Modelling and optimization of gear shifting mechanism, Application to heavy vehicles transmission systems

Licentiate thesis, 2016

Without an efficient transmission system the idea of an efficient vehicle is incomplete. During running of the vehicle especially in case of heavy vehicles the transmission system has to face different situations during which the system possibly can lose its efficiency. Definitely variations in efficiency of the transmission system demand from engine to vary its power to maintain the system efficiency to regulate speed of the vehicle. Gear shifting mechanism of the transmission system is one of the responsible agents for losing rotational speed of the system. The engine needs to increase its power to compensate such kind of losses by injecting the more fuel. Ultimately there will be more emissions on exhaust side. In this scenario the conducted research is concentrated on the gear shifting mechanism. To start with the well-defined aim a generic cone synchronizer mechanism modelled by a mechanical system with five degrees of freedom and comprising three rigid bodies is studied to understand the gear shifting process. To resolve complexity of the complete gear shifting processes detailed kinematic description of the phases and sub-phases gives an opportunity to capture the nature of bodies’ interaction and forces arise during their interaction. In the project a mathematical model to represent the whole gear shifting process is developed based on Constrained Lagrangian Formalism. The developed model went through validation test by using experimental data. Because the developed mathematical model is flexible to adopt other relevant models, the friction model is applied to the developed mathematical model and analyzed the differences in the results. The next step is to optimize the gear shifting process based on the input parameters. Using the developed model the analysis is performed in two steps; in first step the sensitivity analysis is considered to study the effect of variations of individual parameter on the system performance and in second step effects of a set of synchronizer mechanism's parameters which vary simultaneously are studied by using the optimization technique. Time duration of the gear shifting and speed difference at end of the main phase of synchronization process are chosen as objective functions of the system. Parameters estimated quickness and smoothness (comfort) of synchronization processes are cone angle, cone coefficient of friction, applied shift force, blocker angle, blocker coefficient of friction, cone radius, gear moment of inertia and ring moment of inertia. Eight cases of the synchronizer mechanism performance are studied under different scenarios of master/slave and different operating conditions. Further analysis on results obtained from the Pareto optimization clarifies the degree of influence of the input parameters. It was found that optimal performance of the system can be obtained by tuning few of the system parameters which have higher degree of influence instead of changing all the parameters together. For example in the case where the sleeve is considered as a master at nominal condition optimal performance of the synchronizer can be obtained by paying attention to applied shift force, cones angle, cones coefficient of friction, blocker angle and blocker coefficient of friction instead of taking all eight input parameters. At the end a graphical user interface is developed to obtain the synchronization performance diagram.