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MTM (Mini Traction Machine)
/ Applications
Fuel Economy Modeling of Automotive Engine Oils
In an automotive engine, approximately 12% of fuel is used in overcoming friction between sliding components. The lubricant regimes range between hydrodynamic in the main bearings, ehl and mixed lubrication in the valve train, timing gears and rolling element bearings and boundary lubrication between piston rings and liners. By choosing suitable specimens and operating parameters it is possible to simulate each of these regimes with the MTM system and therefore model and predict the frictional losses in the engine.
When studying ehl, mixed and boundary regimes the traction (friction) data can be displayed as traction v slide/roll ratio and traction v rolling speed (Stribeck curves) as shown.
Traction Results using fully formulated synthetic oil at 2000mm/s
Stribeck results using fully formulated synthetic oil at 50% SSR
To evaluate performance in the ehl, mixed and boundary regime, a selection of eight fully formulated synthetic oils from different manufacturers and one regular multigrade mineral oil have been tested for their traction coefficients over a range of temperatures, rolling speeds and slide / roll ratios.
Some of this data is shown as Stribeck curves at two temperatures, 60°C and 125°C. A greater weighting has been applied to the traction coefficients in the important low speed mixed regime by plotting the traction coefficient against the log of the rolling speed.
Comparison of automotive lubricants at 60°C
Comparison of automotive lubricants at 125 °C
A comparison of the performance of each oil can be made by integrating the area under each Stribeck curve. The value of this integral, TC.log(u), is known as the Stribeck Friction Coefficient (SFC). Lower values of SFC indicate that less energy will be absorbed by the lubricant under mixed and ehl regimes. Lower values would therefore be expected to correlate with better performance in fuel economy engine tests. The values for each oil are plotted below. The coefficient of the best oil is 33% less than the poorest, both are synthetics!.
Comparisons of SFC at low and high temperatures
