Structural Optimization Design Of Heavy Vehicle Mainshaft

Mainshaft as the key basic parts of heavy vehicles,its core value is self-evident.Due to the large load and volume of the heavy vehicle,the mainshaft strength design is particularly prominent when it works in complex conditions.The shaft studied in this thesis often leads to the failure due to the restrictions of its structure and space in the process of starting/stopping.Aiming at the weakness of insufficient dynamic strength of the shaft,this thesis firstly analyzes the shaft strength under impact torsional load,and then optimizes the shaft structure to improve its working life.In the analysis of the shaft structure stress,a simplified analysis model of the shaft is established.The short shaft part was subtly meshed and the convergence of meshing results was analyzed.By means of finite element and theoretical analysis,the influences of the groove,the ratio of the length of the long shaft to that of the short shaft,and the diameter of the short shaft on the mainshaft stress is calculated.Based on finite element method,the influence of the pressure angle of involute spline,tooth root shape,and transient fillets radius on spline stress are studied.It is found that it is more reasonable to choose a circular root spline with a pressure angle of 30°.Increasing the transient fillets radius at the junction of the groove and shaft can decrease the Mises stress and cyclic stress of the shaft.Because of the machining error,the tooth thickness tolerance of spline is designed.The stress distribution of spline is calculated when spline tooth thickness is normally distributed.A reasonable range of tooth thickness is obtained.In order to reduce the contact inhomogeneity between the internal and external splines during the shaft rotation,the involute spline surface is designed with variable tooth thickness along the axial direction.Spline tooth modification is carried out based on the elastic torsional deformation curve of spline tooth surface.Through the optimization,there are more load-bearing areas on spline tooth surface of the short shaft.The stress concentration in the transient region of shaft and spline is reduced.The stress distribution in the most dangerous area of the spline surface is improved.The working life and impact resistance of the shaft are enhanced effectively.Finally,in order to verify the simplified analysis method of the shaft impact dynamics proposed in this thesis,the dynamic impacting simulation is carried out for the limiting case of the shaft under impact torsion load.It is found that the dynamicstress in the root region of spline is the largest,which is consistent with the simplified analysis results,and thus the feasibility of the simplified analysis method is verified.Early fatigue fracture and failure in the originally designed shaft occurred easily in the transition region in the spline of short shaft and root region,which are completely consistent with the actual situation.In this thesis,the impact dynamics of the shaft of heavy vehicle is studied and analyzed.There is guiding significance to improve the strength and working life of the mainshaft of heavy vehicle.