This paper presents a methodology for the assessment of the NVH (noise vibration and harshness) performance of Dual Clutch Transmissions (DCTs) depending on some transmission design parameters, e.g. torsional backlash in the synchronizers or clutch disc moment of inertia, during low speed maneuvers.
A 21-DOFs nonlinear dynamic model of a C-segment passenger car equipped with a DCT is used to simulate the torsional behavior of the driveline and to estimate the forces at the bearings. The impacts between the teeth of two engaging components, e.g. gears and synchronizers, generate impulses in the forces, thus loading the bearings with force time-history characterized by rich frequency content. A broadband excitation is therefore applied to the gearbox case, generating noise and vibration issues.
The metric used to assess the severity of a specific test and to compare, at least qualitatively, the NVH performance related to different design parameters sets, is based on the RMS (root-meansquare) value of each bearing force time-history. Variations from one test to another allow assessing the benefit introduced by specific design parameter modifications. Applications of the proposed methodology aimed at evaluating the effects of reducing the clutch discs moment of inertia, the synchronizers backlash and the internal backlash in the differential are presented.
Finally the paper shows that results not only depend on the gearbox design but also on the specific maneuver chosen to excite the dynamic system under test: a clear trend may be seen in some cases while only negligible effects are observed in other conditions.