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The paper reports a numerical investigation on the dynamic behaviour of a vehicle driveline, equipped with a Torsional Vibration Damper (TVD) based on Magneto-Rheological Elastomeric (MRE) spring elements, during the start-up transient considering an abrupt manoeuvre of clutch engagement. The TVD device consists of a flywheel and a damper disk, with interposed some elastomeric samples which react for relative angular displacements of the two disks. The dynamical parameters of the TVD can be properly tuned by varying the magnetic field surrounding the MRE springs to mitigate the torsional oscillations of the flywheel, causes of many undesired inconveniences as critical speeds or vibro-acoustic issues. The present study promotes the use of the MRE torsional vibration damper to reduce the annoying vibroacoustic phenomenon of “gear rattle” arising in the unloaded gear pairs of the gear box, during and after the rapid clutch engagement transients in the vehicle start-up phase and is conducted on a simplified automotive driveline equipped with a dry clutch. The possibility of quickly tuning the mechanical properties of the MRE-TVD, makes this device particularly eligible for suppressing the above disturbance, adapting to the various operative conditions of the automotive driveline. Results of the analysis, by the help of a Gear Rattle Index (GRI), demonstrate the effectiveness of the proposed device in reducing the vibroacoustic phenomenon during the transient phases of the vehicle start-up, until the vehicles speed conditions are reached.

An innovative device consisting of a flywheel equipped with a torsional vibration damper, based on the magnetorheological effect in elastomeric spring elements, is proposed in this paper. The feasibility study reports the dynamic behaviour of an automotive driveline equipped with the device aiming to explore the effectiveness of the damper in reducing the torsional oscillations of the flywheel, at low-speed regime, responsible for the vibro-acoustic phenomenon known as “gear rattle”. The spring elements of the device are constituted by magneto-rheological elastomeric samples, interposed between the flywheel and the damper disk, working for shear strains. Their dynamical characteristics can be properly tuned by varying the magnetic field surrounding the springs in order to mitigate the forced vibration causes of gear tooth impacts. The good attitude of the device in mitigating the rattle phenomenon is demonstrated by comparing the results provided by a numerical drive line model, equipped with a “monolithic” flywheel, with those obtained by adopting the present innovative vibration damper. The angular accelerations, resulting from the collisions between the teeth during the operation under “idle” conditions at different angular speeds, are thus compared.

The paper reports the stages of development of an innovative torsional vibration damper employing magnetorheological elastomers as spring elements. Such device could be adopted for reducing torsional vibrations of a vehicle powertrain. The device consists of two disks, a main flywheel and a damper disk, with interposed some spring elements, constituted by Magneto-Rheological Elastomeric (MRE) samples, working for transversal stress under relative angular displacements. The dynamical characteristics of the MRE samples can be properly tuned to mitigate the torsional vibrations which cause many undesired inconveniences as critical speeds or vibro-acoustic noise in gears. A numerical analysis, conducted on a simplified model of an automotive driveline, has been performed to evaluate the goodness of the device in reducing torsional resonances of the powertrain. An early experimental test rig to characterize the magnetorheological elastomer’s properties, is now under construction at the Dept. of Industrial Eng. of “Federico II” University. By a multibody code, developed in Adams® env., some simulations have been carried out with the aim to verify the behavior of the designed experimental test rig.

This paper describes the feasibility analysis of a methodology based on the Hilbert transform in order to detect the gear rattle phenomenon of automotive transmissions. The technique adopts the Hilbert transform to analyze experimental signals of the relative angular motion of gears starting from high-resolution optical encoder measurements. By this procedure it is possible to evaluate the severity of impacts occurring between the teeth of unloaded gears, by examining the root mean square value of the signal. The Hilbert transform is largely adopted in the detection of gear defects, such as tooth cracks, but it has not yet been used to detect gear rattle. This feasibility study highlights the capability in discriminating between impacts occurring on the two different sides of the tooth. The method puts in evidence the influence of oil lubricant between the teeth in reducing the severity of the impacts, by comparing many experimental tests performed with two different oils for transmission gears. Moreover, in order to evaluate the reliability of the proposed methodology some comparisons are conducted with a metric based on the fast Fourier transform, often adopted in this field, to highlight the goodness and simplicity of the technique based on the Hilbert transform.

