A rail operator in Israel had a systemic problem with the powertrain that drives the backup power pack (BPP) on their entire train fleet. They would incur cardan shaft breakdowns every 6–9 months when the BPP was disengaged. The service provider for the rail operator struggled with this problem for the past 6 years.
Off-Highway Powertrain Services (OHP Services), who was the product supplier, offered to investigate the problem. Our service experts performed vibration analysis on the diesel engine and torque measurement on the BPP for two trains and compared the results to calculate the operating loads on the cardan shaft.
The torque measurements had very high variances on the alternating torque amplitude, significantly above the allowable limit for the cardan shaft being used. Therefore the lifetime of the cardan shaft was limited.
Also, the vibration analysis clearly indicated non-uniform speed output of cardan shaft caused by misalignment. This would increase wear and accelerate breakdowns. The following measures were suggested based on the findings:
- To shift the natural frequency out of the current operating range; redesign and recalculate the cardan shaft to the measured loads and conditions of the train
- To reduce the second order excitation; realign the BPP to the diesel engine so that the deflection angle of the cardan shaft is brought down to <1 degree
- A follow up torque measurement was also recommended to verify the new design
OHP Services is currently implementing the recommendations and working on the redesign.