Daimler : Less fuel consumption and CO2 emissions, even more power – the latest generation of the Mercedes-Benz OM 471 engine in buses and coaches

• Consumption reduced, driving dynamics enhanced
• Latest generation of the X-Pulse injection system
• High torque even in the lowest rev range
• Tailor-made asymmetric turbocharger manufactured in-house
• Even more robust thanks to the omission of sensors and pilot-actuated operation

The three-axle premium touring coaches from Mercedes-Benz and Setra are now even more dynamic and economical. They further expand their lead in efficiency with the new generation of the Mercedes-Benz OM 471 heavy-duty engine - fuel expenses drop again by up to four percent with further enhanced driving dynamics. Last but not least, the engines are more robust than ever. In short, the latest generation of the OM 471 engine once more sets standards among heavy-duty engines for top-class buses and coaches.

Top-of-the-range engine for Travego, TopClass 500/400, ComfortClass 500

In the three-axle versions of the Mercedes-Benz Travego and the Setra ComfortClass 500, the version with an output of 350 kW (476 hp) is used as an option. This output stage of the OM 471 is actually standard in the Setra TopClass 500 top-of-the-range model series. A power output of 375 kW (510 hp) is optionally available for these super-high-deckers.

The Setra double-decker S 431 DT impresses not only with its height, but also with the superior power of its engine: it is powered as standard by the Mercedes-Benz OM 471 engine rated at 375 kW (510 hp).

OM 471 in-line six-cylinder engine: a new era in engine manufacturing

A perfect blend of economy and ecology: in spring of 2011, Mercedes-Benz presented a new engine generation developed from the ground up in anticipation of the Euro VI emission standard. The first member of the new engine family is the OM 471. It is being introduced gradually in the three-axle premium touring coaches Mercedes-Benz Travego, Setra TopClass 500 and Setra ComfortClass 500 as well as in the Setra S 431 DT double-decker coach of the TopClass 400.

With its technical features and the resulting capabilities and qualities, the heavy-duty engine took engine manufacturing for heavy-duty commercial vehicles into a brand new era. The 12.8-litre in-line six-cylinder engine impresses with a robust design and technical innovations with significant benefits for the customer. Key features include the double overhead camshafts, the unique common-rail injection system with X-Pulse pressure boost, the asymmetric turbocharger, emission control based on SCR technology with exhaust gas recirculation and particulate filter in order to meet the stringent Euro VI emissions requirements.

The OM 471 series engines now have a proven track record in practical operation in Mercedes-Benz trucks and in the buses and coaches from Mercedes-Benz and Setra. Including the closely related engines for overseas markets, production output has now reached the 250,000 mark - no other heavy-duty engine platform sells better.

Systematic focus on low costs for the customer

The engine development engineers have built on all the great qualities of the OM 471 with a raft of individual measures for the latest generation. The overriding goal for the engines' further development was to ensure they are systematically geared towards low operating costs.

As a result, costs for diesel fuel and AdBlue drop again by up to four percent and the almost proverbial robustness is further increased. At the same time, the engineers significantly upped torque at low engine speeds.

The Mercedes-Benz OM 471 is now available in the two basic versions for buses and coaches:

One of the essential components of the new engine generation is the latest generation of the X-Pulse injection system with pressure boost in the injector. Maximum rail pressure has been increased from 900 to 1160 bar, resulting in a maximum injection pressure of 2700 bar.

The injection nozzle is a new eight-hole injector. Also new is the geometry of the piston bowl, a compression ratio increased from 17.3:1 to 18.3:1 and the reduced exhaust gas recirculation rate (EGR rate). All measures together add up to a further improvement in efficiency across the entire range of the engine mapping.

Systematically configuring the engine for low fuel consumption means that untreated NOxemissions rise in return. This is countered by SCR technology featuring an innovative and efficient SCR catalytic converter. AdBlue consumption is therefore on par with earlier Euro V engines at around five percent of fuel consumption.

The costs work out: the reduction in fuel consumption (diesel + AdBlue) resulting from the in-engine measures and the improved shift strategy of the fully automated GO 250-8 PowerShift transmission amounts to four percent overall. To put it differently, driving an annual distance of 100,000 km with a fuel consumption of about 25 l/100 km, every touring coach equipped with the latest engine generation saves around 1000 l of fuel a year and consequently emits approximately 2.5 t less CO2. Despite the increased AdBlue consumption, this results in a cost advantage of more than 1000 euros a year.

High torque even in the lowest rev range

Although the maximum output and peak torque figures for the engines remain nominally unchanged, the output and torque curves in the lowest rev range rise far more sharply, endowing the engines with quite different performance characteristics. Regardless of the output stage, all engines now produce a torque of at least 2000 Nm at just under 800 rpm.

Consequently, the output curves of the new engines look just as favourably. The rated engine speed is now 1600 rpm, yet even at the previous speed of 1800 rpm output is just one percent below maximum.

What this means in practice is outstanding drivability under all conceivable conditions across an extremely wide usable engine speed range of about 1000 rpm. At low rev speeds in particular, the already powerful engines now rank at least one output category higher than previously.

New shift characteristics save fuel

Mercedes-Benz and Setra take advantage of this fact to employ modified shift characteristics for the fully automated GO 250-8 PowerShift bus and coach transmission. It contributes noticeably to the lower fuel consumption. The transmission now shifts up even earlier and thereby uses lower engine speeds. Thanks to the new power delivery characteristics, it does so without sacrificing vehicle performance. On the contrary: the engines now have significantly higher power reserves on uphill stretches.

Patented solution for exhaust gas recirculation

The special features of the OM 471 engine include an asymmetric turbocharger. This solution has been further advanced decisively: the new EGR flap in the exhaust manifold has been repositioned far forward and allows infinitely variable and highly precise adjustment of the distribution of the exhaust gases across the entire range of the engine mapping. This results in an effective thermal management and a lower EGR rate with advantages for fuel consumption. The EGR flap controls not just the flow of exhaust gases for the exhaust gas recirculation system, but also for the turbocharger.

Supremely efficient turbocharger manufactured in-house

The turbocharger is also new. It was developed by Mercedes-Benz and is manufactured at the Mannheim engine plant. The proprietary turbocharger ensures precise adaptation to the requirements of the OM 471. The turbocharger excels with its outstanding efficiency. Very tight production tolerances are a guarantee for supreme quality and durability.

As before, the asymmetric turbocharger features a fixed turbine geometry. From a technical standpoint, this variant is far less complex and thereby less prone to fail than a turbocharger with variable turbine geometry, for instance.

New: even more robust thanks to the omission of sensors and pilot-actuated operation

Apart from a wastegate valve for the turbocharger, Mercedes-Benz has also dispensed with boost pressure control and the EGR sensor in the latest generation of the OM 471. This means that the thermodynamically thoroughly optimised engine is always operated in pilot-actuated mode and is thus even more efficient.

At the same time, the engine has become even more robust owing to the omission of numerous components and parts. The fundamental idea here is perfectly simple and makes perfect sense: anything that's not fitted in the first place can't cause a malfunction.

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