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MANUEL TENTARELLI
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Pubblicazioni
2023
- A new approach to the study and prevention of the clutch judder
[Relazione in Atti di Convegno]
Tentarelli, Manuel; Cantelli, Stefano; Sorrentino, Silvio; DE FELICE, Alessandro
abstract
The clutch judder observed in hydraulically actuated dual clutch transmissions cannot be fully explained by the current scientific literature.
Using a new methodological approach for the analysis of clutch judder, this study shows that a fluctuating oil pressure makes the clutch a parametrically excited system and gives rise to regions of instability as a function of the operating conditions of the clutch.
The system’s dynamic behaviour, characterized by both mechanical and structural high complexity, is here investigated through stability analysis of a mathematical model of the driveline. In particular, stability boundaries are identified by means of Floquet analysis, as well as the occurrence of both parametric resonance regions and linear resonance conditions.
This opens a new perspective on NVH of automotive drivelines, showing that clutch judder can potentially occur in a much wider range of conditions than documented in the current scientific literature.
The results of the experiments in progress on a test bench, designed in partnership with CNH Industrial, are validating the proposed model and will allow to calibrate the parameters of a predictive mathematical model to avoid the phenomenon of clutch judder in the design phase.
2023
- Friction-induced parametric oscillations in automotive drivelines: experimental analysis and modelling
[Relazione in Atti di Convegno]
Tentarelli, Manuel; Cantelli, Stefano; Sorrentino, Silvio; De Felice, Alessandro
abstract
Clutch judder is a friction-induced self-excited vibration occurring in automotive drivelines, an NVH issue studied for more than forty years and attributed by the scientific community to three possible causes: stick-slip, negative gradient of the coefficient of friction and geometric disturbances. However, these explanations fail to describe the kind of judder studied in this contribution, arising in presence of an oscillating component (dither) in the clutch actuation pressure. The analysis of experimental data collected on a dual-clutch transmission mounted on a specific test bench suggested the presence of a parametric resonance, generated by the dither. A specific 4 degrees of freedom model was then developed, able to predict with good accuracy the unstable parametric region in which judder occurs and useful in the design stage.
2023
- Parametric excitation as a cause of clutch judder: theoretical study and experimental validation
[Articolo su rivista]
Tentarelli, Manuel; Cantelli, Stefano; Sorrentino, Silvio; DE FELICE, Alessandro
abstract
Judder is a friction-induced torsional vibration generated during clutch engagement in automotive drivelines. To the best of the authors’ knowledge, three are the causes attributed by the scientific community to the onset of the clutch judder: stick-slip phenomena, negative gradient of the coefficient of friction and geometric disturbances.
With the help of a methodological approach that integrates the analysis of a mathematical model with the experimental data obtained on a specially designed test bench, this paper shows that, in some cases, the clutch judder may also be due to the presence of parametric excitation.
This new understanding overcomes the limits of the existing explanations because it does not preclude the occurrence of clutch judder at high slip speeds, with positive gradients of the friction coefficient and at excitation frequencies different from the eigenfrequencies of the system.
The four degrees of freedom model developed for the study of the transmission provides maps that allow to identify the instability conditions of the system. The analysis described in this paper has been aimed at solving a judder problem in a transmission already in production, but the same approach can be used to avoid the conditions that cause the onset of clutch judder on other transmissions in the design phase.
2022
- Cold Judder in Tractor Drivelines: An Essential Model for Stability Analysis
[Relazione in Atti di Convegno]
Tentarelli, M.; Cantelli, S.; De Felice, A.; Sorrentino, S.
abstract
Current scientific literature classifies the well-known clutch judder phenomenon in friction judder and pressure-induced judder, based on the mechanisms that generate it. Friction judder is associated to a negative gradient of the friction coefficient and to stick-slip phenomena, while pressure-induced judder is mainly caused by geometric disturbances. The peculiarities of the torsional oscillations experimentally observed in dual-clutch transmissions of tractors, incompatible with the explanations found in the current literature, led to consider parametric excitation as a possible cause of instability. Consequently, the clutch was modelled by means of a system of three coupled linear differential equations with time-periodic coefficients. Stability analysis, performed by adopting Floquet theory, allowed to draw stability maps as functions of the two excitation parameters, i.e. the frequency and the amplitude of the dither signal in the clutch actuation pressure. Stability maps proved to be particularly promising to explain the experimentally observed phenomenon. In addition, it was possible to show that clutch judder can also arise for positive gradients of the friction coefficient.
2022
- Experimental stability analysis of tractor drivelines affected by cold judder
[Relazione in Atti di Convegno]
Tentarelli, Manuel; Cantelli, Stefano; Sorrentino, Silvio; DE FELICE, Alessandro
abstract
Clutch judder is a friction-generated self-excited vibration affecting automotive drivelines. Stick-slip, negative gradient of the friction coefficient and geometric disturbances are the only causes currently identified in the scientific literature. Nevertheless, they are not sufficient to explain the vibration occurring in drivelines (typically of tractors) with dither (oscillating component) added to clutch hydraulic actuation signals. In this study, experimental data acquired on a specifically designed test bench are processed to show that this particular kind of judder is an instability due to parametrical excitation exerted by the actuation pressure signal. A minimal model with four degrees of freedom is proposed, able to fit the experimental data, to explain the onset of the parametrically excited vibration, and to identify which parameters have a major role in controlling this phenomenon. Stability charts obtained from the proposed model also represent a useful tool to prevent instability already in the design phase.