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Mercedes M 254 / OM 654 M: ​​electrified high-tech four-cylinder

Mercedes M 254 and OM 654 M with ISG
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E For the first time there is an integrated starter generator (ISG) found the way into a four-cylinder gasoline engine from Mercedes. As part of the facelift, the new OM 654 M (diesel) and M 254 (petrol) engines with 48-volt sub-electrical systems are being introduced into the E-Class. The gasoline engine is first used in the new 272 hp and a maximum of 400 Newton-meter strong E 350. And it presents many technical refinements.

Additional compressor minimizes turbo lag

The electric machine combines starter and generator and, as a component, is not part of the engine, like previous starter-generators, but of the transmission. This means that in future this unit can be combined with numerous drive options - right up to a hybrid. Because the ISG can also be combined with a high-voltage network. In the E 350 unit called M 254, however, it is supplied by the 48-volt electrical system, so it is one of the mild hybrids. After all, the ISG's electric motor also recuperates into the on-board network with up to 15 kW. On the other hand, the ISG can support the drive with 12 kW and 180 Nm, thus masking the turbo lag when starting up or after overrun phases.

Daimler AG
The new ISG four-cylinder M 254 and OM 654 M are being used for the first time in the revised E-Class.

The electrical auxiliary compressor does a similar thing. Behind it is a water-cooled electric motor with an output of five kW. It sits on the so-called cold side of the turbocharger and compresses the intake air until the exhaust gas flow is sufficient to drive the turbocharger's turbine. This ensures a response behavior that gets by without turbo lag. In the network, Mercedes speaks of two-stage charging. The system is not with oneConfusing electrically assisted charger, in which the electric motor sits on the main shaft of the exhaust gas turbocharger and drives the compressor wheel directly. This technology will Use AMG .

41 additional horsepower via overboost

In order to make optimum use of the exhaust gas energy, Mercedes uses a multi-flow turbine housing in the two-liter E 350. The so-called segment charger separates the exhaust gas flows from cylinders one and four as well as two and three. In contrast to the twin-scroll loader, the augers do not sit next to each other, but one inside the other. This technology is tested and successfully used by the in-house Formula 1 team Mercedes-AMG Petronas.

Completely new: The M 254 four-cylinder petrol engine

Die The double-flow turbine can be flooded by a flap controlled by both burst and accumulation charging - the former at low speeds, the latter at high speeds. The accumulation charge brings the exhaust gases together before they are sent to the turbine, whereas the impulse charging takes a shorter route and thus uses the kinetic energy of the exhaust gases more effectively to compress the fresh air. According to Mercedes, this results in a very high degree of efficiency, although no variable turbo geometry (VTG) is used.

Four boost levels at full throttle from standstill

The M 254 also has one Overboost function in stock. By increasing the boost pressure and adapting the fuel injection, the control unit allows 41 additional horsepower - over a period of up to 30 seconds. The boost pressure is increased until the exhaust gas temperature reaches a threshold value.

Strictly speaking, there are four boost levels at full throttle from a standstill: First, the electric motor of the starter generator pushes, then the additional compressor follows. The mechanical charger and the overboost take over. The Mercedes engineers are particularly proud of the imperceptible cross-fading of these four levels - the power delivery is strongly reminiscent of that of a large-volume naturally aspirated engine.

The M 254 also receives the trumpet honing

But it also pulls internally Mercedes did all the stops to make the M 254 as efficient as thatpossible to handle the fuel. The gasoline engine, for example, has cylinders whose cylinder liners are widened in the lower part. Mercedes calls the technology, which was first used in 2018 in the M 260 four-cylinder of the then new A-Class, Conicshape or - quite clearly - trumpet honing. Because the conical shape of the liners, which should minimize friction and thereby reduce fuel consumption, visually resembles the bell of a trumpet.

The modular OM 654 M is the diesel equivalent to the M 254 petrol engine.

In addition to the M 254, its diesel equivalent OM 654 M also has the new generation of the ISG integrated into the 9G-Tronic automatic transmission. The engines have a modular structure, hence the name 'FAME' (Family of Modular Engines). This means they are also suitable for use in plug-in hybrid environments.

OM 654 M as the world's first ISG diesel

With the OM 654 M, Mercedes claims to deliver the worldwide first diesel engine with integrated starter generator. The revised two-liter turbodiesel four-cylinder was given a new crankshaft for electrification, increasing the displacement by 43 to 1,993 cubic centimeters. At the same time, the injection pressure will be increased from 2,500 to 2,700 bar. The maximum power is now 265 hp, the maximum torque 550 Newton meters. On the exhaust side, a NOX storage catalytic converter, particle filter and two SCR catalytic converters have been retrofitted.

For the E-Class revision, the in-line six-cylinder M 256 with ISG is also being used for the first time in this model family. In the Mercedes-AMG E 53 4MATIC + models, the engine has an output of 320 kW (435 hp) and a maximum torque of 520 Newton meters. The starter generator briefly supplies an additional 16 kW of power and 250 Newton meters of torque.


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