It seems that being the first to wheel out a Euro6 compliant engine (mandatory from 2014) in March last year was not enough for Georg Weiberg, head of truck product engineering at Daimler Trucks. He’s had a taste of it and he wants more. Just 12 months later, he took the covers off the mid-range engines that will replace the current 900 series, which retire from duty in the Atego, Econic and other mid range products. The new engines are available with nine different outputs, derived from either a 5.1-litre four-cylinder unit, or a 7.7-litre six. Starting at 156hp, they top out at 354hp.

Trends

Some trends are beginning to emerge, most notably that of ‘downsizing.’ With a four-cylinder engine being able to work where previously you would have demanded a six. This theory also applies up the line so that a six-cylinder engine, now with an output of up to 354hp and 1,400Nm from a swept volume of only of 7.7-litres, can find its way into applications that would previously have demanded a 10-litre. The higher pressures in cylinder bores, rails and injectors that have produced this effect, need new materials and construction techniques to go with them. Common-rail injectors now operate at up to 2,400 bar and cylinder bores are tolerating 250 bar, producing up to 50 tonnes pressure on each piston crown.

These forces need tougher materials and tighter tolerances than ever. Much of the investment at the Mannheim engine plant has been in the development of new, stronger materials and modified construction techniques. The cylinder head is made from grey cast iron, with lamellar graphite (GJL). Developed at Mannheim, it gives higher strength and better thermal properties for those components that have to feel the burn.

The cylinder head is secured with six bolts per cylinder, up from the previous four. Keeping a lid on these pressures, and adding the necessary EGR peripherals to cope with Euro6, has meant an increase in complexity, but new tolerances and a €500 million make-over at the Mannheim engine plant will bring improvements in fuel and operating costs, Daimler claims. Engineers have designed a new crossflow cylinder head that now has four valves per cylinder, up from the previous three, and the inclusion of a DOHC design that uses composite camshafts, pioneered last year in the larger OM471 engine from the new Actros.

Half the weight of conventional camshafts, and 30% cheaper to make, they are not turned from solid steel castings, but assembled from a hollow tube with their cam lobes shrink-fitted. The energy saved by the lower rotating masses is passed on in fuel returns. A new idea not purloined from their heavier engines is that of an adjustable exhaust camshaft. Claimed as another ‘first fit’ for a diesel engine, the variable camshaft phaser (VCP) is used to control exhaust gas temperature and maintain the heat required to regenerate the particulate filter. This will be necessary on low-speed and low ambient temperature operating conditions where exhaust temperatures will naturally drop.

The Global View

With additional engine plants in Brazil, South Africa, Japan and the USA, Daimler has no need to bin the successful 900 series units that these engines will replace. 

In the same way that the outgoing Actros model continues in production now the new model has arrived, so engines that have been operating perfectly well in Europe, will find an extended life beyond our shores. This is especially true of some of the fast expanding, so-called, BRIC (Brazil, Russia, India and China) markets where emissions legislation has some catching-up to do. 

Talking Dirty

In the same way that there will be no ‘world truck’, because market requirements are just too diverse, there will be no world engine either. Apart from the manufacturing economics, one of the issues that will prevent the birth of such a beast is the variable quality of diesel fuel around the world.

As European emissions regulations get ever tougher, the engines get less tolerant of high sulphur levels. In Europe we live with less than 15 ppm (parts per million) of sulphur in our diesel, but elsewhere in the world it can climb to 5,000 ppm making it a liability to be running anything with even a tinge of green.

In operational terms, there is promise of lower fuel bills, better driving dynamics from increased torque and higher safety levels from boosted auxiliary braking. The higher torque values that drivers benefit from have a flip side and it looks like fleet operators will win on both counts. The extra grunt proves very useful in holding the vehicle back with an enhanced engine exhaust brake. The last decade has seen dramatic improvements in auxiliary brakes, engine brakes and retarders, and there’s a big operational gain to be had.

As well as extra safety, the ability to drive a truck without recourse to the service brakes over long distances is now a realistic proposition. We suggest that you interrogate your telematics data and see if the driver training is bringing you the benefit of reduced friction lining costs. With every new truck launched, there’s even less excuse to be using the brake pedal with any regularity.  

Family Line-up

As these two new engines were introduced, M-B included a bigger power unit, which sits at the bottom of the heavy-duty engine group. The 10.7-litre OM470 is the straight six that sits between these new middleweights and the big guns. The new family portrait now has a 5.1-litre and 7.7-litre as the juveniles, a 10.7-litre unit bigger brother and the 12.8-litre parents.