Mercedes-Benz powering ahead with €3B strategic engine initiative; increasing electrification, 48V; diesel and gasoline; cylinder deactivation
Following the launch of the new Mercedes-Benz four-cylinder OM 654 diesel engine in spring 2016 in the E 220d (earlier post), 2017 will see the addition of four more members to the all-new family of engines: six-cylinder in-line engines in both diesel (OM 656) and gasoline (M 256) versions; a new four-cylinder gasoline engine (M 264); and a new biturbo V8 (M 176) with cylinder deactivation. Mercedes-Benz is investing a total of around €3 billion (US$3.3 billion) in its strategic engine initiative.
The scaling of state-of-the-art technologies and electrification options from 12 V to 48 V to high-voltage plug-in applications makes it possible to configure the appropriate powertrain for every vehicle. There will be world premieres for new advanced technologies, such as the Integrated Starter-Alternator (ISG); the 48 V electrical system; and the electric auxiliary compressor (eZV).
These new technologies are tuned to the vehicles on state-of-the-art test rigs at the equally new Powertrain Integration center (AIZ) in Sindelfingen.
The optimization of advanced high-tech engines plays a key role in our road map towards sustainable mobility. For the mobility of the future, we are deliberately not committing ourselves to one solitary form of drive system, but to a coexistence of efficient and clean petrol engines, diesels, plug-in hybrids, battery and hydrogen drive systems. Each of these types of drive system has its justification and future prospects.
[The new engines] also need to be designed with a view to all current and future requirements. A key success factor in this regard is the extensive electrification of the powertrain.—Prof. Dr Thomas Weber, Member of the Daimler Board of Management with responsibility for Group Research at Daimler AG and Mercedes-Benz Cars Development
Systematic electrification: new M 256. The new six-cylinder in-line gasoline engine M 256 features a 48 V electrical system. New, intelligent turbocharging, e.g. with an electric auxiliary compressor (eZV), as well as an Integrated Starter-Alternator (ISG) provide excellent drivability with no turbo lag.
The new six-cylinder in-line engine comes with an intelligent form of turbocharging: assisted by the ISG at start-off, the electric auxiliary compressor (eZV) guarantees immediate high torque when driving off and accelerating, bridging the time before the large exhaust turbocharger cuts in. The electric turbocharger accelerates to 70,000 rpm within 300 milliseconds, ensuring an extremely spontaneous reaction from the engine. The result is a dynamic engine response with no turbo lag.
|Cross-sections of the M256. Click to enlarge.|
The M 256 is the first member of a new family of premium gasoline engines that have for the first time been systematically designed for electrification from the outset. The 48 V electrical system serves not only high power consumers, such as the water pump and air-conditioning compressor, but also the Integrated Starter-Alternator (ISG), which also supplies energy to the battery by means of highly efficient energy recovery.
The ISG dispenses with the need for a belt drive for these components. This not only reduces the overall length of the engine and its complexity, but also paves the way for new, efficient control possibilities. The still existing 12 V system supplies power to consumers such as lights, cockpit, infotainment and control units.
The ISG is a key component of the 48 V system and not only serves as an alternator, but is also responsible for hybrid functions. This allows fuel savings that were previously reserved for high-voltage hybrid technology. For the first time, the ISG is also responsible for idle speed control. The hybrid functions include:
- Boost (15 kW)
- Energy recovery
- Shifting of the load point: the engine can be operated in a more favorable area of the engine map; load increase/reduction depending on the state of charge of the battery
- Almost imperceptible restart of the engine
Another feature of the new family of premium gasoline engines is near-engine exhaust aftertreatment. The as-standard particulate filter is the only part of the exhaust system that is under the floor.
An additional bonus is the refinement of the six-cylinder in-line engine. Output and torque are similar to the current eight-cylinder engine, i.e. more than 300 kW (408 hp) and more than 500 N·m. In comparison with the previous V6, the CO2 emissions from the engine have been reduced by around 15%.
At 500 cc, the new machine has the same displacement per cylinder as the premium diesel engine family unveiled last year as well as the family of four-cylinder gasoline engines.
The M 256 is produced at the Untertürkheim plant; it launches next year in the new S-Class.
Most powerful passenger-car diesel engine: OM 656. The new top-of-the-line engine in the premium diesel family is likewise a six-cylinder in-line machine. The characteristics of the OM 656 include the stepped-bowl combustion process introduced with the OM 654, two-stage exhaust turbocharging and, for the first time, the use of CAMTRONIC variable valve timing.
