Determining the load distribution by measuring the tooth root stresses

A main goal in the design of modern gearboxes is to achieve an equal load distribution within the gear meshes for a certain nominal load. A measurement of the tooth root stress with strain gauges along the face width allows evaluating the occurring load distribution. In case of a gear mesh consisting of spur gears, the measurement of equal strain along the face width is sufficient to document equal load distribution. For helical gears, the transverse operating contact line leads to an unequal strain distribution in the tooth root, even for equal load distribution over the face width. Besides, the exact position of the measurement units at the tooth root profile is influencing the measurement noticeable. For many applications, e.g. the gearboxes in wind energy plants, an exact measurement of the load distribution is necessary before the gearboxes may enter the market. Therefore, a very precise method to determine the load distribution would be a very useful tool to fulfill these requirements. This paper shows a method to determine the load distribution of spur and helical gear stages based on the tooth root strain along the face width. Furthermore, the exact location of the local strain is taken into account for the determination of the load distribution. Another focus is the exact mesh condition especially for helical gear stages.