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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.

Carbon-based coatings are used in several industrial applications, usually to promote improved wear and friction behaviors. In this work, two carbons based coatings are analyzed: a non-doped amorphous Diamond Like Carbon (DLC), produced by a Plasma-Enhanced Chemical Vapor Deposition (PECVD) process, and a Tungsten doped DLC (W-DLC), produced by a Physical Vapor Deposition (PVD) process. Mechanical properties (hardness and modulus of elasticity) are measured by nanoindentation technique using the Hysitron TI950 triboindenter, while the tribological aspects of the coatings (wear behavior and coefficient of friction) are evaluated by reciprocating motion tests on an Optimol SRV v4 tribometer. The DLC presented higher indentation hardness and modulus of elasticity when compared to the W-DLC. Results also indicate that the DLC shows lower coefficient of friction and higher critical loads to present coating delamination when compared with W-DLC.