Piston pin
The piston pin is a construction element in crank mechanisms for the transmission of forces between the piston and the connecting rod . In combustion engines and compressors , gas and inertia forces act on the bolt. In general, a distinction is made between chamfer pins and radius pins, and weight-lightened piston pins are increasingly being used. These are characterized by a relatively oversized inner bevel of standard bolts, but without weakening the material of the highly stressed central part.
The piston pin is floatingly mounted in the pin eye of the piston and the connecting rod for power transmission. Depending on the machine type, needle bearings or plain bearings take over the power transmission from the pin to the connecting rod. In addition to oil lubrication, coatings made of amorphous carbon have also been used since around 2010 to minimize friction between the piston pin and the connecting rod or its bearings. This means that there is almost no need for oil lubrication on the piston pin, and this carbon-containing coating provides very good emergency running properties . Pin locks on both sides prevent axial migration, which is particularly important with slot-controlled two-stroke engines. The fuse can be taken over by the piston on one side. In many smaller Otto engines , the pins are also held in the connecting rod by means of shrinkage tension, so that there is no need for an additional piston pin retainer.
The material used for these highly stressed components is primarily case-hardening steels such as 16MnCr5 and 17Cr3 and, under certain circumstances, nitriding steel . Other materials have also proven themselves in racing or in other areas that make extreme demands. The starting form is a tube, the dimensions being selected as small as possible due to the inertia forces . The parts are manufactured with very high demands on accuracy in terms of roundness, cylindrical shape and the dimensional accuracy of the outer diameter. The length is largely tolerated in the minus, that is, the bolt is a few 1/10 mm shorter than the nominal size. This avoids jamming due to the high thermal loads during the combustion or compression process. The outer surfaces are only case-hardened or surface-hardened during the hardening process (the hardening depth is only a few 1/10 mm up to a maximum of 2 mm), because a change in the direction of force would lead to an immediate material breakage in hardened parts. After the hardening process, the outside diameter is brought to the nominal size using suitable processes such as grinding with subsequent lapping or honing . Depending on the size and application, tolerances in the diameter of a few 1/100 mm to 1/1000 mm must be adhered to, this also applies to the roundness and cylindrical shape. Even the slightest damage in the area of the plane or side surfaces, if not noticed, leads to damage to the piston itself, despite the fact that it can be installed, and leads to premature failure or wear.
Individual evidence
- ↑ Richard van Basshuysen, Fred Schäfer (Ed.): Handbook internal combustion engines. Vieweg Braunschweig, Wiesbaden 2002, ISBN 3-528-13933-1 , pp. 97f.
- ^ Franz Pischinger: Internal combustion engines , lecture reprint, Volume 1, self-published printing, Aachen, October 1986, p. 253f.