The complex eigenvalue analysis is currently a common approach to predict squealing vibration and noise. There are two methods for modeling friction contact in the complex eigenvalue analysis of friction systems. In o...The complex eigenvalue analysis is currently a common approach to predict squealing vibration and noise. There are two methods for modeling friction contact in the complex eigenvalue analysis of friction systems. In one method, contact springs are used to simulate friction contact. In another method, no contact spring is used. However, it has been uncertain whether these two modeling methods can predict approximately identical results. In order to clarify the uncertainty, two finite element models of the same brake system for the brake squeal prediction are established and simulated by using ABAQUS and NASTRAN software tools, respectively. In the ABAQUS model, friction coupling is applied to determine normal contact force and no contact spring is assumed. Whilst in the NASTRAN model, the contact spring is assumed by the penalty method to simulate contact connection. Through the numerical simulations, it is recognized that even if the same mesh geometry is applied, generally, these two finite element approaches are not capable of predicting approximately identical unstable frequencies. The ABAQUS approach can predict instabilities of high frequency up to 20 kHz or more, while the NASTRAN approach can only predict some instabilities of high frequency, not all. Moreover, the simulation results also show that both the contact spring stiffness and mesh size have influences to some extent on the prediction results of squeal. The present comparative work illuminates that the modeling method without contact springs is more suitable to predict squealing vibration and noise, comparing to the modeling method with contact springs. It is proposed that one should prefer using the modeling method without contact springs to predict squealing vibration and noise. The proposed study provides the reference for predicting squealing vibration and noise.展开更多
Drum brake squeal is usually due to the unstable oscillation excited by the dry friction between the drum and linings. In order to understand the mechanisms of drum brake squeal, a new drum brake dynamics model in clo...Drum brake squeal is usually due to the unstable oscillation excited by the dry friction between the drum and linings. In order to understand the mechanisms of drum brake squeal, a new drum brake dynamics model in closed form is presented for analyzing the modes and stability of drum brake vibration, so as to judge whether a squeal will happen or not. Then, a non contact experimental vibration analysis procedure based on nearfield acoustical holography technique is developed for measuring the operating deflection shape of drum. The measured ODS of drum is nearly the same as the unstable oscillation with the largest real component of eigenvalue among all the complex modes of brake drum.展开更多
Brake squeal is one of the main NVH （vibration harshness） challenges in the brake development of passenger cars. The conflict of goals in the development process and the late testability leads to the need of a deepe...Brake squeal is one of the main NVH （vibration harshness） challenges in the brake development of passenger cars. The conflict of goals in the development process and the late testability leads to the need of a deeper basic understanding of the squeal phenomenon and definition of design rules. On the other hand, brake squeal is still a very interesting field of research also for the universities because of its combination of different fundamentals, such as friction and stability behaviour of systems with local nonlinearities. Major nonlinearities of the brake system are the joints, especially the contact areas formed by the oscillating brake pad and the caliper. The state-of-the-art calculation method, which still is the ＂complex eigenvalue analysis＂, linearizes these joints, hence, neglecting its nonlinear influence in the stability analysis. Vehicle and bench experiments show that special driving manoeuvres like parking, where the brake pad often leaves the steady state, are likely causing brake squeal. The system in these manoeuvres sometimes behaves opposed to the linearized stability analysis, indicating a limit cycle beyond the Hopf point. Therefore, these states must be investigated more closely. This paper investigates the nonlinear influence of the pad caliper joint in a fixed brake caliper, also called abutment. Bench tests with pressure foils at the abutment of the brake caliper and mode shape analysis were done and a simple FE （finite element） model for a transient simulation is proposed. It is shown that the joint activity varies with driving manoeuvres, leading to different stability behaviours and limiting cycle amplitudes.展开更多
The poppet valve is a fundamental component in fluid power systems. Under particular conditions, annoying ＂squeal＂ noises may be generated in hydraulic poppet valves. In the present study, the frequency spectrum of ...The poppet valve is a fundamental component in fluid power systems. Under particular conditions, annoying ＂squeal＂ noises may be generated in hydraulic poppet valves. In the present study, the frequency spectrum of the squeal noise is obtained by analyzing the sampling data from the accelerometer mounted on the valve body. It is found that the flow velocity, pressure, and structural parameters have crucial effects on the properties of squeal noise, especially frequency. Larger valve chamber volume or lower backpressure leads to lower fundamental frequency of the squeal noise. An explanation for the squeal noise, as a result of Helmholtz resonance, is suggested and proved by experimental results.展开更多
