Optimizing the gear shifting mechanism of heavy vehicles
Automotive industry face a big challenge to reduce carbon dioxide emissions and to sell competitive trucks that comply with current and future emissions standards. The engine design, drivetrain and other transmission systems components must be further developed. The gear shifting mechanism which is a part of drivetrain needs also to be updated.
The transmission system including gear shifting mechanism has a key role to drive a vehicle which transmits power from engine to rotational motion at wheels. Particularly in case of heavy vehicles gear shifting needs to be more frequent and quick for the low energy consuming and high performing vehicles. The gear shifting process is optimized based upon the developed models and genetic algorithm with particular settings (master/slave) and conditions (nominal, road grade and excitation).
To support development of the gear shifting mechanism, detailed description of kinetics and kinematics are needed. To this end, a mechanical system with 5 degrees of freedom modelling a generic synchronizer consisting of engaging sleeve, synchronizer ring and gearwheel is considered. Due to design of the different components and their interactions the synchronizing process is described in terms of different phases; presynchronization, main synchronization, blocker transition and engagement. The four main phases are further divided into sub-phases.
To model the whole process in a unified manner, Constrained Lagrangian Formalism (CLF) turns out to be a suitable method in which the interactions between components (sleeve, synchronizer ring and gearwheel) are described by unilateral or/and bilateral constraints imposed on generalized coordinates of the system during different phases. The generic synchronizer computational model is adapted to available experimental setup and validated using obtained measurement data.
For heavy vehicles, particularly under certain circumstances, avoiding failure modes of the gear shifting mechanism is also a challenge. A model of the gear shifting mechanism is developed in GT-Suite software. Failure modes are identified via sensitivity analysis by using four system response characteristics.
The gear shifting process is optimized based upon the GT-Suite model with particular settings and conditions. Three conditions of nominal, road grade and vibrational motion of the master are studied in six cases by considering the sleeve and the gear as a master (constant rotational speed) alternatively. The optimization is performed for each case to find out minimum gear shifting time based on variations of the structural design parameters. Seventeen structural design parameters of the sleeve, the ring and the gear are considered to be optimized. The optimization results are plotted in correlations of synchronization time and structural design parameters. Minimum synchronization time is found almost same in all cases. It is concluded from closeness of the optimization results, average of the parameter values can be considered as optimized values for all cases. At the end, robustness of the optimized structural design parameters are analyzed with respect to the road grade, amplitude and frequency of excitation.