by Adrian-Liviu Dorofte

The new Mercedes-Benz Actros: Engines and powertrain - More dynamic, cleaner and more economical

The new Mercedes-Benz Actros is the very first truck to receive the newly-premiered Blue Efficiency Power units that fully comply with the stringent Euro VI emission standard. These diesel engines boast excellent technical characteristics, low fuel consumption, exemplary robustness and longevity and provide high levels of output and torque across a wide range of rpm. Engineers have also mastered the X-PULSE, a new commonrail system with pressure booster, and a powerful and dynamic three-stage engine brake. Furthermore, the new powerplants feature efficient emission control solutions: the SCR technology, exhaust gas recirculation and the particulate filter. Power is sent to wheels thanks to the introduction of the third generation of Mercedes-Benz PowerShift fully-automated transmissions, tweaked for faster and more effective gear shifts.

The launch of the new Mercedes-Benz Actros heralds the arrival of a completely redesigned range of heavy-duty engines which set new standards in many respects. The new Mercedes-Benz BlueEfficiency Power engine generation has been developed specifically for use in Europe and, from the outset, will meet Euro VI requirements. The first member of the new engine family to be in the spotlight is the Mercedes-Benz OM 471 six-cylinder in-line unit, with an output range that covers the bulk of European long-distance-transport requirements. The OM 471 counters the unavoidable extra expense for Euro VI by incorporating state-of-the-art technology. As a result, the new Actros is not only cleaner, it also consumes far less diesel than its predecessor.

New engine already meets the requirements of the forthcoming Euro VI emissions standard
With this new engine generation, Mercedes-Benz continues its tradition as a trailblazer in terms of environmental compatibility. The OM 471 is the first engine in its class to be homologated in accordance with the future Euro VI emissions standard, so marking the start of a new era a full two years before Euro VI actually becomes law. Euro VI brings further significant reductions in, above all, nitrogen oxides and particulates in the exhaust gas.

The new Mercedes-Benz OM 471 covers an output range of 310 kW (421 hp) to 375 kW (510 hp), with peak torques between 2100 and 2500 Nm. During development of the OM 471, the Mercedes-Benz engineers were able to call upon a wealth of experience: the core design of the engine is based on the new platform used for Daimler Trucks' heavy-duty engines. These have been used very successfully since 2007 in trucks produced by Daimler's North American Freightliner brand (built by company-owned engine manufacturer Detroit Diesel) and since last year by Fuso in Japan.

BlueEfficiency Power: top class from Mercedes-Benz

Operators as well as drivers of the new Actros want powerful engines with good traction and low fuel consumption, along with high overall economic efficiency. They expect the best possible performance as well as refined, quiet running and exhaust gases that are low in pollutants. The new engine generation meets these requirements thanks to its robust construction and high-grade engineering, including four valves per cylinder, two overhead camshafts and a fully electronically controlled injection system with pressure booster that is unique in the world.
Like the Actros itself, the new Mercedes-Benz engines are top class in every respect. Top class in terms of the outstanding and innovative engine technology with exceptional economy and refinement thanks to the new, unique X-PULSE injection system. Top class in terms of excellent engine dynamics thanks to turbocharger technology. Top class in terms of low emissions thanks to the combination of SCR technology, exhaust gas recirculation and a particulate filter. And top class in terms of the powerful, new engine brake. Not to mention the new engines' serviceability and durability.

A wealth of output and torque variants

The Mercedes-Benz OM 471 is available with a choice of four outputs and torques for the new Actros. These configurations are suitable for typical European application conditions and meet operators' and drivers' requirements. The following versions of the Mercedes-Benz OM 471 are available for the new Actros:

Output (kW) - Output (hp) - Torque (Nm)
310 - 421 - 2100
330 - 449 - 2200
350 - 476 - 2300
375 - 510 - 2500

One of the particular highlights of the new OM 471 is the fact that, if the standard rear-axle ratio of 2.611 is specified, 200 Nm of extra torque are provided when the automated transmission is in top gear so as to prevent downshifts when driving uphill.

