Synchroniser analysis and shift dynamics of powertrains equipped with dual clutch transmissions

University of Technology, Sydney. Faculty of Engineering and Information Technology.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

Human cytomegalovirus (HCMV) replication dynamics in HCMV-naive and -experienced immunocompromised hosts

Human cytomegalovirus (HCMV) can infect both HCMV-naive and -experienced transplant patients. In this study, the growth rate of HCMV in HCMV-naive hosts (1.82 units/day; 95% confidence interval [CI], 1.44-2.56 units/day) was shown to be significantly faster than the growth rate of virus in HCMV-experienced hosts undergoing recurrent infection (0.61 units/ day; 95% CI, 0.55-0.7 units/day; P93% (95% CI, 89%-98%) is required to eliminate viral growth during infection of HCMV-naive liver transplant recipients, whereas lower efficacy levels are sufficient to reduce the R-0 value to <1 in hosts with prior HCMV immunity

Engagement and control of synchroniser mechanisms in dual clutch transmissions

The study of synchroniser engagements in dual clutch transmissions is undertaken in this paper, identifying limitations to the repeatability of actuation, demonstrating one popular solution for positive synchroniser control and offering an alternate engagement tool. Principally, high wet clutch drag and the synchroniser design have lead to detrimental alignments conditions, where indexing chamfers on sleeve and target gear delay engagement of the mechanism and lead to potential sleeve block out. This paper focuses on the investigation of different control methods for overcoming these detrimental alignment conditions. The application of a closed loop control method to overcome block out related engagements is studied, and, for comparison, a novel engagement tool for overriding all chamfer alignment conditions is introduced and evaluated. Results have demonstrated that both techniques have some limitations, with the novel tool being capable of providing direct control of all chamfer engagements with limited extension of the duration of synchroniser engagements; however, some tuning of mechanism parameters is required for different engagement conditions. © 2011 Elsevier Ltd. All rights reserved

Active damping of transient vibration in dual clutch transmission equipped powertrains: A comparison of conventional and hybrid electric vehicles

The purpose of this paper is to investigate the active damping of automotive powertrains for the suppression of gear shift related transient vibrations. Conventionally, powertrain vibration is usually suppressed passively through the application of torsional dampers in dual clutch transmissions (DCT) and torque converters in planetary automatic transmissions (AT). This paper presents an approach for active suppression of transient responses utilising only the current sensors available in the powertrain. An active control strategy for manipulating engine or electric machine output torque post gear change via a proportional-integral-derivative (PID) controller is developed and implemented. Whilst conventional internal combustion engine (ICE) powertrains require manipulation of the engine throttle, for HEV powertrains the electric machine (EM) output torque is controlled to rapidly suppress powertrain transients. Simulations for both conventional internal combustion engine and parallel hybrid vehicles are performed to evaluate the proposed strategy. Results show that while both the conventional and hybrid powertrains are both capable of successfully suppressing undesirable transients, the EM is more successful in achieving vibration suppression. © 2014 Elsevier Ltd

Investigation of synchroniser engagement in dual clutch transmission equipped powertrains

Transient response of a dual clutch transmission (DCT) powertrain to synchroniser mechanism engagements is investigated using a lumped inertia model of the powertrain. Original research integrates lumped inertia powertrain models for the DCT with a detailed synchroniser mechanism model and two separate engine models, comprising of a mean torque model and a harmonic torque model, using torque derived from piston firing. Simulations are used to investigate the synchroniser mechanism engagement process in a previously unscrutinised operating environment. Simulations are performed using both engine torque models, with the mean torque model demonstrates the highly nonlinear nature of synchroniser mechanism engagement, and the powertrain response to the engagement process. Through the introduction of harmonic engine torques, additional excitation is present in the mechanism during engagement, and increased vibration of the synchroniser sleeve results. The impact of vibrations is particularly important to the increased wear of indexing chamfer contact surfaces. © 2011 Elsevier Ltd All rights reserved

Parameter study of synchroniser mechanisms applied to Dual Clutch Transmissions

The modelling, simulation and analysis of a synchroniser mechanism as a component of wet Dual Clutch Transmissions (DCT) is presented in this paper. Mechanism engagement is demonstrated using rigid body models with a detailed drag torque model, to establish its variation over the process. Dimensionless equivalent cone and chamfer torques are used to study the impact of drag torque from a design perspective, and parameter studies performed to verify this method. Outcomes suggest the high dependency of speed synchronisation on both cone angle and friction coefficient, while the chamfer torque are highly dependent on chamfer angle, but not friction coefficient

Control of gear shifts in dual clutch transmission powertrains

To achieve the best possible responses during shifting in dual clutch transmissions it is commonplace to integrate clutch and engine control, while the clutch is used to match speeds between the engine and wheels via reduction gears, poor engine control can lead to extended engagement times and rough/harsh shift transients. This paper proposes a method for combined speed and torque control of vehicle powertrains with dual clutch transmissions for both the engine and clutches. The vehicle powertrain is modelled as a simple four degree of freedom system with reduction gears and two clutches. Including a detailed clutch hydraulic model, comprising of the direct acting solenoids and clutch piston with the hydraulic fluid modelled as a compressible fluid. Powertrain control is realised through control of clutch solenoids and manipulation of the engine throttle input. Sensitivity study of clutch performance evaluating inaccurate torque estimation demonstrated variance in the response of the hydraulic system, with an indicative simulation of poor estimation resulting in increased powertrain vibration during and after shifting. Simulations are conducted to demonstrate the capacity for this method of engine and clutch control to further reduce shift transients developed in dual clutch transmission powertrains. The obtained results also show that the adoption of torque based control techniques for both the clutch and engine, which makes use of the estimated target clutch torque, significantly improves the powertrain response as a result of reduction in the lockup discontinuities. © 2010 Elsevier Ltd. All rights reserved

Comparison of Powertrain System Configurations for Electric Passenger Vehicles

Copyright © 2015 SAE International. Electric vehicles (EV) are considered a practical alternative to conventional and hybrid electric passenger vehicles, with higher overall powertrain efficiencies by omitting the internal combustion engine. As a consequence of lower energy density in the battery energy storage as compared to fossil fuels powered vehicles, EVs have limited driving range, leading to a range phobia and limited consumer acceptance. Particularly for larger luxury EVs, electric motors with a single reduction gear typically do not achieve the diverse range of function needs that are present in multi-speed conventional vehicles, most notably acceleration performance and top speed requirements. Subsequently, multi-speed EV powertrains have been suggested for these applications. Through the utilization of multiple gear ratios a more diverse range of functional needs can be realized without increasing the practical size of the electric motor. The major limitation of multi-speed EV powertrains is that the increased transmission complexity introduces additional losses to the vehicle. Through a number of simulations this paper studies the integration of multispeed transmission with EV platforms. Particularly, it investigates the performance improvements of both B and E class vehicle platforms realized through utilization of two and three speed transmissions. Also the potential application of hybrid energy storage systems (i.e. batteries combined with super-capacitors) is studied. Results demonstrate that there can be significant benefits attained for both small and large passenger vehicles through the application of multi-speed transmissions. However, optimization of these ratios must be considered in the analysis