Kolbenschmidt Pierburg Group KS Aluminum Pistons for Truck Applications

Requirements The development of on- and off-highway diesel engines for a wide spectrum of applications is affected by global emission requirements and the minimization of friction losses. The high cylinder pressures and specific powers of modern direct injection diesel engines cause high mechanical and thermal loads. Aluminum pistons with conventional material and cooling gallery are pushed beyond their limits by these increased loads. Fig. 1 shows the application limits of different piston types for light, medium, and heavy duty applications with respect to specific power. For heavy duty trucks...

As a reinforcement of the top ring groove and occasionally the second groove, highly loaded aluminum diesel pistons are strengthened by a ring carrier made out of an austenitic gray cast iron. The ring carrier and the aluminum base material are bonded by an intermetallic Alfin layer. The combustion bowl, especially the bowl rim, is another critical zone of today’s highly loaded diesel pistons. The combination of low cycle fatigue (LCF), caused by the cold and hot swings of the engine, and the high cycle fatigue (HCF) mode, resulting from the gas force, can lead to crack initiation at the bowl...

The higher oil flow increases the heat transfer significantly. In comparison to the ContureKS® cooling gallery that has been proven in multiple applications and features a variable cross section, the temperatures at the bowl rim is reduced by 15 °C and at the top ring groove by 10 °C (see Fig. 5). The reliable and established production technology using lost salt cores can also be used for these complex cooling gallery shapes. The production process for the salt cores and for the piston castings has been optimized. New Material Although steel pistons are traditionally used for the highest power...

Other advantages are the increased process stability compared to casting and an improved surface quality in machining. The re-melting process is a tailored solution that increases the durability and the quality of diesel pistons significantly. Results from engine tests at KS and at OEMs have confirmed the potential of this technology. the re-melted bowl rim before final machining. The resulting fine and homogenous microstructure in the re-melted area improves the thermal fatigue properties in the critical range of up to 200 % as shown in Fig. 8. Number of Cycles Until Macroscopic Crack liner...

With targeted recent developments in the areas of design, materials, coatings, and manufacturing processes, KS Kolbenschmidt has prepared for the future requirements in diesel engines for commercial vehicles. Current series developments and strong market demands for new solutions confirm our strategy. The resulting new piston coating, NanofriKS®, reduces the dry friction coefficient as well as the wear by approximately 50 % (see Fig. 9). With this development, KS Kolbenschmidt has underlined its role as the leader in coating technology. Outlook The many good reasons for the continued use of aluminum...

KS Kolbenschmidt GmbH · Karl-Schmidt-Straße · 74172 Neckarsulm · GERMANY Tel. +49 7132 33-0 · Fax +49 7132 33-2796 · www.kspg.com Subjects to alterations. Printed in Germany. A|I