It seems that many gearbox companies design against static load cases over a design life. These load cases are only snap shots and will only provide a accurate life prediction if the change in load is smooth.
The change in load within a wind turbine gearbox can be far from smooth. The transients are also not predictable. With this in mind the calculation process for wind turbine gearboxes should be based upon transient / dynamic loading and the certification standards should reflect this.
Current calculation standards for gears and bearings do not go far enough to deal with transient loads effects. I am looking for consortium members to be involved in a study into these effects and whether corrective factors can be used to improve the calculation standards.

So what do the professionals think about this problem:

Dinesh Barwey, Aviation & Aerospace Professional:

One can still design with static load conditions, however, knowing extreme loadings is paramount and is an art, especially for systems that may overspeed. Transient models will surely help and need not be that complicated structurally.

 

Alex Tylee-Birdsall , Technical Director, Drive System Design Ltd:

The key difference in automotive is the the gearbox has a lot of protection. The torsional damper at the clutch protects it from torsional vibration. The driveshafts act as torsional spring dampers. Therefore the torsional connection to the engine and the wheels are not that stiff. In my experience in wind turbine the design what the entire driveline to be as stiff a possible (I assume for control reasons – maybe someone can explain more). This means the gearbox is rigidly connected to high inertia components and it is not protected.

Also in a vehicle the gearbox is mounted on rubber mounts that isolates the vehicle from its vibrations and vice versa. Vibrations into the gearbox from things such as tower vibration would also damage contacting surfaces such as bearings.

Load transients are not so extreme in automotive and torsional vibrations from the engine are predicable and can be reduced using torsional dampers in the clutch assembly.

For unpredictable load transients you would need adaptive damping which is probably best achieved using some form of fluid coupling.

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