Research On The Hysteretic Nonlinear Features Of PZT Actuator In Direct Acting Fuel Injector

The electronic fuel injector directly actuated by piezoelectric actuator can achieve an accurate injection under the situation of high fuel pressure, which will significantly improve the fuel efficient of the combustion engine, reduce the working noises, and decrease the harmful emissions. However, as a subset of poly crystal ferroelectric materials, the hysteretic nonlinear features and the bias pressure dependence and the loading frequency dependence will pose many great challenges to model building and model-based controller design.According to the above engineering backgrounds, the current paper conducted an intensively analysis to the domain structures and the orientation switchings, and give an explanation to the hysteretic phenomena from the perspective of domain orientation switchings. In order to providing the theoretic supports to the control algorithm design, a dynamic coupled differential model based on the theory of Landau phase transition was proposed with referring to the existing hysteretic models and the requirements of engineering applications. In the current paper, a nonconvex constitutive curve was constructed and the hysteretic behaviors can be mimic as the bifurcation was introduced into dynamic system by the nonconvex law. So, the contents are listed as followings:In the first chapter, the background and significance of the current paper were presented. The advantages and technical bottlenecks were explained in details and several popular fuel injector products were introduced briefly. Then, the theme of the current paper was introduced which was to construct a model to capture the hysteretic nonlinear curves and also will be convenient in engineering applications.In the second chapter, a further research of the features of hysteresis and the formation mechanism of the hysteresis in PZT materials were conducted. A brief explanation of the relationships and differences among the piezoelectric effect, electrostrictive effect and ferroelectric effect in piezoelectric ceramics was provided. Then, a deeper analysis on the spontaneous polarization, domain structure and the orientation switching processes on the micro-structures was provided. Finally, a brief introduction and the analyses of advantages and disadvantages of the popular hysteretic models in existing applications and researches were presented, which would be the comparisons to the proposed model.In the third chapter, a single crystal differential model was proposed on the basis of Landau theory of phase transition and the nonconvex constitutive relation. The hysteretic behaviors were captured through introducing the bifurcation into the dynamic system. Then, a poly crystal model was constructed through adopting a weight function of domain distribution, which was consistent with the physical essences of poly crystal materials. The parameter estimation strategies of both models were provided systematically, which were conducted with basing on the least squared error.In the fourth chapter, the numerical simulations of bias stress dependence and loading frequency dependence were conducted. Then the comparisons of modelling results and experimental results under different bias pressures and loading frequencies shows the superiority of the proposed dynamic differential model.In the final chapter, a conclusion of the current paper was presented, and perspective of the future research work were mentioned.