Function
The connecting rod connects the piston to the crankshaft, it consists of the small and the large connecting rod eye and the shaft.
The rotation of the crankshaft causes a rotating movement of the large connecting rod eye. The small connecting rod eye follows the axial stroke movement of the piston in the cylinder. The connecting rod is therefore a component that converts the axial movement of the piston into rotation of the crankshaft.
Strains
As the element that transmits forces and movements between the piston and the crankshaft, the connecting rod is exposed to large, changing loads. The piston pushes and pulls the connecting rod. In addition, the connecting rod is subjected to bending stresses due to its pivoting movement. It should be as light as possible but still sufficiently dimensionally stable. In addition, sufficient component and design strength must be guaranteed.
Requirements
In principle, moving masses should be small in favor of efficiency and vibration excitation. The weight can be minimized by reducing the component length. However, the changed lateral forces on the piston skirt and in the connecting rod must be taken into account.
Guide of the connecting rod
The connecting rod is usually axially guided via the large connecting rod eye on the crank web. This is referred to as "bottom led". Less common is the guide via the piston and the small connecting rod eye "guided at the top". This requires a contact surface on the piston and the clearance must be reduced.
Vorteile des „oben geführten“ Pleuel sind: Die Anlaufscheiben an der Kurbelwelle entfallen und die länge des Kolbenbolzens kann reduziert werden. Dies führt zu einer Gewichtsreduzierung. Aufgrund der kleineren Anlaufflächen entstehen geringere Reibungsverluste.
Nachteile des „oben geführten“ Pleuel sind: Schwingungen und Bewegungen von der Kurbelwelle werden direkt in den Kolben übertragen, was die Lebensdauer des Kolben mindert. Weiterhin verschlechtern sich die Schmierbedingungen im kleinen Auge, da weniger Öl durch den schmalen Spalt zwischen Pleuel und Kolben gelangt.
Werkstoffe
Für die Verwendung von Serien Pleuel hat sich das Sinterschmiedeverfahren durchgesetzt. Um die Porosität zu verringert wird hier ein Schmiedeprozess nachgeschaltet. Das verwendete Material 3Cu6c hat einen Kohlenstoffgehalt von 0,5-0,6% Über das zulegieren von Kupfer mit bis zu 3% kann die Festigkeit gesteigert werden. Für hochbelastete Motoren haben sich Stahlpleuel, welche im Gesenkschmiedeverfahren hergestellt werden, durchgesetzt.
Advantages of the "top guided" connecting rod are: There are no thrust washers on the crankshaft and the length of the piston pin can be reduced. This leads to a reduction in weight. Due to the smaller contact surfaces, there are fewer friction losses.
Disadvantages of the "top-guided" connecting rod are: Vibrations and movements from the crankshaft are transmitted directly to the piston, which reduces the service life of the piston. Furthermore, the lubrication conditions in the small eye deteriorate because less oil gets through the narrow gap between the connecting rod and the piston.
Materials
The sinter forging process has become established for the use of series connecting rods. In order to reduce the porosity, a forging process is carried out downstream. The 3Cu6c material used has a carbon content of 0.5-0.6% The strength can be increased by alloying copper with up to 3%. Steel connecting rods, which are manufactured using the drop forging process, have become established for highly stressed engines.