The knowledge of tires tread viscoelastic behaviour plays a fundamental role in automotive to optimize vehicle performance and safety. These properties are usually characterized by means of Dynamic Mechanical Analysis [1] which implies the testing of compound sample that can be obtained by destroying the tire of interest or manufactured in different condition respect to the final product provided by tiremakers. Nowadays, the non-destructive analysis procedures are an attractive solution. These techniques are essentially advantageous for being employed in testing the whole tire, allowing the analysis of a great number of them without affects costs. The purpose of this work is the experimental analysis of the tire tread response, in different working condition, evaluated by a commercial dial indicator [2] considering the measured displacement values of the device. Experimental tests have been carried out on different tread compounds and, being the tire performance strictly affected by the working temperature, additional tests have been performed by heating and cooling each sample in a range of interest [3, 4]. Moreover, the effects of aging on a tire has been studied. The comparison of the testing activity results shows the reliability of the dynamic dial indicator to capture the tires tread different behaviour within the operating condition of interest. These encouraging results lead to next step of the research activity which will focus on the evaluation of properties characterizing the hysteretic behaviour of tires.

The present paper aims to propose performance indices able to characterize the driving abilities of a car driver in the motorsport ambit. These indices could be used both to improve drivers performances and to conduct comparative analyses between professional and non-professional drivers. The data used for the analysis come from a Formula 4 vehicle and have been acquired by means of a specific data logger. Some indices, suggested by the specific literature in the motorsport vehicles, have been analyzed and employed on the data acquired on track during races. The results were not so satisfactory especially to evaluate the performance of a non-professional driver. The proposed indicators defined as the product of the accelerations along one determined direction (longitudinal or lateral) for the corresponding velocities seem to be suitable to be used as performance indices for the pilot in all the three main phases of a curve. The analysis of the data shows that these indices are quite reliable even if, in some particular cases, they show little discrepancies. This happens because the indices must be interpreted differently in dependence of the various types of curve, which are diversely approached (e.g. a chicane or a hairpin). Further development will improve the indicators according to the type of curve, trying to give an overall performance indicator for each curve.

The paper reports a feasibility study of car suspensions equipped with an innovative bushing composed by an elastomer having magneto-rheological characteristics in order to improve the performances in terms of handling and comfort. The analysis focuses on the effects produced by the variations in stiffness due to the magneto-rheological effect on the elastomeric material of the bushing. This magneto- rheological effect is designed to act on the performances of the vehicle particularly during the transients of the dynamic behavior. The performances can be achieved by acting on the characteristics of the suspension bushing on the car body. The desired suspension performances, in terms of camber or steering angle, can be obtained by controlling the characteristics of the magneto-rheological bushings. The diagrams of these characteristics, obtained through an Elasto-kinematic analysis, synthetically show the changes of performances due to the variations in the magnetic field produced by the current applied in the inside coil of the bushing. The feasibility analysis could be particularly considered for industrial application of high performance vehicles.

The paper reports a wide vibro-acoustic experimental investigation of the gear rattle phenomenon induced by multi-harmonic excitation. The analysis is performed by using different measurement techniques which allow some of the significant parameters in this type of investigation to be acquired on a specific test rig: the angular rotations of the gears by using encoders; the accelerations obtained from a triaxial accelerometer; the sound pressure level determined by employing both acoustic microphones; the correct evaluation of the acoustic sources by utilizing a p–v sound intensity probe. Performance indices were adopted to compare the dynamic behaviours of the system with respect to some parameters, such as the speed of the pinion, the fluctuations in the speed of the pinion and the lubrication conditions. The results of the comparative analysis show very good agreement between the vibro-acoustic measurements and the results from the encoder-based method; this has helped us to interpret the physical behaviour of the gear pair with respect to the impacts occurring between the teeth during the different phases of the phenomenon. Moreover, the study indicates interesting aspects of the effects of multi-harmonic excitation on the rattle phenomenon, with particular attention to the influence of lubrication on the reduction in the rattle noise.

