In the paper a new approach is presented for the design of the synchroniser and selector mechanism of a road vehicle gearbox. The main aim is to improve shiftability and driver comfort. The new approach is based not only on the theory of multi-objective optimisation but also on robust design. A multi-body physical system model of the synchroniser and selector mechanism has been developed and validated experimentally. The physical model is stochastic being many of the system parameters defined by stochastic processes. The fifty-eight parameters of the system model have been tuned in order to achieve the desired dynamic behaviour of the synchroniser and selector mechanism during a reference shift action, defined by nine performance indices. The new approach is characterised both by the optimisation of the objective functions (corresponding to system performance indices) and by the reduction (or minimisation) of the sensitivity (variance) of the performance indices to stochastic perturbations. Such variances are computed (very quickly) by means of an original procedure based on the global approximation of the objective functions. Additionally, with respect to the mentioned features, the new approach is based on both a special study to explore all of the feasible design solutions, and on a global sensitivity procedure to analyse (in a stochastic context) the influence of each design variable on each objective function. Pareto-optimal design solutions for different levels of "robustness" have been computed in a very short time. The optimisation method has been applied with successful results. A number of optimised synchronisers and selector mechanisms have been defined, all of them featuring relevant improvements in terms of performance and robustness with respect to the reference system, already effective and under production.
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