Minimum friction losses in wind turbine gearboxes

Improving the mechanical efficiency is not the most important objective in the design of wind turbine gearboxes since the available wind energy is abundant and costless. The most important criteria for dimensioning the gearbox are the fatigue strength-bending and pitting-, noise emission, vibrations, and maintenance requirements. Nevertheless, mechanical losses increase the lubricant temperature and induce thermal stresses, which increases wear and cracking risk. This means that friction losses should be reduced as much as possible, but always regarding the contact and tooth-root stress levels, as well as the other operating parameters which should be kept for ensuring the required operating conditions. In this paper, a study on the variation of the friction losses with the tooth shift coefficients is presented. All the other geometrical parameters-number of teeth, tooth height, pressure angle, helix angle, face width, and center distance-are unalterable, since all of them have been chosen according to more important design requirements. In addition, to keep the contact and tooth-root stress levels, the shift coefficients of the sun, planets and ring are calculated in such a way that the transverse contact ratios are kept, and therefore the critical load points for bending and pitting are also unchanged. The radial clearance is also kept in order to allow the proper evacuation of the lubricant. Finally, all the geometrical constraints (undercut, pointing, root interference, secondary interference, backlash) are also imposed. With all these restrictions, the optimal shift coefficients for all the gears are calculated to minimize the friction losses.

Automated summary

When designing wind turbine gearboxes, the most important criteria to consider are fatigue strength, noise emission, vibrations, and maintenance requirements. In order to minimize friction losses, it is crucial to reduce friction losses while considering the impact on contact and tooth-root stress levels.