A novel design of semi-active hydraulic mount with wide-band tunable notch frequency

Hydraulic engine mount is advanced vibration isolator with superior performance to reduce vibration transferred from engine to chassis. As the stiffness at notch frequency is small, some semi-active or active hydraulic mounts tune some parameters to let notch frequency coincide with exciting frequency for better vibration isolation performance. It is discovered the current semi-active mounts can tune the notch frequency in narrow frequency band when only one parameter is tuned. A novel semi-active hydraulic engine mount design which introduces screw thread is proposed and researched in the paper. This hydraulic mount can control both cross section area and the length of inertia track and the theoretical tunable notch frequency band is [0, ∞). Theoretical work is carried out to uncover the capability for the proposed design to tune notch frequency. Simulation work is performed to understand its high vibration isolation performance. For the purpose of energy conservation, the friction self-locking is introduced. This denotes once the mount is tuned at optimal condition, the energy can be cut off and the optimal condition will never change. We also determine the best time to tune the parameters of the proposed mount in order to decrease the acting force. The proposed semi-active mount has capability to obtain wide band tunable notch frequency and has merit of energy conservation.     

Optimal design of engine mount using an artificial life algorithm

When designing fluid mounts, design parameters can be varied in order to obtain a desired notch frequency and notch depth. The notch frequency is a function of the mount parameters and is typically selected by the designer to occur at the vibration disturbance frequency. Since the process of choosing these parameters can involve some trial and error, it seems to be a great application for obtaining optimal performance of the mount. Many combinations of parameters are possible to give us the desired notch frequency, but the question is which combination provides the lowest depth? Therefore, an automatic optimal technique is needed to optimize the fluid mount.In this study, the enhanced artificial life algorithm (EALA) is applied to minimizing transmissibility of a fluid mount at the desired notch frequency, and at the notch and resonant frequencies. The present hybrid algorithm is the synthesis of a conventional artificial life algorithm with the random tabu search (R-tabu) method and then, the time for searching optimal solution could be reduced from the conventional artificial life algorithm and its solution accuracy became better.The results show that the performance of the optimized mount by using the hybrid algorithm has been better than that of the conventional fluid mount.     

A new type of semi-active hydraulic engine mount using controllable area of inertia track

Automotive engine mounts function to constrain the engine shake motion resulting at low-frequencies, as well as to isolate noises and vibrations generated by the engine with unbalanced disturbances at the high frequencies. The property of the mount depends on vibration amplitude and excitation frequency. It means that the excitation amplitude is large in low excitation frequency range and small in high frequency range. In this paper, a new hydraulic engine mount with a controllable area of inertia track is proposed and investigated. Theoretical works with the mount model to isolate the engine-related vibrations were conducted by an optimal algorithm to control the area of the inertia track under shocks and multi-signal force excitations. This research clearly gives an analysis of the considerable changes in the mount dynamic properties according to the changes in the inertia track area. Consequently, when the inertia track area is tuned, the transmissibility of the mount is effectively reduced.     

The effects of nonlinearity on the output frequency response of a passive engine mount

In this paper, the new concept of output frequency-response function (OFRF) that was derived recently by the authors from the Volterra-series theory of nonlinear systems is briefly introduced. An effective algorithm is proposed to determine the monomials in the OFRF-based representation of the output frequency response of nonlinear systems. The results are then used to analyze the output frequency response of a passive engine mount. Important conclusions regarding the effects of system nonlinearity on the output frequency-response behaviors of the engine mount are reached via theoretical analysis and verified by simulation studies. These conclusions are of significant importance for the analysis and design of vibration isolators such as engine mounts in practice.     

Experimental Investigation and Semi-Active Control Design of A Magnetorheological Engine Mount

In this paper; the dynamic characteristics of a semi-active magnetorheological fluid (MRF) engine mount are studied. To do so, the performance of the MRF engine mount is experimentally examined in higher frequencies (50~170 Hz) and the various amplitudes (0.01 ~ 0.2 mm). In such an examination, an MRF engine mount along with its magnetically biased is fabricated and successfully measured. In addition, the natural frequencies of the system are obtained by standard hammer modal test. For modelling the behavior of the system, a mass-spring-damper model with tuned PID coefficients based on Pessen integral of absolute error method is used. The parameters of such a model including mass, damping ratio, and stiffness are identified with the help of experimental modal tests and the recursive least square method (RLS). It is shown that using PID controller leads to reducing the vibration transmissibility in the resonance frequency (=93.45 Hz) with respect to the typical passive engine mount by a factor of 58%. The average of the vibration transmissibility decreasing is also 43% within frequency bandwidth (50~170 Hz).     

