Abstract
Optimizing the surface topography of cast iron crankshafts offers the opportunity to use this material as an alternative to steel in high-performance combustion engines. In the past, this was not possible due to the higher wear on bearing shells and the higher friction losses in relation to forged steel shafts. In order to find an optimized shaft micro topography, the friction and wear behavior of steel and cast iron shafts with different surface treatments were compared to each other, using a combined physical (experimental) and a virtual (computational) simulation approach. The experiments were carried out with a rotary tribometer using a journal bearing test configuration with the possibility to test real-life bearing shells and shaft specimens, manufactured from real-life crankshafts. In the experiments, a polished steel shaft with low bearing wear was effective. The optimization of cast iron crankshafts by a novel surface treatment showed a significant reduction of bearing wear in relation to the classical surface finishing procedures of cast iron shafts. A computational simulation approach, considering the real-life micro topography by using the Navier–Stokes equations for the calculation of micro hydrodynamics, supports the assessment of fluid friction. The virtual simulation shows, in accordance to the experimental results, only a minor influence of the investigated shaft topographies on the fluid friction. Further optimization of shaft surfaces for journal bearing systems seems possible only by the usage of patterned micro topographies.
Highlights
Hydrodynamic journal bearings are widely used machine elements, and due to their advantages, they are standard bearings in internal combustion engines
Besides finding an optimization potential for crankshaft surface topographies, this study allows for comparison and validation between physical and virtual simulation approaches
A comparison between the fluid friction properties of the shaft variants used for the virtual simulation, as well as to the experimental data from the physical simulation is possible in that way
Summary
Hydrodynamic journal bearings are widely used machine elements, and due to their advantages, they are standard bearings in internal combustion engines. The combination of physical and virtual simulation, and experimental and computational results, shows high potential for increasing our basic understanding of tribosystems [26,27] This combination can be used for the optimization of critical journal bearing systems, for example, the crankshaft bearings of automotive combustion engines. To make use of casted crankshafts in high-performance engines possible, different surface treatments are compared in this article with the goal of comparing and understanding wear and friction properties under application-near conditions This task is carried out by a physical simulation on a rotational tribometer together with a virtual simulation, using a novel approach for modeling surface topography effects in hydrodynamic lubrication [25]. Besides finding an optimization potential for crankshaft surface topographies, this study allows for comparison and validation between physical and virtual simulation approaches
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