ABSTRACT

Careful rating of drive systems is a critical task to prevent premature failure. Any failure is a very adverse event. Priority elements in a drive system are gears, but – for example in wind turbines – often bearings or shafts may be more critical. Calculation methods for lifetime evaluation given in ISO, AGMA, FKM use the S-N characteristics of the material (Woehler line), therefore with damage accumulation and a proper load spectrum the service life can be evaluated. On the other hand, for many drives measured torque-speed data exists - from test drives, from the field or from simulations. To be able to perform a rating, measured data must be converted into a load spectrum. 

The appropriate method to generate a load spectrum from a measurement varies between gears, bearings, and shafts. For gears the load on a single tooth must be extracted, then converted into a load spectrum with respect to the alternating stress obtained from torque-variation (21FTM07, Use of duty cycles or measured torque-time data with AGMA ratings). For bearings the speed-torque distribution over time is the determining effect for a correct lifetime evaluation. And for rotating shafts alternate bending and shearing stresses are combined with rarely varying torsional and axial stresses.

In this paper the method discussed is how torque-speed data given at the input or output coupling of a drive system can be converted in a specific load spectrum for the rating of every gear mesh, bearing and shaft of the system. The procedure for a gear stage was presented in an earlier paper (21FTM07). So, the focus is on the adaptation to bearing calculations (ISO 281 and ISO 16281) and to shafts (FKM Guideline). 

In the final section, practical applications of the above method with a 3-stage-bevel/helical-gearbox and with a wind turbine is discussed.

Author(s): Ulrich Kissling

ISBN: 978-1-64353-162-5