Daimler Trucks ushers in a new era: the launch of the Mercedes-Benz OM 47x, under the name “Blue Efficiency Power”, heralds the arrival of a completely redesigned range of heavy-duty engines that sets a new benchmark in so many ways. The Blue Efficiency Power generation of Mercedes-Benz engines has been specifically developed for use in Europe and is the first of its type to meet, from the outset, the Euro VI emission standard.
New family of exceptionally fuel-efficient and robust engines
The new engines set the benchmark for fuel consumption, thanks amongst other things to the new X-PULSE injection system with pressure booster. The six-cylinder in-line engines are characterised by their exceptional robustness and feature a powerful exhaust brake. The new generation comprises three model series with varying displacements. The three series share a common basic design, although the technical details vary according to the differing requirements made of them.
The Blue Efficiency Power engines have been designed from scratch, completely without compromise and without consideration to engines that already existed. This opened up the possibility to design them to be exceptionally future-proof. Thought was first given to the creation of a new engine generation in 2002, with development work on the special engines for Mercedes-Benz beginning in Stuttgart five years ago.
First truck engine to meet the forthcoming Euro VI emission standard
The first member of the new engine generation to be in the spotlight is the Mercedes-Benz OM 471, with its 12.8 l displacement. With this new generation of engines, Mercedes-Benz continues its tradition as a trailblazer in terms of environmental compatibility. The OM 471 is the first engine in its class to have received type approval and already be available with the future Euro VI emission standard, so marking the start of a new era a full two years before Euro VI becomes law. Euro VI brings further significant reductions in, above all, nitrogen oxides and particulates in the exhaust gas.
With its power output range of 310 kW (421 hp) to 375 kW (510 hp) and maximum torque of between 2100 and 2500 Nm, the new Mercedes-Benz OM 471 fulfils all the most common requirements. During the development of the OM 471, and of the other two engines, the engineers at Mercedes-Benz were able to draw on a considerable store 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 built by the Group’s North American Freightliner brand (manufactured by company-owned engine manufacturer Detroit Diesel) and since last year by Fuso in Japan.
Common platform, individual design: a true Mercedes-Benz
Like their predecessors, the new Mercedes-Benz engines are built at the company’s Mannheim plant. This plant also produces key components for the Detroit Diesel engines and complete engines for Fuso.
The platform concept used for the new generation of engines involves an identical basic design, which can be varied significantly with different emission-related components or through the addition of regional applications or assemblies for specific markets or customers. By being custom-built in this way, the engines are able to achieve the balancing act of fulfilling the very different requirements of the world’s markets and yet, whilst maintaining a high level of common parts, still to offer considerable scope for individuality and keep the standard of quality extremely high.
However, the different emission standards and usage profiles that apply in Europe, together with the different installation position in the cab-over-engine truck as opposed to the conventional model, means that some essential components of the engine do differ. These include the injection nozzles, turbocharger, flywheel, control electronics, exhaust system, air compressor and the overall tuning, including that of the various output and torque variants. All in all, the engines differ in more than 200 components from the engines produced in North America or for Japan. They are therefore true Mercedes-Benz engines, developed by Mercedes-Benz engineers in Stuttgart and with every right to bear the three-pointed star on their cylinder head cover.
The new Blue Efficiency Power engines: top class from Mercedes-Benz
Operators as well as truck drivers want powerful engines with good traction and low fuel consumption, along with high overall economic efficiency. They expect the best possible performance; refined, quiet running and exhaust gases that are low in pollutants. The new generation of engines lives up to these requirements thanks to its robust construction and high-grade engineering with four valves per cylinder, two overhead camshafts and a fully electronically controlled injection system with pressure booster that is unique in the world.
The new Mercedes-Benz engines are top class in every respect. Top class describes the engine’s outstanding and innovative technology, delivering a high level of fuel economy and smooth running thanks to its unique new X-PULSE injection system (technically this is an amplified common-rail system). Top class describes the excellent dynamics of the engines, delivered by their turbocharger technology; and the low emissions that result from a combination of SCR technology, exhaust gas recirculation and particulate filter. And top class also describes the powerful new exhaust brake, the ease of maintenance and the durability of the new engines.
