# Image-Based Analysis of Plate Separation and Clearance Distribution in Wet Clutches
## 5 Conclusions  
This study investigated the axial movements of the plates and the clearance distribution in wet clutches under different operating conditions and modes. Based on the findings, the effects of the separation behavior on the drag loss behavior were evaluated. An image-based measurement methodology was applied to record the movements of the plates on a drag torque test rig. The measurements show that the axial movements of the plates comprise main and superimposed non-periodic movements of much smaller amplitude. The separation of the plates is primarily driven by the applied differential speed so that the set total clearance is only utilized mainly in the higher differential speed range. The plates can even remain in contact in the low differential speed range. The separation behavior, therefore, decisively influences the drag loss behavior. It can be summarized that 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. The investigations also show that the separation behavior and, thus, the drag loss behavior can be improved by using waved plates, especially in the low differential speed range. The spring-like effect provided by the waved plates ensures rapid separation during clutch disengagement. Furthermore, in applications with a low differential speed, a temporary increase in speed can be performed to improve separation and reduce drag losses. It was also found that a high plate number and a large set total clearance lead to a non-uniform distribution of the plates. Based on the investigations conducted, it is possible to expand our fundamental understanding of wet clutches' drag loss behavior. The findings can thus contribute to the development of efficient clutch systems. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app14209270/s1](https://www.mdpi.com/article/10.3390/app14209270/s1)]([https://www.mdpi.com/article/10.3390/app14209270/s1](https://www.mdpi.com/article/10.3390/app14209270/s1)), Video S1: Test 1-R; Video S2: Test 1-1; Video S3: Test 1-2; Video S4: Test 1-3; Video S5: Test 2-R; Video S6: Test 2-1; Video S7: Test 3-R.  
Conceptualization, L.P.-G.; methodology, L.P.-G. and S.F. ; investigation, L.P.-G. and S.F. ; formal analysis, L.P.-G. and S.F. ; visualization, L.P.-G. and S.F. ; writing--original draft, L.P.-G.; writing--review and editing, S.F., K.V., and K.S. ; supervision, K.V. and K.S. ; resources, K.S. ; project administration, L.P.-G. All authors have read and agreed to the published version of the manuscript. The presented results are based on the research project FVA no. 671/III; self-financed by the Research Association for Drive Technology e. V. (FVA). **Data Availability Statement:** Data are contained within the article or Supplementary Material. **Acknowledgments:** The authors would like to express thanks for the sponsorship and support received from the FVA and the members of the project committee. **Conflicts of Interest:** The authors declare no conflicts of interest. **Nomenclature** \begin{tabular}{l l l} \hline \hline Symbol & Unit & Meaning \\ \hline \(h_{i}\) & mm & Clearance of gap \(i\) \\ \(\overline{h}_{i}\) & mm & Mean clearance of gap \(i\) \\ \(h_{\text{nom}}\) & mm & Nominal clearance \\ \(h_{\text{tot}}\) & mm & Set total clearance \\ \(\overline{h}_{\text{utz}}\) & mm & Mean utilized total clearance \\ \(i\) & - & Gap number \\ \(n\) & rpm & Rotational speed \\ \(N\) & - & Number of gaps \\ \(r_{\text{utz}}\) & \% & Utilization rate \\ \(s\) & mm & Position of plate \\ \(s_{i}\) & mm & Standard deviation of clearance of gap \(i\) \\ \(t\) & s & Time \\ \(T\) & Nm & Torque \\ \(T_{\text{d}}\) & Nm & Drag torque \\ \(\Delta n\) & rpm & Differential speed \\ \hline \hline \end{tabular}   
**Appendix A**  
\begin{tabular}{l l l} \hline \hline \multicolumn{1}{c}{**Figure A1.