# Image-Based Analysis of Plate Separation and Clearance Distribution in Wet Clutches
## 4 Discussion  
In general, the results show that the separation of the plates immediately after disengaging the clutch is mainly driven by increasing differential speed. In contrast to the simulation results presented in Ref. [16], plate separation was not analyzed in the context of the different lubrication stages during the disengagement process, but as an general phenomenon after disengaging the clutch. At a low differential speed, small clearances form, and the set total clearance is not utilized (see results for OM-2). A high differential speed, on the other hand, supports the plate separation, generally leading to a higher clearance utilization rate (see results for OM-1). It is assumed that with increasing differential speed, increasing viscous forces in the gaps are mainly responsible for forming larger clearances. When operating a wet clutch at a low differential speed level, a temporary increase in speed can--if the application permits--improve separation and, thus, significantly reduce the drag torque during operation (see results for OM-3). The plates largely remain in their positions after separation is completed. It was also shown that waved plates show better separation behavior due to the spring-like effect generated by the plates during the disengaging process. This finding is in line with the results presented in Ref. [11]. Therefore, using waved plates can be particularly effective in applications with low differential speeds to reduce drag losses. It can be assumed that the separation process is more distinct in the case of a typical axial force in the range of several kilometres, as in this case, the plates are entirely pressed planar in the engaged state. Accordingly, an increased spring-like effect can be assumed during disengagement. The axial force on the LK-4 test rig is limited due to the pneumatic actuation. The investigated clutch is typically actuated with an axial force of several kilometres. The utilized total clearance mainly depends on the clutch design and operating conditions. This finding can be used in future clutch development processes to adequately set the total clearance, leading to a more compact design. Furthermore, the results of the test series for OM-1 show that specific operating conditions and clutch configurations can lead to a non-uniform distribution of the plates within the set total clearance. In the case of dip lubrication, the clutch is not actively lubricated. In contrast, in the case of injection lubrication, the oil is injected uniformly over the entire width of the clutch pack from the inside. It is conceivable that active lubrication generally improves the separation and leads to a more uniform distribution of the plates (see Reference Test 1-R versus Test 1-2). The mechanical system becomes more complex with more plates composing the clutch pack. Therefore, it is evident that the distribution of the plates is less uniform as the plate number increases (see Reference Test 1-R versus Test 1-3). Also, in the case of a high plate number, it is evident that the separation process takes longer because the piston-sided plates must travel a longer distance. In the case of a small set total clearance, the plates are generally guided more closely, which generally leads to a more uniform distribution (see Reference Test 1-R versus Test 1-1). Moreover, the measurements show that larger clearances occur between the plates located on the piston side in particular. CFD simulation can be used in future research studies to validate the explanatory approaches and conduct in-depth investigations. Forces of different origins cause the plates to move. Friction forces acting in the spline contact of the carrier and plates act against the direction of movement. Moreover, viscous forces occur in the gaps depending on the oil and the operating conditions. Forces can also arise from an imbalance of rotating components. It is assumed that the superimposed oscillations are caused by, e.g., part unbalances or flow irregularities in the gaps.