This case study presents the vibration analysis for a locomotive diesel engine based on different measurement methods. The author will shortly explain the initial situation starting from customer complaints, followed by the structural approach of the root cause analysis. After an engine overhaul high vibration amplitudes occurred in the low engine speed range.
For initial evaluation purpose velocity vibration spectra during engine idle speed sweep were analyzed. Based on the dominant first order, an unbalance issue was suspected. Therefore, engine mounting as well as vibration damper were check without any findings. Next step was the analysis of the time signals, especially the relative phases between engine front and rear end in all three directions. The results show a 180 degree out of phase lag between engine front and rear in the horizontal direction. The corresponding operating deflection shape mode will also be presented in this case study.
Based on this information further acceleration spectra are taken at the engine front and flywheel housings. The measurements showed gear mesh frequencies with multiple harmonics in the radial and axial direction. Because of the known teeth number the frequency could be assigned to the crankshaft gear driving the camshafts via a balance gear with same teeth number.
Therefore, front as well as flywheel housings were checked for timing calibration. The following survey discovered the root cause for first order vibrations. Both balance gears were incorrectly installed. After the correction of timing the unbalance was gone.
The audience will learn about the importance of vibration measurement the frequency as well as time domain. Also the analysis of relative phase is a great tool for troubleshooting purpose.

Takeaways

– Structured approach of troubleshooting
– Importance of different vibration measurements (time signals, spectra, phases)
– Operating deflection shape as analysis tool

Technical Background
▪ M.Sc. in Electrical Engineering and Automation Systems
▪ Electronic Technician
▪ Vibration Analyst Cat II

Work Experience (> 10 years)
▪ Head of Application & Product Support for CATERPILLAR diesel engine driven powertrains
➢ Segments: Industrial (construction, agriculture, etc.), locomotive, marine, electric power generation, oil & gas
➢ Applications: Prototype evaluation of engines / machines, NPIs (new product introductions), CPIs
(continuous product improvements), troubleshooting and root cause failure analysis
➢ Tools: Spectral analysis, time signal analysis, phase analysis, modal analyis, operational deflection shape analysis, alignment, balancing