Development of a novel hybrid-piston for application in high performance two-stroke engines

The current development trends for high performance two-stroke engines have been identified in raising combustion pressures and therefore higher cylinder temperatures [1] [2]. Thus, the requirements on piston assembly are increased in such a way that pistons based on aluminium-silicon alloys- A s most commonly used in high performance two-stroke engines-reach their application limit. A suitable solution has been shown by research work such as that conducted by Mahle König, by using a piston consisting of different materials. With this approach, the higher stressed piston crown consists of steel, while the lower stressed piston skirt is made out from aluminium. Previous basic examinations showed the high potential of the hybrid piston concept in terms of pressure and temperature increase, while also showing the need for a temperature-stable and pressure-tight joint between crown and skirt. This paper will focus on the development of two novel hybrid-piston concepts, where the piston crown and the piston skirt are connected in different ways. The first hybrid concept presented uses the piston pin in order to realize a plug connection between piston crown and piston skirt (a conjunction hereafter known as plug-connection). A second approach is a material joint between piston crown and piston skirt, with the result that the two parts are integrally joined to one another (a conjunction hereafter known as multimaterial joint). During the predevelopment phase the design and dimensioning of the hybrid concepts were carried out with reference to mechanical and thermal operation loads, as well as joining aspects. A specific joining concept using a bimetal transition joint was created, along with the development of a special adapted laser beam welding procedure. The multi-material joint properties were further verified by FEM simulations as well as by mechanical and thermal tests. Finally, hybrid-piston prototypes were produced in time for first bench tests. In this paper the design concept of the hybrid piston and the joining technology will be presented, along with the results of FEM simulations and material testing.