Evaluating the performance of 3-piece bogies on short defects and with unequal wheel diameters

Suspension tests on three piece bogies were conducted at the Centre for Railway Engineering Heavy Testing Laboratory. Two 3–piece bogies were tested; both had constant force type friction wedge dampers. One bogie had constant force wedges housed in the bolster. The other bogie had constant force wedges housed in the sideframes. The bogies tested were not reconditioned with wedges half worn or more. Tests were completed using a coal wagon ballasted with scrap steel to simulate a loaded wagon. Track profile inputs were simulated using position controlled hydraulic cylinders. Both bogies were subjected to bounce tests at 3 and 7 Hz and sinusoidal rail profile inputs of wavelengths 3.0 m with simulated vehicle speeds of 40 and 80 kph. Further variation in suspension behaviour was investigated by simulating variations in wheelset wheel diameters. Wheelset diameter mismatches of 24mm were simulated for first and second axles on the bogie. Rail profile magnitudes tested were 24 mm peak to peak.The bounce tests illustrated the inadequacy of the friction damping at resonance. The simulation of rail profile inputs, which resulted in pitch motion of the bogie sideframes resulted in unexpected hysteresis performance. The work demonstrates the limitations of the friction dampers commonly used on freight bogies and highlights the need for more detailed mathematical models in wagon simulation.