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Analyzing Gearbox Degradation Using Time-Frequency Signature Analysis

Lin Liu, Zhuang Li & Suri Ganeriwala
SpectraQuest Inc., 8227 Hermitage Road, Richmond, VA 23228
Published: March, 01 2006


In this work, vibration signature caused by gear tooth seeded fault is studied in the time and frequency domains. The experiment was conducted on a Machinery Fault SimulatorTM(MFS). The pinion gear in the gearbox was intentionally faulted with increasing severities, and a vibration signal was collected for each case. The signal was analyzed in a time and frequency domain. The results indicated that the vibration signature of a faulted bevel gear tooth is a pulse in time domain. Because of this impulse signal, strong sidebands arise in the spectrum around the mesh frequency.

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The experiment is conducted on a Machinery Fault Simulator TM (MFS). The vibration data was collected by a tri-axial accelerometer installed on the top of the gearbox. The frequency limit was set to 5 KHz during data acquisition. During the test, the motor speed was kept at 1000 RPM and the brake loader was set to 2.5. First, the baseline of the gearbox vibration data is collected. Then the gearbox is disassembled and the pinion gear is taken out. The surface of one of the pinion’s teeth on the meshing side is milled using a drill mill. After the damage is done to the tooth, the pinion gear is put back into the gearbox. Vibration data is collected again under the same running conditions (speed and load) as before. This process is repeated four more times with additional damage applied to the same pinion tooth for each case scenario. The five damage severities are denoted as Severity Level 1 to Level 5, from the least to the most.

Fig 1: Baseline Vibration Signal Spectrum around Mesh Frequency Component


Fig 2: Vibration Signal Spectrum (Damage Severity Level 5)-Spectrum around Mesh Frequency Component