Performance Study On Fatigue And Endurance Of Steering Assist Mechanism In Electric Power Steering System Of Automobile

With the rapid development of automobile technology,people put forward higher requirements for the operation stability,safety,reliability and sensitivity of vehicles.The electric power steering system of the automobile assists the driver to control the steering of the automobile through the deceleration and twisting action of the steering assist mechanism,making the steering of the automobile more light at low speed and more stable at high speed,which can reduce the driver's fatigue and ensure the control stability during the driving process.The stability and reliability of the output torque of the steering assist mechanism are particularly important.As the transmission mechanism of the steering assist mechanism,the movement characteristics and fatigue endurance performance of the nylon worm gear are the key to the realization of the function of the steering assist mechanism and the safe and reliable operation of the entire automobile steering system.Therefore,this paper establishes a multi-body dynamic model of the steering system assist mechanism,studies the dynamic performance of the steering mechanism and the fatigue endurance performance of the nylon worm gear under multi-load conditions,and carries out fatigue tests on the steering assist mechanism.The specific contents are as follows:(1)Using the theory of multi-rigid-body dynamics and parametric modeling method,the multi-rigid-body dynamics model of the entire steering assist mechanism was established,including worm gear and worm,bearing,elastic element,etc.The multi-body dynamics software RecurDyn was used for dynamic simulation and verification.Through the experimental verification of the worm drive torque,worm gear speed and the theoretical verification of the force on the worm gear,the comparison shows that the error of the simulation results are less than 5%,which verifies that the modeling accuracy of the multi-rigid dynamics simulation model is relatively high,which lays a theoretical foundation for the analysis of the stress on the tooth root of nylon worm gear and the research on the fatigue endurance performance.(2)The rigid and flexible coupling dynamics simulation model of steering assist mechanism was established by the flexible treatment of nylon worm gear and the contact analysis of the rigid and flexible coupling of worm and worm gear.Based on the curve comparison of acceleration test data and simulation results,it is found that the simulation model is in good agreement with the actual working state of steering assist mechanism.The worm gear tooth root stress is obtained by dynamicsimulation,comparing the static simulation and theoretical calculation of tooth root stress again,the error of value is 3.52% and 4.08% respectively,showed that under certain modeling accuracy,built by the coupled simulation model can get the exact worm gear tooth root dynamic stress results.(3)The fatigue test bench of steering assist mechanism was built,and its fatigue endurance test was carried out according to three load spectrum loading schemes.By lognormal distribution,the two parameter weibull distribution and three parameter weibull distribution of fatigue life under different load spectrum,found that the correlation coefficient of three parameter weibull distribution is superior to other distribution types,with the fit of the inspection,found that in 5% of the significant degree of request,three parameter weibull distribution can be accepted,determine its fatigue life distribution type.Finally,the fatigue life distribution function under different loading schemes is obtained,and the bending fatigue life of worm gear under different failure probabilities is obtained by the distribution function.(4)The dynamic simulation results of nylon worm gear root stress under different load spectrum loading schemes were obtained by transforming the load spectrum loading scheme of the fatigue test into the dynamic simulation boundary conditions.Then,the S-N curve of worm gear material nylon 66 was modified by combining the fatigue damage influence factor and MM correction rule.The fatigue life and life cloud diagram of nylon worm gear under the same three load spectrum loading schemes as the fatigue test were obtained by using the modified S-N curve and the dynamic simulation results of tooth root stress.Finally,the Offset Test method is used to verify the simulated fatigue life,which shows that the simulation results of fatigue life meet the test statistic standard of 95% confidence,and the feasibility and accuracy of the simulation model of steering assist mechanism to replace the fatigue test are verified.Based on vehicle steering assist mechanism of the coupled dynamics analysis and fatigue durability of the nylon worm gear research,enrich the design method of steering assist mechanism,also reveals the main factors influencing the steering assist mechanism of fatigue endurance.It provides reference for the application and research of electric power steering system assist mechanism in practical engineering.