Developing a completely new gearbox range is a huge undertaking, especially when you are set to outperform what is already an industry benchmark. That is why the new Scania Opticruise gearbox range has no parts in common with the existing range. With its wealth of performance enhancements, it will stay com¬pet¬i¬tive throughout this decade.
“I hate to use the worn cliché about starting from a blank sheet of paper, but that was actually the case,” says Jimmy Larsson, Senior Manager, Head of Gearbox Deve¬lopment, Scania R&D. “The teams assignment was to develop gearboxes that could handle all the diverse demands of the next decade, especially in fuel con-sumption, drivability and sustainability. And with the new range, also vehicles with high GTW can use fast axle gearing while still maintaining the required startability.”
Scania has a longstanding tradition of offering powertrains with low-revs and high torque as key elements for achieving low fuel consumption. Why? If the engine has the torque and stamina to propel the truck at low engine speeds, less fuel is used (simply since fuel needs to be injected in a cylinder on every fourth piston stroke).
In practise, it entails highly complex computations with a multitude of factors to consider, but that nail the core of it. If a favourable cruising speed can be maintained at around, or just above, 1050 engine revolutions per minute, fuel will definitely be saved. Just until recently, a typical long-distance truck operated on a 1400 rev-per-minute-level. Scania’s new gearbox range has a significantly wider spread with a true overdrive gear on top and can handle both low and high revs in an efficient way.
A prominent feature of the new gearboxes is their fuel-saving capability. That is why Scania’s engineers have particularly focused on internal friction when designing and developing the new range. The planned target was reached, the internal losses was reduced with no less than 50%. This was accomplished through polishing some of the gears, by using low viscosity MTF oil and by setting aside the lion’s share of the oil in a separate, dry sump-like part on top of the gearbox. This reduces internal oil splash since the gears are not continuously exposed to oil (think about a water wheel). Certain cog areas that are vulnerable to hard wear when absorbing force are supplied with extra oil by spray pipes for increased cooling and lubrication.
All aluminium and quiet
The first edition in the range, G33CM, is some 60 kg lighter than the current gearboxes, mainly due to the all-aluminium housings and somewhat smaller dimensions. Another key achievement is lowered noise, a prerequisite for meeting future regulations. The average noise reduction is up to 3.5 dB, quite a considerable reduction when considering that the dB scale is logarithmic.
The new gearboxes are shorter than the most common Scania gearbox at present, GRS905. By only using two synchronisers (compared to seven), between low and high range split, the new gearboxes are shorter and sturdier, with shafts capable of handling more torque. This also enables opportunities to use gears with slightly wider cogs that can handle more load and are more durable.
However, removing synchs also place higher demands on the gearbox management system and the overall gearshifting strategy. All the electronics are therefore new and manage the pneumatic actuators and the shaft brakes (three in total) that are instru¬mental for swift, smooth and accurate gearshifts.
Eight gears for reverse
Scania’s engineers adopted a new approach to reversing. In most gearboxes, going in reverse entails letting a separate cog wheel rotate the mainshaft in the opposite direction. In the new Scania range, by contrast, the planetary engagement at the output shaft is used instead, and reversing is effectuated by locking up the planetary wheel carrier. This solution allows having eight gears for going in reverse at speeds up to 54 km/h (optional). This is useful when, for instance, tipper trucks need to go in reverse for long dist¬ances (such as at tunnel construction sites).
The oil change intervals have been greatly improved, due to higher precision and the use of bigger oil filters and high-quality oil.
Clever PTO solutions
No truck gearbox range would be worth mentioning without also citing its PTO (Power Take-Off) capabilities. Scania’s new range comes with an abundance of newly developed and clever PTO solutions aiming to fulfil any number of advanced PTO needs asked for by Scania’s customers, regardless of their application.
A whole range, in fact nine different PTOs, will be available, characterised by in-creased per¬formance, less drag losses and great flexibility via modularity. The EG PTOs are driven directly by the layshaft and are pressure-lubricated by the gearbox. The new interface on the gearbox with a lubrication port means that they can power heavier equipment such as hydraulic pumps.
The EK PTO’s (flywheel driven) will consist of a separate unit, mounted between the engine and the gearbox. Four different ratios will be available and the output tower is possible to mount in three different positions.
“All-in-all, we have every reason to believe that our new gearbox range is state-of- the-art for powerful truck engines,” says Alexander Vlaskamp, Executive Vice President, Head of Sales and Marketing at Scania. “We hope it will support our customers in fulfilling their transportation tasks in a seamless and sustainable way for many years to come”.