Abstract: A crank drive has a crankshaft having at least one crank pin having a bearing surface with a concavely curved shape in a longitudinal crankshaft section and a conrod having a big end fitted to the crank pin and having a bearing surface with a convex shape in contact with the concave shape of the bearing surface of the crank pin in a load-bearing area that transmits forces acting between the big end of the conrod and the crank pin when the drive is in use. The shapes of the bearing surfaces are in accordance with the principle of uniformly distributed stresses such that essentially the same equivalent stress is distributed overall in the bearing surfaces in time average.

Abstract: The invention relates to a device comprising a crankshaft (100) and least one conrod (200) having a big end (202) mounted on a crank pin (102) of the crankshaft (100). The crank pin (102) and the big end (201) of the conrod (200) comprise bearing surfaces (108, 202) which are in close contact to one another in a load-bearing area that bear the forces acting between the big end (201) of the conrod and crank pink (102) when the device is operated. According to the invention the bearing surface (108) of the crank pin (102) in its load-bearing area features a concavely curved profile in the longitudinal shaft section and the bearing surface of the big end (201) features a convex profile being in close contact with the concave profile of the crank pin (102).