Research On Shafting Dynamics And Fault Anlysis Of The Marine Diesel Engine With Timing Gears

In this thesis,two types of faults will be discussed.One is the timing gear fractual of the main diesel engine of the diesel propulsion apparatus fails freqeunently after three to eight months' operation.The other is the failure of the flexible coupling.According to the existing theories and specifications,such two types of faults have to be analyzed and researched separately.The relevance of those two types of faults will be investigated.Furthermore,in order to provide effective suggestions to solve those problems,the inherent coupling relationship by considering the whole system will be given.At first,the typical fracture of the timing gear near the prongs and tooth root is observed using the scanning electron microscopy and optical microscopy.Meanwhile,the surface hardness of the gear is also measured using the Vickers hardness tester.At last,the universal testing machine is used for testing the mechanical properties.It will be concluded that the fatigue is the main reason for the gear failure.It is found that the natural frequency obtained through calculating the stiffness of the flexible coupling torsional is larger than the test data.To fix this problem,the torsional stiffness online identification method based on the amendment of the natural frequency will be proposed.Such method will be verified to make sure that it can improve the accuracy of the model.Different from the existing ship regulatory requirements,the torsional vibration model of diesel engine propulsion system containing camshaft system is constructed.Meanwhile,the timing gear and flexible coupling is also coupled for the torsional vibration.It is found that the natural frequencies of the lower orders are sensitive to the torsional stiffness of flexible coupling.However,the natural frequencies of the higher orders are sensitive to the torsional rigidity of the timing gear.In the condition of working evenly for the each cylinder for the diesel engine,the torsional stiffness of the flexible coupling has great effects on the addional torque,which may cause the tear of the flexible coupling.The additional torque of timing gear is very sensitive to the torsional stiffness,and it can also be affected by elastic coupling torsional rigidity at some harmonic orders.The change of the additional torque of the elastic coupling and timing gear will be discussed in the condition of working unevenly,flameout of single cylinder,and the failure of the torsional vibration damper,etc.It is found that these common abnormal operating conditions have a great influence on the additional torque of failure point.And it is proposed that the shaft system should be operated in a normal condition.Finally,the effect of engine control parameters on shafting stability and fault additional torque will also be discussed.It is found that the stiffness of the flexible coupling has a large effect on the stability of hosts.If the stiffness of the flexible coupling is different from the design value,it will make the hosts operate unstably and the additional torque of the timing gear fluctuates largely.Engine control parameters for the normal operation condition will be given in this thesis.After adjusting the torsional stiffness of the flexible coupling and operating the test for 17 months,timing gear and flexible couplings can still operate smoothly and reliably.By researching the torsional vibration,the intrinsic relationship between the flexible coupling and the timing gear will be found.The influence of the working parameters of the engine and control parameters on the additional torque of the failure points of the shaft will also be obtained,which can provide a new analytical method for the fault diagnosis and treatment of the diesel engine.