CFD Simulations of windage losses of a gearbox

Concli Franco - Politecnico di Milano (Italy)
Gorla Carlo- Politecnico di Milano (Italy)
Politecnico Milano


Efficiency is becoming more and more a main concern in the design of power transmissions and the demand for high efficiency gearboxes is continuously increasing. Also the more and more restrictive euro standards for the reduction of
pollutant emissions from vehicles impose to improve the efficiency of the engines but also of the gear transmissions. For this reason the resources dedicated to this goal are continuously increasing.

The first step to improve efficiency is to have appropriate models to compare different design solutions. Even if the efficiency of transmissions is quit high if compared to the efficiency of the engines and appropriate models to predict the power losses due to gear meshing, to bearings and to seals already exist, in order to have a further improvement, some aspects like the power losses related to the oil churning, oil squeezing and windage are still to be investigated. These losses rise from the interaction between the moving or rotating elements of the transmission and the air/oil lubricant mixture. In previous papers, the authors have investigated the churning losses of planetary speed reducers (in which there is a relative motion between the "planets + planet carrier" and the lubricant) and the oil squeezing power losses. This report is focused on the windage power losses. This losses are related to the interaction between the rotating gears and the air. This losses became important for high rotational speeds.

For this reason the phenomena has been investigated by means of CFD simulations in order to understand the influence of some operating and geometric parameters like rotational speed, gear depth, tip diameter and helix angle.

The results of this study have been included in a model to predict the efficiency of the whole transmission.