# An Experimental and Numerical Study on Reduction of Generated Axial Force
## 6 Conclusions  
An experimental and numerical study to reduce GAF of a tripod CVJ is presented in this study. Based on the complete GAF model, which has been developed from the kinematic and friction coefficient analysis on the tripod CVJ, the parameter analysis is carried out to find the key parameters of the GAF. Then, design optimization analysis is performed to reduce the GAF.  
From the GAF model, it can be known that the rolling-sliding ratio and friction coefficient between the track and the spherical roller are the key parameters, and this fact also suggests that GAF can be reduced by decreasing them. These two parameters are related to normal pressure and sliding velocity which are also highly related to design parameters such as track curvature and contact angle. In this study, the track curvature and contact angle of a CVJ were modified and their impact on the GAF is estimated. As track curvature changes from \(-20\) to 20%, GAF increases with the increase of track curvature. On the other hand, GAF does not show significant changes with the change of contact angle.  
In this study, the estimation results are compared with the experiment results to verify the estimated GAF reduction. Several tripod CVJs with different design parameters were manufactured, and their GAF was measured. A system was built to measure GAF. The measurement system has force sensors between the CVJ and the servo motors so that they can measure its GAF. From the verification results, the measurement results nearly showed the same results as the estimation, and throughout the entire driving torque range, the GAF has its lowest value at +20% contact angle and \(-20\%\) track curvature. Finally, the GAF with the optimized design parameters was compared with the GAF with the existing design parameters, which shows 9.85% reduction.  
Conceptualization, S.H.K.; Methodology, S.H.K. and G.H.J.; Software, S.H.K. and G.H.J.; Validation, S.H.K. and G.H.J.; Formal Analysis, S.H.K. and D.H.K.; Investigation, S.H.K. and G.H.J.; Resources, G.H.J.; Data Curation, G.H.J.; Writing-Original Draft Preparation, S.H.K.; Writing-Review & Editing, G.H.J.; Visualization, G.H.J.; Supervision, G.H.J.; Project Administration, S.H.K.; Funding Acquisition, S.H.K. All authors have read and agreed to the published version of the manuscript.  
This research was supported by Korea Institute for Advancement of Technology (KIAT) grant funded by the Korea Government (MOTIE) (N0002431, The Competency Development Program for Industry Specialist). This research was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (2020R1C1C1008068). This research was supported by the MSIT (Ministry of Science and ICT), Korea, under the ITRC (Information Technology Research Center) support program (IITP-2021-2016-0-00312) supervised by the IITP (Institute for Information & communications Technology Planning & Evaluation).  
Not applicable.  
Figure 15: GAF comparison between existing and optimized parameters.  
Informed Consent Statement: Not applicable. Conflicts of Interest: The authors declare no conflict of interest.