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ONYX and NREL’s Next Generation Drivetrain – Part 1: Design and Assembly

Dr. Chris Halse, our gearbox lead designer and Head of Engineering Services inspecting the assembly of the flexible pins and journal bearing spindles.  During assembly we had to take care not to damage the many strain and temperature sensors.

ONYX InSight has been involved in the design, manufacturing and testing of a Next Generation Drivetrain for the US Department of Energy (DOE). The $3M project is facilitated by NREL (National Renewable Energy Laboratory) with additional industry partners specializing in power electronics and control systems. The platform of the drivetrain is a medium speed generator, single stage gearbox and main shaft integrated into a single housing. The innovation is the use of journal bearings in the planetary stage of the gearbox. Journal bearings can be thought of as brass bushings with oil lubrication. This technology has been around many decades but wind turbine gearboxes have always used traditional roller element bearings.

The DOE is funding journal bearing research as a means to improve wind gearbox reliability. There are challenges to overcome thus the research, but there is one clear advantage – a whole lot less moving parts!

How it all started

The Next Generation Drivetrain project began with simulations followed by the detailed design of the gearbox. We had to model, simulate and design the journals to optimize the performance. Then procure and assemble the gearbox for testing.

In the winter of 2015 the metal cutting began.The single planetary stage gearbox utilizes a flexible pin design to equalize the load sharing between each of the four planet gears. The flexible pin configuration is supported on only one side by the carrier plate. The assembled drivetrain has been tested on the 2.5MW dynamometer at NREL’s National Wind Test Center near Boulder, Colorado. Testing commenced late last year and we installed a lot of instrumentation. It’s performed well during numerous torque sequences, grid fault simulations and start-stop cycles. We’ve got great data to analyse on the limits of planet journal bearings in this wind turbine application.


 Travis Histed, from our Colorado office, pleased to confirm the data feed is looking good from over 50 channels of sensors. The journal bearing gearbox is the shiny metal ring between the generator and input shaft. 

A recent presentation about the project is here, including pictures of assembly >>

And NREL put a nice video together about the project >>

Read the second installment of this Next Generation Drivetrain story here >>

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