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Transient vibrations from dry clutch operation in heavy-duty truck powertrains

Modelling, simulation and validation

Time: Fri 2021-12-17 10.00

Location: Hugin, Teknikringen 8, Stockholm

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Language: English

Subject area: Engineering Mechanics

Doctoral student: Jakob Sjöstrand , Strömningsmekanik och Teknisk Akustik

Opponent: Per Erik Austrell, Lunds universitet

Supervisor: Leif Kari, Marcus Wallenberg Laboratoriet MWL; Ines Lopez Arteaga, Marcus Wallenberg Laboratoriet MWL

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For internal combustion engines used in heavy-duty vehicles, increased engine efficiency and consequently reduced CO2 emissions can be obtained if the engine speed can be kept within an optimal speed range. This requires swift and frequent gear shifts where the dry friction clutch is utilized. Enhanced dry clutch simulation models and a better understanding of the involved phenomena can assist the development towards swifter gear shifts and help reduce CO2 emissions. The work presented in this thesis focuses on the modelling of dry clutch systems for heavy-duty applications and their effect on the torsional response of the driveline during transient events such as clutch engagement and disengagement. During these events it is primarily the first vibration mode of the driveline that is active and consequently it is possible to greatly reduce theof degrees of freedom (DOFs) of the powertrain model and still capture the relevant dynamics of the powertrain. The reduced set of differential equationsdescribe the torsional motion of the powertrain and the equations of motion are solved numerically in the time-domain. From a mathematical point ofview, the equations of motion turn "stiff" when the clutch is locked. This issue is resolved by utilizing numerical solution techniques suitable for stiff differential equations. In the simulations it was observed that no engine torque fluctuations were transferred through the slipping clutch. Consequently the response of the driveline is purely modal during sliding. If the gradient of the coefficient of friction is negative the modal response is possibly unstable with exponentially growing vibration amplitudes as an effect. Moreover, the way in which the clamp load evolves during clutch engagement is found to severely effect the excitation of transient vibrations during clutch synchronization. It can be shown that reducing the gradient of the evolving clamp load at the onset of sliding will reduce the amplitude of the friction induced vibrations. Reducing the torsional vibration amplitudes will help avoid the jerky motion of the vehicle during launch and increase comfort for driver and passengers.