Dissertation: Predictions available for planetary gearbox power loss

Charles Nutakor's doctoral dissertation aims to experimentally and theoretically investigate the power losses of planetary gearboxes. The dissertation is titled "An experimental and theoretical investigation of power losses in planetary gearboxes".

Gearboxes based on planetary gear sets are preferred for their advantages, such as higher gear ratios, improved self-centering capabilities, kinematic flexibility, favorable bearing support conditions and higher power densities with less noise in a more compact size. The multiple-planet branches of planetary gear sets are usually symmetric about their axes, so they are a more suitable choice in the design of a drivetrain configuration where there is high demand for low-speed high torque, high-speed low torque or both operating conditions. Meeting the design requirements for such drivetrain configurations can result in a compromise between the reliability and efficiency of the gearbox. 

In the dissertation, a planet-sun gear mesh power loss model is first developed to quantify the influence of micro and macro geometry on a single planet--sun gear mesh power loss. In addition, several base oil types were investigated to understand their influence on planet gear bearing power loss.

Considering that the next generation gearboxes for wind turbines and heavy-duty off-road working machines have a planetary gear set incorporated with a permanent magnet synchronous machine, two groups of power losses initially defined for conventional planetary gearboxes had to be extended to accommodate the power losses arising because of the conventional mechanical gear interaction with permanent magnet electric motors. For this, a methodology for predicting power losses in an integrated planetary gearbox is developed and validated with measurement data from a prototype-integrated gearbox.

Realizing that the friction coefficient values at the gear and rolling element contacts play a major role in predicting the efficiency of wind turbine gearboxes, two new closed-form formulae for predicting friction coefficients have been proposed. The new closed-form friction coefficient formulae are based on a comprehensive experimental friction coefficient measurement database, which considers a wide range of rolling and sliding speeds, surface roughness, oil temperature, and lubrication conditions.

Improving wind power efficiency is essential because the cumulative increase in electricity production would increase by several gigawatts per hour if the wind turbine gearbox power losses were reduced even by one percent.  Similarly, reducing the power losses in heavy duty off-road vehicles is beneficial because any improvement in the gearbox efficiency has the potential of impact the carbon emission and energy consumption.


Charles NutakorMaster of Science in Technology, will defend his doctoral dissertation titled "An experimental and theoretical investigation of power losses in planetary gearboxes" at LUT on October 12, 2018 at noon, in Auditorium 2305. Professor Arto Lehtovaara, Tampere University of Technology, Tampere-Finland and Professor Petri Kuosmanen, Aalto University-Finland will act as opponent. Professor Jussi Sopanen of LUT will act as custos.


Library information

The dissertation has been published in the Acta Universitatis Lappeenrantaensis research series and the details are as follows

Acta Universitatis Lappeenrantaensis 815

ISBN 978-952-335-273-5

ISBN 978-952-335-274-2 (PDF) 


ISSN-L 1456-4491

ISSN 1456-4491


A printed version of the dissertation may be purchased from the Aalef bookstore, tel. +358 44 744 5511, or at kirjakauppa@aalef.fior online from the LUT Shop: https://lutshop.lut.fi/.