Test drive New Mercedes 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 Mercedes-Benz's return to the brand's original row of 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 Chrysler's Pentastar engines. 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 that complements the turbocharger (similar to that of Audi's 4.0 TDI engine) - 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 more of an integral element of the engine itself and was designed as a part of it from the very beginning of the development work on the bike. With its 15kW of power and 220Nm of torque, the ISG helps deliver dynamic acceleration and early peak torque, along with the aforementioned electric supercharger, reaching 70rpm in 000ms. In addition, the system recovers energy during braking, allows constant speed movement with electric power only and engine operation in a more efficient zone with a higher load, respectively a wider throttle opening or using the battery as a charging buffer. With a 300 volt power supply are also large consumers such as the water pump and the compressor of the air conditioner. Thanks to all this, the M 48 does not need a peripheral mechanism to drive a generator, nor a starter, thus freeing up space on its exterior. The latter is occupied by the forced filling system with a complex system of air ducts encircling the engine. The new M256 will be officially introduced 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 layout with the separation of the intake and exhaust systems also allows for a closer arrangement of the catalyst and the new system for cleaning solid particles (used so far only in diesel engines). In its initial version, the new machine has power and torque reaching the level of the 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 its displacement of 500 cc per cylinder, the new unit has the same optimal, and according to BMW engineers, displacement as that of the two-liter the diesel engine introduced last year and the new two-litre 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 a layout of 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. "

The M 176 has a smaller displacement than its predecessor M 278 (4,6 liters) and is a derivative of the AMG M 177 (Mercedes C63 AMG) and M 178 (AMG GT) units with outputs in the range of 462 hp . up to 612 hp Unlike the latter, which are assembled on a one-man-one-engine basis in Affalterbach, the M 176 will be more widespread, assembled in Stuttgart-Untertürkheim and will initially have a power output of 476 hp, maximum torque of 700 Nm and will consume 10 percent less fuel. In no small measure, this is 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 valve timing system, in which the operation of the four cylinders switches to a mode of greater load with a wider open throttle valve. Eight actuators axially shift the elements with the cams so that the valves of four of them stop opening. The four-cylinder operation mode takes place in rev modes from 900 to 3250 rpm, but when more power is needed, it switches off within milliseconds.

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