Abstract
Traditional procedures to calculate efficiency on gear transmissions generally consider sliding friction as the only dissipative effect, and what is more, they are based on the usage of constant friction coefficients. Although this approach gives acceptable efficiency values depending on the transmission application, the utilisation of a variable friction coefficient provides more reliable results of the friction behavior. Within this framework, the influence of the choice of the friction coefficient on the efficiency of shifted spur gears is assessed in this study. The Niemann’s friction coefficient formulation, which is constant and commonly applied to traditional approaches, was implemented in this proposal, in order to compare it with two hybrid formulations, which are based on elastohydrodynamic lubrication fundamentals and capable to reproduce the friction coefficient in dry contact, boundary, mixed and fluid film conditions of lubrication. These friction coefficient formulations are dependent on the load applied in the conjunction, therefore an enhanced load sharing allows for a better modelling of sliding friction, not only because it depends directly on the normal forces, but due to the friction coefficient load dependence. In this regard, the Load Contact Model previously developed by the authors, which considers the deflections of the adjacent teeth and shifting profile to calculate the load sharing and the friction coefficient, is used, allowing for efficiency values with a high level of accuracy. The efficiency results obtained when hybrid formulations are implemented provides lower values than those determined including Niemann’s formulation. Furthermore, there is a shifting profile which makes optimal the efficiency. This shift factor depends on the implemented friction coefficient formulation, concluding the remarkable importance of the friction coefficient choice.
Highlights
Energy saving has been one of the major concerns in Industry for the last decades, since a cost reduction has been always pursued
With these two accurate formulations, the dissimilarities with the acceptable Niemann friction coefficient related to efficiency and friction coefficient values can be established. It is inferred the importance of utilising accurate formulations of the contact forces and friction coefficients along the mesh cycle to determine the efficiency. This is the reason why, in this work, the efficiency results implementing the Niemann′s Friction Coefficient (F C), which were presented in previous works [10], are used as reference to show the benefits of employing an advanced friction coefficient formulation, correlating in this manner the obtained friction and efficiency results with ISO/TC 60 standard [10]
An efficiency assessment of shifted gear transmissions was performed in each shifting case study, using the Load Contact Model (LCM) and three F C specified in the previous sections
Summary
This is the reason why, in this work, the efficiency results implementing the Niemann′s F C, which were presented in previous works [10], are used as reference to show the benefits of employing an advanced friction coefficient formulation, correlating in this manner the obtained friction and efficiency results with ISO/TC 60 standard [10] Another aspect assessed in this work is the profile shifting, which is widely employed in several sectors of the Industry to balance the durability of gear transmissions with a gear ratio different from the unity.
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