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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.

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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.