Abstract
Three main concerns are in the focus of the development of geared transmissions nowadays: load carrying capacity, noise–vibration–harshness (NVH) behavior, and efficiency. Increasing the efficiency of modern gearboxes contributes significantly to the reduction of energy consumption and the saving of resources. Gearboxes are frequently designed conservatively with an oversupply of oil to guarantee operational reliability. An oversupply of oil results in an unnecessarily high amount of oil kept in motion and to high no-load losses. Detailed information on the oil distribution in the early design stages of gearboxes would help to optimize the lubrication and to increase the efficiency. Thereby, CFD (computational fluid dynamics) methods offer a very flexible way to visualize the oil flow inside gearboxes with much fewer restrictions compared to measurements with transparent gearbox designs. In this study, a verified CFD model based on the finite volume method is used to investigate the oil flow in a single-stage gearbox. Different oil viscosities and circumferential speeds are considered. The investigations focus on the oil flow. The gear churning loss, as part of the no-load loss, is additionally considered. Experimental validation is obtained by high-speed camera recordings and measurements at the FZG no-load power loss test rig. The results show very strong agreement between simulation and measurement. The results show that CFD simulations can visualize the oil flow behavior with a very high degree of detail.
Highlights
Improving the efficiency of geared transmissions is one of the most significant goals in the development of current drive systems
Liu et al [20] applied a CFD simulation model based on the smooth particle hydrodynamics (SPH) method to investigate the oil flow and the churning power loss of a single-stage dip-lubricated gearbox
On the other hand, the churning losses cannot be resolved from measurements at the low circumferential speeds, the higher circumferential speeds are selected for additional comparison of measured churning losses with CFD simulation results
Summary
Improving the efficiency of geared transmissions is one of the most significant goals in the development of current drive systems. The no-load losses of dip-lubricated gears can be categorized based on their mechanism of formation into churning, squeezing and windage (Mauz [2]): PLG0 = PLG0,C + PLG0,S + PLG0,W (1). The loss caused by gears dipping and circulating in the oil sump is identified as churning loss. The squeezing loss PLG0,S originates from the oil squeezed out of the tooth gaps at the gear meshing zone. One part is caused by the displacement of the oil film on the tooth flank in the rolling direction and the second part by the axial squeezing of excessive oil out of the tooth gap. Figure churning, squeezing andand windage loss in a dip-lubricated gearbox based. Figure 11exemplifies exemplifiesthe the churning, squeezing windage loss in a dip-lubricated gearbox on CFD simulation results obtained by the model of.
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