Investigations on Oil Flow Rates Projected on the Casing Walls by Splashed Lubricated Gears

In order to investigate the oil projected by gears rotating in an oil bath, a test rig has been set up in which the quantity of lubricant splashed at several locations on the casing walls can be measured. An oblong-shaped window of variable size is connected to a tank for flow measurements, and the system can be placed at several locations. A series of formulae have been deduced using dimensional analysis which can predict the lubricant flow rate generated by one spur gear or one disk at various places on the casing. These results have been experimentally validated over a wide range of operating conditions (rotational speed, geometry, immersion depth, etc.). 1. Introduction Splash lubrication is traditionally used in low- to medium-speed enclosed gears such as automotive gearboxes in which the lubricant is projected by the rotation of the gears. The main disadvantages are (i) the generation of significant power losses by churning and (ii) the absence of precise control in terms of lubricant supply. Based on a number of studies [1–10], there is general agreement on the fact that losses increase with rotational speed and immersion depth. Although lubricant churning can be considered as a major source of power loss in gearboxes, splash lubrication also contributes to the regulation of gear bulk temperature since some heat is removed from the tooth faces by centrifugal fling-off as demonstrated by Blok [11]. Using a general thermal model of an automotive manual gearbox, Changenet et al. [12] have confirmed the influence of the heat exchanges between the oil sump and several rotating elements on the global thermal behaviour and emphasized, in particular, the role of the immersion depth. H？hn et al. [13] have conducted a number of experiments showing that lowering the oil level in the sump reduces churning losses but also leads to higher gear bulk temperatures. These results have been theoretically confirmed by Durand de Gevigney et al. [14]. From the above-mentioned studies, it seems possible to define an optimal lubricant level in the sump in order to reduce churning losses and, from a thermal viewpoint, ensure satisfactory gear-lubricant heat exchanges. However, as far as the authors know, the influence of the oil level on the lubricant circulation and flow has received scant attention in the open literature despite the practical importance of ensuring sufficient lubrication and cooling of sensitive elements such as bearings. Because of its intrinsically chaotic nature, splash lubrication properties are hardly predictable and a lot of the development for