The stepped-bowl combustion process is named after the shape of the combustion bowl in the piston. The stepped bowl has a positive effect on the combustion process, the thermal loading of critical areas of the pistons and the introduction of soot into the engine oil.
The efficiency is increased by the higher burning rate in comparison with the previous omega combustion bowl. The characteristic feature of the specifically configured combination of bowl shape, air movement and injector is its very efficient utilisation of air, which allows operation with very high air surplus. This means that particulate emissions can be reduced to an especially low level.
A special feature of the family of premium diesel engines is the combination of steel pistons with an all-aluminum engine block. The lower expansion of steel as operating temperatures rise ensures an increasing clearance between piston and aluminum block, thereby reducing the friction by 40 to 50%. At the same time, the fact that steel is stronger than aluminum allows very compact, lightweight pistons that even offer additional strength reserves. Finally, the lower thermal conductivity of steel leads to higher component temperatures, thereby improving the thermodynamic efficiency, increasing combustibility and reducing combustion duration.
The combination of innovative steel pistons and the optimized piston ring package with the further-improved NANOSLIDE coating of the cylinder walls results in benefits in terms of fuel consumption and CO2 emissions, especially in the lower and medium engine-speed ranges, which are of relevance for day-to-day vehicle use.
Although there is a significant increase in output compared with the previous OM 642 (more than 230 kW/313 hp instead of 190 kW/258 hp), the new engine consumes more than 7% less fuel.
The new diesel engine is designed to meet future emissions legislation (RDE – Real Driving Emissions). All the components of relevance for efficient emissions reduction are installed directly on the engine. Supported by insulation measures and improved catalyst coatings, there is no need for engine temperature management during cold starting or at low load.
In addition to the advantages in terms of emissions, this results in fuel savings, especially on short journeys. Thanks to the near-engine configuration, exhaust aftertreatment has a low heat loss and extremely favorable operating conditions. This is reinforced by the CAMTRONIC switchable exhaust camshaft, which supports the consumption-neutral heating of the exhaust system.
The new engine is equipped with multi-way exhaust gas recirculation (EGR). It combines cooled high-pressure and low-pressure EGR. This makes it possible to significantly further reduce the untreated emissions from the engine across the entire engine map, with the center of combustion being favorable for fuel economy.
New four-cylinder gasoline engine M 264. With a specific output of around 100 kW:, the new Toptype 2.0 liter gasoline engine from Mercedes-Benz advances into output regions previously reserved for high-displacement six-cylinder machines. At the same time, it consumes significantly less fuel than a comparable six-cylinder engine. The engine's special features include twin-scroll turbochargers, belt-driven 48 V starter-alternator (BSA) and electric 48 V water pump.
The BSA is also responsible for fuel-saving hybrid functions:
- Easy start: virtually imperceptible starting and acceleration of the engine
- Boost in the engine-speed range up to 2500 rpm
- Energy recovery up to 12.5 kW
- Shifting of the load point: allows operation in a more favorable area of the engine map
- Coasting with engine off
- iECO: extended stop/start with intelligent engine shutoff even at low speeds
In the interests of high power output and a spontaneous engine response, Mercedes-Benz opted for twin-scroll turbocharging. Unlike conventional systems, a twin-scroll turbocharger merges the exhaust gas ducts of cylinder pairs in the flow-optimized manifold. This turbocharging concept with systematic cylinder flow separation produces high torque in the low-rpm range together with high specific output. Further efficiency measures include intake CAMTRONIC and a friction loss reduction package.
At the very top of the list of requirements for developers were comfort and NVH (noise, vibration, harshness). Plastic engine mounts and the BSA contribute to exemplary refinement, as do numerous insulation measures. These include insulation of the engine block and extensive covering of the engine with an acoustic insert as well as further NVH optimisation in relation to the injection hydraulics.
To guarantee excellent exhaust emissions, use is made of tried-and-tested piezo injectors with good mixture preparation, a further-improved combustion chamber and a particulate filter for gasoline engines.
New V8 biturbo gasoline engine M 176. The new biturbo is one of the most economical V8 gasoline engines in the world. Its special features include cylinder shutoff at part load as well as the positioning of the turbochargers in the V between the cylinder banks.
From its 3982 cc displacement, the new V8 biturbo produces more than 350 kW (476 hp) with a maximum torque of around 700 Nm from 2000 rpm. The new engine will consume more than 10% less fuel than its predecessor, which is rated at 335 kW (455 hp). The new V8 will launch with this technology next year in the new S-Class.