BlueEfficiency Power: high torque even below 1000 rpm

The rated engine speed of the new engines is set at 1800 rpm for all output variants, with the maximum torque available at just 1100 rpm. But these figures can only be a guide: as a result of the very steep output curve immediately before the main operating range, most of this maximum torque is already available at an engine speed of just 1000 rpm. Even below 1000 rpm, the torque is surprisingly high. This results in an extension of the usable engine speed range at the bottom end – down to around 800 to 900 rpm, depending on the route profile – with a correspondingly positive effect on fuel consumption.

Excellent driveability: high output across a wide rpm range

The same is true of the output curve: even at 1400 rpm, the engines deliver almost 100 percent of their full output. In reality, on the road, the output and torque curves combine to ensure excellent driveability with a high output in all key engine speed ranges. The Mercedes-Benz OM 471 reinforces this sense of dynamism with its quiet, smooth running, which is nevertheless characterised by the brand's hallmark sonorous and distinctive sound.

Compact six-cylinder in-line engine

The design of the new Mercedes-Benz OM 471 is based on six cylinders mounted vertically in-line – a platform that bodes well for the smooth running of the engine. The long-stroke design of the Mercedes-Benz OM 471, which has a bore of 132 mm and stroke of 156 mm, gives it excellent pulling power. The engine is categorised in the heavy-duty class for heavy-duty commercial vehicles. The dry weight of the Euro VI version is 1146 kg, while the weight to DIN 70020-A is 1126 kg.

Exemplary robustness and longevity

In order to meet the demands made of the new Actros class of high-powered heavy-duty trucks, exceptional robustness and durability are among the outstanding characteristics of the engine. The crankcase, for example, is made of a grey-cast-iron material developed and patented specifically for this engine generation and includes vertical structures and ribbing to make it very rigid. This design also reduces noise emissions.

The single-piece pistons, made from steel to maximise their service life, each feature two compression rings, an oil control ring and splash-oil cooling. A protective coating ensures that the engine will perform under load, even while it is being run-in. The almost negligible distortion of the pistons and the rigid crankcase keep oil consumption and blow-by losses to a minimum – so reducing costs and improving environmental acceptability. The fine plateau honing of the cylinder liners likewise reduces oil consumption as well as friction losses.

Optimum engine cooling is ensured by wet cylinder liners. The main cooling flow circulates around the upper third of the liner, while a secondary flow cools the lower section, which is not subject to such high temperatures. In general, the distances travelled by the coolant are kept short, making the cooling process here very efficient. The cooling thermostat is located at the intake end to ensure precise control. Larger radiators with a higher output reduce the thermal load whilst the fan does not have to operate as frequently, thus reducing fuel consumption.

Smooth running and an extremely rigid design

The "cracked" connecting rods are split at the connecting rod eye. In this process, the connecting rods are broken at a defined point, producing an extremely robust, close-fitting join with a large surface area when they are screwed back together. A precisely balanced seven-bearing crankshaft ensures exceptionally smooth running of the engine.

The highly rigid crankcase, steel pistons, and reinforced connecting rods and bearings were selected with the high engine ignition pressures in mind. To maximise efficiency, these have been increased from their previous level of 180 bar to over 200 bar.

The turbocharger, starter motor and crankcase ventilation system are all located on the hot side of the engine, while the engine control unit, the oil coolant module with filter and coolant pump, the fuel pumps for the high- and low-pressure system, and the consumption-optimised two-cylinder air compressor with on-demand control are grouped together on the cold side of the engine for ease of maintenance.

Exceptionally robust cast-iron cylinder head

The one-piece cylinder head for the new engine is made of grey cast iron with vermicular graphite (also known as CGI). It is exceptionally robust and designed for the high ignition pressures in the new engines.

Efficient gear drive, double overhead camshafts

At the front end of the engine, poly-V-belts drive the alternator, the coolant pump, the refrigerant compressor and the fan. The now closed-loop coolant pump is only activated as and when needed so as to reduce fuel consumption.

