Siemens AG has commissioned PROSE to carry out wheelset torsional vibrations on its Desiro ÖBB cityjet in Austria. The aim of the measurement is to determine the maximum dynamic torsional moments of the wheelset shafts occurring under the most unfavourable friction conditions.
Wheelset torsional vibrations occur at certain slip velocities and unfavourable friction conditions due to falling coefficients of friction. This can lead to an unstable system state that triggers a self-excited (friction) vibration. This counter-phase oscillation between the left and right wheel disc causes torsional amplitudes at the wheelset shaft that exceed the torsional momentum due to maximum traction and braking force during start-up and braking by a multiple.
The maximum torque value of the torsional moment determined by this measurement is used by the manufacturer to validate the load assumptions of the wheelset shaft. In Germany, this measurement is part of the wheel set shaft approval.
PROSE has installed an irrigation system on the vehicle to produce these unfavourable force-fastening conditions or the necessary slip for provoking wheelset torsional vibrations in dry rails, which irrigates a total of 8 wheel-rail contact points by means of controllable solenoid valves. The flow rate is infinitely variable.
In addition, PROSE records the angular speeds of the measured driving wheel sets with high-resolution magnetic tape sensors (over 8000 increments per revolution). The slip velocity formed from these angular velocities is a decisive evaluation parameter (dynamic torsional moment as a function of slip velocity) of how intensively torsional vibrations were provoked during the tests.
Approval is granted on the basis of the evaluation of the torsional signals, whereby the criteria according to DIN-Taschenbuch 491/1 must be fulfilled.
In recent years, PROSE has developed a software that enables an assessment of the fulfilment of the approval criteria during the measurement on the test vehicle. This enables immediate adaptation of the drive programs and setting parameters (e. g. irrigation) and saves our customers time and money.