variant with 350 kW (476 hp) and maximum torque of 2300 Newton metres has been added, BlueTEC generally gives the existing V8 engines a higher output. The most powerful OM 502 LA now develops 440 kW (598 hp) at 1800 rpm and has maximum torque of 2800 Newton metres.

The 900-series engines with BlueTec likewise cover the entire range of variants previously offered as Euro 3 engines. The OM 904 LA in the basic version as water-cooled in-line four-cylinder with three valves per cylinder develops 95 kW (129 hp) at 2200 rpm. The engine features a turbocharger, intercooler and fully electronic engine management with nine-hole injection nozzles which achieve injection pressure ratings of up to 2000 bar. The maximum torque of 500 Newton metres is available at 1200 to 1600 rpm.

The most powerful BlueTec engine of the Atego is the OM 906 LA, a water-cooled in-line six-cylinder with three valves per cylinder. The technical details are similar to those of the four-cylinder unit; however, this engine gets 210 kW (286 hp) at 2200 rpm with 6.4 litres displacement. This is good for torque of 1120 Newton metres at 1200 to 1600 rpm.

The OM 457 LA and the OM 906 LA in the Axor also give a good account of themselves as environment-friendly BlueTec engines. The water-cooled in-line six-cylinders in four-valve-per-cylinder design work with a turbocharger and intercooler, a central, high-set camshaft, fully electronic engine management with single-cylinder injection pumps, and centrally arranged seven-hole or nine-hole nozzles providing an injection pressure of up to 2000 bar. In its basic version the Euro 4 OM 906 LA develops 188 kW (256 hp) at 2200 rpm. The engine attains its torque of 970 Newton metres at 1200 to 1600 rpm. The most powerful version of the Euro 5 OM 457 LA engine with its twelve litres displacement develops 315 kW (428 hp) at 1800 rpm, and the torque of 2100 Newton metres is available at 1100 rpm.

In the past, the Euro 1 through to Euro 3 emission norms always required compromises as combustion processes designed for low particulate emissions and high fuel economy inevitably produced larger quantities of nitrogen oxides – and vice versa. The external SCR exhaust gas aftertreatment eliminated this conflict of goals caused by thermodynamic laws and permitted the next generation of engines from the 900 series to be developed for both low consumption and low particulate emissions. The success of this technology speaks for itself: as per July 2007, as many as 80,000 BlueTec trucks were already operating on our roads – the majority of these already comply with the Euro 5 emission norm which would come into force in October 2009. And in 2008 more than 160,000 vehicles with BlueTec were in operation – with a great many more to come.

The continuous improvement of this technology by the Mercedes-Benz engineers guarantees the sustained success of BlueTec in the commercial vehicle field. In October 2010 Fleet Transport Magazine honoured this achievement with the presentation of the “Green Commercial of the Year“ award to the Atego BlueTec Hybrid.

The platform of this short-radius distribution truck with hybrid drive is the Atego 1222 L EEV. The basic vehicle satisfies the EEV (Enhanced Environmentally Friendly Vehicle) standard and operates on German roads toll-free. Its compact and light four-cylinder diesel engine with a displacement of 4.8 litres develops 160 kW (218 hp). It is paired with a water-cooled electric motor with a peak output of 44 kW (60 hp) which is supplied with power by high-energy, high-capacity lithium-ion batteries.

The electric motor is arranged behind the internal combustion engine and clutch but in front of the transmission. In this set-up, engine and motor can drive the truck individually or in combination. This architecture (parallel hybrid drive) permits moving off under electric power, recuperation, boosting with the electric motor, and optimisation of the diesel engine’s characteristics. The driving power of the diesel engine is cut in by means of the clutch between the diesel engine and the electric motor. Up until then the internal combustion engine serves exclusively to power the auxiliary units. The result is not only a clear-cut reduction in fuel consumption and exhaust emissions by up to 15 percent, but also lower noise emissions.

A fleet of 50 Atego BlueTec Hybrid will be delivered to German customers in the short-radius distribution sector at the start of 2011 in order to prove the workaday suitability of this important technology of the future. The vehicles will be included in the “Electric Mobility Advancement Programme” of the German Federal Ministry for Transport, Construction and Urban Development.