Stress Analysis of the Piston Skirt with Vertical Plane Ribs

Abstract

In respect to the stresses on the pin boss of a piston skirt which has vertical ribs, we carried out a series of analyses, namely, 3-dimensional stress calculation by the F.E.M, 3-dimensional photoelasticity, strain measurement under static load, and strain measurement under service condition.
Through these analyses the following matters were clarified.
(1) Suitable taper given to the inner surface of the pin boss is effective for reducing the tangential tensile stress, due to gas pressure, on the boss end.
(2) It is possible to calculate the degree of stress reduction due to above mentioned taper processing, by suitably estimating the contact pressure distribution along the inner surface of the pin boss.
(3) It is possible to change a load transmitting path by changing an intersecting angle between the vertical rib and the pin boss. Consequently, when attaching the ribs perpendicularly to the pin boss as well as increasing the thickness of boss wall, the tangential tensile stress on the boss end is reducible.