Optimal Design Research Of Railway Vehicle Wheel Profile

Wheel/rail profile geometric matching relationship exerts direct influence on railway vehicle running performance, transportation costs and operation safety. It has always been an important research subject for railways researchers in home and abroad. While very rich results have been obtained by wheel/rail profile optimal design, this problem has not yet been well settled. With the increase of train speed, wheel/rail interface dynamic interaction intensified, and the wheel/rail wear phenomenon becomes more prominent. Therefore, for the purpose of reducing wheel/rail dynamic interaction forces and improving wheel/rail contact status, wheel/rail profile optimal design combined with vehicle system dynamics research has important engineering application value and theoretical meaning for railway wheel/rail damage comprehensive prevention and control.The2profile design approaches for railway vehicle wheels are developed. One is the designing railway wheel profile based on existing rail profile method, and another is the wheel profile numerical optimal design model.The wheel profile design based on the rail profile method further improves the rail profile expansion design method originally proposed by Leary et al. The improved design method utilizes the rail profile expansion factor to build an analytical expression for the relationship between wheelset equivalent conicity, characterizing railway vehicle dynamics performance, and rail profile expansion factor, representing wheel/rail contact conformity. Taking the expansion factor as a design variable, can design the wheel profiles with different equivalent conicities matching different rail cants and wheel/rail nominal clearances.And the numerical optimal design model of wheel profile is based on the works of Shevtsov and Jahed et al. The present paper puts forward the numerical optimization design constrains by exploiting the cubic Spline theory. And it also proposes an objective wheelset rolling radius difference (RRD) design technique according to the wheel/rail creep theory.The designing wheel profile based on the existing rail profile method is, hereafter, extensively utilized to design railway wheel profiles. Combined with wheel/rail contact characteristic analysis and vehicle dynamics calculation, the effects of wheelset equivalent conicities, wheel/rail nominal clearances and rail cants on the vehicle dynamics performance and wheel/rail interaction features are studied in detail in Chapters4,5, and6, respectively.Chapter7analyzes the continuously measured wheel profile wear data of a high-speed electric multiple unit (EMU) train in an interval between two wheel reprofilings in detail. A new wheel profile design proposal is put forward, considering the wheel wear problems found in the site measurements and the foregoing research results.The main results obtained and conclusions reached of this dissertation are as follows.(1) The railway vehicle critical speed does not strictly in inverse proportion to the square root of wheelset equivalent conicity. There exists a low wheelset equivalent conicity range with relatively high vehicle critical speed. The variation of equivalent conicity within this range would not cause a great change in the vehicle critical speed. The vehicle critical speed does in inverse proportion to the square root of wheelset equivalent conicity, if the wheelset has higher equivalent conicity than this range. A wheelset with very low conicity would cause it insufficiency in the ability of going back to track central position, the vehicle critical speed drops rapidly. The analysis found that a wheelset with worn shape profile can achieve nearly the same vehicle critical speed as the wheelset with conical profile in the above mentioned low equivalent conicity range. A good behavior wheelset should has an important characteristics that its equivalent conicity increase as the wheelset lateral displacement increases, and the wheelset should has a higher equivalent conicity transition region before its flanging action. This would improve the vehicle curving performance and reduce the occurrence of wheel flanging action effectively.(2) Regarding the influence of wheel/rail nominal clearance on railway vehicle dynamics performance and wheel/rail contact. The analyses of worn shape wheel profile designed with different wheel/rail nominal clearance indicate that, a decrease in wheel/rail nominal clearance would cause the vehicle critical speed drops obviously. And, under track irregularity excitations a profile with smaller nominal clearance is prone to wheelset flange contact. But, if the wheelset equivalent conicity is designed appropriately, the wheelset with worn shape wheel profile can still has sufficiently high critical speed and lower chance of flange contact. For a conical profile wheelset with smaller wheel/rail nominal clearance, the vehicle critical speed drops more quickly than a worn one. As, in case of larger lateral displacement excited by track irregularities, a conical profile wheelset cannot generate enough radius difference, and flange contact becomes inevitable. Hence, the wheel/rail nominal clearance exerts significant effects on both vehicle dynamics performances and wheel/rail contact status.(3) The rail cant variation has little effect on the equivalent conicity of a wheelset with conical wheel profile. So, the rail cant has no substantial influence on the vehicle critical speed, curving performance, and wheel/rail forces when the vehicle uses conical profile wheelsets. But, there is a significant difference among the equivalent conicities of the worn profile wheelsets designed based on different rail cants, namely, the rail cant has a great influence on the equivalent connicity of the wheelset with worn shape wheel profile. The larger rail cant the larger difference of the equivalent conicities. The wheelsets with worn profiles designed based on small rail cant always have a low equivalent conicity range, in which there is a high critical speed. As the rail cant increases the equivalent conicity of the worn profile wheelset increases, the low equivalent conicity range preserving high critical speed and desirable wheel/rail forces becomes narrower. For wheelsets with the same equivalent conicity designed based on different rail cants, their curving performance and wheel/rail interaction forces exhibit no obvious differences. Therefore, based on different rail cants, wheelsets with designed wheel profiles have difference in vehicle critical speeds.(4) The analysis on the wheel profile wear tracking measurement results shows that the change of the average accumulated wear depths on both the wheel tread and the wheel flange are close, which indicates that the abnormal wear of wheel profile main working region is alleviated. The tracking measurement results reveal that the train application pattern has a very important influence on wheel profile wear. The analysis also shows that, after the initial operation period of about40,000km, the average accumulated wear depth on both the wheel tread and the flange amounts to nearly half of one turning cycle of the wheel.