So, it's now slowly becoming plausible, also the Euro-6 engines are again being made even more thrifty than their predecessors. The difference is indeed, much smaller, but in view of the huge NOX-emission reduction, it's an enormous achievement.
Let's describe, e.g., the OM 471. 12,8 litres distributed over 6 cylinders is normal, also four valves per cylinder, indeed, two overhead cams in a truck is not the standard. The resulting performance is, 310 - 370 kW (422 - 503 HP) at 1800 RPM and 2100 - 2500 Nm of torque at 1100 RPM.
The engine is usable at as little as 800 to 900 RPM and is always striving to reduce the fuel consumption. This also explains the effect of the GPS-based engine- and transmission management. If it can be foreseen that the top of the hill will be reached very soon, then downshifting is no longer worthwhile.
Diesel engines still always have a tendency towards having a long-stroke. This is particularly valid for truck engines, where torque is more important than performance. In this respect, the OM 471 with its 132 mm bore and 156 mm stroke, is no exception. And, give it some thought, a truck like this clocks up an average of approx. 1,4 million kilometres, generally with only one crankshaft.
The engine is not even twice as long as the sum of its six cylinders. This includes the web-widths of the wet-sleeves, the timing casing at the rear and the ventilator clutch up front. By the way, because of the above required longevity, the crankshaft is made from inductively tempered steel.
The innovations, compared with the former engine blocks, are the numerous weight-saving ribbings, the plastic oil-sump and the so called plateau-honing, which promises a more specific and shallower surface treatment and shorter running in periods, thus reducing the oil consumption.
The stringent NOX-restrictions required by the Euro 6 classification, which have doubtlessly caused higher consumptions, have led to even higher ignition pressures. Mercedes gives a value of 200 bar, which not only strains against the crankshaft itself but against the entire crankcase.
Oddly enough, there is a hot side and a cold side of the engine, indeed, what is meant, is not the engine itself but the side where external components like the turbo-charger and starter on one side and the control device, fuel-pump, oil-cooling module and the air compressor on the other side are installed.
Aluminium is, despite the search for weight-saving, not the preferred material for the cylinder head. In this case, vermicular- is used instead of nodular-graphite. This suits the heat expansion of the engine block better. . Read more about this here.
Recently we're coming across more and more split cooling systems. In this case, it's not the separation between the head and the bushings, but a bit more between the top bushing and a bit less at the bottom. Surprisingly, there is not only the transversal scavenging which treats all the cylinders equally, but also a longitudinal scavenging which compensates for any inequalities which may still be present.
One of the two coolant pumps is regulated, which in a truck engine, can mean as much as 4,4 kW (6 HP). By the way, not only in the warm-up phase, but also in normal running operation is a cut-off desired.
We've already mentioned amazing things about the engine-control. Indeed, there is still more to come. The truck, unlike the motor car, doesn't actually need an engine with a lower construction height. Nonetheless, the two shafts over the already mentioned timing casing, are driven from the rear.
On top of this, the shafts are also hollow, something which can't be taken for granted in truck engines. There is however, one further difference, since in the motor car engine, the rocker-arms, if still required, would have roller-bearings. In the case of the OM 471, they've used plain bearings.
Mercedes is particularly proud of the injection system used here. While the pressure with Common Rail is generally regulated through the high-pressure pump, this occurs here in the injectors themselves, with their constant pressure of 900 bar, where then, pressures of up to 2100 bar are possible.
It is a system with magnetic valves, two per injector. These make not only unbelievably short-period and short term injecting possible but virtually also allow each individual injector to be varied. We'll be dealing with the so called pressure amplification and its effects separately. 01/15