Parametric Design Theory Of Railway Wheel Profile

The dissertation is sponsored by the fund of wheel rail profile optimizing design(50475059). Railway wheel profile design is an important part which determines the dynamic performances of the locomotive and vehicle such as hunting stability, curve negotiation performance, wheel and rail surface wear and derailment safety. In wheel profile optimizing design, profile shape modification and performance calculation will be done repeatedly. So wheel profile parametric modeling is required to realize wheel profile parametric design. Parametric design was widely applied in machinery, car, aviation, and building industries, but the effective and useful parametric design theory hasn't formed in the study of wheel profile. Non-Uniform Rational B-Spline (NURBS) is suitable for parametric design of wheel profile because its good characters and advantage of generating smooth curve using small characteristic parameters. In the paper, the method of constructing wheel profile with NURBS curve was studied. The properties of the wheel profile described by NURBS such as local approximation, strong convex hull property and geometric continuity solve the difficult problems in the wheel profile design such as tread shape local modification, realizing hollow or convex parts and smooth of the profile. Weight and control point were taken as design variables in the railway wheel profile parametric design. The geometric meaning and the influence on vehicle dynamic performances of the weights and control points were analysized. The value fields were determined. Furthermore, according to wheel profile design principles, different dynamic performance was required for wheel flange and tread. Boundary conditions of wheel flange and tread curve was determined, and parametric models were built by NURBS curve fitting. Finally combined NURBS curve method was used to build parametric model of the whole wheel profile. On the basis of the parametric model, a theory of railway wheel profile parametric design was proposed with the object of improving vehicle dynamic performances. According to this theory, a smooth wheel profile with good performances will be obtained through selecting suitable weights and control points which were design variables. Software was developed in according with this parametric design theory and procedure, and applied to the worn wheel profile design for Beijing subway. The final profile named DM which had good curve negotiating performance and wear performance was obtained. The result proved the engineering practicality of this parametric design theory.