Engine manufacturers are now under constant pressure to reduce development times and costs. At MAHLE Technology, Inc., we work with customers to optimize components already in the concept and design phase in order to reduce testing iteration. The best way to do this is through the intensive use of simulation tools.
Faster computers with larger memories have yielded more sophisticated simulation codes and reduced computing times. This opened the door for T10 (tetrahedron) mesh models with large numbers of elements. These models can be generated automatically and allow faster turnaround times. The precision is very close to the accuracy of hexahedron mesh models.

Hexahedron mesh models lead to the most accurate results. These, however, allow only a limited amount of automated mesh generation. Complicated components usually require a time-consuming hand-generated mesh model. We use both the T10 and hexahedron mesh models in our investigations.

We also use the latest technology simulation tools. Our piston development process, for example, begins with linear elastic finite element analysis. In this FEA, we determine the component temperature, deformation, stresses, safety factors and piston skirt contact pattern.

Linear elastic FEA's do not consider stress relief through plastic deformation. Therefore, our calculated safety factors in highly stressed areas with plastic deformation are smaller than in actuality. In order to overcome this problem, we perform a lifetime prediction for these areas. This prediction is based on the relevant test cycle used for validation. We calculate the effect of the stress relief due to plastic deformation and also calculate the accumulated damage that occurs due to the test cycle and temperature of the component. With this accumulated damage rate, we can predict the minimum lifetime of the component under this test cycle.

Standard finite element analysis cannot define surface stresses in areas like the pin bore. These surface stresses determine the formation of pin bore cracks. In order to determine these stresses, we simulate the elasto hydrodynamic oil film pressure. MAHLE developed tools that facilitate this process. This program runs with the standard FEA since we need convergence between the component deformation and the oil film.

We can then determine oil film pressure distribution, oil film thickness, pin bore surface stress and safety factors. In order to optimize NVH behavior, we then apply secondary motion calculations.

In this process, we define tilt angles, contact forces and pressures between piston and bore, deformations, contact patterns and clearances. We then run an animation that makes it easier to understand the piston motion. MAHLE developed evaluation criteria to optimize the pin offset for NVH reductions. We further optimize the crevice volume still under consideration of avoiding topland contact. The secondary motion calculation is also used for the dynamic optimization of the skirt contact pattern.

Since the majority of our pistons are cast, we also apply solidification simulation modeling. In this model, we determine material flow during the filling of the casting mold, porosity, material density and thermal stresses. It allows optimizing the casting quality before the first parts have been cast.

All of these tools contribute strongly to reduced development for new engines from approximately 48 months just a few years ago to 24 months today, and it will enable manufacturers to achieve the projected 18 months.

At the same time, the tools have improved the quality of products, allowed increasing the robustness against NVH and opened the door for possible further weight reduction in MAHLE components.

As computer technology progresses, we will be offered even more sophisticated simulation tools which allow refining our predictions even more so that we can offer our customers products with shorter development time and even higher quality.