For even lower fuel consumption, when operated at part load the new M 176 shuts off four cylinders simultaneously by means of CAMTRONIC valve timing. This reduces the pumping losses while improving the overall efficiency of the remaining four cylinders by shifting the operating point towards higher loads.
The cylinders are turned on and off by the interplay between engine control and actuators on the cylinder head. The switchover to four-cylinder operation is accomplished by eight actuators that act on the axially movable cam parts of the intake and exhaust camshafts via a selector.
These cam parts are held on the carrier shaft by gears and are locked in the respective end positions by means of a locking mechanism. The intake and exhaust valves of cylinders 2, 3, 5 and 8 do not open due to the zero-lift cams of the cam parts. At the same time, the fuel supply and ignition are deactivated, so that no unburned mixture is left in the deactivated combustion chamber.
Cylinder shutoff is active in the engine-speed range between 900 and 3250 rpm, provided the driver has selected mode C or E with the DYNAMIC SELECT switch. Cylinder shutoff is inactive in all other transmission modes. As soon as the driver requests higher engine power via the position of the accelerator or as soon as the engine speed goes above 3250 rpm, cylinders 2, 3, 5 and 8 are reinstated within a matter of milliseconds.
The transition between the two operating modes is seamless and with no loss of comfort for the occupants. The main menu in the instrument cluster shows whether the engine is currently in four- or eight-cylinder mode.
The new V8 biturbo employs a centrifugal pendulum to reduce both the fourth-order vibrations in eight-cylinder mode as well as the second-order vibrations in four-cylinder mode.
A combination of biturbocharging and direct gasoline injection with spray-guided combustion increases the thermodynamic efficiency, thereby reducing the fuel consumption and exhaust emissions. Particularly fast and precise piezo injectors spray the fuel at high pressure into the eight combustion chambers. Multiple injection occurs on-demand, ensuring a homogeneous fuel/air mixture. The delivery of fuel is electronically controlled and fully variable for a fuel pressure between 100 and 200 bar.
The engine is of closed-deck construction—i.e., the engine block cover plate is extensively closed in the area around the cylinders. The engine block is of an aluminum alloy and produced by permanent mould casting. This ensures extreme strength while keeping the weight as low as possible, and allows high injection pressures of up to 140 bar. The further-improved NANOSLIDE coating of the cylinder liners reduces the friction loss while contributing to excellent efficiency. The cylinder head uses an aluminum-zirconium alloy, which is a better conductor of heat than the standard aluminum alloy.
“Spectacle honing” is another measure for reducing the friction and therefore consumption: in this complex process, the cylinder liners receive their mechanical surface treatment when already bolted in place. A jig resembling spectacles is bolted to the engine block in place of the cylinder head, which is mounted later. The honing of the engine block already produces the same state of stress as when the cylinder heads are mounted. For this reason, the tension of the piston rings can be reduced, which leads to a further reduction in friction loss and lower oil consumption.
For an exceptional engine response and low exhaust emissions, the two turbochargers are positioned not on the outside of the cylinder banks, but between them in the “V” – experts call this the “hot inside V”. In the interests of thermal protection for the engine components, the manifolds and exhaust turbochargers are specially insulated.
The efficiency-raising measures include the low-friction drive of alternator and refrigerant compressor by means of two short four-groove belts. The water pump is chain-driven by the timing assembly. A two-stage feedback-controlled oil pump circulates the engine oil. It varies the flow rate depending on the required load and engine speed, thereby helping to save fuel.
The M 176 has exhaust aftertreatment with two catalysts directly mounted on the engine and on the underfloor. The as-standard particulate filter is part of the exhaust system under the floor.
48 V electrical system. The introduction of the new engine generation blurs the lines between gasoline and hybrid models. Looking to the future, all Mercedes-Benz passenger cars will be electrified, because the company is at the same time systematically advancing the development of the 48 V electrical system. The technology will be gradually rolled out in various model series, initially as a sub-system for the functions inside the engine compartment.
The 48 V electrical system supplies four times the power of its 12 V predecessor at the same current, but does not require the additional safety architecture of a high-voltage system. This allows fuel savings that were previously the exclusive domain of high-voltage hybrid technology, for the key hybrid functions of “energy recovery” and “boost” can thus be made available without high-voltage components.
The engineers also enjoy new freedoms with regard to the design of the operating strategies for the high-tech engine, with the result that it can be operated even more frequently in an area of the map that is favorable in terms of fuel consumption.