The extremely compact and rigid gear drive is located at the engine's output end, where it operates exceptionally efficiently, quietly and smoothly. Each of the camshafts controls two intake and exhaust valves arranged vertically in the cylinder head via low-friction rocker arms mounted in friction bearings. Rather than being milled from a solid piece of material, the camshafts are of "composite" or "assembled" design – a premiere for engines of this size – and are based on a hollow construction to save weight. They are mounted in a die-cast aluminium camshaft frame with seven bearings.

X-PULSE: unique common-rail system with pressure booster

One of the key aspects of the new engine generation for the new Actros is clean and efficient fuel combustion based on a flexible, fully electronically controlled common-rail system. Flexible in this case means that not only can the injection pressure, timing and quantity of fuel injected be varied, but also the injection rate, thanks to the new X-PULSE injection system with pressure booster that has been developed exclusively with Daimler Trucks.

Maximum injection pressure of 2100 bar

In the X-PULSE common-rail system with pressure booster, the twin-piston high-pressure pump produces a maximum pressure of around 900 bar in the common rail. This pressure is then boosted to up to 2100 bar in the individual injectors. The X-PULSE pressure booster can be varied on the engine map and adjusts continuously to the current engine operating conditions – for example to the demand for torque from the accelerator pedal. The engine control unit manages the injection point, injection quantity, injection rate, number of injections and injection pressure separately for each injector, enabling it to even out any differences between the various cylinders.

Pilot, main and post injections

X-PULSE allows an exceptionally high maximum injection pressure to be achieved as well as enabling free adjustment of the pressure and pressure distribution during main injection by means of two solenoid valves. As all the parameters are variable, each individual injection can be precisely adjusted to the specific situation.

Smooth running, economical, clean: main injection rate can be freely shaped

Many different forms of injection are possible with the new X-PULSE injection system. Their use depends on various parameters, such as the engine load: injection without pressure boosting but with just the pressure in the rail, injection with very early pressure boosting ("square" injection rate) or injection with late pressure boosting ("boot" rate). A variant in between ("ramp" rate) is also possible.

All in all, this means that for the first time it is possible to control fully the injection sequence at each engine operating point. As the highest pressure is only produced actually inside the injectors, the injections are exceptionally stable. In the case of the new Mercedes‑Benz engine generation, this results in quiet and smooth running with a high level of refinement, extremely low fuel consumption and minimal exhaust emissions.

Swirl-free turbulence, efficient combustion

The injection process takes place in a geometrically optimised combustion chamber with a shallow piston recess. The X-PULSE injector is positioned vertically and centrally between the vertically arranged intake and exhaust valves. It features an injection nozzle with seven injection orifices designed as miniature blind-orifice nozzles. The high maximum injection pressure and extremely fine fuel atomisation in the combustion chamber are the keys to efficient combustion. The combustion chamber is shaped to prevent swirl and tumble and to make the combustion of the fuel/air mixture as efficient as possible. The engines' relatively high compression ratio of 17:1 is also aimed at maximising economy.

Asymmetric exhaust gas turbocharger

The new Mercedes-Benz OM 471 has a turbocharger with an asymmetric turbine housing and fixed geometry as well as an intercooler. The asymmetric flow is an advantage, as the exhaust gases from the first three cylinders go directly through the exhaust gas recirculation system to the turbine without any losses. This process improves engine response.

Powerful and dynamic three-stage engine brake

Superb efficiency is one of the key characteristics of the new Mercedes-Benz OM 471, and this is also true of the engine brake. Mercedes-Benz uses a turbocharged decompression brake, which operates extremely effectively and quietly. The fast response time of less than 150 milliseconds is also remarkable.

The engine brake is controlled in three stages through the steering column stalk. In the first stage, the engine brake is activated on three of the cylinders. The remaining three cylinders are then activated in a second stage. In the third and highest stage, the EGR valve and wastegate are activated to increase the engine's charging level and so achieve the maximum brake power of 2300 rpm at 400 kW (544 hp). In addition to this manual actuation, the engine brake is also used in cruise control mode.

