To develop a non-linear dynamic model for gear interaction including frictional effects to better understand the gear vibration responses under different operating conditions.
To implement advanced signal modelling and data analysis techniques capable of enhancing vibration signatures to achieve more accurate detection and reliable diagnosis of different lubricant deteriorations.
Achieving these aims and experimentally verifying the noise reduction, signal analysis and feature optimisation, will provide for more efficient fault detection and diagnosis for the monitoring of multistage gearboxes.
1.7.2 Research Objectives
In order to fulfil this research, a number of objectives have been identified as follows: Objective 1. To review existing condition monitoring techniques and assess the
performance of the most common techniques used for online CM and early fault detection of gearboxes.
Objective 2. To review the main sources of gear vibration to obtain an in-depth understanding of the dynamic interactions between transmission components. Objective 3. To design and construct a mechanical transmission test rig for the evaluation
of industrial gearboxes under different operating conditions, which allow different faults to be introduced into the gearbox components, enabling subsequent system behaviour to be characterised.
Objective 4. To develop numerical dynamic model with the help of MATLAB, and compute the periodic mesh stiffness variation of helical gears as a function of the contact position of the meshing teeth. Also, to characterise the vibration signature changes, enabling more reliable diagnostics under different operating conditions. Objective 5. To calibrate the linear and nonlinear responses of the dynamic model and
evaluate the model for different frictional modes with progressive tooth breakages. Objective 6. To develop an efficient computation and stable analysis of the dynamic
responses of a tooth surface worn in a two-stage helical gearbox using a run-to failure experimental test and a comprehensive dynamic model including EHL friction effects.
Objective 7. To investigate nonlinearities in vibration transmission and viscoelastic properties of gearbox lubrication, and hence develop effective signal processing methods for online monitoring and diagnosis of different gearbox oil deterioration conditions under different gear operating conditions, and any constraints on its usage that should be considered.
Objective 8. To develop guidelines for future research activity relating to this field.
Structure of the Thesis
The thesis is divided into nine chapters including the current chapter. A brief synopsis of each subsequent chapter is as follows:
explains gear failure modes, the status of gearbox lubrication and the conditions for lubricant deterioration.
Chapter 3 -This chapter gives an introduction to vibration analysis techniques commonly
used for CM and fault diagnostics of the gear system. It starts with main characteristics of time and frequency domain analysis followed by an explanation of TSA and the effect of modulation. After that, higher order spectra analysis methods are introduced due to their ability to suppress background noise and improve the gear fault detection and diagnosis.
Chapter 4 –This chapter explains the test facility and fault simulation used in this study. It
describes the gearbox test rig components and control systems that are used to carry out the investigation with the vibration measurement specifications. Fault simulation and data collection procedure are discussed at the end of this chapter.
Chapter 5 -This chapter presents a numerical dynamic model of a two-stage helical gearbox
with the inclusion of time-varying friction based on the EHL model. An in-depth calculation of helical gear mesh stiffness is also developed including the dynamics of the system under various possible failure conditions. In addition, different tooth breakage (TB) severities have been simulated to evaluate the model performance under different tooth stiffness excitation models.
Chapter 6 -This chapter illustrates parameter identification and validation of the numerical
model with the experimental results for the purpose of CM. It examines the gear dynamic responses from both experimental and numerical studies with increasing tooth surface wear from its earliest phase. A description of the experimental setup of a run-to- failure test arrangement is developed. The numerical model is developed to simulate time-varying mesh stiffness, coupled with an EHL frictional model and tooth wear characteristics.
Chapter 7 - This chapter defines the diagnostic relationship between vibration signature
and lubrication status of the gearbox. Different lubrication problems such as contamination with water, starvation and change in oil viscosity have been simulated under different operating conditions. To establish online health monitoring of the gearbox oil condition based on vibration signal analysis, effective analysis methods have been used to normalise the condition indicator and investigate any measurable changes correlated with the variation of gearbox oil condition for future preventive maintenance.
Chapter 8 - This chapter evaluates the performance of the MSB method for monitoring
excessive bearing clearance based on vibration analysis in the presence of gear wear. Three bearings with different standard clearances have been used to investigate the effect of bearing clearance variations on the characteristics of helical gear vibration characteristics.
Chapter 9 – This chapter draws conclusions based on the key findings of the research. The
objectives are reviewed and a summary of the author’s contribution to knowledge and the novel aspects of the research are presented. This chapter also gives suggestions and recommendations for future work in related research areas.