An Analysis of Longitudinal Vibration for Bogie Vehicle : Effects of the Lowered Stiffness of Rubber Vibration Isolators Used for Fixing Dampers in the Primary Suspension

When the new Shinkansen train, the series 100EC, came into service, lasting longitudinal vibration with a constant frequency arose frequently near the maximum operation speed. The lasting vibration was the first modal vibration excited by vertical track irregularities through the pitching motion of bogie trucks. This paper describes analytical results of the effects of the rubber stiffness on the longitudinal vibration characteristics. The rubber used for fixing the primary damper is a type of vibration isolator acting in series with the damper, and its stiffness must be reduced in order to allow the damper to incline with relative horizontal displacement between the truck frame and the axle box. However, when the stiffness is too low, the damping effect deteriorates. In the realistic range of reduced stiffness, the first modal longitudinal vibration increases with the decreasing stiffness, and when the stiffness is further reduced, the vibration due to truck pitching grows markedly.