Dual Clutch Transmission vibrations during gear shift: a simulation-based approach for clunking noise assessment 2019-01-1553
A novel methodology for the assessment of DCT vibrations during gear shifts is proposed. It is based on the capability to predict through simulation a typical dynamic quantity used to objectively evaluate the vibrational behaviour of a gearbox during experimental tests, i.e. the acceleration of a point on the external surface of the gearbox housing. To achieve this result, a two-step approach is proposed: an accurate simulation of the internal transmission dynamics and an offline uncoupled computation of the gearbox housing acceleration from the output of the simulation.
The first step required the definition of a suitable nonlinear lumped parameter model of the car equipped with a DCT that was implemented in Amesim software. Complex physical models of synchronizers are used with the aim of predicting, with high fidelity, gears forces exchanged during gear shift transients. Forks displacements together with engine torque and clutches transmissible torques are the model inputs; the time histories for these quantities are extracted from experimental tests with both upshifts and downshifts and considering low engine load conditions. Time histories of the forces applied in every transmission bearings (on primary and secondary shafts and on the differential), are computed by the model; they are the information exchanged between the two step of the proposed method.
The second step, developed as a post processing tool in Matlab, is based on the knowledge of the inertance Frequency Response Functions (FRFs) between the single component of force (X,Y,Z direction in a global reference frame) applied in a bearing and a single component of acceleration (X,Y,Z direction) in the measurement point. By combining the FRFs and the time-histories of the calculated forces, and by applying the superposition principle, the multiple-input single-output response of the dynamic system is evaluated.
The indices used to assess the clunk severity are peak to peak amplitude and RMS of the gearbox housing acceleration. The efficacy of this method is proved by comparing trends of the subjective ratings of gear shift quality with trends of clunk indices computed by the proposed methodology.