某商用车怠速油底壳异响问题分析研究*

针对产品开发过程中某柴油车型发动机油底壳怠速时“呜呜”异响问题,通过噪声与振动的测试及仿真分析,对油底壳异响原因进行分析。结果表明,怠速时机油泵的工作激励频率与油底壳模态频率耦合,形成“呜呜”声,并通过油底壳表面辐射出来。进一步实验研究表明,随着机油温度的升高,机油泵功率、工作激励幅值会逐步减小,异响逐步减小。同时实验研究表明,机油量对油底壳模态频率有影响,油底壳内机油加注量越多,油底壳模态频率越低,油底壳表面振动幅值及异响均逐步减小。针对该异响问题,明确该发动机机油加注上限及下限时油底壳对应频率范围后,通过优化怠速转速,提高油底壳模态频率等使机油泵激励频率与油底壳模态频率避频,解决了该异响问题。     

面向传递路径分析方法研究的试验系统设计*

在传递路径分析理论研究中,经典传递路径分析要求在传递函数测量时拆卸激励源,为了减少工作量,设计一套面向传递路径分析方法研究的实验系统。以简化发动机模型作为激励源,真实汽车发动机悬置作为传递路径,简化车身内的响应为目标响应,建立一套完整的传递路径分析模型。在保留主要激励特征情况下简化发动机机体结构,将NI Compact RIO作为控制核心,激振器作为激励施加装置,以缸压信号和机体振动信号为激励信号对机体加载,实现发动机激励特征的模拟。最终验证该实验系统可模拟出发动机的结构噪声,采集信号中阶次成分明显,主要噪声频段基本吻合,可从阶次信号中提取对应转速信息。整个实验系统结构简单,可作为载体用于传递路径分析方法的研究。     

Effects of internal mass distribution and its isolation on the acoustic characteristics of a submerged hull

The primary aim of machinery isolation in marine vessels is to isolate structural vibration of the onboard machinery from the hull and to reduce far-field radiation of underwater noise. A substantial proportion of the total submarine mass is on flexible mounts that isolate supported masses from the hull at frequencies above the mounting system resonant frequency. This reduces the dynamically effective mass of the hull and affects the signature of the marine vessel due to propeller excitation. A fully coupled finite element/boundary element (FE/BE) model has been developed to investigate the effect of mass distribution and isolation in a submerged hull. The finite element model of the structure includes internal structures to represent the machinery and other flexibly mounted components. Changes in the radiated sound power demonstrate the effect of machinery isolation on the acoustic signature of the submerged hull due to the external propeller forces. Results are also presented to show how the arrangement of flexible mounts for a large internal structure can influence the radiation due to machinery forces.     

某汽车传动系扭振测试、诊断与数据处理分析

本文针对某轻型卡车由于传动系扭振导致加速过程中驾驶室内出现异常振动与轰鸣噪声现象进行研究。首先,为弄清车内振动噪声产生机理,对整车的扭振和车内振动噪声进行了实车道路试验;其次,对整车试验异常数据进行后处理,通过低通滤波和设置电压波动缓冲区的方法对其进行去噪和再生成,消除了加速工况下转速曲线失速和异常峰值的现象;最后,通过分析转速、振动和噪声数据得出：样车加速过程中发动机2阶激励频率达到整车传动系的固有频率时,引起了传动系扭转共振,连同传动轴的不平衡转动自振,通过悬置、中间支撑和后桥板簧传入到车内,引起驾驶室异常振动和轰鸣噪声。     

A nonlinear spring mechanism incorporating a bistable composite plate for vibration isolation

The High Static Low Dynamic Stiffness (HSLDS) concept is a design strategy for a nonlinear anti-vibration mount that seeks to increase isolation by lowering the natural frequency of the mount whilst maintaining the same static load bearing capacity. It has previously been proposed that an HSLDS mount could be implemented by connecting linear springs in parallel with the transverse flexure of a composite bistable plate — a plate that has two stable shapes between which it may snap. Using a bistable plate in this way will lead to lightweight and efficient designs of HSLDS mounts. This paper experimentally demonstrates the feasibility of this idea. Firstly, the quasi-static force–displacement curve of a mounted bistable plate is determined experimentally. Then the dynamic response of a nonlinear mass–spring system incorporating this plate is measured. Excellent agreement is obtained when compared to theoretical predictions based on the measured force–displacement curve, and the system shows a greater isolation region and a lower peak response to base excitation than the equivalent linear system.     

