The concept of active technology in rail vehicles has been studied theoretically and experimentally for several decades and has now reached the stage of implementation. Active Lateral Suspension (ALS) is the active technology that leads the development in active secondary suspensions if carbody tilting is disregarded.

Active suspension systems may have an influence on running safety of the vehicle. The requirements to fulfil are related to forces between wheel and rail. The safety must be assured by the manufacturer by a safety assessment, which must be sent to the authorities before entering service. An important part of the assessment is to show that the active system, under all conditions, is part of a vehicle that runs safely on the track. The passive components in the vicinity of the active system have an important role in assuring that even a defective active system fulfils the required safety.

This master thesis aims to set requirements on the passive suspension components for the failed ALS.

The study has been conducted by varying various parameters of the vehicle with different running conditions and failure cases. The study highlights that the secondary lateral bumpstop is the most important parameter for the vehicle safety.

With soft bumpstop (low stiffness) the vehicle runs within safe limits for all studied conditions, and the effect of varying other parameters, running conditions and failure cases, is marginal. For somewhat higher stiffness (medium bumpstop), the effect of other parameters plays a critical role in ensuring safe run. For hard bumpstop, the track shift forces are above the limit values, independently of the passive component settings.

High vertical forces have been observed for certain cases with medium bumpstop, due to primary vertical bumpstop contact, which can be prevented by increasing the primary vertical damping or by increasing the vertical play. Reduction in track shift forces has been observed with the increase of primary vertical damping. The reason for the effect is not known and is proposed for further study.