Gear oil influences on efficiency of gear and fuel economy of cars

Abstract

1. First of all, it should be considered that the fuel consumption of a car depends on a set of parameters only partly related to tribology. Their influence is much more pronounced than that of the lubricant. 2. Only the mechanical losses can be decreased by lubricant-related measures. Therefore, the fuel economy improvement that possibly might be realized is rather limited, especially when taking into account the rather high efficiency of gears. 3. When evaluating the influence of viscosity on fuel consumption, the so-called effective viscosity must be taken into account. This is most important for non-Newtonian oils. 4. Reducing the gear oil viscosity by one SAE viscosity grade will result in fuel consumption reductions of 0.2-1.5 per cent at high temperatures and 0.4-2.5 per cent at low temperatures. 5. Using friction modifiers in gear oils, fuel consumption reductions of between 1.0 and 6.0 per cent are realistic. 6. On the basis of a 50 per cent friction reduction maximum fuel consumption reductions between 1.0 and 5.1 per cent by other gear oils are possible, considering different driving programmes. 7. Tests with a real automobile gear resulted in fuel economy improvements of the order of magnitudes of 1 per cent by other gear oils. 8. The results of measurements confirm in principle the calculated estimations.