There are also entirely new technologies, such as the electric auxiliary compressor (eZV), which is celebrating its premiere as part of the intelligent turbocharging of the new six-cylinder in-line gasoline engine (M 256). This compressor delivers charge-air pressure in fractions of a second, independently of engine speed and engine load. Connected in tandem with a large exhaust turbocharger, the eZV ensures a balanced engine response in all rpm ranges and eliminates the turbo lag.
The integration of a 48 V electrical system also offers advantages for in-vehicle consumers, such as air conditioning, electric heating elements or extractor fan—these, too, could be operated at a higher voltage in future. The advantage is that the same power requires only a quarter of the current of a conventional system. This means that the wiring can be thinner and therefore lighter, which indirectly contributes to saving fuel. The 48 V electrical system also paves the way for the further expansion of infotainment and assistance systems.
NANOSLIDE. Mercedes-Benz and Mercedes-AMG have been using the innovative NANOSLIDE (earlier post) coating in more and more engines over the past three years. This technology, which is protected by more 40 patents, will also help to save fuel in the new family of premium gasoline and diesel engines. NANOSLIDE is even used to reduce the internal friction in the latest Mercedes Formula One engine.
An extremely thin, low-friction coating is applied to the inner surfaces of the cylinders in an aluminum engine block. As up to 25% of the energy in fuel is used to overcome in-engine friction, particularly at part load, fuel savings of several percent are attainable.
Twin-wire arc spraying (TWAS) is used to apply an extremely thin coating based on an iron-carbon alloy to the inner surfaces of the cylinders in aluminum engine blocks. This produces a nano to ultra-fine, highly wear-resistant material structure with microporosity. This microporosity ensures effective lubrication in operation. It means that the heavy cast-iron liners measuring several millimeters in thickness can be replaced in aluminum cylinder blocks.
The result is a mirror-smooth surface, with friction between piston, piston rings and cylinder wall reduced by up to 50% and weight savings of several kilograms.
In 2015, the production process was changed and made even more environment-friendly. Previously, prior to coating, the cylinder contact surfaces had to be activated (“roughened”) using a high-pressure water jet (up to 3000 bar). The same effect is now achieved by means of a specially developed machining technique. With even wider application of the technology, this not only saves the company considerable sums of investment, but also reduces environmental pollution, with annual savings of around 10 million liters of water, about 10 tonnes of aluminum-containing slurry and around 900 MWh of electrical energy.
Overall, the NANOSLIDE process reduces the use of cast iron by around 1000 tonnes and of aluminum by around 8000 tonnes per year.
NANOSLIDE was developed by Mercedes-Benz and Gebr. Haller GmbH, a manufacturer of machine tools and complete production systems, which has industrialized all stages of the process for reliable worldwide application in series production.
Particulate filter for gasoline engines as standard. Mercedes-Benz is the first manufacturer to opt for the large-scale use of particulate filters for gasoline engines to further improve their environmental compatibility. After more than two years of positive experience in the field with the S 500, in 2017 further S-Class variants will be equipped with the new M 256 and M 176 gasoline engines with this technology. The filter will then be gradually introduced in other new vehicle models, facelifted models and new engine generations, such as the M 264.
The particulate filter for gasoline engines reduces the emissions of fine soot particles. The exhaust-gas stream is supplied to a particulate filter system. The filter has a honeycomb structure with alternately sealed inlet and outlet channels. This forces the exhaust gas to flow through a porous filter wall, which traps the soot. The filter can be continuously regenerated under corresponding driving conditions.
New Powertrain Integration center (AIZ). With its new Powertrain Integration center (AIZ), in summer 2016 Mercedes-Benz took into service one of the automotive industry’s most advanced test facilities. A total of ten vehicle test rigs inside the all-new state-of-the-art building in Sindelfingen are used for such purposes as the fine tuning of engine and transmission—comfort, dynamics and agility are matched to each other.
The highlights include test rigs with high-precision torque measurement directly at the wheels of the vehicle as well as a test rig with a climatic altitude chamber, which uses partial vacuum to simulate an altitude of up to 5000 meters at temperatures of down to -30°C, while the vehicle operates fully automatically on a chassis dynamometer.
The new Powertrain Integration center is part of extensive additions and conversions to the Mercedes-Benz Technology center (MTC) in Sindelfingen. The new driving simulator, climatic wind tunnels and a high-tech aero-acoustic wind tunnel are already in operation. By 2018, there will also be a state-of-the-art technology center for vehicle safety, an electronics testing center and a computer center. Housed on the upper floor of the AIZ, the computer center will directly use the electricity generated downstairs on the test rigs in order to operate and cool the computers.
The MTC is home to the headquarters of the company’s global Group Research and passenger car development, including design.