DETERMINATION OF SLIDING FRICTION LOSSES IN A GEAR PAIR
Keywords:sliding friction, empirical and analytical modeling, friction coefficient, work of friction forces, two-pair engagement, single-pair engagement, losses coefficient
Increasing the performance of gear drives of machines is an urgent task, so to estimate the total losses in engagement, it is worth considering all components of losses. To solve this problem, the article proposes a method for determining the sliding friction losses in a gear pair. At present, the effect of sliding in the tooth's direction contact line on the friction coefficient and lubrication conditions has not been studied sufficiently. There are two groups of semi-analytical models in the published works. The first group of authors studied the efficiency of spur gears, assuming that the friction coefficient is constant along the entire contact surface of the friction surfaces in any position of the gears during their rotation. The second group of semi-analytical models can be considered as an improvement of the models of the first group with a constant friction coefficient. The accuracy of the empirical formulas used in them limited the accuracy of the description using these models. These empirical formulas are not general and are often a function of certain types of lubricant, available temperatures, speed and load limits, and surface fineness of the test specimens. The coefficient of sliding friction depends on the speed of the mating teeth and the properties of the lubricant; it can also consider such factors as the values of the normal load, the roughness of the tooth surfaces, and the radii of curvature of the tooth profiles. The dependencies have been got to determine the work consumed by friction along the entire meshing line, considering the friction coefficients in the tooth pair for single and double meshing. In this case, the friction coefficient in the gear transmission can be variable by the speed of the mating surfaces, but is the same for two-pair and single-pair meshing. Analytical dependencies have been obtained that make it possible to calculate power losses because of sliding friction depending on kinematic, force, and strength factors, properties of lubricants and gear materials.
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