DE VELO PMENT G A S OLINE ENGINES
THE NEW MERCEDES-BENZ 3.0-L V6 DI GASOLINE ENGINE WITH TWIN TURBO With the launch of the 3.0-l V6 gasoline engine with direct injection and twin turbocharging, called M276 DELA 30, a new member has been added to the approved M276 V6 gasoline engine series, which effortlessly embodies the highest of comfort requirements, superior driving performance and efficiency. Its initial use was in the new Mercedes-Benz E 400 in spring 2013.
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AUTHORS
DIPL.-ING. MARKUS SCHÜTZ is Project Manager for M276 DELA Powertrain Development at the Daimler AG in Sindelfingen (Germany).
DIPL.-ING. GERHARD DOLL is Head of Basic Engine Development for Gasoline V-engines at the Daimler AG in Stuttgart (Germany).
DIPL.-ING. ANTON WALTNER is Head of Thermodynamic Development for Gasoline Engines at the Daimler AG in Stuttgart (Germany).
OBJECTIVE
The new Mercedes-Benz gasoline engine family has successfully been launched onto the market with the BlueDirect combustion system and a modular technology portfolio, ❶, since fall 2010. The objective for the new top variant of the M276 V6 engine series, presented in the following, was the fulfillment of the highest comfort requirements and the realisation of further improved driving performance, particularly in the lower and middle engine speed ranges without increasing fuel consumption. The combustion system and charge cycle components have been optimised for the new twin turbocharging with the aim of optimising delay-free engine response behaviour to load change, while at the same time retaining the basic design features of the M276 naturally aspirated engine and its compact installation dimensions with enginemounted control unit and air filter for uniform use in several vehicle model series. The most stringent emission regulations, including Euro 6, had to be fulfilled so that this engine could be used worldwide. ENGINE ENCAPSULATION DESIGN AND MAIN GEOMETRY DATA
DIPL.-ING. ROLAND KEMMLER is Head of Vehicle Applications for Gasoline V-engines at the Daimler AG in Sindelfingen (Germany).
The displacement has been reduced to 3.0 l for the same stroke/bore ratio for the supercharged M276 DELA 30 in com-
parison to the 3.5-l variants of the M272 predecessor series with port injection and 90° cylinder angle as well as the M276 naturally aspirated engine with 60° cylinder angle. The fiscal constraints of the increasingly important Chinese market, among other things, have thus been taken into account. The compression ratio of the combustion chamber optimised for twin turbocharging is 10.7:1, while the cylinder-bore spacing is 106 mm, ❷. CYLINDER BARREL
As a consistent advancement of the already extensively optimised, extremely finely honed gray cast iron cylinder barrel, the Nanoslide cylinder barrel – which has again been further developed by Daimler – will, for the first time, be used in the M276 DELA 30 on a die-cast crankcase. Nanoslide technology consists of a twin-wire arc spraying method, whereby iron-carbon wires are melted and then sprayed onto the cylinder barrel – here the pretreated aluminium surface – using an inert gas flow; this allows for the development of a characteristically porous surface, whose surface oil retention volume results in an extremely smooth, mirror-like honing structure. The Nanoslide cylinder barrel thus offers tribological reserves for optimised low-viscosity engine oils with low HTHS (high-temperature-high-shear) viscosity values as well as for biofuels
❶ The technology portfolio of the V6/V8 engine families M276 and M278 06I2013
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and low fuel grades. The main differences in the macro structure of widely available, modern gray cast iron cylinder barrels and their influence on the friction between the piston and cylinder barrel in comparison to the Nanoslide cylinder barrel are shown in ❸. A further advantage of the Nanoslide technology is the further improved wear characteristic in comparison to the extremely finely honed gray cast iron cylinder barrels. The cast alloy was optimised with regard to porosity and cast density via the addition of strontium for the implementation on the die-cast crankcase, among other things. CYLINDER HEAD AND TURBOCHARGER
The exhaust ports have already been optimised in the cylinder head for short gas paths and a consistent orientation vis-à-vis the turbine housing in line with the objective of achieving an optimal response behaviour of the twin turbo engine to load change. Pulse turbocharging, with an almost loss-free use of the exhaust-gas enthalpy in the turbine, is facilitated through the continuation in the exhaust manifold and the omission of a manifold collecting section. The exhaust manifold and integrated turbine housing must have a cast steel design due to the resulting high thermomechanical load, ❹.
