Investigation of the Energy Losses Generated by the Oil Churning, the Bearing and the Tooth Friction in Planetary Gear Drives

摘要

In some applications it is necessary to use transmission systems having high gear ratio, which can be solved by using planetary gears. There are simple planetary gear constructions which are able to result high gear ratio, for example the Wolfrom type planetary gear drive (KB+B). However, the power flow in the Wolfrom gear drive is unbeneficial at high gear ratio, because much higher rolling power circulate between in the planetary gear than the input power increasing the friction loss and decreasing the efficiency. During design of a planetary gear having high gear ratio and useless inner power circulation it is necessary to find a compromise between the complexity of the construction and the allowable friction losses. The efficiency of a planetary gear depends on many factors, first of all on the construction of the planetary gear drive determining the power flow and on the tooth- and bearing friction losses. In practice the tooth friction loss of mating gears are taken into consideration mainly by using the known formulas of the tooth efficiency. The friction loss of bearings can be determined by the methods suggested by the bearing manufacturers. Beside these two main constituents of friction also the oil churning losses have to be taken into consideration. We developed a model for calculation of the oil churning loss containing the loss of oil expel, the loss of splashing and the disc churning loss. This article shows the equations derived by us to calculate these components of power losses. Using our method the oil churning loss, the bearing friction loss and the tooth friction loss of Wolfrom type (KB+B) planetary gears having high gear ratios were calculated and the influence of these types of power losses on the efficiency of the planetary gears were evaluated.