Analytical and Experimental Study of Lateral Vibrations in a High-Speed Gear Unit

This paper presents a comprehensive investigation into a significant lateral vibration issue encountered in a high-speed industrial gearbox used as the central unit of an electro-compressor train. During initial commissioning, the gearbox was unable to reach its rated operating speed due to excessive vibration levels (> ۵۰ μm peak-to-peak), prompting a detailed diagnostic analysis. The root-cause study identified that the critical frequency of the pinion shaft was very close to the gearbox's operating speed, resulting in resonance. Two potential solutions were considered to shift the first critical speed outside the operating range. Increasing the mass of the pinion to lower its critical speed was deemed impractical due to design constraints and standard limitations. Consequently, the alternative approach of increasing the shaft diameter to enhance stiffness and elevate the critical frequency was implemented. Numerical simulations confirmed that this modification successfully moved the critical speed well above the operating range, ensuring safe operation in a subcritical regime. Subsequent mechanical running tests validated the effectiveness of the redesign, showing a substantial reduction in radial vibration amplitudes. Measured vibration levels at both the low-speed and high-speed shafts were below ۲۰ μm (peak-to-peak), confirming the successful mitigation of resonance. The study demonstrates the value of integrating analytical modeling, simulation, and targeted engineering modifications to resolve complex vibration problems in geared rotor systems. The implemented solution not only restored reliable gearbox operation but also provides a practical industrial experience for addressing similar high-speed vibration challenges in industrial mechanical drives.

Keywords:

High-speed gearbox , Shaft critical frequency , Vibration analysis , Critical Frequency Shifting