Chafing against engine friction

Friction is enemy No. 1 for powertrain engineers striving to meet rising fuel-economy standards.

"As engines get smaller, eliminating friction becomes even more important," says Dave Lancaster, a General Motors technical fellow who works at the automaker's powertrain engineering operations in suburban Detroit. "Every component in every engine is designed with all the analytical tools we have to reduce friction."

Lower friction enables engines to efficiently produce more horsepower per liter of displacement. And by re-engineering parts at modest cost, automakers can boost mileage without the massive investment of redesigning an engine. In the 2025 model year, each automaker's fleet miles per gallon must reach 54.5.

Engineers have made significant strides reducing friction. A GM four-cylinder engine from the early 1980s, called the Iron Duke, generated about 45 percent more friction than GM's current Ecotech four-cylinder -- even though the Ecotech engine has more moving parts, the automaker says.

Now, to further reduce friction, low-tech, off-the-shelf commodity parts such as piston rings, engine bearings, seals and oil pumps are evolving into premium hardware.

Suppliers are playing a big role. "Certainly there are many more areas where we can improve efficiency," says Wolfgang Rein, Mahle North America's senior vice president of r&d for engine systems and components. "Every small improvement counts when it comes to friction." Mahle is a leading piston and bearing manufacturer.

Here are five main engine components on which automakers and suppliers are working to reduce engine friction.

• What: Smaller bearing shells with special coatings. The bearing shells, installed between the crankshaft and block and on the connecting rods, have a steel backing coated with layers of copper, tin, lead, aluminum and other compounds.
• How they reduce friction: Engine designers are using smaller bearings to cut surface area. And engine oil is getting thinner and more slippery. Suppliers such as Federal-Mogul Corp. have developed special coatings that further reduce friction. Federal-Mogul's IROX coating for engine bearings, a 2013 Automotive News PACE Award winner, is a polymer coating that can reduce friction by up to 50 percent compared with older, larger bearings without coating. Coated bearings particularly help vehicles with stop-start systems, which increase wear and tear on bearings. The redesigned engine in the 2014 Chevrolet Corvette uses Federal-Mogul's IROX coating.

• What: Eliminating the balance shaft, used to cancel engine vibration
• How it reduces friction: If a Ford innovation catches on, the balance shaft could get the shaft in the coming wave of three-cylinder engines. Ford has eliminated the power-robbing balance shaft in the 1.0-liter, three-cylinder engine for the Fiesta coming this fall. To reduce vibration, Ford channels the engine's shaking forces in a different direction with patented motor mounts coupled with precisely placed weights on the engine pulley and flywheel. Ford says eliminating the balance shaft reduces engine friction by about 6 percent. Four-cylinder engines with balance shafts are now being fitted with roller bearings, which reduce friction by about 2 percent.

• What: Low-friction valvetrains. Engineers are polishing and coating tappets, the bucket-shaped part underneath the cam that activates the valves. They are also cutting tension on valve springs, using smaller camshaft chains and immersing camshaft belts in oil.
• How they reduce friction: Nissan uses a coating called Diamond-Like on valve lifters and tappets and elsewhere in the engine to reduce friction by as much as 10 percent in engines in the Altima, Juke, Sentra and others. General Motors has reduced the size of timing chains and switched to slippery chain guides on its overhead-cam engines. On pushrod engines, engineers have developed rocker arms with low-friction rollers, which activate the valves.

• What: Pistons with smaller skirts, special coatings and low-tension rings
• How they reduce friction: Pistons account for more than a quarter of the energy lost to friction in an engine, Ford Motor Co. says. Engine designers and suppliers are attacking piston friction by reducing the size of the skirt, the section below the rings, and by coating it with ceramic or polymer. Coatings enable the piston to slide easier up and down the bores. Some of the coatings used by Mahle and other piston suppliers include graphite, carbon fiber and molybdenum disulfide. Mahle's latest piston rings exert about 50 percent less pressure against the cylinder bore than rings from just a few years ago. Smoother, coated cylinder bore surfaces are also reducing piston friction.

• What: Low-friction crankshaft seals. These flexible discs fit over each end of the crankshaft and keep the oil inside the engine.
• How they reduce friction: Suppliers, including SKF Group and Freudenberg-NOK, have developed several types of low-friction seals that eliminate the spring inside the disc that squeezes the lip of the disc against the highly polished ends of the crankshaft. The SKF Low Friction Engine Seal uses sealing tips made of elastomer, a highly flexible polymer. Suppliers also make Teflon seals for use in engines in which an oil film is unneeded on the end of the crankshaft. Low-friction seals reduce friction more than 50 percent from the old-style, spring-loaded seals. Low-friction seals are being introduced with new engines. BMW has embraced the technology as part of its EfficientDynamics program and uses low-friction seals in all of its engines.