Reduction of vibration and noise radiation of an underwater vehicle due to propeller forces using periodically layered isolators

Using periodic structure theory, the suppression of vibration and noise radiation from an underwater vehicle due to excitation from propeller forces is investigated. The underwater vehicle is modelled in two parts (the hull and the propeller/shafting system). A model of the propeller/shafting system is constructed using a modular approach and considers the propeller, shaft, thrust bearing, isolation structure and foundation. Different forms of isolator are considered – a simple spring-damper system, a continuous rod and a periodically layered structure. The dynamic properties of the underwater vehicle and the isolation performances of various isolators are compared and analysed. The stop band properties of the periodic isolator are used to enhance the passive control performance. Furthermore, an integrated isolation device is proposed that consists of the periodic isolator and a dynamic absorber, and its isolation performance is investigated. The effects of the absorber parameters on the performance of the integrated device are also analysed. Finally, the radiated sound pressure is calculated to verify the attenuation. The numerical results show that the vibration and noise radiation are greatly attenuated in the stop bands. By optimising the design of the periodic isolators and its integrated structures, the suppression of the vibration and noise radiation can be improved effectively.     

NON-LINEAR MODELLING OF HYDRAULIC MOUNTS: THEORY AND EXPERIMENT

This paper focuses on the development of a complete non-linear model of a hydraulic engine mount and the evaluation of the model using a unique experimental apparatus. The model is capable of capturing both the low- and high-frequency behavior of hydraulic mounts. The results presented here provide a significant improvement over existing models by considering all non-linear aspects of a hydraulic engine mount. Enhancements to already published non-linear models include a continuous function that follows a simplistic yet effective approach to capture the switching effect and leakage through the decoupler, and upper chamber bulge damping. It is shown that the model developed here provides the appropriate system response over the full range of loading conditions (frequency and amplitude) encountered in practice. In order to obtain the parameter values for the non-linear model, a unique test apparatus is introduced. Using the experimental set-up, it is possible to verify the model of individual components of the mount, and later on test the behavior of the whole assembly. These data also establish the relative importance of several damping, inertia and stiffness terms. In addition, the measured responses of the mounts to loading at various frequencies and amplitudes are compared to the predictions of the mathematical model. The comparisons generally show a very good agreement (better than 10%), which corroborate the non-linear model of the mount. It is felt that this work will help engineers in reducing mount design time, by providing insight into the effects of various parameters within the mount.     

Design and analysis of an intelligent vibration isolation platform for reaction/momentum wheel assemblies

This study focuses on design and analysis of an intelligent vibration isolation platform for reaction wheel assemblies (RWAs) and momentum wheel assemblies (MWAs). A passive platform consisting of four folded beams is designed and analysed for MWAs. A simple and effective mathematical model is developed for the system consisting of the platform and MWAs, and this model is used to investigate the passive vibration isolation performance. Further development is performed to produce an intelligent platform for RWAs, with piezoelectric sensors and actuators bonded to the vertical beams. The flywheel imbalance and impulse load are assumed to be input disturbances for the investigation of the active vibration isolation performance by the finite element method (FEM). The simulation results show that the passive vibration isolation platform is particularly effective for the suppression of a high frequency range vibration for MWAs, and the intelligent platform using velocity feedback control effectively attenuates the dynamic amplification of amplitude at resonance for RWAs. Thus, it is concluded that the passive platform can be used as a vibration isolation platform for MWAs and that the intelligent one can be used for RWAs.     

Passive vibration isolation of reaction wheel disturbances using a low frequency flexible space platform

Reaction wheel assemblies (RWAs) are momentum exchange devices used in fine pointing control of spacecrafts. Even though the spinning rotor of the reaction wheel is precisely balanced to minimize emitted vibration due to static and dynamic imbalances, precision instrument payloads placed in the neighborhood can always be severely impacted by residual vibration forces emitted by reaction wheel assemblies. The reduction of the vibration level at sensitive payloads can be achieved by placing the RWA on appropriate mountings. A low frequency flexible space platform consisting of folded continuous beams has been designed to serve as a mount for isolating a disturbance source in precision payloads equipped spacecrafts.Analytical and experimental investigations have been carried out to test the usefulness of the low frequency flexible platform as a vibration isolator for RWAs. Measurements and tests have been conducted at varying wheel speeds, to quantify and characterize the amount of isolation obtained from the reaction wheel generated vibration. These tests are further extended to other variants of similar design in order to bring out the best isolation for given disturbance loads. Both time and frequency domain analysis of test data show that the flexible beam platform as a mount for reaction wheels is quite effective and can be used in spacecrafts for passive vibration control.     

H∞ Feedback control and Fx-LMS feedforward control for car engine vibration attenuation

The attenuation of the low frequency noise produced by the car engine vibration has been the major concern of the automotive community with the objective to increase the comfort of the driver and the passengers. The chassis subframe is the part responsible for transmission of the engine vibration to the car body through the engine mounts. At the beginning of this paper, we briefly describe the test rig we used and which has been experimentally investigated by using system identification. Then the experimental results of the feedforward control strategy and the achieved performance are briefly presented. These results are then compared to the feedback control method utilizing H_∞ strategy which allows us to design a robust controller requiring less sensors. Furthermore, a broadband noise attenuation could be achieved by using a robust feedback controller in the real time test.     

