Cyclic Harmonic Ratio Defined in Squared Envelope Spectrum and Log-Envelope Spectrum for Gearbox Fault Diagnosis

Gearboxes are widely used in many industrial fields, and their faults may bring serious economic losses or even casualties. Therefore, two new indexes, namely, cyclic harmonic ratio (CHR) and log-CHR, are proposed in this article for gearbox fault diagnosis, which can effectively measure the degree of specific second-order cyclostationary components from squared envelope spectrum and log-envelope spectrum, respectively. CHR and log-CHR are the improved forms of indicator of second-order cyclostationary (ICS2) and log-cycligram (LC) index, respectively. They are also the simplified form of discolored CHR (DCHR). The proposed indexes are more robust than the available ICS2 and LC index, and the relevant comparisons are also conducted by using an acoustic emission signal of the planetary gearbox and a vibration signal of the fixed-axis gearbox. In addition, a noise resistance study is conducted to evaluate the robustness of the proposed methods. As a result, the proposed methods are proved to have better performances than ICS2gram and LC, and they can be regarded as effective methods for gearbox fault diagnosis.