Examples of the main engine components on which vehicle manufacturers and suppliers are working to reduce friction components include the following (Truett 2013):
Smaller, low friction bearings: Smaller bearings are being designed to reduce surface area. Special coatings, such as Federal-Mogul’s IROX polymer coating, have been applied to engine bearings for 2014 model year engines and these coatings can reduce friction by up to 50% compared with older, larger bearings without coatings. Coated bearings particularly help in stop-start systems, which increase wear on bearings.
Pistons: Pistons account for more than a quarter of the energy lost to friction in an engine. Piston friction is being reduced by reducing the size of the skirt and coating it with ceramic or polymer (other examples include graphite, carbon fiber, and molybdenum disulfide). Low tension piston rings currently exert about 50 percent less pressure against the bore than rings from a few years ago. Smoother, coated cylinder bore surfaces also reduce piston friction.
Valve train: Coatings, such as “Diamond-Like” on valve lifters and tappets and other engine components have been shown by Nissan to reduce friction by as much as 10 percent. Timing chains have been reduced in size and slippery guides have been applied to reduce valve train friction. Rocker arms with low friction rollers are being applied.
Seals: Low friction crankshaft seals have been developed that eliminate the spring inside the disc that squeezes the lip of the disc against the crankshaft and provide more than 50 percent reduction in friction.
Balance shaft: Ford has eliminated the balance shaft in their three-cylinder 1.0L engine by placing balance weights on the engine pulley and flywheel and using patented motor mounts. Eliminating the balance shaft reduced friction by 6 percent. Four-cylinder engines with balance shafts are being fitted with roller bearings, which reduce friction by about 2 percent.
ESTIMATION OF EFFECTIVENESS OF FUEL CONSUMPTION REDUCTION TECHNOLOGIES
Low Friction Lubricants—Level 1 (LUB1)
The effectiveness of low friction lubricants was estimated as follows. Approximately 75 percent of the friction loss is due to piston, crank, and rotating components, with approximately half of this loss due to hydrodynamic lubrication (Heywood 1988). Power loss in hydrodynamic lubrication is proportional to the lubricant viscosity. The viscosity at 100°C is reduced by approximately 25 percent by replacing the 5W-30 oil with 5W-20 oil, as indicated in Table 2.3. This viscosity reduction would be effective after the oil had fully warmed up, which is approximately a quarter of the EPA urban cycle and highway drive cycles.
Total engine friction consumes approximately 8 percent of the fuel energy. Hydrodynamic lubrication consumes half of the 75 percent of the friction loss.
8% fuel energy × 0.75 × 0.5 = 3% fuel energy consumed by hydrodynamic lubrication
A 25 percent reduction in oil viscosity, which would be effective over a quarter of the drive cycles, would result in the following reduction in engine friction:
3% fuel energy consumed by hydrodynamic lubrication × 0.25 × 0.25 = 0.19% fuel energy
The 0.19 percent reduction in fuel energy due to friction represents approximately a 2.5 percent reduction in overall engine friction (0.19 percent fuel energy/8 percent total fuel energy due to friction × 100), which would result in a 0.5 percent reduction in fuel consumption, obtained by applying 36 percent ITE.
0.19% fuel energy reduction/0.36 indicated work/fuel = 0.5% increase in indicated work
The 0.5 percent reduction in fuel consumption is within the range of EPA/NHTSA estimates in the final CAFE rule.
Low Friction Lubricants—Level 2 (LUB2)
The low friction lubricants identified for level 2 consist of 0W-20, 0W-16 or 0W-12 oils instead of 5W-20 oils. This change results in two changes. First, changing to the 0W classification reduces low temperature viscosity, as shown in Table 2.3. With an estimated 12 percent reduction in low temperature viscosity, extrapolated from Table 2.3, and assuming that this reduction would be effective over half of the drive cycles in which the oil is not fully warmed up, applying similar calculations used for level 1 for the energy consumed by hydrodynamic lubrication, above, yields a 0.5 percent reduction in fuel consumption, as follows:
3% fuel energy consumed by hydrodynamic lubrication × .12 × 0.5 = 0.18% fuel energy
0.18% fuel energy reduction/0.36 indicated work/fuel = 0.5% increase in indicated work
The second change is the reduction in oil viscosity measured at 100°C. By changing from 5W-20 to 0W12, viscosity would be reduced by an estimated 25 percent. The calculation for level 1 indicates that this reduction in viscosity could provide a 0.5 percent reduction in fuel consumption.
Combining the 0.5 percent reduction for low temperature viscosity reduction with the 0.5 percent reduction for 100°C viscosity reduction provides an overall estimate of 1.0 percent reduction for low friction lubricants - level 2.
Heywood, J.B. 1988. Internal Combustion Engine Fundamentals. New York: McGraw-Hill.
Truett, R. 2013. Chafing against engine friction. Automotive News, May 20.