ORIGINALARBEITEN/ORIGINALS DOI 10.1007/s10010-017-0221-5 Forsch Ingenieurwes (2017) 81:207–213 Investigation on the flank surface durability of gears with increased pressure angle Christian Weber 1 · Thomas Tobie 1 · Karsten Stahl 1 Received: 10 April 2017 © Springer-Verlag GmbH Deutschland 2017 Abstract Within a funded research project (reference num- ber 0325244C, BMWi – Federal Ministry for Economic Af- fairs and Energy of Germany), the load-carrying capacity of alternative involute gears was investigated. To find qualified variations for use in gear drives, increased pressure angles (αn > 20°) and/or asymmetric tooth shapes (αn < 20° and αn > 20°) have been examined experimentally. Optimization goals were the power to weight ratio of the transmission and the power density in the drive train. In this report gears with reference tooth shape (αn = 20°) as well as gears with modified tooth shape (αn = 28°) are dis- cussed with focus on the load carrying capacity of the tooth flank with special regard to the damage mechanisms pitting, micro-pitting and scuffing. The results of experimental and test accompanying studies are shown. They allow a direct comparison between standard and special gears as well as a classification in context of the actual state of knowledge. 1 Introduction and objective Mechanical engineering uses almost exclusively symmetric involute gears with pressure angles αn  20° according to the basic rack as specified in ISO 53 [7] in today’s power transmitting gear drives. Besides the economic advantages of the manufacturing process using straight-flank hobbing tools the broad application of this toothing is due to its uniform transmission of motion. This even applies to shaft center distance deviations from the setpoint.  Christian Weber c.weber@fzg.mw.tum.de 1 Gear Research Centre (FZG), Technical University of Munich, Garching, Germany For the design of symmetric involute toothings with αn  20° comprehensive calculation tools and methods such as ISO 6336 [6] are available. These calculation methods are based on extensive theoretical and experimental stud- ies on appropriate standard gears and are well-proven for years. Nevertheless, these calculation methods do not claim to universal validity. The calculation method according to ISO 6336 [6] for example is limited to a pressure angle of αn  25° according to the basic rack specified in ISO 53 [7]. However, for a reliable application of special involute gears with an increased pressure angle in industrially run- ning transmissions a comprehensive and confirmed iden- tification and verification of the load-carrying capacities is needed for such toothings. This also requires an experimen- tal verification of existing tooth flank load-carrying capacity calculation methods. 2 Investigated failure mechanisms The herein described experimental investigations were car- ried out in order to determine the flank load carrying ca- pacity against the most common gear failures, i. e. pitting, micro-pitting, and scuffing. For all tests regarding the listed types of flank failures, selective tests have been performed. The operating conditions were adjusted to cause the desired type of flank failures, if necessary. Furthermore, investigations concerning the tooth root bending strength of gears with increased pressure angles as well as of gears with asymmetric tooth shape were done [14]. The aim of these investigations was amongst others the validation of the advanced calculation method for tooth root bending strength according to FZG/Fröh [13]. The re- sults of these investigations are no object of this paper. K