【作者】 应广驰；

【导师】 孟光；

【作者基本信息】 上海交通大学 ， 机械设计及理论， 2008， 博士

【摘要】 涡轮增压器通过增压增加了气缸的进气量,使燃油燃烧得更多更充分,提高燃油的经济性,增加发动机的输出功率,极大地改善了发动机的性能,因而获得了广泛的应用。涡轮增压器是发动机的重要子系统,其工作性能、使用可靠性和稳定性有着很高的技术要求。涡轮增压器转子转速快,工作温度高。此外,由于涡轮增压器是安装在发动机上的,相比于涡轮增压器转子的高速旋转,发动机运转时产生的低频的大位移的振动会通过油膜轴承传递给涡轮增压器的转子。尽管发动机的振动频率远远低于涡轮增压器转子的转速,但这些振动还是会通过非线性油膜轴承对涡轮增压器的转子振动产生很大的影响。传统的转子动力学研究主要是针对地面旋转机械的,并假设基础的刚性足够大且是固定不动的。对于涡轮增压器这样的转子系统,这种假设显然是不太合理的,必须考虑基础振动的影响。因此,考虑到涡轮增压器转子的高速高温的工作条件,加上发动机基础激励的影响,对涡轮增压器进行转子动力学研究就显得非常重要。本论文旨在研究考虑基础激励的涡轮增压器转子动力学建模与分析方法,进行发动机对涡轮增压器的基础激励辨识,开展发动机–排气管–涡轮增压器系统的模态分析,探讨基础激励与非线性油膜力耦合作用下的转子动力学问题,应用有效方法实现系统仿真,提供在基础激励作用下的故障诊断和状态监测方法。论文的研究围绕这些内容展开。对于本文应用三种方法进行了发动机对于涡轮增压器的基础激励的辨识。第一,考虑到发动机给涡轮增压器转子的基础激励是通过中间室和浮动轴承对转子起作用的,如果能得到发动机工作时轴承座(即中间室内部)的振动响应,就可以用它作为发动机的基础激励,进行涡轮增压器转子的动力学研究。然而中间室的温度高,振动响应不易测量。只在中间室的注油孔部位受润滑油的循环冷却作用温度较低,振动响应可以测量的。考虑到中间室是一个刚度很大的空心柱体,那么就可以假设中间室注油孔(即中间室外部)的振动响应就等同于中间室内部的振动响应,可以通过直接测量注油孔的振动响应方法获得发动机的基础激励。因此,通过对中间室的实验模态分析、中间室内部和外部的频响函数测定和比较以及振动台上中间室内部和外部的振动响应比较等方式,验证了中间室外部注油孔的振动响应与中间室内部的振动响应是等同的,因此可以用直接测量中间室外部振动响应的方法获得发动机对涡轮增压器转子的基础激励。第二,通过测量涡轮增压器可测量点的振动和激励点至这些可测量点的频响函数,利用频响函数矩阵求逆法得到轴承座内部难以测量的振动响应。对涡轮增压器进行自由悬挂实验和振动台实验验证了此方法的有效性和可行性,并且用来反演的可测量点越多,获得的不可测点的响应越精确。这是第二种获得基础激励的方法。第三,利用对发动机–排气管–涡轮增压器整体系统理论建模的方法,获得涡轮增压器中间室的响应。在对整体发动机悬置系统建立动力学模型时,将发动机整体系统分解成发动机主体和排气管+涡轮增压器两个子系统,发动机主体子系统用刚体运动建模,排气管+涡轮增压器子系统用实验和有限元模态分析相结合的方法建模,然后用自由界面模态综合法对各子系统进行综合,获得整体系统的固有频率和振动响应。计算得到的与实验测量的固有频率非常吻合,而计算得到的与实验测量的振动响应也很接近。在考虑基础激励的涡轮增压器转子动力学研究方面,主要包括三方面内容。第一,对涡轮增压器的转子建立线性动力学模型,进行进行转子的振动特性研究,包括模态分析和临界转速计算,以确保涡轮增压器的工作转速能远离转子的各阶临界转速,从而获得安全平稳的运行。计算得到的自由转子的固有频率和模态振型与实验结果非常吻合,验证了动力学模型的可靠性。此外,还对含基础的转子进行临界转速分析,研究不同的基础的质量和支承刚度对转子的临界转速的影响。计算表明,基础的质量和支承刚度只对基础自由度振动的固有频率有影响,而对转子的临界转速没有影响。第二,考虑发动机的基础激励和非线性油膜力,建立涡轮增压器转子–轴承系统的动力学方程,计算转子在偏心惯性力作用下的动力学响应,研究了转子随转速变化的分叉规律以及基础激励对转子非线性动力学行为的影响,并与没有基础激励时的转子动力学行为进行对比,发现考虑基础激励的转子动力学行为明显不同于没有基础激励的情况。基础激励会通过非线性油膜力非常显著的影响转子的动力学行为,例如基础激励会使转子振动响应产生众多分频和倍频成分,在低转速时会使原本单周期的运动变为周期2运动,基础激励会降低转子发生油膜涡动和混沌运动的转速。但由于基础激励本身的频率就比较低,基础激励对转子动力学的影响主要体现在转子转速较低的阶段,随着转子转速的提高,基础激励的影响也逐渐减小。第三,研究含有裂纹故障和碰摩故障的转子在基础激励的作用下的动力学问题,提取在基础激励下的故障特征信息,进一步揭示基础激励对转子动力学的影响。研究发现,基础激励对裂纹转子的动力学响应有着复杂的影响,特别是转子开始发生油膜涡动的时候,基础激励的存在使裂纹力的作用更显著。基础激励的存在会增加转子发生碰摩的可能性,也会加剧转子碰摩的程度。最后,对全文的工作进行了总结,并对今后的研究方向进行了展望。更多还原

【Abstract】 A turbocharger has a broad application on the engine because it can improve the property of an engine by charging more air into the cylinders, burning more fuels and more sufficiently, and subsequently carrying out more power. As an important component of an engine, the turbocharger has a high command on the working performance, reliability and stability. The turbocharger is a rotational machine with extremely high rotational speed and under high temperature situation. As the turbocharger is always founded on the engine, low frequency, with respect to engine’s running speed, large deflection vibrations are transferred from the engine to the turbocharger rotor through the hydrodynamic bearings. Even though these low frequency vibrations are far below from the rotor’s running speed, they do affect its operation in a nonlinear way through the journal bearing clearance variation. Uptodate, many efforts have been made to investigate the nonlinear behaviors of rotor dynamics, including bifurcation, chaos, oil whirl and whip, stability, and so on. However, the traditional rotor dynamics mainly aims at the ground rotational