SECTOR FOCUS: AUTOMOTIVE GREASES
Rolling Bearing Greases for Enhanced Demands in Today’s and Future
Automotive Applications – Anti-False-Brinelling Performance and reduced Friction Torque in Passenger Car Wheel Bearings
C. Specht, Schaeffler Technologies AG & Co. KG, Schweinfurt, Germany New Trends in Mobility
For several years now all car manufacturers and their suppliers have been facing more and more new trends in mobility and transport. Due to ecological concerns traditional combustion engines for passenger cars will have to be replaced by more eco-friendly drive systems. Depending on future technological progress, and also on legislative regulations, different drive technologies will prevail to achieve significant reductions in exhaust emissions and energy consumption. Today a pure electric drive system is believed to be the best final solution – if supplied with “green” energy. But definitely the coming years will be a kind of transition phase in which different approaches such as hybrid drives, fuel cells or synthetic fuels will play their role.
Enhanced Demands for Lubricants Following the above mentioned general trends lubricating greases in rolling bearings will have to stand significantly higher demands in future automotive applications. Especially rolling bearings in future hybrid or pure electric drives must show reliable operation at much higher speeds and temperatures as today. At the same time these bearing greases also have to protect rolling bearings from stand-still damages during transport at very low temperatures down to -30 or even -40 °C. And for maximizing
cruising ranges of new alternative drive concepts, rolling bearings are also in the focus of optimisation regarding friction. All these demands cannot be met without optimised lubricating greases. The products available today are not able to meet the requirements of tomorrow.
Greases for Passenger Car Wheel Bearings (PC Hub Units) During the previous decades standard greases for passenger car wheel bearings were designed as lithium-complex or polyurea greases with a mineral base oil. These combinations were able to meet all requirements regarding life time, load, speed and temperature in sealed double-row angular contact ball bearings. However when car manufacturers started to produce cars also in significantly colder regions, the original European or American requirements turned out to be insufficient especially with regard to bearing protection against false brinelling. This specific rolling bearing damage type typically occurs during vehicle transport on railway or trailers at low temperatures. The interaction of constant vibrations, micro-movements of rollers on raceways in the bearings and temperatures below -20 °C finally results in markings on wheel bearing raceways. Markings deeper than appr. 5 µm create unacceptable noise in bearing operation and so leads to customer complaints.
Fig 1. False Brinelling due to Car Transport: Vibration + low Temperature = Markings Continued on page 16 14 LUBE MAGAZINE NO.144 APRIL 2018
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