Simulation and optimization of wet double clutch transmission (DCT)

This work focused on the longitudinal seven-speed wet DCT that is used in some high performance sports cars due to its capability to handle high rev and high torque output engine. Although a wet DCT has many advantages, it still has to be improved to increase efficiency and use-ability. One of the inefficiencies arises from the use of clutch fluid as a coolant to lengthen the lifetime of the clutch pad. The clutch fluid tends to stick the clutch pairs, causing the drag torque when the fluid sheared by the clutch pair that rotates with different speed after the gear preselection. The other disadvantage is in the manual shift mode, when the gear that is automatically preselected by the TCU before the gear shifting does not match the next gear as desired by the driver. The thesis starts by introducing the DCT. The introduction chapter is followed by a chapter on the state of the art which focuses on DCT design, an empirical system model and on objectification and optimization methods using a simulation environment to prepare the virtual optimization of gear shifting. In chapter three, the concept of the wet DCT is explained including the double clutch and the mechatronics system. A complete vehicle drivetrain model is developed using Matlab -Simulink and -Simscape in chapter four. After the model is confirmed, the optimization of wet DCT gear shifting using the genetic algorithm method is explained in chapter five. The vehicle acceleration during gear shifting as a simulation result was assessed to derive the shift spontaneity and shift comfort scores using the objectification method. The new gear preselection strategy is particularly recommended for manual shift modes where the gears are preselected just after the driver pushes/pulls the shift lever.