In the article an investigation about the feasibility of a wavelet analysis for gear rattle metric in transmission gears, due to tooth impacts under unloaded conditions, is conducted. The technique adopts the discrete wavelet transform (DWT), following the Multi-resolution analysis, to decompose an experimental signal of the relative angular motion of gears into an approximation and in some detail vectors. The described procedure, previously developed by the authors, permits the qualitative evaluation of the impacts occurring between the teeth by examining in particular the detail vectors coming out from the wavelet decomposition. The technique enables discriminating between the impacts occurring on the two different sides of tooth. This situation is typical of the double-sided gear rattle produced in the automotive gear boxes. This paper considers the influence of oil lubricant, inserted between the teeth, in reducing the impacts. Analysis is performed by comparing three different lubrication conditions, and some of the classical wavelet functions adopted in literature are tested as “mother” wavelet. Moreover, comparisons with a metric based on the harmonic analysis by means of the Fast Fourier Transform (FFT), often adopted in this field, are conducted to put in evidence the advantages of the Wavelet technique with reference to the influence of some fundamental operative parameters. The experimental signals of the relative angular rotation of gear are acquired by two high resolution incremental encoders on a specific test rig for lightly loaded gears. The results of the proposed method appear optimistic also in the detection of defects that could produce little variations in the dynamic behavior of unloaded gears.

The paper reports a feasibility study for the detection of automotive gear rattle induced by multi-harmonic excitation through the use of a wavelet multi-resolution analysis. The analysis adopts experimental data coming from a helical gear pair under unloaded conditions. The excitation of gear rattle is of periodic type with two harmonic components, which is similar to the excitation of an actual automotive I.C. engine. The dynamic behavior of the gear pair has been analyzed by varying the second order harmonic amplitude of the excitation, for two mean speed values. The analysis gives useful information to develop an index of performances based on the wavelet theory that could be adopted for comparative analyses with respect to the severity of the tooth impacts occurring during the rattle phenomenon.

The paper provides an investigation into the influence of the periodic variation in the boundaries of the dead-zone between the teeth, caused by the Transmission Error, on the gear rattle phenomenon. The study represents an evolution of a theoretical model, which has already been developed by the authors, to analyze lightly loaded gear pairs, accounting for oil squeeze effects between the gear teeth. An experimental test rig and a methodology to estimate the transmission error parameters, starting from an experimental acquisition, are described. A number of experimental–theoretical correlations concerning the influence of transmission errors on gear dynamics are reported in order to validate the theoretical model.

The article describes an experimental investigation into the “gear rattle” phenomenon in automotive manual transmissions with a special focus on the influence that lubricant oil may have in reducing this undesirable event. The experimental analysis has been conducted in order to validate a theoretical model developed by the authors that accounts for the presence of oil between the meshing gear teeth of unloaded gear pairs during the no-contact phase. An original measurement technique has been adopted for the tests that consist of the acquisition of the angular relative motion of a gear pair by two high resolution encoders. The experimental test rig designed for this analysis offers the possibility of varying the distance between the wheel axes so that the influence of the backlash variation on the rattle phenomenon can be investigated. The paper presents the results of a series of experiments conducted on helical gear pairs from an automotive gear box in the “idle gear rattle” condition by varying the lubrication mechanism. The experimental results show good agreement with the expectations provided by the theoretical model.

