Optimisation of a Railway Wheel Profile

During the last decades substantial progress has been made in design of railway vehicles and running gears. Tilting trains, high speed trains, active steering wheelsets and many other sophisticated solutions have been implemented in recent years on the railways. But despite this progress, the mechanics of railway wheelset remains the same and an inappropriate combination of wheel and rail profiles can easily diminish all this technological advances. Besides, many old fashioned vehicles are still in too good condition to be replaced. They have a special need for appropriate combinations of wheel/rail profiles since such vehicles do not have high-tech devices which improving performance. The paper presents a procedure for optimal design of a wheel profile based on geometrical wheel/rail contact characteristics such as the rolling radii difference (RRD). The procedure uses an optimality criteria based on a RRD function. The criteria accounts for stability of wheelset, cost efficiency, minimum wear of wheels and rails as well as safety requirements. The shape of the wheel profile approximated by a piecewise cubic Hermite interpolating polynomial is varied during the optimisation process in order to satisfy the optimality criteria. The optimization problem described above has been solved using the MARS method (Multipoint Approximations based on Response Surface fitting). The method has been specifically developed for problems where multiple response analyses and (time consuming) simulations are involved. Finally dynamic simulations of vehicle with obtained wheel profile have been performed in ADAMS/Rail program package in order to control wheel/rail wear and safety requirements. A solution of the optimization problem is then taken as a new wheel profile. Wheels with such profile have the given contact characteristics, which results in improved wheelset dynamics and in reduction of wheel wear. The proposed optimum design procedure has been applied to improve the performance of the metro trains in Rotterdam, The Netherlands (RET), which were suffering from severe wheel wear and as a result the hunting of the vehicles. The results of the optimisation have shown that the performance of railway vehicle can be improved by improving the contact properties of the wheel and rail. Using the proposed procedure a new wheel profile has been obtained and applied to the RET metro trains. Due to the application of the optimised wheel profile the instability of the metro trains has been eliminated and the lifetime of the wheels has been increased from 15000 km to 114000 km.