Nodular cast iron pistons for Medium Duty Applications 2018-01-1275
Today, especially medium duty engine platforms have to fulfill a wide spread of applications and thus also power ratings. With heavy duty engines being already for a long time in a peak cylinder pressure range above 20MPa, forged steel pistons have become an industry wide standard. However, for medium duty, many engines still utilize Aluminium piston technologies due to mainly economic reasons and operating conditions at lower peak cylinder pressures. The drawback of this situation is a lower performance in terms of thermal efficiency and thus fuel consumption. This becomes even more important, when CO2-based regulations might come into action. Recently, medium duty platforms are developed with variants that need forged steel pistons due to their peak cylinder pressure requirements, causing rather a high degree of fragmentation of engine components. Typically, steel pistons have lower compression heights, causing also different part numbers for connecting rods, crankshafts and even up to different cooling oil supply. Nodular cast iron pistons are therefore an interesting technology, able to provide some of the benefits of forged steel pistons also to lower power ratings and creating a synergetic scenario for engine platform design. Usually, forged steel pistons require a high amount of machining effort from the raw part to the finished part and offer performance that is overengineered for some of the engines in a platform. Therefore, the commercial aspect of switching completely to forged steel pistons is not compensated by the performance potential. Nodular cast iron solutions, as successfully provided by MAHLE (former Izumi) since decades, are therefore developed further to fit the range as mentioned. A key aspect being the similarity to modern forged steel piston designs and hence, enabling streamlined engine platform designs from top to moderate power while enabling best total cost of ownership performance.