In this paper a non-linear one-degree-of-freedom model for analysis of gear rattle vibrations in automotive manual transmissions is presented. In order to take into account the damping effects owing to the oil in the gap between two teeth of a meshing gear, a simple one-dimensional model for the oil-film squeeze effects is proposed. The squeeze model assumes that the damping force is proportional to the oil viscosity and to the extension of the oil film in the plane of curvature of the teeth, which may depend on the lubrication conditions (dry sump, splash, bath). The results provided from several numerical simulations, carried out with reference to helical involute tooth pairs, confirm the capability of oil in reducing the high-frequency vibrations subsequent to the impact between the teeth. In particular, the influence exerted by oil viscosity and gap extension on the rattle characteristics is investigated through the analysis of the transient response of the driven gear by imposing a harmonic motion to the driving gear.

This paper describes an experimental investigation conducted on WRS-BTU seismic isolators that are constituted by a wire rope spring coupled with a ball transfer unit. The device can be considered rigid along the vertical direction while the horizontal stiffness can be independently chosen to shift the natural period away from the period range having the most of earthquake energy. Two kinds of tests were carried out: the first ones regard the isolator characterization; then, to evaluate the isolation efficiency, a small laboratory structure was equipped with four isolators and several tests on a shake-table were performed.

The stability of a rigid rotor supported on radial tilting pad journal bearings is analysed. This study has been tackled both for small unbalance values by linearising the equations of motion, and also in the case where, because of the high unbalance value, the rotor axis describes orbits with an amplitude such that the system's non-linearity cannot be ignored. In both cases the system's stable operation maps have been obtained and verified through numerical integration of the differential equations of motion.

This paper describes a method for conducting non-linear stability analysis on the synchronous motion of the journal axis and tilting pads in a system consisting of a symmetrical rigid rotor mounted on tilting pad journal bearings with two pads. The method makes it possible to obtain the limit curves separating the stable operating condition, characterized by the above motion, from the so-called unstable one characterized by motions of the pads and journal with a fundamental frequency equal to one half the rotor angular speed. A variational method is used to carry out stability analysis on the synchronous solution of the non-linear equations of motion, obtained in an approximated analytical form using a particularized harmonic balance method.

In the paper a wavelet-based signals processing technique for the experimental detection of the gear rattle produced by the teeth impacts in lightly loaded gears is proposed. The Discrete Wavelet Transform is used to decompose the signal of the angular relative motion of an helical gear pair, and the wavelet decomposition details are adopted to analyze the dynamic behavior under rattle condition. In particular the procedure permits to evaluate the quality of the impacts between the teeth, discriminating between the two different sides of teeth contacts when there is a double-sided rattle condition. This technique enables, moreover, to define new indices for metrics of gear rattle especially useful in order to conduct comparisons for different operative conditions. Some examples of application of the proposed technique are reported in the paper adopting experimental signals acquired by two high resolution incremental encoders on a specific gear pair test rig. The experimental investigations regard comparative analyses with respect to the speed fluctuations amplitude, the rattle frequency and the lubrication regime.

Wire rope springs (WRS) are widely used to protect sensitive equipment from shock or vibrations but they do not have the characteristics of a seismic isolator that must have a high vertical stiffness to support the vertical load with an acceptable vertical deflection and, at the same time, a low horizontal stiffness to isolate low frequency ground horizontal acceleration of an earthquake. To take advantage of their peculiar characteristics due to the dry friction that arises among the wires, they can be adopted in parallel with a Ball Transfer Unit (BTU), able to support vertically the weight of the sensitive equipment and to allow the equipment itself to move in any horizontal direction with low friction. The WRS-BTU isolator can be considered rigid in the vertical direction and the horizontal stiffness can be properly chosen to give the isolated system a low natural frequency and a suitable re-centering force. In order to evaluate the feasibility of adopting an isolator based on WRS and BTU, a prototype was developed and tested. In this paper, the description of the seismic isolator prototype and some experimental results are presented; it is also presented a procedure to identify the restoring force by means of the Bouc-Wen model. Finally, adopting this analytical description of the restoring force, the non-linear behavior of sensitive equipment suspended on these isolators, for different operational conditions, is simulated.

