Vanja Ranogajec

Optimal Shift Control of an Automatic Transmission with a Large Number of Gears

Doctoral thesis (in Croatian), Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb, Croatia, 2019
A trend of increasing the number of forward gears of step-gear automatic transmissions (ATs) has emerged recently due to the legislative and market pressure for CO2 reduction and improved fuel economy. For the increased number of AT gears (up to ten, nowadays), the number of shift types and shift events grows significantly. The increasing shift complexity makes the development of AT control system more demanding, which calls for the development of new shift control optimisation tools and requires more exhaustive control system simulation and optimisation studies. The thesis firstly presents modelling of vehicle powertrain system, where the emphasis is on automated AT modelling and automated AT model-order reduction. Next, numerical optimisation of AT control trajectory is conducted by using a pseudospectral collocation method. The main aim of this activity is to gain insights into the optimal behaviour of AT for various single-transition and double-transition shifts. The thesis also proposes a method for multi-objective parameter optimisation and assessment of piecewise linear time profiles of AT control trajectories, which are easy to interpret, implement and calibrate. The optimisation is aimed to find parameters defining the piecewise linear shift control profiles, which provide a good trade-off between the shift comfort and performance. As an extension of the parameter optimisation approach, a method for robust parameter optimisation is proposed, which aims at ensuring high shift quality and robustness in the presence of transmission actuation parameter variations. The method for multi-objective parameter optimisation of piecewise linear control profiles is also applied to the case of more demanding double-transition power-on downshift. Different viable definitions of control variable profiles (i.e. different open-loop control strategies) are proposed and assessed based on several performance indices extracted from parameter optimisation results. Finally, the obtained optimisation results are employed for designing a more realistic control system that interacts with driver commands and accounts for various driving conditions. The use of the developed methods for modelling and optimisation is demonstrated based on the example of an advanced 10-speed AT.