We’ve already told you about Mercedes’ plans to bring back straight-six engines, but following a future technology presentation by the brand we can add that all versions of the new gasoline six will be equipped with a beefy 48-volt motor-generator unit that will, in effect, make any car equipped with it a mild hybrid.
This new M256 engine will be launched in the facelifted S-class that will make its debut next year, although as the current entry-level U.S. S-class ships with a V-8 the six-cylinder variant is unlikely to come here. But Mercedes-Benz says that the new engine will quickly go on to replace almost all applications of the existing gasoline V-6. Although we don’t have any power figures for the internal combustion side of the powertrain, the company says that the starter-generator can deliver up to 18 horsepower of assistance and harvest up to 20 horsepower of regenerative braking. Being mounted directly to the crankshaft, it can also be used to start the engine in a fraction of a second, although the lack of any clutch to disengage it means that the system can’t provide electric-only operation and can only assist while the gasoline engine is turning at less than 2000 rpm. Despite the 48 volt battery having a paltry 0.9-kWh capacity, the carmaker tells us that the system delivers economy improvements of between 10 percent and 15 percent.
What it doesn’t have is an official moniker. “We’re still searching for a name for it,” Jurgen Schenk, the E-class drivetrain boss admitted, although he also said that cars fitted with it are unlikely to carry any kind of “hybrid” badging. We’re told the 48V system will effectively replace all non-plug-in hybrids among Mercedes models with a north-south engine orientation, save for the S-class hybrid.
The straight six is the second engine spun off from Mercedes’s new modular architecture, and is closely related to the OM654 four-cylinder diesel that the company recently introduced in Europe-market versions of the new E-class. A straight-six diesel will follow—bringing back memories of the immortal 300D models that Mercedes sold here in the Eighties—featuring the same motor-generator, although this is unlikely to make it to the States. There also will be four-cylinder versions fitted with a less complex belt-driven motor generator that can also add assistance. The M256 engine will get a particulate filter, being the first engine to get this diesel-cleaning technology, which will enable it to meet forthcoming ultra-tough emissions standards on both sides of the Atlantic.
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