Dr.-Ing. Thomas Tobie studied mechanical engineering at the Technical University of Munich (TUM), Germany. Today he is head of the Load Carrying Capacity of Cylindrical Gears department at the Gear Research Centre (FZG), where he specializes in gear materials, heat treatment, gear lubricants and gear load carrying capacity research. Concurrently, Tobie brings to that work a particular focus on all relevant gear failure modes such as tooth root breakage, pitting,
micropitting and wear, as well as sub-surface-initiated fatigue failures.
To increase cost efficiency in wind turbines, the wind industry
has seen a significant rise in power density and an increase in the overall size of geared components. Current designs for multimegawatt turbines demand levelized cost of energy (LCOE) reduction, and the gearbox is a key part of this process. Since fatigue failures nearly always occur at or near the surface, where the stresses are greatest, the surface condition strongly affects the gear life. Consequently, an improved surface condition effectively avoids major redesign or increased material cost due to an increase in part size. Additional finishing methods such as shot peening (SP) and superfinishing (SF) significantly increase the gear load capacity, but these effects have not yet been adequately considered in the current ISO 6336 standard or in any other gear standards. The combination of SP followed by SF will be described here as an “improved gear surface” (IGS).
Standardized methods, like AGMA 2001-D04 or ISO 6336 for the calculation of the load carrying capacities of gears are intentionally conservative to ensure broad applicability in industrial practice. However, new applications and higher requirements often demand more detailed design calculations nowadays; for example: long operating lives in wind power gearboxes or fewer gear stages and higher speeds in e-mobility applications result in higher load cycles per tooth in a gearbox.