Motor control module MCM: everything under control

As the engine's "brain", the MCM (motor control module) is not only responsible for translating the demand for power governed by the driver's foot on the accelerator, but also for controlling and monitoring all the engine functions, from the start and rate of injection through to actuation of the engine brake.

By way of example: in order to achieve perfect synchronisation during gear changes, the engine needs to reach the requisite nominal speed as quickly as possible. To do so, it is even possible to fire individual cylinders whilst other cylinders are being decelerated by the engine brake. Very fast and smooth gear changes are therefore possible.

The control module uses sensors to constantly check factors such as oil level, the position of crankshaft and camshafts, the pressure in the common-rail system and the injectors, the turbocharger turbine speed, the temperature of the engine oil, coolant, fuel and charge air, the charge pressure, and the exhaust gas recirculation rate. As a result of this extensive monitoring, the engine always operates in its optimum range – the prerequisite for good performance, low fuel consumption, a long service life and low exhaust gas emissions.

Efficient emission control: SCR technology, exhaust gas recirculation, particulate filter
Conscious of the stringent requirements imposed by the Euro VI emissions standard, Mercedes-Benz has developed a combination of SCR technology with AdBlue insertion, cooled exhaust gas recirculation (EGR) and a particulate filter for the new BlueEfficiency Power engine generation in the new Actros. This solution has already proved successful on the road in commercial vehicles from Daimler Trucks on other continents. However, the configuration here is adapted specifically to comply with European emissions legislation, while the particulate filter, including its regeneration strategy, is also a special European development. All of the systems combine to ensure extremely efficient emission control.

The differences between the optionally available Euro V versions and the standard Euro VI variant include the omission of the particulate filter, a reduced recirculation rate in the EGR system and a smaller EGR cooler. To meet customer demand, there are also EEV variants in the line-up. These are based on the Euro V version. EEV and Euro V versions are available with a choice of three power outputs: 310 kW (421 hp), 330 kW (449 hp) or 375 kW (510 hp).

Low fuel consumption despite Euro VI: a milestone in engine development

Along with a high level of environmental compatibility, one of the key aims during the development of the new engine generation was to minimise lifecycle costs. First of all, this involves low fuel consumption. Despite the added complexity that was necessary to meet the requirements of the Euro VI emissions standard, these versions of the Mercedes-Benz OM 471 boast exceptionally low fuel consumption and achieve record figures in all versions of the new Actros. AdBlue consumption is also reduced drastically in the Euro VI versions.

The Euro V version of the OM 471 has even lower fuel consumption. It has a lower exhaust gas recirculation rate and dispenses with the particulate filter.

Exceptionally long service intervals ensure low lifecycle costs

At the same time, the developers have been concentrating on keeping maintenance costs down. The service intervals have now been extended to up to 150,000 kilometres, the precise figure depending on the vehicle type and its usage profile. This interval is an exceptionally good figure for an engine with exhaust gas recirculation. In reality, this means the new Actros models in many long-distance transport fleets will require just one annual maintenance call with an engine oil change. The generally maintenance-free particulate filter in the new Euro VI Actros only needs to be changed after 450,000 km and subsequently cleaned after every 300,000 km. The service interval for the air filter in the new Actros is likewise 300,000 km.

The excellent serviceability of the new engine generation also helps to reduce operating costs. A filter module fitted to the cold side of the engine includes the oil filter as well as the filter module for the fuel supply, itself comprising prefilter, main filter and the water separator for the fuel system, grouped closely together in an easily accessible position. The oil refill point is also accessibly located on the cylinder head cover – although the low oil consumption of these engines means that, in reality, the oil will only rarely need refilling.

