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Secondary air injection after cold start gives two effects for reduced exhaust emissions: An exothermic reaction at the hot exhaust valves occurs, which increases the temperature of the exhaust gas. It gives sufficient air to the catalyst during the cold start fuel enrichment that is necessary to prevent driveability problems. Handicaps for the wide use of air injection include space constraints, weight and price. An electrical air blower was choosen to best satisfy all these requirements. The development steps are described. The result is a three stage radialblower with extremly high revolutions of about 18000 rpm. The system configuration and the outcome are demonstrated on the new C-Class of Mercedes-Benz. The results show emission reductions higher than 50 %, while also satisfying the development goals of noise, volume, weight and cost requirements.

Lubrication of moving parts becomes less efficient in those areas where close fit limits the amount of lubricant to a very thin oil film. Journal bearings are particularly vulnerable in this respect. To test the degree of wear, a radioisotope technique was applied in which shafts and bearings were deuteron activated. Not only did the tests prove sufficiently sensitive to determine the full range of hydrodynamic lubrication, but they also identified the transition point at which poor lubrication caused journal-bearing wear. It was also found that materials of the shaft and bearings greatly influenced the amount of wear.