3. Vertical damper to suppress decrease in wheel load on container wagon bogies

When a carbody rolls due to track irregularity, there is a decrease in wheel load. This can become a factor leading to derailment in the case of container wagons. Consequently, the vertical damper on the bogie was improved.

On container wagon bogies, vertical dampers are mounted in parallel with secondary suspension to manage the switch in attenuation characteristics between the loaded and empty state of the wagon.

However, depending on the load conditions, etc., even if the mass including the load corresponds to empty vehicle damper characteristics, there are cases where rolling can easily occur.

In such cases, if the vibration frequency caused by continuous irregularity at a constant wavelength and the natural frequency of the vehicle rolling coincide, resonance can occur, and the more rigid the secondary suspension, the greater the relative attenuation force insufficiency of the damper, causing a cyclical decrease in wheel load.

Investigations were carried out using dynamic vehicle simulation, to examine the attenuation characteristics of compliant dampers under different loading conditions, from empty to maximum loaded state. As a result, an improved damper was proposed for vehicles with relatively rigid springs, excluding empty state attenuation properties, corresponding to unified loaded state characteristics which strengthened the attenuation force in the operating speed region below 10cm/s (Fig. 1). (Fig. 1).

In order to confirm the effect of the improved dampers, stationary vibration tests were performed on a container wagon on a rolling stock test plant (Fig. 2). Cross-level irregularity track measurement data was input to the roller rig, to reproduce in a test, the conditions that led to the past derailment.
As a result, when the speed of roller rig was 60 km/h, it was found that the improved damper had lowered the wheel-load reduction ratio on the third axle by approximately 20% (Fig. 3).

Following main line running tests to confirm the validity of the new design with different loading conditions, a proposal will be made to introduce the improved damper into service as a way to improve the operating safety of freight wagons.