Search Results

Tortuosity, viscous characteristic length and thermal characteristic length are three important parameters for estimating the acoustic performance of porous materials, and it is usually measured by ultrasonic measurement technology, which is costly. In this paper, a method for identifying the tortuosity, viscous characteristic length and thermal characteristic length for the porous fiber materials mixed with kapok fiber and two kinds of other fiber materials is proposed. The tortuosity is calculated by using the porosity and high-frequency normal sound absorption coefficient of porous materials. According to the normal sound absorption coefficient curve of porous materials under plane wave incidence, viscous characteristic length and thermal characteristic length are identified through the Johnson-Champoux-Allard-Lafarge (JCAL) model and genetic algorithm by using the measured parameters, the calculated tortuosity and static thermal permeability.

A new proportional electromagnetic dynamic vibration absorber (EDVA) is proposed for control of engine vibration during idling. The device consists of an electromagnetic actuator attached to the primary structure through elastic element, where the driving force pair is implemented between the reaction-mass and the primary structure. The design of the proportional electromagnetic actuator is realized considering the geometric parameters of the core to achieve nearly constant magnetic force over a broad range of its dynamic displacement but proportional to square of the current. A methodology is proposed to achieve magnetic force proportional to square of current and consistent with the disturbance frequency. The proportional EDVA is subsequently applied to a single-degree-of-freedom primary system with an acceleration feedback control algorithm for attenuation of primary system vibration in a frequency band around the typical idling vibration frequencies.

Membrane-type acoustic metamaterials consist of a tensioned membrane fixed on the frame and an additional mass attached to the membrane. The sound insulation performance of membrane-type acoustic metamaterials is much better than the acoustic mass law predictions at transmission loss (TL) peak frequencies. In this paper, an equivalent mechanical model of membrane-type metamaterials is established. Through the vibration analysis of the membrane with tensile force as the main elastic restoring force, an approximate estimation method of the TL peak frequency of Membrane-type acoustic metamaterials is proposed, the effects of membrane tension, membrane size, mass and size of additional mass on the peak frequency of TL were analyzed quantitatively. The COMSOL software was used to establish a finite element analysis model and calculate the TL curve of the metamaterial at a frequency of 100-1600 Hz.

An Inline 4-cylinder engine is equipped with second-order balance shafts. When the engine is running under no-load acceleration conditions, the gear system of the balance shaft generated whine noise. In this paper, an analysis and experiment method for reducing the whine noise is presented. First, a flexible multi-body dynamic model of the engine is established, which includes shaft and casing deformation, micro-modification of the gears. Taking the measured cylinder pressure as input, the load on each gear of balance shaft gear system is calculated. In addition, the influence of tooth surface micro-modification on the meshed noise was analyzed. The results show that the dynamic meshing force between the crank gear and the shim gear is large under the original tooth surface micro-modification parameters, which is the main reason of the whine noise.

A road test on semi-trailers is carried out, and accelerations of some characteristic points on the braking system,axles,and truck body is measured,also brake pressure and noise around the support frame is acquired.The measured data was analyzed to determine the causes of the brake noise, and the mechanism of the noise of the drum brake of semi-trailers during low-speed braking was investigated. The following conclusions are obtained: (1) Brake noise of the drum brake of the semi-trailer at low-frequency is generated from vibrations of the brake shoes, axle, and body, and the vibration frequency is close to 2nd natural frequency of the axle. (2) Brake noise is generated from stick-slip motion between the brake shoes and the brake drum, where the relative motion between the brake drum and the brake shoes is changed alternately with sliding and sticking, resulting in sudden changes in acceleration and shock vibration.

In this paper, the influence of the decoupler-cage structure on the hitting noise of the hydraulic mount is studied, the abnormal noise of the hydraulic mount is mainly caused by the collision impact between the decoupler and the cage, the hitting noise was simulated and evaluated using calculation and experiment. a finite element model of the collision impact between the decoupler and the cage is developed, and an explicit finite element analysis is performed to obtain the time history of the vibration acceleration of the model, which is used as the boundary condition of the noise analysis. The acoustic boundary element method is used to analyze the impact noise of the decoupler-cage, and the frequency domain distribution characteristics of the impact sound pressure are obtained. The influence of different decoupler structure on the hitting noise is studied, and the recommended values for each parameter for a structure are given.

Tuned mass dampers (TMD) are frequently used in vehicles to resolve vibration and interior booming noise issues arising from powertrain's vibration and road excitation. This paper describes a driveshaft NVH case study in which analysis and test were used to solve the NVH problem. A TMD simulation package that utilizes a database of measured elastomeric material propertied. This facilitates the designing of optimized damper systems for a wide variety of vehicle applications. The simulation software takes into account frequency effects on elastomer properties while designing dampers. And the approach has proven to accurately predict performance in vehicles prior to manufacture. Rules of thumb for TMD design are discussed including locations for placement of dampers in automotive structures, determining the needed mass, and measurements and simulations that can greatly improve the success and reducing time-cost for TMD design.

