Research On Vibration Signal Processing Techniques And Applications To Fault Diagnosis Of Helicopter Gearbox

Gearboxes are kernels of helicopter transmitting systems. Their faults threaten the safety o f helicopter flights. So there have been greatinterests in theoretical and pradical research on detection and diagnosis of such failures. With the faint characteristic signal and strong environment noise, the vibration signal of helicopter gearbox have often low signal-to-noise ratio, which makes it difficult to extract information about gearbox condition. So denoising methods are key techniques for fault diagnosis of helicopter gearbox.Time Synchronous Averaging is useful to enhance vibration signal of gearbox. To improve fault diagnosis of helicopter gearbox, the intermediate gearbox of some helicopter is taken as diagnostic object. Empirical Mode Decomposition and Time-Frequency distribution are applied as processing tools, classic Time Synchronous Averaging is advanced in the aspect of tachometer signals. These techniques are investigated in this dissertation to enhance vibration signals. Based on these researches, a prototype condition monitoring and fault diagnosis system for helicopter gearbox is constructed. The detailed contents and innovative work are shown in the following sections.1 To process vibration data without tachometer signals using period-based Time Synchronous Averaging, Phase Error Accumulation Effect is analyzed thoroughly. Phase Error Accumulation Factor is defined to estimate the rule of round estimation error and frequency e stimation error on Phase Error Accumulation E ffect. The influencing rules on Time Synchronous Averaging signal are achieved by Phase Error Accumulation Factor, component order and averaging number.2, To separate vibration from different sources, Empirical Mode Decomposition is studied intensively. The validity of Empirical Mode Decomposition is probed with the definition of valid decomposition. The conditions of valid decomposition are deduced for sine signal and applied to fault diagnosis of faulty bearing in a gearbox. It is proved that the component of gear vibration is compliant to resultant expression of Empirical Mode Decomposition. So a fundamental problem is settled for its applications to diagnosis of gearbox fault. A sufficient condition of valid decomposition is established based on deduction of Empirical Mode Decomposition for modulated signals.3 To fulfill the requirements of time-frequency information extraction, Wigner distribution is mended based on Empirical Mode Decomposition. Short-time Fourier transform and Wigner distribution are compared with their shortcomings and merits. The crossterm of Wigner distribution is examined. Mended Wigner distribution based on Empirical Mode Decomposition is brought out. Experiment analysis demonstrates this...