Keywords: curving, steering, railway vehicles.

The paper investigates what is the reasonable index to evaluate curving abilities of railway vehicles. A definition is suggested: the curving abilities refer to the ability of a vehicle to run on curves against all wheelset flange contacts to the high rails. Based on this definition a study is undertaken through the wheel profile, wheelset and primary assembly and a bogie. Basic requirements for the wheel profiles are reviewed: (1) A steering index of a wheelset, with primary suspension, is used to evaluate the key component of the bogie is studied; (2) A radial adjustment index of a bogie is also studied to evaluate the curving ability of the bogie design. Computer simulations based on a utopia linear and nonlinear model have been made to evaluate the feasibilities of the indexes.

With an understanding of the wheelset guiding mechanism, the steering ability can be defined: Here it is the ability to balance the lateral suspension force by applying a yaw angle to the wheelset with less lateral movement to the high rail on a curved track. The defined "steering ability index" is equal to the lateral creep forces on a wheelset over the external force applied to the wheelset

Normally all wheelsets are installed in a bogie with two or three axles. The adjacent wheelsets will restrict each other according to the different axle base. So besides the above radial steering index, an index is needed to consider the wheelset restriction. The radial adjustment index is defined in the paper.

With the above suggested two indexes, a bogie design is to be evaluated with respect to the curving abilities by considering wheel profiles, primary suspension stiffness, load conditions, adhesion levels, axle base, rolling radius of wheelset etc.

One advantage is that the two indexes are all independent on track curve radius with the linear parameters, which are dominated by the basic curving performances of the bogie. The calculation can be made easily using a calculator. For more detailed values of indexes, nonlinear model of the wheelset and bogie can be employed to obtain the indexes using computer simulations.

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