machine, and presumes the base is stationary and the supporting stiffness is efficiently large. This presumption is obviously unreasonable for the turbocharger rotor system. The influence of the engine’s base excitation must be taken into account in the turbocharger rotor dynamics.In this effort, this dissertation deals with the engine’s base excitation identification and the turbocharger rotor dynamics investigation with the base excitation. The base excitation identification method is presented, the modal analysis of the engine-manifold-turbocharger system is carried out, the dynamic model of turbocharger rotor-bearing system is established, including the engine’s base excitation and nonlinear oil film force, the nonlinear dynamic behavior of unbalance mass is investigated, and the fault diagnosis and state monitor with the base excitation are studied.Three methods are applied for the engine’s base excitation identification in this dissertation.Firstly, based on the fact that the engine’s base excitation affects the turbocharger rotor dynamics through the center housing and the hydrodynamic bearings, if the vibration responses of bearing block (center housing inner) when the engine is running on can be obtained, we can use these responses as base excitation for the turbocharger rotor dynamics. However, the responses of center housing inner can hardly be measured directly due to its high temperature and too small room to place accelerometers. Only the responses of center housing lubricant nut (center housing outer) can be measured owing to the cyclic lubricant cool. Considering that the center housing is an extremely stiff hollow cylinder, we assume that the vibration responses of center housing outer are identical to the vibration responses of center housing inner, and the base excitation can be obtained by measuring the responses of center housing outer directly. In order to validate this assumption, the modal analysis of center housing is carried out, the test and comparison of frequency response functions (FRF) of center housing inner and center housing outer are processed, and the test and comparison of vibration responses of the engine on the vibrator table are made. The results show that the responses of center housing outer are identical to the responses of center housing inner, and the base excitation can be obtained by measuring the responses of center housing outer directly.Secondly, an FRF matrix inverse method is applied to acquire the vibration responses of turbocharger center housing inner by means of testing the responses of measurable points on the compressor housing shell and their FRFs. This method is verified by free hanging experiment and vibrator table experiment, and thus proved to be efficient and applicable. The factors that influence the accuracy are analyzed, and the more measurable points that are used to inverse, the more accurate the inversed immeasurable responses of center housing inner.Thirdly, a theoretical dynamic model of the engine-manifold-turbocharger is constructed, and the responses of center housing inner can be derived from this model. The whole engine system is divided into two subsystems: engine main body subsystem and manifold-turbocharger subsystem. The engine main body subsystem is modeled by rigid body movement, and