The new Mercedes-Benz OM 651 2.2 litre, four-cylinder diesel engine sets new standards in terms of performance and fuel consumption, thanks in part to weight reduction of key components such as the balancer shaft and bearing assembly, designed and manufactured by Schaeffler.
By analysing engine load conditions, Schaeffler was able to optimise weight distribution, enabling the width of the bearing to be reduced. This meant that the weight of the shaft could be cut by more than a third, equating to a weight saving of 0.75kg for the engine. Moreover, by replacing conventional plain bearings with needle rolling bearings, friction is reduced by up to 50% over the whole speed range.
The lower mass moment of inertia reduces the load in the power train, therefore improving the acoustic characteristics. In addition, the narrower raceway improves the oil mist supply to the rolling bearings, enabling a simpler system design without oil feed holes, reducing manufacturing costs. The engine requires a lower throughput of oil, so the oil pump can also be made smaller. All of these technical improvements meant that the balancer shaft alone contributed around 0.5% to 1% to fuel consumption reduction.
With the global market for four-cylinder engines standing at almost 50 million units per year, the new INA lightweight balancer shaft assembly offers huge potential for reducing engine fuel consumption and emissions. For example, based on an average reduction in fuel consumption of 1% over the life of an engine, and calculated for a vehicle mileage of 250,000km, this would lead to approximately 175 litres of fuel savings.
Even if only 25% of all four-cylinder engines were fitted with lightweight balancer shaft assemblies, this would still reduce harmful CO2 emissions by around six million tonnes per year.