Mercedes PowerShift fully-automated transmission

In all versions of the new Actros, the power is sent to the wheels through a Mercedes-Benz PowerShift G211 or G281 fully-automated transmission. These transmissions have already proven successful in the predecessor models. And they now offer even faster and more precise response thanks to their highly sensitive shift sensors. The ratios of the twelve-speed transmissions have been optimised for the new engines, the direct ratio in top gear serving as a basis for highly economical long-distance driving. As was the case with the predecessor, application-oriented extra functions such as EcoRoll mode, rocking mode and power mode make the driver's job easier.

New functions for transmission individualisation

New features include a crawler function in place of the previous manoeuvring mode. As in a passenger car with an automatic transmission, the clutch closes when the brake pedal is released. So the new Actros can now be driven at walking pace with a gear engaged but without the need to press the accelerator – making the driver's job even easier when stuck in traffic or when manoeuvring.

Likewise new is the range of freely selectable application-oriented drive programs. The Economy Drive package, installed as standard, offers the driver the already economical Standard drive program as well as an Economy program for significantly reducing fuel consumption on the road. The Economy program does not use kickdown, while the EcoRoll function cannot be deactivated, and the top speed is limited to 85 km/h. The optional Power Drive package includes the fuel-saving Standard program as well as a Power shift program which offers the driver optimum performance. Furthermore, this program allows a GCW of up to 120 t in heavy-duty applications. These individualised shift programs mean that the Actros can be ideally adapted to the particular application conditions.

Faster gear change, controlled by the steering column stalk

Another factor behind the top performance achieved by the new Actros is even faster gear changes with less loss of road speed, which has a positive effect on both average road speed and fuel consumption.

The transmission controls are also new: as every new Actros is supplied with a fully-automated transmission, a steering column stalk is now provided – for the rare occasions on which the driver has to intervene manually.

Tried-and-tested axles, longer ratios

The new Actros is available exclusively with fuel-saving hypoid axles. Although the tried-and-tested HL6 axle from the predecessor has been retained, it now has a new hypoid gear to reduce friction losses. This improvement in efficiency is reflected in lower fuel consumption.

The new high-torque engines with a far wider usable speed range and the "Top-Torque" torque increase in top gear combined with the optimised Mercedes PowerShift with shorter shift times allow a longer rear axle ratio to be used. The standard ratio for semitrailer tractors is now i=2.611 rather than i= 2.846 with a correspondingly lower engine speed level. At a speed of 85 km/h in twelfth gear, the engine in the new Actros runs at just 1260 rpm rather than 1370 rpm – another factor behind the lower fuel consumption achieved by the new Actros.

Furthermore, Mercedes-Benz has extended the range of available rear axle ratios once more. There are now five versions of the HL6 rear axle available for semitrailer tractors with a standard frame height and 315/70 R 22.5 tyres, ranging from i=2.533 to i=3.077. There are also five versions available for lowliner versions with 295/55 R 22.5 tyres, ranging from i=2.2278 to i=2.733.

Economy Packs: economical miracles in package form

If a fleet's main priority is maximum economy, Mercedes-Benz makes it easier to select the right components by offering ready-made Economy Packs at attractive prices. The Classic Economy Pack includes a tyre pressure monitoring system, wind deflectors and side panelling, while the Top Economy Pack also includes a retarder.

FleetBoard and service contracts further boost cost-effectiveness

It's not just the vehicle technology in the new Actros that boosts cost-effectiveness, telematic systems do their bit, too: FleetBoard is included as standard for the first time. The FleetBoard vehicle computer is fitted as standard on board every new Actros. The extensive FleetBoard services can be used free of charge for the first four months. Only after this period does a fee become payable, should the customer decide to continue using FleetBoard. FleetBoard services include trip recording, driving analysis, telediagnosis and maintenance management. What's more, the driver – and only the driver – receives short-time analyses of his or her driving style from the trip computer on the instrument panel display as part of FleetBoard EcoSupport. FleetBoard makes it possible to cut costs by five to 15 percent.

Customised service contracts likewise help to boost the cost-effectiveness of the new Actros. Given the longer service intervals, these are notably less expensive.

Source: Daimler AG

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