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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.

During gear shifting, the contact between teeth composes a tribological system of considerable importance regarding energy dissipation in road vehicles. Improvement of tribological system efficiency leads to costs and pollutant emission reductions. Powder metallurgy (PM) is a near-net-shape technique that allows the production of parts with complex geometry - such as gears, lower costs and larger range of material utilization compared to other manufacturing processes. Furthermore, the presence of pores in sintered material could be a beneficial factor for friction reduction and wear resistance, due to oil reservoir and debris trapping effects, and film thickness variation that could enhance lubricant load support capacity. This work aims to evaluate the lubricant effect on support capacity due to surface pores in sintered steel with different levels of porosity. Results were compared with standard gear material based on friction coefficient results.

The differences between tribological performance of nitrided and non-nitrided samples of SAE XEV-F valve steel were investigated in dry sliding conditions. Experimental tests were conducted using an SRV-4 tribometer in a ball-on-disc configuration (i.e. non-conformal contact) with reciprocating type of movement. Two kinds of samples (discs) were tested: valve steel and nitrided valve steel. The ball (i.e. the counter-body) was made of AISI 52100 bearing steel. Room temperature and fixed conditions of time, load, frequency and stroke were used. Wear was evaluated by means of mass loss, from both disc and ball, and post examination of the worn surfaces. Post examination was conducted using scanning electron microscopy (SEM), coherence correlation interferometry (CCI), and X-Ray diffraction (XRD). Wear debris resulting from tribological interaction were also investigated using SEM and XRD.

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.