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Scuffing Resistance of Vehicle Transmission Gears Collenberg
In many transmission types, the lubricant fulfills other functions apart from lubricating the gearing, for example in friction elements (synchronizer unit, clutch) in vehicle transmissions, or as a hydraulic fluid (torque converter, retarder, steering system). The modern trends are now high contact ratio gearing as well as the use of low viscosity lubricants to reduce churning losses. Therefore, at the gear design and lubricant additive stages, compromises are now necessary which require the most precise information possible on scuffing resistance of the gearing and lubricant. It will be demonstrated that the normal test procedures for determining scuffing resistance are not suitable for lubricant classification for vehicle transmissions (GL 4 and GL 5). By reducing the tooth width as well as doubling the speed, the scuffing test to DIN 51354 standards was increased in severity to such an extent, that the parameters necessary for transmission dimensioning could be determined for even higher scuffing resistant oils. The oil data necessary for sufficient scuffing resistance will be shown for different transmission design types. Within the scope of lifetime oil fills, attention should be paid to oil aging processes. The profile and tooth trace of gears on modern transmissions are nowadays corrected, almost without exception, to compensate for load-related deformation and production discrepancies. In the current calculation procedures these corrections, which tend to increase scuffing resistance, are not considered to an adequate extent. A process is being presented, in which scuffing resistance is calculated for every point on the tooth flank, based on the “flash temperature method”, and taking all variations and corrections into account. It will be demonstrated with practical examples, that, as early as the design stage, this method can be used to detect flank areas at risk, and to eliminate them with a specific correction design.
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