Experimental vibro-acoustic analysis of the gear rattle induced by multi-harmonic excitation

The paper reports a wide vibro-acoustic experimental investigation of the gear rattle phenomenon induced by multiharmonic 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

Banco Tensore d'Inerzia

Nella presente relazione si descrive il Banco Tensore d'Inerzia realizzato presso il Dipartimento al fine di soddisfare la richiesta, avanzata in particolar modo dalle aziende del settore automotive, di disporre della misura dei parametri d'inerzia di interi veicoli o di suoi componenti. Dopo aver descritto il principio di funzionamento, si illustreranno le procedure di prova e le tecniche adottate per la calibrazione

Delineation and Diagnostic Criteria of Oral-Facial-Digital Syndrome Type VI

Oral-Facial-Digital Syndrome type VI (OFD VI) represents a rare phenotypic subtype of Joubert syndrome and related disorders (JSRD). In the original report polydactyly, oral findings, intellectual disability, and absence of the cerebellar vermis at post-mortem characterized the syndrome. Subsequently, the molar tooth sign (MTS) has been found in patients with OFD VI, prompting the inclusion of OFD VI in JSRD. We studied the clinical, neurodevelopmental, neuroimaging, and genetic findings in a cohort of 16 patients with OFD VI. We derived the following inclusion criteria from the literature: 1) MTS and one oral finding and polydactyly, or 2) MTS and more than one typical oral finding. The OFD VI neuroimaging pattern was found to be more severe than in other JSRD subgroups and includes severe hypoplasia of the cerebellar vermis, hypoplastic and dysplastic cerebellar hemispheres, marked enlargement of the posterior fossa, increased retrocerebellar collection of cerebrospinal fluid, abnormal brainstem, and frequently supratentorial abnormalities that occasionally include characteristic hypothalamic hamartomas. Additionally, two new JSRD neuroimaging findings (ascending superior cerebellar peduncles and fused thalami) have been identified. Tongue hamartomas, additional frenula, upper lip notch, and mesoaxial polydactyly are specific findings in OFD VI, while cleft lip/palate and other types of polydactyly of hands and feet are not specific. Involvement of other organs may include ocular findings, particularly colobomas. The majority of the patients have absent motor development and profound cognitive impairment. In OFD VI, normal cognitive functions are possible, but exceptional. Sequencing of known JSRD genes in most patients failed to detect pathogenetic mutations, therefore the genetic basis of OFD VI remains unknown. Compared with other JSRD subgroups, the neurological findings and impairment of motor development and cognitive functions in OFD VI are significantly worse, suggesting a correlation with the more severe neuroimaging findings. Based on the literature and this study we suggest as diagnostic criteria for OFD VI: MTS and one or more of the following: 1) tongue hamartoma(s) and/or additional frenula and/or upper lip notch; 2) mesoaxial polydactyly of one or more hands or feet; 3) hypothalamic hamartoma

Studio e realizzazione di un modello sperimentale di robot planare a due bracci

Dottorato di ricerca in ingegneria dei sistemi termomeccanici. 8. ciclo. A.a. 1994-95Consiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7, Rome; Biblioteca Nazionale Centrale - P.za Cavalleggeri, 1, Florence / CNR - Consiglio Nazionale delle RichercheSIGLEITItal

Indirect Estimation of Tire Pressure on Several Road Pavements via Interacting Multiple Model Approach

Generally, tire deflation results in a decrease in both handling performance and tire lifetime, and in fuel consumption increment. Therefore, the real-time knowledge of the pressure is important. Direct approaches via pressure sensors mounted on the rim of each tire are not practical, due to technical and economic reasons. Cost-effective solutions with real-time estimation of tire pressure are generally less accurate and reliable than direct ones. Dynamical estimators based on a suspension model need road surface topology information to compute disturbances on the suspension system as an input, which is typically unknown. This paper proposes an innovative approach to estimate tire pressure indirectly, without actual road surface roughness information. A vertical suspension dynamic model is used to build several unscented Kalman filters, parametrised around different road surface topologies. These estimators are combined following the Interacting Multiple Model approach, which gives an acceptable estimation of tire stiffness through a weighted average obtained from a probabilistic model. A known linear static relationship between the tire stiffness and inflation pressure is utilized to indirectly estimate the tire inflation pressure. A Monte Carlo analysis has been performed on a wide range of driving scenarios and vehicle manoeuvres. The results of the estimation have been compared to those of a single unscented Kalman filter, in order to validate the effectiveness of the proposed solution and to highlight the improved performances in monitoring tire pressure

Motion Planning of a Robot Arm with Non-Rigid Transmission

In this paper some aspects of the dynamical behaviour of a two degree of freedom plain manipulator with non rigid transmission between servomotors and links are reported. A technique to compute appropriate servomotors laws of motion to obtain the planned end effector trajectories is also presented. By means of a mathematical model we report the results of a series of tests show the dynamic effects of the transmission elasticity. The simulation results show that the law of motion can induce significant link and end effector vibrations. These are due to the law of motion itself and to the occurrence of resonance. We will demonstrate that, by an appropriate computing of the servomotors laws of motion, the end-effector trajectories can be followed precisely enough, even if the transmission are not very stiff (e.g. timing belt). The simulation results, obtained with the proposed mathematical model, have been tested by means of Simulink codes; the agreement was good

A Theoretical Model For The Gear Rattle Analisys In Automotive Manual Transmissions Accounting For The Gears Lubrication

Due to the irregularity of the I.C. engine torque, the impacts between the tooth of the unloaded gear pairs of a gear box produce vibrations originating an acoustic phenomenon, known as “gear rattle noise”. The paper presents a theoretical study on the dynamic behaviour of automotive transmissions focusing on the presence of oil between the impacting tooth of the meshing gears. This rattle phenomenon is particularly audible at low regimes and regards all the gear pairs different from the gear inserted to transmit the power. Another operating condition that manifests the gear rattle phenomenon is typically the “idle condition”, when all the gear pairs are meshing but without loading. The presence of oil between the impacting tooth of the gear pairs can play a positive role to decrease the vibrations and than the rattle noise level. In the paper some driveline complete models comprising many components as flywheel, clutch, primary and secondary shafts, are described accounting for the presence of oil lubricant between the teeth of the unloaded gear pairs. The described models consider an oil film lubrication between the tooth of the gear pairs, starting from the Reynolds equation and adopting some hypotheses regarding in particular the oil squeeze effect and also hypotheses about the teeth shape. Moreover some dissipative terms as friction and hysteresis in the clutch springs together with the oil drag torque in the gear box elements have been considered and modelled in the article