Paper IX (ii) Seals for Passenger Car Wheel Bearing Units

The modern concept of a car wheel bearing is a complete unit that is ready to use, greased and sealed for life. Thus today the lubricant and the seal form an integral part of the bearing. With ongoing improvement in bearing internal geometry and materials, the performance of the seal can even replace rolling contact fatigue as the limiting factor for bearing service life. At the same time, demands for reliability and long, service-free running periods are continuously increasing. Systematic efforts during recent years have resulted in improved seal designs and have provide deeper insight into their functioning and the tribology effects involved. Seals for grease lubricated bearings are defined as active hydrodynamic engineering elements, with a preferential outward pumping effect to prevent penetration of foreign matter into a bearing unit. Seal life is thus governed by the existence of preferential pumping effects. When these have vanished, the seal transforms from an active into a passive engineering element. Bearing life from then depends on environmental factors only. Several mechanisms were identified which influence these effects negatively and thus restrict seal life: of these ageing of the seal lip material and counterface abrasive wear are described. Limiting factors were found and incorporated in a seal life model.