Turning Instead of Sliding: Rolling Bearings in Engines Save Fuel

In the search for technical possibilities to save fuel consumption, relatively small and apparently inconsiderable components in vehicles are subjected to critical examination – sometimes with extraordinary success.

One example that “turning a small wheel” also offers potential for reduction in fuel consumption and thus emissions is provided by Schaeffler KG in Herzogenaurach. Following the increasing interest in replacing plain bearings in the engine with rolling bearings, which cause less friction, the experts in the company, belonging to the Schaeffler Group, hit on the cam shaft bearing – and found potential for savings.

“In principle it is easy to replace the traditional plain bearings of the cam shafts in the engine with rolling bearings – in our case needle bearings, which save space,” Dr. Peter Solfrank, who is responsible for the application of rolling bearings in automobile engines at Schaeffler KG, explains.

“For example, we were able to save around 0.5% fuel consumption by exchanging six bearings in a vehicle with two overhead cam shafts,” he continues. Anyone who thinks that “turning” instead of “sliding” results in acoustic disadvantages is mistaken. “This exchange does not result in any losses with regard to engine acoustics,” Solfrank says.

And he can demonstrate that the theoretical principle also works in practice: at the beginning of the year, the two overhead camshafts, which until then merely turned in the housing, were equipped with rolling bearings in a Fiat Stilo 1.4 l with a 4-cylinder gasoline engine (70 kW/95 HP). The INA needle bearings that were used reduce friction and save fuel – other than that the driver doesn’t notice anything.

But rolling bearings in the engine offer even more potential: currently, a number of projects are underway with customers to furnish the crankshaft with rolling bearings. The loads on the bearings are disproportionately higher here, the available design space is very limited, and the continuously rising power density needs to be taken into account. Still, Solfrank is optimistic that rolling bearings will be used here in the medium-term as well.

Already successful is the use of rolling bearing in mass balance shafts that compensate for vibrations in the engine. Here plain bearings in new series production launches are increasingly replaced by roller bearings. Already, the balance shafts in the BMW 4-cylinder diesel engine (2.0 l, 143 or 177HP, respectively) are equipped with INA rolling bearings in series production. Here the balance shafts turn twice as fast as the crankshaft – no problem for the rolling bearing. Aside from the needle bearing, INA also has the know-how to produce the balance shafts themselves – but it doesn’t stop there.

“We offer our customers balance shafts with significant reductions in both mass and mass moment of inertia. This way we not only save on the shafts, but we also save weight in the drive train, and thus fuel,” Dr. Peter Solfrank reports.

He does not yet specify in what order of magnitude – in a best-case scenario, a clear one-digit saving is feasible: similar, for example, to the maximum savings potential by reduction of the dynamic pressure in the exhaust section, i.e. the optimisation of the catalytic converter. Sometimes even small steps lead to the energy-saving vehicle of the future

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