To overcome the defects of the traditional time-domain synchronous average(TSA)technique

such asrequirements of key-phase signal and constant operating speed of gearbox in application

a new method for implementing TSA of vibration signal without key-phase signal for varying speed condition gearbox is proposed. By time frequency domain filtering and computing the instantaneous phase of filtered signal

the instantaneous speed estimation of gearbox is gained. The influence of speed variation is eliminated by equal angular interval re-sampling of the vibration signal. The re-sampled signal is used to implement the TSA processing. An experimental investigation on a variable speed gearbox test rig indicates that the accurate instantaneous speed of gearbox is estimated and the influence of speed variation of gearboxes is eliminated

and the effective monitoring and diagnostic information is provided by the TSA result of re-sampled vibration signal.