Synchroniser analysis and shift dynamics of powertrains equipped with dual clutch transmissions
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Transient dynamic investigations of dual clutch transmission equipped powertrains are conducted in this thesis through the development and application of torsional multi-body models incorporating multiple nonlinearities. Shift control studies are performed using detailed hydraulic model integrated with a 4DOF powertrain model. Results illustrate that accuracy of torque estimation, time delay in engine and clutches, and torque balance in the powertrain all influence the shift quality. Powertrain transient studies have been carried out to investigate the impact of multiple nonlinearities on powertrain dynamics and shift quality. This makes use of the clutch friction stick-slip algorithm to model nonlinearity in clutch engagements, with other nonlinearities including mean and harmonic engine torque models and dual mass flywheel with hysteresis. Comparisons between 4 and 15 DOF powertrain models are made, and the impact of using engine harmonics for the DCT powertrain identified. Results of these studies are also discussed with respect to stick-slip response clutches and the effect on post shift transient response. Finally, a backlash model is introduced for gears and synchronisers to study response under a variety of operating conditions, including synchroniser engagement, shift transients and engine tip-in/tip-out. Investigations of synchroniser mechanism dynamics and control are undertaken with a rigid body mechanism model, and as part of the DCT powertrain using a 15 DOF multi-body model. Broad ranging parameter studies are undertaken for design and environmental variables that impact on synchroniser performance, and dimensionless torques are introduce for the study of synchroniser design parameters. Slip regeneration is identified as a significant issue in mechanism actuation, in terms of engagement repeatability and damage to chamfer friction surfaces. Alignment control methods are studied to attempt to reduce the impact of chamfer alignment and regenerated slip on engagement performance. Finally two design modifications are suggested for the mechanism to eliminate the slip issue, and provide higher synchroniser torques for a similar design envelope. Powertrain simulation results suggest that under nominal actuation, using the mean engine torque model, vibrations of the sleeve increase during indexing alignment of chamfers, indicating increased wear of friction surfaces. With the inclusion of the harmonic engine torque model, vibrations in the transmission increases significantly throughout the engagement process; however these results do not indicate that there is an increased likelihood of clash during speed synchronisation.
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