Due to its function as the link between the piston and the connecting rod, the piston pin must fulfill a wide range of requirements. In addition to exhibiting sufficient rigidity, it must still be light in order to keep the inertia forces low in the engine. MAHLE has developed a composite piston pin that optimally meets these contradictory requirements by combining a high-strength steel sleeve with a lightweight aluminum core.
In modern passenger car engines, the oscillating masses or inertia forces of the moving drive unit components must be kept as low as possible. Low oscillating masses are not only the basis for a smooth-running engine, it also greatly affects the operational safety and service life of the components. The lower the oscillating mass in the crank mechanism, the weaker the vibration and friction—and consequently the wear on the components. The proportion of oscillating mass made up by the piston pin can be between ten and thirty percent. The effect of reducing the weight of the piston pin is correspondingly significant.
In comparison with the previously typical steel pin, the newly developed MAHLE composite piston pin has a press-fit aluminum core. In the passenger car segment, this leads to weight savings for the piston pin of up to twenty percent in gasoline engines and as much as thirty percent in diesel engines.
Since the production of piston pins should be kept as simple and thus economical as possible, the new composite piston pin from MAHLE is manufactured using a forming process. The aluminum core is inserted in the existing steel sleeve and then pressed in place. Another advantage of the press fit is design freedom for the ends of the core, resulting in material savings at the ends of the piston pin that are subject to lower mechanical loads, which in turn leads to additional reductions in weight.
One special feature of the composite piston pin is its variability. Depending on the stress level in the engine, particularly associated with peak pressures, for example, the wall thickness of the steel sleeve and therefore the strength of the pin can be adjusted. If unusually high demands are placed on the surface of the composite piston pin, the friction and wear can be substantially reduced with an additional coating of DLC (diamond-like carbon), thereby increasing operational safety.
