ABSTRACT

For a wind turbine main gearbox (MGB) of the 3MW class, the planetary type low-speed stage (LSS) was designed with five planets and the planet carrier was designed as a single sided carrier. To avoid planet tilting, the planets were supported on flexible planet pins (Flexpin). The Flexpin was optimized, analyzed and tested beyond the prior known state of the art. Objective of the optimization was lowest stiffness at acceptable stress level resulting in the best possible load distribution in the LSS.

For this, different shapes for a Flexpin pin were compared and an optimized geometry was found by parameter variation. The resulting pin geometry combines a low stiffness with acceptable stress levels. The deformation behavior and resulting stress state were determined first using a simple beam model and compared to 3D FEM analysis results. The latter was required to consider the influence of the press fit between Flexpin and planetary carrier and between the pin and sleeve of the Flexpin.

A spring-based model was established representing the planetary stage with the five. Manufacturing and position tolerances as well as the Flexpin, bearing and gear mesh stiffness are considered. 20 different, random tolerance distributions were created and the load distribution among the five planets was calculated. Due to the low stiffness of the Flexpin, low values for Kg at Kg = 1.10 to 1.15 resulted. 

On prototypes, fatigue tests were performed for a single Flexpin under full load for 1*10^6 load cycles, confirming the pin strength and displacement predictions. 

The assembled gearbox containing a set of five Flexpins, integrated into the drive train of Ming Yang SCD turbine, China designed by aerodyn GmbH, Germany was tested at the CWD of the RWTH Aachen, Germany. After temperature stability was achieved, full load test and bending load tests were run and the gearbox was inspected by DNV-GL and the author. The resulting tooth contact patterns (and other parameters) yielded the desired results, and the inspection could be successfully closed. Flexpin displacement was measured in situ, and load distribution factors were computed at Kg = 1.12 (only torque applied to the drive train) and Kg = 1.23 (torque and bending moment applied to the drive train). The measured values confirmed the assumptions and models used in the design process. 

In the meantime, several sizes (3MW and higher) and a considerable number of MGB are in operation without any known issues. Higher ratings are in the design phase.

Author(s): Hanspeter Dinner

ISBN: 978-1-64353-165-6