M 272 KE 35 TRANSMISSION
–
NUMBER OF CYLINDERS
–
CYLINDER ANGLE
°
VALVES/CYLINDER
–
M 276 DE 35
7G-Tronic
M 276 DELA 30
7G-Tronic Plus 6
90
60 4
DISPLACEMENT
cm 3
3499
BORE
mm
92.9
88
STROKE
mm
86
82.1
STROKE/BORE RATIO CYLINDER OFFSET
–
2996
0.93
mm
106
–
10.7
12.2
RATED POWER
kW
200
225
245
AT RPM
rpm
6000
6500
5250 – 6000
COMPRESSION RATIO
10.7
MAX. TORQUE
Nm
350
370
480
AT RPM
rpm
2400 – 5000
3500 – 5250
1600 – 4000
kg
165.2
170.6
179.2
ENGINE WEIGHT DIN 70020 GZ
❷ Comparison of the M276 DELA 30 technical data with that of the M276 DE 35 and M272 KE 35
The difference in the turbocharger rotor speeds between the left and right cylinder banks is minimised by the wastegate ports, which have been optimised through CFD simulation. A spoiler is also created around the wastegate outlet with dual function due to the fluid optimisation: On the one hand, it minimises the negative interference of the bypass mass flow for the turbine wheel outflow, which is expressed by a reduction in the exhaust back pressure. On the other hand, it smoothes the effective pulse-like forces on the wastegate plate, which is actuated by means of a yoke via a vacuum cell.
Due to the compact design and consistent harmonisation of the wall thicknesses, a significantly lower unit weight for the exhaust manifold and turbine housing could be achieved in comparison to the competition. Blank casting as well as machining are performed inhouse, while the overall exhaust-gas turbocharger is completed at ICSI. CRANKCASE VENTILATION SYSTEM
Increasing demands are being made with regard to the oil separation quality in crankcase ventilation due to the increas-
❸ Comparison of Nanoslide technology
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engine output and significantly increased torque. It was possible here to take over, unchanged, one of the two high-pressure pumps from the 4.6-l V8 engine M278 into the V6 engine package. This is directly driven via a four-fold cam by the intake camshaft of the right cylinder bank. The M276 DELA 30 injection system has been designed for fuel types with variable ethanol proportions up to E85. High acoustic damping comfort requirements due to noise caused by high-pressure injection with quick injectors are taken into account by the specially designed foam pieces in the area of the high-pressure pump as well as under the engine design cover. ❹ Exhaust port design: Section through cylinder head and turbocharger
ing requirements relating to emission performance, longer oil change intervals without the customer having to add oil as well as the use of turbochargers. The M276 DELA 30 has a two-stage ventilation system, consisting of a centrifuge for coarse and fine separation and a complex separator for extremely fine oil separation, which is located downstream in the inside V of the engine, ❺. The centrifuge itself, which rotates at camshaft speed and is supplied at both partial and full load independent of the load and speed as well as the static and dynamic geodetic engine situation, achieves a very high level of oil separation. A separator for extremely fine oil separation is located downstream in the inside V of the engine; this has miniature cyclones and is divided into a partial-load and a full-load branch. Crankcase ventilation at partial load operation thus offers additional benefits with regard to oil aging. The system selected offers the following advantages: : improved oil separation due to coarse/ fine and extremely fine oil separators in series : optimal utilisation of existing pressure gradient at partial load : integrated engine ventilation without additional lines and valves.
