Application of similarity theory to load capacity of gearboxes

This study suggests the theoretical methodology to construct a small-sized similarity model having the same load capacity as a large gearbox. The prototype gearbox was a 2-MW wind turbine gearbox consisting of two planetary gear stages and one parallel shaft gear stage, and the specifications of its 1/4 scale similarity model were determined by applying similarity theory. The constructed similarity model was validated by comparing load capacity parameters with those of the prototype gearbox using analysis tool. The validation results showed that the nominal tooth root and contact stresses of the similarity model and prototype gearbox were identical, whereas the tooth root and contact stresses satisfied the similarity condition within 2% difference. Furthermore, most factors that influenced the tooth root and pitting stress limits were identical. Thus, information related to load capacity, one of the major design evaluation criteria for gears, of large-size gearbox can be replicated by its similarity model. Although this is a theoretical methodology and still has many difficulties to apply to practical situations, these results have opened up the possibility of applying similarity theory to load capacity of gearboxes. Because the load capacity is the primary cause of commercial gearbox failure, this result also shows the possibility of life similarity in the gearbox application, although some further study is needed.