Measurement of contact pattern displacement of hypoid gears with optical thermal camera

When optimizing the micro geometry in the development process of a gear set, the deflection behavior under load situations is important to predict the realistic component life span and acoustic behavior. Most common experimental deflection tests are extraordinarily complex and need special preparation of the whole drive unit to be able to measure the deflection precisely. On the other hand, purely simulation approaches need to be validated because the models are getting extensive through many boundary conditions between the different components of the drive unit. To address these challenges, this paper presents a method for measuring the deflection of hypoid gear sets by an evaluation of thermographic contact pattern. This method is based on measuring the contact pattern via a thermographic camera and transferring the optical information of the images into objective parameters to describe the properties of the contact pattern such as position, size and inner temperature. Through experimental study the influence of different load and rotation speed combination on the contact pattern are investigated. With increasing load, the size and the inner temperature of the contact pattern rise and a deflection to the heel is detected for drive and coast flank. Using a linear approach, the load and contact pattern parameters are showing a high correlation (R2 > 0.9) coefficient. Although a higher rotational speed did not show any influence on the positioning of the contact pattern, an increased temperature leads to an enlargement contact pattern size. This is considered as disruptive effect which can be compensated by optimizing segmentation threshold in the image processing. As part of the publication, the experimental results are compared to a loaded tooth contact analysis (LTCA) conducted with the software BECAL. After optimizing the deflection for LTCA, the results in the different loading points are showing a high agreement in a direct comparison.