With reference to a rigid symmetrical unbalanced rotor on lubricated journal bearings and adopting the short bearing theory, synchronous orbits and orbits with a 1/2 component described by the journal are determined as approximated solutions of the system of non-linear motion equations. The method also makes it possible to evaluate the stability of the above solutions and thus of the journal orbital motion. For different values of dimensionless unbalance of the rotor, examples of orbits thus obtained are given and, in the modified Sommerfeld number-stability parameter plane, the stability areas of the solutions are identified, in particular, the area of stability of the small synchronous orbits corresponding to the stable operating condition of the rotor-bearings system.

The “gear rattle” phenomenon is a research topic of great interest for the NVH (Noise, Vibration and Harshness) automotive sector, concerning driveline noise and vibrations coming from the manual gear boxes. It is due to the internal combustion engine variable torque producing impacts and rebounds, and consequently noise, between the teeth of the unloaded gear pairs of the gear box because of the unavoidable presence of backlashes. Discrete Wavelet Transform (DWT) is used to decompose the angular relative motion signal and the wavelet decomposition details are adopted to analyze the dynamic behaviour of gears under rattle conditions. The DWT has been chosen because it is a particularly suitable instrument to recognize discontinuities, such as jumps or instantaneous changes in the slope of the signals, due to their localization in the time domain. Wavelet analysis allows to characterize an event by the localization, the kind, and the amplitude of the event. This technique enables, moreover, to define new indices for metrics of gear rattle especially useful in order to conduct comparisons among different operative conditions. Some examples of application of the proposed technique are reported in the paper. The theoretical investigations regard comparative analysis with respect to the amplitude and to the frequency of speed fluctuations and to the gears lubrication regime.

In this paper a theoretical analysis concerning the influence of the oil damping effects on the dynamic behaviour of manual automotive transmissions, in the “idle” operating condition, is proposed. The study presents an analytical model that accounts both for the hysteretic friction in the clutch springs and for the oil squeeze effect between the impacting teeth of the meshing gears. This last dissipative term, generally neglected in the literature, has been modelled by the authors in order to consider its influence on the “gear rattle” phenomenon. The results provided by a wide numerical investigation are presented and enable a qualitative comparison between the effects due to the oil and those due to the hysteretic friction in the clutch on the rattle level.

In order to study the dynamic behaviour of systems comprising low-loaded rotors on tilting pad journal bearings, a numerical simulation model has been developed and two experimental test rigs have been set up at the D.I.M.E. of the University of Naples. The theoretical model allows the system's dynamic behaviour to be described in the above conditions and is based on the hypothesis of a rigid rotor and rigid bearing supports. Bearings' hydrodynamic forces are calculated adopting the Reynolds equation for laminar and isothermal flows. The two test rigs and the particular features of each one are described in the present paper which also reports some of the test results, interpreted in the light of the results obtained by numerical simulation.

The results of a survey conducted on an experimental system consisting of a rigid rotor supported on two radial bearings each with five tilting pads is presented. In particular, the system was set up in order to assess the dynamic behaviour of the bearing in unusual operating conditions. The response of the bearing to different unbalance values was determined after acquiring and analysing the orbits described by the journal axis for assigned unbalance values in different operating conditions. Analysis of the results shows some particular operating features that were not entirely predicted by the theoretical model and which may give rise to malfunctions in the rotor-tilting pad bearings system. The tests were carried out in the rotor dynamics laboratory of the Dipartimento di Ingegneria Meccanica per l'Energetica at the University of Naples.

The dynamic behaviour of a rigid rotor on tilting-pad journal bearings system is analysed for balanced and unbalanced rotors. The study mainly regards a two-pad journal bearing symmetric with respect to the external static load. Both linear and non-linear behaviours have been analysed, with particular reference to the stability of the journal and pads equilibrium positions in the case of balanced or slightly unbalanced rotors, and to the stability of their synchronous motions in the case of considerable unbalance.