Innenpassung

Innenpassung is a German term used in mechanical engineering to describe an interference fit where one part fits tightly inside another. It refers to a condition where the diameter of a shaft or pin is intentionally made larger than the diameter of the hole it is to be inserted into. This intentional oversizing creates a high-pressure contact between the two mating surfaces, resulting in a strong and secure connection.

The principle behind Innenpassung relies on the elastic deformation of both the outer and inner components. When the shaft is pressed into the hole, the outer part (e.g., a housing or sleeve) expands slightly, while the inner part (e.g., a shaft or pin) is compressed. Upon assembly, the residual stresses from this deformation provide the clamping force that holds the parts together. This method is often preferred over other fastening techniques like keyways or threads when a smooth, continuous outer surface is required or when high torque transmission is necessary.

Achieving a successful Innenpassung requires precise control over the dimensions and tolerances of both mating parts, as well as the appropriate application of force during assembly. Factors such as material properties, temperature, and lubrication can influence the ease of assembly and the resulting holding power. Common applications include bearings fitted into housings, gears pressed onto shafts, and pins inserted into holes. The strength of an Innenpassung can be significant, often making disassembly difficult or requiring destructive methods.