Modeling and Contact Stress Analysis of Crossed-Axes Helical Gear System

Crossed helical gears are susceptible to pitting damage resulting from contact stress, primarily due to the theoretical point contact between the gears. The contact point transforms into an ellipse due to the deformation of the elastic material under varying loading conditions. The overheating between the tooth profiles during the engagement process contributes to the proliferation of pits, deteriorating the tooth surface and causing premature tooth failure. This study investigates the influence of two modifications: the tip relief design, and the compound profile design, which combines involute and epicycloid profiles. A shaping process generates both standard and modified helical gears. The results indicate that increasing the amount of misalignment with a smaller harmonic waveform reduces the transmission error. The involute-epicycloid profile reduces the sliding velocity with the most significant improvement of approximately 16%. A decrease in the angle of pressure and an increase in the helix angle of 1.5 and 1.7, respectively, enhance the total contact ratio. The maximum contact stress observed for the modified involute-epicycloid surface decreased by 6%, 6%, and 2%, while the tooth root stress reduced by 6%, 8%, and 12% for the three positions, respectively. Meanwhile, the maximum contact stress for tip relief modification decreased by 2%, 6%, and -6%, whereas the tooth root stress reduced by 2%, 7%, and -1% for the three positions, respectively. Consequently, the modified crossed helical gear drive demonstrates superior performance compared to the standard gear drive for a given helix angle. Furthermore, the stress concentration factor decreased through the use of the modified helical teeth by about 2% and 6%.