In the variable axial transmission system of an automobile, the power output of the segmented transmission shaft changes, which affects the vibration of the rear axle to a certain extent. As an important component of the drive shaft system, the intermediate support has an important effect on reducing the vibration transmission path of the drive shaft and the vibration of the rear axle system. In this paper, the vibration characteristics of the intermediate support of a certain vehicle's transmission shaft and the transmission shaft system are studied, and the vibration damping performance of the intermediate support rubber is theoretically analyzed and design optimized. In order to solve the vibration problem in the high frequency range of this car, a rubber pad was added at the position of the installation hole of the intermediate support bracket assembly to form a structure with double-layer vibration isolation effect, and the stiffness of this structure was optimized.

The driving pulley is often used as a Torsional Vibration Damper (TVD) for the crankshaft in the front end accessory drive (FEAD) system. Although the crankshaft torsional vibrations are dampened, they are transmitted to the belt transmission and therefore to the driven accessories. The isolation pulley is a new device to reduce the belt tension fluctuation by isolating the belt transmission from the crankshaft torsional vibrations. A five-pulley system with isolation pulley is presented and a non-linear model is established to predict the dynamic response of the pulleys, tensioner motion, tension fluctuation and slippage. The model works in the time domain with Runge-Kutta time-stepping algorithm. The numerical simulation results of harmonic excitations show that the amplitudes of the belt tension fluctuation and the vibrations of each component are reduced significantly. Moreover, the effect of isolation pulley parameters on the system natural frequencies is demonstrated.

The application of turbochargers in fuel vehicles brings high-frequency noise, which seriously affects the vehicle's ride comfort. The hiss noise of a turbocharged car is improved in this paper. Firstly, under different operating conditions and whether the air intake system is wrapped, the noise in the vehicle cabin and the driver's right ear is tested, and the noise sources and noise characteristics are identified. Then, the acoustic calculation model of the muffler is established, and the transmission loss (TL) of the original muffler behind the turbocharger (MBT) is calculated. The TL of the muffler is measured by the double-load impedance tube method. The finite element calculation model is verified by comparing the TL of muffler calculated with tested. Thirdly, the MBT is redesigned. The improved muffler significantly improves the performance of eliminating high-frequency noise, and its TL beyond 20 dB is expanded to the band of 1600 ~ 3500 Hz.

Electromagnetic semi-active hydraulic engine mount (HEM) with double inertia tracks can realize the opening and closing of the inertia tracks through the control of electromagnetic actuator, so as to meet the needs of vibration isolation in different working conditions, but the cost is high. In this paper, without using electromagnetic actuator, a mechanical semi-active HEM with double inertia tracks is designed and manufactured with simple structure and low cost. In this study, the feature of mechanical semi-active HEM with double inertia tracks is that a baffle-current limiting column structure is added in the inertia track. Under different excitation amplitudes, the baffle-current limiting column structure can open and close the inertia track passively. Several mechanical semi-active HEM with double-inertia tracks samples and conventional inertia tracks HEM samples are manufactured and the dynamic characteristics of these samples under low frequency excitation are tested.

The identification of vehicle noise is the basis for studying the acoustic characteristics of vehicles. In this paper, both excitation of noise sources and response of interior noise were identified. Firstly, a transfer path analysis (TPA) model was established to identify the excitation of noise sources, which includes vehicle main noise sources, such as engine, tire, exhaust pipe and muffler. Based on the operational signals and transfer function which were tested in the vehicle semi-anechoic room, the excitation of noise sources was identified using inverse matrix method. Identify result indicated that tires have higher excitation amplitude than engine in high frequency band. Therefore, the transfer path between the tire and the cabin, such as carpet and windshield, should be taken as the focus of acoustic performance improvement. By improving the acoustic material on the transfer path, the loss of sound in the transfer path will be increase.

A rumbling noise is audible in a vehicle passenger compartment during acceleration. Mechanism detail of the rumbling noise is studied. A series of preliminary transfer path experiments investigation on chassis dynamometer shows that the interior rumbling noise is mainly induced by abnormal crankshaft impact at particular crank angle. Spectrum analysis indicates that high level half order harmonic components significantly affects the rumbling noise. Multi-body dynamics model of the powertrain is developed to further investigate the root cause of the abnormal crankshaft impact. Experiment results are used to verify the numeric model. High deviation of main bearing forces at the crank angle 0° to 180° after the Fire Top Dead Center of the no.l cylinder is considered to fundamentally induces the high level half order components. The force ripple coupled with the crankshaft resonance induces the crankshaft rumbling.

