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To quantify the intensity of automobile brake creep groan, both experimental and analytical studies are innovatively conducted on the friction-induced vibration and noise of the disc brake in this paper. Experimentally, three factors, brake disc initial temperature, terrain, and gear position, are comprehensively contemplated to design six different test conditions, based on which a creep groan vehicle road test is conducted. Depending on the subjective evaluation and statistical analysis of the annoyance degree caused by vibration and noise in the starting and braking process under different test conditions, the influence of each factor on creep groan intensity is obtained. By processing the brake caliper and lower suspension arm acceleration and the interior sound pressure signals acquired in the test, the occurrence conditions and transient dynamic characteristics of creep groan are explored. One of the creep groan vibration modes is triggered by the rapid removal of the force exerted on the brake pedal when the vehicle starts at an extremely low speed, which presents intermittent impact and chaotic characteristics. The other vibration mode shows periodic harmonic characteristics, whose energy is concentrated on specific frequencies in the form of frequency doubling. This vibration mode occurs when continuously maintaining a low brake oil pressure or slowly releasing the force exerted on the brake pedal during the vehicle low-speed starting process, the velocity-displacement phase-plane portrait of which shows a stable limit cycle of stick-slip motion. Analytically, four vibration indexes and four noise indexes are established to evaluate the intensity of creep groan, the validity of which is verified by linear regression analysis. Finally, by combining all effective indexes, multiple linear regression analysis is performed, based on which the mapping relationship between the subjective evaluation of creep groan and effective indexes is obtained. The results demonstrate that the combination of the logarithmic vibration dose value of maximum brake caliper acceleration pulse and the loudness of interior noise can accurately describe the annoying degree caused by creep groan. The regression model can quantify and predict creep groan intensity of the test vehicle under different test conditions, which has guiding significance for engineering applications.

Brake creep groan is getting more and more attention in vehicle brake design and development. However, many complex motions of brake creep groan have not been comprehensively, which are critical for the understanding and prevention of the problem. In this paper, brake creep groan dynamics are studied and analysed to research the mechanisms of creep groan. Vehicle road experiments on a slope road are performed to record creep groans using two tri-axial accelerometers, which are install at the caliper and suspension strut. History curves of oil pressure and caliper accelerations, time–frequency spectrogram of the vibrations, and largest Lyapunov exponent are calculated using Hilbert–Huang transform and empirical mode decomposition methods. This study reveals that the sources of the brake creep groan include unstable sliding in addition to transient and steady-state motions of stick–slip between disc and pad. It is found that one of the important sources of the creep groan is the unstable sliding, which has impulsive and discontinuous nature and has effects of hammering leading to strong excitation and wideband vibrations. It is also found that when creep groan occurs, multiple modes of the brake system and subsystems contribute to the complex vibrations. The existences and the properties of the stable, unstable, and chaotic vibrations associated with the creep groan are characterized, which depend on the system natures, excitations, and tribological conditions.

To determine the interior noise reduction mechanism of car body cavity filler block, the noise reduction researches were conducted experimentally. By comparing the BIW modal characteristic and transfer functions before and after removing cavity filler block, the influence of cavity filler block on vehicle low frequency vibration was investigated. To investigate the effect of cavity filler block on engine noise and road-tire noise, a full vehicle test using drum tester was carried out. Another full vehicle test in the wind tunnel was conducted to determine how it influences wind noise. Based on the above test results, the noise reduction mechanisms were analyzed. On the one hand, it helps to increase the damping of BIW, thus suppress the vibration and reduce low frequency noise. On the other hand, it cuts off the propagation of the noise outside the vehicle which may invades the passenger compartment, thereby reducing the high frequency noise.

Contact stiffness and friction coefficient are excitation sources and key influencing factors to frictional squeal with obvious inhomogeneous characteristic that is always neglected. In this paper, a multipoint contact flexible pin-on-disc system is established considering tangential stiffness. Then influence of contact stiffness and friction coefficient with heterogeneous distribution on frictional squeal is studied using the complex modal analysis. The research shows that contact stiffness and friction coefficient heterogeneities influence the likelihood of occurrence of the squeal, the frequency of the squeal, and the real part of the complex eigenvalue of the system. And when the contact stiffness and friction coefficient are close to the boundary of the region of mode-coupling instability, flexible pin-on-disc system with homogeneous contact stiffness and friction coefficient cannot predict whether frictional squeal occurs or not. Besides, uncertain distribution of contact stiffness and friction coefficient can induce the uncertainty of brake squeal.

In this paper, a flexible pin-on-disk system is used to simulate how squeal noise can be generated in frictional contact. As the research object, the modeling process and transient simulation method of the flexible pin-on-disk system are introduced. By means of numerical simulation, the time-varying frictional squeal reappears by introducing periodic frictional coefficient generated from rotation. Afterward, the features of time-varying squeal are studied including time-domain features, frequency-domain features, transient deformation features of the disk and the pin on the occurrence of squeal, as well as energy features. Finally, the conception and mathematical expressions of modal contribution factor are defined, and the transient modal contribution factor features of every mode are studied to make clear the function of every mode. The relationship between mode contribution factors and the vibration is revealed. It reveals that modal contribution factors between squeal and not are quite different from each other. On no occurrence of squeal, the modal contribution factors of sine and cosine modes of the disk fluctuate in the way similar to harmonic wave, and the phase difference between the contribution factors of sine and cosine mode with the same nodal circle and the same nodal diameter is 90 deg. During squeal, the coupling mode may play the most important role but not all the time. At any time, the low-frequency modes play the leading role.

Strain gage sensors have been used to evaluate the local behavior of structures; however, there are limited studies for its application in bridge dynamic feature identification. In this study, fiber Bragg grating strain gages were installed on the lower chord members of a bridge, and dynamic features were identified successfully using strain gage readings when vehicles passed over the bridge. The results were also verified using a finite element model. The innovation presented in this article is the use of fiber Bragg grating strain gage readings to identify the dynamic features of a long-span, steel-girder bridge. To clarify the effect of truck dynamic load, the load spectrum of the truck is characterized. This article introduces a new method for identifying the dynamic parameters of bridges.