28/9/11

Overview: Schaeffler roller-bearing shafts

The Schaeffler Group’s lightweight balancer shaft with roller-bearing supports has won the PACE Award in the Product category for outstanding innovation.

Presented annually since 1994 by Automotive News magazine in conjunction with audit and consulting firm Ernst & Young and the Transportation Research Center (TRC), the PACE Award recognises outstanding product innovations from automotive suppliers.

Schaeffler roller-bearing balancer shafts in situ.

Lightweight balancer shafts with roller-bearing supports contribute to reducing fuel consumption improving refinement.

For example, the power consumed internally in a four-cylinder diesel engine already in volume production is reduced by up to 2.0PS when roller-bearings are specified in place of plain bearings. Additionally, the requirement for cooling by engine oil is reduced, and the need for pressure lubrication is eliminated. These characteristics, along with the design’s superior emergency running properties, make lightweight balancer shafts with roller-bearings ideal for engines with start-stop systems.

The use of roller-bearings in itself allows lighter balancer shafts to be used, saving roughly a third of the mass compared with a plain bearing installation. This means that the two balancer shafts mounted in a four-cylinder engine reduce engine mass by more than 1kg.

Schaeffler’s lightweight roller-bearing balancer shafts appeared for the first time in Daimler’s 2.2-litre OM 651 four-cylinder diesel engine, which was proclaimed Engine of the Year in 2009, and is also used in Fiat’s Twin Air engine, which received this year’s Engine of the Year award. In 2010, the Schaeffler roller-bearing balancer shafts won the Steel Innovation Prize.

Turbochargers

Because of the lower frictional losses of roller-bearing mountings in comparison with plain bearings, increased torque can be achieved with given diameters and geometry of turbines. Also, response is improved — the blower accelerates faster — and fuel consumption is reduced.

The reduced frictional losses offer higher maximum bearing shaft speeds, not least in the partial load range. Turbo lag in petrol engine applications is also reduced somewhat. Additionally, because of the more rapid acceleration of the turbine under transient loads, the emissions spikes inherent in these conditions are reduced. Schaeffler claims that the ‘raw’ emissions in the low and partial load ranges are reduced by a factor of two compared with comparable engines using turbochargers with plain bearings. The reduction in fuel consumption is around four per cent. over the NEDC.

Camshafts

One of the requirements of modern engines is that they must now be suitable for use with stop-start systems. roller-bearing supports also offer the advantage that they prevent ‘mixed friction’ conditions, and suffer less from the wear associated with frequent starts with only a partial oil supply.

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