Elastohydrodynamischer schmierfilm im Wälzkontakt beim Rollen mit überlagertem Gleiten

Attempts to explain the EHD procedure by fluidic laws lead to a hypothesis. According to this Hypothesis, under pure rolling conditions the lubricant flow is turbulent before entering the gap, laminar up to the pressure peak, turbulent again after the narrow passage. The boundary layers sticking to the gap walls drag the lubricant through the gap. In the areas of increasing pressure the central lubricant stream flows against the lateral streams. In the areas of increasing pressure the central stream flows ahead of the lateral streams. Thus flow speeds and wall shear stresses vary along the gap. These procedure are symmetrical to the X-axis. By superposing the rolling motion with a sliding motion, flow speeds and thus the shear stresses are distributed asymmetrically to the X-axis over the cross-section. The effects are as follows: Firstly, under pure rolling the frictional moment is very low because the shear stresses along the gap, caused by flowing of the lubricant forward and backward nearly balance the shear stresses. Slippage disturbs this equilibrium, the frictional moment rises steeply. Secondly, once the slippage has reached a critical value, the lubricant flow becomes turbulent also in the area between gap entrance and the pressure peak. At that point, the frictionel moment passes through its maximum value and decreases afterwards. The hypothesis says that shear stresses of locally varying magnitude are created along the gap. The material stressing changes particularly in the layers near the surfaceees. An additional material stressing is caused by the sound wave that is released by the pressure decrease after the pressure peak.