Mercedes-Benz OM 471: development specifically for Europe
Heralding the arrival of the new generation of engines for Europe is the new Mercedes-Benz OM 471. From introduction, this meets the Euro VI emission standard. Featuring a combination of exhaust gas recirculation, SCR catalytic converter and particulate filter to reduce emissions, the engine has been designed to meet the specific requirements of the European emission standard Euro VI and the particular needs of European customers.
The new Mercedes-Benz OM 471 will be available in various output and torque versions, ranging from 310 kW to 375 kW and from 2100 to 2500 Nm. Its outstanding attributes, as well as the bundling of sophisticated and advanced engine technology, ensure that the OM 471 is an engine that meets all expectations in terms of performance, economic efficiency and environmental compatibility, in Europe as well as in other markets across the world.
Comprehensive range of power and torque variants
Among the special features of the Mercedes-Benz OM 471 are its particularly broad range of four power and four torque variants, as well as two different brake power configurations. Typical of the specifically European design of the engine are the variants with enhanced power and torque, which are configured to suit typical usage here as well as to the needs of operators and drivers.
The four basic power variants, with 310, 330, 350 and 375 kW, are complemented by three variants that have been given the name “Top Torque”. With these engines, for example when used in trucks, an additional 200 Nm of torque is released in the highest gear of the automatic transmission.
Blue Efficiency Power: high torque even below 1000 rpm
The rated engine speed of the new engines is set at 1800 rpm for all power 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 speed range downwards – depending on the profile of the route – to around 800 to 900 rpm, with a correspondingly positive effect on fuel consumption.
Excellent driveability: high output over a broad engine speed range
The same is true of the power curve: even at 1400 rpm, the engines deliver almost 100 percent of their full output. In reality, on the road, the power 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 a sonorous and distinctive sound that is typical of the brand.
Compact design for in-line six-cylinder engine
The design of the Mercedes-Benz OM 471 is based on six cylinders mounted vertically in-line. This platform bodes well for the smooth-running of the engine. The compact dimensions of the engine, at 1531 mm long (valve body assembly to fan coupling), mean that it fits neatly underneath the driver’s cab on cab-over-engine models. 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.
A model of robustness and durability
In order to meet the demands made of this class of high-powered heavy-duty trucks, exceptional robustness and durability are among the outstanding characteristics of the engine. This is already evident in its basic design. The crankcase, for example, includes vertical structures and ribbing to make it very rigid. This design also helps to reduce noise emissions.
To optimise weight, the sump is made out of a synthetic material. The oil level is checked by a special sensor linked to the engine control unit.
In order to keep the design compact, the spacing of the cylinders has been kept to a minimum. With a view to a long service life, the one-piece pistons are made out of steel. They have two compression rings and one oil control ring each, along with 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.
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 third, 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 thermostat for the cooling system is located at the input end to ensure sensitivity of adjustment. The fine plateau honing of the cylinder liners reduces oil consumption as well as friction losses.
Smooth running, with good rigidity
The connecting rods, also made of steel, are split at the eye in a process called “cracking”. This involves the connecting rod being broken at a pre-determined point and then screwed together again to form a particularly stable, close-fit join with a larger surface area. The crankshaft is made out of induction-tempered steel. Seven main bearings and a careful balancing process with counterweights ensure the smooth running of the engine.
The high rigidity of the crankcase, the steel pistons, reinforced connecting rods and bearings were all selected with the high ignition pressures of the engine in mind. These increased from 180 bar, as hitherto, to more than 200 bar, so improving efficiency.
The turbocharger, starter motor and crankcase ventilation system are all located on the hot side of the engine. The motor control module (MCM), oil/coolant module including filter and coolant pump, the fuel pumps for the high and low pressure system and the consumption-optimised two-cylinder air compressor are grouped together for ease of maintenance on the cold side.
The crankcase has a very carefully machined surface. This, in conjunction with the cylinder head gasket, results in a smooth and thus close-fit and leakproof join to the cylinder head.
