Study On Wheel-Rail Contact Relationship Of High Speed Railway Vehicle

With the train speed increasing, the wheel-rail relationship, one of the basic problems on railway vehicle dynamics, has become very prominent. It is acknowledged that the wheel-rail contact is the basic content of the research on wheel-rail relationship. Thus, starting from calculating the simplest wheel-rail contact point, this paper gives a new geometric wheel-rail contact algorithm-the space vector mapping method, which is based on the space vector mapping principle and the basic characteristics of wheel-rail shape. It can solve the contact problem between stretching body and revolving body of any shape. Also, it can quickly and accurately determine the contact point between the wheel and the track in different postures, such as wheel-rail contact, wheel-wheel contact, groove-rail contact and wheel-rail contact with worn shape. Besides, the effectiveness and accuracy of this algorithm have been verified by the simulation of 3D model. In addition, here is some other work which has been done.(1) The contact points directly calculated by the space vector mapping method are rigid ones, and the distribution of them have large fluctuation. Quasi-elastic contact method takes into consideration the elastic deformation of the whole wheel-rail contact area and gets a better contact point distribution which is smooth, even and continuous. Thereby, it better meets the wheel-rail contact conditions and the actual tread wear characteristics. Meanwhile, three equivalent conicity computing methods have been presented:simplified method, harmonic method and UIC519 method. Then they have been used to calculate the equivalent conicity of four typical treads of high speed train in china. The results demonstrate that the harmonic and UIC519 methods are more accurate to calculate the equivalent conicity of the standard tread shape, which has been verified by different software. As for the worn tread shape, UIC519 method will be a better choice.(2) As for the wheel-rail contact problem of railway vehicles, based on the contact theories of Hertz and Non-Hertz, an analysis of the contact area and contact stress between wheel and rail under different wheelset lateral displacement has been made. It turned out that Non-Hertz method has better results. When the Non-Hertz contact area is similar to an ellipse, the computing result of Hertz contact area is compatible with that of Non-Hertz. Whereas, when Non-Hertz contact area is not an ellipse shape, the Hertz result shows large error. What’s more, hunting motion of free wheelset has been simulated by using the given wheel-rail contact table and the creep rate formulas.(3) In order to quantify the wheel-rail contact geometry relationship, the calculation methods of contact bandwidth and its change rate are given. They are applied to evaluate the reprofiling quality of wheel tread and to analyze the regulation of wheel-rail contact state and tread wear state. In one tread reprofiling cycle, the change regulations of some wheel-rail contact indexes for the measured shapes of S1002CN tread and LMA tread have been analyzed respectively. It is shown that, compared with the equivalent conicity index, the same change regularity for the worn tread has been obtained, but contact bandwidth and its change rate can better evaluate the tread reprofiling quality.(4) In order to improve the contact relationship of the current wheel tread and rail profile, a new reverse optimal tread design method is developed according to the characteristics of wheel-rail contact indexes, such as the wheel-rail shape, the change of roll radius difference and the distribution of contact point. This method combines the reference tread shape with a given initial wheel-rail contact position and roll radius difference, with the result that an optimizing model of tread reverse design is established, which is verified by S1002CN and LMA tread reverse design respectively. The validation results indicate that by adopting varying design parameters, different design tread shapes can be obtained, all of which meet the initial wheel-rail contact position and the change of roll radius difference. Besides, according to the shape error and the contact point distribution between design tread and reference tread, the design parameter of tread design has been gained. Based on this parameter, a better tread shape can be designed by modifying the curve of roll radius difference and the initial wheel-rail contact position so that the accuracy and adaptability of the new reverse tread design method can get verified.(5) Based on the wheel tread reverse design method stated above, three new tread reverse design methods are proposed, which are respectively designed for different initial wheel-rail contact positions, different equivalent conicity and different equivalent conicity slope, for the purpose of validating the effects of different wheel tread shapes on vehicle dynamic performance. Take CRH3 type’s high speed EMUs for example. The critical velocity and variation law of this vehicle have been calculated under different initial wheel-rail contact positions, different equivalent conicity and different equivalent conicity slope respectively. Finally, the tread design scheme for increasing vehicle critical velocity has been given, and also a wheel tread shape with high critical speed has been presented.