Low-loss gears for precision planetary gearboxes: Influence of the gear design on the meshing and the churning power losses
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In the field of automation, extremely accurate gearboxes are mandatory in order to ensure the adequate precision required by the automatic processes. For these kinds of applications, planetary gearboxes represent one of the most attractive solutions. This type of gear set ensures at the same time high power density and high reduction ratios. The low backlash required in the field of automation is obtained by changing the chordal thickness of the teeth. This has the main disadvantage to increase the power dissipation and causing limitation due to excessive temperature. In order to overcome this problem new gear designs have been studied by means of analytical and numerical approaches by Bonfiglioli Mechatronic Research S.p.A.. The efficiency increase is based on an extreme reduction of the module of the gears. This change, together with other modifications of the tooth form (pressure angle, profile shift, etc.), allows to reduce the relative sliding between the tooth flanks and therefore the power dissipation. CFD simulations have shown that the sliding optimized design has a positive impact also on the churning power losses. The global winning in terms of the reduction of the gear meshing power losses can be assumed with about 50%, depending on the reduction ratio. Besides an energy saving, the modifications imply a reduction of the operating temperature which allows higher performances without reaching excessive temperatures. The new design has been validated by means of experimental tests performed in the internal laboratory of the Bonfiglioli Mechatronic Research S.p.A. (BMR). The results have fully validated both the CAE approach and the new design. Introduction The increasing demand on more efficient and productive solutions represents a big challenge for the gear manufacturers. In many application fields one of the most attractive solutions is the planetary gearing. This configuration provides high power density as well as high reduction ratios. The disadvantage is the thermal power limit of the gearbox. This characteristic is enforced by the requirement of low backlash. For this reason a new and more efficient solution that is able to improve the overheating problem was studied by BMR (Bonfiglioli Mechatronic Research S.p.A.) for its low-backlash gearboxes for mechatronic applications. The operating temperature reduction was achieved not by increasing the heat exchange with the surrounding environment but by reducing the power dissipation of the gearbox itself.
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