DESIGN SENSITIVITY ANALYSIS AND OPTIMIZATION OF AN ENGINE MOUNT SYSTEM USING AN FRF-BASED SUBSTRUCTURING METHOD

The FRF-based substructuring method is one of the most powerful methods in analyzing the responses of complex built-up structures with high modal density. In this paper, a general procedure for the design sensitivity analysis of a vibro-acoustic system has been presented using the FRF-based substructuring formulation. For an acoustic response function, the proposed method gives a parametric design sensitivity expression in terms of the partial derivatives of the connection element properties and the transfer functions of the substructures. The derived noise sensitivity formula is combined with a non-linear programming module to obtain the optimal design for the engine mount system of a passenger car. The objective function is defined as the area of the interior noise graph integrated over a concerned r.p.m. range. The interior noise variations with respect to the dynamic characteristics of the engine mounts and bushings have been calculated using the proposed sensitivity formulation and transferred to a non-linear optimization software. To obtain the FRFs, a finite element analysis was used for the engine mount structures and experimental techniques were used for the trimmed body including the cabin cavity. The optimization based on the sensitivity analysis gives the ideal stiffness of the engine mount and bushings. The resultant interior noise in the passenger car shows that the proposed method is efficient and accurate.     

Recent applications of viscoelastic damping for noise control in automobiles and commercial airplanes

In this paper, the application of passive damping technology using viscoelastic materials to control noise and vibration in vehicles and commercial airplanes is described. Special damped laminates and spray paints suitable for mass production and capable of forming with conventional techniques are now manufactured in a continuous manner using advanced processes. These are widely used in the automotive and aerospace industry in a variety of applications to reduce noise and vibration and to improve interior sound quality. Many of these recent applications are not readily available for dissemination in academe and archival literature. It is hoped that the material presented in this paper will be useful for instruction and further research in developing new and innovative applications in other industries.     

Application of multi-channel spectral analysis to identify the source of a noise amplitude modulation in a diesel engine operating at idle

We are interested in the low frequency amplitude modulation of the noise generated by an engine operating at idle. This phenomenon, perceived inside the car, is particularly annoying. Modulated vibrations are transmitted to the frame mainly by one of the three engine mounts. The combustion is the first potential source to be inspected, but pragmatic observations on consecutive measurements show that it is not the cause of the amplitude modulation. Spectral analysis tools are applied on multi-channel measurements to identify the source of the phenomenon. A sensor is placed on each potential noise and vibration source. A virtual source analysis show that several uncorrelated sources are contributing to the operating response, particularly on frequencies for which a high amplitude modulation is observed. The computation of residual spectra obtained by means of conditioned spectral analysis proves that the diesel pump is involved in the amplitude modulation. Experiments are carried out to validate this diagnosis. Added masses appropriately placed on the injection circuit strongly attenuate the phenomenon.     

Indirect measurement of dynamic force transmitted by a nonlinear hydraulic mount under sinusoidal excitation with focus on super-harmonics

Direct measurement of forces is not practical in many real-life applications since the interfacial conditions may change. Thus indirect force estimation methods must be developed though they pose special difficulty for nonlinear mounts or isolators. The hydraulic engine mount is examined as an illustrative example in this article since it exhibits spectrally varying and amplitude-sensitive parameters. First, we propose linear time-invariant, nonlinear and quasi-linear fluid and mechanical system models. Second, models are utilized to predict the transmitted force time history under sinusoidal excitation conditions given measured (or calculated) motion and/or internal pressure time histories. Experimental data from the non-resonant dynamic stiffness test is investigated in both time and frequency domains. In particular, the super-harmonic contents in fluid chamber pressure and force time histories are investigated using both measurements and mathematical models. This paper examines several alternate indirect schemes for estimating dynamic forces and highlights their strengths. The quasi-linear model with effective system parameters, say in terms of force to pressure or force to motion transfer functions, is found to correlate well with measured dynamic forces though linear and nonlinear models could be employed as well.     

Auto-tuning of a two-degree-of-freedom rotational pendulum absorber

A dynamic vibration absorber is effective in suppressing harmonic excitation by tuning its natural frequency to match the excitation frequency. The rotational pendulum absorber (RPA) has a wide-range of natural frequencies that are continuously tunable by setting a suitable rotational speed. In this paper it is shown how to automatically tune the rotational speed of a two-degree-of-freedom RPA by detecting the phase between the vibration of the primary structure and that of the RPA. For this purpose the speed response of the RPA is introduced in addition to the frequency response. It is seen that if the excitation frequency is above a critical value dependent on the parameters of the RPA, the second vibration mode of the RPA is effective, allowing a relatively low rotational speed for the pendulums. The speed tuning algorithm is tested on a flexible plate that is subject to excitations of around 80 Hz, which do not generate visible oscillations but emit audible noise instead. Experimental results confirm the noise-level reduction effect of the RPA.