Other Reports

Technical Documentation: Locomotive Truck Hunting Model

  • 26
  • Oct
  • 1976
AUTHOR: V. K. Garg, G. C. Martin, P. W. Hartmann, J. G. Tolomei
SUBJECT: Tracks & Structures
KEYWORDS: Computer Programs, Critical Velocity, Dynamic Tests, Mathematical Models, Vehicle Design
ABSTRACT: Two very different modes of hunting behavior are frequently observed; body hunting and truck hunting. Body hunting or primary hunting is often characterized by violent motions of the carbody. Truck hunting, or secondary hunting, is inherent in the vehicle design. Theoretically, with a perfect cylindrical wheel profile, truck hunting can be eliminated, but cylindrical wheel profile has a number of operating drawbacks. This type of hunting is characterized by severe oscillations of the truck or wheel axle set relative to the carbody. Once truck hunting starts, it continues to worsen as locomotive speed increases. A complete analysis of the hunting of a locomotive should take into consideration the carbody, truck, primary and secondary suspensions, and the wheel-rail contact forces. This requires a dynamic system with multi-degrees of freedom. Five mathematical models were developed with the objective of evaluating primary and secondary hunting of four or six-axle locomotive. A two degree of freedom model was developed for a single wheel-axle set. Seven and nine degree of freedom models were developed for trucks with two or three axles. Combining two of the trucks models with the carbody seventeen and twenty-one degree of freedom locomotive models were obtained. A characteristics equation, based on linear equations of motion was obtained for each model. This equation is a function of velocity. A computer program was written to compute the complex roots (eigenvalues) and the corresponding nonmalized modes shapes (eigenvectors) of the characteristics equation. This computer program can determine the critical velocity, which is the velocity that coincides with the advent of instability. The resulting computer model would be used primarily as a design tool.