A model is presented which makes it possible to predict power losses in a six-speed manual gearbox. The following sources of dissipation, i.e., power inputs in the model, are considered: (i) tooth friction; (ii) rolling element bearings; (iii) oil shearing in the synchronizers and at the shaft-free pinion interfaces; and (iv) oil churning. Based upon the first principle of Thermodynamics for transient conditions, the entire gearbox is divided into lumped elements with a uniform temperature connected by thermal resistances which account for conduction, convection, and radiation. The numerical predictions compare favorably with the efficiency measurements from the actual gearbox at different speeds and torques. The results also reveal that, at lower temperatures (about 40°C), power loss estimations cannot be disassociated from the accurate prediction of temperature distributions.

A series of formulas are presented which enable accurate predictions of churning losses for one pinion characteristic of automotive transmission geometry. The results are based on dimensional analysis and have been experimentally validated over a wide range of speeds, gear geometries, lubricants, and immersion depths. The case of a pinion-gear pair in mesh has been considered, and it has been proved that, depending on the sense of rotation, the superposition of the individual losses of the pinion and of the gear leads to erroneous figures. A new formula devoted to a pinion and gear rotating anticlockwise has been derived and validated by comparison with experimental evidence.

Power losses in high-speed gears come from the friction between the teeth (sliding and rolling), the lubrication process (dip or jet lubrication), the pumping of a gas-lubricant mixture during the meshing and the losses associated with windage effects. The objective of this paper is to present a number of preliminary experimental and theoretical findings on the prediction of windage losses. Experiments were conducted on a test bench whose principle consists in driving a gear to a given speed and then measuring its deceleration once it has been disconnected from the motor. Results are presented for a disk and 4 different gears with no enclosure and in the absence of lubricant at speeds ranging from 0 to 12, 000 rpm. Two different theoretical approaches have been developed: i) a dimensional analysis based upon the dimensionless groups of terms which account for the flow characteristics (Reynolds number), the gear geometry (tooth number, pitch diameter, face width) and the speed, ii) a quasi-analytical model considering in detail the fluid flow on the gear faces and inside the teeth. It is found that both approaches give good results in comparison with the experimental evidence and two analytical formulas aimed at predicting windage losses in high-speed gears are proposed.

Temperature levels and distributions in rolling element bearings (REBs) depend on many parameters such as load, rotational speed, lubricant, etc. In this context, the understanding of power loss and heat generation mechanisms is a major issue especially for REBs operating at high speeds, since they largely control the component behaviour, its capacity to operate at high temperatures, and ultimately its integrity. It is commonly accepted that the power losses in high-speed bearings can be divided into (a) sliding friction losses in the contacts between the rolling elements and races, (b) sliding friction losses (Couette flow) at the cage/race and cage/rolling elements contacts, (c) oil churning losses for splash and dip lubrication. However, there is no general agreement about two other sources namely rolling friction and drag forces, but it seems that whatever the chosen model be the resulting total power losses are equivalent. In the present study, a thermal network approach is presented in order to estimate the temperatures at different locations within a thrust angular ball bearing. Several power loss distributions inside the REBs are considered and their influences on different power losses and on temperatures along with the important role of the oil—air mixture are highlighted.