Improved ring pack lowers fuel consumption and CO2 emissions

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Stuttgart, September 2011—MAHLE has once again substantially reduced friction loss in the engine with optimized piston rings while improving ring properties. The fruit of these efforts is a reduction in fuel consumption by one to two percent—just from the piston rings!

The piston rings—perhaps unimpressive components at first glance—take on several important tasks in the engine.

The compression ring is the uppermost, and thus closest to the combustion chamber; it seals off the combustion chamber and bears the gas pressure during the combustion cycle. The second ring, located in the middle, mainly dissipates heat. The oil control ring—as the name suggests—scrapes off the oil to keep oil consumption in the engine as low as possible, while ensuring that some lubricating film remains on the cylinder wall. It is also known as the third ring, and is the lowest of the piston rings.

When the three piston rings are optimized with respect to the least possible friction against the cylinder wall, this helps reduce fuel consumption. There are three ways to optimize: first by reducing ring stress, second by reducing the ring axial width, and third by means of materials and surfaces with a lower friction coefficient. MAHLE has continuously developed these three aspects for many years, achieving efficiency gains in all areas.

Ring stress is the load that the ring exerts against the cylinder wall to seal it off and scrape off the oil. It has a significant effect on the total friction in the engine. The latest downsizing gasoline engines have a total ring stress of about 0.6 to 0.7 Newtons per millimeter. MAHLE has now developed a new, two-piece "x-taper" oil control ring, which improves scraping with directional contact surfaces. This reduces the load on the scraper ring by about half. Altogether, this reduces the total stress on the ring pack by up to 0.25 Newtons per millimeter. The oil control ring nevertheless retains its excellent scraping performance, as the contact pressure remains unchanged.

The engineers at MAHLE also reduced friction by improving the running face profiles of the other rings. The third way to reduce friction is a chromium nitride PVD coating, now on the oil control ring as well, which also increases the service life of the ring. PVD (Physical Vapor Deposition) is a vacuum coating process, whereby a gaseous material is brought into contact with the substrate to be coated, where it condenses and forms the intended coating.

MAHLE has already tested piston ring packs that have been optimized using these three methods in the latest downsizing engine, reducing fuel consumption and CO2 emissions by up to an additional two percent. Combined with optimized and specially tuned cylinders and pistons, even greater savings are possible.

The MAHLE Group is one of the 30 largest companies in the automotive supply industry worldwide. With its two business units Engine Systems and Components and Filtration and Engine Peripherals, MAHLE ranks among the top three systems suppliers worldwide for piston systems, cylinder components, as well as valve train, air management, and liquid management systems. MAHLE's industrial activities are combined in the Industry business unit. These include, among others, the areas of large engines, industrial filtration, as well as cooling and air conditioning systems. The Aftermarket business unit serves the independent parts market, supplying MAHLE products in original equipment quality. In 2010, the MAHLE Group generated sales of approximately EUR 5.3 billion; around 47,000 employees work at over 100 production plants and eight research and development centers.