Robust cylinder head in cast iron
The one-piece cylinder head of the new engine is made of cast iron with vermicular graphite (also known as compacted graphite iron, or CGI). This material is extremely resistant to temperature fluctuations, has excellent damping characteristics and is subject to only minimal expansion at high temperatures. It is also extremely robust and well suited to cope with the high ignition pressures of more than 200 bar in the new generation of engines.
The materials used for the cylinder head and crankcase respectively have virtually the same expansion coefficient. This means that there is no distortion between the components, regardless of the conditions. The water jacket (the cooling ducts) in the cylinder head is arranged in two layers. The basic principle behind the cylinder head cooling is that of cross-flow. In the upper part of the water jacket, this is overlaid by an added longitudinal flow that, amongst other things, ensures an even distribution between the cylinders. The cylinder head cover is fastened in place with 14 screws.
Efficient gear drive, double overhead camshaft
The alternator, cooling-water pump, air conditioning compressor and fan are driven by up to three poly-V belts located at different levels on the front of the engine. The number of levels depends on the specific configuration, whereby the third level can also be used as a power take-off for optional ancillary equipment. There is a choice of two cooling-water pumps. The closed-loop cooling-water pump kicks in as needed to help reduce fuel consumption. Both the closed-loop cooling-water pump and the fan are among the many components that were specially developed for the Mercedes-Benz OM 471.
At the power take-off end of the engine is the very compact and rigid gear drive. This is extremely efficient, as well as quiet and smooth-running. The gear drive drives the oil pump, the very fuel-efficient two-cylinder air compressor, the common rail high-pressure pump, the power steering pump and the double overhead camshaft.
Each camshaft controls two intake and outlet valves mounted vertically in the cylinder head via low-friction rocker arms supported on friction bearings. The camshafts are not milled from a solid piece of material but assembled – a premiere for engines of this size – on the basis of a shaft that, for weight reasons, is hollow. They are mounted on seven bearings, without the need for bearing shells, in a diecast aluminium camshaft frame.
Unique common-rail system with X-PULSE pressure booster
One of the key priorities for the new generation of Mercedes-Benz engines is the clean and efficient combustion of fuel. The system used is based on a fully electronic, flexible common-rail system. Flexible in this case means that not only can the injection pressure, timing and the 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. In general, high-pressure injections in a common-rail system are comparatively quiet, giving the advantage of a smooth-running engine. In conventional common-rail systems, however, the maximum injection pressure is produced purely via the high-pressure pump in the common rail, which feeds the injectors of each cylinder.
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 boosted within the individual injectors to up to 2100 bar. The X-PULSE pressure boost varies according to the engine mapping and adjusts continuously to the the actual operating conditions of the engine – for example to the demand for torque from the accelerator. Control of the injection timing, quantity, rate and number of injections and of the injection pressure is managed for each individual injector separately through the engine control unit. It is thus able to even out any differences between the various cylinders.
Pilot, main and post-injections
X-PULSE not only makes it possible to achieve extremely high maximum pressures but both the pressure and the pressure distribution can also – unlike in conventional common-rail systems – be freely adjusted during the main injection with the help of two solenoid valves. Since all parameters are variable, each individual injection can be precisely adjusted to the specific situation.
Each injection process is made up of a series of separate injections. Up to two pilot injections precede a gradual increase of pressure, so reducing noise levels and ensuring excellent smooth running characteristics. The very flexible rate-shaping of the subsequent main injection ensures that fuel consumption is kept as low as possible, while continuing to meet emissions regulations. A post-injection ensures the almost complete combustion of the particulates. A further post-injection can also be made, as necessary, in order to regenerate the particulate filter. The Mercedes-Benz OM 471, however, has a separate injection valve for this purpose – known as the HC doser – located in the exhaust nozzle. This is used to control the active regeneration of the filter.
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 engine load: injection without pressure boost but with just the pressure in the rail, injection with early-stage pressure boost (a “square” injection rate) or late boost (“boot” rate). And of course there is a possible version in between (the “ramp” rate).