cylinder engine to the AMG V8 with 5.5 l of displacement – the third generation of the spray-guided GDI system, with the BlueDirect combustion process and identical piezo injectors, is also used in the M276 DELA 30. In comparison to the M276 naturally aspirated engine, the injection system layout has been optimised with regard to both the engine package and assembly aspects. The fuel is now introduced after the high-pressure pump via a short high-pressure line in the right rail and is distributed from there via a connecting line to the left rail; i.e. it is no longer distributed via one line to both rails. The delivery rate of the high-pressure pump has been adjusted to the higher
AIR DUCTING AND CHARGE-AIR COOLING
Air ducting and charge-air cooling are shown in ❻. The M276 DELA 30 has two engine-mounted intake muffler modules with raw and clean air ducting. The wedge-shaped gap between the engine and engine hood is used for the symmetrical dual layout for both filter housings and contains, in each case, a single-chamber resonator on the raw air side as well as a three-chamber resonator on the clean air side. These have been adjusted to the frequency ranges by 1 kHz and 2 to 5 kHz and serve for the suppression of the dominating intake noise, which is perceived as a wide-band roaring noise, in supercharged engines at high load and low engine speed. These modules have been designed as one assembly unit from the
INJECTION SYSTEM
Similar to all modern Mercedes-Benz gasoline engines – from the 1.6-l four06I2013
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❺ Overall view of M276 DELA 30 crankcase ventilation
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❻ General layout of fresh gas routing with water/air charge-air cooler
separation point to the on-vehicle cold air intake to the compressor inlet. A gas path design without compromise, similar to the exhaust side, was also of chief importance during the design and positioning of the charge-air distributor after the central throttle valve. The intake ports continued in the chargeair distributor are just long enough so that undesired cross-talking is excluded between the cylinders. The water/air charge-air cooler, which has a counterflow design, is also enginemounted and has a separate low-temperature coolant circuit with its own expansion tank. This layout, which is the same
in all target vehicles, achieves – in limited installation space – very good response behaviour and charge-air cooling values via short gas paths with low volume. EXHAUST SYSTEM
Greater comfort and appealing sound have always been important features of the Mercedes-Benz E-Class. The new E 400 with the M276 DELA 30 also lives up to this standard. The development objective was to support well-balanced NVH tuning with the acoustic design of the exhaust system to ensure a high level of
driving comfort and a reasonable level of sportiness. The stainless steel exhaust system shown in ❼ has a globally uniform twinline design with, in each case, two front catalytic converters and 1.55 l of total volume per cylinder bank. The air/fuel ratio is monitored and controlled for both cylinder banks using two lambda sensors for each. A joint front and centre muffler as well as two rear mufflers are located afterwards. Active exhaust system flaps to influence the acoustics were not necessary. The flow-optimised design supports engine performance and efficiency. ENGINE CONTROL UNIT
❼ M276 DELA 30 exhaust system in the E-Class
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A further development of the MED17 engine control unit from Bosch of the M276 naturally aspirated engine is used in the M276 DELA 30. In line with the higher requirements, the processor cycle frequency has been increased by 20 % to 180 MHz, and an additional 2 MB flash memory is used. The installation location has been moved from the lateral position in the M276 naturally aspirated engine to the inside V above the charge air distributor in the M276 DELA 30 in order to retain engine-mounted positioning of the control unit. Air ducting from in front of the cooler – using the dynamic pressure – to the engine control unit was integrated in the engine design cover to
ensure compliance with the required temperature limits for electronic components of at most 90 °C at continuous load and 120 °C for a short-term load. COMBUSTION AND EXHAUST- GAS EMISSIONS CALIBRATION
After its launch in the new M276/M278 V6 and V8 engine families in 2010 and use in the new four-cylinder engine generation M270/M274 starting last year, the Mercedes-Benz BlueDirect combustion system will now also be used in the new M276 DELA 30 with twin turbocharging. Basic features of this combustion process are gasoline direct injection by means of a central piezo injector, which opens outwards, with tapered spray, a pressure level of 20 MPa and the spray-guided layout of the injector and spark plug. The supercharged engine was designed based on the homogeneous combustion system to ensure use on a global scale. Due to the outstanding mixture formation of the piezo injectors with minimum wall wetting and excellent fuel quantity dosability, the spray-guided layout can reliably ignite the smallest injection quantities, almost independently of the injection timing point. These properties, which can be utilised especially during cold start and transient mode, allow for keeping within the new Euro 6 particle concentration limit for gasoline engines with direct injection – solely via an optimisation of the operating parameters without using secondary measures. The basic data input was used to compile an optimised distribution of the injection timing points and the breakdown of the respective fuel quantities. The achieved reduction of over 70 % in particle concentration in the catalyst heating by means of a detailed optimisation of the multiple injection is shown in ❽. A reduction in the particle concentration by around 90 % in comparison to the original level will, in the future, be possible with a further increase in the number of fuel injections. Mercedes-Benz believes that the piezo ignition system, together with multi-spark ignition, offers by far the greatest future viability in comparison to all other injection systems.
