Gearbox efficiency is a topic of rising interest amongst both OEM and end-users due to an increased
sensitivity to gearbox performance, reliability, total cost of ownership (energy cost), overall impact on the
environment, and also anticipating future regulations.
Agearboxis bynature aquite efficientasset: aparallel shaftgearunitissaid in literature tohave typical losses
of 1 to 2% per stage. As an example, a single stage gearbox could have a nominal efficiency of 98 to 99%.
Anyhow, due to the high power/ torque transferred by the system, it could be interesting to minimize the
absolute losses as they could be significant (1 % of 1 MW is still 1 kW), especially when existing technology
allows it at very reasonable cost and without much complexity.
In a gearbox, there are difference sources of losses: gear, lubrication, seal and bearing loss. The use of
modern simulation tools makes easier the evaluation of losses in various load case conditions.
It has been demonstrated that the contribution of bearing loss on the system efficiency is dependant on the
load cases. Even ifthebearing isbyfarnottheprimarysourceoflosses, theoptimization ofthebearing setcan
significantly improve the gearbox performance.
Simulation ofa single stage gearboxusing tapered roller bearings, shows thatthe running temperature ofthe
gearbox can be reduced up to 1 0C, by using latest bearing generation. Such a saving could improve the
thermal rating of the gearbox by up to 30%.
Experiment also demonstrated that different design of tapered roller bearing shows significant variation in
friction performance.

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