车用离心风机转子系统振动特性分析

为分析风机转子系统的振动特性,利用扰动力法建立了水润滑轴承刚度阻尼的非线性模型,完成了轴承-转子系统的动力学建模;基于转子系统的有限元模型,计算了转子系统的临界转速并进行了试验验证;分析了离心风机振动激励源,之后对转子在质量不平衡激励和轴承不对中激励下的振动特性进行了分析。结果表明,在质量不平衡激励下,转子系统振动的峰值频率主要位于整数倍频及半倍频处,其中以旋转基频和半倍频的振动为主;在轴承不对中激励下,转子系统振动的峰值频率主要位于整数倍频处,其中最主要的振动频率为旋转基频,其次为2倍频。该文对风机转子系统振动特性的分析对后续的整车振动与噪声分析,以及整车乘坐舒适性的改进提供了参考。

Analysis on vibration characteristics of vehicle centrifugal fan rotor system

Abstract: The high-speed centrifugal fan used in the air supply system is a key noise and vibration source of vehicle. Therefore, it is important for the centrifugal fan to achieve low vibration level. In previous studies, analyses of vibration characteristics are mainly based on the finite element method. But those models neglect the influence of bearing characteristics as well as the distribution form of different excitation sources in a bearing-rotor system. The focal point of this paper was to analyze the vibration characteristic of centrifugal fan system on the basis of the vibration analysis of the bearing-rotor system. Firstly, the nonlinear stiffness damping model of the water-lubricated bearing was solved by the disturbing force method. Then a dynamic model of rotor system was proposed based on the nonlinear stiffness damping model of water-lubricated bearing above. The first three-order critical speeds were calculated by the QR damped method based on the dynamic model of rotor system. The calculated first three-order critical speeds were 11 594, 12 272 and 64 646 r/min, respectively. Secondly, a measurement for the vibration spectrum of the rotor system was conducted to verify the proposed dynamic model of rotor system. A high-speed centrifugal fan was manufactured for the experiment, in which the motor vibration acceleration spectrum of rotating half fundamental frequency was extracted. The results showed that the calculated critical speed was 63 000 r/min, which agreed well with the measured one. This means that the finite element model of rotor system is effective for the analysis of rotor system. Thirdly, for the purpose of resource saving, the finite element model of rotor system above was further simplified to a one-dimensional beam model of rotor system. Comparing the first three-order critical speeds of one-dimensional beam model with the original model, the errors were 1.2%, 1.3% and 4%, respectively, which showed a good agreement. Therefore, the simplified one-dimensional beam model was used for the vibration analysis below. The vibration characteristics of the rotor system with imbalance masses were analyzed. The results showed that the excitation of single imbalance mass led to the vibration of rotating fundamental frequency. Multiple imbalance masses of rotor system led to the vibration at fundamental frequency and its frequency doubling as well as half fundamental frequency. The main vibration frequencies hardly changed when phase difference between the unbalanced masses was different. In addition, resonance happened at the natural frequency of 1 137 Hz. Total vibration amplitude significantly increased when the system speed exceeded the third order critical speed of 64 646 r/min. It also showed that under the excitation of bearing misalignment, the peak frequency of vibration was also mainly located at its integer frequencies, in which rotating fundamental frequency was dominant, followed by the rotating double fundamental frequency. The same as the excitation of imbalance masses, resonance also happened at the natural frequency of 1 140 Hz. Total vibration amplitude had also an obvious increase when the system speed exceeded the first order critical speed of 11 733 r/min. The analysis of vibration characteristics of rotor system in this paper is of great significance for the analysis of vehicle acoustics and vibration behavior as well as optimizing the vehicle ride comfort.