Pistons usually have at least one pin bore in which a pin, for example for the purpose of connecting to a connecting rod, is rotatably mounted. In order to support the high loads that occur during the operation it is desirable to form a surface of the pin bore as smooth as possible. Although this results in the said better load bearing capacity of the pin bore, such flat surfaces nevertheless have a negative effect on the supply of the pin bore with a lubricant, which is needed for lubrication between the piston and the pin. In order to achieve a better lubrication it is known to provide the surface of the pin bore with grooves which serve as reservoir for the lubricant and thus improve the lubrication. Providing the surface with such types of grooves diminishes the proportion of the surface designed flat and thus the load bearing characteristics of the surface. In addition, such grooves offer an inadequate storage of lubricant.
For solving this problem, DE 10 2006 050 246 A1 and U.S. Pat. No. 6,089,756 A propose providing the surface of the pin bore with a groove structure, having deep grooves and grooves that are less deep. Both types of grooves serve for storing the lubricant, wherein the shallower grooves contribute more to the load bearing capacity of the surface. In the case of these pistons, the grooves of the groove structure are arranged in parallel or run in parallel. The depth of the respective groove can also vary along the associated groove.
From DE 44 42 218 A1 a fine boring machine for creating shaped bores with non-cylindrical geometry is known, in the case of which the bore radius can be varied through suitable activation in circumferential direction (ovality) and/or axial direction (trumpet shape). The fine boring machine includes as rotatable boring tool a boring bar with a cutting tool that is advanced into the bore and a work piece chuck that can be synchronously moved with the boring bar. With such a fine boring machine, a helical groove according to the present invention could be introduced into the inner surface of the bore upon suitable activation, for example constant radial deflection of the cutting tool and constant feed speed.
Disadvantageous with such groove structures according to the prior art is in particular their expensive production by means of a separate operation which leads to high production costs and/or production durations.