基金supported by National Natural Science Foundation of China (Grant No. 50875220, Grant No. 50675181)Innovative Research Group Program of National Natural Science Foundation of China (Grant No. 50821063)Development Project of Ministry of Education for Elitists in the New Century of China (Grant No. NCET-06-0798)
文摘The complex eigenvalue analysis is currently a common approach to predict squealing vibration and noise. There are two methods for modeling friction contact in the complex eigenvalue analysis of friction systems. In one method, contact springs are used to simulate friction contact. In another method, no contact spring is used. However, it has been uncertain whether these two modeling methods can predict approximately identical results. In order to clarify the uncertainty, two finite element models of the same brake system for the brake squeal prediction are established and simulated by using ABAQUS and NASTRAN software tools, respectively. In the ABAQUS model, friction coupling is applied to determine normal contact force and no contact spring is assumed. Whilst in the NASTRAN model, the contact spring is assumed by the penalty method to simulate contact connection. Through the numerical simulations, it is recognized that even if the same mesh geometry is applied, generally, these two finite element approaches are not capable of predicting approximately identical unstable frequencies. The ABAQUS approach can predict instabilities of high frequency up to 20 kHz or more, while the NASTRAN approach can only predict some instabilities of high frequency, not all. Moreover, the simulation results also show that both the contact spring stiffness and mesh size have influences to some extent on the prediction results of squeal. The present comparative work illuminates that the modeling method without contact springs is more suitable to predict squealing vibration and noise, comparing to the modeling method with contact springs. It is proposed that one should prefer using the modeling method without contact springs to predict squealing vibration and noise. The proposed study provides the reference for predicting squealing vibration and noise.
文摘Drum brake squeal is usually due to the unstable oscillation excited by the dry friction between the drum and linings. In order to understand the mechanisms of drum brake squeal, a new drum brake dynamics model in closed form is presented for analyzing the modes and stability of drum brake vibration, so as to judge whether a squeal will happen or not. Then, a non contact experimental vibration analysis procedure based on nearfield acoustical holography technique is developed for measuring the operating deflection shape of drum. The measured ODS of drum is nearly the same as the unstable oscillation with the largest real component of eigenvalue among all the complex modes of brake drum.
文摘Brake squeal is one of the main NVH （vibration harshness） challenges in the brake development of passenger cars. The conflict of goals in the development process and the late testability leads to the need of a deeper basic understanding of the squeal phenomenon and definition of design rules. On the other hand, brake squeal is still a very interesting field of research also for the universities because of its combination of different fundamentals, such as friction and stability behaviour of systems with local nonlinearities. Major nonlinearities of the brake system are the joints, especially the contact areas formed by the oscillating brake pad and the caliper. The state-of-the-art calculation method, which still is the ＂complex eigenvalue analysis＂, linearizes these joints, hence, neglecting its nonlinear influence in the stability analysis. Vehicle and bench experiments show that special driving manoeuvres like parking, where the brake pad often leaves the steady state, are likely causing brake squeal. The system in these manoeuvres sometimes behaves opposed to the linearized stability analysis, indicating a limit cycle beyond the Hopf point. Therefore, these states must be investigated more closely. This paper investigates the nonlinear influence of the pad caliper joint in a fixed brake caliper, also called abutment. Bench tests with pressure foils at the abutment of the brake caliper and mode shape analysis were done and a simple FE （finite element） model for a transient simulation is proposed. It is shown that the joint activity varies with driving manoeuvres, leading to different stability behaviours and limiting cycle amplitudes.
基金Project supported by the National Natural Science Foundation of China （No. 51475415）, the Science Fund for Creative Research Groups of the National Natural Science Foundation of China （No. 51221004）, and the Fundamental Research Funds for the Central Universities, China
文摘The poppet valve is a fundamental component in fluid power systems. Under particular conditions, annoying ＂squeal＂ noises may be generated in hydraulic poppet valves. In the present study, the frequency spectrum of the squeal noise is obtained by analyzing the sampling data from the accelerometer mounted on the valve body. It is found that the flow velocity, pressure, and structural parameters have crucial effects on the properties of squeal noise, especially frequency. Larger valve chamber volume or lower backpressure leads to lower fundamental frequency of the squeal noise. An explanation for the squeal noise, as a result of Helmholtz resonance, is suggested and proved by experimental results.
