Simulation of traction and curving for passive steering hauling locomotives

In a heavy haul train operations the ruling grades that set the tractive power requirements for train consists are often associated with tight curvatures. Past studies of passive or active bogie steering developments have been mostly directed towards high speed rail applications or light rail and commuter rail applications and hence studies have focused on two axle bogies. Linked passive steering three axle locomotive bogies such as produced by General Motors EMD for the SD70 class locomotive are in widespread use however, there are few publications on traction and curving, and few papers on linked passive steering bogies.This paper presents a simulation study three axle bogie locomotives on various curve radii with traction and variable rail friction conditions. Curving performance is assessed showing body linked radial bogies to have considerable advantages over axle linked bogies that are significantly better than yaw relaxation bogies at improving steering under traction. As traction adhesion approaches the rail friction coefficient steering performance of all bogies without forced steering deteriorates to the same levels as a rigid bogie.