Churning losses of spiral bevel gears at high rotational speed

In the present study, no-load losses of different splash lubricated spiral bevel gears were measured. The authors used a specific test rig, and a set of gears, to investigate churning losses at higher tangential speeds: up to 60 m/s. An uncommon behavior of the drag torque was highlighted: the torque increased with the rotational speed until a local maximum was reached; then the torque decreased and a local minimum was noticed; at higher rotational speed the torque increased. The torque decrease seems to be linked with a windage phenomenon, which becomes non-negligible at such speeds. In this work, efforts were made to characterize this reduction of gear immersion depth in order to be able to predict no-load losses. It was found that the evolution of oil immersion was linked to a Froude number. Finally a new analytical model of no-load losses was developed for churning losses combined with windage effects. This formulation takes into account several parameters such as rotational speed, gear immersion depth, oil properties, and gear geometrical parameters.