196 BEARING CONCEPTS 12 19712 BEARING CONCEPTSSchaeffler Symposium 2018 New bearing concepts Friction optimized tapered roller bearings and locating non locating bearing supports Modern transmissions are unthinkable without high performance rolling bearings The bearings are designed for specific applications and with the overall system in mind Schaeffler has deve loped its own calculation programs 1 Many transmission shafts are currently suppor ted by tapered roller bearings The reason for this lies in the high robustness of this bearing type and in its very good ability to support loads In addition tapered roller bearings are characte rized by a comparatively small cross section as well as mostly simple assembly Tapered roller bearings are continuously refined by Schaeffler to increase their performance and reduce the friction torque level Its latest designs combine individual application specific designs with the best possible manufacturing standard These include the optimized design of the contact angle special raceway profiling the use of ta pered rollers with optimum length and diameter the right number of rollers for a specific load nar Introduction Modern rolling bearings are indispensable when it comes to the refinement of transmissions with regard to friction and power density New design space conditions and requirements that this key component will be confronted with by develop ments such as powertrain electrification may re sult in optimized designs as well as new bearing types and concepts This paper deals with a new bearing design that makes it possible to use low friction locating non locating bearing supports even more fre quently than before It also shows that the con sistent optimization of known bearing designs can help further reduce friction decrease design space requirements and also reach the high speed level of electric drives at moderate tempera tures In addition the paper describes ways in which application limits can be extended through the use of coatings Future requirements for rolling bearings The increasing regulation of CO2 emissions de fines essential trends including the develop ment of transmissions largely independently of the transmission design Faster than was pre dicted only a few years ago it is the new electric drives in particular that have changed the re quirements for bearing technology They are driven by hybridization the development of dedicated hybrid transmissions DHT and elec tric axles For this reason the discussion of fu ture transmission bearings also includes the electric motor as a drive in particular since it will be combined with the transmission to form one drive unit This results in new requirements for bearings in cluding Higher load capacity with even less friction Higher speeds Today the speed parameter that is the product of the speed and the mean bearing pitch circle is at around 0 2 0 5 million mm min for oil lubricated transmission bea rings and will increase to up to 1 3 million mm min for grease lubricated bearings in electric motors Noise reduction Greater temperature differences between the bearing rings The temperature differences be tween the bearing inner and outer ring in crease from 15 20 K to up to 70 K due to the more frequent starts and stops as well as the heat transferred from the rotor This large tem perature difference must be taken into consi deration when dimensioning the internal clearance and the heat treatment of the bea ring rings Protection from electric current and resistance to non operate currents Increased power density Grease lubrication The temperature limit of available high speed greases is too low Clas sic high temperature greases are thermally very stable but they are limited to speed para meters n x dm up to 1 million mm min Schaeff ler has resolved this conflict of goals between speed parameters and temperature stability by means of a newly developed grease Oil lubrication In transmission bearings the use of oils with ever lower viscosity leads to more frequent operation in mixed friction The probability of surface induced damage in creases Some modern transmission oils even promote the occurrence of white etching cracks in the bearings The Durotect B coating developed by Schaeffler counteracts both ef fects row tolerances and improved surfaces as well as the use of improved materials and heat treatment processes 2 The OPTIKIT program developed at Schaeffler as an optimization tool for CAE models allows ta pered roller bearings to be designed in relation to freely definable target parameters and auxiliary conditions Due to the use of this automated opti mizer that is integrated in BEARINX much better solutions have been found than would be possi ble manually in the same time period 1 The la test result of this computer assisted optimization is the ultra low friction ULF tapered roller bearing that is based on the T29D manufacturing standard and has a very low friction torque Fi gure 1 In spite of the progress that has been achieved in the development of tapered roller bearings changing to locating non locating bearing sup ports can further reduce the friction power be cause there is no axial preload of the bearing The time and money invested in the reconfiguration of the transmissions justifies the change in the bearing concept for fundamental revisions of exis ting transmissions or new designs Due to such successor transmissions manufacturers succes sively change their transmissions to locating non locating bearing supports 3 Figure 2 Deep groove ball bearings are used as locating bearings and cylindrical roller bearings or radial ly compact drawn cup cylindrical roller bearings are used as non locating bearings One advan tage here is that the point contact of the deep groove ball bearing in partial load operation pro duces less friction than the line contact of the ta pered roller bearing However deep groove ball bearings have a comparatively low capacity for supporting loads In addition they have a certain axial and radial clearance That is why their suita bility for specific applications must be checked on a case by case basis Friction torque Standard X Life T29D ULF 1 Comparison of ultra low friction tapered roller bearings

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