Mount is a component used to connect the powertrain and the body, which plays an important role in isolating vibration from motor of electrical vehicles. As for traditional rubber mounts, the dynamic stiffness increases significantly with the increase of excitation frequency and will have a peak value, which is called "internal resonance" phenomenon. Compared with the traditional rubber mount, the rubber mount with second-stage isolators has a smaller dynamic stiffness at high-frequency ranges and is usually used to enhance NVH (Noise, Vibration and Harshness) performance of electric vehicles at high-frequency ranges. This paper investigates a rubber mount with second-stage isolators. The second-stage isolators are assembled with bolt holes connecting with mount and car body.

Two-layer engine front end accessory drive systems (TEFEADS) are adopted generally by commercial vehicles due to the characteristics of the accessory pulleys, which have large torque and moment of inertia. An overrunning alternator decoupler (OAD) is an advanced vibration isolator which can reduce the amplitude of torsional vibration of alternator rotor effectively by an one-way transmission and they are more and more widely used in vehicles. This paper established a model of a generic layout of a TEFEADS with an OAD. The coupling effect between the TEFEADS, the nonlinear characteristics of OAD, the torsional vibration of crankshaft and the creeping on the belt were taken into account. A nine pulleys model was provided as a study example, the dynamic responses, which are respectively under steady and accelerating conditions, of the system were calculated by the established method and compared with the bench experiment.

The generator is an important loaded component of an engine front end accessory drive system (EFEADS). With a huge moment of inertia and a highest running speed, the vibration and noise often occurs in operation, which has an effect on the service life. Thus an overrunning alternator decoupler (OAD) is used in the EFEADS for reducing the vibration of system. In this paper, a model of EFEADS with an OAD is established. The impact of the OAD on the dynamic responses of pulley of generator and the system are analyzed, and is verified by bench experiments. And the influence of parameters, such as spring stiffness, moment of inertia of generator and loaded torque on the dynamic performances of the system are studied. The influence of misalignment in pulleys on the dynamic performance of system is also discussed. The presented method is useful for optimizing the dynamic performance of system, such as the oscillation of tensioner arm and the slip ratio of the belt-generator pulley.

With the popularity of battery electric vehicles, the engine of the vehicle disappears, so the problem of road noise in cars is becoming more and more prominent. Road noise into the car can be divided into structure-borne noise and airborne noise, this paper only focuses on the airborne noise above 500Hz, completely ignoring the structure-borne noise. A transfer path analysis model with “Intermediate Response Points” is proposed to accurately represent the transfer path of each airborne noise through the setting of “Intermediate Points”. In the Vehicle Semi-Anechoic Room With 4×4 NVH Chassis Dyno, it is possible to create a working condition with only four tires running, so only the tire noise is considered in this paper. The frequency response function is tested in the Semi-Anechoic Chamber and the operating data is tested in the Vehicle Semi-Anechoic Room With 4×4 NVH Chassis Dyno.

The vehicle will produce certain shock and vibration during the braking process, which will affect the driving experience of the driver. Aiming at the problems of pitch vibration, longitudinal vibration and shock during the braking process, this paper proposes a planning and following control method for target longitudinal acceleration in post-braking phase, and designs control trigger strategies. Target longitudinal acceleration planning takes minimizing longitudinal shock as the design goal. The following control takes the brake pressure as the control object, and adopts the “feedforward +PID feedback” method to follow the target longitudinal acceleration. Besides, considering the safety of braking process, the trigger condition of control is designed which utilizes BP neural network method to judge whether the control has to be triggered. Based on Simulink software, the simulation model of straight-line braking is established.

In the automotive industry, testing the sound absorption coefficient of acoustic materials through reverberation chambers has been widely used. The advantage of this method is that sound waves are incident on the surface of acoustic materials randomly, which is more in line with actual engineering. At present, most of the reverberation chamber design and construction refers to the international standard ISO 354-2003. However, although the design indicators of the reverberation chamber have already met the requirements of the standard ISO 354-2003, there are still some differences between the test results of different reverberation chambers on the same group of samples to be tested, and sometimes the differences are so big they affect the engineering applications. In this paper, the sound absorption coefficients of the same group of samples in different reverberation chambers are tested, and there are some differences in the sound absorption coefficients.

Aiming at the problem of middle and low frequency noise absorption, a combined sound-absorbing structure is designed based on porous material and a coiled-up cavity resonance structure. Combined with the sound absorption principle of porous materials and coiled-up cavities, a theoretical analytical model was established. By the finite element method, the sound absorption coefficient curve of the combined structure in a frequency range of 500-2000Hz is calculated, and the correctness of the analytical calculation and the finite element simulation calculation was verified in the impedance tube experiment. The results show that the combined structure has good sound absorption performance in the 500Hz-2000Hz frequency band, and the sound absorption peak appears near the 1108Hz frequency, reaching nearly perfect sound absorption. Compared with a single porous material, the sound absorption performance of the combined structure is better.