Temporary noise on Jungfrau train transmission

Fig. 1: A historic train of the Jungfrau Railway in the Swiss Alps
Fig. 1: A historic train of the Jungfrau Railway in the Swiss Alps
Fig. 2: Rack and pinion gear with mounted accelerometer
Fig. 2: Rack and pinion gear with mounted accelerometer

The Jungfraujoch in the Swiss Alps is a must-see attraction. The Jungfraujoch is a particular favorite of tourists from the Far East. To see Jungfraujoch, you can now go via modern or historic railways. However it is annoying, if on the way to this fantastic place, noises suddenly occur in one of the railcars. But how dangerous these noises are, was a question to be answered using measurement technology. Or better yet, what can be done to eliminate this noise? A diagnostic order that is undertaken with glee. Fig. 2 shows a rack and pinion drive found in historic railcars. Accelerometers were mounted to characteristic measurement points of several drives, and a microphone installed inside the train. For data acquisition a mobile online CMS was temporarily installed in the train, to enable real-time measurement evaluation and diagnosis during the measuring run. Then the run began with an additionally coupled, fully filled water truck to simulate the passenger mass. It was apparent that the train changed gear in narrow curve sections both during the ascent and the descent, which needed to be considered as part of the evaluation.

Fig. 3: Open replacement gearbox
Fig. 3: Open replacement gearbox
Fig. 4: Open replacement gearbox
Fig. 4: Open replacement gearbox

The noise and vibration measurement clearly indicated that the dominant noise occurred only when the generator was descending at a speed of 24 km/h. And from the sound pattern we could deduce that gearing noise was the likely cause. The next step was to find out the gear stage responsible, using frequencies analysis and excitation frequencies calculation. The acoustically dominant frequency 1197 Hz was quickly identified. Unfortunately, the number of teeth was not documented anywhere, and the gearbox manufacturer no longer existed. The Jungfrau Railway technicians quickly presented a solution. A spare standby gearbox was opened at Eigergletscher railway station office. Subsequently associated teeth were counted (Fig. 3, Fig. 4). The respective meshing frequencies were calculated, and the abnormal gear stage identified. That same evening a targeted inspection of the abnormal gear stage took place in the depot, via a small inspection hole cover. A non-uniform wear was identified. Since the bearing vibrations were without abnormalities, a manufacturing defect in the initial production phase was the conclusion. A gear manufacturer then got the order to rebuild the gear in the affected gear stage. Regrinding of the affected gear stage, was all that was required.

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