Researches On Identification Method And Applications Of Angular Vibratig Modal For Internal Combustion Engine Crankshaft

Crankshaft is one of the most important structure parts of internal combustion engine (ICE), which withstands complex and alternating impact loads resulting in torsinal vibration. The crankshaft torsional vibration not only affects the fatigue strength of crankshafts, but also is relative to many other failures and performance deteriorations of ICE. Therefore the crankshafts torsional vibration has been become one of key in designs and applications of ICE as well as its power equipments. The crankshaft torsional vibration characteristic is determined by its angular vibration modality, and the modal analysis on crankshafts angular vibration can not only provide theory foundation for dynamic analysis and optimized design for crankshafts, but also the angular vibration modal parameters identified can be used to operating condition monitoring, fault diagnosis of ICE and torsional vibration evaluation and check.Aimed at the problems presented in the identification on crankshafts angular modal parameters, a method of identifying the crankshafts angular vibration modal parameters (natural frequency, vibration mode and damping ratio) in running ICE is developed in this dissertation. The identification on crankshafts damping coefficients, state monitoring and fault diagnosis on ICE and other issues are researched sufficiently based on this method. The identification techniques of crankshafts angular vibration modal parameters and the fault diagnosis can be improved and the condition monitoring technique of ICE based on crankshafts angular vibration can be enriched by the research results.An experimental method of identifying crankshaft angular vibration modal parameters in running ICE was presented. Taking into account the interactive effect of each angular vibration mode, the functional relationship between the harmonic angular vibration of a measuring point and the harmonic moment of a cylinder is derived; the influences of rigid vibration and other modes can be eliminated or reduced by quadrature component method; and a misfiring method is presented to identify the crankshafts angular vibration mode in operating condition of ICE. The identified angular vibration mode of crankshaft is correspond to the practical state of the crankshaft angular vibration in running ICE without complex test equipments and a great amount of experiments. And the effect of power nonuniformity on identification precision of crankshaft angular vibration mode and the method of solution are also analyzed.A new method of identifying the damping coefficient of crankshafts using the modal damping ratio of crankshaft angular vibration is presented based on the principle that the system vibration energy is unchangeable, and the relationship between the modal damping ratio of crankshaft and each crankshafts damping coefficient is derived, as well as the relationship between the modal damping ratio of crankshaft angular vibration and external damping coefficient of cylinder, damping coefficient of flexible coupling and damping coefficient of shock absorber. When the crankshafts damping coefficients are identified, the crankshafts damping characteristics are analyzed, the main damping coefficients of engine are determined and proper vibration mode of crankshaft angular vibration is selected firstly, and then the main damping coefficients can be identified. The main damping coefficients of ICE can be calculated more accurately without a great deal of experiments.Aimed at the limitation of the fault cylinder diagnosis method on basis of crankshaft vibration mode such as "quasi-rigid body model" or "quasi-trapeziform model", a new vector method to diagnose individual misfiring cylinder based on the vibration mode characteristic of crankshaft angular vibration is proposed. That is, at a certain rotational speed, if there is no node in the crankshaft angular vibration mode of an order, and the misfiring cylinder can be diagnosed accurately by making vector calculation on angular vibration displacement of measuring point in normal condition and random trouble condition. In this method, the diagnostic dynamic model of crankshaft harmonic angular vibration needs not to be established, and the crankshafts structure parameters and a great deal of experiments are not needed. This is also suitable for the case when the firing interval angle of each cylinder distributes asymmetrically.A new method of online monitoring ICE powers based on the crankshaft angular vibration response is proposed. When each cylinder works uniformly at a certain rotating speed, the relationship between an order's angular vibration displacement amplitude of the crankshafts measuring point and the engine powers can be represented by a cubic polynomial;thereby through fitting the variational curve of an order's angular vibration displacement amplitude for crankshaft measuring point against the engine powers, the angular vibration displacement amplitude of the order could be used to online monitor engine powers. This method is simple in measurement, no special apparatus needed, low cost and can satisfy engineering application.All new methods in this paper are deduced theoretically and proved strictly, and tested and verified sufficiently by a great deal of simulated researches and experimental verification.The research efforts not only resolves the problems presented in identification on experimental modal parameters of crankshaft angular vibration in running engine successfully, improves the identification techniques for modal parameters of crankshafts angular vibration, but enriches the fault diagnosis and state monitoring techniques for ICE. Furthermore some generalized meaning research results can also be used to resolve the problems in other relevant fields.