Squeal Noise Reduction and Dynamic Analysis of Stick-Slip Vibration in a Rotor System

Abstract

The cause of squeal noise in a water pump, a rotor system, was investigated and the stick-slip torsional vibration was analyzed using a mathematical model. In order to analyze the stick-slip phenomenon, the single-degree-of-freedom equivalent torsional vibration model and the continuous torsional beam were modelled. The simple torsional model is used to identify design parameters sensitive to squeal noise generation and suggest design guideline to reduce squeal noise. Also, dynamic characteristics of stick-slip torsional vibration were analyzed by continuous model, and nonlinearity and discontinuity of friction torque were considered. Main issues for this study are as follows: In chapter 2, a cause of the squeal noise of the automotive water pump is identified by the experiment and modal analysis. The squeal noise component was extracted by the signal analysis experiment. A finite element analysis model was constructed and used to analyze mode shapes and natural frequencies corresponding to squeal noise. The primary cause of squeal noise was analyzed as the first torsional natural frequency of the water pump shaft. In chapter 3, a method to reduce the squeal noise generated by the automotive water pump is presented. The water pump rotor system was modelled as an equivalent single-degree-of-freedom model for torsional vibration, and the stability coefficient was established for this model. From the parametric study, I suggested design strategies to reduce the possibility of squeal noise. Sensitivity analysis showed whether the design parameters of the water pump have a significant effect on the stability coefficient variation within a given design range. A design for reducing squeal noise was proposed through design optimization. Prototypes were fabricated, and the results of this study were experimentally verified. In chapter 4, I present a study on the stick-slip torsional vibration of the spinning shaft in an automotive water pump. To analyze the stick-slip vibration of a water pump, a dynamic rotor model with a pulley, an impeller, a mechanical seal and a shaft are proposed as a dynamic rotor model. The dynamic states of the mechanical seal are classified into stick and slip states depending on whether the seal and mating rings of the mechanical seal have relative motion or not. I derived the partial differential equations of motion and the corresponding boundary conditions for each state of the seal. In addition, I established a judgement criterion for the stick and slip states of the seal. After the equations of motion were discretized by a proposed finite element procedure, the dynamic responses of the rotor system of a water pump were computed by using the generalized- time integration method. Furthermore, I analyzed the effects of various system parameters on stick-slip vibration, including the mass moment of inertia for the pulley, the drag torque at the impeller, the external torque at the pulley, and the normal force between the seal and mating rings.