Abstract
The phenomenon clutch judder describes vibrations, normally with or near the first eigenfrequency of a powertrain, during the slip phase of a friction clutch. These vibra-tions can be self excited due to a dependency of the friction coefficient from the sliding veloc-ity, and there can underlie a forced excitation caused by axial crankshaft oscillations or geo-metrical deviations within the tolerance range.
This paper is focused on the effects of misalignments and geometrical deviations of the clutch system and the surrounding powertrain components. On the basis of previous examinations relevant deviations are identified and categorized. This classification contains “deviations ro-tating with engine speed”, e.g. radial or axial run-out of the crankshaft, “deviations rotating with gearbox (input) speed”, e.g. a thickness variation of the clutch disc, and “static devia-tions”, e.g. a misalignment of the gearbox input shaft and the clutch. The appearance of devia-tions belonging to different categories leads to an excitation torque. The frequency of this al-ternating torque also results from the categories mentioned above.
In this paper experimental methods are shown, which allow the measurement and the varia-tion of different geometrical qualities as well as the measurement of their effects on the judder vibrations. The judder vibrations are examined on a clutch component test bench; this test as-sembly contains a torsional spring, which represents a variable powertrain stiffness and there-fore allows the tuning of a certain resonance frequency.
The benefit of these methods is demonstrated at the superposition of exemplary geometric deviations like crankshaft axial run-out, pressure plate evenness and lift behaviour of the clutch plate. It can be shown that the excitation torque caused by these deviations can be minimized by subtle angular superposition. The knowledge of these superposition mecha-nisms can be used to conduct mounting instructions e.g. for the ideal angular position of the clutch relative to the crankshaft.
These experimental methods are also applied in the validation of a simulation model, which is used for the calculation of the excitation torque based on given geometrical deviations. This model is shortly introduced in this paper.
Keywords: clutch, judder, forced excitation, geometrical deviations, powertrain