Mercedes' new engines: Part III - Petrol

Mercedes' new engines: Part III - Petrol

We continue the series for the advanced technical solutions in the range of units

The new six-cylinder petrol engine M 256

The M256 also marks the return of Mercedes-Benz to the brand's original row arrangement of the six cylinders. Several years ago, the M272 KE35 six-cylinder atmospheric units with injection in the intake manifolds (KE-kanaleinspritzung) were replaced at the same time with an angle between the cylinder rows of 90 degrees and M276 DE 35 with direct injection (DE-direkteinspritzung) with an angle of 60 was borrowed from Pentastar's engines Chrysler. The successor to the two naturally aspirated units is the M276 DELA30 with V6 architecture, with a displacement of three liters and forced charging with two turbochargers. Despite the relative youth of the latter, Mercedes will replace it with the in-line six-cylinder M 256 engine, originally equipped with a 48-volt electrical system. The main task of the latter is to drive the electric mechanical compressor (similar to that of the 4.0 TDI engine of the turbocharger). Audi) - the first such solution in the petrol segment. The power source is the Integrated Starter Generator (ISG), placed in place of the flywheel and lithium-ion battery. At the same time, the ISG plays the role of an element of a hybrid system, but with a much lower voltage than previous similar solutions.

In fact, it is rather an integral element of the engine itself and has been designed as part of it from the very beginning of the development work on the engine. With its 15 kW of power and 220 Nm of torque, the ISG helps to dynamically accelerate and reach maximum torque early, together with the aforementioned electric compressor, reaching 70 rpm in 000 milliseconds. In addition, the system recovers braking energy, allowing uniform speed travel only with power supply and engine operation in a more efficient area with a higher load, respectively a wider open throttle valve or using the battery as a charging buffer. With 48 volt power supply are also large consumers such as the water pump and air conditioning compressor. Thanks to all this, the M 256 does not need a peripheral mechanism to drive the generator, nor a starter, which frees up space on the outside. The latter is occupied by the charging system with a complex system of air ducts surrounding the engine. The new M256 will be officially unveiled next year in the new S-Class.

Thanks to the ISG, the external starter and generator are saved, which reduces the length of the engine. The optimal arrangement with separation of the intake and exhaust system allows for a closer location of the catalyst and the new system for cleaning particulate matter (used so far only in diesel engines). In its original version, the new machine has power and torque reaching the level of current eight-cylinder engines with its 408 hp. and 500 Nm, with a 15 percent reduction in fuel consumption and emissions compared to the current M276 DELA 30. With a working volume of 500 cubic meters. cm per cylinder, the new unit has the same optimal and according to the engineers of BMW displacement such as that of the two-liter diesel engine introduced last year and the new two-liter four-cylinder petrol engine.

New, smaller but more powerful 4.0 liter V8 engine

When presenting his team's creation in the form of the new M 176, the head of the eight-cylinder engine development department, Thomas Ramsteiner, spoke with a touch of pride. "Our job is the most difficult. We need to create an eight-cylinder engine that can fit under the hood of the C-Class. The problem is that colleagues developing four- and six-cylinder engines have plenty of space to optimally design elements such as intake and exhaust systems and air cooling. We have to fight with every cubic centimeter. We have placed the turbochargers on the inside of the cylinders and the air coolers in front of them. Due to the accumulation of heat, we continue the circulation of coolant and keep the fans on even after the engine is stopped. To protect the engine components, the exhaust manifolds and turbochargers are thermally insulated. "

M 176 has a smaller displacement than its predecessor M 278 (4,6 liters) and is a derivative of the units of AMG M 177 (Mercedes C63 AMG) and M 178 (AMG GT) with power in the range of 462 hp . up to 612 k.s. Unlike the latter, which are assembled on the principle of "one man one engine" in Affalterbach, M 176 will be more widespread, assembled in Stuttgart-Unterturkheim and will initially have a power of 476 hp, maximum torque of 700 Nm and will consume 10 percent less fuel. This is largely due to the ability to turn off four of the eight cylinders at partial engine load. The latter is done with the help of the CAMTRONIC variable gas distribution system, in which the operation of the four cylinders switches to a higher load mode with a wider throttle valve. Eight activating devices axially displace the cam elements so that the valves of four of them stop opening. The mode of operation with four cylinders is carried out in revolutions from 900 to 3250 rpm, but at the moment of need for more power turns off within milliseconds.

A special centrifugal pendulum in the flywheel has the task of reducing both the fourth-order vibration forces in 8-cylinder mode and the second-order vibration forces in 4-cylinder mode. Thermodynamic efficiency is also improved by the combination of biturbo filling and direct injection with a centrally located injector (see box) and NANOSLIDE coating. It allows multiple injections for better mixing, and the Closed deck engine is made of aluminum alloys and can withstand a pressure of 140 bar.

Four-cylinder petrol M 264 with Miller cycle

The new four-cylinder petrol turbocharger is from the same modular engine generation as the M 256 and has the same cylinder architecture. According to Nico Ramsperger from the four-cylinder engine department, it is based on the relatively new M 274, which we have already talked about. In the name of the faster reaction of the engine, a double-jet turbocharger is used, as in AMG's M 133, and the liter power is over 136 hp / l. Like the larger M 256, it uses a 48-volt power supply system, but unlike it, it is external, belt-driven and acts as a starter-generator, assisting the car in starting and accelerating and allowing flexible change of operating point. The variable gas distribution system provides operation on our Miller cycle.

Text: Georgy Kolev



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