Research On The Application Of Prevailing Torque Nut In Mini Vehicle

Prevailing torque nuts are normal friction lock types,and widely used in automobile industry.And connection quality of threaded fasteners is related to the safety of the vehicle.Meanwhile for screw parts,domestic automobile manufactures adopt empirical design and comparative analysis to vehicles which are designed by foreign car makers,which results in improper design of fastening torques and loosening failure.Due to lack of theoretical reserves of lock nuts,the efficiency of solving problems of fastener loosening failure is low,and the repair cost is high.These things are not conductive to quality,safety and cost controls.In order to solve application problems of prevailing torque nuts in some mini-vehicle company,this thesis will conduct a research from two aspects of fastening torque designs and anti-loosening characteristics.By means of experimental and statistic method,prevailing torque nuts for their fastening characteristics were analyzed in order to devise a formula of torque-clamping force relationship.And the anti-loosening effects were also considered.Finally,the influenced factors of anti-loosening performance of locking screw connection were summarized.And results of theoretical analysis and experimental research were adopted to improve locking performance.The main achievements are as follows:1.Force model of screw fasteners was established.Based on anti-loosening principle of prevailing torque nuts,fastening torque and loosening torque formulas of such nuts were proposed,which can lay a theoretical foundation for analyzing fastening characteristics and influenced factors of lock performance.2.Through the torque-clamping force experiments,the data for torques and corresponding clamping forces of sample screws in some mini-vehicle company were gained.Then linear regression analysis was taken.For the prevailing torque nuts,the formula relating to torque and clamping relationship need to be modified,and this is different to normal threaded connection.By means of boxplot and stem leaf chart,the regularities of distribution of torque coefficient and friction torque increments were gained.And traditional torque design formula was optimized to improve reliability of threaded connection.3.Through transverse vibration tests and contractions prevailing torque nuts to other anti-loosening methods,prevailing torque nuts are better than most of them from locking aspects.And effects of repeated uses and disassembles on anti-loosening performance and tightening characteristics were tested to guide usage of the nuts.4.Aiming at influenced factors of anti-loosening performance for threaded connection,theoretical,experimental,one-way ANOVA statistical method and LSD mean value multiple comparison method were adopted.As for improving the locking performance,only relying on using lock nuts is not enough,other things that improving utilization rate of the bolts and stability of pre-tightening force,changing ontological characteristics of fasteners and ensuring manufacturing precision of the connection parts need be done meantime.Improvements for full use of prevailing torque nuts were indicated.