Mercedes-Benz is not generally given to hyperbole to detail its technology, so when company engineers describe a program as “the biggest strategic engine initiative” in the automaker's long history, it is worth taking notice. And electrification is very much to the fore.
The company's latest propulsion blitz opened with the new 4-cylinder 2.0-L diesel now used in the E-Class. It will continue in 2017 with the appearance of a new gasoline 4.0-L V8 biturbo for the S-Class, new 6-cylinder units in gasoline and diesel forms with 48V technology, and a 2.0-L 4-cylinder gasoline which also uses 48V to power auxiliaries. The sixes are inline, not "vee"-arranged, because Mercedes’ engineers reckon in combination with 48V electric systems, the return to the hallowed inline-six layout delivers meaningful packaging advantages.
The V8 has capacity reduced by about 0.7-L from the outgoing V8 and gets cylinder deactivation, becoming a "four-pot" unit under light loads while cruising. With a claimed output of “over” 350 kW (469 hp) with “about” 700 N·m (516 lb·ft) peak torque, the engine has received attention from Mercedes’ AMG tuning specialists.
Some premium car makers are fixated on reduction of cylinder count—for example Volvo, with its aim of being accepted by the market as a premium producer, reckoning four cylinders is the maximum for all its models—to achieve required fuel consumption and emissions targets. Mercedes, though, while demonstrating what can be achieved with four cylinders on many models, is not being seduced by the prospect of drastic cubic-capacity reduction. Instead, it is using advanced complementary technology to meet the unremitting demands for cleaner, more-frugal engines while maintaining the level of performance and refinement expected of its powertrains in their higher-level models.
As well as 48V, those complementary technologies also include an integrated starter generator (ISG) and electric auxiliary turbocharger compressor (eZV) to assist the exhaust-driven compressor.
To help continue maximum efficiency systems cohesion, Mercedes has opened a new powertrain integration center (AIZ) at its Sindelfingen assembly complex.
All-new I6 replaces V6
Prof. Dr. Thomas Weber, responsible for group research for Daimler AG and Mercedes cars’ development, says of the strategic power unit initiative: “Our high-tech engines need to be (and are) designed with a view to all current and future requirements. A key success factor is the extensive electrification of the powertrain."
Of the new engines, it is the 3.0-L inline sixes that are the real attention-grabbers. The gasoline version (M256) produces a claimed 300 kW (402 hp) and delivers maximum torque of “more than” 500 N·m (369 lb·ft)—the qualifying words, which the company uses extensively in its initial talk about the new engine architectures, shows either a caution about claims or a plan to surprise later. Mercedes has chosen 500 cm3 per cylinder as the optimum swept volume, the same as that for the new 4-cylinder diesel.
The gasoline inline 6-cylinder (the S-Class gets that too, next year) uses a 48V system and forced air via an eZV and has an ISG to look after hybrid aspects, including energy recovery.
Mercedes' first V6, the M112, was introduced in 1998 as a response to new frontal-crash requirements, replacing the company's classic gasoline I6 family. For the move back to inline cylinders for 2017, Mercedes engineers cite performance akin to an 8-cylinder, which should make next year’s S-Class something very special. It also brings design opportunities, such as eliminating the need for a front-end accessory belt drive, that help reduce overall length.
Near-engine exhaust aftertreatment for low heat loss helps reduce emissions. The 48V system looks after the high-power demands of the water pump and air-conditioning compressor and the ISG. With this setup, emissions are down some 15% against the outgoing V6, engineers claim.
48V with new I4
The diesel version (OM656) of the new I6 family incorporates the Camtronic variable valve timing, with steel stepped-bowl pistons and 2-stage turbocharging.
The stepped-bowl piston has a positive effect on the combustion process, engineers explain, in terms of thermal loading of critical areas of the pistons and the introduction of soot into the engine oil. Efficiency is increased by the higher burn 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 utilization of air, which allows operation with high air surplus. This means that particulate emissions can be reduced to an especially low level, engineers said.
The engine’s block is aluminum and what is described as “improved” Nanoslide coating is used to line the cylinders. The engine also uses near-engine exhaust treatment. A Camtronic switchable exhaust camshaft is integrated.
Output is “over” 230 kW (308 hp) to make it the most powerful passenger-car diesel in Mercedes-Benz history. Maximum torque is “over” 650 N·m (479 lb·ft).
Topping the muscle chart for the new engine group is the M176 gasoline V8 4.0-L, claimed to deliver a hefty 350 kW (469 hp) and “around 700 Nm (516 lb·ft) from 2000 rpm.
Cylinder shut-off via Camtronic at part load effectively creates a V4. For added efficiency, the engine’s two turbochargers are placed between the cylinder banks.
Less glamorous than the sixes and V8 but very significant for Mercedes’ higher-volume models is the new gasoline 2.0-L 4-cylinder (M264). Also known as the Toptype, it follows downsizing/rightsizing philosophy by offering a specific output of 100 kW (134 hp) per liter. It is technology-dense with a twin-scroll turbocharger, belt-driven 48V starter-generator and 48V water pump. Energy recovery capability is claimed to be some 12.5 kW (17 hp).
The design enables engine-off coasting and Camtronic is used on the intake side. And Mercedes plans to expand its application of particulate filters across its gasoline engine range.
M256 "designed for electrification"
Prof. Weber underlined the importance of Mercedes continuing to develop and offer a wide range of co-existing drive systems: “Efficient and clean gasoline engines, diesels, plug-in hybrids, battery and hydrogen drives—each has its justification and future prospects. The M256 is the first engine that we have systematically designed for electrification from the outset.”
The ISG, responsible for hybrid functions, achieves boost or energy recovery while allowing fuel savings that were previously reserved for high-voltage hybrid technology, he added: “And the electric auxiliary compressor makes for an impressive step-off with the M256, bridging the time lag before the large exhaust turbocharger cuts in to full effect.”
Weber always talks of “rightsizing” rather than downsizing. “Instead of trimming the number of cylinders from the outset, thereby foregoing refinement and output, there are much more intelligent solutions," he noted. The M176 V8 uses cylinder shutoff; at part-load up to 3600 rpm it is an especially efficient 4-cylinder, he claims. Then, imperceptibly for the vehicle’s occupants, cylinders 2, 3, 5 and 8 cut in.
Mercedes’ new Powertrain Integration Center houses 10 test rigs fitted with high-precision torque measurement directly at the wheels. Integration covers engine and transmission, comfort, dynamics and overall agility—essentially ride and handling. The center includes a climatic altitude chamber and fully automatic operation of the vehicle on a dynamometer.
Mercedes is just starting work on a vehicle safety, electronics, and computer technology center. Just revealed is Mercedes EQ pure electric SUV coupe concept, with motors on front and rear axles to give all-wheel drive and front/rear variable torque distribution. A battery is positioned between the axles in the car's floor.
Mercedes has talked of a maximum 300-kW (402-hp) output and up to 700-N·m for the concept, and a potential 500-km (310 mi) range.Continue reading »