Effect of helical tooth geometry on gear efficiency using numerical analyses in lubricated contact

The gearbox is the main component for adjustment of speed and torque in automotive powertrain systems. In this work, numerical simulations were conducted to analyze the effect of the gear tooth geometry on the slide-to-roll ratio (SRR) and friction coefficient along the gear engagement, as well as on the overall transmission efficiency. Simulations were carried out using the AVL Excite Power Unit software. Elastohydrodynamic theory was applied to model the lubricated contact conditions. This model considers lubricant viscosity and the entraining velocity, curvature and roughness of the contacting surfaces. The simulated system is based on a manual transmission model coupled to a differential and a rigid wheel driver, which imposes rotation and torque profiles to the gears. The radius of curvature of tooth profile and angular velocity of the gear were varied, while maintaining the same characteristics of the lubricating oil. Results indicate a correlation between the increase in the output torque (efficiency) and the reduction of SRR for different tooth profiles investigated. Furthermore, the simulations allowed the evaluation of the friction coefficient and lubrication regimes along the gearing cycle.