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Friction losses in complex tribo-technical system are revealed primarily through their effect on the operating temperature level. In order to assess the influence of the oil formulation on the temperature level comprehensive tests were run in a model test apparatus consisting of a special adapter for the 4-ball test rig. More than ten with different formulations (different base oils, additive packages and viscosity modifiers) were tested. The resulting temperature levels varied by nearly 25 %. The objective of this model testing is to assess the influence of the oil formulation on the operating temperature of vehicle manual transmission. The correlation to the real tribotechnical system was confirmed by a VW Polo transmission test.

Decreasing viscosity for improving the fuel economy by reducing the mechanical friction under hydrodynamic conditions simultaneously will cause increased areas of mixed film lubrication regimes. As a consequence, higher wear has to be taken into account. Therefore, a balance between improved fuel economy on one side and increasing wear by lower viscosities on the other side has to be established. Based on an efficiency analysis of automobil gears and engines the influence of the mechanical efficiencies on the fuel economy will be estimated. In doing so, influences of viscosity, of viscosity index, of temperature and shear rate on viscosity will be analyzed regarding their effect on fuel economy.

In order to meet the viscosity requirements of multigrade engine oils, mineral and synthetic base oils of various viscosities and viscosity index improvers having various chemical compositions are used. As a consequence of both the viscosity-temperature behaviour of different base oils and the unique thickening effect of a given type of VI improver, the high- and low-temperature viscosity characteristics of a formulated oil are a function of the base-oil/VI-improver combination. The viscosity characteristics can be more or less optimized to meet the desired viscosity requirements. To provide acceptable rheological behaviour in practical formulations, it may be necessary to accept low-temperature performance that is less than optimum in order to achieve greater shear stability at a lower VI improver concentration.

Experimental investigations of stationary and instationary bearings - Measuring temperature distribution in the bearing, oil pressure distribution within the bearing gap, and bearing eccentricity and friction-Calculating shear rate distribution and mean shear rate using eccentricity and speed-Determining viscosity distribution using temperature, pressure, and shear rate - Calculating the effective viscosity and investigating its effects on bearing performance Using Newtonian and non-Newtonian oils having the same as well different properties regarding viscosity-temperature, pressure and shear rate behaviour.

Up to the present, the “W” portion of multigrade engine oils were classified only with regard to their low temperature startability by viscosity measurements at -18 C in the Cold Cranking Simulator. Because of the low shear rates encountered at the suction side of the oil pumps, the low temperature pumpability of the oils in the engine were not being considered. The investigations which were promoted by the DGMK were conducted to correlate the low-temperature pumpability of multigrade oils in a full-scale engine with suitable viscosity measurements and with results of tests in laboratory pumping rigs. Comparative measurements of viscosities were obtained with different viscometers. A critical shear rate of G = 50 s-1 was found for the borderline pumping conditions of the test engine. Good correlations were obtained between viscosity data of a rotational viscometer and engine pumping data.