the manifold-turbocharger subsystem is modeled by the combination of finite element method (FEM) and experiment method. These two subsystems are synthesized by free interface component modal synthesis method. The vibration modes and vibration responses are obtained from the synthesized system equations. The calculated results agreed well with the experiment results. Through this study, the response of turbocharger bearing block, which is regard as the base excitation for turbocharger rotor dynamics, can be determined.On the investigation of the turbocharger rotor dynamics with base excitation, there are three aspects of contents.Firstly, the linear dynamic model of the turbocharger bearing-rotor is constructed for the modal analysis and critical speeds calculation, so that the working speed of turbocharger can be far away from the critical speeds. The predicted natural frequencies and mode shapes of the free rotor agree with the experiment results, which validates the dynamic model of turbocharger rotor. Further more, the critical speeds of base-bearing-rotor system are analyzed, and the base mass and supporting stiffness variation influences on the critical speeds are investigated. The results show that the base mass and supporting stiffness variation can only affect the base’s natural frequency, and cannot affect the rotor’s critical speeds.Secondly, in order to investigate the influence of the base excitation on the nonlinear rotor dynamic behavior of turbocharger, a dynamic model of turbocharger rotor-bearing system including the engine’s base excitation and nonlinear lubricant force is established. The rotor vibration response of unbalance mass is simulated by numerical calculation of Runge-Kutta method. The bifurcation disciplinarian and chaos behaviors of nonlinear rotor dynamics with various rotational speeds are studied. The results obtained by numerical simulation show that the difference of dynamic behavior between the turbocharger rotor systems with/without base excitation is obvious. The base excitation will affect the rotor dynamic behavior in a complicated way, e.g. the base excitation will change the rotor dynamic behavior from period-1 motion to period-2 motion at a low rotational speed, and the base excitation will lower the rotational speeds at which the oil whirl begins and chaos motion occurs. Since the frequency of base excitation is much lower than the rotational speed of the turbocharger rotor, the influences of base excitation on the rotor dynamic behavior are mainly at the low rotational speed. The influences of base excitation lessen gradually with the increase of rotor rational speed.Thirdly, on the purpose of revealing more influences of base excitation on the rotor dynamics, the crack rotor dynamics and rub-impact rotor dynamics with base excitation are investigated, and the characteristic information of fault with base excitation are abstracted. The investigations show that base excitation will complicate the cracked rotor dynamics. Especially at the rotational speed that the oil whirl begins, the base excitation will make the crack forces more distinct. The base excitation will increase the possibility and extent that the rub-impact fault of rotor happens.Finally, the dissertation is summarized, and the prospect is presented.更多还原