3.5-l M276 naturally aspirated engine is shown in ❾. This documents, in particular, the significant torque increase in the lower and middle engine speed ranges, which allows for superior driving performance even for a driving style at lower engine speed and with fewer gearshifts, and at the same time offers additional performance for a sporty driving style at higher engine speeds. RESPONSIVENESS AND FUEL CONSUMPTION
The new M276 DELA 30 is combined in all vehicle variants with the fuel consumption-optimised 7G-Tronic Plus automatic transmission and Eco start/stop function, which excels due to extremely
short start times and high comfort in the case of automatic engine on/off. Significantly improved driving performance is achieved in spite of the longer drive ratio in comparison to the M276 naturally aspirated engine. Due to the optimised overall gas path as well as supercharging component design with regard to the transient performance, a delay-free response behaviour of the supercharged engine to load change is achieved, which does not differ from the performance of good naturally aspirated engines. Particular attention was placed on the use of accelerator pedal curves and transmission shift programmes. An important development objective in the vehicle application was the provision of different transmission modes for different cus-
❽ Comparison of particle concentration emissions during catalyst heating for different injection strategies
FULL LOAD
The torque and output of the M276 DELA 30 engine in comparison to the 06I2013
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❾ Comparison of full-load performance maps
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❿ Consumption plotted against performance in the competitive comparison (manufacturers data)
tomer requirements with a significantly larger spread than previously typical for the E-Class. In this connection, the following “guiding principles” form the basis for the design of the transmission modes in the new E-Class: : Mode E: “The right transmission mode for fun, safety and comfort for everyday driving”. : Mode S: “Superior driving pleasure and responsiveness”. A wide range of measures were implemented in order to achieve these objectives. These include, among others, the significantly steeper accelerator pedal characteristic design in the S-transmission mode in comparison to the E-transmission mode. Variably assigned idle speeds already allow for a significant differentiation between the transmission modes during startup. It was even possible to further improve the spontaneity of the response to load change in the S-transmission mode in comparison to the very good basic tuning of the E-transmission mode. Furthermore, the increase in shift points and the reduction in shift times significantly contribute to
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the sporty characteristics of the S-transmission mode; the customers can thus call up different vehicle characteristics at the touch of a button. The scatter of competitor vehicles with six-cylinder gasoline engines shown in ❿ verifies the excellent fuel economy numbers of the new M276 DELA 30 in the E 400 saloon. The comparison value of the M276 naturally aspirated engine is also based on the homogeneous combustion process, which is used here outside Western Europe, in line with the design of the M276 supercharged engine, which is based on the homogeneous combustion process, to ensure use worldwide.
consistently designed for global use and the increasingly stringent requirements for the emission performance of modern gasoline engines. It represents a typical Mercedes-Benz brand premium product with regard to its performance, NVH and fuel consumption. EU6 emissions regulations are already fulfilled. The basic design features of the M276 naturally aspirated engine as well as the BlueDirect combustion system with piezo direct injection have been further developed and adjusted to meet the requirements of twin turbocharging and reduced displacement. The following must, in particular, be mentioned here: The adjustment of the combustion chambers, a further friction loss optimisation due to Nanoslide cylinder barrel technology as well as the modifications to the gas cycle components for consistent implementation of pulse turbocharging, which allows for very quick engine response behaviour to load change. After market launch, which started in spring 2013 with the new E-Class, the new M276 DELA 30 will also be used successively in other Mercedes-Benz model series under the model designation “400”.
THANKS
SUMMARY
The authors would like to thank Dr.-Ing. Harald
As the new top variant of the M276 V6 gasoline engine series, which has successfully been launched since 2010, the M276 DELA 30 with twin turbocharging and 3.0 l displacement joined the Mercedes-Benz engine portfolio in spring 2013. The shown engine with its superior performance characteristics has been
Ing. (grad. eng.) Roland Schulte, Dipl.-Ing. (grad.
Scheib, Dipl.-Ing. (grad. eng.) Jens Bieler, Dipl.eng.) Uwe Schaupp, Dr.-Ing. Frank Altenschmidt, Dr.-Ing. Daniel Hertler, Dipl.-Ing. (grad. eng.) Georg Thomann and Dipl.-Ing. (grad. eng.) Christian Henrich, all Daimler AG, for their support during the compilation of this article.
