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A thermo-mechanical model of a splash lubricated one-stage gear unit is presented. This system corresponds to a first step towards the design of a hybrid vehicle gearbox which can operate up to 40,000 rpm on its primary shaft. The numerical model is based on the thermal network method and takes into account power losses due to tooth friction, rolling elements bearings and oil churning. Some calculations underline that oil churning causes a high amount of power loss. A simple method to reduce this source of power losses is presented, and its influence on the gear unit efficiency and its thermal capacity is quantified.

In Rolling Contact Fatigue (RCF), understanding initiation and propagation failure mechanisms remains a challenge. A cohesive Finite Element model has been developed to investigate microstructure role on initiation mechanisms. The approach consists in modelling the Grain Boundary (GB) progressive damage (from initial undamaged state to failure). In this paper, numerical singularities at triple junctions are highlighted and cohesive stiffness values (for undamaged and fully damaged GB) are defined. Preliminary results underscore the influence of damage application: a linear relation between cohesive stiffness and damage is not suitable to simulate progressive damage.

This paper presents an original method to investigate the power losses distribution into a planetary gear unit. A thermal model, which allows the estimation of power losses linked to the temperature distribution, is established. This model is used to analyse some experimental results obtained on a specific test rig. For the planetary gear set studied here, it is demonstrated that load-independent power losses are mainly due to hydrodynamic power losses generated in planets bearings and that gears windage effects are negligible.