All in all, this means that for the first time it is possible to control fully the injection sequence at every operating point of the engine. As the highest pressure is only produced actually inside the injectors, injection delivery is exceptionally stable. The result in the Mercedes-Benz engine generation is quiet and easy-running engines with excellent smooth running characteristics, very low fuel consumption and minimal exhaust emissions. This first appearance in Mercedes-Benz engines is only the first stage for X-PULSE, so the scope for future development is almost unlimited. As an example, the X-PULSE injection system with pressure booster has the potential for an injection pressure of 2500 bar.
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 developed specially for the Mercedes-Benz engines is not the same component as the injectors used in Daimler Trucks’ engines on other continents. As part of the overall injection strategy, it is designed specifically for typical operating conditions in Europe, with a higher proportion of heavy-duty use.
The injector is positioned vertically and centrally between the vertically arranged intake and outlet valves. It features an injection nozzle, also specially designed for Mercedes-Benz, with seven injection orifices, executed here as miniature blind orifice nozzles. The high maximum pressure of injection and the extremely fine atomisation of the fuel in the combustion chamber are the keys to efficient combustion. The shape of the combustion chamber is such that there is no swirl or tumble, so ensuring that the combustion of the fuel/air mixture takes place in an extremely efficient way. The intake valves and load-change behaviour have also been configured especially for Mercedes-Benz to suit European conditions.
The engines’ comparatively high compression ratio of 17:1 similarly leads to a high level of economic efficiency. As does their capability of withstanding high ignition pressures of more than 200 bar, which requires considerable stability from the components involved.
Asymmetric exhaust gas turbocharger
The turbocharger on the Mercedes-Benz OM 471 is characterised by its asymmetric turbine casing, fixed geometry and charge air cooling system. The advantage of the asymmetric flow: 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.
With the asymmetric turbine, the exhaust gases from the first three cylinders flow directly through the exhaust gas recirculation system to the turbine, without any losses. Only three of the cylinders are linked with the exhaust gas recirculation duct, and the asymmetric design of the turbine means that a higher pressure level can be maintained in them for the recirculation process. As a result, the engine can be operated across a broad range of parameters with an economical, positive scavenging gradient, despite the exhaust gas recirculation.
A wastegate valve is used to limit the charge pressure and further improve engine response during acceleration. This is actuated according to the operating point directly from the engine control unit via a pressure control valve.
Powerful and dynamic three-stage exhaust brake
Superb efficiency is one of the key characteristics of the new Mercedes-Benz OM 471, and this is also true of its exhaust brake. In order to improve performance – particularly in the intermediate speed range – Mercedes-Benz has here dispensed with conventional technology in the form of an exhaust brake with exhaust throttle valve or a constantly open throttle in favour of a turbocharged decompression brake. This has been an integral feature of the engine’s design and control system from the outset. It is configured to meet European requirements and is extremely effective and quiet in its operation. The short response time of less than 150 milliseconds is also remarkable.
The exhaust brake can be controlled in three stages through a steering column stalk. In the first stage, the exhaust brake is activated on three of the cylinders. The remaining three cylinders are then brought in as a second stage. In the third and highest stage, the EGR valve and wastegate controls are used to increase the charging level of the engine and so achieve the maximum brake power of 2300 rpm at 400 kW (544 hp). In addition to this manual actuation, the exhaust brake is also used in cruise control mode, whereby here the ideal braking torque is adjusted continuously.
As is already the case in the current vehicle generations, the exhaust brake is also used to synchronise the engine speed when the automatic transmission shifts up. As well as shortening the synchronisation time, the use of the exhaust brake during shifting ensures that the charge pressure level in particular is maintained, ensuring that the subsequent build-up of torque occurs faster – so giving the engine noticeably more “bite”.
Exhaust gas recirculation, particulate filter and SCR technology
Conscious of the stringent requirements of the Euro VI emissions level, Mercedes-Benz has developed a cooled exhaust gas recirculation system (EGR), particulate filter and SCR technology for use in the new Blue Efficiency Power generation of engines. This combination has already proved successful in real-life use in vehicles from Daimler Trucks on other continents. The configuration here has however been specifically adjusted to European emissions legislation, while the particulate filter, including the strategy for its regeneration, is a special European development. All these separate steps add up to ensure a highly effective emission control system. The differences between the optionally available Euro V versions and the standard Euro VI emissions-level variant include the omission of the particulate filter, a reduced recirculation rate in the EGR system and a smaller EGR cooler.
