Shifting strategy for step change transmission vehicle : a comparative study and design method

In this paper, gear shifting characteristics of vehicles equipped with an Automated Manual Transmission (AMT) and PowerShift-AMT (PS-AMT) are analyzed and compared in order to study their effects on the fuel economy. A "rapid" upshift strategy proposed for PS-AMT shows that relative fuel saving can be achieved up to 8.5% compared to the case of the AMT with prescribed gear shifting schedule over NEDC. To fully explore potential fuel savings with respect to gear shifting strategy, Dynamic Programming (DP) is utilized for PS-AMT system to derive a globally optimal shifting schedule. Simulation result reveals that relative fuel economy improvement can be reached up 10.7%. A systematic approach is proposed to study a tradeoff between fuel consumption and driveability with respect to gear shifting strategy. The optimization problem of which the cost function consists of fuel consumption, power reserve and shifting cost is formulated and solved for optimal gear shifting strategies by the DP algorithm. In this study, it is found that fuel consumption benefit can be obtained at a certain loss or even benefit of accumulative power reserve by an approximated linear slope factor of -5. This design method is verified through simulations of forward facing dynamic powertrain model. Finally, in order to further improve the fuel saving potential and the driveability, a Hybrid Electric PS-AMT prototype is introduced and design consideration concerning the optimal control strategy is discussed