Predicted scuffing Risk to spur and Helical Gears in Commercial Vehicle Transmissions

(Printed with permission of the copyright holder, the American Gear Manufacturers Association, 1001 N. Fairfax Street, Fifth Floor, Alexandria, VA 22314-1587. Statements presented in this paper are those of the author(s) and may not represent the position or opinion of the American Gear Manufacturers Association.) introduction The risk of gear tooth scuffing in commercial vehicle transmissions has gained more attention because of increasing demand for fuel-efficient powertrain systems in which diesel engines run at lower speeds, power density is higher, and lubricants are modified to improve efficiency and compatibility with components of new technologies, such as dual-clutch transmissions. Accordingly, predicting scuffing risk during the design phase is vital for the successful development of commercial vehicle transmissions. AGMA 925–A03 (Ref. 1) is a comprehensive method for predicting the probability of gear scuffing. This paper presents the AGMA 925–A03 (Ref. 1) scuffing risk predictions for 50 spur and helical gear sets in transmissions used in commercial vehicles ranging from SAE Class 3 through Class 8. Limiting scuffing temperatures using two mineral and three synthetic gear lubricants was determined from FZG scuffing tests. The risk of scuffing was determined for each gear set according to AGMA 925–03 (Ref. 1). The predictions were compared with field and warranty data, and dynamometer test results. The predictor was correct in all cases. High scuffing risk was predicted for gears known to scuff, and low scuffing risk was predicted for all other cases with no history of scuffing. The document correlation between prediction, test results and actual usage instills confidence in the predictor of scuffing risk for gears in commercial vehicle transmissions.