In order for them to meet the Euro VI emissions level, the engines are fitted with a sophisticated emission control system. BlueTec engine technology has now been successfully used at Mercedes-Benz for around six years. This is a system that cleans the exhaust gases using SCR (Selective Catalytic Reduction) technology. The process involves AdBlue, now widely available, being added to the exhaust system. Harmful nitrogen oxides are then converted into the harmless elements of nitrogen and water in a downstream SCR catalytic converter. Mercedes-Benz’s BlueTec technology makes it possible to optimise the combustion process and has been proved to deliver excellent fuel consumption.
Low 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 keep its overall life-cycle costs low. First of all, this involves low fuel consumption. Despite the added complexity that was necessary to meet emissions level Euro VI, the fuel consumption on these models is excellent and will produce top figures in everyday vehicle use.
With an eye to saving resources, environmental aspects and the rising trend in the price of diesel fuel, the work of the Mercedes-Benz engineers on the new generation of engines represented a real milestone in engine development.
Motor Control Module MCM: everything under control
The Motor Control Module is a logical further development of the MR2 control module. It comes from the 500 series of engines where it – as well as in the OM 457 series – has now been fitted more than a million times. The control module is attached by screws to the cold side of the engine, near the crankcase. As the “brain” of the engine, the MCM 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 functions of the engine, from the start and rate of injection through to the actuation of the exhaust brake.
Just one example: in order to achieve perfect synchronisation during gear changes, the engine needs to reach the requisite rated speed as quickly as possible. To do so, it is possible here to fire individual cylinders while others are being decelerated at the same time by the exhaust brake. This very short and gentle gear changes can be achieved.
Sensors in the control module are constantly checking factors such as oil level, the position of crankshaft and camshaft, the pressure in the common-rail system and the injectors, the turbine speed of the turbocharger, 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 is always operating in the optimum range – the prerequisite for good performance, low fuel consumption, a long service life and low exhaust gas emissions.
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 in comparison with the predecessor engines 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 will mean just one annual maintenance call with engine oil change for many long-distance transport fleets.
The ease of maintenance in 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.
Intensive testing over 60 million kilometres
The outstanding quality of the new engine generation was evident even during its development. Extreme reliability and durability were among the most important development objectives. In order to achieve this, the engines were tested under the toughest of conditions, all over the world. Up until now, the engines have undergone endurance testing over more than 60 million kilometres, on test rigs as well as in real-life operation, for all emissions classes – no engine ever before has been as intensively tested.
Mercedes-Benz was able to benefit from its global development operations: endurance testing of European engines according to the emissions standards valid here were conducted not only in Germany but also in a parallel process at Detroit Diesel in the US. This intensified the test phase, whilst also making it shorter.
Tested under the harshest conditions, from the polar circle to South Africa
The real-life road tests also covered all climatic conditions as well as extreme road conditions and gradients, including the arctic winter and the searing heat of the desert. Installed in vehicles, the new engines have also visited all the climatic zones you can think of, from the polar circle to South Africa. Real-life testing also included customer driving tests in the Mercedes-Benz Actros.
On top of all this came customer driving tests of a very special nature, from Mercedes-Benz’s point of view: in North America and Japan, meanwhile, more than 70,000 engines are working successfully in Freightliner and Fuso heavy-duty trucks. New-generation engines – albeit in a special configuration for the respective region – have already been in daily customer use there since 2007 (North America) and 2010 (Japan). So, on top of all the test kilometres covered, the basic technology has also been proven over several hundred thousands of kilometres in a large number of trucks.
The findings from the tests conducted under extreme conditions have proved very positive. The new engine series thus meets the figure of 1.2 million kilometres in European long-distance transport operations, in other words 20% more than hitherto. This means: the engines can cover at least this distance without the need for a major overhaul.
Source: Daimler AG